CN1306668C - Semiconductor used in laser module - Google Patents

Semiconductor used in laser module Download PDF

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CN1306668C
CN1306668C CNB021161909A CN02116190A CN1306668C CN 1306668 C CN1306668 C CN 1306668C CN B021161909 A CNB021161909 A CN B021161909A CN 02116190 A CN02116190 A CN 02116190A CN 1306668 C CN1306668 C CN 1306668C
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grating
diffraction grating
active layer
semiconductor device
laser unit
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CN1453910A (en
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筑地直树
吉田顺自
舟桥政树
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Furukawa Electric Co Ltd
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Furukawa Electric Co Ltd
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Abstract

The present invention discloses a semiconductor laser device, a module and a method, which is used for providing light rays that are suitable for providing a pump light source for a Raman amplifier. The semiconductor laser device comprises an active layer, a spacing layer and a diffracting grating, wherein the active layer is constructed for emitting light rays; the spacing layer is in contact with the active layer; the diffracting grating is formed in the spacing layer, and is constructed for emitting light beams with a plurality of longitudinal modes which are positioned in the predetermined spectrum width of an oscillation spectrum of the semiconductor device. The longitudinal modes are arranged in the predetermined spectrum width of an oscillation wavelength spectrum by changing the wavelength interval between every two longitudinal modes and/or widening the predetermined spectrum width of the oscillation wavelength spectrum. The wavelength interval is set by the length of a resonant cavity in the semiconductor laser device. Meanwhile, the predetermined spectrum width of the oscillation wavelength spectrum is set by shortening the diffracting grating or changing the spacing of grating elements in the diffracting grating.

Description

The semicondcutor laser unit that uses in the laser module
Technical field
The present invention relates to a kind of semicondcutor laser unit that is used for semiconductor laser module, described semiconductor laser module is suitable for use as the pump light source in Raman's amplification system.
Background technology
In the last few years, along with multimedia in the increase on the internet, produced a kind of like this demand, i.e. the bigger data transmission capabilities of light communication system.Traditional light communication system is that the single wavelength with 1310nm or 1550nm transmits data on simple optical fiber, and this system has reduced the absorbing properties of optical fiber.But,, must increase the number of fibers of being laid on the transmission path, thereby cause cost that undesirable increase takes place in order to improve the data transmission capabilities of this simple optical fiber system.
In light of this situation, developed wavelength division multiplexing (WDM) light communication system in recent years, such as dense wavelength division multiplexing (DWDM) system, wherein a plurality of optical signallings with different wave length can transmit by simple optical fiber simultaneously.These systems utilize a kind of erbium-doped fiber amplifier (EDFA) according to the needs of long-distance transmissions the data light signal to amplify usually.Utilize the wdm system of EDFA originally to carry out work at the wave band of 1550nm, this wave band is the service band of erbium-doped fiber amplifier, and is easy to obtain stable gain homogenizing (gain flattening) under this wave band.Though utilize the application of the WDM communication system of EDFA to be extended to the little gain coefficient wave band of 1580nm in recent years, but still wish to have a kind of optical amplifier that can carry out work outside the EDFA wave band, this is because the low-loss band of optical fiber will be wider than the wave band that can be amplified by EDFA; A kind of so just optical amplifier of Raman amplifier.
In Raman's amplification system, a branch of very strong pump beam is gone into a light that carries the light data-signal by pumping and is conducted in the cable.As known in those skilled in the art, the Raman scattering effect causes the gain that frequency is approximately the light signal of 13THz, and this frequency is less than the frequency of pump beam.When the data-signal on the light conduction cable had the wavelength of this length, this data-signal will be exaggerated.Therefore, different with EDFA is that the gain wavelength wave band of Raman amplifier is determined by the wavelength of pump beam, therefore, can amplify the optional wavelength wave band by the wavelength of pump beam is selected, wherein in EDFA, the gain wavelength wave band is determined by the energy level of erbium ion.Therefore, the light signal in the optical fiber in the whole low-loss band can be amplified by the WDM communication system that has utilized Raman amplifier, and compares with the communication system that utilizes EDFA, and the number of active lanes of signal beams can increase.
Though Raman amplifier can amplify signal in the wavelength range of broad, the gain of Raman amplifier is but less relatively, therefore, preferably utilizes the laser aid of a high output to be used as pump light source.But, the power output that only increases the monotype pump light source can cause again do not wish the stimulated Brillouin scattering that takes place, and can increase the noise at performance number place, peak.Therefore, Raman amplifier needs a pump light source, and this pump light source has a plurality of oscillation longitudinal modes.Shown in Figure 15 A and 15B, the stimulated Brillouin scattering phenomenon has a threshold value P Th, at this threshold value P ThThe time, will produce stimulated Brillouin scattering.For the pump light source with the single vertical pattern that resembles the spectrum of oscillation wavelength shown in Figure 15 A (oscillation wavelengthspectrum), the height of Raman amplifier output demand such as 300mw, causes the maximum output of this single-mode to be higher than P ThThereby, produce undesirable stimulated Brillouin scattering.On the other hand, the pump light source with a plurality of vertical patterns can be distributed to power output on a plurality of patterns, and each pattern all has relatively low peak value.Thereby, shown in Figure 15 B, can be at threshold value P ThIn obtain a multiple longitudinal mode pump light source with required 300mw power output, thereby avoided the generation of stimulated Brillouin scattering problem, and provide bigger Raman gain.
In addition, because the amplification process in the Raman amplifier takes place fast, therefore when the pumping light intensity was unstable, Raman gain also can be unstable.These fluctuations of Raman gain cause the fluctuation on the amplifying signal intensity, and this does not wish to take place for transfer of data.Therefore, except a plurality of vertical patterns were provided, the intensity of the pump light source of Raman amplifier must be more stable.
Also have, the Raman in the Raman amplifier amplifies and only the signal light component with polarization identical with pump light is carried out.That is to say, when Raman amplifies,, therefore must make owing to the different influences that cause between the polarization of the polarization of signal beams and pump beam reduce to minimum because gain amplifier is decided by polarization.Though because the different meetings of the polarization state between the pump light of signal light and reverse conduction are neutralized in the transmission course, and make reverse pumping method not produce polarization problem, but the polarization difference owing between the light wave of two collaborative conduction in transmission course can make the forward pumping method depend on the pumping polarisation of light more consumingly.Thereby when using the forward pumping method, the technology that Raman gain must utilize to the dependence of pump light polarization that the pump beam polarization is compound, depolarization is shaken and other is used to reduce polarization degree (DOP) is reduced.Aspect this, be well known that the multiple vertical pattern that is provided by pump light source helps to realize minimizing of this polarization degree.
Figure 16 is a block diagram, shows a structure that is used in the traditional Raman amplifier in the WDM communication system.In Figure 16, semiconductor laser module 182a to 182d, include paired Fabry-Perot (Fabry-Perot) N-type semiconductor N light-emitting component 180a to 180d, these semiconductor light-emitting elements 180a to 180d has fiber grating (fiber gratings) 181a to 181d respectively.Laser module 182a and 182b have the long laser beam of same wave by polarization-maintaining fiber 71 (polarization maintaining fiber) to the compound coupler 61a of polarization (polarization-multiplexing coupler) output.Equally, laser module 182c and 182d have the long laser beam of same wave by polarization-maintaining fiber 71 to the compound coupler 61b output of polarization.Each polarization-maintaining fiber 71 has included a single fiber optical fiber (a single threadoptical fiber), is carved with fiber grating 181a to 181d on this optical fiber.Compound coupler 61a of polarization and 61b be the laser beam after 62 outputs of WDM coupler are compound through polarization respectively.These laser beams by compound coupler 61a of polarization and 61b output have different wavelength.
62 pairs of laser beams by compound coupler 61a of polarization and 61b output of WDM coupler carry out compound, and will be delivered to external isolation device 60 (a externalisolator) as pump beam through the light beam after compound, this external isolation device 60 is delivered to amplifying fiber 64 by WDM coupler 65 with light beam.The signal beams that need be exaggerated inputs to the amplifying fiber 64 from signal light input optical fibre 69 by independent polarization isolator 63 (polarization-independentisolator)., and be input among monitoring light branch road coupler 67 (a monitor light branchingcoupler) by carrying out compound with pump beam and amplified through the signal beams after amplifying by WDM coupler 65 and independent polarization isolator 66 by Raman.This monitoring light branch road coupler 67 will be delivered to through the part of amplifying signal light beam in the control circuit 68, and be delivered in the signal light output optical fibre 70 as outgoing laser beam through the signal beams after amplifying remaining.Control circuit 68 is based on the amplifying signal light beam in the described that part of input control circuit 68, luminance to for example light intensity of each semiconductor light-emitting elements 180a to 180d is carried out FEEDBACK CONTROL (feedback control), makes final Raman's gain amplifier no longer responsive to wavelength change.
Figure 17 shows the ordinary construction of a traditional fiber raster pattern semiconductor laser module (fiber gratingsemiconductor laser module) 182a to 182d, and this semiconductor laser module 182a to 182d is used in traditional Raman's amplification system shown in Figure 16.As being seen in Figure 17, semiconductor laser module 201 includes 202 and optical fiber 203 of a semiconductor light-emitting elements (laser diode).Semiconductor light-emitting elements 202 has an active layer (a active layer) 221, is provided with a light reflective surface 222 at the place, an end of this active layer, and is provided with a light radiation surface 223 at its place, another one end.The light beam that is produced in active layer 221 inside reflects on light reflective surface 222, and 223 outputs from the light radiation surface.
Optical fiber 203 is placed on the light radiation surface 223 of semiconductor light-emitting elements 222, and with this light radiation surface 223 optical coupling.Fiber grating 233 is formed on the core 232 of optical fiber 203 apart from 223 1 preset distance places, light radiation surface, and fiber grating 233 reflects the light beam with specific wavelength selectively.That is to say that fiber grating 233 is as the external resonator between this fiber grating 233 and the light reflective surface 222, and the laser beam with specific wavelength selected and amplified that this laser beam is exported as outgoing laser beam 241 subsequently.
Though providing, traditional fiber Bragg grating type semiconductor laser module 182a to 182d is used for the necessary multiple vertical pattern of Raman amplifier, but the problem of the fiber Bragg grating type module shown in Figure 17 is, the value of its relative intensity noise (RIN) is bigger, and this just means fluctuating widely of light intensity.Such just as previously discussed, for Raman amplifier, this fluctuation of pump light intensities is not wished to take place, because it will make that Raman gain fluctuates, thereby causes fluctuating through the signal after amplifying.For the Raman amplifier that utilizes the forward pumping method, bigger RIN especially do not wish to take place, in this Raman amplifier, the strength retrogression signal light and the higher pump light of intensity propagate in the same direction.Therefore, even traditional fiber Bragg grating type laser module provides multiple vertical pattern, these vertical patterns allow to reduce degree of polarization according to the needs of forward pumping method, but because this module has higher RIN, so the forward pumping method can't together be used with the fiber Bragg grating type module regularly.
The mechanical structure of fiber Bragg grating type laser module also makes traditional pump light source instability.More particularly, since the optical fiber 203 that has a fiber grating 233 by laser welding on capsule, therefore the mechanical oscillation of this device or optical fiber 203 all can cause the variation of its oscillating characteristic and a unsettled light source with respect to the slight shift of light-emitting component 202.This skew that optical fiber 203 is aimed at light-emitting component 202 is normally because the variation of environment temperature is caused.Aspect this, the variation of environment temperature also can cause by the minor variations on the fiber grating 233 selected oscillation wavelengths, and then also can make the pump light source instability.
With the fiber Bragg grating type laser module mutually the another one problem of association be, owing to needing the high energy losses that the external isolation device causes.In having the laser module of fiber grating, isolator can't be placed between semicondcutor laser unit and the optical fiber, because the reflection of fiber grating is depended in the external resonant cavity oscillations.That is to say that described isolator will stop the light of being returned by optical grating reflection to turn back in the semicondcutor laser unit.Therefore, the problem of fiber Bragg grating type laser module is to be affected to reflecting sensitivity and being easy to.In addition, as shown in Figure 16, utilize Raman's amplification system of fiber Bragg grating type module must utilize external isolation device 60.Just as well known in the field in this technique, because being connected of the output optical fibre in convergent lens and the external isolation device, isolator causes relatively large energy loss to pump light.
Summary of the invention
Therefore, one object of the present invention is to provide a kind of laser aid and method, is used for providing a light source that is suitable for as the pump light source of Raman's amplification system, but this light source can overcome and the fiber Bragg grating type laser module foregoing problems of association mutually.
According to a first aspect of the invention, a semiconductor device is provided, this semiconductor device has one and is configured the active layer of launching light, and one is formed in diffraction grating in the wall with the contacted wall of this active layer (a spacerlayer) and one.Aspect this, described semiconductor device is configured launches the light beam with a plurality of vertical patterns, and these vertical patterns are arranged in the predetermined spectral width (predetermined spectral width) of this semiconductor device oscillation wavelength spectrum.
In the embodiment of the present invention aspect this, this semiconductor device includes a reflectance coating, this reflectance coating is positioned at the first end place of active layer and substantially vertical with this active layer, with an antireflecting coating, this antireflecting coating is positioned at the active layer the second end place relative with described first end, and perpendicular with active layer substantially, this can form a resonant cavity in active region.In this aspect, the length of resonant cavity is at least 800 microns, and is no more than 3200 microns.
In the another one embodiment of first aspect present invention, diffraction grating can be substantially forms along the whole length of active layer, or forms a short diffraction grating (shortened diffraction grating) along the part of the whole length of this active layer.In any in these structures, diffraction grating all can include a plurality of optical grating elements, and these optical grating elements have spacing (pitch) constant or fluctuation.When forming a short diffraction grating along the part of active layer length, this weak point diffraction grating can be placed in reflectance coating one side and/or antireflecting coating one side in the semicondcutor laser unit.When being placed in a side of antireflecting coating, short diffraction grating has relatively low reflectivity, and antireflecting coating has 2% or lower ultralow reflectivity, and reflectance coating then has at least 80% reflectivity.If be placed in a side of reflectance coating, so short diffraction grating has higher relatively reflectivity, antireflecting coating have about 1% to 5% than antiradar reflectivity, reflectance coating then has about 0.1% to 2% ultralow reflectivity, and preferably has 0.1% or lower ultralow reflectivity.
According to a further aspect in the invention, provide a kind of method of emitting beam from semicondcutor laser unit of being used for, comprised the steps: to launch light by the active layer in this semicondcutor laser unit; A diffraction grating is set in this semicondcutor laser unit, is used for the part of radiation laser beam is selected, so that it is sent by this semicondcutor laser unit as output beam; And the physical parameter of this semicondcutor laser unit selected, make output beam have oscillation wavelength spectrum, this oscillation wavelength spectrum has a plurality of vertical patterns in the predetermined spectral width of oscillation wavelength spectrum.
In this aspect of the invention, the step that physical parameter is selected includes: the length to the resonant cavity of this semicondcutor laser unit is set, so that between a plurality of vertical patterns, form presetted wavelength at interval, a chirped FM grating (chirped grating) perhaps is set or the length setting of diffraction grating is the length less than active layer, thereby widen the predetermined spectral width of oscillation wavelength spectrum.When being provided with a chirped FM grating, provide periodicity or randomness on the spacing of an optical grating element to change.When the length of diffraction grating is set to when being shorter than active layer,, come the reflecting properties of reflectance coating in diffraction grating and this laser aid and antireflecting coating is set based on this position of short diffraction grating in device.
Of the present invention aspect another in, a kind of semicondcutor laser unit is provided, this semicondcutor laser unit includes: the device that is used for emission light in this semicondcutor laser unit; A part that is used for selective radiation light is with its device that sends as output beam and by this semicondcutor laser unit; Be used to guarantee that output beam has the device of oscillation wavelength spectrum, this oscillation wavelength spectrum has a plurality of vertical patterns of the predetermined spectral width that is positioned at the oscillation wavelength spectrum.Aspect this, be used to guarantee that device that output beam has this oscillation wavelength spectrum can include is used for device that the wavelength interval between a plurality of vertical patterns is set, perhaps be used for the device that the predetermined spectral width of oscillation wavelength spectrum is set.
In still another aspect of the invention, provide a kind of semiconductor laser module.Aspect this, semicondcutor laser unit in this laser module includes a semiconductor device, and this semiconductor device has one and is configured the active layer of launching light, one and the contacted wall of this active layer and a diffraction grating that is formed in this wall inside.Aspect this, described semiconductor device is configured launches a light beam, and this light beam has a plurality of vertical patterns in the predetermined spectral width of the oscillation wavelength spectrum of this semiconductor device.
Description of drawings
When considering in conjunction with the accompanying drawings, by the reference following detailed, can understand the present invention and many attached advantages thereof more all sidedly, wherein:
Fig. 1 is a fragmentary, perspective view, shows an ordinary construction of semicondcutor laser unit according to an embodiment of the invention;
Fig. 2 is the vertical sectional view along semicondcutor laser unit length direction shown in Figure 1;
Fig. 3 is the transverse sectional view along semicondcutor laser unit center line A-A intercepting shown in Figure 2 of semicondcutor laser unit;
Fig. 4 is a curve chart, shows the output characteristic of the multiple longitudinal oscillation mode (multiple oscillation longitudinal mode) of a diffraction grating formula semicondcutor laser unit among the present invention;
Fig. 5 is a vertical sectional view on the length direction, shows a semicondcutor laser unit that has short diffraction grating according to an embodiment of the invention, and this weak point diffraction grating is positioned at antireflecting coating one side;
Fig. 5 A is a curve chart, shows an optical output power of semicondcutor laser unit according to an embodiment of the invention, and light output power is the function of oscillation wavelength;
Fig. 6 is a vertical sectional view along its length, shows a semicondcutor laser unit that has short diffraction grating according to an embodiment of the invention, and this weak point diffraction grating is positioned at a side of reflectance coating;
Fig. 7 is a vertical sectional view along its length, show a semicondcutor laser unit according to an embodiment of the invention with the first short diffraction grating and second short diffraction grating, the first short diffraction grating is positioned at a side of antireflecting coating, and the second short diffraction grating is positioned at a side of reflectance coating;
Fig. 8 is a vertical sectional view along its length, shows an ordinary construction that has the semicondcutor laser unit of linear frequency modulation diffraction grating according to an embodiment of the invention;
Fig. 9 is a curve chart, shows the combined cycle Λ by Fig. 8 1And Λ 2Produce the principle of complex oscillation wavelength spectrum;
Figure 10 illustrates a cyclic fluctuation according to the grating cycle of linear frequency modulation diffraction grating of the present invention;
Figure 11 A to 11C illustrates the example that is used to realize the diffraction grating cyclic fluctuation according to of the present invention;
Figure 12 is a vertical sectional view, shows a structure according to semiconductor laser module of the present invention;
Figure 13 is a block diagram, shows a structure of Raman amplifier according to an embodiment of the invention, wherein, and by the pump beam by two semicondcutor laser unit outputs is carried out the compound polarization dependence of having eliminated of polarization;
Figure 13 A is a block diagram, show a structure of Raman amplifier according to an embodiment of the invention, wherein, be used as depolariser by utilizing a polarization-maintaining fiber, the pump beam of being exported by single semicondcutor laser unit is carried out depolarization, eliminated the dependence of polarization;
Figure 14 is a block diagram, shows the ordinary construction of a WDM communication system, has used the Raman amplifier shown in Figure 13 in this WDM communication system;
Figure 15 A and 15B are two curve charts, show the relation between laser beam power output and single longitudinal oscillation mode and a plurality of longitudinal oscillation mode, and show the threshold value of stimulated Brillouin scattering;
Figure 16 is a block diagram, shows the ordinary construction of a traditional Raman amplifier; And
Figure 17 is the view that shows the structure of a semiconductor laser module, and this semiconductor laser module is used for the Raman amplifier shown in Figure 16.
Embodiment
(wherein components identical is identified by identical Reference numeral) with reference to the accompanying drawings, specifically with reference to Fig. 1,2 and 3, here show a semicondcutor laser unit according to an embodiment of the invention, this semicondcutor laser unit is used for providing a light source that is suitable for as the pump light source of Raman's amplification system.Fig. 1 is a fragmentary, perspective view, shows an ordinary construction of semicondcutor laser unit according to an embodiment of the invention.Fig. 2 is a vertical sectional view along semicondcutor laser unit length direction shown in Figure 1, and Fig. 3 then is the transverse sectional view of this semicondcutor laser unit along Fig. 2 center line A-A intercepting.
The semicondcutor laser unit 20 of Fig. 1 to 3 includes a n-InP matrix 1, has stacked 4, one p-InP coverings 6 of 3, one p-InP walls of 2, one active layers of a n-InP resilient coating on this matrix 1 in turn, and an InGaAsP cover layer 7.Resilient coating 2 is not only a resilient coating that is formed by the n-InP material, and as a following wrap, and active layer 3 is a kind of gradient factor independent restraining multiple quantum trap (a graded index separate confinement multiple quantum well (GRIN-SCH-MQW)).A diffraction grating 13 of being made by the p-InGaAs material periodically forms within the p-InP wall 4 along the whole length of active layer 3 substantially.The film thickness of the diffraction grating 13 in embodiment illustrated in fig. 1 is 20nm, and spacing is 220nm, and to select centre wavelength be the laser beam of 1480m, by semicondcutor laser unit 20 it is launched.
As in Fig. 3, know see, the top with p-InP wall 4, GRIN-SCH-MQW active layer 3 and n-InP resilient coating 2 of diffraction grating 13 is processed to table top ribbon (amesa strip shape).The side of this table top band is embedded among the p-InP barrier layer 8 and n-InP barrier layer 9 that is shaped as current barrier layer.In addition, a p-lateral electrode 10 is formed on the upper surface of InGaAs cover layer 7, and a n-lateral electrode 11 is formed on the lower surface of n-InP matrix 1.
As in Fig. 2, being seen, have than high reflectance, such as 80% or higher reflective film 14 be formed on the light reflection end surface, this end surface is an end surface on semicondcutor laser unit 20 length directions.Have low luminous reflectivity, the antireflecting coating 15 such as 1% to 5% is formed on the light radiation end surface of the semicondcutor laser unit 20 relative with described light reflection end surface.Reflective film 14 forms an optical resonantor with antireflecting coating 15 in the active region 3 of semicondcutor laser unit 20.As being seen in Fig. 2, this resonator has predetermined length L, and these will be described further below.The light beam that GRIN-SCH-MQW active layer 3 inside in this optical resonator are produced is by reflective film 14 reflection, and radiate as outgoing laser beam via antireflecting coating 15.
Therefore, as being seen in Fig. 1 to 3 illustrated embodiment, a diffraction grating has been shaped within the wall 4 of the present invention in semicondcutor laser unit 20.The inventor has realized that this integral type diffraction grating that is comprised in semicondcutor laser unit inside provides some advantages with respect to for the described external fiber raster pattern of reference Figure 17 laser module.
At first, semiconductor laser module illustrated in fig. 17 provides a light source with higher RIN, and that crosses just as previously discussed is such, and this is opposite with the demand of Raman amplifier just.Still with reference to Figure 17, the inventor has been found that, because the resonance between the reflecting surface 222 of external fiber grating 233 and semiconductor laser radiated element 202 is so fiber Bragg grating type semiconductor laser module 201 (182a to 182d among Figure 16) has bigger RIN.That is to say and since between fiber grating 233 and the semiconductor light-emitting elements 202 than long spacing, so can't stably carry out Raman's amplification.But, because the semicondcutor laser unit 20 among the present invention is in that need not to utilize under the condition of external fiber grating directly will be by the laser beam of low 15 radiation of the reflectance coating pump light source as Raman amplifier, so RIN is less.Therefore, the fluctuation of Raman gain becomes less, and in the system that has utilized according to integral type diffraction grating semicondcutor laser unit of the present invention, can stably carry out Raman and amplify.
In addition, because RIN is little, so when being used for Raman's amplification system, the whole raster pattern semicondcutor laser unit among the present invention can not resemble the use that limits reverse pumping method the fiber Bragg grating type semiconductor laser module.The applicant has realized that, because the forward pumping method has this problem, the association fluctuation noise (fluctuation-associated noises) that is pump light is easy to be modulated onto on the signal, so reverse pumping method is used for existing fiber Bragg grating type Raman amplification system more continually, wherein, in the forward pumping method, faint signal beams is advancing on the identical direction of light beam with strong being excited.That crosses just as previously discussed is such, and the semicondcutor laser unit among the present invention provides a kind of being used to carry out the stable pump light source that Raman amplifies, thereby can be applicable to the forward pumping method easily.
The mechanically stable problem of semiconductor laser module shown in Figure 17 is also weakened by the present invention.Because the resonator in the diffraction grating device is no longer separated with the semicondcutor laser unit physical property, but integral body is incorporated into wherein, the variation of the laser generation characteristic that the variation of mechanical oscillation or environment temperature causes so the semicondcutor laser unit among this first embodiment can not occur again, and can obtain stable light and export and Raman gain.In addition, because the diffraction grating among the present invention is incorporated into semiconductor device, so the temperature of grating is by semiconductor device being provided temperature controlled temperature control unit control.This has not only been avoided environment temperature to change the influence by the selected oscillation wavelength of grating, and a mechanism is provided, and is used for controlling as the following oscillation wavelength to multiplex mode laser aid according to the present invention that will further describe.
Though the integral type diffraction grating device among the present invention is compared with the fiber Bragg grating type laser module aforementioned advantages is provided, main application of the present invention remains the pump light source in the Raman amplifier.Therefore, the integral type diffraction grating device among the present invention also must provide multiple vertical mode of operation.Except traditional integral type grating device only provides the single mode of operation that is suitable for single light source, the inventor finds that also integral type diffraction grating device can provide the multi-job pattern of the pump light source that is suitable for use in Raman's amplification.
Fig. 4 shows the multiple longitudinal oscillation mode output characteristic of diffraction grating formula semicondcutor laser unit among the present invention.As being seen in the figure, oscillation wavelength spectrum 30 provides a plurality of vertical patterns that separated by wavelength interval Δ λ, such as 31,32 and 33.Because the integral type diffraction grating among the present invention in the laser aid utilizes its bragg wavelength (Bragg wavelength) to select a kind of vertical pattern, therefore Fig. 4 also shows the predetermined spectral width w of oscillation wavelength spectrum 30, and this spectral width w is limited by the half-power point hp of oscillation wavelength spectrum.Predetermined spectral width w is a predetermined spectral width, and wide the defining on the oscillation wavelength spectrum of these bands of a spectrum includes that part of of laser work pattern.Therefore, though the full bandwidth (FWHM) that predetermined spectral width w illustrated in fig. 4 is half maximum power point place should be understood that this predetermined spectral width w can be limited by any bandwidth that oscillation wavelength is composed on 30.For example, another is used for being scheduled to the known method that spectral width limits, and is to move down 10db from the maximum power point that oscillation wavelength is composed on 30.From this specification can understand be, according to how predetermined spectral width w is limited, for given oscillation wavelength spectrum, the number of laser work pattern can change.Therefore, as the inventor recognized, in order to be provided for reducing the required multiple longitudinal oscillation mode characteristic of stimulated Brillouin scattering in the Raman amplifier, whole diffraction grating formula laser aid among the present invention must provide a plurality of longitudinal oscillation modes, and these longitudinal oscillation modes are arranged within the predetermined spectral width w of oscillation wavelength spectrum 30.
In addition, the inventor has realized that as the mode 3 shown in Fig. 41,32 and 33 the number that is included in the vertical pattern in the predetermined spectral width w should be three at least.That crosses just as previously discussed is such, and adopting the existing problem of Raman's amplification system of forward pumping method is that final gain is decided by the pumping polarisation of light of incident.Polarization is compound to be eliminated this dependence by the pump light by 20 outputs of two semicondcutor laser units is carried out, perhaps the pump light of being exported by single semicondcutor laser unit is carried out depolarization handle and eliminated (these alternate embodiments respectively shown in Figure 13 and the 13A, and will be described further below) by utilizing polarization-maintaining fiber to be used as depolariser.Under latter event, the polarization axle of polarization-maintaining fiber is approximately 45 degree with respect to the angle by the semicondcutor laser unit emitted light.Utilize this structure, can be by conducting a small distance through polarization-maintaining fiber, and make the output of laser aid obtain polarization at random with single polarization.Usually, the number increase of longitudinal oscillation mode is many more, and the length of polarization-maintaining fiber can be short more.Especially, when the number of longitudinal oscillation mode greater than three, preferably four or 5 o'clock, the coherence length of laser will shorten, and is used for that this laser is carried out depolarization and handles the length of necessary polarization-maintaining fiber and also can shorten greatly.Therefore, to be easy to obtain the laser of low degree of polarization (DOP), reduce the polarization dependence of Raman amplifier, make this Raman amplifier be suitable for substituting two and carry out the compound laser module of polarization with single laser module with higher-wattage, thus and the cost of reduction laser and polarization-maintaining fiber.
In order to obtain required a plurality of oscillation modes in the predetermined spectral width in oscillating curve (the oscillation profile), the inventor has realized that and can control predetermined spectral width w and/or wavelength interval Δ λ.But there is restriction in Raman's amplification system to the value of the predetermined spectral width w of wavelength interval Δ λ and oscillation wavelength spectrum 30.At wavelength interval Δ λ, as shown in Fig. 4, the inventor has determined this value should be 0.1nm or bigger.This be because, under the situation of utilizing semicondcutor laser unit 20 as the pump light source in the Raman amplifier, if wavelength interval Δ λ is 0.1nm or bigger, so unlikely generation stimulated Brillouin scattering.At the predetermined spectral width w in the oscillation wavelength spectrum 30, if the predetermined spectral width of oscillation wavelength is wide, the coupling loss that is caused by the compound coupler of wavelength will increase so.In addition, because the fluctuation of wavelength in the described spectral width of oscillation wavelength, so also can produce noise and change in gain.Therefore, as shown in Fig. 4, the inventor determines, and the predetermined spectral width w of oscillation wavelength spectrum 30 should be 3nm or littler, and 2nm or littler preferably.
Usually, the wavelength interval Δ λ by the vertical pattern that resonator produced of semiconductor device can be represented by following formula:
Δλ＝λ 0 2/(2·n·L)
Wherein, n is an effective refractive index, λ 0Be oscillation wavelength, L then be as the front referring to figs. 1 through 3 discuss by reflectance coating 14 length with antireflecting coating 15 formed resonators.Can see that from this formula ignore the reflectivity n that only Δ λ is had edge effect, then the length of resonator is long more, wavelength interval Δ λ is just narrow more, and the optional condition with laser beam of single vertical pattern that is used to vibrate becomes more strict.But in order to provide required a plurality of vertical patterns in 3nm or littler predetermined spectral width w, the length L of resonator can not be done too shortly.For example, in the diffraction grating device shown in Fig. 1 to 3, oscillation wavelength lambda 0Be 1480nm, and effective reflection coefficient is 3.5, when the length of resonator was 800 microns, the wavelength separation delta λ of vertical pattern was approximately 0.39nm.When resonator length is 800 microns or when bigger, be easy to obtain the power output of a plurality of patterns and Geng Gao.Equally, resonator length L must not do oversizely, so that can't realize the wavelength interval of required 0.1nm.Still referring to figs. 1 through 3 shown examples, when the length of resonator was 3200 microns, the wavelength interval Δ λ of vertical pattern was approximately 0.1nm.
Thereby, for oscillation wavelength lambda with 1480nm 0And the semicondcutor laser unit of effective reflection coefficient 3.5, as shown in Fig. 2, the length L of resonant cavity must approximately be positioned at 800 to 3200 microns scope.It is pointed out that the whole diffraction grating formula semicondcutor laser unit with such resonator length L is not used for traditional semicondcutor laser unit because when resonator length L be 800 microns or when bigger, be difficult to realize single vertical pattern vibration.But, semicondcutor laser unit 20 of the present invention, by making that on one's own initiative the length of resonator is 800 microns or longer, a laser output is provided artificially, this laser output has a plurality of longitudinal oscillation modes that are arranged in the predetermined spectral width w of oscillation wavelength spectrum.And the laser diode that has this long resonator length is suitable for obtaining high power output.
According to another embodiment of the invention, by widening the predetermined spectral width w in the oscillating curve 30, be implemented in the purpose that a plurality of mode of operations are provided in the predetermined spectral width w of oscillating curve 30.In this embodiment, by changing the grating length Lg of coupling coefficient (coupling coefficient) K and/or diffraction grating, change the predetermined spectral width w of oscillation wavelength spectrum 30.Specifically, suppose that compound coupling coefficient K*Lg (is that coupling coefficient K and diffraction grating length L g are long-pending, hereinafter being called " coupling coefficient ") fixing and predetermined spectral width w limited by the FWHM point, so when the grating length Lg of resonator reduces, predetermined spectral width w will increase, thereby allow a large amount of vertical patterns to occupy this predetermined spectral width w, as the mode of operation of laser.Aspect this, should be noted that traditional integral type grating device only uses total length formula optical grating construction (a full length grating structure).This is because these traditional devices only provide single mode of operation, in these mode of operations, does not wish to increase predetermined spectral width.The inventor has been found that the length that shortens grating helps to form the multi-job pattern.By this way, widening predetermined spectral width w according to the present invention when, can be less by the reflectance coating 14 and the influence of antireflecting coating 15 formed Fabry-Perot type resonators.
Fig. 5 is a vertical sectional view along its length, shows an ordinary construction of semicondcutor laser unit according to an embodiment of the invention.The oscillation wavelength of the semicondcutor laser unit shown in Fig. 5 is 980 to 1550nm, 1480nm preferably, and except the reflecting properties of short diffraction grating 43 and reflectance coating 14 and antireflecting coating 15, similar to the structure shown in Fig. 1 to 3.Diffraction grating 43 is short gratings, and the distance between this grating and the antireflecting coating 15 is predetermined length L g1.Aspect this, the inventor has been found that if diffraction grating 43 is formed in the zone of antireflecting coating 15 substantially, so ultralow optical reflection coating should be used as antireflecting coating 15, and high optical reflection coating should be used as reflectance coating 14.Thereby the reflectance coating 14 of Fig. 5 and antireflecting coating 15 preferably have 80% or higher reflectivity and 2% or lower reflectivity respectively.In addition, when diffraction grating is formed in antireflecting coating 15 sides like that as shown in Figure 5, preferably be set at diffraction grating 43 reflectivity own quite low; Thereby coupling coefficient K*Lg preferably is set to 0.3 or littler, and preferably is set to 0.1 or littler.
As a specific example of the formula of diffraction grating shown in Fig. 5 semicondcutor laser unit, be that the length L of resonator can be set to 1300 microns, and the grating length of diffraction grating 43 can be set to 100 microns under 0.1 the condition at coupling coefficient K*Lg.Utilizing a reflectivity is that 0.1% leading flank 15 and reflectivity are 97% trailing flank 14, and the predetermined spectral width of oscillation wavelength spectrum 30 is 0.5 to 0.6nm, and can include 3 kinds of oscillation modes in this predetermined spectral width.Fig. 5 A is a curve chart, shows the optical output power of this semicondcutor laser unit, and light output power and oscillation wavelength are a functional relation.Shown this laser aid also has one and is lower than when the 10GHz left and right sides-RIN of 140db/Hz and surpass 300 milliamperes drive current.
Fig. 6 is a vertical sectional view along its length, shows an integral type diffraction grating 44, and this diffraction grating 44 is formed in reflectance coating 14 sides (being trailing flank), rather than diffraction grating 43 shown in Figure 5.The inventor determines, if diffraction grating 44 is formed within the zone of reflectance coating 14 substantially, reflectivity is 1% to 5% so, and preferably 0.1% to 2% ultralow optical reflection coating should be as embodiment illustrated in fig. 5, as antireflecting coating 15.But different with laser aid shown in Fig. 5, the reflectance coating 14 among Fig. 6 has 1% to 5% low light reflectivity, preferably 0.1% to 2%, more preferably 0.1% or lower.In addition, when being formed in reflectance coating 15 sides diffraction grating resembles shown in Fig. 6, preferably be set at diffraction grating 44 reflectivity own quite high; Thereby K*Lg preferably is set to 1 or bigger.
Fig. 7 is a vertical sectional view along its length, shows a structure that is combined with the semicondcutor laser unit of structure shown in Fig. 5 and 6.That is to say, this semicondcutor laser unit has a diffraction grating 45 and a diffraction grating 46, wherein diffraction grating 45 is formed in and antireflecting coating 15 position of predetermined length Lg3 at interval, this antireflecting coating 15 has 0.1% to 2% ultralow light reflectivity, preferably 0.1% or lower, and diffraction grating 46 is formed in and reflectance coating 14 position of predetermined length Lg4 at interval, this reflectance coating 14 also has 0.1% to 2% ultralow light reflectivity, and preferably 0.1% or lower.In addition, because diffraction grating 45 and 46 is formed in antireflecting coating 15 sides and reflectance coating 14 sides respectively, therefore, diffraction grating 45 reflectivity own are set to quite low, and diffraction grating 46 reflectivity own are set to quite high.More particularly, the K*Lg of leading flank is set to 0.3 or lower, and the K*Lg of trailing flank is 1 or higher.
Therefore, as shown in Fig. 5 to 7, shorten the diffraction grating in the semicondcutor laser unit, widened the predetermined spectral width w of oscillation wavelength spectrum, even thereby under the situation that wavelength interval Δ λ fixes, the multiple vertical pattern that still allows this semicondcutor laser unit to provide the required Raman of being used for to amplify.In addition, though Fig. 5 to 7 shows the diffraction grating 43 to 46 that is formed in antireflecting coating 15 sides and/or reflectance coating 14 sides, but should be understood that, diffraction grating is not limited to these structures, and so long as considered the reflectivity of diffraction grating, reflectance coating and antireflecting coating, a diffraction grating that has partial-length with respect to resonator length L can be shaped in any position along GRIN-SCH-MQW active layer 3.
In aforesaid each embodiment, diffraction grating all has the fixing grating cycle.In another one embodiment of the present invention, come the predetermined spectral width w in the oscillating curve 30 is controlled by the spacing that changes diffraction grating.More particularly, the inventor has realized that when the width (being grating space) when optical grating element increased, oscillation wavelength spectral curve 30 will be offset to long wavelength.
Similarly, when grating space reduced, oscillation wavelength spectral curve 30 will be offset to shorter wavelength.Based on this understanding, the inventor has been found that linear frequency modulation diffraction grating (wherein the grating cycle of this diffraction grating 13 periodically changes) forms at least two oscillating curves by same laser aid.These two oscillating curves combine and form a composite curve, and this composite curve has the predetermined spectral width w of a relative broad, thereby have increased the number of vertical pattern in the predetermined spectral width w effectively.
Fig. 8 is a vertical sectional view along its length, shows an ordinary construction with semicondcutor laser unit of linear frequency modulation diffraction grating.As shown in the figure, diffraction grating 47 is made into to comprise at least two grating periods lambda 1And Λ 2Fig. 9 is a curve chart, shows the combined cycle Λ that utilizes among Fig. 8 1And Λ 2Produce the principle of a complex oscillation wavelength spectrum.As shown in Fig. 9, because spacing Λ 1Greater than Λ 2So, with corresponding Λ 2Oscillation wavelength spectrum compare, corresponding to Λ 1Oscillation wavelength spectrum result from long wavelength place.When make these independently oscillation wavelength spectrum be superimposed together, make and Λ 2Long wavelength's half-power point of wave spectrum is compared Λ 1When short wavelength's half-power point of wave spectrum is positioned at shorter wavelength place, will form a complex oscillation wavelength spectrum 900 as shown in Figure 9.This compound wave spectrum 900 has limited a complex wave spectral width, thereby widens the predetermined spectral width in the oscillation wavelength spectrum effectively, to comprise the more longitudinal oscillation mode of big figure.
Figure 10 shows the cyclic fluctuation in grating cycle in the diffraction grating 47.As shown in Figure 10, diffraction grating 47 has such structure, and wherein be 220nm average period, and by the cyclic fluctuation (deviation) of cycle C repetition ± 0.15nm.In this example, the reflected waveband of diffraction grating 47 with this ± difference of the cyclic fluctuation of 0.15nm and have the half width of about 2nm, thereby can include three to six longitudinal oscillation modes in the compound width wc in this complex oscillation wavelength spectrum.
Though the grating cycle of chirped FM grating changes with fixing cycle C in the aforementioned embodiment, structure of the present invention is not limited thereto, and the grating cycle can be in periods lambda 1(220nm+0.15nm) and periods lambda 2Change at random (220nm-0.15nm).In addition, as shown in Figure 11 A, diffraction grating can be made into alternately repetition period Λ 1And periods lambda 2, and can have given fluctuation.In addition, as shown in Figure 11 B, diffraction grating can be made into respectively repeatedly alternately repetition period Λ 1And periods lambda 2, and have given fluctuation.As shown in Figure 11 C, diffraction grating can be made with a plurality of continuous periods lambda 1 and a plurality of continuous periods lambda 2, and can have given undulate quantity.In addition, can diffraction grating be set by adding such cycle, this cycle is in periods lambda 1And periods lambda 2Between have discrete different value.
Thereby, as Fig. 8 to 11 is shown, by making the diffraction grating that provides in the semicondcutor laser unit have the cyclic fluctuation with respect to several nm that add deduct average period on whole chirped FM grating, the predetermined spectral width of complex oscillation wavelength spectrum wc can be configured to required value.Therefore, utilize the semicondcutor laser unit in the present embodiment that an outgoing laser beam that has a plurality of longitudinal oscillation modes within predetermined spectral width can be provided.In addition, though the chirped FM grating of previous embodiment is set equal to the length L of resonator substantially, but should be understood that structure of the present invention is not limited thereto, and chirped FM grating can be as described above along the part (being active layer) of resonator L and be shaped.
Figure 12 is a vertical sectional view, shows the structure of a semiconductor laser module, and this semiconductor laser module has one according to semicondcutor laser unit of the present invention.This semiconductor laser module 50 includes a semicondcutor laser unit 51, one first lens 52, internal insulation device 53, second lens 54 and an optical fiber 55.Semicondcutor laser unit 51 is the integral type grating devices that any aforesaid semiconductor laser aid structure of basis forms, and imports the optical fiber 55 via first lens 52, internal insulation device 53 and second lens 54 from the laser beam that this semicondcutor laser unit 51 sends.Second lens 54 are set on the optical axis of laser beam, and with optical fiber 55 optical coupled.
The inventor has realized that, in semiconductor laser module 50 with semicondcutor laser unit described in the present invention 51, because diffraction grating is formed in the inside of semicondcutor laser unit 51, so internal insulation device 53 can occupy between semicondcutor laser unit 51 and the optical fiber 55.This has just had an advantage, i.e. the light beam that is reflected by other optical module or in the light beam that semiconductor laser module 50 external reflections are come in will can not incide resonator this laser aid 51 once more.Thereby even have reflection from the outside, the vibration of semicondcutor laser unit 51 still can be stablized.In addition, internal insulation device 53 is placed between laser aid 51 and the optical fiber 55, can not introduce energy loss this laser module.Just as well known in the field in this technique, the loss of isolator mainly is in the convergent lens zone, and this convergent lens piece is positioned at beam convergence on the optical fiber at place, isolated material output end.This loss is owing to the coupling between this output lens and the output optical fibre causes.But by utilizing an internal insulation device 53, second lens 54 of this laser module 50 have had the function of the output lens of isolator.Because even without the internal insulation device, second lens 54 also are that laser module 50 is necessary, so internal insulation device 53 can not introduced any energy loss to laser module 50.In fact, as following will further describe, utilize the internal insulation device to reduce the energy loss of Raman's amplification system.Another advantage that internal insulation device 53 is brought is that it provides stable isolation characteristic.More particularly, because internal insulation device 53 contacts with Peltier (Peltier) module 58, so internal insulation device 53 remains under the stationary temperature, thereby do not have the fluctuation isolation characteristic of external isolation device, this external isolation device places under the ambient temperature usually.
Back side monitoring photodiode 56 is set on the matrix 57 as heat abstractor, and is connected on the temperature control equipment 58, and this temperature control equipment 58 is installed on the metal capsule 59 of laser module 50.The light that back side monitoring photodiode 56 detects from the reflectance coating side of semicondcutor laser unit 51 leaks.Temperature control equipment 58 is peltier modules.Though the electric current (not shown) is supplied to peltier module 58 to utilize its polarization and cool off and to heat, but peltier module 58 is main as cooling devices, and the oscillation wavelength that causes is offset because the temperature of semicondcutor laser unit 51 raises to prevent.That is to say, if the wavelength of a laser beam is greater than required wavelength, Peltier element 58 will cool off this semicondcutor laser unit 51 so, and controlling it is under the lower temperature, if but the wavelength of a laser beam is less than required wavelength, Peltier element 58 will heat this semicondcutor laser unit 51 so, and control it and be under the higher temperature.By carrying out this temperature control, can improve the wavelength stability of this semicondcutor laser unit.Optionally, can utilize a thermistor 58a to come the characteristic of laser aid is controlled.If the temperature of this laser aid that is determined by the thermistor 58a that is positioned at laser aid 51 1 sides is higher, peltier module 58 will cool off this semicondcutor laser unit 51, if temperature is lower, this peltier module 58 will heat this semicondcutor laser unit 51.By carrying out this temperature control, the wavelength of described semicondcutor laser unit and power output intensity are stablized.
Utilized the laser module 50 according to integral type laser aid of the present invention also to have the another one advantage, promptly peltier module can be used to the oscillation wavelength of this laser aid is controlled.Just as previously described, the wavelength selectivity of diffraction grating is decided by temperature, integral body is incorporated into diffraction grating in the semicondcutor laser unit according to the present invention in utilization, peltier module 58 can be used to effectively the temperature of grating be controlled, thereby, the oscillation wavelength of this laser aid is controlled.
Figure 13 is a block diagram, shows a structure according to the Raman amplifier of the WDM of being used for communication system of the present invention.In Figure 13, semiconductor laser module 60a to 60d all belongs to the type described in embodiment illustrated in fig. 2. Laser module 60a and 60b have the long laser beam of same wave via polarization-maintaining fiber 71 to the compound coupler output of polarization.Similarly, also have identical wavelength with the laser beam that 60d is exported, and it is compound to utilize the compound coupler 61b of polarization to come that they are carried out polarization by each semiconductor laser module 60c.According to the present invention, each laser module 60a to 60d all exports the laser beam with a plurality of longitudinal oscillation modes via polarization-maintaining fiber 71 to compound coupler 61a of corresponding polarization and 61b.
Compound coupler 61a of polarization and the 61b laser beam after 62 outputs of a WDM coupler are compound through polarization, these laser beams have different wavelength.62 pairs of laser beams from compound coupler 61a of polarization and 61b output of WDM coupler carry out compound, and via the laser beam of WDM coupler 65 after amplifying fiber 64 output processes are compound, are used as pump beam.Thereby, as shown in Figure 13, utilized a Raman amplifier not comprise the such external isolation device of isolator 60 shown in Figure 17 according to laser module of the present invention.Therefore, Raman's amplification system of Figure 13 has been avoided and the external isolation device foregoing energy loss of association mutually.Need carry out the amplifying signal light beam is input in the amplifying fiber 64 from signal light input optical fibre 69 via independent polarization isolator (polarization-independent isolator) 63., and be input among monitoring light branch road coupler 67 (the monitor light branching coupler) by carrying out compoundly being able to Raman and amplifying through the signal beams after amplifying via WDM coupler 65 and independent polarization isolator 66 with pump beam.Monitoring light branch road coupler 67 will be delivered to control circuit 68 through the part of amplifying signal light beam, and be delivered in the signal light output optical fibre 70 as outgoing laser beam through the amplifying signal light beam remaining.
Control circuit 68 based on that part of be transported in this control circuit 68 through the amplifying signal light beam, the luminance of each semiconductor light-emitting elements 180a to 180d is controlled, such as light intensity is controlled.In addition, the gain band that 68 couples of Ramans of control circuit amplify is carried out FEEDBACK CONTROL, makes gain band no longer responsive to wavelength.
Raman amplifier described in Figure 13 has been realized all advantages of foregoing semicondcutor laser unit.For example, though the Raman amplifier shown in Figure 13 has adopted reverse method for pumping, but, because the pump beam that semiconductor laser module 60a to 60d output is stable, so what no matter Raman amplifier adopted is forward pumping method or two directional pump method, all can carries out stable Raman and amplify.
It is compound that described Raman amplifier can be configured to that the compound pump light of a plurality of unpolarized is carried out wavelength.That is to say that the semiconductor laser module among the present invention can be used to one not to carry out in the compound Raman amplifier of polarization pump light.Figure 13 A is a block diagram, show a structure of Raman amplifier according to an embodiment of the invention, wherein handle, eliminated polarization dependence by utilizing polarization-maintaining fiber to come that as depolariser the pump beam of being exported by single semicondcutor laser unit is carried out depolarization.As being seen in the figure, laser module 60A and 60C directly are connected on the WDM coupler 62 by a polarization-maintaining fiber 71.In this structure, the polarization axle of polarization-maintaining fiber is approximately 45 degree with respect to the angle by the light that semicondcutor laser unit sent.Such just as previously mentioned, owing to comprise at least three vertical patterns in the predetermined spectral width in laser output wave spectrum, so the coherence length of laser becomes shorter, and this laser is carried out the also shortening greatly of length of the necessary polarization-maintaining fiber of depolarization.Thereby, be easier to obtain the lower laser of degree of polarization (DOP), reduced the polarization dependence of Raman amplifier.Therefore, laser aid among the present invention provides the another one advantage, promptly can utilize two to be polarized compound laser module unit (as shown in figure 13) and to substitute one and have more powerful depolarization laser module unit (as shown in FIG. 13A), but can not make the DOP deterioration, and can correspondingly reduce cost simultaneously.
Raman amplifier shown in Figure 13 and the 13A can be used in the foregoing WDM communication system.Figure 14 is a block diagram, shows the ordinary construction of a WDM communication system, has used the Raman amplifier shown in Figure 13 or Figure 13 A in this WDM communication system.
In Figure 14, wavelength is λ 1To λ nLight signal from a plurality of reflector Tx 1To Tx nBe passed in the compound coupler 80, it is compound they to be carried out wavelength here, and is transported in the optical fiber 85, to be delivered in the remote communication unit.On the transmission path of optical fiber 85, be provided with a plurality of Raman amplifiers 81 and 83, so that the light signal that decay has taken place is amplified corresponding to the Raman amplifier shown in Figure 13.The signal of transmission is divided into by optical demultiplexer 84 and has a plurality of wavelength X on optical fiber 85 1To λ nLight signal, a plurality of receiver Rx of these optical signals 1To Rx nReceive.In addition, can on optical fiber 85, insert an ADM (interpolation/deletion multiplexer (Add/Drop Multiplexer)), to insert and to remove light signal with any wavelength.
Obviously, under aforementioned enlightenment, can carry out multiple improvement and modification to the present invention.Therefore, should be understood that within the scope of the appended claims, the present invention can be by implementing with the mode that specifically described mode is different herein.For example, as the pump light source that Raman amplifies, the present invention is discussed, and still, structure of the present invention obviously is not limited to this purposes, and can be as having the EDFA pump light source of 980nm and 1480nm oscillation wavelength.

Claims (63)

1. semiconductor device includes:
One is configured the active layer of launching light;
A diffraction grating;
A reflectance coating, this reflectance coating are positioned at the first end place of described active layer, and vertical with this active layer substantially; And
An antireflecting coating, this antireflecting coating be positioned at described active layer with described first end opposite second end place, and vertical with described active layer substantially,
Wherein, described reflectance coating and described antireflecting coating have limited a resonant cavity in described active area, and, the length of described resonant cavity is not less than 800 μ m and is not more than 3200 μ m, makes described semiconductor device emitted light beams have a plurality of vertical patterns within the predetermined spectral width of the oscillation wavelength spectrum of this semiconductor device.
2. semiconductor device as claimed in claim 1, wherein, described diffraction grating forms along the whole length of described active layer substantially.
3. semiconductor device as claimed in claim 2, wherein, described diffraction grating includes a plurality of optical grating elements with constant space.
4. semiconductor device as claimed in claim 2, wherein, described diffraction grating includes a chirped FM grating, and this chirped FM grating has a plurality of optical grating elements with fluctuation spacing.
5. semiconductor device as claimed in claim 4, wherein, described chirped FM grating is so formed, and makes that the fluctuation of spacing of described a plurality of optical grating elements is random fluctuation.
6. semiconductor device as claimed in claim 4, wherein, described chirped FM grating is so formed, and makes that the fluctuation of spacing of described a plurality of optical grating elements is cyclic fluctuation.
7. semiconductor device as claimed in claim 1, wherein, described diffraction grating is a short diffraction grating, this diffraction grating forms along the part of the whole length of described active layer.
8. semiconductor device as claimed in claim 7, wherein, described diffraction grating includes a plurality of optical grating elements with constant space.
9. semiconductor device as claimed in claim 7, wherein, described diffraction grating includes a chirped FM grating, and this chirped FM grating has a plurality of optical grating elements with fluctuation spacing.
10. semiconductor device as claimed in claim 9, wherein, described chirped FM grating is so formed, and makes that the fluctuation of spacing of described a plurality of optical grating elements is random fluctuation.
11. semiconductor device as claimed in claim 9, wherein, described chirped FM grating is so formed, and makes that the fluctuation of spacing of described a plurality of optical grating elements is cyclic fluctuation.
12. semiconductor device as claimed in claim 7, wherein, described short diffraction grating is positioned a side of described antireflecting coating along the part of active layer.
13. semiconductor device as claimed in claim 12, wherein, described antireflecting coating has about 0.1% to 2% ultralow reflectivity.
14. semiconductor device as claimed in claim 12, wherein, described antireflecting coating has about 0.1% or lower ultralow reflectivity.
15. semiconductor device as claimed in claim 12, wherein, described reflectance coating has at least 80% high reflectance.
16. semiconductor device as claimed in claim 12, wherein, described short diffraction grating has and is approximately 0.3 or the long-pending K*Lg of littler coupling coefficient and grating length.
17. semiconductor device as claimed in claim 12, wherein, described short diffraction grating has and is approximately 0.1 or the long-pending K*Lg of littler coupling coefficient and grating length.
18. semiconductor device as claimed in claim 7, wherein, described short diffraction grating is positioned a side of described reflectance coating along the part of active layer.
19. semiconductor device as claimed in claim 18, wherein, described antireflecting coating has about antiradar reflectivity of 1% to 5%.
20. semiconductor device as claimed in claim 18, wherein, described reflectance coating has about 0.1% to 2% ultralow reflectivity.
21. semiconductor device as claimed in claim 18, wherein, described reflectance coating has about 0.1% or lower ultralow reflectivity.
22. semiconductor device as claimed in claim 18, wherein, described short diffraction grating has and is approximately 1 or the long-pending K*Lg of higher coupling coefficient and grating length.
23. semiconductor device as claimed in claim 18, wherein, described short diffraction grating has and is approximately 3 or the long-pending K*Lg of higher coupling coefficient and grating length.
24. semiconductor device as claimed in claim 7, wherein, described short diffraction grating includes the first short diffraction grating and the second short diffraction grating, wherein the first short diffraction grating is positioned a side of described antireflecting coating along the part of active layer, and the second short diffraction grating is positioned a side of described reflectance coating along the part of active layer.
25. semiconductor device as claimed in claim 24, wherein, described antireflecting coating and described reflectance coating have about 0.1% to 2% ultralow reflectivity.
26. semiconductor device as claimed in claim 24, wherein, described antireflecting coating and described reflectance coating have about 0.1% or lower ultralow reflectivity.
27. semiconductor device as claimed in claim 24, wherein, the described first short diffraction grating comprise have be approximately 0.3 or the long-pending K*Lg of littler coupling coefficient and grating length first lack diffraction grating.
28. semiconductor device as claimed in claim 24, wherein, the described second short diffraction grating comprise have be approximately 1 or the long-pending K*Lg of higher coupling coefficient and grating length second lack diffraction grating.
29. a method that is used for providing from semicondcutor laser unit light includes:
Active layer by described semicondcutor laser unit is launched light;
A diffraction grating is set in described semicondcutor laser unit, is used as exporting light and launches by described semicondcutor laser unit with a part of selecting the described light of launching; And
Physical parameter to described semicondcutor laser unit is selected, and makes described output beam have oscillation wavelength spectrum, and this oscillation wavelength spectrum has a plurality of vertical patterns within the predetermined spectral width of this oscillation wavelength spectrum,
Wherein, the described step that physical parameter is selected comprises length setting with the resonant cavity of described semicondcutor laser unit for being not less than 800 μ m and being not more than 3200 μ m, makes wavelength interval between described a plurality of vertical pattern for 0.1nm and described a plurality of vertical pattern might be formed within the described predetermined spectral width of oscillation wavelength spectrum at least.
30. method as claimed in claim 29, wherein, the described step that physical parameter is selected comprises that the length setting with described diffraction grating is the length less than described active layer, thereby widens the described predetermined spectral width of oscillation wavelength spectrum.
31. method as claimed in claim 30, wherein said semicondcutor laser unit comprises antireflecting coating, and described method also comprises a side that described diffraction grating is arranged on the described antireflecting coating of this semicondcutor laser unit.
32. method as claimed in claim 31 comprises that also the reflectivity with described antireflecting coating is set to about 0.1% to 2%.
33. method as claimed in claim 31 comprises that also the reflectivity with described antireflecting coating is set to about 0.1% or lower.
34. method as claimed in claim 31, wherein said semicondcutor laser unit also comprise the reflectance coating relative with described antireflecting coating, described method comprises that also the reflectivity with described reflectance coating is set at least 80%.
35. method as claimed in claim 31 also comprises the coupling coefficient of described diffraction grating and the long-pending K*Lg of grating length are set at about 0.3 or littler.
36. method as claimed in claim 31 also comprises the coupling coefficient of described diffraction grating and the long-pending K*Lg of grating length are set at about 0.1 or littler.
37. method as claimed in claim 30, wherein said semicondcutor laser unit comprises reflectance coating, and described method also comprises a side that described diffraction grating is arranged at the described reflectance coating of this semicondcutor laser unit.
38. method as claimed in claim 37 comprises that also the reflectivity with described reflectance coating is set at about 0.1% to 2%.
39. method as claimed in claim 37 comprises that also the reflectivity with described reflectance coating is set at about 0.1% or lower.
40. method as claimed in claim 37 comprises that also the reflectivity with the antireflecting coating relative with described reflectance coating is set at about 1% to 5%.
41. method as claimed in claim 37 also comprises the coupling coefficient of described diffraction grating and the long-pending K*Lg of grating length are set at about 1 or higher.
42. method as claimed in claim 37 also comprises the coupling coefficient of described diffraction grating and the long-pending K*Lg of grating length are set at about 3 or higher.
43. method as claimed in claim 30, wherein said semicondcutor laser unit comprises antireflecting coating and the reflectance coating relative with described antireflecting coating, described method also comprises described diffraction grating is arranged at antireflecting coating one side of this semicondcutor laser unit as the first short diffraction grating along the part of described active layer, and the second short diffraction grating is arranged at described reflectance coating one side along the part of described active layer.
44. method as claimed in claim 41, wherein said semicondcutor laser unit also comprise the antireflecting coating relative with described reflectance coating, described method comprises that also the reflectivity with described antireflecting coating and described reflectance coating is set at about 0.1% to 2%.
45. method as claimed in claim 41, wherein said semicondcutor laser unit also comprises the antireflecting coating relative with described reflectance coating, and described method comprises that also the reflectivity with described antireflecting coating and described reflectance coating is set at about 0.1% or lower.
46. method as claimed in claim 43 also comprises the coupling coefficient of described first and second diffraction grating and the long-pending K*Lg of grating length are set at about 0.3 or littler and about 1 or higher respectively.
47. method as claimed in claim 29, wherein, the described step that physical parameter is selected comprises described diffraction grating is formed a chirped FM grating, this chirped FM grating has a plurality of optical grating elements with fluctuation spacing, thereby widens the described predetermined spectral width of oscillation wavelength spectrum.
48. method as claimed in claim 47, wherein, the step of the described chirped FM grating of described formation comprises this chirped FM grating of formation like this, makes that the fluctuation of spacing of described a plurality of optical grating elements is random fluctuation.
49. method as claimed in claim 47, wherein, the step of the described chirped FM grating of described formation comprises this chirped FM grating of formation like this, makes that the fluctuation of spacing of described a plurality of optical grating elements is cyclic fluctuation.
50. a semicondcutor laser unit includes:
The device that is used for emission light in described semicondcutor laser unit;
Be used to select the part of the described light of launching, with its device of launching as output beam and by described semicondcutor laser unit; And
Be used to guarantee that described output beam has the device of oscillation wavelength spectrum, this oscillation wavelength spectrum has a plurality of vertical patterns within the predetermined spectral width that is positioned at the oscillation wavelength spectrum,
Wherein, the described device that is used to guarantee that described output beam has this oscillation wavelength spectrum comprises and is used for device that the wavelength interval between described a plurality of vertical patterns is set, and the described device that is used to set the wavelength interval comprises and is used for the wavelength interval is set at the device of 0.1nm at least; And the described device that is used to guarantee that described output beam has this oscillation wavelength spectrum comprises and is used for device that the predetermined spectral width of described oscillation wavelength spectrum is set, described be used for the device that the predetermined spectral width of described oscillation wavelength spectrum is set comprised be used for this predetermined spectral width is set at the device that is no more than 3nm.
51. a semiconductor laser module includes:
A semicondcutor laser unit, this semicondcutor laser unit comprises:
One is configured the active layer of launching light;
A diffraction grating;
A reflectance coating, this reflectance coating are positioned at the first end place of described active layer, and vertical with this active layer substantially; And
An antireflecting coating, this antireflecting coating be positioned at described active layer with described first end opposite second end place, and vertical with described active layer substantially,
Wherein, described reflectance coating and described antireflecting coating have limited a resonant cavity in described active area, and, the length of described resonant cavity is not less than 800 μ m and is not more than 3200 μ m, makes described semiconductor device emitted light beams have a plurality of vertical patterns within the predetermined spectral width of the oscillation wavelength spectrum of this semiconductor device.
52. semiconductor laser module as claimed in claim 51 also comprises an internal insulation device, this internal insulation device is clipped in described semicondcutor laser unit and one and is coupling between the optical fiber on the output of described semiconductor laser module.
53. semiconductor laser module as claimed in claim 52 also comprises a temperature control equipment, this temperature control equipment is configured to be controlled the isolation characteristic of described internal insulation device.
54. semiconductor laser module as claimed in claim 51 also comprises a temperature control equipment, this temperature control equipment is configured to be controlled the oscillation wavelength of described semicondcutor laser unit.
55. semiconductor laser module as claimed in claim 54, wherein, described temperature control equipment comprises peltier module.
56. semiconductor laser module as claimed in claim 54, wherein, described temperature control equipment includes a thermistor.
57. semiconductor laser module as claimed in claim 51 comprises that also is used for the device that the oscillation wavelength of described semicondcutor laser unit is controlled.
58. semiconductor laser module as claimed in claim 51 also comprises a polarization-maintaining fiber, wherein the polarization axle of this polarization-maintaining fiber is approximately 45 degree with respect to the angle by the light that this semicondcutor laser unit sent.
59. a fiber amplifier includes:
A semicondcutor laser unit, this semicondcutor laser unit comprises:
One is configured the active layer of launching light;
A diffraction grating;
A reflectance coating, this reflectance coating are positioned at the first end place of described active layer, and vertical with this active layer substantially; And
An antireflecting coating, this antireflecting coating be positioned at described active layer with described first end opposite second end place, and vertical with described active layer substantially,
Wherein, described reflectance coating and described antireflecting coating have limited a resonant cavity in described active area, and, the length of described resonant cavity is not less than 800 μ m and is not more than 3200 μ m, makes described semiconductor device emitted light beams have a plurality of vertical patterns within the predetermined spectral width of the oscillation wavelength spectrum of this semiconductor device.
60. a wavelength-division multiplex system includes:
A fiber amplifier, this fiber amplifier include a semicondcutor laser unit, and this semicondcutor laser unit comprises:
One is configured the active layer of launching light;
A diffraction grating;
A reflectance coating, this reflectance coating are positioned at the first end place of described active layer, and vertical with this active layer substantially; And
An antireflecting coating, this antireflecting coating be positioned at described active layer with described first end opposite second end place, and vertical with described active layer substantially,
Wherein, described reflectance coating and described antireflecting coating have limited a resonant cavity in described active area, and, the length of described resonant cavity is not less than 800 μ m and is not more than 3200 μ m, makes described semiconductor device emitted light beams have a plurality of vertical patterns within the predetermined spectral width of the oscillation wavelength spectrum of this semiconductor device.
61. a Raman amplifier includes:
A semicondcutor laser unit, this semicondcutor laser unit comprises:
One is configured the active layer of launching light;
A diffraction grating;
A reflectance coating, this reflectance coating are positioned at the first end place of described active layer, and vertical with this active layer substantially; And
An antireflecting coating, this antireflecting coating be positioned at described active layer with described first end opposite second end place, and vertical with described active layer substantially,
Wherein, described reflectance coating and described antireflecting coating have limited a resonant cavity in described active area, and, the length of described resonant cavity is not less than 800 μ m and is not more than 3200 μ m, makes described semiconductor device emitted light beams have a plurality of vertical patterns within the predetermined spectral width of the oscillation wavelength spectrum of this semiconductor device.
62. Raman amplifier as claimed in claim 61, wherein, described semicondcutor laser unit is directly connected on the wave division multiplex coupler (62) by a polarization-maintaining fiber.
63. Raman amplifier as claimed in claim 62, wherein, the polarization axle of this polarization-maintaining fiber is approximately 45 degree with respect to the angle by the light that described semicondcutor laser unit sent.
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