US20110183450A1 - Surface emitting semiconductor laser, method for fabricating surface emitting semiconductor laser, module, light source apparatus, data processing apparatus, light sending apparatus, optical spatial transmission apparatus, and optical spatial transmission system - Google Patents
Surface emitting semiconductor laser, method for fabricating surface emitting semiconductor laser, module, light source apparatus, data processing apparatus, light sending apparatus, optical spatial transmission apparatus, and optical spatial transmission system Download PDFInfo
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- US20110183450A1 US20110183450A1 US13/078,031 US201113078031A US2011183450A1 US 20110183450 A1 US20110183450 A1 US 20110183450A1 US 201113078031 A US201113078031 A US 201113078031A US 2011183450 A1 US2011183450 A1 US 2011183450A1
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
- H01S5/18322—Position of the structure
- H01S5/18327—Structure being part of a DBR
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- H01S2301/00—Functional characteristics
- H01S2301/18—Semiconductor lasers with special structural design for influencing the near- or far-field
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- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/0225—Out-coupling of light
- H01S5/02251—Out-coupling of light using optical fibres
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- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/0225—Out-coupling of light
- H01S5/02253—Out-coupling of light using lenses
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
- H01S5/18311—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement using selective oxidation
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
- H01S5/18322—Position of the structure
- H01S5/18325—Between active layer and substrate
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
- H01S5/18322—Position of the structure
- H01S5/1833—Position of the structure with more than one structure
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18341—Intra-cavity contacts
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18355—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a defined polarisation
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- H—ELECTRICITY
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18361—Structure of the reflectors, e.g. hybrid mirrors
- H01S5/18369—Structure of the reflectors, e.g. hybrid mirrors based on dielectric materials
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- H—ELECTRICITY
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18397—Plurality of active layers vertically stacked in a cavity for multi-wavelength emission
Definitions
- This invention relates to a surface emitting semiconductor laser, a method for fabricating a surface emitting semiconductor laser, a module, a light source apparatus, a data processing apparatus, a light sending apparatus, an optical spatial transmission apparatus, and an optical spatial transmission system.
- VCSELs Vertical-Cavity Surface-Emitting Lasers
- VCSELs have excellent characteristics which edge-emitting semiconductor lasers do not have.
- VCSELs feature lower threshold current and smaller power consumption.
- VCSELs With VCSELs, a round light spot can be easily obtained, and evaluation can be performed while they are on a wafer, and light sources can be arranged in two dimensional arrays. With these characteristics, demands for VCSELs as light sources in the communication field have especially been expected to grow.
- a VCSEL In a case where a VCSEL is used as a light source or the like for optical transmission, selection of mode of laser light is required. For example, in a case where a VCSEL is coupled to an optical fiber and a long-distance communication is to be performed, single-mode is more preferable. To obtain single-mode, in general, it is required to make the diameter of a current confining layer of the VCSEL to about 3 to 4 micrometers.
- a VCSEL of a selective oxidation type AlAs or AlGaAs having a high Al-composition is used for the current confining layer, and a portion of the current confining layer is oxidized to form an aperture in the current confining layer. Because the aperture is formed by an oxidizing reaction of Al, it is difficult to accurately control the diameter, and especially, it is difficult to reproduce a small aperture diameter for obtaining single-mode, resulting in a reduction in yield of the VCSEL.
- the present invention aims to provide a surface emitting semiconductor laser in which mode control can be performed more effectively than the mode control by surface processing of a light emitting surface of a related art, and a module, a light source apparatus, a data processing apparatus, a light sending apparatus, an optical spatial transmission apparatus, and an optical spatial transmission system, which use the surface emitting semiconductor laser, and a method for fabricating a surface emitting semiconductor laser.
- An aspect of the present invention provides a surface emitting semiconductor laser including a substrate; a lower reflective mirror formed on the substrate; an active layer formed on the lower reflective mirror, and emitting light; an upper reflective mirror formed on the active layer, and forming a resonator between the lower reflective mirror and the upper reflective mirror; an optical mode controlling layer formed between the lower reflective mirror and the upper reflective mirror, and optically controlling mode of laser light; and a current confining layer formed between the lower reflective mirror and the upper reflective mirror, and confining current that is applied during driving.
- the optical mode controlling layer an opening is formed for selectively absorbing or reflecting off light that is emitted in the active layer.
- FIGS. 1A and 1B are cross sectional views illustrating a configuration of a VCSEL according to a first example of the present invention, wherein FIG. 1A illustrates a status before an upper DBR is formed, and FIG. 1B illustrates a status after the upper DBR is formed;
- FIGS. 2A to 2D are plan views illustrating a profile of an optical mode controlling layer
- FIGS. 3A and 3B illustrate light intensity distributions in which transverse mode control is performed by an optical mode controlling layer
- FIG. 4 is a graph illustrating the relation between the diameter of the opening of the optical mode controlling layer and the oscillation wavelength
- FIG. 5 is a schematic cross sectional view illustrating a configuration of a VCSEL according to a second example of the present invention.
- FIG. 6 is a schematic cross sectional view illustrating a modified example of a VCSEL according to a second example of the present invention.
- FIG. 7 is a schematic cross sectional view illustrating a configuration of a VCSEL according to a third example of the present invention.
- FIGS. 8A to 8C are cross sectional views illustrating a process of a method for fabricating a VCSEL according to a first example of the present invention
- FIGS. 9A to 9C are cross sectional views illustrating a process of a method for fabricating a VCSEL according to a first example of the present invention.
- FIGS. 10A and 10B are schematic cross sectional views each illustrating a configuration of a module in which an optical component is implemented in a VCSEL of according to an example
- FIG. 11 illustrates an example of a configuration of a light source apparatus in which a VCSEL is used
- FIG. 12 is a schematic cross sectional view illustrating a configuration of a light sending apparatus in which the module shown in FIG. 10A is used;
- FIG. 13 illustrates a configuration in which the module shown in FIG. 10A is used for an optical transmission system
- FIG. 14A illustrates a block diagram of a configuration of an optical transmission system
- FIG. 14B illustrates an outer configuration of an optical transmission apparatus
- FIG. 15 illustrates a video transmission system in which the optical transmission apparatus of FIG. 14B is used.
- FIG. 1A and FIG. 1B are schematic cross sectional views illustrating a configuration of a VCSEL according to an example of the present invention.
- a VCSEL 100 according to an example includes a p-side electrode 104 on a back surface of a p-type GaAs substrate 102 .
- a lower DBR (Distributed Bragg Reflector) 106 that composes a reflective mirror of multilayer films in which two types of p-type Al x Ga 1-x As having different x values are overlaid one another; a current confining layer 108 made of p-type Al 0.98 Ga 0.02 As; a p-type lower spacer layer 110 ; an active layer 112 having a quantum well structure; an n-type upper spacer layer 114 ; an intermediate DBR 116 that composes a partial reflective mirror of multilayer films in which a few periods of two types of n-type Al x Ga 1-x As having different x values are overlaid; an optical mode controlling layer 120 made of n-type GaAs, in which an opening 118 is formed at a center portion thereof; an n-side electrode 122 ohmic-contacted to the optical mode controlling layer 120 ; an upper DBR 124 that composes a reflective mirror of dielectric multilayer films in which SiO 2 and Ti
- the semiconductor layers on the substrate from the lower DBR 106 to the optical mode controlling layer 120 are formed by a series of epitaxial growth. Then, by etching the semiconductor layers from the optical mode controlling layer 120 to the lower DBR 106 , a cylindrical post structure P is formed.
- the optical mode controlling layer 120 being the uppermost layer of the post structure P is a GaAs layer. By not exposing Al on the surface, oxidation is prevented.
- the current confining layer 108 is oxidized from the side surface of the post structure P.
- the current confining layer 108 has a higher Al-composition than other semiconductor layers do, and thus has a higher oxidation speed than other semiconductor layers.
- a highly reflective portion is formed at periphery of the current confining layer 108 , and a conductive portion 128 surrounded by the highly reflective portion is formed.
- the conductive portion 128 confines current during operation, and the diameter thereof may be about 8 to 6 micrometers.
- the current confining layer may be made of AlAs.
- the optical mode controlling layer 120 performs light absorption or light reflection of oscillation wavelength near the active layer 112 that is sandwiched between the lower DBR 106 and the upper DBR 124 .
- the optical mode controlling layer 120 may change refractive index near the active layer 112 that is sandwiched between the lower DBR 106 and the upper DBR 124 .
- the optical mode controlling layer 120 controls lasing mode, especially controls transverse mode, by optically absorbing or reflecting off light.
- the oscillation at around 850 nm is contemplated, and the thickness of the optical mode controlling layer 120 is about 200 nm.
- the opening 118 is formed by etching the GaAs layer at a center portion of the optical mode controlling layer 120 . In the opening 118 , absorption of light of 850 nm does not occur; however, at a portion where GaAs is remained, light absorption occurs, and thus gain is reduced during laser oscillation.
- the opening 118 of the optical mode controlling layer 120 is formed by a photolithography process. By this process, the opening 118 may become an accurate pattern depending on the accuracy of the photolithography. Each of the centers of the opening 118 and the conductive portion 128 coincides with an optical axis. Preferably, the diameter of the opening 118 is 4 to 3 micrometers, and smaller than the diameter of the conductive portion 128 . By accurately forming the diameter of the opening 118 , the control of lasing mode can be more accurately performed.
- the optical mode controlling layer 120 is disposed in proximity to the active layer 112 through the intermediate DBR 116 .
- the intermediate DBR 116 is interposed to perform gettering of gold or the like diffused from the n-side electrode 122 that is ohmic-contacted to the optical mode controlling layer 120 .
- the optical mode controlling layer 120 may be formed on the active layer 112 or the upper spacer layer 114 .
- the optical mode controlling layer 120 is formed in a gain medium, not on the top surface being the light emitting surface of laser light, and thus lasing mode can be extremely effectively controlled. In other words, a slight change in shape of the opening 118 can significantly affect lasing mode.
- FIGS. 2A to 2D are plan views of examples of a profile of an optical mode controlling layer.
- the optical mode controlling layer shown in FIGS. 2A to 2C controls mainly transverse mode
- the optical mode controlling layer shown in FIG. 2D controls mainly polarization.
- the optical mode controlling layer 120 is formed in a round shape when the post structure P is formed, and the round-shaped opening 118 being nearly concentric with outer profile of the round shape is formed.
- the center of the opening 118 coincides with the center of the conductive portion 128 of the current confining layer 108 as described above, and coincides with the optical axis.
- transverse mode can be controlled, and single-mode laser light can be obtained.
- the light intensity distribution in which transverse mode control by the example of FIG. 2A is performed is shown in FIG. 3A . As shown in FIG. 3A , the light intensity distribution of laser light becomes a single-peaked single-mode.
- the optical mode controlling layer 120 shown in FIG. 2B has two semicircular openings 140 that are line-symmetric and divided along a center line of the round-shaped opening. By this configuration, gain at a portion where GaAs is remained becomes smaller. As shown in FIG. 3B , the light intensity distribution of laser light becomes a double-peaked single-mode having peaks that correspond to the two semicircular openings 140 .
- the optical mode controlling layer 120 shown in FIG. 2C has four fan-shaped openings 142 that are point-symmetric in which a round-shaped opening is divided into four. By this configuration, the light intensity distribution of laser light becomes a single-mode having four peaks that correspond to the openings 142 .
- the optical mode controlling layer 120 shown in FIG. 2D is formed by dividing a round-shaped opening in a direction of a straight line to form three slits 144 .
- the light intensity distribution of laser light becomes a pattern having three peaks that correspond to the three slits.
- emitted laser light is aligned in a direction of the slits 144 , which is effective in controlling polarization.
- the optical mode controlling layer 120 is capable of controlling vertical mode of laser light. In other words, by changing the diameter of the opening 118 of the optical mode controlling layer 120 , oscillation wavelength can be selected.
- FIG. 4 illustrates the relation between the diameter of the opening 118 of the optical mode controlling layer 120 and the oscillation wavelength, when the diameter of the conductive portion 128 of the current confining layer 108 is kept constant.
- the diameter of the opening 118 GaAs aperture diameter shown in the horizontal axis
- the oscillation wavelength increases from about 827 nm to 839 nm. Therefore, laser light having a desired oscillation wavelength can be obtained by selecting the diameter of the opening 118 .
- the opening 118 is formed by etching the GaAs layer that is the optical mode controlling layer.
- etching selectivity between the GaAs layer and an AlGaAs layer underlying thereof is small, and thus the underlying AlGaAs layer is over etched. This alters the thickness of the intermediate DBR 116 , which is undesirable. Therefore, in the second example, a configuration that can avoid such damage in thickness due to etching is adopted.
- FIG. 5 illustrates a schematic cross sectional view of a VCSEL according to a second example, wherein same reference numerals are used for a same configuration as that of the first example.
- a VCSEL 100A of the second example as a cap layer of the post structure P, that is, the final layer by epitaxial growth, an n-type GaAs layer 160 having a thickness of 20 nm is formed.
- the n-side electrode 122 is ohmic-contacted, and a ring shaped optical mode controlling layer 162 is formed spaced apart from the n-side electrode 122 .
- a round-shaped opening 164 is formed in a center portion of the optical mode controlling layer 162 .
- the center of the opening 164 coincides with the optical axis, and the diameter of the opening 164 is equal to or slightly smaller than the diameter of the conductive portion 128 .
- the optical mode controlling layer 162 may be made of a metal, such as gold, titanium, tungsten, or the like, and is formed with high accuracy by lift-off. In a lift-off process, a resist is etched when a resist pattern is formed. The selectivity between the resist and the GaAs layer 160 is sufficient, and the damage in thickness of the intermediate DBR 116 can be prevented.
- the GaAs layer 160 being the cap layer has an extremely thin thickness, and thus it passes light emitted in the active layer 112 .
- the light that is passed through the GaAs layer 160 is reflected off in a portion where the metal of the optical mode controlling layer 162 exists on interface thereof, and is passed through the opening 164 in which no metal exists.
- the optical mode controlling layer 162 is formed spaced apart from the n-side electrode 122 ; however, for example, in a case where gold (Au) that can be ohmic-contacted to the GaAs layer 160 is used for the n-side electrode 122 , the n-side electrode 122 and the optical mode controlling layer 162 can be formed simultaneously by lift-off, such that they are connected each other as shown in FIG. 6 .
- the optical mode controlling layer that reflects off light having an oscillation wavelength may be formed.
- the optical mode controlling layer shown in FIG. 5 may be formed of amorphous silicon. The amorphous silicon absorbs a wavelength of 1 micrometer. Therefore, similarly to a case where light is reflected off, control of transverse mode of oscillation wavelength, control of polarization, and control of vertical mode can be performed.
- the n-side electrode 122 is formed between the optical mode controlling layer 120 and the upper DBR; however, in a VCSEL 100 B according to a third example, as shown in FIG. 7 , after forming the optical mode controlling layer 120 , an n-type upper DBR 170 is formed thereon, and an n-side electrode 172 is formed thereon.
- the upper DBR 170 may be formed of semiconductor multilayer films such as ITO, and the n-side electrode 172 is electrically coupled to the optical mode controlling layer 120 through the upper DBR 170 .
- Other configuration is same as that of the first example.
- FIGS. 8A to 8C and FIGS. 9A to 9C a method for fabricating a VCSEL according to a first example will be described.
- MOCVD Metal Organic Chemical Vapor Deposition
- sequentially stacked on the p-type GaAs substrate 102 are: the p-type lower DBR 106 having a carrier concentration of 1 ⁇ 10 18 cm ⁇ 3 in which 40.5 periods of, for example, Al 0.9 Ga 0.1 As and Al 0.12 Ga 0.88 As, each having a film thickness of 1 ⁇ 4 of the wavelength in the medium, are alternately stacked; the current confining layer 108 made of p-type Al 0.98 Ga 0.02 As; the lower spacer layer 110 made of p-type Al 0.6 Ga 0.4 As; the undoped quantum well active layer (made of three GaAs quantum well layers each having a thickness of 70 nm and four Al 0.3 Ga 0.7 As barrier layers each having a thickness of 50 nm) 112 ; the
- the substrate is taken out from the chamber, and then as shown in FIG. 8B , a round-shaped photoresist pattern M is formed on the optical mode controlling layer 120 . Then, as shown in FIG. 8C , by using the photoresist pattern, the semiconductor layers are dry etched to form a cylindrical post structure P on the substrate 102 .
- the post structure P exposes at least the current confining layer 108 .
- oxidation of the substrate is performed in an oxidation furnace for a predetermined time.
- a specified distance from the side surface of the post P is oxidized, and an oxidized area 108 a is formed in the current confining layer 108 .
- the area surrounded by the oxidized area 108 a becomes the conductive portion 128 that performs current confining during operation.
- the photoresist pattern M is removed, and the insulating layer 126 of SiN or the like is formed on the entire surface of the substrate.
- the insulating layer 126 is etched by a photolithography process to form a round-shaped opening 126 a at a top portion of the post structure P, and the GaAs layer 120 is exposed.
- a top portion of the GaAs layer 120 appearing at a top portion of the post structure P is etched by a photolithography process, and as shown in FIG. 9C , a round-shaped opening 118 is formed to obtain the optical mode controlling layer 120 .
- the n-side electrode 122 is formed by lift-off.
- Au or Cu may be used.
- the dielectric multilayer films are formed by vapor deposition or electron beam deposition. In the deposition, SiO 2 and TiO 2 are alternately deposited such that each of them has a predetermined thickness, by performing thickness management using an optical monitor.
- the p-side electrode 104 is formed on a back surface of the substrate 102 . As such, a VCSEL that emits laser light having an oscillation wavelength of about 850 nm can be obtained.
- the thickness of the GaAs layer being the final layer is made to 20 nm, and after that, an optical mode controlling layer that absorbs or reflects off light having an oscillation wavelength is formed on the GaAs layer by a photolithography process.
- a single post structure P is formed on the substrate; however, the VCSEL may be of a multi-beam or multi-spot type in which plural post structures P are formed on the substrate, and laser light is emitted from the plural post structures P.
- a VCSEL in which an AlGaAs system is used is used; however, the present invention can also be applicable to a VCSEL in which other III-V group compound semiconductor is used.
- the shape of the post structure may be rectangular, other than cylindrical shape.
- FIG. 10A is a cross sectional view illustrating a configuration of a package (module) in which a VCSEL is mounted.
- a chip 310 in which a VCSEL is formed is fixed on a disk-shaped metal stem 330 through a conductive adhesive 320 .
- Conductive leads 340 , 342 are inserted into through holes (not shown) in the stem 330 .
- One lead 340 is electrically coupled to an n-side electrode of the VCSEL, and the other lead 342 is electrically coupled to a p-side electrode.
- a rectangular hollow cap 350 is fixed to contain the chip 310 , and a ball lens 360 is fixed in a center opening of the cap 350 .
- the optical axis of the ball lens 360 is positioned to match an approximate center of the chip 310 .
- a forward voltage is applied between the leads 340 and 342 , laser light is emitted vertically from the chip 310 .
- the distance between the chip 310 and the ball lens 360 may be adjusted so that the ball lens 360 is contained within the divergence angle ⁇ of the laser light from the chip 310 .
- a light sensing element or a thermal sensor may be contained to monitor the emitting status of the VCSEL.
- FIG. 10B illustrates a configuration of another package.
- a flat-plate glass 362 is fixed in a center portion of the cap 350 .
- the center of the flat-plate glass 362 is positioned to match an approximate center of the chip 310 .
- the distance between the chip 310 and the flat-plate glass 362 may be adjusted so that the opening diameter of the flat-plate glass 362 is equal to or greater than the divergence angle ⁇ of the laser light from the chip 310 .
- FIG. 11 illustrates an example in which a VCSEL is used as a light source.
- a light source apparatus 370 includes the package 300 in which a VCSEL is implemented as in FIG. 10A or FIG. 10B , a collimator lens 372 that receives multi-beam laser light emitted from the package 300 , a polygon mirror 374 that rotates at a certain speed and reflects off light rays from the collimator lens 372 with a certain divergence angle, an f ⁇ lens 376 that receives laser light from the polygon mirror 374 and projects the light on a reflective mirror 378 , a line-shaped reflective mirror 378 , and a light sensitive drum 380 that forms a latent image based on the reflected light from the reflective mirror 378 .
- a VCSEL can be used as a light source for an optical data processing apparatus, such as a copy machine or printer, equipped with an optical system that collects laser light from the VCSEL onto a light sensitive drum, and a mechanism that scans the collected laser light on the light sensitive drum.
- an optical data processing apparatus such as a copy machine or printer
- FIG. 12 is a cross sectional view illustrating a configuration in which the module shown in FIG. 10A is applied to a light sending device.
- a light sending device 400 includes a cylindrical housing 410 fixed to the stem 330 , a sleeve 420 formed integrally with the housing 410 on an edge surface thereof, a ferrule 430 held in an opening 422 of the sleeve 420 , and an optical fiber 440 held by the ferrule 430 .
- a flange 332 formed in a direction of the circumference of the stem 330 , an edge portion of the housing 410 is fixed.
- the ferrule 430 is positioned exactly in the opening 422 of the sleeve 420 .
- the optical axis of the optical fiber 440 is aligned with the optical axis of the ball lens 360 .
- the core of the optical fiber 440 is held.
- Laser light emitted from the surface of the chip 310 is concentrated by the ball lens 360 .
- the concentrated light is injected into the core of the optical fiber 440 , and transmitted.
- the ball lens 360 is used in the above example, other lens such as a biconvex lens or a plano-convex lens may be used.
- the light sending device 400 may include a driving circuit for applying an electrical signal to the leads 340 , 342 .
- the light sending device 400 may have a receiving function for receiving an optical signal via the optical fiber 440 .
- FIG. 13 illustrates a configuration in which the module shown in FIG. 12 is used in a spatial transmission system.
- a spatial transmission system 500 includes a package 300 , a condensing lens 510 , a diffusing plate 520 , and a reflective mirror 530 .
- the light concentrated by the condensing lens 510 is reflected off the diffusing plate 520 through an opening 532 of the reflective mirror 530 .
- the reflected light is reflected toward the reflective mirror 530 .
- the reflective mirror 530 reflects off the reflected light toward a predetermined direction to perform optical transmission.
- FIG. 14A illustrates an exemplary configuration of an optical transmission system in which a VCSEL is used as a light source.
- An optical transmission system 600 includes a light source 610 that contains the chip 310 in which a VCSEL is formed, an optical system 620 , for example, for concentrating laser light emitted from the light source 610 , a light receiver 630 for receiving laser light outputted from the optical system 620 , and a controller 640 for controlling the driving of the light source 610 .
- the controller 640 provides a driving pulse signal for driving the VCSEL to the light source 610 .
- the light emitted from the light source 610 is transmitted through the optical system 620 to the light receiver 630 by an optical fiber or a reflective mirror for spatial transmission.
- the light receiver 630 may detect the received light by a photo-detector, for example.
- the light receiver 630 is capable of controlling operations (for example, the start timing of optical transmission) of the controller 640 , by a control signal 650 .
- FIG. 14B illustrates a general configuration of an optical transmission apparatus used for an optical transmission system.
- An optical transmission apparatus 700 includes a case 710 , an optical signal transmitting/receiving connector 720 , a light emitting/light receiving element 730 , an electrical signal cable connector 740 , a power input 750 , an LED 760 for indicating normal operation, an LED 770 for indicating an abnormality, and a DVI connector 780 .
- a transmitting circuit board/receiving circuit board is contained inside the apparatus.
- a video transmission system is shown in FIG. 15 in which the optical transmission apparatus 700 is used.
- a video transmission system 800 uses the optical transmission apparatus shown in FIG. 14B for transmitting a video signal generated at a video signal generator 810 to an image display 820 such as a liquid crystal display. More specifically, the video transmission system 800 includes the video signal generator 810 , the image display 820 , an electrical cable 830 for DVI, a transmitting module 840 , a receiving module 850 , a connector 860 for a video signal transmission optical signal, an optical fiber 870 , an electrical cable connector 880 for a control signal, a power adapter 890 , and an electrical cable 900 for DVI.
- a surface emitting semiconductor laser according to the present invention can be used in fields such as an optical data processing, or optical high speed data communication.
Abstract
A surface emitting semiconductor laser includes a substrate, a lower reflective mirror formed on the substrate, an active layer formed on the lower reflective mirror, an upper reflective mirror formed on the active layer, an optical mode controlling layer formed between the lower reflective mirror and the upper reflective mirror, and a current confining layer formed between the lower reflective mirror and the upper reflective mirror. The active layer emits light. The upper reflective mirror forms a resonator between the lower reflective mirror and the upper reflective mirror. In the optical mode controlling layer, an opening is formed for selectively absorbing or reflecting off light that is emitted in the active layer. The optical mode controlling layer optically controls mode of laser light. The current confining layer confines current that is applied during driving.
Description
- This application is a division of U.S. application Ser. No. 11/946,327 filed Nov. 28, 2007, which is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2007-126571 filed May 11, 2007.
- 1. Technical Field
- This invention relates to a surface emitting semiconductor laser, a method for fabricating a surface emitting semiconductor laser, a module, a light source apparatus, a data processing apparatus, a light sending apparatus, an optical spatial transmission apparatus, and an optical spatial transmission system.
- 2. Related Art
- In technical fields such as optical communication or optical storage, there has been a growing interest in surface emitting semiconductor lasers, i.e., Vertical-Cavity Surface-Emitting Lasers (hereinafter referred to as VCSELs). VCSELs have excellent characteristics which edge-emitting semiconductor lasers do not have. For example, VCSELs feature lower threshold current and smaller power consumption. With VCSELs, a round light spot can be easily obtained, and evaluation can be performed while they are on a wafer, and light sources can be arranged in two dimensional arrays. With these characteristics, demands for VCSELs as light sources in the communication field have especially been expected to grow.
- In a case where a VCSEL is used as a light source or the like for optical transmission, selection of mode of laser light is required. For example, in a case where a VCSEL is coupled to an optical fiber and a long-distance communication is to be performed, single-mode is more preferable. To obtain single-mode, in general, it is required to make the diameter of a current confining layer of the VCSEL to about 3 to 4 micrometers.
- For a VCSEL of a selective oxidation type, AlAs or AlGaAs having a high Al-composition is used for the current confining layer, and a portion of the current confining layer is oxidized to form an aperture in the current confining layer. Because the aperture is formed by an oxidizing reaction of Al, it is difficult to accurately control the diameter, and especially, it is difficult to reproduce a small aperture diameter for obtaining single-mode, resulting in a reduction in yield of the VCSEL.
- The present invention aims to provide a surface emitting semiconductor laser in which mode control can be performed more effectively than the mode control by surface processing of a light emitting surface of a related art, and a module, a light source apparatus, a data processing apparatus, a light sending apparatus, an optical spatial transmission apparatus, and an optical spatial transmission system, which use the surface emitting semiconductor laser, and a method for fabricating a surface emitting semiconductor laser.
- An aspect of the present invention provides a surface emitting semiconductor laser including a substrate; a lower reflective mirror formed on the substrate; an active layer formed on the lower reflective mirror, and emitting light; an upper reflective mirror formed on the active layer, and forming a resonator between the lower reflective mirror and the upper reflective mirror; an optical mode controlling layer formed between the lower reflective mirror and the upper reflective mirror, and optically controlling mode of laser light; and a current confining layer formed between the lower reflective mirror and the upper reflective mirror, and confining current that is applied during driving. In the optical mode controlling layer, an opening is formed for selectively absorbing or reflecting off light that is emitted in the active layer.
- Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
-
FIGS. 1A and 1B are cross sectional views illustrating a configuration of a VCSEL according to a first example of the present invention, whereinFIG. 1A illustrates a status before an upper DBR is formed, andFIG. 1B illustrates a status after the upper DBR is formed; -
FIGS. 2A to 2D are plan views illustrating a profile of an optical mode controlling layer; -
FIGS. 3A and 3B illustrate light intensity distributions in which transverse mode control is performed by an optical mode controlling layer; -
FIG. 4 is a graph illustrating the relation between the diameter of the opening of the optical mode controlling layer and the oscillation wavelength; -
FIG. 5 is a schematic cross sectional view illustrating a configuration of a VCSEL according to a second example of the present invention; -
FIG. 6 is a schematic cross sectional view illustrating a modified example of a VCSEL according to a second example of the present invention; -
FIG. 7 is a schematic cross sectional view illustrating a configuration of a VCSEL according to a third example of the present invention; -
FIGS. 8A to 8C are cross sectional views illustrating a process of a method for fabricating a VCSEL according to a first example of the present invention; -
FIGS. 9A to 9C are cross sectional views illustrating a process of a method for fabricating a VCSEL according to a first example of the present invention; -
FIGS. 10A and 10B are schematic cross sectional views each illustrating a configuration of a module in which an optical component is implemented in a VCSEL of according to an example; -
FIG. 11 illustrates an example of a configuration of a light source apparatus in which a VCSEL is used; -
FIG. 12 is a schematic cross sectional view illustrating a configuration of a light sending apparatus in which the module shown inFIG. 10A is used; -
FIG. 13 illustrates a configuration in which the module shown inFIG. 10A is used for an optical transmission system; -
FIG. 14A illustrates a block diagram of a configuration of an optical transmission system; -
FIG. 14B illustrates an outer configuration of an optical transmission apparatus; and -
FIG. 15 illustrates a video transmission system in which the optical transmission apparatus ofFIG. 14B is used. - Referring to the accompanying drawings, exemplary embodiments for implementing the present invention will be now described.
-
FIG. 1A andFIG. 1B are schematic cross sectional views illustrating a configuration of a VCSEL according to an example of the present invention. A VCSEL 100 according to an example includes a p-side electrode 104 on a back surface of a p-type GaAs substrate 102. Stacked on thesubstrate 102 are: a lower DBR (Distributed Bragg Reflector) 106 that composes a reflective mirror of multilayer films in which two types of p-type AlxGa1-xAs having different x values are overlaid one another; acurrent confining layer 108 made of p-type Al0.98Ga0.02As; a p-typelower spacer layer 110; anactive layer 112 having a quantum well structure; an n-typeupper spacer layer 114; anintermediate DBR 116 that composes a partial reflective mirror of multilayer films in which a few periods of two types of n-type AlxGa1-xAs having different x values are overlaid; an optical mode controllinglayer 120 made of n-type GaAs, in which anopening 118 is formed at a center portion thereof; an n-side electrode 122 ohmic-contacted to the optical mode controllinglayer 120; anupper DBR 124 that composes a reflective mirror of dielectric multilayer films in which SiO2 and TiO2 are alternately stacked; and aninsulating layer 126 of SiN or the like that covers a bottom portion, a side surface, and a portion of a top portion of a post structure P formed on thesubstrate 102. - The semiconductor layers on the substrate from the
lower DBR 106 to the optical mode controllinglayer 120 are formed by a series of epitaxial growth. Then, by etching the semiconductor layers from the optical mode controllinglayer 120 to thelower DBR 106, a cylindrical post structure P is formed. The optical mode controllinglayer 120 being the uppermost layer of the post structure P is a GaAs layer. By not exposing Al on the surface, oxidation is prevented. - After the post structure P is formed, the current confining
layer 108 is oxidized from the side surface of the post structure P. The current confininglayer 108 has a higher Al-composition than other semiconductor layers do, and thus has a higher oxidation speed than other semiconductor layers. By this oxidation, a highly reflective portion is formed at periphery of the current confininglayer 108, and aconductive portion 128 surrounded by the highly reflective portion is formed. Theconductive portion 128 confines current during operation, and the diameter thereof may be about 8 to 6 micrometers. The current confining layer may be made of AlAs. - The optical
mode controlling layer 120 performs light absorption or light reflection of oscillation wavelength near theactive layer 112 that is sandwiched between thelower DBR 106 and theupper DBR 124. Alternatively, the opticalmode controlling layer 120 may change refractive index near theactive layer 112 that is sandwiched between thelower DBR 106 and theupper DBR 124. The opticalmode controlling layer 120 controls lasing mode, especially controls transverse mode, by optically absorbing or reflecting off light. - In the VCSEL of this example, the oscillation at around 850 nm is contemplated, and the thickness of the optical
mode controlling layer 120 is about 200 nm. Theopening 118 is formed by etching the GaAs layer at a center portion of the opticalmode controlling layer 120. In theopening 118, absorption of light of 850 nm does not occur; however, at a portion where GaAs is remained, light absorption occurs, and thus gain is reduced during laser oscillation. - The
opening 118 of the opticalmode controlling layer 120 is formed by a photolithography process. By this process, theopening 118 may become an accurate pattern depending on the accuracy of the photolithography. Each of the centers of theopening 118 and theconductive portion 128 coincides with an optical axis. Preferably, the diameter of theopening 118 is 4 to 3 micrometers, and smaller than the diameter of theconductive portion 128. By accurately forming the diameter of theopening 118, the control of lasing mode can be more accurately performed. - The optical
mode controlling layer 120 is disposed in proximity to theactive layer 112 through theintermediate DBR 116. Theintermediate DBR 116 is interposed to perform gettering of gold or the like diffused from the n-side electrode 122 that is ohmic-contacted to the opticalmode controlling layer 120. However, the opticalmode controlling layer 120 may be formed on theactive layer 112 or theupper spacer layer 114. The opticalmode controlling layer 120 is formed in a gain medium, not on the top surface being the light emitting surface of laser light, and thus lasing mode can be extremely effectively controlled. In other words, a slight change in shape of theopening 118 can significantly affect lasing mode. -
FIGS. 2A to 2D are plan views of examples of a profile of an optical mode controlling layer. The optical mode controlling layer shown inFIGS. 2A to 2C controls mainly transverse mode, and the optical mode controlling layer shown inFIG. 2D controls mainly polarization. - In
FIG. 2A , the opticalmode controlling layer 120 is formed in a round shape when the post structure P is formed, and the round-shapedopening 118 being nearly concentric with outer profile of the round shape is formed. The center of theopening 118 coincides with the center of theconductive portion 128 of the current confininglayer 108 as described above, and coincides with the optical axis. By making the diameter of theopening 118 nearly equal to or smaller than the diameter of theconductive portion 128, transverse mode can be controlled, and single-mode laser light can be obtained. The light intensity distribution in which transverse mode control by the example ofFIG. 2A is performed is shown inFIG. 3A . As shown inFIG. 3A , the light intensity distribution of laser light becomes a single-peaked single-mode. - The optical
mode controlling layer 120 shown inFIG. 2B has twosemicircular openings 140 that are line-symmetric and divided along a center line of the round-shaped opening. By this configuration, gain at a portion where GaAs is remained becomes smaller. As shown inFIG. 3B , the light intensity distribution of laser light becomes a double-peaked single-mode having peaks that correspond to the twosemicircular openings 140. - The optical
mode controlling layer 120 shown inFIG. 2C has four fan-shapedopenings 142 that are point-symmetric in which a round-shaped opening is divided into four. By this configuration, the light intensity distribution of laser light becomes a single-mode having four peaks that correspond to theopenings 142. - The optical
mode controlling layer 120 shown inFIG. 2D is formed by dividing a round-shaped opening in a direction of a straight line to form threeslits 144. By this configuration, the light intensity distribution of laser light becomes a pattern having three peaks that correspond to the three slits. In addition, emitted laser light is aligned in a direction of theslits 144, which is effective in controlling polarization. - Other than the control of transverse mode or polarization of laser light as described above, the optical
mode controlling layer 120 is capable of controlling vertical mode of laser light. In other words, by changing the diameter of theopening 118 of the opticalmode controlling layer 120, oscillation wavelength can be selected. -
FIG. 4 illustrates the relation between the diameter of theopening 118 of the opticalmode controlling layer 120 and the oscillation wavelength, when the diameter of theconductive portion 128 of the current confininglayer 108 is kept constant. As obvious fromFIG. 4 , when the diameter of the opening 118 (GaAs aperture diameter shown in the horizontal axis) is increased from 6 micrometers to 10 micrometers, in approximate proportion to the increase, the oscillation wavelength increases from about 827 nm to 839 nm. Therefore, laser light having a desired oscillation wavelength can be obtained by selecting the diameter of theopening 118. - A second example of the present invention will be now described. In the first example, the
opening 118 is formed by etching the GaAs layer that is the optical mode controlling layer. However, etching selectivity between the GaAs layer and an AlGaAs layer underlying thereof is small, and thus the underlying AlGaAs layer is over etched. This alters the thickness of theintermediate DBR 116, which is undesirable. Therefore, in the second example, a configuration that can avoid such damage in thickness due to etching is adopted. -
FIG. 5 illustrates a schematic cross sectional view of a VCSEL according to a second example, wherein same reference numerals are used for a same configuration as that of the first example. In aVCSEL 100A of the second example, as a cap layer of the post structure P, that is, the final layer by epitaxial growth, an n-type GaAs layer 160 having a thickness of 20 nm is formed. On the periphery of theGaAs layer 160, the n-side electrode 122 is ohmic-contacted, and a ring shaped opticalmode controlling layer 162 is formed spaced apart from the n-side electrode 122. In a center portion of the opticalmode controlling layer 162, a round-shapedopening 164 is formed. The center of theopening 164 coincides with the optical axis, and the diameter of theopening 164 is equal to or slightly smaller than the diameter of theconductive portion 128. The opticalmode controlling layer 162 may be made of a metal, such as gold, titanium, tungsten, or the like, and is formed with high accuracy by lift-off. In a lift-off process, a resist is etched when a resist pattern is formed. The selectivity between the resist and theGaAs layer 160 is sufficient, and the damage in thickness of theintermediate DBR 116 can be prevented. - The
GaAs layer 160 being the cap layer has an extremely thin thickness, and thus it passes light emitted in theactive layer 112. The light that is passed through theGaAs layer 160 is reflected off in a portion where the metal of the opticalmode controlling layer 162 exists on interface thereof, and is passed through theopening 164 in which no metal exists. By this configuration, similarly to the case of the first example, control of transverse mode, control of polarization, and control of vertical mode of laser light being oscillated can be performed. - In the example shown in
FIG. 5 , the opticalmode controlling layer 162 is formed spaced apart from the n-side electrode 122; however, for example, in a case where gold (Au) that can be ohmic-contacted to theGaAs layer 160 is used for the n-side electrode 122, the n-side electrode 122 and the opticalmode controlling layer 162 can be formed simultaneously by lift-off, such that they are connected each other as shown inFIG. 6 . - In addition, in the second example, the optical mode controlling layer that reflects off light having an oscillation wavelength; however, an optical mode controlling layer that absorbs light having an oscillation wavelength may be formed. For example, if the oscillation wavelength is around 1 micrometer, the optical mode controlling layer shown in
FIG. 5 may be formed of amorphous silicon. The amorphous silicon absorbs a wavelength of 1 micrometer. Therefore, similarly to a case where light is reflected off, control of transverse mode of oscillation wavelength, control of polarization, and control of vertical mode can be performed. - A third example of the present invention will be now described. In the first example, the n-
side electrode 122 is formed between the opticalmode controlling layer 120 and the upper DBR; however, in aVCSEL 100B according to a third example, as shown inFIG. 7 , after forming the opticalmode controlling layer 120, an n-typeupper DBR 170 is formed thereon, and an n-side electrode 172 is formed thereon. Theupper DBR 170 may be formed of semiconductor multilayer films such as ITO, and the n-side electrode 172 is electrically coupled to the opticalmode controlling layer 120 through theupper DBR 170. Other configuration is same as that of the first example. - Referring now to
FIGS. 8A to 8C andFIGS. 9A to 9C , a method for fabricating a VCSEL according to a first example will be described. As shown inFIG. 8A , by Metal Organic Chemical Vapor Deposition (MOCVD), sequentially stacked on the p-type GaAs substrate 102 are: the p-typelower DBR 106 having a carrier concentration of 1×1018 cm−3 in which 40.5 periods of, for example, Al0.9Ga0.1As and Al0.12Ga0.88As, each having a film thickness of ¼ of the wavelength in the medium, are alternately stacked; the current confininglayer 108 made of p-type Al0.98Ga0.02As; thelower spacer layer 110 made of p-type Al0.6Ga0.4As; the undoped quantum well active layer (made of three GaAs quantum well layers each having a thickness of 70 nm and four Al0.3Ga0.7As barrier layers each having a thickness of 50 nm) 112; theupper spacer layer 114 made of n-type Al0.6Ga0.4As; the n-typeintermediate DBR 116 in which plural periods of Al0.9Ga0.1As and Al0.15Ga0.85As, each having a film thickness of ¼ of the wavelength in the medium, are alternately stacked; the n-type GaAs layer (optical mode controlling layer) 120 having a carrier concentration of 1×1019 cm−3 and thickness of 200 nm. - After stopping the epitaxial growth, the substrate is taken out from the chamber, and then as shown in
FIG. 8B , a round-shaped photoresist pattern M is formed on the opticalmode controlling layer 120. Then, as shown inFIG. 8C , by using the photoresist pattern, the semiconductor layers are dry etched to form a cylindrical post structure P on thesubstrate 102. The post structure P exposes at least the current confininglayer 108. - Then, as shown in
FIG. 9A , oxidation of the substrate is performed in an oxidation furnace for a predetermined time. By this oxidation, a specified distance from the side surface of the post P is oxidized, and anoxidized area 108 a is formed in the current confininglayer 108. The area surrounded by the oxidizedarea 108 a becomes theconductive portion 128 that performs current confining during operation. - Then, the photoresist pattern M is removed, and the insulating
layer 126 of SiN or the like is formed on the entire surface of the substrate. After that, as shown inFIG. 9B , the insulatinglayer 126 is etched by a photolithography process to form a round-shapedopening 126 a at a top portion of the post structure P, and theGaAs layer 120 is exposed. - Then, a top portion of the
GaAs layer 120 appearing at a top portion of the post structure P is etched by a photolithography process, and as shown inFIG. 9C , a round-shapedopening 118 is formed to obtain the opticalmode controlling layer 120. - Then, on the optical
mode controlling layer 120, the n-side electrode 122 is formed by lift-off. For a material for the electrode, Au or Cu may be used. Then, on the opticalmode controlling layer 120, theupper DBR 124 of dielectric multilayer films made of SiO2 and TiO2, which are dielectric and alternately stacked, is formed. The dielectric multilayer films are formed by vapor deposition or electron beam deposition. In the deposition, SiO2 and TiO2 are alternately deposited such that each of them has a predetermined thickness, by performing thickness management using an optical monitor. Finally, on a back surface of thesubstrate 102, the p-side electrode 104 is formed. As such, a VCSEL that emits laser light having an oscillation wavelength of about 850 nm can be obtained. - For a material of the layer that performs mode control, other than GaAs, a material that is lattice matched, such as InGaAs, can be used instead. For a VCSEL according to the second example, the thickness of the GaAs layer being the final layer is made to 20 nm, and after that, an optical mode controlling layer that absorbs or reflects off light having an oscillation wavelength is formed on the GaAs layer by a photolithography process.
- In the examples described above, a single post structure P is formed on the substrate; however, the VCSEL may be of a multi-beam or multi-spot type in which plural post structures P are formed on the substrate, and laser light is emitted from the plural post structures P. In addition, in the examples described above, a VCSEL in which an AlGaAs system is used; however, the present invention can also be applicable to a VCSEL in which other III-V group compound semiconductor is used. In addition, the shape of the post structure may be rectangular, other than cylindrical shape.
- Referring to drawings, a module, a light sending apparatus, a spatial transmission system, an optical transmission apparatus or the like, which use a VCSEL of an example, will be described.
FIG. 10A is a cross sectional view illustrating a configuration of a package (module) in which a VCSEL is mounted. In apackage 300, achip 310 in which a VCSEL is formed is fixed on a disk-shapedmetal stem 330 through aconductive adhesive 320. Conductive leads 340, 342 are inserted into through holes (not shown) in thestem 330. Onelead 340 is electrically coupled to an n-side electrode of the VCSEL, and theother lead 342 is electrically coupled to a p-side electrode. - On the
stem 330, a rectangularhollow cap 350 is fixed to contain thechip 310, and aball lens 360 is fixed in a center opening of thecap 350. The optical axis of theball lens 360 is positioned to match an approximate center of thechip 310. When a forward voltage is applied between theleads chip 310. The distance between thechip 310 and theball lens 360 may be adjusted so that theball lens 360 is contained within the divergence angle θ of the laser light from thechip 310. In addition, in the cap, a light sensing element or a thermal sensor may be contained to monitor the emitting status of the VCSEL. -
FIG. 10B illustrates a configuration of another package. In apackage 302 shown inFIG. 10B , instead of using theball lens 360, a flat-plate glass 362 is fixed in a center portion of thecap 350. The center of the flat-plate glass 362 is positioned to match an approximate center of thechip 310. The distance between thechip 310 and the flat-plate glass 362 may be adjusted so that the opening diameter of the flat-plate glass 362 is equal to or greater than the divergence angle θ of the laser light from thechip 310. -
FIG. 11 illustrates an example in which a VCSEL is used as a light source. A light source apparatus 370 includes thepackage 300 in which a VCSEL is implemented as inFIG. 10A orFIG. 10B , acollimator lens 372 that receives multi-beam laser light emitted from thepackage 300, apolygon mirror 374 that rotates at a certain speed and reflects off light rays from thecollimator lens 372 with a certain divergence angle, anfθ lens 376 that receives laser light from thepolygon mirror 374 and projects the light on areflective mirror 378, a line-shapedreflective mirror 378, and a lightsensitive drum 380 that forms a latent image based on the reflected light from thereflective mirror 378. As such, a VCSEL can be used as a light source for an optical data processing apparatus, such as a copy machine or printer, equipped with an optical system that collects laser light from the VCSEL onto a light sensitive drum, and a mechanism that scans the collected laser light on the light sensitive drum. -
FIG. 12 is a cross sectional view illustrating a configuration in which the module shown inFIG. 10A is applied to a light sending device. Alight sending device 400 includes acylindrical housing 410 fixed to thestem 330, asleeve 420 formed integrally with thehousing 410 on an edge surface thereof, aferrule 430 held in anopening 422 of thesleeve 420, and anoptical fiber 440 held by theferrule 430. In aflange 332 formed in a direction of the circumference of thestem 330, an edge portion of thehousing 410 is fixed. Theferrule 430 is positioned exactly in theopening 422 of thesleeve 420. The optical axis of theoptical fiber 440 is aligned with the optical axis of theball lens 360. In a throughhole 432 of theferrule 430, the core of theoptical fiber 440 is held. - Laser light emitted from the surface of the
chip 310 is concentrated by theball lens 360. The concentrated light is injected into the core of theoptical fiber 440, and transmitted. While theball lens 360 is used in the above example, other lens such as a biconvex lens or a plano-convex lens may be used. In addition, thelight sending device 400 may include a driving circuit for applying an electrical signal to theleads light sending device 400 may have a receiving function for receiving an optical signal via theoptical fiber 440. -
FIG. 13 illustrates a configuration in which the module shown inFIG. 12 is used in a spatial transmission system. Aspatial transmission system 500 includes apackage 300, a condensinglens 510, a diffusingplate 520, and areflective mirror 530. The light concentrated by the condensinglens 510 is reflected off the diffusingplate 520 through anopening 532 of thereflective mirror 530. The reflected light is reflected toward thereflective mirror 530. Thereflective mirror 530 reflects off the reflected light toward a predetermined direction to perform optical transmission. -
FIG. 14A illustrates an exemplary configuration of an optical transmission system in which a VCSEL is used as a light source. Anoptical transmission system 600 includes alight source 610 that contains thechip 310 in which a VCSEL is formed, anoptical system 620, for example, for concentrating laser light emitted from thelight source 610, alight receiver 630 for receiving laser light outputted from theoptical system 620, and acontroller 640 for controlling the driving of thelight source 610. Thecontroller 640 provides a driving pulse signal for driving the VCSEL to thelight source 610. The light emitted from thelight source 610 is transmitted through theoptical system 620 to thelight receiver 630 by an optical fiber or a reflective mirror for spatial transmission. Thelight receiver 630 may detect the received light by a photo-detector, for example. Thelight receiver 630 is capable of controlling operations (for example, the start timing of optical transmission) of thecontroller 640, by acontrol signal 650. -
FIG. 14B illustrates a general configuration of an optical transmission apparatus used for an optical transmission system. An optical transmission apparatus 700 includes acase 710, an optical signal transmitting/receivingconnector 720, a light emitting/light receiving element 730, an electricalsignal cable connector 740, apower input 750, anLED 760 for indicating normal operation, anLED 770 for indicating an abnormality, and aDVI connector 780. Inside the apparatus, a transmitting circuit board/receiving circuit board is contained. - A video transmission system is shown in
FIG. 15 in which the optical transmission apparatus 700 is used. A video transmission system 800 uses the optical transmission apparatus shown inFIG. 14B for transmitting a video signal generated at avideo signal generator 810 to animage display 820 such as a liquid crystal display. More specifically, the video transmission system 800 includes thevideo signal generator 810, theimage display 820, anelectrical cable 830 for DVI, a transmittingmodule 840, a receivingmodule 850, aconnector 860 for a video signal transmission optical signal, anoptical fiber 870, anelectrical cable connector 880 for a control signal, apower adapter 890, and anelectrical cable 900 for DVI. - A surface emitting semiconductor laser according to the present invention can be used in fields such as an optical data processing, or optical high speed data communication.
- The foregoing description of the examples has been provided for the purposes of illustration and description, and it is not intended to limit the scope of the invention. It should be understood that the invention may be implemented by other methods within the scope of the invention that satisfies requirements of a configuration of the present invention.
Claims (3)
1. A method for fabricating a surface emitting semiconductor laser, comprising:
stacking semiconductor layers that include at least a lower reflective mirror, a current confining layer, and an active layer, on a substrate;
forming an optical mode controlling layer that optically controls mode of laser light by forming an opening on the uppermost layer of the stacked semiconductor layers by a photolithography process; and
forming an upper reflective mirror that composes a resonator between the lower reflective mirror and thereof, on the optical mode controlling layer.
2. The method for fabricating a surface emitting semiconductor laser according to claim 1 , the method further comprising:
forming a post structure that extends from at least the optical mode controlling layer to the current confining layer, on the substrate; and
forming a conductive portion surrounded by an oxidized area by oxidizing a portion of the current confining layer from a side surface of the post structure.
3. The fabrication method according to claim 1 , wherein the lower reflective mirror, the active layer, the current confining layer, and the optical mode controlling layer are formed by epitaxial growth.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US13/078,031 US20110183450A1 (en) | 2007-05-11 | 2011-04-01 | Surface emitting semiconductor laser, method for fabricating surface emitting semiconductor laser, module, light source apparatus, data processing apparatus, light sending apparatus, optical spatial transmission apparatus, and optical spatial transmission system |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
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JP2007126571A JP2008283028A (en) | 2007-05-11 | 2007-05-11 | Surface light emission type semiconductor laser, manufacturing method of the same, module, light source device, information processing apparatus, optical transmission apparatus, optical space transmission apparatus, and optical space transmission system |
JP2007-126571 | 2007-05-11 | ||
US11/946,327 US7944957B2 (en) | 2007-05-11 | 2007-11-28 | Surface emitting semiconductor laser, method for fabricating surface emitting semiconductor laser, module, light source apparatus, data processing apparatus, light sending apparatus, optical spatial transmission apparatus, and optical spatial transmission system |
US13/078,031 US20110183450A1 (en) | 2007-05-11 | 2011-04-01 | Surface emitting semiconductor laser, method for fabricating surface emitting semiconductor laser, module, light source apparatus, data processing apparatus, light sending apparatus, optical spatial transmission apparatus, and optical spatial transmission system |
Related Parent Applications (1)
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US13/078,031 Abandoned US20110183450A1 (en) | 2007-05-11 | 2011-04-01 | Surface emitting semiconductor laser, method for fabricating surface emitting semiconductor laser, module, light source apparatus, data processing apparatus, light sending apparatus, optical spatial transmission apparatus, and optical spatial transmission system |
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JP (1) | JP2008283028A (en) |
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Also Published As
Publication number | Publication date |
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CN101304157A (en) | 2008-11-12 |
CN101304157B (en) | 2012-09-05 |
JP2008283028A (en) | 2008-11-20 |
KR20080100118A (en) | 2008-11-14 |
US20080279229A1 (en) | 2008-11-13 |
US7944957B2 (en) | 2011-05-17 |
KR101121114B1 (en) | 2012-03-19 |
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