WO2000076035A1 - Optical amplifier - Google Patents

Optical amplifier Download PDF

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Publication number
WO2000076035A1
WO2000076035A1 PCT/FR2000/001584 FR0001584W WO0076035A1 WO 2000076035 A1 WO2000076035 A1 WO 2000076035A1 FR 0001584 W FR0001584 W FR 0001584W WO 0076035 A1 WO0076035 A1 WO 0076035A1
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WO
WIPO (PCT)
Prior art keywords
optical amplifier
amplifier according
optical
cavity
signal
Prior art date
Application number
PCT/FR2000/001584
Other languages
French (fr)
Inventor
Serge Gidon
Original Assignee
Commissariat A L'energie Atomique
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Publication date
Application filed by Commissariat A L'energie Atomique filed Critical Commissariat A L'energie Atomique
Priority to EP00940470A priority Critical patent/EP1183757A1/en
Publication of WO2000076035A1 publication Critical patent/WO2000076035A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2308—Amplifier arrangements, e.g. MOPA
    • H01S3/2316—Cascaded amplifiers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06754—Fibre amplifiers
    • H01S3/06758—Tandem amplifiers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/1608—Solid materials characterised by an active (lasing) ion rare earth erbium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/1611—Solid materials characterised by an active (lasing) ion rare earth neodymium

Definitions

  • the invention relates to an optical amplifier.
  • the invention • finds a particularly advantageous application in various fields such as, for example, the field of telecommunications by optical fibers or even the field of marking in ocular safety.
  • optical signals are transmitted using optical fibers arranged in the form of networks.
  • the optical signals thus transmitted need to be amplified, either because of the linear attenuation due to the propagation in the fibers, or because of the successive divisions of the signal due to the various ramifications of the network.
  • This amplification of the optical signal is carried out by means of electronic amplifiers or by means of optical amplifiers.
  • FIG. 1 describes the structure of an optical amplifier according to the known art.
  • the optical amplifier comprises, cascades in series, a first isolator 1, a first optical fiber 2, a first multiplexer 3, a second optical fiber 5, a second multiplexer 6 and a second isolator 8.
  • the optical fibers 2 and 5 are the more often doped with 'Erbium ions.
  • a first pump diode 4, placed on a channel of the first multiplexer 3, sends a first pump signal, for example at the wavelength of 0.98 ⁇ , in the fiber 2.
  • a second pump diode 7, placed on a channel of the second multiplexer 6, sends a second signal of the pump, for example at the wavelength of 1.48 ⁇ m, in the fiber 5.
  • the first and second pump signals create a population inversion of the Erbium ions, thereby making these ions active.
  • the optical fibers 2 and 5 are generally of a different nature from each other in order to widen the bandwidth of the amplification.
  • the isolators 1 and 8 make it possible to avoid the establishment of parasitic reflections and, consequently, the appearance of parasitic oscillations.
  • Optical fibers have the lowest attenuation for signals whose wavelength is around 1.5 ⁇ m. The wavelength used for the propagation of signals over optical fibers is thus chosen so as to be around 1.5 ⁇ m.
  • the Erbium ions are practically the only ones capable of producing a laser emission around 1.5 ⁇ m. This is the reason why the Erbium ions are chosen to make the amplifier.
  • Erbium ions require significant pump power to reach the level of population inversion necessary for a laser effect.
  • the silica fibers cannot be heavily doped. It is then necessary - to use a relatively high pump signal power, for example 100 / cm 2 , to 'reach the threshold of the laser effect. Long optical fibers (several tens of meters) are then necessary to obtain amplification factors of the order of 20 dB.
  • the invention does not have this drawback.
  • the invention relates to an optical amplifier for amplifying an optical signal by stimulated emission of rare earth ions made active under the action of a pump signal.
  • the optical amplifier comprises a laser cavity consisting of two mirrors, one of which is an output mirror for the amplified optical signal, the cavity containing optical amplification means doped with rare earth ions and mode conversion means to pump rare earth ions.
  • all the energy originating from the pump signal ends up being absorbed in the amplification means doped by the rare earth ions.
  • the invention advantageously makes it possible to increase the efficiency of optical amplifiers.
  • FIG. 1 represents an optical amplifier according to the prior art
  • FIGS. 2A and 2B represent two variants of an optical amplifier according to a first embodiment of the invention
  • - Figure 3 shows a first improvement of one optical amplifier according to the first embodiment of the invention.
  • FIG. 4 represents a second improvement of the optical amplifier according to the first embodiment of the invention
  • FIG. 5 represents a first application of an optical amplifier according to the first embodiment of the invention
  • FIG. 6 represents a second application of an optical amplifier according to the first embodiment of the invention
  • FIG. 7 represents a third application of an optical amplifier according to the first embodiment of the invention.
  • FIG. 8 represents an optical amplifier according to a second embodiment of the invention
  • FIG. 9 represents a first example of an optical amplifier according to the second embodiment of the invention.
  • FIG. 10 shows a second example of an optical amplifier according to the second embodiment of the invention.
  • FIGS. 2A and 2B represent two variants of an optical amplifier according to a first embodiment of the invention.
  • the optical amplifier according to the first embodiment of the invention comprises a laser cavity C and means 13 for introducing a pump signal P into the cavity C.
  • the laser cavity C includes two mirrors 9 and 10, mode conversion means 11 and an amplifying medium 12.
  • the mirrors 9 and 10 are totally or partially transparent for the wavelengths to be amplified.
  • the mirrors 9 and 10 preferably consist of stacks of multi-electric layers optimized, for example, for wavelengths in the telecommunications field.
  • the mode conversion means 11 are pumped by the pump signal P which is applied to them.
  • the mode conversion means 11 are made of a YAG crystal: Nd.
  • the pump signal P has a wavelength of 0.808 ⁇ m and the YAG crystal: Nd emits at the wavelength of
  • the amplifier material 12 is pumped by the signal from the mode conversion means 11. Under the action of the signal from the mode conversion means 11, the amplifier material 12 emits a signal whose wavelength is the length d wave of the signal E to be amplified which enters the cavity C.
  • the amplifier material 12 is preferably a co-doped glass Erbium and Ytterbium.
  • the thickness of the amplifier material 12 is, for example, equal to 1 cm. Generally, the thickness of the amplifier material depends on the concentration of Erbium ions.
  • the laser cavity C is, preferably, a microlaser cavity allowing a compact realization of the amplification function.
  • the pump signal P can be introduced into the cavity C, axially, by means of a dichroic blade 13 as shown in FIGS. 2A and 2B.
  • the signal to be amplified E crosses the dichroic mirror 13 before entering the cavity by the mirror 9 and the amplified signal S leaves the cavity by the mirror 10.
  • the signal to be amplified E and the amplified signal S are located on the same side of the cavity.
  • the signal to be amplified E enters the cavity by the mirror 10 and the amplified signal leaves the cavity by this same mirror 10.
  • the pump signal is then introduced into the cavity, for example, on the side where the mirror 9 is located.
  • the pump signal can also be introduced into the cavity on the side where the mirror 10 is located.
  • FIG. 3 represents a first improvement of the optical amplifier according to the first embodiment of the invention.
  • the cavity comprises a stage 14 for wavelength conversion.
  • the wavelength conversion stage 14 is pumped by the signal from the mode conversion means 11 and the amplifier material 12 is pumped by the signal from the wavelength conversion stage 14 wave.
  • the mode conversion means 11 are made of a YAG: Nd crystal which emits a wavelength of 1.06 ⁇ m
  • the stage 14 of wavelength conversion is made of a crystal of YAG: Cr which emits a wavelength of 1.48 ⁇ m.
  • the wavelength line 1.48 ⁇ m makes it possible to efficiently pump the amplifying medium 12.
  • the amplifying medium 12 then emits a signal of wavelength substantially equal to 1.5 ⁇ m which constitutes the output signal S of the cavity.
  • FIG. 4 represents a second improvement of the optical amplifier according to the first embodiment of the invention.
  • the cavity is a stable cavity.
  • One of the two mirrors, reference 15 in FIG. 4 is then a concave mirror making it possible to focus the signal of pump P inside the mode conversion means 16 and of the amplifier material 12.
  • the power density of the pump signal is then very significantly increased in the amplifier material.
  • the stability of the cavity can also be obtained by a lens device inside the cavity.
  • the improvement described in FIG. 4 applies to an optical amplifier according to the first embodiment of the invention described in FIG. 2A.
  • the improvement according to which the cavity is stable also applies to an optical amplifier such as that described in FIG. 2B.
  • various matrices silicon, fluorinated glass, etc.
  • active ions can be cascaded to widen the amplification band. These dies are then placed within the laser cavity.
  • the absorption of the pump signal can be increased in the amplifier material, on the one hand, by favoring the line at 0.946 ⁇ m of the YAG by cavity mirrors which are totally reflective at this wavelength and weakly reflective at d other wavelengths, on the other hand, by co-doping the amplifying medium with Ytterbium (Yb) which widens the absorption band.
  • Yb Ytterbium
  • optical elements can be associated with the optical amplifiers described above.
  • the structures obtained then constitute complex components in three-dimensional optics advantageously having a high compactness.
  • FIG. 5 represents a first application of the optical amplifier according to the first embodiment of the invention.
  • the device of FIG. 5 comprises an optical amplifier such as that shown in FIG. 2A associated with an isolator.
  • the isolator 17 is positioned between the amplifier material 12 and the output mirror 10.
  • the isolator 17 can be produced, for example, by means of a rod of Faraday effect material placed between optical polarizers immersed in a magnetic field .
  • the isolator is dimensioned to "block" the strip of laser material (for example 1.5 ⁇ m) and to allow the wavelength of the converter 11 to pass.
  • Such a device has the advantage of being very compact.
  • the device represented in FIG. 5 comprises an optical amplifier such as that described in FIG.
  • the invention also relates to cases where an isolator is associated with an optical amplifier such as those described in FIGS. 2B, 3 or 4.
  • FIG. 6 represents a second application of an optical amplifier according to the first embodiment of the invention.
  • the device shown in FIG. 6 is a three-way lossless distributor.
  • FIG. 6 shows by way of example a three-way distributor. More generally, the invention relates to a distributor with n channels, n being an integer which can reach, for example, the value 64.
  • the distributor with three channels successively comprises a mirror 9, mode conversion means 11, an amplifying medium 12, an insulator 17, a mirror 18, a diffractive optical element 19, a spacer 20, and means 21 for positioning distribution channels such as, for example, optical fibers.
  • FIG. 7 represents a third application of the optical amplifier according to the first embodiment of the invention.
  • the device of FIG. 7 represents an amplified microlaser source. It is then possible to produce a source of wavelength l, 55 ⁇ m whose power can reach, for example, several Watts.
  • the amplified microlaser source comprises a microlaser source M and an optical amplifier A according to the first embodiment of the invention.
  • the microlaser source M comprises an active laser zone 23 comprised between two mirrors 22 and 24.
  • the active area 23 as well as the mirrors 22 and 24 are made, for example, of Erbium / Ytterbium doped glass. Under the action of a pump signal Pi applied to the active area 23, the source M emits a signal S M of wavelength l, 5 ⁇ m.
  • the signal S M is transmitted at the input of amplifier A.
  • the optical amplifier A is an amplifier with stable cavity, the output mirror 25 of which is a concave mirror.
  • the mode conversion means 16 are pumped by a pump signal P 2 introduced into the cavity, for example by the output mirror 25, using a dichroic mirror 26.
  • the structure of the microlaser source according to the invention advantageously makes it possible to preserve, after amplification, the characteristics of the initial beam such as the quality of the beam or else
  • Wavelength tunability if necessary.
  • FIG. 8 represents an optical amplifier according to a second embodiment of the invention.
  • the optical amplifier comprises two mirrors 28 and 29, a laser diode 30 and optical amplification means 27 doped with rare earth ions.
  • the mirrors 28 and 29 and the laser diode 30 constitute an extended diode cavity beyond the exit face of the diode.
  • the mirror 29 is completely reflecting for the signal from the laser diode.
  • the laser diode 30 constitutes the mode conversion means.
  • the laser diode 30 can be, for example, a multimode laser diode which, introduced into the extended cavity, becomes quasi-single mode.
  • the optical amplification means 27 are placed in the cavity formed by the mirrors 28 and 29 and absorb the pump signal from the diode 30.
  • the optical amplification means 27 also receive the signal E to be amplified using coupling means.
  • the amplified signal S passes through the output mirror 29, which is transparent or partially transparent for the amplified signal.
  • the coupling between the pump wave coming from the diode and the amplification means is made effective due to the multiple passages of the pump wave in the amplifying medium, by cavity effect.
  • the amplification means are in the form of an optical guide 32 advantageously single-mode.
  • the cavity of the diode is then closed by a mirror 33 placed at the end of the guide 32.
  • the mirror 33 is produced, for example, by a periodic index structure, commonly called Bragg grating, obtained by etching the surface or by photo inscription of the guide 32.
  • the guide 32 can be an optical fiber or a guide obtained by ion exchange in glasses.
  • the signal E to be amplified is coupled to the amplifier, for example, by a Y junction or by a dichroic coupler 31 of the directional coupler type optimized to be transparent to the signal to be amplified E and not inducing losses of the pump signal .
  • the coupling of the diode to the guide can be optimized by the presence of at least one anti-reflective layer between the diode 30 and the guide 32.
  • the diode 30 has an opposite face FI of a face F2 of the guide 32.
  • An anti-reflective layer can then be formed by an appropriate treatment of the face FI and / or of the face F2.
  • a microlens may be interposed between the diode 30 and the guide 32 in order to adapt the dimensions of the diode to the dimensions of the guide.
  • the adaptation of the dimensions of the diode and of the guide can also be carried out using a guide with progressive coupling, commonly called "tapping".
  • FIG. 10 represents a second example of an optical amplifier according to the second embodiment of the invention.
  • the coupling of the diode to the guide is then optimized by producing a double-core guide (zones Z1 and Z2 of different indices), which makes it possible to relax the alignment constraints and to increase the coupling.
  • an extended cavity coupled to a guide advantageously makes it possible to benefit from a self-alignment effect of the elements which constitute the cavity. It is therefore not necessary to align the laser diode and the guide with great precision (a precision of 1 ⁇ m to 100 ⁇ m may, for example, be sufficient).
  • the assembly of the cavity is thereby simplified. Due to the multiple passages of the pump wave in the amplifying medium, the operation of the intracavity type of the laser diode and of the amplifying medium advantageously allows almost complete absorption of the pump power in the active medium, independently of the linear absorption coefficient of the active medium.
  • the operation in an extended cavity also makes it possible to transform an intrinsically multimode diode into a quasi-single-mode diode, thus promoting coupling to the single-mode guide.

Abstract

The invention concerns an optical amplifier for amplifying an optical signal (E) by stimulated emission of rare earth ions activated by the action of a pump signal. The optical amplifier comprises a laser cavity (C) consisting of two mirrors (28, 29) whereof one is an output mirror (28) for the amplified signal, the cavity containing optical amplifying means (27) doped with rare earth ions and mode converting means (30) to pump the rare earth ions. The invention is applicable, for example, in the field of optical fibre telecommunications.

Description

AMPLIFICATEUR OPTIQUE OPTICAL AMPLIFIER
Domaine technique et art antérieurTechnical field and prior art
L'invention concerne un amplificateur optique.The invention relates to an optical amplifier.
L'invention • trouve une application particulièrement avantageuse dans différents domaines tels que, par exemple, le domaine des télécommunications par fibres optiques ou encore le domaine du marquage en sécurité oculaire.The invention • finds a particularly advantageous application in various fields such as, for example, the field of telecommunications by optical fibers or even the field of marking in ocular safety.
Dans le domaine des télécommunications par fibres optiques, les signaux optiques sont transmis à l'aide de fibres optiques agencées sous forme de réseaux. Les signaux optiques ainsi transmis ont besoin d'être amplifiés, soit du fait de l'atténuation linéique due à la propagation dans les fibres, soit du fait des divisions successives du signal dues aux diverses ramifications du réseau.In the field of telecommunications by optical fibers, optical signals are transmitted using optical fibers arranged in the form of networks. The optical signals thus transmitted need to be amplified, either because of the linear attenuation due to the propagation in the fibers, or because of the successive divisions of the signal due to the various ramifications of the network.
Cette amplification du signal optique, communément appelée régénération, est effectuée au moyen d'amplificateurs électroniques ou au moyen d'amplificateurs optiques.This amplification of the optical signal, commonly called regeneration, is carried out by means of electronic amplifiers or by means of optical amplifiers.
La figure 1 décrit la structure d'un amplificateur optique selon l'art connu. L'amplificateur optique comprend, cascades en série, un premier isolateur 1, une première fibre optique 2, un premier multiplexeur 3, une deuxième fibre optique 5 , un deuxième multiplexeur 6 et un deuxième isolateur 8. Les fibres optiques 2 et 5 sont le plus souvent dopées par' des ions Erbium. Une première diode de pompe 4 , placée sur une voie du premier multiplexeur 3, envoie un premier signal de pompe, par exemple à la longueur d'onde de 0,98 μ , dans la fibre 2. Une deuxième diode de pompe 7 , placée sur une voie du deuxième multiplexeur 6 , envoie un deuxième signal de pompe, par exemple à la longueur d'onde de l,48μm, dans la fibre 5. Les premier et deuxième signaux de pompe créent une inversion de population des ions Erbium permettant ainsi de rendre ces ions actifs. Les fibres optiques 2 et 5 sont généralement de nature différente l'une de l'autre afin d'élargir la bande passante de l'amplification. Les isolateurs 1 et 8 permettent d'éviter l'établissement de réflexions parasites et, partant, l'apparition d'oscillations parasites. Les fibres optiques présentent l'atténuation la plus faible pour les signaux dont la longueur d'onde se situe autour de l,5μm. La longueur d'onde retenue pour la propagation des signaux sur fibres optiques est ainsi choisie de façon à se situer autour de l,5μm. Par ailleurs, les ions Erbium sont pratiquement les seuls à pouvoir réaliser une émission laser autour de l,5μm. C'est la raison pour laquelle les ions Erbium sont choisis pour réaliser l'amplificateur. Cependant, les ions Erbium requièrent une puissance de pompe importante pour atteindre le niveau d'inversion de population nécessaire à un effet laser.FIG. 1 describes the structure of an optical amplifier according to the known art. The optical amplifier comprises, cascades in series, a first isolator 1, a first optical fiber 2, a first multiplexer 3, a second optical fiber 5, a second multiplexer 6 and a second isolator 8. The optical fibers 2 and 5 are the more often doped with 'Erbium ions. A first pump diode 4, placed on a channel of the first multiplexer 3, sends a first pump signal, for example at the wavelength of 0.98 μ, in the fiber 2. A second pump diode 7, placed on a channel of the second multiplexer 6, sends a second signal of the pump, for example at the wavelength of 1.48 μm, in the fiber 5. The first and second pump signals create a population inversion of the Erbium ions, thereby making these ions active. The optical fibers 2 and 5 are generally of a different nature from each other in order to widen the bandwidth of the amplification. The isolators 1 and 8 make it possible to avoid the establishment of parasitic reflections and, consequently, the appearance of parasitic oscillations. Optical fibers have the lowest attenuation for signals whose wavelength is around 1.5 μm. The wavelength used for the propagation of signals over optical fibers is thus chosen so as to be around 1.5 μm. In addition, the Erbium ions are practically the only ones capable of producing a laser emission around 1.5 μm. This is the reason why the Erbium ions are chosen to make the amplifier. However, Erbium ions require significant pump power to reach the level of population inversion necessary for a laser effect.
Les fibres de silice ne peuvent pas être fortement dopées. Il est alors nécessaire - d' utiliser une puissance de signal de pompe relativement élevée, par exemple 100 /cm2, pour ' atteindre le seuil de l'effet laser. Des fibres optiques de grandes longueurs (plusieurs dizaines de mètres) sont alors nécessaires pour obtenir des facteurs d'amplification de l'ordre de 20 dB.The silica fibers cannot be heavily doped. It is then necessary - to use a relatively high pump signal power, for example 100 / cm 2 , to 'reach the threshold of the laser effect. Long optical fibers (several tens of meters) are then necessary to obtain amplification factors of the order of 20 dB.
L'invention ne présente pas cet inconvénient. En effet, l'invention concerne un amplificateur optique pour amplifier un signal optique par émission stimulée d'ions de terre rare rendus actifs sous l'action d'un signal de pompe. L'amplificateur optique comprend une cavité laser constituée de deux miroirs dont l'un est un miroir de sortie pour le signal optique amplifié, la cavité contenant des moyens d'amplification optique dopés par des ions de terre rare et des moyens de conversion de mode pour pomper les ions de terre rare. Selon l'invention, toute l'énergie provenant du signal de pompe finit par être absorbée dans les moyens d'amplification dopés par les ions de terre rare.The invention does not have this drawback. Indeed, the invention relates to an optical amplifier for amplifying an optical signal by stimulated emission of rare earth ions made active under the action of a pump signal. The optical amplifier comprises a laser cavity consisting of two mirrors, one of which is an output mirror for the amplified optical signal, the cavity containing optical amplification means doped with rare earth ions and mode conversion means to pump rare earth ions. According to the invention, all the energy originating from the pump signal ends up being absorbed in the amplification means doped by the rare earth ions.
L'invention permet avantageusement d'accroître le rendement des amplificateurs optiques.The invention advantageously makes it possible to increase the efficiency of optical amplifiers.
Brève description des figuresBrief description of the figures
D'autres caractéristiques et avantages de l'invention apparaîtront à la lecture d'un mode de réalisation préférentiel de 1 ' invention fait en référence aux figures ci-annexées parmi lesquelles :Other characteristics and advantages of the invention will appear on reading a preferred embodiment of the invention made with reference to the appended figures among which:
- la figure 1 représente un amplificateur optique selon l'art antérieur,FIG. 1 represents an optical amplifier according to the prior art,
- les figures 2A et 2B représentent deux variantes d'un amplificateur optique selon un premier mode de réalisation de l'invention, - la figure 3 représente un premier perfectionnement de 1 ' amplificateur optique selon le premier mode de réalisation de l'invention.FIGS. 2A and 2B represent two variants of an optical amplifier according to a first embodiment of the invention, - Figure 3 shows a first improvement of one optical amplifier according to the first embodiment of the invention.
- la figure 4 représente un deuxième perfectionnement de 1 ' amplificateur optique selon le premier mode de réalisation de l'invention,FIG. 4 represents a second improvement of the optical amplifier according to the first embodiment of the invention,
- la figure 5 représente une première application d'un amplificateur optique selon le premier mode de réalisation de l'invention, - la figure 6 représente une deuxième application d'un amplificateur optique selon le premier mode de réalisation de l'invention,FIG. 5 represents a first application of an optical amplifier according to the first embodiment of the invention, FIG. 6 represents a second application of an optical amplifier according to the first embodiment of the invention,
- la figure 7 représente une troisième application d'un amplificateur optique selon le premier mode de réalisation de l'invention,FIG. 7 represents a third application of an optical amplifier according to the first embodiment of the invention,
- la figure 8 représente un amplificateur optique selon un deuxième mode de réalisation de 1 ' invention,FIG. 8 represents an optical amplifier according to a second embodiment of the invention,
- la figure 9 représente un premier exemple d'amplificateur optique selon le deuxième mode de réalisation de l'invention,FIG. 9 represents a first example of an optical amplifier according to the second embodiment of the invention,
- la figure 10 représente un deuxième exemple d'amplificateur optique selon le deuxième mode de réalisation de l'invention.- Figure 10 shows a second example of an optical amplifier according to the second embodiment of the invention.
Description détaillée de modes de mise en oeuyre deDetailed description of methods of implementing
1 ' inventionThe invention
Sur toutes les figures, les mêmes repères désignent les mêmes éléments. La figure 1 a été décrite précédemment. Il est donc inutile d'y revenir. Les figures 2A et 2B représentent deux variantes d'un amplificateur optique selon un premier mode de réalisation de l'invention.In all the figures, the same references designate the same elements. Figure 1 has been described previously. There is therefore no point in coming back to it. FIGS. 2A and 2B represent two variants of an optical amplifier according to a first embodiment of the invention.
L'amplificateur optique selon le premier mode de réalisation de 1 ' invention comprend une cavité laser C et des moyens 13 pour introduire un signal de pompe P dans la cavité C.The optical amplifier according to the first embodiment of the invention comprises a laser cavity C and means 13 for introducing a pump signal P into the cavity C.
La cavité laser C comprend deux miroirs 9 et 10, des moyens de conversion de mode 11 et un milieu amplificateur 12.The laser cavity C includes two mirrors 9 and 10, mode conversion means 11 and an amplifying medium 12.
Les miroirs 9 et 10 sont totalement ou partiellement transparents pour les longueurs d'onde à amplifier. Les miroirs 9 et 10 sont préférentiellement constitués d'empilements de couches multidiélectriques optimisées, par exemple, pour des longueurs d'onde du domaine des télécommunications.The mirrors 9 and 10 are totally or partially transparent for the wavelengths to be amplified. The mirrors 9 and 10 preferably consist of stacks of multi-electric layers optimized, for example, for wavelengths in the telecommunications field.
Les moyens de conversion de mode 11 sont pompés par le signal de pompe P qui leur est appliqué.The mode conversion means 11 are pumped by the pump signal P which is applied to them.
Selon le premier mode de réalisation de l'invention, les moyens de conversion de mode 11 sont faits d'un cristal de YAG:Nd. Préférentiellement, le signal de pompe P a une longueur d'onde de 0,808 μm et le cristal de YAG:Nd émet à la longueur d'onde deAccording to the first embodiment of the invention, the mode conversion means 11 are made of a YAG crystal: Nd. Preferably, the pump signal P has a wavelength of 0.808 μm and the YAG crystal: Nd emits at the wavelength of
1,06 μm. Le matériau amplificateur 12 est pompé par le signal issu des moyens de conversion de mode 11. Sous l'action du signal issu des moyens de conversion de mode 11, le matériau amplificateur 12 émet un signal dont la longueur d'onde est la longueur d'onde du signal E à amplifier qui pénètre dans la cavité C. Le matériau amplificateur 12 est, préférentiellement, un verre co-dopé Erbium et Ytterbium. L'épaisseur du matériau amplificateur 12 est, par exemple, égale à 1 cm. De façon générale, l'épaisseur du matériau amplificateur dépend de la concentration en ions Erbium. La cavité laser C est, préférentiellement, une cavité microlaser permettant une réalisation compacte de la fonction d'amplification.1.06 μm. The amplifier material 12 is pumped by the signal from the mode conversion means 11. Under the action of the signal from the mode conversion means 11, the amplifier material 12 emits a signal whose wavelength is the length d wave of the signal E to be amplified which enters the cavity C. The amplifier material 12 is preferably a co-doped glass Erbium and Ytterbium. The thickness of the amplifier material 12 is, for example, equal to 1 cm. Generally, the thickness of the amplifier material depends on the concentration of Erbium ions. The laser cavity C is, preferably, a microlaser cavity allowing a compact realization of the amplification function.
Le signal de pompe P peut être introduit dans la cavité C, de manière axiale, au moyen d'une lame dichroïque 13 telle que représentée sur les figures 2A et 2B.The pump signal P can be introduced into the cavity C, axially, by means of a dichroic blade 13 as shown in FIGS. 2A and 2B.
Selon la première variante du premier mode de réalisation de l'invention représentée en figue 2A, le signal à amplifier E traverse le miroir dichroïque 13 avant de pénétrer dans la cavité par le miroir 9 et le signal amplifié S sort de la cavité par le miroir 10.According to the first variant of the first embodiment of the invention shown in FIG. 2A, the signal to be amplified E crosses the dichroic mirror 13 before entering the cavity by the mirror 9 and the amplified signal S leaves the cavity by the mirror 10.
Selon la deuxième variante du premier mode de réalisation de l'invention représentée en figure 2B, le signal à amplifier E et le signal amplifié S sont situés du même côté de la cavité. Le signal à amplifier E pénètre dans la cavité par le miroir 10 et le signal amplifié sort de la cavité par ce même miroir 10. Le signal de pompe est alors introduit dans la cavité, par exemple, du côté ou se situe le miroir 9. Selon cette deuxième variante du premier mode de réalisation de l'invention, le signal de pompe peut également être introduit dans la cavité du côté où se situe le miroir 10.According to the second variant of the first embodiment of the invention shown in FIG. 2B, the signal to be amplified E and the amplified signal S are located on the same side of the cavity. The signal to be amplified E enters the cavity by the mirror 10 and the amplified signal leaves the cavity by this same mirror 10. The pump signal is then introduced into the cavity, for example, on the side where the mirror 9 is located. According to this second variant of the first embodiment of the invention, the pump signal can also be introduced into the cavity on the side where the mirror 10 is located.
La figure 3 représente un premier perfectionnement de 1 ' amplifi'cateur optique selon le premier mode de réalisation de l'invention. En plus des miroirs 9 et 10, des moyens de conversion de mode 11 et du matériau amplificateur 12, la cavité comprend un étage 14 de conversion de longueur d'onde. Selon cette configuration, l'étage 14 de conversion de longueur d'onde est pompé par le signal issu des moyens de conversion de mode 11 et le matériau amplificateur 12 est pompé par le signal issu de l'étage 14 de conversion de longueur d'onde.FIG. 3 represents a first improvement of the optical amplifier according to the first embodiment of the invention. In addition to mirrors 9 and 10, mode conversion means 11 and amplifier material 12, the cavity comprises a stage 14 for wavelength conversion. According to this configuration, the wavelength conversion stage 14 is pumped by the signal from the mode conversion means 11 and the amplifier material 12 is pumped by the signal from the wavelength conversion stage 14 wave.
Préférentiellement, les moyens de conversion de mode 11 sont faits d'un cristal de YAG:Nd qui émet une longueur d'onde de l,06μm, et l'étage 14 de conversion de longueur d'onde est fait d'un cristal de YAG:Cr qui émet une longueur d'onde de l,48μm. La raie de longueur d'onde l,48μm permet de pomper efficacement le milieu amplificateur 12. Le milieu amplificateur 12 émet alors un signal de longueur d'onde sensiblement égale à l,5μm qui constitue le signal de sortie S de la cavité.Preferably, the mode conversion means 11 are made of a YAG: Nd crystal which emits a wavelength of 1.06 μm, and the stage 14 of wavelength conversion is made of a crystal of YAG: Cr which emits a wavelength of 1.48 μm. The wavelength line 1.48 μm makes it possible to efficiently pump the amplifying medium 12. The amplifying medium 12 then emits a signal of wavelength substantially equal to 1.5 μm which constitutes the output signal S of the cavity.
Selon le perfectionnement représenté en figureAccording to the improvement represented in figure
3, le signal d'entrée à amplifier E et le signal de pompe P pénètrent dans la cavité par le miroir 9 et le signal amplifié S sort de la cavité par le miroir 10 situé à l'opposé du miroir 9. L'invention concerne cependant également le cas où les signaux E et S se situent du même côté de la cavité. La figure 4 représente un deuxième perfectionnement de 1 ' amplificateur optique selon le premier mode de réalisation de l'invention.3, the input signal to be amplified E and the pump signal P enter the cavity by the mirror 9 and the amplified signal S leaves the cavity by the mirror 10 situated opposite the mirror 9. The invention relates however also the case where the signals E and S are located on the same side of the cavity. FIG. 4 represents a second improvement of the optical amplifier according to the first embodiment of the invention.
Selon le perfectionnement représenté en figureAccording to the improvement represented in figure
4, la cavité est une cavité stable. Un des deux miroirs, référence 15 sur la ' figure 4, est alors un miroir concave permettant de focaliser le signal de pompe P à l'intérieur des moyens de conversion de mode 16 et du matériau amplificateur 12. La densité de puissance du signal de pompe est alors très sensiblement accrue dans le matériau amplificateur. La stabilité de la cavité peut également être obtenue par un dispositif à lentille intérieur à la cavité.4, the cavity is a stable cavity. One of the two mirrors, reference 15 in FIG. 4, is then a concave mirror making it possible to focus the signal of pump P inside the mode conversion means 16 and of the amplifier material 12. The power density of the pump signal is then very significantly increased in the amplifier material. The stability of the cavity can also be obtained by a lens device inside the cavity.
Le perfectionnement décrit en figure 4 s'applique à un amplificateur optique selon le premier mode de réalisation de l'invention décrit en figure 2A. Le perfectionnement selon lequel la cavité est stable s ' applique également à un amplificateur optique tel que celui décrit en figure 2B.The improvement described in FIG. 4 applies to an optical amplifier according to the first embodiment of the invention described in FIG. 2A. The improvement according to which the cavity is stable also applies to an optical amplifier such as that described in FIG. 2B.
Quel que soit le mode de réalisation, diverses matrices (silice, verre fluoré, ...) dopées en ions actifs peuvent être cascadées pour élargir la bande d'amplification. Ces matrices sont alors placées au sein de la cavité laser.Whatever the embodiment, various matrices (silica, fluorinated glass, etc.) doped with active ions can be cascaded to widen the amplification band. These dies are then placed within the laser cavity.
Par ailleurs, l'absorption du signal de pompe peut être augmentée dans le matériau amplificateur, d'une part, en privilégiant la raie à 0,946μm du YAG par des miroirs de cavité totalement réflecteurs à cette longueur d'onde et faiblement réflecteurs à d'autres longueurs d'onde, d'autre part, en co-dopant le milieu amplificateur avec de 1 ' Ytterbium (Yb) qui élargit la bande d'absorption.Furthermore, the absorption of the pump signal can be increased in the amplifier material, on the one hand, by favoring the line at 0.946 μm of the YAG by cavity mirrors which are totally reflective at this wavelength and weakly reflective at d other wavelengths, on the other hand, by co-doping the amplifying medium with Ytterbium (Yb) which widens the absorption band.
Comme cela est connu de l'homme de l'art, par miroir totalement réflecteur, il faut entendre un miroir dont le coefficient de réflexion est, par exemple, de l'ordre de 99,5%. Selon l'invention, différents éléments optiques peuvent être associés aux amplificateurs optiques décrits ci-dessus. Les structures obtenues constituent alors des composants complexes en optique tridimensionnelle ayant avantageusement une forte compacité.As is known to those skilled in the art, by fully reflecting mirror is meant a mirror whose reflection coefficient is, for example, of the order of 99.5%. According to the invention, different optical elements can be associated with the optical amplifiers described above. The structures obtained then constitute complex components in three-dimensional optics advantageously having a high compactness.
De telles structures sont décrites aux figures 5, 6 et 7.Such structures are described in Figures 5, 6 and 7.
La figure 5 représente une première application de l'amplificateur optique selon le premier mode de réalisation de l'invention.FIG. 5 represents a first application of the optical amplifier according to the first embodiment of the invention.
Le dispositif de la figure 5 comprend un amplificateur optique tel que celui représenté en figure 2A associé à un isolateur. L'isolateur 17 est positionné entre le matériau amplificateur 12 et le miroir de sortie 10. L'isolateur 17 peut être réalisé, par exemple, au moyen d'un barreau de matériau à effet Faraday placé entre des polariseurs optiques immergés dans un champ magnétique. L'isolateur est dimensionné pour "bloquer" la bande du matériau laser (par exemple 1,5 μm) et pour laisser passer la longueur d'onde du convertisseur 11. Un tel dispositif présente l'avantage d'être très compact.The device of FIG. 5 comprises an optical amplifier such as that shown in FIG. 2A associated with an isolator. The isolator 17 is positioned between the amplifier material 12 and the output mirror 10. The isolator 17 can be produced, for example, by means of a rod of Faraday effect material placed between optical polarizers immersed in a magnetic field . The isolator is dimensioned to "block" the strip of laser material (for example 1.5 μm) and to allow the wavelength of the converter 11 to pass. Such a device has the advantage of being very compact.
Le dispositif représenté en figure 5 comprend un amplificateur optique tel que celui décrit en figureThe device represented in FIG. 5 comprises an optical amplifier such as that described in FIG.
2A. L'invention concerne également les cas où un isolateur est associé à un amplificateur optique tel que ceux décrits aux figures 2B, 3 ou 4.2A. The invention also relates to cases where an isolator is associated with an optical amplifier such as those described in FIGS. 2B, 3 or 4.
La figure 6 représente une deuxième application d'un amplificateur optique selon le premier mode de réalisation de l'invention. Le dispositif représenté en figure 6 est un répartiteur sans pertes à trois voies. La puissance du signal Si (i=l, 2, 3) qui sort sur chaque voie i est alors égale à la puissance du signal d'entrée E. La figure 6 représente à titre d'exemple un répartiteur à trois voies. Plus généralement, l'invention concerne un répartiteur à n voies, n étant un nombre entier pouvant atteindre, par exemple, la valeur 64. Le répartiteur à trois voies comprend successivement un miroir 9, des moyens de conversion de mode 11, un milieu amplificateur 12, un isolateur 17, un miroir 18, un élément d'optique diffractive 19, un espaceur 20, et des moyens 21 pour le positionnement de voies de répartition telles que, par exemple, des fibres optiques.FIG. 6 represents a second application of an optical amplifier according to the first embodiment of the invention. The device shown in FIG. 6 is a three-way lossless distributor. The power of the signal Si (i = 1, 2, 3) which leaves on each channel i is then equal to the power of the input signal E. FIG. 6 shows by way of example a three-way distributor. More generally, the invention relates to a distributor with n channels, n being an integer which can reach, for example, the value 64. The distributor with three channels successively comprises a mirror 9, mode conversion means 11, an amplifying medium 12, an insulator 17, a mirror 18, a diffractive optical element 19, a spacer 20, and means 21 for positioning distribution channels such as, for example, optical fibers.
La figure 7 représente une troisième application de 1 ' amplificateur optique selon le premier mode de réalisation de l'invention. Le dispositif de la figure 7 représente une source microlaser amplifiée. Il est alors possible de réaliser une source de longueur d'onde l,55μm dont la puissance peut atteindre, par exemple, plusieurs Watts.FIG. 7 represents a third application of the optical amplifier according to the first embodiment of the invention. The device of FIG. 7 represents an amplified microlaser source. It is then possible to produce a source of wavelength l, 55 μm whose power can reach, for example, several Watts.
La source microlaser amplifiée comprend une source microlaser M et un amplificateur optique A selon le premier mode de réalisation de l'invention. La source microlaser M comprend une zone laser active 23 comprise entre deux miroirs 22 et 24.The amplified microlaser source comprises a microlaser source M and an optical amplifier A according to the first embodiment of the invention. The microlaser source M comprises an active laser zone 23 comprised between two mirrors 22 and 24.
La zone active 23 ainsi que les miroirs 22 et 24 sont constitués, par exemple, de verre dopé Erbium/Ytterbium. Sous l'action d'un signal de pompe Pi appliqué à la zone active 23, la source M émet un signal SM de longueur d'onde l,5μm.The active area 23 as well as the mirrors 22 and 24 are made, for example, of Erbium / Ytterbium doped glass. Under the action of a pump signal Pi applied to the active area 23, the source M emits a signal S M of wavelength l, 5 μm.
Le signal SM est transmis en entrée de l'amplificateur A. A titre d'exemple non limitatif, 1 ' amplificateur optique A est un amplificateur à cavité stable dont le miroir de sortie 25 est un miroir concave.The signal S M is transmitted at the input of amplifier A. By way of nonlimiting example, the optical amplifier A is an amplifier with stable cavity, the output mirror 25 of which is a concave mirror.
Les moyens de conversion de mode 16 sont pompés par un signal de pompe P2 introduit dans la cavité, par exemple par le miroir de sortie 25, à l'aide d'un miroir dichroïque 26.The mode conversion means 16 are pumped by a pump signal P 2 introduced into the cavity, for example by the output mirror 25, using a dichroic mirror 26.
La structure de la source microlaser selon l'invention permet avantageusement de conserver, après amplification, les caractéristiques du faisceau initial telle que la qualité du faisceau ou encoreThe structure of the microlaser source according to the invention advantageously makes it possible to preserve, after amplification, the characteristics of the initial beam such as the quality of the beam or else
1 ' accordabilité en longueur d'onde si nécessaire.Wavelength tunability if necessary.
La figure 8 représente un amplificateur optique selon un deuxième mode de réalisation de l'invention.FIG. 8 represents an optical amplifier according to a second embodiment of the invention.
L'amplificateur optique comprend deux miroirs 28 et 29, une diode laser 30 et des moyens d'amplification optiques 27 dopés par des ions de terre rare.The optical amplifier comprises two mirrors 28 and 29, a laser diode 30 and optical amplification means 27 doped with rare earth ions.
Les miroirs 28 et 29 et la diode laser 30 constituent une cavité à diode étendue au-delà de la face de sortie de la diode. Le miroir 29 est totalement réfléchissant pour le signal issu de la diode laser. Selon le deuxième mode de réalisation de l'invention, la diode laser 30 constitue les moyens de conversion de mode. La diode laser 30 peut être, par exemple, une diode laser multimode qui, introduite dans la cavité étendue, devient quasi-monomode.The mirrors 28 and 29 and the laser diode 30 constitute an extended diode cavity beyond the exit face of the diode. The mirror 29 is completely reflecting for the signal from the laser diode. According to the second embodiment of the invention, the laser diode 30 constitutes the mode conversion means. The laser diode 30 can be, for example, a multimode laser diode which, introduced into the extended cavity, becomes quasi-single mode.
Les moyens d'amplification optiques 27 sont placés dans la cavité constituée par les miroirs 28 et 29 et absorbent le signal de pompe issu de la diode 30.The optical amplification means 27 are placed in the cavity formed by the mirrors 28 and 29 and absorb the pump signal from the diode 30.
Les moyens d'amplification optiques 27 reçoivent par ailleurs le signal E à amplifier à l'aide de moyens de couplage. Le signal amplifié S traverse le miroir de sortie 29, lequel est transparent ou partiellement transparent pour le signal amplifié. Avantageusement, le couplage entre l'onde de pompe issue de la diode et les moyens d'amplification est rendu efficace du fait des multiples passages de l'onde de pompe dans le milieu amplificateur, par effet cavité.The optical amplification means 27 also receive the signal E to be amplified using coupling means. The amplified signal S passes through the output mirror 29, which is transparent or partially transparent for the amplified signal. Advantageously, the coupling between the pump wave coming from the diode and the amplification means is made effective due to the multiple passages of the pump wave in the amplifying medium, by cavity effect.
Dans le cas particulier représenté en figure 9, les moyens d'amplification se présentent sous la forme d'un guide optique 32 avantageusement monomode. La cavité de la diode est alors fermée par un miroir 33 placé à l'extrémité du guide 32. Le miroir 33 est réalisé, par exemple, par une structure périodique d'indice, communément appelée réseau de Bragg, obtenue par gravure de la surface ou par photo inscription du guide 32. Le guide 32 peut être une fibre optique ou un guide obtenu par échange d'ions dans des verres.In the particular case represented in FIG. 9, the amplification means are in the form of an optical guide 32 advantageously single-mode. The cavity of the diode is then closed by a mirror 33 placed at the end of the guide 32. The mirror 33 is produced, for example, by a periodic index structure, commonly called Bragg grating, obtained by etching the surface or by photo inscription of the guide 32. The guide 32 can be an optical fiber or a guide obtained by ion exchange in glasses.
Le signal E à amplifier est couplé à l'amplificateur, par exemple, par une jonction Y ou par un coupleur dichroïque 31 de type coupleur directionnel optimisé pour être transparent' au signal à amplifier E et n'induisant pas de pertes du signal de pompe. Selon un perfectionnement de 1 ' amplificateur représenté en figure 9, le couplage de la diode au guide peut être optimisé par la présence d'au moins une couche antireflet entre la diode 30 et le guide 32. La diode 30 présente une face FI en regard d'une face F2 du guide 32. Une couche antireflet peut alors être constituée par un traitement approprié de la face FI et/ou de la face F2.The signal E to be amplified is coupled to the amplifier, for example, by a Y junction or by a dichroic coupler 31 of the directional coupler type optimized to be transparent to the signal to be amplified E and not inducing losses of the pump signal . According to an improvement of the amplifier shown in FIG. 9, the coupling of the diode to the guide can be optimized by the presence of at least one anti-reflective layer between the diode 30 and the guide 32. The diode 30 has an opposite face FI of a face F2 of the guide 32. An anti-reflective layer can then be formed by an appropriate treatment of the face FI and / or of the face F2.
Une microlentille peut être interposée entre la diode 30 et le guide 32 afin d'adapter les dimensions de la diode aux dimensions du guide. L'adaptation des dimensions de la diode et du guide peut également être réalisée à l'aide d'un guide à raccord progressif, communément appelé "taper". La figure 10 représente un deuxième exemple d'amplificateur optique selon le deuxième mode de réalisation de l'invention.A microlens may be interposed between the diode 30 and the guide 32 in order to adapt the dimensions of the diode to the dimensions of the guide. The adaptation of the dimensions of the diode and of the guide can also be carried out using a guide with progressive coupling, commonly called "tapping". FIG. 10 represents a second example of an optical amplifier according to the second embodiment of the invention.
Le couplage de la diode au guide est alors optimisé en réalisant un guide à double cœur (zones Zl et Z2 d'indices différents), ce qui permet de relâcher les contraintes d'alignement et d'augmenter le couplage.The coupling of the diode to the guide is then optimized by producing a double-core guide (zones Z1 and Z2 of different indices), which makes it possible to relax the alignment constraints and to increase the coupling.
L'utilisation d'une cavité étendue couplée à un guide permet avantageusement de bénéficier d'un effet d'auto-alignement des éléments qui constituent la cavité. Il n'est alors pas nécessaire d'aligner avec une grande précision la diode laser et le guide (une précision de 1 μm à 100 μm peut, par exemple, suffire). Le montage de la cavité s'en trouve simplifié. Du fait des multiples passages de l'onde de pompe dans le milieu amplificateur, le fonctionnement de type intracavité de la diode laser et du milieu amplificateur permet avantageusement une absorption quasi-complète de la puissance de pompe dans le milieu actif, indépendamment du coefficient d'absorption linéique du milieu actif.The use of an extended cavity coupled to a guide advantageously makes it possible to benefit from a self-alignment effect of the elements which constitute the cavity. It is therefore not necessary to align the laser diode and the guide with great precision (a precision of 1 μm to 100 μm may, for example, be sufficient). The assembly of the cavity is thereby simplified. Due to the multiple passages of the pump wave in the amplifying medium, the operation of the intracavity type of the laser diode and of the amplifying medium advantageously allows almost complete absorption of the pump power in the active medium, independently of the linear absorption coefficient of the active medium.
Par ailleurs, le fonctionnement en cavité étendue permet également de transformer une diode intrinsèquement multimode en diode quasi-monomode, favorisant ainsi le couplage au guide monomode. Furthermore, the operation in an extended cavity also makes it possible to transform an intrinsically multimode diode into a quasi-single-mode diode, thus promoting coupling to the single-mode guide.

Claims

REVENDICATIONS
1. Amplificateur optique pour amplifier un signal optique (E) par émission stimulée d'ions de terre rare rendus actifs sous l'action d'un signal de pompe, caractérisé en ce qu'il comprend une cavité laser (C) constituée de deux miroirs (9, 10 ; 24, 25) dont l'un est un miroir de sortie (10, 25) pour le signal optique amplifié, la cavité contenant des moyens d'amplification optique (12, 27, 32) dopés par des ions de terre rare et des moyens de conversion de mode (11, 30) pour pomper les ions de terre rare.1. Optical amplifier for amplifying an optical signal (E) by stimulated emission of rare earth ions made active under the action of a pump signal, characterized in that it comprises a laser cavity (C) consisting of two mirrors (9, 10; 24, 25), one of which is an output mirror (10, 25) for the amplified optical signal, the cavity containing optical amplification means (12, 27, 32) doped with ions of rare earth and mode conversion means (11, 30) for pumping rare earth ions.
2. Amplificateur optique selon la revendication2. Optical amplifier according to claim
1, caractérisé en ce que les moyens de conversion de mode (11, 30) sont constitués d'une diode laser (30). 1, characterized in that the mode conversion means (11, 30) consist of a laser diode (30).
3. Amplificateur optique selon la revendication3. Optical amplifier according to claim
2, caractérisé en ce que les moyens d'amplification optique (12, 27, 32) sont constitués d'un guide d'onde (32).2, characterized in that the optical amplification means (12, 27, 32) consist of a waveguide (32).
4. Amplificateur optique selon la revendication 3, caractérisé en ce qu'il comprend des moyens de couplage (31) du signal à amplifier dans le guide d'onde (32).4. Optical amplifier according to claim 3, characterized in that it comprises coupling means (31) of the signal to be amplified in the waveguide (32).
5. Amplificateur optique selon la revendication 4, caractérisé en ce que les moyens de couplage sont constitués d'un coupleur dichroïque (31).5. Optical amplifier according to claim 4, characterized in that the coupling means consist of a dichroic coupler (31).
6. Amplificateur optique selon la revendication 4, caractérisé en ce que les moyens de couplage sont constitués d'une jonction en Y.6. An optical amplifier according to claim 4, characterized in that the coupling means consist of a Y-junction.
7. Amplificateur optique selon l'une quelconque des revendications 3 à 6, caractérisé en ce qu'il comprend au moins une couche antireflet (Fl, F2 ) entre la diode laser (30) et le guide d'onde (32).7. Optical amplifier according to any one of claims 3 to 6, characterized in that it comprises at least one antireflection layer (F1, F2) between the laser diode (30) and the waveguide (32).
8. Amplificateur optique selon la revendication 7, caractérisé en ce qu'une microlentille est positionnée entre la diode laser (26) et le guide d'onde (32).8. An optical amplifier according to claim 7, characterized in that a microlens is positioned between the laser diode (26) and the waveguide (32).
9. Amplificateur optique selon la revendication 7, caractérisé en ce que le guide d'onde (32) est un guide à raccord progressif pour adapter les dimensions de la diode (30) aux dimensions du guide d'onde (32).9. An optical amplifier according to claim 7, characterized in that the waveguide (32) is a guide with progressive coupling to adapt the dimensions of the diode (30) to the dimensions of the waveguide (32).
10. Amplificateur optique selon l'une quelconque des revendications 3 à 9, caractérisé en ce que le guide (32) est un guide à double cœur pour coupler la diode laser et le milieu amplificateur. 10. An optical amplifier according to any one of claims 3 to 9, characterized in that the guide (32) is a double-core guide for coupling the laser diode and the amplifying medium.
11. Amplificateur optique selon l'une quelconque des revendications 3 à 10, caractérisé en ce que le miroir de sortie (29) est un réseau de Bragg (33) placé à une extrémité du guide d'onde (32).11. An optical amplifier according to any one of claims 3 to 10, characterized in that the output mirror (29) is a Bragg grating (33) placed at one end of the waveguide (32).
12. Amplificateur optique selon l'une quelconque des revendications 2 à 11, caractérisé en ce que la diode laser (30) est une diode à réseau d'émetteurs juxtaposés.12. An optical amplifier according to any one of claims 2 to 11, characterized in that the laser diode (30) is a diode with an array of juxtaposed emitters.
13. Amplificateur optique selon l'une quelconque des revendications 2 à 12, caractérisé en ce que la diode laser est une diode multimode et en ce que la cavité laser (C) est une cavité étendue au-delà de la face de sortie de la diode.13. An optical amplifier according to any one of claims 2 to 12, characterized in that the laser diode is a multimode diode and in that the laser cavity (C) is a cavity extended beyond the output face of the diode.
14. Amplificateur optique selon la revendication 1, caractérisé en ce que les moyens de conversion de mode (11) génèrent le signal de pompe sous l'action d'un second signal de pompe (P). 14. Optical amplifier according to claim 1, characterized in that the mode conversion means (11) generate the pump signal under the action of a second pump signal (P).
15. Amplificateur optique selon la revendication 14, caractérisé en ce que les moyens de conversion de mode (11) sont constitués d'un cristal de YAG:Nd. 15. Optical amplifier according to claim 14, characterized in that the mode conversion means (11) consist of a YAG: Nd crystal.
16. Amplificateur optique selon l'une des revendications 14 ou 15, caractérisé en ce que le miroir (9) qui n'est pas le miroir de sortie (10) est transparent ou partiellement transparent pour le signal optique à amplifier. 16. Optical amplifier according to one of claims 14 or 15, characterized in that the mirror (9) which is not the output mirror (10) is transparent or partially transparent for the optical signal to be amplified.
17. Amplificateur optique selon l'une quelconque des revendications 14 à 16, caractérisé en ce qu'il comprend un étage de conversion de longueur d'onde supplémentaire (14).17. An optical amplifier according to any one of claims 14 to 16, characterized in that it comprises an additional wavelength conversion stage (14).
18. Amplificateur optique selon la revendication 17, caractérisé en ce que l'étage de conversion de longueur d'onde supplémentaire (14) est constitué d'un cristal de YAG:Cr.18. Optical amplifier according to claim 17, characterized in that the additional wavelength conversion stage (14) consists of a YAG: Cr crystal.
19. Amplificateur optique selon l'une quelconque des revendications 14 à 18, caractérisé en ce que la cavité est stable.19. An optical amplifier according to any one of claims 14 to 18, characterized in that the cavity is stable.
20. Amplificateur optique selon l'une quelconque des revendications précédentes, caractérisé en ce que les ions de terres rares sont des ions d' Erbium. 20. Optical amplifier according to any one of the preceding claims, characterized in that the rare earth ions are Erbium ions.
21. Amplificateur optique selon l'une quelconque des revendications précédentes, caractérisé en ce que les moyens d'amplification optique sont codopés avec de l' Ytterbium (Yb).21. Optical amplifier according to any one of the preceding claims, characterized in that the optical amplification means are codoped with Ytterbium (Yb).
22. Structure amplificatrice, caractérisée en ce qu'elle comprend un amplificateur optique selon l'une quelconque des revendications 14 à 21 et en ce qu'un isolateur (17) est placé, dans la cavité laser, entre les moyens d'amplification (12) et le miroir de sortie ( 10) .22. Amplifying structure, characterized in that it comprises an optical amplifier according to any one of claims 14 to 21 and in that that an isolator (17) is placed in the laser cavity between the amplification means (12) and the output mirror (10).
23. Répartiteur sans pertes, caractérisé en ce qu'il comprend une structure amplificatrice selon la revendication 22 et une structure constituée d'un élément d'optique diffractive (19), d'un espaceur (20) et de moyens (21) pour le positionnement de voies de répartition. 24. Source microlaser, caractérisée en ce qu'elle comprend :23. Lossless distributor, characterized in that it comprises an amplifying structure according to claim 22 and a structure consisting of a diffractive optical element (19), a spacer (20) and means (21) for the positioning of distribution channels. 24. Microlaser source, characterized in that it comprises:
- une cavité microlaser (M) pour générer un signal optique sous l'action d'un signal de pompe (PI), la cavité microlaser étant constituée d'un bloc de verre dopé par des ions de terre rare (23) et de deux miroirs transparents ou partiellement transparents pour le signal optique (22, - a microlaser cavity (M) for generating an optical signal under the action of a pump signal (PI), the microlaser cavity consisting of a glass block doped with rare earth ions (23) and two transparent or partially transparent mirrors for the optical signal (22,
24), et24), and
- un amplificateur optique selon l'une quelconque des revendications 14 à 21 pour amplifier le signal optique issu de la cavité microlaser (M) .- An optical amplifier according to any one of claims 14 to 21 for amplifying the optical signal coming from the microlaser cavity (M).
25. Source microlaser selon la revendication 24, caractérisée en ce que les ions de terre rare sont des ions d 'Erbium et en ce que le bloc de verre est codopé avec de 1 ' Ytterbium (Yb) . 25. microlaser source according to claim 24, characterized in that the rare earth ions are Erbium ions and in that the glass block is codoped with 1 Ytterbium (Yb).
PCT/FR2000/001584 1999-06-09 2000-06-08 Optical amplifier WO2000076035A1 (en)

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EP00940470A EP1183757A1 (en) 1999-06-09 2000-06-08 Optical amplifier

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FR99/07261 1999-06-09
FR9907261 1999-06-09

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WO2000076035A1 true WO2000076035A1 (en) 2000-12-14

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3615312A (en) * 1969-04-21 1971-10-26 American Optical Corp End fusion of glass laser rods of dissimilar chemistry
EP0426221A1 (en) * 1989-10-30 1991-05-08 PIRELLI CAVI S.p.A. Low-noise optical amplification unit with reflection of the pumping power
US5182759A (en) * 1990-05-16 1993-01-26 Amoco Corporation Apparatus and method for pumping of a weakly absorbing lasant material
US5530710A (en) * 1995-05-15 1996-06-25 At&T Corp. High-power pumping of three-level optical fiber laser amplifier
US5754570A (en) * 1993-05-19 1998-05-19 Telstra Corporation Limited Co-doped optical material emitting visible/IR light
WO1998059399A1 (en) * 1997-06-20 1998-12-30 Parkhurst Warren E Multi-media solid state laser
US5923684A (en) * 1996-09-26 1999-07-13 Lucent Technologies Inc. Fiber amplifier with multiple pass pumping

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3615312A (en) * 1969-04-21 1971-10-26 American Optical Corp End fusion of glass laser rods of dissimilar chemistry
EP0426221A1 (en) * 1989-10-30 1991-05-08 PIRELLI CAVI S.p.A. Low-noise optical amplification unit with reflection of the pumping power
US5182759A (en) * 1990-05-16 1993-01-26 Amoco Corporation Apparatus and method for pumping of a weakly absorbing lasant material
US5754570A (en) * 1993-05-19 1998-05-19 Telstra Corporation Limited Co-doped optical material emitting visible/IR light
US5530710A (en) * 1995-05-15 1996-06-25 At&T Corp. High-power pumping of three-level optical fiber laser amplifier
US5923684A (en) * 1996-09-26 1999-07-13 Lucent Technologies Inc. Fiber amplifier with multiple pass pumping
WO1998059399A1 (en) * 1997-06-20 1998-12-30 Parkhurst Warren E Multi-media solid state laser

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