INTEGRATED HIGH-POWER LASER EMISSION DEVICE

Description

DOMAINE TECHNIQUE

[0001] The technical field of the invention is integrated optics and more specifically the design of a high-power laser emission circuit intended to be used, without limitation, in LIDAR or telecom applications, or other photonic applications. ART ANTERIEUR

[0002] In the field of optics, the trend is towards technologies that enable large-scale manufacturing and assembly. By integrating optical components onto a single chip, it is possible to reduce the size and cost of systems while increasing their performance.

[0003] In the field of LiDAR, for example, the use of wavelength-modulated laser sources is common. According to the principles of a frequency-modulated continuous wave (FMCW), it is possible to perform continuous modulation of the emission wavelength, for example, according to a triangular shape, as shown in the... figure 1 A portion of an emitted laser beam is captured and directed towards a photodetector. The laser beam reflected by a target is also directed towards the photodetector. Since the captured and reflected beams are coherent, their interference can be detected by the photodetector, resulting in a frequency difference directly proportional to the distance from the target. The operation of such devices is described, for example, in C. Poulton's publication "Coherent solid-state LIDAR with silicon photonic optical phased arrays".

[0004] The use of wavelength-modulated lasers can also be relevant to the field of optical telecommunications.

[0005] Whether for LiDAR or telecom applications, the demand is for compact systems with high transmission power, for example, exceeding 100 mW. Currently, laser sources integrated on a chip cannot achieve such power levels. Hybrid systems enable increased transmission power through a coherent combination of beams emitted by different laser sources. The publications Zhu Y., "Loss-induced coherent combining in InP-Si3N4 hybrid platform," Sci. Rep., vol. 8, no. 1, Art. 1, Jan. 2018, and Zeng S., "Watt-level beam combined diode laser systems in a chip-scale hybrid photonic platform," Optics Express, Vol. 30, no. 13 / 20, June 2022, describe hybrid architectures in which multiple laser sources are connected to a single photonic chip. The beams emitted by each source are combined within the substrate to obtain a high-power beam.However, such architectures have the disadvantage of high manufacturing costs due to the assembly required between each laser source and the substrate. Another difficulty is the alignment between each laser source and the substrate, which can be delicate and lead to losses.

[0006] The US2020 / 161831 document describes a laser source designed to emit a wavelength while minimizing drift under the effect of temperature variation.

[0007] The invention described below provides a laser source integrated into a monolithic substrate. Depending on the arrangement, either a single high-power laser source or multiple laser sources can be obtained. Preferably, the laser source is continuously wavelength-modulated, enabling its use in LiDAR systems. EXPOSE DE L'INVENTION

[0008] One object of the invention is a laser emission device, integrated into a substrate, comprising: a primary waveguide, formed in the substrate, and extending from a primary reflector, the primary reflector being configured to reflect light in a spectral reflection band; several secondary waveguides, optically connected to the primary waveguide, each secondary waveguide extending between a coupling end, optically connected to the primary waveguide, and a secondary reflector, each secondary reflector being configured to reflect light in the spectral reflection band;the device being characterized in that each secondary waveguide is optically coupled to an amplifying medium, connected to a laser pumping system, the amplifying medium being conducive to laser emission under the effect of pumping exerted by the laser pumping system, the amplifying medium being disposed between the coupling end and the secondary reflector of said secondary waveguide such that the device forms as many Fabry-Pérot cavities as there are secondary waveguides, each Fabry-Pérot cavity being configured to allow multiple reflections of light at the same resonant wavelength, in the spectral reflection band, between the main reflector and each secondary reflector; the device comprising an extractor, for extracting the light from the device, at the resonant wavelength, said resonant wavelength forming an emission wavelength of the device.

[0009] According to one embodiment, the main reflector or each secondary reflector is adjustable, so as to modulate the spectral band of reflection.

[0010] In one scenario, the spectral reflection band of the primary reflector is adjustable, the primary reflector being a Bragg mirror coupled to a modulator configured to modulate the refractive index of said Bragg mirror. Each secondary reflector can reflect light within a fixed secondary reflection spectral band that is wider than, and contains, the reflection spectral band of the primary reflector.

[0011] In one scenario, the spectral reflection band of each secondary reflector is adjustable, each secondary reflector being a Bragg mirror coupled to a modulator configured to modulate the refractive index of said Bragg mirror. The primary reflector can reflect light within a fixed spectral reflection band that is wider than, and contains, the reflection band of each secondary reflector.

[0012] Preferably, at least one secondary waveguide includes a secondary phase modulator, configured to modulate a refractive index along a portion of said secondary waveguide, the secondary phase modulator being disposed between the coupling end of said secondary waveguide and the secondary reflector of said secondary waveguide, so as to modulate an optical path in said secondary waveguide.

[0013] Preferably, each secondary waveguide includes a secondary phase modulator, configured to modulate a refractive index along a portion of said secondary waveguide, the secondary phase modulator being disposed between the coupling end of said secondary waveguide and the secondary reflector of said secondary waveguide, so as to modulate an optical path in each secondary waveguide.

[0014] The main waveguide may include a main phase modulator, configured to modulate a refractive index along a portion of the main waveguide, the main phase modulator being disposed between each secondary waveguide and the main reflector, so as to modulate the resonant wavelength of each Fabry-Pérot cavity of the device.

[0015] According to one possibility: The main reflector reflects more than 90% of the light, in the spectral reflection band; each secondary reflector transmits at least 20% of the light, in the spectral reflection band, so that the secondary reflector forms the extractor of the device.

[0016] According to one possibility: Each secondary reflector reflects more than 90% of the light, in the spectral reflection band; the main reflector transmits at least 20% in the spectral reflection band, so that the main reflector forms the extractor of the device.

[0017] The main waveguide can be formed by a first material, and surrounded by a first auxiliary material, whose refractive index is lower than the refractive index of the first material.

[0018] Each secondary waveguide can be formed by a second material, and surrounded by a second auxiliary material, whose refractive index is lower than the refractive index of the second material.

[0019] According to one possibility: the first material is identical to the second material; the first auxiliary material is identical to the second auxiliary material.

[0020] According to one possibility: the first material and the second material are Si; the first auxiliary material to the second auxiliary material are SiO2.

[0021] According to one possibility: the first material is SiN; the second material is Si; the first auxiliary material is identical to the second auxiliary material.

[0022] Preferably, the main waveguide and at least one secondary waveguide, or each secondary waveguide, are formed in the same substrate, each amplifying medium being transferred onto said substrate.

[0023] The invention will be better understood by reading the explanation of the examples of embodiment presented, in the continuation of the description, in connection with the figures listed below. FIGURES

[0024] There figure 1 This represents an example of continuous wavelength modulation. The y-axis corresponds to the wavelength and the x-axis corresponds to time. figure 2 shows a first method of implementation. The figures 3A et 3B They schematically represent a cross-section of the substrate at the level of the active material. figure 4A The diagram schematically represents a spectral reflection band of a narrow, adjustable primary reflector, included within the broad spectral reflection band of a secondary reflector. The light energy propagated within the Fabry-Pérot cavity formed by the primary and secondary reflectors is also shown. figure 4B shows a configuration in which the spectral reflection band of the secondary reflector coincides with a resonance wavelength of the Fabry-Pérot cavity. figure 4C shows a configuration in which, with respect to the figure 4B The spectral reflection band of the secondary reflector is modified. figure 4D shows a configuration in which, with respect to the figure 4C The resonance wavelength of the Fabry-Pérot cavity is modified. figure 5 outlines a second embodiment. EXPOSE DE MODES DE REALISATION PARTICULIERS

[0025] There figure 2 Figure 1 illustrates a first embodiment of a laser emission device 1 according to the invention. The device 1 is formed in a monolithic substrate 2. The figure 2 This represents a cross-sectional view of the device, in the plane of the substrate. Substrate 2, for example, is of the SOI (Silicon on Insulator) type. SOI is a well-known substrate in microelectronics, but it is also widely used in the fabrication of integrated optical circuits. Silicon is transparent at telecom wavelengths (1.3 µm - 1.5 µm), and the strong refractive index contrast with its oxide (nSi = 3.51 - nSiO2 = 1.45, or Δn = nSi - nSiO2 = 2) makes it suitable for compact passive functions: mirrors, waveguides, and resonant cavities. Furthermore, current manufacturing processes are well-established and allow for the production of large substrates.

[0026] Other types of substrates can be used, for example SiNOI (acronym for Silicon Nitride on Insulator) or LNOI (acronym for Lithium Niobate on Insulator).

[0027] The device comprises a main waveguide 10, formed within the substrate, and extending from a main reflector 15, configured to reflect a wavelength of interest. In the examples described, the main reflector 15 is a Bragg mirror, referred to as the main Bragg mirror. Other types of reflectors, for example Sagnac loops, are possible. The main waveguide 10 is formed of a first material 11, in this case Si, around which extends a first auxiliary material 12, in this case SiO₂. Other variants are described later.

[0028] The main waveguide 10 is formed by conventional photolithography / etching techniques. It is typically produced by etching the surface silicon layer of an SOI wafer, which is in contact with an oxide layer 3. The resulting Si waveguide is then coated with a top layer of a lower refractive index material 12, for example, SiO2. The top layer can be thinned and planarized. The thickness of the top layer can be reduced to 100 nm. The channel is arranged on the SiO2 layer 3. An example of channel geometry is described later, in connection with the figures 3A et 3B The height of the waveguide 10 is typically between 220 and 500nm, and its width can vary between 100nm and 5µm.

[0029] As is well known, the principal Bragg mirror 15 is formed by a periodic alternation of two materials with different refractive indices. The periodic variation of the index generates a series of reflections that add together when they are in phase. In this example, the principal Bragg mirror 15 is formed by partially etching silicon followed by the deposition of SiO₂. The periodicity of the etched areas determines a spectral band of reflection, at which the Bragg mirror reflects light, with a period on the order of a few hundred nanometers. The number of periods is typically from several tens to several hundred or even thousands.

[0030] In this example: The main Bragg mirror 15 is a mirror exhibiting a narrow spectral reflection band, the full width at half maximum (FWHM) of the spectral reflection band being, for example, less than 1 nm. The spectral reflection band is centered on the wavelength of interest. λ i The main Bragg mirror 15 is a total mirror, in the sense that it reflects almost all the light in the spectral reflection band. By almost all, we mean more than 90%, or even more than 95%, or even more than 99%. The main Bragg mirror 15 is adjustable, as the spectral reflection band is variable. The variation of the spectral reflection band is obtained by modulating the refractive indices, under the effect of a modulator 17, in the materials forming the Bragg mirror. Such modulation can be obtained by a local variation of the temperature, the modulator of the Bragg mirror 17 then being a heating resistor. The modulation can also be obtained by a local injection of charges at the Bragg mirror. Indeed, the refractive index of a semiconductor material depends on the charge density. On the figure 2 , modulator 17 of the main Bragg mirror is represented by an arrow.

[0031] The device 1 comprises several secondary waveguides 20, whose structure is preferably, but not necessarily, identical to that of the main waveguide 10: same material, same dimensions. Generally, each secondary waveguide 20 is formed of a second material 21, in this case Si, around which extends a second auxiliary material 22, in this case SiO2.

[0032] In this example, device 1 has four secondary waveguides 20. The number of secondary waveguides can be between 2 and 10, or even several dozen.

[0033] Each secondary waveguide 20 extends between a coupling end 23, intended to be optically connected to the primary waveguide 10, and a secondary reflector 25. In this example, the secondary reflector is a Bragg mirror, called a secondary Bragg mirror. Preferably, the secondary Bragg mirrors are identical to each other. They are preferably made of the same materials as the primary Bragg mirror 15, so as to reflect light at the wavelength of interest defined by the primary Bragg mirror 15. Preferably, the spectral reflection band of each secondary Bragg mirror 25 is the same as, or wider than, that of the primary reflector, and includes the spectral reflection band of the primary reflector 15. In this example: Each secondary Bragg mirror 25 is a mirror with a broad spectral reflectance band, the full width at half maximum (FWHM) of the spectral reflectance band being, for example, greater than or equal to 10 nm. Each secondary Bragg mirror 25 is a partial mirror, in that it only partially reflects light within the spectral reflectance band. By partially, we mean less than 80%, or even less than 50%, for example, 40%. The unreflected light is transmitted to a photonic circuit. For example, each secondary Bragg mirror 25 is connected to one of the inputs of an optical phased array (OPA), which, in the context of a LiDAR system, allows the beam to be scanned in space. The secondary Bragg mirrors form the light extractor of the device.

[0034] The length of each Bragg mirror can range from a few hundred microns to several millimeters.

[0035] It goes without saying that the spectral reflection band of the primary Bragg mirror extends into the spectral reflection band of each secondary Bragg mirror. This results in reflections of at least one wavelength of interest. λ i , which corresponds to the intersection of the spectral reflection band of the main Bragg mirror and each secondary Bragg mirror.

[0036] Between the main waveguide 10 and each secondary waveguide 20, there extend transmission waveguides 13, whose function is to ensure optical coupling between the main waveguide 15 and each secondary waveguide 25. A coupler is used at each coupling end 23 to connect / combine the beams from the different secondary guides 20 to the main waveguide 10. The coupler can be, for example, a directional coupler or a multimode interferometer (MMI).

[0037] Each secondary waveguide 20 forms, with the main waveguide 10, a Fabry-Pérot cavity, allowing successive reflections of light in the wavelength of interest. λ i The wavelength of interest λ i must also correspond to a resonance wavelength λ r of each Fabry-Pérot cavity, as described below. In this example, the wavelength of interest λ i is defined by the Bragg mirror having the narrowest spectral reflection band. In this case, it is the main Bragg mirror 15. It can be observed that the device allows the formation of as many Fabry-Pérot cavities as there are secondary waveguides 20. Each Fabry-Pérot cavity is formed by the main waveguide 10 and a secondary waveguide 20.

[0038] An important aspect of the invention is that each secondary waveguide is optically coupled to an amplification medium 24. The amplification medium 24, or active medium, is a laser light-emitting medium under the effect of pumping. It can, for example, consist of layers of III-V materials formed opposite the secondary waveguide 20.

[0039] The light generated by the amplification medium 24 is injected into the secondary waveguide 20, to which it is optically coupled. The amplification medium 24 can be separated from the secondary waveguide 20 by a low-index bonding layer. It is known that III-V material assemblies of the AlGaAs / GaAs type allow emission in the 600-800 nm range, and that III-V material assemblies of InGaAsP / InP allow emission in the 1300 / 1500 nm range.

[0040] The amplification layer 24 is created by transferring a III-V laser epitaxy onto the substrate, allowing the formation of active layers a few microns thick. This stack is then etched to form a waveguide above the photonic guide 20, which is itself also optimized to facilitate light transfer to / from the III-V guide. The transfer of III-V material layers onto a Si waveguide formed on a SOI-type substrate is described, for example, in Roelkens G., "III-V / silicon photonics for on-chip and inter-chip optical interconnect," Laser Photonics Rev. 4 No. 6, 751-779 (2010).

[0041] THE figures 3A et 3B schematic cross-sectional views of substrate 2 are shown respectively at the level of the main waveguide 10 and at the level of the secondary waveguide 20. figure 3B Figure 24 shows a cross-sectional view of an amplification medium. The amplification medium is configured to be coupled to a pumping system. The latter is actuated to achieve a population inversion of charge carriers in the active material. This can be optical pumping, in which case the inversion results from the absorption of a pump laser beam. Preferably, it can be electrical pumping, allowing the injection of charge carriers via a current into a pin-diode whose intrinsic region (i) is formed by the active material. Electrical pumping is simpler to implement.

[0042] The amplifying medium 24 is arranged between the coupling end 23 and the secondary Bragg mirror 25. This allows the emission of laser light, at the wavelength of interest, which is then amplified by the Fabry-Pérot cavity, since each amplifying medium 24 is arranged between two Bragg mirrors: the main Bragg mirror 15 and a secondary Bragg mirror 25.

[0043] The emission device 1 enables the emission of high-power, spatially distributed laser light, the emission resulting from the transmission of each secondary Bragg mirror 25. In the example shown, emission waveguides 29 allow the light to be emitted from the device. As previously described, the reflection by the secondary Bragg mirrors 25 is partial. The unreflected portion of the light is transmitted. Each secondary Bragg mirror 25 is positioned between a secondary waveguide 20 and at least one emission waveguide 29. The light waves emitted by each secondary waveguide 20 are coherent, at the wavelength of interest.

[0044] The use of a modulator on the main Bragg mirror 17 allows for the control of a variation in the emission wavelength of the device. A control unit 30 allows the modulator 17 to be controlled in order to regulate the spectral band of reflection of the main mirror 15.

[0045] Each Fabry-Pérot cavity is defined by resonance wavelengths, defined by the relation: λ r = 2 Ln m Or λ r is the resonance wavelength; L is the length of the Fabry-Perot cavity; n is the effective index of the waveguide formed by the main waveguide 10, the transition waveguide 13 and the secondary waveguide 20: m is an integer designating a mode of resonance.

[0046] In order to obtain a continuous variation of the emission wavelength of the device, it is advantageous for the device to include, in each Fabry-Pérot cavity, at least one modulator, called a phase modulator, so as to modulate the resonance wavelength λ r so that the latter corresponds to the wavelength of interest λ i reflected by Bragg mirrors.

[0047] In each Fabry-Pérot cavity, at least one of the reflectors is configured to address only one resonance peak.

[0048] THE figures 4A à 4D illustrate a variation in the emission wavelength of the device. On the figure 4A The spectral reflection band of the primary Bragg mirror 15 and the spectral reflection band of each secondary Bragg mirror 25 are shown. It can be observed that the primary Bragg mirror 15 reflects approximately 100% of the light, along a narrow spectral band, while each secondary Bragg mirror 25 reflects approximately 50% of the light, along a broad spectral band, which includes the narrow spectral band of the primary Bragg mirror 15. figure 4A The left-hand y-axis represents reflectance (%), and the x-axis represents wavelength (nm). The intensity of light propagating in the Fabry-Pérot cavity formed by the primary Bragg mirror 15 and the secondary Bragg mirror 25 is also shown at different wavelengths (right-hand y-axis, arbitrary unit).

[0049] On the figure 4B The spectral band of the main Bragg mirror 15, centered on a wavelength of interest, has been represented. λ i close to 1550 nm. Resonance wavelengths are also represented on the reference curve FP. λ r of each Fabry-Pérot cavity. In the example of the figure 4B the wavelength of interest λ i corresponds to a resonance wavelength λ r and the emission wavelength of the device. On the figure 4B The left y-axis represents reflectance (%), and the x-axis represents wavelength (m). figure 4C We have represented a spectral band shift of the main Bragg mirror 15. The emission wavelength of the device corresponds to a resonance wavelength λ r belonging to the spectral reflection band of the Bragg mirror, i.e. 1555 nm. This wavelength corresponds to the resonance wavelength of the Fabry-Pérot cavity included in the spectral reflection band. We then observe a discrete variation of the emission wavelength, with a jump of approximately 1548 nm ( figure 4B ) at 1555 nm ( figure 4C This allows the emission wavelength of the device to be modified according to discrete values. The emission wavelength of the device then corresponds to a resonance wavelength present in the spectral reflection band of the main Bragg mirror. On the figure 4C The left y-axis represents reflectance (%), and the x-axis represents wavelength (m). The dashed lines represent the maxima of the spectral bands reflecting the main Bragg mirror before and after the shift, respectively.

[0050] In order to obtain a continuous variation of the emission wavelength of the device, it is advantageous to accompany the variation of the spectral band of reflection of the Bragg mirror 15 with a progressive variation of resonance wavelengths λ r of the Fabry Perot cavity, as depicted on the figure 4D This allows for a resonance wavelength λ r always corresponds to a maximum of the spectral reflection band of the Bragg mirror 15.

[0051] The variation in resonance wavelength λ r The refractive index of each Fabry-Perot cavity in the device can be obtained by placing a modulator, called the main phase modulator 18, at the level of the main waveguide 10. The main phase modulator 18 is configured to vary the refractive index of the main waveguide 10. The variation in the refractive index can be achieved by localized heating or by charge injection. The main phase modulator 18 can extend over a length ranging from a few hundred microns to a few millimeters.

[0052] For a silicon waveguide, it is estimated that the spectral shift can reach 0.1 nm per K. Thus, by changing the temperature by 30°C, a spectral shift of 3 nm can be covered.

[0053] Secondary phase modulators 28 can be arranged in each secondary waveguide. Their function is to equalize the optical paths in each secondary waveguide 20. It should be noted that it is also possible to directly modulate the current (electrical pump signal) of each amplifying medium 24, which produces a variation in the amplifier's charge, and therefore a modification of the optical path. Individual adjustment allows for variabilities resulting from device manufacturing. The arrangement of secondary phase modulators 28 in each secondary waveguide allows for individual adjustment of each Fabry-Pérot cavity of the device, so that all cavities have, at any given instant, the same resonant wavelength. λ r .

[0054] Alternatively, the device shown schematically on the figure 2 can be such that the primary mirror 15 is fixed and has a broad spectral reflection band, while each secondary mirror 25 is variable and has a narrow spectral reflection band. However, such a configuration has the disadvantage of requiring the simultaneous control of several secondary mirrors 25. The configuration shown on the figure 2 has the advantage of only having to control a single Bragg mirror, in this case Bragg mirror 15, simultaneously with the control of the variation of the resonance wavelength of each Fabry-Pérot cavity, using the main modulator 18 and / or the secondary modulators 28.

[0055] The device includes a photodiode 10', positioned at the output of the primary mirror 10, which detects light leakage transmitted by the latter. When the optical paths of the secondary waveguides 20 are equal, each Fabry-Pérot cavity in the device allows the emission of phase-locked lasers, leading to a significant increase in laser power. This increase can be detected by the photodiode 10', indicating proper device operation. The optical path length of each Fabry-Pérot cavity can be equalized sequentially, by adjusting each modulator and each amplifying medium individually, to maximize the power collected at the photodiode 10'.

[0056] The device described in connection with the figure 2 is intended to obtain a spatially distributed coherent laser emission, at the level of each emission guide 29 connected to a secondary guide 20. One advantage is that the light guide carrying all the laser power is limited to the main light guide 10: the maximum power of the laser is carried over a relatively short length, typically over a few hundred microns.

[0057] Concentrating a high power density in a single silicon waveguide can lead to beam absorption through Two-Photon Absorption (TPA). This can limit the optical power emitted by the device. Distributing the beam across multiple secondary waveguides helps to mitigate the impact of this type of absorption.

[0058] One possibility is that the main waveguide 10, which concentrates the laser power, can be made from a material less susceptible to TPA-type absorption phenomena and better suited to transporting high-power light. Thus, the first material 11, forming the main waveguide, could be SiN, which does not exhibit TPA at the wavelengths of interest.

[0059] The device described in connection with the figure 2 It allows for increased laser power while multiplying the emission points. It can be used in LIDAR-type systems to increase their range.

[0060] According to another possibility, represented on the figure 5 The invention can be implemented to concentrate coherent laser waves, so as to produce a high-power beam. On the figure 5 The components, not discussed below, are identical to those described in connection with the figure 2 and have the same function.

[0061] A notable difference compared to the device shown on the figure 2Each secondary reflector 25 is fully reflective (reflection coefficient greater than 90%, or even close to 100%), while the primary reflector 15 is partially reflective, with a reflection coefficient less than 80%, or even 50%. Light is emitted by an emission waveguide 19, connected to the primary waveguide 10. The primary reflector 15 acts as a light extractor. It extends between the primary waveguide 10 and the emission waveguide 19. Light is emitted from the light transmitted by the primary Bragg mirror. A coupler 19' directs a small percentage of light, for example 1%, to the photodiode 10'. This photodiode is used to monitor the laser power emitted by the device. It verifies that phase locking of the different lasers has been achieved.

[0062] Regardless of the embodiment, the device can be used to emit a high-power laser beam without necessarily varying the emission wavelength over time. In this case, it is not necessary for at least one reflector, specifically the main reflector, to be modulated. Similarly, it is not necessary to modulate the resonant frequency of the Fabry-Pérot cavities. The main modulator 18 is not required. The use of secondary modulators 28 remains preferable for adjusting the optical paths in each secondary waveguide 20. The device can be used for photonic computing applications, in which mathematical operations are performed by generating destructive or constructive interference between several coherent laser beams. Constructive interference can be described as addition. Destructive interference can be described as subtraction.

Claims

1. Laser emission device (1, 1') integrated into a substrate (2), comprising: - a primary waveguide (10), formed in the substrate, and extending from a primary reflector (15), the primary reflector being configured to reflect light in a reflection spectral band; - a plurality of secondary waveguides (20), optically connected to the primary waveguide (10), each secondary waveguide extending between a coupling end (13), optically connected to the primary waveguide (10), and a secondary reflector (25), each secondary reflector being configured to reflect light in the reflection spectral band; - each secondary waveguide (20) is optically coupled to a gain medium (24) connected to a laser-pumping system (26), the gain medium being conducive to laser emission under the effect of pumping exerted by the laser-pumping system, the gain medium being placed between the coupling end and (23) the secondary reflector (25) of the secondary waveguide so that the device forms as many Fabry-Pérot cavities as secondary waveguides, each Fabry-Pérot cavity being configured to allow multiple reflections of light at a given resonant wavelength, in the reflection spectral band, between the primary reflector and each secondary reflector; - the device comprises an extractor (15, 25), for extracting light from the device, at the resonant wavelength, said resonant wavelength forming an emission wavelength of the device; the device being characterized in that - the secondary waveguides define optical path lengths that are equal to one another.

2. Device according to Claim 1, wherein the primary reflector or each secondary reflector is adjustable, so as to modulate the reflection spectral band.

3. Device according to Claim 2, wherein the reflection spectral band of the primary reflector is adjustable, the primary reflector being a Bragg mirror, coupled to a modulator (17) configured to modulate a refractive index in said Bragg mirror.

4. Device according to Claim 3, wherein the secondary reflector reflects light in a set secondary reflection spectral band wider than the reflection spectral band of the primary reflector.

5. Device according to Claim 4, wherein the reflection spectral band of each secondary reflector is adjustable, each secondary reflector being a Bragg mirror, coupled to a modulator (27) configured to modulate a refractive index in said Bragg mirror.

6. Device according to Claim 5, wherein the primary reflector reflects light in a set reflection spectral band wider than the reflection spectral band of each secondary reflector.

7. Device according to any one of the preceding claims, wherein at least one secondary waveguide (20) comprises a secondary phase modulator (28), configured to modulate a refractive index along a portion of said secondary waveguide (25), the secondary phase modulator being placed between the coupling end (23) of said secondary waveguide and the secondary reflector (25) of the secondary waveguide, so as to modulate an optical path length in said secondary waveguide.

8. Device according to Claim 7, wherein each secondary waveguide comprises a secondary phase modulator, configured to modulate a refractive index along a portion of said secondary waveguide, the secondary phase modulator being placed between the coupling end of said secondary waveguide and the secondary reflector of said secondary waveguide, so as to modulate an optical path length in each secondary waveguide.

9. Device according to any one of the preceding claims, wherein the primary waveguide comprises a primary phase modulator (18), configured to modulate a refractive index along a portion of the primary waveguide, the primary phase modulator being placed between each secondary waveguide and the primary reflector, so as to modulate the resonant wavelength of each Fabry-Pérot cavity of the device.

10. Device according to any one of the preceding claims, wherein: - the primary reflector (15) reflects more than 90% of the light, in the reflection spectral band; - each secondary reflector (25) transmits at least 20% of the light, in the reflection spectral band, so that the secondary reflector forms the extractor of the device.

11. Device according to any one of claims 1 to 9, wherein: - each secondary reflector (25) reflects more than 90% of the light, in the reflection spectral band; - the primary reflector transmits at least 20% in the reflection spectral band, so that the primary reflector forms the extractor of the device.

12. Device according to any one of the preceding claims, wherein the primary waveguide is formed by a first material (11), and surrounded by a first auxiliary material (12,3), the refractive index of which is lower than the refractive index of the first material.

13. Device according to any one of the preceding claims, wherein each secondary waveguide (20) is formed by a second material (21), and surrounded by a second auxiliary material (22,3), the refractive index of which is lower than the refractive index of the second material.

14. Device according to claims 12 and 13, wherein: - the first material is identical to the second material; - the first auxiliary material is identical to the second auxiliary material.

15. Device according to any one of the preceding claims, wherein the primary waveguide and each secondary waveguide are formed in the same substrate (2), each gain medium (24) being transferred to said substrate.