FR3068527A1 - LASER SOURCE WITH SEMICONDUCTOR - Google Patents

Abstract

A semiconductor laser source in which, for optically coupling a third waveguide (15, 36) to a first waveguide (28) via a second waveguide (25), a resonant optical cavity comprises at least one network-assisted contra-directional coupler (24, 34) adapted to convert the bulk of the optical signal to a wavelength λ Li which propagates in one direction along the third waveguide (15, 36), in an optical signal of the same wavelength, which propagates in opposite directions in the first (28) or the second (25) waveguide, this contra-directional coupler comprising for this purpose at at least one part made in the third waveguide (15, 36) and an array of repeating units with a regular pitch, this array of patterns being realized in the second (25) or the third (15, 36) guide. wave.

Description

SEMICONDUCTOR LASER SOURCE [001] The invention relates to a semiconductor laser source capable of emitting at at least one wavelength Au.

Known laser sources include:

a substrate on which are stacked, in order, a first, a second and a third layer, this substrate extending essentially in a plane called “plane of the substrate” and the different layers extending parallel to the plane of the substrate ,

an optical cavity capable of causing the optical signal to resonate at the wavelength Au, this optical cavity comprising:

A first waveguide whose heart is made of III-V gain material to amplify the optical signal at the wavelength A _Li which propagates along the heart of this first waveguide, this first guide wave being located inside the first layer, • a second wave guide whose core is made of silicon, this second wave guide being located inside the second layer, • a third guide wave whose core is made of a material less sensitive to temperature, that is to say made of a material whose variation dn _f / dT of its refractive index as a function of temperature is at least twice less than the variation dn _S i / dT of the refractive index of silicon as a function of the temperature, this third waveguide being located inside the third layer and optically coupled to the first waveguide by l second waveguide.

For example, such a laser source is disclosed in application US2014153600. In this known laser source, the resonant cavity is a Fabry-Pérot cavity. The ends of the resonant cavity are defined by reflectors between which the optical signal goes back and forth. In application US2014153600, these reflectors are Bragg gratings also known by the acronym DBR (“Distributed Bragg Reflector”) and the material of the third waveguide is silicon nitride. The reflectors are made in the third waveguide of material less sensitive to temperature. Conventionally, the filter which is responsible for selecting the emission wavelength Au of the laser source is produced in the silicon waveguide. The temperature sensitivity of this laser source is quite high.

By "sensitivity to the temperature of the laser source" is meant here the fact that the emission wavelength A _Li of this laser source varies as a function of the temperature of the laser source.

Also known from application FR2954638 is another laser source in which the resonant cavity is not a Fabry-Perot cavity. This resonant cavity is constructed using contra-directional couplers and not using reflectors. In this case, inside the resonant cavity, the optical signal circulates along a loop, part of which is made in the waveguide of III-V material and the other part of which is made in the guide. silicon wave.

Counter-directional couplers are also known by the acronym GACC ("Grating-Assisted Contra-directional Coupler"). These contradirectional couplers are known. For example, the operating principle and examples of embodiment of contra-directional couplers in silicon photonics are described in the following article: Wei Shi et Al, “Silicon photonic grating-assisted contra-directional couplers”, Optics Express. Flight. 21, no 3, February 2013.

This known laser source also works correctly. However, its sensitivity to temperature is also quite important.

The invention therefore aims to provide a semiconductor laser source less sensitive to temperature. It therefore relates to such a laser source in which to optically couple the third waveguide to the first waveguide via the second waveguide, the optical cavity comprises at least one contra-directional coupler assisted by network capable of transforming most of the optical signal at wavelength A _Li which propagates in one direction along the third waveguide, into an optical signal of the same wavelength Au, which propagates in direction opposite in the first or second waveguide, this contra-directional coupler comprising for this purpose at least one part made in the third waveguide and an array of repeating patterns with a regular pitch "a" in the direction of propagation of the optical signal at wavelength Au, this network of patterns being produced in the second or third waveguide.

The embodiments of this laser source can have one or more of the following characteristics:

the network of repeated patterns is only produced inside the second waveguide;

the second waveguide has a first region optically coupled, by adiabatic or evanescent coupling, to a first region opposite the first waveguide so as to allow the optical signal at wavelength A _Li to pass from the second waveguide to the first waveguide and vice versa; the third waveguide comprises a first region optically coupled, via the contra-directional coupler, to a second region opposite the second waveguide so as to allow the optical signal at the length d Au wave to pass from the third waveguide to the second waveguide and vice versa, the regular pitch "a" of the network of repeated patterns of the directional coupler being for this purpose equal to mA _L i / (n _e ff-si + neff-f) more or less 5%, where:

- rieff-si and rieff-f are the effective propagation indices, respectively, of the second and third waveguides, and

- M is an integer strictly greater than zero, the first and second regions of the second waveguide being offset relative to each other along the second waveguide;

the optical cavity is able to resonate an optical signal at at least one possible wavelength A _Rj , and the laser source also includes:

a tuning device capable of shifting the wavelength A _Rj in response to an electrical control signal,

a sensor capable of measuring a physical quantity representative of the difference between the wavelength Au and the wavelength A _Rj possible, and

an electronic circuit capable of generating, as a function of the physical quantity measured by the sensor, the electrical control signal of the tuning device to maintain the wavelength A _Rj equal to the wavelength A _Li ;

the optical cavity is capable of causing the optical signal to resonate at several possible resonant frequencies, the possible wavelengths A _Rj of these possible resonant frequencies being regularly spaced from one another by an interval Δλ _κ and all included in the inside a reflective strip of width AR, and the width of the passband of the contra-directional coupler is less than the interval Δλ _κ ;

the optical cavity is capable of causing the optical signal to resonate at several possible resonant frequencies, the possible wavelengths A _Rj of these possible resonant frequencies being regularly spaced from one another by an interval Δλ _κ and all included in the inside a reflective strip of width AR, and the passband of the contradirectional coupler is greater than twice the interval Δλ _κ , and the optical cavity comprises, in addition to the contra-directional coupler, an additional bandpass filter entirely produced in the material less sensitive to temperature and arranged to be traversed by the resonant optical signal, this additional bandpass filter having a passband centered on the wavelength A _Li and of width less than the interval Δλ _κ , this additional bandpass filter comprising a resonant ring for this purpose;

the optical cavity is capable of causing the optical signal to resonate at several possible resonant frequencies, the possible wavelengths A _Rj of these possible resonant frequencies being regularly spaced from one another by an interval Δλ _κ and all included in the inside a reflective band of width AR, and the passband of the contradirectional coupler is greater than twice the interval Δλ _κ , and the optical cavity is devoid of additional bandpass filter capable of reducing the passband of the counter coupler directional;

the optical cavity includes:

a fourth waveguide, the heart of which is made of the same material as the third waveguide, this fourth waveguide being located inside the third layer,

- a front reflector and a rear reflector optically connected to each other via the first, second, third and fourth waveguides, these front and rear reflectors forming the ends of a Fabry optical cavity- Perot able to resonate the optical signal at the wavelength A _u , the front and rear reflectors being produced inside, respectively, the third and fourth waveguides;

the first region of the third waveguide is optically coupled, via a first contra-directional coupler, to the second region of the second waveguide, and the third waveguide has a second optically coupled region , via a second contra-directional coupler, to a third region facing the second waveguide so as to allow the optical signal at the wavelength Au to pass from the third guide wave towards the second waveguide and vice versa, the first and third regions of the second waveguide being located on either side of the second region of the second waveguide;

the contra-directional coupler comprises first, second and third parts produced inside, respectively, the first, second and third waveguides, these three parts being stacked one above the other in a direction perpendicular to the plane of the substrate and the regular pitch "a" of the network of repeated patterns being equal to mA _u / (neff-m-v + neff-f) to within plus or minus 5%, where:

- n _e ff-iii-v and n _e ff-f are the effective propagation indices, respectively, of the first and third waveguides, and

- m is an integer strictly greater than zero, the network of repeated patterns being produced in the second or third part of the contra-directional coupler;

the laser source comprises first and second contradirectional couplers, and the networks of repeated patterns of these first and second contra-directional couplers are separated from each other by a region devoid of repeated pattern, the width of this region being equal to (n + l) a, where "a" is the pitch of the repeated pattern networks of the first and second contra-directional couplers;

the material less sensitive to temperature is silicon nitride or aluminum nitride.

The invention will be better understood on reading the description which follows, given solely by way of nonlimiting example and made with reference to the drawings in which:

- Figures 1 to 3 are schematic representations of the position of the reflective strip of the reflectors of a semiconductor laser source with respect to the pass band of a filter of this semiconductor laser source;

- Figure 4 is a schematic illustration of the architecture of a semiconductor laser source;

- Figure 5 is a schematic illustration from above of an example of a resonant ring filter that can be used in the laser source of Figure 4;

- Figure 6 is a graph schematically illustrating the position of the reflective band of the reflectors relative to the pass band of the filter of Figure 5;

- Figures 7A and 7B are schematic illustrations in vertical section along, respectively, a longitudinal plane and a transverse plane, of a contradirectional coupler implemented in the laser source of Figure 4;

- Figure 8 is a schematic illustration, in vertical section, of a first embodiment of the laser source of Figure 4;

- Figures 9 to 11 are schematic illustrations, in vertical section, of several possible variants of the laser source of Figure 8;

- Figure 12 is a schematic illustration of the architecture of a multi-wavelength laser source;

- Figure 13 is a graph schematically illustrating the position of the reflective band of the reflectors of the laser source of Figure 12 relative to the pass bands of a filter of this laser source;

- Figures 14 and 15 are schematic illustrations in vertical section along, respectively, a longitudinal plane and a transverse plane, of another embodiment of a laser source;

- Figure 16 is a schematic illustration, in vertical section, of another embodiment of a laser source.

In these figures, the same references are used to designate the same elements. In the remainder of this description, the characteristics and functions well known to those skilled in the art are not described in detail.

In this description, a material which is less sensitive to temperature is a material whose variation dn _f / dT of its refractive index n _f as a function of temperature is at least twice less, under the same conditions, than the variation dn _S j / dT of the index n _s , of refraction of the silicon as a function of the temperature. Typically, the variation dn _S j / dT is equal to 2.3 x 10 ^_4 / ° C to within plus or minus 20%. Thus, the variation dn _f / dT is at least less than 1 x 10 ^-4 / ° C and, preferably, less than 0.5 x 10 ^-4 / ° C. Subsequently, the main embodiments are described in the particular case where the material less sensitive to temperature is silicon nitride (Si ₃ N ₄ ) whose variation dn _f / dT is equal to 0.4 x 10 ^-4 / ° C. However, as described in detail at the end of this description, other materials are possible. The refractive index of silicon nitride varies depending on the temperature six to seven times slower than that of silicon.

In this description, when it is indicated that a waveguide is made of material X, this means that the core of this waveguide is made of this material X. The sheath of this guide wave is made of another material with a lower refractive index.

Thereafter, the description is divided into three chapters, each chapter corresponds to a family of possible embodiments.

Chapter I: Laser source with a contra-directional Si / SiN coupling The reason why the production of the filter in a waveguide made of material less sensitive to temperature decreases the sensitivity of the laser source to the temperature will first be explained in detail with reference to FIGS. 1 to 3. Next, the general architecture of a semiconductor laser source using such a filter is described followed by several specific examples of embodiment.

Figure 1 shows a reflective strip 4 of the front and rear reflectors of a Fabry-Pérot optical cavity of a semiconductor laser source. This bandwidth 4 is represented on a graph where the abscissa axis represents the wavelength and is expressed in nanometers and the ordinate axis corresponds to the power of the optical signal expressed in Watt.

The reflective strip 4 is characterized by its width AR and its central wavelength A _C r. The width AR is the width of the reflective strip 4 at -3 dB. It is the wavelength band containing all the wavelengths A _Rj capable of being reflected by the front and rear reflectors with a power greater than or equal to 50% of the maximum power l _max reflected by these reflectors . The power l _ma x is equal to the power of the reflected optical signal for the wavelength A _Rj for which this power is maximum.

The central wavelength A _C r is the wavelength located in the middle of the reflective strip 4.

In the context of a Fabry-Pérot cavity, the different wavelengths A _{Rj to} which this cavity is likely to resonate are regularly spaced from each other by an interval Δλ _κ . In FIG. 1, the wavelengths A _{Rj at} which the Fabry-Pérot cavity can resonate and which are located inside the passband 4 are represented by vertical lines.

In the context of a monochromatic laser source which emits at a single wavelength A _Li , the filter selects from the set of possible wavelengths A _Rj only one of these wavelengths A _Rj . The wavelength A _Rj selected is equal to the emission wavelength Au of the laser source. For this purpose, the filter has a single narrow passband 6 centered on the wavelength Au. This passband 6 is characterized by its width AA _f and by its central wavelength A _C f. The width AA _f is the width of the passband 6 at -3 dB. The central wavelength A _C t is the wavelength located in the middle of the passband 6. To select the only wavelength Au, the width AA _f is less than or equal to the interval Δλ _κ . To select the wavelength Au, one of the wavelengths Arj, typically the closest to A _C t, is tuned to be equal to this wavelength A _C f. This wavelength A _Rj which is equal to the wavelength A _C f corresponds to the wavelength A _Li .

The graph of Figure 1 is shown for an operating temperature of the laser source equal to 20 ° C.

In known laser sources, the optical signal is guided between the front and rear reflectors by waveguides in silicon and in III-V gain materials and the filter is made in the silicon waveguide. Under these conditions, it is known that the wavelengths A _Rj move as a function of the temperature of about 0.07 nm / ° C.

To illustrate this, the graph in Figure 2 represents the same elements as the graph in Figure 1, but for an operating temperature of the laser source equal to 33 ° C. It can be observed :

- that the passband 4 and the wavelength A _CR have moved by about 0.13 nm (= 0.01 x 13 ° C) because the reflectors are here produced in the waveguide made of silicon nitride, and

- that the passband 6 has moved by about 0.9 nm (about 0.07 x 13 ° C) because the filter is made in the silicon waveguide.

The wavelength A _Li of the laser source has therefore moved about 0.9 nm.

To limit this drift in the wavelength A _Li , the solution proposed here consists in making at least part of the filter in the material less sensitive to temperature. Under these conditions, for example, the central wavelength A _C f of the filter moves, as a function of the temperature, only about 0.01 nm / ° C.

Figure 3 shows the position of the reflective strip 4 and the pass band 6 in the case where the filter is made in a silicon nitride waveguide and for an operating temperature of the laser source of 33 ° C. As shown in the graph in Figure 3, the central wavelength A _C f of the filter only moves 0.13 nm (= 0.01 x 13 ° C) in response to a 13 ° C increase in the temperature of operation of the laser source. On the other hand, the amplitude of the displacement of the central wavelength A _CR is the same as in the case represented in FIG. 2. However, the fact of only making at least part of the filter in a material less sensitive to the temperature is already sufficient to limit the sensitivity of the wavelength A _C f to temperature. However, since it is the filter which selects the emission wavelength Au of the laser source, it becomes possible to obtain an emission wavelength Au of the laser source that is less sensitive to temperature.

Figure 4 schematically shows the general architecture of a laser source 10 with monochromatic semiconductor which emits at the wavelength A _u . The laser source 10 comprises a rear reflector 12 and a front reflector 14 which define the ends of the Fabry-Pérot cavity inside which the optical signal resonates. For example, the reflector 12 has a reflection factor strictly greater than that of the reflector 14. The reflection factor is equal to the ratio between the power of the optical signal reflected by the reflector on the power of the optical signal incident on this reflector. Typically, the reflectance of the reflector 12 is greater than or equal to 90% or 95% for the wavelength Au. The reflectance of the reflector 14 is generally between 30% and 70% and is typically 50%.

The reflectors 12 and 14 are, for example, broadband reflectors. In this embodiment, this means that the width AR of the reflective strip 4 of the reflectors 12 and 14 is strictly greater than AA _f + DT x (dA _C R / dT), where:

- Δλ (is the width of the passband 6 of the filter which selects the wavelength A _Li , expressed in nanometers,

DT is the width of the predetermined range of operating temperatures of the laser source 10, expressed in ° C,

- dAcR / dT is the variation of the central wavelength A _C r of the reflecting band of the reflectors 12 and 14 as a function of the temperature, expressed in nm / ° C.

The range of operating temperatures of a laser source is often chosen today so that, whatever the operating temperature of the laser source located within this range, this does not cause a variation in the wavelength A _Li greater than 0.35 nm. Thus, for example, the width DT of this range is greater than 10 ° C or 30 ° C. To comply with this criterion, here the operating temperature range is chosen to be between + 20 ° C and + 55 ° C. The width DT is therefore here equal to 35 ° C. Thereafter, the smallest and the largest temperatures in the operating temperature range are noted, respectively, T mm and T _ma x. In this embodiment, the reflectors 12 and 14 are produced in a waveguide made of silicon nitride. Thus, the variation dA ^ / dT is here equal to 0.01 nm / ° C. As described with reference to Figures 1 to 3, the width AA _f is less than the interval Δλ _κ . Typically, the interval Δλ _κ is less than or equal to 0.5 nm. For example, here, the interval Δλ _κ is equal is 0.3 nm to 15% or 30%. Thus, in this embodiment, the width Δλ ₍ is less than or equal to 0.3 nm. The width AR is therefore here strictly greater than 0.65 nm (= 0.01 x 35 + 0.3).

Here, the reflectors 12 and 14 are for example reflectors such as Bragg gratings.

Between the reflectors 12 and 14, the laser source successively comprises the following photonic components going from the reflector 12 to the reflector 14:

an optical waveguide 15 made of silicon nitride (Si ₃ N ₄ ) in which the reflector 12 is made,

- an optional bandpass filter 22 able to select the wavelength Au of the laser source 10 operating among the different wavelengths A _Rj possible inside the Fabry-Pérot cavity, this filter 22 being produced in the waveguide 15 made of silicon nitride,

a contra-directional coupler 24 which optically connects a first region of the waveguide 15 to a first region facing a silicon waveguide 25,

the silicon waveguide 25,

- an optional tuning device 16 produced in the waveguide 25, this tuning device 16 being able to move the wavelengths A _Rj as a function of an electrical control signal and using the properties of silicon waveguide 25,

an adiabatic or evanescent coupler 26 which optically connects a second region of the waveguide 25 to a first region opposite a waveguide 28 of gain material III-V,

a semiconductor optical amplifier 30 better known by the acronym SOA (“Semiconductor Optical Amplifier”) produced in the waveguide 28 and capable of generating and amplifying the resonant optical signal inside the cavity of FabryPérot at each wavelength A _Rj ,

an adiabatic or evanescent coupler 32 which optically connects a second region of the waveguide 28 to a third region facing the waveguide 25,

a contra-directional coupler 34 which optically connects a fourth region of the waveguide 25 to a first region facing a waveguide 36 of silicon nitride (Si ₃ N ₄ ), and

the reflector 14 produced in the end of the waveguide 36.

In this description, by "opposite" means the fact that the orthogonal projection of a part or region or area in the plane of the substrate is entirely included inside the orthogonal projection, in the same shot, of the other party or region or zone located opposite. These parts or regions or zones are therefore opposite one another in the vertical direction, that is to say in a direction perpendicular to the plane of the substrate on which the laser source is produced and separated from one another. the other only by a dielectric material whose index of refraction n _S io2 is smaller than the indices n _s , and n _f . Typically, the index n _S io2 is less than or equal to 0.85 x Min (n _S j; n _f ) or less than or equal to 0.75 x Min (n _si ; n _f ), where Min (n _S i ; n _f ) is the function which returns the smallest of the indices n _S i and n _f .

Thereafter, only the features of the laser source 10 are described in detail. For general information on the production and operation of a semiconductor laser source using waveguides made of silicon and of gain material III-V, the reader can consult the following article: B. Ben Bakir and al., "Hybrid Si / lll-V lasers with adiabatic coupling", 2011.

For a detailed description of an adiabatic coupler, the reader is referred to the following article: Amnon Yariv et al., "Supermode Si / lll-V hybrid Lasers, optical amplifiers and modulators: proposai and analysis" Optics Express 9147, vol. 14, No. 15, 07/23/2007.

In particular, an adiabatic coupler is capable of transferring almost all of the optical signal present in a first waveguide to a second waveguide located above or below, without reflection. For example, the power of the optical signal transferred in the second waveguide is greater than or equal to 95% of the power of the optical signal which flows in the first waveguide. Such an adiabatic coupler is, for example, obtained by modifying the width of the first waveguide relative to the width of the second waveguide. Typically for an adiabatic coupling of a silicon waveguide to a waveguide of lll-V material, the width of the silicon waveguide is gradually reduced as the waveguide of lll material is approached -V. Conversely, to transfer by adiabatic coupling an optical signal from the waveguide of III-V material to the first silicon waveguide, the width of the silicon waveguide is for example gradually increased. In addition, the waveguides made of silicon and of material III-V generally have a width such that there are zones of these waveguides opposite where their respective effective propagation indices are equal. The effective propagation index n _e tf is also known as the "phase phase constant". It is defined by the following relation: n _g = ηθ "- Adn _e tf / dA, where n _g is the group index and λ is the wavelength of the optical signal guided by the guide. The effective propagation index of a waveguide depends on the dimensions of the core of this waveguide and on the materials forming this core and the sheath of this waveguide. It can be determined experimentally or by numerical simulation.

In this embodiment, the filter 22 is a resonant ring filter whose ring is made in a waveguide 50 (Figure 5) in Si ₃ N ₄ . Preferably, the waveguide 50 in which the ring is made is directly optically connected to two ends of the waveguide 15 by evanescent coupling. Evanescent coupling is obtained by bringing the two waveguides closer to one another.

To generate the electrical control signal of the tuning device 16, the laser source 10 also includes:

a sensor 40 capable of measuring a physical quantity representative of the difference between the wavelength A _C t and the closest to the wavelengths A _RJ , and

an electronic circuit 42 capable of generating the electrical control signal of the tuning device 16 so as to permanently maintain a wavelength A _Rj at the center of the passband 6 of the filter 22.

For this purpose, here, the sensor 40 measures the power of the optical signal emitted by the laser source 10. In this embodiment, the laser source 10 has two possible outputs for the resonant optical signal, namely by crossing the reflector 14 either by crossing the reflector 12. Since the reflectance of the reflector 12 is greater than that of the reflector 14, the optical signal which leaves when passing through the reflector 12 has a much weaker power than that which leaves when passing through the reflector 14. Conventionally, the optical signal which leaves by passing through the reflector 14 is called “useful optical signal” and that which leaves by passing through the reflector 12 is called “optical piloting signal” or “optical monitoring signal”. Here, the sensor 40 measures the power of the optical signal which passes through the reflector 12. For example, the sensor 40 comprises a photo-detector which measures the power of the optical signal. The power thus measured is transmitted to the electronic circuit 42. This measured power is representative of the difference between the wavelengths A _C f and the closest to the wavelengths A _Rj . Indeed, the power measured is maximum when the wavelength A _C f is aligned with one of the wavelengths A _Rj . This power decreases continuously as the wavelength A _Rj moves away from the wavelength A _C f as long as one remains within a width interval Δλ _κ centered on the wavelength A _C f.

The electronic circuit 42 constructs the control signal which makes it possible to maintain a wavelength A _Rj at the center of the passband 6 as a function of the physical quantity measured by the sensor 40. For this purpose, it is electrically connected to the sensor 40. In addition, it is electrically connected to the tuning device 16 to transmit to it the electrical control signal generated. Typically, the sensor 40 is produced on the same substrate as the other photonic components of the laser source 10. For example, the sensor 40 is a germanium photodiode. The electronic circuit 42 is often attached to this substrate.

The light that emerges through the reflectors 12 and 14 is then guided, for example, to a photodiode or an optical fiber. For this additional optical components are used. Since these additional optical components are conventional, they are not described here in detail and, to simplify the figures, they are also not shown. For example, if a photodiode is produced in a silicon layer situated above the layer in which the reflectors 12 and 14 are produced, then an optical coupler optically connects the output of the reflector 12 or 14 to this photodiode. If the output of the laser source 10 is connected to an optical fiber, then an optical coupler optically directly connects the output of the reflector to this optical fiber. In the latter case, such a coupler can be produced on the edge of the reflector or it can also be a surface network made of silicon nitride.

Figure 5 shows in more detail the filter 22 in the case where it is produced using a resonant ring. To this end, the waveguide 50 forms a ring directly optically connected to two respective ends of the waveguide 15 only by evanescent couplings. This ring is made of silicon nitride. In this figure 5 the two ends of the guide 15 optically connected to the filter 22 are denoted, respectively, ZZE and ZZS.

Figure 6 shows the transmission spectrum of the filter 22. This spectrum has several bandwidths regularly spaced from each other. Here, the central frequencies of two successive passbands are spaced from each other by an interval Av _f . This Av _f interval is better known by the acronym FSR ("Free Spectral Range"). In the graph of FIG. 6, only three bandwidths 6, 52 and 54 all located inside the bandwidth 4 are shown.

In this embodiment, the dimensions of the filter 22 are determined by numerical simulation or experimentally so that the interval Av _f is strictly less, and for example at least two times less, when the AR is released from the reflective strip 4 Thus, several of the passbands of the filter 22, that is to say here the passbands 6, 52 and 54, are located inside the reflective strip 4 whatever the operating temperature. Consequently, the filter 22 makes it possible to simultaneously select several wavelengths A _Rj , denoted A _Rj _ ₂ , A _Li and A _{Rj + 2} in FIG. 6. Thus, if no additional filter is used, the laser source 10 is a polychromatic laser source and not a monochromatic laser source of wavelength Au.

For example, the values of the wavelength A _C f and of the interval Av _f of the filter 22 are fixed on the basis of the following parameters: the perimeter of the ring, the effective index n _e tf of propagation in the waveguide 50, the index n _g of the group in the waveguide 50 (“refractive group index” in English) and the order of resonance K. By way of illustration, the length of wave A _C f and the interval Av _f are estimated using the following relationships:

perimeter <n ^ (J,) Ay _K * At ² Δν, "'perimeter. not

where “perimeter” is the perimeter of the ring produced in the waveguide 50 and A is the wavelength of the optical signal for which the wavelength A _C f and the interval Av _f are calculated.

The width AA _f can be determined by the propagation losses in the waveguide 50 of the ring and the evanescent coupling coefficients of the waveguide 50 with the ends ZZE and ZZS of the waveguide 15 .

The dimensions of the filter 22 are also determined to obtain the desired properties of the evanescent couplings between the waveguide 50 of the ring and the ends ZZE and ZZS of the waveguide 15 and in particular the transfer rate of power between the waveguides 15, 50.

In this embodiment, to obtain a monochromatic laser source of wavelength Au, an additional filter is combined with the filter 22. The passband 56 of this additional filter is shown in FIG. 6. The passband 56 is centered on the wavelength Au. The width of the passband 56 is shown in the particular case where it is greater than 2Δλκ, where Δλρ is the interval between two successive wavelengths A _Rj . It is mainly in this case that it is advantageous to combine the filter 22 and an additional filter. Indeed, in this case, only the combination of these two filters makes it possible to obtain a monochromatic laser source. Conversely, if one of these two filters alone was able to select only the wavelength Au, then the use of the other filter would be useless. In this embodiment, the function of the additional filter is fulfilled by one or both of the couplers 24 and 34. Indeed, a contra-directional coupler, in addition to providing an optical coupling between two waveguides, also fulfills the function of a filter. It is therefore not necessary to provide in the laser source 10 an additional filter other than the coupler 24 or 34. The passband 56 here corresponds to the passband of the coupler 24 or 34.

Figures 7A and 7B show in detail an exemplary embodiment of the coupler 24. The coupler 34 is, for example, made as the coupler 24. The coupler 24 has a lower part 44 and an upper part 46, made , respectively, in the regions facing the waveguides 15 and 25. Here, the dielectric material interposed between the parts 44 and 46 is silicon oxide. In FIGS. 7A and 7B as well as in all the figures showing a vertical section, this dielectric material is not shown. This dielectric material also forms the sheath of the waveguides of silicon and silicon nitride. In FIGS. 7A and 7B and in the following figures in vertical section, only the core of these waveguides is shown.

In FIG. 7A, the double arrows Ss, and Ss, n represent the directions of propagation of the optical signal in the waveguides, 25 and 15 respectively.

The coupler 24 comprises an array 48 of patterns repeated at regular intervals with a pitch "a" along the direction of propagation of the optical signal. In this particular embodiment, the network 48 is only produced in the part 46. The part 44 is devoid of a network of repeated patterns.

The repeated pattern is for example a groove 49 hollowed out in the lower face of the part 46. The lower face of the part 46 is that which is turned towards the part 44. Two successive grooves delimit between them a tooth or a stud 51. These grooves 49 and teeth 51 extend mainly in a direction perpendicular to the direction of propagation of the optical signal.

So that an optical signal at the wavelength A _u can be transferred from the waveguide 15 to the waveguide 25 and vice versa thanks to the coupler 24, the pitch "a" is chosen to be equal at mA _L i / (n _e ff-si + ηθη-Ο within plus or minus 5% near or 2% near, where:

- neff-si and n _e tf-f are the effective propagation indices, respectively, of the waveguides 25 and 15, and

- m is a positive integer.

Preferably, m is equal to 1. Such a coupler 24 has a passband Δλ ₂₄ centered on a wavelength A _C24 . The coupler 24 is here designed so that its passband Δλ ₂₄ corresponds to the passband 56 previously described and that the wavelength A _C24 is equal to Au. The coupler 24 therefore fulfills the function of an additional bandpass filter. As with filter 22, its bandwidth moves as a function of temperature. However, the displacement of its bandwidth is here clearly less than what would be observed if this coupler were entirely made of silicon. Indeed, the part 44 is made of a material less sensitive to temperature.

In known manner, the width of the passband of the coupler 24 can be adjusted by adjusting different dimensions of the coupler 24, such as for example:

- the depth of the grooves 49,

- the number of repeated patterns,

- the width of the network 48,

the width and the length of the parts 44 and 46 in a plane parallel to the plane of the substrate,

the distance between the parts 44 and 46 in a direction perpendicular to the plane of the substrate,

- ... etc.

In this embodiment, the filter 22 is used above all to further reduce the spectrum of the optical signal which would be generated by the laser source 10 in the absence of this filter 22.

Figure 7B shows in a cross section the different dimensions of the coupler 24. In this embodiment, the guide 25 is an edge waveguide comprising a slab ("slab" in English thickness e _46i and an edge of thickness e ₄₆₃ . The width of the edge is denoted La ₄₆ i and the width of the slab is denoted La ₄₆₂ in this figure. The depth of the grooves 49 is denoted e ₄₆₂ . The grooves 49 are only hollowed out in the edge and over the entire width of this edge.

The thickness and the width of the part 44 are noted, respectively e ₄₄ and La ₄₄ . The thickness of the dielectric material between the teeth 51 and the part 44 is denoted e _S io2. By way of illustration, when the wavelength Au is equal to 1310 nm, the dimensions of the coupler 24 can have the following values: La 46i - 400 nm, La ₄ 62 = 5 pm, e ₄ 6i = 200 nm, e ₄ 62 = 150 nm, e ₄ 63 = 300 nm, e _S io2 = 200 nm, Θ44 = 600 nm and La ₄₄ = 700 nm.

When the wavelength A _Li is equal to 1310 nm, the pitch "a" is equal to 280 nm. For example, the number of grooves 49 is greater than or equal to 100, and preferably greater than or equal to 300. Generally, the number of grooves 49 is less than 1000 or 5000.

Figure 8 shows a first embodiment of the laser source 10. Here, the laser source 10 is fabricated on a silicon substrate 60 which mainly extends in a horizontal plane corresponding to the plane of the substrate.

In FIG. 8, the laser source 10 successively comprises stacked above the substrate 60, going from the bottom to the top:

a layer 64 of silicon nitride encapsulated in silicon oxide and which contains the waveguides 15 and 36,

a layer 66 of monocrystalline silicon encapsulated in silicon oxide in which the waveguide 25 is made, and

a layer 68 comprising the waveguide 28 inside which the amplifier 30 is produced.

The substrate 60 is for example made of crystalline silicon.

The adiabatic couplers 26 and 32 are produced in part in the waveguide 25 and in the waveguide 28.

Preferably, the amplifier 30 is a broadband amplifier, that is to say capable of generating and amplifying a large range of wavelengths. This range includes the wavelength Au. Typically, it is centered on this wavelength Au at temperature (T _m ax + T _m in) / 2. The width of this wavelength range at -3 dB is for example at least 10 nm or 25 nm or 35 nm and remains wide with the increase in temperature. For example, the III-V materials constituting the amplifier 30 are those described in the following article: Dimitris Fitsios et al. "High-gain 1.3 pm GalnNAs semiconductor optical amplifier with enchanced temperature stability for all-optical processing at 10 Gb / s", Applied optics, May 2015 vol. 54, no. 1, January 1, 2015. The fact of producing the amplifier 30 as described in this article also makes it possible to obtain a broadband amplifier stable in temperature. This improves the operation of the laser source and in particular it makes it possible to maintain a power emitted by the laser source almost constant throughout the range of operating temperatures [T _min ; T _ma x]. In this case, the waveguide 28 and the amplifier 30 are in the form of a stack of alternating sublayers in GalnNAs and in GaNAs interposed between a lower sublayer 70 and an upper sublayer in doped GaAs. P. The sublayer 70 is a sublayer of III-V doping material opposite to the upper sublayer. For example, here it is an N doped GaAs sublayer.

The amplifier 30 includes a socket 74 directly in mechanical and electrical contact with the sublayer 70. The P-doped GaAs sublayer is in mechanical and electrical contact with a socket 76. When a current greater than the current threshold of the laser source is applied between the taps 74 and 76, the amplifier 30 generates and amplifies the optical signal which resonates inside the Fabry-Perot cavity.

The tuning device 16 is here a heater capable of heating the waveguide 25 to move the wavelengths A _Rj .

In this embodiment, the tuning device 16 comprises a resistor 80 electrically connected to two sockets 82 and 84 of electrical contact. The sockets 82, 84 allow a current to flow in this resistor 80 so as to transform electrical energy into heat. These sockets 82 and 84 are electrically connected to a current or voltage source controlled by the electronic circuit 42 according to the measurements of the sensor 40. The control of the tuning device 16 therefore here consists in adjusting the electric power passing through the resistor 80. Circulating a current in the resistor 80 makes it possible to heat the waveguide 25 and therefore to move the wavelengths A _Rj .

The resistor 80 is here a strip produced in the sublayer 70. This strip is therefore a strip of GaAs doped N. In this embodiment, it is located above the waveguide 25 whose variation of index dn _S i / dT is clearly greater than the variation of index dn _f / dT.

The tuning device 16, the waveguide 28 and the amplifier 30 are covered with a protective envelope 90 which mechanically isolates them from the outside. Only the taps 74, 76, 82, 84 protrude beyond the casing 90. For example, the casing 90 is made of silicon nitride.

The path of the resonant optical signal in the laser source 10 is shown in Figure 8 by a double arrow.

The laser source 10 can be manufactured using the same manufacturing processes as those used to manufacture CMOS ("Complementary Metal-Oxide Semiconductor") components. For example, the laser source 10 is manufactured by adapting the method described with reference to Figure 9 of the application filed in France on January 08, 2016 under number 1650171.

The following figures schematically represent different possible variants of the laser source 10. In these figures, the elements already described with reference to Figures 4 and 8 have the same reference numerals but are shown more schematically. In addition, to simplify these figures, the tuning device 16, the sensor 40 and the circuit 42 are not shown.

FIG. 9 represents a laser source 100 identical to the laser source 10 except that the filter 22 is omitted and that the couplers 24 and 34 are replaced, respectively, by couplers 102, 104. The filtering function is here only filled by the couplers 102 and 104. The couplers 102, 104 are identical to the couplers 24, 34 except that, so that the laser source 100 is monochromatic, the dimensions of the couplers 102 and 104 are adjusted so that the width Δλ ₂₄ of their strip bandwidth is less than the interval Δλ _κ . This embodiment is preferred because it eliminates the need for the filter 22.

In the particular case of Figures 9 and 10, another possibility for outputting the optical signal from the resonant cavity has also been shown. For this, here, the coupler 104 does not transmit the entire optical signal at the wavelength Au from the guide 25 to the guide 36 is vice versa but only a part. For example, the power of the optical signal transmitted from one waveguide to the other is between 30% and 70% of the optical power of the incident optical signal. The optical power here is the optical power of the optical signal at the wavelength A _u . Typically, the part of the optical signal transmitted from one waveguide to the other by the coupler 102 or 104 is adjusted as described for the reflection factors of the reflectors 12 and 14. The part of the optical signal which leaks from the coupler 104 here is guided by a waveguide 35 to other optical components such as a photodiode. Preferably, this guide 35 is produced in the same silicon layer as the guide

25. To adjust the proportion of the optical signal transmitted from one guide to the other, for example, it is possible to adjust the length of the coupler 104. In general, the shorter the length of the coupler 104 the lower the proportion of the signal optical which leaks towards the guide 35 increases.

FIG. 10 represents a laser source 110 identical to the laser source 100 except that:

- reflectors 12 and 14 are omitted, and

the waveguides 15 and 36 are replaced by a single waveguide 112 which directly connects the lower parts of the couplers 24 and 34.

The waveguide 112 is made of silicon nitride. In this figure, the arrows 114 represent the direction of circulation of the optical signal inside the resonant cavity. Here, the optical signal propagates from the amplifier 30 to the upper part of the coupler 102 along the waveguide 25. The coupler 102 then transfers the optical signal into the waveguide 112. It then propagates to the lower part of the coupler 104 which transfers it again to the waveguide 25. It then propagates from the upper part of the coupler 104 to the amplifier 30. In this embodiment, the circulation of the optical signal inside the resonant cavity forms a loop.

FIG. 11 represents a laser source 120 identical to the laser source 100 except that:

the coupler 104 is replaced by a reflector 122, and

- the waveguide 36 is omitted.

The reflector 122 fulfills the same function as the reflector 14 but it is produced in one end of the waveguide 25. For this purpose, for example, the reflector 122 is a Bragg grating. Consequently, in this embodiment, the laser source 120 comprises a single contra-directional coupler 102.

Figure 12 shows a laser source 220 at N-wavelengths or polichromatic. The laser source 220 is identical to the laser source 10, except that:

the filter 22 is omitted, and

- The reflectors 12 and 14 are replaced, respectively, by reflectors 224 and 226.

The graph of Figure 13 is identical to that of Figure 6 except that the passbands 6, 52 and 54 of the filter 22 are omitted. The passband 56 of the couplers 24 and 34 extends over more than twice the interval Δλ _κ and therefore includes three frequencies of resonances of the cavity denoted, respectively, Ali, A _L2 and A _L3 in FIG. 13. In these conditions, the laser source 220 is a multi-wavelength laser source which emits simultaneously at the wavelengths Ali, A _L2 and A _L3 .

For example, the width AR of the reflective strip 234 of the reflectors 224 and 226 is:

- greater than DT x (dA _CR / dT) if N x Av _f <DT x (dA _CR / dT), and

- greater than N x Av _f + DT x (dA _C f / dT) if N x Av _f > DT x dA _CR / dT, where N is an integer greater than or equal to two and equal to the number of wavelengths A _Rj selected by filter 222.

The operation of the laser source 220 is identical to that of the laser source 10 except that it simultaneously emits N wavelengths noted here A _L i, A _L2 and A _L3 .

Chapter II: laser source comprising a contra-directional coupler SiN / III-V [0083] FIG. 14 represents a laser source 130 comprising a stack, one above the other, starting from the top to the bottom

- a waveguide 132 made of III-V material,

- a silicon waveguide 134, and

- A waveguide 136 made of a material less sensitive to temperature.

The waveguide 132 is for example identical to the waveguide 28 and includes in particular the optical amplifier 30. Here, the waveguide 136 is made of silicon nitride. The waveguide 132 is optically connected to the waveguide 136 by two contra-directional couplers 138 and 139. These couplers 138, 139 directly connect the waveguides 132 and 136 via the waveguide 134 Here, the optical signal at the wavelength A _Li propagates from the wave guide 132 to the wave guide 136 and vice versa by crossing the wave guide 134. These couplers 138 and 139 are for example symmetrical from each other with respect to a vertical plane. Therefore, only the coupler 138 is described in more detail.

The coupler 138 has three parts 141 to 143 opposite and stacked one above the other in the vertical direction. These parts 141 to 143 are produced, respectively, in the waveguides 136, 134 and 132. In this embodiment, the coupler 138 comprises an array 146 of patterns repeated at regular intervals with a pitch "a". The network 146 is only produced in the part 142 in silicon. To optically connect the waveguide 136 directly to the waveguide 132, the step "a" is here equal to mA _L i / (n _e ff f + ηθη-ιιι-ν) to within ± 5% or 2% near, where:

- m is a positive integer preferably equal to 1, and

- n _e ff-f and netf-iii-v are the propagation indices, respectively, of guides 136 and 132.

Here, m is equal to 1.

The repeated patterns are for example identical to those described with reference to Figures 7A and 7B.

So that the laser source 130 is monochromatic, the networks of repeated patterns of the couplers 138 and 139 are spaced from one another, in the waveguide 134, by a region 148 devoid of repeated patterns with the not "a". For example, here, this region 148 does not include any pattern such as those used in the networks of the couplers 138 and 139. This region 148 is often called "quarter-wave plate". The horizontal width A _De f of region 148 is equal to (n + l) a, where n is a positive or zero integer. Preferably, n is equal to 0. Here, n is equal to 0 and the two networks of repeated patterns are spaced from each other by a horizontal distance equal to a.

The laser source 130 operates as described in application FR2954638. In particular, inside the resonant cavity, the optical signal circulates in a loop. This loop and its direction of circulation are represented by arrows 150 in FIG. 14.

The fact that part of each coupler 138, 139 is made of a material less sensitive to temperature limits the temperature sensitivity of the laser source 130. It will also be noted that the laser source 130 is devoid of reflector and tuning device such as device 16.

FIG. 15 shows the different dimensions of the coupler 138 on a transverse and vertical section. In this figure, we denote La ^ i, Lai ₄₂ and La ^ s the widths, respectively, of the parts 141, 142 and of the edge of the part 143. In this embodiment, the part 143 is shaped as an edge waveguide, like the part 46 previously described. A material of low index n _S io2 of refraction is interposed between the parts 141 to 143. Here, this material is also silicon oxide.

The thicknesses of silicon oxide between the parts 143, 142 and the parts 142, 141 are denoted, respectively, e _S io2-i and e _S io2-2. The thickness of the parts 141 and 142 are denoted, respectively, e 141 θΐ Θ142. For example, when the wavelength Au is equal to 1310 nm, the following dimensions are suitable for the coupler 138: La ^ i = Lai ₄ 2 = La ^ s = 5 pm, e _S io2i = 80 nm, ei ₄₂ = 500 nm, e _S io2-2 = 200 nm, ei ₄ i = 600 nm. For a wavelength A _Li = 1310 nm, the pitch "a" is equal to 260 nm. The length of the array 146 in the direction of propagation of the optical signal is for example greater than or equal to 1 μm or 2 μm and generally less than 500 μm.

This laser source 130 can be manufactured by the same manufacturing processes as those which can be used to manufacture the embodiments of chapter I.

It will also be noted that the embodiments of Chapter II do not require a tuning device, sensor and electronic circuit such as those described in Chapter I.

Chapter III: laser source with contra-directional couplers SiN / Si and SiN / III-V [0096] FIG. 16 represents a laser source 150 identical to the laser source 130, except that the waveguides 132, 134 and 136 are replaced, respectively, by waveguides 152, 154 and 156.

The waveguide 152 is made of III-V material and includes an optical amplifier such as the optical amplifier 30.

The waveguides 154 and 156 are made, respectively, of silicon and of silicon nitride.

The left end of the waveguide 152 is optically connected to the left end of the waveguide 156 by a contra-directional coupler 158. The coupler 158 is for example identical to the coupler 138.

The right end of the waveguide 152 is connected to the waveguide 154 by an adiabatic coupler 160, for example identical to the coupler 32.

The right end of the waveguide 154 is connected to the right end of the waveguide 156 by a contra-directional coupler 162, for example identical to the coupler 104.

The operation of this laser source is deduced from the explanations given in Chapters I and II. The arrows in bold in Figure 16 represent the flow of the optical signal within the resonant cavity.

Variants of the contra-directional coupler:

In all the embodiments described here, a network of repeated patterns of the contra-directional coupler can be produced in the silicon waveguide and another network of repeated patterns can be produced opposite in the silicon nitride waveguide. In another variant, the network of repeated patterns of the contra-directional coupler is produced only in the waveguide made of silicon nitride. Other forms of repeated patterns are possible. For example, the grooves 49 can be replaced by holes aligned one next to the other or by cylindrical studs aligned in rows.

Alternatively, one of the couplers 24, 34, 102 or 104 is replaced by an adiabatic or evanescent coupler.

Alternatively, the couplers 138, 139 are replaced by a single contra-directional coupler as described in application FR2954638. However, this single coupler is always produced in three parts, as described for the laser source 130.

Other variants of the laser source:

The tuning device is not necessarily a heater. For example, it is also possible to use as a tuning device a P-N junction made in one of the silicon waveguides. The refractive index of silicon at this P-N junction varies as a function of the polarization of this junction. The electronic control signal of the tuning device then varies the polarization of this P-N junction. This way of varying the refractive index of silicon is for example described in more detail in the following article: GT Reed et al., "Silicon optical modulators", Natures photonics, Vol 4, August 2010. Other variants Possible arrangements are described in the application filed in France on January 08, 2016 under number 1650171.

Alternatively, the tuning device, the sensor 40 and the electronic circuit 42 are omitted in the embodiments described in Chapter I and III. This is especially possible when the silicon waveguide is short. In fact, in this case, the temperature variation only very slightly varies the wavelengths A _Rj .

In another embodiment, in place of or in addition to the tuning device 16, the sensor 40 and the electrical circuit 42, an external device for regulating the temperature of the laser source is implemented.

The reflection factors of the front and rear reflectors can also be equal.

As a variant, the reflectors are made partly of silicon nitride and partly of silicon. Typically, each reflector is then formed of two opposite Bragg gratings, one in the waveguide made of silicon nitride and one in the waveguide made of silicon.

The waveguide 25 can be replaced by two silicon waveguides as described in the application US2014153600.

Other embodiments of the filter 22, the waveguide 28 and the amplifier 30 and the sensor 40 are possible. For example, such other possible embodiments are described in the application filed in France on January 08, 2016 under number 1650171.

Alternatively, the waveguide 28 and the amplifier 30 are optically connected to the waveguide 25 by an evanescent coupling. In this case, the adiabatic couplers 26 and 32 are omitted. Such an optical connection between the amplifier and silicon waveguides is for example described in the following article: A. W. Fang et al., "Electrically pumped hybrid AIGalnAs-silicon evanescent laser", Optics Express, Vol. 14, pp. 9203-9210 (2006).

The order in which the various photonic components are arranged inside the resonant cavity can be modified. For example, the filter 22 can be placed between the coupler 34 and the reflector 14.

It is possible to use different types of silicon nitride. For example, it is possible, as described above, to use stoichiometric silicon nitride (Si ₃ N ₄ ). It is also possible to use non-stoichiometric silicon nitride (SiNx).

It is also possible to use other materials than silicon nitride. For example, it is also possible to use, as a material less sensitive to temperature, aluminum nitride.

Everything that is taught here in the particular case where the reflective band of the reflectors is narrower than that of the amplifier 30, also applies to the opposite case. In the opposite case, the width of the reflective strip 4 is then limited by the width of the pass band of the amplifier 30.

A laser source which emits at several wavelengths Au can also be produced as described, for example, with reference to Figures 2 or 6 of the following article: Katarzyna Lawmiczuk et al. "Design of integrated photonic transmitter for application in fiber-to-the-home Systems", Photonics Applications in Astronomy, Communications, Industry and High-Energy Physics Experiments 2010 Proceedings of SPIE, vol 7745, 2010. In this case, the filter is a demultiplexer multiplexer known by the acronym AWG ("Array Waveguide Grating"). It is then this AWG component which is produced in the material which is less sensitive to temperature.

Variants of the manufacturing process:

Other manufacturing methods are possible. For example, the method described with reference to FIG. 17 of the following article can be easily adapted to manufacture the laser sources described here: Martijn JR Heck et al, "Ultra-low loss waveguide platform and Its integration with silicon photonics", Laser photonics rev. 8, n ° 5, pages 667-686 (2014).

Other variants:

In the case of the embodiments described in Chapters I and III, the waveguides 15 and 36 can be made of a material which is not necessarily a material less sensitive to temperature. Indeed, even without this characteristic, the use of contra-directional couplers in place of adiabatic couplers already has the advantage of making it possible to reduce the size of the resonant cavity. Indeed, for equal performance, a contra-directional coupler is shorter than an adiabatic coupler.

Advantages of the described embodiments:

A contra-directional coupler in addition to providing an optical coupling between two waveguides, simultaneously performs a filtering function. Indeed, the contra-directional coupler has a bandwidth centered on an Acgacc wavelength whose value depends on the pitch of the network of repeated patterns. By making part of this contra-directional coupler in a material less sensitive to temperature, the movement of the Acgacc wavelength is limited as a function of temperature and therefore the sensitivity of the laser source to temperature is limited.

In addition, in the case of the embodiments of chapters I or III, the fact of using a contra-directional coupler makes it possible to reduce the size of the resonant cavity. Indeed, a contra-directional coupler achieves an optical coupling between two waveguides with the same efficiency as an adiabatic coupling but over a shorter distance. Furthermore, unlike an adiabatic coupling, the performance of the contra-directional coupler can be adjusted independently of the thickness of the silicon waveguide. Thus, replacing the adiabatic coupling between the silicon and silicon nitride waveguides with a contra-directional coupler makes it possible to choose the thickness of the silicon waveguide only as a function of the performance desired for the adiabatic coupling between this waveguide in silicon and the waveguide in material III-V. It is therefore no longer necessary:

either to provide different thicknesses of the silicon waveguide at the level of the Si / SiN and Si / III-V couplings,

- or to choose a uniform thickness for the silicon waveguide which makes it possible to obtain a compromise between the performance levels of the adiabatic couplings between the waveguides in silicon and in material III-V and between the waveguides wave of silicon and silicon nitride.

In the case of the embodiments of Chapter II, the use of the contra-directional coupler, part of which is at least made of silicon nitride, makes it possible to limit the temperature sensitivity of the laser source.

In addition, since the effective propagation index of the silicon nitride is lower than that of the silicon, the fact of making part of the silicon nitride coupler therefore increases the size of the step "a" of the network of repeated patterns . However, the larger the size of the step “a”, the more it simplifies the manufacture of the contradirectional coupler.

The fact of making the pattern pattern repeated only in the silicon waveguide facilitates the manufacture of the laser source in particular, when the manufacturer has better control over the etching of silicon than silicon nitride. In addition, in this case, the production of the silicon nitride waveguide requires the implementation of a single etching level and not two, as in the case where the network of repeated patterns would be produced in this guide. wave of silicon nitride.

The tuning device, the sensor and the electronic circuit make it possible to permanently maintain a wavelength A _RJ at the center of the passband of the contra-directional coupler. In the case of the embodiments of chapters I or III, this has the consequence of further reducing the temperature sensitivity without the need to have recourse to a device for regulating the temperature of the laser source.

The use of an additional bandpass filter produced in the silicon nitride waveguide makes it possible to limit, if necessary, the bandwidth of the contra-directional couplers and this without increasing its temperature sensitivity. Indeed, the filter is made of the material less sensitive to temperature.

The use of a resonant ring as a filter limits the size of the additional filter and therefore the size of the semiconductor laser source.

The fact of making the reflectors at least in part in the material which is less sensitive to temperature makes it possible to limit their sensitivity to temperature. This allows the use of reflectors whose width AR of the reflective strip is smaller.

The use of two contra-directional couplers each coupling one end of the silicon nitride waveguide to the silicon waveguides makes it possible to produce a resonant cavity without using front and rear reflectors.

Spacing from (n + 1) a the repeated pattern networks in the laser source 130 makes it possible to obtain a single-mode laser source.

The use of silicon nitride or aluminum nitride as a material less sensitive to temperature makes it possible to divide by at least five the sensitivity of the laser source to temperature.

Claims (12)

1. Semiconductor laser source capable of emitting at least one wavelength Au, this laser source comprising: - a substrate (60) on which are stacked, in order, a first (68), a second (66) and a third (64) layers, this substrate extending essentially in a plane called "plane of the substrate" and the different layers extending parallel to the plane of the substrate, an optical cavity capable of causing the optical signal to resonate at the wavelength A _Li , this optical cavity comprising: • a first waveguide (28; 132; 152) whose heart is made of a gain material III-V to amplify the optical signal at the wavelength Au which propagates along the heart of this first guide wave, this first waveguide being located inside the first layer, • a second waveguide (25; 134; 154) whose core is made of silicon, this second waveguide being located inside the second layer, • a third waveguide (15, 36; 112; 136; 156) whose core is made of a material less sensitive to temperature, that is to say made of a material whose variation dn _f / dT of its refractive index as a function of temperature is at least two times less than the variation dn _S i / dT of the refractive index of silicon as a function of temperature, this third guide wave being located inside the third layer and optically coupled to the first waveguide by the interior intermediate of the second waveguide, characterized in that, to optically couple the third waveguide to the first waveguide via the second waveguide, the optical cavity comprises at least one contra-directional coupler (24, 34; 102, 104; 138, 139; 158; 228, 229) assisted by a network capable of transforming most of the optical signal at the wavelength Au which propagates in one direction along the third waveguide, into an optical signal of the same wavelength Au, which propagates in opposite directions in the first or second waveguide, this contra-directional coupler comprising for this purpose at least one part (44; 141) produced in the third waveguide and a network (48; 146 ) of repeated patterns with a regular pitch “a” in the direction of propagation of the optical signal at the wavelength Au, this network of patterns being produced in the second or third waveguide. 2. A laser source according to claim 1, in which the network (48; 146) of repeated patterns is produced only inside the second waveguide (25; 134; 154). 3. Laser source according to any one of the preceding claims, in which: - The second waveguide (25; 154) comprises a first region optically coupled, by adiabatic or evanescent coupling, to a first region opposite the first waveguide (28; 152) so as to allow the optical signal at wavelength Au to pass from the second waveguide to the first waveguide and vice versa, - the third waveguide (15, 36; 112; 156) comprises a first region optically coupled, via the contra-directional coupler (24, 34; 102, 104; 162), to a second region in screw -in relation to the second waveguide (25; 154) so as to allow the optical signal at the wavelength Au to pass from the third waveguide to the second waveguide and vice versa, the regular step “a” of the repeating pattern network of the directional contract coupler being for this purpose equal to mA _L i / (n _e ff-si + neff-f) to within plus or minus 5%, where: • n _e ff-si and n _e fff are the effective indices of propagation, respectively, of the second and third waveguides, and • m is an integer strictly greater than zero, - The first and second regions of the second waveguide being offset relative to each other along the second waveguide. 4. Laser source according to claim 3, in which: the optical cavity is capable of causing an optical signal to resonate at at least one possible wavelength A _Rj , and - the laser source also includes: • a tuning device (16) capable of shifting the wavelength A _Rj in response to an electrical control signal, • a sensor (40) capable of measuring a physical quantity representative of the difference between the length of wave A _Li and wavelength A _Rj possible, and • an electronic circuit (42) capable of generating, as a function of the physical quantity measured by the sensor, the electrical control signal of the tuning device to maintain the length wave A _Rj equal to the wavelength Au. 5. Laser source according to claim 3 or 4 emitting only at a single wavelength Au, in which: the optical cavity is capable of causing the optical signal to resonate at several possible resonant frequencies, the possible wavelengths A _Rj of these possible resonant frequencies being regularly spaced from one another by an interval Δλ _κ and all included in l '' inside a reflective strip of width AR, and - The width of the passband of the contra-directional coupler (102, 104) is less than the interval Δλ _κ . 6. Laser source according to claim 3 or 4 emitting only at a single wavelength Au, in which: the optical cavity is capable of causing the optical signal to resonate at several possible resonant frequencies, the possible wavelengths A _Rj of these possible resonant frequencies being regularly spaced from one another by an interval Δλ _κ and all included in l '' inside a reflective strip of width AR, the bandwidth of the contra-directional coupler (24, 34) is greater than twice the interval Δλ _κ , - the optical cavity comprises, in addition to the contra-directional coupler (24, 34), an additional bandpass filter (22) entirely made of the material less sensitive to temperature and arranged to be crossed by the resonant optical signal, this additional bandpass filter having a passband centered on the wavelength Au and of width less than the interval Δλ _κ , this additional bandpass filter comprising for this purpose a resonant ring. 7. A laser source according to claim 3 or 4 emitting simultaneously at several wavelengths Au, in which: the optical cavity is capable of causing the optical signal to resonate at several possible resonant frequencies, the possible wavelengths A _Rj of these possible resonant frequencies being regularly spaced from one another by an interval Δλ _κ and all included in l '' inside a reflective strip of width AR, the bandwidth of the contra-directional coupler (24, 34) is greater than twice the interval Δλ _κ , - The optical cavity is devoid of additional bandpass filter capable of reducing the bandwidth of the contra-directional coupler (24, 34). 8. Laser source according to any one of claims 3 to 7, in which the optical cavity comprises: a fourth waveguide (36), the heart of which is made of the same material as the third waveguide (15), this fourth waveguide being located inside the third layer, - a front reflector (14; 226) and a rear reflector (12; 224) optically connected to each other via the first, second, third and fourth waveguides, these front and rear reflectors forming the ends of a Fabry-Pérot optical cavity capable of making the optical signal resonate at the wavelength Au, the front and rear reflectors being produced inside, respectively, the third (15) and fourth (36) wave guides. 9. Laser source according to any one of claims 3 to 8, in which: the first region of the third waveguide is optically coupled, via a first contra-directional coupler (102), to the second region of the second waveguide (25), and the third waveguide (112) comprises a second region optically coupled, via a second contra-directional coupler (104), to a third region facing the second waveguide ( 15) so as to allow the optical signal at wavelength Au to pass from the third waveguide to the second waveguide and vice versa, the first and third regions of the second waveguide (15) being located on either side of the second region of the second waveguide (15). 10. Laser source according to any one of claims 1 to 2, in which the contra-directional coupler (138, 139; 158) comprises a first (143), a second (142) and a third (141) parts made at the interior, respectively, of the first (132; 160), the second (134; 154) and the third (136; 156) waveguides, these three parts being stacked one above the other in a perpendicular direction in the plane of the substrate and the regular pitch "a" of the network (146) of repeated patterns being equal to mA _L i / (n _e ff-iii-v + neff-f) to within plus or minus 5%, where: - neff-mv and n _e tf-f are the effective propagation indices, respectively, of the first and third waveguides, and - m is an integer strictly greater than zero, the network of repeated patterns being produced in the second or third part of the contra-directional coupler. 11. The laser source according to claim 10, in which: the laser source comprises a first (138) and a second (139) contradirectional couplers, and the networks of repeating patterns of these first and second contradictory couplers are separated from each other by a region (148) devoid of repeating pattern, the width of this region (148) being equal to (n + l) a , where “a” is the pitch of the repeated pattern networks of the first (138) and second (139) contradirectional couplers. 12. Laser source according to any one of the preceding claims, in which the material less sensitive to temperature is silicon nitride or aluminum nitride.