Semiconductor laser chip for gas sensor

Abstract

Semiconductor laser chip for gas sensor. Semiconductor laser chip comprising an optical cavity which includes: A waveguide extending along an Ox axis and configured to amplify an electromagnetic wave of wavelength λ, A reflector placed at one longitudinal end of the optical cavity, said reflector being arranged to close the waveguide, said reflector being configured to reflect at least partially the electromagnetic wave back into the waveguide, A distributed feedback grating disposed in the optical cavity, said distributed feedback grating comprising periodic patterns arranged at a regular pitch, said grating comprising at least one reference point corresponding to an extremum of one of the Fourier components of said grating, said Fourier component being responsible for the distributed feedback effect of the grating.the reflector at the end of the optical cavity being positioned such that the electromagnetic wave propagating in the waveguide from this reference point and reflecting off the reflector has a phase that changes by π / 8 [π / 4] when said electromagnetic wave passes through said reference point after being reflected off the reflector. Figure for the abbreviation: Figure 1,

Description

Title of invention: Semiconductor laser chip for gas sensor

[0001] The present invention relates to the field of semiconductor lasers, and more particularly to semiconductor laser chips with distributed feedback, in particular for gas sensors. The invention also relates to a method for manufacturing such a semiconductor laser chip.

[0002] A quantum cascade laser, or QCL, acronym for "Quantum Cascade Laser", is a semiconductor laser capable of emitting a photon in a wavelength range from mid-infrared to far-infrared, the laser emission being obtained by inter-subband transitions of a quantum confinement structure.

[0003] Generally, a semiconductor laser chip is obtained by a complex series of steps of depositing layers on a monocrystalline substrate (also called substrate in the present description) forming a wafer (generally called wafer in English) and by cutting this wafer to obtain laser chips. This deposition of layers is carried out either by liquid or gas phase epitaxy, or by molecular beam on the substrate. The substrate is made of a pure crystal (generally InP or InAs or GaAs or other semiconductor material). A series of chemical or physicochemical etching steps and deposition of materials which may be non-crystalline or crystalline are then intended to constitute the laser cavity as well as the diffraction grating and structure the laser chip.Laser chip cleavage steps are then carried out to, on the one hand, delimit the dimensions of the laser chip, and on the other hand to form the front and rear facets of the laser chip which will act as a reflector.

[0004] A distributed feedback semiconductor laser, or DFB for "Distributed Feedback" in English, is understood to mean a semiconductor laser implementing an optical guide and having a grating allowing distributed feedback, which may be metallic or surface grating. The counter-grating grating is a periodic grating in at least one direction of space, such that one of its non-zero Fourier components has a period giving it its DFB effect.

[0005] It is known that the first objective of distributed feedback is to eliminate as much as possible the secondary modes of the laser. A second objective is generally to reduce mirror losses, i.e. losses due to the finite length of the laser cavity.

[0006] Currently, there are two main technologies for producing counter- distributed feedback. These two known technologies are, on the one hand, the use of buried networks, in order to carry out modulation by the index, and on the other hand the use of surface metallic networks, in order to carry out modulation by the gain.

[0007] The technology that we will call "buried gratings" consists of etching a periodic grating of thickness in slots after the growth of the active zone of the semiconductor laser. Then the upper layer of the laser guide is produced by a new growth step on the grating. This technology introduces a coupling by the index because the wave propagating in the active zone perceives a modulation of the effective index of the cavity and evolves with the thickness. It makes it possible to obtain a strong distributed counter-feedback without degrading the threshold of the laser, that is to say without introducing additional loss.

[0008] The second known technology for producing distributed feedback lasers is that of "metallized surface gratings". This technology allows for gain coupling (or loss coupling). This involves growing all the layers of the laser: active zone, guides and contact layers. A pattern is then etched in the upper guide and then metallized. Compared to buried grating technology, this technology has the advantage that the steps introducing distributed feedback, in particular the etching of the pattern in the upper guide, are carried out after all the layers have grown.

[0009] It is well known that a semiconductor laser comprises two facets delimiting the optical cavity of said laser, a facet with high reflectivity, configured to reflect the optical wave, said facet being generally called a "back facet", and a facet with low reflectivity configured to allow the optical wave to pass outside the optical cavity, generally called a "front facet". The facets are generally obtained by cleaving or etching and the imprecision of this step has the effect of causing a reduction in the distributed feedback effect of the distributed feedback network and reducing the performance of the laser chip.

[0010] The present invention aims to overcome this problem by providing a laser chip having improved performance and an optimized distributed feedback effect.

[0011] For this, the invention proposes a semiconductor laser chip comprising an optical cavity which comprises: - A waveguide extending along an axis Ox and configured to amplify an electromagnetic wave of wavelength X, - A reflector placed at a longitudinal end of the optical cavity, said reflector being arranged to close the waveguide, said reflector being configured to at least partially reflect the electromagnetic wave in the waveguide, - A distributed feedback grating arranged in the optical cavity, said distributed feedback grating comprising periodic patterns, said patterns being arranged at a regular pitch A, said grating comprising at least one reference point corresponding to an extrema of one of the Fourier components of said grating, said Fourier component being responsible for the distributed feedback effect of the grating, the reflector at the end of the optical cavity being positioned so that the electromagnetic wave propagating in the waveguide from this reference point and reflecting on the reflector has a phase which evolves from jr / 8 [jt / 4] when said electromagnetic wave passes through this reference point after being reflected on the reflector.

[0012] In other words, the reflector is positioned so that the electromagnetic wave propagating in the waveguide has a phase which evolves from jr / 8 [jt / 4] when said electromagnetic wave passes through a reference point after having been reflected by the reflector.

[0013] By [jt / 4], "modulo jr / 4", it is understood that the phase of the electromagnetic wave evolves to within jr / 4. In other words, when the phase of the electromagnetic wave evolves by ji / 4, it passes through a reference point, for example from one reference point to another.

[0014] The laser chip according to the invention makes it possible to obtain a phase difference at the reference point of the distributed feedback network after reflection of the electromagnetic wave on the reflector ensuring optimized optical power of the laser chip. By controlling this phase difference, this makes it possible to obtain reproducibility in the manufacture of laser chips and therefore homogeneous optical power between laser chips, as well as between laser cavities of the same chip.

[0015] In one aspect according to the invention, the network comprises a plurality of reference points, said reference points each corresponding to extrema of one of the Fourier components of said network, said Fourier component being responsible for the distributed feedback effect of the network.

[0016] In this case, when the phase of the electromagnetic wave evolves by ji / 4, it passes from one reference point to another.

[0017] In one aspect according to the invention, the reference point is located on an extrema of a pattern of the distributed feedback network, for example on a minima or a maxima of said pattern.

[0018] In one aspect of the invention, each pattern of the distributed feedback network comprises a minima and a maxima separated by a thickness el, the minima being the point closest to the waveguide and the maxima being the point furthest from the waveguide.

[0019] In one aspect according to the invention, the patterns of the distributed feedback network are slots, each slot comprising a trough and a peak substantially parallel to the optical cavity and substantially parallel to each other, the trough and the peak being separated by the thickness el, said slots being arranged continuously in the optical cavity in a periodic manner.

[0020] In one aspect of the invention, the extrema of the distributed feedback grating pattern correspond to the point in the middle of the trough of the slot for the minima, and to the point in the middle of the peak of the slot for the maxima. The minima is here located closer to the waveguide than the maxima.

[0021] In one aspect of the invention, the reference point is located on the distributed feedback grating pattern closest to the reflector.

[0022] In one aspect according to the invention, the reference point is located on the extrema, in particular the minima or the maxima, of the pattern of the distributed feedback network closest to the reflector.

[0023] In one aspect of the invention, the distributed feedback slot pattern has a shape selected from a square, a rectangle, a trapezoid, a triangle, a half-sphere, an ellipse.

[0024] In one aspect according to the invention, the waveguide has a refractive index ni. Preferably, the waveguide has a refractive index ni of 3.2.

[0025] In one aspect according to the invention, the distributed feedback grating is configured to decompose into Fourier components such that the Fourier component has a pitch A specific to the wavelength X. In other words, the distributed feedback grating is a periodic grating in at least one direction of space, the direction Ox, such that one of its non-zero Fourier components has a pitch specific to the wavelength X of the electromagnetic wave amplified in the waveguide. It is this Fourier component which is responsible for the distributed feedback effect.

[0026] In one aspect according to the invention, the distributed feedback network is configured to decompose into a Fourier component such that its step A is equal to X / (2.nl).

[0027] In one aspect according to the invention, the reflector is arranged to at least partially reflect the electromagnetic wave, thus forming a reflected wave, said reflector being arranged to generate a phase difference of ir / 8 [ji / 4] between the wave reflected by said deflector and the Fourier component of the distributed feedback network.

[0028] In one aspect according to the invention, the reference point is an extrema of the order of the Fourier component of the distributed feedback network, this order being that closest to X / (2.nl).

[0029] In one aspect according to the invention, the semiconductor laser chip comprises a dielectric layer disposed between the reflector and the waveguide so that the wave propagating in the waveguide passes through this dielectric layer before reaching the reflector.

[0030] In one aspect according to the invention, this dielectric layer comprises an electrically insulating material. In this way, electrical short circuits between the distributed feedback network and the reflector are avoided. This is particularly important when the reflector is a metallic reflective surface.

[0031] In one aspect according to the invention, the dielectric layer comprises SiO2.

[0032] In one aspect according to the invention, the dielectric layer has a length L2 extending along the Ox axis.

[0033] In one aspect according to the invention, the dielectric layer has a refractive index n2 lower than the refractive index of the waveguide.

[0034] In one aspect according to the invention, the dielectric layer has a refractive index n2 of 1.5.

[0035] In one aspect of the invention, the distributed feedback network is etched into the optical cavity.

[0036] In one aspect according to the invention, the reflector is a metallic reflective surface, in particular a metallic mirror.

[0037] Alternatively, the reflector is a surface that can be likened to a metallic reflective surface. It may in particular be a stack of layers comprising a dielectric material generating high reflectivity that can be likened to a metallic reflective surface such as a metallic mirror.

[0038] In one aspect according to the invention, the waveguide has a length L1 extending along the axis Ox between the dielectric layer and the reference point and a refractive index ni, the dielectric layer has a length L2 extending along the axis Ox and a refractive index n2, the laser chip comprising a spacing E between the reflector and the reference point of the distributed feedback grating such that E = nl.Ll+n2.L2 = X / 16 [X / 8].

[0039] In other words, the length L1 and the length L2 are defined so as to have a desired spacing E between the reflector and the reference point of the network. This spacing E extends in the direction along the Ox axis between the reflector and the reference point.

[0040] By [X / 8], “modulo 7 / 8”, we mean here to within X / 8.

[0041] In one aspect according to the invention, the length L1 of the waveguide is between 1 and 5 mm.

[0042] In one aspect according to the invention, the length L2 of the dielectric layer is between 0.5 and 2 pm.

[0043] Such a spacing E makes it possible to obtain a phase difference at the reference point of the distributed feedback network before and after the reflection of the electromagnetic field against the reflector such that the optical power of the laser chip is optimized. This spacing being controlled, it is easier to produce laser chips in a reproducible manner and having a homogeneous power.

[0044] In one aspect according to the invention, the laser chip is a quantum cascade laser chip.

[0045] In one aspect according to the invention, the laser chip is configured to emit light radiation in pulsed mode. This makes it possible in particular to reduce the energy consumption for powering said laser units compared to a continuous mode. The efficiency of the laser chip (optical energy / electrical energy required) is therefore improved.

[0046] In one aspect according to the invention, the laser chip is configured to emit light radiation at a wavelength in the infrared, preferably in the mid-infrared.

[0047] In one aspect according to the invention, the laser chip is configured to emit light radiation in a wavelength range between 3 and 15 microns, preferably between 4 and 10 microns, preferably equal to 8 microns.

[0048] In one aspect according to the invention, when the wavelength of the electromagnetic wave is 8 microns, the spacing E is 0.5 micrometers [1 micrometer].

[0049] In one aspect according to the invention, the optical cavity is delimited at each longitudinal end along Ox by a front facet and a rear facet, the front facet of the cavity being the facet by which the electromagnetic wave is recovered, and the rear facet being the other facet arranged longitudinally opposite the optical cavity along the axis Ox of the front facet, said rear facet being reflective so as to return the electromagnetic wave into the optical cavity.

[0050] In one aspect according to the invention, the rear facet has a reflectivity of between 0.3 and 1, preferably between 0.5 and 1, preferably greater than 0.8.

[0051] In one aspect according to the invention, the front facet has a reflectivity of between 0 and 1, preferably between 0 and 0.5, preferably less than 0.3.

[0052] In one aspect according to the invention, the rear facet is obtained by etching the laser chip.

[0053] In one aspect according to the invention, the reflector is adjacent to the rear facet. In other words, the reflector is arranged on the rear facet between said rear facet and the waveguide. The reflective property of the rear facet can therefore be obtained thanks to the reflector arranged on said rear facet.

[0054] In one aspect according to the invention, the reflector is bonded to the rear facet. This is particularly the case when the reflector is a metal surface.

[0055] In another aspect according to the invention, the reflector is deposited on the rear facet by deposition of layers. This is particularly the case when the rear facet is a stack of layers comprising a dielectric material generating high reflectivity which can be likened to a metallic reflective surface.

[0056] In one aspect according to the invention, the reflector is obtained by etching the rear facet of the optical cavity and stacking layers on said rear facet of a material having a reflectivity of between ...

[0057] In one aspect according to the invention, the optical cavity has a distance d between the rear facet and the reference point, said distance d extending along the axis Ox, the dielectric layer being included in this distance d.

[0058] In one aspect according to the invention, the length of the dielectric layer is chosen such that the spacing E between the reflector and the reference point makes it possible to obtain the desired phase shift. In other words, the quantity of dielectric deposited is adapted to the desired spacing.

[0059] In one aspect according to the invention, the optical cavity comprises at least one confinement layer extending along the Ox axis comprising a dielectric material configured to confine the electromagnetic wave in the waveguide, said layer extending along the Ox axis, said confinement layer being adjacent to being superimposed on the waveguide and adjacent to it. This confinement layer makes it possible to confine the propagation of electromagnetic waves in the waveguide.

[0060] In one aspect according to the invention, the confinement layer comprises SiO2.

[0061] In one aspect according to the invention, the front facet is obtained by cleaving the cavity optical.

[0062] In one aspect according to the invention, the laser chip comprises a substrate on which a set of layers forming the optical cavity are deposited.

[0063] In one aspect according to the invention, the laser chip comprises at least two optical cavities, each optical cavity comprising at least one waveguide arranged for the propagation of an electromagnetic wave.

[0064] In one aspect according to the invention, the laser chip according to the invention comprises at least one electrode formed by deposition of an electrically conductive material, in particular gold.

[0065] The present invention also relates to a gas sensor comprising: - A cell forming a resonator, comprising a gas inlet duct, a gas outlet duct and at least one opening called a laser inlet, - At least one laser chip as described above, the laser chip being configured to emit, into the cell, light radiation having a wavelength whose value is specifically adapted to the excitation of a gas to be detected, such that an interaction between the radiation light and the gas to be detected contained in the cell induces the generation of a signal characteristic of the presence of said gas at a resonance frequency of the cell, and - A signal detection device.

[0066] The invention also relates to a method for manufacturing a semiconductor chip as described above, comprising the following steps: - Deposition of layers of material on a substrate to form at least one optical cavity comprising a waveguide arranged for the propagation of an electromagnetic wave, said waveguide extending between two ends along an axis Ox, - Etching of a distributed feedback network on the waveguide, said confinement layer being included in the optical cavity, the distributed feedback network comprising a succession of periodic patterns, a reference point being defined on said network, - Etching of the optical cavity so as to delimit one of the longitudinal ends of the waveguide along the Ox axis by a rear facet, said etching being carried out at a distance d from the reference point of the distributed feedback network, - Deposition of a reflector between the waveguide and the rear facet.

[0067] Advantageously, the step of etching the optical cavity is carried out before the step of etching the distributed feedback network.

[0068] Advantageously, the network patterns are manufactured by structuring a single layer by electronic lithography or by photolithography and selective etching.

[0069] In one aspect according to the invention, the method comprises a step of cleaving the laser cavity so as to delimit the other longitudinal end of the waveguide along the Ox axis by a front facet.

[0070] In one aspect according to the invention, the reflector is deposited on the rear facet by bonding said reflector.

[0071] Alternatively, the reflector is deposited on the rear facet by depositing layers of at least one dielectric material having a reflectivity of between 0.9 and 1.

[0072] In one aspect according to the invention, the method comprises a step of depositing a layer of dielectric between the waveguide and the reflector.

[0073] In one aspect according to the invention, the step of depositing layers of material on the substrate comprises a sub-step of depositing at least one confinement layer adjacent to the waveguide, said confinement layer extending over the entire length of the waveguide.

[0074] In one aspect according to the invention, the reflector is deposited at a spacing E from the point of reference, said spacing E being such that the electromagnetic wave propagating in the waveguide from this reference point and reflecting on the reflector has a phase which evolves from ir / 8 [ji / 4] when said electromagnetic wave passes through this reference point after being reflected on the reflector.

[0075] In one aspect according to the invention, the spacing E between the reflector and the reference point of the distributed feedback network arranged on the minima of the pattern closest to the reflector is such that E = nl.Ll+n2.L2.

[0076] In one aspect according to the invention, the spacing E is such that E = X / 16 [X / 8].

[0077] Other characteristics, details and advantages of the invention will emerge on reading the description given below for information purposes in relation to drawings in which:

[0078] [Fig. 1][Fig. 1] represents a semiconductor laser chip according to the invention.

[0079] [Fig.2][Fig.2] represents the way in which the Fourier component is decomposed of the distributed feedback network of the laser chip according to the invention.

[0080] [Fig.l] represents a semiconductor laser chip according to the invention. The laser chip 1 comprises an optical cavity 2 which comprises: - a waveguide 3 extending along an axis Ox, the waveguide being configured to amplify an electromagnetic wave of wavelength X, - a reflector 9 placed at a longitudinal end of the optical cavity 2, said reflector 9 being arranged to close the waveguide 3, said reflector 9 being configured to at least partially reflect the electromagnetic wave in the waveguide 3, - a distributed feedback effect grating 4 arranged in the optical cavity 2, said grating 4 comprising periodic patterns which are arranged according to a regular pitch A, said grating 4 comprising at least one reference point 5 corresponding to an extrema of one of the Fourier components of said grating, said Fourier component being responsible for the distributed feedback effect of the grating.

[0081] The reflector 9 at the end of the optical cavity 2 is arranged so that the electromagnetic wave propagating in the waveguide 3 from this reference point 5 and reflecting on the reflector 9 has a phase which evolves from ir / 8 [ji / 4] when said electromagnetic wave passes through this reference point 5 after being reflected on the reflector 9.

[0082] The waveguide 3 has a length L1 along the axis Ox between the reflector and the reference point and has a refractive index ni. For example, the refractive index ni of the waveguide 3 is 3.2.

[0083] The wavelength of the amplified electromagnetic wave is here between 4 and 10 micrometers. It is for example 8 micrometers.

[0084] Between the reflector 9 and the waveguide 3, a dielectric layer 8 is deposited. This dielectric layer 8 comprises a dielectric material such as SiO2 which has a refractive index n2 of 1.5. The dielectric layer has a length L2 along the Ox axis. This dielectric layer between the waveguide 3 and the reflector 9 makes it possible to avoid electrical short circuits.

[0085] The distributed feedback network 4 is composed of periodic patterns which are here slots. The slots are spaced apart by a pitch A specific to the wavelength of the electromagnetic wave which propagates in the waveguide 3. This pitch A is equal to X / (2.nl), so for a wavelength of 8 micrometers and a refractive index of the waveguide of 3.2 the pitch is 1.25 micrometers. The network here comprises a multitude of reference points which correspond to the minima of each of the slot patterns, preferably in the middle of the hollow of the slot closest to the reflector 9.

[0086] The position of the reflector 9 is such that a spacing E between said reflector 9 and the reference point 5, here the minimum of the pattern closest to the reflector 9, is equal to L1.n1 + L2.n2, L1 being the length of the waveguide between the reflector and the reference point 5 in the direction of the axis Ox, n1 the refractive index of the waveguide, L2 the length of the dielectric layer 8 and n2 the refractive index of the dielectric layer.

[0087] This spacing E is equal to X / 16 [X / 8], X being the wavelength of the electromagnetic wave which propagates in the waveguide 3. For an electromagnetic wave of wavelength 8 micrometers, the spacing E is therefore 0.5 micrometers. Thus, the length L1 of the waveguide 3 and the length L2 of the dielectric layer 8 are chosen so as to obtain the desired spacing E making it possible to obtain the phase evolution of ir / 8 [ji / 4] when the electromagnetic wave passes through the reference point 5 after having been reflected by the reflector 9.

[0088] The reflector may be a metallic surface such as a metallic mirror, or a stack of layers comprising a dielectric material having a high reflectivity which can be likened to a metallic reflective surface such as a metallic mirror.

[0089] The optical cavity 2 is delimited at each longitudinal end along the axis Ox by a front facet 12 and a rear facet 13, the front facet 12 of the optical cavity 2 being the facet by which the electromagnetic wave is recovered, and the rear facet 13 being the other facet arranged longitudinally opposite the optical cavity 2 along the axis Ox of the front facet 12, said rear facet 13 being reflective so as to return the electromagnetic wave into the optical cavity 2. This reflective characteristic is in particular obtained by depositing the reflector 9 on said rear facet 13. Indeed, the reflector 9 is adjacent to the rear facet 13. The rear facet 13 is obtained by etching (generally using a physicochemical method adapted to etched semiconductors, in our case in an ICP (Inductively Coupled Plasma) frame), which allows for a more precise definition of said rear facet. The rear facet 13 has, for example, a reflectivity of 1.

[0090] The front facet 12 has a reflectivity of 0.3 so as to allow the electromagnetic wave to exit the waveguide. This front facet 12 is generally obtained by cleavage.

[0091] The etched rear facet 13 is at a distance d from the reference point. The length L2 of the dielectric layer must be adapted according to the desired spacing E between the rear facet and the reference point 5.

[0092] The laser chip 1 here also comprises two confinement layers 6 of the electromagnetic wave on either side of the waveguide 3. These confinement layers comprise a dielectric material, for example SiO2. They make it possible to confine the electromagnetic wave in the waveguide 3.

[0093] The laser chip also comprises a substrate 10 on which the layers forming the optical cavity are deposited. This substrate 10 serves as a support.

[0094] The laser chip 1 also comprises at least one electrode formed from an electrically conductive material 7 allowing an electric current to pass through said laser chip. This material is for example gold.

[0095] The laser chip 1 is obtained for example by: - Deposition of layers of material on a substrate to form at least one optical cavity comprising a waveguide arranged for the propagation of an electromagnetic wave, said waveguide extending between two ends along an axis Ox, the deposition of layers comprising in particular at least one step of deposition of a confinement layer adjacent to the waveguide, said confinement layer extending over the entire length of the waveguide, - Etching of a distributed feedback network on the waveguide, said confinement layer being included in the optical cavity, the distributed feedback network comprising a succession of periodic patterns, a reference point being defined on said network, - Etching of the optical cavity so as to delimit one of the longitudinal ends of the waveguide along the Ox axis by a rear facet, said etching being carried out at a distance d from the reference point of the distributed feedback network, - Deposition of a reflector between the waveguide and the rear facet.

[0096] The patterns of the distributed feedback network are for example manufactured by structuring a single layer by electronic lithography and selective etching.

[0097] Advantageously, the etching of the optical cavity is carried out before the etching of the grating.

[0098] The method comprises a step of cleaving the laser cavity so as to delimit the other longitudinal end of the waveguide along the Ox axis by a front facet.

[0099] The reflector is deposited on the rear facet either by bonding said reflector when it is a reflective surface, or by depositing layers of at least one dielectric material having a reflectivity of between ... when it is a reflector comparable to a reflective surface obtained by depositing layers of a dielectric material.

[0100] The method comprises a step of depositing a dielectric layer between the waveguide and the reflector.

[0101] The reflector is deposited at a spacing E from the reference point, said spacing E being such that the electromagnetic wave propagating in the waveguide from this reference point and reflecting on the reflector has a phase which evolves by ir / 8 [jt / 4] when said electromagnetic wave passes through this reference point again after being reflected on the reflector.

[0102] The spacing E between the reflector and the reference point of the distributed feedback network arranged on the minima of the pattern closest to the reflector is such that E = nl.Ll+n2.L2. The spacing E is such that E = X / 16 [X / 8].

[0103] [Fig.2] shows more precisely how the component of Fourier of the distributed feedback network of the laser chip according to the invention. Each reference point 5 is here located on an extrema, more precisely on a minima of the Fourier component of the periodic pattern of the network allowing the distributed feedback effect. In this example, each pattern comprises a reference point which is arranged in the middle of each slot pattern of the network.

Claims

Claims

1. Semiconductor laser chip (1) comprising an optical cavity (2) which comprises: - A waveguide (3) extending along an axis Ox and configured to amplify an electromagnetic wave of wavelength X, - A reflector (9) placed at a longitudinal end of the optical cavity (2), said reflector (9) being arranged to close the waveguide (3), said reflector (9) being configured to at least partially reflect the electromagnetic wave in the waveguide (3), - A distributed feedback grating (4) arranged in the optical cavity (2), said distributed feedback grating (4) comprising periodic patterns arranged at a regular pitch A, said grating comprising at least one reference point (5) corresponding to an extrema of one of the Fourier components of said grating, said Fourier component being responsible for the distributed feedback effect of the grating (4),the reflector (9) at the end of the optical cavity (2) being positioned so that the electromagnetic wave propagating in the waveguide (3) from this reference point (5) and reflecting on the reflector (9) has a phase which evolves by ir / 8 [ir / 4] when said electromagnetic wave passes through said reference point after being reflected on the reflector (9).,

2. Semiconductor laser chip (1) according to the preceding claim, characterized in that it comprises a dielectric layer (8) arranged between the reflector (9) and the waveguide (3) so that the wave propagating in the waveguide (3) passes through this dielectric layer (8) before reaching the reflector (9).

3. Laser chip (1) according to the preceding claim, characterized in that the waveguide (3) has a length L1 extending along the axis Ox between the dielectric layer (8) and the reference point (5) and a refractive index ni, the dielectric layer (8) has a length L2 extending along the axis Ox and a refractive index n2, the laser chip (1) comprising a spacing E between the reflector (9) and the reference point (5) of the distributed feedback network (4) such that E = nl.Ll+n2.L2 = X / 16 [X / 8].

4. Laser chip (1) according to one of the preceding claims, characterized in that the reflector (9) comprises a metallic reflective surface, in particular a metallic mirror.

5. Laser chip (1) according to one of claims 1 or 2, characterized in that the reflector (9) is a surface which can be likened to a metallic reflective surface.

6. Laser chip (1) according to one of the preceding claims, characterized in that the optical cavity (2) is delimited at each longitudinal end along Ox by a front facet (12) and a rear facet (13), the front facet (12) of the cavity being the facet by which the electromagnetic wave is recovered, and the rear facet (13) being the other facet arranged longitudinally opposite the optical cavity (2) along the Ox axis of the front facet (12), said rear facet (13) being reflective so as to return the electromagnetic wave into the optical cavity (2).

7. Laser chip (1) according to the preceding claim, characterized in that the rear facet (13) is obtained by etching the laser chip.

8. Laser chip (1) according to one of claims 6 or 7, characterized in that the reflector (9) is adjacent to the rear facet (13).

9. A method of manufacturing a semiconductor chip (1) according to one of the preceding claims, comprising the following steps: - Deposition of layers of material on a substrate (10) to form at least one optical cavity (2) comprising a waveguide (3) arranged for the propagation of an electromagnetic wave, said waveguide extending between two ends along an axis Ox, the deposition of layers comprising in particular at least one step of depositing a confinement layer adjacent to the waveguide (3), said confinement layer extending over the entire length of the waveguide (3), - Etching of a distributed feedback grating (4) on the waveguide (3), said confinement layer being included in the optical cavity (2), the distributed feedback grating (4) comprising a succession of periodic patterns, a reference point (5) being defined on said grating, Etching of the optical cavity (2) so as to delimit one of the longitudinal ends of the waveguide along the Ox axis by a rear facet (13), said etching being carried out at a distance d from the reference point of the distributed feedback network (4), Deposition of a reflector (9) between the waveguide and the rear facet.

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