Semiconductor laser chip for gas sensor

Abstract

The invention relates to a semiconductor laser chip comprising an optical cavity comprising: - a waveguide extending along an axis Ox and configured to amplify electromagnetic waves of a wavelength λ, - a reflector placed at a longitudinal end of the optical cavity, - a distributed negative feedback grating placed in the optical cavity, the reflectors at the ends of the optical cavity being positioned such that the electromagnetic waves propagating through the waveguide from this reference point and reflected from the reflectors have a phase change of π / 8 [π / 4] when passing through the reference point after reflection from the reflector.

Description

Technical Field

[0001] This invention relates to the field of semiconductor lasers, and more specifically, to distributed feedback semiconductor laser chips, particularly for use in gas sensors. The invention also relates to a method for manufacturing such a semiconductor laser chip. Background Technology

[0002] Quantum cascade lasers, or QCLs, are semiconductor lasers capable of emitting photons in the mid-infrared to far-infrared wavelength range. Laser emission is achieved through inter-subband transitions in a quantum-confined structure.

[0003] Typically, a semiconductor laser chip is obtained by a complex sequence of steps involving the deposition of layers on a single-crystal substrate (also referred to as the substrate in this specification) on which the wafer is formed, and by dicing the wafer to obtain the laser chip. This layer deposition is performed on the substrate via liquid-phase or vapor-phase epitaxy, or via molecular beam epitaxy. The substrate is composed of a pure crystal (typically InP, InAs, GaAs, or another semiconductor material). A series of chemical or physicochemical etching steps and the deposition of materials, which may be amorphous or crystalline, are then performed to form the laser cavity and diffraction grating and to construct the laser chip. A dicing step is then performed on the laser chip to define its dimensions and to form the front and rear faces of the laser chip that will serve as reflectors.

[0004] A distributed feedback semiconductor laser, or DFB, is understood as a semiconductor laser that implements an optical waveguide and has a grating that allows distributed feedback. This grating can be metallic or surface-based. The feedback grating is a periodic grating in at least one spatial direction, such that one of its non-zero Fourier components has a period that imparts the DFB effect.

[0005] As is well known, the first objective of distributed feedback is to eliminate secondary modes of the laser as much as possible. The second objective is usually to reduce mirror loss, which is the loss caused by the finite length of the laser cavity.

[0006] Currently, there are two main technologies used to produce distributed feedback lasers. One known technology uses buried gratings to perform refractive index modulation, and the other uses metallized surface gratings to perform gain modulation.

[0007] The technique, known as "buried grating," involves etching a periodic grating with a square-wave thickness after growth in the active region of a semiconductor laser. The upper layer of the laser waveguide is then created through a new growth step on the grating. This technique introduces refractive index coupling because the wave propagating in the active region senses modulation of the cavity's effective refractive index and evolves with thickness. It allows for strong distributed feedback without lowering the laser threshold, i.e., without introducing additional losses.

[0008] The second known technique capable of generating distributed feedback lasers is the "metallized surface grating." This technique enables gain coupling (or loss coupling). This involves growing all the layers of the laser: the active region, the waveguide, and the contact layer. A pattern is then etched in the upper waveguide, followed by metallization. Compared to buried grating techniques, this technique has the advantage of performing the step of introducing distributed feedback after all layers have been grown, particularly the step of etching the pattern in the upper waveguide.

[0009] As is well known, a semiconductor laser includes two end faces defining an optical cavity of the laser: an end face with high reflectivity configured to reflect light waves, commonly referred to as the "rear end face," and an end face with low reflectivity configured to allow light waves to pass outside the optical cavity, commonly referred to as the "front end face." The end faces are typically obtained through cleaving or etching, and inaccuracies in this process can lead to a reduction in the distributed feedback effect of the distributed feedback grating and consequently, a decrease in the performance of the laser chip. Summary of the Invention

[0010] The present invention aims to solve this problem by proposing a laser chip with improved performance and optimized distributed feedback effect.

[0011] To this end, the present invention provides a semiconductor laser chip including an optical cavity, the optical cavity comprising:

[0012] - A waveguide that extends along axis Ox and is configured to amplify electromagnetic waves with wavelength λ.

[0013] A reflector, positioned at the longitudinal end of the optical cavity, is arranged to enclose the waveguide and configured to at least partially reflect the electromagnetic waves in the waveguide.

[0014] A distributed feedback grating, disposed in the optical cavity, comprises a periodic pattern arranged at a regular pitch. The grating includes at least one reference point corresponding to an extremum of one of the Fourier components responsible for the distributed feedback effect of the grating.

[0015] The reflector at the end of the optical cavity is positioned such that the electromagnetic wave propagating from the reference point in the waveguide and reflected on the reflector has a phase offset of π / 8 [π / 4] when it passes through the reference point after being reflected on the reflector.

[0016] In other words, the reflector is positioned such that when an electromagnetic wave propagating in the waveguide passes through the reference point after being reflected by the reflector, the electromagnetic wave has a phase offset of π / 8 [π / 4].

[0017] The term [π / 4], or "mod π / 4," can be understood as the phase of an electromagnetic wave shifting within [π / 4]. In other words, when the phase of an electromagnetic wave shifts by [π / 4], it passes through a reference point, for example, from one reference point to another.

[0018] The laser chip according to the invention enables a phase difference to be obtained at a reference point of the distributed feedback grating after the electromagnetic wave is reflected on the reflector, thereby ensuring optimized optical power of the laser chip. By controlling this phase difference, it allows for reproducibility in the fabrication of the laser chip, and thus allows for uniform optical power between laser chips and between laser cavities within the same chip.

[0019] In one aspect of the invention, the grating includes a plurality of reference points, each of which corresponds to an extremum of one of the Fourier components of the grating, the Fourier component being responsible for the distributed feedback effect of the grating.

[0020] In this case, when the phase of the electromagnetic wave shifts by [π / 4], it travels from one reference point to another.

[0021] In one aspect of the invention, the reference point is located at an extreme value of the pattern of the distributed feedback grating, for example, at the minimum or maximum value of the pattern.

[0022] In one aspect of the invention, each pattern of the distributed feedback grating includes a minimum value and a maximum value separated by a thickness e1, wherein the minimum value is the point closest to the waveguide and the maximum value is the point furthest from the waveguide.

[0023] In one aspect of the invention, the pattern of the distributed feedback grating is a square wave, each square wave comprising troughs and peaks substantially parallel to and substantially parallel to each other, the troughs and peaks being separated by a thickness e1, the square waves being arranged continuously in the optical cavity in a periodic manner.

[0024] 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 square wave for the minimum value, and to the point in the middle of the crest of the square wave for the maximum value. Here, the minimum value is closer to the waveguide than the maximum value.

[0025] In one aspect of the invention, the reference point is located on the pattern of the distributed feedback grating closest to the reflector.

[0026] In one aspect of the invention, the reference point is located at the extreme value of the pattern of the distributed feedback grating closest to the reflector, particularly at the minimum or maximum value.

[0027] In one aspect of the invention, the pattern of the distributed feedback square wave has a shape selected from square, rectangle, trapezoid, triangle, hemisphere, and ellipse.

[0028] In one aspect of the invention, the waveguide has a refractive index n1. Preferably, the waveguide has a refractive index n1 of 3.2.

[0029] In one aspect of the invention, the distributed feedback grating is configured to decompose into Fourier components such that the Fourier components have a pitch specific to wavelength λ. In other words, the distributed feedback grating is a periodic grating in at least one spatial direction (direction Ox) such that one of its non-zero Fourier components has a pitch specific to wavelength λ of the electromagnetic wave amplified in the waveguide. It is this Fourier component that is responsible for the distributed feedback effect.

[0030] In one aspect of the invention, the distributed feedback grating is configured to be decomposed into Fourier components such that its pitch Λ is equal to λ / (2.n1).

[0031] In one aspect of the invention, a reflector is arranged to at least partially reflect electromagnetic waves, thereby forming a reflected wave, the reflector being arranged to produce a phase difference of π / 8 [π / 4] between the wave reflected by the reflector and the Fourier component of the distributed feedback grating.

[0032] In one aspect of the invention, the reference point is the extremum of the order of the Fourier component of the distributed feedback grating, which is the order closest to λ / (2.n1).

[0033] In one aspect of the invention, a semiconductor laser chip includes a dielectric layer disposed between a reflector and a waveguide, such that a wave propagating in the waveguide passes through the dielectric layer before reaching the reflector.

[0034] In one aspect of the invention, the dielectric layer comprises an electrically insulating material. In this way, an electrical short circuit between the distributed feedback grating and the reflector is avoided. This is particularly important when the reflector is a metallic reflective surface.

[0035] In one aspect of the invention, the dielectric layer comprises SiO2.

[0036] In one aspect of the invention, the dielectric layer has a length L2 extending along the axis Ox.

[0037] In one aspect of the invention, the dielectric layer has a refractive index n2 that is lower than that of the waveguide.

[0038] In one aspect of the invention, the refractive index n2 of the dielectric layer is 1.5.

[0039] In one aspect of the invention, a distributed feedback grating is etched into the optical cavity.

[0040] In one aspect of the invention, the reflector is a metallic reflective surface, particularly a metallic mirror.

[0041] Alternatively, a reflector can be a surface that can be likened to a metallic reflective surface. In particular, it can be a stack of layers comprising dielectric materials that produce high reflectivity, which can be likened to a metallic reflective surface such as a metal mirror.

[0042] In one aspect of the invention, the waveguide has a length L1 and a refractive index n1 extending along the axis Ox between the dielectric layer and the reference point, the dielectric layer has a length L2 and a refractive index n2 extending along the axis Ox, and the laser chip includes a spacing E between the reference point of the reflector and the distributed feedback grating, such that E = n1.L1 + n2.L2 = λ / 16 [λ / 8].

[0043] In other words, lengths L1 and L2 are defined to have a desired spacing E between the reflector and the reference point of the grating. This spacing E extends between the reflector and the reference point in a direction along the axis Ox.

[0044] By [λ / 8], “modulo λ / 8” means within λ / 8.

[0045] In one aspect of the invention, the waveguide length L1 is between 1 and 5 mm.

[0046] In one aspect of the invention, the length L2 of the dielectric layer is between 0.5 and 2 μm.

[0047] This spacing E allows for a phase difference to be obtained at the reference point of the distributed feedback grating before and after the electromagnetic wave is reflected to the reflector, thereby optimizing the optical power of the laser chip. By controlling this spacing, it is easier to produce laser chips with uniform power in a reproducible manner.

[0048] In one aspect of the invention, the laser chip is a quantum cascade laser chip.

[0049] In one aspect of the invention, the laser chip is configured to emit optical radiation in a pulsed mode. Compared to a continuous mode, this significantly allows for a reduction in the energy consumption used to supply the laser unit. This thus improves the efficiency of the laser chip (optical energy / required electrical energy).

[0050] In one aspect of the invention, the laser chip is configured to emit light radiation with a wavelength in the infrared, preferably in the mid-infrared.

[0051] In one aspect of the invention, the laser chip is configured to emit light radiation with a wavelength range of 3 to 15 micrometers, preferably between 4 and 10 micrometers, and more preferably equal to 8 micrometers.

[0052] In one aspect of the invention, when the wavelength of the electromagnetic wave is 8 micrometers, the spacing E is 0.5 micrometers [1 micrometer].

[0053] In one aspect of the invention, the optical cavity is defined at each longitudinal end along Ox by a front end face and a rear end face, the front end face being the end face through which electromagnetic waves are acquired, and the rear end face being another end face disposed longitudinally opposite to the optical cavity along the axis Ox of the front end face, the rear end face being reflective so as to transmit electromagnetic waves back into the optical cavity.

[0054] In one aspect of the invention, the rear end face has a reflectivity between 0.3 and 1, preferably between 0.5 and 1, and preferably greater than 0.8.

[0055] In one aspect of the invention, the front end face has a reflectivity between 0 and 1, preferably between 0 and 0.5, and preferably less than 0.3.

[0056] In one aspect of the invention, the back end face is obtained by etching a laser chip.

[0057] In one aspect of the invention, the reflector is adjacent to the rear end face. In other words, the reflector is disposed on the rear end face between the rear end face and the waveguide. Therefore, due to the reflector disposed on the rear end face, the reflection characteristics of the rear end face can be obtained.

[0058] In one aspect of the invention, the reflector is integrated into the rear end face. This is especially true when the reflector is a metallic surface.

[0059] In another aspect of the invention, the reflector is deposited on the rear end face by layer deposition. This is especially true when the rear end face is a stack of layers comprising a dielectric material that produces high reflectivity, which can be likened to a metallic reflective surface.

[0060] In one aspect of the invention, the reflector is obtained by etching the rear end face of the optical cavity and stacking a material layer on the rear end face, the reflectivity of which is particularly greater than that of the front end face (i.e., the interface without the reflector), particularly greater than 0.3 and particularly between 0.8 and 1.

[0061] In one aspect of the invention, the optical cavity has a distance d between the rear end face and the reference point, the distance d extending along the axis Ox, and the dielectric layer is included in the distance d.

[0062] In one aspect of the invention, the length of the dielectric layer is chosen such that the spacing E between the reflector and the reference point allows for a desired phase shift. In other words, the amount of deposited dielectric is suited to the desired spacing.

[0063] In one aspect of the invention, the optical cavity includes at least one confinement layer extending along an axis Ox, the confinement layer comprising a dielectric material configured to confine electromagnetic waves within a waveguide, the layer extending along the axis Ox, the confinement layer being adjacent to and superimposed on the waveguide. This confinement layer allows the propagation of electromagnetic waves to be confined within the waveguide.

[0064] In one aspect of the invention, the confining layer comprises SiO2.

[0065] In one aspect of the invention, the front end face is obtained by cleaving the optical cavity.

[0066] In one aspect of the invention, the laser chip includes a substrate on which a set of layers forming an optical cavity are deposited.

[0067] In one aspect of the invention, the laser chip includes at least two optical cavities, each optical cavity including at least one waveguide arranged for the propagation of electromagnetic waves.

[0068] In one aspect of the invention, the laser chip according to the invention includes at least one electrode formed by depositing a conductive material, particularly gold.

[0069] The present invention also relates to a gas sensor, comprising:

[0070] - The unit forming the resonator includes a gas inlet conduit, a gas outlet conduit, and at least one opening called the laser inlet.

[0071] - At least one laser chip as described above, configured to emit light radiation into the cell, the wavelength of which is particularly suitable for the excitation of the gas to be detected, such that the interaction between the light radiation and the gas to be detected contained in the cell causes a signal characterizing the presence of the gas to be generated at the cell's resonant frequency, and

[0072] - A device for detecting the signal.

[0073] The present invention also relates to a method for manufacturing a semiconductor chip as described above, comprising the following steps:

[0074] - A material layer is deposited on a substrate to form at least one optical cavity, the optical cavity including waveguides arranged for propagating electromagnetic waves, the waveguides extending between their two ends along an axis Ox.

[0075] - A distributed feedback grating is etched on the waveguide, the confinement layer being included in the optical cavity, the distributed feedback grating comprising a series of periodic patterns defining reference points on the grating.

[0076] - Etching the optical cavity to define one of the longitudinal ends of the waveguide along the axis Ox via the rear end face, the etching being performed at a distance d from the reference point of the distributed feedback grating.

[0077] A reflector is deposited between the waveguide and the rear end face.

[0078] Advantageously, the step of etching the optical cavity is performed before the step of etching the distributed feedback grating.

[0079] Advantageously, the pattern of the grating is fabricated by electron beam lithography or by lithography and selective etching to construct a single layer.

[0080] In one aspect of the invention, the method includes the step of cleaving the laser cavity to define another longitudinal end of the waveguide along axis Ox via a front face.

[0081] In one aspect of the invention, the reflector is deposited on the rear end face by incorporating the reflector.

[0082] Alternatively, the reflector can be deposited on the back end face by depositing a layer of at least one dielectric material having a reflectivity between 0.9 and 1.

[0083] In one aspect of the invention, the method includes the step of depositing a dielectric layer between the waveguide and the reflector.

[0084] In one aspect of the invention, the step of depositing a material layer on a substrate includes a sub-step of depositing at least one confinement layer adjacent to the waveguide, the confinement layer extending over the entire length of the waveguide.

[0085] In one aspect of the invention, a reflector is deposited at a distance E from a reference point, the distance E being such that an electromagnetic wave propagating from the reference point in the waveguide and reflected on the reflector has a phase offset of π / 8 [π / 4] when it passes through the reference point after being reflected on the reflector.

[0086] In one aspect of the invention, the spacing E between the reflector and the reference point of the distributed feedback grating disposed on the minimum of the pattern closest to the reflector is such that E = n1.L1 + n2.L2.

[0087] In one aspect of the invention, the interval E is such that E = λ / 16 [λ / 8]. Attached Figure Description

[0088] Other features, details, and advantages of the invention will become apparent from the following description, given with reference to the accompanying drawings, in which:

[0089] Figure 1 This refers to a semiconductor laser chip according to the present invention.

[0090] Figure 2 This describes the Fourier component decomposition of the distributed feedback grating of the laser chip according to the present invention. Detailed Implementation

[0091] Figure 1 This describes a semiconductor laser chip according to the present invention. The laser chip 1 includes an optical cavity 2, which includes:

[0092] - Waveguide 3, extending along axis Ox, is configured to amplify electromagnetic waves with wavelength λ.

[0093] - A reflector 9, which is placed at the longitudinal end of the optical cavity 2, is arranged to enclose the waveguide 3, and is configured to at least partially reflect electromagnetic waves in the waveguide 3.

[0094] - A distributed feedback grating 4 is disposed in an optical cavity 2. The grating 4 includes a periodic pattern arranged at regular pitches. The grating 4 includes at least one reference point 5 corresponding to an extremum of one of the Fourier components of the grating, which is responsible for the distributed feedback effect of the grating.

[0095] The reflector 9 at the end of the optical cavity 2 is arranged such that the electromagnetic wave propagating from the reference point 5 in the waveguide 3 and reflected on the reflector 9 has a phase offset of π / 8 [π / 4] when it passes through the reference point 5 after being reflected on the reflector 9.

[0096] Waveguide 3 has a length L1 along the axis Ox between the reflector and the reference point, and has a refractive index n1. For example, the refractive index n1 of waveguide 3 is 3.2.

[0097] The wavelengths of the amplified electromagnetic waves here are between 4 and 10 micrometers. For example, 8 micrometers.

[0098] A dielectric layer 8 is deposited between the reflector 9 and the waveguide 3. This dielectric layer 8 comprises a dielectric material, such as SiO2, with a refractive index n2 of 1.5. The dielectric layer has a length L2 along the axis Ox. This dielectric layer between the waveguide 3 and the reflector 9 prevents electrical short circuits.

[0099] The distributed feedback grating 4 consists of a periodic pattern, in which the periodic pattern is a square wave. The square waves are spaced apart by a pitch specific to the wavelength of the electromagnetic wave propagating in the waveguide 3. This pitch Λ is equal to λ / (2.n1), so for a wavelength of 8 micrometers and a waveguide refractive index of 3.2, the pitch is 1.25 micrometers. The grating here includes multiple reference points corresponding to the minimum value of each square wave pattern, preferably at the middle of the trough of the square wave closest to the reflector 9.

[0100] The position of reflector 9 is such that the interval E between reflector 9 and reference point 5 (which is the minimum value of the pattern closest to reflector 9) is equal to L1.n1 + L2.n2, where L1 is the length of the waveguide between reflector and reference point 5 in the direction of axis Ox, n1 is the refractive index of the waveguide, L2 is the length of dielectric layer 8, and n2 is the refractive index of dielectric layer.

[0101] The spacing E is equal to λ / 16 [λ / 8], where λ is the wavelength of the electromagnetic wave propagating in waveguide 3. For an electromagnetic wave with a wavelength of 8 micrometers, the spacing E is therefore 0.5 micrometers. Therefore, the length L1 of waveguide 3 and the length L2 of dielectric layer 8 are chosen to obtain the desired spacing E such that a phase shift of π / 8 [π / 4] can be obtained when the electromagnetic wave passes through reference point 5 after being reflected by reflector 9.

[0102] A reflector can be a metal surface, such as a metal mirror, or a stack of layers comprising a dielectric material with high reflectivity, which can be compared to a metal reflective surface, such as a metal mirror.

[0103] Optical cavity 2 is defined at each longitudinal end along axis Ox by a front end face 12 and a rear end face 13. The front end face 12 is the end face through which electromagnetic waves are received, and the rear end face 13 is another end face disposed longitudinally opposite to the optical cavity 2 along the axis Ox of the front end face 12. The rear end face 13 is reflective in order to transmit electromagnetic waves back into optical cavity 2. This reflective property is obtained in particular by depositing a reflector 9 on the rear end face 13. In fact, the reflector 9 is adjacent to the rear end face 13. The rear end face 13 is obtained by etching (typically using physicochemical methods suitable for etching semiconductors, and in our case, in an ICP (inductively coupled plasma) system), which allows for more precise definition of the rear end face. The rear end face 13 has a reflectivity of, for example, 1.

[0104] In itself, the front surface 12 has a reflectivity of 0.3 so that electromagnetic waves can leave the waveguide. This front surface 12 is typically obtained through cleavage.

[0105] The distance between the etched rear end face 13 and the reference point is d. The length L2 of the dielectric layer must be adjusted according to the desired spacing E between the rear end face and the reference point 5.

[0106] The laser chip 1 also includes two layers 6 for confining electromagnetic waves on either side of the waveguide 3. These confining layers comprise dielectric materials, such as SiO2. They allow electromagnetic waves to be confined within the waveguide 3.

[0107] The laser chip also includes a substrate 10 on which the layer forming the optical cavity is deposited. The substrate 10 serves as a support.

[0108] The laser chip 1 also includes at least one electrode formed of a conductive material 7 that allows current to pass through the laser chip. This material is, for example, gold.

[0109] Laser chip 1 is obtained, for example, in the following manner:

[0110] - A material layer is deposited on a substrate to form at least one optical cavity, the optical cavity including a waveguide arranged for propagating electromagnetic waves, the waveguide extending between two ends along an axis Ox, the layer deposition specifically including the step of depositing at least one confinement layer adjacent to the waveguide, the confinement layer extending along the entire length of the waveguide.

[0111] - A distributed feedback grating is etched on the waveguide, the confinement layer being included in the optical cavity. The distributed feedback grating comprises a series of periodic patterns defining reference points on the grating.

[0112] - Etching the optical cavity to define one of the longitudinal ends of the waveguide along the axis Ox via the rear end face, the etching being performed at a distance d from the reference point of the distributed feedback grating.

[0113] - Deposit a reflector between the waveguide and the rear end face.

[0114] For example, patterns of distributed feedback gratings can be fabricated by constructing a single layer using electron beam lithography and selective etching.

[0115] Advantageously, the etching of the optical cavity is performed before the etching of the grating.

[0116] The method includes the step of cleaving the laser cavity to define another longitudinal end of the waveguide along the axis Ox via the front face.

[0117] When the reflector is a reflective surface, the reflector is deposited on the rear end face by bonding the reflector, or when the reflector is a reflective surface equivalent to that obtained by depositing a dielectric material layer, the reflector is deposited on the rear end face by depositing at least one dielectric material layer with a reflectivity greater than 0.3 and particularly between 0.8 and 1.

[0118] The method includes the step of depositing a dielectric layer between the waveguide and the reflector.

[0119] The reflector is deposited at a distance E from the reference point, such that an electromagnetic wave propagating from the reference point in the waveguide and reflected on the reflector has a phase offset of π / 8 [π / 4] when it returns to the reference point after being reflected on the reflector.

[0120] The spacing E between the reflector and the reference point of the distributed feedback grating is such that E = n1.L1 + n2.L2, where the reference point of the distributed feedback grating is set at the minimum value of the pattern closest to the reflector. The spacing E is such that E = λ / 16[λ / 8].

[0121] Figure 2 A more precise illustration shows how the Fourier components of the distributed feedback grating of the laser chip according to the invention are decomposed. Each reference point 5 here is located at an extremum, more precisely at the minimum of the Fourier components of the periodic pattern of the grating that realizes the distributed feedback effect. In this example, each pattern includes a reference point disposed at the middle of each square wave pattern of the grating.

Claims

1. A semiconductor laser chip (1) comprising an optical cavity (2), the optical cavity (2) comprising: • Waveguide (3), which extends along axis Ox and is configured to amplify electromagnetic waves with wavelength λ. • A reflector (9), placed at the longitudinal end of the optical cavity (2), the reflector (9) being arranged to enclose the waveguide (3), the reflector (9) being configured to at least partially reflect the electromagnetic waves in the waveguide (3). • A distributed feedback grating (4), disposed in the optical cavity (2), the distributed feedback grating (4) comprising a periodic pattern arranged at regular pitches, the grating comprising at least one reference point (5) corresponding to an extremum of one of the Fourier components of the grating, the Fourier component being responsible for the distributed feedback effect of the grating (4). The reflector (9) at the end of the optical cavity (2) is positioned such that the electromagnetic wave propagating from the reference point (5) in the waveguide (3) and reflected on the reflector (9) has a phase offset of π / 8 [π / 4] when it passes through the reference point after being reflected on the reflector (9).

2. The semiconductor laser chip (1) according to the preceding claim, characterized in that, The semiconductor laser chip (1) includes a dielectric layer (8) disposed between the reflector (9) and the waveguide (3) such that a wave propagating in the waveguide (3) passes through the dielectric layer (8) before reaching the reflector (9).

3. The laser chip (1) according to the preceding claim, characterized in that, The waveguide (3) has a length L1 and a refractive index n1 extending along the axis Ox between the dielectric layer (8) and the reference point (5), the dielectric layer (8) has a length L2 and a refractive index n2 extending along the axis Ox, and the laser chip (1) includes a spacing E between the reflector (9) and the reference point (5) of the distributed feedback grating (4) such that E = n1.L1 + n2.L2 = λ / 16 [λ / 8].

4. The laser chip (1) according to any one of the preceding claims, characterized in that, The reflector (9) includes a metallic reflective surface, particularly a metallic mirror.

5. The laser chip (1) according to any one of claims 1 or 2, characterized in that, The reflector (9) is a surface that can be compared to a metallic reflective surface.

6. The laser chip (1) according to any one of the preceding claims, characterized in that, The optical cavity (2) is defined at each longitudinal end along Ox by a front end face (12) and a rear end face (13), the front end face (12) of the cavity being the end face through which the electromagnetic wave is received, and the rear end face (13) being another end face disposed longitudinally opposite to the optical cavity (2) along the axis Ox of the front end face (12), the rear end face (13) being reflective to send the electromagnetic wave back into the optical cavity (2).

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

8. The laser chip (1) according to any one of claims 6 or 7, characterized in that, The reflector (9) is adjacent to the rear end face (13).

9. A method for manufacturing a semiconductor chip (1) according to any one of the preceding claims, comprising the following steps: • A material layer is deposited on a substrate (10) to form at least one optical cavity (2), the at least one optical cavity (2) comprising a waveguide (3) arranged for propagating electromagnetic waves, the waveguide extending between its two ends along an axis Ox, the deposition of the layer specifically comprising the step of depositing at least one confinement layer adjacent to the waveguide (3), the confinement layer extending over the entire length of the waveguide (3). • A distributed feedback grating (4) is etched on the waveguide (3), the confinement layer is included in the optical cavity (2), the distributed feedback grating (4) comprises a series of periodic patterns, and a reference point (5) is defined on the grating. • Etching the optical cavity (2) to define one of the longitudinal ends of the waveguide along the axis Ox via the rear end face (13), the etching being performed at a distance d from the reference point of the distributed feedback grating (4). • Deposit a reflector (9) between the waveguide and the rear end face.

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