Infrared light source optimized for gas sensors and method for its production

Description

DOMAINE TECHNIQUE

[0001] The invention relates to an infrared light source, in particular intended for use in a gas sensor. ART ANTERIEUR

[0002] The use of optical methods for gas analysis is quite common. Devices allow the composition of a gas to be determined based on the fact that the species composing a gas have different absorption spectral properties from each other. Thus, knowing the absorption spectral band of a gaseous species, its concentration can be determined by estimating the absorption of light passing through the gas, using the Beer Lambert law. This principle allows an estimation of the concentration of a gaseous species present in the medium.

[0003] The light source is usually an infrared source, the method used being usually referred to by the English term "NDIR detection", the acronym NDIR meaning Non Dispersive Infra-Red. Such a principle has been frequently implemented, and is for example described in numerous documents, for example in US5026992 or WO2007064370.

[0004] According to the most common methods, the gas being analyzed extends between a light source and a photodetector, called a measuring photodetector, the latter being intended to measure a light wave transmitted by the gas to be analyzed, and partially absorbed by the latter. The methods generally include a measurement of a light wave, called a reference light wave, emitted by the source, and not absorbed by the gas being analyzed.

[0005] Comparing the light wave in the presence of gas with the light wave without gas allows the gas to be characterized. For example, this involves determining the quantity of a gaseous species in the gas, using the technology known as "NDIR by absorption." It can also involve estimating the quantity of particles in the gas by detecting light scattered by the gas over a predetermined angular scattering range.

[0006] To design an NDIR sensor, it is common to use a light source in the form of an incandescent filament. This type of light source is inexpensive and has a spectral emission close to that of a black body.

[0007] Examples of gas sensors have been described in documents WO2018162848, or WO2019081838. These sensors comprise an enclosure, intended to be occupied by the gas to be analyzed. Conventionally, the enclosure is delimited by reflective walls. When the light propagates between the light source and a photodetector, it can undergo numerous reflections on the reflective walls.

[0008] Other gas sensors, of the NDIR type, have been described in US2015 / 192517, EP1612540 as well as US10386298. US5285131 describes an infrared light source.

[0009] The inventors have designed a light source particularly suitable for integration into NDIR gas sensors, and for example the sensors described in the previously cited documents. The light source designed by the inventors makes it possible to increase a quantity of light detected by the photodetector. The inventors also propose a simple production method to implement, making it possible to obtain an optimized light source. EXPOSE DE L'INVENTION

[0010] A first object of the invention is an infrared light source, in particular for a gas sensor, comprising: an emission element, extending along a radial plane, around a center of the emission element, the emission element being configured to heat up, the heating leading to an emission of infrared light; a cavity, in which the emission element extends, the cavity being delimited by a cover, arranged facing the emission element, the cover comprising an internal face, arranged opposite the emission element and an external face, defining an interface between the cover and a medium external to the light source; the cover extending, parallel to a transverse axis, perpendicular to the radial plane, along a thickness, between the internal face and the external face; the external face comprising: a flat central part, extending around a center of the external face, the center of the external face being aligned with the center of the emission element, along the transverse axis;the light source being characterized in that the external face comprises: at least one peripheral portion, adjacent to the central portion, the peripheral portion being inclined relative to the central portion at an angle of inclination, such that in the peripheral portion, the thickness of the cover decreases as a function of a distance relative to the central portion.;

[0011] The peripheral part can extend on either side of the central part.

[0012] The emitting element may be a membrane. The emitting element may have a conductive track passing through it, such that under the effect of an electric current flowing in the conductive track, the light emitting element heats up.

[0013] According to one embodiment, the central portion preferably extends parallel to the radial plane.

[0014] The peripheral portion is preferably inclined, relative to the central portion, at an angle of inclination of between 5° and 30°, and preferably between 5° and 25° or between 5° and 20°. According to one embodiment, the central portion extends parallel to a radial longitudinal axis and to a lateral axis, the longitudinal axis being perpendicular to the lateral axis; the peripheral portion extends parallel to a first longitudinal axis and to a first lateral axis; the first longitudinal axis is inclined, according to the angle of inclination, with respect to the longitudinal axis; the first lateral axis is parallel to the lateral axis.

[0015] According to one possibility, the light source comprises a second peripheral part, adjacent to the central part, such that: the second peripheral portion extends parallel to a second longitudinal axis and a second lateral axis; the second lateral axis is inclined, at a second angle of inclination, relative to the lateral axis; the second longitudinal axis is parallel to the longitudinal axis.

[0016] The second peripheral part can extend on either side of the central part.

[0017] According to one embodiment, the peripheral portion extends along a length of between 100 µm and 600 µm, on either side of the central portion, the length being determined along the longitudinal axis or along the lateral axis. More generally, the peripheral portion may extend along a length of between 5% and 50% of the length of the cover, the length being determined along the longitudinal axis and / or along the lateral axis.

[0018] According to one embodiment, at least one peripheral portion, or even each peripheral portion, is inclined, relative to the central portion, according to different angles of inclination, the angles of inclination increasing with the distance relative to the central portion.

[0019] Preferably, the central portion is centered relative to the emitting element, along the transverse axis.

[0020] The external face may extend, along an axis parallel to the radial plane, in a length of between 500 µm and 2500 µm.

[0021] A second subject of the invention is a gas sensor, comprising an enclosure configured to contain a gas, as well as a light source and at least one photodetector, the light source being configured to emit light radiation propagating, through the enclosure, towards the photodetector, the light source being a light source according to the first subject of the invention.

[0022] The gas sensor may be such that the enclosure is delimited by at least a first reflective wall, extending perpendicular to the radial plane of the light source, parallel to the transverse axis.

[0023] The gas sensor may be such that the external face of the light source cover has a flat central portion, extending along a plane parallel to the radial plane and passing through the center of the external face, and in which: the central portion extends parallel to a longitudinal axis and a lateral axis, the longitudinal axis being preferably perpendicular to the lateral axis; the peripheral portion extends parallel to a first longitudinal axis and to a first lateral axis; the first longitudinal axis is inclined, at an angle of inclination, relative to the longitudinal axis; the first lateral axis is parallel to the lateral axis; the light source being arranged such that the longitudinal axis is perpendicular to the first reflecting wall.

[0024] The gas sensor may be such that the enclosure is delimited by a second reflective wall, extending parallel to the first reflective wall, the light source extending between the two reflective walls. It is then preferable for the peripheral part to extend on either side of the central part.

[0025] A third object of the invention is a method for producing an infrared light source, which is the subject of the first embodiment, comprising: a) obtaining a light source, the light source comprising an emission element, extending parallel to a radial plane, around a center of the emission element, the emission element being configured to heat up, the heating leading to an emission of infrared light, and arranged in a cavity delimited by a cover, the cover extending between an internal face, arranged facing the emission element, and an external face, the external face extending parallel to the radial plane, around a center of the external face, the center of the external face being aligned with the center of the emission element, along a transverse axis, perpendicular to the radial plane, the distance between the internal face and the external face defining a thickness of the cover;b) machining the external face, so as to form, in the external face, at least one peripheral part, adjacent to a flat central part of the external face, passing through the center of the external face, and parallel to the radial plane, the peripheral part being inclined relative to the central part so that in the peripheral part, the thickness of the cover decreases as a function of a distance from the center of the external face.;

[0026] The method may comprise, during step b), a formation of several peripheral parts, extending respectively from the central part, and inclined relative to a plane parallel to the radial plane and passing through the center of the external face.

[0027] Machining may involve the application of a cutting tool comprising a blade inclined relative to the radial plane, against the external face of the cover.

[0028] The method may comprise a translation of the cutting tool relative to the external face. The method may comprise a successive use of several cutting tools, each cutting tool comprising a blade inclined relative to the radial plane at an angle of inclination, the angles of inclination of two different cutting tools being different.

[0029] The process can be as follows: step a) comprises obtaining a plurality of light sources, such that the respective emission elements of each light source are coplanar, and extend respectively in a cavity, the respective cavities of each light source being delimited by the same cover, each cavity being centered relative to a center of the external face; step b) is implemented around each center of the external face, so as to form, at each center, at least one peripheral portion, adjacent to a planar central portion, passing through said center of the external face, and parallel to the radial plane, the peripheral portion being inclined relative to the central portion such that in the peripheral portion, the thickness of the cover decreases as a function of a distance from the center of the external face.

[0030] A fourth unclaimed subject matter of the present disclosure is a method of producing a light source, comprising: i. obtaining a base light source, the base light source comprising an emitting element, extending parallel to a radial plane, around a center of the emitting element, and arranged in a cavity delimited by a base cover, the base cover extending between an inner face, arranged facing the emitting element, and a first face, the first face of the base cover extending parallel to the radial plane; ii. obtaining an auxiliary cover, extending between a second face and an outer face, the distance between the second face and the outer face defining a thickness of the auxiliary cover, the outer face comprising a center of the outer face; iii.machining the outer face of the auxiliary cover, so as to provide, in the outer face, at least one peripheral portion, adjacent to a flat central portion, the central portion passing through the center of the outer face, and being parallel to the second face, the peripheral portion being inclined relative to the central portion such that in the peripheral portion, the thickness of the auxiliary cover decreases as a function of a distance from the center of the outer face; iv. assembling the auxiliary cover against the base cover, the second face being in contact with the first face, the assembly being carried out such that the center of the outer face is aligned relative to the center of the emitting element, parallel to a transverse axis perpendicular to the radial plane.

[0031] According to the fourth object, the method may comprise: during step i), obtaining a plurality of basic light sources, distributed along the radial plane, each basic light source comprising an emission element, extending parallel to a radial plane around a center of the emission element, and arranged in a cavity delimited by a base cover, the base cover extending between an internal face, arranged facing each emission element, and a first face, the first face of the base cover extending parallel to the radial plane; during step ii), obtaining an auxiliary cover such that the external face of the auxiliary cover comprises several centers of the external face;during step iii) forming, in the outer face of the auxiliary cover, a plurality of peripheral portions, respectively around a plurality of central portions, each central portion passing through a center of the outer face, and being parallel to the second face, each peripheral portion being inclined relative to the central portion to which it is adjacent, such that in each peripheral portion, the thickness of the auxiliary cover decreases as a function of a distance from the central portion to which the peripheral portion is adjacent; during step iv), assembling the auxiliary cover on the base cover, the first face being assembled against the second face, the assembly being carried out in such a way that at least one center of the outer face is aligned relative to the center of an emitting element, parallel to a transverse axis perpendicular to the radial plane. ;

[0032] The invention will be better understood by reading the description of the exemplary embodiments presented in the remainder of the description, in conjunction with the figures listed below. FIGURES

[0033] There figure 1A shows an example of a gas sensor which may comprise a light source according to the first subject of the invention. The figure 1B represents a propagation of light, from a light source, between two parallel reflecting walls. The figure 2A schematizes an infrared light source according to the prior art. The figure 2B schematizes a light-emitting element taking the form of a membrane traversed by a conductive track. The figure 2C shows a first embodiment of a light source according to the invention. The figures 2D et 2E illustrate a propagation of a light ray on either side of the external face of the cover of the light source, respectively considering a light source according to the prior art and a light source according to the invention. The figure 2F is a top view of a light source according to the first embodiment. The figure 2G is a perspective view of a light source according to the first embodiment. The figure 2H is a detail of the external face of a light source according to the first embodiment. The figure 3A shows a setup used to model the rays emerging from the light source. The figures 3B And 3C are histograms of ray angles detected by a modeled photodetector. These histograms were obtained following modeling of a light source respectively according to the prior art and according to the first embodiment of the invention. The figures 3D And 3Erepresent ray tracings made by placing a light source between two flat, parallel reflective walls. On the figures 3D And 3E , the light source is respectively a light source according to the prior art and according to the first embodiment. The figures 4A à 4C show a light source according to a second embodiment. The figure 4D illustrates results of an optimization of geometric parameters of the external face, the objective being to increase a proportion of rays extending within an angular range of ± 30° around a transverse axis. The figure 4E represents a histogram of ray angles detected by a modeled photodetector. This histogram was obtained following modeling of a light source according to the second embodiment of the invention. The figure 5A shows a light source according to a third embodiment. The figure 5B represents a histogram of ray angles detected by a modeled photodetector. This histogram was obtained following modeling of a light source according to the third embodiment of the invention. The figure 5C shows a light source according to a fourth embodiment. The figure 5D represents a histogram of ray angles detected by a modeled photodetector. This histogram was obtained following modeling of a light source according to the fourth embodiment of the invention. The figure 5E shows a radiation diagram of light sources respectively according to the prior art, the first embodiment and the third embodiment. The figures 6A et 6B represent a variant of the first embodiment. The figures 6C et 6D represent a variant of the second embodiment. The figure 7 shows a production method for obtaining a light source according to the first embodiment or according to the second embodiment. The figure 8 shows a production method for obtaining a light source according to the third embodiment or according to the fourth embodiment. The figure 9 schematizes a deposition of an anti-reflective layer on a light source according to the invention. The figure 10 shows a fifth embodiment of a light source. The figure 11A represents another, unclaimed, method for obtaining a light source. The figure 11B schematizes a collective manufacturing process allowing the production of different light sources. figures 12A, 12B et 12C schematize a method for obtaining a light source according to the prior art. The figures 13A à 13D show steps in machining the top cover of a light source. The figures 14A et 14B schematize substrates forming the light source cover, respectively according to the first embodiment and the second embodiment, resulting from a collective formation process. EXPOSE DE MODES DE REALISATION PARTICULIERS

[0034] We have represented, on the figure 1A , an example of a gas sensor 1, of the NDIR type, this sensor being described in WO2018162848. The sensor comprises an enclosure 2, capable of receiving a gas to be analyzed. The enclosure is delimited by two walls 3 1 , 3 2 , called transverse walls, extending along a transverse plane XZ. On the figure 1A , a first transverse wall 3 1 has been shown, the second transverse wall 3 2 being shown transparently so as to visualize the interior of the enclosure 2. The transverse walls 3 1 and 3 2 are shown on the figure 1B .

[0035] The transverse walls may be parallel to the transverse plane P XZ , or substantially parallel to it, the term substantially indicating that an angular tolerance, for example + / - 20° or + / - 30° is allowed. They may be flat or curved.

[0036] The gas sensor 1 also comprises a peripheral wall 4, delimiting the enclosure 2, and extending between the first transverse wall 3 1 and the second transverse wall 3 2 . The peripheral wall 4 extends around a longitudinal axis Y, perpendicular to the transverse plane Pxz. The peripheral wall 4 takes the form of a cylindrical wall, the section of which, in the plane P XY , comprises curved portions 4 1 , 4 2 and flat portions. The curved portions may in particular be elliptical. An elliptical portion follows, according to the transverse plane Pxz, the contour of a part of an ellipse.

[0037] The gas sensor 1 comprises a light source 10, capable of emitting a light wave according to an emission cone Ω, the emission cone extending around an emission axis Δ. The light source 10 is configured to emit the light wave according to an illumination spectral band Δλ. The illumination spectral band Δλ extends into the infrared, for example between 1 µm and 10 µm.

[0038] The first curved portion 4 1 is reflective. It is configured to receive a first part Ω 1 of the emission cone Ω, so as to reflect it towards a measurement photodetector 20. The light wave thus passes through the gas present in the enclosure 2, before being detected by the measurement photodetector 20. In the example considered, the measurement photodetector 20 is a thermopile, capable of delivering a signal dependent on the intensity of the light wave to which the photodetector is exposed. It may also be a photodiode or another type of photodetector. The measurement photodetector 20 may be coupled to a bandpass filter 21, the spectral band of which corresponds to a spectral band of a gaseous species G s of which we wish to determine a quantity C s in the gas mixture. The intensity I of the light wave detected by the measuring photodetector 20 depends on the quantity C s according to the Beer-Lambert relation: att = I I 0 = e − μ C S l Or : µ( C s ) is an attenuation coefficient, depending on the quantity C s sought; 1 is the thickness of gas crossed by the light wave in the enclosure; I 0 is the intensity of the incident light wave, which corresponds to the intensity of the wave that would reach the measuring photodetector 20 in the absence of absorbing gas in the enclosure.

[0039] The comparison between I And I 0 , taking the form of a ratio I I 0 , corresponds to an attenuation att generated by the gaseous species considered.

[0040] For each pulse of the light source 10, we can thus determine µ( C s ), which makes it possible to estimate Ĉ s knowing that the relationship between C s and µ( C s ) is known.

[0041] Expression (1) assumes control of the intensity I0 of the light wave emitted by the light source 10. For this purpose, the device may comprise a reference photodetector 23, arranged such that it detects a light wave, called a reference light wave, reaching the reference photodetector 23 without interacting with the gas present in the enclosure 2, or without significantly interacting with the latter. The peripheral wall 4 comprises for this purpose the second reflecting portion 4 2 , configured to receive a second part of the emission cone Ω emitted by the light source 10, so as to reflect it towards the reference photodetector 23. The intensity of the reference light wave, detected by the reference photodetector 23, is designated by the term reference intensity I ref . In this example, the reference photodetector 23 is associated with an optical filter, called the reference optical filter 22. The reference optical filter 22 defines a bandwidth corresponding to a range of wavelengths not absorbed by the sample. The reference bandwidth is for example centered around the wavelength 3.91 µm. The measurement of I ref allows to correct the value of I 0 , which allows us to determine µ( C s ), then estimate Ĉ s . The measure of I ref in particular allows for taking into account temporal variations in intensity I 0 of the light wave emitted by the light source 10.

[0042] On the figure 1B , a section of the enclosure 2 is shown, along the emission axis Δ, between the light source 10 and the first elliptical part 4 1 of the peripheral wall 4. The section is shown along a transverse plane YZ. In the transverse plane YZ, the radiation is emitted by the light source according to an angular range grouping emission angles α distributed at ±90° on either side of the emission axis Δ. The transverse walls 3 1 and 3 2 are reflective. Thus, depending on the emission angle α, the radiation can undergo numerous reflections on the transverse walls before reaching the reflective elliptical part 4 1 . Downstream of the latter, the radiation propagates to the measurement photodetector 20, also undergoing reflections on the transverse walls.

[0043] By reflective wall is meant a wall whose reflection coefficient, in all or part of the spectral band Δλ of the light wave emitted by the light source 10, is greater than 50%, and preferably greater than 80%. A reflective wall can be formed using a reflective material such as a metal, for example gold.

[0044] It is understood that the higher the emission angle α, the greater the number of reflections by the reflecting walls 3 1 and 3 2. However, the higher the number of reflections, the more the intensity of the emitted radiation decreases, due to losses at each reflection. In addition, the measuring photodetector 20 is generally coupled to a bandpass filter 21. The bandpass filter delimits a spectral band corresponding to the absorption spectral band of the gaseous species sought. It is preferable that the angle of the incident radiation at the bandpass filter 21 is as close as possible to a normal to the filter. In other words, it is preferable that the angle of incidence of the radiation, relative to the transverse axis Z, is as small as possible. When the angle of incidence relative to the filter is high, the bandwidth defined by the filter can be modified, which degrades the filtration performance.Finally, the variability of the emission angles α relative to the transverse axis Z, in the plane P YZ causes a variability of the optical paths of the different rays propagating between the light source 10 and the measuring photodetector 20. Indeed, the higher the emission angle α, the higher the number of reflections in the optical path between the light source 10 and the measuring photodetector 20. The rays with a high emission angle α are therefore more attenuated than the rays emitted at a lower angle.

[0045] The findings described in the previous paragraph are also valid for the radiation propagating from the light source to the second elliptical part 4 2 , then from the latter to the reference photodetector 23.

[0046] Considering the consequences set out in the previous paragraph, it is preferable to reduce as much as possible the emission angles α, relative to the emission axis Δ of the light source (which corresponds to the transverse axis Z), while maintaining the intensity level of the light source 10. This is an important aspect of the invention.

[0047] The light source 10 may in particular be pulsed, the incident light wave being a pulse with a duration generally between 100 ms and 1 s. It may in particular be a light source comprising a membrane-type emission element 11, traversed by a filament, the latter being traversed by a pulsed electric current. The filament is a conductive track 11' heated to a temperature between 400°C and 800°C so as to emit infrared light.

[0048] An example of a prior art light source 10 A, or base light source, is shown in FIG. figure 2A The light source comprises an emission element 11 in the form of a membrane connected to a substrate 12 and suspended over an opening 12' formed in the latter. The membrane 11 extends into a cavity 15, placed under vacuum. The cavity 15 is delimited by an annular wall 13 and is closed by a cover 14 A. The emission element 11, in this example the membrane, extends along a radial plane P XY , perpendicular to a transverse axis Z. The annular wall 13 connects the cover 14 A to the substrate 12. The cover 14 A extends between an internal face 17, adjacent to the cavity 15, and an external face 16. The internal face 17 and the external face 16 are parallel to the membrane 11, i.e. parallel to the radial plane P XY .

[0049] On the figure 2B , a disc-shaped membrane 11 is shown, traversed by a conductive track 11'. The membrane 11 extends along the radial plane P XY . The membrane 11 is attached, by arms 11", to the substrate 12. When the conductive track 11' is traversed by an electric current, it heats up and produces a heating of the membrane 11. The heating of the membrane 11 can be considered as homogeneous. Under the effect of the heating, the membrane 11 emits infrared radiation in all directions (i.e. according to a solid angle of 4π steradians). The spectrum of the infrared radiation, i.e. the intensity as a function of the wavelength, is usually considered as the emission spectrum of a gray body.

[0050] On the figure 2A , arrows represent ray paths emitted from the center 11 c of the membrane 11 and propagating through the cavity 15. In reality, the rays are emitted from the entire surface of the membrane. The emission angle α relative to the transverse axis Z is also represented. The cover of the light source is made of a material whose refractive index is higher than that of air in the spectral emission band of the membrane 11. This is, for example, silicon. Due to the variation in refractive index between vacuum and silicon on the one hand, and between silicon and air on the other, the angle α is reduced at the interface between vacuum and silicon, then increases at the interface between silicon and air.

[0051] The invention relates to an optimization of the light source, so as to increase the quantity of radiation emerging from the cover 14 by having an emission angle α, relative to the transverse axis Z, less than ± 30° or ± 10°.

[0052] A first embodiment is shown in the figure 2C . In this figure, the light source 10 comprises the same elements as those described in connection with the light source 10 A of the prior art, with the exception of the cover 14, the latter being modified as described below. The membrane 11 extends around a center 11 c . The external face 16 extends around a center 16 c . Along the transverse axis Z, the center of the external face 16 c is aligned with the center of the membrane 11 c . The distance between the internal face 17 and the external face 16, along the transverse axis Z, corresponds to a thickness e of the cover 14.

[0053] The external face 16 comprises a central portion 16 1 , comprising the center of the external face 16 c and extending around the latter, along a length d 1 , parallel to the longitudinal axis Y. The central portion 16 1 extends parallel to the radial plane P XY , that is to say parallel to the membrane 11. In general, the external face 16 comprises at least one peripheral portion 16 2 , adjacent to the central portion 16 1 . The peripheral portion 16 2 is inclined, at an angle of inclination θ, relative to the central portion 16 1 . The inclination is such that as one moves away from the central portion 16 1 , (or from the center of the external face 16 c ), along the longitudinal axis Y, the thickness e of the cover 14 is reduced.

[0054] In the example shown, the dimensions L, Φ, ε, e, t, d represented on the figure 2C are: L = 800 µm; Φ = 300 µm; ε = 675 µm; t = 120 µm; e = 280 µm; d = 1140 µm.

[0055] On the embodiment shown on the figure 2C , the light source comprises a peripheral part 16 2 inclined at the angle θ on either side of the central part 16 1 , along the longitudinal axis Y. Each peripheral part 16 2 extends, from the central part 16 1 , along a length d 2 , defined parallel to the longitudinal axis Y. The length d 2 as well as the angle of inclination θ can be subject to optimization, as described in connection with the figure 4D .

[0056] The inclination of the peripheral portion 16 2 of the external face 16 has the effect of inclining the normal to the silicon / air interface defined by the external surface 16. If α denotes the angle with which a ray emerges from the external face 16 relative to the transverse axis Z, the inclination of the peripheral portion 16 2 of the external face 16 makes it possible to reduce the angle α, compared to the configuration of the prior art, according to which the external face 16 is not inclined. This effect is illustrated in the figures 2D et 2E .

[0057] There figure 2D illustrates a configuration of the prior art. A ray propagating through the cover 14 is shown. The angles α 1 , α 2 and α are respectively: the angle of incidence of the ray with respect to the normal N 1 to the internal face 17; the angle of incidence of the ray with respect to the normal N 2 to the external face 16; the angle of the ray emerging from the external face 16 with respect to the transverse axis Z.

[0058] In this example, the transverse axis Z is parallel to the normal N 2 . The cover 14 is made of silicon, whose optical refractive index is between 3.4 and 3.5. The cavity 15 is under vacuum, the refractive index of vacuum being 1. Beyond the external face 16, the ray propagates in the gas to be analyzed, the latter being able to be assimilated to air, with a refractive index equal to 1: Therefore α = α 1 . Due to the change in refractive index on either side of the interface, the angle α 2 , in the cover 14, is less than the angles α and α 1 .

[0059] There figure 2E illustrates a configuration as shown in the figure 2C . As on the figure 2D , a ray propagating through the cover 14 is represented. The angles α 1 , α 2 and α correspond to the definitions given in connection with the figure 2D . On the figure 2E , the ray emerges from the peripheral portion 16 2 of the external face. The peripheral portion 16 2 is inclined relative to a plane parallel to the radial plane P XY and passing through the center 16 c of the external face 16, at an angle of inclination θ. As a result, the normal N 2 to the hood 14 / air interface is also inclined at an angle θ relative to the transverse axis Z. The angle α, relative to the transverse axis Z, is less than that of the configuration of the prior art. Comparison of the figures 2D et 2E shows that the inclination of the outer face 16 results in a reduction of the angle α compared to the prior art. Thus, the inclination of the peripheral portion 16 2 of the outer face 16 results in a reduction of the angles with which the rays emerge from the peripheral portion 16 2 , compared to the configuration of the prior art, according to which the outer face 16 is planar.

[0060] There figure 2F illustrates a top view, that is to say along a plane parallel to the radial plane P XY , of the light source shown on the figure 2C . The membrane 11 is shown in dotted lines. The figure 2G is a perspective view of the light source shown in the figure 2C . On the figure 2H , the central part 16 1 of the external face is shown, flat, and parallel to the radial plane P XY . A peripheral part 16 2 is also shown. The radial plane is defined by a lateral axis X orthogonal to a longitudinal axis Y. The peripheral part 16 2 extends parallel to a plane defined by a first lateral axis X 1 orthogonal to a first longitudinal axis Y 1 (or Y 1 ')According to the embodiment shown: the first lateral axis X 1 is parallel to the lateral axis X; the first longitudinal axis Y 1 (or Y' 1 ) is inclined relative to the lateral axis Y, in a transverse plane P YZ . The acute angle of inclination θ between the axes Y 1 (or Y' 1 ) and Y corresponds to the angle of inclination of the peripheral part 16 2 relative to the central part 16 1 .

[0061] We modeled, by ray tracing, different configurations corresponding to the embodiment illustrated in the figure 2C . The inclination angle θ and the length d 2 of the peripheral part 16 2 were varied. The objective is to maximize a quantity of rays emerging from the external face 16 and propagating at an angle α less than ±30° relative to the transverse axis Z.

[0062] There figure 3A shows a configuration implemented to perform the modeling. The light source 10 is arranged facing a modeled photodetector 20 m extending infinitely around the transverse axis Z of the light source 10. The light source is assumed to emit radiation at a solid angle of 2π steradians in a half-space delimited by the light source 10 and comprising the photodetector 20 m . The modeling is defined so that the angle α of each ray emitted by the source is the opposite of the angle received by the modeled photodetector 20 m .

[0063] THE figures 3B And 3C are histograms of the angles α, with respect to the transverse axis Z, of the rays detected by the photodetector 20 m, considering respectively: a prior art light source, as described in connection with the figure 2A ; a light source according to the configuration shown in the figure 2C .

[0064] On the figures 3B And 3C , the abscissa and ordinate axes represent respectively the angles, with respect to the Z axis, of the rays detected by the photodetector 20 m , respectively in the transverse planes P XZ and P YZ . The center of each figure, marked by a cross, corresponds to rays parallel to the Z axis. On each figure, the gray level represents a number of detected rays. On the figure 3B , the histogram is relatively homogeneous. The angular distribution of the detected photons is considered homogeneous. On the figure 3C , we observe a tightening of the histogram around the small angles, in the transverse plane P YZ . This shows that the invention makes it possible to increase the proportion of rays, emitted by the light source 10, and emerging from the cover in an angular range of ±30°, or even ±25° relative to the transverse axis Z.

[0065] The inventors carried out modeling by varying the parameters d 2 (length of each peripheral part parallel to the longitudinal axis Y), and θ (angle of inclination of each peripheral part). The optimal parameters are d 2 = 494 µm and θ = 11°. According to these optimal parameters, 54.6% of the rays emitted by the light source 10, in the half-space comprising the photodetector, emerge from the cover 14 at angles α, relative to the transverse axis Z, within the angular range ±30°. By using a light source of the prior art, as described in connection with the figure 2A , this proportion is 31%.

[0066] THE figures 3D And 3E represent ray tracings by respectively arranging a light source 10 A according to the prior art (cf. figure 2A ), and a light source 10 according to the configuration shown in the figure 2C . In each of these figures, the light source is arranged as shown in the figures 1A et 1B : It opens into the enclosure 2 of the gas sensor. In this example, the light source is arranged between two reflective walls 3 1 and 3 2 spaced from each other by a distance h = 1.2 mm. The transverse axis Z of the light source 10 is parallel to the transverse walls, and centered relative to the latter. The comparison of the figures 3D And 3E show that the invention makes it possible to increase the quantity of rays emerging from the light source 10 at an angle α of ±30° relative to the transverse axis Z. On the figures 3D And 3E , we bypassed areas corresponding to rays emitted at an angle α greater than 30°. The configuration according to the invention ( figure 3E ) allows to reduce the proportion of rays passing through these areas.

[0067] THE figures 4A à 4C show a second embodiment of the invention. According to this embodiment, the external face 16 of the light source 10 comprises a central part 16 1 which is planar, extending along a plane parallel to the radial plane P XY and passing through the center 16 c of the external face 16. The central part 16 1 extends along a lateral axis X orthogonal to a longitudinal axis Y. The light source 10 also comprises: two peripheral parts, 16 2,1 , called first peripheral parts, extending on either side of the central part 16 1 , along the longitudinal axis Y. As described in connection with the embodiment shown in the figure 2C , each peripheral portion extends along a first lateral axis X 1 orthogonal to a first longitudinal axis Y 1 (or Y' 1 ). The first lateral axis X 1 is parallel to the lateral axis X. The first longitudinal axis Y 1 (or Y' 1 ) forms a first acute inclination angle θ 1 relative to the longitudinal axis Y. two second peripheral portions 16 2,2 , extending on either side of the central portion 16 1 , along the lateral axis X. Each second peripheral portion extends along a second lateral axis X 2 (or X' 2 ) orthogonal to a second longitudinal axis Y 2 . The second longitudinal axis Y 2 is parallel to the longitudinal axis Y. The second lateral axis X 2 forms a second acute inclination angle θ 2 relative to the lateral axis X.

[0068] The first inclination angle θ 1 and the second inclination angle θ 2 can form the same inclination angle θ.

[0069] There figure 4A is a perspective view of the second embodiment. The figure 4B is a top view of the second embodiment. On the figure 4C , the lateral and longitudinal axes of the central part and of each peripheral part are represented.

[0070] Such an embodiment may for example be adapted to a gas sensor as described in connection with the figure 1A , but also to a gas sensor in which the enclosure 2, separating the light source from the photodetector, is cylindrical, around the transverse axis Z.

[0071] There figure 4D represents a result of the modeling carried out by varying the parameters d 2 (length of each peripheral part parallel to the longitudinal axis Y or to the lateral axis X) and θ (angle of inclination of each peripheral part). The ordinate axis corresponds to the variation range of d 2 , (unit: mm) and the abscissa axis corresponds to the variation range of θ (unit: degree). The gray level corresponds to a percentage of rays emerging from the cover 14 in an angular range of ±30° around the transverse axis Z. The objective of the modeling is to determine the parameters maximizing this percentage. The optimal parameters correspond to the cross drawn on the figure 4D : d 2 = 494 µm and θ = 11°. According to these optimal parameters, 74.5% of the rays emitted by the light source 10, in the half-space comprising the photodetector, emerge from the cover 14 at angles α, relative to the transverse axis Z, within the angular range ±30°. By using a light source of the prior art, as described in connection with the figure 2A , this proportion is 31%.

[0072] There figure 4E is a histogram of the angles α, relative to the transverse axis Z, of the rays detected by the 20 m photodetector. The histogram was produced in the same way as those of the figures 3B And 3C , considering a light source as represented on the figures 4A à 4C , according to the optimized parameters reported in the previous paragraph.

[0073] There figure 5A shows a third embodiment. According to this embodiment, the external face 16 of the light source 10 comprises a peripheral part 16 2 extending, on either side of the central part, at a first angle of inclination θ 1 over a part of the length of the peripheral wall 16 2 , then at a second angle of inclination θ 1 ' over another part of the length of the peripheral wall 16 2 , with θ' 1 > θ 1 . According to this embodiment, the angles of inclination θ 1 , θ 1 ' correspond to the acute angles between the longitudinal axis Y and the first longitudinal axis Y 1 of each peripheral part. This embodiment corresponds to an improvement of the first embodiment, each peripheral part successively comprising two angles of inclination.

[0074] An optimization was carried out, as described in connection with the figure 4D . It has been shown that according to such a configuration, taking into account the dimensions described in connection with the figure 2C , the optimal angles θ 1 and θ' 1 are respectively equal to 7.5° (along a length, parallel to the longitudinal axis Y, of 400 µm), and to 16° (along a length, parallel to the longitudinal axis Y, equal to 120 µm).

[0075] There figure 5B is a histogram of the angles α, relative to the transverse axis Z, of the rays detected by the 20 m photodetector. The histogram was produced in the same way as those of the figures 3B And 3C , considering a light source as represented on the figure 5A , according to the optimized parameters reported in the previous paragraph.

[0076] On the figure 5B , the abscissa and ordinate axes represent respectively the angles, with respect to the Z axis, of the rays detected by the photodetector 20 m , respectively in the planes P XZ and P YZ . The center figure 5B , marked by a cross, corresponds to rays parallel to the Z axis. The gray level represents a number of detected rays. A tightening of the histogram is observed around low angles. This shows that the invention makes it possible to increase the proportion of rays, emitted by the light source 10, and emerging from the cover 14 in an angular range of ±30°, or even ±20° relative to the transverse Z axis.

[0077] There figure 5C represents a fourth embodiment according to which the external face 16 comprises two first peripheral parts 16 2,1 and two second peripheral parts 16 2,2 as described in connection with the second embodiment.

[0078] Each first peripheral portion 16 2,1 extends along a first longitudinal axis Y 1 forming, with the longitudinal axis Y, a first acute angle of inclination θ 1 over a portion of the length of the peripheral wall, then along a second acute angle of inclination θ 1 ' over another portion of the length of the peripheral wall, with θ' 1 > θ 1 .

[0079] Each second peripheral portion 16 2,2 extends along a second lateral axis X 2 forming, with the lateral axis X, the first acute angle of inclination θ 1 over a part of the length of the peripheral wall, then according to the second angle of inclination θ 1 ' over another part of the length of the peripheral wall, with θ' 1 > θ 1 .

[0080] An optimization was carried out, as described in connection with the figure 4D . It has been shown that according to such a configuration, taking into account the dimensions described in connection with the figure 2C , the optimal angles θ 1 and θ' 1 are respectively equal to 7.5° (along a length, parallel to the longitudinal axis Y, of 400 µm), and to 16° (along a length, parallel to the longitudinal axis Y, equal to 120 µm). According to these optimal parameters, 76.7% of the rays detected by the 20 m photodetector emerge from the light source at angles, relative to the transverse axis Z, included in the angular range ±30°. By using a light source of the prior art, as described in connection with the figure 2A , this proportion is 31%.

[0081] There figure 5D is a histogram of the angles α, relative to the transverse axis Z, of the rays detected by the 20 m photodetector. The histogram was produced in the same way as those of the figures 3B , 3C , 4E Or 5B , considering a light source as represented on the figure 5C , according to the optimized parameters reported in the previous paragraph.

[0082] On the figure 5D , the abscissa and ordinate axes respectively represent the angles, with respect to the Z axis, of the rays detected by the photodetector 20 m , respectively in the planes P XZ and P YZ . The center figure 5D , marked by a cross, corresponds to rays parallel to the Z axis. The gray level represents a number of detected rays. A tightening of the histogram is observed around low angles. This shows that the invention makes it possible to increase the proportion of rays, emitted by the light source 10, and emerging from the cover 12 in an angular range of ±30°, or even ±20° relative to the transverse Z axis.

[0083] The comparison between the histograms of the figures 5D , 5B , 4E And 3C , representing two embodiments of the invention, with the histogram of the figure 3B , shows the technical effect of the invention, namely an increase in the proportion of rays emerging from the light source 10 in an angular range of ±30°.

[0084] There figure 5E shows the emission diagrams, along a transverse plane P YZ (or P XZ depending on the embodiments), of a light source respectively: according to a configuration of the prior art, described in connection with the figure 2A : curve a; according to a configuration according to the first embodiment of the invention, described in connection with the figures 2C à 2H , according to the optimized parameters (θ 1 = 11°).: curve b; according to a configuration according to the third embodiment of the invention, described in connection with the figure 5A , according to the optimized parameters (θ 1 = 7.5°, θ' 1 = 16°): curve c.

[0085] On the figure 5E , the abscissa axis corresponds to a standardized luminous intensity. The angular range corresponds to the angle α between the rays emitted by the light source (i.e. emerging from the external face 16) and the transverse axis Z. Using each curve, the angular range Δθ 0.5 was estimated for which the standardized luminous intensity is equal to 0.5. The values ​​of Δθ 0.5 from curves a, b and c are respectively ± 58°, ± 24°, ± 20°. This confirms the fact that the invention makes it possible to narrow the light beam emitted by the emission element 11 by reducing the angular range relative to the transverse axis Z. As could be seen by comparing the figures 3C And 5B , there figure 5E confirms that the tightening is more pronounced when implementing the third embodiment compared to the first embodiment.

[0086] THE figures 6A et 6B illustrate a variant of the first embodiment, according to which the external face 16 comprises only one peripheral part 16 2 extending around the central part 16 1 . The figures 6C et 6D illustrate a variant of the second embodiment, according to which the external face 16 comprises three peripheral parts: two parts 16 2,1, and one part referenced 16 2,2.

[0087] The inventors modeled the use of a light source according to the first and second embodiments, using the optimized parameters θ, d 2 as described in connection with the figure 4D , on a gas sensor as shown in the figure 1A . The light source 10 is arranged such that the transverse axis Z corresponds to the central axis Δ shown in the figure 1A . A quantity of light detected by the measuring photodetector 20 and by the reference photodetector 23 was estimated. It was considered that the transverse walls 3 1 and 3 2 are reflective, and distant from each other by a distance h = 1.2 mm. The longitudinal axis Y of the light source 10 is orthogonal to the reflective walls 3 1 and 3 2 .

[0088] Table 1 represents, for the first and second embodiments, a relative increase in the intensity ΔI detected by the photodetector and by the reference photodetector, in the absence of absorbing gas in the enclosure. The relative increase in relative intensity is defined such that: Δ I = I − I A I A where I and I A correspond respectively to an intensity detected by the photodetector considered by respectively implementing a light source according to the invention (first embodiment or second embodiment) and a light source according to the prior art, cf. figure 2A . Table 1 Mode de réalisation Photodétecteur de mesure Photodétecteur de référence 1 ( figure 2G ) 74% 44 % 2 ( figure 4A ) 146 % -35 %

[0089] The results reported in Table 1 show that the first embodiment makes it possible to increase the quantity of light detected by the measurement photodetector and by the reference photodetector. The second embodiment makes it possible to further increase the quantity of light detected by the measurement photodetector (+ 146%), to the detriment of the quantity of light detected by the reference photodetector (- 35%).

[0090] In view of these results, the inventors consider that the first embodiment is particularly suitable for a gas sensor as shown in the figure 1A The second embodiment appears more suitable for gas sensor configurations comprising a cylindrical enclosure extending around the transverse axis Z.

[0091] The simulations carried out show that the angle of inclination of a peripheral part, or of each peripheral part, relative to the central part, is preferably between 5° and 30°, and preferably between 5° and 25° or between 5° and 20°.

[0092] There figure 7 schematizes a method of manufacturing a light source according to the first or second embodiments, cf. figures 2C , 2G Or 4A. The cover 14 can be machined, for example cut, using a cutting tool 41, so as to form a peripheral portion 16 2 inclined relative to the central portion 16 1 . The cutting tool comprises a beveled blade 51, making it possible to form the inclination of the peripheral portion 16 2 . According to the first embodiment, the cutting tool 41 is translated parallel to the lateral axis X to form the peripheral portions 16 2 . According to the second embodiment, the cutting tool 41 is translated parallel to the lateral axis X to form the first peripheral portions 16 2,1 , then parallel to the longitudinal axis Y to form the second peripheral portions 16 2,2 . It can be a cutting tool of the "Dicing blade ZH05 Series - Disco corporation - Japan" type.

[0093] There figure 8 shows a method of manufacturing a light source according to the third or fourth embodiments, cf. figure 5A Or5C . The cover 14 can be machined, for example cut, using a first cutting tool 41 and a second cutting tool 42 so as to form a peripheral portion 16 2 inclined relative to the central portion 16 1 , according to two different angles of inclination. Each cutting tool comprises a blade 51, 52, arranged to form a peripheral portion inclined successively according to the angles of inclination θ 1 and θ' 1 . First of all, the first cutting tool 41 is used, as shown in the figure 7 , then the second cutting tool 42.

[0094] There figure 9 illustrates a deposition of an anti-reflective layer 19 (Anti-reflective coating) on ​​the external face of a light source as described in connection with the first or third embodiment. Given the small inclination angles θ, which are generally less than 25°, or even 20°, the inclination of each peripheral face has little impact on the thickness of the anti-reflective layer 19. Considering for example an angle of 12°, the thickness on each peripheral part is 0.98 times equal to the thickness of the anti-reflective layer deposited on the central part. Thus, the performances of the anti-reflective layer 19 can be considered as spatially homogeneous, because the thickness of the latter varies little. This conclusion is valid whatever the embodiment, in particular as long as the inclination angle θ remains sufficiently small, typically less than 25° and preferably 20°.

[0095] There figure 10 illustrates a fifth embodiment. According to this embodiment, the substrate 12 is also structured. The substrate thus comprises a rear external face 12 R, structured in the same way as the external face 16 of the cover 14. The objective is to obtain an increase in the radiation emitted by the source and emerging from the substrate 12 with a low incidence relative to the transverse axis Z. According to such an embodiment, the light source can be arranged in a gas sensor, the reference photodetector 23 facing the substrate 12.

[0096] There figure 11A illustrates a manufacturing method, in which the cover 14 comprises a base cover 14 1 and an auxiliary cover 14 2 . The base cover 14 1 extends between an inner face 17 and a first face 17 1 . The inner face 17 and the first face 17 1 extend parallel to each other. The base cover 14 1 is assembled on a substrate 12, the base cover and the substrate enclosing a cavity 15 comprising an emission element 11, for example a membrane. The emission element extends along a radial plane around a center 11 c .

[0097] The auxiliary cover 14 2 extends between a second face 17 2 and an external face 16. The latter is structured, around a center 16 c , as described in connection with the previous embodiments. The auxiliary cover 14 2 is then assembled to the base cover 14 1 , such that the first face 17 1 is arranged against the second face 17 2 . The assembly is carried out such that the center 11 c of the emission element 11 is aligned with the center 16 c of the external face, parallel to the transverse axis Z. On the figure 11A , the alignment is materialized by a mixed line.

[0098] The base cover 14 1 and the auxiliary cover 14 2 may be formed from the same material, for example silicon. Alternatively, the auxiliary cover 14 2 may be formed from a different material than the base cover 14 1 . The auxiliary cover 14 2 may for example be made of glass, while the base cover is made of silicon.

[0099] The assembly of the auxiliary cover 14 2 on the base cover 14 1 forms a cover 14 of the light source 10.

[0100] There figure 11B illustrates a method of collectively manufacturing a plurality of light sources according to the embodiment similar to that described in connection with the figure 11A . According to this method, a base cover 14 1 and an auxiliary cover 14 2 are available. As in the method shown schematically in the figure 11A , the base cover 14 1 extends between an inner face 17 and a first face 17 1 . The inner face 17 and the first face 17 1 extend parallel to each other. The base cover 14 1 is assembled on a substrate 12, the base cover and the substrate contain a plurality of cavities 15, each cavity 15 comprising an emission element 11, for example a membrane. Each emission element 11 extends along a radial plane around a center 11 c . The assembly formed by the base cover, the substrate 12, the cavity 15 and the membrane 11 corresponds to a basic light source.

[0101] The auxiliary cover 14 2 extends between a second face 17 2 and an external face 16. The latter is the subject of a structuring, around centers 16 c , distinct from each other. The structuring comprises the production of at least one peripheral part 16 2 inclined relative to central parts, parallel to the second face 17 2 , each central part passing respectively through each center 16 c . The auxiliary cover 14 2 is then assembled to the base cover 14 1 , such that the first face 17 1 is arranged against the second face 17 2 . The assembly is carried out such that each center 11 c of an emission element is aligned with a center 16 c of the external face 16, parallel to the transverse axis Z. On the figure 11B , the alignment is materialized by a mixed line. Such a method allows simultaneous formation of several light sources 10, the latter being able to be separated from each other. On the figure 11B , each light source 10 is represented by a dotted frame.

[0102] THE figures 12A à 12C schematize a method for collectively manufacturing light sources 10 A according to the prior art, called basic light sources. According to such a method, each basic light source is formed by an emission element 11 (in particular a membrane), extending along a radial plane, in a cavity 15 delimited by a cover 14 A and a substrate 12. The cover 14 A extends between two parallel faces. The figures 12B et 12C represent a separation of each basic light source 10 A, by a cutout of the cover 14 A (cf. figure 12B ) then the substrate ( figure 12C ). On the figure 12C , a 10 A light source thus obtained has been materialized by a dotted frame.

[0103] THE figures 13A à 13C represent different ways of structuring an external face 16, the latter being able to be: an external face of a substrate 14, the latter being initially such as the substrate 14 A shown in the figure 12A ; an external face of an auxiliary substrate 14 2 , as described in connection with the figure 11B .

[0104] On the figures 13A et 13B , the structuring is carried out by using a cutting tool 41, as described in connection with FIG. 7A. This makes it possible to provide, on the same external face, different peripheral parts 16 2 extending respectively around different central parts 16 1 .

[0105] On the figure 13C , the structuring is carried out by using a tool 44, comprising a V-shaped blade 54. This makes it possible to simultaneously form two peripheral parts 16 2 on the external face. The figure 13D shows the application of a cutting tool 44 to a substrate 14, which initially has a shape corresponding to the substrate 14A shown in the figure 12A .

[0106] The structures represented on the figures 13A à 13C can be carried out on the external face 16 2 of a cover described in connection with the figure 11B .

[0107] THE figures 14A et 14B show a result of the application of collective manufacturing processes of light sources 10. The collective manufacturing processes are those described in connection with the figure 11B , Or 13A à 13D . On the figure 14A , a production of light sources according to the first embodiment is shown. On the figure 14B , a production of light sources according to the second embodiment is shown.

[0108] The light sources according to the invention may be used in gas sensors, the latter being applied to different fields, for example the environment, in particular the control of atmospheric pollution, industry, for example the chemical, petroleum or agri-food industry, or health.

Claims

1. An infrared light source (10), comprising: - an emitting element (11), extending as a radial plane (PXY), about a center of the emitting element (11c), the emitting element being configured to heat up, the heating leading to an emission of infrared light; - a cavity (15), in which the emitting element lies, the cavity being bounded by a cover (14), placed facing the emitting element (11), the cover having an internal face (17), placed facing the emitting element (11), and an external face (16), defining an interface between the cover (14) and a medium outside the light source; - the cover occupying, parallel to a transverse axis (Z), perpendicular to the radial plane (PXY), a thickness (e), between the internal face (17) and the external face (16); - the external face comprising • a planar central portion (161), extending about a center (16c) of the external face, the center of the external face being aligned with the center of the emitting element (11c), along the transverse axis (Z); the light source being characterized in that the external face comprises : • at least one peripheral portion (162, 162,1, 162,2), adjacent to the central portion, the peripheral portion being inclined with respect to the central portion by an angle of inclination (θ); - such that, in the peripheral portion, the thickness (e) of the cover (14) decreases as a function of a distance from the central portion (161).

2. The light source as claimed in claim 1, wherein the peripheral portion (162, 162,1, 162,2) lies on either side of the central portion (161).

3. The light source as claimed in either one of the preceding claims, wherein the peripheral portion (162, 162,1, 162,2) is inclined, with respect to the central portion (161), by an angle of inclination comprised between 5° and 30°, and preferably comprised between 5° and 20°.

4. The light source as claimed in any one of the preceding claims, wherein: - the central portion (161) lies parallel to a longitudinal axis (Y) and to a lateral axis (X), the longitudinal axis being perpendicular to the lateral axis; - the peripheral portion (162, 162,1) lies parallel to a first longitudinal axis (Y1) and to a first lateral axis (X1); - the first longitudinal axis (Y1) is inclined, by the angle of inclination (θ), with respect to the longitudinal axis (Y); - the first lateral axis (X1) is parallel to the lateral axis (X).

5. The light source as claimed in claim 4, comprising a second peripheral portion (162,2), adjacent to the central portion, such that: - the second peripheral portion lies parallel to a second longitudinal axis (Y2) and a second lateral axis (X2); - the second lateral axis (X2) is inclined, by a second angle of inclination (θ2), with respect to the lateral axis (X); - the second longitudinal axis (Y2) is parallel to the longitudinal axis (Y).

6. The light source as claimed in any one of the preceding claims, wherein the peripheral portion (162) extends a length comprised between 5% and 50% of a length of the cover (14), this length being measured parallel to the lateral axis or to the longitudinal axis.

7. The light source as claimed in any one of the preceding claims, wherein at least one peripheral portion is inclined, with respect to the central portion, by various angles of inclination (θ1, θ'1), the angles of inclination increasing with distance from the central portion (161).

8. The light source as claimed in any one of the preceding claims, wherein the central portion (16) is centered with respect to the emitting element (11), along the transverse axis (Z).

9. The light source as claimed in any one of the preceding claims, wherein the external face (16) extends, along an axis parallel to the radial plane (PXY), a length comprised between 500 µm and 2500 µm.

10. A gas sensor (1), comprising an enclosure (2) configured to contain a gas, a light source (10) and at least one photodetector (20), the light source being configured to emit light radiation that propagates, through the enclosure, to the photodetector, the light source being a light source as claimed in any one of claims 1 to 9.

11. The gas sensor as claimed in claim 10, wherein the enclosure (2) is bounded by at least a first reflective wall (31), which lies perpendicular to the radial plane (PXY) of the light source, parallel to the transverse axis (Z).

12. The gas sensor as claimed in claim 11, wherein the external face (16) of the cover (14) of the light source (10) comprises a planar central portion (161), extending as a plane parallel to the radial plane and passing through the center (16c) of the external face, and wherein: - the central portion (161) lies parallel to a longitudinal axis (Y) and to a lateral axis (X), the longitudinal axis being perpendicular to the lateral axis; - the peripheral portion (162) lies parallel to a first longitudinal axis (Y1) and to a first lateral axis (X1); - the first longitudinal axis (Y1) is inclined, by an angle of inclination (θ), with respect to the longitudinal axis (Y); - the first lateral axis (X1) is parallel to the lateral axis (X); the light source being arranged such that the longitudinal axis (Y) is perpendicular to the first reflective wall.

13. The gas sensor as claimed in any one of claims 10 to 12, wherein the enclosure is bounded by a second reflective wall (32), lying parallel to the first reflective wall, the light source lying between the first and second reflective walls.

14. The gas sensor as claimed in claim 13, wherein the center of the emitting element (11c) of the light source (10) is located at an equal distance from each reflective wall.

15. A method for producing an infrared light source as claimed in any one of claims 1 to 9, comprising: - a) obtaining a light source, the light source comprising an emitting element (11), lying parallel to a radial plane (PXY), about a center of the emitting element (11c), the emitting element being configured to heat up, the heating leading to an emission of infrared light, and placed in a cavity (15) bounded by a cover, the cover extending between an internal face (17), placed facing the emitting element, and an external face (16), the external face lying parallel to the radial plane (PXY), about a center (16c) of the external face, the center of the external face being aligned with the center of the emitting element (11c), along the transverse axis (Z) perpendicular to the radial plane, the distance between the internal face and the external face defining a thickness (e) of the cover; - b) machining the external face (16), so as to form, in the external face, at least one peripheral portion (162, 162,1, 162,2), adjacent to a planar central portion (161) of the external face, passing through the center (16c) of the external face, and parallel to the radial plane, the peripheral portion being inclined with respect to the central portion such that, in the peripheral portion, the thickness of the cover decreases as a function of a distance from the center of the external face.