Optical substrate having integrated antennas, and spectrometer comprising same

Abstract

The invention relates to an optical substrate (1) having an integrated waveguide (2), at least one antenna (330) being formed in the optical substrate (1), the at least one antenna being formed by a plurality of nanoholes (341, 342, 343), at least one of the nanoholes (341, 342, 343) differing from the other nanoholes (341, 342, 343) by at least one of: its diameter, its spacing of the waveguide (2) in the height direction of the optical substrate (1), and its distance from an adjacent nanohole of the same antenna in the longitudinal direction of the optical substrate (1). The invention also relates to a spectrometer (S) that integrates an optical substrate (1) of this kind.

Description

[0001]Description Title of the invention: Optical substrate with integrated antennas and spectrometer comprising it The present invention relates to the field of integrated optics, and relates more particularly to an optical substrate with integrated antennas and to a spectrometer comprising it. In the field of integrated optics, when it is desired to send guided light in a planar guided structure, buried or on the surface of an optical component, towards an optical detector, in particular of the infrared (IR) or camera type, outside the optical component, in a direction close to the normal to the surface of the optical component, the light will naturally diverge from the emission point to the detection point. If several distinct sources are formed on the surface of the optical component, and it is desired to associate each source with a different pixel or group of pixels of the optical detector, the signal coming from these distinct sources will spread over several pixels.This induces a superposition on a pixel (or group of pixels) of the signals from the different sources at the optical detector, creating crosstalk and reducing the signal-to-noise ratio. This large angular divergence is due to the source points, considered as punctate and therefore very divergent, and to the active zone in optical detectors (particularly IR type), which can be several hundred micrometers below the physical surface of the optical detector. A first solution to overcome these drawbacks is to space the source points. However, the density of information that can be processed is thus reduced. Another solution is to act on the extraction of light from the waveguide to the optical detector. For example, a Bragg grating (physical alternation of high / low refractive index zones) placed on the surface in the waveguide can be used. The stronger the interaction between the guided mode and the Bragg grating isThe higher the intensity, the greater the extracted signal intensity. This principle is widely known in integrated optics. Most solutions for improving the directivity of the radiated flux are thus based on two-dimensional antennas of the surface grating type, by electron beam lithography, a focused ion beam, or polymerization. The following publications disclose such solutions: - 3D optical YagiUda nanoantenna array, Dregely D. et al., Nat. Communications 2, 267 (2011), - Hybrid nanoantennas for directional emission enhancement, Usak, E. et al., Appl. Phys. Lett., 105, 221109 (2014), - Dielectric antennas - a suitable platform for controlling magnetic dipolar emission, Schmidt MK et al., Opt. Express 20, 13636-13650(2012), - All-dielectric antenna wavelength router with bidirectional scattering of visible light, Li, J. et al., Nano Lett, 4396-4403 (2016), - All Integrated Lithium Niobate Standing Wave Fourier Transform Electro-Optic Spectrometer, Loridat & al., Journal of Lightwave Technology, Volume: 36, Issue: 20, Oct.15 (2018). There are three-dimensional solutions of the single-antenna type, similar to surface microlenses that are relatively complex to implement, as described in "Broadband highly directive 3D nanophotonic lenses", Johlin, E. et al., Nature Communications 9 (2018), - Improvement of the vertical radiation pattern emitted by broadcasting centers atMultiple nanogrooves acting as an antenna for future integrated optics Fourier transform spectrometers in the near IR (Improving the vertical radiation pattern emitted from multiple nano-groove scattering centers acting as an antenna for future integrated optics Fourier transform spectrometers in the near IR), Morand & al., Opt Lett. 2019, Feb 1;44(3):542-545. The Bragg grating according to the state of the art is however only made in a planar manner, on the surface. It is then only possible to control the period or the duty cycle of the periods to control the extraction power of the grating. Another possibility for manufacturing the Bragg grating is to make periodically spaced nano "air holes" (which are similar to air cylinders) in the material constituting the component. Such a technique for forming nano-holes is for example described in the following publications: - Machining of high aspect ratio nanochannels usingHigh aspect ratio nanochannel machining using single shot femtosecond Bessel beams, Bhuyan et al., Appl. Phys. Lett. 97, 081102 (2010), - Single shot high aspect ratio bulk nanostructuring of fused silica using chirp controlled ultrafast laser Bessel beams, Bhuyan et al., Appl. Phys. Lett. 104, 0201107 (2014), - Spatio-temporal dynamics in nondiffractive Bessel ultrafast laser nanoscale volume structuring, Velpula et al., Las. Photon Rev. 2, 230 (2016), - Near-infrared spectro-interferometer using integrated waveguides and nano-scatterers, fabricated by laser photo-inscription in the GLS, (Near-infrared spectro-interferometer usingfemtosecond laser written GLS embedded waveguides and nano- scatterers), Martin & al., Optics Express, Vol. 25, Issue 7, pp. 8386-8397 (2017). According to these techniques, a non-diffractive irradiation procedure is used to photo-write nanoholes in the optical substrate comprising a waveguide using focused Bessel beams that locally generate in the optical substrate a sufficient concentration of energy to create localized one-dimensional micro-explosions, the lateral pressure release creating axially uniform one-dimensional cavities, to create extended uniform nanoholes (sometimes called nano-Bessel holes). It is possible according to this technique to use two lasers facing each other with the optical substrate in the middle, or a single laser aimed at the substrate. The main advantage of laser writing for the fabrication of elongated nanoholes is that it is possible to cover a sampling length of 1 cm,without mask replacement, in a very short time (a few seconds). In addition, the position of the hole can be adjusted relative to the waveguide. The geometry and length of the nano-holes can be controlled "at will", but with a compromise between length and diameter. The fabrication of air nano-holes by laser photo-inscription techniques, for example, allows this type of planar network to be realized. Similarly to the two-dimensional antennas described above, only the period or the duty cycle of the periods can be modified to control the extraction power of the network. The publication Spectro-interféromètre 3D 3T inscrit par laser : étude et optimisation de la nano-antenne inscrite par laser (Laser written 3D 3T spectro-interferometer : Study and optimisation of the laser written nano-antenna), Bonduelle & al., SPIE Astronomical Telescopes + Instrumentation, Dec 2020, France. pp.82, <10.1117 / 12.<2562179>, describes the use of nano-holes forthe extraction of optical flow in a waveguide. The present invention aims to optimize the extraction of an optical flow confined in a waveguide integrated in an optical substrate in order to direct it towards a detector located on the surface of the optical substrate integrating the waveguide, by using three-dimensional nano-antennas of the nano-air hole type formed by laser photo-inscription. Unlike conventional lithographic technologies, which are surface techniques, it is in fact possible with the laser photo-inscription described above to produce a Bragg grating at any depth in an optical substrate integrating a waveguide, making it possible in particular to protect the diffracting structures as well as the waveguide from surface effects (scratches, dust, etc.). It is also envisaged according to the present invention to produce diffracting nano-structures by other techniques, for example in resins deposited above the waveguidewaveguide: a photosensitive resin is deposited on a surface waveguide, then exposed with a laser, for example a UV laser (simpler than the femtosecond lasers of the laser photo-inscription technique), then degraded in the exposed areas, which are then removed with a solvent to also form nano-air holes. The approach according to the present invention using laser photo-inscription or other equivalent techniques to produce nanoantennas (typically 100 nm in diameter) in three dimensions is more versatile than the state of the art. The result is similar to three-dimensional stacks that can be produced by the Microlight 3D ® or Nanoscribe ® tools in polymers, by two-photon absorption for example. The nanoantennas are thus formed directly in the material in which the waveguide is located, without requiring an additional resin deposition step as in the case of Microlight 3D®. The invention provides access to an additional degree of freedom. Indeed, the nanoholes can be made at different heights relative to each other. The extraction of the optical flux from the waveguide by these three-dimensional antennas made of nanoholes can therefore be controlled by several parameters: the period, the duty cycle with the diameter of the nanoholes, the offset, the spacing or the superposition of periodic nanoholes in height. This has the effect of reducing the angular cone of emission, making it possible to direct the flux extracted from the waveguide towards a very small number of pixels of an associated optical detector. The divergence is then almost zero, independently of the depth of the active zone in the optical detector, and the signal can be measured without crosstalk. The invention thus makes it possible to control the power extracted with a two-dimensional grating for a given number of nanoholes by controlling the vertical position of the grating byrelative to the waveguide. The angular divergence of the radiation decreases with the number of nanoholes or the length of the grating. The period of the nanoholes is in this case preferably λ / n, with λ the wavelength of the signal and n the refractive index of the substrate in which the waveguide and the nanoholes are formed. To obtain a more homogeneous shape of the vertical radiation, it may be possible to use an apodized grating. This apodization can be done in two ways: either by controlling the diameter of the nanoholes, or by vertically shifting the position of the nanoholes. Finally, when the period of the nanoholes is 2 to 3 times greater than λ / n, there are several radiated Bragg orders (i.e. several directions of light radiation in addition to the normal direction). It is also possible to distribute the nanoholes horizontally and vertically to reduce the influence of radiation in directions other than the vertical.The invention can thus make it possible to develop a compact optical spectrometer, without any moving parts, the detector being bonded to the photon-collecting waveguide to be characterized, with a Bragg grating as the only relay optic. The subject of the present invention is therefore an optical substrate with an integrated waveguide, the optical substrate having a longitudinal direction, a transverse direction and a height direction and being made of a material with a refractive index n, the waveguide being formed in the optical substrate along the longitudinal direction of the optical substrate, at least one antenna being formed in the optical substrate offset from the waveguide in the height direction, the at least one antenna being configured to diffract, in the height direction of the optical substrate, an evanescent wave produced on the surface of the waveguide by a standing wave generated by the injection of an optical signal of wavelength λ into the waveguide,characterized in that the at least one antenna is formed by several nano-holes formed along the transverse direction of the optical substrate, at least one of the nano-holes differing from the other nano-holes by at least one of its diameter, its spacing from the waveguide along the height direction of the optical substrate and its spacing from an adjacent nano-hole of the same antenna along the longitudinal direction of the optical substrate. The distribution of the nano-holes in the height direction and / or their apodization makes it possible to improve the extraction of the flux from the waveguide towards the outside of the substrate. According to one embodiment, the at least one antenna comprises an odd number of nano-holes, preferably between three and five nano-holes, more preferably comprises five nano-holes. The width (angular flare) and the intensity of the diffracted signal are related to the number of nano-holes: the more holes there are, the more coherent the signal, with a finer peak and lesscrosstalk. Thus, the signal intensity is proportional to the number of holes, while the diffraction width is inversely proportional to the number of holes. Increasing the number of holes introduces constraints on repeatability. A compromise between signal coherence and repeatability is achieved with around five nanoholes per antenna. The at least one antenna can be formed between the waveguide and the detector, in which case the at least one antenna diffracts the evanescent wave away from the waveguide, or the at least one antenna can be formed opposite the detector relative to the waveguide, in which case the at least one antenna diffracts the evanescent wave towards the waveguide and the detector. The standing wave formed in the waveguide by the injection of an optical signal of wavelength λ can be obtained either by reflection at the end of the waveguide using a mirror, or by injection of two sources on either side of the waveguide(therefore injection from the left and right of the waveguide simultaneously), which requires a prior division of the optical flow of the source to make a 50 / 50 distribution then a separation of the optical paths to inject through the two opposite inputs of the waveguide. According to one embodiment, the nano-holes have diameters decreasing symmetrically from a central nano-hole of the antenna towards the end nano-holes. A variable nano-hole diameter (apodization) within the same antenna makes it possible to adjust the envelope of the diffracted signal. For example, a larger hole in the center of the antenna makes it possible to reduce the secondary lobes of the signal diffracted by the antenna to improve the quality of extraction of the signal diffracted towards the outside of the optical substrate, making it possible for example to switch from a diffracted signal having the shape of a cardinal sine to a Gaussian shape. According to one embodiment, the nano-holes are in parallel planes according tothe height direction of the optical substrate. According to one embodiment, the nano-holes have a V-shaped arrangement, the central nano-hole constituting the tip of the V being opposite the waveguide and the other nano-holes being arranged symmetrically along each branch of the V in planes perpendicular to the height direction of the optical substrate moving away from the waveguide depending on whether the nano-holes they contain are approaching the ends of the branches of the V, the spacing separating two adjacent nano-holes in projection in a plane perpendicular to the height direction of the optical substrate being equal to λ / n or to an integer multiple of λ / n. Within the same antenna, the spacing separating each pair of adjacent nano-holes may be the same, but the invention is not limited in this respect, the spacings within the same antenna may differ provided that each spacing spacing two adjacent nano-holes in projection in a plane perpendicular to theheight direction of the optical substrate is equal to λ / n or to an integer multiple of λ / n. According to one embodiment, the at least one antenna comprises five nano-holes having a W-shaped arrangement and arranged in two planes parallel to each other and perpendicular to the height direction of the optical substrate, a first plane comprising the central nano-hole and the two end nano-holes, the distance between each end nano-hole and the central nano-hole in the longitudinal direction of the optical substrate in the first plane being equal to a characteristic distance equal to λ / n or to an integer multiple of λ / n, a second plane arranged between the waveguide and the first plane comprising the other two nano-holes spaced apart by a distance equal to the characteristic distance in the longitudinal direction of the optical substrate, the first plane and the second plane being separated by half the characteristic distance in the height direction of the optical substrate. The distancecharacteristic is preferably equal to λ / n, but can also take the value of an integer multiple of λ / n. According to one embodiment, the optical substrate comprises several antennas formed on the same side of the waveguide in the height direction and constituting an antenna array, the antenna array being configured to diffract one or more wavelengths. The different antennas formed in the optical substrate can thus either be formed, in the height direction of the optical substrate, between the waveguide and the detector, or opposite the detector relative to the waveguide, the waveguide then being between the antennas and the detector. The present invention also relates to a spectrometer comprising a light source, an optical substrate as defined above and a detector, the substrate having two parallel planar faces opposite in the height direction of the optical substrate, the light source being configured toinjecting light into the waveguide of the optical substrate, the detector being arranged opposite the flat face of the substrate towards which the light diffracted by the at least one antenna is directed. The injection of light can be done using an optical fiber glued to the substrate, opposite the waveguide, or using microlenses glued to the waveguide, or by focusing the beam coming from the light source with microscope objectives or any suitable optical lens assembly. According to one embodiment, fluid reservoirs are formed on the surface of the optical substrate, on the face of the optical substrate opposite the detector, in order to allow a spectrometric analysis of the light diffracted by the at least one antenna and passing through the reservoirs. According to one embodiment, a microfluidic circuit is formed between the face of the optical substrate opposite the detector and the detector, in order to allow aspectrometric analysis of the light diffracted by the at least one antenna and passing through the microfluidic circuit. To better illustrate the subject of the present invention, embodiments, given for illustrative and non-limiting purposes, will now be described with reference to the accompanying drawings. In these drawings: [Fig. 1] is a sectional view of an optical substrate integrating a waveguide according to the prior art; [Fig. 2] is a schematic view of an antenna according to the prior art; [Fig. 3] is a view similar to Figure 2 of an antenna according to a first embodiment of the present invention; [Fig. 4] is a curve illustrating the differences in performance between an antenna according to the prior art and an antenna according to the first embodiment; [Fig. 5] is a view similar to Figure 2 of an antenna according to a second embodiment of the present invention; [Fig. 6] is a view analogous to theFigure 2 of an antenna according to a third embodiment of the present invention; [Fig. 7] is a curve illustrating the differences in performance between an antenna according to the prior art and an antenna according to the third embodiment of the invention; and [Fig. 8] is a schematic representation of a spectrometer according to the invention integrating an antenna according to a fourth embodiment of the invention. Referring to Figure 1, it can be seen that an optical substrate 1 with an integrated waveguide according to the prior art has been shown. In Figure 1, the longitudinal direction of the optical substrate 1 is the direction from left to right of Figure 1, the height direction is the direction from top to bottom of Figure 1 and the transverse direction is the direction perpendicular to the plane of Figure 1. The optical substrate 1 is a material of refractive index n, and comprises an integrated waveguide 2 formed according to thelongitudinal direction of the optical substrate 1. The waves enter the integrated waveguide 2 from the left of Figure 1 and are reflected by a mirror 2a formed at the right end of the integrated waveguide 2, to form inside the integrated waveguide 2 a standing wave with the propagating and counter-propagating wave generated by the mirror 2a, the evanescent wave from this standing wave being diffracted in the direction of an antenna 3 formed of several nano-holes 4 (five nano-holes 4 in Figure 1 spaced by λ / n, λ being the wavelength of the optical signal injected into the waveguide 2) in the form of tubes which extend in the transverse direction of the optical substrate 1. As can be seen in Figure 1, a nano-hole designates a hole on the nanometric scale which is formed inside the substrate, i.e. in the thickness of the optical substrate 1. A nanohole is therefore completely enveloped by material at least in the height direction and inthe longitudinal direction. A nanohole is not a surface structuring or an indentation formed on the surface of the optical substrate 1. A nanohole may comprise a circular section in a plane perpendicular to the transverse direction. Each nanohole may be filled with empty space, air, or even any material having a refractive index different from the refractive index of the optical substrate 1. Each nanohole may be fabricated, for example, using a focused laser beam. The focused laser beam is configured to create micro-explosions that cause material compressions leading to the formation of nanoholes. By modifying the laser power, the refractive index can also be locally modified to obtain an index contrast large enough to generate diffraction (for example, by locally amorphizing the initial material). Alternatively, nanoholes could also be obtained by using a substrate in twoparts: the surface of a first part could be etched before being covered by the second part of the substrate. The antenna 3 samples a point of the propagating wave by converting the evanescent part of the propagating wave in interaction with the nano-holes 4 into a vertically radiated wave to vertically extract a part of the propagating wave, the same behavior being obtained for the counter-propagating wave. The waves thus diffracted by the antenna 3 are extracted towards a detector 5 on the upper part of which is formed a layer of optical sensors 6. The sum of the two waves radiated on the layer of optical sensors 6 makes it possible to generate an interference which will be contrasted in this case. As a non-limiting example, the detector can be made of InP, the layer of optical sensors 6 in the upper part being an array of IngaAs pixels. It should be noted that in Figure 1 there is an air gap between the optical substrate 1 and the detector 5, but that asuch air gap is not necessarily mandatory, the detector 5 being able to be bonded to the surface of the optical substrate 1. In addition, an anti-reflection layer can be provided on the face of the detector 5 facing the optical substrate 1. Figure 2 shows more schematically the antenna 3 of Figure 1, only shown in relation to the waveguide 2 with the optical substrate 1 and the detector 5 of Figure 1 omitted for greater readability of the drawing, composed of five nano-holes 4, arranged in the same plane in the height direction of the optical substrate, the nano-holes 4 of the antenna 3 having the same dimensions, and diffusing the evanescent wave coming from the incident optical wave E, in the left part of the integrated waveguide 2 and moving in it according to the arrow shown in the waveguide 2 from left to right, towards the detector (not shown in Figure 2). Figure 3 is a view similar to Figure 2 of an antenna 30 according to a first mode ofembodiment of the invention, in which the nano-holes 41, 42, 43 are arranged in a V, with the tip of the V constituted by the nano-hole 41 closest to the integrated waveguide 2 and the other nano-holes 42, 43 extending symmetrically in the height direction of the optical substrate 1 towards the detector (also not shown in Figure 3). As shown in Figure 3, the antenna 30 comprises five nano-holes 41, 42, 43, the first nano-hole 41 constituting as indicated the tip of the V at a first height relative to the optical waveguide 2, two nano-holes 42 in the same plane located at a second height relative to the optical waveguide 2 greater than the first height, and two nano-holes 43 in the same plane located at a third height relative to the optical waveguide 2 greater than the second height and constituting the ends of the branches of the V formed by the antenna 30. As a remark, the height of a nano-hole can be defined as the distance separatingthe center of a nano-hole of the optical waveguide 2. Whatever their height, all the nano-holes nevertheless remain distant from the surface of the optical substrate 1 opposite the detector 5. The spacing between two nano-holes can be defined as the distance separating the center of these two nano-holes. Two adjacent nano-holes 41, 42, 43 in Figure 3 are spaced 2λ / n in the longitudinal direction and 2λ / n in the height direction. The invention is however not limited in this respect. Thus, if one wishes to make it larger for size constraints, if the lateral separation between two holes in the same plane is K*λ / n, with K a natural integer, then the vertical separation must be K*2λ / n. Figure 4 shows the difference in performance of antenna 3 of Figure 2 and antenna 30 of Figure 3, by representing the shape of the radiation obtained above each antenna (wavelength on the abscissa and intensity on the ordinate), the curve in solid linerepresenting the performance of antenna 3 in Figure 2 and the broken line curve representing the performance of antenna 30 in Figure 3. Figure 4 thus shows an improvement in the extraction cone and a reduction in secondary peaks, therefore a better performance of antenna 30 in terms of reduction in crosstalk between neighboring pixels of a detector placed opposite the antenna. Figure 5 is a view similar to Figure 2 of an antenna 130 according to a second embodiment of the invention, in which the nano-holes 141, 142, 143 are configured in a W, with two nano-holes 142 in a first plane, and three nano-holes 141, 143 in a second plane parallel to the first plane and further from the waveguide 2 than the first plane, the nano-holes 141, 142, 143 in each plane being spaced apart by λ / n, the two planes being spaced apart by λ / (2n), each nano-hole 142 of the first plane being arranged at the center, in orthogonal projection on the waveguide 2, of twonano-holes 141, 143 of the second plane. As before, the invention is however not limited in this respect. Thus, if one wishes to make it larger for size constraints, if the lateral separation between two holes of the same plane is K*λ / n, with K a natural integer, then the vertical separation must be K*2λ / n. Figure 6 is a view similar to Figure 2 of an antenna 230 according to a third embodiment of the invention, in which the nano-holes 241, 242, 243 are arranged in the same plane at a certain distance from the waveguide 2 in the height direction of the substrate. The difference between the nano-holes 241, 242, 243 in the antenna 230 of this third embodiment comes from apodization: the nano-holes 241, 242, 243 have different diameters, the central nano-hole 241 having the largest diameter, the two adjacent nano-holes 242 have a diameter smaller than that of the central nano-hole 241 and the two end nano-holes 243 have a diameter evenlower than that of the nano-holes 242. The effect of apodization is shown in Figure 7, representing the shape of the radiation obtained above each antenna (wavelength on the abscissa and intensity on the ordinate). In particular, the dotted curve represents an antenna 3 according to Figure 2 and the light gray curve represents an antenna 230 according to the third embodiment of Figure 6. Apodization allows a significant reduction of the secondary peaks, once again reducing the crosstalk effect on the neighboring pixels of a detector placed opposite the antenna. Figure 7 also shows the effect of improving the extraction cone as a function of the increasing number of nano-holes in the antenna (1 nano-hole corresponds to the solid line curve with a very flattened extraction cone, 3 nano-holes corresponds to the broken line curve with a more pronounced extraction cone, the best extraction cone being obtained with five nano-holes (curve indotted lines), the five apodized holes having a less pronounced extraction cone but more attenuated secondary lobes than the antenna with 5 holes without apodization). Generally speaking, as the nano-holes are buried in the optical substrate, a symmetry of the optical medium is obtained around the nano-holes. The flux extracted from the waveguide thus has symmetry properties which make it possible to increase the optical flux diffracted towards the pixels, and therefore to improve the signal-to-noise ratio. The association of several nano-holes makes it possible to reduce the angular emission cone, making it possible to direct the flux extracted from the waveguide towards a very reduced number of pixels of an associated optical detector. Although the antenna 3 is shown in the Figures of the different embodiments between the waveguide 2 and the detector 5, the antenna 3 could also be formed in the optical substrate 1 under the waveguide 2, namely opposite the detector 5 with respect to thewaveguide 2, without departing from the scope of the present invention. It is also clearly understood that the invention is not limited, in its various embodiments, with regard to the generation of the standing wave and that the standing wave could be created in the waveguide 2 by any other means, in the absence of the mirror 2a at the end of the waveguide 2 opposite the injection end of the optical signal, for example by injection of two optical sources on either side of the waveguide 2 (therefore injection by the left and by the right of the waveguide 2 simultaneously), with a prior division of the optical flux of the source to obtain a 50 / 50 distribution on the two sources, then separation of the optical paths to inject the signals from the two optical sources created by the two opposite inputs of the waveguide 2. If we now refer to Figure 8, we can see that a spectrometer S according to the present invention has been shown there.As for Figure 1, the spectrometer S according to the present invention comprises an optical substrate 1 with an integrated waveguide 2, having a mirror 2a at its end opposite to the input end of the optical wave, an optical source 7 and a signal processing device 8. An antenna 330 according to a fourth embodiment is formed in the optical substrate 1, above the waveguide 2 in the height direction of the optical substrate 1, the antenna 330 being a combination of the first and third embodiments, namely consisting of five nano-holes 341, 342, 343, formed in a V as in the first embodiment and apodized as in the third embodiment, the central nano-hole 341 being the nano-hole which constitutes the base of the V and of larger diameter, the other nano-holes, respectively 342 and 343, being arranged above and having smaller diameters as one moves away from the waveguide 2. The optical signal emitted bythe optical source 7 in the waveguide 2 generates, by circulation in the waveguide 2, an evanescent wave directed by the antenna 330 towards the detector 5, and in particular towards the pixel network represented by the layer 6 in the upper part of the detector 5, the resulting signals being sent to the signal processing device 8. The signal processing device 8 may be a microprocessor, a microcontroller, a processor, a digital signal processor (DSP), a field programmable gate array (FPGA), an application-specific component (ASIC), or even a computer having software enabling the signals emitted by the pixels of the layer 6 to be processed and analyzed. Thus, an optical wave injected into the waveguide 2 by the optical source 7 forms an evanescent wave diffracted by the antenna 330 to be captured by the pixels 6 and then processed by the signal processing device 8 to form the optical spectrometer S. As a variant,fluid circulation channels 9 may be formed on the surface of the optical substrate 1 and connected to a fluid circulation device (not shown in Figure 7) to circulate in the channels 9 a fluid to be analyzed by the spectrometer S according to the invention, by analyzing the influence of the fluid on the optical wave captured by the pixels 6 of the detector 5. It is understood that the antenna according to the invention has been shown schematically in the Figures, but that its dimensions are not necessarily to scale, both in relation to the dimensions of the optical substrate 1 and of the waveguide 2. Also, it is envisaged according to the invention that there may be more or fewer nanoholes per antenna, several antennas per optical substrate / spectrometer to capture different wavelengths, and different antenna configurations, provided that at least one of the diameter, the spacing of the waveguide according to the height direction of the substrateoptical and the spacing between two adjacent nanoholes varies for the nanoholes of the same antenna.

Claims

Claims

1. – Optical substrate (1) with an integrated waveguide (2), the optical substrate (1) having a longitudinal direction, a transverse direction and a height direction and being made of a material with a refractive index n, the waveguide (2) being formed in the optical substrate (1) along the longitudinal direction of the optical substrate (1), at least one antenna (30; 130; 230; 330) being formed in the optical substrate (1) offset from the waveguide (2) in the height direction, the at least one antenna (30; 130; 230; 330) being configured to diffract, in the height direction of the optical substrate (1), an evanescent wave produced on the surface of the waveguide (2) by a standing wave generated by injecting an optical signal of wavelength λ into the waveguide (2), characterized in that that the at least one antenna (30; 130; 230; 330) is formed by several nano-holes (41, 42, 43; 141, 142, 143; 241, 242, 243;341, 342, 343) formed along the transverse direction of the optical substrate (1), at least one of the nano-holes (41, 42, 43; 141, 142, 143; 241, 242, 243; 341, 342, 343) differing from the other nano-holes (41, 42, 43; 141, 142, 143; 241, 242, 243; 341, 342, 343) by at least one of its diameter, its spacing from the waveguide (2) along the height direction of the optical substrate (1) and its spacing to an adjacent nano-hole of the same antenna along the longitudinal direction of the optical substrate (1).

2. – Optical substrate (1) according to claim 1, characterized in that the at least one antenna (30; 130; 230; 330) comprises an odd number of; nano-holes, preferably between three and five nano-holes, more preferably comprises five nano-holes.

3. – Optical substrate (1) according to claim 2, characterized in that the nano-holes (141, 142, 143; 341, 342, 343) have diameters decreasing symmetrically from a central nano-hole (141; 341) of the antenna (130; 330) towards the end nano-holes (142, 143; 342, 343).

4. – Optical substrate (1) according to one of claims 1 to 3, characterized in that the nano-holes (41, 42, 43; 141, 142, 143; 341, 342, 343) are in parallel planes along the height direction of the optical substrate (1).

5. – Optical substrate (1) according to claim 4 taken in dependence on claim 2 or claim 3, characterized in that the nano-holes (41, 42, 43; 341, 342, 343) have a V-shaped arrangement, the central nano-hole (41; 341) constituting the tip of the V being opposite the waveguide (2) and the other nano-holes (42, 43; 342, 343) being arranged symmetrically along each branch of the V in planes perpendicular to the height direction of the optical substrate (1) moving away from the waveguide (2) depending on whether the nano-holes (42, 43; 342, 343) which they contain approach the ends of the branches of the V, the spacing separating two adjacent nano-holes in projection in a plane perpendicular to the height direction of the optical substrate (2) being equal to λ / n or to an integer multiple of λ / n.

6. – Optical substrate (1) according to claim 4 taken in dependence on claim 2 or claim 3, characterized in that the at least one antenna (130) comprises five nano-holes (141, 142, 143) having a W-shaped arrangement and arranged in two planes parallel to each other and perpendicular to the height direction of the optical substrate (1), a first plane comprising the central nano-hole (141) and the two end nano-holes (143), the distance between each end nano-hole (143) and the central nano-hole (141) in the longitudinal direction of the optical substrate (1) in the first plane being equal to a characteristic distance equal to λ / n or to an integer multiple of λ / n, a second plane arranged between the waveguide (2) and the first plane comprising the other two nano-holes (142) spaced apart by a distance equal to the characteristic distance in the direction longitudinal of the optical substrate (1),the first plane and the second plane being separated by half the characteristic distance along the height direction of the optical substrate (1).

7. – Optical substrate (1) according to one of claims 1 to 6, characterized in that it comprises several antennas formed on the same side of the waveguide (2) in the height direction and constituting an antenna array, the antenna array being configured to diffract one or more wavelengths.

8. – Spectrometer (S) comprising a light source (7), an optical substrate (1) according to one of claims 1 to 7 and a detector (5), the optical substrate (1) having two parallel plane faces opposite each other along the height direction of the optical substrate (1), the, light source (7) being configured to inject light into the waveguide (2) of the optical substrate (1), the detector (5) being arranged opposite the flat face of the optical substrate (1) towards which the light diffracted by the at least one antenna (30; 130; 230; 330) is directed.

9. – Spectrometer (S) according to claim 8, characterized in that fluid reservoirs (9) are formed on the surface of the optical substrate (1), on the face of the optical substrate (1) opposite the detector (5), in order to allow a spectrometric analysis of the light diffracted by the at least one antenna (330) and passing through the reservoirs (9).

10. – Spectrometer (S) according to one of claims 8 or 9, characterized in that a microfluidic circuit is formed between the face of the optical substrate (1) opposite the detector (5) and the detector (5), in order to allow an analysis by spectrometry of the light diffracted by the at least one antenna (330) and passing through the microfluidic circuit.

Images