FR3140451A1 - Optical substrate with integrated antennas and spectrometer comprising it - Google Patents

Abstract

Optical substrate with integrated antennas and spectrometer comprising it The invention relates to an optical substrate (1) with an integrated waveguide (2), at least one antenna (330) being formed in the optical substrate (1), the at least one antenna being formed by several nano-holes (341, 342, 343), at least one of the nano-holes (341, 342, 343) differing from the other nano-holes (341, 342, 343) by at least one of its diameter, and its spacing of the waveguide (2) in the height direction of the optical substrate (1) and its spacing to an adjacent nano-hole of the same antenna in the longitudinal direction of the optical substrate (1). The invention also relates to a spectrometer (S) integrating such an optical substrate (1). Figure to be published with the abstract: Figure 8

Description

Optical substrate with integrated antennas and spectrometer comprising it

The present invention relates to the field of integrated optics, and more particularly to an optical substrate with integrated antennas and to a spectrometer comprising it.

In the field of integrated optics, when we want 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) type or camera, 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 we want 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 coming 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 (notably of the 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 of the waveguide can be used. The greater the interaction between the guided mode and the Bragg grating, the greater the intensity of the extracted signal. 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 M. K. 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 relatively complex surface microlenses to implement, as described in "Broadband highly directive 3D nanophotonic lenses", Johlin, E. et al., Nature Communications 9 (2018),

- 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, however, is only implemented in a planar manner, on the surface. It is then only possible to control the period or the duty cycle of the periods in order 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:

- High 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 & al., Las. Photon Rev. 2, 230 (2016),

- Near-infrared spectro-interferometer using femtosecond laser written GLS embedded waveguides and nano-scatterers, Martin et al., Optics Express, Vol. 25, Issue 7, pp. 8386-8397 (2017).

In 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 uniform extended nanoholes (sometimes called nano-Bessel holes). It is possible in 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 interest of laser inscription 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 nanoholes can be controlled “at will”, but with a trade-off between length and diameter.

The fabrication of nano-air holes by laser photo-inscription techniques, for example, makes it possible to produce this type of planar network. As with 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 Laser written 3D 3T spectro-interferometer: Study and optimization 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 nanoholes for optical flow extraction 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, 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 indeed 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 waveguide: 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 eliminated 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 Microlight 3D ® or Nanoscribe ® tools in polymers, for example by two-photon absorption.

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 flow 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, allowing the flux extracted from the waveguide to be directed 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 relative 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 vertical shifting of 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 glued to the photon collector waveguide to be characterized, with a Bragg grating as the only relay optics.

The present invention therefore relates to 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 in 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 in 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 in the height direction of the optical substrate and its spacing at an adjacent nanohole of the same antenna along the longitudinal direction of the optical substrate.

The distribution of nanoholes 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 nanoholes, preferably between three and five nanoholes, more preferably comprises five nanoholes.

The width (angular flare) and intensity of the diffracted signal are related to the number of nanoholes: the more holes there are, the more coherent the signal is, with a finer peak and less crosstalk. Thus, the signal intensity is proportional to the number of holes, the diffraction width being 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 may 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 may be formed opposite the detector relative to the waveguide, in which case the at least one antenna diffracts the evanescent wave toward 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 by the left and by the 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 by the two opposite inputs of the waveguide.

According to one embodiment, the nanoholes have diameters decreasing symmetrically from a central nanohole of the antenna towards the end nanoholes.

A variable nanohole diameter (apodization) within the same antenna allows to adjust the envelope of the diffracted signal. For example, a larger hole in the center of the antenna allows to reduce the side lobes of the signal diffracted by the antenna to improve the quality of extraction of the diffracted signal towards the outside of the optical substrate, allowing for example to pass from a diffracted signal having the shape of a cardinal sine to a Gaussian shape.

According to one embodiment, the nanoholes are in parallel planes along the height direction of the optical substrate.

According to one embodiment, the nanoholes have a V-shaped arrangement, the central nanohole constituting the tip of the V facing the waveguide and the other nanoholes 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 nanoholes they contain approach the ends of the branches of the V, the spacing separating two adjacent nanoholes 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 nanoholes may be the same, but the invention is not limited in this regard, the spacings within the same antenna being able to differ provided that each spacing separating two adjacent nanoholes in projection in a plane perpendicular to the height 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 two other 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 characteristic distance 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 various 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 flat faces opposite in the height direction of the optical substrate, the light source being configured to inject 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.

Light injection can be done using an optical fiber bonded to the substrate, in front of the waveguide, or using microlenses bonded 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 facing the detector, in order to allow 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 facing the detector and the detector, in order to allow spectrometric 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.

On these drawings:

is a sectional view of an optical substrate integrating a waveguide according to the prior art;

is a schematic view of an antenna according to the prior art;

is a view analogous to the of an antenna according to a first embodiment of the present invention;

is a curve illustrating the performance differences between an antenna according to the prior art and an antenna according to the first embodiment;

is a view analogous to the of an antenna according to a second embodiment of the present invention;

is a view analogous to the of an antenna according to a third embodiment of the present invention;

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

is a schematic representation of a spectrometer according to the invention integrating an antenna according to a fourth embodiment of the invention.

If we refer to the , it can be seen that an optical substrate 1 with integrated waveguide according to the prior art has been shown.

On the , the longitudinal direction of the optical substrate 1 is the direction from left to right of the , the height direction is the up and down direction of the and the transverse direction is the direction perpendicular to the plane of the .

The optical substrate 1 is a material of refractive index n, and comprises an integrated waveguide 2 formed along the longitudinal direction of the optical substrate 1. The waves enter the integrated waveguide 2 from the left of the 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 counterpropagating wave generated by the mirror 2a, the evanescent wave resulting from this standing wave being diffracted in the direction of an antenna 3 formed of several nano-holes 4 (five nano-holes 4 on the spaced λ/n apart, 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.

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 vertical 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 there is on the an air gap between the optical substrate 1 and the detector 5, but that such an air gap is not necessarily mandatory, the detector 5 being able to be bonded to the surface of the optical substrate 1. Furthermore, an anti-reflection layer can be provided on the face of the detector 5 facing the optical substrate 1.

There more schematically represents antenna 3 of the , only shown relative to the waveguide 2 with the optical substrate 1 and the detector 5 of the 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 resulting from the incident optical wave E, in the left part of the integrated waveguide 2 and moving in the latter according to the arrow shown in the waveguide 2 from left to right, towards the detector (not shown in the figure). ).

There is a view analogous to the of an antenna 30 according to a first embodiment of the invention, in which the nano-holes 41, 42, 43 are arranged in a V, with the tip of the V formed 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 the ). As shown in the , 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. Two adjacent nano-holes 41, 42, 43 on the 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 it is desired for size constraints to make it larger, 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.

There shows the difference in performance of antenna 3 from the and antenna 30 of the , representing the shape of the radiation obtained above each antenna (wavelength on the abscissa and intensity on the ordinate), the solid line curve representing the performance of antenna 3 of the and the dashed line curve representing the performance of antenna 30 of the . There thus shows an improvement in the extraction cone and a reduction in secondary peaks, therefore a better performance of the antenna 30 in terms of reduction in crosstalk between neighboring pixels of a detector placed opposite the antenna.

There is a view analogous to the 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 shape, 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 two nano-holes 141, 143 of the second plane. As previously, the invention is however not limited in this regard. So, if we want to make it bigger 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 will have to be K*2λ/n.

There is a view analogous to the 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 nanoholes 241, 242, 243 in the antenna 230 of this third embodiment comes from the apodization: the nanoholes 241, 242, 243 have different diameters, the central nanohole 241 having the largest diameter, the two adjacent nanoholes 242 have a diameter smaller than that of the central nanohole 241 and the two end nanoholes 243 have a diameter even smaller than that of the nanoholes 242.

The effect of apodization is shown in , 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 the and the light gray curve represents an antenna 230 according to the third embodiment of the . Apodization allows a significant reduction of secondary peaks, once again reducing the crosstalk effect on neighboring pixels of a detector placed opposite the antenna. also shows the effect of the extraction cone improvement as a function of the increasing number of nanoholes in the antenna (1 nanohole corresponds to the solid curve with a very flattened extraction cone, 3 nanoholes corresponds to the dashed curve with a more pronounced extraction cone, the best extraction cone being obtained with five nanoholes (dotted curve), the five apodized holes having a less pronounced extraction cone but more attenuated secondary lobes than the antenna with 5 holes without apodization).

Although the antenna 3 is shown in the Figures of the different embodiments between the waveguide 2 and the detector 3, the antenna 3 could also be formed in the optical substrate 1 under the waveguide 2, namely opposite the detector 5 with respect to the waveguide 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 end of injection 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 flow 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 the , it can be seen that a spectrometer S according to the present invention is shown there.

As for the , 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 nanoholes 341, 342, 343, formed in a V shape as in the first embodiment and apodized as in the third embodiment, the central nanohole 341 being the nanohole which constitutes the base of the V and of larger diameter, the other nanoholes, respectively 342 and 343, being arranged above and having smaller diameters as one moves away from the waveguide 2.

The optical signal emitted by the 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 schematized 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 for processing and analyzing the signals emitted by the pixels of the layer 6.

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 then processed by the signal processing device 8 to form the optical spectrometer S. As a variant, fluid circulation channels 9 can be formed on the surface of the optical substrate 1 and connected to a fluid circulation device (not shown in the figure). ) to circulate in the channels 9 a fluid to be analyzed by the spectrometer S according to the invention, by analysis of 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 optical substrate and the spacing between two adjacent nanoholes varies for the nanoholes of the same antenna.

Claims (10)

– 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) in 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 the injection of an optical signal of wavelength λ into the waveguide (2), characterized in that the at least one antenna (30; 130; 230; 330) is ... ; 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 nanoholes (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) in the height direction of the optical substrate (1) and its spacing from an adjacent nanohole of the same antenna in the longitudinal direction of the optical substrate (1). – 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. – 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). – 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 in the height direction of the optical substrate (1). – 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) that 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. – 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 two other nano-holes (142) spaced apart by a distance equal to the characteristic distance in the longitudinal direction of the optical substrate (1), the first plane and the second plane being separated by half the characteristic distance according to the height direction of the optical substrate (1). – 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. – 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 planar faces opposite in 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 planar face of the optical substrate (1) towards which the light diffracted by the at least one antenna (30; 130; 230; 330) is directed. – 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) facing the detector (5), in order to allow spectrometric analysis of the light diffracted by the at least one antenna (330) and passing through the reservoirs (9). – 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) facing the detector (5) and 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 microfluidic circuit.