Photoacoustic or photothermal detector with optical transducer

Abstract

Name: Photoacoustic or photothermal detector with optical transducer. The present invention is an apparatus and method for detecting an analyte in a medium. An excitation light source generates an excitation light wave, which propagates through the medium and heats the medium. The apparatus includes a transducer for detecting the heating of the medium. According to one embodiment, the transducer is a thermal transducer configured to detect changes in the temperature of the medium. According to another embodiment, the transducer is an acoustic transducer configured to detect photoacoustic waves propagating from the medium. Regardless of the embodiment, the transducer uses a membrane in which a waveguide is placed. The waveguide includes a resonant optical cavity. Transduction is achieved by analyzing changes in the resonant wavelength of the optical cavity.

Description

[Technical field]

[0001] The technical field of the invention is the detection of analytes in a medium by the principle of photoacoustic or photothermal detection. [Background technology]

[0002] Photoacoustic detection is based on the detection of sound waves generated under the influence of absorption by the analysis medium of a pulsed or amplitude-modulated excitation electromagnetic wave, called the excitation wave. The sound waves are formed after heating under the influence of absorption of the excitation wave by absorbing molecules present in the analysis medium. This heating leads to a modulated thermal expansion of the medium, which expansion is the origin of the sound waves.

[0003] Photoacoustic detection can be made specific to one particular analyte by setting the wavelength of the excitation wave to the absorption wavelength of the analyte. Photoacoustic detection has applications in the detection of gas species in gases or the presence of specific molecules in biological tissues. The wavelength of the incident wave is often located in the infrared.

[0004] Photoacoustic detection is then a non-invasive analytical technique that can be applied to scattering or opaque media.

[0005] The application of photoacoustic detection to biological tissue is described, for example, in the following publications: -Bauer AJ. “IR-spectroscopy for skin in vivo: Optimal skin sites and properties for non-invasive glucose measurement by photoacoustic and photothermal spectroscopy”;Journal of Biopohtonics 11 (2018) -“Windowless ultrasound photoacoustic cell for in-vivo mid-IR spectroscopy of human epidermis: Low interference by changes of air pressure, temperature, and humidity caused by skin contact opens the possibility for a non-invasive monitoring glucose in the interstitial fluid”; Rev.Sci.Instrum.84, 084901 (2013)

[0006] In these documents, a pulsed laser source is used that is activated at a frequency of several tens of kilohertz. The object of the present invention is to estimate the glucose concentration in the interstitial fluid at a depth between 10 μm and 50 μm below the user's skin. For this purpose, a photoacoustic detection device is used that is placed against the user's skin.

[0007] The technique of photothermal detection is also known, which is based on the detection of the temperature change of the analyzed medium under the effect of absorption by the medium of a pulsed or amplitude-modulated excitation electromagnetic wave, which results from the heating of absorbing molecules present in the analyzed medium under the effect of absorption of the excitation wave.

[0008] The periodic temperature modulation can be detected, for example, by estimating the change in the refractive index of the medium under the effect of a temperature change, as described, for example, in EP 3359949 B1.

[0009] Whether photothermal or photoacoustic detection is used, the sample may be a gas sample and the target objective is the detection of a particular gas species or a particular particle, for example considered as a pollutant. It may also be a matter of liquid or solid samples, with possible applications in the industrial field (for example in the food industry) or in the health field as mentioned above. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] European Patent No. 3359949B1 [Non-patent literature]

[0011] [Non-Patent Document 1] Bauer AJ. “IR-spectroscopy for skin in vivo: Optimal skin sites and properties for non-invasive glucose measurement by photoacoustic and photothermal spectroscopy”;Journal of Biopohtonics 11 (2018) [Non-Patent Document 2] “Windowless ultrasound photoacoustic cell for in-vivo mid-IR spectroscopy of human epidermis: Low interference by changes of air pressure, temperature, and humidity caused by skin contact opens the possibility for a non-invasive monitoring glucose in the interstitial fluid”; Rev.Sci.Instrum.84, 084901 (2013) Summary of the Invention [Problem to be solved by the invention]

[0012] We have designed a transducer that can be used in either applications using photoacoustic or photothermal detection, resulting in a specialized device with high detection sensitivity and simple design. [Means for solving the problem]

[0013] A first subject of the invention is a detection device intended to be applied, via a contact surface, to an analytical medium prone to contain an analyte absorbing light of at least one absorption wavelength, an opening formed in the contact surface; an excitation light source configured to emit an excitation light wave that is pulsed or amplitude modulated at an excitation frequency in an excitation spectral band that includes the absorption wavelength, the device being positioned such that the excitation light wave propagates through the aperture towards the analysis medium; a transducer intended to measure the response of the medium after a portion of the excitation light wave has been absorbed by the analyte, The transducer is a membrane carrying a waveguide; a waveguide including a first reflector and a second reflector, each reflector reflecting light in a reflection spectral band; a first reflector and a second reflector spaced apart from one another to form a resonant optical cavity, the first reflector and the second reflector defining a resonant wavelength in a reflection spectral band; The waveguide is It transmits light at the resonant wavelength, Reflects light in the reflection spectrum band, not at the resonant wavelength, The transducer is an auxiliary laser light source configured to emit an auxiliary light wave in the reflection spectral band into the waveguide; a photodetector positioned to detect light waves transmitted by the waveguide at the resonant wavelength; a servo circuit coupled to the photodetector and configured to determine a periodic time-dependent modulation of a resonant wavelength of the resonant optical cavity.

[0014] The device is connected to a servo circuit, Estimate the amplitude of the time-dependent modulation of the resonance wavelength, A processing unit may be provided that is configured to detect the presence of an analyte in the medium depending on the estimated amplitude.

[0015] The processing unit may be configured to estimate a concentration of the analyte in the medium depending on the estimated amplitude.

[0016] According to one embodiment, referred to as the photoacoustic embodiment, the device comprises a hollow cavity opening at an aperture, and a transducer is connected to the hollow cavity, the transducer being an acoustic transducer configured to detect the amplitude of a photoacoustic wave propagating through the hollow cavity from the aperture, such that under the effect of illumination of the medium by an excitation light wave, the membrane vibrates at an excitation frequency, resulting in a time-dependent modulation of the resonant wavelength at a modulation frequency equal to the excitation frequency.

[0017] The membrane may be parallel to the contact surface. The membrane may bound a portion of the hollow cavity.

[0018] According to one embodiment, referred to as the photothermal embodiment, the device is as follows. The membrane of the transducer forms the contact surface of the device, which is intended to be applied in contact with the medium. An opening extends through the membrane. The transducer is a thermal transducer, and under the effect of irradiation of the medium by an excitation light wave, the temperature of the membrane exhibits periodic time-dependent variations, resulting in a periodic time-dependent modulation of the resonant wavelength.

[0019] Regardless of the embodiment, at least one or each reflector is a Bragg mirror formed by a periodic modulation of the refractive index along the waveguide.

[0020] Regardless of the embodiment, the servo circuit includes a servo loop coupled to the auxiliary light source and configured to servo control a wavelength of the light wave emitted by the auxiliary light source at a resonant wavelength of the resonant optical cavity. The servo circuit may, among other things, implement a Pond-Drever-Hall servo technique.

[0021] Regardless of the embodiment, the apparatus may be as follows. The first reflector is a first Bragg mirror. The second reflector is a second Bragg mirror. The first Bragg mirror and the second Bragg mirror form an identical Bragg mirror having a defect, the first Bragg mirror and the second Bragg mirror corresponding to portions of the Bragg mirror located on either side of the defect, respectively.

[0022] In a photoacoustic embodiment, the device may be as follows. Under the effect of vibration, the membrane exhibits at least one vibration antinode, the amplitude of the vibration being maximum at each antinode. The waveguide is flush with at least one antinode.

[0023] Regardless of the embodiment, the waveguide may be formed directly on the film. The first and second reflectors may be obtained by inscribing the waveguide with laser light to obtain a periodic modulation of the refractive index in the waveguide.

[0024] Regardless of the embodiment, the waveguide may be a microstructured optical fiber deposited on the film.

[0025] A second object of the invention is a method for detecting an analyte in a medium, the analyte absorbing at least one absorption wavelength, comprising the steps of: a) applying a device according to the first subject of the invention to a medium such that a contact surface of the device is held against the medium; b) activating an excitation light source, the excitation light source emitting pulsed or amplitude modulated excitation light waves at an excitation frequency having a wavelength corresponding to an absorption wavelength of the analyte; c) determining, using a servo circuit, a periodic modulation of a resonant wavelength of the transducer waveguide at a modulation frequency corresponding to the excitation frequency, the resonant wavelength corresponding to a transmission peak of the waveguide; and d) detecting the presence of an analyte in the medium in response to the periodic modulation determined by the servo circuit.

[0026] The apparatus may be as described with respect to the photoacoustic embodiment. The method of the present invention thus comprises: After step b), periodically heating the medium with an excitation frequency to cause the emission of a photoacoustic wave, which propagates through the hollow cavity and, under the effect of the transducer membrane vibrating with the excitation frequency, causes the resonant frequency of the transducer's waveguide to be modulated with a modulation frequency equal to the excitation frequency; In step d), estimating an amplitude of a periodic modulation of the resonant wavelength at a modulation frequency; and detecting the presence of the analyte as a function of the estimated amplitude.

[0027] The apparatus may be as described with respect to the photothermal embodiment. Thus, the method of the present invention comprises: After step b), periodically heating the medium with an excitation frequency to periodically heat the membrane with the excitation frequency such that the resonant frequency of the transducer waveguide is modulated with a modulation frequency corresponding to the excitation frequency; In step d), estimating the amplitude of the periodic modulation of the resonant wavelength at the modulation frequency; and detecting the presence of the analyte as a function of the estimated amplitude.

[0028] Regardless of the embodiment, step d) may also comprise estimating the concentration of the analyte in the analysis medium.

[0029] A third subject of the invention is a manufacturing process for producing a device according to the first subject of the invention, in which the waveguide is formed directly on the membrane, the manufacturing process comprising the steps of: depositing a thin layer of a first material onto the membrane so as to form a waveguide; inscribing the waveguide with femtosecond laser light to obtain a periodic modulation of the refractive index of the waveguide.

[0030] The invention will be better understood upon reading the description of examples of embodiments described in the remainder of the description with reference to the following figures, in which: [Brief description of the drawings]

[0031] [Figure 1A] 1 shows a schematic of the main components of the device according to one embodiment, referred to as the optoacoustic embodiment. [Figure 1B] 1 shows a schematic of the main components of the device according to one embodiment, referred to as the optoacoustic embodiment. [Figure 1C] 1 shows a schematic of the main components of the device according to one embodiment, referred to as the optoacoustic embodiment. [Figure 1D] 1 shows a schematic of the main components of the device according to one embodiment, referred to as the optoacoustic embodiment. [Figure 1E] 1 shows a schematic of the main components of the device according to one embodiment, referred to as the optoacoustic embodiment. [Figure 2A] 1 shows a microstructured optical fiber forming a Bragg mirror. [Figure 2B] 2B shows the reflectance spectral band of the optical fiber shown diagrammatically in FIG. 2A. [Figure 2C] A microstructured optical fiber is shown forming a resonant optical cavity based on two spaced apart Bragg mirrors. [Figure 2D] 2D shows the reflectance spectral band of the optical fiber shown diagrammatically in FIG. 2C. [Figure 3A] 1 illustrates a waveguide that includes a resonant optical cavity, where the waveguide is undeformed. [Figure 3B] 1 shows a waveguide that includes a resonant optical cavity, where the waveguide has been deformed. [Figure 3C] 1 shows a waveguide with non-uniform deformation. [Figure 3D] 3D shows the change in the reflection spectral band of a waveguide as shown in FIG. 3C under the effect of deformation. [Figure 3E] 4 shows the deformation amplitude of the membrane along the diameter of the membrane. [Figure 3F] Optimally positioned waveguides are shown for the deformation shown in FIG. 3D. [Figure 4A] 1 shows a schematic diagram of a circuit for servo-controlling the wavelength of an assist light source using a wavelength locking method. [Figure 4B] The change in the error function obtained using the wavelength locking method is shown. [Figure 5A] 1 shows the shift of the resonant wavelength of a resonant optical cavity under the effect of a membrane vibration. [Figure 5B] 1 shows the time-dependent modulation of the optical resonance wavelength. [Figure 5C] 13A-B show schematic diagrams illustrating the estimation of the vibration amplitude of the membrane based on the time-dependent modulation of the resonant wavelength. [Figure 6A] 1 illustrates the main steps of the manufacturing process that allows contacting the membrane to form a microstructured waveguide. [Figure 6B] 1 illustrates the main steps of the manufacturing process that allows contacting the membrane to form a microstructured waveguide. [Figure 6C] 1 illustrates the main steps of the manufacturing process that allows contacting the membrane to form a microstructured waveguide. [Figure 6D] 1 illustrates the main steps of the manufacturing process that allows contacting the membrane to form a microstructured waveguide. [Figure 7A] 4 illustrates the main steps of a detection method using a device according to an optoacoustic embodiment. [Figure 7B] 4 illustrates the main steps of a detection method using a device according to a photothermal embodiment. [Figure 8A] 1 shows a schematic of the main components of a device according to one embodiment, referred to as the photothermal embodiment. [Figure 8B] 1 shows a schematic of the main components of a device according to one embodiment, referred to as the photothermal embodiment. [Figure 8C] 1 shows a schematic of the main components of a device according to one embodiment, referred to as the photothermal embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] 1A to 1E show a first embodiment, called the optoacoustic embodiment, of a device 1 according to the invention. The device 1 is adapted to be applied to an analysis medium 2.

[0033] The device comprises an excitation light source 10 configured to emit excitation light 11 which propagates through the analysis medium 2. The light source 10 has an excitation frequency f 11 The light wave 11 is pulsed or amplitude modulated at Δλ 2 . The light wave 11 is focused in an excitation spectral band Δλ 2 , which includes the absorption wavelength λ 4 of the analyte 4 present in the medium. 11 One purpose of the device 1 is to detect the presence of an analyte 4 and potentially estimate its concentration.

[0034] The excitation spectral band is preferably in the visible or infrared and extends, for example, between wavelengths of 3 μm and 15 μm. Preferably, the excitation spectral band Δλ 11 is narrow enough for the device 1 to be specific to a single analyte. For example, the width of the emission spectrum band is 1 cm -1 When the analyte is glucose, the emission spectrum band is the absorption wavelength of glucose, e.g., 1034 cm -1 The excitation light source 10 may in particular be a pulsed laser light source, for example a tunable quantum cascade laser (QCL). The emission spectral band Δλ is located in the infrared.

[0035] The analyte 4 may be a molecule present in the analysis medium. If the medium is a biological tissue, it may be a glucose problem present in the biological tissue's body fluids. As mentioned in the prior art, the analyte may be a gas molecule and the medium is a gas. It may be, for example, a gas molecule that is considered a pollutant. The medium may be a liquid and the analyte is a molecule potentially present in the liquid.

[0036] The device 1 comprises a contact surface 3 which is intended to be applied to an analysis medium 2 so as to come into contact with the analysis medium 2. The contact surface 3 is designed to match the medium 2 to which it is intended to be applied, for example being flat.

[0037] The apparatus 1 comprises an enclosure 17 extending from the contact surface 3 and defining a hollow cavity 16. The hollow cavity 16 comprises an opening 13 formed in the contact surface 3 to open into the medium 2. The excitation light source 10 is configured such that an excitation light wave 11 propagates through the hollow cavity 16 and through the opening 13 into the medium 2.

[0038] Under the influence of the presence of an analyte 4 in the medium 2, a photoacoustic wave 6 is formed. The photoacoustic wave 6 is an acoustic wave formed as a result of the cyclic heating of the medium by an incident light wave 11, which has an excitation frequency f 11 A portion of the photoacoustic wave 6 propagates through the hollow cavity 16 to be detected by the transducer 15.

[0039] In the photoacoustic embodiment, the transducer 15 is an acoustic transducer. Its function is to measure the amplitude and / or frequency of the photoacoustic wave 6. More precisely, in the targeted application, the transducer 15 is arranged to measure the amplitude and / or frequency of the excitation light wave 6 at the excitation frequency f 11 This makes it possible to estimate the amplitude of the photoacoustic wave 6 at

[0040] The transducer 15 comprises a flexible membrane 18 configured to vibrate when exposed to photoacoustic waves 6. The membrane 18 is oriented in a radial plane P XY The diameter of the membrane or its largest diagonal is preferably between 1 mm and 10 mm. The thickness of the membrane, parallel to the transverse axis Z and perpendicular to the radial plane, is preferably between 10 μm and 500 μm, preferably between 10 μm and 100 μm. The thickness of the membrane is preferably between 1 / 10 and 1 / 200 of the radius of the membrane (or its largest semi-diagonal).

[0041] The excitation light source 10 is configured such that excitation light 11 propagates through the hollow cavity 16 into the medium 2. In the example shown in Figure 1A, the excitation light wave 11 propagates through a secondary aperture 19 formed through the membrane 18.

[0042] The secondary openings 19 formed in the membrane also allow the pressures on both sides of the membrane 18 to be in equilibrium at low frequencies. This makes it possible to avoid potential deformations of the membrane 18 under the effect of low-frequency fluctuations of pressure on both sides of the membrane 18. Low-frequency fluctuations of pressure mean pressure differences occurring at frequencies below the operating frequency range of the membrane. The diameter of the secondary openings 19 is, for example, less than 1 / 10 of the membrane diameter. For example, it is of the order of 10 μm or 20 μm.

[0043] The transducer 15 includes a waveguide 20 extending over, in contact with and parallel to the membrane 18. The waveguide has an inlet 20 i and Exit 20 o The waveguide is made from a first material 21 having a first refractive index n1.

[0044] The waveguide 20 may be an optical fiber, in which case the first material is the material of the core of the optical fiber. It may also be a matter of a waveguide formed from a deposit of a thin layer of a first material 21, for example SiON (silicon oxynitride), which corresponds to the example shown in Figures 1A to 1E. The waveguide is surrounded by a confining material 23 whose refractive index is lower than the refractive index n3 of the first material n1. If the waveguide 20 is an optical fiber, the confining material 23 is the cladding of the optical fiber.

[0045] The waveguide 20 is advantageously formed from a thin layer of a first material 21, and the confining material 23 may simply be air surrounding the first material. The thickness along the transverse axis Z of the waveguide is preferably less than 10 μm or 5 μm. The manufacturing steps used to form such a waveguide are described with reference to Figures 6A to 6D. By forming the waveguide directly on the membrane, it is possible to avoid the step of bonding an optical fiber to the membrane. Another advantage of the use of optical fibers is that a less rigid waveguide is obtained.

[0046] Regardless of the configuration selected, the refractive index n3 of the confinement material 23 is lower than the refractive index n1 of the first material 21. If the first material 21 is deposited directly on the film 18, then the refractive index n1 of the first material 21 is preferably higher than the refractive index of the material from which the film 18 is formed.

[0047] An example of a waveguide 20 is shown in FIG. 1B. In this example, a first material 21 is deposited on the film 18. The waveguide comprises segments of a second material 22 of a second refractive index n2, which are periodically distributed along the waveguide 20. The second refractive index n2 is different from the first refractive index n1. It may be higher than the first refractive index n1. The relative change between the first and second refractive indices is less than 0.01% (10 -4 ) to 0.1% (10 -3 )

[0048] Along the axis defined by the waveguide, the refractive index is periodically modulated between n1 and n2, resulting in a reflection spectral band Δλ 20 The structure of the Bragg mirror is known to those skilled in the art. The structure has a periodic change in refractive index, with two segments of different refractive indexes alternating along the axis along which light propagates, and the optical thickness of each segment is λ B / 4n i where λ B is the reflection spectrum band Δλ 20 is the central wavelength of n i is the refractive index of the material in question (n i =n1 or n i = n2). The lower the refractive index contrast, the higher the number of periods.

[0049] Reflectance spectrum band Δλ 20 is the resonant wavelength λ r The latter is as follows:

number

number

[0050] The waveguide 20 is such that the Bragg mirror formed by alternating segments 21 and 22 contains a defect. By defect is meant a local break in the periodicity of the refractive index modulation. This defect corresponds for example to a continuous space 25 made of a given material, for example a first material 21, and extending the length of one period Λ or the length of several consecutive periods. At the same level as the defect, the waveguide contains a single material and extends a distance d along the axis of the waveguide 20. The distance d is defined as:

number

[0051] d>kλ B / n eff If, the reflectance spectrum band Δλ 20 is the Bragg wavelength λ B Other resonant wavelengths λ r In this case, it is preferable to keep the resonance wavelength at which the resonance peak is narrowest.

[0052] This allows the defect to separate the first Bragg mirror 241 and the second Bragg mirror 242 in the waveguide 20. The assembly formed by the first Bragg mirror 241, the second Bragg mirror 242 and the space 25 between the Bragg mirrors forms a resonant cavity 26.

[0053] Next, the waveguide 20 is Resonance wavelength λ r Instead, the reflection spectrum band Δλ of the Bragg mirrors 241 and 24220 Reflects the light of The resonant wavelength λ of the resonant cavity 26 r The optical fiber is configured to transmit light through the optical fiber.

[0054] The transducer 15 is disposed at the entrance 20 of the waveguide 20. i The auxiliary light source 30, in particular a laser diode, is arranged to emit an auxiliary light wave 32 towards the 32 Emission spectrum band Δλ centered at 32 The emission spectrum band Δλ 32 is the reflection spectrum band Δλ 20 It is preferred that the fluorine-containing compound is included in the formula (I).

[0055] Preferably, the emission spectral band Δλ 32 The width of the reflection spectrum band Δλ 20 For example, the emission spectrum band Δλ 32 The width of the emission spectrum band Δλ may be 1 nm, or may be smaller than 500 PM or 100 PM. 32 The width of the emission spectrum band refers to the full width at half maximum of the emission spectrum band.

[0056] The auxiliary light source 30 is preferably a continuous wave laser. It may be, for example, a DFB laser diode (DFB is the acronym for distributed feedback) with a power of 1 mW, emitting at a wavelength of 1.55 μm and having a spectral width of the order of 1 pm. This type of laser diode is commonly used in the field of telecommunications.

[0057] The transducer 15 comprises a photodetector 36, preferably a high-speed photodetector, and here a photodiode. The photodetector detects a reflection spectral band Δλ 20 A detection spectral band Δλ including 36 has.

[0058] The transducer 15 is coupled to a resonant cavity 26 at a resonant wavelength λ r Time-dependent modulation of λ rThe servo circuit 41 is configured to control the emission wavelength λ of the auxiliary light wave 32 emitted by the auxiliary light source 30. 32 The resonant wavelength λ of the resonant cavity 26 r The auxiliary light source can be servo-controlled, for example to correspond to the

[0059] The device is driven by a time-dependent modulation λ determined by a servo circuit 41. r Frequency of (t) TIFF0007607661000004.tif7150 or Amplitude The processing unit 42 comprises or is connected to a processing unit 42 configured to calculate the excitation frequency f of the excitation light wave 11. 11 The corresponding frequency The processing unit 42 is designed or programmed to estimate the amplitude of the modulation of the resonant wavelength at TIFF0007607661000006.tif7150. The operation of the processing unit 42 is described in further detail with reference to Figures 5A to 5C.

[0060] The device comprises a cover 48 defining a rear volume, which corresponds to the volume extending between the membrane 18 and the cover 48. In general, the waveguide 20 comprises a resonant cavity 26 formed from a first reflector 241 and a second reflector 242, said reflectors being obtained by microstructuring the waveguide 20. In the example given in this description, the first reflector 241 and the second reflector 242 are Bragg mirrors, although other types of microstructuring are also conceivable.

[0061] One important aspect of the present invention, as explained below, relates to the following fact. The auxiliary light source 30 is activated and emits light at wavelength λ 32 is the resonant wavelength λ of the waveguide 20 r (or more precisely, the resonant wavelength of the resonant cavity 26), the waveguide 20 will reflect a reflected wave 32'. The auxiliary light source 30 is activated and emits light at wavelength λ 32 is the resonant wavelength λ of the resonant cavity 26 r , the waveguide 20 transmits a transmitted wave 34 to a photodetector 36. 32 is the resonant wavelength λ r The closer it is to , the higher the intensity of the transmitted wave 34 becomes.

[0062] The present invention relates to an acoustic frequency f a When exposed to a photoacoustic wave 6 of frequency f a The amplitude of vibration is A a As a result, the waveguide 20 undergoes periodic deformation, and under the influence of this deformation, the resonant wavelength λ r is a periodic time-dependent modulation λ r (t) shows the amplitude of the time-dependent modulation of the resonance wavelength. TIFF0007607661000007.tif7150 depends on the amplitude of the membrane vibration, which is the acoustic amplitude A a The frequency of the time-dependent modulation is proportional to TIFF0007607661000008.tif7150 is the acoustic frequency f a which corresponds to the excitation frequency f 11 Also supports frequency Amplitude of modulation in TIFF0007607661000009.tif7150 By calculating TIFF0007607661000010.tif7150, the device makes it possible to detect the presence of an analyte in a medium and, optionally, to estimate its concentration, as described with reference to Figures 5A to 5C.

[0063] FIG. 1C illustrates the radial plane P XY 1 shows a diagram of certain elements in. In this example, membrane 18 takes the form of a thin disk whose thickness is 1 / 100th of its radius.

[0064] FIG. 1D is a three-dimensional view showing the position of the membrane 18 and the waveguide 20 relative to the analysis medium 2.

[0065] FIG. 1E shows an example of an apparatus in which an excitation light source 10 is associated with a reflector 14. The excitation light 11 is directed toward an emission surface P XY , and is reflected by reflector 14 towards aperture 13 where it propagates towards medium 2. An auxiliary light source 30 and a photodetector 36 are aligned with respect to waveguide 20. Alternatively, the auxiliary light source 30 and / or the photodetector 36 may be coupled to waveguide 20 by a photonic crystal.

[0066] According to one variant, the membrane 18 of the transducer 15 is connected to the cavity by an acoustic channel, the cavity 16 transmitting a portion of the photoacoustic waves 6 to the membrane 18 .

[0067] FIG. 2A shows an embodiment in which the waveguide 20 is a microstructured optical fiber in which a Bragg grating is formed. This type of microstructure in an optical fiber is usually called a fiber Bragg grating (FBG). The optical fiber comprises a first material 21 forming the core and a confinement material 23 forming the cladding. In the core of the optical fiber, inclusions or cavities of a second material 22, whose refractive index differs from that of the first material, are formed. FIG. 2B shows the reflection spectrum of such a microstructured optical fiber. The reflection spectrum corresponds to the reflection intensity normalized by the illumination intensity (y-axis) as a function of wavelength (x-axis - in nm). Reflection spectrum band Δλ 20 Such a waveguide, when illuminated with a light wave 32, has a reflection spectral band Δλ 20 So, the total reflection spectral band Δλ 20 32' reflects the light wave 32'.

[0068] FIG. 2C shows a similar optical fiber, in which two Bragg mirrors 241 and 242 are separated by a space 25 filled with a first material 21, as described with reference to FIG. 1B. The length of the space 25 is determined by the number of resonant wavelengths included in the reflection spectral band.

number

[0069] Figure 2D shows the reflection spectrum of the optical fiber thus miniaturized. r Except for the reflectance spectrum band Δλ 20 Such a waveguide has a reflection spectrum band Δλ 2 where the light wave 32 emitted from the auxiliary light source 30 is reflected. 20 When illuminated with a wavelength λ 32 is different from the resonant wavelength, the light wave 32' is reflected, and the wavelength λ 32 is located at a resonance peak, a light wave 34 called a transmitted light wave is transmitted.

[0070] Figure 2 B and 2D were obtained using a model written in Matlab (registered trademark, Mathworks), in which the structure is considered to extend along a length L of 3 mm and the refractive index contrast between the first and second materials is 10 -3 and the period of each Bragg mirror was taken to be about 0.5 μm. Each Bragg mirror therefore has a number of periods equal to 3000.

[0071] Figure 3 D is the resonant wavelength λ resulting from the deformation of the waveguide 20 as shown in FIG. 1B or FIG. 2C. r 3A and 3B show the undeformed and deformed waveguides 20, respectively. Under the effect of the deformation, the spatial period of the refractive index modulation changes from Λ to Λ'=Λ+dΛ. Applying equation (1), the Bragg wavelength λ B Shift dλ in B This wavelength broadens the reflection spectral band Δλ. B The shift is as follows:

number

number

[0072] Equation (3) assumes that film 18 is made of SiO2 and the exponential jump between the first and second materials is 10 -3 This is based on the uniform deformation of each Bragg mirror, as shown in Figure 3B. According to equation (3), for a deformation of 1 microstrain, the Bragg wavelength λ B Shift dλ in B is 1.2 pm.

[0073] In FIG. 3C, non-uniform deformation of the waveguide 20 is shown, with some segments of the Bragg mirror being less deformed than other segments.

[0074] Figure 3D is a model showing the change in the reflection spectrum of the Bragg mirror in a configuration such as that described with reference to Figure 3C. Curves a, b and c correspond, respectively, to no deformation, a deformation between 0 and 10 microstrains, and a deformation between 4 and 6 microstrains. The spectral shift is small, less than 10 pm. Curves b and c correspond to the same average deformation of the waveguide, equal to 5 microstrains. The shift in the resonant wavelength between these two configurations is due to the variation of the strain along the axis of the waveguide, which ranges from 0 to 10 microstrains and from 4 to 6 microstrains, respectively. The more uniform the deformation, the greater the spectral shift of the resonant wavelength under the effect of the deformation.

[0075] Preferably, the waveguide 20 extends over the portion of the membrane 18 that undergoes the greatest deformation. The membrane 18 exhibits one or more vibration antinodes where the amplitude of the vibration is greatest. The respective antinodes can be determined by modeling and / or experiment. Preferably, the waveguide 20 extends over at least one antinode of the membrane's vibration. This maximizes the deformation of the waveguide 20, further increasing the spectral shift due to the deformation. This results in better sensitivity.

[0076] We modeled the deformation of a membrane 18 as shown diagrammatically in Figures 1A and 1D. The modeled membrane was made of SiO2 with a radius of 1 mm and a thickness of 10 μm and was subjected to a pressure of 1 Pa. The deformation along one of the membrane's diameters is shown in Figure 3E. The x-axis corresponds to the distance (mm) from the center of the membrane and the y-axis corresponds to the deformation in microstrain. The resonant cavity 26 is preferably placed at the level with the largest amplitude of deformation, i.e. at the center of the membrane 18. The simulation shown in Figure 3E shows that for this membrane, the application of a pressure of 1 Pa causes several 10 -2 This indicates that microstrain deformation is induced.

[0077] In Figure 3E, the deformation of the membrane is c Negative, peripheral part 2 p The resonant cavity 26 is advantageously placed on a segment of the membrane 2 so that, under the effect of the vibrations of the membrane, the deformations have the same sign, whether it is a matter of compression or expansion.

[0078] FIG. 3F shows that the resonant cavity 26 is located in the central part 2 of the membrane 2. c 3E, which shows a schematic of a waveguide 20 located at ε 0.5 mm away from the center of the membrane, extending on either side of the center of the membrane at a distance of ±0.5 mm from the center. Under the effect of the vibration of the membrane, the deformation alternately becomes negative (ε<0) and then positive, as shown in FIG. 3E. When the deformation is negative, the optical cavity is compressed and the segments of the second material 22 move closer to each other. When the deformation is positive, the optical cavity is expanded and the segments of the second material 22 move away from each other.

[0079] 4A and 4B show the operation of the servo circuit 41, which functions to regulate the resonant wavelength λ of the resonant cavity 26 formed in the guide 20. r at wavelength λ 32 The servo circuit 41 controls the wavelength λ 32 is the resonant wavelength λ r The locking is usually of the type called top-of-the-fringe locking. This is a problem for circuits using Pound-Drever-Hall servo technology, for example, as described in Chow JH ”Phase-sensitive interrogation of fiber Bragg grating resonators for sensing applications”, J. Light. Technol., vol.23, No.5, pp.1881-1889, May 2005 or Black E” An introduction to Pound-Drever-Hall laser frequency stabilization”, Am.J.Phy.69(1), January 2001.

[0080] The servo circuit 41 detects the wavelength λ of the auxiliary light wave 32 emitted by the auxiliary light source 30. 32 The modulator 411 modulates the light emitted from the laser 410 at a modulation frequency of 10 kHz to several hundred MHz. 32 The modulation frequency of is much higher than the maximum acoustic frequency addressed by the device. It may be, for example, ten times higher than the maximum acoustic frequency addressed by the device. The intensity of the light wave 34 emerging from the waveguide 20 and detected by the photodetector 36 is communicated to a servo circuit 41, which measures a function h that represents the change in intensity detected by the photodetector 36 as a function of the wavelength modulation.

[0081] Depending on the sign of the function h, an error signal is sent to the light source, which determines the emission wavelength λ 32increases or decreases. For example, if the change in detected intensity as the wavelength increases is negative, the emission wavelength will gradually decrease. If the change in detected intensity as the wavelength increases is positive, the emission wavelength will increase. If the detected change in intensity due to modulation is close to zero, the emission wavelength corresponds to the resonant wavelength of the waveguide. The servo circuit 41 uses the following facts: λ 32 <λ r In the case of 32 As the wavelength λ increases, the intensity of the transmitted wave 34 increases. 32 A decrease in the intensity of the transmitted wave 34 results. λ 32 >λ r In the case of 32 As wavelength λ increases, the intensity of the transmitted wave 34 decreases. 32 A decrease in results in an increase in the intensity of the transmitted wave 34.

[0082] Therefore, the wavelength λ of the auxiliary light wave 32 32 and observing the effect of the modulation on the intensity of the transmitted light wave 34, the assist light source 30 can be servo-controlled to change the wavelength λ of the assist light wave 32. 32 is the resonant wavelength λ of the waveguide 20 r can be made to track.

[0083] By tracking the resonance wavelength by top-of-fringe locking, the resonance wavelength can be reduced by 10 -6 pm, or 10 for acoustic frequencies below 1 kHz -3 It can be tracked with a wavelength sensitivity of the order of pm. Considering equation (3) applied to SiO2 films, it is estimated that such sensitivity allows estimation of film deformations of the order of a few pico-strains, or equivalent to a few mPa. Therefore, considering that the spectral shift of the resonant cavity 26 is small, and that this spectral shift is probably of the order of a few pm, the Pond-Drever-Hall method is appropriate.

[0084] Tracking the resonant wavelength by top-of-fringe locking also makes the tracking insensitive to variations in the resonant wavelength of the cavity 26 under the influence of variations in environmental parameters such as temperature and humidity.

[0085] 5A to 5C show the resonant wavelength λ of the membrane 18 when it vibrates under the influence of the photoacoustic wave 6. r Periodic time-dependent fluctuations in λ r Due to the servo control performed by the servo circuit 41, the emission wavelength λ 32 The periodic time-dependent fluctuation in (t) is the resonant wavelength λ caused by the membrane vibration. r 5A shows the spectrum of the transmitted light wave 34 under the effect of the deformation of the waveguide 20 and the spectral shift dλ r FIG. 5B shows the resonant wavelength λ resulting from the deformation of the waveguide 20. r , which shows a time-dependent modulation of the acoustic frequency f a The corresponding frequency The servo circuit 41 modulates the resonant wavelength by a wavelength λ 32 This modulation can be determined by servo-controlling the amplitude of the modulation of the resonant wavelength. The processing unit 42 calculates the acoustic frequency f of the photoacoustic wave 6 based on the amplitude. a Based on the amplitude of the membrane vibration, estimate the amplitude of the membrane vibration corresponding to the acoustic frequency f a With this, it is possible to determine whether analyte 4 is present in the medium or to estimate the concentration of analyte 4 in the medium.

[0086] The estimation of the concentration of analyte 4 in the medium is between the concentration of the analyte and the amplitude of the membrane oscillations, Alternatively, a prior calibration may be required to establish a relationship between the concentration of the analyte and the amplitude of the modulation of the resonant wavelength.

[0087] acoustic amplitude A a The determination of does not necessarily require the determination of the value of the resonant wavelength, but the modulation amplitude Note that we only need to determine exactly TIFF0007607661000016.tif7150.

[0088] 6A to 6D show the main steps that make it possible to form a non-optical fiber waveguide 20 on the membrane 18. In FIG.

[0089] A substrate 100, for example a Si substrate, is provided, on which a first layer 101, for example 4 μm thick of SiO2 (index 1.44), and a second layer 102, for example SiON (silicon oxynitride - index 1.60), for example 1 μm thick, are deposited, see FIG.

[0090] The method comprises the following. Etching the second layer 102 using photolithography to form the waveguides 20, see Figure 6B. In this example, SiON corresponds to the first material 21 of the waveguide. Etching the back side of the substrate 100 to release a portion of the first layer 101 to form a hanging membrane 18. This process can also form an enclosure 17 surrounding the hollow cavity 16. See Figure 6C. Exposing the waveguide 20 point-by-point to femtosecond laser pulses, an operation traditionally called inscription, in order to form cavities in the second material 22, see FIG. 6D. Under the effect of the laser irradiation, the index of the SiON changes locally. The exposed SiON then corresponds to a second material 22 whose refractive index n2 differs from that of the unexposed SiON. In particular, the exposure generates microbubbles, which cause a change in the refractive index. As a result, the refractive index of the waveguide 20 is modulated within the waveguide along the axis of light propagation. The duration of each pulse is, for example, equal to 100 fs at a wavelength of 800 nm and the energy of each pulse is 30 nJ. The pulse frequency can be configured between a few Hz and 200 kHz. Another exposure technique is UV photoinscription, which is described in Chow JH “Phase-sensitive interrogation of fiber Bragg grating resonators for sensing applications”, J. Light. Technol., vol.23, No.5, pp.1881-1889, May 2005. For example, UV photoinscription makes it possible to microstructure optical fibers.

[0091] The refractive index modulation caused by exposure is 10 -3 The width of the resonant peak is relatively small, on the order of 10 pm. However, femtosecond laser inscription makes it possible to produce Bragg mirrors over short lengths, for example on the order of 1 mm. This type of exposure makes it possible to obtain high-finesse resonant cavities 26, with widths of the resonant peaks smaller than a few tens of pm, or even smaller than 10 pm, and in some cases smaller than 5 pm.

[0092] The length that each Bragg mirror extends can be increased, which reduces the width of the resonance peak.

[0093] Thus, when employing the first photoacoustic embodiment, it is possible to detect the presence of an analyte in an analysis medium, or even to estimate its concentration, by carrying out the following steps shown in FIG. 7A: Step 110: applying the device 1 to the medium such that the contact surface is held against the medium; Step 120: Activate the excitation light source 10, which emits an excitation light of an excitation frequency f having a wavelength corresponding to the absorption wavelength λ of the analyte. 11 activating an excitation light source, which emits a pulsed or amplitude modulated excitation light wave 11 at Step 130: Under the effect of illumination of the medium by an excitation light wave, the emission of a photoacoustic wave 6 propagating through the hollow cavity 16 is obtained, such that the membrane of the transducer emits an excitation light of the excitation frequency f 11 The transducer vibrates at a resonant frequency λ r is the excitation frequency f 11 Modulation frequency equal to TIFF0007607661000017.tif7150 to be periodically modulated; Step 140: The servo circuit 41 controls the excitation frequency f 11 The resonant wavelength λ of the waveguide 20 at r determining the resonant wavelength corresponding to the time-dependent modulation of Step 150: calculating the amplitude of the modulation of the resonant wavelength at a frequency that depends on the excitation frequency, in particular at a frequency that is twice higher than the excitation frequency, in response to the time-dependent modulation determined by the servo circuit; Step 160: Detecting the presence of an analyte in the medium and / or estimating the analyte concentration depending on the amplitude of the modulation.

[0094] The presence of the analyte may be detected, or its concentration may be estimated, by a calibration performed with a calibration sample representative of the medium 2 and containing a known amount of the analyte.

[0095] 8A to 8C show a second embodiment, called photothermal embodiment, of a device 1' according to the invention. The device 1' is adapted to be applied to an analysis medium 2.

[0096] The device 1' comprises the components as described with reference to the first embodiment. One difference is that the membrane 18 forms the support wall 3 in which the opening 13 is formed.

[0097] The device 1' comprises an excitation light source 10 emitting an excitation light wave 11. It is of the nature of a pulsed laser source, the pulse frequency being, for example, between 10 Hz and 500 Hz, for example equal to 100 Hz. The excitation light 11 propagates into the medium 2. According to an embodiment, the excitation light source is configured such that the excitation light wave 11 propagates into the medium 2 through an opening 13 formed in the membrane 18.

[0098] Under the effect of the presence of an analyte 4 in the medium, part of the excitation wave is absorbed. This results in a heating 5 of the medium 4. If the analyte is present in the surface part of the medium, the heating 5 of the medium propagates via thermal diffusion to the membrane 18 forming the interface. By surface part of the medium is meant the part comprised between the interface and a depth ranging up to two or three times the heat penetration depth of the material forming the analysis medium.

[0099] The membrane 18 is preferably thermally conductive such that the temperature of the membrane will follow, possibly after a time lag, changes in temperature of the medium 2. The membrane is thin enough to have such thermal conductivity.

[0100] According to this embodiment, the transducer 15 is a thermal transducer whose function is to detect, and preferably quantify, the periodic modulation of the temperature of the film under the effect of periodic excitation of the medium 2 by the excitation light wave 11.

[0101] The transducer 15 comprises an auxiliary light source 30, a waveguide 20, a photodetector 36 and a servo circuit 41 as described with respect to the optoacoustic embodiment.

[0102] Under the effect of heating of the membrane 18, the temperature of the waveguide 20 changes. As a result, the resonant wavelength λ r This variation is due in particular to the variation in the refractive index of the materials 21, 22 from which the waveguides are made.

[0103] The change in resonant wavelength under the influence of temperature can be expressed as:

number

[0104] Wavelength λ of auxiliary source 32 32 If is equal to 1.55 μm, the sensitivity of the transducer can be estimated to be 11 pm / °C.

[0105] When a photothermal embodiment is used, it is possible to detect the presence of an analyte in the analyzed medium, or even to estimate its concentration, by carrying out the following steps shown in FIG. 7B. Step 110: Applying the device 1 to the medium such that the contact surface (in this case the membrane) is held against the medium; Step 120: activating the excitation light source 10, where the excitation light source is irradiated with an excitation frequency f having a wavelength corresponding to the absorption wavelength λ of the analyte. 11 activating an excitation light source 10, which emits an excitation light wave 11 at Step 135: Under the effect of illumination of the medium by the excitation light wave, a periodic heating of the medium 2 is obtained, the generated heat being propagated to the membrane 18 via thermal diffusion and reaching the resonant frequency λ of the waveguide 20 of the transducer. r is the excitation frequency f 11 Modulation frequency equal to TIFF0007607661000019.tif7150 to be periodically modulated; Step 140: The servo circuit 41 controls the excitation frequency f 11 The resonant wavelength λ of the waveguide 20 is r determining a time dependent modulation of the waveguide, the resonant wavelength corresponding to a transmission peak of the modulation; Step 155: calculating the amplitude of the variation of the resonant wavelength in response to the time-dependent variation determined by the servo circuit; Step 165: Detecting the presence of the analyte in the medium and / or estimating the analyte concentration as a function of the variation.

[0106] The presence of the analyte may be detected, or its concentration may be estimated, by a calibration performed with a calibration sample representative of the medium 2 and containing a known amount of the analyte.

[0107] The invention may be implemented on gas, liquid or solid samples in analyte detection applications in the environmental, industrial (eg, food industry) or biomedical fields.

Claims

1. A detection device (1, 1') intended to be applied via a contact surface (3) to an analysis medium (2) which may contain an analyte (4) absorbing light of at least one absorption wavelength, The detection device includes an opening (13) formed in the contact surface (3); The excitation spectral band containing the absorption wavelengths (Δλ １１ ), at the excitation frequency (f １１ an excitation light source (10) configured to emit an excitation light wave (11) pulsed or amplitude modulated at 1000 Hz, the detection device being arranged such that the excitation light wave (11) propagates through the opening (13) towards the analysis medium; a transducer (15) intended to measure the response of the medium after cyclic heating of the medium caused by the absorption of a portion of said excitation light wave (11) by the analyte, The transducer (15) a membrane (18) carrying a waveguide (20); The first reflector (24 １ ), and a second reflector (24 ２ ), each reflector having a reflection spectral band (Δλ ２０ ) the waveguide reflecting light of A first reflector and a second reflector spaced apart from one another to form a resonant optical cavity (26), the resonant optical cavity having a resonant wavelength (λ) within a reflection spectral band. ｒ a first reflector and a second reflector defining a The waveguide has a resonant wavelength (λ ｒ ) and transmits light at a wavelength other than the resonant wavelength (Δλ ２０ ) and reflects the light of The transducer comprises: Reflectance spectrum band (Δλ ２０ an auxiliary laser source (30) configured to emit an auxiliary light wave (32) of Resonance wavelength (λ ｒ a photodetector (36) arranged to detect light waves (34) transmitted through the waveguide at A periodic time-dependent modulation (λ) of the resonant wavelength of the resonant optical cavity (26) is coupled to the photodetector (36). ｒ and a servo circuit (41) configured to determine The waveguide (20) is formed directly on the membrane; The membrane (18) is configured to deform under the effect of cyclic heating of the medium.

2. a processing unit (42) connected to the servo circuit; The resonant wavelength (λ ｒ ) amplitude of the time-dependent modulation ( ) is estimated, 2. The detection device according to claim 1, adapted to detect the presence of the analyte in the medium (2) depending on the estimated amplitude.

3. The processing unit is 3. The detection device according to claim 2, configured to estimate the concentration of the analyte in the medium (2) as a function of the concentration of the analyte in the medium (2).

4. The membrane (18) comprises a hollow cavity (16) opening onto the opening (13), the transducer being connected to the hollow cavity, the transducer (15) being an acoustic transducer configured to detect the amplitude of a photoacoustic wave (6) propagating through the hollow cavity from the opening, and wherein under the effect of irradiation of the medium by the excitation light wave (11), the membrane (18) is excited at the excitation frequency (f １１ ) and a modulation frequency ( ) at the resonant wavelength (λ ｒ 4. The detection device (1) according to claim 1, which provides a time-dependent modulation of the light intensity.

5. 5. The detection device according to claim 4, wherein the membrane (18) is parallel to the contact surface (3).

6. 6. Detection device according to claim 4 or 5, wherein the membrane bounds a portion of the hollow cavity (16).

7. the membrane (18) of the transducer (15) forms the contact surface (3) of the detection device, the contact surface being intended to be applied in contact with the medium (2), The opening (13) extends through the membrane (20); The transducer (15) is a thermal transducer, and under the effect of irradiation of the medium by the excitation light wave (11), the temperature of the membrane exhibits periodic time-dependent variations, which are related to the resonant wavelength (λ ｒ 4. The detection device (1') according to claim 1, wherein a periodic time-dependent modulation of the signal intensity (A) occurs.

8. 8. A detection apparatus according to any preceding claim, wherein the or each reflector is a Bragg mirror formed via a periodic modulation of the refractive index along the waveguide.

9. The servo circuit (41) is connected to the auxiliary laser light source (30) and controls the wavelength (λ) of the light wave (32) emitted by the auxiliary laser light source (30). ３２ ) to the resonant wavelength (λ) of the resonant optical cavity (26). ｒ 9. The detection apparatus of claim 1 , further comprising a servo loop configured to servo control the

10. 10. The detection device of claim 9, wherein the servo circuit (41) implements the Pond-Dreber-Hall servo technique.

11. The first reflector (24 １ ) is the first Bragg mirror, The second reflector (24 ２ ) is the second Bragg mirror, 11. The detection device according to claim 1, wherein the first and second Bragg mirrors form a same Bragg mirror including a defect (25), the first and second Bragg mirrors corresponding to portions of the Bragg mirror located on either side of the defect, respectively.

12. the membrane (18) exhibits at least one vibration antinode when deformed, the amplitude of vibration being maximum at each antinode; 7. The detection device according to any one of the preceding claims, wherein the waveguide (20) is flush with at least one antinode.

13. 13. The detection device according to any one of the preceding claims, wherein the first and second reflectors are obtained by inscribing the waveguide with laser light so as to obtain a periodic modulation of the refractive index of the waveguide.

14. 1. A method for detecting an analyte (4) in a medium (2), in which the analyte (4) absorbs light at at least one absorption wavelength, comprising: a) applying a detection device (1, 1') according to any one of claims 1 to 13 against the medium (2) such that the contact surface (3) of the detection device is held against the medium; b) activating an excitation light source (10), said excitation light source providing an excitation frequency (f １１ activating an excitation light source (10) which emits a pulsed or amplitude modulated excitation light wave (11) at c) by a servo circuit (41), modulating the resonant wavelength (λ) of the waveguide (20) of the transducer (15) at a modulation frequency corresponding to the excitation frequency. ｒ ) wherein the resonant wavelength corresponds to a transmission peak of the waveguide; d) detecting the presence of said analyte in the medium in response to the periodic modulation determined by said servo circuit.

15. The detection device is a detection device (1) according to any one of claims 4 to 6, The method comprises: Step b) is followed by the excitation frequency (f １１ ) to periodically heat the medium (2) and emit photoacoustic waves (6) that propagate through the hollow cavity (16) and cause the membrane (18) of the transducer (15) to emit the photoacoustic waves at the excitation frequency (f １１ ) of the transducer, the resonant wavelength (λ ｒ ) is the excitation frequency (f １１ ) equal to the modulation frequency ( ) modulated by In step d), The modulation frequency ( ) the amplitude of the periodic modulation of the resonant wavelength ( ) and estimating and detecting the presence of the analyte as a function of the estimated amplitude.

16. The detection device is a detection device (1') according to claim 7 and the method comprises the steps of: After step b), cyclically heating the medium (2) at the excitation frequency and regulating the resonant wavelength λ of the waveguide (20) of the transducer. ｒ is the modulation frequency ( ) to be modulated at the excitation frequency (f １１ cyclically heating the membrane (18) at In step d), estimating an amplitude of a periodic modulation of the resonant wavelength at the modulation frequency; and detecting the presence of the analyte as a function of the estimated amplitude.

17. 17. The method of any one of claims 14 to 16, wherein step d) also comprises the step of estimating the concentration of the analyte in the analysis medium.

18. A manufacturing process for producing a detection device according to any one of claims 1 to 13, comprising the steps of: depositing a thin layer of a first material on the membrane so as to form a waveguide; inscribing the waveguide with femtosecond laser light to obtain a periodic modulation of the refractive index of the waveguide.

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