Improved multi-sensor MEMS or NEMS type measurement system

Abstract

The invention relates to a measurement system (10) of the MEMS and / or NEMs type comprising: a resonant assembly (RE) comprising a plurality of N indexed OMRi resonators i, at least one resonant mechanical element MEij coupled to each OMRi resonator, and at least one waveguide (WG) to which the optical resonators are coupled, an emission device (ED), an injection device (ID), each OMRi resonator of the resonant assembly being further configured to be excited at a mechanical excitation frequency (fex / o(i)) and to modulate the light beam associated with said first excitation frequency (fex / o(i)), a resonant mechanical element (MEij) being configured to be excited at a mechanical excitation frequency (fex / e(i,j)) and to modify an optical transmission or reflection in the vicinity of the optical resonance of said associated resonator, said modification being a function of a physical quantity (u) to be measured,at least one detector (Det) and a demodulation device (DDM) comprising a plurality of synchronous detection demodulation modules (11), referred to as LIA. Figure 11,

Description

Title of the invention: Improved multi-sensor MEMS or NEMS type measurement system. FIELD OF THE INVENTION

[0001] The present invention relates to the field of MEMS or NEMS based sensors, and more particularly to sensors using an optical resonator coupled with at least one mechanical element, and the networking of these sensors. STATE OF THE ART

[0002] MEMS or NEMS-based sensors, which rely on the interaction of a quantity to be measured with an optical resonator, have recently experienced significant growth and are highly varied in nature. A MEMS or NEMS sensor is defined as any sensor utilizing microfabrication techniques from microelectronics.

[0003] A sensor of this type comprises an optical resonator RO, also called a photonic cavity, and one or more waveguides GO coupled to the optical resonator, as illustrated in [Fig. 1]. The optical resonator is characterized by at least one resonance wavelength Xr associated with a resonance bandwidth of width Xr / Qopt (Qopt being the quality factor of the optical cavity) as illustrated in [Fig. 2], which describes the energy E stored in the resonator as a function of wavelength.

[0004] The propagation properties of EM waves in the optical resonator are affected by a measurand u (physical quantity to be measured) or a parameter u whose response depends on a measurand of interest z. A readout light beam Fin is injected into the sensor input, and the amplitude and / or phase of the light beam propagating in the waveguide(s) coupled to the optical resonator RO is perturbed by the quantity u. The optical transmission or reflection function of the sensor is thus modified, directly or indirectly, by the physical quantity to be measured. The beam Fout exits the sensor and is detected by a photodetector, and a measurement of the quantity u is deduced from the detected beam.

[0005] In the example of [Fig. 1], the optical resonator RO is a ring whose effective propagation index neff(u) depends on u for its real and / or imaginary part. The propagation speed and / or the dissipation rate of the light wave in the optical resonator thus depend on u.

[0006] For example, for a sensor intended to identify biological objects, the absorption of a biological or other body at the surface of the resonator modifies its effective propagation index and changes the position of the resonance wavelength Xr(w), u being the quantity absorbed. From the quantity absorbed, the nature of the body (measurand z) is determined.

[0007] Thus, the identification of the absorbed substance is achieved by the functionalization layer, which selects the particles to be detected. To give an example of the measurand z in this sensor case, a relationship can be established between the parameter u, which corresponds to a quantity of material to be detected, and the measurand z, which can be the concentration of this material. The two are linked by an absorption-desorption process and can be described by a biochemical equilibrium equation.

[0008] According to another example, the sensor comprises an optical resonator RO coupled with a mechanical element whose displacement is measured. This type of sensor is called an optomechanical sensor.

[0009] Figure 3 illustrates such a sensor in which the mechanical element is a cantilever beam P fixed at one end to a pad CP. The reading beam is injected into the waveguide GO and recovered at the waveguide output by a grating coupler GC. The displacement x of the beam (parameter u) in the evanescent field of the optical resonator perturbs the effective index (variation of the gap between the beam and the ring). From the displacement x, one can measure, for example, the acceleration of a body (measurand z).

[0010] According to yet another example, the resonant mechanical element is confused with the optical resonator, which then exhibits an optical resonance and a mechanical resonance.

[0011] Some sensors are said to be active, because these sensors use the energy supplied by the measurand to carry out the transduction, no external excitation is applied to the sensor: The force of an ultrasonic wave activates the membrane, the inertial force sets a moving mass in motion, etc.

[0012] For another class of sensors, called passive sensors, one of their physical parameters is modified. For example, the resonant frequency of the mechanical system or its quality factor, the electrical resistance of a strain gauge, etc. In this case, it is necessary to provide an external excitation (a bias) to obtain a reading of this parameter. This excitation method is necessary for certain types of sensors.

[0013] For example the resonant mechanical element is excited at an external excitation frequency fex included in the mechanical resonance band BPm around a mechanical resonance frequency frm.

[0014] In another example of a passive sensor, the optical resonator and the mechanical resonator are combined. This is, for example, a vibrating disk exhibiting both optical and mechanical resonance: for example, a sensor operating in a liquid medium to detect biological objects (viruses, proteins, etc.) that are deposited on this disk. The additional mass absorbed on these disks is measured (using a functionalization layer or not), which allows us to determine the concentration of the biological species. The mass weighs down the disk, which modifies its mechanical resonance frequency. Another example is an atomic force sensor in the form of a ring with a resonating tip, as described in the publication by Allain et al., "Optomechanical resonating probe for very high frequency sensing of atomic forces," Nanoscale, 2020, 12, 2939.

[0015] In order to increase the number of measurements and / or enhance the accuracy or functionality of the sensor, it is advantageous to network these active or passive sensors. This then raises the issue of how to read the information associated with each sensor.

[0016] Document EP4109049 describes an SM0 measurement system comprising several optical resonators coupled to a waveguide and elements associated with the optical resonators, as illustrated [Fig. 4]. This measurement system allows the simultaneous retrieval of individual information from each elementary optical resonator / element sensor, and thus access to all the values ​​measured by all the sensors.

[0017] The SM0 system comprises a resonant assembly ENR including an input E and an output S, a plurality of N indexed optical resonators Ri each having a resonance wavelength Xr,i, and at least one waveguide GO to which the optical resonators are coupled.

[0018] The SM0 system also includes at least one element Eij coupled to each resonator Ri and configured to modify optical transmission or reflection in the vicinity of the resonance of the associated optical resonator Ri, the modification being a function of a physical quantity to be measured. The optical resonators are indexed i ranging from 1 to N, and the elements associated with a resonator i are indexed j: Eij. An Eij / Ri assembly forms an elementary sensor Cij, and the ENR assembly forms a sensor array. Within an ER assembly, several types of sensors can be mixed. Examples of resonators Ri are: a waveguide looped back on itself (such as a ring), a disk, and a photonic crystal.

[0019] As explained above, the optical transmission / reflection of a resonator Ri is modified by a physical quantity u, which can be either directly the final physical quantity that one wishes to measure, or a parameter on which the final quantity to be measured z depends. The measurement system SM0 aims to measure the physical quantity u. The measured value of this parameter u by the element Eij associated with the resonator Ri (sensor Cij) is denoted uij, and it is understood that when u is an intermediate parameter, the measurement zij is then determined from uij.

[0020] The measurement system SM0 also includes an emission device DE configured to emit a plurality of N light beams, each having an emission wavelength Xi within the resonance band of the associated optical resonator Ri. The spectral resonance band of the resonator Ri is defined as the band The spectral BPopt around the resonance frequency is characterized by the parameter Qopt as illustrated in [Fig. 2]: BPopt = Xr / Qopt. The different wavelengths Xi must be chosen so as to have disjoint resonance spectral bands, to prevent a wavelength emitted by a laser from addressing two different resonance sources.

[0021] The system also includes a modulation device DM configured to modulate each of the light beams at a modulation frequency fmod(i) and an injection device DI configured to superimpose the N light beams to form an input beam Bin and to inject the beam into the input of the resonant assembly ER. The input beam Bin is the probe, or readout, beam that will read the measurements taken by the sensors Cij, via the modification of the optical response of the resonators Ri. The beam at the output of the ER assembly is called Bout.

[0022] Beam superposition is achieved, for example, using blades or cubes called "beam splitters," or with a multiplexer called Arrayed Waveguide Grating (AWG). Injection into the waveguide is carried out, for example, with an optical fiber coupled to a diffraction grating ("grating coupler") or by edge coupling, with an optical fiber positioned in the same plane as the substrate.

[0023] The system also includes at least one detector Det, for example a photodiode, configured to detect a light beam from the output beam Bout, and generate an electrical output signal Sout.

[0024] In [Fig. 4] and the following figures, the optical beams are symbolized by a line solid and electrical signals by a dotted line, to make the diagrams more readable.

[0025] According to one example, the emission device DE comprises, for example, N Li lasers emitting Bini(i) beams, and the modulation device DM comprises N modulators arranged respectively on the optical paths of the N light beams emitted by the N lasers, and configured to modulate each light beam at the frequency fmod(i). The modulators are, for example, electro-optical modulators EOM(i) (see [Fig. 5]).

[0026] The DM modulation device performs intensity modulation. This intensity modulation is carried out, for example, directly (modulated lasers), via absorption (electro-optical modulators), via Mach-Zender (MZ) interference, or resonator interference.

[0027] The SM0 system finally includes a DDM demodulation device comprising a plurality of synchronous detection type demodulation modules 11 for demodulating the output signal, so as to extract characteristic signals Sdemod(i,j) associated with each element Eij, the measured values ​​uij of the physical quantity u being determined from the characteristic signals.

[0028] The principle of the SMO system is that information relating to a wavelength Xi is encoded by frequency modulation at fmod(i), allowing the recovery of this information not by wavelength demultiplexing but by electronic demodulation processing of the synchronous detection type. The signals at the frequencies of interest are extracted electronically with a very good signal-to-noise ratio. The extraction is carried out by analog or digital blocks.

[0029] This document demonstrates that the information of interest uij is encoded on the components of the optical output intensity Iout with angular frequency Ai+ / -Qij, where:

[0030] Ai = 2.ir.fmod(i) ; Qÿ = 2.ir.fc(ij) ; fc(i,j) excitation frequency applied to the resonant element Eij.

[0031] Thanks to the linearization of the transmission functions, the signals of interest are accessible via modulation / demodulation encoding / decoding. The use of synchronous detection allows the phase signal to be extracted directly with a very good signal-to-noise ratio (SNR). The demodulated signals Sdemod(i,j) allow the measurands associated with each individual photonic sensor Cij to be isolated because the signals are positioned on different spectral bands.

[0032] Synchronous detection is typically implemented by a Synchronous Detection Amplifier (SDA), or "Lock-In Amplifier" (LIA) in Anglo-Saxon terminology. The signal is amplified and multiplied by a reference signal (generated by an internal or external oscillator). A low-pass filter with a suitable cutoff frequency performs the integration. Synchronous detection can be implemented in analog or digital mode. It can be improved by integrating two quadrature channels.

[0033] The number of LIA 11 demodulation modules and the choice of the different modulation and demodulation frequencies depend on the type of sensors in the ER assembly and the chosen demodulation architecture.

[0034] According to a first option illustrated [Fig. 5], demodulation is performed in a single stage. The SMO resonant array comprises M resonant elements Eij (Mi per resonator Ri). According to an example illustrated [Fig. 5], the DDM demodulation device comprises M LIA demodulation modules configured to perform M demodulations at frequencies fmod(i) + / - fc(i,j). The advantage is that this architecture comprises only one stage, the information being obtained by a single processing step. The constraint for choosing the modulation frequencies is that they should preferably be greater than 10 times the bandwidth of the sensor. In the example of [Fig. 5], N=3 and Mi=3 for all resonators Ri, i.e., M=9. The demodulation device in this case comprises 9 LIA demodulators 1 l(i,j).

[0035] According to a second option illustrated [Fig. 6], demodulation is carried out in two stages. According to one example, the DDM demodulation device comprises a first stage including N LIA demodulation modules l(i) configured to perform N demodulations at frequencies fmod(i) and includes, for each channel i, a second stage. The second stage comprises either LIA demodulation modules 12(i,j) at characteristic frequencies fc(i,j) or BPF(i,j) spectral filters configured to perform spectral filtering around the characteristic frequency fc(i,j).

[0036] The choice between the two options depends on the signal to be extracted.

[0037] Document EP4109049 also describes an SM0 measurement system illustrated [Fig. 7] in which the ENR resonant assembly comprises three disks constituting both the optical and mechanical resonators. The three disks are excited respectively at frequencies fex(1), fex(2), and fex(3), generated respectively by three oscillators Oscex1, Oscex2, and Oscex3. The three excitation frequencies are respectively contained within the mechanical spectral bands BP1m, BP2m, and BP3m around the mechanical resonance frequencies fr1m, frm2, and frm3 of the disks. The signals V1(t), V2(t), and V3(t) from the oscillators are carried on the same bus and injected into the three disks, each disk operating a filter and responding only at its own resonance. Here there are no Eij elements associated with each resonator, it is the resonator Ri itself which acts as a resonating mechanical element, the disk being named in this case Ri / Ei (dual function).

[0038] The modulation frequencies fmod(1), fmod(2), and fmod(3) are generated respectively by three source oscillators Oscs1, Oscs2, and Oscs3. The demodulation frequency fdemod(i) = fmod(i) + / - fex(i) is synthesized from the two signals from the two oscillators Oscsi and Oscexi. The modulation frequencies are typically chosen to be between a few kHz and a few GHz.

[0039] One drawback of the SM0 measurement system is the use of external modulators for modulating the light beams injected into the resonant assembly. This makes fabrication complex and prevents the realization of a fully integrated system on a single chip. Furthermore, the modulators are often sensitive to the polarization of the light, thus requiring additional components (polarization controllers), which increases the system's complexity. In addition, the modulators can exhibit significant insertion losses, which must be compensated by the laser, resulting in additional power consumption.

[0040] One object of the present invention is to remedy the aforementioned drawbacks by proposing an improved measurement system which does not include external modulators and which features an original resonant assembly. DESCRIPTION OF THE INVENTION

[0041] The present invention primarily relates to a measurement system of the MEMS and / or NEMs type comprising: - a resonant system comprising: • an input and an output, • a plurality of N indexed OMRi resonators i, each resonator being configured to exhibit both an optical resonance at an optical resonance wavelength and a mechanical resonance at an associated mechanical resonance frequency frm / o(i), said optical resonance wavelengths and said mechanical resonance frequencies all being different, • at least one resonant mechanical element MEij coupled to each OMRi resonator, j being the index of the resonant mechanical element associated with the OMRi resonator, said resonant mechanical element having a mechanical resonance frequency, said mechanical resonance frequency being, where appropriate, different from the mechanical resonance frequencies of the other resonant mechanical elements coupled to the same resonator, • at least one waveguide to which the optical resonators are coupled, - an emitting device configured to emit a plurality of N light beams, each having an emission wavelength Xi within an optical resonance band of the associated optical resonator, - an injection device configured to superimpose N light beams to form an input beam (Bin) and to inject the input beam into the input of the resonant assembly, each OMRi resonator of the resonant assembly being further configured to be excited at a mechanical excitation frequency called the first excitation frequency, contained within a first mechanical resonance band of said resonator, and to modulate the light beam associated with said first excitation frequency, a resonant mechanical element being configured to be excited at a mechanical excitation frequency called the second excitation frequency, and to modify an optical transmission or reflection in the vicinity of the optical resonance of said associated resonator, said modification being a function of a physical quantity (u) to be measured, - at least one detector configured to detect a light beam emanating from the output beam of the resonant assembly (Bout) and generate an output signal, - a demodulation device comprising a plurality of synchronous detection type demodulation modules, called LIA, to demodulate the output signal, so as to extract characteristic signals associated with each resonating mechanical element, measured values ​​of said physical quantity being determined from said characteristic signals.

[0042] According to one embodiment, the resonators are configured such that the path lengths of light in said resonators are different from one resonator to another, a path length being related to the associated optical resonance wavelength by the following formula:

[0043] , _ PUneffj With PLi the optical path length of the light in the resonator r' m'i) OMRi, neffi effective refractive index of the OMRi resonator material, m(i) integer greater than or equal to 1 chosen for each i.

[0044] According to one embodiment, the resonators are disks of radius Ri made of the same material, and which satisfy the relation:

[0045] , _ 2^Rî-neff with nrff effective refractive index of the disk material. Ari-

[0046] The present invention also relates to a measurement system of the MEMS and / or NEMs type comprising: - a resonant system comprising: • an input and an output, • a plurality of N indexed i OMRi resonators, each resonator being configured to exhibit both an optical resonance at a common optical resonance wavelength for all resonators and a mechanical resonance at a mechanical resonance frequency specific to each resonator, said mechanical resonance frequencies all being different, • at least one resonant mechanical element MEij coupled to each OMRi resonator, j being the index of the resonant mechanical element associated with the OMRi resonator, said resonant mechanical element having a mechanical resonance frequency, said mechanical resonance frequency being, where appropriate, different from the mechanical resonance frequencies of the other resonant mechanical elements coupled to the same resonator, • at least one waveguide to which the optical resonators are coupled, • an emitting device configured to emit a light beam called the input beam having an optical wavelength Xini within an optical resonance band identical for all optical resonators, - an injection device (ID) configured to inject said input beam into the input of the resonant assembly, each OMRi resonator of the resonant assembly being further configured to be excited at a mechanical excitation frequency, called the first excitation frequency, contained within a first mechanical resonance band of said resonator, and to modulate the light beam at said first excitation frequency, a resonant mechanical element being configured to be excited at a mechanical excitation frequency, called the second excitation frequency, and to modify an optical transmission or reflection in the vicinity of the optical resonance of said resonator, said modification being a function of a physical quantity to be measured, - at least one detector configured to detect a light beam emanating from the output beam of the resonant assembly and generate an output signal, - a demodulation device (DDM) comprising a plurality of synchronous detection type demodulation modules, called LIA, to demodulate the output signal, so as to extract characteristic signals associated with each resonating mechanical element, measured values ​​of said physical quantity being determined from said characteristic signals.

[0047] According to one embodiment, the resonators are made of the same material and configured so that the path lengths of light in said resonators are different from one resonator to another, a path length being related to the optical resonance wavelength by the following formula:

[0048] , _ PLineff With PLi optical path of light in each of the resonators rm(i) OMRi, neff effective refractive index of the material of said resonator OMRi, m(i) integer greater than or equal to 1 chosen for each i.

[0049] According to one embodiment, the resonators are disks of radius Ri made of the same material, and which satisfy the relation:

[0050] 2jtRineff ”...........

[0051] According to another embodiment, the resonators are made of the same material and have identical dimensions, the different frequencies of mechanical resonances being obtained by modifying, from one resonator to another, the positions of the anchoring elements of said discs.

[0052] According to one embodiment (common to both objects), a resonator is chosen from: a disk, a ring, a racecourse.

[0053] According to one embodiment (common to both objects), a resonator is excited via an actuation chosen from electrostatic, piezoelectric, optical actuation.

[0054] According to one embodiment (common to both objects), a resonant mechanical element is chosen from a beam, a disc, a suspended platform.

[0055] According to one embodiment (common to both objects) a resonant mechanical element is excited via an actuation chosen from electrostatic, piezoelectric, thermal actuation.

[0056] According to one embodiment (common to both objects) a second excitation frequency of a resonant mechanical element coupled to a resonator is identical to a second excitation frequency of a resonant mechanical element coupled to another resonator.

[0057] According to one embodiment (common to both objects), the resonators are excited at said first associated excitation frequencies via dedicated oscillators, said oscillators forming a first set of oscillators, and said resonant mechanical elements are excited at said second excitation frequencies via dedicated oscillators, said oscillators forming a second set of oscillators.

[0058] According to an embodiment (common to both objects) signals from the oscillators of the first set pass over a first common bus for the excitation of the resonators and / or signals from the oscillators of the second set pass over a second common bus for the excitation of the resonant mechanical elements.

[0059] According to one embodiment (common to both objects) the resonators are activated via first electrodes connected to each other and connected to the first bus.

[0060] According to one embodiment (common to both objects) the resonant mechanical elements are actuated via second electrodes (ELI) connected to each other and connected to the second bus (B2).

[0061] According to one embodiment (common to both objects) said oscillators of the first and second set are used to generate demodulation frequencies.

[0062] The present invention also relates to a measuring sensor comprising a plurality of M measuring systems according to the second object of the invention, a measuring system being indexed k and forming a channel k, each channel having an associated resonant wavelength, • said inputs and outputs being combined so that the different channels operate in parallel, • the injection device, the detector and the demodulation device being common to all channels, • each emission device being configured to emit a light beam having an emission wavelength Xk within a resonance band of the associated channel and the injection device being configured to superimpose the M light beams to form said input beam.

[0063] The following description presents several embodiments of the device of the invention: these examples are not limiting to the scope of the invention. These embodiments present both the essential features of the invention and additional features related to the embodiments considered.

[0064] The invention will be better understood and other features, objectives and advantages thereof will become apparent from the following detailed description and with reference to the accompanying drawings given by way of non-limiting examples and in which:

[0065] The [Fig. 1] already cited describes a ring optical resonator according to the state of the art.

[0066] Figure [Fig. 2] already cited describes the energy E stored in the resonator as a function of the wavelength.

[0067] The [Fig.3] already cited illustrates an optomechanical sensor according to the state of the art comprising an optical resonator coupled with a mechanical element whose displacement is measured, in which the mechanical element is a cantilever beam P fixed at one end to a pad.

[0068] The [Fig.4] already cited describes a measurement system according to the state of the art comprising several optical resonators coupled to a waveguide and elements associated with the optical resonators.

[0069] The [Fig.5] already cited illustrates a first variant of the measurement system of [Fig.4] in which the demodulation takes place in a single stage.

[0070] The [Fig.6] already cited illustrates a second variant of the measurement system of [Fig.4] in which the demodulation takes place in two stages.

[0071] The [Fig.7] already cited describes a variant of the measurement system of [Fig.4] in which the resonating assembly comprises discs constituting both the optical resonator and the mechanical resonator.

[0072] Figure 8 illustrates a resonator coupled to a waveguide and comprising an associated mechanical element according to the invention.

[0073] Figure 9 illustrates, for a resonator vibrating at the mechanical resonance frequency, the light power detected at the output of the waveguide as a function of wavelength.

[0074] Figure 10 illustrates three examples of an optomechanical resonator according to the invention.

[0075] Figure 11 illustrates a first variant of the measurement system according to the invention, in which the optomechanical resonators are configured to exhibit optical resonance wavelengths that are all different.

[0076] Fig. 12 illustrates a second variant of the measurement system according to the invention, in which the optomechanical resonators are configured to exhibit a common optical resonance wavelength.

[0077] Figure 13 illustrates a compatible embodiment of the two variants in which the demodulation mode is said to be "single-stage".

[0078] Figure 14 illustrates another compatible embodiment of the two variants in which the demodulation mode is said to be "two-stage".

[0079] Fig. 15 illustrates an embodiment of the system according to the invention in which the first excitation frequencies of the resonators and the second excitation frequencies of the resonant mechanical elements are generated via dedicated oscillators.

[0080] Fig. 16 illustrates an embodiment of the system according to the invention in which signals from the oscillators of the first set pass over a first common bus and / or signals from the oscillators of the second set pass over a second common bus.

[0081] Fig. 17 illustrates an embodiment of the system according to the invention in which the resonators are actuated via first electrodes connected to each other and connected to the first bus, and the resonant mechanical elements are actuated via second electrodes connected to each other and connected to the second bus.

[0082] Figure 18 illustrates an example of a system according to the first variant of the invention in which the resonant assembly is integrated on a chip.

[0083] Fig. 19 illustrates a measuring sensor according to another aspect of the invention comprising a plurality of systems according to the second variant of the system according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0084] The invention relates to a measurement system of type MEMS and / or NEMs comprising a resonant assembly, the system according to the invention incorporating certain aspects of the system described in document EP4109049 but presenting certain differences and improvements.

[0085] The ENR resonant assembly according to the invention comprises an input E, an output S, and a plurality of N indexed OMRi resonators i, each resonator being configured to exhibit an optical resonance at an optical resonance wavelength (Xr or Xri, see below) and a mechanical resonance at an associated mechanical resonance frequency frm / o(i). The mechanical resonance frequencies frm / o(i) are all different from each other. The OMR resonator is an opto resonator, also called optomechanical (existence of optical and mechanical resonance).

[0086] Each OMRi resonator is coupled to at least one resonant mechanical element MEij, where j is the index of the resonant mechanical element associated with the OMRi resonator. The resonant mechanical element MEij has a mechanical resonance frequency frm / e(i,j). In the case where a resonator is coupled to several resonant mechanical elements, the mechanical resonance frequencies of the resonant mechanical elements coupled to the same resonator are all different from each other.

[0087] This is a difference from the structure of the resonant assembly in document EP4109049 in which the optical resonators are: • either coupled to resonant mechanical elements, in which case they do not have mechanical resonance ([Fig.4] cited above in this application), • either configured to also exhibit mechanical resonance, and in this case they are not coupled to any resonant mechanical element ([Fig.7] cited above in this application).

[0088] The OMRi optical resonators are coupled to at least one GO waveguide. It is the (OMRi, MEij) combination that forms an elementary sensor Cij.

[0089] An OMR resonator coupled to a waveguide GO and comprising an associated mechanical element ME is illustrated [Fig. 8]. The incoming laser beam, with wavelength Xa, is denoted Fin, and the outgoing laser beam is denoted Fout. The OMR resonator has a resonant wavelength Xr and a resonant frequency frm / o.

[0090] The resonance wavelength Xr is expressed by the equation:

[0091] , ^LL ^-12 3 (1)

[0092] With PL the length of the optical path traveled by the light on the perimeter of the resonator, neff the effective index of the resonator material, and m an integer greater than or equal to 1 chosen. This gives us several accessible optical resonance wavelengths.

[0093] As a mechanical resonator, the OMR resonator can vibrate at the resonance frequency frm / o. The originality of this elementary sensor according to the invention is that this vibrational capacity of the OMR optical resonator is used as a transduction mechanism to modulate the light beam passing through it, as illustrated in [Fig. 9], which describes the light power Pout detected at the output of the waveguide as a function of wavelength. Curve 90 represents the resonance at Xr. The wavelength Xiaser is contained within the optical resonance band BPro of the resonator with width Xr / Qopt, i.e., Xkser is located on one side of the optical resonance peak. When the OMR resonator vibrates mechanically by performing a displacement Ax, it induces a periodic change in the length PL of the optical path traveled by light, which induces a variation dX of the resonance wavelength (equation (1)). The modulation of the resonance wavelength dX induces a modulation APout of the output light wave at the vibration frequency of Ax, i.e. the resonance frequency frm / o, as illustrated [Fig.9].

[0094] Preferably, the optomechanical resonator is chosen from a disk D, a ring RG or a racetrack RT, as illustrated [Fig. 10].

[0095] Preferably, the resonators are excited via an actuation chosen from electrostatic, piezoelectric, optical actuation.

[0096] The ME element is a resonant mechanical element at the frequency frm / e. The movement of the resonant mechanical element ME near the optomechanical resonator OMR (ME-OMR coupling) causes a change in its effective refractive index neff (see equation 1), therefore a change in the resonant wavelength, and thus modulates the optical output power at the frequency frm / e. It is this frequency frm / e which, through its perturbation, will allow the measurement of u or z (see prior art).

[0097] Indeed, each ME exhibits a resonant frequency sensitive to the measurand. Typically, the excitation frequency fex / e(i,j) is adapted, via feedback, to the frequency of each element, which varies during the measurement, in order to maintain the resonance of the mechanical element despite the disturbance. This is done, for example, using an oscillator and a frequency measurement, or a phase-locked loop.

[0098] Thus, in the system according to the invention, there is a double modulation of the output power via the modulation of the resonance wavelength: • on the one hand, via the mechanical vibration of the optomechanical resonator OMR itself, which modifies the optical path length PL of the optomechanical resonator, and • on the other hand via the vibration of the resonant mechanical element ME, which modifies the effective refractive index neff of the optomechanical resonator to which it is coupled (displacement near the resonator but not in contact).

[0099] The double modulation can be performed on the transmission of the light wave as illustrated [Fig. 10], or on its reflection.

[0100] The resonant mechanical element is preferably chosen from a beam (in cantilever), a disc, a suspended platform.

[0101] Preferably a resonant mechanical element is excited via an actuation chosen from electrostatic, piezoelectric, thermal actuation.

[0102] This dual modulation associated with the couple (OMRi, MEij) is applied in a resonant ENR assembly according to the invention illustrated in Figures 11 and 12, which comprises, As explained above, the plurality of optomechanical resonators OMRi, each resonator being associated with at least one resonant mechanical element MEij. An elementary sensor Cij consisting of the pair (OMRi, ME(i,j)) allows the measurement of uij / zij.

[0103] To implement the resonant assembly in the measurement system, the resonator must be excited within its mechanical resonance band. Thus, each OMRi resonator in the resonant assembly is configured to be excited at an excitation frequency fex / o(i), referred to as the first excitation frequency, and to modulate the light beam associated with the first excitation frequency fex / o(i). The first excitation frequency fex / o(i) lies within a first mechanical resonance band BPrm / o(i) of the resonator. The best response is obtained for fex / o(i) = frm / o(i), but operation with excitation in the vicinity of frm / o is also possible.

[0104] Similarly, a resonant mechanical element should be excited within its mechanical resonance band. A resonant mechanical element MEij is configured to be excited at an excitation frequency fex / e(i,j), referred to as the second excitation frequency. The value of the resonance frequency frm / e is perturbed by the measurand, and the second excitation frequency is adjusted accordingly to maintain the ME element in resonance.

[0105] The best response is obtained when the excitation is on the resonance frequency of the resonant mechanical element, but operation with an excitation in the vicinity of the resonance frequency is also possible (second resonance bandwidth).

[0106] The resonant mechanical element is configured to modify an optical transmission or reflection in the vicinity of the optical resonance of the associated resonator, the modification being a function of a physical quantity u to be measured.

[0107] Note that several physical quantities can be measured, with mechanical elements sensitive to different physical quantities.

[0108] Subjected to these two excitations the output beam is thus modulated at the frequencies fex / o(i) + / - fex / e(i,j).

[0109] We denote Ai = 2.ir.fex / o(i) and Qij = 2.ir.fex / e(i,j)

[0110] The pulsation Ai is derived from the modulation by the optomechanical resonator OMRi, and the pulsation Qij is derived from the modulation by the resonant mechanical element MEij.

[0111] The measurement system also includes a light wave emission device DE, an injection device for injecting this light wave into the input of the resonant assembly, at least one detector Det configured to detect the light beam Bout from the beam at the output of the resonant assembly and to generate an output signal Sout.

[0112] Following the same principle as that of document EP4109049, the measurement system also includes a DDM demodulation device comprising a plurality of synchronous detection demodulation modules 11, designated LIA, to demodulate the output signal in order to extract characteristic signals Sdemod(i,j) associated with each resonant mechanical element. The measured values ​​(uij, zij) of the physical quantity (associated with the resonant mechanical element) are determined from these characteristic signals. As explained above, it is possible to measure several physical quantities from mechanical elements sensitive to different physical quantities.

[0113] According to one example, demodulation is performed with at least N demodulation modules. According to another example, the number of demodulation modules is reduced by performing time-division multiplexing.

[0114] It can be seen that, compared to the measurement system of document EP4109049, the measurement system according to the invention no longer includes an external modulator to modulate the light at the frequency fmod(i), since the OMRi optomechanical resonators themselves perform this function. This simplifies the system architecture and makes it more integrable.

[0115] The measurement system according to the invention is available in two variants.

[0116] The measurement system 10 according to the first embodiment of the invention is illustrated [Fig. 11]. In this first embodiment, the optomechanical resonators OMRi are configured to exhibit optical resonance wavelengths Xri, all of which are different. The emission device DE is then configured to emit a plurality of N light beams Bini(i), each having an associated emission wavelength Xi within the resonance band of the associated optical resonator BPro(i) (centered on Xri). In one embodiment, the emission device comprises N lasers configured to emit the N light beams.

[0117] The measurement system 20 according to the second embodiment of the invention is illustrated [Fig. 12]. In this second embodiment, the optomechanical resonators OMRi are configured to exhibit a common optical resonance wavelength Xr. The emitting device DE is then configured to emit a light beam having the emission wavelength Xini within the resonance band of the associated optical resonator BPro (identical for all optomechanical resonators and centered on Xr), and forming the input beam Bin.

[0118] The mechanical resonance frequencies of the optomechanical resonators are chosen so that the mechanical resonance bands do not overlap.

[0119] Note, as explained above, that in both variants each OMRi optomechanical resonator is configured to exhibit a mechanical resonance frequency different from those of the other OMRk^i optomechanical resonators.

[0120] The first variant has the advantage of simplicity of implementation, but includes several lasers, and the laser is an expensive component and consumes a significant amount of power.

[0121] The second variant is more complex to implement, but has the advantage of requiring only one laser.

[0122] According to an embodiment compatible with both variants and illustrated [Fig. 13], the ENR resonant assembly comprises a total of P resonant mechanical elements, and the DDM demodulation device comprises P LIA 11(i,j) demodulation modules configured to perform P demodulations at frequencies fex / o(i) + / -fex / e(i,j). This so-called "single-stage" demodulation mode is described in document EP4109049.

[0123] According to another embodiment compatible with both variants and illustrated [Fig. 14], the demodulation mode is said to be "two-stage" (also described in document EP4109049). The ENR resonant assembly comprises a first stage comprising N LIA 1 l(i) demodulation modules configured to perform N demodulations respectively at the frequencies fex / o(i).

[0124] According to a first option, the ENR assembly comprises, for each channel i, a second stage including demodulation modules 12(i,j) at frequencies fex / e(i,j). According to yet another embodiment, the ENR assembly comprises, for each channel i, a second stage including spectral filters BPF(i,j) configured to perform spectral filtering around the frequency fex / e(i,j).

[0125] According to an embodiment also described in document EP4109049, an LIA demodulation module comprises a reference oscillator at a demodulation frequency and a first demodulation chain comprising a mixer and a low-pass filter. Preferably, an LIA demodulation module also comprises a second demodulation chain in quadrature with the first chain.

[0126] For the design and realization of the optomechanical resonators according to the first variant, according to one embodiment the OMRi resonators are configured such that the path lengths of the light in the PLi resonators are different from one resonator to another, a PLi path length being related to the associated optical resonance wavelength Xri by the following formula, derived from equation 1:

[0127] , PU.n^ (2) ri nij} With : PLi optical path length of light in the OMRi resonator neffi effective refractive index of the OMRi resonator material m(i) integer greater than or equal to 1 chosen for each i.

[0128] According to an embodiment that facilitates the fabrication of the ENR resonant assembly, the resonators are disks of radius Ri made of the same material, and which satisfy the relation:

[0129] , _ With effective refractive index of the disc material. ri m(f)

[0130] Indeed, in the case of a disk or track in the shape of a circle of radius R the length PL of one turn of resonator (i.e. of the perimeter) is equal to 2.ir.R.

[0131] According to a practical implementation example for a set of two resonators made of silicon disks (effective index n=3.47), the radius of the first optical resonator is R\ = 5 finite, and that of the second resonator Rz - 5.05 / tm, so that = 1557 nm and 22 = 1573 nm , with m = 70 for both cases.

[0132] In practice, the parameter Ri / m(i) is adapted to obtain a chosen resonance length.

[0133] For the design and production of the optomechanical resonators according to the second variant, according to a first embodiment the OMRi resonators are configured so that the OMRi resonators are made of the same material and configured so that the path lengths PLi of the light in the resonators are different from one resonator to another, a path length being related to the optical resonance wavelength Xr by the following formula:

[0134] , _ PLineff With: Âr “ mù) PLi optical path of light in each of the OMRi resonators neff effective refractive index of the material of said OMRi resonators m(i) integer greater than or equal to 1 chosen for each i.

[0135] According to one option, the resonators are disks of radius Ri made of the same material, and which satisfy the relation:

[0136] _ 2îrRineff r mù)

[0137] According to a practical implementation example, for a set of two resonators made of silicon disks and for a single resonance wavelength for both resonators Δr — 1557.33 nm, we have: Resonator 1: Rt = 70 Resonator 2: Rz = 5.07 / wn, m2=71

[0138] Thus, by changing the two parameters R and m, it is possible to fix ^r. In this case, the sensors are separated by the first excitation frequency (optical modulation frequency), which is fixed by the radius R, and the measurement system then operates with a single laser.

[0139] According to a second embodiment, the resonators are made of the same material and have identical dimensions (for example, discs of the same radius), the different mechanical resonance frequencies being obtained by modifying, from one resonator to another, the positions of the anchoring elements of the resonators.

[0140] For this embodiment, only one laser is required, since all optical resonators have the same resonant wavelength. Selection is made by the mechanical resonant frequency, which varies from one resonator to another. Consequently, the complexity of the reading system is reduced.

[0141] According to one embodiment, at least a second excitation frequency of a resonant mechanical element coupled to a resonator is identical to a second excitation frequency of a resonant mechanical element coupled to another resonator. Indeed, what is important is that the mechanical resonance frequencies, and therefore the excitation frequencies, of the mechanical elements coupled to the same optomechanical resonator are all different, so that demodulation is performed correctly.

[0142] For the implementation of the system (10 or 20) according to the invention, the first excitation frequencies fex / o(i) of the OMRi resonators are preferably generated via dedicated oscillators Oscoi, as illustrated in [Fig. 15] for a set of two optomechanical resonators, each coupled to three resonant mechanical elements. Similarly, the second excitation frequencies fex / e(i,j) of the resonant mechanical elements MEij are preferably generated via dedicated oscillators Osceij. The signal generated by the Oscoi oscillator is denoted Voi(t), and the signal generated by the Osceij oscillator is denoted Vij(t).

[0143] The Oscoi oscillators form a first set of EO1 oscillators and the Osceij oscillators form a second set of EO2 oscillators.

[0144] Each OMRi resonator or EMij resonant mechanical element only resonates mechanically with a frequency within its mechanical resonance band, and it is therefore possible to transmit all or part of the excitation signals via a common bus. A resonator excited with several signals "recognizes" its excitation signal and ignores the others.

[0145] Thus, according to an embodiment illustrated [Fig. 16], signals from the oscillators of the first set travel on a first common bus B1 for the excitation of the resonators and / or signals from the oscillators of the second set travel on a second common bus B2 for the excitation of the resonant mechanical elements. The signals can be placed on a common bus of any kind, depending on the implementation constraints.

[0146] The implementation of common buses simplifies the fabrication and integration of the resonant assembly and its excitation.

[0147] According to one embodiment, the OMRi resonators are actuated via first ELI electrodes connected to each other and to the first bus B1, as illustrated in [Fig. 17] (i=3, j=3). In [Fig. 17], the ELI electrodes and their connections are symbolized by surface 71. Similarly, according to another embodiment, the resonant mechanical elements MEij are actuated via second EL2 electrodes connected to each other and to the second bus B2 (surface 70 symbolizes the EL2 electrodes and their connections).

[0148] This electrode and bus structure simplifies the implementation of the system according to the invention.

[0149] Preferably, the oscillators of the first and second set are used to generate demodulation frequencies.

[0150] Preferably, the oscillators are integrated into the DDM demodulation device, as illustrated [Fig. 17].

[0151] According to one embodiment, the ENR resonant assembly is integrated onto a CHIP chip as illustrated [Fig. 18] for an example according to the first variant. In this example, the DI injection device comprises a fiber coupler FC that superimposes the N light beams to form the Bin beam and a coupling grating GC that injects Bin into the GO waveguide, and which is also integrated onto the CHIP chip.

[0152] The invention also relates to a CM measurement sensor illustrated [Fig. 19] comprising M systems according to the second embodiment. The system is indexed k and is referred to as a channel. [Fig. 19] illustrates the case M=3, each resonant assembly comprising N=3 optomechanical resonators, each coupled to 3 resonant mechanical elements. The ENRk resonant assemblies operate in parallel: the inputs Ek and the outputs Sk of the M systems are combined so that the different channels operate in parallel. The DI injection device, the Det detector, and the DDM demodulation device are common to all channels.

[0153] Aki is the angular frequency of the mechanical excitation frequency of resonator n°i of system k and Qkij is the angular frequency of the mechanical excitation frequency of resonant element n°j coupled to resonator n°i of system k.

[0154] Each channel k has an associated resonance wavelength Àr(Ck).

[0155] Each DEk emission device is configured to emit a light beam having an emission wavelength Xk within a resonance band of the associated channel and the DI injection device is configured to superimpose the M light beams, to form the input beam Bin.

[0156] We have thus achieved wavelength multiplexing, which makes it possible to multiply the number of elementary sensors Ckij (OMRki, MEkij) without adding complexity to the system, and keeping only one input and one output.

Claims

1. Demands Measurement system (10) of type MEMS or NEMs comprising: - a resonant system (RES) comprising: • an input (E) and an output (S), • a plurality of N indexed OMRi resonators i, each resonator being configured to exhibit both an optical resonance at an optical resonance wavelength (Xri) and a mechanical resonance at an associated mechanical resonance frequency (frm / o(i)), said optical resonance wavelengths and said mechanical resonance frequencies all being different, • at least one resonant mechanical element MEij coupled to each OMRi resonator, j being the index of the resonant mechanical element associated with the OMRi resonator, said resonant mechanical element having a mechanical resonance frequency (frm / e(i,j)), said mechanical resonance frequency being, where appropriate, different from the mechanical resonance frequencies of the other resonant mechanical elements coupled to the same resonator, • at least one waveguide (WG) to which the optical resonators are coupled, - a transmitting device (ED) configured to emit a a plurality of N light beams, each with an emission wavelength Xi within an optical resonance band (BPro(i)) of the associated optical resonator, - an injection device (ID) configured to superimpose the N light beams to form an input beam (Bin) and to inject the input beam into the input of the resonant assembly, each OMRi resonator of the resonant assembly being further configured to be excited at a mechanical excitation frequency (fex / o(i)) called the first excitation frequency, contained within a first mechanical resonance band (BPrm / o(i)) of said resonator, and to modulate the light beam associated with said first excitation frequency (fex / o(i)), a resonant mechanical element (MEij) being configured to be excited at a mechanical excitation frequency (fex / e(i,j)), called the second excitation frequency, and to modify an optical transmission or reflection in the vicinity of the optical resonance of said associated resonator, said modification being a function of a physical quantity (u) to be measured, - at least one detector (Det) configured to detect a light beam from the beam at the output of the resonant assembly (Bout) and generate an output signal (Sout), - a demodulation device (DDM) comprising a plurality of synchronous detection type demodulation modules (11), called LIA, to demodulate the output signal, so as to extract characteristic signals (Sdemod(i,j)) associated with each resonant mechanical element, from the measured values ​​(uij,zij) of said physical quantity being determined from said characteristic signals.

2. A measurement system according to the preceding claim wherein the resonators are configured such that path lengths of light in said resonators (PLi) are different from one resonator to another, a path length being related to the associated optical resonance wavelength by the following formula: PUncffi ri m(i) With PLi optical path length of light in the resonator OMRi, neffi effective refractive index of the material of the resonator OMRi, m(i) integer greater than or equal to 1 chosen for each i.

3. A measurement system according to the preceding claim in which the resonators are disks of radius Ri made of the same material, and which satisfy the relation: ^Ri-neff ri miï) with neff the effective refractive index of the disk material.

4. Measurement system (20) of the MEMS or NEMs type comprising: - a resonant assembly (RE) comprising: • an input (E) and an output (S), • a plurality of N indexed OMRi resonators i, each resonator being configured to exhibit both an optical resonance at an optical resonance wavelength (Xr) common to all resonators and a mechanical resonance at a mechanical resonance frequency (frm / o(i)) specific to each resonator, said mechanical resonance frequencies all being different, • at least one resonant mechanical element MEij coupled to each OMRi resonator, j being the index of the resonant mechanical element associated with the OMRi resonator, said resonant mechanical element having a mechanical resonance frequency (frm / e(i,j)), said mechanical resonance frequency being, where appropriate, different from the mechanical resonance frequencies of the other resonant mechanical elements coupled to the same resonator, • at least one waveguide (WG) to which the optical resonators are coupled, an emitting device (ED) configured to emit a light beam called the input beam (Bin) having an optical wavelength Xini within an optical resonance band (BPro) identical for all optical resonators, an injection device (ID) configured to inject said input beam (Bin) into the input of the resonant assembly, Each OMRi resonator of the resonant assembly is further configured to be excited at a mechanical excitation frequency (fex / o(i,j)), referred to as the first excitation frequency, contained within a first mechanical resonance band (BPrm / o(i)) of said resonator, and to modulate the light beam at said first excitation frequency (fex / o(i,j)), a mechanical resonant element being configured to be excited at a mechanical excitation frequency (fex / e(i,j)), referred to as the second excitation frequency, and to modify a transmission or an optical reflection in the vicinity of the optical resonance of said resonator, said modification being a function of a physical quantity (u) to be measured, - at least one detector (Det) configured to detect a light beam from the beam at the output of the resonant assembly (Bout) and generate an output signal (Sout), - a demodulation device (DDM) comprising a plurality of demodulation modules (11) of the synchronous detection type, called LIA, to demodulate the output signal, so as to extract characteristic signals (Sdemod(i,j)) associated with each resonant mechanical element, measured values ​​(uij, zij) of said physical quantity being determined from said characteristic signals.

5. A measurement system according to the preceding claim wherein the resonators are made of the same material and configured so that the path lengths (PLi) of the light in said resonators are different from one resonator to another, a path length being related to the optical resonance wavelength by the following formula: _ PLi ne ffm(i) With PLi optical path length of the light in each of the OMRi resonators, neff effective refractive index of the material of said OMRi resonators, m(i) integer greater than or equal to 1 chosen for each i.

6. A measurement system according to the preceding claim in which the resonators are disks of radius Ri made of the same material, and which satisfy the relation: m(i)

7. A measurement system according to claim 4 in which the resonators are made of the same material and have identical dimensions, the different mechanical resonance frequencies being obtained by modifying, from one resonator to another, the positions of the anchoring elements of said discs.

8. System according to any one of the preceding claims wherein a resonator is selected from: a disk, a ring, a racetrack.

9. System according to any one of the preceding claims wherein a resonator is excited via an actuation selected from electrostatic, piezoelectric, optical actuation.

10. System according to any one of the preceding claims in which a resonant mechanical element is selected from a beam, a disc, a suspended platform.

11. System according to any one of the preceding claims wherein a resonant mechanical element is excited via an actuation selected from electrostatic, piezoelectric, thermal actuation.

12. System according to any one of the preceding claims wherein at least a second excitation frequency of a resonant mechanical element coupled to a resonator is identical to a second excitation frequency of a resonant mechanical element coupled to another resonator.

13. System according to any one of the preceding claims wherein the resonators (OMRi) are excited at said first excitation frequencies (fex / o(i)) associated via dedicated oscillators (Oscoi), said oscillators forming a first set of oscillators (EO1), and wherein said resonant mechanical elements (MEij) are excited at said second excitation frequencies (fex / e(i,j)) via dedicated oscillators (Osceij), said oscillators forming a second set of oscillators (EO2).

14. System according to the preceding claim in which signals from the oscillators of the first set pass over a first common bus (B1) for the excitation of the resonators and / or signals from the oscillators of the second set pass over a second common bus (B2) for the excitation of the resonant mechanical elements.

15. System according to the preceding claim in which the resonators are actuated via first electrodes (ELI) connected to each other and connected to the first bus (Bl).

16. System according to claims 14 or 15 wherein the resonant mechanical elements are actuated via second electrodes (ELI) connected to each other and connected to the second bus (B2).

17. Measurement system according to any one of claims 13 to 16 wherein said oscillators of the first and second set are used to generate demodulation frequencies.

18. Measurement sensor (30) comprising a plurality of M measurement systems (20) according to any one of claims 4 to 7, a measurement system being indexed k and forming a channel k, each channel having an associated resonance wavelength (XrC(k)), said inputs (Ek) and said outputs (Sk) being coincident so that the different channels operate in parallel, the injection device (DI), the detector (Det) and the demodulation device (DDM) being common to all channels, each emission device (DEk) being configured to emit a light beam having an emission wavelength Xk included in a resonance band of the associated channel and the injection device (DI) being configured to superimpose the M light beams to form said input beam (Bin).

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