Temperature-stabilized opto-mechanical oscillator

Abstract

Optomechanical oscillator, comprising: a first laser light source (11), emitting a first beam of light (F1) at a first wavelength (); a resonator (30) configured to oscillate according to a resonance frequency (), optically coupled to the first beam of light, so that the resonator collects a fraction of the light propagating in the first beam, said fraction of light being modulated according to the resonance frequency; a processing circuit (40), configured to: receive, at an input, the first beam of light having propagated along the resonator (30); address a feedback signal (Sr) intended to power the resonator; form, at an output, an output signal (Sout), amplitude modulated, at a stabilized modulation frequency.

Description

Title of the invention: Temperature-stabilized optomechanical oscillator Technical field

[0001] The technical field of the invention concerns opto-mechanical oscillators. PREVIOUS ART

[0002] The use of an optomechanical oscillator allows the formation of a periodic electronic signal whose amplitude and period are controlled. One possible application is the formation of a clock signal.

[0003] In the devices of the prior art, the optomechanical oscillators comprise a mechanically oscillating structure optically coupled to a beam of light. Under the effect of the optical coupling, a portion of the light propagating in the waveguide is mechanically extracted. Under the effect of the mechanical oscillation, at a resonant frequency, the efficiency of the optical coupling varies at the resonant frequency. This results in a periodic variation in the quantity of light propagating in the waveguide.

[0004] The publication Xu et al “Ultra-sensitive chip-based photonic temperature sensor using ring resonator structures” describes an optical cavity, coupled to a straight waveguide. The cavity is ring-shaped. It is optically coupled to the straight waveguide, by evanescent coupling. Under the effect of a temperature variation, the optical resonance wavelength is modified. Thus, an increase in temperature leads to an increase in the resonance wavelength. The beam propagating in the straight waveguide is a probe beam. The fluctuations in the light power transmitted by the probe beam, which depend on the resonance frequency, are used to determine the temperature variation of the resonant structure. The device described in the publication thus forms a photonic thermometer.

[0005] The publication Lee et al “Low jitter and temperature stable MEMS oscillators” describes an electromechanical oscillator comprising a thermistor of an oscillating structure. The temperature resulting from the thermistor is used to electronically correct a signal modulated by the oscillating structure. However, the thermistor is separate from the oscillating structure: the temperature it measures may be different from the temperature within the oscillating structure itself.

[0006] The publication Huang et al. 2017. “Direct stabilization of optomechanical oscillators” describes an optomechanical oscillator operating in a regime in which a temperature change induces a perturbation of the resonant frequency mechanical, but also a modification of the oscillation amplitude. The oscillator is controlled by keeping the oscillation amplitude constant, which indirectly plays a role in frequency stability.

[0007] The Gavartin 2013 publication “Stabilization of a linear nanomechanical oscillator to its thermodynamic limit” describes a resonator operating at two different mechanical frequencies. The actuation is said to be multimode. The frequency drift of a first mode serves to compensate for that of the second mode. However, this alternative is only possible by using other ultra-stable oscillators. This configuration is possible for sensor applications, but not for time bases.

[0008] The inventors propose an optomechanical oscillator allowing better consideration of temperature variation. The objective may be to generate an amplitude-modulated signal whose power and period are stable. Presentation of the invention

[0009] An object of the invention is an optomechanical oscillator, comprising: - a first laser light source, emitting a first beam of light at a first wavelength; - a resonator configured to oscillate according to a resonant frequency, the resonator being configured to be optically coupled to the first beam of light, according to a first coupling bandwidth comprising the first wavelength, such that the resonator collects a fraction of the light propagating in the first beam, said fraction of light being modulated according to the resonant frequency; - a processing circuit, configured to: • receive, at an input, the first beam of light having propagated along the resonator; • send a feedback signal intended to power the resonator; • form, at one output, an amplitude-modulated output signal, at a modulation frequency corresponding to the resonance frequency;

[0010] the oscillator being characterized in that the processing circuit comprises: - a photodetection circuit, forming the input of the processing circuit, and configured to detect at least a first part of the first beam of light so as to form a frequency-modulated detection signal at the resonant frequency, the processing circuit being configured to form the output signal as a function of the detection signal; - a low-pass filter, connected to the photodetection circuit, configured to form a correction signal, at a frequency lower than the frequency of resonance, the correction signal being representative of a variation in temperature of the resonator; - a corrector, connected to the low-pass filter and configured to correct the modulation frequency of the detection signal as a function of the correction signal.

[0011] According to one embodiment, the photodetection circuit comprises a first photodetector, connected to: - a detection branch, carrying the detection signal; - a correction branch, comprising the low-pass filter and the corrector.

[0012] According to one embodiment, the photodetection circuit comprises: - a first photodetector, opening onto a detection branch, carrying the detection signal; - a second detector, leading to a correction branch, the correction branch comprising the low-pass filter and the corrector.

[0013] The corrector can be configured to apply the correction signal: - to the detection signal, resulting from the first photodetector; - or to the resonator; - or to the first source of light.

[0014] According to one possibility, the corrector is configured to: - estimate a variation of the resonance frequency as a function of the correction signal; - correcting a frequency of the detection signal resulting from the first photodetector, as a function of the variation of the estimated resonant frequency.

[0015] The corrector can be configured to apply a response function to the correction signal to estimate the variation of resonant frequency.

[0016] According to one possibility, the corrector is connected to the first laser light source, so as to modify an emission power of the first light beam as a function of the correction signal.

[0017] According to one possibility, the corrector is connected to the resonator, so as to modify the resonance frequency as a function of the correction signal.

[0018] According to one possibility, the resonator comprises a regulation unit, configured to be powered by the corrector, so as to adjust the resonance frequency, by thermal or electrostatic effect.

[0019] According to one possibility, the second photodetector is configured to detect a second portion of the first light beam having propagated through the waveguide.

[0020] According to one possibility, the waveguide is configured to receive the first beam of light and propagate the latter along the resonator, towards the processing circuit.

[0021] According to one possibility, the oscillator comprises: - a second laser light source, emitting a second beam of light at a second wavelength, different from the first wavelength, the oscillator being such that: - the processing circuit is configured to receive the second laser beam having propagated along the resonator; - the second wavelength is included in a second coupling bandwidth of the resonator, so that the resonator collects a fraction of the light propagating in the second beam, said fraction of light being modulated according to the resonance frequency; - the second photodetector is configured to detect all or part of the second light beam having propagated along the resonator, so that the correction signal is established from a low-frequency component of the second light beam.

[0022] The processing circuit may comprise a separator configured to: - direct all or part of the first beam towards the first photodetector; - direct all or part of the second beam towards the second photodetector.

[0023] The oscillator may comprise: - an optical path, extending between the second light source and the processing circuit; the optical path being configured to transport a portion of the second light beam from the light source to the processing circuit; - an interferometer, configured to form an interference signal between: • the second beam having propagated along the resonator; • the part of the second beam of light emerging from the optical path; - the processing circuit being such that the second photodetector is configured to detect the interference signal resulting from the interferometer.

[0024] The waveguide may be configured to receive the second beam of light and propagate the latter along the resonator, towards the processing circuit.

[0025] The oscillator may comprise a high-pass filter, arranged between the first photodetector and the resonator, and whose cut-off frequency is less than or equal to the resonance frequency.

[0026] The invention will be better understood upon reading the description of the exemplary embodiments presented in the remainder of the description, in conjunction with the figures listed below. FIGURES

[0027] [Fig.lA] and [Fig.lB] diagram a waveguide and an optomechanical resonator, forming an optomechanical oscillator

[0028] [Fig.2A] illustrates the harmonic shift of the optical coupling bandwidth, under the effect of a mechanical oscillation, generating an oscillation of optical power delivered by the oscillator as described in connection with figures 1A and 1B.

[0029] [Fig.2B] illustrates an effect of a temperature variation on the optical power delivered by the mechanical oscillator.

[0030] [Fig.3A] shows a diagram of a first embodiment of the invention.

[0031] [Fig.3B] shows a diagram of a variant of the first embodiment of the invention.

[0032] [Fig.3C] shows schematically another variant of the first embodiment of the invention.

[0033] [Fig.3D] shows another variant of the first embodiment of the invention.

[0034] [Fig.4] illustrates two optical coupling bandwidths addressed by two different wavelengths.

[0035] [Fig.5A] shows a diagram of a second embodiment of the invention.

[0036] [Fig.5B] shows a diagram of a variant of the second embodiment of the invention.

[0037] [Fig.5C] shows schematically another variant of the second embodiment of the invention.

[0038] [Fig.5D] shows schematically another variant of the second embodiment of the invention. PRESENTATION OF SPECIAL EMBODIMENTS

[0039] Figures 1A and 1B diagram an example of an optomechanical oscillator. The oscillator comprises a waveguide 20 configured to guide a light beam F. The waveguide 20 extends between a first optical coupler 21 and a second optical coupler 22. The first optical coupler 21 is configured to allow the admission of a light beam, in particular a laser beam, into the power waveguide. The light beam is produced by a laser source 10. The second optical coupler 22 is configured to allow extraction of the light having propagated in the waveguide 20. The first and second optical couplers are for example diffraction gratings, this type of structure being known to those skilled in the art.

[0040] The oscillator comprises a resonator 30 extending along the waveguide 20, between the first coupler 21 and the second coupler 22. The resonator 30 is configured to oscillate at a resonance frequency f . The resonator 30 is, in this example, a structure capable of being driven by a planar movement, called contour mode, according to the resonance frequency, under the effect of an electrostatic actuation imparted by an actuator 33. The actuator 33, shown in [Fig.lB], is fixed relative to the resonator 30. The actuator 33 is located on either side of the resonator 30. Electrostatic actuation is effected through an air gap 34, extending between the actuator 33 and the resonator 30. The electrostatic actuation is controlled by a control unit 35.

[0041] The waveguide 20 can be produced on the surface Si layer of a SOI (Silicon on Insulator) type substrate. The cross-section can for example be a few hundred nm by a few hundred nm, for example of the order of 600 nm x 200 nm. By cross-section, we mean a section in a plane perpendicular to the axis of propagation of the light in the waveguide. Preferably, the waveguide 20 is configured to carry out propagation according to a single mode, at a wavelength which can be 1550 nm, the usual wavelength in the field of telecommunications.

[0042] The resonator may have a diameter of the order of 10 μm, a thickness of the order of 220 nm. The dimension of the air gap 34 is for example of the order of 100 nm.

[0043] The resonator 30 is optically coupled to the waveguide 20, for example by evanescent coupling. The minimum distance between the resonator 30 and the waveguide 20 is for example 60 nm, and typically between 100 and 150 nm. Thus, when a light beam propagates along the waveguide 20, a portion of the light beam is extracted and propagates in and around the resonator 30, or in the near field around the latter.

[0044] The oscillator comprises a processing circuit 40, intended to produce an output signal Sout modulated in amplitude, according to a modulation frequency that is as stable as possible. The processing circuit comprises a feedback loop, connecting the processing circuit 40 to the control unit 35, so as to maintain the oscillation of the resonator at the resonance frequency.

[0045] [Fig.2A] illustrates an optical coupling bandwidth between the waveguide 20 and the resonator 30. Subsequently, this coupling is designated waveguide 20 / resonator 30 coupling, the latter forming an optical cavity. The abscissa axis corresponds to the optical wavelength. The ordinate axis corresponds to the light power extracted from the waveguide 20: this represents the fraction of light collected by the resonator. The solid line curve represents a configuration in which the resonator is fixed. Under the effect of the oscillation, the resonator is deformed, which results in a modification of the optical coupling waveguide 20 / resonator 30. In [Fig.2A], this results in a periodic shift of the coupling bandwidth, between the two dashed curves, reflecting a spectral shift of the optical coupling waveguide 20 / resonator 30.The coupling bandwidth can also widen or narrow, without the center wavelength of the bandwidth being shifted.

[0046] In Figure 2A, the dotted vertical line corresponds to the wavelength X of the beam F propagating in the waveguide 20. Under the effect of the variation pe- periodicity of the coupling bandwidth, the fraction of light optically coupled to the resonator varies. The power of the optical beam F propagating in the waveguide is then modulated according to a pulsation (ûr, according to the expression:

[0047] P = P0 + acos(mx) (1)

[0048] where: - Pq corresponds to a power, called static power, propagating in the waveguide “at equilibrium”, that is to say in the absence of oscillation of the resonator 30; - a corresponds to the modulation amplitude; r(2)

[0049] Preferably, the wavelength X corresponds to the steepest part of the curve describing the coupling bandwidth A 2. This makes it possible to maximize the variation in power extracted by the optical coupling relative to the periodic spectral variation of the coupling bandwidth.

[0050] As described in connection with the prior art, under the effect of a variation in the temperature AT of the resonator, the optical coupling bandwidth varies. This results in a spectral shift of the coupling bandwidth, shown diagrammatically in [Fig.2B]. Thus, the power of the beam propagating in the waveguide 20 is temporally modulated, according to the expression:

[0051] P = (PQ + AP0) +acos((uv+ Aay)r) (3)

[0052] where: - A Pq translates a shift in the power, called static, propagating through the waveguide, under the effect of the temperature variation; - A corresponds to a pulsation shift translating the frequency shift of the power modulation, under the effect of the temperature variation AT.

[0053] The oscillators described below, in connection with figures 3A, 3B, 3C, 3D, 5A, 5B, 5C, 5D, aim to provide a correction to correct the frequency shift, represented here by the shift of the pulsation A wr.

[0054] A first embodiment of a temperature-stabilized oscillator is shown in FIG. 3A. The oscillator 1 comprises a waveguide 20 and a resonator 30 as described in connection with FIGS. 1A and 1B. The device comprises a first laser source 11, intended to produce a first light beam Fi intended to be power modulated by the resonator 30. The first laser beam Fi is coupled to the waveguide 20 by the first coupler 21. The first light beam is for example emitted at a first wavelength ^included in the spectral band 1520 nm - 1580 nm when the oscillator is intended for telecom-type applications. communications.

[0055] Downstream of the resonator 30, all or part of the first laser beam Fi is extracted from the waveguide 20 by the second coupler 22, to form an extracted beam F'p. The extracted beam F'i is representative of the power modulation carried out by the resonator 30. The extracted beam F\ is directed towards a processing circuit 40. As previously described, the processing circuit 40 is configured to establish an output signal Sout, periodic and intensity modulated. An important aspect of the processing circuit 40 is that it is configured so that the output signal is amplitude modulated according to a modulation frequency that is as stable as possible.

[0056] Whatever the embodiment, the processing circuit 40 comprises an input formed by a photodetection circuit 40'. The photodetection circuit comprises one or more photodetectors, depending on the embodiments. The processing circuit extends between the photodetection circuit 40' and an output, delivering the output signal Sou.

[0057] The extracted beam F'i is directed towards a 40s splitter. The 40s splitter, usually referred to as a “power splitter”, is configured to direct: - a first part F' of the extracted beam F' i towards a first branch, called the detection branch, intended to form the output signal S and to form a feedback signal Sr supplying the control unit 35 of the resonator 30. - a second part F' i2 of the extracted beam F' i towards a second branch, called the correction branch, intended to generate a correction signal Sc. The correction signal is representative of a variation of the first spectral coupling band as a function of the temperature variation. The correction branch comprises, in this example, a second photodetector 42, a low-frequency pass filter 44 and a corrector 46.

[0058] The first part F'n of the extracted beam F\ is intended to generate the output signal Sout, amplitude modulated. It can represent 50% of F'i. Preferably, the first part F'n is larger than the second part F'i2. The first part F'n can correspond to at least 80% or at least 90% of the beam F'i, the second part F'i2 corresponding to the complementary portion.

[0059] In this example, the first photodetector 41 is a photodiode. The first photodetector 41 generates a detection signal Sd, of pulsation (+ A ttv ), which is an image of the optical beam. A portion of the detection signal Sd is directed to the control unit 35 of the resonator 30, and forms the feedback signal Sr. The feedback loop comprises a high-pass filter 43. The high-pass filter 43 is configured to extract a high-frequency component from the detection signal resulting from the first photodetector 4L. By high-frequency component is meant a component in a frequency range comprising the resonance / of the re- sonator 30.

[0060] The second photodetector 42 is for example a photodiode. The low-pass filter 44 is configured to extract a low-frequency component of the signal resulting from the second photodetector, forming the correction signal Sc. By low-frequency component, we mean a component strictly lower than the resonance frequency / of the resonator 30, for example at a frequency lower than 100 Hz, or even 10 Hz, or even 1 Hz. This makes it possible to estimate the low-frequency component, corresponding to the variation of the modulation amplitude A Po under the effect of the progressive drift of the coupling bandwidth A 2 between the waveguide 20 and the resonator 30, under the effect of a progressive variation of the temperature of the resonator 30. The low-frequency component, forming the correction signal Sc, is representative of the variation of optical power A PQ. It depends on the variation of temperature dT of the resonator.

[0061] The processing circuit 40 is configured to extract the correction signal Sc resulting from the low-pass filter 44, and to correct, from the correction signal, the detection signal Sd propagating downstream of the first photodetector 4L. For this, the processing circuit comprises a correction component 46, supplied by: - ​​the correction signal Sc resulting from the low-pass filter 44; - the detection signal Sd resulting from the photodetector 41, from which the processing circuit forms the output signal Sout.

[0062] The correction component 46 takes into account a pre-established transfer function h, linking the low frequency drift, corresponding to the variation of the static power A Po , under the effect of the temperature, to the high frequency drift, corresponding to the variation of the modulation frequency. The correction component may comprise a digital part, allowing the estimation of A and its taking into account to correct the pulsation of the detection signal.

[0063] The transfer function makes it possible to estimate A ov as a function of A Po; A = h(Sc ), knowing that the correction signal Sc corresponds to A Po; the correction signal Sc is representative of the temperature variation on A Po.

[0064] For example, we can assume a simplifying hypothesis according to which the frequency drifts linearly with the temperature: A = y AT where V is a known positive coefficient. The coefficient P can be determined by modeling and / or experimentally. We also assume that the variation in optical power A Po is also a linear function of the temperature: A Po = fi AT. fi is a known positive coefficient. The coefficient fi can be determined by modeling and / or experimentally.

[0065] Thus, .

[0066] This reasoning can be generalized to nonlinear dependencies of frequency and optical power variation with respect to temperature. For example, if A®,- = g^T)a A«>,.= A / >0) = / i(AP0).Lk functions and ^2 are established experimentally and / or by modeling, h — g og^

[0067] Thus, the corrector 46 is configured to estimate A wr, from Sc, and to correct the modulation frequency of the detection signal sd as a function of A ( / ¼ We thus obtain an output signal Sout modulated in amplitude and stabilized on the pulsation

[0068] An advantage of the oscillator described in connection with [Fig.3A] is that correction of the output signal is carried out from the light beam having been amplitude modulated by the resonator 30. This allows better consideration of the temperature variation than by carrying out a correction from an external measurement of the temperature. This advantage is verified for the other configurations described subsequently.

[0069] [Fig.3B] represents a variant of the oscillator described in connection with [Fig.3A]. The processing circuit 40 comprises a correction branch, similar to that described in [Fig.3A]. The processing circuit 40 comprises the photodetector 41 and the high-pass filter 43 and described in connection with [Fig.3A], forming the detection branch. A particularity of this variant is that the low-frequency component, forming the correction signal Sc, is not used directly to estimate the drift of the modulation frequency, but to power a correction component 48, the latter being configured to modulate the power supply of the laser 11. Thus, the power of the laser can be reduced, when the temperature increases, so as to cause a drop in temperature. The correction signal Sc is used to feedback on the power supply of the laser 11.

[0070] [Fig.3C] represents a variant of the oscillator described in connection with [Fig.3B]. According to this variant, the processing circuit 40 comprises a correction branch, similar to that described in [Fig.3A]. The processing circuit 40 comprises the photodetector 41 and the high-pass filter 43 and described in connection with [Fig.3A], forming the detection branch. The correction signal Sc is used to feedback on the resonator 30, via the corrector 48, acting on a regulation unit 36. The regulation unit 36 ​​may comprise a resistor, making it possible to modulate the temperature near the resonator, or an electrode facing the air gap 34, so as to modulate the rigidity of the resonator 30, by electrostatic effect, usually called "electrostatic tuning". In this variant, the correction signal Sc is configured to feedback directly on the resonator 30.

[0071] [Fig.3D] shows a variant of the configuration described in connection with [Fig.3A], in which the photodetection circuit 40' comprises a single photodetector 41, supplying both the correction branch, which comprises the low-pass filter 44 connected to the corrector 46, and the detection branch, which carries the detection signal, intended to form the output signal. It is understood that the use of a photodetection circuit 40' comprising only a single photodetector can be transposed to the configurations described in connection with Figures 3B and 3C.

[0072] Figure 4 illustrates a coupling spectral band A À comprising a succession of different elementary bandwidths, without overlap. A first wavelength 2] is represented in a first bandwidth A and a second first wavelength in a second bandwidth A 22. In [Fig.4], each slope is shown by a double arrow.

[0073] Figures 5A to 5D relate to an embodiment in which the oscillator comprises two different light sources: a first light source 11, as previously described, and a second light source 12, emitting a second beam F2, preferably a laser beam, at a second wavelength ^2, different from the first wavelength 2b as described in connection with [Fig.4]. Thus, a fluctuation of the coupling bandwidth at one wavelength can be used to determine the fluctuation of the coupling spectral band at the other wavelength.

[0074] The second wavelength is sufficiently offset from the first wavelength so that the two wavelengths can be spectrally separated by a conventional spectral separator. For example, the spectral shift is greater than 1 nm and less than 100 nm. The spectral shift is preferably sufficiently small to allow coupling into the waveguide 20 with the first coupler and extraction to the processing circuit 40 using the second coupler.

[0075] In the examples shown in Figures 5A to 5D, the beams Fi and F2 are introduced into the waveguide 20 at the level of the first coupler 21. They are extracted from the waveguide 20 by the second coupler 22. According to other possibilities: - there are two first couplers 21, addressing respectively the first beam Fi and the second beam F2; - and / or two second couplers 22 are available, allowing the separate extraction of the first beam Fi and the second beam F2.

[0076] The second laser beam F2 acts as a probe beam. Also, the optical power P2 of the second beam F2 is preferably lower than the optical power Pi of the first beam Fp. We can have P2 < 0.5 Pi or P2 < 0.01 Pp. It is preferable for the probe beam to work at low intensity to avoid the phenomenon of self-heating. The beam F1 works at high power in order to be able to generate a greater amplitude modulation.

[0077] Under the effect of a temperature variation, the power of the second beam propagating in the waveguide is temporally modulated according to the expression:

[0078] p - (Po + AP0) +acos( (“>•+ A a)r)t) (3')

[0079] where - AP\} translates a shift in the static power propagating through the waveguide, under the effect of the temperature variation; - A ü)r corresponds to the pulsation shift translating the frequency shift of the power modulation, under the effect of the temperature variation

[0080] The embodiment described in FIGS. 5A to 5D is based on an extraction of the first beam Fb so as to form a first extracted beam F'b and a second extraction of the second beam F2, so as to form a second extracted beam F'2. The second extracted beam F'2 is intended to measure the low-frequency drift AP of the modulation of the second optical beam, so as to estimate the temperature variation. The first extracted beam F' i is intended to form a detection signal Sd, the latter being used to feedback on the resonator 30 and to form the output signal Sout.

[0081] In the examples described in FIGS. 5A to 5D, the first and second beams are extracted at the same second coupler 22. The photodetection circuit 40' comprises two photodetectors 41 and 42. The processing circuit 40 comprises a splitter 40s configured to allow spectral separation of the extracted beams F'i and F'2. The extracted beam F'b at the wavelength is directed towards the first photodetector 41 of the processing circuit 40. The extracted beam F'2, at the wavelength is directed towards the second photodetector 42 of the processing circuit.

[0082] As in the embodiments shown in FIGS. 3A to 3C, the processing circuit advantageously comprises a high-pass filter 43 arranged in the feedback loop supplying the resonator 30.

[0083] The processing circuit 40 comprises a second photodetector 42, for example of the photodiode type, connected to a low-pass filter 44. The low-pass filter 44 is intended to extract a low-frequency component of the signal resulting from the photodetector 42, considered representative of the variation in optical power AP\h and forming the correction signal Sc.

[0084] In the embodiment shown in [Fig.5A], the processing circuit comprises a correction component 46, supplied by: - the correction signal Sc resulting from the low-pass filter 44: the correction signal corresponds to the static power variation in the second spectral band. Thus, the signal is representative of a variation in the temperature resonator temperature. - the detection signal Sd resulting from the photodetector 41.

[0085] The correction component 46 takes into account a pre-established response function h', linking the low frequency drift, corresponding to the variation of the static power A P'o of the second beam, under the effect of the temperature, to the high frequency drift, corresponding to the variation of the modulation frequency.

[0086] The response function makes it possible to estimate A œr as a function of A P'Q; A wr = h'(Sc ), knowing that Sc corresponds to A P'^ which is representative of A T.

[0087] Thus, the corrector 46 is configured to estimate A o.)r, from the correction signal Sc, and to correct the modulation frequency of the detection signal Sd as a function of A Wr. An output signal is thus obtained that is modulated in amplitude and stabilized on the pulsation wr.

[0088] [Fig.5B] represents a variant of the oscillator described in connection with [Fig.5A]. The processing circuit 40 comprises a photodetector 42 and a low-pass filter 44, as described in [Fig.5A], generating a correction signal Sc. The processing circuit comprises the photodetector 41 and the high-pass filter 43 and described in connection with [Fig.5A]. The correction signal Sc is not used directly to estimate the drift of the modulation frequency, but to modulate the power supply of the laser 11, through a correction component 48 regulating the latter. Thus, the power of the laser can be reduced, when the temperature increases, so as to cause a regulation of the temperature.

[0089] [Fig.5C] represents a variant of the oscillator described in connection with [Fig.5B]. According to this variant, the processing circuit 40 comprises a photodetector 42 and a low-pass filter 44, similar to that described in [Fig.5A]. The processing circuit 40 comprises the photodetector 41 and the high-pass filter 43 and described in connection with [Fig.5A]. The correction signal Sc is used to feedback on the resonator 30, as described in connection with [Fig.3C]. The correction signal is addressed, via a correction component, to a regulation unit 36, for example a resistor, making it possible to modulate the temperature near the resonator, or an electrode, facing the air gap, so as to modulate the stiffening of the resonator 30, by electrostatic effect, usually called "electrostatic tuning". In this variant, the correction signal is configured to feed back directly to the resonator 30.

[0090] In [Fig.5D], a variant of the embodiment described in connection with [Fig.5C] is shown. In [Fig.5D], the electronic analysis circuit 40 comprises an interferometer 40i, configured to allow interference between: - a part of the beam F2, taken between the second light source 12 and the waveguide 20; - the beam F'2 extracted from the waveguide 20.

[0091] The beams F2 and F'2 are at the same wavelength x2. They are combined in the interferometer 40; so as to form an interference signal F';. The latter is directed towards the low frequency branch of the processing circuit. The interference signal F', is representative of a phase shift between the beams F2 and F'2. It is considered that a measurement of a phase variation is more sensitive than a measurement of a power variation.

[0092] The use of an interferometer 40, as described in [Fig.5D], is compatible with the embodiments described in FIGS. 5A to 5C.

[0093] The invention makes it possible to generate an amplitude-modulated output signal Sout, according to a stabilized frequency. It is particularly suitable for the formation of a clock signal, intended for electronic circuits.

Claims

Claims

1. Optomechanical oscillator, comprising: - a first laser light source (11), emitting a first beam of light (FJ at a first wavelength (^0; - a resonator (30) configured to oscillate according to a resonance frequency ( / ), the resonator being configured to be optically coupled to the first beam of light, according to a first coupling bandwidth comprising the first wavelength, so that the resonator collects a fraction of the light propagating in the first beam, said fraction of light being modulated according to the resonance frequency; - a processing circuit (40), configured to: • receive, at an input, the first beam of light having propagated along the resonator (30); • send a feedback signal (Sr) intended to power the resonator; • form, at an output, an amplitude-modulated output signal (Sout), at a modulation frequency corresponding to the resonance frequency; the oscillator being characterized in that the processing circuit comprises: - a photodetection circuit (40'), forming the input of the processing circuit, and configured to detect at least a first part (F'b F'n) of the first beam of light so as to form a detection signal (Sd) frequency modulated at the resonance frequency, the processing circuit being configured to form the output signal as a function of the detection signal; - a low-pass filter (44), connected to the photodetection circuit, configured to form a correction signal (Sc), at a frequency lower than the resonance frequency, the correction signal being representative of a variation in temperature of the resonator; - a corrector (46, 48), connected to the low-pass filter and configured to correct the modulation frequency of the detection signal according to the correction signal.

2. Oscillator according to claim 1, in which the photodetection circuit comprises a first photodetector (41), connected to: - a detection branch, carrying the detection signal; - a correction branch, comprising the low-pass filter (44) and the corrector (46, 48).

3. Oscillator according to claim 1, in which the photodetection circuit comprises: - a first photodetector (41), opening onto a detection branch, carrying the detection signal; - a second detector (42), opening onto a correction branch, the correction branch comprising the low-pass filter (44) and the corrector (46, 48).

4. Oscillator according to any one of the preceding claims, wherein the corrector (46, 48) is configured to apply the correction signal: - to the detection signal (Sd), resulting from the first photodetector; - or to the resonator (30); - or to the first light source (11).

5. Oscillator according to claim 4 wherein the corrector (46) is configured to: - estimate a variation of the resonance frequency (A mr) as a function of the correction signal; - correct a frequency of the detection signal ((Vr + A wr) resulting from the first photodetector, as a function of the variation of the estimated resonance frequency (A).

6. Oscillator according to claim 5, in which the corrector is configured to apply a response function (h) to the correction signal to estimate the resonance frequency variation

7. Oscillator according to claim 4 wherein the corrector (48) is connected to the first laser light source (11), so as to modify an emission power of the first light beam as a function of the correction signal.

8. Oscillator according to claim 4 wherein the corrector (48) is connected to the resonator (30), so as to modify the resonance frequency as a function of the correction signal.

9. Oscillator according to claim 8, in which the resonator comprises a regulation unit (36), configured to be powered by the corrector (48) so as to adjust the resonance frequency, by thermal or electrostatic effect.

10. An oscillator according to any one of claims 1, 4 to 9, and claim 3, wherein the second photodetector (42) is configured to detect a second portion of the first light beam (F'i2).

11. Oscillator according to any one of the preceding claims, comprising a waveguide (20) configured to receive the first beam of light and propagate the latter along the resonator, towards the processing circuit.

12. Oscillator according to any one of claims 1, 4 to 11, and claim 3, comprising - a second laser light source (12), emitting a second beam of light (F2) at a second wavelength (22), different from the first wavelength, the oscillator being such that: - the processing circuit is configured to receive the second laser beam having propagated along the resonator; - the second wavelength is included in a second coupling bandwidth of the resonator, so that the resonator collects a fraction of the light propagating in the second beam, said fraction of light being modulated according to the resonance frequency; - the second photodetector is configured to detect all or part of the second light beam (F'2) having propagated along the resonator, so that the correction signal is established from a low-frequency component of the second light beam.

13. Oscillator according to claim 12, in which the processing circuit comprises a separator (50s), configured to: - direct all or part of the first beam (F' i) towards the first photodetector; - direct all or part of the second beam (F'2) towards the second photodetector.

14. Oscillator according to any one of claims 12 or 13, comprising: - an optical path (48), extending between the second light source and the processing circuit; the optical path being configured to transport a portion of the second light beam (F2) from the light source to the processing circuit; - an interferometer (40;), configured to form an interference signal between: • the second beam having propagated along the resonator; • the portion of the second light beam emerging from the optical path; - the processing circuit being such that the second photodetector is configured to detect the interference signal resulting from the interferometer.

15. An oscillator according to any one of claims 12 to 14 and claim 11, wherein the waveguide is configured to receive the second beam of light and propagate the latter along the resonator, towards the processing circuit.

16. Oscillator according to any one of the preceding claims, comprising a high-pass filter (43), arranged between the first photodetector and the resonator, and whose cut-off frequency is less than or equal to the resonance frequency.

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