Optical stability transfer device, optical system and associated optical stabilization method
Patent Information
- Application Number
- FR2024015383
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-12-30
- Publication Date
- 2026-07-03
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
Title of the invention: Optical stability transfer device, optical system and associated optical stabilization method
[0001] The present invention relates to an optical stability transfer device, as well as an optical system and an optical stabilization method.
[0002] High-stability and high-coherence optical sources are of great interest for applications involving measurements over long integration or interrogation times. This is the case, for example, in inertial sensors or for memories, particularly those using quantum states. To achieve the desired levels of stability, optical sources must be stabilized at a few reference frequencies, which generally correspond to an atomic transition of an element or molecule in gaseous form, such as rubidium or acetylene.
[0003] Devices exist for transferring the frequency stability of a reference light source to a light source whose frequency, and therefore wavelength, is suitable for the intended application. For example, devices using a frequency comb, a Fabry-Pérot transfer cavity, or fiber-reinforced cavity devices are known. However, in the first case, optical frequency comb devices are complex and expensive systems with a limited intrinsic spectral width, in other words, the range of wavelengths that can be stabilized. Devices using Fabry-Pérot cavities are difficult to implement because they are sensitive to external disturbances, such as vibrations or temperature variations, which generally necessitate a monolithic cavity whose length cannot be finely adjusted to compensate for long-term drifts.On the other hand, the spectral width of such a device is also reduced, generally less than 50 nm. While fiber-cavity devices are less complex to implement, particularly with regard to length control, their spectral width remains limited to 100 nm at best.
[0004] The aim of the invention is then to propose an optical stability transfer device, allowing the stabilization of light sources with wavelengths far removed from the wavelength of the reference light source, which is robust and simple to implement.
[0005] To this end, the invention relates to an optical stability transfer device comprising:
[0006] - an interferometer comprising: • an acousto-optical filter, configured for: • receive a reference optical signal, emitted by a reference light source, and at least one target optical signal, the target optical signal or each target optical signal being emitted by a respective target light source, a frequency of the target optical signal or each target optical signal being distinct from a frequency of the reference optical signal; • emit a plurality of acoustic signals of distinct frequency and amplitude, each acoustic signal being independently associated with a single optical signal from among the reference optical signal and the target optical signal(s); and • independently diffract each optical signal to form respectively zero-order and first-order reference and target optical signals, • a first arm, configured to receive and propagate the reference and target optical signals of the same given order among the zero order and the first order; • a second arm, configured to receive and propagate the reference and target optical signals of the other given order, the first and second arms being configured to impose a predetermined optical delay between the optical signals propagating in the first arm and the optical signals propagating in the second arm; • an optical coupler, arranged at the output of the first and second arms, and configured to combine the zero- and first-order reference optical signals into a recombined reference optical signal on the one hand, and the zero- and first-order target optical signal(s) into a recombined target optical signal(s) on the other hand;
[0007] - a photodetector, configured to convert the reference optical signal recombined and the target optical signal or signals respectively recombined into the output reference electrical signal and the output target electrical signal or signals; and
[0008] - a control unit, configured to convert the reference electrical signal output and the target electrical output signal or signals respectively into a reference error signal and a target error signal, so as to keep the optical delay of the interferometer constant and to keep the frequency of the target optical signal or signals constant, depending on the reference and target error signals.
[0009] Thanks to the invention, it is possible to stabilize light sources whose wavelength is far from the wavelength of the reference light source. In particular, the wavelengths of the target light signals are separated, for example, by several hundred nanometers from the reference optical signal.
[0010] The use of an acousto-optical filter in an unbalanced interferometer-type discriminator advantageously extends the operating range to typically one octave, and offers a resolved acousto-optical coupling, allowing a correspondence between a particular wavelength and a particular acoustic frequency, and an independent diffraction efficiency optimization for each wavelength involved.
[0011] Furthermore, the device allows for the simultaneous stabilization of several target optical signals, that is, the stabilization of the frequency, and therefore the wavelength, of each target optical signal, without significantly affecting the device's performance. In particular, it is possible, for example, to stabilize more than two target light sources at different wavelengths. The wavelengths of the target light signals can also be separated by more than 100 nm from each other.
[0012] Finally, since the device maintains a constant optical delay of the interferometer, it is adaptable to varying environmental conditions, such as temperature variations or vibrations. It is therefore robust and compatible with applications in embedded systems.
[0013] According to other advantageous aspects of the invention, the device comprises one or more of the following features, taken individually or in all technically possible combinations:
[0014] - the control unit is further configured to adjust the amplitude of the signals acoustics as a function of reference and target error signals;
[0015] - the first arm has a predetermined length, and in which the control unit includes an interferometer correction module, configured to receive the reference error signal and to adjust at least one of the following parameters as a function of the reference error signal: the length of the first arm, an interferometer temperature and a phase of the acoustic signals emitted by the acousto-optic filter, in order to keep the optical delay of the interferometer constant;
[0016] - the control unit includes a correction module for the source or sources target light source, configured to receive the target error signal(s) and to adjust at least one of the following parameters according to the target error signal(s): a temperature of the target light source(s) or at least one of the target light sources, an electrical intensity of an electrical supply current to the target light source(s) or at least one of the target light sources, and a voltage of the electrical supply current to the target light source(s) or at least one of the target light sources, to keep the frequency of the target optical signal(s) constant;
[0017] - the first arm includes a waveguide, configured so that the signals reference optics and target of the same given order among zero order and first order propagate through the waveguide;
[0018] - the first arm is configured to receive and propagate optical signals from zero-order reference and target and the second arm is configured to receive and propagate first-order reference and target optical signals.
[0019] The invention also relates to an optical system comprising:
[0020] - a reference light source, configured to emit an optical signal of reference ;
[0021] - at least one target light source, the target light source or each target light source being configured to emit a target optical signal, the target optical signal(s) having a frequency distinct from a frequency of the reference optical signal; and
[0022] - an optical stability transfer device, the acousto-optical filter being configured to receive the target optical signal(s) emitted by the target light source(s) and the reference optical signal emitted by the reference light source.
[0023] According to other advantageous aspects of the invention, the optical system comprises one or more of the following features, taken individually or in all technically possible combinations:
[0024] - the reference and target light sources are laser sources;
[0025] - comprising a plurality of target light sources, preferably more than two target light sources, each target light source being configured to emit a target optical signal of a frequency distinct from the other target light sources;
[0026] - the target optical signal from each target light source is an optical signal auxiliary target, each target light source being configured to further emit a main target optical signal, of the same frequency as the frequency of the auxiliary target optical signal emitted by the target light source, and further comprising an optical combining module, configured to combine the main target optical signals into a combined optical signal, of a combined frequency, distinct from the frequencies of the main target optical signals;
[0027] - the optical combination module is a summing or subtracting device of frequencies.
[0028] The invention also relates to an optical stabilization method, implemented by a device, the method comprising the following steps:
[0029] - reception of a reference optical signal and at least one target optical signal, by the acousto-optical filter;
[0030] - emission of the plurality of acoustic signals by the acousto-optical filter;
[0031] - diffraction of each optical signal by the acousto-optical filter to form the zero-order and first-order reference optical signals, and the zero-order and first-order target optical signal(s);
[0032] - reception and propagation of reference and target optical signals of the same order given between zero order and one order in the first arm and optical reference and target signals of the other given order in the second arm;
[0033] - combination of zero-order and first-order reference optical signals into the signal recombined reference optics, and zero-order and first-order target optical signals into the recombined target optical signal(s), by the optical coupler;
[0034] - conversion of the recombined reference optical signal into the electrical signal of output reference and of each target optical signal recombined into the target electrical output signal(s) by the photodetector; and
[0035] - conversion of the output reference electrical signals and of each signal target electrical output respectively in the reference error signal and in the target error signal(s), so as to keep the optical delay of the interferometer constant and to keep a frequency of the target optical signal(s) constant, depending on the reference and target error signals.
[0036] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which: - [Fig.1] [Fig.1] is a diagram of an optical system according to the invention; - [Fig.2] [Fig.2] is a diagram of a stability transfer device according to the invention; and - [Fig. 3] [Fig. 3] is a flowchart of an optical stabilization method according to the invention.
[0037] Throughout this description, "equal to" means a relationship of equality plus or minus the indicated range of variation or uncertainty. In the absence of an indicated range of variation, the range of variation is plus or minus 5%.
[0038] Fig. 1 represents schematically an optical system 5. The optical system 5 advantageously comprises a reference light source 10, as well as two target light sources 11 and 12.
[0039] The light sources 10, 11 and 12 are advantageously monochromatic sources. In particular, the light sources 10, 11 and 12 are laser sources.
[0040] The reference light source 10 is advantageously a source configured to emit a Soref reference optical signal, originating from a reference atomic transition, which makes it possible to obtain a Soref reference optical signal of frequency The reference atomic transition frequency (foref) is constant, meaning its relative variation is less than or equal to 1012 over measurement times between 1 and 10,000 s. Advantageously, the reference atomic transition is that of acetylene. The reference light source is then configured to emit a reference optical signal (Soref) with a foref frequency of 195.337 THz, corresponding to a wavelength (Xoref) of 1542.38 nm. Of course, other reference atomic transitions besides acetylene can be used to generate the reference optical signal (Soref).
[0041] The target light sources 11 and 12 are, for example, laser diodes. The target light sources 11 and 12 are configured to emit target optical signals. Advantageously, the target light source 11 is configured to emit an auxiliary target optical signal Soi and a main target optical signal Soi', of frequency foi. Similarly, the target light source 12 is configured to emit an auxiliary target optical signal SO2 and a main target optical signal SO2' of frequency fo2. Advantageously, in practice, the target light sources 11 and 12 each emit a single initial optical signal of frequency foi, respectively fo2, which is then separated to form the auxiliary target optical signal Soi, respectively SO2, and the main target optical signal Soi', respectively So2'.
[0042] The target light sources 11 and 12 are less stable than the reference light source, i.e., the relative variation of the frequencies fo and fo2 is much greater, i.e., at least twice greater than 1012 over measurement times between 1 and 10,000 s. The frequencies fo and fo2 are distinct from the frequency foref of the reference optical signal Soref. The frequencies fo1 and fo2 are advantageously distinct from each other.
[0043] In the example described here, the frequency fol is equal to 187.4 THz, corresponding to a wavelength Xoi of 1.6 pm, and the frequency fo2 is equal to 305.9 THz, corresponding to a wavelength Xo2 of 980 nm. The wavelengths Xoi and Xo2 are thus separated by several hundred nanometers, and the wavelengths Xoref and Xo2 are also separated by several hundred nanometers.
[0044] In an alternative not shown, system 5 comprises a single target light source, or more than two target light sources.
[0045] The system 5 further comprises an optical stability transfer device 16, associated with the light sources 10, 11, and 12. The optical stability transfer device 16 comprises an interferometer 20, a photodetector 22, disposed at the output of the interferometer 20, and a control unit 24, electrically connected to the photodetector 22. The system 5 is configured to stabilize frequencies within a frequency range or spectral range, also called the operating frequency range, which is as wide as possible, corresponding, for example, to an octave. optical, that is to say, for a given frequency, an interval ranging from that frequency to twice that frequency.
[0046] The interferometer 20 comprises an acousto-optical filter 26, a first arm 31 and a second arm 32, the acousto-optical filter being disposed at the input of arms 31 and 32, and an optical coupler 34, disposed at the output of arms 31 and 32.
[0047] The interferometer 20 is advantageously a Mach-Zehnder type interferometer.
[0048] The acousto-optic filter 26 is advantageously a broadband acousto-optic filter. The acousto-optic filter 26 advantageously comprises an acoustic wave emitter 36, visible in [Fig. 2], for example a piezoelectric transducer, in contact with a filtering element 38 made of a material having acousto-optic properties, for example a paratellurite crystal. The acousto-optic filter 26 is advantageously connected to the reference light sources 10 and target light sources 11 and 12 by optical fibers 33a, 33b, 33c, respectively. The acousto-optic filter 26 is configured to receive optical signals and to emit a plurality of acoustic signals of distinct and predetermined frequencies and amplitudes in order to diffract the optical signals it receives. More specifically, it is the transmitter 36 which is configured to emit the plurality of optical signals, which then propagate into the filtering element 38.To this end, each acoustic signal emitted by the acousto-optic filter 26 is associated with a unique optical signal received by the acousto-optic filter 26. In other words, a single acoustic signal, of predetermined frequency, is independently associated with a single optical signal. By independently, we mean that the association of an acoustic signal with an optical signal is independent of other acoustic and / or optical signals.
[0049] The arms 31 and 32 are configured to receive and propagate optical signals transmitted and diffracted at the output of the acousto-optical filter 26, and to impose a predetermined optical delay T between the optical signals propagating in arm 31 and the optical signals propagating in the second arm 32. For this purpose, arm 31 advantageously has a predetermined length. Advantageously, arm 31 includes a waveguide 40 of predetermined length L. The waveguide 40 is, for example, an optical fiber.
[0050] Advantageously, the arm 31 further includes a piezoelectric stretcher 42, configured to stretch the waveguide 40.
[0051] Advantageously, the arm 31 further comprises an injection module 44, connected at the input of the waveguide 40, and an output module 45, connected at the output of the waveguide 40. The injection module 44 allows optical signals to be injected into the input of the waveguide 40 in such a way as to minimize losses, and the output module 45 allows optical signals to be extracted from the output of the waveguide 40, also in such a way as to minimize losses.
[0052] The second arm 32 is for example made in free space, that is to say that the signals which propagate through the arm 32 propagate in the air.
[0053] The optical coupler 34 is for example a polarization splitter cube or a broadband coupler, advantageously with a coupling ratio of 50 / 50.
[0054] The photodetector 22 is for example a photodiode, possibly a plurality of photodiodes.
[0055] The control unit 24 advantageously comprises a correction module 46 for the interferometer 20 and a correction module 48 for each target light source 11, 12, shown in [Fig. 2]. The correction module 46 for the interferometer 20 and the correction module 48 for each target light source 11, 12 are advantageously each implemented as a programmable logic component, such as an FPGA (Field Programmable Gate Array), or as an integrated circuit, such as an ASIC (Application-Specific Integrated Circuit).
[0056] In an alternative not shown, the control unit 24 includes an information processing unit formed, for example, of a memory and a processor associated with the memory. The correction module 46 of the interferometer 20 and the correction module 48 of each target light source 11, 12 are then advantageously each implemented as software, or a software component, executable by the processor.
[0057] The memory of the control unit 24 is then capable of storing interferometer correction software and correction software for each target light source.
[0058] When the control unit is implemented in the form of one or more software programs, that is, in the form of a computer program, also called a computer program product, it is further capable of being stored on a computer-readable medium (not shown). A computer-readable medium is, for example, a medium capable of storing electronic instructions and being connected to a bus of a computer system. For example, a readable medium is an optical disc, a magneto-optical disc, ROM, RAM, any type of non-volatile memory (e.g., FLASH or NVRAM), or a magnetic card. A computer program comprising software instructions is then stored on the readable medium.
[0059] The correction module 46 of the interferometer 20 advantageously comprises a demodulator 52a, a filter 55a and a corrector 56a.
[0060] The correction module 46 of the interferometer 20 is advantageously connected to the piezoelectric stretcher 42, in order to control the piezoelectric stretcher 42 and to control the length L of the waveguide 40.
[0061] Alternatively or in addition, the correction module 46 of the interferometer 20 is advantageously connected to the acousto-optical filter 26, in order to control the phase of the acoustic signals emitted by the acousto-optical filter 26.
[0062] The correction module 46 of the interferometer 20 is advantageously connected to a temperature control module 58, included in the optical system 5. The temperature control module 58 is, for example, a Peltier effect module, on which the interferometer 20 is placed. The correction module 46 of the interferometer 20 is advantageously configured to control a temperature in the temperature control module 58, and thus, a temperature of the interferometer 20.
[0063] The correction module 48 of each target light source 11, 12 advantageously comprises a demodulator, a filter and a corrector for each target light source 11 and 12. In other words, the correction module 48 of each target light source 11, 12 comprises a demodulator 52b, a filter 55b and a corrector 56b, associated with the target light source 11, and a demodulator 52c, a filter 55c and a corrector 56c, associated with the target light source 12. The filters 55a, 55b and 55c are advantageously low-pass filters, and the correctors 56a, 56b and 56c are advantageously PID type correctors.
[0064] The correction module 48 is advantageously connected to each target light source 11, 12, in order to control the fob frequency fo2 of the optical signals Soi and SO2 emitted by the target light source 11 and the target light source 12, respectively.
[0065] The system 5 further comprises an optical combining module 60, external to the optical stability transfer device 16. The optical combining module 60 is, for example, a frequency adder or a frequency subtractor. If the optical combining module 60 is a frequency adder, it is configured to combine optical signals into a combined optical signal, whose frequency is the sum of the frequencies of the optical signals. If the optical combining module 60 is a frequency subtractor, it is configured to combine optical signals into a combined optical signal, whose frequency is the difference between the frequencies of the optical signals. The optical combining module 60 is, for example, a nonlinear crystal.
[0066] In an alternative not shown, the optical combination module 60 includes a frequency modulator, in order to modulate an optical signal, and a frequency summing or subtracting device, which adds or subtracts the optical signal modulated by the modulator, with another optical signal.
[0067] The operation of system 5 is now described in detail. In this context, an optical stabilization method, implemented by device 16, is also described.
[0068] The reference light source 10 is powered by an electric supply current and emits the reference optical signal Soref. The target light source 11 is powered by an electric supply current and emits the auxiliary target optical signal Soi and the main target optical signal Soi'. The target light source 12 is powered and advantageously emits the auxiliary target optical signal So2 and the main target optical signal So2' in a manner similar to that described for the target light source 11, i.e., by separating a single optical signal.
[0069] Advantageously, the reference optical signal So ref, and the auxiliary target optical signals Soi and So2 propagate respectively in the optical fiber 33a, 33b, 33c linking respectively the reference light source 10 and the target light sources 11, 12 to the acousto-optic filter 26.
[0070] The acousto-optical filter 26 receives the reference optical signal Sref and the auxiliary target optical signals Soi and So2 during a reception stage S102.
[0071] The acousto-optic filter 26 emits a plurality of acoustic signals of distinct frequencies and amplitudes during an emission step S104. Each acoustic signal emitted during the emission step S104 is associated with a unique optical signal from among the reference optical signal Soref and the target optical signals Soi and So2, as described previously. Thus, in the example of Figures 1 and 2, the acousto-optic filter 26 is configured to emit three distinct acoustic signals: a reference acoustic signal S^f, associated with the reference optical signal Soref; a target acoustic signal Sab associated with the target optical signal Soi; and a target acoustic signal S^, associated with the target acoustic signal So2. In particular, the reference acoustic signal S^f, the target acoustic signal Sai, and the target acoustic signal Sa2 have distinct frequencies f^f, fal, and fa2, respectively.The frequencies f^f, fal and fa2, for example, are between 10 and 100 MHz.
[0072] The acousto-optical filter 26 then diffracts the reference optical signal Soref and the auxiliary target optical signals Soi and So2 during a diffraction step S106. The type of diffraction is advantageously Bragg diffraction, each optical signal Soref, Soi, So2 being diffracted through its interaction with the acoustic signal S^f, Sai, Sa2 with which it is associated in the acousto-optical filter 26. The diffraction step S106 allows the formation, for each optical signal, of a zero-order and a first-order optical signal. In addition, the first-order optical signal is frequency-shifted by the Doppler effect, by the frequency of the acoustic signal with which the optical signal interacted. More precisely, the reference optical signal Soref is diffracted to form a zero-order reference optical signal Soref(0) and a first-order reference optical signal Soref(1). The zero-order optical reference signal has a The frequency is equal to fOTef, and the first-order reference optical signal has a frequency equal to f0 + f1. The target optical signal Si is diffracted to form a zero-order target optical signal Si(0), with frequency f0b, and a first-order target optical signal Si(1), with frequency f0 + fi. Similarly, the target optical signal S02 is diffracted to form a zero-order target optical signal S02(0), with frequency f02, and a first-order target optical signal S02(1), with frequency f02 + fi2. The diffraction of each optical signal S0, Si, S2 is independent of the other optical signals. In particular, the diffraction efficiency of a given optical signal S0, Si, Si2 depends only on the frequency and amplitude of the acoustic signal Sf, Si, Si2.
[0073] At the output of the acousto-optical filter 26, the arm 31 receives and propagates optical signals of the same given order among zero-order and first-order signals, and the arm 32 receives and propagates the reference and target optical signals of the other given order, during a reception and propagation step S108. In the example of Figures 1 and 2, the zero-order reference optical signal Soref(0), and the zero-order target optical signals Soi(0) and So2(0) are received and propagated in the arm 31, more precisely injected into the waveguide 40 via the injection module 44.
[0074] The first-order reference optical signal Soref(l), as well as the first-order target optical signals Soi( 1 ) and So2( 1 ) are received and propagated in the arm 32, advantageously in free space.
[0075] The length L of the fiber 40 induces the optical delay T between zero-order optical signals propagating in the arm 31 and first-order optical signals propagating in the arm 32. The optical delay T creates a spectral transfer function periodic in 1 / T. L is advantageously between 2 and 100 m. It is thus possible to discriminate optical signals with frequencies spaced proportionally to 1 / T, advantageously every 2 to 50 MHz, depending on the value of the optical delay T chosen. The presence of the waveguide 40 in the arm 31 makes it easy to adjust the optical delay T, simply by changing the length L, without having to modify the spatial arrangement of the various components of the interferometer 20.Furthermore, the 40 waveguide, particularly if it is a polarization-maintaining fiber, allows a delay T of several tens of meters with very low propagation losses, over a spectral range covering several hundred nanometers, optimal spatial overlap, and polarization conservation.
[0076] Zero-order and first-order optical signals are combined in a combination step S110. Advantageously, the zero-order optical signals Soref(0), Soi(0) and So2(0) propagate from the waveguide 40 to the output module 45 before being sent to the optical coupler 34. The first-order optical signals Soref(1), Soi(1) and So2(1) advantageously propagate directly to the optical coupler 34.
[0077] The zero-order reference optical signals Soref(0) and Soref(1), the zero-order target optical signals Soi(0) and Soi(1), and the zero-order target optical signals So2(0) and So2(1) are respectively combined into a combined reference optical signal Soref(comb), a recombined target optical signal Soi(comb), and a combined target optical signal So2(comb). Furthermore, due to the frequency shift of the first-order optical signals, in addition to the interference caused by recombination, the recombined signals Soref(comb), Soi(comb), and So2(comb) form optical beats with a frequency equal to the frequency difference between the zero-order and first-order optical signals. In other words, the recombined reference optical signal Soref(comb) has a beat frequency f^f, the recombined target optical signal Soi(comb) has a beat frequency fa[ and the recombined target optical signal So2(comb) has a beat frequency fa2.The recombined optical signals Soref(comb), Soi(comb) and So2(comb) thus have a distinct beat frequency.
[0078] An amplitude of the beat signal, in other words of the recombined optical signals Soref(comb), Soi(comb) and So2(comb) is independent of the other recombined optical signals, and depends in particular on the amplitude of the acoustic signals Saref, Sai and Sa2, in other words, on the power of the acoustic signals 8^, Sa[ and Sa2.
[0079] The combined reference optical signal Soref(comb), the combined target optical signal Soi(comb), and the combined target optical signal So2(comb) are converted respectively into the output reference electrical signal Seref, the target electrical signal Sei, and the target electrical signal Se2 by the photodetector 22 during a conversion step S112. Advantageously, the recombined optical signals Soref(comb), Soi(comb), and So2(comb) are sent to the same photodetector 22 without being spatially separated. Indeed, since the beat frequencies are distinct for the three combined optical signals Soref(comb), Soi(comb), and So2(comb), they can be converted into three independent output electrical signals without the need for spatial separation to avoid noise or crosstalk.
[0080] The output reference electrical signal Seref is converted into a reference error signal Eref, and the target electrical signals Sei and Se2 are converted into target error signals Eiet E2 by the control unit 24 during a conversion step SI 14.
[0081] Advantageously, the output reference electrical signal Seref is received by the correction module of the interferometer 46. Advantageously, the output reference electrical signal Seref is received by the demodulator 52a, which converts the output reference electrical signal Seref into the reference error signal Eref. Advantageously, the reference error signal Eref is filtered by the low-pass filter 55a and then received by the corrector 56a.
[0082] Similarly, the target electrical signal Sei and the target electrical signal Se2 are received by the correction module 48 from each target light source 11, 12. Advantageously, the target electrical signal Sei is received by the demodulator 52b, which converts the output target electrical signal Sei into the target error signal Ei. The target error signal Ei is then filtered by the low-pass filter 55b and received by the corrector 56b. The target electrical signal Se2 is received by the demodulator 52c, which converts the output target electrical signal Se2 into the target error signal E2. Advantageously, the target error signal E2 is filtered by the low-pass filter 55c and received by the corrector 56c.
[0083] Advantageously, after receiving the error signals Eref, Ei and E2, the correctors 56a, 56b and 56c emit control signals during a control step SI 16. The corrector 56a emits a control signal in order to control the piezoelectric stretcher 42, so as to adjust the length of the arm 31. For example, the piezoelectric stretcher 42 tensions the waveguide 40 to maintain its length L constant.
[0084] Alternatively or in addition, the compensator 56a outputs a control signal to control the temperature control module 58, for example, to maintain a constant temperature in the temperature control module 58, and therefore a constant interferometer temperature. The control signal is represented by a dashed arrow in [Fig. 2]. This allows, in particular, compensation for changes in the optical delay T due to thermal expansion.
[0085] Alternatively or in addition, the corrector 56a emits a control signal to control the acousto-optical filter 26, more precisely to adjust the phase of the acoustic signals S^f, Sai, and Sa2 emitted by the acousto-optical filter 26. The control signal is represented by a dashed arrow in [Fig. 2]. In particular, the phase of the acoustic signals S^f, Sai, and Sa2 can be chosen to compensate for changes in the optical delay T.
[0086] Thus, the control unit 24 adjusts at least one of the following parameters according to the reference error signal: the length L of the arm 31, a temperature of the interferometer 20 and a phase of the acoustic signals S^f, Sai and Sa2 emitted by the acousto-optical filter 26, in order to maintain the optical delay T of the interferometer 20 constant.
[0087] The corrector 56b outputs a control signal to adjust at least one of the following parameters of the target light source 11: the temperature of the target light source 11, the electrical current supplying the target light source 11, and the voltage of the electrical current supplying the target light source 11, in order to maintain the frequency of the target optical signal Soi constant. Alternatively, the control signal allows adjustment of other parameters of the target light source 11, for example, in the case where the light source includes a cavity, a cavity length, or an electrical voltage applied to an electro-optical crystal, if the light source 11 includes such a crystal.
[0088] Alternatively, the corrector 56b emits several control signals in order to adjust several parameters of the target light source 11 simultaneously.
[0089] Similarly, the corrector 56c emits a control signal in order to adjust at least a temperature of the target light source 12, an electrical intensity of the electrical current supplying the target light source 12, and a voltage of the electrical current supplying the target light source 12, to maintain the frequency of the target optical signal So2 constant.
[0090] Alternatively, as described for the corrector 56b, the corrector 56c emits several control signals in order to adjust several parameters of the target light source 12 simultaneously.
[0091] The frequency foi and fo2 of the optical signals Soi and So2 is thus kept constant, that is to say that the relative variation of the frequencies fol and fo2 is less than or equal to 10 12 over measurement times between 1 and 10000 s, which is the same as the relative variation of the frequency fOTef of the reference optical signal Soref from the reference light source 10.
[0092] Advantageously, the control unit 24 further adjusts the amplitude of the acoustic signals Saref, Sai, and Sa2, in other words, the acoustic power of the signals Sf, Sa1, and Sa2, in order to optimize the amplitude of the recombined optical signals SOref(comb), Soi(comb), and So2(comb), via a control signal. This optimization is performed independently for each of the three recombined optical signals Soref(comb), Soi(comb), and So2(comb). It is carried out by adjusting the acoustic power of the signals Sf, Sai, and Sa2 so as to adjust the diffraction efficiency of the optical signals Soref, Soi, and So2. Thus, the power between the zero-order reference optical signals Soref(0) and a Soref(l), the zero-order target optical signals Soi(0) and a Soi(1), and the zero-order target optical signals So2(0) and a So2(l) are equal at the time of their recombination on the photodetector 22.This allows the power of the error signals ErefEiet E2 to be optimized and ensures that the stability transfer is effective regardless of the frequency of the target optical signal, within the operating frequency range of device 16. In particular, such optimization makes it possible to correct imperfections of the interferometer 20, related to the use of a wide range of frequencies.
[0093] The reference source 10 thus ensures that the interferometer 20 operates in the same way over time, regardless of external conditions, and thus to be able to use it to precisely measure the frequency variations of the target optical signals Soi, So2 in order to stabilize their frequency fol and fo2.
[0094] Stabilizing the frequencies foi and fo2, from the auxiliary optical signals Soi and So2, makes it possible in particular to stabilize the frequency of the main target optical signals Soi' and So2'. Indeed, advantageously, the control signal emitted by the correction module 48 of each target light source 11, 12 makes it possible to adjust the frequency of the initial optical signal emitted by each target light source 11, 12, an initial signal which is separated into main optical signals Soi' and So2' and auxiliary optical signals Soi and So2, as described above.
[0095] The main target optical signals Soi' and So2' are advantageously sent to the optical combination module 60. The optical combination module 60 combines the main target optical signals Soi' and So2' into a combined optical signal Soc. In the case where the optical combination module 60 is a frequency summing , it is possible to obtain a combined optical signal Soc whose frequency fœ is in the visible range by summing the main target optical signal Soi' of frequency fol equal to 187.4 THz and the main target optical signal So2' of frequency fo2 equal to 305.9 THz.
[0096] The combined optical signal Soc thus has a stability frequency foc comparable to a reference light source, because the frequencies fol and fo2 are stabilized by means of the device 16. The combined optical signal Soc is used for example to carry out measurements requiring high stability of the light source enabling the measurement, for example because of a long integration time, as in inertial navigation applications or in gyroscopic sensors, or in applications involving quantum states, for example in the interrogation of quantum memories.
[0097] Any feature described for an embodiment or variant in the foregoing may be implemented for the other embodiments and variants described above, provided that it is technically feasible.
Claims
1. Demands Optical stability transfer device (16) comprising: an interferometer (20) comprising: • an acousto-optical filter (26), configured for: • receive a reference optical signal (Soref), emitted by a reference light source (10), and at least one target optical signal (Sob So2), the target optical signal or each target optical signal (Soi, So2) being emitted by a respective target light source (11, 12), a frequency (fob fo2) of the target optical signal or each target optical signal (Sob So2) being distinct from a frequency (foref) of the reference optical signal (SOTef); • emit a plurality of acoustic signals (S^f, Sab Sa2) of distinct frequency (f^, fai, f^) and amplitude, each acoustic signal (S^* Sab Sa2) being independently associated with a single optical signal among the reference optical signal (Soref) and the target optical signal(s) (Sob So2); and • independently diffract each optical signal (Soref, Sob So2) to form respectively zero-order reference and target optical signals (Soref(0), Sol(0), So2(0)) and first-order (Soref(1), Soi(1), So2(1)), • a first arm (31), configured to receive and propagate the reference and target optical signals of the same given order among zero order and one order; • a second arm (32), configured to receive and propagate the reference and target optical signals of the other given order, the first and second arms (31, 32) being configured to impose a predetermined optical delay (T) between the optical signals propagating in the first arm (31) and the optical signals propagating in the second arm (32); • an optical coupler (34), disposed at the output of the first and second arms (31, 32), and configured to combine the zero-order reference optical signals (Soref(0)) and a (Soref(l)) into a recombined reference optical signal (Soref(comb)) on the one hand, and the zero-order target optical signal(s) (Soi(0),So2(0)) and a (Soi(l),So2(l)) into a recombined target optical signal(s) (Soi(comb), So2(comb)) on the other hand; - a photodetector (22), configured to convert the recombined reference optical signal (Soref(comb)) and the or each recombined target optical signal (Soi(comb), So2(comb)) respectively into an output reference electrical signal (Seref) and into an output target electrical signal or signals (Sei, Se2);and - a control unit (24), configured to convert the output reference electrical signal (Seref) and the output target electrical signal(s) (Seb Se2) respectively into a reference error signal (Eref) and a target error signal (Eb E2), so as to keep the optical delay (T) of the interferometer (20) constant and to keep the frequency (fob fo2) of the target optical signal(s) (Sob So2) constant, as a function of the reference error signal(Eref) and target error signal(Eb E2).
2. Device (16) according to claim 1, wherein the control unit (24) is further configured to adjust the amplitude of the acoustic signals (S^f, Sab Sa2) as a function of the reference error signals (Eref) and target (Eb E2).
3. A device (16) according to any one of claims 1 to 2, wherein the first arm (31) has a predetermined length (L), and wherein the control unit (24) comprises a correction module (46) for the interferometer (20), configured to receive the reference error signal (Eref) and to adjust at least one of the following parameters as a function of the reference error signal (Eref): the length (L) of the first arm (31), a temperature of the interferometer (20) and a phase of the acoustic signals (S^, Sab S^) emitted by the acousto-optic filter (26), in order to keep the optical delay (T) of the interferometer (20) constant.
4. Device (16) according to any one of claims 1 to 3, wherein the control unit (24) comprises a correction module (48) for the target light source or each target light source (11, 12), configured to receive the target error signal or each target error signal (Eb E2) and to adjust at least one of the following parameters as a function of the target error signal or each target error signal (Eb E2): a temperature of the target light source or at least one target light source (11, 12), an electric intensity of an electric current supplying the target light source or at least one target light source (11, 12), and a voltage of the electric current supplying the target light source or at least one target light source (11, 12), to maintain the frequency (fol, fo2) of the target optical signal or each target optical signal (Soi, So2) constant.
5. Device (16) according to any one of claims 1 to 4, wherein the first arm (31) comprises a waveguide (40), configured so that reference and target optical signals of the same given order among zero order and first order propagate through the waveguide (40).
6. Device (16) according to any one of claims 1 to 5, wherein the first arm (31) is configured to receive and propagate zero-order reference and target optical signals (Soref(0), Soi(0), So2(0)) and the second arm (32) is configured to receive and propagate first-order reference and target optical signals (Soref(l), Sol(l), So2(l)).
7. Optical system (5) comprising:
8.
9.
10. - a reference light source (10), configured to emit a reference optical signal (Soref); - at least one target light source (11, 12), the target light source or sources (11, 12) being configured to emit a target optical signal (Sob So2), the target optical signal or signals (Sob So2) having a frequency (fob foi) of the °u of each target optical signal (Sob So2) distinct from a frequency (fOTef) of the reference optical signal (SOTef); and - an optical stability transfer device (16) according to any one of claims 1 to 6, the acousto-optical filter (26) being configured to receive the target optical signal or each target optical signal (Sob So2) emitted by the target light source or each target light source (11, 12) and the reference optical signal (SOTef) emitted by the reference light source (10). System (5) according to claim 7, wherein the reference and target light sources (11, 12) are laser sources. System (5) according to any one of claims 7 to 8, comprising a plurality of target light sources (11, 12), preferably more than two target light sources (11, 12), each target light source (11, 12) being configured to emit a target optical signal (Sob So2) of frequency (fob fo2) distinct from the other target light sources (11, 12). System (5) according to claim 9, wherein the target optical signal (Soi, So2) of each target light source is an auxiliary target optical signal (Sob So2), each target light source (11, 12) being configured to further emit a main target optical signal (Soi', So2'), of frequency (fob fo2) identical to the frequency (foi, fo) of the auxiliary target optical signal (Sob So2) emitted by the target light source (11, 12), and further comprising an optical combining module (60), configured to combine the main target optical signals (Soi', So2') into a combined optical signal (Sœ), of frequency (fœ) a combined frequency, distinct from the frequencies of the main target optical signals (fob fo2).
11. System (5) according to claim 10, wherein the optical combining module (60) is a frequency summing or subtracting module.
12. An optical stabilization method, implemented by a device (16) according to any one of claims 1 to 6, the method comprising the following steps: reception (S 102) of a reference optical signal (Soref) and at least one target optical signal (Sob So2), by the acousto-optical filter (26); emission (S 104) of the plurality of acoustic signals (Saref, Sab Sa2) by the acousto-optical filter (26); diffraction (S 106) of each optical signal (Soref, Sob So2) by the acousto-optical filter (26) to form the zero-order (Soref(0)) and first-order (Soref(l)) reference optical signals, and the zero-order (Sol(0),So2(0)) and first-order (Sol(l),So2(l)) target optical signal(s); reception and propagation (S 108) of reference and target optical signals of the same given order among zero order and first order in the first arm (31) and of reference and target optical signals of the other given order in the second arm (32); combination (SI 10) of the zero-order reference optical signals (Soref(0)) and one (Soref(l)) into the recombined reference optical signal (Soref(comb)), and of the zero-order target optical signals (Soi(0),So2(0)) and one (Soi(l),So2(l)) into the recombined target optical signal(s) (Soi(comb), So2(comb)), by the optical coupler (34); conversion (SI 12) of the recombined reference optical signal (Soref(comb)) into the output reference electrical signal (Seref) and of each recombined target optical signal(s) (Soi(comb), So2(comb)) into the output target electrical signal(s) (Seb Se2) by the photodetector (22); and conversion (SI 14) of the electrical reference output signals (Seref) and of the or each electrical target output signal (Seb Se2) respectively into the reference error signal (Eref) and into the target error signal(s) (Ei, E2), so as to keep the optical delay (T) of the interferometer (20) constant and to keep a frequency (foi, €2) of the or each optical target signal (Sob So2) constant, as a function of the reference error signal (Eref) and target error signal(Eb E2).