Laser frequency stabilization device based on active feedback control

Abstract

The application provides a laser frequency stabilization device based on active feedback control, comprising: a local laser configured to generate and output a laser signal; an optical phase modulator configured to modulate a microwave signal onto the laser signal to obtain a modulated optical signal; an optical filter configured to perform a notch filtering on the modulated optical signal; a photodetector configured to perform beat frequency on the notch filtered optical signal to obtain a first radio frequency signal; a radio frequency amplifier configured to amplify the first radio frequency signal to obtain a second radio frequency signal; a radio frequency power divider configured to divide the second radio frequency signal into two third radio frequency signals with equal power, and input one of the third radio frequency signals into the optical phase modulator; a feedback control loop configured to mix a radio frequency reference signal with the other third radio frequency signal input into the radio frequency power divider to generate an error signal, and generate a feedback signal based on the error signal to adjust the frequency of the laser signal output by the local laser.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser frequency stabilization, in particular to a laser frequency stabilization device based on active feedback control. BACKGROUND

[0002] Ultra-stable lasers with extremely high frequency stability have important applications in scientific measurement, coherent communication and frequency metrology. However, the current lasers are generated by resonant cavities, and the frequency stability of the generated laser is affected by the stability of the resonant cavity. The resonant cavity of the laser is an active cavity, and the light transmitted in the cavity needs to satisfy the condition that the gain is greater than the loss to generate a stable lasing light signal. However, the active resonant cavity is easily affected by factors such as current noise, environmental noise and temperature fluctuations, which reduces the stability of the resonant cavity and further deteriorates the frequency stability and linewidth of the generated laser. Passive vibration isolation and active temperature control can improve the frequency stability of the laser, but the effect is limited. The linewidth of the current commercial laser is in the order of kHz to MHz, and the frequency instability is generally greater than 10^-12@1s, which is difficult to meet the needs of some application scenarios that require high frequency stability. SUMMARY

[0003] In view of the above problems, the present application provides a laser frequency stabilization device based on active feedback control.

[0004] The embodiment of the present application provides a laser frequency stabilization device based on active feedback control, which comprises: a local oscillator laser configured to generate and output a laser signal; an optical phase modulator configured to modulate a microwave signal onto the laser signal to obtain a modulated optical signal; an optical filter configured to perform notch filtering on the modulated optical signal to obtain a notch-filtered optical signal; a photodetector configured to perform beat frequency on the notch-filtered optical signal to obtain a first radio frequency signal; a radio frequency amplifier configured to amplify the first radio frequency signal to obtain a second radio frequency signal; a radio frequency power divider configured to divide the second radio frequency signal into two third radio frequency signals with equal power, and input one of the third radio frequency signals into the optical phase modulator; a feedback control loop configured to mix a radio frequency reference signal with the other third radio frequency signal input into the radio frequency power divider to generate an error signal, generate a feedback signal based on the error signal, and input the feedback signal into the local oscillator laser to adjust the frequency of the laser signal output by the local oscillator laser.

[0005] According to an embodiment of the present disclosure, the feedback control loop comprises: a frequency mixer configured to mix the radio frequency reference signal with another third radio frequency signal input by the radio frequency power divider, to extract a change of the center angular frequency of the local laser relative to the center angular frequency of the optical filter, to obtain an error signal; and a controller configured to generate a feedback signal based on the error signal and feed back the feedback signal to a current input port or a tuning port of the local laser, to adjust the frequency of the laser signal output by the local laser, the frequency of the laser signal output by the local laser being equal to an absolute value of a difference between the center angular frequency of the optical filter and an angular frequency of the oscillating radio frequency signal or a sum of the difference and the angular frequency.

[0006] According to an embodiment of the present disclosure, the apparatus further comprises: an electro-optical modulator configured to input the laser signal output by the local laser after modulation; and the feedback control loop comprises: a frequency mixer configured to mix the radio frequency reference signal with another third radio frequency signal input by the radio frequency power divider, to extract a change of the center angular frequency of the local laser relative to the center angular frequency of the optical filter, to obtain an error signal; and a controller configured to generate a feedback signal based on the error signal and feed back the feedback signal to the electro-optical modulator, to adjust the frequency of the laser signal output by the local laser, the frequency of the laser signal output by the local laser being equal to an absolute value of a difference between the center angular frequency of the optical filter and an angular frequency of the oscillating radio frequency signal or a sum of the difference and the angular frequency.

[0007] According to an embodiment of the present disclosure, the feedback control loop comprises: a frequency mixer configured to mix the radio frequency reference signal with another third radio frequency signal input by the radio frequency power divider, to extract a change of the center angular frequency of the local laser relative to the center angular frequency of the optical filter, to obtain an error signal; a controller configured to generate a feedback signal based on the error signal; and a combiner configured to combine the third radio frequency signal input by the radio frequency power divider and the feedback signal into one feedback input to a radio frequency input port of the optical phase modulator, to adjust the frequency of the laser signal output by the local laser, the frequency of the laser signal output by the local laser being equal to an absolute value of a difference between the center angular frequency of the optical filter and an angular frequency of the oscillating radio frequency signal or a sum of the difference and the angular frequency.

[0008] According to an embodiment of the present disclosure, the feedback control loop comprises: a frequency divider configured to divide the other third radio frequency signal input by the radio frequency power divider; a frequency mixer configured to mix the radio frequency reference signal with the third radio frequency signal divided by the frequency divider, to extract a change of the center angular frequency of the local laser relative to the center angular frequency of the optical filter, to obtain an error signal; and a controller configured to generate a feedback signal based on the error signal and feed back the feedback signal to a current input port or a tuning port of the local laser, to adjust the frequency of the laser signal output by the local laser, the frequency of the laser signal output by the local laser being equal to an absolute value of a difference between the center angular frequency of the optical filter and an angular frequency of the oscillating radio frequency signal or a sum of the difference and the angular frequency.

[0009] According to an embodiment of the present disclosure, the feedback control loop comprises: a frequency multiplier configured to multiply the other third radio frequency signal input by the radio frequency power divider; a frequency mixer configured to mix the radio frequency reference signal with the multiplied third radio frequency signal to extract the change of the center angular frequency of the local laser relative to the center angular frequency of the optical filter, to obtain an error signal; and a controller configured to generate a feedback signal from the error signal and feed the feedback signal into the current input port or the tuning port of the local laser to adjust the frequency of the laser signal output by the local laser, wherein the frequency of the laser signal output by the local laser is equal to the absolute value of the difference between the center angular frequency of the optical filter and the angular frequency of the radio frequency oscillation signal or the sum of the two.

[0010] According to an embodiment of the present disclosure, the device further comprises an optical coupler arranged between the output of the local laser and the input of the optical phase modulator and configured to couple the laser signal output by the local laser to output a first super-stable laser having the same angular frequency as the local laser.

[0011] According to an embodiment of the present disclosure, the device further comprises an acousto-optic frequency shifter or an intensity modulator or a phase modulator configured to process the first super-stable laser output by the optical coupler and the third radio frequency signal output by the radio frequency power divider to output a second super-stable laser after frequency shift.

[0012] According to an embodiment of the present disclosure, the optical filter further comprises a transmission filter port configured to output a third super-stable laser having the same center angular frequency as the optical filter, wherein, in the case where the frequency of the laser signal output by the local laser is equal to the absolute value of the difference between the center angular frequency of the optical filter and the angular frequency of the oscillation radio frequency signal, the third super-stable laser comprises the +1 order sideband of the modulated optical signal after transmission filtering by the optical filter; and in the case where the frequency of the laser signal output by the local laser is equal to the sum of the center angular frequency of the optical filter and the angular frequency of the oscillation radio frequency signal, the third super-stable laser comprises the -1 order sideband of the modulated optical signal after transmission filtering by the optical filter.

[0013] According to an embodiment of the present disclosure, the optical filter further comprises a notch filter port, wherein, in the case where the frequency of the laser signal output by the local laser is equal to the absolute value of the difference between the center angular frequency of the optical filter and the angular frequency of the oscillation radio frequency signal, the notch filter port is configured to output the optical carrier and the -1 order sideband of the modulated optical signal after notch filtering; and in the case where the frequency of the laser signal output by the local laser is equal to the sum of the center angular frequency of the optical filter and the angular frequency of the oscillation radio frequency signal, the notch filter port is configured to output the optical carrier and the +1 order sideband of the modulated optical signal after notch filtering.

[0014] The laser frequency stabilization device based on active feedback control provided by the present application has at least the following technical effects:

[0015] The radio frequency reference signal is mixed with the third radio frequency signal input into the radio frequency power divider through a feedback control loop to generate an error signal, a feedback signal is generated based on the error signal, and the feedback signal is input into the local laser to adjust the frequency of the laser signal output by the local laser. Under the action of the feedback loop, the frequency can be kept stable, so that the oscillator system can always be in a stable working state and continuously output super-stable laser. Moreover, the feedback loop can further suppress the phase noise of the laser signal output by the local laser, and the phase noise suppression effect is superimposed on the suppression effect without feedback control, so that the output super-stable laser has lower phase noise.

[0016] Due to the addition of the feedback control loop, the frequency of the local laser after locking is equal to the sum or difference of the center frequency of the optical filter and the frequency of the oscillating radio frequency signal. The output of the local laser after locking is super-stable laser.

[0017] The laser frequency obtained by the device has greater freedom. By tuning the radio frequency frequency of the optoelectronic oscillator, the frequency of the super-stable laser can be arbitrarily tuned.

[0018] The device can simultaneously obtain two single-frequency super-stable lasers at different frequencies, one of which has the same frequency as the local laser, and the other of which has the same frequency as the center frequency of the optical filter.

[0019] The device can divide the oscillating radio frequency signal to reduce the locking difficulty of the feedback control loop, improve the stability of the system after locking, and further reduce the frequency stability requirement of the local laser source itself. The device can also multiply the oscillating radio frequency signal, amplify the error signal, and realize higher-precision feedback control. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application, taken in conjunction with the accompanying drawings, in which:

[0021] Figure 1 A structure diagram of a laser frequency stabilization device with active feedback control according to a first embodiment of the present application is schematically shown;

[0022] Figure 2 A structure diagram of a laser frequency stabilization device with active feedback control according to a second embodiment of the present application is schematically shown;

[0023] Figure 3 A structure diagram of a laser frequency stabilization device with active feedback control according to a third embodiment of the present application is schematically shown;

[0024] Figure 4A structure diagram of the active feedback control laser frequency stabilization device according to the fourth embodiment of the present application is schematically shown;

[0025] Figure 5 A structure diagram of the active feedback control laser frequency stabilization device according to the fifth embodiment of the present application is schematically shown;

[0026] Figures 6A-6D A spectrum diagram corresponding to each signal in the active feedback control laser frequency stabilization process according to the embodiments of the present application is schematically shown;

[0027] Figure 7 A phase noise comparison result diagram of the laser before and after the active feedback control laser frequency stabilization device stabilizes the frequency according to the embodiments of the present application is schematically shown;

[0028] Figure 8 A laser line width comparison result diagram of the laser before and after the active feedback control laser frequency stabilization device stabilizes the frequency according to the embodiments of the present application is schematically shown. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It is to be understood, however, that these descriptions are merely exemplary and are intended to illustrate the scope of the present application, not to limit it. In the following detailed description of the embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to one skilled in the art that the embodiments of the present application can be practiced without these specific details. In other instances, well-known structures and functions have not been described in detail in order to avoid obscuring aspects of the present application.

[0030] The terms used herein are merely used to describe specific embodiments, and are not intended to limit the present application. The terms "include" and "have" and the like used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0031] All terms used herein, including technical and scientific terms, have the same meanings as those generally understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having meanings consistent with the context of the present specification, and should not be interpreted in an idealized or overly formal manner.

[0032] In the case of using expressions similar to "at least one of A, B, and C, etc.", it should be generally interpreted as including one or more of the corresponding items (for example, "a system having at least one of A, B, and C" should include but not be limited to a system having A alone, a system having B alone, a system having C alone, a system having both A and B, a system having both A and C, a system having both B and C, and / or a system having A, B, and C together, etc.).

[0033] In the related art, in order to generate laser with higher frequency stability, a series of active control methods are proposed, including saturated absorption spectrum technology, fiber active frequency stabilization scheme, and PDH laser frequency stabilization technology based on super stable Fabry-Perot cavity. Among them, the saturated absorption spectrum technology locks the frequency of the laser with the absorption spectrum of the molecular atom, so it can only be applied to the frequency stabilization of a specific wavelength laser. The active frequency stabilization scheme based on the optical fiber locks the frequency of the laser with the long optical fiber, but the use of the long optical fiber reduces the detection bandwidth while improving the detection accuracy. At the same time, the optical fiber is easily affected by temperature changes and environmental noise, which deteriorates the frequency stability of the locked light source. The PDH frequency stabilization technology locks the frequency of the laser with the mode frequency of the super stable cavity, but it has high requirements for the frequency stability and linewidth of the locked laser. At the same time, the bandwidth of the lock is limited by the signal-to-noise ratio of the link and the bandwidth of the feedback excitation, and multiple feedback excitations are often needed to achieve a large feedback bandwidth. At the same time, the actual locking process of the PDH frequency stabilization technology is difficult, and it is easy to lose lock due to environmental disturbances. In addition, due to the principle of error signal generation, the active frequency stabilization scheme based on the optical fiber and the PDH laser frequency stabilization technology have poor response to low-frequency frequency fluctuations of the laser source, and cannot effectively detect and feedback control the low-frequency frequency fluctuations.

[0034] Therefore, the embodiments of the present disclosure provide an active feedback control based laser frequency stabilization device, which can include: a local oscillator laser configured to generate and output a laser signal; an optical phase modulator configured to modulate a microwave signal onto the laser signal to obtain a modulated optical signal; an optical filter configured to notch filter the modulated optical signal to obtain a notch filtered optical signal; a photodetector configured to beat the notch filtered optical signal to obtain a first radio frequency signal; a radio frequency amplifier configured to amplify the first radio frequency signal to obtain a second radio frequency signal; a radio frequency power divider configured to split the second radio frequency signal into two third radio frequency signals with equal power, and input one of the third radio frequency signals into the optical phase modulator; a feedback control loop configured to mix a radio frequency reference signal with the other third radio frequency signal input into the radio frequency power divider to generate an error signal, generate a feedback signal based on the error signal, and input the feedback signal into the local oscillator laser to adjust the frequency of the laser signal output by the local oscillator laser.

[0035] The device obtains an error signal by extracting the phase of the oscillating radio frequency signal, and outputs a feedback signal after the error signal passes through a feedback controller. The feedback signal adjusts the frequency of the local oscillator laser, and outputs a super stable laser signal.

[0036] The active feedback control based laser frequency stabilization device will be described below in conjunction with specific embodiments.

[0037] Figure 1A schematic diagram of a laser frequency stabilization device with active feedback control according to a first embodiment of the present invention is shown.

[0038] like Figure 1 As shown, in embodiments of this disclosure, the active feedback controlled laser frequency stabilization device may include: a phase modulation-intensity modulation-based optoelectronic oscillator and a phase-locked feedback control link. The phase modulation-intensity modulation-based optoelectronic oscillator includes: a local oscillator laser, an optical phase modulator, an optical filter, a photodetector, an RF amplifier, and an RF power divider. The phase-locked feedback control link includes: a mixer and a controller.

[0039] The local oscillator laser is configured to generate and output a laser signal.

[0040] An optical phase modulator is configured to modulate a microwave signal onto a laser signal to obtain a modulated optical signal.

[0041] An optical filter is configured to perform concave filtering on a modulated optical signal to obtain a concave-filtered optical signal. Optical filters can be grating filters, fiber optic filters, ultra-stable vacuum optical cavities, optical microrings, etc.

[0042] A photodetector is configured to beat the dimmed filtered optical signal to obtain a first radio frequency signal.

[0043] The radio frequency amplifier is configured to amplify the first radio frequency signal to obtain the second radio frequency signal.

[0044] The radio frequency power divider is configured to split the second radio frequency signal into two third radio frequency signals with equal power, and input one of the third radio frequency signals into an optical phase modulator.

[0045] The mixer is configured to mix the RF reference signal with another third RF signal input from the RF power divider, extract the change in the center angular frequency of the local oscillator laser relative to the center angular frequency of the optical filter, and obtain the error signal.

[0046] The controller is configured to generate an error signal feedback signal and feed it back to the current input port or tuning port of the local oscillator laser to adjust the frequency of the laser signal output by the local oscillator laser. The frequency of the laser signal output by the local oscillator laser is equal to the absolute value of the difference between the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, or the sum of the two.

[0047] Figure 2 A schematic diagram of a laser frequency stabilization device with active feedback control according to a second embodiment of the present invention is shown.

[0048] like Figure 2The active feedback control laser frequency stabilization device shown can include a phase modulation-intensity modulation based optoelectronic oscillator and a phase-locked feedback control link.

[0049] The local laser is configured to generate and output a laser signal.

[0050] The electro-optical modulator is configured to modulate the laser signal output by the local laser and input the optical phase modulator. The type of the electro-optical modulator can be a voltage-controlled oscillator driven acousto-optic modulator or a general phase modulator.

[0051] The optical phase modulator is configured to modulate a microwave signal onto the electro-optically modulated laser signal to obtain a modulated optical signal.

[0052] The optical filter is configured to notch filter the modulated optical signal to obtain a notch filtered optical signal. The optical filter can be a grating filter, a fiber filter, an ultra-stable vacuum optical cavity, an optical micro-ring, etc.

[0053] The photodetector is configured to beat the notch filtered optical signal to obtain a first radio frequency signal.

[0054] The radio frequency amplifier is configured to amplify the first radio frequency signal to obtain a second radio frequency signal.

[0055] The radio frequency power divider is configured to divide the second radio frequency signal into two third radio frequency signals with equal power, and input one of the third radio frequency signals into the optical phase modulator.

[0056] The frequency mixer is configured to mix the radio frequency reference signal with the other third radio frequency signal input by the radio frequency power divider to extract the change of the center angular frequency of the local laser relative to the center angular frequency of the optical filter, and obtain an error signal.

[0057] The controller is configured to generate a feedback signal from the error signal and feed back the feedback signal to the electro-optical modulator to adjust the frequency of the laser signal output by the local laser. The frequency of the laser signal output by the local laser is equal to the absolute value of the difference between the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal or the sum of the two.

[0058] Figure 3 The structure diagram of the active feedback control laser frequency stabilization device according to the third embodiment of the present application is schematically shown.

[0059] As Figure 3The active feedback control laser frequency stabilization device shown can include a phase modulation-intensity modulation based optoelectronic oscillator and a phase-locked feedback control link. The phase modulation-intensity modulation based optoelectronic oscillator includes a local laser, an optical phase modulator, an optical filter, an optical detector, a radio frequency amplifier and a radio frequency power divider. The phase-locked feedback control link includes a frequency mixer, a controller and a combiner.

[0060] The local laser is configured to generate and output a laser signal.

[0061] The optical phase modulator is configured to modulate a microwave signal onto the laser signal to obtain a modulated optical signal.

[0062] The optical filter is configured to notch filter the modulated optical signal to obtain a notch filtered optical signal. The optical filter can be a grating filter, a fiber filter, an ultra-stable vacuum optical cavity, an optical micro-ring, etc.

[0063] The optical detector is configured to beat the notch filtered optical signal to obtain a first radio frequency signal.

[0064] The radio frequency amplifier is configured to amplify the first radio frequency signal to obtain a second radio frequency signal.

[0065] The radio frequency power divider is configured to split the second radio frequency signal into two third radio frequency signals with equal power, and input one of the third radio frequency signals into the optical phase modulator.

[0066] The frequency mixer is configured to mix the radio frequency reference signal with the other third radio frequency signal input by the radio frequency power divider to extract a change of a center angular frequency of the local laser relative to a center angular frequency of the optical filter, and obtain an error signal.

[0067] The controller is configured to generate a feedback signal based on the error signal. The combiner can adopt a frequency diplexer, or can adopt a radio frequency coupler instead to achieve the same function.

[0068] The combiner is configured to combine the third radio frequency signal input by the radio frequency power divider and the feedback signal into one third radio frequency signal, and input the third radio frequency signal into a radio frequency input port of the optical phase modulator as a feedback input to adjust a frequency of the laser signal output by the local laser. The frequency of the laser signal output by the local laser is equal to an absolute value of a difference between the center angular frequency of the optical filter and an angular frequency of the oscillation radio frequency signal, or a sum of the center angular frequency of the optical filter and the angular frequency of the oscillation radio frequency signal.

[0069] Figure 4 A structure diagram of the active feedback control laser frequency stabilization device according to the fourth embodiment of the present application is schematically shown.

[0070] As Figure 4The active feedback control laser frequency stabilization device shown can include a phase modulation-intensity modulation based optoelectronic oscillator and a phase-locked feedback control link. The phase modulation-intensity modulation based optoelectronic oscillator includes a local laser, an optical phase modulator, an optical filter, an optical detector, a radio frequency amplifier and a radio frequency power divider. The phase-locked feedback control link includes a frequency divider, a frequency mixer and a controller.

[0071] The local laser is configured to generate and output a laser signal.

[0072] The optical phase modulator is configured to modulate a microwave signal onto the laser signal to obtain a modulated optical signal.

[0073] The optical filter is configured to notch filter the modulated optical signal to obtain a notch filtered optical signal. The optical filter can be a grating filter, a fiber filter, an ultra-stable vacuum optical cavity, an optical micro-ring, etc.

[0074] The optical detector is configured to beat the notch filtered optical signal to obtain a first radio frequency signal.

[0075] The radio frequency amplifier is configured to amplify the first radio frequency signal to obtain a second radio frequency signal.

[0076] The radio frequency power divider is configured to split the second radio frequency signal into two third radio frequency signals with equal power, and input one of the third radio frequency signals into the optical phase modulator.

[0077] The frequency divider is configured to divide the other third radio frequency signal input by the radio frequency power divider.

[0078] The frequency mixer is configured to mix the radio frequency reference signal with the divided third radio frequency signal to extract a change of a center angular frequency of the local laser relative to a center angular frequency of the optical filter to obtain an error signal.

[0079] The controller is configured to generate a feedback signal from the error signal and feed the feedback signal into a current input port or a tuning port of the local laser to adjust a frequency of the laser signal output by the local laser. The frequency of the laser signal output by the local laser is equal to an absolute value of a difference between the center angular frequency of the optical filter and an angular frequency of the oscillating radio frequency signal or a sum of the two.

[0080] According to the implementation of the present disclosure, the radio frequency oscillating signal after the radio frequency power divider is mixed with the radio frequency reference signal to generate the error signal after the radio frequency divider. The use of the frequency divider can reduce the difficulty of locking the feedback loop, reduce the requirement for the frequency stability of the local laser and improve the long-term stability of the system after locking.

[0081] Figure 5A structure diagram of the active feedback control laser frequency stabilization device according to the fifth embodiment of the present application is schematically shown.

[0082] As shown in Figure 5 , the active feedback control laser frequency stabilization device can include a phase modulation-intensity modulation based optoelectronic oscillator and a phase-locked feedback control link. The phase modulation-intensity modulation based optoelectronic oscillator includes a local laser, an optical phase modulator, an optical filter, an optical detector, a radio frequency amplifier and a radio frequency power divider. The phase-locked feedback control link includes a frequency multiplier, a frequency mixer and a controller.

[0083] The local laser is configured to generate and output a laser signal.

[0084] The optical phase modulator is configured to modulate a microwave signal onto the laser signal to obtain a modulated optical signal.

[0085] The optical filter is configured to notch filter the modulated optical signal to obtain a notch filtered optical signal. The optical filter can be a grating filter, a fiber filter, an ultra-stable vacuum optical cavity, an optical micro-ring, etc.

[0086] The optical detector is configured to beat the notch filtered optical signal to obtain a first radio frequency signal.

[0087] The radio frequency amplifier is configured to amplify the first radio frequency signal to obtain a second radio frequency signal.

[0088] The radio frequency power divider is configured to split the second radio frequency signal into two third radio frequency signals with equal power, and input one of the third radio frequency signals into the optical phase modulator.

[0089] The frequency multiplier is configured to multiply the other third radio frequency signal input by the radio frequency power divider.

[0090] The frequency mixer is configured to mix the radio frequency reference signal with the multiplied third radio frequency signal to extract a change of the center angular frequency of the local laser relative to the center angular frequency of the optical filter, and obtain an error signal.

[0091] The controller is configured to generate a feedback signal from the error signal and feed the feedback signal into a current input port or a tuning port of the local laser to adjust the frequency of the laser signal output by the local laser. The frequency of the laser signal output by the local laser is equal to the absolute value of the difference between the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, or the sum of the two.

[0092] According to the implementation of the present disclosure, the radio frequency divider is replaced by a radio frequency multiplier, which can amplify the error signal and realize higher precision feedback control.

[0093] Continuing to refer to Figures 1-5On the basis of the above embodiment, the laser frequency stabilization device of active feedback control can further comprise an optical coupler arranged between the output end of the local laser and the input end of the optical phase modulator, configured to couple the laser signal output by the local laser, and output the first super-stable laser with the same angular frequency as the local laser.

[0094] On the basis of the above embodiment, the laser frequency stabilization device of active feedback control can further comprise a local laser frequency shift link, which can be composed of an acousto-optic frequency shifter or an intensity modulator or a phase modulator, configured to process the first super-stable laser output by the optical coupler and the third RF signal output by the RF power divider, and output the second super-stable laser after frequency shift.

[0095] It should be noted that since the first super-stable laser output by the feedback control only suppresses the phase noise of the local laser within the bandwidth of the feedback loop, the second super-stable laser generated after the addition of the frequency shift link can achieve a greater frequency range of phase noise suppression of the local laser. And under the dual action of the oscillator and the feedback loop, a higher compression ratio of the noise of the local laser is achieved.

[0096] On the basis of the above embodiment, the optical filter further comprises a transmission filter port configured to output the third super-stable laser with the same center angular frequency as the optical filter, and the third super-stable laser comprises the +1 order sideband of the modulated optical signal.

[0097] On the basis of the above embodiment, the optical filter further comprises a notch filter port configured to output the optical carrier and the -1 order sideband of the modulated optical signal.

[0098] On the basis of the above embodiment, the feedback control loop can further comprise a low-pass filter arranged between the mixer and the controller, configured to low-pass filter the error signal obtained by the mixer.

[0099] Figures 6A-6D The spectral diagram corresponding to each signal in the laser frequency stabilization process of active feedback control according to the embodiment of the application is schematically shown.

[0100] As Figures 6A-6D shown, it can be understood that when the link gain is sufficient, the phase modulation-intensity modulation optoelectronic oscillator generates a RF signal, i.e. the oscillation RF signal. The frequency of the oscillation RF signal is jointly regulated by the frequency of the local laser and the center frequency of the optical filter. Specifically, under the condition of satisfying the RF phase self-reproduction, the frequency of the oscillation RF signal will be as close as possible to the difference between the center angular frequency of the local laser and the center angular frequency of the optical filter, i.e. wherein The angular frequency of the oscillating radio frequency signal is given by the center angular frequency of the local oscillator laser. The center angular frequency of the optical filter is Without loss of generality, we assume... Ignoring higher-order sidebands, the spectrum of the modulated signal output by the optical phase modulator is as follows: Figure 6A As shown. The modulated signal is input to the optical filter and output through the transmission filter port and the notch filter port. The angular frequency of the optical signal output from the transmission filter port is... ,like Figure 6B As shown. The angular frequencies of the output spectrum at the concave filter port are respectively ,like Figure 6C As shown. The second and third optical signals output from the concave filter port, after passing through the photodetector, have an output angular frequency of... radio frequency signals, such as Figure 6D As shown.

[0101] The angular frequency of the ultra-stable laser signal output from the transmission filter port is That is, the angular frequency of the output ultra-stable laser signal is aligned with the center angular frequency of the optical filter.

[0102] According to an embodiment of the present invention, the angular frequency of the oscillating radio frequency signal The center angular frequency of the local oscillator laser and the center angular frequency of the optical filter The frequency of the oscillating radio frequency signal is determined jointly. When any one of the frequencies changes, the angular frequency of the oscillating radio frequency signal... This will also change accordingly. When the center angular frequency of the optical filter is stable, that is... When stable, the center angular frequency of the local oscillator laser The change will be directly reflected in the angular frequency of the oscillating radio frequency signal. The frequency variation of the oscillating RF signal is extracted using a mixer through a radio frequency reference signal, and an error signal is output. This error signal reflects the center angular frequency of the local oscillator laser. Relative optical filter center angular frequency The frequency of the laser signal output by the local oscillator laser can be stabilized by the controller, thereby obtaining an optical signal with a frequency relatively stable to the center angular frequency of the optical filter.

[0103] It should be noted that there are two possible relationships between the local oscillator laser frequency, the radio frequency signal frequency, and the optical filter frequency:

[0104] The first case is that the frequency of the laser signal output by the local laser oscillator is equal to the absolute value of the difference between the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, at this time the optical filter notch filter port outputs the optical carrier and the -1 order sideband, and the third frequency stabilized laser output by the optical filter transmission corresponds to the +1 order sideband.

[0105] The second case is that the frequency of the laser signal output by the local laser oscillator is equal to the sum of the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, at this time the optical filter notch filter port outputs the optical carrier and the +1 order sideband, and the third frequency stabilized laser output by the optical filter transmission corresponds to the -1 order sideband.

[0106] The two cases finally achieve the same purpose, but the frequency relationship of the signals generated in the middle is different.

[0107] Taking the first case as an example:

[0108] The transmission filter port outputs the super-stable laser signal including the +1 order sideband of the modulation signal. The optical filter has a transmission filter port corresponding to the transmission filter output. The transmission filter output filters one of the sidebands of the modulation signal, which can be the +1 order sideband, and the angular frequency of the +1 order sideband is determined by the center angular frequency of the optical filter, which is , that is, the sideband is automatically locked with the center frequency of the optical filter. It can be understood that the optical filter as an etalon determines the stability of the super-stable laser output by the transmission filter.

[0109] The optical signal filtered by the optical filter notch filter includes the optical carrier and the -1 order sideband of the modulation signal. The optical filter also has a notch filter port corresponding to a notch filter output. The notch filter output filters the optical carrier and the -1 order sideband of the modulation signal, so that the phase-modulated optical signal is converted into an intensity-modulated optical signal, and the frequency of the modulation is converted into a radio frequency signal with an angular frequency of When the frequency of the local laser oscillator changes, for example, from to , the angular frequency of the oscillating radio frequency signal will also change, and through the radio frequency reference signal and the mixer, the change of the angular frequency of the oscillating radio frequency signal, that is, the error signal, is obtained. Through the controller, the center angular frequency of the local laser oscillator is adjusted, so that the center frequency of the local laser oscillator is relatively locked with the center angular frequency of the optical filter, thereby achieving the effect of frequency stabilization.

[0110] Figure 7 A schematic diagram of the relative phase noise of the laser before and after frequency stabilization of the active feedback controlled laser frequency stabilization device according to an embodiment of the present application is shown.

[0111] As shown in Figure 7As shown, compared with using an ultra-stable FP cavity as a reference, more than 120 dB of phase noise suppression is achieved at low frequency positions, greatly reducing the phase noise of the laser.

[0112] Figure 8 A comparison chart of laser linewidth before and after frequency stabilization of the active feedback control laser frequency stabilization device according to the embodiment of the present application is schematically shown.

[0113] As Figure 8 shown, the left graph is the local oscillator laser linewidth of the related art, which is 2.8 kHz, and the right graph is the laser linewidth after locking of the active feedback control laser frequency stabilization device according to the embodiment of the present application, which is 0.7 Hz. It can be found that after active feedback control, the laser linewidth is reduced from 2.8 kHz to 0.7 Hz.

[0114] The flowcharts and block diagrams in the drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present application. In this regard, each block in the flowcharts or block diagrams can represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical functions. It should also be noted that in some alternative implementations, the functions noted in the blocks can occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustrations, and combinations thereof, can be implemented by a dedicated hardware-based system that performs the specified functions or operations, or combinations of hardware and computer instructions.

[0115] Those skilled in the art can understand that the features described in various embodiments and / or claims of the present application can be combined or / and integrated, even if such combinations or integrations are not explicitly described in the present application. In particular, the features described in various embodiments and / or claims of the present application can be combined and / or integrated in various combinations, without departing from the spirit and teachings of the present application. All such combinations and / or integrations fall within the scope of the present application.

[0116] The embodiments of the present application are described above. However, these embodiments are merely for illustrative purposes, and are not intended to limit the scope of the present application. Although each embodiment is described above separately, this does not mean that the measures in each embodiment cannot be used advantageously in combination. The scope of the present application is defined by the appended claims and their equivalents. Without departing from the scope of the present application, those skilled in the art can make various substitutions and modifications, which all fall within the scope of the present application.

Claims

1. A laser frequency stabilization device based on active feedback control, characterized in that, The device comprises: a local oscillator laser configured to generate and output a laser signal; an optical phase modulator configured to modulate a microwave signal onto the laser signal to obtain a modulated optical signal; an optical filter configured to notch filter the modulated optical signal to obtain a notch filtered optical signal; a photodetector configured to beat the notch filtered optical signal to obtain a first radio frequency signal; a radio frequency amplifier configured to amplify the first radio frequency signal to obtain a second radio frequency signal; a radio frequency power divider configured to split the second radio frequency signal into two third radio frequency signals with equal power, and input one of the third radio frequency signals into the optical phase modulator; a feedback control loop configured to mix a radio frequency reference signal with the other third radio frequency signal input into the radio frequency power divider to generate an error signal, and generate a feedback signal based on the error signal, and input the feedback signal into the local oscillator laser to adjust a frequency of the laser signal output by the local oscillator laser.

2. The apparatus of claim 1, wherein, The feedback control loop comprises: a mixer configured to mix the radio frequency reference signal with the other third radio frequency signal input into the radio frequency power divider to extract a change of a center angular frequency of the local oscillator laser relative to a center angular frequency of the optical filter, and obtain the error signal; a controller configured to input the feedback signal into a current input port or a tuning port of the local oscillator laser based on the error signal to adjust the frequency of the laser signal output by the local oscillator laser, wherein an angular frequency of the laser signal output by the local oscillator laser is equal to a sum or an absolute value of a difference of the center angular frequency of the optical filter and an angular frequency of an oscillating radio frequency signal.

3. The apparatus of claim 1, wherein, The device further comprises: an electro-optical modulator configured to modulate the laser signal output by the local oscillator laser and input the modulated laser signal into the optical phase modulator; the feedback control loop comprises: a mixer configured to mix the radio frequency reference signal with the other third radio frequency signal input into the radio frequency power divider to extract a change of a center angular frequency of the local oscillator laser relative to a center angular frequency of the optical filter, and obtain the error signal; a controller configured to input the feedback signal into the electro-optical modulator based on the error signal to adjust the frequency of the laser signal output by the local oscillator laser, wherein the frequency of the laser signal output by the local oscillator laser is equal to a sum or an absolute value of a difference of the center angular frequency of the optical filter and an angular frequency of an oscillating radio frequency signal.

4. The apparatus of claim 1, wherein, The feedback control loop comprises: a mixer configured to mix the radio frequency reference signal with the other third radio frequency signal input into the radio frequency power divider to extract a change of a center angular frequency of the local oscillator laser relative to a center angular frequency of the optical filter, and obtain the error signal; a controller configured to generate the feedback signal based on the error signal; The combiner is configured to combine one of the third radio frequency signals input by the radio frequency power divider with the feedback signal to form a feedback input to a radio frequency input port of the optical phase modulator, so as to adjust a frequency of the laser signal output by the local oscillator laser, wherein the frequency of the laser signal output by the local oscillator laser is equal to an absolute value of a difference between a center angular frequency of the optical filter and an angular frequency of the oscillating radio frequency signal or a sum of the absolute value and the angular frequency.

5. The apparatus of claim 1, wherein, The feedback control loop comprises: The frequency divider is configured to divide another of the third radio frequency signals input by the radio frequency power divider; The frequency mixer is configured to mix a radio frequency reference signal with the divided third radio frequency signal, so as to extract a change in the center angular frequency of the local oscillator laser relative to the center angular frequency of the optical filter, to obtain the error signal; The controller is configured to generate a feedback signal from the error signal and feed the feedback signal to a current input port or a tuning port of the local oscillator laser, so as to adjust the frequency of the laser signal output by the local oscillator laser, wherein the frequency of the laser signal output by the local oscillator laser is equal to an absolute value of a difference between the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal or a sum of the absolute value and the angular frequency.

6. The apparatus of claim 1, wherein, The feedback control loop comprises: The frequency divider is configured to divide another of the third radio frequency signals input by the radio frequency power divider; The frequency mixer is configured to mix a radio frequency reference signal with the divided third radio frequency signal, so as to extract a change in the center angular frequency of the local oscillator laser relative to the center angular frequency of the optical filter, to obtain the error signal; The controller is configured to generate a feedback signal from the error signal and feed the feedback signal to a current input port or a tuning port of the local oscillator laser, so as to adjust the frequency of the laser signal output by the local oscillator laser, wherein the frequency of the laser signal output by the local oscillator laser is equal to an absolute value of a difference between the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal or a sum of the absolute value and the angular frequency.

7. The device of any one of claims 1-6, wherein, The apparatus further comprises: The optical coupler is arranged between an output of the local oscillator laser and an input of the optical phase modulator and is configured to couple the laser signal output by the local oscillator laser, to output a first super-stable laser having the same angular frequency as the local oscillator laser.

8. The apparatus of claim 7, wherein, The apparatus further comprises: The acousto-optic frequency shifter or the intensity modulator or the phase modulator is configured to process the first super-stable laser output by the optical coupler and one of the third radio frequency signals output by the radio frequency power divider, to output a second super-stable laser after frequency shifting.

9. The device of any one of claims 1-6, wherein, The optical filter further comprises a transmission filter port configured to output a third ultra-stable laser with the same center angular frequency as the optical filter, wherein, in the case that the frequency of the laser signal output by the local laser oscillator is equal to the absolute value of the difference between the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, the third ultra-stable laser comprises the +1 order sideband of the modulated optical signal after transmission filtering by the optical filter; in the case that the frequency of the laser signal output by the local laser oscillator is equal to the sum of the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, the third ultra-stable laser comprises the -1 order sideband of the modulated optical signal after transmission filtering by the optical filter.

10. The device of any one of claims 1-6, wherein, The optical filter further comprises a notch filter port configured to output the optical carrier and the -1 order sideband of the modulated optical signal after notch filtering by the optical filter in the case that the frequency of the laser signal output by the local laser oscillator is equal to the absolute value of the difference between the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal; The notch filter port is configured to output the optical carrier and the +1 order sideband of the modulated optical signal after notch filtering by the optical filter in the case that the frequency of the laser signal output by the local laser oscillator is equal to the sum of the center angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal.

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