Laser frequency stabilization device based on active feedback control

Abstract

The invention provides a laser frequency stabilization device based on active feedback control, and the device comprises a local oscillator laser which is configured to generate and output a laser signal; the optical phase modulator is configured to modulate the microwave signal onto the laser signal to obtain a modulated optical signal; an optical filter configured to perform sag filtering on the modulated optical signal; the photoelectric detector is configured to perform beat frequency on the optical signal subjected to recess filtering to obtain a first radio frequency signal; the radio frequency amplifier is configured to amplify the first radio frequency signal to obtain a second radio frequency signal; the radio frequency power divider is configured to divide the second radio frequency signal into two paths of third radio frequency signals at equal power and input one path of third radio frequency signal into the optical phase modulator; and the feedback control loop is configured to perform frequency mixing on the radio frequency reference signal and the other path of third radio frequency signal input by the radio frequency power divider to generate an error signal, and generate a feedback signal based on the error signal so as to adjust the frequency of the laser signal output by the local oscillator laser.

Description

Technical Field

[0001] The invention relates to the technical field of laser frequency stabilization, and in particular to a laser frequency stabilization device based on active feedback control. Background Art

[0002] Ultra-stable lasers with extremely high frequency stability have important applications in scientific measurement, coherent communication, and frequency metrology. However, current lasers are generated through resonant cavity oscillation, and the frequency stability of the directly generated laser is affected by the stability of the resonant cavity. The laser's resonant cavity is an active cavity, and the light transmitted in the cavity needs to satisfy the gain greater than the loss to produce a stable laser 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 then leads to the deterioration of the frequency stability and linewidth of the generated laser. The frequency stability of the laser can be improved through passive vibration isolation and active temperature control, but the effect is limited. The linewidth of commercial lasers is currently in the kHz to MHz range, and the frequency instability is generally greater than 10^-12@1s, which is difficult to meet the needs of some application scenarios that require higher frequency stability. Summary of the invention

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

[0004] An embodiment of the present invention provides a laser frequency stabilization device based on active feedback control, comprising: 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 an optical signal after notch filtering; a photodetector, configured to perform beat frequency on the optical signal after notch filtering 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 another third radio frequency signal input by 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, a feedback control loop includes: a mixer, configured to mix an RF reference signal with another third RF signal input by an RF power divider, extract a change in the center angular frequency of the local oscillator laser relative to the center angular frequency of the optical filter, and obtain an error signal; a controller, configured to generate a feedback signal from the error signal and feed it back to a current input port or a tuning port of the local oscillator laser to adjust the frequency of the laser signal output by the local oscillator laser, wherein the angular 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 RF signal or the sum of the two.

[0006] According to an embodiment of the present disclosure, the device also includes: an electro-optical modulator, which is configured to modulate the laser signal output by the local oscillator laser and input it into the optical phase modulator; the feedback control loop includes: a mixer, which is configured to mix the RF reference signal with another third RF signal input by the RF power divider, extract the change of the central angular frequency of the local oscillator laser relative to the central angular frequency of the optical filter, and obtain an error signal; a controller, which is configured to generate a feedback signal from the error signal and feed it back to the electro-optical modulator to adjust the frequency of the laser signal output by the local oscillator laser, and the frequency of the laser signal output by the local oscillator laser is equal to the absolute value of the difference between the central angular frequency of the optical filter and the angular frequency of the oscillating RF signal or the sum of the two.

[0007] According to an embodiment of the present disclosure, a feedback control loop includes: a mixer configured to mix an RF reference signal with another third RF signal input by an RF power divider, extract a change in the center angular frequency of the local oscillator laser relative to the center angular frequency of the optical filter, and 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 RF signal input by the RF power divider with the feedback signal into one signal and then feed it back to the RF input port of the optical phase modulator 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 RF signal or the sum of the two.

[0008] According to an embodiment of the present disclosure, a feedback control loop includes: a frequency divider configured to divide the frequency of another third RF signal input by the RF power divider; a frequency mixer configured to mix the RF reference signal with the divided third RF signal, extract the change of the center angular frequency of the local oscillator laser relative to the center angular frequency of the optical filter, and obtain an error signal; a controller configured to generate a feedback signal from the error 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 RF signal or the sum of the two.

[0009] According to an embodiment of the present disclosure, a feedback control loop includes: a frequency multiplier configured to multiply the frequency of another third RF signal input by the RF power divider; a frequency mixer configured to mix the RF reference signal with the third RF signal after multiplication, extract the change of the center angular frequency of the local oscillator laser relative to the center angular frequency of the optical filter, and obtain an error signal; a controller configured to generate a feedback signal from the error 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 RF oscillation signal or the sum of the two.

[0010] According to an embodiment of the present disclosure, the device also includes: an optical coupler, which is arranged between the output end of the local oscillator laser and the input end of the optical phase modulator, and is configured to couple the laser signal output by the local oscillator laser to output a first ultra-stable laser with the same angular frequency as the local oscillator laser.

[0011] According to an embodiment of the present disclosure, the device also includes: an acousto-optic frequency shifter or an intensity modulator or a phase modulator, which is configured to process the first ultra-stable laser output by the optical coupler and a third RF signal output by the RF power divider, and output a second ultra-stable laser after frequency shifting.

[0012] According to an embodiment of the present disclosure, the optical filter also includes a transmission filter port, which is configured to output a third ultra-stable laser having the same central angular frequency as the optical filter, wherein, when the frequency of the laser signal output by the local oscillator laser is equal to the absolute value of the difference between the central angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, the third ultra-stable laser includes a +1-order sideband of the modulated optical signal after transmission filtering by the optical filter; and when the frequency of the laser signal output by the local oscillator laser is equal to the sum of the central angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, the third ultra-stable laser includes a -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 also includes a notch filter port. When 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, the notch filter port is configured to output the optical carrier and -1-order sideband of the modulated optical signal after notch filtering; when the frequency of the laser signal output by the local oscillator laser 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 notch filter port is configured to output the optical carrier and +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 invention has at least the following technical effects:

[0015] The RF reference signal is mixed with the third RF signal input by the RF power divider through the feedback control loop to generate an error signal, and a feedback signal is generated based on the error signal. The feedback signal is input into the local oscillator laser to adjust the frequency of the laser signal output by the local oscillator 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 ultra-stable laser. In addition, the feedback loop can further suppress the phase noise of the laser signal output by the local oscillator laser. The phase noise suppression effect is superimposed on the suppression effect of the non-feedback control, so that the output ultra-stable laser can have lower phase noise.

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

[0017] The laser frequency obtained by this device has a greater degree of freedom. By tuning the radio frequency oscillating from the optoelectronic oscillator, arbitrary frequency tunability of the ultra-stable laser frequency can be achieved.

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

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

[0020] The above contents and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

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

[0022] Figure 2 A schematic diagram showing the structure of a laser frequency stabilization device with active feedback control according to a second embodiment of the present invention;

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

[0024] Figure 4A schematic diagram showing the structure of a laser frequency stabilization device with active feedback control according to a fourth embodiment of the present invention;

[0025] Figure 5 A schematic diagram showing the structure of a laser frequency stabilization device with active feedback control according to a fifth embodiment of the present invention;

[0026] Figures 6A-6D Schematically showing the spectrum graph corresponding to each signal in the laser frequency stabilization process of active feedback control according to an embodiment of the present invention;

[0027] Figure 7 A diagram schematically shows a comparison result of the phase noise of the laser before and after frequency stabilization of the laser frequency stabilization device with active feedback control according to an embodiment of the present invention;

[0028] Figure 8 The figure schematically shows the comparison result of the laser line width before and after frequency stabilization of the laser frequency stabilization device with active feedback control according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0030] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0031] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0032] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

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

[0034] In view of this, an embodiment of the present disclosure provides a laser frequency stabilization device based on active feedback control, which may 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 perform notch filtering on the modulated optical signal to obtain an optical signal after notch filtering; a photodetector, configured to perform beat frequency on the optical signal after notch filtering to obtain a first radio frequency signal; an radio frequency amplifier, configured to amplify the first radio frequency signal to obtain a second radio frequency signal; an 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 an radio frequency reference signal with another third radio frequency signal input by 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 an oscillating radio frequency signal. The error signal outputs a feedback signal after passing through a feedback controller. The feedback signal adjusts the frequency of a local oscillator laser and outputs an ultra-stable laser signal.

[0036] The laser frequency stabilization device with active feedback control is introduced below in conjunction with specific embodiments.

[0037] Figure 1The structure of the laser frequency stabilization device with active feedback control according to the first embodiment of the present invention is schematically shown.

[0038] like Figure 1 As shown, in an embodiment of the present disclosure, the laser frequency stabilization device with active feedback control may include: an optoelectronic oscillator based on phase modulation-intensity modulation, and a phase-locked feedback control link. The optoelectronic oscillator based on phase modulation-intensity modulation includes: a local oscillator laser, an optical phase modulator, an optical filter, a photodetector, a radio frequency amplifier, and a radio frequency 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] The optical phase modulator is configured to modulate the microwave signal onto the laser signal to obtain a modulated optical signal.

[0041] The optical filter is configured to perform notch filtering on the modulated optical signal to obtain a notch filtered optical signal. The optical filter can be a grating filter, an optical fiber filter, an ultra-stable vacuum optical cavity, an optical microring, etc.

[0042] The photoelectric detector is configured to perform a beat frequency on the optical signal after the notch filtering to obtain a first radio frequency signal.

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

[0044] The radio frequency power splitter 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.

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

[0046] The controller is configured to generate a feedback signal from the error signal and feed it back to the current input port or the 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 central 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 The structure of the laser frequency stabilization device with active feedback control according to the second embodiment of the present invention is schematically shown.

[0048] like Figure 2As shown, the laser frequency stabilization device with active feedback control may include: an optoelectronic oscillator based on phase modulation-intensity modulation, and a phase-locked feedback control link. The optoelectronic oscillator based on phase modulation-intensity modulation includes: a local oscillator laser, an electro-optical modulator, an optical phase modulator, an optical filter, a photodetector, a radio frequency amplifier, and a radio frequency power divider. The phase-locked feedback control link includes: a mixer and a controller.

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

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

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

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

[0053] The photoelectric detector is configured to perform a beat frequency on the optical signal after the notch filtering 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 splitter 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.

[0056] The mixer is configured to mix the RF reference signal with another third RF signal input by the RF power divider, extract the change of the central angular frequency of the local oscillator laser relative to the central 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 it back to the electro-optic modulator 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 central 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 of the laser frequency stabilization device with active feedback control according to the third embodiment of the present invention is schematically shown.

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

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

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

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

[0063] The photoelectric detector is configured to perform a beat frequency on the optical signal after the notch filtering 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 splitter 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 mixer is configured to mix the RF reference signal with another third RF signal input by the RF power divider, extract the change of the central angular frequency of the local oscillator laser relative to the central 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 beam combiner can be replaced by a frequency duplexer or a radio frequency coupler to achieve the same function.

[0068] The combiner is configured to combine a third RF signal input from the RF power divider with the feedback signal into one signal, which is then fed back to the RF input port of the optical phase modulator 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 central angular frequency of the optical filter and the angular frequency of the oscillating RF signal or the sum of the two.

[0069] Figure 4 The structure of a laser frequency stabilization device with active feedback control according to a fourth embodiment of the present invention is schematically shown.

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

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

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

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

[0074] The photoelectric detector is configured to perform a beat frequency on the optical signal after the notch filtering 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 splitter 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 frequency of another third radio frequency signal input by the radio frequency power divider.

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

[0079] The controller is configured to generate a feedback signal from the error signal and feed it back to the current input port or the 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 central angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal or the sum of the two.

[0080] According to the implementation of the present disclosure, the RF oscillation signal after the power divider is mixed with the RF reference signal after passing through the RF frequency divider to generate an error signal. The use of the frequency divider can also reduce the difficulty of locking the feedback loop, reduce the requirements for the frequency stability of the local oscillator laser, and improve the long-term stability of the system after locking.

[0081] Figure 5The structure of a laser frequency stabilization device with active feedback control according to the fifth embodiment of the present invention is schematically shown.

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

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

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

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

[0086] The photoelectric detector is configured to perform a beat frequency on the optical signal after the notch filtering 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 splitter 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 frequency of another third radio frequency signal input by the radio frequency power divider.

[0090] The mixer is configured to mix the radio frequency reference signal with the frequency-multiplied third radio frequency signal, extract the change of the central angular frequency of the local oscillator laser relative to the central 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 it back to the current input port or the 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 central 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 RF frequency divider is replaced with a RF frequency multiplier, so that the error signal can be amplified to achieve higher-precision feedback control.

[0093] Continue reading Figure 1-Figure 5On the basis of the above embodiments, the laser frequency stabilization device with active feedback control may further include: an optical coupler, which is arranged between the output end of the local oscillator laser and the input end of the optical phase modulator, and is configured to couple the laser signal output by the local oscillator laser to output a first ultra-stable laser with the same angular frequency as the local oscillator laser.

[0094] On the basis of the above embodiments, the laser frequency stabilization device with active feedback control may further include: a local oscillator laser frequency shifting link, which may be composed of an acousto-optic frequency shifter or an intensity modulator or a phase modulator, and is configured to process the first ultra-stable laser output by the optical coupler and a third RF signal output by the RF power divider, and output a second ultra-stable laser after frequency shifting.

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

[0096] Based on the above embodiment, the optical filter further includes a transmission filter port, which is configured to output a third ultra-stable laser having the same central angular frequency as the optical filter, and the third ultra-stable laser includes a +1-order sideband of the modulated optical signal.

[0097] Based on the above embodiment, the optical filter further includes a notch filter port, and the notch filter port is configured to output the optical carrier and -1 order sideband of the modulated optical signal.

[0098] On the basis of the above embodiment, the feedback control loop may further include a low-pass filter, which is arranged between the mixer and the controller and is configured to perform low-pass filtering on the error signal obtained by mixing.

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

[0100] like Figures 6A-6D As shown, it can be understood that when the link gain is sufficient, the phase modulation-intensity modulation optoelectronic oscillator generates a radio frequency signal, that is, the oscillating radio frequency signal. The frequency of the oscillating radio frequency signal is jointly regulated by the frequency of the local oscillator laser and the center frequency of the optical filter. Specifically, under the condition of satisfying the self-reproduction of the radio frequency phase, the frequency of the oscillating radio frequency signal will be as close as possible to the difference between the center angular frequency of the local oscillator laser and the center angular frequency of the optical filter, that is, ,in is the angular frequency of the oscillating RF signal, and the central angular frequency of the local oscillator laser is , the central angular frequency of the optical filter is Without loss of generality, assume Ignoring the high-order sidebands, the spectrum of the modulated signal output by the optical phase modulator is as follows: Fig. 6A As shown. The modulated signal is input into the optical filter. And output through the transmission filter port and the recessed filter port. The angular frequency of the optical signal output from the transmission filter port is ,like Figure 6B The angular frequencies of the output spectrum of the notch filter port are ,like Figure 6C After the second optical signal and the third optical signal output from the notch filter port pass through the photodetector, the output angular frequency is RF signals, such as Fig.6D 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 central 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 central angular frequency of the local oscillator laser and the central angular frequency of the optical filter When any of the frequencies changes, the angular frequency of the oscillating RF signal When the central angular frequency of the optical filter is stable, that is, When stable, the central angular frequency of the local oscillator laser is The change will directly reflect the angular frequency of the oscillating RF signal The frequency change of the oscillating RF signal is extracted by a mixer using an RF reference signal, and an error signal is output. The error signal reflects the central angular frequency of the local oscillator laser. Relative optical filter center angular frequency Through the controller, the error signal can be used to stabilize the frequency of the laser signal output by the local oscillator laser, thereby obtaining an optical signal with a relatively stable frequency and the central angular frequency of the optical filter.

[0103] It should be noted that there are two situations in which the relationship between the local oscillator laser frequency, the RF signal frequency and the optical filter frequency is:

[0104] The first case is: the frequency of the laser signal output by the local oscillator laser is equal to the absolute value of the difference between the central angular frequency of the optical filter and the angular frequency of the oscillating RF signal. At this time, the optical filter recessed filter port outputs the optical carrier and the -1st order sideband, and the third frequency-stabilized laser output by the optical filter corresponds to the +1st order sideband.

[0105] The second case is: the frequency of the laser signal output by the local oscillator laser is equal to the sum of the central angular frequency of the optical filter and the angular frequency of the oscillating RF signal. At this time, the optical filter recessed filter port outputs the optical carrier and the +1-order sideband, and the third frequency-stabilized laser output by the optical filter corresponds to the -1-order sideband.

[0106] Both situations can ultimately achieve the same goal, but the frequency relationship of the signals generated in the middle is different.

[0107] Take the first case as an example:

[0108] The ultra-stable laser signal outputted from the transmission filter port includes the +1-order sideband of the modulated signal. The optical filter has a transmission filter port corresponding to the transmission filter output. The transmission filter output filters out one of the sidebands of the modulated signal, which can be a +1-order sideband. The angular frequency of the +1-order sideband is determined by the central angular frequency of the optical filter and is , that is, the sideband is automatically locked with the center frequency of the optical filter. It can be understood that the optical filter here acts as an etalon to determine the stability of the ultra-stable laser output by the transmission filter.

[0109] The optical signal after notch filtering by the optical filter includes the optical carrier of the modulated signal and the -1 order sideband. The optical filter also has a notch filter port corresponding to the notch filter output. The notch filter output filters out the optical carrier of the modulated signal and the -1 order sideband, so that the phase modulated optical signal is converted into an intensity modulated optical signal, and its modulated frequency is received by the photodetector and converted into an angular frequency of When the frequency of the local oscillator laser changes, for example, becomes , then the angular frequency of the oscillating RF signal is The angular frequency of the oscillating RF signal will also change. Through the RF reference signal and the mixer, the change of the angular frequency of the oscillating RF signal, that is, the error signal, is obtained. The central angular frequency of the local oscillator laser is adjusted through the controller feedback, so that the central frequency of the local oscillator laser and the central angular frequency of the optical filter are relatively locked, thereby achieving the effect of frequency stabilization.

[0110] Figure 7 A diagram schematically shows a comparison result of the phase noise of a laser before and after frequency stabilization of a laser frequency stabilization device with active feedback control according to an embodiment of the present invention.

[0111] like Figure 7As shown, by using the ultra-stable FP cavity as a reference, a phase noise suppression of more than 120 dB was achieved at the low frequency position, greatly reducing the phase noise of the laser.

[0112] Figure 8 The figure schematically shows the comparison result of the laser line width before and after frequency stabilization of the laser frequency stabilization device with active feedback control according to an embodiment of the present invention.

[0113] like Figure 8 As shown, the left figure shows that the line width of the local oscillator laser in the related technology is 2.8kHz, and the right figure shows that the laser line width is 0.7Hz after locking using the laser frequency stabilization device with active feedback control of the embodiment of the present disclosure. It can be found that after using active feedback control, the laser line width is reduced from 2.8kHz to 0.7Hz.

[0114] The flowcharts and block diagrams in the accompanying drawings illustrate the possible implementation architecture, functions and operations of the systems and methods according to various embodiments of the present invention. In this regard, each box in the flowchart or block diagram may represent a module, a program segment or a part of a code, and the above-mentioned module, a program segment or a part of a code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box may also occur in an order different from that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram or flowchart, and the combination of boxes in the block diagram or flowchart, can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0115] It will be appreciated by those skilled in the art that the features described in the various embodiments and / or claims of the present invention may be combined and / or combined in various ways, even if such combinations and / or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments and / or claims of the present invention may be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All of these combinations and / or combinations fall within the scope of the present invention.

[0116] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment is described above, it does not mean that the measures in each embodiment cannot be used in combination. The scope of the present invention is defined by the attached claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A laser frequency stabilization device based on active feedback control, characterized in that: include: A local oscillator laser is 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 an optical signal after notch filtering; a photoelectric detector configured to perform a beat frequency on the optical signal after the notch filtering 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 splitter 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; The feedback control loop is configured to mix the RF reference signal with another third RF signal input by the RF 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.

2. The device according to claim 1, characterized in that The feedback control loop includes: A mixer is configured to mix the radio frequency reference signal with another third radio frequency signal input by the radio frequency power divider, extract the change of the central angular frequency of the local oscillator laser relative to the central angular frequency of the optical filter, and obtain the error signal; The controller is configured to generate a feedback signal from the error signal and feed it back to the current input port or the tuning port of the local oscillator laser to adjust the frequency of the laser signal output by the local oscillator laser, wherein the angular frequency of the laser signal output by the local oscillator laser is equal to the sum of the central angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal or the absolute value of the difference between the two.

3. The device according to claim 1, characterized in that The device also includes: an electro-optical modulator, configured to modulate the laser signal output by the local oscillator laser and then input the modulated laser signal into the optical phase modulator; The feedback control loop includes: A mixer is configured to mix the radio frequency reference signal with another third radio frequency signal input by the radio frequency power divider, extract the change of the central angular frequency of the local oscillator laser relative to the central angular frequency of the optical filter, and obtain the error signal; The controller is configured to generate a feedback signal from the error signal and feed it back to the electro-optic modulator 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 the sum of the central angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal or the absolute value of the difference between the two.

4. The device according to claim 1, characterized in that The feedback control loop includes: A mixer is configured to mix the radio frequency reference signal with another third radio frequency signal input by the radio frequency power divider, extract the change of the central angular frequency of the local oscillator laser relative to the central angular frequency of the optical filter, and obtain the error signal; a controller configured to generate a feedback signal based on the error signal; A beam combiner is configured to combine a third RF signal input by the RF power divider with the feedback signal into one beam and then feed it back to the RF input port of the optical phase modulator 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 central angular frequency of the optical filter and the angular frequency of the oscillating RF signal or the sum of the two.

5. The device according to claim 1, characterized in that The feedback control loop includes: A frequency divider configured to divide the frequency of another third radio frequency signal input by the radio frequency power divider; A mixer configured to mix the radio frequency reference signal with the frequency-divided third radio frequency signal, extract the change of the central angular frequency of the local oscillator laser relative to the central angular frequency of the optical filter, and obtain the error signal; The controller is configured to generate a feedback signal from the error signal and feed it back to the current input port or the 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 central angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal or the sum of the two.

6. The device according to claim 1, characterized in that The feedback control loop includes: a frequency multiplier configured to multiply the frequency of another third radio frequency signal input by the radio frequency power divider; A mixer is configured to mix the radio frequency reference signal with the frequency-multiplied third radio frequency signal, extract the change of the central angular frequency of the local oscillator laser relative to the central angular frequency of the optical filter, and obtain the error signal; The controller is configured to generate a feedback signal from the error signal and feed it back to the current input port or the 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 central angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal or the sum of the two.

7. The device according to any one of claims 1 to 6, characterized in that: The device also includes: The optical coupler is arranged between the output end of the local oscillator laser and the input end of the optical phase modulator, and is configured to couple the laser signal output by the local oscillator laser to output a first ultra-stable laser with the same angular frequency as that of the local oscillator laser.

8. The device according to claim 7, characterized in that The device also includes: The acousto-optic frequency shifter or intensity modulator or phase modulator is configured to process the first ultra-stable laser output by the optical coupler and a third radio frequency signal output by the radio frequency power divider, and output a frequency-shifted second ultra-stable laser.

9. The device according to any one of claims 1 to 6, characterized in that: The optical filter also includes a transmission filter port, which is configured to output a third ultra-stable laser having the same central angular frequency as the optical filter, wherein, when the frequency of the laser signal output by the local oscillator laser is equal to the absolute value of the difference between the central angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, the third ultra-stable laser includes a +1-order sideband of the modulated optical signal after transmission filtering by the optical filter; and when the frequency of the laser signal output by the local oscillator laser is equal to the sum of the central angular frequency of the optical filter and the angular frequency of the oscillating radio frequency signal, the third ultra-stable laser includes a -1-order sideband of the modulated optical signal after transmission filtering by the optical filter.

10. The device according to any one of claims 1 to 6, characterized in that: The optical filter further comprises a notch filter port, and when the frequency of the laser signal output by the local oscillator laser is equal to the absolute value of the difference between the central 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 -1st order sideband of the modulated optical signal after notch filtering; When the frequency of the laser signal output by the local oscillator laser is equal to the sum of the central 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 +1-order sideband of the modulated optical signal after notch filtering.

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