High-precision single-cavity multi-comb frequency measurement and control system and method

Abstract

This invention relates to the fields of laser technology and optoelectronic control technology, and discloses a high-precision single-cavity multi-comb frequency measurement and control system and method. The system includes: a single-cavity multi-comb pulse oscillator, a frequency detection module, and a frequency feedback control module. The single-cavity multi-comb pulse oscillator outputs at least two mode-locked pulse trains with a certain difference in both center wavelength and repetition frequency. The frequency detection module simultaneously detects the frequencies of the mode-locked pulse trains and outputs electrical signals. The frequency feedback control module processes the electrical signals from the frequency detection module and then sends them to the frequency response point in the single-cavity multi-comb pulse oscillator to control the strain at the frequency response point, thereby achieving feedback control of the frequency (repetition frequency, repetition frequency difference, carrier envelope offset frequency) of the mode-locked pulse trains. The method and system of this invention can solve the problem of frequency drift in multi-comb lasers and achieve precise control and stabilization of multiple frequencies.

Description

Technical Field

[0001] This invention relates to the fields of laser technology and optoelectronic control technology, specifically to a high-precision single-cavity multi-comb frequency measurement and control system and method. Background Technology

[0002] The emergence of optical frequency comb technology has provided a new solution for precise optical measurements and is a significant achievement recognized by the 2005 Nobel Prize laureates in Physics. Optical frequency combs are typically based on mode-locked pulsed lasers, appearing in the frequency domain as a series of frequency components with equal frequency intervals (laser repetition frequency) and in the time domain as pulse trains with equal time intervals. Optical frequency comb technology has been widely applied in spectroscopy, among which coherent spectroscopy based on multiple optical combs has demonstrated enormous application potential due to its advantages of fast acquisition time, high sensitivity, and high resolution accuracy.

[0003] Traditionally, multi-comb spectroscopy relies on multiple independent mode-locked pulsed lasers with a certain repetition rate difference. Their frequency information is locked using complex and specialized photoelectric conversion and detection techniques to achieve a multi-comb light source. This entire system is large, complex, specialized, and fragile, hindering the development and widespread adoption of multi-comb spectroscopy.

[0004] In recent years, researchers have invented a multi-wavelength laser that can greatly simplify the implementation of multi-comb light sources. Taking a dual-wavelength laser as an example, as the name suggests, a dual-wavelength mode-locked pulse laser can simultaneously output two mode-locked pulses of different wavelengths (λ1 and λ2), and the mode-locked pulses of different wavelengths have different repetition frequencies (f1 and f2, f1≠f2, f1-f2=Δf). Dual-wavelength lasers are usually implemented based on a common resonant cavity, and their common-mode noise is effectively suppressed. The coherence between the two wavelength pulses is greatly improved, and the trends of f1 and f2 are consistent, with Δf (repetition frequency difference) fluctuating within a very small range (on the order of Hz). The carrier envelope offset frequencies (fceo1 and fceo2) corresponding to different wavelength pulse trains also follow relatively, but their positions are not fixed, and the difference between them, Δfceo, has a certain degree of fluctuation. Therefore, for such multi-comb lasers, how to achieve precise control and stability of all frequencies is a key factor in realizing high-precision multi-comb light sources. Summary of the Invention

[0005] The present invention aims to provide a high-precision single-cavity multi-comb frequency measurement and control system and method, which can solve the problem of frequency drift in multi-comb lasers and achieve precise control and stabilization of multiple frequencies.

[0006] The technical solution provided by this invention is a high-precision single-cavity multi-comb frequency measurement and control system, comprising: a single-cavity multi-comb pulse oscillator, a frequency detection module, and a frequency feedback control module. The single-cavity multi-comb pulse oscillator includes a laser, an output port, and a frequency response point. The laser is used to output at least two mode-locked pulse trains with a certain difference in both center wavelength and repetition frequency. The output port is used to split the mode-locked pulse trains according to the laser wavelength and transmit them to the frequency detection module. The frequency response point is used to respond to the electrical signal processed by the frequency feedback control module, thereby achieving separate locking of each frequency signal. The frequency detection module is used to simultaneously detect the frequencies of the mode-locked pulse trains and output electrical signals. The frequency feedback control module is used to standardize the electrical signal from the frequency detection module and then send it to the frequency response point in the single-cavity multi-comb pulse oscillator to control the strain of the frequency response point, thereby achieving feedback control of the frequency of the mode-locked pulse trains.

[0007] The working principle and advantages of this invention are as follows: For a single-cavity multi-comb pulse oscillator outputting several mode-locked pulse trains with repetition frequencies and certain differences (different wavelengths correspond to different repetition frequencies and carrier envelope offset frequencies), a frequency detection module simultaneously detects each mode-locked pulse train and outputs an electrical signal. A frequency feedback control module provides feedback and controls the frequency response point set within the pulse oscillator to achieve stable control of each frequency signal of the output dual-wavelength pulse train, solving the frequency drift problem of multi-comb lasers and achieving precise control and stabilization of multiple frequencies. The frequency-stable single-cavity multi-comb light source can serve as a highly stable, highly coherent, and outdoor-use ultrafast optical comb light source for applications such as high-precision distance detection, high-precision spectral measurement, high-speed fiber optic communication, and high-precision frequency metrology.

[0008] Furthermore, the single-cavity multi-comb pulse oscillator is a dual-wavelength pulse oscillator, and the frequency response points include repetition frequency response points, repetition frequency difference response points, and carrier envelope offset frequency difference response points, and the frequency response points do not interfere with each other.

[0009] For any mode-locked pulsed laser, the repetition frequency can be characterized by the following formula:

[0010]

[0011] Where c is the speed of light, n is the refractive index of the medium, and L is the cavity length. Therefore, the factors affecting the repetition frequency include the overall cavity length and the refractive index.

[0012] Simultaneously, due to the difference between the phase velocity and group velocity in the dispersive medium inside the laser cavity, the pulse envelope drifts relative to the carrier phase between pulses, resulting in an overall shift in the frequency comb, known as the carrier envelope shift frequency (fceo). Correspondingly, the frequency of the optical mode is:

[0013] f n =fceo+N*f

[0014] Where n is the conversion coefficient between optical frequency and radio frequency. It is evident that precise control and locking of f and fceo can directly realize a high-precision optical frequency comb.

[0015] For dual-wavelength lasers, since there are two pulse trains oscillating within the cavity, the repetition frequency f1 is not equal to f2, resulting in a repetition frequency difference (frequency difference):

[0016]

[0017] Where D is the average dispersion within the cavity, Δλ is the wavelength difference, and L is the cavity length. Let L be the average repetition period of the two optical combs. D, L, and Δλ are the three key factors affecting the repetition rate difference Δf. Furthermore, L is also a key factor affecting the laser's repetition frequency (f1 or f2). Therefore, simply controlling the laser cavity length L only allows for precise control of the repetition frequency of one pulse, making it difficult to simultaneously lock all repetition rate information of a dual-wavelength laser. Moreover, if feedback control is applied to L for both repetition frequency and repetition rate difference locking, crosstalk will undoubtedly occur between the two locking signals, preventing either from locking. Therefore, if L is controlled to lock a specific repetition frequency of the dual-wavelength laser, the locking of the repetition rate difference can only be achieved by feedback control of either D or Δλ, thus realizing a dual-wavelength optical comb source with stable repetition rate information.

[0018] Furthermore, due to a slight difference in repetition frequency between the two pulses, the paths they traverse within the cavity are not entirely identical, resulting in some jitter in the carrier envelope offset frequency. The carrier envelope offset frequencies of the two pulse trains are denoted as fceo1 and fceo2, respectively, and their difference is denoted as Δfceo. Controlling fceo1 and fceo2 separately would create crosstalk, affecting overall stability. Therefore, to prevent crosstalk between frequency response points, this invention controls the carrier envelope offset frequency difference Δfceo. Combining the above control of all repetition frequency information, all frequency information of the dual-wavelength optical comb source can be stabilized.

[0019] Furthermore, the response parameters at the frequency response point are one or more of the following: laser cavity length, medium refractive index, cavity dispersion coefficient, center wavelength spacing of dual-wavelength pulses, pump power, and cavity nonlinear coefficient.

[0020] According to the above formula, by adjusting the response parameters at frequency response points such as cavity length, medium refractive index, cavity dispersion coefficient, center wavelength spacing of dual-wavelength pulses, pump power, and cavity nonlinear coefficient, precise control of repetition frequency, repetition frequency difference, and carrier envelope offset frequency difference can be achieved.

[0021] Furthermore, the gain medium of the dual-wavelength pulse oscillator is a gain fiber or a gain crystal, wherein the gain fiber includes one or more of erbium, ytterbium, and thulium, and the gain crystal is one or more of Yb:YAG, Yb:CaF2, and Yb:KYW.

[0022] Using gain fiber or gain crystal can alleviate the thermal effects of lasers, improve the quality of the output laser beam, and enhance the stability of the laser system.

[0023] Furthermore, the dual-wavelength pulse oscillator is a dual-wavelength fiber pulse oscillator. The repetition frequency response point responds according to the fiber refractive index to control the repetition frequency, and the fiber refractive index is controlled by an all-optical method. The repetition frequency difference response point responds according to the intracavity dispersion coefficient to control the repetition frequency difference, and the intracavity dispersion coefficient is controlled by a motor stretching an intracavity chirped fiber grating. The carrier envelope offset frequency difference response point responds according to the pump power to control the carrier envelope offset frequency difference.

[0024] For the control methods of each response point, the repetition frequency is controlled by an all-optical method, the repetition frequency difference is achieved by stretching the length of the chirped fiber grating in the cavity using a motor, and the carrier envelope offset frequency difference is achieved by controlling the output power of the pump source using a power feedback control module.

[0025] Furthermore, the dual-wavelength pulse oscillator is a dual-wavelength solid-state pulse oscillator. The repetition frequency response point responds according to the laser cavity length, controlling the repetition frequency. The laser cavity length is adjusted by piezoelectric ceramic expansion and contraction. The repetition frequency difference response point responds according to the intracavity dispersion coefficient, controlling the repetition frequency difference. The intracavity dispersion coefficient is controlled by piezoelectric ceramic displacement stretching of the intracavity chirped fiber grating. The carrier envelope offset frequency difference response point responds according to the pump power, controlling the carrier envelope offset frequency difference.

[0026] Another approach to the control method for each response point is to use piezoelectric ceramics to control the repetition frequency, and to use piezoelectric ceramic displacement to control the chirped fiber grating in the cavity to control the repetition frequency difference. Additionally, a power feedback control module is used to control the output power of the pump source to control the carrier envelope offset frequency difference.

[0027] Furthermore, the dual-wavelength pulse oscillator is a dual-wavelength fiber pulse oscillator. The repetition frequency response point responds according to the fiber refractive index, controlling the repetition frequency. The fiber refractive index is controlled by an all-optical method. The repetition frequency difference response point responds according to the intracavity dispersion coefficient, controlling the repetition frequency difference. The intracavity dispersion coefficient is controlled by adjusting the temperature of the chirped fiber grating. The carrier envelope offset frequency difference response point responds according to the pump power, controlling the carrier envelope offset frequency difference.

[0028] In addition to stretching the length of the chirped fiber grating to control the dispersion coefficient within the cavity, it can also be placed on a semiconductor cooling chip or a temperature controller to adjust the temperature of the chirped fiber grating, thereby controlling the repetition rate difference.

[0029] Furthermore, the frequency detection module includes two independent repetition frequency detection units and two independent carrier envelope offset frequency detection units. Each repetition frequency detection unit includes a beam splitter, a photodetector, a bandpass filter, an RF amplifier, a frequency divider, and a counter. The beam splitter is used to split the optical signal output by the oscillator into multiple beams according to the laser wavelength. The photodetector converts the optical signal into an electrical signal, realizing photoelectric conversion. The bandpass filter is used to select the fundamental frequency signal or harmonic signal of the repetition frequency of the electrical signal and filter out noise. The RF amplifier is used to amplify the power of the filtered electrical signal. The frequency divider is used to divide the electrical signal into multiple beams according to the laser wavelength. The system is divided into two beams: one beam is used for detection and monitoring signals, and the other beam is used for applications. The counter is used to observe and collect frequency information of electrical signals in real time. Each carrier envelope offset frequency detection unit includes an f-2f detector, a photodetector, a bandpass filter, and an RF amplifier. The f-2f detector is used to detect the carrier envelope offset frequency of the optical signal output by the oscillator. The photodetector converts the optical signal from the f-2f detector into an electrical signal, realizing photoelectric conversion. The bandpass filter is used to select the fundamental frequency signal or harmonic signal of the repetition frequency of the electrical signal and filter out noise. The RF amplifier is used to amplify the power of the filtered electrical signal.

[0030] The frequency detection module includes two independent repetition frequency detection units and two independent carrier envelope offset frequency detection units, which detect the repetition frequency and carrier envelope offset frequency respectively, thus improving the detection accuracy. For fceo (frequency offset frequency), the current mainstream method is the f-2f method. Photoelectric conversion, filtering, amplification, frequency division, and counting are performed separately to prepare for the next control step.

[0031] Furthermore, the frequency feedback control module includes a repetition frequency feedback control module, a repetition frequency difference feedback control module, and a carrier envelope offset frequency difference feedback control module. The repetition frequency control module includes a signal generator, a mixer, a low-pass filter, and an RF amplifier. The repetition frequency difference feedback control module includes a carrier modulator, a signal generator, a mixer, a low-pass filter, and an RF amplifier. The carrier envelope offset frequency difference feedback control module includes a carrier modulator, a signal generator, a mixer, a low-pass filter, and an RF amplifier. The carrier modulator is used to add carrier modulation to the input signal. The signal generator is used to output a standard frequency signal. The mixer is used to mix the modulated signal with the standard frequency signal to obtain an error signal. The filter and the RF amplifier are used to select and amplify the error signal to achieve feedback control.

[0032] The repetition frequency feedback control module, the repetition frequency difference feedback control module, and the carrier envelope offset frequency difference feedback control module respectively provide feedback control for the repetition frequency, repetition frequency difference, and carrier envelope offset frequency difference. The carrier modulator adds carrier modulation to the input signal to make it fall within the operating range of the relevant RF components, and then performs mixing, filtering, and amplification processing to achieve feedback control.

[0033] This invention also provides a high-precision single-cavity multi-comb frequency measurement and control method, which uses the above-mentioned system and includes the following steps:

[0034] S1: A single-cavity multi-comb pulse oscillator outputs at least two mode-locked pulse trains with a certain difference in both center wavelength and repetition frequency;

[0035] S2: The output pulse train optical signal is split into multiple beams according to the laser wavelength by the beam splitter, and then converted into electrical signals by the photodetector, and then filtered and amplified.

[0036] S3: The processed electrical signal is divided into several paths by a frequency divider, and each electrical signal is processed by mixing, filtering and amplification respectively;

[0037] S4: The processed electrical signal is used as a feedback signal to drive the frequency response point of the single-cavity multi-comb pulse oscillator, thereby realizing feedback control of the frequency of the mode-locked pulse train. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the high-precision single-cavity multi-comb frequency measurement and control system of the present invention;

[0039] Figure 2 This is a structural diagram of the dual-wavelength pulse oscillator of the high-precision single-cavity multi-comb frequency measurement and control system of the present invention. Detailed Implementation

[0040] The following detailed explanation illustrates the specific implementation methods:

[0041] The markings in the accompanying drawings include: dual-wavelength pulse oscillator 100, laser 101, repetition frequency response point 102, temperature control module 103, repetition frequency difference response point 104, beam splitter 105, carrier envelope offset frequency difference response point 106, frequency detection module 200, repetition frequency feedback control module 310, repetition frequency difference feedback control module 320, and carrier envelope offset frequency difference feedback control module 330.

[0042] Beam splitters 201, 211; photodetectors 202, 212, 232, 242; bandpass filters 203, 213, 233, 243; RF amplifiers 204, 214, 234, 244, 314, 325, 336; frequency dividers 205, 206, 215; counters 207, 216, 222, 252; f-2f detectors 231, 241; mixers 311, 321, 323, 331, 334; signal generators 312, 326, 337; low-pass filters 313, 324, 335; carrier modulators 322, 323.

[0043] Semiconductor laser diode 109, plano-concave mirror 110, gain crystal 111, semiconductor saturable absorber mirror 112, grating pair 1024, motor controller 1025, 1047, piezoelectric ceramic 1046.

[0044] (For ease of distinction, in this embodiment, the beam splitter, photodetector, bandpass filter, RF amplifier, frequency divider, counter, f-2f detector, mixer, signal generator, low-pass filter, carrier modulator, and motor controller are each labeled with different figures, but all components are of the same model number.)

[0045] Example 1:

[0046] like Figure 1 As shown, a high-precision single-cavity multi-comb frequency measurement and control system includes a single-cavity multi-comb pulse oscillator, a frequency detection module 200, and a frequency feedback control module. The frequency feedback control module includes a repetition frequency feedback control module 310, a repetition frequency difference feedback control module 320, and a carrier envelope offset frequency difference feedback control module 330. The single-cavity multi-comb pulse oscillator is a dual-wavelength pulse oscillator 100 (in this embodiment, the dual-wavelength pulse oscillator 100 can be any one of fiber lasers, solid-state lasers, semiconductor lasers, or gas lasers capable of achieving dual-wavelength dual-pulse mode-locking), specifically including a laser 101, an output port, and frequency response points. The output port is a beam splitter 105, and the frequency response points include a repetition frequency response point 102, a repetition frequency difference response point 104, and a carrier envelope offset frequency difference response point 106.

[0047] The dual-wavelength pulse oscillator 100 includes a laser 101, a repetition frequency response point 102, a temperature control module 103, a repetition frequency difference response point 104, a beam splitter 105, and a carrier envelope offset frequency difference response point 106. The laser 101 generates two mode-locked pulse trains with different center wavelengths, λ1 = 1530 nm and λ2 = 1560 nm, with a center wavelength spacing Δλ = 30 nm. Assuming their corresponding repetition frequencies are f1 = 25.001 MHz and f2 = 25 MHz, the repetition frequency difference Δf = 1 kHz; their carrier envelope offset frequencies are fceo1 = 10 MHz and fceo2 = 10.001 MHz, with a carrier envelope offset frequency difference Δfceo = 1 kHz. The output signal is split by wavelength by the beam splitter 105, and then the two pulse trains pass through beam splitters 201 and 211 respectively. One of the repetition frequency signals is as follows: λ1 (1530nm) is detected by photodetector 202 and converted into an electrical signal; λ2 (1560nm) is detected by photodetector 212 and also converted into an electrical signal. The other is the carrier envelope offset frequency signal: both pulses will enter the carrier envelope offset frequency difference detection module.

[0048] The dual-wavelength pulse oscillator 100 is stabilized by the temperature control module 103 to stabilize the oscillator's operating wavelength. The repetition frequency response point 102, the repetition frequency difference response point 104, and the carrier envelope offset frequency difference response point 106 are used to stabilize the repetition frequency, the repetition frequency difference, and the carrier envelope offset frequency difference, respectively. The beam splitter 105 is used to separate the dual-wavelength mode-locked pulse train signal according to wavelength so that it can be measured independently.

[0049] The frequency detection module 200 includes two independent repetition frequency detection units and two independent carrier envelope offset frequency detection units. Next, for one repetition frequency signal, dual-wavelength mode-locked pulse trains enter the frequency detection module 200, which includes beam splitters 201 and 202, photodetectors 202 and 212, bandpass filters 203 and 213, RF amplifiers 204 and 214, frequency dividers 205, 206 and 215, and counters 207, 216 and 222. The 1530nm signal light pulse passes sequentially through beam splitter 201, photodetector 202, bandpass filter 203, RF amplifier 204, and frequency dividers 205 and 206. One output signal of frequency divider 206 is connected to counter 207 to detect its pulse repetition frequency signal. The 1560nm signal light pulse passes sequentially through beam splitter 211, photodetector 212, bandpass filter 213, RF amplifier 214, and frequency divider 215. One output signal of frequency divider 215 is connected to counter 216 to detect its pulse repetition frequency signal.

[0050] The beam splitters 201 and 211 are used to split the 1530nm and 1560nm beams according to intensity, with a splitting ratio of 5:5. Photodetectors 202 and 212 convert the optical signal into an electrical signal to detect the pulse signal. Various types of photodetectors, such as PIN or APD, can be used. Bandpass filters 203 and 213 are both bandpass filters with a center frequency of 25MHz. The RF amplifier 204 has a gain of 23dB and is used to amplify the 1530nm signal; the RF amplifier 214 has a gain of 20dB and is used to amplify the 1560nm signal. The frequency divider 205 splits the 1530nm signal amplified by the RF amplifier 204 into two paths: one path connects to the repetition frequency feedback control module 310, and the other path connects to the frequency divider 206. The frequency divider 206 further splits the 1530nm signal into two paths. One path is connected to the counter 207 for repetition frequency detection, and the other path is connected to the mixer 321 for mixing, before entering the subsequent repetition frequency difference feedback control module 320. The frequency divider 215 splits the 1560nm signal, amplified by the RF amplifier 214, into two paths. One path is connected to the counter 216 for repetition frequency detection; the other path is connected to the mixer 321 and mixed with the 1530nm signal to obtain a repetition frequency difference signal Δf = 1kHz. One path is connected to the counter 222 for repetition frequency difference detection, and the other path is connected to the repetition frequency difference feedback control module 320.

[0051] For the carrier envelope offset frequency path, the split dual-wavelength pulses are fed into f-2f carrier envelope offset detection modules 231 and 241, photodetectors 232 and 242, bandpass filters 233 and 243, and RF amplifiers 234 and 244, respectively. The f-2f carrier envelope offset detection modules 231 and 241 are used to detect the carrier envelope offset frequencies of the 1530nm and 1560nm signals, respectively. The photodetectors convert the optical signals from the f-2f carrier envelope offset detection modules into electrical signals for subsequent detection; here, an APD-type photodetector is used.

[0052] The bandpass filters 233 and 243 are bandpass filters with a center frequency of 10MHz and a bandwidth of 2MHz. The RF amplifiers 234 and 244 both have a gain of 20dB and are used to amplify the fceo1 and fceo2 signals. The two amplified signals are connected to mixer 331 for mixing to obtain a carrier envelope offset frequency difference signal Δfceo = 1kHz. One path is then connected to counter 252 to detect the carrier envelope offset frequency difference, and the other path is connected to carrier envelope offset frequency difference feedback control module 330.

[0053] The frequency feedback control module includes a repetition frequency feedback control module 310, a repetition frequency difference feedback control module 320, and a carrier envelope offset frequency difference feedback control module 330. The repetition frequency feedback control module 310 includes a mixer 311, a signal generator 312, a low-pass filter 313, and an RF amplifier 314. The repetition frequency difference feedback control module 320 includes a mixer 321, a carrier modulator 322, a mixer 323, a signal generator 326, a low-pass filter 324, and an RF amplifier 325. The carrier envelope offset frequency difference control module 330 includes a mixer 331, a carrier modulator 332, RF amplifiers 333 and 336, a mixer 334, a low-pass filter 335, and a signal generator 337.

[0054] A 1530nm pulse signal output from the frequency divider 205 enters the repetition frequency feedback control module 310. After signal processing by the mixer 311, low-pass filter 313 and RF amplifier 314, the signal is fed back to control the repetition frequency response point 102 in the dual-wavelength pulse oscillator 100, thereby achieving stable control of the repetition frequency signal of the dual-wavelength laser of the present invention.

[0055] The repetition frequency difference signal Δf output by mixer 321 enters the repetition frequency difference feedback control module 320. After signal processing by carrier modulator 322, mixer 323, low-pass filter 324 and RF amplifier 325, it is used to feedback control the repetition frequency difference response point 104 in the dual-wavelength pulse oscillator 100, thereby realizing stable control of the repetition frequency difference signal of the dual-wavelength laser of the present invention.

[0056] The carrier modulator 322 generates a modulation frequency of 15MHz to boost the frequency of the frequency difference signal to 15.001MHz, placing it within the operating range of the mixer 323. The RF mixers 311 and 323 perform mixing operations on the repetition frequency signal or the frequency difference signal, respectively, and perform frequency difference operations with the standard frequency signals output by signal generators 312 and 326 to obtain error signals, which are used as feedback signals to drive the corresponding frequency response points. The signal generator 312 outputs a standard frequency signal of 25MHz with a sine wave waveform; the signal generator 326 outputs a standard frequency signal of 15MHz with a sine wave waveform.

[0057] The low-pass filter 313 and the radio frequency amplifier 314 are used to extract and amplify the repetition frequency error signal to achieve feedback control of the repetition frequency response point 102.

[0058] The low-pass filter 324 and the radio frequency amplifier 325 are used to extract and amplify the repetition frequency difference error signal to realize feedback control of the repetition frequency difference response point 104.

[0059] For carrier envelope offset frequency detection and locking, the carrier envelope offset frequency difference signal Δfceo after the two detected carrier envelope offset frequencies fceo1 and fceo2 pass through mixer 331 enters the carrier envelope offset frequency difference feedback control module 330. After signal processing by carrier modulator 332, RF amplifier 333, mixer 334, low-frequency filter 335 and RF amplifier 336, the signal is fed back to control the carrier envelope offset frequency difference response point 106 in the dual-wavelength pulse oscillator 100, thereby achieving stable control of the carrier envelope offset frequency difference signal of the dual-wavelength laser of the present invention.

[0060] The carrier modulator 322 generates a 15MHz modulation frequency to boost the carrier envelope offset frequency difference signal to 15.001MHz, placing it within the operating range of the RF mixer 334, and then passes it through an RF amplifier 333 with a gain of 20dB. The mixer 334 mixes the 15MHz sinusoidal standard signal generated by the signal generator 337 with the modulated carrier envelope offset frequency difference signal to obtain an error signal. The low-pass filter 335 and the RF amplifier 336 with a gain of 20dB are used to extract and amplify the carrier envelope offset frequency difference error signal, achieving feedback control of the frequency response point 106.

[0061] The dual-wavelength pulse oscillator 100 is a dual-wavelength fiber pulse oscillator, and the laser 101 includes a 980nm semiconductor laser diode (LD). Its output pump laser is pumped through a four-port wavelength division multiplexer to obtain a 1550nm band signal light, which is then passed through a mode-locked modulator to obtain a mode-locked pulse signal. In this embodiment, all optical fibers and optical fiber components used are polarization-maintaining elements (polarization-maintaining fibers).

[0062] The repetition frequency response point 102 employs an all-optical method to control the oscillator repetition frequency, including a circulator, wavelength division multiplexer, semiconductor laser diode, gain fiber, and chirped fiber grating. The circulator introduces the intracavity signal into the grating and guides the reflected signal light back into the laser cavity. The center wavelength of the semiconductor laser diode should be 980nm. A 980 / 1550 type three-port wavelength division multiplexer 1042 pumps the gain fiber 1044, generating a refractive index change to control the repetition frequency within the oscillator cavity. The repetition frequency feedback control module 310 controls the refractive index change of the gain fiber by changing the pump power of the laser diode, affecting the optical path and thus controlling the repetition frequency. The chirped fiber grating should be highly reflective at 1530nm and 1560nm, and highly transparent at 980nm.

[0063] The frequency response point for the repetition rate difference (CGBG) includes a circulator, a chirped fiber grating (CGBG), and a pressure controller. The circulator introduces the intracavity signal into the grating and guides the reflected signal light back into the laser cavity. The feedback signal generated by the CGBG feedback control module 320 controls the length of the CGBG via a motor stretching control, thereby controlling the overall intracavity dispersion and achieving stable control of the CGBG of the dual-wavelength laser. The parameters of the chirped fiber grating are as follows: operating wavelength of 1520nm to 1560nm, bandwidth of 40nm, reflectivity greater than 80%, and polarization-maintaining fiber. Length stretching or temperature control allows the provided second-order dispersion parameter to be adjustable within the range of 0.01-0.2 ps².

[0064] The motor can also be replaced by a temperature controller or a semiconductor cooling chip to adjust the temperature of the chirped fiber grating to control the dispersion coefficient inside the cavity, thereby controlling the repetition frequency difference.

[0065] The carrier envelope offset frequency difference frequency response point is controlled by controlling the pump power to control the carrier envelope offset frequency difference of the oscillator. The carrier envelope offset frequency difference feedback control module 330 changes the power of the semiconductor laser diode, thereby altering the magnitude of the nonlinear coefficient within the cavity, ultimately achieving control of the carrier envelope offset frequency difference.

[0066] In addition to the frequency response point combinations mentioned above, the repetitive frequency response point 102 can also be achieved by using a chirped fiber grating with an electrically controlled polarization controller, a grating pair with an all-optical method to control the cavity length, a chirped fiber grating with a piezoelectric ceramic controller, or a grating pair with an electrically controlled polarization controller. The carrier envelope offset frequency difference response point 106 can also be achieved by controlling nonlinear devices within the cavity.

[0067] The gain fiber described in this embodiment includes one or more of erbium, ytterbium, and thulium.

[0068] Example 2:

[0069] The difference between this embodiment and embodiment one is that the dual-wavelength pulse oscillator 100 is a dual-wavelength solid-state pulse oscillator, and the output port is a coupler. Its pulse oscillator structure is as follows: Figure 2 As shown, the system includes a laser 101, a coupler, a plano-concave mirror 110, a gain crystal 111, a grating pair 1024, a motor controller 1025, a motor controller 1047, and a piezoelectric ceramic 1046. The laser 101 is a semiconductor laser diode 109, and the coupler is a semiconductor saturable absorber mirror 112.

[0070] A 980nm semiconductor laser diode 109, through a 980nm anti-reflection and a 1030nm high-reflectivity plano-concave mirror 110, pumps a gain crystal 111 to generate a 1030nm signal light. This signal light then passes through a semi-transparent, semi-reflective semiconductor saturable absorber mirror 112 for signal output. A grating pair 1024 is used to compensate for the dispersion coefficient within the oscillator cavity and serves as the repetition frequency response point 102 to stabilize the repetition rate difference. The semiconductor saturable absorber mirror 112, in addition to serving as an output coupling mirror, also acts as a saturable absorber material to generate dual-wavelength mode-locked pulse output and as the repetition frequency response point 102, achieving stable control of the laser's repetition frequency.

[0071] The repetition frequency response point 102 includes a grating pair 1024 and a motor controller 1025. One grating from the grating pair 1024 is attached to the motor controller 1025 and can follow its position and angle changes. The feedback signal generated by the repetition frequency difference feedback control module 320 controls the angle and distance of the grating pair 1024 through the motor controller 1025, thereby changing the overall dispersion within the cavity and achieving locking of the repetition frequency difference of the dual-wavelength pulses.

[0072] The repetition frequency difference response point 104 includes a semiconductor saturable absorber mirror 112, a piezoelectric ceramic 1046, and a motor controller 1047. The semiconductor saturable absorber mirror 112 is adhered to the piezoelectric ceramic 1046. The repetition frequency feedback control module 310 generates a feedback signal, which controls the piezoelectric ceramic 1046 through the motor controller 1047, thereby changing the position of the semiconductor saturable absorber mirror 112, thus changing the overall cavity length and achieving stable control of the repetition frequency of the dual-wavelength pulse oscillator 100.

[0073] The carrier envelope offset frequency difference frequency response point 106 uses the pump power control to control the carrier envelope offset frequency difference of the oscillator. The carrier envelope offset frequency difference feedback control module 330 changes the power of the semiconductor laser diode 109, thereby changing the magnitude of the nonlinear coefficient in the cavity, and ultimately achieving control of the carrier envelope offset frequency difference.

[0074] The gain crystal is one or more of Yb:YAG, Yb:CaF2, and Yb:KYW.

[0075] Example 3:

[0076] The difference between this embodiment three and embodiment two is that the carrier envelope offset frequency response point 106 is achieved by inserting an output cavity mirror between the gain crystal 111 and the grating pair 1024. In this embodiment, the output cavity mirror is a glass wedge. By controlling and adjusting the angle of the glass wedge, the magnitude of the nonlinear coefficient in the cavity is changed, thereby realizing the control of the carrier envelope offset frequency difference.

[0077] This invention also discloses a high-precision single-cavity multi-comb frequency measurement and control method, which uses the above-mentioned system.

[0078] The above are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, based on the inspiration derived from this application, improve and implement this solution in combination with their own capabilities. Some typical well-known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A high-precision single-cavity multi-comb frequency measurement and control system, characterized in that, include: The system comprises a single-cavity multi-comb pulse oscillator, a frequency detection module, and a frequency feedback control module. The single-cavity multi-comb pulse oscillator includes a laser, an output port, and a frequency response point. The laser outputs at least two mode-locked pulse trains with a certain difference in center wavelength and repetition frequency. The output port splits the mode-locked pulse trains according to laser wavelength and transmits them to the frequency detection module. The frequency response point responds to the electrical signal processed by the frequency feedback control module, enabling separate locking of each frequency signal. The frequency detection module simultaneously detects the frequencies of the mode-locked pulse trains and outputs electrical signals. The frequency feedback control module processes the electrical signal from the frequency detection module and then sends it to the frequency response point in the single-cavity multi-comb pulse oscillator, controlling the strain of the frequency response point to achieve feedback control of the frequency of the mode-locked pulse trains. The frequency detection module includes two independent repetition frequency detection units and two independent carrier envelope offset frequency detection units. Each repetition frequency detection unit includes a beam splitter, a photodetector, a bandpass filter, an RF amplifier, a frequency divider, and a counter. The beam splitter splits the optical signal output from the oscillator into multiple beams according to the laser wavelength. The photodetector converts the optical signal into an electrical signal, achieving photoelectric conversion. The bandpass filter selects the fundamental frequency signal or harmonic signal of the repetition frequency of the electrical signal and filters out noise. The RF amplifier amplifies the power of the filtered electrical signal. The frequency divider divides the electrical signal into two equal parts. Second, one beam serves as the detection and monitoring signal, and the other beam serves as the application. The counter is used to observe and collect the frequency information of the electrical signal in real time. Each carrier envelope offset frequency detection unit includes an f-2f detector, a photodetector, a bandpass filter, and a radio frequency amplifier. The f-2f detector is used to detect the carrier envelope offset frequency of the optical signal output by the oscillator. The photodetector converts the optical signal from the f-2f detector into an electrical signal to achieve photoelectric conversion. The bandpass filter is used to select the fundamental frequency signal or harmonic signal of the repetition frequency of the electrical signal and filter out noise. The radio frequency amplifier is used to amplify the power of the filtered electrical signal.

2. The high-precision single-cavity multi-comb frequency measurement and control system according to claim 1, characterized in that: The single-cavity multi-comb pulse oscillator is a dual-wavelength pulse oscillator. The frequency response points include repetition frequency response points, repetition frequency difference response points, and carrier envelope offset frequency difference response points. The frequency response points do not interfere with each other.

3. The high-precision single-cavity multi-comb frequency measurement and control system according to claim 2, characterized in that: The response parameters at the frequency response point are one or more of the following: laser cavity length, medium refractive index, cavity dispersion coefficient, center wavelength spacing of dual-wavelength pulses, pump power, and cavity nonlinear coefficient.

4. The high-precision single-cavity multi-comb frequency measurement and control system according to claim 2, characterized in that: The gain medium of the dual-wavelength pulse oscillator is a gain fiber or a gain crystal. The gain fiber includes one or more of erbium, ytterbium, and thulium, and the gain crystal is one or more of Yb:YAG, Yb:CaF2, and Yb:KYW.

5. The high-precision single-cavity multi-comb frequency measurement and control system according to claim 2, characterized in that: The dual-wavelength pulse oscillator is a dual-wavelength fiber pulse oscillator. The repetition frequency response point responds according to the fiber refractive index, controlling the repetition frequency. The fiber refractive index is controlled by an all-optical method. The repetition frequency difference response point responds according to the intracavity dispersion coefficient, controlling the repetition frequency difference. The intracavity dispersion coefficient is controlled by a motor stretching an intracavity chirped fiber grating. The carrier envelope offset frequency difference response point responds according to the pump power, controlling the carrier envelope offset frequency difference.

6. The high-precision single-cavity multi-comb frequency measurement and control system according to claim 2, characterized in that: The dual-wavelength pulse oscillator is a dual-wavelength solid-state pulse oscillator. The repetition frequency response point responds according to the laser cavity length, controlling the repetition frequency. The laser cavity length is adjusted by piezoelectric ceramic expansion and contraction. The repetition frequency difference response point responds according to the intracavity dispersion coefficient, controlling the repetition frequency difference. The intracavity dispersion coefficient is controlled by piezoelectric ceramic displacement stretching of the intracavity chirped fiber grating. The carrier envelope offset frequency difference response point responds according to the pump power, controlling the carrier envelope offset frequency difference.

7. The high-precision single-cavity multi-comb frequency measurement and control system according to claim 2, characterized in that: The dual-wavelength pulse oscillator is a dual-wavelength fiber pulse oscillator. The repetition frequency response point responds according to the fiber refractive index to control the repetition frequency, and the fiber refractive index is controlled by an all-optical method. The repetition frequency difference response point responds according to the intracavity dispersion coefficient to control the repetition frequency difference, and the intracavity dispersion coefficient is controlled by adjusting the temperature of the chirped fiber grating. The carrier envelope offset frequency difference response point responds according to the pump power to control the carrier envelope offset frequency difference.

8. The high-precision single-cavity multi-comb frequency measurement and control system according to any one of claims 5-7, characterized in that: The frequency feedback control module includes a repetition frequency feedback control module, a repetition frequency difference feedback control module, and a carrier envelope offset frequency difference feedback control module. The repetition frequency control module includes a signal generator, a mixer, a low-pass filter, and an RF amplifier. The repetition frequency difference feedback control module includes a carrier modulator, a signal generator, a mixer, a low-pass filter, and an RF amplifier. The carrier envelope offset frequency difference feedback control module includes a carrier modulator, a signal generator, a mixer, a low-pass filter, and an RF amplifier. The carrier modulator is used to add carrier modulation to the input signal. The signal generator is used to output a standard frequency signal. The mixer is used to mix the modulated signal with the standard frequency signal to obtain an error signal. The filter and the RF amplifier are used to select and amplify the error signal to achieve feedback control.

9. A high-precision single-cavity multi-comb frequency measurement and control method, characterized in that, This method uses the aforementioned system and includes the following steps: S1: A single-cavity multi-comb pulse oscillator outputs at least two mode-locked pulse trains with a certain difference in both center wavelength and repetition frequency; S2: The output pulse train optical signal is split into multiple beams according to the laser wavelength by the beam splitter, and then converted into electrical signals by the photodetector, and then filtered and amplified. S3: The processed electrical signal is divided into several paths by a frequency divider, and each electrical signal is processed by mixing, filtering and amplification respectively; S4: The processed electrical signal is used as a feedback signal to drive the frequency response point of the single-cavity multi-comb pulse oscillator, thereby realizing feedback control of the frequency of the mode-locked pulse train.

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