Device for generating double optical frequency combs based on nonlinear amplification loop mirror mode-locked laser

Abstract

The invention relates to the technical field of optical frequency combs, in particular to a device for generating a double-optical frequency comb based on a nonlinear amplification loop mirror mode-locked laser, and the device comprises a femtosecond mode-locked fiber laser module which is used for providing stable frequency comb teeth and pulse signals; the optical fiber amplifier module is used for increasing the power of the output laser; the repetition frequency detection module is used for extracting repetition frequency signals of comb tooth intervals through photoelectric conversion; and the frequency reference and controller module is used for realizing traceable repetition frequency locking. According to the double-optical frequency comb generation device, optical frequency comb output with different repetition frequencies and high stability can be generated through the two nonlinear amplification loop mirror mode-locked laser modules, and working parameters of each laser module can be accurately regulated and controlled through the control module; therefore, the stability and adjustability of the optical frequency comb are ensured. The technology can significantly improve the performance of the optical frequency comb in high-precision distance measurement and spectral measurement applications, and has important application values and development prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of optical frequency combs, and in particular to a device for generating dual optical frequency combs based on a nonlinear amplifying loop mirror mode-locked laser. Background Art

[0002] The optical frequency comb is an advanced light source for precise frequency transfer and measurement. In the time domain, it consists of femtosecond laser pulses with uniform time intervals, while in the frequency domain, it appears as a longitudinal mode structure with fixed frequency intervals. The carrier frequency of the pulse sequence corresponds to the optical frequency f of the optical frequency comb. n , the period of the pulse envelope is the inverse of the repetition frequency 1 / f rep Correspondingly. In each cycle, the phase of the carrier and the envelope will undergo a constant phase change, that is, the carrier envelope phase shift φ, and the corresponding frequency is f ceo The frequency of any tooth in the optical frequency comb can be expressed as f n =f ceo +n×f rep The core of an optical frequency comb is a seed source that generates femtosecond laser pulses.

[0003] For the optical frequency comb generated by a low-noise mode-locked fiber laser, the fluctuation of the repetition frequency is the main factor causing the change of the optical frequency offset. Therefore, in order to achieve high-performance dual optical frequency comb applications, it is generally necessary to actively lock and control the repetition frequency of the laser. The dual optical comb system with locked repetition frequency can provide absorption spectrum resolution and accuracy exceeding MHz for gas absorption and spectral detection applications. In large-range ranging applications, the measurement accuracy of this method has reached the sub-micron level. The fluctuation of the carrier envelope offset frequency is another factor that affects the performance of the dual optical frequency comb. Controlling and reducing the relative carrier envelope offset frequency fluctuation between the two optical frequency combs is the key to achieving high-precision spectroscopy and ranging applications.

[0004] In order to achieve low-noise femtosecond mode-locked laser output, nonlinear polarization rotation and material-based saturable absorbers (such as semiconductor saturable absorber mirrors SESAM) are usually used as mode-locked media. However, these methods have limitations. For example, nonlinear polarization rotation mode locking is subject to the reproducibility and long-term stability problems brought about by the technology itself, and material-based saturated absorbers are subject to the material life. In addition, when using a free-running dual-comb, the two lasers have large repetition frequency difference noise and relative carrier envelope offset fluctuations due to the different working ring mirrors and pump lasers, which is not conducive to the measurement accuracy of applications such as dual-comb spectroscopy and precision ranging. Summary of the invention

[0005] In order to solve the problems of long-term stability of current dual optical frequency combs and consistency of carrier-envelope offset frequency between the dual combs, the present invention proposes a dual optical frequency comb generating device to overcome the limitations of existing optical frequency comb technology and realize a low-noise, high-precision, long-term stable dual optical frequency comb system, thereby meeting the growing needs of high-precision spectral analysis and ranging.

[0006] The technical solution of the present invention is as follows:

[0007] A dual optical frequency comb generating device comprises: a femtosecond mode-locked fiber laser module for providing stable frequency comb teeth and pulse signals; a fiber amplifier module for increasing the power of the output laser; a repetition frequency detection module for extracting the repetition frequency signal of the comb tooth interval through photoelectric conversion; and a frequency reference and controller module for achieving traceable repetition frequency locking.

[0008] The femtosecond mode-locked fiber laser module comprises: two dispersion-managed femtosecond mode-locked fiber lasers based on nonlinear amplifying ring mirrors with the same cavity structure; a single-mode 976nm semiconductor laser and its driving circuit that simultaneously pump the two fiber lasers through optical fiber coupler splitting, so as to reduce the relative carrier envelope offset frequency fluctuation between the dual optical combs; and a packaging mechanical shell and a temperature-controlled driving circuit for maintaining the two femtosecond mode-locked fiber lasers in the same ring mirror, so as to reduce the relative repetition frequency fluctuation between the dual optical combs.

[0009] The femtosecond mode-locked fiber laser module has a cavity length tuning structure composed of a fiber collimator, piezoelectric ceramics (PZT), and a total reflection mirror, or has a cavity length tuning structure in which an optical fiber in a resonant cavity is wound around or attached to a piezoelectric ceramic.

[0010] The femtosecond mode-locked fiber laser module has a resonant cavity formed by connecting a fiber coupler, a wavelength division multiplexer, a gain fiber, a dispersion compensation module, a phase biaser and a polarization-maintaining fiber.

[0011] The femtosecond mode-locked fiber laser module generates a mode-locked laser pulse with a repetition frequency of 1 MHz to 10 GHz and a central wavelength of 1030 nm, 1064 nm or 1550 nm.

[0012] The fiber amplifier module comprises: two all-fiber rare earth ion-doped fiber amplifiers to achieve 50mW to 10W laser output; full polarization-maintaining dispersion-compensating fiber (DCF) provides ultrashort pulse output achieved by dispersion.

[0013] Furthermore, a wide supercontinuum spectrum covering 600nm to 2400nm can be generated by injecting amplified high-peak power pulsed laser into highly nonlinear optical fiber or highly nonlinear waveguide crystal, and a mid-infrared optical frequency comb covering 3100nm to 3400nm can be obtained by optical difference frequency technology.

[0014] The repetition frequency detection module includes: a photodiode that completes photoelectric conversion of the laser pulse output by the femtosecond mode-locked laser; a low-pass filter that filters the radio frequency signal output by the photodiode; and a radio frequency amplifier that amplifies the power of the filtered radio frequency signal.

[0015] The frequency reference and controller module includes: a reference RF frequency source, which provides an ultra-stable frequency; an arbitrary signal generator configured to transmit the ultra-stable frequency reference stability and generate an RF signal mixed with the RF repetition frequency generated by the frequency repetition frequency detection module; an analog proportional integral differential (PID) controller, which is configured to process the mixing signal and control the movement of the piezoelectric ceramics in the femtosecond mode-locked fiber laser module.

[0016] The beneficial effects of the technical solution provided by the present invention are:

[0017] 1) Compared with the existing technology, it is possible to produce a dual optical frequency comb with full polarization-maintaining fiber structure, long-term stability, low noise, repetition frequency locking and traceability; the system robustness and environmental interference resistance of the present invention are enhanced, which is conducive to the practical application of the dual optical frequency comb system outside the laboratory.

[0018] 2) Pumping two optical frequency combs with the same semiconductor laser and encapsulating them in the same temperature-controlled mechanical housing is beneficial to the instantaneous and long-term consistency between the two combs, and is beneficial to the interference signal acquisition and subsequent phase correction calculation in dual optical comb precision ranging and spectral measurement applications, thereby improving the accuracy of optical comb measurement applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the structure of a dual optical frequency comb generation device based on a nonlinear amplified loop mirror mode-locked laser;

[0020] Figure 2 This is a schematic diagram of the structure of a dual optical frequency comb generation device based on a nonlinear amplifying ring mirror mode-locked laser.

[0021] Figure 3 It is a dual optical frequency comb generation device based on nonlinear amplifying ring mirror mode-locked laser, and the basic parameters of the output lasers of two mode-locked fiber lasers.

[0022] Figure 4The repetition frequency stability of a dual optical frequency comb generator based on a nonlinear amplified loop mirror mode-locked laser was measured for free operation.

[0023] Figure 5 The repetition frequency stability of a dual optical frequency comb generation device based on a nonlinear amplifying loop mirror mode-locked laser is measured after locking the repetition frequency. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0025] The embodiment of the present invention provides a device for generating a dual optical frequency comb based on a nonlinear amplifying loop mirror mode-locked laser, the device comprising: a femtosecond mode-locked fiber laser module (101) for providing stable comb teeth and pulse signals; a fiber amplifier module (102) for increasing the output power of a relatively small seed to hundreds of milliwatts; a repetition frequency detection module (103) for extracting a comb tooth interval signal through photoelectric conversion to achieve repetition frequency stability; and a frequency reference and controller module (104) for achieving traceable optical frequency repetition frequency locking. The dual optical frequency comb generating device of the present invention can generate optical frequency comb outputs with different repetition frequencies and high stability through two nonlinear amplifying loop mirror mode-locked laser modules, and can accurately control the working parameters of each laser module through a control module to ensure the stability and adjustability of the optical frequency comb.

[0026] More specifically, the schematic diagram of the nonlinear amplifying loop mirror mode-locked laser structure used in the femtosecond mode-locked fiber laser module can be found in Figure 2 , consisting of a nonlinear amplifying ring mirror loop and a linear arm with a cavity length tuning mechanism. They are connected by a 2×2 polarization-maintaining fiber coupler with a splitting ratio of 30:70 at 1550nm. The cavity length tuning mechanism consists of a reflector and a collimator mounted on piezoelectric ceramics. The nonlinear amplifying ring mirror loop includes a 976 / 1550nm polarization-maintaining wavelength division multiplexer and an erbium-doped fiber as the gain medium. A section of PM1550 fiber is used to induce the nonlinear phase shift difference between clockwise and counterclockwise propagation, and a section of dispersion compensation fiber with matching length is used to adjust the net dispersion in the cavity to zero. A nonreciprocal phase shifter (PS) provides a -π / 2 linear phase bias. The 0.5m erbium-doped fiber is core-pumped by a single-mode 976nm laser through a 976 / 1550 wavelength division multiplexer. The rest of the fiber cavity is composed of PM1550 fiber. The laser cavity is entirely composed of PM fiber and fiber components to improve the long-term stability of the output pulse. In addition, the two lasers are packaged together in the same mechanical housing and subjected to two-level gradient temperature control. The pump source uses the same single-mode 976nm semiconductor diode, which is split by a 976nm fiber coupler and then pumped to achieve long-term common-mode consistency of the two optical combs.

[0027] The fiber amplifier module consists of two erbium-doped fiber amplifiers with the same structure. The single-channel structure is as follows: the erbium-doped fiber with a length of 1m is core-pumped by a single-mode 976nm laser diode through a 976 / 1550 wavelength division multiplexer, and two 1550nm polarization-maintaining fiber isolators are used at the seed input port and the amplifier output port, respectively. The output end isolator has a 1% tap monitoring end. The negative dispersion introduced by the balanced amplification link using a 2m long dispersion-compensating fiber is used to achieve amplified femtosecond pulse output, with an output power of >50mW.

[0028] The repetition frequency detection module consists of two indium gallium arsenide photodiodes that are applied with a reverse bias voltage. The bias voltage is 12V. The photodiodes are coupled to the monitoring end of the amplifier module output isolator through optical fiber. The RF signal output port is equipped with a 200MHz low-pass filter to filter out and retain the baseband repetition frequency signal. The RF amplifier is used to increase the signal power.

[0029] The frequency reference and controller module includes a reference RF frequency source, which is a commercial rubidium atomic clock that can stably output a clock signal with a stable frequency of 10MHz. Based on the clock signal, a direct digital frequency synthesizer based on the AD9959 chip is used to realize two-way tuning stepping sub-Hz arbitrary frequency generation between 0-100MHz, and the generation frequency is the target repetition frequency of the dual optical frequency comb. After the generation frequency is mixed with the repetition frequency signal of the mode-locked laser obtained by photoelectric detection, a 1MHz low-pass filter is used to obtain the error signal; the analog proportional integral differential (PID) controller is a second-order proportional integral differential controller composed of an AD825 operational amplifier chip and capacitors and resistors. The error signal is calculated by the controller to output a low-voltage control signal; the low-voltage control signal is amplified by 20 times in phase through the high-voltage operational amplifier OPA455 and output to the piezoelectric ceramic tuning cavity length.

[0030] like Figure 3 As shown in the figure, when the pump power intensity of the femtosecond mode-locked fiber laser module is adjusted to 268mW, the two lasers can achieve stable self-starting, and the pump power can be stable in single pulse operation between 268mW and 470m. The spectrum analyzer measured that the repetition frequency of the two lasers is about 102.3MHz, and the signal-to-noise ratio reaches 70dB, which is due to the excellent stability brought by the full polarization-maintaining fiber structure. Figure 4As shown in the figure, the maximum repetition frequency change of the two optical combs within 40 hours under constant temperature control is only 27Hz, and they always maintain synchronous fluctuations. Using the frequency reference and controller module, the two optical combs can be locked to the same reference rubidium clock. As shown in the figure, the repetition frequencies of the dual combs are 102.342850MHz and 102.340250MHz respectively, and the repetition frequency difference of the two lasers is stable at 2.6KHz. The standard deviation frequency fluctuation within 6 hours is only 18uHz and 17uHz, which verifies the effectiveness of this method.

[0031] This embodiment generates dual optical frequency combs through two nonlinear amplifying loop mirror mode-locked lasers with the same structure, and uses a shared pump source and temperature control technology to achieve long-term common mode consistency, effectively reducing the relative frequency fluctuation between the dual optical combs. Using a commercial rubidium atomic clock as the reference frequency source, combined with a direct digital frequency synthesizer and a PID controller, high-precision locking of the repetition frequency of the dual optical comb is achieved, and the locking accuracy reaches the sub-Hz level, ensuring the long-term stability and traceability of the frequency comb. The laser cavity and amplifier all use polarization-maintaining fiber and fiber components, which effectively reduces the impact of polarization noise and external environment on system performance and improves the stability and signal-to-noise ratio of the output pulse. The cavity length tuning mechanism composed of a reflector and a collimator installed on a piezoelectric ceramic can accurately adjust the cavity length of the laser, thereby achieving flexible control of the repetition frequency and enhancing the adjustability and applicability of the system. The fiber amplifier module uses two erbium-doped fiber amplifiers with the same structure, and achieves efficient and high-quality pulse amplification by balancing the negative dispersion introduced by the dispersion compensation fiber amplification link. The output power can reach hundreds of milliwatts, meeting the needs of a variety of application scenarios.

Claims

1. A device for generating dual optical frequency combs based on a nonlinear amplified loop mirror mode-locked laser, characterized in that: include: A femtosecond mode-locked fiber laser module is used to provide stable frequency comb teeth and pulse signals, including at least two nonlinear amplifying ring mirror mode-locked lasers, each of which includes a nonlinear amplifying ring mirror loop and a linear arm with a cavity length tuning mechanism, which are connected through a polarization-maintaining fiber coupler. The two nonlinear amplifying ring mirror mode-locked lasers are packaged together in the same mechanical housing and subjected to two-stage gradient temperature control. The pump source uses the same single-mode 976nm semiconductor diode for pumping after splitting through a fiber coupler to achieve long-term common-mode consistency of the two optical combs. The fiber amplifier module is connected to the femtosecond mode-locked fiber laser module to increase the power of the output laser; A repetition frequency detection module, used for extracting the repetition frequency signal of the comb tooth interval through photoelectric conversion; Frequency reference and controller module for traceable, repetitive frequency locking.

2. The device for generating dual optical frequency combs based on a nonlinear amplified loop mirror mode-locked laser according to claim 1, characterized in that: The femtosecond mode-locked fiber laser module has a cavity length tuning structure, which is composed of a fiber collimator, piezoelectric ceramics (PZT), and a total reflection mirror, or is composed of an optical fiber wound in a resonant cavity or attached to a piezoelectric ceramic.

3. The device for generating dual optical frequency combs based on a nonlinear amplifying loop mirror mode-locked laser according to claim 1, characterized in that: The femtosecond mode-locked fiber laser module has a resonant cavity formed by connecting a fiber coupler, a wavelength division multiplexer, a gain fiber, a dispersion compensation module, a phase biaser and a polarization-maintaining fiber.

4. The device for generating dual optical frequency combs based on a nonlinear amplified loop mirror mode-locked laser according to claim 1, characterized in that: The femtosecond mode-locked fiber laser module generates a mode-locked laser pulse with a repetition frequency of 1 MHz to 10 GHz and a central wavelength of 1030 nm, 1064 nm or 1550 nm.

5. The device for generating dual optical frequency combs based on a nonlinear amplified loop mirror mode-locked laser according to claim 1, characterized in that: The nonlinear amplifying loop mirror mode-locked laser can achieve stable self-starting when the pump power reaches a certain threshold, and can maintain stable single-pulse operation within a wider pump power range. The repetition frequencies of the two lasers are highly consistent and the signal-to-noise ratio is excellent.

6. According to the device for generating dual optical frequency combs based on nonlinear amplifying loop mirror mode-locked lasers as claimed in claim 1, the fiber amplifier module comprises: Two all-fiber rare-earth ion-doped fiber amplifiers, achieving 50mW to 10W laser output; Using the dispersion compensation module, ultra-short pulse output is provided.

7. According to the device for generating dual optical frequency combs based on nonlinear amplified loop mirror mode-locked lasers as claimed in claim 1, the repetition frequency detection module comprises: A photodiode for performing photoelectric conversion on the laser pulse output by the femtosecond mode-locked laser; A low-pass filter for filtering the radio frequency signal output by the photodiode; The radio frequency amplifier amplifies the power of the filtered radio frequency signal.

8. According to the device for generating dual optical frequency combs based on nonlinear amplified loop mirror mode-locked lasers as claimed in claim 1, the frequency reference and controller module comprises: Reference clock source, providing ultra-stable RF clock signal; Arbitrary signal generator or direct digital frequency synthesizer, used to generate arbitrary RF frequency signal while delivering the stability of the clock source; An analog proportional integral derivative (PID) controller is configured to process the mixing signal and control the movement of the piezoelectric ceramic in the femtosecond mode-locked fiber laser module.

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