An optical frequency comb automatic recovery device and method

Abstract

The application discloses an optical frequency comb automatic recovery device and method, and belongs to the field of silicon-based nonlinear optical photoelectric modulation. The application comprises a laser, an IQ modulator, an acousto-optic modulator, a fiber amplifier, a polarization controller, a micro-ring resonator, a phase-locked loop, an arbitrary waveform generator, a photoelectric detector, a PID module and an upper computer. Transmission loss of an optical frequency comb debugging system is tested, which comprises fiber loss before laser enters a microcavity and transmission loss after the laser enters the microcavity; the output frequency range of the phase-locked loop is adjusted, and frequency scanning is performed on the microcavity; laser wavelength is entered from blue detuning, the output power of the laser is gradually reduced through the acousto-optic modulator, and the wavelength is kept unchanged; when the PID detects a power rise, the laser power is quickly raised until the PID detects a rising step; the laser frequency is slowly increased and the power is kept unchanged until a single soliton optical frequency comb is observed; when the single soliton disappears, the control steps after the laser wavelength is entered from blue detuning are repeated, and the optical frequency comb is automatically recovered.

Description

TECHNICAL FIELD

[0001] The application discloses an optical frequency comb automatic generation recovery device and method based on an optical microcavity, and belongs to the technical field of silicon-based nonlinear optical photoelectric modulation. BACKGROUND

[0002] In recent years, microcavity optical frequency combs have attracted extensive attention due to their high bandwidth and high repetition frequency characteristics, and can be used for large-scale coherent optical communication and high-speed ranging applications. The optical frequency comb generated based on a microcavity is divided into several different states, such as a Turing state, a subcomb, a noise state, a multi-soliton state, a soliton crystal and a single-soliton state, according to the stage of dynamic evolution. The single-soliton state has the characteristics of low noise and phase stability, and is the most important state in applications. However, due to the existence of certain loss and dispersion of the microcavity material, the laser entering the microcavity needs to satisfy a certain optical power, and after overcoming the waveguide loss, the strong optical field intensity induces a third-order nonlinear polarization, and the generated nonlinear effect can be balanced with the dispersion of the waveguide material itself. When the microcavity satisfies the double balance of gain and loss and dispersion and nonlinear effect, the single-soliton state can be realized. Moreover, the waveguide material has a thermal-optic effect to a certain extent, so that the temperature change of the material caused by high-power laser in the debugging process causes the drift of the resonant wavelength, and therefore, the optical debugging of the microcavity optical frequency comb has a certain difficulty.

[0003] In order to reduce the influence of the thermal-optic effect on the soliton debugging process, the currently used method mainly uses two lasers to pump the microcavity, the pump laser and the auxiliary laser enter the microcavity at the same time from the blue detuning, the pump laser frequency is scanned to gradually enter the red detuning, in this process, the resonant wavelength is red-shifted due to the increase of the cavity power, the auxiliary laser is still in the blue detuning, and the detuning amount is increased, so that the cavity power decrease caused by the auxiliary laser leads to the blue shift of the resonant wavelength. The pump laser frequency is continuously scanned to enter the red detuning, the cavity power decreases after entering the soliton state, and the blue shift of the resonant wavelength reduces the detuning amount of the auxiliary laser, and the cavity power increases. In this way, under the action of the auxiliary laser, the total power in the microcavity can be maintained at a constant value, and the influence of the thermal-optic effect on the soliton state is reduced. Although this device can obtain a single-soliton optical frequency comb, the configuration of two lasers makes the device large, and the operation process is relatively complicated, which hinders the miniaturization development of the microcavity optical frequency comb, and further hinders the progress of the application verification outside the laboratory.

[0004] A robust and miniaturized microcavity optical frequency comb system is of great significance for the subsequent application of the optical frequency comb. A high-quality factor microcavity can provide higher optical localization and high gain, which can provide sufficient cavity optical field intensity to realize parametric oscillation on the one hand, and effectively reduce the input power to realize the integration of a chip semiconductor laser and a microcavity device on the other hand, which is the development trend of the future microcavity optical frequency comb application. Therefore, optimizing the microcavity device preparation method to obtain a high-quality factor silicon nitride microcavity is an urgent problem to be solved in the application of the optical frequency comb. SUMMARY

[0005] In order to solve the problem that the existing microcavity optical frequency comb single soliton state debugging process is complicated and cannot be automatically recovered, the purpose of the present application is to provide an optical frequency comb automatic recovery device and method, which quickly tunes the wavelength of the laser through an IQ modulator; modulates the intensity of the laser through an acousto-optic modulator; detects the rising and falling edges of the output power detected by the photodetector through a PID, and feeds back the laser, phase-locked loop and arbitrary waveform generator through the host computer to realize the monitoring and automatic searching of the optical frequency comb soliton state, thereby automatically generating and recovering the soliton state, and improving the debugging accuracy and efficiency of the microcavity optical frequency comb single soliton state.

[0006] The purpose of the present application is realized through the following technical solutions.

[0007] The optical frequency comb automatic recovery device disclosed by the present application comprises a laser, an IQ modulator, an acousto-optic modulator, a fiber amplifier, a polarization controller, a microcavity, a voltage-controlled oscillator, an arbitrary waveform generator, a photodetector, a PID module and a host computer.

[0008] The laser is a narrow linewidth laser serving as a pump light source; the IQ modulator is a Mach-Zehnder modulator based on a double-parallel structure of lithium niobate, which is used to generate a carrier-suppressed single sideband and realize the tuning of the optical wavelength of the laser; the acousto-optic modulator is used to modulate the optical power of the laser; the fiber amplifier is an erbium-doped or erbium-ytterbium co-doped fiber amplifier, which is used to amplify the optical power of the laser; the polarization controller is used to adjust the polarization direction of the laser to match the polarization direction in the microcavity; the microcavity is a nonlinear optical passive device, which is used to generate a nonlinear Kerr effect to produce an optical frequency comb; the output oscillation frequency of the voltage-controlled oscillator is used as the radio frequency input of the IQ modulator, i.e., the tuning range; the arbitrary waveform generator is used to generate a linear voltage signal to control the acousto-optic modulator; the photodetector is used to receive the optical signal output from the microcavity and convert it into an electrical signal; the PID module is used to monitor the output electrical signal, judge the rising and falling edges, and feed back signals to the laser, the IQ modulator and the acousto-optic modulator; and the host computer is used to control the laser and the arbitrary waveform generator and the like.

[0009] The optical frequency comb automatic recovery method disclosed by the present application is realized based on the optical frequency comb automatic recovery device and comprises the following steps.

[0010] Step one: test the transmission loss of the optical frequency comb debugging system, wherein the transmission loss comprises the coupling alignment loss before the laser enters the microcavity and the waveguide transmission loss after the laser enters the microcavity, and the difference in optical power before and after the laser enters the microcavity is the sum of the two-end coupling loss and the waveguide loss;

[0011] Step two: adjust the bias voltage of the voltage-controlled oscillator in the phase-locked loop to change its output frequency, which is applied to the IQ modulator as a radio frequency signal, and the laser passes through the IQ modulator in the single sideband modulation state, and the output light is a single sideband that moves the output frequency by the input laser frequency, the amplitude change and the change rate of the bias voltage of the voltage-controlled oscillator in the phase-locked loop, that is, the sweep range and the scanning rate of the laser, thereby realizing the effect of frequency scanning of the microcavity, and obtaining the transmission curve of the microcavity;

[0012] Step three: control the bias voltage of the voltage-controlled oscillator in the phase-locked loop to make the laser wavelength from the blue detuning into the microcavity, at this time the output optical power of the microcavity gradually decreases, the output power of the laser is gradually reduced by adjusting the bias voltage of the acousto-optic modulator, and the wavelength is kept unchanged, when the PID detects that the optical power rises, the bias voltage of the acousto-optic modulator is controlled to make the laser power rise rapidly until the PID detects the rising step, at this time the power of the radio frequency input signal of the IQ modulator is slowly increased to increase the laser frequency and keep the input power unchanged until the single soliton optical frequency comb is observed;

[0013] Step four: when the PID detects that the output optical power rises again, it means that the single soliton disappears, at this time the host computer repeats step three, that is, the laser and the arbitrary waveform generator are controlled to return to the initial state again, thereby realizing the automatic recovery of the optical frequency comb.

[0014] Advantages:

[0015] 1. The optical frequency comb automatic recovery device and method disclosed by the application realizes the frequency sweeping function of the laser by using the phase-locked loop, can realize large-range and rapid frequency scanning, and realizes the accurate control of the frequency change of the laser through time series.

[0016] 2. The optical frequency comb automatic recovery device and method disclosed by the application detects the change of the output power of the microcavity by using the PID, can quickly and accurately detect the weak change of the output power of the microcavity, and realizes the accurate feedback control of the laser.

[0017] The modulation device can automatically generate and recover the soliton state, solves the problems that the existing microcavity optical frequency comb single soliton state debugging process is complicated and cannot be automatically recovered, can realize the robust microcavity optical frequency comb single soliton state, and has important significance for realizing the programmed control of the optical frequency comb system and small-sized application. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a schematic diagram of an optical system of the optical frequency comb automatic recovery device of the application;

[0019] Figure 2 It is a flow chart of the optical frequency comb automatic recovery method of the application. DETAILED DESCRIPTION

[0020] The application will be further described below in connection with the accompanying drawings and embodiments.

[0021] Embodiment 1

[0022] Please refer to Figure 1 and Figure 2 The embodiment discloses an optical frequency comb automatic recovery device, which comprises a laser 1, an IQ modulator 2, an acousto-optic modulator 3, a fiber amplifier 4, a polarization controller 5, a micro-ring resonator 6, a photodetector 7, a PID module 8, an arbitrary waveform generator 9, a phase-locked loop 10 and an upper computer 11.

[0023] The laser 1 is a narrow linewidth laser, which is used as a pump light source and has a wavelength range of 1540 nm to 1570 nm; the IQ modulator 2 is a Mach-Zehnder structure modulator based on a double-parallel structure of lithium niobate, which is used to generate a carrier-suppressed single sideband and realize the tuning of the wavelength of the laser, and generally adopts a modulator with a modulation bandwidth of more than GHz; the acousto-optic modulator 3 is used to realize the modulation of the optical power of the laser; the fiber amplifier 4 is an erbium-doped or erbium-ytterbium co-doped fiber amplifier, which is used to amplify the optical power of the laser, and the amplified power is in the order of watts; the polarization controller 5 is used to adjust the polarization direction of the laser to match the polarization direction in the microcavity; the micro-ring resonator 6 is a nonlinear optical passive device, which is used to generate a nonlinear Kerr effect to generate an optical frequency comb, and is generally made of silicon nitride, silicon oxide, magnesium fluoride, aluminum nitride, gallium nitride or lithium niobate, and the quality factor is required to be at least in the order of 10 6 The output oscillation frequency of the voltage-controlled oscillator function of the phase-locked loop 10 is used as the radio frequency input of the IQ modulator 2, that is, the tuning range, and generally requires a tuning range of more than GHz; the arbitrary waveform generator 9 is used to generate a linear voltage signal to control the acousto-optic modulator 3; the photodetector 7 is used to receive the optical signal output from the micro-ring resonator 6 and convert it into an electrical signal; the PID module 8 is used to monitor the output electrical signal and determine the rising and falling edges to feed back signals to the laser 1, the IQ modulator 2 and the acousto-optic modulator 3; and the upper computer 11 is used to program control the laser 1, the phase-locked loop 10 and other devices.

[0024] 3. The optical frequency comb automatic recovery method comprises:

[0025] Step one: test the transmission loss of the optical frequency comb debugging system, wherein the transmission loss includes the coupling alignment loss before the laser 1 enters the micro-ring resonator 6 and the waveguide transmission loss after entering the microcavity, and the difference between the optical power before and after entering the microcavity is the sum of the two-end coupling loss and the waveguide loss;

[0026] Step two: adjust the bias voltage of the voltage-controlled oscillator in the phase-locked loop 10 to change its output frequency, which is applied to the IQ modulator 2 as a radio frequency signal, the laser passes through the IQ modulator 2 in the single sideband modulation state, and the output light is a single sideband that moves the output frequency by the input laser frequency, the amplitude change and the change rate of the bias voltage of the voltage-controlled oscillator, that is, the sweep range and the scanning rate of the laser 1, so as to realize the frequency scanning effect of the micro ring resonant cavity 6, and obtain the transmission curve of the micro cavity;

[0027] Step three: control the bias voltage of the voltage-controlled oscillator in the phase-locked loop 10 to make the laser wavelength from the blue detuning into the microcavity, at this time the output optical power of the microcavity gradually decreases, by adjusting the bias voltage of the acousto-optic modulator 3 to gradually reduce the output power of the laser, and keeping the wavelength unchanged, when the PID module 8 detects the rising of the optical power, the acousto-optic modulator 3 is controlled to make the laser power rise rapidly until the PID module 8 detects the rising step, at this time the radio frequency signal frequency of the IQ modulator 2 is adjusted, the laser frequency is slowly increased and the input power is kept unchanged, until the single soliton optical frequency comb is observed;

[0028] Step four: when the PID module 8 detects the rising of the output optical power again, it means that the single soliton disappears, at this time the host computer 11 repeats step three, that is, the laser and the arbitrary waveform generator 9 are controlled to return to the initial state again, so as to realize the automatic recovery of the optical frequency comb.

[0029] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any modification, equivalent replacement, improvement, etc. made by those skilled in the art within the technical scope disclosed by the present application shall be included in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. An automatic recovery method for an optical frequency comb, characterized in that: An automatic recovery device for optical frequency combs includes a laser, an IQ modulator, an acousto-optic modulator, an optical fiber amplifier, a polarization controller, a micro-ring resonator, a phase-locked loop, an arbitrary waveform generator, a photodetector, a PID module, and a host computer. The automatic recovery method for optical frequency combs includes the following steps: Step 1: Test the transmission loss of the optical frequency comb tuning system. The transmission loss includes the coupling alignment loss before the laser enters the micro-ring resonator and the waveguide transmission loss after entering the micro-ring resonator. The difference in optical power before and after entering the micro-ring resonator is the sum of the coupling loss at both ends and the waveguide loss. Step 2: Adjust the bias voltage of the voltage-controlled oscillator in the phase-locked loop to change its output frequency. This output frequency is applied as an RF signal to the IQ modulator. The laser passes through the IQ modulator in single-sideband modulation mode, and its output light is a single-sideband shifted by the same amount as the input laser frequency. Control the amplitude and rate of change of the bias voltage of the voltage-controlled oscillator in the phase-locked loop, which corresponds to the sweep frequency range and scanning rate of the laser, thereby achieving the effect of frequency scanning of the micro-ring resonator and obtaining the transmission curve of the micro-ring resonator. Step 3: Control the bias voltage of the voltage-controlled oscillator in the phase-locked loop to allow the laser wavelength to enter the micro-ring resonator from blue detuning. At this time, the output optical power of the micro-ring resonator gradually decreases. By adjusting the bias voltage of the acousto-optic modulator, the output power of the laser is gradually reduced while keeping the wavelength constant. When the PID module detects an increase in optical power, the bias voltage of the acousto-optic modulator is controlled to make the laser power rise rapidly until the PID module detects the rising step. At this time, the frequency of the RF input signal of the IQ modulator is adjusted to slowly increase the laser frequency while keeping the input power constant until a single soliton optical frequency comb is observed. Step 4: When the PID module detects an increase in output optical power again, it indicates that the soliton has disappeared. At this time, the host computer repeats step 3, that is, controls the laser and arbitrary waveform generator to return to the initial state, thereby realizing the automatic recovery of the optical frequency comb.

2. The automatic recovery method for an optical frequency comb as described in claim 1, characterized in that: The laser is a narrow-linewidth laser, serving as the pump source; the IQ modulator is a Mach-Zehnder structure modulator based on a lithium niobate double parallel structure, used to generate a carrier-suppressed single sideband to tune the laser wavelength; the acousto-optic modulator is used to modulate the laser power; the fiber amplifier is an erbium-doped or erbium-ytterbium co-doped fiber amplifier, used to amplify the laser power; the polarization controller is used to adjust the laser's polarization direction to match the polarization direction within the microring resonant cavity; the microring resonant cavity is a nonlinear optical passive device used to generate a nonlinear Kerr effect to produce an optical frequency comb; the output oscillation frequency of the voltage-controlled oscillator within the phase-locked loop serves as the RF input of the IQ modulator, i.e., the tuning range; and the arbitrary waveform generator is used to generate a linear voltage signal to control the acousto-optic modulator. Photodetectors are used to receive optical signals output from a microring resonant cavity and convert them into electrical signals; The PID module is used to monitor the output electrical signal and determine the rising and falling edges to provide feedback signals to the laser, IQ modulator, and acousto-optic modulator; the host computer is used to control the laser and arbitrary waveform generator.

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