All-lithium niobate-based integrated optical frequency synthesizer

Abstract

The invention relates to an all-lithium niobate-based integrated optical frequency synthesizer. The structure of the all-lithium niobate-based integrated optical frequency synthesizer comprises a pump laser module, a modulator module, a tunable laser module, a frequency doubling laser module, a high repetition frequency optical frequency comb, a low repetition frequency optical frequency comb, a photoelectric detector module and the like, all the modules are lithium niobate bases and are all integrated on the same lithium niobate chip. By using the electro-optical effect and the nonlinear optical effect of lithium niobate, the generation of an optical frequency comb and a super-continuum spectrum is facilitated, further frequency coverage and accurate frequency synthesis in a wide spectrum range are realized, a self-reference microwave-optical link is constructed, and accurate interconnection and synchronization of signals are realized. A cooperative double-frequency comb technology is adopted, and fine tuning of wavelength is realized through a cross feedback mechanism and integrated signal processing. The process not only optimizes the performance of the optical frequency synthesizer, but also significantly improves the working bandwidth of the optical frequency synthesizer, and ensures high precision and high stability of the synthesized signal.

Description

Technical Field

[0001] The invention relates to an optical frequency synthesizer, in particular to an all-lithium niobate-based integrated optical frequency synthesizer. Background Art

[0002] With the continuous progress of electronic integrated circuit technology, the line width of integrated circuits prepared by traditional photolithography has approached the atomic scale, which makes electronic chips gradually reach their physical limits in key performance indicators such as bandwidth and energy consumption. Faced with this challenge, photonic technology, with its significant advantages such as high bandwidth, low loss and parallel transmission, has become the key to promoting the development of next-generation information processing technology. At present, the research on integrated photonic chips has become a hot topic in the global scientific research field. The development of integrated photonic chips depends on the high-density integration of optical components with different functions on the photonic platform. These components include but are not limited to light sources, electro-optical modulators, optical amplifiers and photodetectors. The integration of these components is the basis for realizing high-density and high-performance photonic chips. Lithium niobate has always received great attention in the field of photonic device manufacturing due to its stable physical and chemical properties, large nonlinear coefficients and electro-optical coefficients, and wide optical transparency window. Since its advent, lithium niobate has been regarded as a photonic chip supporting material with great potential, providing a solid material foundation for realizing more efficient and advanced photonic integration technology.

[0003] Frequency synthesizers are the product of the demand for precise frequency sources in modern communications, navigation, radar and other fields. Microwave frequency synthesizers generate the required frequency in the microwave band and are widely used in scientific research and industry. As a technological innovation, optical frequency synthesizers have great potential in satellite communications, environmental monitoring and other fields. However, traditional equipment is mainly limited to laboratory use due to size, weight, power consumption and cost. Summary of the invention

[0004] The purpose of the present invention is to provide a full lithium niobate based integrated optical frequency synthesizer to solve the problems of complex structure and high power consumption of traditional frequency synthesizers.

[0005] The present invention is achieved in that: A fully lithium niobate-based integrated optical frequency synthesizer, comprising: A pump laser module is connected to the modulator module and serves as a pump source for exciting the optical frequency comb; A modulator module is connected to the pump laser module, the high repetition rate optical frequency comb and the low repetition rate optical frequency comb respectively, and is used to independently control the high repetition rate optical frequency comb and the low repetition rate optical frequency comb; A high repetition rate optical frequency comb is connected to the modulator module and the photodetector module respectively to provide a self-reference of the frequency-doubled signal; The frequency-doubling laser module is connected to the photodetector module to broaden the overall working spectrum range of the device; The low repetition rate optical frequency comb is connected to the modulator module and the photodetector module respectively, and is used to match the comb tooth frequency of the high repetition rate frequency comb, providing a precise frequency synthesis reference and signal relay; A photodetector module, connected to the high repetition rate optical frequency comb, the low repetition rate optical frequency comb and the tunable laser module, respectively, for detecting optical signals and providing feedback; and A tunable laser module is connected to the photodetector module and is used to output an optical synthesis signal; All of the above modules are based on lithium niobate and are all integrated on a lithium niobate chip.

[0006] Furthermore, a signal generation region of an integrated optical frequency synthesizer is formed by a pump laser module, a modulator module, a high repetition rate optical frequency comb and a low repetition rate optical frequency comb, which are used to generate two dissipative Kerr optical frequency combs and lock them to a stable micro-comb reference source.

[0007] Furthermore, an optical frequency comb dual-comb system is formed by a low repetition rate optical frequency comb and a high repetition rate optical frequency comb to precisely control the comb teeth spacing and realize coherent multiplication from microwaves to light waves; the low repetition rate optical frequency comb has a mode spacing at the GHz level; the high repetition rate optical frequency comb has a mode spacing at the THz level; both adopt a lithium niobate micro-resonant cavity structure.

[0008] Furthermore, by adjusting the relative comb lines of the low repetition rate optical frequency comb, the terahertz frequency interval of the high repetition rate optical frequency comb is locked to guide the tuning of the tunable laser module.

[0009] Furthermore, the frequency of the carrier-envelope detuning is determined by measuring the optical heterodyne beat note between the high-repetition-rate optical frequency comb and the low-repetition-rate optical frequency comb, and the measured signal is fed back to the pump laser module, and the frequency is stabilized by phase-locking to the synthetic radio frequency.

[0010] Furthermore, lithium niobate waveguides are used to achieve efficient coupling between individual optoelectronic devices and modules.

[0011] In the optical frequency synthesizer of the present invention, the pump laser module is first processed by a high repetition rate optical frequency comb and a low repetition rate optical frequency comb to generate two sets of optical frequency comb signals respectively. The two sets of optical frequency comb signals are then combined and input into a tunable laser module to jointly constitute the output source of the frequency synthesizer. The high repetition rate optical frequency comb has the ability of self-calibration due to its wide spectral coverage, ensuring the accuracy of frequency synthesis. The low repetition rate optical frequency comb provides a finer frequency resolution with its narrow comb line width and limited expansion range. The comb tooth spacing of these frequency combs is set by a precise microwave reference clock to ensure the precise interval of the frequency. By precisely controlling the comb tooth spacing and the phase stability of the octave optical frequency comb, high-precision control of the optical frequency synthesizer is achieved. This process not only improves the performance of the optical frequency synthesizer, but also enhances its application potential in fields such as precision measurement and high-speed communication.

[0012] The present invention helps to generate optical frequency combs and supercontinuum spectra by utilizing the electro-optical effect and nonlinear optical effect of lithium niobate, thereby achieving frequency coverage and accurate frequency synthesis in a wide spectral range, constructing a self-referenced microwave-optical link, and realizing accurate interconnection and synchronization of signals. The collaborative dual-frequency comb technology is adopted to achieve fine tuning of the wavelength through a cross-feedback mechanism and integrated signal processing. This process not only optimizes the performance of the optical frequency synthesizer, but also significantly improves its operating bandwidth, ensuring high precision and high stability of the synthesized signal. The design of the present invention simplifies the structure, reduces energy consumption, solves the shortcomings of traditional equipment in terms of complexity and power consumption, and provides a more efficient, compact and reliable solution for the development of optical frequency synthesis technology.

[0013] The optical frequency synthesizer of the present invention proposes a new paradigm of high and low repetition frequency interlocked optical combs and a new mechanism of frequency relay transmission, fundamentally breaking through the bottleneck of the multi-wave frequency synthesis light source that requires both frequency doubling and large bandwidth and precise tunability, and realizing the organic integration of high efficiency, broadband, stability, and tunability in integrated optical frequency synthesis. The optical frequency synthesizer effectively utilizes the excellent electro-optical properties and nonlinear optical effects of lithium niobate materials through full lithium niobate integration, and can achieve large bandwidth, high precision, and high stability optical frequency synthesis, effectively solving the problems of complex structure and high power consumption of traditional frequency synthesizers. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the working principle of the optical frequency synthesizer of the present invention.

[0015] Figure 2 It is a system configuration diagram of the optical frequency synthesizer of the present invention.

[0016] Figure 3 This is the spectral output of a high-repetition-rate optical frequency comb.

[0017] Figure 4 It is a diagram of the optical signal output of the integrated optical frequency synthesizer of the present invention.

[0018] In the figure: 1. Pump laser module, 2. Modulator module, 3. Tunable laser module, 4. Frequency doubling laser module, 5. High repetition rate optical frequency comb, 6. Low repetition rate optical frequency comb, 7. Photodetector module. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings.

[0020] like Figure 1 As shown, the all-lithium niobate-based integrated optical frequency synthesizer of the present invention includes a pump laser module 1, a modulator module 2, a tunable laser module 3, a frequency doubling laser module 4, a high repetition rate optical frequency comb 5, a low repetition rate optical frequency comb 6 and a photodetector module 7. Among them, the output of the pump laser module 1 is connected to the modulator module 2 as a pump source for exciting the optical frequency comb; the output of the modulator module 2 is connected to the high repetition rate optical frequency comb 5 and the low repetition rate optical frequency comb 6 for independent control of the high repetition rate optical frequency comb 5 and the low repetition rate optical frequency comb 6; the output of the high repetition rate optical frequency comb 5 is connected to the photodetector module 7 for providing a self-reference of the frequency doubling signal; the output of the low repetition rate optical frequency comb 6 is connected to the photodetector module 7 to match the comb tooth frequency of the high repetition rate frequency comb 5, providing a precise frequency synthesis reference and signal relay; the output of the frequency doubling laser module 4 is connected to the photodetector module 7 for broadening the overall working spectrum range of the device; the output of the photodetector module 7 is connected to the tunable laser module 3 for detecting optical signals and providing feedback; the tunable laser module 3 is used to output optical synthesis signals. All of the above modules are lithium niobate-based and are all integrated on the same lithium niobate chip.

[0021] The pump laser module 1, the modulator module 2, the high repetition rate optical frequency comb 5 and the low repetition rate optical frequency comb 6 constitute the signal generation area of ​​the optical frequency synthesizer of the present invention. Among them, the pump laser module 1 adopts a lithium niobate narrow linewidth tunable laser chip, which is responsible for generating high-quality optical signals with C-band tunability, narrow linewidth and fast frequency control capabilities. In order to generate two dissipative Kerr optical frequency combs, they are required to have high laser power output performance and be locked to a stable micro-comb reference source. The low repetition rate optical frequency comb 6 and the high repetition rate optical frequency comb 5 constitute an optical frequency comb dual-comb system. These two optical combs realize the coherent multiplication from microwaves to light waves by precisely controlling the comb tooth spacing. This process not only improves the synchronization accuracy of the signal, but also greatly enhances the frequency synthesis capability of the entire system. The pump laser module 1 acts as a shared pump source for two micro-resonant comb generators in this dual-comb system. The low repetition rate optical frequency comb 6 has a GHz-level mode comb tooth spacing; the high repetition rate optical frequency comb 5 has a THz-level comb tooth spacing, both of which use lithium niobate micro-resonant cavity structures. By precisely controlling the comb spacing, coherent multiplication from microwaves to light waves is achieved, ensuring accurate synchronization of signals.

[0022] In the optical frequency synthesizer of the present invention, the high repetition rate optical frequency comb 5 successfully excites the octave single pulse soliton comb, and its spectral output is as follows: Figure 3 As shown. Through carefully designed waveguide dispersion engineering, dispersion peaks at 1 micron and 2 microns are generated in the optical power, which is attributed to the zero-integrated dispersion starting from the pump wavelength. A high side mode suppression ratio is achieved by adjusting the radius of the microresonator to select the desired longitudinal mode. However, the comb tooth spacing of the high repetition rate optical frequency comb 5 reaches the terahertz level, which is a challenge for light detection and difficult to reduce to microwave frequency using traditional electronic equipment. Therefore, the present invention uses a low repetition rate optical frequency comb 6 to make up for the spacing between high repetition rate terahertz comb modes. By adjusting the relative comb lines of the low repetition rate optical frequency comb 6, the terahertz frequency spacing of the high repetition rate optical frequency comb 5 is locked, thereby accurately guiding the tuning of the tunable laser module 3. The frequency of the carrier-envelope detuning is determined by measuring the optical heterodyne beat tone between the two combs, and the measured signal is fed back to the pump laser module 1, and the frequency is stabilized by phase locking to the synthetic radio frequency.

[0023] The optical frequency synthesizer of the present invention has a f-2f frequency stabilization region, and utilizes the x (2)Characteristics, performing frequency doubling operation on the amplified laser signal, not only achieves a high signal-to-noise ratio, but also successfully transfers the stability of the micro-comb reference source to the terahertz comb line by phase-locking to the radio frequency. The frequency is accurately measured by measuring the optical heterodyne beat note between the two optical frequency combs, and this measurement signal is fed back to the pump laser module 1, and the frequency stability is further ensured by phase-locking to the synthetic radio frequency. On this basis, the signal is phase-locked to the radio frequency, and the pump laser power is adjusted through a feedback mechanism. The heterodyne signal generated by the DKS dual-comb signal in the relative mode of the pump is input into a phase-locked loop based on a field programmable gate array and processed by digital division. Finally, the laser is locked to the DKS dual comb, producing a fully stable and adjustable optical frequency synthesizer output. The adjustable output range of the optical frequency synthesizer of the present invention is as follows Figure 4 shown.

[0024] The optical frequency synthesizer of the present invention adopts a specific locking technology to ensure the stability and accuracy of frequency synthesis. By accurately controlling the optical frequency comb spacing and bias frequency, coherent multiplication from microwave to light wave is achieved to ensure accurate synchronization of signals. The frequency is measured by measuring the optical heterodyne beat tone between the two combs and fed back to the frequency of the pump laser to achieve frequency stability.

[0025] The pump laser module 1 simultaneously serves as a shared pump source for two micro-resonant comb generators. The resonant frequency detuning of each micro-comb is precisely controlled by an amplified voltage-controlled oscillator and an arbitrary waveform generator to produce a linear voltage ramp. Using this approach, single soliton pulses can be successfully excited on both high-repetition-rate optical frequency combs and low-repetition-rate optical frequency combs. Once a soliton is formed, the system will precisely control the frequency of each voltage-controlled oscillator through a feedback mechanism to ensure optimal device matching in the GHz and THz frequency ranges. On a high-repetition-rate micro-comb, fine-tuning is performed by modulator module 2. . Lithium niobate waveguides are used to achieve efficient coupling between various optoelectronic devices and modules. Through precise control and optimized design, not only the stability and repeatability of soliton pulses are improved, but also the performance of the optical frequency synthesizer of the present invention is significantly improved, and efficient and accurate optical frequency synthesis is achieved, providing strong technical support for applications in the fields of precision measurement, high-speed communication and quantum information technology.

[0026] The working process of the optical frequency synthesizer of the present invention is: (1) starting the pump laser and the tunable laser to provide a laser source; (2) generating high repetition rate and low repetition rate optical frequency combs through the frequency generation and transmission module; (3) using the self-reference locking module to lock the two optical frequency combs; (4) outputting a stable optical signal through the frequency synthesis module.

[0027] like Figure 1As shown, the working principle of the optical frequency synthesizer of the present invention is: a high repetition rate optical frequency comb 5 and a low repetition rate optical frequency comb 6 are integrated on the same lithium niobate chip, and the two optical frequency combs are locked to each other, and a narrow linewidth adjustable laser is integrated to form a frequency synthesis module to output optical signals. The high repetition rate optical frequency 5 has a wider spectral range, but the comb line width is relatively large; the comb line width of the low repetition rate optical frequency comb 6 is narrower and the expansion range is also narrower. These comb tooth spacings are set by a microwave reference clock. High-precision optical frequency synthesis is achieved by phase stabilization of the comb spacing and the octave optical frequency comb. The pump laser module 1 acts as a pump source for the two optical frequency combs, and the modulator module 2 is used to perform detailed independent control of each comb. Since the comb tooth spacing in the high repetition rate optical frequency comb 5 is difficult to identify on the spectrum analyzer, the present invention uses the low repetition rate optical frequency comb 6 to fill this mode gap. By measuring the optical heterodyne beat sound of the two optical frequency combs separated by 1 terahertz from the pump laser, the frequency can be accurately measured. This measurement result is fed back to the pump laser module 1, and the signal is locked to the synthetic radio frequency. The precise locking of the signal can be achieved by using the frequency doubling span relationship between the terahertz peak at 2 microns and the dispersion peak at 1 micron. Finally, with these two optical frequency combs as the backbone, the tunable laser is guided to perform flexible arbitrary optical frequency synthesis.

Claims

1. A fully lithium niobate-based integrated optical frequency synthesizer, characterized in that: include: A pump laser module is connected to the modulator module and serves as a pump source for exciting the optical frequency comb; A modulator module is connected to the pump laser module, the high repetition rate optical frequency comb and the low repetition rate optical frequency comb respectively, and is used to independently control the high repetition rate optical frequency comb and the low repetition rate optical frequency comb; A high repetition rate optical frequency comb is connected to the modulator module and the photodetector module respectively to provide a self-reference of the frequency-doubled signal; The frequency-doubled laser module is connected to the photodetector module to broaden the overall working spectrum range of the device; The low repetition rate optical frequency comb is connected to the modulator module and the photodetector module respectively, and is used to match the comb tooth frequency of the high repetition rate frequency comb, providing a precise frequency synthesis reference and signal relay; A photodetector module, connected to the high repetition rate optical frequency comb, the low repetition rate optical frequency comb and the tunable laser module, respectively, for detecting optical signals and providing feedback; A tunable laser module is connected to the photodetector module and is used to output an optical synthesis signal; All of the above modules are based on lithium niobate and are all integrated on a lithium niobate chip.

2. The all-lithium niobate-based integrated optical frequency synthesizer according to claim 1, characterized in that: The signal generation area of ​​the integrated optical frequency synthesizer is composed of a pump laser module, a modulator module, a high repetition rate optical frequency comb and a low repetition rate optical frequency comb, which are used to generate two dissipative Kerr optical frequency combs and lock them to a stable micro-comb reference source.

3. The all-lithium niobate-based integrated optical frequency synthesizer according to claim 1, characterized in that: An optical frequency comb dual-comb system is formed by a low repetition rate optical frequency comb and a high repetition rate optical frequency comb, which is used to precisely control the comb teeth spacing and realize coherent multiplication from microwaves to light waves; the low repetition rate optical frequency comb has a mode spacing at the GHz level; the high repetition rate optical frequency comb has a mode spacing at the THz level; both use a lithium niobate micro-resonant cavity structure.

4. The all-lithium niobate-based integrated optical frequency synthesizer according to claim 1, characterized in that: By adjusting the relative comb lines of the low repetition rate optical frequency comb, the terahertz frequency spacing of the high repetition rate optical frequency comb is locked to guide the tuning of the tunable laser module.

5. The all-lithium niobate-based integrated optical frequency synthesizer according to claim 1, characterized in that: The frequency of carrier-envelope detuning is determined by measuring the optical heterodyne beat note between the high-repetition-rate optical frequency comb and the low-repetition-rate optical frequency comb. The measured signal is fed back to the pump laser module and phase-locked to the synthetic radio frequency to achieve frequency stabilization.

6. The all-lithium niobate-based integrated optical frequency synthesizer according to claim 1, characterized in that: Lithium niobate waveguides are used to achieve efficient coupling between individual optoelectronic devices and modules.

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