System and method for generating electro-optic frequency comb by dual-frequency driving lithium niobate thin film modulator

Abstract

This invention discloses a system and method for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator, belonging to the fields of optical communication and precision measurement technology. Addressing the limitations of traditional electro-optic frequency combs in terms of the limited number of teeth and scalability, this invention employs two radio frequency signals of different frequencies to drive a cascaded thin-film lithium niobate modulator, achieving a significant multiplication of the number of teeth. The first-stage modulator generates a large-pitch initial comb pattern, while the second-stage modulator fills each initial tooth with finer teeth using a lower-frequency radio frequency signal. The number of teeth multiplied is linearly proportional to the frequency ratio of the two radio frequency signals. Experiments successfully generated an electro-optic frequency comb with a line spacing of 2.5 GHz, a flatness of approximately 10 dB, and 432 teeth. This invention provides a simple, high-performance electro-optic frequency comb generation scheme with flexible adjustable center wavelength and line spacing, significantly overcoming the tooth number limitations of traditional schemes, and can be used in fields such as optical communication and precision measurement.

Description

Technical Field

[0001] This invention belongs to the field of optical communication and precision measurement technology, specifically relating to a system and method for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator. Background Technology

[0002] Optical frequency combs, with their uniform spacing and coherent phase stability across frequencies, are widely used in optical atomic clocks, absolute distance measurement, precision spectroscopy, and optical communications. In optical atomic clocks, optical frequency combs establish a direct connection between optical and microwave frequencies, providing an unprecedented tool for pushing the precision of atomic clocks to their limits. In absolute distance measurement, dual-comb ranging based on integrated microcavity coherent soliton pairs achieves nanometer-level precision and can be applied to surface profile measurement, strain sensing, and satellite formation. In precision spectroscopy, optical frequency combs map absorption and dispersion information to the radio frequency domain through coherent heterodyne detection, achieving high-resolution molecular spectroscopy with measurement deviations below 1% without the need for active stabilization. In optical communication systems, each comb tooth can function as an independent communication channel, enabling high-speed data transmission across multiple channels through wavelength division multiplexing, significantly improving channel capacity.

[0003] Currently, the main methods for generating optical frequency combs include mode-locked lasers, microcavity Kerr frequency combs, and electro-optic modulation. Mode-locked lasers can generate optical frequency combs with high power and high repetition rates, but the tunability of their repetition rate is limited by the cavity length. Microcavity Kerr frequency combs offer advantages such as compact size and low power consumption, and their ultrawide spectrum has the potential to exceed the capacity limits of optical communication; however, their line spacing is determined by the physical dimensions of the microcavity. Electro-optic frequency combs use radio frequency signals to drive electro-optic modulators, modulating the intensity and phase of continuous-wave lasers to generate sidebands. They offer several advantages, including continuously tunable center wavelength and line spacing, controllable phase noise, high system stability, and ease of integration.

[0004] Electro-optic frequency combs based on bulk lithium niobate modulators are typically limited by large half-wave voltages, resulting in a relatively small number of comb teeth, which restricts their applicability in high-speed communications and precision measurements. The advent of thin-film lithium niobate modulators, with their lower half-wave voltages, has made it possible to significantly increase the number of comb teeth. However, most existing methods for increasing the number of comb teeth rely on cascading multiple phase modulators. This method requires more modulators, increasing system cost. While this method achieves a significant increase in the number of comb teeth, the increased number of devices limits its scalability. Summary of the Invention

[0005] To address the limitations of traditional electro-optic frequency combs in terms of the limited number of teeth and scalability, this invention provides a system and method for generating electro-optic frequency combs using a dual-frequency driven thin-film lithium niobate modulator. This solves the problems of limited tooth count and high system complexity associated with traditional electro-optic frequency combs. By employing two radio frequency signals of different frequencies to drive a cascaded thin-film lithium niobate modulator, this invention achieves a significant increase in the number of teeth, with the increase being linearly related to the frequency ratio of the two radio frequency signals. This solution is applicable to generating electro-optic frequency combs with various line spacings within the bandwidth of the electro-optic modulator, providing a practical solution for the application of high-performance comb sources.

[0006] To achieve the above objectives, the present invention employs the following technical solutions:

[0007] A system for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator, the system comprising: a continuous-wave laser, a first-stage thin-film lithium niobate modulator, a second-stage thin-film lithium niobate modulator, a first radio frequency source, a second radio frequency source, a first radio frequency amplifier, a second radio frequency amplifier, and a phase shifter; wherein:

[0008] The continuous wave laser is used to output continuous light;

[0009] The first-stage thin-film lithium niobate modulator, driven by a first radio frequency signal, is used to modulate the continuous light to generate an initial electro-optic frequency comb with a first line spacing.

[0010] The second-stage thin-film lithium niobate modulator is cascaded with the first-stage thin-film lithium niobate modulator and driven by a second radio frequency signal to further modulate the initial electro-optic frequency comb;

[0011] The first-stage thin-film lithium niobate modulator includes a first-stage intensity modulator and a first-stage phase modulator;

[0012] The second-stage thin-film lithium niobate modulator includes a second-stage intensity modulator and a second-stage phase modulator;

[0013] The bias voltage and RF voltage amplitude applied to the first-stage intensity modulator and the second-stage intensity modulator are respectively modulated to optimize the flatness of the final output electro-optic frequency comb.

[0014] The first radio frequency source is used to generate a first radio frequency signal, and the second radio frequency source is used to generate a second radio frequency signal;

[0015] The first radio frequency amplifier is used to amplify the first radio frequency signal, and the second radio frequency amplifier is used to amplify the second radio frequency signal;

[0016] The first phase shifter is used to control the phase synchronization between the radio frequency signals of the first-stage intensity modulator and the first-stage phase modulator in the first-stage thin-film lithium niobate modulator; the second phase shifter is used to control the phase synchronization between the radio frequency signals of the second-stage intensity modulator and the second-stage phase modulator in the second-stage thin-film lithium niobate modulator; and the third phase shifter is used to control the phase synchronization between the first-stage thin-film lithium niobate modulator and the second-stage thin-film lithium niobate modulator.

[0017] The frequency of the first radio frequency signal is different from that of the second radio frequency signal. By secondary modulation, fine comb teeth with a second line spacing are generated around each comb tooth of the initial electro-optic frequency comb, thereby multiplying the total number of comb teeth.

[0018] The frequency of the first radio frequency signal Frequency greater than the second radio frequency signal The final electro-optic frequency comb has a total number of teeth and a frequency ratio of [missing information]. Proportional.

[0019] The continuous wave laser is a high-performance continuous single-frequency laser with a linewidth of 100 Hz and a wavelength of 1550.12 nm.

[0020] The frequency of the first radio frequency signal is 25 GHz, and the frequency of the second radio frequency signal is 2.5 GHz.

[0021] A method for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator, the method comprising the following steps:

[0022] 1) Continuous light is output from a continuous-wave laser;

[0023] 2) Continuous light is input into the first-stage thin-film lithium niobate modulator, and a frequency of is applied. The first radio frequency signal is modulated;

[0024] 3) Input the initial electro-optic frequency comb into the second-stage thin-film lithium niobate modulator and apply a frequency of The second radio frequency signal is further modulated, wherein ;

[0025] 4) The second-stage thin-film lithium niobate modulator modulates each tooth of the initial frequency comb, generating a spacing and frequency around it. The second radio frequency signal is the same fine comb teeth, thus outputting a final electro-optic frequency comb with a multiplied number of comb teeth.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] This invention presents an electro-optic frequency comb generation scheme based on a dual-frequency driven cascaded thin-film lithium niobate modulator. It requires only two cascaded modulators and achieves a significant increase in the number of comb teeth through a simple dual-frequency driving method. The increase in the number of comb teeth is linearly related to the frequency ratio of the two radio frequency signals, allowing the system to greatly expand the number of comb teeth while maintaining a relatively simple structure. Experiments show that this scheme, using 25GHz and 2.5GHz radio frequency signals, successfully generated an electro-optic frequency comb with a line spacing of 2.5GHz, a flatness of 10dB, and up to 432 comb teeth. The number of comb teeth is ten times that of the single-frequency driving scheme, consistent with the tenfold frequency ratio.

[0028] This invention overcomes the problem of limited number of teeth in traditional electro-optic frequency combs, and has the advantages of high performance, high stability, flexible adjustment of center wavelength and line spacing, and easy integration, providing strong support for fields such as optical communication and precision measurement. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the system for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator in this invention.

[0030] Figure 2 The simulation results of the dual-frequency drive scheme of the present invention are shown in the figure.

[0031] Figure 3 The figure shows the experimental results of the dual-frequency drive scheme of the present invention. Detailed Implementation

[0032] To gain a deeper understanding of this invention, we will provide a comprehensive and detailed description. However, this invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a full understanding of the disclosure of this invention.

[0033] To increase the number of teeth in a frequency comb, this invention proposes using two radio frequency signals of different frequencies to drive a cascaded thin-film lithium niobate modulator, such as... Figure 1 As shown. The system for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator includes a continuous wave laser, a first-stage thin-film lithium niobate modulator (including a first-stage intensity modulator and a first-stage phase modulator), a second-stage thin-film lithium niobate modulator (including a second-stage intensity modulator and a second-stage phase modulator), a first radio frequency source, a second radio frequency source, a first radio frequency amplifier, a second radio frequency amplifier, and a phase shifter;

[0034] The continuous-wave laser outputs continuous light with a linewidth of 100Hz and a wavelength of 1550.12nm. The first radio frequency signal RF1 (frequency...) The signal, after being amplified by the first RF amplifier, drives the first-stage thin-film lithium niobate modulator to generate an initial optical frequency comb with a comb tooth pitch of 25 GHz. The second RF signal RF2 (frequency...) After being amplified by the second RF amplifier, it drives the second-stage thin-film lithium niobate modulator to perform secondary modulation on the initial frequency comb. The first RF signal RF1 and the second RF signal RF2 maintain clock synchronization. Three phase shifters ensure phase synchronization between the modulators.

[0035] The first-stage thin-film lithium niobate modulator generates the spacing and frequency. The first radio frequency signal is the same as the initial frequency comb. The second-stage thin-film lithium niobate modulator further modulates each tooth of the initial frequency comb, generating a spacing and frequency around each original tooth. The second radio frequency signal has the same fine comb teeth. The spacing is The fine comb teeth filled the original spacing. The gaps between the comb teeth allow for a doubling of the number of teeth. The doubling is determined by the frequency ratio of the two radio frequency signals applied to the cascaded thin-film lithium niobate modulator. The flatness of the final output electro-optic frequency comb is optimized by adjusting the bias voltage and radio frequency voltage amplitude applied to the first-stage and second-stage intensity modulators.

[0036] In this embodiment, for the dual-frequency driving scheme, the RF voltage modulation depth and bias voltage modulation depth of the first-stage intensity modulator are set as follows: , The RF voltage modulation depth and bias voltage modulation depth of the second-stage intensity modulator are as follows: , The modulation depth of the first and second phase modulators is , Set the modulation frequency , . Figure 2 Simulation results of the dual-frequency drive scheme were presented, producing a frequency comb with a line spacing of 2.5 GHz, a flatness of 10 dB, and 437 comb teeth.

[0037] In the experiment, a dual-frequency driven cascaded thin-film lithium niobate modulator system was built for verification. A 1550.12nm continuous-wave laser with a linewidth of 100Hz was used as the light source. Radio frequency signals of 25GHz and 2.5GHz were amplified and used to drive two cascaded thin-film lithium niobate modulators. A narrowband bandpass filter was introduced to suppress parasitic second harmonics in the radio frequency source and amplifier. Measurements were performed using a high-resolution spectrometer (accuracy 0.04pm). The same modulation parameters as in the simulation were used in the experiment. The experimental results are as follows: Figure 3 As shown, the fabricated frequency comb exhibits a tooth pitch of 2.5 GHz, a flatness of 10 dB, and a total of 432 teeth. The total output power of the frequency comb is approximately -10 dBm, corresponding to a power of approximately -35 dBm per tooth. Figure 3 The top right corner shows a magnified view of a portion of the spectrum. Analysis reveals that the power fluctuation of most comb teeth is within 5 dB, with only about 8% fluctuating around 10 dB. The number of comb teeth generated by the dual-frequency drive scheme is proportional to the frequency ratio of the two RF signals (25 / 2.5=10), achieving a tenfold increase in the number of comb teeth. In the experiment, the accuracy of phase control and clock synchronization both affect the flatness of the frequency comb; therefore, these parameters require careful tuning.

[0038] In summary, this invention proposes and experimentally demonstrates a simple and efficient electro-optic frequency comb generation scheme. By employing a cascaded thin-film lithium niobate modulator driven by dual-frequency radio frequency signals, a significant increase in the number of comb teeth is achieved, with the number of comb teeth being linearly proportional to the frequency ratio of the two radio frequency driving signals. Experimentally, an electro-optic frequency comb with a line spacing of 2.5 GHz, a flatness of approximately 10 dB, and 432 comb teeth was generated. The electro-optic frequency comb generated using a dual-frequency driven thin-film lithium niobate modulator features flexible adjustment of the center wavelength and line spacing, high system stability, and ease of integration. The results of this invention overcome the limitation of the limited number of comb teeth in traditional electro-optic frequency combs, providing strong support for the application of electro-optic frequency combs in fields such as optical communication and precision measurement.

[0039] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A system for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator, characterized in that, The system includes: a continuous wave laser, a first-stage thin-film lithium niobate modulator, a second-stage thin-film lithium niobate modulator, a first radio frequency source, a second radio frequency source, a first radio frequency amplifier, a second radio frequency amplifier, a first phase shifter, a second phase shifter, and a third phase shifter; wherein: The continuous wave laser is used to output continuous light; The first-stage thin-film lithium niobate modulator, driven by a first radio frequency signal, is used to modulate the continuous light to generate an initial electro-optic frequency comb with a first line spacing. The second-stage thin-film lithium niobate modulator is cascaded with the first-stage thin-film lithium niobate modulator and driven by a second radio frequency signal to further modulate the initial electro-optic frequency comb; The first-stage thin-film lithium niobate modulator includes a first-stage intensity modulator and a first-stage phase modulator; The second-stage thin-film lithium niobate modulator includes a second-stage intensity modulator and a second-stage phase modulator; The bias voltage and RF voltage amplitude applied to the first-stage intensity modulator and the second-stage intensity modulator are respectively modulated to optimize the flatness of the final output electro-optic frequency comb. The first radio frequency source is used to generate a first radio frequency signal, and the second radio frequency source is used to generate a second radio frequency signal; The first radio frequency amplifier is used to amplify the first radio frequency signal, and the second radio frequency amplifier is used to amplify the second radio frequency signal; The first phase shifter is used to control the phase synchronization between the radio frequency signals of the first-stage intensity modulator and the first-stage phase modulator in the first-stage thin-film lithium niobate modulator; the second phase shifter is used to control the phase synchronization between the radio frequency signals of the second-stage intensity modulator and the second-stage phase modulator in the second-stage thin-film lithium niobate modulator; and the third phase shifter is used to control the phase synchronization between the first-stage thin-film lithium niobate modulator and the second-stage thin-film lithium niobate modulator.

2. The system for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator according to claim 1, characterized in that, The frequency of the first radio frequency signal is different from that of the second radio frequency signal. By secondary modulation, fine comb teeth with a second line spacing are generated around each comb tooth of the initial electro-optic frequency comb, thereby multiplying the total number of comb teeth.

3. The system for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator according to claim 2, characterized in that, The frequency of the first radio frequency signal Frequency greater than the second radio frequency signal The final electro-optic frequency comb has a total number of teeth and a frequency ratio of [missing information]. Proportional.

4. The system for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator according to claim 3, characterized in that, The continuous wave laser is a high-performance continuous single-frequency laser with an output linewidth of 100Hz and a wavelength of 1550.12nm.

5. The system for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator according to claim 4, characterized in that, The frequency of the first radio frequency signal is 25 GHz, and the frequency of the second radio frequency signal is 2.5 GHz.

6. A method for generating an electro-optic frequency comb using a dual-frequency driven thin-film lithium niobate modulator, characterized in that, The method is based on a system implementation using a dual-frequency driven thin-film lithium niobate modulator to generate an electro-optic frequency comb. The method includes the following steps: 1) Continuous light is output from a continuous-wave laser; 2) Continuous light is input into the first-stage thin-film lithium niobate modulator, and a frequency of is applied. The first radio frequency signal is modulated; 3) Input the initial electro-optic frequency comb into the second-stage thin-film lithium niobate modulator and apply a frequency of The second radio frequency signal is further modulated, wherein ; 4) The second-stage thin-film lithium niobate modulator modulates each tooth of the initial frequency comb, generating a frequency band around it with a spacing and frequency of [missing information]. The second radio frequency signal is the same fine comb teeth, thus outputting a final electro-optic frequency comb with a multiplied number of comb teeth.

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