A large bandwidth ultra-fine high-flat electro-optic frequency comb generating device

Abstract

The application provides a large-bandwidth ultra-fine high-flatness electro-optical frequency comb generating device. The device generates ultra-narrow linewidth laser with a kHz-level linewidth, then transmits the generated laser to two-stage cascaded electro-optical modulators, and uses a cyclic discrete sweep signal to modulate the first electro-optical modulator to generate a wideband optical frequency comb with periodically changed comb tooth spacing, and the second electro-optical modulator uses a frequency-time conversion signal to modulate the comb tooth generated by the first electro-optical modulator. The comb tooth is detected based on a heterodyne beat frequency method, the modulation signal is feedback adjusted by using an error analysis processing module, and finally the wideband narrow comb tooth spacing high flatness electro-optical optical frequency comb output is realized. The application has the characteristics of small comb tooth spacing, large number of comb teeth, large bandwidth range and high flatness.

Description

Technical Field

[0001] This invention relates to the field of laser source technology, and in particular to a device for generating a high-bandwidth, ultra-fine, highly flat electro-optic frequency comb. Background Technology

[0002] Optical frequency combs are laser beams with uniformly spaced, coherently stable phases and discretely distributed across the spectrum. They provide a time and frequency reference bridge between the optical and microwave domains, and have broad application prospects in fields such as optical atomic clocks, atmospheric science, and precision measurement. However, different applications require different optical frequency comb characteristics. In particular, optical frequency combs with narrow tooth spacing and high flatness can effectively improve the detection accuracy of precision optical metrology. For example, an ultra-narrow tooth spacing of 1 MHz can be equivalent to a spectral resolution of less than 0.01 pm, which is difficult to achieve with traditional spectral detection methods. Therefore, how to generate ultra-fine, highly flat optical frequency combs has become a hot topic in the field of laser technology.

[0003] Currently, the main methods for generating optical frequency combs can be divided into three categories: those based on mode-locked lasers, those based on nonlinear effects, and those based on external modulation. Mode-locked laser-based methods generate periodic optical pulses by synchronously locking the repetition frequency and carrier envelope phase. In the frequency domain, this manifests as an optical frequency comb with equal tooth spacing. The advantage of this method is its large tooth bandwidth, but it is difficult to adjust the tooth spacing, and the dual-locking technique for the tooth center frequency and tooth spacing is quite complex. Nonlinear effects-based methods mainly utilize the nonlinear characteristics of four-wave mixing and Brillouin scattering to generate higher-order spectral components. Its advantage is the large generated tooth bandwidth, but in experiments, its gradually expanding dynamic bandwidth expansion mechanism makes it difficult to guarantee the flatness of the optical frequency comb. External modulation methods use radio frequency signals to directly modulate the fundamental frequency light (phase modulation or intensity modulation) to generate multiple optical frequency combs. This is a relatively simple method in terms of structure, and its advantage is stable tooth position. However, as the tooth bandwidth increases, the flatness deteriorates. Meanwhile, in related patents (applications): (1) In 2021, the University of Science and Technology of China applied for a high-flatness optical frequency comb generating device based on an electro-optic modulator (publication number: CN202110729158.2), which generates a flat optical frequency comb by using a sine wave to modulate the phase modulator and the Mach-Zehnder modulator. The current electro-optic frequency comb is limited by the output capability of a single radio frequency modulation signal, making it difficult to further expand the bandwidth. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies and achieve optical frequency comb output with large bandwidth, high flatness, and narrow tooth spacing, this invention proposes a cascaded electro-optic modulation technology based on discrete sweep frequency signals and frequency-time conversion signals. The discrete sweep frequency signal is used to modulate and expand the comb tooth bandwidth, followed by frequency-time conversion signal modulation to reduce the comb tooth gap. Finally, feedback adjustment is combined to improve the comb tooth flatness. This technology features small tooth spacing, a large number of comb teeth, a wide bandwidth range, and high flatness.

[0005] The objective of this invention is achieved by at least one of the following technical solutions.

[0006] A high-bandwidth, ultra-fine, high-flat electro-optic frequency comb generating device includes: a narrow-linewidth laser, a first beam splitter coupler, a first electro-optic modulator, a second electro-optic modulator, a signal generator, an arbitrary waveform generator, a signal amplifier, a frequency shifter, a second beam splitter coupler, a beam combiner, a photodetector, a spectrum analyzer, and an error analysis and processing module.

[0007] A narrow-linewidth laser is split into beams by a first beam splitter. One output beam is frequency-shifted by a frequency shifter and used as a reference beam input to a beam combiner. The other beam is sequentially modulated by a cascaded first electro-optic modulator and a second electro-optic modulator to generate an electro-optic frequency comb. The first electro-optic modulator receives a discrete sweep frequency modulation signal generated by a signal generator and performs discrete sweep frequency modulation to broaden the bandwidth of the electro-optic frequency comb. The second electro-optic modulator receives a frequency-time transformation signal generated by an arbitrary waveform generator and performs fine modulation to achieve ultra-fine narrow comb tooth characteristics.

[0008] The electro-optic frequency comb laser generated by the second electro-optic modulator is split into two beams by the second beam splitter. One beam is output directly, while the other beam beats with the reference beam through a beam combiner. The beat-frequency optical signal is converted into an electrical signal by a photodetector, and then the spectrum is analyzed by a spectrum analyzer to obtain the comb tooth data. Subsequently, it is transmitted to the error analysis and processing module for feedback adjustment to further improve the flatness of the comb teeth, and finally realize the output of a large bandwidth, ultra-fine, and highly flat electro-optic frequency comb laser.

[0009] Furthermore, the narrow linewidth laser is a fixed wavelength or a tunable single-frequency laser.

[0010] Furthermore, the first electro-optic modulator can be a phase modulator or an intensity modulator.

[0011] Furthermore, the first electro-optic modulator receives the discrete sweep frequency modulation signal generated by the signal generator and performs discrete sweep frequency modulation. The discrete sweep frequency modulation signal includes a sine or triangular wave signal with cyclically changing frequency.

[0012] Furthermore, the frequency range of the discrete sweep frequency modulation signal is 1kHz to 20GHz, and the cycle period range is 1ns to 100s.

[0013] Furthermore, the type of the second electro-optic modulator includes a phase modulator or an intensity modulator.

[0014] Furthermore, the modulation signal received by the second electro-optic modulator includes a frequency-time conversion signal, a square wave signal, a triangular wave signal, or a sine wave signal.

[0015] Furthermore, the frequency-time transformed signal generated by the arbitrary waveform generator is amplified by a signal amplifier and then output to the second electro-optic modulator.

[0016] Furthermore, after receiving the actual output spectrum data, the error analysis and processing module compares and calculates it with the required spectrum to obtain the error between the actual output electro-optical comb envelope, the comb teeth in the optical comb envelope, and the required spectrum.

[0017] Furthermore, the modulation voltage of the signal generator and the flatness of the envelope follow the relationship of Bessel function. The modulation voltage of the signal generator is adjusted based on the spectral error between the envelopes to improve the flatness between the envelopes of each comb tooth. Based on the spectral error between individual envelope comb teeth, the signal strength of the corresponding frequency point in the corresponding frequency-time conversion signal is adjusted to improve the flatness between the comb teeth inside the envelope.

[0018] Compared with the prior art, the technical effects and advantages of the present invention include:

[0019] This invention employs electro-optic modulation of narrow-linewidth lasers, enabling the output of ultra-fine optical combs. It utilizes discrete frequency sweep signals to electro-optically modulate the narrow-linewidth laser, significantly widening the bandwidth of the comb teeth. Combined with a frequency-to-time conversion signal, it performs secondary modulation on the high-bandwidth optical comb, generating an ultra-fine, high-bandwidth optical frequency comb. Furthermore, it optimizes the flatness of the comb teeth through feedback adjustment, achieving ultra-fine, high-bandwidth, and highly flat optical frequency comb laser output. Compared to existing electro-optic modulation methods for generating optical frequency combs, this invention solves the problems of limited comb teeth in sinusoidal modulation and the decrease in flatness with increasing optical frequency comb bandwidth encountered in pseudo-random code and frequency-to-time conversion signal modulation. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following description is provided with accompanying drawings of the relevant technical solutions in the embodiments of the present invention or the prior art. It should be understood that the accompanying drawings described below are only for the purpose of clearly illustrating some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the time domain of a frequency-to-time converted signal;

[0022] Figure 2 This diagram illustrates the process of generating comb teeth through modulation with a discrete frequency sweep signal and a 900MHz frequency-time conversion signal, as well as the final output of the comb teeth.

[0023] Figure 3 This diagram illustrates the process of generating comb teeth through modulation with a discrete frequency sweep signal and a 600MHz frequency-time conversion signal, as well as the final state of the generated comb teeth.

[0024] Figure 4 This diagram illustrates the process of generating comb teeth through modulation with a discrete frequency sweep signal and a 300MHz frequency-time conversion signal, as well as the final state of the generated comb teeth.

[0025] Figure 5 This is a schematic diagram of the structure of a large bandwidth, ultra-fine, high-flat electro-optic frequency comb generation device and method provided by the present invention. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and specific examples. It should be noted that the scope of protection of the present invention is not limited to the scope described in the embodiments. Any processes not specifically described below are those that can be implemented by those skilled in the art with reference to the prior art.

[0027] Example:

[0028] A time-domain schematic diagram of a frequency-to-time conversion signal is shown below. Figure 1 As shown, a high-bandwidth, ultra-fine, highly flat electro-optic frequency comb generating device, such as... Figure 5 As shown, it includes: a narrow linewidth laser 01, a first beam splitter 02, a first electro-optic modulator 03, a second electro-optic modulator 04, a signal generator 05, an arbitrary waveform generator 06, a signal amplifier 07, a frequency shifter 08, a second beam splitter 09, a beam combiner 10, a photodetector 11, a spectrum analyzer 12, and an error analysis and processing module 13.

[0029] Among them, the narrow linewidth laser 01 is used to output a single-frequency laser with a linewidth in the kHz range, providing a basis for achieving ultra-narrow comb tooth spacing;

[0030] The first optical splitter 02 splits the narrow linewidth laser into two paths. One path is modulated to generate an optical comb, and the other path is frequency-shifted by the frequency shifter 08 and then beats the laser of the optical comb to obtain the comb tooth spectrum.

[0031] The first electro-optic modulator 03 receives the cyclic discrete sweep frequency modulation signal generated by the signal generator 05 and generates periodically frequency-shifted comb teeth.

[0032] The second electro-optic modulator 04 receives the frequency-time conversion modulation signal generated by the arbitrary waveform generator 06 and amplified by the signal amplifier 07, and performs secondary modulation on the comb teeth generated by the first electro-optic modulator 03 to generate an optical frequency comb with a large bandwidth and narrow comb tooth spacing.

[0033] Signal generator 05 generates a sweep frequency modulation signal whose frequency cycles with time;

[0034] Arbitrary waveform generator 06 generates the frequency-time conversion modulation signal corresponding to the second electro-optic modulator 04;

[0035] Signal amplifier 07 amplifies the signal generated by arbitrary waveform generator 06;

[0036] Frequency shifter 08 performs frequency shifting and decoherence on the fundamental frequency light;

[0037] The second optical splitter 09 splits the optical frequency comb laser into two paths, one of which is directly output, and the other is beat-frequency with the frequency-shifted and decohered fundamental frequency light.

[0038] Beam combiner 10 combines the optical comb laser with the frequency-shifted light to beat the frequency;

[0039] The photodetector 11 converts the beat-frequency optical signal into an electrical signal;

[0040] The spectrum analyzer 12 analyzes the electrical signal to obtain the spectrum information of the comb teeth;

[0041] After receiving the spectrum information data, the error analysis and processing module 13 performs calculations to obtain a correction signal and provides feedback adjustment to the signals generated by the signal generator 05 and the arbitrary waveform generator 06.

[0042] Narrow linewidth laser 01 is split into beams by the first beam splitter 02. One output beam after splitting is frequency shifted by the frequency shifter 08 and used as a reference beam input to the beam combiner 10. The other beam is successively modulated by the cascaded modulation of the first electro-optic modulator 03 and the second electro-optic modulator 04 to generate an electro-optic frequency comb. The first electro-optic modulator 03 receives the discrete sweep frequency modulation signal generated by the signal generator 05 and performs discrete sweep frequency modulation to broaden the bandwidth of the electro-optic frequency comb. The second electro-optic modulator 04 receives the frequency-time transformation signal generated by the arbitrary waveform generator 06 and performs fine modulation to achieve ultra-fine narrow comb tooth characteristics.

[0043] The electro-optic frequency comb laser generated by the second electro-optic modulator 04 is split into two beams by the second beam splitter 09. One beam is output directly, and the other beam beats with the reference beam through the beam combiner 10. The beat-frequency optical signal is converted into an electrical signal by the photodetector 11, and then the spectrum is analyzed by the spectrum analyzer 12 to obtain the comb tooth data. Subsequently, it is transmitted to the error analysis and processing module 13 for feedback adjustment to further improve the flatness of the comb teeth, and finally realize the output of a large bandwidth, ultra-fine, and highly flat electro-optic frequency comb laser.

[0044] In one embodiment, the narrow linewidth laser 01 is a tunable single-frequency laser; in another embodiment, the narrow linewidth laser 01 is a fixed-wavelength single-frequency laser.

[0045] In one embodiment, the first electro-optic modulator 03 is an intensity modulator; in another embodiment, the first electro-optic modulator 03 is an intensity modulator.

[0046] Furthermore, the first electro-optic modulator 03 receives the discrete sweep frequency modulation signal generated by the signal generator 05 and performs discrete sweep frequency modulation. In one embodiment, the discrete sweep frequency modulation signal is a triangular wave signal with cyclically changing frequency, and in another embodiment, the discrete sweep frequency modulation signal is a sine wave signal with cyclically changing frequency.

[0047] Furthermore, the frequency range of the discrete sweep frequency modulation signal is 1kHz to 20GHz, and the cycle period range is 1ns to 100s.

[0048] In one embodiment, the second electro-optic modulator 04 is an intensity modulator; in another embodiment, the second electro-optic modulator 04 is a phase modulator.

[0049] In one embodiment, the modulation signal received by the second electro-optic modulator 04 is a frequency-time transformed signal; in another embodiment, the modulation signal received by the second electro-optic modulator 04 is a square wave signal; in another embodiment, the modulation signal received by the second electro-optic modulator 04 is a triangular wave signal; in yet another embodiment, the modulation signal received by the second electro-optic modulator 04 is a sine wave signal.

[0050] Furthermore, the frequency-time conversion signal generated by the arbitrary waveform generator 06 is amplified by the signal amplifier 7 and then output to the second electro-optic modulator 04.

[0051] Furthermore, after receiving the actual output spectrum data, the error analysis and processing module 13 compares and calculates it with the required spectrum to obtain the error between the actual output electro-optical comb envelope, the comb teeth in the optical comb envelope, and the required spectrum.

[0052] Furthermore, the modulation voltage of the signal generator 05 and the flatness of the envelope follow the relationship of Bessel function. The modulation voltage of the signal generator 05 is adjusted based on the spectral error between the envelopes to improve the flatness between the envelopes of each comb tooth. Based on the spectral error between individual envelope comb teeth, the signal strength of the corresponding frequency point in the corresponding frequency-time conversion signal is adjusted to improve the flatness between the comb teeth inside the envelope.

[0053] In one embodiment, such as Figure 2 The diagram shows the process of generating comb teeth through modulation with discrete sweep frequency signal and 900MHz frequency-time conversion signal, as well as the final comb teeth.

[0054] Figure 2 In the diagram, Figures a, b, and c show the intermediate process of comb generation, and Figure d shows the final acquired spectrum. A 900MHz bandwidth frequency-to-time conversion modulation signal is used to modulate the second electro-optic modulator 04. The first electro-optic modulator 03 is modulated using cyclic discrete frequency sweep modulation at 1.8GHz, 3.6GHz, and 5.4GHz. Figure a corresponds to the 1.8GHz frequency point in the discrete frequency sweep modulation, Figure b corresponds to the 3.6GHz frequency point, and Figure c corresponds to the 5.4GHz frequency point. Finally, by matching the acquisition rate of the acquisition card in the spectrum analyzer with the cycle rate of the cyclic discrete frequency sweep modulation, a broadband optical frequency comb with a bandwidth of 12.6GHz is acquired.

[0055] In one embodiment, such as Figure 3 The diagram shows the process of generating comb teeth through modulation with discrete sweep frequency signal and 600MHz frequency-time conversion signal, as well as the final comb teeth.

[0056] Figure 3 In the diagram, Figures a, b, and c represent the intermediate process of comb tooth generation, and Figure d shows the final acquired spectrum. A 600MHz bandwidth frequency-to-time conversion modulation signal is used to modulate the second electro-optic modulator 04. Cyclic discrete frequency sweep modulation at 1.2GHz, 2.4GHz, and 3.6GHz is applied to the first electro-optic modulator 03. Figure a corresponds to the 1.2GHz frequency point in the discrete frequency sweep modulation, Figure b corresponds to the 2.4GHz frequency point, and Figure c corresponds to the 3.6GHz frequency point. Finally, by matching the acquisition rate of the acquisition card in the spectrum analyzer with the cycle rate of the cyclic discrete frequency sweep modulation, broadband optical frequency comb acquisition with a bandwidth of 8.4GHz is achieved.

[0057] In one embodiment, such as Figure 4 The diagram shows the process of generating comb teeth through modulation with discrete sweep frequency signal and 300MHz frequency-time conversion signal, as well as the final comb teeth.

[0058] Figure 4 In the diagram, Figures a, b, and c represent the intermediate process of comb tooth generation, and Figure d shows the final acquired spectrum. A 300MHz bandwidth frequency-to-time conversion modulation signal is used to modulate the second electro-optic modulator 04. The first electro-optic modulator 03 is modulated using cyclic discrete frequency sweep modulation at 600MHz, 1.2GHz, and 1.8GHz. Figure a corresponds to the 600MHz frequency point in the discrete frequency sweep modulation, Figure b corresponds to the 1.2GHz frequency point, and Figure c corresponds to the 1.8GHz frequency point. Finally, by matching the acquisition rate of the acquisition card in the spectrum analyzer with the cycle rate of the cyclic discrete frequency sweep modulation, broadband optical frequency comb acquisition with a bandwidth of 4.2GHz is achieved.

[0059] Compared with the aforementioned patented high-flatness optical frequency comb generating device based on an electro-optic modulator (Publication No.: CN202110729158.2), the present invention has the following significant differences: 1. The types and combinations of modulators used are different; 2. The modulation signals used are different; 3. The present invention introduces feedback adjustment to improve the flatness of the comb teeth; 4. The present invention uses a narrow linewidth seed source as the fundamental frequency light to achieve the output of an ultra-fine optical comb.

[0060] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0061] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A device for generating a large bandwidth, ultra-fine, highly flat electro-optic frequency comb, characterized in that, include: Narrow linewidth laser (01), first beam splitter (02), first electro-optic modulator (03), second electro-optic modulator (04), signal generator (05), arbitrary waveform generator (06), signal amplifier (07), frequency shifter (08), second beam splitter (09), beam combiner (10), photodetector (11), spectrum analyzer (12), and error analysis and processing module (13); The narrow linewidth laser (01) is split into beams by the first beam splitter (02); one output beam after splitting is frequency shifted by the frequency shifter (08) and used as the reference beam input to the beam combiner (10); the other beam is successively modulated by the cascaded modulation of the first electro-optic modulator (03) and the second electro-optic modulator (04) to generate an electro-optic frequency comb. The first electro-optic modulator (03) receives the discrete sweep frequency modulation signal generated by the signal generator (05) and performs discrete sweep frequency modulation to broaden the bandwidth of the electro-optic frequency comb; the second electro-optic modulator (04) receives the frequency-time transformation signal generated by the arbitrary waveform generator (06) and performs fine modulation to achieve ultra-fine narrow comb tooth characteristics. The electro-optic frequency comb laser generated by the second electro-optic modulator (04) is split into two beams by the second beam splitter (09). One beam is output directly, and the other beam beats the reference beam through the beam combiner (10). The beat-frequency optical signal is converted into an electrical signal by the photodetector (11), and then the spectrum is analyzed by the spectrum analyzer (12) to obtain the comb tooth data. Subsequently, it is transmitted to the error analysis and processing module (13) for feedback adjustment to further improve the flatness of the comb teeth, and finally realize the output of a large bandwidth ultra-fine high flat electro-optic frequency comb laser. The modulation voltage of the signal generator (05) and the flatness of the envelope follow the relationship of the Bessel function. The modulation voltage of the signal generator (05) is adjusted based on the spectral error between the envelopes to improve the flatness between the envelopes of each comb tooth. Based on the spectral error between individual envelope comb teeth, the signal strength at the corresponding frequency point in the corresponding frequency-time conversion signal is adjusted to improve the flatness between comb teeth inside the envelope.

2. The large bandwidth ultra-fine high flatness electro-optic frequency comb generating device according to claim 1, characterized in that: The narrow linewidth laser (01) is a fixed wavelength or a tunable single-frequency laser.

3. The large bandwidth ultra-fine high flatness electro-optic frequency comb generating device according to claim 1, characterized in that: The first electro-optic modulator (03) includes phase modulators and intensity modulators.

4. The large bandwidth ultra-fine high flatness electro-optic frequency comb generating device according to claim 1, characterized in that: The first electro-optic modulator (03) receives the discrete sweep frequency modulation signal generated by the signal generator (05) and performs discrete sweep frequency modulation. The discrete sweep frequency modulation signal includes a sine or triangular wave signal with cyclically changing frequency.

5. The device for generating a large bandwidth, ultra-fine, highly flat electro-optic frequency comb according to claim 1, characterized in that: The frequency range of the discrete sweep frequency modulation signal is 1 kHz to 20 GHz, and the cycle period range is 1 ns to 100 s.

6. The large bandwidth ultra-fine high flatness electro-optic frequency comb generating device according to claim 1, characterized in that: The second electro-optic modulator (04) can be a phase modulator or an intensity modulator.

7. The large bandwidth ultra-fine high flatness electro-optic frequency comb generating device according to claim 1, characterized in that: The modulation signal received by the second electro-optic modulator (04) includes frequency-time conversion signal, square wave signal, triangular wave signal or sine wave signal.

8. The device for generating a large bandwidth, ultra-fine, highly flat electro-optic frequency comb according to claim 1, characterized in that: The frequency-time conversion signal generated by the arbitrary waveform generator (06) is amplified by the signal amplifier (7) and then output to the second electro-optic modulator (04).

9. The device for generating a large bandwidth, ultra-fine, highly flat electro-optic frequency comb according to claim 1, characterized in that: After receiving the actual output spectrum data, the error analysis and processing module (13) compares and calculates the actual output electro-optical comb envelope, the comb teeth in the optical comb envelope and the required spectrum.

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