A high-precision optical frequency measurement system based on frequency shift splicing

Abstract

The application discloses a high-precision optical frequency measurement system based on frequency shift splicing, which comprises a seed light laser, an integrated lithium niobate electro-optic comb chip, an acousto-optic frequency shifter, a first I / Q coherent detection module and a second I / Q coherent detection module, wherein the seed light output by the seed light laser is sent to the integrated lithium niobate electro-optic comb chip to generate an electro-optic comb with a repetition frequency of 10 GHz; the electro-optic comb is divided into two paths, one of which is output to the first I / Q coherent detection module, and the other of which is output to the second I / Q coherent detection module after frequency shift by the acousto-optic frequency shifter; a sweep laser is used for dividing the output sweep laser into two paths and sending the two paths to the first I / Q coherent detection module and the second I / Q coherent detection module respectively; the first I / Q coherent detection module and the second I / Q coherent detection module respectively acquire beat signals between the sweep laser and the electro-optic comb before and after frequency shift, and realize the measurement of the frequency of the sweep laser based on the beat signals.

Description

Technical Field

[0001] This invention relates to the field of optical metrology, and more specifically to a high-precision optical frequency measurement system based on frequency shifting and splicing. Background Technology

[0002] With the development of cutting-edge fields such as optical communication, lidar, and spectroscopy, frequency-sweeping lasers with linearly modulated frequencies over time have played a crucial role in applications such as high-speed optical communication, high-resolution lidar imaging, and high-sensitivity spectral analysis. However, in practical applications, the frequency tuning process of frequency-sweeping lasers is often affected by both device characteristics and the external environment, exhibiting tuning nonlinearity. These nonlinearities introduce distortions into the time and frequency domain signals, causing systematic errors in processing methods based on the linear frequency sweep assumption. These errors manifest as signal demodulation and coherent detection errors, resolution degradation, and inaccurate spectral localization. Therefore, there is an urgent need to develop a technique for real-time, high-precision calibration of the frequency of frequency-sweeping lasers under dynamic frequency sweeping conditions to effectively compensate for nonlinear errors and ensure the measurement accuracy and stability of the system under broadband and dynamic operating conditions.

[0003] In the field of nonlinear calibration of swept-frequency lasers, many mature solutions exist, including the reference interferometer method, the etalon method, the gas cell method, and the optical comb calibration method. Among these, the reference interferometer method has a simple structure, but its calibration relies on a known optical path difference, making it susceptible to environmental disturbances and dispersion, and difficult to maintain stability under large modulation bandwidths. The etalon method can provide equally spaced relative frequency scales for swept-frequency lasers, with its transmission peaks determined by the free spectral range. However, the cavity length and refractive index of the etalon are sensitive to environmental factors such as temperature and vibration, limiting its long-term stability and affecting the stability of frequency calibration. The gas cell method uses the absorption spectral lines of gas molecules as an absolute frequency reference, possessing natural traceability and high stability. However, gas absorption peaks are typically broad, limiting the resolution of frequency measurements; simultaneously, the spectral lines are discretely distributed, allowing calibration only at specific frequency points and failing to cover the entire swept frequency range. The optical comb calibration method, with its equally spaced frequencies and high stability, can provide absolute and highly accurate frequency scales. However, in the entire frequency calibration process, it is usually necessary to strictly match the comb tooth interval (repetition frequency) with the data sampling rate to avoid crosstalk between the sweep laser and the beat frequencies of different comb teeth. When the frequency of the sweep laser is exactly between two comb teeth, the accuracy of the beat frequency measurement will be limited by the sampling theorem and become ambiguous, thus affecting the accuracy and robustness of the entire calibration process.

[0004] Therefore, conducting high-precision frequency calibration throughout the entire process is a crucial step in the application of swept-frequency lasers, and it is of great significance for ensuring the accuracy, stability and reliability of swept-frequency interferometry. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, in view of the above-mentioned problems, the object of the present invention is to provide a high-precision optical frequency measurement system based on frequency shifting and stitching capable of real-time frequency measurement of swept-frequency lasers.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention is as follows: This invention provides a high-precision optical frequency measurement system based on frequency shifting and splicing. This system includes a seed laser, an integrated lithium niobate optical comb chip, an acousto-optic frequency shifter, a first I / Q coherent detection module, and a second I / Q coherent detection module, wherein: the seed light output from the seed laser is sent to the integrated lithium niobate optical comb chip to generate a repetition rate of... An electro-optical comb is used; the electro-optical comb is divided into two paths, one path is output to the first I / Q coherent detection module, and the other path is output to the second I / Q coherent detection module after frequency shifting by the acousto-optic frequency shifter; a swept laser is used to split the output swept laser into two paths and send them to the first I / Q coherent detection module and the second I / Q coherent detection module respectively; the first I / Q coherent detection module and the second I / Q coherent detection module respectively acquire the beat frequency signal between the swept laser and the electro-optical comb before and after frequency shifting, and measure the frequency of the swept laser based on the beat frequency signal.

[0007] In some possible implementations, the frequency shift amount of the acousto-optic frequency shifter is: Used to shift the overall frequency of the input electro-optic comb. .

[0008] In some possible implementations, the first I / Q coherent detection module and the second I / Q coherent detection module respectively acquire the beat frequency signal between the swept laser and the electro-optical comb before and after frequency shifting, and measure the frequency of the swept laser based on the beat frequency signal. The process is as follows: Two sets of zero-frequency sequences were obtained based on two-channel I / Q coherent synchronous detection, and both sets of zero-frequency sequences followed the same frequency interval rule; Two sets of zero-frequency point sequences, one before and one after the frequency shift, with a time interval from 0 to t, are obtained, sorted as a whole, and four adjacent zero-frequency points are selected to define the time interval. , These are two consecutive zero-frequency points before frequency shifting. , These are two consecutive zero-frequency points after frequency shifting; A set of clear regions before and after frequency shift is obtained based on four zero-frequency points, wherein: the time interval of the clear region before frequency shift is defined as: arrive ; The time interval of the clear region after frequency shifting is defined as follows: arrive ; By proceeding in this manner, several time intervals from 0 to t before and after frequency shift are obtained and spliced ​​together to obtain a reference sequence based on the global equally spaced beat frequency. Based on the reference frequency formed by the global equally spaced beat frequency reference sequence and the electro-optic comb teeth, the continuous sweep laser instantaneous frequency sequence is obtained. That is, the sweep laser instantaneous frequency sequence is spliced ​​together by several sets of frequencies calculated from the clear regions before and after frequency shift.

[0009] In some possible implementations, the instantaneous frequency sequence of the swept laser is formed by splicing together frequencies calculated from several sets of sharp regions before and after frequency shift, specifically: The sweeping optical frequency of the clear region before frequency shifting The calculation formula is: ; Frequency of the sweeping light in the clear region after frequency shift The calculation formula is: ; In the formula, The frequency of the comb teeth of the electro-optical comb. and The instantaneous frequency of the beat frequency signal of the sweep laser and the electro-optical comb before and after frequency shift is denoted as .

[0010] Some possible implementations, the instantaneous frequency of the beat frequency signal and The calculation formula is: ; In the formula, and These are the instantaneous phases of the beat frequency signals from the swept laser and the electro-optical comb before and after frequency shifting, respectively.

[0011] In some possible implementations, the seed laser is a narrow-linewidth, fiber-coupled continuous light source, including a composite feedback external cavity laser, a distributed feedback fiber laser, or a non-planar ring cavity laser.

[0012] In some possible implementations, the integrated lithium niobate electro-optic comb chip is realized based on the linear electro-optic effect of thin-film lithium niobate material. When a radio frequency signal is applied to the electro-optic modulator on the integrated lithium niobate electro-optic comb chip, the electro-optic modulator periodically modulates the phase and / or intensity of the input seed light, thereby generating multiple equally spaced sidebands in the spectrum to form an electro-optic comb.

[0013] In some possible implementations, the first I / Q coherent detection module and the second I / Q coherent detection module have the same structure, both including an optical 90° mixer and a pair of balanced detectors, wherein: The 90° optical mixer is used to coherently mix two input beams. The phase differences between its four output ports are 0°, 90°, 180° and 270° respectively. By combining them in pairs, mutually orthogonal I-path and Q-path coherent signals are obtained. The balanced photodetector is used to detect the I-channel and Q-channel signals.

[0014] In some possible implementations, the swept laser is a vertical cavity surface-emitting laser, a Fourier domain mode-locked laser, or an external cavity swept laser.

[0015] Some possible implementations also include a first coupler and a second coupler, wherein the first coupler is used to split the electro-optical comb into two paths, and the second coupler is used to split the light emitted by the swept laser into two paths.

[0016] Because the present invention adopts the above technical solution, it has the following characteristics: 1. Compared with existing calibration schemes based on interferometers, etalons or gas absorption spectra, the present invention does not rely on specific environmental conditions and can achieve high-precision nonlinear frequency calibration throughout the entire process under large modulation bandwidth and high-speed scanning conditions. Combined with the frequency shifting and splicing strategy of the present invention, the calibration accuracy and robustness of the system can be significantly improved.

[0017] 2. The present invention has a compact structure and a high degree of integrability, providing a new technical path for the promotion of electro-optical combs in engineering applications.

[0018] 3. This invention overcomes the shortcomings of traditional methods in terms of stability, continuity and sampling theorem limitations, and provides an efficient and scalable solution for engineering applications and scientific research.

[0019] In summary, this invention is applicable to scenarios such as real-time frequency calibration, high-precision ranging, and high-speed spectral measurement of wide-bandwidth swept-frequency lasers. Attached Figure Description

[0020] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings: Figure 1 This is a schematic diagram of the high-precision optical frequency measurement system based on frequency shifting and splicing according to an embodiment of the present invention.

[0021] Figure 2This is a schematic diagram illustrating the frequency measurement principle based on frequency shifting according to an embodiment of the present invention. Detailed Implementation

[0022] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0023] Although terms such as first, second, third, etc., may be used in this document to describe multiple elements, components, regions, layers, and / or segments, these elements, components, regions, layers, and / or segments should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or segment from another. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or segment discussed below may be referred to as the second element, component, region, layer, or segment without departing from the teachings of the exemplary embodiments.

[0024] For ease of description, spatial relative terms may be used in the text to describe the relationship of one element or feature relative to another element or feature as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "above," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure.

[0025] Because the accuracy of beat frequency measurement in the optical comb calibration method is limited by the sampling theorem and becomes fuzzy when the frequency of the sweeping laser is exactly between two comb teeth, thus affecting the accuracy and robustness of the entire calibration process. This invention provides a high-precision optical frequency measurement system based on frequency shifting and splicing, including a seed laser, an integrated lithium niobate optical comb chip, an acousto-optic frequency shifter, a first I / Q coherent detection module, and a second I / Q coherent detection module, wherein: the seed light output from the seed laser is sent to the integrated lithium niobate optical comb chip to generate a repetition rate of... An electro-optical comb is used; the electro-optical comb is split into two paths, one output to the first I / Q coherent detection module, and the other output to the second I / Q coherent detection module after frequency shifting by an acousto-optic frequency shifter. A swept laser is used to split the output swept laser into two paths and send them to the first I / Q coherent detection module and the second I / Q coherent detection module respectively. The first I / Q coherent detection module and the second I / Q coherent detection module respectively acquire the beat frequency signal between the swept laser and the electro-optical comb before and after frequency shifting, and measure the frequency of the swept laser based on the beat frequency signal. Therefore, this invention does not rely on specific environmental conditions and can achieve high-precision nonlinear frequency calibration throughout the entire process under large modulation bandwidth and high-speed scanning conditions. Combined with the frequency shifting and splicing strategy of this invention, the calibration accuracy and robustness of the system can be significantly improved.

[0026] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0027] like Figure 1 As shown, the high-precision optical frequency measurement system based on frequency shifting and splicing provided in this embodiment includes a seed laser 1, an integrated lithium niobate optical comb chip 2, a first coupler C1, an acousto-optic frequency shifter 3, a first I / Q coherent detection module 4, a second I / Q coherent detection module 5, and a second coupler C2, wherein: The seed light output from seed laser 1 is sent to integrated lithium niobate electro-optical comb chip 2 to generate a repetition rate of 1. The electric comb.

[0028] The electro-optic comb is split into two beams of equal power by the first coupler C1. One beam is directly output to the first I / Q coherent detection module 4, and the other beam is output to the second I / Q coherent detection module 5 after being subjected to a known frequency shift by the acousto-optic frequency shifter 3.

[0029] The frequency-sweeping laser 6 is used to send the output frequency-sweeping laser to the second coupler C2. The second coupler C2 splits the frequency-sweeping laser into two equal-power paths, which are sent to the first I / Q coherent detection module 4 and the second I / Q coherent detection module 5, respectively.

[0030] The first I / Q coherent detection module 4 and the second I / Q coherent detection module 5 respectively acquire the beat frequency signal between the swept laser and the electro-optic comb before and after frequency shift, so as to realize the accurate measurement of the frequency of the swept laser.

[0031] In a preferred embodiment of the present invention, the seed laser 1 may be a narrow-linewidth, fiber-coupled continuous light source, including a composite feedback external cavity laser, a distributed feedback fiber laser, or a non-planar ring cavity laser, and is not limited thereto.

[0032] In a preferred embodiment of the present invention, the integrated lithium niobate electro-optical comb chip 2 includes several cascaded phase modulators and an intensity modulator to generate a broadband, power-flat, and repetition-frequency-adjustable electro-optical comb, with a driving frequency traceable to a time reference. The integrated lithium niobate electro-optical comb chip 2 is based on the linear electro-optic effect of thin-film lithium niobate material. When an RF signal is applied to the electro-optic modulator of the integrated lithium niobate electro-optical comb chip 2, the electro-optic modulator periodically modulates the phase and / or intensity of the input continuous light, thereby generating multiple equally spaced sidebands in the spectrum to form an electro-optical comb. By optimizing the cascaded structure and driving parameters of the intensity modulator and phase modulator, a broadband, highly flat, and stable electro-optical comb can be obtained; the detailed principle is not elaborated here.

[0033] In a preferred embodiment of the present invention, the frequency shift amount of the acousto-optic frequency shifter 3 can be... That is, it is used to shift the overall frequency of the input electro-optic comb. .

[0034] In a preferred embodiment of the present invention, the first I / Q coherent detection module 4 and the second I / Q coherent detection module 5 have the same structure, both including an optical 90° mixer and a pair of balanced detectors, wherein: Each 90° optical mixer is used to coherently mix two input beams. The phase differences between its four output ports are 0°, 90°, 180° and 270° respectively. By combining them in pairs, mutually orthogonal I-path and Q-path coherent signals can be obtained.

[0035] Each pair of balanced photodetectors is used to detect the I and Q signals, suppress common-mode noise, and improve the signal-to-noise ratio.

[0036] In a preferred embodiment of the present invention, both the first coupler C1 and the second coupler C2 can be fiber optic couplers.

[0037] In a preferred embodiment of the present invention, the swept laser 6 refers to an output optical frequency that varies with time and is often accompanied by nonlinear characteristics. It can be a vertical cavity surface-emitting laser, a Fourier domain mode-locked laser, or an external cavity swept laser, and is used as an example, but is not limited thereto.

[0038] In summary, this invention achieves continuous calibration of the beat spectrum frequency shifting and splicing and the frequency scanning process by cascading the electro-optical comb output from the integrated lithium niobate electro-optical comb chip with an acousto-optical frequency shifter. This fundamentally solves the problems of frequency measurement ambiguity and unwrapping errors caused by the limitations of the sampling theorem in traditional optical comb calibration methods.

[0039] The frequency shifting and splicing frequency measurement mechanism of the high-precision optical frequency measurement system based on frequency shifting and splicing of the present invention will be explained in detail below through specific embodiments.

[0040] like Figure 2 As shown, this invention can simultaneously acquire the beat frequency signals of the swept laser and the electro-optical comb before and after frequency shifting. Through high-precision time synchronization and data stitching processing, it achieves continuous reconstruction of the entire frequency change process of the swept laser, thereby accurately characterizing its nonlinear characteristics. When the output light frequency of the swept laser 6 changes continuously, its light frequency will sequentially sweep across each tooth of the electro-optical comb. Whenever the swept light is adjacent to the light frequency of a certain tooth, a beat frequency signal is generated between them. This invention uses a 90° optical mixer to achieve orthogonal coherent detection, which can simultaneously obtain the in-phase (I) and quadrature (Q) components of the beat frequency signal, thus forming a complex signal with a symmetrical distribution of positive and negative frequencies. Therefore, this invention effectively avoids the problem of positive and negative frequency aliasing in traditional intensity detection methods, and can directly extract the phase information of the beat frequency signal without Hilbert transform, thereby improving demodulation accuracy and system stability.

[0041] To prevent aliasing of the beat frequency signal during sampling, this invention sets the data sampling rate to the repetition frequency of the electro-optical comb, ensuring that the sweep light beats only with the nearest comb tooth at any given time, with the beat frequency ranging from 0 to... The frequency of the swept laser varies within a certain range. However, according to the Nyquist sampling theorem, when the optical frequency of the swept laser is near the midpoint frequency of two adjacent comb teeth, the beat frequency signal frequency approaches the sampling bandwidth limit, easily leading to aliasing and frequency ambiguity, thus affecting the accurate determination of phase and instantaneous frequency. When the swept laser is located between two adjacent comb teeth before frequency shifting, causing ambiguity and phase uncertainty in the beat frequency signal, the beat frequency after frequency shifting will move to the vicinity of the nearest comb tooth, close to zero frequency, thereby eliminating the original frequency ambiguity and achieving accurate measurement of instantaneous frequency. This invention, through high-precision time alignment and splicing processing of the beat frequency signals before and after frequency shifting, can continuously reconstruct the complete frequency change process of the swept laser, ensuring high accuracy and high stability of the nonlinear frequency calibration throughout the process.

[0042] Specifically, the implementation process of the frequency shift alignment and splicing method is as follows: Assume at time... t The instantaneous frequency of the swept light is The corresponding frequency of the comb teeth in the electro-optical comb is By utilizing the I / Q coherent detection module to obtain complex signals, the beat frequency signals of the frequency-sweeping laser under test and the electro-optical comb before and after frequency shift can be detected simultaneously, thereby obtaining the instantaneous phase of the beat frequency signal. , By differentiating the instantaneous phase, the instantaneous frequency of the beat frequency signal can be obtained: .

[0043] Instantaneous beat frequency reflects the frequency difference between the swept light and the comb teeth. This is because there is an inherent frequency difference between the two optical combs. Set time The comb teeth that interfere with the swept frequency light are numbered as follows: Then the instantaneous frequencies of the two beat frequency signals can be expressed as: .

[0044] Furthermore, after obtaining the instantaneous beat frequency, this invention constructs a beat frequency reference frequency sequence using the zero-frequency point position of the beat frequency signal. In practical processing, the time position of the zero-frequency point can be determined by the instantaneous frequency crossing of the beat frequency signal. The comb teeth of the electro-optical comb operate at a repetition frequency... The frequency spacing is fixed, therefore the frequency interval between adjacent zero-frequency points is equal to the repetition frequency. Two I / Q coherent detectors can simultaneously obtain two sets of zero-frequency sequences, both of which follow the aforementioned frequency spacing rule. This is combined with acousto-optic frequency shifting. The resulting frequency domain complementarity allows for the joint construction of a global equally spaced beat frequency reference sequence based on two sets of beat frequency data, with a sequence frequency step size of [missing value]. Furthermore, adjacent zero-frequency points possess excellent time positioning accuracy. Based on this, the expression for the instantaneous frequency of the swept light is obtained as follows: .

[0045] Due to the limitations of the sampling theorem, single-channel beat frequency signals exhibit measurement ambiguity. The following section will analyze how to select effective measurement results from two signals at different time periods and stitch them together to obtain high-precision frequency measurement data for the entire process.

[0046] like Figure 2 As shown in the frequency domain section on the left, the electro-optical comb teeth before frequency shifting operate at a repetition frequency. Equally spaced distribution; a fixed frequency shift is applied via acousto-optic frequency shifter 3. Afterwards, the overall spectrum of the electro-optical comb shifts after frequency shifting, while the spacing between the comb teeth remains unchanged. Unchanged. The frequency of the swept light changes continuously with time, beating with the two electro-optical combs respectively. For example... Figure 2 The right side shows the actual measured beat frequencies of the two channels. and The change process, the upper part is the beat frequency signal before frequency shift, which is limited by the Nyquist sampling theorem, and the beat frequency value is close to The region marked with dashed lines experiences aliasing distortion, forming a measurement ambiguity area; the remaining portion constitutes the effective measurement range. The lower half represents the beat frequency signal after frequency shift. Due to the overall spectral shift, the original ambiguity area transforms into the effective measurement range, perfectly complementing the clear region of the original signal on the time axis. (Using zero frequency...) Using 0 as the time reference, the clear area data of the two beat frequency signals are smoothly spliced ​​together to obtain a non-aliased, continuous beat frequency reference sequence. Combined with the reference frequency formed by the comb teeth of the electro-optical comb, the instantaneous frequency sequence of the sweep frequency laser can be restored, effectively solving the frequency ambiguity problem caused by the sampling theorem in single-channel measurement.

[0047] Furthermore, such as Figure 2 As shown, two sets of zero-frequency sequences are obtained based on two-channel I / Q coherent synchronous detection, and both sets of zero-frequency sequences follow the same frequency interval rule. Since the zero-frequency points of the two signals appear alternately, the zero-frequency points of the signals before and after frequency shift from time 0 to t are obtained, sorted, and four adjacent zero-frequency points are selected. The absolute time base is defined as the subscript size for sorting, where the time is defined as... , These are two consecutive zero-frequency points of the signal before frequency shifting. , Given two consecutive zero-frequency points of the frequency-shifted signal, a set of clear regions before and after the frequency shift is obtained based on the four zero-frequency points, where: The time interval of the clear region before frequency shift is defined as follows: arrive ; The time interval of the clear region after frequency shifting is defined as follows: arrive ; By proceeding in this manner, several time intervals from 0 to t before and after frequency shift are obtained and spliced ​​together to obtain a reference sequence based on the global equally spaced beat frequency. Based on the reference frequency formed by the global equally spaced beat frequency reference sequence and the electro-optic comb teeth, the continuous sweep laser instantaneous frequency sequence is obtained. That is, the sweep laser instantaneous frequency sequence is spliced ​​together by several sets of frequencies calculated from the clear regions before and after frequency shift.

[0048] Furthermore, the instantaneous frequency sequence of the swept laser is composed of frequencies calculated from several sets of sharp regions before and after frequency shift, specifically: The sweeping optical frequency of the clear region before frequency shifting The calculation formula is: ; Frequency of the sweeping light in the clear region after frequency shift The calculation formula is: .

[0049] Therefore, the above method not only effectively solves the frequency ambiguity problem caused by the Nyquist sampling limitation, but also ensures the continuous tracking of the nonlinear frequency changes of the frequency-sweeping laser under high-speed frequency sweeping, providing reliable high-precision frequency tracing for subsequent applications such as spectral analysis, lidar and optical communication.

[0050] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In the description of this specification, the terms "a preferred embodiment," "furthermore," "specifically," "in this embodiment," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments in this specification. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-precision optical frequency measurement system based on frequency-shift splicing, characterized in that, The system includes a seed laser, an integrated lithium niobate electro-optical comb chip, an acousto-optic frequency shifter, a first I / Q coherent detection module, and a second I / Q coherent detection module, wherein: The seed light output from the seed laser is sent to the integrated lithium niobate electro-optical comb chip to generate a repetition rate of... The electro-optical comb is divided into two paths, one of which is output to the first I / Q coherent detection module, and the other is output to the second I / Q coherent detection module after being frequency-shifted by the acousto-optic frequency shifter. The frequency-sweeping laser is used to split the output frequency-sweeping laser into two paths and send them to the first I / Q coherent detection module and the second I / Q coherent detection module respectively. The first I / Q coherent detection module and the second I / Q coherent detection module respectively acquire the beat frequency signal between the swept laser and the electro-optic comb before and after frequency shift, and measure the frequency of the swept laser based on the beat frequency signal.

2. The high-precision optical frequency measurement system based on frequency shifting and splicing according to claim 1, characterized in that, The frequency shift amount of the acousto-optic frequency shifter is: Used to shift the overall frequency of the input electro-optic comb. .

3. The high-precision optical frequency measurement system based on frequency shifting and splicing according to claim 2, characterized in that, The first I / Q coherent detection module and the second I / Q coherent detection module respectively acquire the beat frequency signal between the swept laser and the electro-optical comb before and after frequency shifting. Based on the beat frequency signal, the frequency of the swept laser is measured. The process is as follows: Two sets of zero-frequency sequences were obtained based on two-channel I / Q coherent synchronous detection, and both sets of zero-frequency sequences followed the same frequency interval rule; Two sets of zero-frequency point sequences, one before and one after the frequency shift, with a time interval from 0 to t, are obtained, sorted as a whole, and four adjacent zero-frequency points are selected to define the time interval. , These are two consecutive zero-frequency points before frequency shifting. , These are two consecutive zero-frequency points after frequency shifting; A set of clear regions before and after frequency shift is obtained based on four zero-frequency points, wherein: the time interval of the clear region before frequency shift is defined as: arrive ; The time interval of the clear region after frequency shifting is defined as follows: arrive ; By proceeding in this manner, several time intervals from 0 to t before and after frequency shift are obtained and spliced ​​together to obtain a reference sequence based on the global equally spaced beat frequency. Based on the reference frequency formed by the global equally spaced beat frequency reference sequence and the electro-optic comb teeth, the continuous sweep laser instantaneous frequency sequence is obtained. That is, the sweep laser instantaneous frequency sequence is spliced ​​together by several sets of frequencies calculated from the clear regions before and after frequency shift.

4. The high-precision optical frequency measurement system based on frequency shifting and splicing according to claim 3, characterized in that, The instantaneous frequency sequence of a swept laser is composed of frequencies calculated from several sets of sharp regions before and after frequency shift, specifically: The sweeping optical frequency of the clear region before frequency shifting The calculation formula is: ； Frequency of the sweeping light in the clear region after frequency shift The calculation formula is: ； In the formula, The frequency of the comb teeth of the electro-optical comb. and The instantaneous frequency of the beat frequency signal of the sweep laser and the electro-optical comb before and after frequency shift is denoted as .

5. The high-precision optical frequency measurement system based on frequency shifting and splicing according to claim 4, characterized in that, instantaneous frequency of beat frequency signal and The calculation formula is: ； In the formula, and These are the instantaneous phases of the beat frequency signals from the swept laser and the electro-optical comb before and after frequency shifting, respectively.

6. The high-precision optical frequency measurement system based on frequency shifting and splicing according to claim 1, characterized in that, The seed laser is a narrow-linewidth, fiber-coupled continuous light source, including a composite feedback external cavity laser, a distributed feedback fiber laser, or a non-planar ring cavity laser.

7. The high-precision optical frequency measurement system based on frequency shifting and splicing according to claim 1, characterized in that, The integrated lithium niobate electro-optic comb chip is realized based on the linear electro-optic effect of thin-film lithium niobate material. When the radio frequency signal is applied to the electro-optic modulator on the integrated lithium niobate electro-optic comb chip, the electro-optic modulator periodically modulates the phase and / or intensity of the input seed light, thereby generating multiple equally spaced sidebands in the spectrum to form an electro-optic comb.

8. The high-precision optical frequency measurement system based on frequency shifting and splicing according to claim 1, characterized in that, The first I / Q coherent detection module and the second I / Q coherent detection module have the same structure, both including an optical 90° mixer and a pair of balanced detectors, wherein: The 90° optical mixer is used to coherently mix two input beams. The phase differences between its four output ports are 0°, 90°, 180° and 270° respectively. By combining them in pairs, mutually orthogonal I-path and Q-path coherent signals are obtained. The balanced photodetector is used to detect the I-channel and Q-channel signals.

9. The high-precision optical frequency measurement system based on frequency shifting and splicing according to claim 1, characterized in that, The swept-frequency laser is a vertical-cavity surface-emitting laser, a Fourier-domain mode-locked laser, or an external-cavity swept-frequency laser.

10. The high-precision optical frequency measurement system based on frequency shifting and stitching according to claim 1, characterized in that, It also includes a first coupler and a second coupler, the first coupler being used to split the electro-optical comb into two paths, and the second coupler being used to split the light emitted by the swept laser into two paths.

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