Ultrahigh-speed measurement system based on magnesium fluoride crystal photonic band structure microcavity optical frequency comb

Abstract

The invention discloses an ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb, which adopts a magnesium fluoride crystal photonic band structure microcavity as a Kerr double-optical-comb generator, simplifies a double-optical-comb high-speed measurement system, and can measure the morphology of an object at a high speed of 10,000 meters per second to the maximum extent. And the single measurement time is maintained at a millisecond magnitude. The influence factors of the response frequency range and sensitivity of the detector, noise interference and measurement precision are considered, meanwhile, distortion or loss of signals in the transmission process is avoided, and the accuracy of high-speed measurement is improved. The measuring system provided by the invention has the advantages of simple structure, high measuring efficiency, high accuracy and high precision.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and in particular to an ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb. Background Art

[0002] LiDAR (Light Detection and Ranging) technology, as a laser-based light detection and ranging method, has become an indispensable high-precision, long-range and fast data acquisition tool in industrial and scientific metrology. Although the existing technology has made remarkable achievements, it still faces challenges in expanding the ranging range, improving the measurement accuracy and speed, and reducing the system size. As a new type of laser source, optical frequency comb has found a usable tool in the field of precision measurement by generating a series of equally spaced comb teeth in the frequency domain.

[0003] The dual-comb scheme combines time-of-flight (TOF) measurement with optical interferometry to achieve multi-heterodyne detection by coherently superposing slightly detuned frequency combs. Although this approach improves the accuracy and resolution of measurements, it still faces challenges in achieving high-speed sampling and system miniaturization. With the development of technology, schemes based on optical frequency combs have been proven to be a feasible way to achieve high-speed sampling, with acquisition times as low as 500ns. However, while existing technologies achieve high-precision and ultrafast acquisition, they are difficult to meet the needs of system miniaturization and chip-level integration.

[0004] Recent advances in photonic integration technology, especially the application of large-scale nanophotonic phased arrays, have provided new possibilities for ultra-compact systems with fast and high-resolution beam guidance. However, existing dual-comb lidar technology relies on resonant cavity-stabilized mode-locked fiber lasers or fiber-based dispersion management schemes, which usually require fine adjustments and intermediate amplifiers, limiting their practicality in integrated optical micro-comb velocimetry systems. The integrated optical micro-comb velocimetry system is a sensor system for ultra-high-speed precision measurement of highly dynamic objects. It has two important influencing parameters: accuracy and sensitivity, which are mainly determined by the mode volume and quality factor of the resonant cavity. How to maintain its high sensitivity and high accuracy while meeting the requirements of system miniaturization and chip-level integration is a key issue that has been sought to be overcome in recent years. Summary of the invention

[0005] The present invention provides an ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb to solve the technical difficulties of the laser radar technology in the above-mentioned background technology in expanding the ranging range, improving the measurement accuracy and speed, and reducing the system size.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: an ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb, comprising a laser, an amplifier, a magnesium fluoride crystal photonic band structure microcavity, a beam splitter, a coupler, a circulator, a fiber delay, a fiber collimator, a target to be measured, a photodetector, a spectrometer and a high-speed signal processing unit;

[0007] There are two groups of lasers and amplifiers. Each group of lasers and amplifiers are connected separately, and two beams are simultaneously connected to the magnesium fluoride crystal photonic band structure microcavity.

[0008] One of the beams is split into two by a beam splitter; one beam is connected to a circulator, and is sequentially connected to a fiber delay device, a fiber collimator, and a target to be measured to form a target detection unit; the other beam is connected to a coupler, and after coupling, is split into two beams by a beam splitter, one beam is connected to a spectrometer for spectrum detection, and the other beam is connected to a photoelectric detector and a high-speed signal processing unit to form a processing module for ultra-high-speed optical signals to be measured;

[0009] The other beam is split into two by a beam splitter; one beam is coupled with the beam from the circulator at a coupler and then connected to a high-speed signal processing unit through a photoelectric detector to form a comparison unit module.

[0010] Furthermore, the magnesium fluoride crystal photonic band structure microcavity provides two Kerr double optical combs with different frequency intervals as a signal comb and a local oscillator comb. After the residual pump light is suppressed by the fiber Bragg grating, the laser signal is amplified by a pair of amplifiers.

[0011] Furthermore, the amplifier is used to amplify tiny optical signals; by amplifying the pump light to a high power level, it is ensured that the magnesium fluoride crystal photonic band structure microcavity produces a frequency comb with a desired power level.

[0012] The beam splitter is used to split the main laser into two parts with a ratio of 50:50;

[0013] The coupler is used to couple light from different branches together;

[0014] The circulator protects the instrument before the branch from damage by preventing the light path from going backwards;

[0015] The optical fiber delay device is used to introduce a controllable time delay to adjust the relative time between the signal comb and the local oscillator comb to optimize the performance of high-speed detection;

[0016] The fiber collimator is used to convert the Kerr double light comb generated by the microcavity into a parallel light beam for transmission and measurement. At the receiving end, the light beam reflected from the target to be measured is focused onto the photodetector to improve the detection efficiency of the signal.

[0017] Photodetectors are used to measure the signal comb and local oscillator comb, which receive the signal comb and local oscillator comb reflected from the target to be measured respectively; by comparing these two signals, the system can calculate the flight time of the light pulse and then determine the distance of the target to be measured.

[0018] Furthermore, the magnesium fluoride crystal photonic band structure microcavity is shaped as a central axis symmetrical figure, with two wedge-shaped protrusions of different radii, which can realize the excitation of different whispering gallery modes by using the two wedge-shaped protrusions as coupling points, and generate the required frequency comb through precise control.

[0019] Furthermore, the magnesium fluoride crystal photonic band structure microcavity is used as a Kerr dual-comb generator, with a beat frequency interval between 100 MHz and 1 GHz, a collection time between 1 ns and 10 ns, and a distance collection rate between 100 MHz and 1 GHz.

[0020] The beneficial effects of adopting the above technical solution are:

[0021] 1. The present invention provides an ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb. The magnesium fluoride crystal photonic band structure microcavity is used as a Kerr dual optical comb generator. Compared with traditional light sources, the volume is smaller, and the microcavity optical frequency comb can be miniaturized, which has a significant effect on simplifying the measurement system. Compared with the single frequency comb technology, the present invention simplifies the system structure, reduces the resolution limit of the instrument, avoids complex electronic control systems, and thus reduces costs and system complexity.

[0022] 2. The present invention provides an ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb, with a beat frequency interval between 100MHz and 1GHz, which can measure the shape of objects at a maximum speed of 10,000 meters per second, and the single measurement time is maintained at the millisecond level. The response frequency range and sensitivity of the detector, noise interference, and the influencing factors of measurement accuracy are taken into account, while avoiding signal distortion or loss during transmission, thereby improving the accuracy of high-speed measurement.

[0023] 3. The present invention provides an ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb. High-speed measurement is achieved through asynchronous optical sampling, which improves the measurement speed. Due to the reduction of the equivalent sampling step length, the measurement accuracy of the femtosecond level can be achieved, while reducing noise interference as much as possible. No displacement element is required, which further improves the measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of an ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb;

[0025] Figure 2This is a schematic diagram of the preparation process of the magnesium fluoride crystal photonic band structure microcavity;

[0026] Figure 3 This is a schematic diagram of the measurement scheme based on the magnesium fluoride crystal photonic band structure microcavity optical frequency comb;

[0027] Figure 4 This is a structural diagram of a magnesium fluoride crystal photonic band structure microcavity;

[0028] Figure 5 This is the quality factor test result of one microcavity protrusion of the photonic band structure of magnesium fluoride crystal;

[0029] Figure 6 This is the test result of the quality factor of two protrusions of the microcavity of the photonic band structure of the magnesium fluoride crystal;

[0030] Figure 7 It is the process of regulating the optical frequency comb of the microcavity of the photonic band structure of magnesium fluoride crystal;

[0031] in:

[0032] 1. Laser; 2. Amplifier; 3. Magnesium fluoride crystal photonic band structure microcavity; 4. Beam splitter; 5. Coupler; 6. Circulator; 7. Fiber delay; 8. Fiber collimator; 9. Target to be measured; 10. Photodetector; 11. Spectrometer; 12. And high-speed signal processing unit. DETAILED DESCRIPTION

[0033] The specific implementation methods of the present invention are further explained in detail below by describing the embodiments with reference to the accompanying drawings, with the aim of helping those skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solution of the present invention and facilitating its implementation.

[0034] like Figures 1 to 7 As shown, the present invention is an ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb. The magnesium fluoride crystal photonic band structure microcavity is used as a Kerr dual-comb generator, which simplifies the dual-comb high-speed measurement system. The maximum object shape measurement at a high speed of 10,000 meters per second can be measured, and the single measurement time is maintained at the millisecond level. The response frequency range and sensitivity of the detector, noise interference, and the influencing factors of measurement accuracy are taken into consideration, while avoiding signal distortion or loss during transmission, thereby improving the accuracy of high-speed measurement. The proposed measurement system has the advantages of simple structure, high measurement efficiency, high accuracy, and high precision.

[0035] The specific working method is described below with specific embodiments:

[0036] Embodiment 1:

[0037] The frequency spacing and bandwidth of the Kerr optical comb are determined by the parameters of the optical microcavity and the characteristics of the pump laser. In order to generate the Kerr double optical comb, the magnesium fluoride crystal photonic band structure microcavity 3 is used as the generator, and its two wedge-shaped protrusions are respectively coupled with the tapered optical fiber, and the optical frequency comb is generated through two branches. The frequency of the pump laser is adjusted so that the frequency combs generated by the two microstructures have different frequency spacings. The two generated frequency combs are used as the signal comb S and the local oscillator comb L respectively.

[0038] In the dual-comb ranging system, the signal comb S and the local oscillator comb L beat each other to produce a beat signal. The final measurement signal contains the information of the target distance. The beat interval is determined by the difference between the line intervals of the local oscillator comb L and the signal comb S. Given, the value is between 100MHz and 1GHz, where Δf r represents the frequency difference between the two frequency combs in Hertz, Δω r Stands for Free Spectral Range (FSR), in Hertz. This determines the acquisition time The value is between 1ns and 10ns, and the distance acquisition rate is between 100MHz-1GHz. min is based on the frequency difference Δf r The calculated minimum measurement time can measure the topography of objects moving at a maximum speed of 145,000 m / s. According to the threshold calculation formula of the soliton optical frequency comb: The threshold power of the pump light is about 462 mW, which is close to the power of 470 mW required for actual measurement. Among them, n is the refractive index of the material, which is about 1.38 for MgF2; ω0 is the angular frequency of the pump light; Calculate, where λ is the wavelength of the pump light, here 1550nm; R is the radius of the microcavity; Δλ is the spectral width of the pump light; c is the speed of light; τ R is the average residence time of light in the microcavity, which can be approximated as Where Q is the quality factor; ε0 is the electric constant in vacuum, which is approximately 8.854×10 -12 F / m.

[0039] The measurement system divides the optical comb signal into two paths: the signal of one path directly interferes with the local oscillator comb L and serves as a reference signal; the signal of the other path is reflected by the target reflector and interferes with the local oscillator comb L to form a measurement signal. In order to neutralize the phase delay of the local oscillator comb L, the system uses optical fiber delay line technology.

[0040] Then, the two interference signals are converted into electrical signals by the photodetector 10, and the signals are collected and amplified by the phase-locked amplifier. The center frequency of the signal comb S is set to γ S , whose deviation from the original laser frequency γ0 is fSo , the comb frequency interval is f Sr , the frequency of the i-th comb tooth is represented by f Si =γ S +if Sr Part of the signal light comb is used to measure the target distance, marked as Mea; the other part is used as a reference to record the distance and phase information, marked as Ref. The center frequency of the local oscillator comb L is γ L , whose offset is f Lo , the comb teeth spacing is f Lr , the i-th comb frequency is represented by f Ri =γ R +if Rr The local oscillator comb L mixes the signal light comb to generate a beat interference signal. The mixed signal is divided into two paths, one is mixed with the measurement light comb, and the other is mixed with the reference light comb. The frequency difference between the center teeth of the two light combs is f0 = γ S -γ L , the difference in comb tooth spacing is f r =γ Sr -γ Lr Finally, the photodetector 10 detects these interference signals and reference signals and converts them into corresponding electrical signals S Mea and S Ref .

[0041] The field strength E of the signal comb S and the local oscillator comb L S (t) and E L (t) can be expressed as the following formulas:

[0042]

[0043]

[0044] After the signal comb S is divided into a distance comb for measurement and a distance comb for reference, each passes through the corresponding measurement path l Mea and reference path l Ref , and are finally sent to the photodetector 10 for detection. The two comb light field intensities E Mea (t) and E Ref The expressions of (t) are as follows:

[0045]

[0046] Here, and Represents the measurement path length l Mea and the reference path length l Ref The resulting optical phase change is:

[0047]

[0048] In the optical frequency comb technique, the corresponding vacuum wavelength λ of the i-th order comb tooth is i and the refractive index n of the air medium i It has a direct impact on the propagation characteristics of light waves in the medium. The distance to be measured l is defined as the measurement distance l Mea The reference distance l Ref The difference, that is, l = l Mea -l Ref .

[0049] Ranging phase of the i-th comb tooth in an optical frequency comb The relationship between the distance l and the target can be determined by analyzing the propagation effect of light waves in the air. Since the propagation speed of light in different media changes due to different refractive indices, the phase delay will also change accordingly. For the i-th order comb teeth, the ranging phase It can be expressed as:

[0050]

[0051] If the phase delay effect of the local oscillator comb is not taken into account, the measured interference signal intensity is converted into the beat interference electrical signal S Mea (t) and the reference electrical signal S Ref (t), after corresponding conversion and filtering, can be expressed as follows:

[0052]

[0053] In the process of converting optical signals into electrical signals, frequency comb technology is used to maintain the interference spectrum of each frequency component related to the measured distance and the reference distance. By accurately separating and measuring the phase of these frequency components, the measured distance can be accurately calculated using formula (9).

[0054] In summary, the ultra-high-speed measurement system based on the magnesium fluoride crystal photonic band structure microcavity optical frequency comb of the present invention meets the measurement requirements of high precision, large size and high dynamics. The present invention adopts the magnesium fluoride crystal photonic band structure microcavity as the Kerr dual-comb generator, simplifies the dual-comb high-speed measurement system, and can measure the morphology of objects at a maximum speed of 10,000 meters per second, and the single measurement time is maintained at the millisecond level. The response frequency range and sensitivity of the detector, noise interference and the influencing factors of measurement accuracy are taken into account, while avoiding signal distortion or loss during transmission, thereby improving the accuracy of high-speed measurement. The proposed measurement system has the advantages of simple structure, high measurement efficiency, high accuracy and high precision.

[0055] The present invention is described above by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention; or the above-mentioned concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. An ultra-high-speed measurement system based on a magnesium fluoride crystal photonic band structure microcavity optical frequency comb, characterized by: It comprises a laser (1), an amplifier (2), a magnesium fluoride crystal photonic band structure microcavity (3), a beam splitter (4), a coupler (5), a circulator (6), an optical fiber delay device (7), an optical fiber collimator (8), a target to be measured (9), a photodetector (10), a spectrometer (11) and a high-speed signal processing unit (12); The laser (1) and the amplifier (2) are provided in two groups, each group of the laser (1) and the amplifier (2) are respectively connected, and are divided into two beams and simultaneously connected to the magnesium fluoride crystal photonic band structure microcavity (3). One of the beams is split into two by a beam splitter (4); one beam is connected to a circulator (6), and is sequentially connected to an optical fiber delay device (7), an optical fiber collimator (8), and a target to be measured (9), forming a target detection unit; the other beam is connected to a coupler (5), and after coupling, is split into two beams by a beam splitter (4), one beam is connected to a spectrometer (11) for spectrum detection, and the other beam is connected to a photoelectric detector (10) and a high-speed signal processing unit (12), forming a processing module for an ultra-high-speed optical signal to be measured; The other beam is split into two by a beam splitter (4); one beam is coupled with the beam from the circulator (6) at a coupler (5) and then connected to a high-speed signal processing unit (12) through a photoelectric detector (10), thereby forming a comparison unit module.

2. The ultra-high-speed measurement system based on the magnesium fluoride crystal photonic band structure microcavity optical frequency comb according to claim 1 is characterized in that: The magnesium fluoride crystal photonic band structure microcavity (3) provides two Kerr dual optical combs with different frequency intervals as a signal comb and a local oscillator comb. After the residual pump light is suppressed by a fiber Bragg grating, the laser signal is amplified by a pair of amplifiers (2).

3. The ultra-high-speed measurement system based on the magnesium fluoride crystal photonic band structure microcavity optical frequency comb according to claim 1 is characterized in that: The amplifier (3) is used to amplify tiny optical signals; The beam splitter (4) is used to split the main laser into two parts with a ratio of 50:50; The coupler (5) is used to couple light from different branches together; The circulator (6) protects the instrument before the branch from being damaged by preventing the light path from going backwards; The optical fiber delay device (7) is used to introduce a controllable time delay to adjust the relative time between the signal comb and the local oscillator comb to optimize the performance of high-speed detection; The optical fiber collimator (8) is used to convert the Kerr double light comb generated by the microcavity into a parallel light beam for transmission and measurement. At the receiving end, the light beam reflected from the target to be measured is focused onto the photodetector (10) to improve the detection efficiency of the signal. The photoelectric detector (10) is used to measure the signal comb and the local oscillator comb, which respectively receive the signal comb and the local oscillator comb reflected from the target to be measured; by comparing the two signals, the system can calculate the flight time of the light pulse and further determine the distance of the target to be measured.

4. The ultra-high-speed measurement system based on the magnesium fluoride crystal photonic band structure microcavity optical frequency comb according to claim 1 is characterized in that: The magnesium fluoride crystal photonic band structure microcavity (3) is shaped as a central axis symmetrical figure, and has two wedge-shaped protrusions with different radii, so that the two wedge-shaped protrusions are used as coupling points to realize the excitation of different whispering gallery modes, and the required frequency comb is generated through precise control.

5. The ultra-high-speed measurement system based on the magnesium fluoride crystal photonic band structure microcavity optical frequency comb according to claim 1, characterized in that: The magnesium fluoride crystal photonic band structure microcavity (3) is used as a Kerr dual light comb generator, the beat frequency interval is between 100 MHz and 1 GHz, the acquisition time is between 1 ns and 10 ns, and the distance acquisition rate is in the range of 100 MHz-1 GHz.

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