Pulse spectrum measurement technology based on chirp grating

Abstract

The invention discloses a pulse spectrum measurement technology based on a chirp grating. An optical fiber beam splitter, a low-dispersion optical fiber, an optical circulator, the chirp fiber grating, an optical fiber beam combiner, a photoelectric detector, a signal conditioning circuit, a signal acquisition circuit and a signal processing unit are adopted. The chirped fiber bragg grating is used for achieving dispersion on the pulsed light in time, and a spectrum corresponding to the pulsed light is obtained through calculation in combination with deconvolution operation.

Description

Technical Field

[0001] The present invention relates to a pulse spectrum measurement technology based on a chirped grating, and more particularly to a method for applying a chirped fiber grating to a coherent laser wind radar. Background Art

[0002] The application of spectral measurement is becoming more and more extensive. Currently, there are two types of spectrometers commonly used: 1. Dispersive spectrometers typically use prisms and gratings as spectral dispersive devices, with common structures including single and double gratings. To achieve spectral separation, matching optical components such as slits and mirrors, as well as a specially designed optical path, are also required. Spectral resolution is primarily determined by the slit width, the structural parameters of the grating, and the size of the photosensitive surface of the photoelectric sensor, and once established, it is difficult to change. The photoelectric sensor in a dispersive spectrometer uses linear or planar arrays such as CMOS and CCD. These linear and planar array sensors can measure the entire spectrum at once. Scanning monochromators use avalanche photodiodes and photomultiplier tubes as photoelectric sensors. Avalanche photodiodes and photomultiplier tubes offer the advantages of high sensitivity and fast response time, but they require matching mechanical scanning components for spectral measurement. Due to their long spectral measurement cycle, they are not suitable for measuring rapidly changing optical signals. Dispersive spectrometers are characterized by a simple and stable optical system, but difficult to adjust spectral resolution.

[0003] 2. Interferometric spectrometers, typically the Fourier transform spectrometer (FTS). FTS offers unmatched advantages over other spectrometer types in terms of multi-channel, high throughput, and high resolution. FTS utilizes optical paths such as Michelson interferometers, Mach-Zehnder interferometers, and crystal birefringence. FTS are categorized as either time-modulated or spatially modulated. Time-modulated FTS requires a scanning mirror and offers advantages such as high spectral sensitivity, high spectral resolution, and a wide spectral measurement range. However, they are complex, bulky, have long measurement cycles, and are expensive. Spatially modulated FTS utilize a static optical path and employ linear or planar arrays such as CMOS and CCD sensors as photoelectric sensors. Currently, due to limitations in the optical path and photoelectric sensor size, key performance indicators such as spectral resolution and measurement range of spatially modulated FTS cannot compare to those of time-modulated FTS.

[0004] In the present invention, a chirped fiber grating is used as a dispersion device.

[0005] A chirped fiber Bragg grating (FBG) is a fiber grating in which the amplitude or period of the refractive index change of the fiber core gradually changes along the fiber axis, causing its Bragg reflection wavelength to change along the length direction. The Bragg reflection wavelength corresponding to a certain point z can be expressed as: λ B (z)=2 n eff (z)Λ(z) , (1) in, n eff (z) and Λ(z) are along z Axis variation of fiber core refractive index and grating period.

[0006] The wavelength of light contained in the pulse light falls within the range of the chirped fiber grating reflection wavelength. The long-wavelength pulse light signal is reflected at the corresponding position of the long chirped fiber grating period, and the short-wavelength pulse light signal is reflected at the corresponding position of the short chirped fiber grating period, thereby dispersing the pulse light in time. Summary of the Invention

[0007] The purpose of the present invention is to provide a pulse spectrum measurement technology based on a chirped grating to solve the problems raised in the above background technology.

[0008] The present invention comprises an optical fiber beam splitter, a low-dispersion optical fiber, an optical circulator, a chirped optical fiber grating, an optical fiber beam combiner, a photoelectric detector, a signal conditioning circuit, a signal acquisition circuit, and a signal processing unit.

[0009] The pulse light to be measured is divided into two paths by the optical fiber beam splitter, one path is the dispersed pulse light, and the other path is the original pulse light.

[0010] After passing through a section of low-dispersion fiber, the dispersed pulsed light is input into the optical circulator port 1 and output to the chirped fiber grating (FBG) through the optical circulator port 2. Within the dispersed pulsed light, short-wavelength pulsed light signals are reflected at locations corresponding to short chirped fiber grating periods, while long-wavelength pulsed light signals are reflected at locations corresponding to long chirped fiber grating periods, thus temporally dispersing the pulsed light. The dispersed light signal is reflected back to the optical circulator port 2 and output from the optical circulator port 3. After passing through a section of low-dispersion fiber, it is superimposed with the original pulsed light in the fiber combiner. Because the optical path length of the original pulsed light differs from that of the dispersed light signal, there is no temporal overlap between the original and dispersed light signals.

[0011] The photodetector converts the original pulse light and the dispersed optical signal into corresponding electrical signals. After amplification, filtering, and impedance matching by the signal conditioning circuit, the signal acquisition circuit converts the electrical signals into digital signals. Using the collected original pulse light data, the signal processing unit performs a deconvolution operation on the collected dispersed optical signal data to calculate the spectrum corresponding to the measured pulse light.

[0012] The shorter the sampling time interval of the signal acquisition circuit is, the higher the spectral resolution of the pulse spectrum measurement based on the chirped grating is. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments of the present invention.

[0014] Figure 1 , Schematic diagram of the pulse spectrum measurement technology based on chirped grating of the present invention Figure 2 The data of the original pulse light and the dispersed optical signal collected by the present invention are Figure: 1. Measured pulse light, 2. Fiber beam splitter, 3. Dispersed pulse light, 4. Original pulse light, 5. Low-dispersion fiber, 6. Optical circulator, 7. Chirped fiber Bragg grating (FBG), 8. Dispersed optical signal, 9. Low-dispersion fiber, 10. Fiber combiner, 11. Low-dispersion fiber, 12. Photodetector, 13 Signal conditioning circuit, 14. Signal acquisition circuit, 15. Signal processing unit, 16. Collected original pulse light data, 17. Collected dispersed optical signal data. DETAILED DESCRIPTION

[0015] The present invention aims to provide a chirped grating-based pulse spectrum measurement technique to address technical problems in related fields. To further clarify the technical problems and technical solutions to be addressed by the present invention, the present invention is further described below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0016] The principle of the pulse spectrum measurement technology based on chirped grating of the present invention is as follows: Figure 1 shown.

[0017] The measured pulse light (1) contains λ1<λ2<···<λ n <···<λ N The multiple wavelength components are divided into two paths by an optical fiber beam splitter (2), one path being the dispersed pulse light (3) and the other path being the original pulse light (4).

[0018] After passing through a section of low-dispersion optical fiber (5), the dispersed pulse light (3) is input to port 1 of the optical circulator (6), and output to the chirped fiber grating (7) through port 2 of the optical circulator (6); in the dispersed pulse light (3), the short-wavelength pulse light signal is reflected at the corresponding position of the short period of the chirped fiber grating (7), and the long-wavelength pulse light signal is reflected at the corresponding position of the long period of the chirped fiber grating (8), thereby dispersing the pulse light in time. The dispersed optical signal (8) is reflected back to port 2 of the optical circulator (7), and is output from port 3 of the optical circulator (7), passes through a section of low-dispersion optical fiber (9), and is superimposed with the original pulse light (4) in the optical fiber combiner (10); because the optical path length experienced by the original pulse light (4) is different from that of the dispersed optical signal (8), the original pulse light (4) and the dispersed optical signal (8) do not overlap in time, as shown in FIG. Figure 2 shown.

[0019] The photodetector (12) converts the original pulse light (4) and the dispersed optical signal (8) into corresponding electrical signals. After amplification, filtering, and impedance matching by the signal conditioning circuit (13), the signal acquisition circuit (14) converts the electrical signals into digital signals. Using the collected original pulse light data (16), the signal processing unit (15) performs a deconvolution operation on the collected dispersed optical signal data (17), thereby calculating the spectrum corresponding to the measured pulse light (1).

[0020] The shorter the sampling time interval of the signal acquisition circuit (14), the higher the spectral resolution of the pulse spectrum measurement based on the chirped grating. Figure 2 In the example, if the sampling time interval is ΔT1, optical signals with wavelengths λ1, λ2, λ3, ... can be measured; if the sampling time interval is ΔT2, optical signals with wavelengths λ1, λ3, ... can be measured.

[0021] It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Those skilled in the art should consider the specification as a whole, and the technical solutions in the embodiments can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A pulse spectrum measurement technology based on a chirped grating, characterized by: It consists of a fiber beam splitter, low-dispersion fiber, an optical circulator, a chirped fiber Bragg grating, a fiber combiner, a photodetector, a signal conditioning circuit, a signal acquisition circuit, and a signal processing unit. The measured pulse light is divided into two paths by the optical fiber beam splitter, one path is the dispersed pulse light and the other path is the original pulse light; After passing through a section of low-dispersion optical fiber, the dispersed pulse light is input into the optical circulator port 1 and output to the chirped fiber grating through the optical circulator port 2. In the dispersed pulse light, the short-wavelength pulse light signal is reflected at the position where the chirped fiber grating period is short, and the long-wavelength pulse light signal is reflected at the position where the chirped fiber grating period is long, thereby achieving temporal dispersion of the pulse light. The dispersed optical signal is reflected back to the optical circulator port 2 and output from the optical circulator port 3. After passing through a section of low-dispersion optical fiber, it is superimposed with the original pulse light in the optical fiber combiner. Because the optical path length traversed by the original pulse light is different from that of the dispersed optical signal, there is no temporal overlap between the original pulse light and the dispersed optical signal. The photodetector converts the original pulse light and the dispersed optical signal into corresponding electrical signals. After amplification, filtering, and impedance matching by the signal conditioning circuit, the signal acquisition circuit converts the electrical signals into digital signals. Using the collected original pulse light data, the signal processing unit performs a deconvolution operation on the collected dispersed optical signal data to calculate the spectrum corresponding to the measured pulse light.

2. The chirped grating-based pulse spectrum measurement technology according to claim 1, characterized in that: The shorter the sampling time interval of the signal acquisition circuit is, the higher the spectral resolution of the pulse spectrum measurement is.

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