Full-field fine spectrum diagnosis system based on IQ coherent detection

Abstract

The invention belongs to the field of optical signal detection, and particularly relates to a full-field fine spectrum diagnosis system based on IQ coherent detection. According to the invention, an IQ coherent detector is innovatively formed by an optical mixer commonly used for coding and decoding and a balanced photoelectric detector, frequency shift is carried out on single-frequency light by using an AOM to obtain local oscillation light, and four paths of frequency mixing signals before and after 90-degree phase shift are obtained after to-be-detected signal light and the local oscillation light pass through a 90-degree optical mixer; detecting signals before and after 90-degree phase shift are respectively obtained by utilizing a balance photoelectric detector; and finally, the detecting signals are processed to obtain a fine spectrogram of the optical signal to be measured. Two paths of orthogonal output are processed through IQ coherent detection, full-field spectrum characterization is achieved, and spectrum intensity and spectrum phase information can be provided at the same time; and secondly, single-shot parallel detection is realized, and the real-time performance of the system is improved. The wavelength accuracy, the frequency spectrum phase accuracy and the frequency spectrum intensity accuracy can reach 0.5 MHz, 0.1 rad and 1% respectively, and the detection rate is larger than 20 MHz.

Description

Technical Field

[0001] The present invention belongs to the field of optical signal detection, and in particular relates to a full-field fine spectrum diagnostic system based on IQ coherent detection. Background Art

[0002] Spectroscopic diagnostic technology has broad applications in numerous fields, including biomedical imaging, environmental monitoring, and materials science. Traditional spectral diagnostic systems typically only detect the amplitude of the spectrum, making it difficult to obtain phase information. However, phase information holds important diagnostic value in many applications. For example, in biomedical imaging, phase changes can reflect changes in the optical properties of tissues; in materials science, phase information can be used to study ultrafast dynamic processes in materials.

[0003] In recent years, with the continuous advancement of optical technology, research on ultra-high-sensitivity photodetectors has made significant progress. These detectors have key applications in optical communications, optical sensing, biosensing, and astronomy, where their sensitivity determines system performance. Furthermore, the development of optical mixing and phase modulation technologies has provided technical support for improving the performance of spectral diagnostic systems. Optical mixing technology can achieve precise measurement of optical signal phase, amplitude, and other information through phase interference between signal light and local oscillator light.

[0004] Furthermore, the use of high-speed signal processors has significantly increased signal processing speed, meeting the demands of real-time data processing. High-resolution oscilloscopes can be used to monitor and analyze signal waveforms, ensuring proper system operation. However, existing spectral diagnostic systems still suffer from several limitations, such as limited detection capabilities, insufficient accuracy, and slow response speed. Therefore, developing a full-field, fine-scale spectral diagnostic system capable of simultaneously detecting both spectral amplitude and phase, with high accuracy and rapid response, is of great significance.

[0005] Full-field fine spectral diagnostic systems based on real-time coherent detection are cutting-edge and groundbreaking technologies in the field of spectral metrology. Previous studies using coherent detection-based fine spectral characterization (COSA) techniques relied on single-frequency local oscillator (LO) light sweeps and low-pass filtering to achieve broadband serial spectral characterization. These methods were unable to achieve single-shot parallel detection and only provided spectral intensity information. Summary of the Invention

[0006] In response to the above-mentioned problems or shortcomings, and to solve the problems of full-field detection and real-time performance of the spectral diagnostic system, the present invention provides a full-field fine spectral diagnostic system based on IQ coherent detection. The optical mixer commonly used for encoding and decoding is innovatively combined with a balanced photodetector to form an IQ coherent detector. The full-field fine spectral diagnostic system of the present invention can achieve 1% spectrum intensity accuracy, 0.1rad phase accuracy, 0.5MHz wavelength accuracy and 20MHz frame rate.

[0007] The present invention adopts the following technical solutions:

[0008] A full-field fine spectrum diagnostic system based on IQ coherent detection includes: a single-frequency laser, an acousto-optic frequency shifter (AOM), a 90-degree optical mixer, a balanced photodetector, a polarization controller and a data processing module.

[0009] The single-frequency laser is used to generate a single-frequency optical signal.

[0010] The acousto-optic frequency shifter performs acousto-optic frequency shift on a single-frequency optical signal to generate a local oscillation optical signal.

[0011] There are two polarization controllers in total, which are dual-port devices with one input port and one output port. The two polarization controllers receive the photometric signal and the local oscillator light signal respectively, adjust the polarization state of the photometric signal and the local oscillator light signal, and after matching the polarization state required by the 90° optical mixer, they are respectively connected to the two input ports of the 90° optical mixer.

[0012] The 90° optical mixer is a six-port device with two input ports and four output ports. The two input ports receive the photometric signal and the local oscillator signal respectively; the local oscillator signal is mixed with the photometric signal to obtain four mixed signals and output them.

[0013] There are two balanced photodetectors in total, which are three-port devices with two input ports and one output port. The two input ports of each balanced photodetector are respectively connected to the two output ports of the 90° optical mixer. One balanced photodetector only receives the mixed signal after phase shift, and the other balanced photodetector only receives the mixed signal before phase shift, thereby achieving background light signal elimination and common-mode noise suppression.

[0014] The data processing module recovers the light signal to be measured from the signals output by the two balanced photodetectors (both containing the amplitude and phase information of the light signal to be measured).

[0015] Furthermore, the four mixed signals are specifically as follows: one output is the sum of the local oscillator light signal and the light signal to be measured, and one output is the difference between the local oscillator light signal and the light signal to be measured; one output is the sum of the local oscillator light signal after 90° phase shift and the light signal to be measured, and one output is the difference between the local oscillator light signal after 90° phase shift and the light signal to be measured.

[0016] Furthermore, the signals output by the two balanced photodetectors both contain amplitude and phase information of the optical signal to be measured.

[0017] Furthermore, the specific process of the data processing module recovering the optical signal to be measured is: the mixed signal after the 90° phase shift is multiplied by the imaginary unit i and added to the mixed signal before the 90° phase shift to obtain the optical signal to be measured, and then the spectrum of the optical signal to be measured is obtained by Fourier transform.

[0018] Furthermore, the polarization controller is a three-ring polarization controller to achieve maximum output of the IQ coherent detector.

[0019] The present invention uses an AOM to frequency-shift single-frequency light to obtain local oscillator light. After the signal light to be measured and the local oscillator light pass through a 90° optical mixer, four mixed signals before and after the 90° phase shift are obtained. Then, a balanced photodetector is used to obtain detection signals before and after the 90° phase shift, respectively. Finally, the detection signals are processed by a data processing module to obtain a fine spectrum of the light signal to be measured.

[0020] In summary, the full-field fine spectral diagnostic system based on IQ coherent detection provided by the present invention can realize wide-spectrum single-shot parallel full-field fine spectral real-time diagnosis, solving the pain points of existing coherent detection fine spectral characterization technology: First, IQ coherent detection processes two orthogonal outputs to realize full-field spectral characterization, that is, it can provide spectrum intensity and spectrum phase information at the same time, making up for the disadvantage of traditional fine spectral characterization technology that can only provide spectrum intensity information due to single-channel signal output; secondly, compared with traditional fine spectral systems that use time averaging to characterize fine spectra, the present invention realizes single-shot parallel detection, improving the real-time performance of the system. The wavelength accuracy, spectrum phase accuracy and spectrum intensity accuracy of the present invention can reach 0.5MHz, 0.1rad and 1% respectively, and the detection rate is greater than 20MHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic block diagram of the overall system architecture of the embodiment;

[0022] Figure 2 The output signal processing effect of the embodiment;

[0023] Figure 3 This is a performance characterization diagram of the embodiment. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] A full-field fine spectrum diagnostic system based on IQ coherent detection, the architecture of which is as follows Figure 1 shown.

[0026] This embodiment uses a phase modulator to modulate 1550nm single-frequency light to obtain sidebands, generating a broadband signal light to be measured. An acousto-optic frequency shifter (AOM) is used to frequency-shift the 1550nm single-frequency light to obtain a local oscillator signal, which shifts the beat frequency signal away from low frequencies, reduces noise impact, and improves the signal-to-noise ratio. Two three-ring polarization controllers (PCs) are used to control the polarization of the signal light to be measured output by the phase modulator and the local oscillator light output by the acousto-optic frequency shifter to match the input polarization of a 90° optical mixer, and then output the polarization to the 90° optical mixer. Two balanced photodetectors are then used to suppress common-mode noise and eliminate background signals. Finally, a data processing module processes the output signal of the balanced photodetector (BPD), recovers the amplitude and phase information of the signal to be measured, and then performs a Fourier transform to complete the fine spectral diagnosis of the signal to be measured.

[0027] In this embodiment, the 1550nm single-frequency laser is pumped by 1550nm single-frequency light, and its maximum output is 10mW. The output of the 1550nm single-frequency laser light source is evenly divided into two paths of 1550nm single-frequency light entering the system through a 50 / 50 beam splitter (coupling device).

[0028] Figure 2 is the signal processing result of the data processing module of the embodiment.

[0029] Figure 3 Graph showing the performance of the full-field fine spectral diagnostic system based on IQ coherent detection in the embodiment. Figure 3 (a) is a spectral intensity fluctuation characterization diagram of the full-field fine spectral diagnostic system based on IQ coherent detection in the embodiment. The calculated relative intensity fluctuation is 0.45%, proving that the spectral intensity fluctuation of this embodiment is less than 1%. Figure 3 (b) is a characterization diagram of the spectral wavelength fluctuation of the full-field fine spectral diagnostic system based on IQ coherent detection in the embodiment. The calculated spectral wavelength fluctuation is 0.34 MHz, proving that the wavelength fluctuation of this embodiment is less than 0.5 MHz. Figure 3 (c) is a spectral phase fluctuation characterization diagram of the full-field fine spectral diagnostic system based on IQ coherent detection in the embodiment. The calculated phase fluctuation is 0.02 rad, which proves that the phase fluctuation of this embodiment is less than 0.1 rad. Figure 3 (d) is a spectral resolution characterization diagram of the full-field fine spectral diagnostic system based on IQ coherent detection in the embodiment. The modulation frequency of 200 MHz can be resolved, proving that the resolution of this embodiment is higher than 200 MHz.

[0030] As can be seen from the above examples, the present invention implements a full-field, fine-spectral diagnostic system based on IQ coherent detection. This system enables real-time spectral diagnosis with high diagnostic accuracy and a fast diagnostic response rate. Compared to traditional fine-spectral characterization techniques based on coherent detection, this system offers full-field spectral detection and single-shot parallel detection, significantly improving the accuracy of spectral information acquisition.

Claims

1. A full-field fine spectral diagnostic system based on IQ coherent detection, characterized by: It includes single-frequency laser, acousto-optic frequency shifter, 90° optical mixer, balanced photodetector, polarization controller and data processing module; The single-frequency laser is used to generate a single-frequency optical signal; The acousto-optic frequency shifter performs acousto-optic frequency shifting on the single-frequency optical signal to generate a local oscillation optical signal; There are two polarization controllers in total, which are dual-port devices, one input port and one output port; the two polarization controllers receive the photometric signal and the local oscillator light signal respectively, adjust the polarization state of the photometric signal and the local oscillator light signal, and after matching the polarization state required by the 90° optical mixer, they are respectively connected to the two input ports of the 90° optical mixer; The 90° optical mixer is a six-port device with two input ports and four output ports. The two input ports receive the photometric signal and the local oscillator signal respectively. The local oscillator signal is mixed with the photometric signal to obtain four mixed signals and output them. There are two balanced photodetectors in total, which are three-port devices with two input ports and one output port. The two input ports of each balanced photodetector are respectively connected to the two output ports of the 90° optical mixer. One balanced photodetector receives only the mixed signal after phase shift, and the other balanced photodetector receives only the mixed signal before phase shift, thereby achieving background light signal elimination and common-mode noise suppression. The data processing module recovers the light signal to be measured from the signals output by the two balanced photoelectric detectors.

2. The full-field fine spectral diagnostic system based on IQ coherent detection according to claim 1, characterized in that: The four mixing signals are specifically: one output is the sum of the local oscillator light signal and the light signal to be measured, and one output is the difference between the local oscillator light signal and the light signal to be measured; one output is the sum of the local oscillator light signal after 90° phase shift and the light signal to be measured, and one output is the difference between the local oscillator light signal after 90° phase shift and the light signal to be measured.

3. The full-field fine spectral diagnostic system based on IQ coherent detection according to claim 1, characterized in that: The signals output by the two balanced photodetectors both contain amplitude and phase information of the optical signal to be measured.

4. The full-field fine spectral diagnostic system based on IQ coherent detection according to claim 1, characterized in that: The specific process of the data processing module recovering the optical signal to be measured is as follows: the mixed signal after 90° phase shift is multiplied by the imaginary unit i and then added to the mixed signal before 90° phase shift to obtain the optical signal to be measured, and then the spectrum of the optical signal to be measured is obtained by Fourier transform.

5. The full-field fine spectral diagnostic system based on IQ coherent detection according to claim 1, characterized in that: The polarization controller is a three-ring polarization controller to achieve the maximum output of the IQ coherent detector.

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