CN113114350B

CN113114350B - Wavelength coding optical time domain reflection testing device and method based on frequency shift heterodyne

Info

Publication number: CN113114350B
Application number: CN202110365976.9A
Authority: CN
Inventors: 张尚剑; 邢贯苏; 徐映; 刘永
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2021-03-30
Filing date: 2021-03-30
Publication date: 2022-06-10
Anticipated expiration: 2041-03-30
Also published as: CN113114350A

Abstract

The invention discloses a wavelength coding optical time domain reflection testing device and method based on frequency shift heterodyne, and belongs to the technical field of optical fiber link testing. The invention uses a coding signal generator to generate a frequency-coded radio-frequency signal to drive an acousto-optic frequency shifter, encodes a narrow-line-width laser through the acousto-optic frequency shifter to generate a wavelength-coded optical signal, the optical signal is divided into a detection optical signal and a reference optical signal through a beam splitter and respectively input into a circulator and a beam combiner, the detection optical signal enters a tested optical fiber and is divided into a breakpoint to generate a reflection optical signal, the reflection optical signal enters the beam combiner through a polarization controller, the reflection optical signal and the reference optical signal enter the photoelectric detector to beat frequency, and the beat frequency signal enters a spectrum analysis module to be analyzed. Compared with the prior art, the invention improves the wavelength tuning speed and the wavelength tuning stability, and can realize narrower pulse and narrower beat signal line width.

Description

Wavelength coding optical time domain reflection testing device and method based on frequency shift heterodyne

Technical Field

The invention relates to the technical field of optical fiber link testing, in particular to a wavelength coding optical time domain reflection testing device and method based on frequency shift heterodyne, which realize quick and stable tuning.

Background

An Optical Time-Domain Reflectometer (Optical Time-Domain Reflectometer) is abbreviated as OTDR. The OTDR utilizes the principle of laser radar, and obtains parameters such as a loss characteristic at a reflection position by injecting a probe light pulse into an optical fiber and by measuring reflected light power and transmission time. The OTDR can perform verification, maintenance, repair, and monitoring on an optical fiber communication system, and is widely used in the optical fiber industry.

In order to improve the performance of the conventional OTDR, a wavelength-coded optical time domain reflection scheme is proposed by xingni et al, and chinese patents are applied, the patent numbers of which are: CN101764646, the patent name "method for measuring optical fiber link by using wavelength-coded optical time domain reflection testing device". The distributed Bragg reflection type laser is used as a light source, the tuning of the optical wavelength is realized by changing the bias current applied to a phase region, and the performance of the OTDR is improved by carrying out wavelength coding on an optical signal. However, since the spatial resolution of the OTDR is determined by the pulse width, in order to achieve high spatial resolution, the tuning time of the laser between two wavelengths is required to reach 200 nanoseconds or even shorter, and meanwhile, the line width of the beat signal is also affected by the instability of the wavelength caused by fast tuning between different wavelengths, and the line width of the beat signal is wider as the tuning speed is faster, and the wider line width affects the dynamic range of the system. The above two problems limit the application of wavelength-coded OTDR.

Disclosure of Invention

In order to solve the technical problems, the invention provides a wavelength coding optical time domain reflection testing device and method based on frequency shift heterodyne, which realize fast and stable optical wavelength tuning and can generate narrower pulses and narrower beat frequency signal line width.

In order to achieve the purpose, the invention specifically adopts the following technical scheme:

the invention provides a wavelength coding optical time domain reflection testing device based on frequency shift heterodyne, which comprises a narrow line width laser (1), a wavelength coding module (4), a beam splitter (5), a circulator (6), a polarization controller (8), a beam combiner (9), a photoelectric detector (10) and a time-frequency analysis module (11), wherein the wavelength coding module (4) consists of an acousto-optic frequency shifter (2) and a coding signal generator (3).

The principle of the wavelength coding optical time domain reflection testing method based on frequency shift heterodyne is as follows:

the code signal generator (3) generates a code signal with a period T_DThe frequency coding signal of N periods in total, two pulses with different frequencies are coded in one period, the pulse width is tau, and the frequency is f respectively₁And f₂Two pulses having a time interval of T₁The filling frequency of the rest of the time is f₃Of the signal of (1). Frequency f₁，f₂，f₃Located near the center frequency of the acousto-optic frequency shifter (2), f₁<f₃<f₂Or f₂<f₃<f₁. The frequency shift efficiency of the acousto-optic frequency shifter (2) at three frequencies is eta respectively₁，η₂，η₃。

The narrow linewidth laser (1) is in a normal lasing state and emits power P₀The optical carrier wave with the frequency v is subjected to frequency shift by the acousto-optic frequency shifter (2), and the light field E after frequency shift is expressed as follows:

rect is a rectangular function:

the optical field after frequency shift is input into a beam splitter (5) from a port a, and is divided into a detection optical signal and a reference optical signal which are respectively output from a port b and a port c of the beam splitter (5); the detection optical signal is input into the circulator (6) from the port d and then input into the tested optical fiber (7) from the port e, and a reflected optical signal is generated after meeting a breakpoint in the tested optical fiber (7) and returns to the circulator (6) and is output from the port f; the reflected light passes through the polarization controller (8), passes through the beam combiner (9) in reference light signals, enters the photoelectric detector (10) for beat frequency, and beat frequency signals enter the time frequency analysis module (11) for analysis. Changing the time interval of two pulses to T₁Simultaneously analyzing the time domain and the frequency domain of the beat signal when the frequency component f₁-f₂When the signal duration reaches the maximum or the power reaches the maximum, extracting the pulse time interval T of the current moment₁And the time of flight (TOF) of the reflected light signal in the optical fiber is obtained, so that the breakpoint positioning of the optical fiber is realized.

The invention has the following beneficial effects: the wavelength coding is carried out on the optical signal by utilizing the acousto-optic frequency shifter, and the wavelength tuning speed is high (the tuning time is less than the rising/falling time of the acousto-optic frequency shifter by 35 ns); by using a narrow linewidth laser and acousto-optic frequency shift, the wavelength of the coded optical signal is stable, so that the width of the generated beat frequency signal line is narrow and is less than 1 MHz.

Drawings

FIG. 1 is a diagram of an optical time domain reflectometry apparatus according to the present invention.

FIG. 2 is a diagram of a short-time Fourier transform of a radio frequency signal generated by the code signal generator of the present invention.

Fig. 3 is a time domain waveform diagram of a beat signal actually measured by the present invention.

Fig. 4 is a frequency spectrum diagram of a beat signal actually measured by the present invention.

Detailed Description

For a better understanding of the present invention, the following detailed description is given in conjunction with the accompanying drawings and the following examples:

example 1

Referring to fig. 1, the wavelength-coded optical time domain reflection testing apparatus based on frequency shift heterodyne of the present invention mainly includes a narrow linewidth laser (1), a wavelength coding module (4), a polarization controller (8), a photodetector (10), a beam splitter (5), a beam combiner (9), and a time-frequency analysis module (11).

Wherein the narrow linewidth laser (1) outputs laser with carrier frequency 193.414THz and linewidth 1 kHz; the wavelength coding module (4) is composed of a coding signal generator (3) and an acousto-optic frequency shifter (2), the coding signal generator (3) is an arbitrary waveform generator, the signal frequencies for coding are 70MHz and 90MHz respectively, the rest filling signal frequencies are 80MHz, and fig. 2 is a short-time Fourier transform diagram of the radio frequency signal.

Coded light pulses generated by the wavelength coding module (4) are input from a port a of the beam splitter (5) and output from a port b and a port c as a detection light signal and a reference light signal respectively; the detection light signal is output from an input port e of a port d of the circulator (6) and enters the tested optical fiber (7), reflected light generated when the detection light signal meets a breakpoint in the optical fiber is output from a port f of the circulator (6), the reflected light passes through the polarization controller (8), enters the beam combiner (9) from the reference light signal, enters the photoelectric detector (10) for beat frequency, and a sampling oscilloscope collects beat frequency signal data and analyzes the beat frequency signal data. The fiber break point distance is about 6230m, and the time interval T between two coded pulses is changed₁When T is₁At 60.98us, an intermediate-frequency beat signal with a frequency equal to 20MHz, which is the difference between the two pulses, can be observed from the time domain and the frequency domain, fig. 3 is the time domain of the global signal and the local beat signal, and fig. 4 is the frequency domain of the global signal.

Claims

1. A wavelength coding optical time domain reflection testing device based on frequency shift heterodyne is characterized in that:

the device comprises a narrow linewidth laser (1), a wavelength coding module (4), a beam splitter (5), a circulator (6), a polarization controller (8), a beam combiner (9), a photoelectric detector (10) and a time-frequency analysis module (11); the wavelength coding module (4) consists of a coding signal generator (3) and an acousto-optic frequency shifter (2); the code signal generator (3) generates a frequency-coded radio-frequency signal to drive the acousto-optic frequency shifter (2), the narrow-line-width laser (1) generates a coded optical pulse signal through the acousto-optic frequency shifter (2) and inputs the coded optical pulse signal into the beam splitter (5) from a port a, and the coded optical pulse signal is divided into a detection optical signal and a reference optical signal which are respectively output from a port b and a port c of the beam splitter (5); the detection optical signal is input into the circulator (6) from the port d and then input into the tested optical fiber (7) from the port e, and a reflected optical signal is generated after meeting a breakpoint in the tested optical fiber (7) and returns to the circulator (6) and is output from the port f; the reflected light passes through the polarization controller (8), then passes through the beam combiner (9) together with the reference light signal, enters the photoelectric detector (10) for beat frequency, and the beat frequency signal enters the time frequency analysis module (11) for analysis.

2. The device for testing the wavelength-coded optical time domain reflection based on the frequency shift heterodyne as recited in claim 1, wherein the code signal generator (3) is an arbitrary waveform generator or a frequency shift keying modulator, and generates a radio frequency signal with a frequency near the center frequency of the acousto-optic frequency shifter (2).

3. The wavelength-coded optical time domain reflectometry test device based on frequency shift heterodyne according to claim 1, characterized in that the time frequency analysis module (11) is a sampling oscilloscope, or a data acquisition card and a microprocessor.

4. A wavelength-coded optical time domain reflection test method based on frequency shift heterodyne, which applies the wavelength-coded optical time domain reflection test device based on frequency shift heterodyne as recited in any one of claims 1-3, characterized in that the method divides the coded optical signal composed of two optical signals with different wavelengths into a probe optical signal and a reference optical signal, the probe optical signal enters the tested optical fiber and then encounters an optical fiber breakpoint to generate a reflected optical signal, the reflected optical signal and the reference optical signal enter a photodetector (10) for beat frequency, the beat frequency signal enters a time-frequency analysis module (11) for analysis; by adjusting the time interval of the two optical pulses and observing the duration of the time domain signal of the corresponding beat frequency signal, when the duration of the time domain signal reaches the maximum, the time delay of the reflected optical signal is equal to the time interval of the two optical pulses, so that the flight time of the probe light in the optical fiber is measured, and the positioning of the breakpoint of the optical fiber is realized.