Frequency synthesis-based optical frequency domain reflectometry method and system
Frequency synthesis-based optical frequency domain reflectometry method and system are disclosed. The method is to implement optical frequency reflectometry and comprises: performing an electro-optic modulation and an acousto-optic modulation on a local light to obtain an optical pulse; inputting the optical pulse as a detection pulse optical signal to a test optical fiber; and detecting an obtained Rayleigh backscattered optical signal under coherent detection with the local light, and then performing a photoelectric conversion and a demodulation, wherein: the electro-optic modulation is performed by using a single frequency signal; the acousto-optic modulation is performed by using a pulse signal; and the optical pulse is obtained by simultaneously sweeping multiple frequency components of an optical comb signal which is obtained by the electro-optic modulation.
1. A frequency synthesis-based optical frequency domain reflectometry method to implement optical frequency reflectometry, comprising:
performing an electro-optic modulation and an acousto-optic modulation on a local light to obtain an optical pulse;
inputting the optical pulse as a detection pulse optical signal to a test optical fiber; and
detecting an obtained Rayleigh backscattered optical signal under coherent detection with the local light, and then performing a photoelectric conversion and a demodulation, wherein:
the electro-optic modulation is performed by using a single frequency signal;
the acousto-optic modulation is performed by using a pulse signal; and
the optical pulse is obtained by simultaneously sweeping multiple frequency components of an optical comb signal which is obtained by the electro-optic modulation.
2. The frequency synthesis-based optical frequency domain reflectometry method according to claim 1 , wherein:
the local light is a narrow-linewidth laser; and
the pulse signal is a chirped pulse signal.
3. The frequency synthesis-based optical frequency domain reflectometry method according to claim 1 , wherein
a frequency interval of the optical comb signal is equal to a sweeping range of the pulse signal.
4. The frequency synthesis-based optical frequency domain reflectometry method according to claim 1 , wherein
the electro-optic modulation modulates a high-frequency sinusoidal electrical signal to a single frequency optical signal in an intensity modulation manner or in a phase modulation manner and generates an optical frequency comb signal.
5. The frequency synthesis-based optical frequency domain reflectometry method according to claim 1 , wherein
the acousto-optic modulation modulates the optical comb signal by using a pulse signal and obtains a multi-frequency sweep optical pulse signal.
6. A frequency synthesis-based optical frequency domain reflectometry method to implement optical frequency reflectometry, comprising:
performing an electro-optic modulation and an acousto-optic modulation on a local light to obtain an optical pulse;
inputting the optical pulse as a detection pulse optical signal to a test optical fiber; and
detecting an obtained Rayleigh backscattered optical signal under coherent detection with the local light, and then performing a photoelectric conversion and a demodulation, wherein:
the electro-optic modulation is performed by using a single frequency signal;
the acousto-optic modulation is performed by using a pulse signal; and
the optical pulse is obtained by simultaneously sweeping multiple frequency components of an optical comb signal which is obtained by the electro-optic modulation, wherein the demodulation includes:
generating a digital frequency-sweep signal having segments as many as frequency components thereof according to an electrical signal obtained by the photoelectric conversion;
multiplying the generated multiple segments of complex signals by a window function respectively and performing cross-correlation operations with the original data respectively to obtain a corresponding correlation function;
adding the obtained multiple complex functions directly and performing modulo operations to obtain a synthesis demodulation result of the multiple segments of digital frequency-sweep signals.
7. The frequency synthesis-based optical frequency domain reflectometry method according to claim 6 , wherein
the window function is a Hanning window function.
8. A frequency synthesis-based optical frequency domain reflectometry system comprising:
a reference optical branch and a modulation optical branch homogenous therewith;
a coupling unit; and
a demodulation unit, wherein:
an output end of the reference optical branch and an output end of the modulation optical branch are both connected with the coupling unit, and an output end of the coupling unit is connected with the demodulation unit;
the modulation optical branch comprises an electro-optic modulator, an acousto-optic modulator, an erbium-doped optical fiber amplifier, an optical fiber circulator and a test optical fiber which are sequentially connected in series;
the electro-optic modulator performs a modulation by a single frequency signal to generate an optical comb signal;
the optical comb signal input into the acousto-optic modulator is modulated by a pulse signal to obtain a multi-frequency sweep optical pulse signal, amplified by the erbium-doped optical fiber amplifier, and then output to the optical fiber circulator and the test optical fiber in turn;
a reflecting end of the optical fiber circulator serves as an output of the modulation optical branch and is connected with the coupling unit.
9. The frequency synthesis-based optical frequency domain reflectometry system according to claim 8 , wherein:
an input end of the reference optical branch and an input end of the modulation optical branch receive a narrow-linewidth laser from a common laser device;
the laser device outputs the narrow-linewidth laser with a splitting ratio of 99:1 to the modulation optical branch and the reference optical branch respectively through an optical fiber coupler.
10. The frequency synthesis-based optical frequency domain reflectometry system according to claim 8 , wherein
the reference optical branch is provided with a polarization controller.
11. The frequency synthesis-based optical frequency domain reflectometry system according to claim 8 , wherein
the electro-optic modulator is an electro-optic intensity modulator or an electro-optic phase modulator.
12. The frequency synthesis-based optical frequency domain reflectometry system according to claim 8 , wherein:
the coupling unit is a 50:50 optical fiber coupler;
a local light from the reference optical branch and a Rayleigh backscattered light output from the optical fiber circulator are coherent-detected in the 50:50 optical fiber coupler.
13. A frequency synthesis-based optical frequency domain reflectometry system comprising:
a reference optical branch and a modulation optical branch homogenous therewith;
a coupling unit; and
a demodulation unit, wherein:
an output end of the reference optical branch and an output end of the modulation optical branch are both connected with the coupling unit, and an output end of the coupling unit is connected with the demodulation unit;
the modulation optical branch comprises an electro-optic modulator, an acousto-optic modulator, an erbium-doped optical fiber amplifier, an optical fiber circulator and a test optical fiber which are sequentially connected in series;
the electro-optic modulator performs a modulation by a single frequency signal to generate an optical comb signal;
the optical comb signal input into the acousto-optic modulator is modulated by a pulse signal to obtain a multi-frequency sweep optical pulse signal, amplified by the erbium-doped optical fiber amplifier, and then output to the optical fiber circulator and the test optical fiber in turn;
a reflecting end of the optical fiber circulator serves as an output of the modulation optical branch and is connected with the coupling unit,
the demodulation unit comprises a photoelectric conversion module, a data acquisition card and a demodulation module; and
the data acquisition card collects electrical signals converted by the photoelectric conversion module, and the demodulation module demodulates the electrical signals.