CN-121678118-B - Optical time domain reflectometer with large dynamic range and optical fiber testing method

CN121678118BCN 121678118 BCN121678118 BCN 121678118BCN-121678118-B

Abstract

The invention discloses an optical time domain reflectometer with a large dynamic range and an optical fiber testing method, which comprise a continuous light source, an optical amplifier for amplifying the gain of continuous laser, an optical attenuator for attenuating the optical power of the continuous laser, a time domain filter for modulating the continuous laser into a periodic pulse optical signal, a circulator for outputting the periodic pulse optical signal to an optical fiber to be tested and receiving a back scattering signal returned from the optical fiber to be tested, an optical signal detection unit for converting the back scattering signal into an electric signal, a signal processing unit for extracting the relation between the back scattering power and the position of the optical fiber from the electric signal, and a control unit for dynamically adjusting the gain of the optical amplifier, setting the attenuation value of the optical attenuator and adjusting the modulation pulse width of the time domain filter. The invention can realize the detection of the back scattering signal with a large dynamic range and is compatible with the conventional quartz optical fiber and hollow optical fiber.

Inventors

LIU YAPING
YU JINGXIONG
ZHANG ZHIHENG
ZHANG PENG
LIAO ZHAOLONG
ZHANG LIYAN
LI PENG
ZHANG LEI
XIONG ZHUANG

Assignees

长飞光纤光缆股份有限公司

Dates

Publication Date: 20260512
Application Date: 20260206

Claims (11)

1. The large dynamic range optical time domain reflectometer is characterized by comprising: a continuous light source for outputting continuous laser; An optical amplifier for gain-amplifying the continuous laser; an optical attenuator for attenuating optical power of the gain-adjusted continuous laser light; a time domain filter for modulating the continuous laser into a periodic pulsed optical signal; The circulator is used for outputting a periodic pulse optical signal to the tested optical fiber and receiving a back scattering signal returned from the tested optical fiber; the optical signal detection unit is used for converting the back scattering signal into an electric signal; A signal processing unit for extracting a relationship between the back scattering power and the optical fiber position from the electrical signal; the control unit is used for dynamically adjusting the gain of the optical amplifier, setting the attenuation value of the optical attenuator and adjusting the modulation pulse width of the time domain filter according to the relation between the back scattering power and the optical fiber position and the power range of the linear working interval of the optical signal detection unit; according to the known parameters and the estimated parameters of the measured optical fiber, the gain of the optical amplifier, the attenuation value of the attenuator and the modulation pulse width of the time domain filter are preliminarily set; The known parameters of the measured optical fiber comprise the type and the backscattering coefficient of the measured optical fiber, and the estimated parameters comprise the length interval of the measured optical fiber, the number of optical fiber fusion points and the number of connection points; The principle of preliminary setting of the gain of the optical amplifier, the attenuation value of the attenuator and the modulation pulse width of the time domain filter is as follows: Estimating estimated total loss of the measured optical fiber according to the known parameters and the estimated parameters of the measured optical fiber; Calculating back scattering signal power pre-estimation values of the beginning end and the tail end of the tested optical fiber according to the initially set gain of the optical amplifier, the attenuation value of the attenuator and the modulation pulse width of the time domain filter, known system loss, parameters of the continuous light source, the back scattering coefficient of the tested optical fiber and the estimated total loss, so that the back scattering signal power pre-estimation values of the beginning end and the tail end of the tested optical fiber are all located in a linearly detectable power interval of the optical signal detection unit; When preliminary setting is carried out, the nonlinear effect of the tested optical fiber is judged according to the type of the tested optical fiber, the combined output power of the optical amplifier and the attenuator is set to a level which does not generate the nonlinear effect, and meanwhile, the modulation pulse width of the time domain filter is set to be 1.5-3 times of the minimum pulse width according with the principle according to the backscattering coefficient and the estimated total loss of the tested optical fiber, so that higher testing resolution and signal-to-noise ratio are realized.
2. The large dynamic range optical time domain reflectometer of claim 1, wherein the optical amplifier is a1 st stage amplifier, or The optical amplifier is formed by cascading at least 2 stages of amplifiers, and a broadband filter is arranged between each two stages of amplifiers.
3. The large dynamic range optical time domain reflectometer as in claim 1, wherein the continuous light source, the optical amplifier, the optical attenuator and the time domain filter are connected in sequence, or The continuous light source, the optical amplifier, the time domain filter and the optical attenuator are sequentially connected.
4. The large dynamic range optical time domain reflectometer of claim 1, wherein the output power range of the continuous light source is-30 dBm-13 dBm, the gain adjustment range of the optical amplifier is 10 dB-70 dB, the maximum output power of the optical amplifier is 43dBm, and the sensitivity range of the optical signal detection unit is-90 dBm to-100 dBm.
5. An optical fiber testing method implemented by using the large dynamic range optical time domain reflectometer according to any one of claims 1 to 4, characterized by comprising the following steps: according to the known parameters and the estimated parameters of the measured optical fiber, the gain of the optical amplifier, the attenuation value of the attenuator and the modulation pulse width of the time domain filter are preliminarily set; Acquiring the relation between the back scattering power and the position of the optical fiber in real time; dynamically adjusting the gain of the optical amplifier, setting the attenuation value of the optical attenuator and adjusting the modulation pulse width of the time domain filter according to the relation between the back scattering power and the optical fiber position and the power range of the linear working interval of the optical signal detection unit; The known parameters of the measured optical fiber comprise the type and the backscattering coefficient of the measured optical fiber, and the estimated parameters comprise the length interval of the measured optical fiber, the number of optical fiber fusion points and the number of connection points; The principle of preliminary setting of the gain of the optical amplifier, the attenuation value of the attenuator and the modulation pulse width of the time domain filter is as follows: Estimating estimated total loss of the measured optical fiber according to the known parameters and the estimated parameters of the measured optical fiber; Calculating back scattering signal power pre-estimation values of the beginning end and the tail end of the tested optical fiber according to the initially set gain of the optical amplifier, the attenuation value of the attenuator and the modulation pulse width of the time domain filter, known system loss, parameters of the continuous light source, the back scattering coefficient of the tested optical fiber and the estimated total loss, so that the back scattering signal power pre-estimation values of the beginning end and the tail end of the tested optical fiber are all located in a linearly detectable power interval of the optical signal detection unit; When preliminary setting is carried out, the nonlinear effect of the tested optical fiber is judged according to the type of the tested optical fiber, the combined output power of the optical amplifier and the attenuator is set to a level which does not generate the nonlinear effect, and meanwhile, the modulation pulse width of the time domain filter is set to be 1.5-3 times of the minimum pulse width according with the principle according to the backscattering coefficient and the estimated total loss of the tested optical fiber, so that higher testing resolution and signal-to-noise ratio are realized.
6. The method of claim 5, wherein during dynamic adjustment, the attenuation value of the optical attenuator is gradually reduced, and then the gain of the optical amplifier is gradually increased, so that the combined output power of the optical attenuator and the optical amplifier is increased, until the backscattering power of different optical fiber positions obtained in real time are all located in the linear working interval of the optical signal detection unit, and when the combined output power of the optical attenuator and the optical amplifier is continuously increased, the detectable position of the tail end of the optical fiber is unchanged, and the adjustment is stopped; If the combined output power of the optical attenuator and the optical amplifier is adjusted to generate a nonlinear effect in the measured optical fiber or to be adjusted to the maximum output power, the backscattering power of different optical fiber positions obtained in real time still cannot be located in the linear working interval of the optical signal detection unit, and then the modulation pulse width of the time domain filter is increased.
7. The method of claim 5, wherein when the optical fiber is a quartz single-mode optical fiber, The combined output power of the optical attenuator and the optical amplifier is set to be a level which does not generate the nonlinear effect of the optical fiber, and the modulation pulse width of the time domain filter is set to be 1.5-3 times of the minimum pulse width according with the principle according to the backscattering coefficient and the estimated total loss of the measured optical fiber.
8. The method of claim 7, wherein the optical attenuation value is set to 0-10dB before the gain of the optical amplifier is adjusted when the combined output power of the optical attenuator and the optical amplifier is set to a level that does not produce the nonlinear effect of the optical fiber.
9. The method of claim 5, wherein the time domain filter is set to a smaller pulse width when the optical fiber is a hollow fiber, and the combined output power of the optical attenuator and the optical amplifier is set to a smaller value according with the principle, the smaller value being 2-5 dB higher than the minimum value.
10. The method of claim 9, wherein the pulse width of the pulse width signal is less than or equal to 100ns.
11. The method of claim 9, wherein the optical attenuation value is set to 0-10 dB when the combined output power of the optical attenuator and the optical amplifier is set to a smaller value according with the principle, and then the gain of the optical amplifier is adjusted.

Description

Optical time domain reflectometer with large dynamic range and optical fiber testing method Technical Field The invention belongs to the field of hollow fiber testing, and particularly relates to an optical time domain reflectometer with a large dynamic range and a fiber testing method. Background The OTDR is a conventional optical fiber detection technology, can be used for representing the attenuation characteristic of optical fibers in a distributed manner, reflects some event points on an optical fiber link, and has important application in the aspects of optical fiber cable production, construction, operation and maintenance and the like. The antiresonant hollow fiber is formed by a plurality of capillary structures to form specific arrangement, thereby generating antiresonant effect and inhibiting light leakage, and restraining light to be transmitted in the middle air medium fiber core. Since the light guiding medium is air, the hollow fiber has obviously better performance in terms of attenuation, dispersion, time delay and nonlinearity than the traditional quartz fiber, and has rapidly developed in recent years, wherein the attenuation coefficient reaches 0.05dB/km. However, hollow core fibers present a significant challenge in OTDR testing. The backscattering coefficient of air (which can be as low as-110 dB/m) is 30-40 dB lower than that of quartz (about-72 dB/m), and the dynamic range of the traditional commercial OTDR is about 40-50 dB (corresponding to 20 mu s pulse width), so that the attenuation of the hollow fiber is difficult to test by the traditional commercial OTDR. In particular, the conventional commercial OTDR test on hollow-core fibers can take the technical approach of using only larger pulse widths, however, using large pulse width tests sacrifices test resolution and dead zones. Even with a pulse width of 1 mus, the dynamic range is still difficult to test for a longer hollow fiber link, and the event condition of the fiber link cannot be accurately represented due to large dead zone and low resolution. Patent application CN118801977a proposes to amplify an optical pulse signal with an optical amplifier and to perform dispersion compensation on the amplified optical signal with a dispersion compensation component, so as to obtain a chirp-free optical signal. The dispersion compensation component adopted by the scheme compresses pulse to boost pulse power, on one hand, the dispersion compensation scheme in the application is usually aimed at fs or ps-level pulse width compression, and the OTDR is ns or mu s-level pulse width, so that the effect of pulse width compression is very little, and on the other hand, the dispersion compensation component usually has larger loss on an optical signal, so that the power of an output optical pulse is limited. In addition, this approach does not take into account the noise problem of the optical amplifier at the time of pulsed light amplification, and although the output optical pulse power can be raised, the dynamic range is not significantly improved. In addition, the scheme is difficult to be compatible with conventional optical fibers and hollow-core optical fibers due to the problem of nonlinear effects of the optical fibers. Disclosure of Invention Aiming at the defects or improvement demands of the prior art, the invention provides an optical time domain reflectometer with a large dynamic range and an optical fiber testing method. To achieve the above object, according to one aspect of the present invention, there is provided a large dynamic range optical time domain reflectometer comprising: a continuous light source for outputting continuous laser; An optical amplifier for gain-amplifying the continuous laser; an optical attenuator for attenuating optical power of the gain-adjusted continuous laser light; a time domain filter for modulating the continuous laser into a periodic pulsed optical signal; The circulator is used for outputting a periodic pulse optical signal to the tested optical fiber and receiving a back scattering signal returned from the tested optical fiber; the optical signal detection unit is used for converting the back scattering signal into an electric signal; A signal processing unit for extracting a relationship between the back scattering power and the optical fiber position from the electrical signal; the control unit is used for dynamically adjusting the gain of the optical amplifier, setting the attenuation value of the optical attenuator and adjusting the modulation pulse width of the time domain filter according to the relation between the back scattering power and the optical fiber position and the power range of the linear working interval of the optical signal detection unit. According to the above scheme, the optical amplifier is a 1-stage amplifier, or The optical amplifier is formed by cascading at least 2 stages of amplifiers, and a broadband filter is arranged between each two stages of amplifiers.