High-precision optical fiber quality detection method and system for deconvolution filtering
Technical Field
The invention belongs to the field of distributed optical fiber quality detection, and particularly relates to a deconvolution filtering high-precision optical fiber quality detection method and system.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
Optical time domain reflectometry, also known as backscatter measurement, was used earlier primarily as a technique to detect loss profiles of fiber lengths. In recent years, the optical time domain reflection detection technology is expanded to other aspects: optical fiber length measurement, loss detection at optical fiber fusion splice, optical fiber break measurement, loss measurement at connector, etc. The quality detection of optical fibers, or diagnosis and fault identification positioning of optical fiber systems, becomes the most important application field of optical time domain reflection detection technology.
In testing an optical communication cable, a relatively high power optical pulse is injected from one end of the cable and scattered and reflected signals are received through the same side. Light propagates in the optical fiber and generates Rayleigh scattering due to the characteristics of the optical fiber itself and the non-uniformity of impurity components; due to the mechanical connection and breakage, fresnel reflection occurs as light is transmitted in the fiber, with some of the scattered and reflected light being transmitted back to the input end. The optical fiber quality distribution condition can be obtained by photoelectric conversion and collecting Fresnel reflection and backward Rayleigh scattering signals.
The optical fiber quality detection device belongs to an optical fiber physical link online detection system, adopts an optical reflection measurement technology to detect and position information such as the length, attenuation (loss), joint, fault position and the like of an optical fiber link, provides fault early warning and fault positioning of the optical fiber through a system platform, and realizes continuous real-time online monitoring and accurate fault positioning of the optical fiber link for 7 multiplied by 24 hours.
The related data show that the problems of bending, breaking and the like of the optical fiber are main problems which lead to the failure of the optical cable line to work normally. For example, industrial or agricultural production, construction in engineering, including factors in nature such as debris flows, slumps, and earthquakes, may cause failure of the fiber network and immeasurable losses.
In the process of practical life application, the optical fiber can fail for various reasons, so that the failure is classified by the optical fiber: one is direct fracture, the fault is serious, if two ends of the point are reserved, the reserved optical fiber is fully utilized, and then the maintenance of the optical fiber is completed; the other type is an incompletely broken optical fiber, and the type can be divided into two types of beam tube breakage and optical fiber breakage in the beam tube, so that the normal operation of other optical fibers is ensured during the maintenance of the faults, and the optical fibers are maintained in a corresponding mode.
The optical time domain reflectometer takes laser pulse signals incident into a measured optical fiber as detection signals, when the laser pulses are transmitted in the optical fiber, rayleigh scattering at all positions on the length of the optical fiber continuously returns to an injection end, when the detection signals pass through the optical fiber fault, fresnel reflection is caused, and reflected light returns to the injection end of pulse laser. The attenuation characteristic and the fault point position of the detected optical fiber can be obtained through correlation processing by selecting a proper optical circulator and a photoelectric detector with high sensitivity to detect the information of the echo signal received at the injection end face.
When pulse signals are transmitted in the tested optical fiber, the non-uniformity on the structure of the optical fiber can cause some energy of the laser signals to change the original transmission direction and spread around, the phenomenon is called Rayleigh scattering, and in 1881, british scientist Rayleigh (Rayleigh) has proposed on the basis of researching the scattering phenomenon of light. This phenomenon is due to the fact that the optical fiber has a different local refractive index due to the random variation of the optical fiber density during its production, resulting in scattering of the optical signal around, and a part of the scattered light is totally opposite to the original transmission direction, which is called rayleigh backscattering. In addition, the Rayleigh scattering magnitude is related to the measured parameters of the scattering points, and corresponding attenuation information can be obtained from the back-scattered light signals.
When the laser pulse encounters a crack or a point of different refractive index due to the fiber optic connector, a portion of the optical signal is reflected to the incident end and the reflected light is much more intense than the scattered light. The reflection of this light during transmission due to a fault is called fresnel reflection. Fresnel reflections are caused by faulty points or connection points in the fiber optic link, and the back-scattered light intensity generated at these points is significant. Therefore, the optical time domain reflectometry technique can perform fault detection by using the reflected signal.
The miniaturized optical fiber network in the market at present enters into daily life, such as aspects of optical fiber links in certain huge systems, optical fiber home networks and the like, so that the optical fiber fault detection is faced with great challenges, such as more accurate detection resolution and the like. The traditional single-pulse OTDR can obtain the attenuation characteristic curve and the fault point position of the tested optical fiber by inputting pulse laser into the tested optical fiber, collecting echo signals through photoelectric conversion and then processing the collected signals. However, the pulse signal width in this manner determines the measurement accuracy, typically in the order of meters, and may decrease to tens of meters as the length of the optical fiber to be detected increases. In addition, related personnel improve the signal-to-noise ratio and the measurement resolution through related technologies such as ultra-short light pulse, but the contradiction that the detection distance and the spatial resolution cannot be improved at the same time still cannot be solved: the measurement is improved by reducing the pulse laser width, but this method reduces the laser pulse energy, making the dynamic range smaller; increasing the peak power of the signal to increase the spatial resolution may lead to the generation of nonlinear effects. Even if the generation of the ultra-short laser pulse is completed through some unusual instruments, the system structure is more complex, the operation difficulty is increased, the miniaturization and marketization of the system cannot be realized, and most OTDR products on the market at present have the problems of high price and low resolution.
Disclosure of Invention
In order to solve the problems, the invention provides a high-precision optical fiber quality detection method and a system for deconvolution filtering.
According to some embodiments, the present invention employs the following technical solutions:
in a first aspect, the present invention provides a method for high-precision optical fiber quality detection with deconvolution filtering.
A deconvolution filtering high-precision optical fiber quality detection method comprises the following steps:
the optical pulse signals emitted by the laser emitter respectively enter the optical cable to be tested and the reflector through the circulator to respectively obtain the optical cable time domain echo signals to be tested and the reflector time domain echo signals;
calculating a reflector frequency domain echo signal corresponding to the reflector time domain echo signal, and obtaining a measured optical cable frequency domain echo signal corresponding to the measured optical cable time domain echo signal according to the combination of the reflector frequency domain echo signal and a system frequency domain transfer function;
determining deconvoluted measured optical cable frequency domain echo signals according to the measured optical cable frequency domain echo signals;
and obtaining a high-resolution echo signal related to the quality of the tested optical cable according to the deconvoluted tested optical cable frequency domain echo signal.
Further, the process of obtaining the time domain echo signal of the tested optical cable comprises the following steps: and generating echo signals when encountering fault points according to the transmission of the optical pulse signals in the tested optical cable, and obtaining the time domain echo signals of the tested optical cable.
Further, the process of obtaining the reflector time domain echo signal includes: the optical pulse signal directly generates a single reflection signal in the reflector to obtain a reflector time domain echo signal.
Further, the process of calculating the reflector frequency domain echo signal corresponding to the reflector time domain echo signal includes: and in a single measurement period, carrying out Fourier transformation on the reflector time domain echo signal to obtain the reflector frequency domain echo signal.
Further, the measurement period=1/repetition frequency of the optical pulse signal.
Further, the obtaining the measured optical cable frequency domain echo signal corresponding to the measured optical cable time domain echo signal according to the combination of the reflector frequency domain echo signal and the system frequency domain transfer function specifically includes: measured optical cable frequency domain echo signal = reflector frequency domain echo signal x system frequency domain transfer function.
Further, determining the deconvoluted measured optical cable frequency domain echo signal according to the measured optical cable frequency domain echo signal specifically includes: deconvolved measured optical cable frequency domain echo signal = measured optical cable frequency domain echo signal x filtered reflector frequency domain echo signal.
Still further, the process of obtaining the filtered reflector frequency domain echo signal includes: and filtering the reflector frequency domain echo signals by using a wiener filter to obtain filtered reflector frequency domain echo signals.
Further, the process of obtaining the high-resolution echo signal related to the quality of the tested optical cable according to the deconvoluted tested optical cable frequency domain echo signal comprises the following steps: and performing inverse Fourier transform on the deconvoluted measured optical cable frequency domain echo signals to obtain high-resolution echo signals related to the measured optical cable quality.
In a second aspect, the present invention provides a deconvolution filtered high-precision optical fiber quality inspection system.
A deconvolution filtered high-precision fiber quality detection system, comprising:
a time domain signal acquisition module configured to: the optical pulse signals emitted by the laser emitter respectively enter the optical cable to be tested and the reflector through the circulator to respectively obtain the optical cable time domain echo signals to be tested and the reflector time domain echo signals;
a frequency domain signal acquisition module configured to: calculating a reflector frequency domain echo signal corresponding to the reflector time domain echo signal; according to the reflector frequency domain echo signals and the system frequency domain transfer function, obtaining measured optical cable frequency domain echo signals corresponding to the measured optical cable time domain echo signals;
a deconvolution module configured to: determining deconvoluted measured optical cable frequency domain echo signals according to the measured optical cable frequency domain echo signals;
an output module configured to: and obtaining a high-resolution echo signal related to the quality of the tested optical cable according to the deconvoluted tested optical cable frequency domain echo signal.
Compared with the prior art, the invention has the beneficial effects that:
in the traditional optical fiber quality detection device and method, echo signals of single-point faults have a certain time width, and if fault points with a relatively close space distance exist, the echo signals are fused into the same echo pulse.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a flow chart of a high-precision fiber quality detection method of deconvolution filtering shown in the present invention;
FIG. 2 is an echo signal of a reflector shown in the present invention;
FIG. 3 is a measured cable echo signal shown in the present invention;
FIG. 4 is a deconvoluted reflector echo signal illustrating the present invention;
fig. 5 is a deconvoluted cable echo signal under test, in accordance with an embodiment of the present invention.
Detailed Description
The invention will be further described with reference to the drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the term "comprising" when used in this specification is taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
In the present invention, terms such as "coupled" and the like are to be construed broadly and mean either directly or indirectly coupled through an intermediary. The specific meaning of the terms in the present invention can be determined according to circumstances by a person skilled in the relevant art or the art, and is not to be construed as limiting the present invention.
Example 1
The embodiment provides a high-precision optical fiber quality detection method for deconvolution filtering.
As shown in fig. 1, a method for detecting the quality of an optical fiber with high precision by deconvolution filtering includes:
the optical pulse signals emitted by the laser emitter respectively enter the optical cable to be tested and the reflector through the circulator to respectively obtain the optical cable time domain echo signals to be tested and the reflector time domain echo signals;
calculating a reflector frequency domain echo signal corresponding to the reflector time domain echo signal, and obtaining a measured optical cable frequency domain echo signal corresponding to the measured optical cable time domain echo signal according to the combination of the reflector frequency domain echo signal and a system frequency domain transfer function;
determining deconvoluted measured optical cable frequency domain echo signals according to the measured optical cable frequency domain echo signals;
and obtaining a high-resolution echo signal related to the quality of the tested optical cable according to the deconvoluted tested optical cable frequency domain echo signal.
Specifically, the present embodiment includes a pulse generator, a signal modulation circuit, a laser transmitter, a 1×2×2 circulator, an optical cable to be tested, a reflector, a detector 1, and a detector 2.
The pulse generator is connected with the signal modulation circuit, the signal modulation circuit is connected with the laser transmitter, the laser transmitter is connected with the 1 multiplied by 2 circulator, the 1 multiplied by 2 circulator enables light waves input by the port 1 to enter the optical cable to be tested through the port 2 and enter the reflector through the port 3 respectively, and echo signals generated when the light waves are transmitted by the optical cable to be tested and meet fault points enter the port 4 through the port 2. The light wave is reflected directly back into port 3 and into port 5 as it propagates in the reflector. The port 4 is commonly transmitted to a computer for processing through the detector 1 and the port 5 through the detector 2.
The specific steps are as follows:
(1) The laser emission repetition frequency is f rep Pulse width T wid Through the circulator and into the fiber optic cable under test and the reflector.
(2) When the optical pulse is transmitted in the optical cable to be tested, echo signals are generated when the optical pulse encounters a fault point, and the time domain signals returned by the optical cable to be tested are recorded as y (t); the light pulse directly generates a single reflection signal in the reflector, which is denoted as x (t). The reflector echo signal and the measured cable echo signal are shown in fig. 2 and 3, respectively.
(3) Within a single measurement period (measurement period
) And carrying out Fourier transform on the echo time domain signal of the reflector to obtain a reflector echo signal of a frequency domain.
X(ω)=∫x(t)e -jωt dt (1)
(4) The echo signal of the reflector is regarded as a reference signal, and the filter is used for filtering in order to avoid the divergence effect caused by the too low signal energy, so as to obtain the filtered reference signal.
Where a represents the ratio of signal power to noise power, which is generally assumed to be constant,
represents the conjugation of X (ω).
(5) The echo signal of the reflector can be regarded as the reflection signal of an infinite small fault point, and theoretically has extremely narrow pulse characteristics, so that the echo y (t) of the tested optical cable can be regarded as the convolution of the system transfer function h (t) and the echo x (t) of the reflector.
In the frequency domain, the frequency domain echo signal Y (ω) of the measured optical cable can be regarded as the multiplication of the system transfer function frequency domain expression H (ω) with the reflector frequency domain echo signal X (ω).
Y(ω)=H(ω)·X(ω) (4)
Thus, multiplying the frequency domain signal of the measured optical cable echo by the wiener filtered reflector frequency domain echo signal can obtain a system transfer function related to the measured optical cable, and the transfer function can be regarded as the deconvolved frequency domain echo signal of the measured optical cable.
(6) And performing inverse Fourier transform on the deconvoluted measured optical cable frequency domain echo signals to obtain echo signals with higher spatial resolution and related to the measured optical cable quality. The deconvoluted reflector and the measured cable echo signals are shown in fig. 4 and 5, respectively.
Wherein FT -1 () Representing the inverse fourier transform.
In the conventional optical fiber quality detection device and method, the echo signal of the single point fault has a certain time width, and is similar to the echo signal of the reflector, as shown in fig. 2, after being processed by the method of the embodiment, the echo signal in an extremely narrow pulse form can be obtained in an ideal condition, so that the spatial resolution of fault location is obviously improved. In the conventional optical fiber quality detection device and method, if the detected optical cable has a fault point with a relatively close spatial distance, the detected optical cable is fused into the same echo pulse, such as the second pulse in fig. 3, and after being processed by the method of the embodiment, the originally fused 2 pulses can be distinguished, as shown in fig. 5, so that the spatial resolution of the optical cable quality detection is significantly improved.
Example two
The embodiment provides a deconvolution filtering high-precision optical fiber quality detection system.
A deconvolution filtered high-precision fiber quality detection system, comprising:
a time domain signal acquisition module configured to: the optical pulse signals emitted by the laser emitter respectively enter the optical cable to be tested and the reflector through the circulator to respectively obtain the optical cable time domain echo signals to be tested and the reflector time domain echo signals;
a frequency domain signal acquisition module configured to: calculating a reflector frequency domain echo signal corresponding to the reflector time domain echo signal; according to the reflector frequency domain echo signals and the system frequency domain transfer function, obtaining measured optical cable frequency domain echo signals corresponding to the measured optical cable time domain echo signals;
a deconvolution module configured to: determining deconvoluted measured optical cable frequency domain echo signals according to the measured optical cable frequency domain echo signals;
an output module configured to: and obtaining a high-resolution echo signal related to the quality of the tested optical cable according to the deconvoluted tested optical cable frequency domain echo signal.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.