CN108020249A - A kind of OTDR structures and methods based on Ramam effect Larger Dynamic scope - Google Patents

Abstract

The invention relates to an OTDR structure and method, belonging to the technical field of optical fiber detection, in particular to an OTDR structure and method based on a large dynamic range of the Raman effect. The present invention amplifies the OTDR signal light online through the integrated Raman gain module, cooperates with the optical filter at the APD receiving end to eliminate the extra ASE noise brought by Raman, so that only the narrow-band spectrum in the wavelength range of the signal light can be collected by the optical detector, thereby improving The optical signal-to-noise ratio of the received signal enables OTDR with a large dynamic range.

Description

An OTDR structure and method based on Raman effect and large dynamic range

technical field

The invention relates to an OTDR structure and method, belonging to the technical field of optical fiber detection, in particular to an OTDR structure and method based on a large dynamic range of the Raman effect.

Background technique

Optical Time Domain Reflectometer (OTDR) is an important test instrument in optical fiber communication system. The optical transmission module of OTDR transmits the set optical pulse signal, according to the backward Fresnel reflection and Rayleigh Based on the principle of scattering, the reflected optical signal is converted and amplified by the optical receiving module (including Avalanche Photodiode (APD)), and then processed and analyzed by the signal processing unit to obtain the average loss and other parameters of the measured optical fiber. It can measure the actual length and average loss of the optical fiber in the optical fiber communication system. At the same time, it can detect, locate and measure many types of events on the optical fiber link, such as the loss caused by fiber fusion, connectors, bending, etc. in the link. point.

Dynamic range is a very important parameter of OTDR, and it is usually used to classify the performance of OTDR. The definition of dynamic range is the difference between the initial level and the noise level on the backscattering curve, which is the maximum attenuation value (in dB) of the backscattering curve that can be tested. The dynamic range indicates the maximum fiber loss information that can be measured, and directly determines the longest fiber distance that can be measured. The calculation of dynamic range usually uses the difference between the initial level on the backscattering curve and the root mean square level of the noise (when the signal-to-noise ratio = 1).

With the development of communication technology, the span of optical fiber is getting larger and larger, and the requirements for the dynamic range of OTDR are also increasing. Usually, improving the dynamic range of OTDR mainly depends on increasing the signal light pulse width and increasing the average number, increasing the signal light pulse width It will lead to poor resolution, increasing the number of averages will increase the measurement time and the improvement of dynamic range is very limited.

Improving the dynamic range of OTDR has always been a research topic of researchers all over the world. Through the improvement of optical path, circuit and algorithm, the performance of OTDR has been improved:

In 2004, in the patent "optical module of optical time domain reflectometer and optical time domain reflectometer and optical fiber test method", Huawei improved the receiving circuit of OTDR, and used different amplification gears of the amplifier to analyze the returned optical signal. Segment amplification, without changing the size of the probe light power, improves the dynamic range of the OTDR.

In 2014, in the patent "OTDR device and method based on multi-wavelength pulsed optical signal", Yinuo Instrument Company used multi-wavelength pulsed optical signals to measure separately, and then analyzed and combined the received multi-wavelength signals to improve OTDR dynamic range.

In 2014, Yinuo Instrument Co., Ltd. patented "OTDR device and method based on pulse-coded optical signal", by using multiple sets of coded pulses, using high-resolution codes for short-distance optical fibers, and using large dynamic range codes for long-distance optical fibers. Events at different distances are tested and analyzed with different codes, which can improve OTDR performance.

In 2017, EXFO provided an OTDR algorithm and device for detecting one or more events in the optical fiber link in the patent "Multiple-acquisition OTDR Method and Device". Through multiple optical acquisitions, test optical pulses with different pulse widths or wavelengths are propagated in the optical link, and the corresponding return optical signals from the optical fiber link are detected to determine the number and location of events.

The Raman signal amplification technology is based on the Raman effect in the optical fiber. If a weak signal light and a strong pump light are transmitted in an optical fiber at the same time, and the wavelength of the weak signal light is within the Raman gain bandwidth of the pump light, The energy of the strong pump light is transferred to the weak signal light through the stimulated Raman scattering effect, so that the weak signal light is amplified, and additional ASE noise is also generated.

Contents of the invention

The present invention mainly solves the above-mentioned technical problems existing in the prior art, and provides an OTDR structure and method based on a large dynamic range of the Raman effect. The structure and method synchronously amplify the OTDR signal light online through the integrated Raman gain module, and cooperate with the optical filter at the receiving end of the APD to eliminate the additional ASE noise caused by Raman, so that only the narrow-band spectrum of the signal light wavelength range can be collected by the optical detector. In this way, the optical signal-to-noise ratio of the received signal is improved, thereby realizing an OTDR with a large dynamic range.

Above-mentioned technical problem of the present invention is mainly solved by following technical scheme:

An OTDR structure based on the large dynamic range of the Raman effect, including:

A pulsed laser is coupled to a WDM module connected to the optical fiber to be tested through the first and second ports of the circulator;

The WDM module is connected with the Raman gain module, and is coupled with the optical detector through the second and third ports of the circulator.

Preferably, in the above-mentioned OTDR structure based on a large dynamic range of the Raman effect, an optical filter is arranged between the optical detector and the circulator.

Preferably, in the aforementioned OTDR structure based on the Raman effect with a large dynamic range, the optical filter is specifically a narrow linewidth filter, and its 30 dB bandwidth is less than or equal to 1 nm.

Preferably, in the above-mentioned OTDR structure based on the large dynamic range of the Raman effect, the pulsed laser and/or the photodetector and/or the Raman gain module are connected to the signal processor.

Preferably, in the above-mentioned OTDR structure based on the large dynamic range of the Raman effect, the Raman pump of the Raman gain module is pulse-driven.

Preferably, the above-mentioned OTDR structure based on the large dynamic range of the Raman effect, the Raman gain module includes first-order Raman and/or second-order Raman and/or third-order Raman; wherein:

The input of the first-order Raman is pumped by two 14xxnm and then output by 14xx IPBCD;

The input of the second-order Raman is connected to four 13xxnm pumps and one 14xxnm pump in parallel, the 13xxnm pumps are divided into two groups, each group is connected to a 13xx IPBCD, and the 13xx IPBCD is connected to a 13xx WDM and then connected to a 13xx /14xx WDM, the 14xxnm pump is connected to the 13xx/14xx WDM, and the WDM is connected to the output terminal;

The input of the third-order Raman is connected in parallel with 12xxnm pumps, 13xxnm pumps, and 14xxnm pumps, and the 13xxnm pumps and 14xxnm pumps are connected to 13xx/14xxWDM and then connected to WDM; the 12xxnm pumps are connected to the WDM, The WDM connection output.

An OTDR method based on the large dynamic range of the Raman effect, including:

The pulse signal light of the pulse laser and the pulse pump light of the Raman gain module are combined by the WDM module and then sent into the optical fiber to be tested;

The backscattered light and/or reflected light of the excited pulse signal light is input to the detector.

Preferably, above-mentioned a kind of OTDR method based on the large dynamic range of Raman effect comprises:

The pulse signal light is sent to the WDM module through the first and second ports of the circulator; the backscattered light and/or reflected light is sent to the photodetector through the second and third ports of the circulator.

Preferably, the above-mentioned OTDR method based on the large dynamic range of the Raman effect uses the WDM module to filter out the Rayleigh scattered light of the pulsed pump light, the Fresnel reflected light, and the pulsed pump light outside the WDM passband of reverse ASE light.

Preferably, in the above-mentioned OTDR method based on the large dynamic range of the Raman effect, an optical filter is used to filter out reverse ASE light outside the filtering bandwidth.

Therefore, the present invention has the following advantages: the present invention uses the Raman effect to amplify the OTDR pulse signal light online, and the advantage of Raman amplification is high gain and low noise, and the OTDR dynamic range can be greatly improved by optimizing the Raman pump power configuration, and it does not Affects measurement time and test resolution.

Description of drawings

Fig. 1 is a kind of OTDR structure schematic diagram based on the large dynamic range of Raman effect provided by the embodiment of the present invention;

FIG. 2 is a structure diagram of the first-order Raman in the Raman gain module provided by the embodiment of the present invention, wherein the input port is connected to the output pulse 2 of the signal processor 107 in FIG. 1 , and the output is connected to the port 3 of the WDM 103 .

3 is a structure diagram of second-order Raman in the Raman gain module provided by the embodiment of the present invention, wherein the input port is connected to the output pulse 2 of the signal processor 107 in FIG. 1 , and the output is connected to the port 3 of the WDM 103.

4 is a structure diagram of the third-order Raman in the Raman gain module provided by the embodiment of the present invention, wherein the input port is connected to the output pulse 2 of the signal processor 107 in FIG. 1 , and the output is connected to the port 3 of the WDM 103.

Fig. 5 is a flowchart of an OTDR method based on a large dynamic range of the Raman effect provided by an embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be further specifically described below through the embodiments and in conjunction with the accompanying drawings.

Example 1:

Embodiment 1 of the present invention provides an OTDR structure based on the Raman effect with a large dynamic range, as shown in Figure 1, including a narrow linewidth pulse laser 101, a circulator 102, a WDM 103, an optical filter 104, and a Raman gain module 105, photodetector 106 and signal processor 107, specifically:

The light exit port of the narrow-linewidth pulsed laser 101 is connected to the first light entrance port of the circulator 102 (the corresponding port marked with 1 in the circulator 102 in FIG. 1 in the circulator 102 marked with the corresponding port 2) connected to the 1 port of the WDM 103 (the corresponding port marked with 1 in the WDM 103 in FIG. 2) to connect the outside optical fiber to be tested, and the 3 ports of WDM (marked with 3 corresponding ports in WDM 103 in Fig. 1) are connected to Raman gain module 105; wherein, the central wavelength of the narrow linewidth pulse laser is 15xx±0.2nm;

The third light outlet of the circulator 102 is connected to the optical filter 104, and the optical filter 104 is connected in series between the third light outlet of the circulator 102 and the photodetector 106;

The narrow-linewidth pulse laser 101, the photodetector 106 and the Raman gain module 105 are all connected to the signal processor 107, and the signal processor provides the pulse driving signal for the narrow-linewidth pulse laser and the Raman gain module, and simultaneously processes the light detection signal detected by the detector.

The Raman gain module includes first-order Raman, second-order Raman or third-order Raman, which is used to amplify OTDR signal light. The higher the order, the better the signal-to-noise ratio and the more obvious the improvement of the dynamic range, but the implementation is more complicated.

The first-order Raman structure diagram in the described Raman gain module is shown in accompanying drawing 2, wherein 201 and 202 are 14xx pumps, and 203 is 14xx IPBCD; 14xx pump, 306 and 307 are 13xx IPBCD, 308 is 13xx WDM, 309 is 13xx/14xx WDM; the third-order Raman structure diagram is shown in Attachment 4, in which 401 is 12xx pump, 402 is 13xx pump, 403 is 14xx Pump, 404 is 13xx/14xx WDM, 405 is 12xx/13xx/14xx WDM; the input port is connected to the output pulse 2 of the signal processor 107 in Figure 1, the output is connected to the port 3 of WDM 103, and the specific wavelength selection of each pump The principle of adjusting the power and size is to make the signal gain as much as possible at the far end of the OTDR signal source.

The narrow-linewidth pulse laser is driven by pulse 1 sent by the signal processor (pulse adjustment range 5-20000ns), and the pump in the Raman gain module is driven by pulse 2 sent by the signal processor, wherein pulse 2 and pulse 1 can be completely Synchronous drive can also be asynchronously driven in a certain coding mode. The Raman pump can effectively reduce the ASE generated by the Raman effect by using a pulse drive mode. The wider the coding pulse width, the greater the Raman gain, but the greater the ASE, the coding The narrower the pulse width, the smaller the Raman gain, but the smaller the ASE. The principle of pulse encoding should optimize the Raman gain and generate ASE.

The optical filter is specifically a narrow-linewidth filter, and its 30dB bandwidth is less than or equal to 1nm (the center wavelength is the same as the narrow-linewidth pulse laser wavelength 15xxnm). The smaller the filter bandwidth, the better the ASE noise performance of eliminating the Raman effect, but At the same time, it should be larger than the signal bandwidth of the narrow-linewidth pulse laser, so that the signal light signal energy can pass through with minimum loss.

The WDM is specifically 15xx/14xx (corresponding to first-order Raman), 15xx/14xx+13xx (corresponding to second-order Raman), 15xx/14xx+13xx+12xx (corresponding to third-order Raman) multiplexer, and its insertion loss Should be less than 1dB. Make the combined signal of pulsed signal light and pulsed pumping light pass through with minimum loss.

Example 2:

Embodiment 2 of the present invention provides a kind of OTDR method based on Raman amplification effect, uses the OTDR as described in Embodiment 1 in the method of the embodiment of the present invention, as shown in Figure 5, described method also comprises:

In step 501, the narrow-linewidth pulsed laser 101 emits pulsed signal light (pulse 1, pulse width 5-20000 ns can be set) under the drive of the signal processor 107, and the Raman gain module 105 is driven by the signal processor 107 Pulsed pump light is emitted (pulse 2).

In this example, the center wavelength of the pulse laser is selected as 1521nm, and the principle of laser wavelength selection: the corresponding Raman gain is large, the fiber attenuation is small, and it is best to avoid the working wavelength; pulse signal 1 and pulse signal 2 can be synchronized or optimized by coding Asynchronous way.

In step 502, the pulse signal light enters WDM 103 port 1 through the first light inlet port and the second light inlet/outlet port of circulator 102, and the pulsed pump light generated by Raman gain module 105 enters 103 port 3 at the same time. The signal light and the pulsed pump light enter the optical fiber under test at the same time after being combined by WDM.

In step 503, during the simultaneous transmission of the pulsed signal light and the pulsed pumping light in the optical fiber to be tested, due to the stimulated Raman effect, the pulsed pumping light transfers energy to the pulsed signal light, and the pulsed signal light is effectively amplified. The pulsed signal light produces Rayleigh scattered light and Fresnel reflected light, while the pulsed pump light also produces Rayleigh scattered light and Fresnel reflected light, as well as reverse ASE light.

In step 504, corresponding to the backscattered light and/or reflected light of the amplified pulsed signal light, the Rayleigh scattered light and Fresnel reflected light of the pulsed pumping light are combined with the reversed ASE light generated by the pulsed pumping light Returning to port 2 of WDM 103, after filtering by WDM 103, only the backscattered light and/or reflected light of the amplified pulse signal light and the reverse ASE light generated by the pulse pump light in the WDM passband can pass through, and the pulse pump The Rayleigh scattered light and Fresnel reflected light of the Pu light are completely filtered out.

In step 505, the reverse ASE light generated by the backscattered light and/or reflected light of the pulsed signal light filtered by the WDM 103 and the pulsed pump light in the WDM passband passes through the second incoming/outgoing light of the circulator 102 port and the third light inlet transmission channel, the reverse ASE light outside the filter bandwidth is filtered through the optical filter 104, and the reverse ASE light within the remaining filter bandwidth and the backscattered light and/or reflection of the amplified pulse signal light The light is collected by detector 106 .

The Raman gain module 105 generates pulsed pumping light in a pulse-driven manner. Compared with continuous pumping light, the pulsed pumping light can greatly reduce the reverse ASE noise level generated by pumping, and then cooperate with the narrow-band optical filter 104 to further Reducing the reverse ASE noise power entering the optical detector 106 can greatly improve the optical signal-to-noise ratio and improve detection performance, and the signal converted by the detector 106 is analyzed and processed by the signal processor 107 .

In step 506, the signal converted by the light detector 106 is analyzed and processed by the processor 107, the physical state of the point is judged according to the light intensity, and the distance of the point is calculated according to the time returned to the processor, so as to describe the length of the optical fiber and Decay distribution curve.

Through the above steps, compared with the OTDR without Raman effect, the dynamic range of OTDR based on Raman effect can be increased by more than 6dB in the synchronous pulse driving mode, and the dynamic range can be increased by more than 9dB in the optimized encoding asynchronous driving mode.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. A kind of OTDR structure based on the large dynamic range of Raman effect, is characterized in that, comprises: A pulsed laser is coupled to a WDM module connected to the optical fiber to be tested through the first and second ports of the circulator; The WDM module is connected with the Raman gain module, and is coupled with the optical detector through the second and third ports of the circulator. 2. a kind of OTDR structure based on the large dynamic range of Raman effect according to claim 1, is characterized in that, optical filter is arranged between described optical detector and circulator. 3. a kind of OTDR structure based on the large dynamic range of Raman effect according to claim 2, is characterized in that, described optical filter is specifically the narrow line width filter, and its 30dB bandwidth is less than or equal to 1nm. 4. a kind of OTDR structure based on the large dynamic range of Raman effect according to claim 1, is characterized in that, described pulsed laser and/or optical detector and/or Raman gain module are connected with signal processor. 5. a kind of OTDR structure based on the large dynamic range of Raman effect according to claim 1, is characterized in that, the Raman pump of Raman gain module is pulse drive. 6. a kind of OTDR structure based on the large dynamic range of Raman effect according to claim 1, is characterized in that, described Raman gain module comprises first-order Raman and/or second-order Raman and/or third-order Raman Man; where: The input of the first-order Raman is output by the polarization combiner IPBCD with depolarization after two 14xxnm pumps; The input of the second-order Raman is connected in parallel with four 13xxnm pumps and one 14xxnm pump, the 13xxnm pumps are divided into two groups, and each group is connected with a 13xx polarization combiner IPBCD with depolarization, and the 13xx with The depolarized polarization combiner IPBCD is connected to a 13xx/14xx WDM after being connected to a 13xx/14xx WDM, the 14xxnm pump is connected to the 13xx/14xx WDM, and the WDM is connected to the output end; The input of the third-order Raman is connected in parallel with 12xxnm pumps, 13xxnm pumps, and 14xxnm pumps, and the 13xxnm pumps and 14xxnm pumps are connected to 13xx/14xxWDM and then connected to WDM; the 12xxnm pumps are connected to the WDM, The WDM connection output. 7. A kind of OTDR method based on the large dynamic range of Raman effect, it is characterized in that, comprising: The pulse signal light of the pulse laser and the pulse pump light of the Raman gain module are combined by the WDM module and then sent into the optical fiber to be tested; The backscattered light and/or reflected light of the excited pulse signal light is input to the detector. 8. a kind of OTDR method based on the large dynamic range of Raman effect according to claim 7, is characterized in that, comprises: The pulse signal light is sent to the WDM module through the first and second ports of the circulator; the backscattered light and/or reflected light is sent to the photodetector through the second and third ports of the circulator. 9. a kind of OTDR method based on the large dynamic range of Raman effect according to claim 7, is characterized in that, utilizes described WDM module to filter out the Rayleigh scattered light of pulse pump light, Fresnel reflected light, WDM The reverse ASE light of the pulsed pump light outside the passband. 10. a kind of OTDR method based on the large dynamic range of Raman effect according to claim 7, is characterized in that, utilizes optical filter to filter out the reverse ASE light beyond filter bandwidth.