CN115733554A - Optical fiber coding method based on swept-frequency laser and weak reflecting grating array - Google Patents
Optical fiber coding method based on swept-frequency laser and weak reflecting grating array Download PDFInfo
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Abstract
The invention discloses an optical fiber coding method based on a frequency-swept laser and a weak reflecting grating array, which comprises the following steps: emitting a C-waveband sweep frequency optical pulse signal by a laser module; after a sweep frequency laser pulse signal is sent out, the sweep frequency laser pulse signal enters an optical link to be tested through a circulator; each coding node on the optical link to be tested is provided with a string of weak reflection grating arrays with different central wavelength combinations, each grating selectively reflects one part of specific wavelength of the pulse, and the residual optical power continues to be transmitted along the optical link to finish coding of the following nodes; the coded pulse signals reflected back to the monitoring end reach a wavelength division demultiplexer through a circulator, the optical pulses are decomposed into more than one path according to the wavelength, converted into electric signals by a photoelectric detector array, converted into digital signals by an acquisition card and processed by an upper computer; the method solves the technical problems that the existing coding technology can not be suitable for realizing serial coding of an all-optical network with large-scale and high reliability requirements and the like.
Description
Technical Field
The invention belongs to the technical field of optical fiber coding, and particularly relates to an optical fiber coding method based on a frequency-swept laser and a weak reflecting grating array.
Background
Optical fiber coding is the basic and core technology for realizing all-optical network digitization. The optical fiber link safety is the basis for ensuring the safety of the optical access network, and researches show that about one third of optical network faults are caused by optical fiber cable faults, so that the digital coding is carried out on the nodes of each optical fiber link in the optical access network, the network state is monitored by utilizing the codes, and the accurate, reliable, intelligent and efficient all-optical network digital management is realized on the premise that the optical access network can operate efficiently and stably. The efficiency of optical fiber coding directly influences the effect of all-optical network digitization, and the optical fiber coding method based on the swept-frequency laser and the weak-reflectivity grating string can code a large number of serial nodes in an optical link, accurately position the nodes, and provide more information support for optical network maintenance.
The optical fiber coding technology used at present mostly uses total reflection gratings, so when node coding is carried out on the same optical link, light with one central wavelength can be used only once at the same node, the number of the nodes determines the number of the types of the central wavelengths of the optical fiber gratings to be used, and the coverage range of the output light pulse wavelength of the laser is also influenced. When the number of nodes increases, the number of the types of the gratings and the bandwidth of the laser increase, and the method cannot be applied to optical fiber links with more nodes.
In the prior art, a laser used in coding is mainly a multi-wavelength pulse light source which can be controlled by an external signal, and a plurality of lasers are generated by a laser array and have the same width, power and period in a time domain; optical pulses with different center wavelengths and the same 3dB bandwidth in the wavelength domain. Because each laser adopts a fixed center wavelength, the center wavelength of the grating used in the link also needs to correspond to the fixed center wavelength, and when the reflection center wavelength of the grating used at the coding node drifts due to the change of the environmental temperature, the reflected light power is greatly reduced or even disappears due to the mismatching of the light source and the grating wavelength, thereby affecting the coding accuracy; the prior art coding technology is not suitable for realizing serial coding of a large-scale and high-reliability all-optical network,
disclosure of Invention
The technical problem to be solved by the invention is as follows: the method is used for solving the problems that the optical fiber coding technology in the prior art cannot be suitable for optical fiber links with more nodes because the number of grating types and the bandwidth of a laser are increased when the number of nodes is increased; because the wavelength of the light source is not matched with that of the grating, the power of reflected light is greatly reduced and even disappears, and the encoding accuracy is influenced; the coding technology in the prior art cannot be suitable for realizing the technical problems of serial coding and the like of a large-scale all-optical network with high reliability requirements.
The technical scheme of the invention is as follows:
a method for encoding an optical fiber based on a swept-frequency laser and a weak reflecting grating array, the method comprising:
and 3, the coded pulse signals reflected back to the monitoring end reach a wavelength division demultiplexer through a circulator, the optical pulses are decomposed into more than one path according to the wavelength, converted into electric signals by a photoelectric detector array, converted into digital signals by an acquisition card and processed by an upper computer.
The encoder is formed by connecting a plurality of weak reflectivity grating strings in series, wherein corresponding weak reflectivity gratings are installed on the wavelength corresponding to the code word of 1, and no grating is installed on the wavelength corresponding to the code word of 0.
The laser module receives an external signal to control and generate a sweep frequency light pulse.
During each optical pulse time, the center wavelength of the light increases or decreases linearly with time, the start-stop range of wavelength change covers the center wavelength used by all the weakly reflective gratings, and the laser power remains constant as the center wavelength changes.
The weak reflection grating array comprises m kinds of weak reflection gratings with central wavelengths, and except for the central wavelengths, the reflectivity and bandwidth parameters of the gratings are the same and the reflectivity is lower than 1% so as to ensure that each kind of central wavelength light pulse can generate reflection light different from noise at each grating connected in series on a link.
The number of channels of the wavelength division demultiplexer, the acquisition card and the photoelectric detector array is the same as the number of the types of the gratings used in the link, and the number of the channels is m; the transmission bandwidth of each channel of the wavelength division demultiplexer completely covers the reflection bandwidth of one grating, the transmission bandwidths of different channels are isolated from each other, the reflected light pulse is completely decomposed into pulses with different wavelengths, the photoelectric conversion is completed by the photoelectric detector array, and the pulses are collected by the collecting card and then sent to the upper computer for processing.
In order to ensure that each encoding node contains an optical pulse signal of at least one wavelength, each encoder contains at least one weak reflectivity grating.
The use of gratings containing m central wavelengths on one optical link yields a total of 2 m 1 code, each code uniquely corresponding to a coding node in the link.
The invention has the beneficial effects that:
the invention takes the detection light pulse output by the pulse sweep frequency laser as a carrier of coding information, and two-dimensionally codes the wavelength of the light pulse through the selective reflection characteristic of the weak reflection grating array, thereby realizing serial coding of a large number of users under the condition of using limited wavelength resources; a C-waveband sweep frequency pulse signal is emitted by a laser module, the wavelength scanning range of sweep frequency laser covers the central wavelength of all gratings for encoding, an optical pulse enters an optical link to be detected through a circulator after being emitted, each encoding node on the link is connected in series with a plurality of weak reflection gratings with different central wavelength combinations, each grating selectively reflects a small part of a specific wavelength of the pulse, reflected light forms a unique wavelength encoding combination of the encoding node, the residual optical power is continuously transmitted along the optical link to complete encoding of subsequent nodes, the reflected light is transmitted back to a monitoring end, reaches a receiving module through the circulator and then is subjected to upper processing; by using the weak reflection grating, only light with small power is reflected when the light passes through the grating every time, more light is stored for the subsequent grating to continuously finish reflection, the light with the same central wavelength can be reflected for many times in a link, the multiplexing of light wavelength is realized, and the use of wavelength resources by the grating and a laser is greatly reduced; the invention provides an optical fiber coding method based on a frequency-swept laser and a weak reflection grating, which improves the efficiency of an optical fiber grating coding technology by utilizing a weak reflection grating string through wavelength multiplexing, overcomes the influence of grating wavelength drift by using the frequency-swept laser, and can meet the requirement of high-reliability optical network link monitoring.
The problem that the optical fiber coding technology in the prior art cannot be applied to an optical fiber link with more nodes because the number of the types of the gratings and the bandwidth of a laser are increased when the number of the nodes is increased is solved; because the wavelength of the light source is not matched with that of the grating, the power of reflected light is greatly reduced and even disappears, and the encoding accuracy is influenced; the coding technology in the prior art cannot be suitable for realizing the technical problems of serial coding and the like of a large-scale all-optical network with high reliability requirements.
Drawings
FIG. 1 is a system diagram of a fiber encoding method based on a swept-frequency laser and a weak reflecting grating array;
FIG. 2 is a spectral diagram of an optical pulse output from a multi-wavelength laser;
FIG. 3 is a block diagram of a weakly reflective grating array encoder with code word 110101;
FIG. 4 is a spectrum diagram of optical pulses before and after encoding when 6 kinds of center wavelength gratings are used;
fig. 5 is a diagram illustrating the optical signal received by each wavelength channel when 6 kinds of center wavelength gratings are used.
Detailed Description
Aiming at the problem that the coding scale is limited by the usable wavelength, the invention combines the existing sweep frequency laser technology and the weak reflection fiber bragg grating array, improves the utilization efficiency of wavelength resources when a large number of nodes are coded on one fiber link, and solves the problem that the coding scale of the prior art is still limited and can not meet the use requirement of a multi-node network.
In order to improve the utilization efficiency of wavelength resources when a large number of nodes are coded on one optical fiber link, the invention provides the following coding method: the method comprises the following steps:
(1) A laser module emits a C-waveband sweep optical pulse signal, and the wavelength range of the sweep laser covers the central wavelength of all the code-used weak reflection gratings;
(2) The optical pulse enters an optical link to be tested through a circulator after being emitted, a string of weak reflection grating arrays with different central wavelength combinations are placed on each coding node on the link, each grating selectively reflects a small part of the specific wavelength of the pulse, the group of reflection light forms the unique pulse wavelength combination of the coding node, and the residual optical power continues to be transmitted along the optical link to finish coding of the subsequent nodes.
(3) The coded pulse signals reflected back to the monitoring end reach the wavelength division demultiplexer through the circulator, the optical pulses are decomposed into multiple paths according to the wavelength, the multiple paths of the optical pulses are converted into electric signals through the photoelectric detector array, the electric signals are converted into digital signals through the acquisition card, and the digital signals are processed through the upper computer.
The pulse frequency-sweeping laser in the scheme can be controlled by an external signal to generate frequency-sweeping light pulses. During each optical pulse time, the center wavelength of the light increases or decreases linearly with time, the start-stop range of the wavelength change covers the center wavelength used by all weak reflection gratings, and the laser power remains constant as the center wavelength changes.
In the scheme, m kinds of weak reflection gratings with central wavelengths are used in total, except for the central wavelength, the reflectivity, the bandwidth and other parameters of the gratings are the same, and the reflectivity is set to be lower than 1%, so that each kind of central wavelength light pulse can generate reflected light different from noise at each grating connected in series on a link.
The channel numbers of the wavelength division demultiplexer, the multi-port acquisition card and the detector array in the scheme are the same as the number of the types of the gratings used in the link and are all m. The transmission bandwidth of each channel of the wavelength division demultiplexer completely covers the reflection bandwidth of one grating, the transmission bandwidths of different channels are isolated from each other, the reflected light pulse is completely decomposed into a plurality of pulses with different wavelengths, the pulses are subjected to photoelectric conversion by a detector, collected by an acquisition card and then processed by an upper computer.
In the above scheme, in order to make each coded signal contain at least one wavelength pulse, the use of a grating containing m central wavelengths on one optical link can generate 2 in total m 1 code, each code can uniquely correspond to one coding node in the link.
The solution of the invention is further explained below with reference to the drawings:
FIG. 1 is a system diagram of a fiber coding method based on a swept-frequency laser and a weak reflecting grating array. A laser module emits a C-waveband sweep frequency light pulse signal, and the wavelength range of the sweep frequency laser covers the central wavelength of all the code weak reflection gratings; the optical pulse enters an optical link to be tested through a circulator after being emitted, a string of weak reflection gratings with different central wavelength combinations are placed on each coding node on the link, each grating selectively reflects a small part of the specific wavelength of the pulse, the group of reflected light forms the unique pulse wavelength combination of the coding node, and the residual optical power continues to be transmitted along the optical link to finish coding of the subsequent nodes. The coded pulse signals reflected back to the monitoring end reach the wavelength division demultiplexer through the circulator, the optical pulses are decomposed into multiple paths according to the wavelength, the multiple paths of the optical pulses are converted into electric signals through the photoelectric detector array, the electric signals are converted into digital signals through the acquisition card, and the digital signals are processed through the upper computer.
Fig. 2 is a graph of the change in wavelength of light output by a swept-frequency laser over time. The central wavelength of the light increases or decreases linearly with time during each pulse time, and the start-stop range of the wavelength change covers the central wavelength (lambda) used by all weak reflection gratings 1 ，λ 2 ，λ 3 ，λ 4 ，λ 5 ，λ 6 ) And the laser power remains constant as the center wavelength changes.
Fig. 3 is a diagram of a weak reflection grating encoder with a code word of 110101. The encoder is composed of a plurality of weak reflectivity grating strings which are connected in series, wherein the corresponding code word is the wavelength (lambda) of 1 1 ，λ 2 ，λ 4 ，λ 6 ) Are provided with corresponding weakly reflecting gratings corresponding to a wavelength (lambda) at which the code word is 0 3 ，λ 5 ) No grating is installed.
In order to ensure that each coding node comprises an optical pulse signal with at least one wavelength, each coder at least comprises a weak reflectivity grating; to ensure that each node has sufficient power for light to reflect, the reflectivity of the weak reflectivity grating is less than 1% or less. The use of optical pulses comprising m wavelengths on an optical link can yield a total of 2 m 1 code, each code can uniquely correspond to a code node in an optical fiber link.
FIG. 4 is a spectrum diagram of an optical pulse of an encoded signal output by an encoder using a 6-center wavelength weak reflectivity grating string. Where plot (a) is a spectral plot of the previous light pulse encoded as a broadband spectrum with a bandwidth covering from λ 1 To lambda 6 The graphs (b), (c) and (d) show the wavelengths (λ) using the 6 kinds of centers 1 ，λ 2 ，λ 3 ，λ 4 ，λ 5 ，λ 6 ) The optical fiber grating is used for encoding, and the code words reflected by the encoder are 001011, 100011 and 110101 encoding pulse spectrumsIn the figure, light peaks exist in several wavelength ranges indicated as coded information 1. Each wavelength combination is unique in each independent network and uniquely corresponds to a subscriber end.
Fig. 5 is a diagram illustrating the optical signal received by each wavelength channel when 6 kinds of center wavelength gratings are used. The link comprises three nodes in total, corresponding code words of the three nodes are 001011, 100011 and 110101 respectively, all wavelengths corresponding to the code word 1 at each node simultaneously generate reflected light signals when optical pulses reach the node, the time of the reflected light reaching a monitoring end is different for different nodes according to the difference of the distances between the nodes and the monitoring end, and the distance between the nodes and the monitoring end can be calculated according to the time of the return light signals of each node reaching the monitoring end.
Claims (8)
1. An optical fiber coding method based on a frequency-swept laser and a weak reflecting grating array is characterized in that: the method comprises the following steps:
step 1, a laser module emits a C-waveband sweep frequency optical pulse signal, and the wavelength range of the sweep frequency optical pulse signal covers the central wavelength of all encoding weak reflection gratings;
step 2, sending out a sweep frequency laser pulse signal and then entering an optical link to be tested through a circulator; each coding node on the optical link to be tested is provided with a series of weak reflection grating arrays with different central wavelength combinations, each grating selectively reflects one part of specific wavelength of the pulse, the group of reflection light forms the unique pulse wavelength combination of the coding node, and the residual optical power continues to be transmitted along the optical link to finish coding the following nodes;
and 3, the coded pulse signals reflected back to the monitoring end reach a wavelength division demultiplexer through a circulator, the optical pulses are decomposed into more than one path according to the wavelength, converted into electric signals by a photoelectric detector array, converted into digital signals by an acquisition card and processed by an upper computer.
2. The optical fiber coding method based on the swept-frequency laser and the weak reflecting grating array as claimed in claim 1, wherein: the encoder is formed by connecting a plurality of weak reflectivity grating strings in series, wherein corresponding weak reflectivity gratings are installed on the wavelengths corresponding to the code words of 1, and no grating is installed on the wavelengths corresponding to the code words of 0.
3. The optical fiber coding method based on the swept-frequency laser and the weak reflecting grating array as claimed in claim 1, wherein: the laser module receives an external signal to control and generate a sweep frequency light pulse.
4. The optical fiber coding method based on the swept-frequency laser and the weak reflecting grating array as claimed in claim 3, wherein: during each optical pulse time, the center wavelength of the light increases or decreases linearly with time, the start-stop range of the wavelength change covers the center wavelength used by all weak reflection gratings, and the laser power remains constant as the center wavelength changes.
5. The optical fiber coding method based on the swept-frequency laser and the weak reflecting grating array as claimed in claim 1, wherein: the weak reflection grating array comprises m kinds of weak reflection gratings with central wavelengths, and except for the central wavelengths, the reflectivity and bandwidth parameters of the gratings are the same and the reflectivity is lower than 1% so as to ensure that each kind of central wavelength light pulse can generate reflection light which is different from noise at each grating which is connected in series on a link.
6. The optical fiber coding method based on the swept-frequency laser and the weak reflecting grating array as claimed in claim 1, wherein: the channel number of the wavelength division demultiplexer, the acquisition card and the photoelectric detector array is the same as the type number of the used grating in the link and is m; the transmission bandwidth of each channel of the wavelength division demultiplexer completely covers the reflection bandwidth of one grating, the transmission bandwidths of different channels are isolated from each other, the reflected light pulse is completely decomposed into pulses with different wavelengths, the photoelectric conversion is completed by the photoelectric detector array, and the pulses are collected by the collecting card and then sent to the upper computer for processing.
7. The optical fiber coding method based on the swept-frequency laser and the weak reflecting grating array as claimed in claim 2, wherein: in order to ensure that each encoding node contains an optical pulse signal of at least one wavelength, each encoder contains at least one weak reflectivity grating.
8. The optical fiber encoding method based on the swept-frequency laser and the weak reflecting grating array as claimed in claim 7, wherein: the use of gratings containing m central wavelengths on one optical link yields a total of 2 m 1 codes, each code uniquely corresponding to a coding node in the link.
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