RU2682659C1 - Device for studying linear dwdm trunk paths by the recirculation loop method - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: invention relates to the optical communication equipment, specifically to the field of measurement equipment for optical information transmission systems, and can be used for complex measurements of the characteristics of the linear path of high-speed DWDM trunks based on the recirculation loop method. Device uses a specialized driver for simulating the DWDM channel mesh into which a test signal is inserted, which modulates the transmitted signal of the 100G module, and a marker signal that ensures synchronization of all operations in load, recirculation cycle counting, output and evaluation of the transmission quality for the initial parameters entered into the ultra-fast processor, which determines the possibility of using the most modern methods of measuring transmission quality taking into account the standard techniques for processing digital streams.EFFECT: creation of the possibility to study trunk paths with periodic retransmission of high-speed linear signals with complex modulation formats used in modern and future transceiver modules, using the automation of measurement mode based on industrial products of modern high-speed microelectronics and program execution of all recirculation cycles in accordance with the initial setting of the parameters of linear equipment.6 cl, 1 dwg

Description

The invention is a device and relates to the field of measurement technology for optical information transmission systems, can be used in complex measurements of the characteristics of the linear path of high-speed DWDM lines using the recirculation loop method.

The main and currently accepted research method at the design stage, up to the transoceanic extent, is the method of using multiple recycling of the optical signal with parameters close to the linear signal of the designed system. A lot of works are known in the specialized literature on this issue, where various options for loop circuits and the results of studying the simulation of long lines with different speeds, modulation formats, and wash line structures are described, which indicates the high efficiency of the method. As a result of the analysis of all available materials, the following sources were selected and considered as known analogues of the proposed device:

1. N.S. Bergano, C.R. Davidson, "Circulating loop transmission experiments for the study of long-haul transmission systems using erbium-doted fiber amplifiers", Journal of Lightwave Technology, v. 13, p. 879, (1995),

2. N.S. Bergano, C.R. Davidson, "Wavelength division multiplexing in long-haul transmission systems", Journal of Lightwave Technology., V. 14, p. 1299-1308, (1996),

3. V. Mikhailov, "Investigation of high-speed WDM optical fiber transmission systems and devices using recirculating loop techniques", a thesis submitted to University of London for the degree of Doctor of Philosophy of Electronic and Electrical Engineering, September (2003),

4. Q. Yu, L.-S. Yan et al. "Loop-Synchronous Polarization Scrambling Technique for Simulating Polarization Effects using Recirculating Fiber Loops", Journal of Lightwave Technology, v. 21, issue 7, p. 1593, (2003),

5. D.C. Kilper et al., "Dynamic Circulating Loop Methods for Transmission Experiments in Optically Transparent Networks", ICTON 2008, Tu. B 1.2, p. 99-102,

6. D.C. Kilper, F. Smith et al. "Applied Constant Gain Amplification in Circulating Loop Experiments," Journal of Lightwave Technology, v. 21 No 1, p. 4686 (2009),

7. A. Morea, F. Leplingard et al., "Advanced Test-beds to Validate Physical Estimators in Heterogeneous Long-Haul Transparent Optical Networks", Journal of Networks, v. 5 No 11, p / 1335-1342, (2010),

8. E. Mutafungwa, "Circulating loop simulations for transmission performance comparison of various node architectures", Journal of Optics A: Pure and Applied Optics, 3 No 4 pp 255-261,

9. "Fiber-Optic Recirculating Loop", O / E Land Inc., www.o-eland.com, p. 1-3,

10. E.G. Bogdanova, A.H. Sigaev “The Loopback Method for Studying the Long DWDM System” First Mile, No. 1 2017, pp. 54-59.

What is characteristic in general for these analogues, united by the commonality of the applied methodology:

1. Most of the experiments with multi-channel DWDM linear signals were carried out with channel speeds of ~ 10.7 Gbit / s, with the NRZ format and incoherent reception, using polarization scramblers in the path spans and using wave-selective WSS devices as equalizers for the linear signal;

2. In the vast majority of experiments with advanced types of linear signals (100 Gb / s and more, complex modulation formats with phase shift keying), standard transceiver modules operating in real lines are not used, but complex and expensive specialized terminals are installed;

3. When forming a multi-channel (dozens of DWDM channels) simulation of a linear signal, the ASE + WSS combination is almost not used, but they are bulky, up to 40 or more, sets of DFB lasers with 10.7 Gbit / s and NRZ;

Known US patent 6271944 (B1) - Laser wavelength control in an optical communication system, H04B 10/02, H04B 10/04, H04B 10/14, H04J 14/02, also published as EP 1105983 (A1), WO 0103337 (A1). The patent describes a method and device for controlling and stabilizing laser wavelengths in a dense wavelength spectrum multiplexer (DWDM) transmission system in which a plurality of test signals are generated, and then a frequency analyzer in the optical receiver analyzes frequency test signals for distortion and / or changes amplitudes.

Known patent JP 2004343692 (A) - Method and apparatus for monitoring channel performance in dense wavelength division multiplexed (dwdm) optical networks, H04B 10/077; H04B 10/079; H04B 17/00; H04J 14/00; H04J 14/02. This monitoring device receives an optical signal from an optical DWDM network. An optical filter for selecting a custom channel is connected to receive an optical signal from the optical network and to isolate and transmit one channel from the network. A tunable optical notch filter receives an isolated channel and scans it with a narrow passband. The entire channel will be transmitted through a custom optical notch filter, which must be processed by the transmission channel analysis system. The scanned narrow-band signal from a tunable notch filter can be output for processing using an optical spectrum analyzer. Filter settings are controlled by the control system.

The disadvantage of these patents is that, in contrast to the claimed invention, only the signal frequency is analyzed in the optical receiver, but the quality of the transmitted digital information at various distances of the trunk lines is not investigated.

Aveiro, Portugal, p. 46 49 (2015). Ее мы приняли в качестве прототипа.The closest in principle and function to the device proposed here and a fairly modern analogue (100 Gbit / s, DP-QPSK) is the experimental setup described in S. Ziaie, FP Guiomar et al., "100 Gbps DP-QPSK Transmission over 8000 km of Standard Single Mode Fiber using Recirculating Loop Technique ",

Aveiro, Portugal, p. 46 49 (2015). We took it as a prototype.

As the terminals in the prototype are used: a transmitter of 100 Gbit / s, built according to the well-known signal generation scheme with polarized signal multiplexing with quadrature phase shift keying, QPSK. The signal is generated by the PSP generator (2 ¹⁵ -1) in continuous mode. Receiving terminal - a coherent receiver having its own laser-local oscillator, and the electrical signal from the output of balanced photodetectors is converted to digital form and then autonomously processed using MATLAB; BER estimation is carried out by direct error counting over an array of 2 ¹⁷ bits. The algorithm of the prototype includes a sequence of steps for loading the loop, the implementation of a given number of cycles (signal revolutions) in the loop, and at each revolution a part of the recycle signal is fed through the 2: 2 coupler to the receiver. The response times of the optical switches Switch 1 (boot), Switch2 (loop mode, recirculation) and the gating window of the signal output to the Real Time oscilloscope for evaluating the reception quality are set approximately, with a small margin in time. The disadvantages of the prototype include:

- lack of universality of the installation: the stand cannot be used to study paths that transmit a multi-channel linear DWDM signal, and is not designed to test with industrially produced standardized modules for transmission systems 100 Gbit / s with DP-QPSK format or with other modulation formats;

- there is no synchronization of the loading mode, the recirculation mode and the removal of the measured signal after the end of the recirculation loop through the loop, which leads to the need to use non-standard techniques for estimating the error coefficient BER; Thus, BER measurements were carried out in a “natural error count”, making it difficult to estimate the gain through the use of FEC coding;

- the procedure for the recirculation process in the loop path is regulated by operators and does not include the use of measurement automation.

The task to be solved by the claimed invention is directed; is the creation of a device for the study of linear paths of DWDM highways by the recirculation loop method, which differs from the prototype by eliminating its indicated drawbacks.

The technical result provided by the combination of features given in the formula is:

- the ability to build a device that allows you to study the characteristics of extended high-speed DWDM lines with periodic amplification of a linear signal in a wide class of modulation formats, moreover, subject to the conditions for transmitting a multi-channel linear signal using standard transmitting and receiving modules;

- the ability to synchronize the functional nodes of the device based on the use of a common marker pulse;

- providing the ability to automate the measurement mode of the parameters of the investigated line using standard methods for measuring the error coefficient (taking into account framing, FEC coding and the use of regular BER testers in the accumulation mode of an array of received characters).

The specified result is achieved in that the output of the pseudo-random test sequence generator, which generates the SRP signal and is part of the programmable microcircuit, is connected to the input of the transmitter, which generates a channel signal at a wavelength λр. The output of the transmitter is connected to the first input of the shaper simulating a linear signal. In addition, the output of the laser generator, in which a pulse signal is generated at a wavelength of λm, which is a synchronization signal, is connected to the second input of the shaper simulating a linear signal. A linear signal is created in the linear signal simulator as a grid of pseudo-channels with wavelengths corresponding to the DWDM grid, and two channels in this grid are replaced by a pulse signal at a wavelength of λm and a channel signal at a wavelength of λр. The generated linear signal through the optical isolator, amplifier, optical switch, four-port optical splitter is fed to the base area under study. In this case, the base section is a series-connected spans, each of which consists of an optical amplifier and an optical fiber corresponding to the span, with the number of spans varying from 1 to N, where N is the specified number of spans to form the required length of the optical line. The output of the base section is connected to the input of the optical coupler, to the control output of which an optical spectrum analyzer can be connected to control the quality of the linear signal. The signal output of the optical coupler is connected to the second input of the four-port optical coupler, the second output of which is connected to the input of the DWDM demultiplexer, where the channel signal at the wavelength λр and the pulse signal at the wavelength λm are extracted from the linear signal. The first output of the DWDM demultiplexer with a dedicated signal λm is connected to the input of the PD photodetector, in which the signal is converted from an optical form to an electric one. The photodetector output is connected to the input of the synchronization manager, in which various control signals are generated by means of an electric signal λm, such as an enable signal supplied to the input of the laser generator, a transmitter start signal supplied to the input of the programmable chip, and a control signal supplied to the input of the control command generator. From the control command generator, control signals are applied to the control inputs of the optical switches. In addition, the channel signal at a wavelength λp allocated by a DWDM demultiplexer from the second output is fed through an optical switch to the input of a coherent receiver for conversion from an optical form to an electric one, from the output of which a signal is fed through a programmable chip to a bit error meter. In order to precisely adjust the signal power level at a wavelength of λm, a variable optical attenuator can be installed between the linear signal simulator and the laser generator. In order to precisely adjust the signal power level at a wavelength λp, a variable optical attenuator can be installed between the linear signal simulator and the transmitter.

These features of the device are essential for solving the task and obtaining the desired technical result. The invention is illustrated in the drawing. The figure shows a structural diagram of the invention.

A device for studying linear paths of DWDM lines by a recirculation loop method contains a pseudo-random test sequence generator 1, which is part of a programmable chip 19, in which a PSP signal is generated, which is transmitted to transmitter 2 to generate a channel signal at a wavelength λp. In addition, the laser generator 10 generates a pulsed signal at a wavelength of λm, which is a synchronization signal. The signals λp and λm are fed to the input of a linear signal simulator 9, in which a linear signal is created as a grid of pseudo-channels with wavelengths corresponding to the DWDM grid, and two channels in this grid are replaced by a pulse signal at a wavelength of λm and a channel signal at a wavelength of λp . The generated linear signal through an optical isolator 3, an amplifier 4, an optical switch 11, a four-port optical splitter 5 is fed to the studied base section 6. In this case, the base section is a series-connected spans, each of which consists of an optical amplifier and the studied length of the optical fiber, this number of spans varies from 1 to N, where N is the specified number of spans to form the required length of the optical line. From the output of the base section, the linear signal is fed to the optical coupler 7, to the control output of which an optical spectrum analyzer can be connected to control the quality of the linear signal. From the output of the optical coupler 7, the signal goes to the second input of the four-port optical coupler 5, from the second output of which the signal goes to the DWDM - demultiplexer 12, where the channel signal at the wavelength is extracted from the linear signal. λp and a pulse signal at a wavelength of λm. The signal λm is fed to the input of the photodetector FD 13 for conversion from optical to electrical form, then the converted signal is fed to the input of the synchronization manager 14, in which various control signals are generated, such as the enable signal supplied to the input of the laser generator 10, the start signal of the transmitter 2, arriving at the input of the programmable microcircuit 19, the control signal supplied to the input of the control command generator 15. The control command generator 15 provides control signals to the optical switches or 11. In addition, the channel signal at a wavelength λp extracted by DWDM - demultiplexer 12 is fed through an optical switch 11 to the input of a coherent receiver 8 for conversion from optical to electrical form, from the output of which a signal is transmitted via programmable chip 19 to a bit error meter 16. C In order to precisely control the signal power level at a wavelength of λm, a variable optical attenuator 17 is installed between the linear signal simulator 9 and the laser generator 10. For the purpose of fine adjustment the signal power level at a wavelength λp between the shaper simulating a linear signal 9 and the transmitter 2 is set to a variable optical attenuator 17.

The invention after power-up works according to the following algorithm.

The program of the cyclic algorithm 19 is loaded into the programmable chip 19, after which the SRP generator 1 starts working in it. The SRP signal is fed to the modulator of transmitter 2, in which the signal is converted into an optical signal with a wavelength λp, which is fed to the input of a linear signal simulator 9. For controlling the output power of the transmitter 2 in accordance with the power of the remaining channels, it is possible to use a variable optical attenuator 17. At the same time, the laser generator 10 generates a pulse signal wavelength λm, which is supplied to the second input of the imager of the linear signal simulation 9. To control the output power, the signal with the wavelength λm in accordance with the power of the remaining channels, you can use a variable optical attenuator 17. In the imager of the linear signal 9, which is a generator of a continuous spectrum of spontaneous noise and a spectrally selective WSS module, an imitation of a linear signal is formed, which is a sequence of noise pseudo-channels in which the channels are suppressed s with wavelengths λp and λm. The signals arriving at the inputs with wavelengths λp and λm are built into the place of the suppressed channels. Thus, at the output of the linear signal simulator 9, a linear signal imitation is formed, the signal λp being a test signal and the signal λm being a cyclic synchronization signal are built-in. The generated signal is fed to the input of the insulator 3, which serves to prevent the reflected echo from the input of the amplifier 4. Having passed the insulator 3 and the amplifier 4, the linear signal is fed to the input of the first optical switch 11, which is connected to the first cycle of loading the base section 6 by a linear signal . From the first optical switch 11, the signal is supplied to the first input of the four-port optical splitter 5. From the first output of the splitter 5, the signal is fed to the input of the base section 6. The base section under study consists of series-connected spans, each of which consists of a linear optical amplifier and an optical fiber corresponding to the span, while the number of spans varies from 1 to N, where N is the specified number of spans to form the required length of the studied optical line. From the output of the base section 6, the signal is fed through the optical coupler 7 to the second input of the optical splitter 5. Simultaneously, from the second output of the coupler 5, the selected signal is sent to the DWDM demultiplexer 12, in which the signal λm is transmitted through the photo detector 13 to the input of the synchronization manager 14, and a signal λp supplied to the input of the second optical switch 11, the output of which the optical signal is fed to the input of the coherent receiver 8. In the receiver 8, the optical signal is converted into an electronic signal, which is recorded tsya in the memory chip 19 as a reference. The synchronization manager 14 generates various control signals, such as an enable signal supplied to the input of the laser generator 10, a start signal of the transmitter 2 supplied to the input of the programmable microcircuit 19, a control signal supplied to the input of the control command generator 15. A signal is sent from the control command generator 15 control for switching the first optical switches 11 so as to disconnect the output of amplifier 4 from 1 input of splitter 5. Thus, the circuit processed 1 cycle of formation and passage of lines A clear signal and is ready for analysis of the base section 6.

In the future, the circuit will work in the mode of passage of the linear signal through the loop: splitter 5; base section 6; coupler 7; splitter 5 and so on. To control the transmission quality of the linear signal of the base section, an optical spectrum analyzer 18 can be connected to the control output of the optical coupler 7.

The synchronization signal λm is used to count the number of cycles specified by the study program of the base section 6.

The test signal λp for the bit error meter 16 in the first cycle is a reference signal, in subsequent cycles a test signal, that is, compared with a reference.

Each time the signal passes through the loop, the signal received on this cycle is recorded in the buffer memory of the microcircuit 19. Thus, an array of M signals is created, received sequentially from 1 to M of the laser generator of the 10th revolution of the linear signal in a loop. After that, the program in the chip 19 instructs the meter 16 to calculate the bit error rate for each revolution separately.

After passing a given number of cycles under study in the base area 6, the signal from the shaper 15 turns off the second switch 11. At the same time, the test signal is no longer received at the input of the receiver 8.

Here is an example implementation of the device.

Programmable microcircuit 19 is a programmable specialized microcircuit with three-dimensional integration, for example, such are produced by a number of companies (Xilinx, Altera, etc.). The functionality (with programmable characteristics) includes: FEC encoding / decoding, frame formation (Framer), GearBox Logic - a processor for logical processing and encoding of information, PMA - interfaces for binding to the physical level of the standard (for example, 10 lines of 11 Gbit / s) from).

Transmitter 2 and receiver 8 are serial 100 Gbps CFP-MSA transceiver modules that generate and receive a standard 100G signal (OIF 100G Ultra Long Haul DWDM Framework Document) with a modulation format of DP-QPSK, and allowing BER estimation in linear signal.

Shaper simulating a linear signal 9 is a combination of:

- source of uniform broadband noise signal (spontaneous emission of erbium fiber) WXZTE, in the band ~ 1530 ... 1560 nm;

- the WSS-100-4 module (Wavelength Selective Switch), a spectrally selective wavelength switch, in combination with Santec's PC: 011 control program, loaded into a Dell laptop.

To implement the optical coupler 7, NAG DWDM modules can be used, which have insertion loss in transit mode <1.22 dB, in Drop mode (Add) <1.1 dB and directivity> 50 dB;

To implement optical switches 11, it is proposed to use compact solid-state fiber-optic switches NSSW 1 × 2, manufactured by Agiltron (speed ~ 300 ns, loss ~ 0.6 dB).

EDFA-1, Span-1, ... EDFA-N, Span-N - a sequence of fiber optic spans and repeater amplifiers, making up the base area L _b . In this scheme, it is assumed that a system with coherent reception, with a powerful DSP capable of providing all the necessary compensatory functions, will be investigated. When researching systems with incoherent reception in the base path, it is necessary to provide compensators (CD, PMD, PC).

Structurally, BALI can provide for the placement of high-speed microelectronic cards, optimal for direct communication with elements controlled through Host MDIO, and in addition to provide all the requirements for docking via a 4 × 25 / 28G PMA with a CFA-MSA module, including module cooling devices. Naturally, the design should include manual controls (data entry, change of modes), BALI programming tools and indication of results on the front panel.

Thus, the present invention fully realizes the task, technologically feasible and industrially applicable.

Claims (6)

1. A device for studying linear paths of DWDM lines by a recirculation loop method, comprising a pseudo-random test sequence generator, a transmitter, an optical isolator, an optical amplifier, a four-port optical splitter, a base section, an optical coupler, a coherent receiver, characterized in that the pseudo-random test sequence generator is included as part of a programmable microcircuit, generates a PSP signal, which is transmitted to the transmitter to form a channel dough signal at a wavelength λр, which is input to a linear signal simulator, to the other input of which a pulse signal at a wavelength λm is received from the laser generator, which is a cyclic synchronization signal, a linear signal is created in a linear signal simulator, like a grid of pseudo-channels with lengths waves corresponding to the DWDM grid, and two channels in this grid are replaced by a pulsed signal at a wavelength of λm and a channel signal at a wavelength of λр, then the generated linear signal through optical the cube isolator and amplifier goes to the first controllable optical switch, the output of which is connected to a four-port optical coupler, from the output of which the signal goes to the base section, from the output of the base section, a linear signal is fed through the optical coupler to the second input of the four-port optical splitter, from the second output of which arrives at the DWDM demultiplexer, where a channel signal at a wavelength λр and a pulse signal at a wavelength λm are extracted from a linear signal, and the signal λm is fed to the input of the PD photodetector for conversion from optical to electrical form, then the converted signal is fed to the input of the synchronization manager, in which various control signals are generated, such as the enable signal supplied to the input of the laser generator, the transmitter start signal received at the input of the programmable chip, a control signal supplied to the input of the control command generator, while the control command generator supplies control signals to the optical switches, in addition On the other hand, a channel signal at a wavelength λр allocated by a DWDM demultiplexer is fed through a second optical switch to the input of a coherent receiver for conversion from optical to electrical form, from the output of which a signal is transmitted through a programmable chip to a bit error meter. 2. A device for studying linear DWDM paths of highways by a recirculation loop method in accordance with Clause 1, characterized in that the base section under investigation is a series of spans, each of which consists of a linear optical amplifier and an optical fiber corresponding to the span the number of spans varies from 1 to N, where N is the specified number of spans to form the required length of the studied optical line. 3. A device for studying linear paths of DWDM lines by a recirculation loop method in accordance with clause 1, characterized in that for the purpose of precisely adjusting the signal power level at a wavelength of λm, a variable optical attenuator is installed between the linear signal simulator and the laser generator. 4. A device for studying linear paths of DWDM highways by a recirculation loop method in accordance with Clause 1, characterized in that for the purpose of precise adjustment of the signal power level at a wavelength λp, a variable optical attenuator is installed between the linear signal simulator and the transmitter. 5. A device for studying linear paths of DWDM lines by a recirculation loop method in accordance with Clause 1, characterized in that an optical spectrum analyzer is connected to control the quality of the linear signal from the output of the base section to the second output of the optical coupler. 6. A device for studying linear paths of DWDM lines by a recirculation loop method in accordance with Clause 1, characterized in that an optical spectrum analyzer is used to control the quality of the linear signal generated by the simulator of the linear signal, which is connected to the control output of the shaper.

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