Optical transmission system and optical transmission system design method

Abstract

To make it possible to optimally design frequency correction in a transponder.SOLUTION: An optical transmission system 1A including a transponder having a transmitter 111 and a receiver 112 includes a transmitting-side station A 100A including a transponder, a receiving-side station B 100B including a transponder, a predetermined path 210 that passes through components of the optical transmission system 1A other than the transponder and connects the station A 100A and the station B 100B, and a server 150 that calculates a correction value for correcting the frequency characteristic of a signal transmitted from the transmitter 111 based on a signal transmitted using the predetermined path 210.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical transmission system and a method for designing an optical transmission system. [Background technology]

[0002] An optical transmission system has an optical transmission layer where multiple nodes are interconnected by links. In this optical transmission layer, optical physical characteristics and analog control characteristics interact in a complex manner, causing faults (anomalies) that are difficult to locate and identify their causes.

[0003] Optical transmission systems utilize digital coherent methods that include electrical signal processing for transmitting and receiving optical signals. Taking advantage of the ability to perform electrical signal processing, a method has been proposed in which the characteristics of optical modules (optical modulators, ICRs (Integrated Coherent Receivers), etc.) and electrical modules (driver amplifiers, TIAs (Trans-Impedance Amplifiers), high-frequency cables, etc.) used in transmitters and receivers are compensated for in the electrical signal processing section to improve the quality of optical signals (see Non-Patent Documents 1 and 2). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] A. Matsushita, et. al., “64-GBd PDM-256QAM and 92-GBd PDM-64QAM Signal Generation using Precise-Digital-Calibration aided by Optical-Equalization“, Proc. OFC2019, W4B.2. [Non-patent document 2] A. Matsushita, et. al., “High-Spectral-Efficiency 600-Gbps / Carrier Transmission Using PDM-256QAM Format”, IEEE JLT, vol.37, no.2, Jan. 15, 2019. Summary of the Invention [Problem to be solved by the invention]

[0005] However, there are multiple variations in parameters and correction methods that must be set on the transmitting and receiving sides, making it difficult to achieve an optimal design.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to optimally design frequency correction in a transponder. [Means for solving the problem]

[0007] As a means for solving the above problems, the present invention provides an optical transmission system including a transponder having a transmitter and a receiver, a first station on the transmitting side that includes the transponder; The transponder and spectrum analyzer and calculation unit a receiving side second station having: a first path connecting the first station and the receiver in the second station; Branching from the first pathway, The first and second station buildings The spectrum analyzer Connect with No. 2 The route, Equipped with The calculation unit Calculating a correction value for correcting the frequency characteristics of the signal transmitted from the transmitter in the first station via the first path at the receiver side of the second station so that the frequency characteristics of the signal transmitted from the transmitter in the first station via the second path approach those of the result of measurement by the spectrum analyzer. It is characterized by: [Effects of the Invention]

[0008] According to the present invention, frequency correction in a transponder can be optimally designed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a configuration diagram showing an optical transmission system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a hardware configuration diagram illustrating an example of a computer that realizes the functions of a server in the optical transmission system according to the first embodiment. [Figure 3] 4 is a diagram illustrating an example of frequency characteristics of an electrical module in the optical transmission system according to the first embodiment. FIG. [Figure 4] FIG. 3 is a diagram illustrating an example of frequency characteristics of an electrical signal in the optical transmission system according to the first embodiment. [Figure 5] FIG. 4 is a diagram illustrating an example of frequency characteristics of a corrected signal in the optical transmission system according to the first embodiment. [Figure 6] 4 is a flowchart showing a design process for an optical transmission system according to the first embodiment. [Figure 7] 4 is an optimization subroutine of the design process of the optical transmission system according to the first embodiment. [Figure 8] FIG. 3 is a diagram illustrating the relationship between the BER and a reference value in the optical transmission system according to the first embodiment. [Figure 9] FIG. 10 is a configuration diagram showing an optical transmission system according to a second embodiment of the present invention. [Figure 10] 10 is a flowchart showing a design process for an optical transmission system according to a second embodiment. [Figure 11] FIG. 10 is a configuration diagram showing an optical transmission system according to a third embodiment of the present invention. [Figure 12] 10 is a flowchart showing a design process for an optical transmission system according to a third embodiment. [Figure 13] FIG. 10 is a configuration diagram showing an optical transmission system according to a fourth embodiment of the present invention. [Figure 14] FIG. 10 is a configuration diagram showing an optical transmission system according to a fifth embodiment of the present invention. [Figure 15] FIG. 10 is a diagram illustrating an optical signal spectrum of the optical transmission system according to the fifth embodiment. [Figure 16] FIG. 10 is a configuration diagram showing an optical transmission system according to a sixth embodiment. [Figure 17]FIG. 13 is a diagram illustrating an optical signal spectrum of the optical transmission system according to the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] An optical transmission system and the like in an embodiment for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described below with reference to the drawings. (First embodiment) FIG. 1 is a configuration diagram showing an optical transmission system according to a first embodiment of the present invention. As shown in FIG. 1, in the optical transmission system 1, a station 100A (first station) and a station 100B (second station) are connected via a component 10 of the optical transmission system other than a transponder. The components 10 of the optical transmission system include an optical multiplexer / demultiplexer, an optical cross-connect unit, an optical amplifier repeater unit, an optical fiber transmission line, and the like. The station 100A and the station 100B each include a transponder 110 and a server 150 (calculation unit). The transponder 110 includes a transmitter (Tx) 111 and a receiver (Rx) 112. The transponder 110 in the station 100A further includes a cross-connect function unit 113. However, the transponder 110 in the station 100B may also be configured to include the cross-connect function unit 113.

[0011] The transmitter (Tx) 111 includes an electric signal generating unit 1111 and an electric signal transmitting unit 1112 . The receiver (Rx) 112 includes an electrical signal receiving unit 1121 and an electrical signal generating unit 1122 . The cross-connect function unit 113 forms a loopback path 200 (first path) that directly connects a signal from the receiver (Rx) 112 to the transmitter (Tx) 111.

[0012] The server 150 of the optical transmission system 1 according to this embodiment is realized by a computer 900, which is a physical device having a configuration as shown in FIG. 2 is a hardware configuration diagram showing an example of a computer that realizes the functions of the server 150 in the optical transmission system 1 according to the first embodiment of the present invention. The computer 900 includes a CPU (Central Processing Unit) 901, a ROM (Read Only Memory) 902, a RAM 903, an HDD (Hard Disk Drive) 904, an input / output I / F (Interface) 905, a communication I / F 906, and a media I / F 907.

[0013] The CPU 901 operates based on a program stored in the ROM 902 or the HDD 904, and performs control by the control unit of the server 150 shown in Fig. 1. The ROM 902 stores a boot program executed by the CPU 901 when the computer 900 is started up, programs related to the hardware of the computer 900, and the like.

[0014] The CPU 901 controls an input device 910 such as a mouse or keyboard, and an output device 911 such as a display, via an input / output I / F 905. The CPU 901 acquires data from the input device 910 via the input / output I / F 905, and outputs generated data to the output device 911. Note that a GPU (Graphics Processing Unit) or the like may be used as a processor together with the CPU 901.

[0015] The HDD 904 stores programs executed by the CPU 901 and data used by the programs. The communication I / F 906 receives data from other devices via a communication network (e.g., NW (Network) 920) and outputs the data to the CPU 901, and also transmits data generated by the CPU 901 to other devices via the communication network.

[0016] The media I / F 907 reads a program or data stored in the recording medium 912 and outputs it to the CPU 901 via the RAM 903. The CPU 901 loads a program related to a target process from the recording medium 912 onto the RAM 903 via the media I / F 907, and executes the loaded program. The recording medium 912 is an optical recording medium such as a DVD (Digital Versatile Disc) or a PD (Phase Change Rewritable Disc), a magneto-optical recording medium such as an MO (Magneto Optical disc), a magnetic recording medium, a conductive memory tape medium, a semiconductor memory, or the like.

[0017] For example, when the computer 900 functions as the server 150 of the optical transmission system 1 according to this embodiment, the CPU 901 of the computer 900 executes a program loaded onto the RAM 903 to realize the functions of the server 150. Furthermore, the HDD 904 stores data in the RAM 903. The CPU 901 reads and executes a program related to a target process from a recording medium 912. Alternatively, the CPU 901 may read a program related to a target process from another device via a communication network (NW 920).

[0018] A method for designing the optical transmission system 1 configured as described above will now be described. The application of the optical transmission system 1 to an optical communication system has the following technical background. Optical communication systems utilize digital coherent methods that include electrical signal processing for transmitting and receiving optical signals. Because DSPs (Digital Signal Processors) are capable of high-speed electrical signal processing, the quality of optical signals can be improved by compensating for the characteristics of the optical modules (optical modulators, ICRs, etc.) and electrical modules (driver amplifiers, TIAs, high-frequency cables, etc.) used in the transmitter and receiver in the electrical signal processing section.

[0019] Figure 3 shows an example of the frequency characteristics of an electrical module in an optical transmission system. The horizontal axis represents frequency (Frequency [GHz]) and the vertical axis represents amplification factor (Amplitude [dB]). As shown in Figure 3, the frequency characteristics of the electrical module show that the higher the frequency, the more easily attenuation occurs.

[0020] 4 is a diagram showing an example of frequency characteristics of an electrical signal in an optical transmission system, where the horizontal axis represents frequency (Frequency [GHz]) and the vertical axis represents amplification factor (Amplitude [dB]). If the frequency characteristics of the electrical module shown in FIG. 3 are known, high frequency components can be boosted by applying an electrical signal having the inverse characteristics shown in FIG.

[0021] 5 is a diagram showing an example of frequency characteristics of a corrected signal, where the horizontal axis represents frequency (Frequency [GHz]) and the vertical axis represents amplification factor (Amplitude [dB]). The frequency characteristics of the electrical module shown in Figure 3 are corrected by applying a signal with the inverse characteristics shown in Figure 4. As shown in Figure 5, the electrical module has flat frequency characteristics from low to high frequencies, which can improve signal quality. Based on the above technical background, frequency correction in the optical transmission system 1 will be described using a flowchart.

[0022] 6 is a flowchart showing the design process of the optical transmission system 1. In this flow, the control unit of the server 150 controls each unit of the transponder 110 (see FIG. 1). In step S11, it is determined whether or not the transmitter (hereinafter referred to as Tx) 111 side is to be optimized. If optimization of the Tx 111 side is not performed, the processing of this flow is terminated. Here, if optimization of the Tx 111 side is performed, the frequency correction on the receiver (hereinafter referred to as Rx) 112 side is fixed. Conversely, if optimization of the Rx 112 side is performed, the frequency correction on the Tx 111 side is fixed.

[0023] When optimizing the Tx 111 side, the function of the electrical signal receiving unit 1121 of the receiver (hereinafter referred to as Rx) 112 is turned on in step S12 (at this time, the correction value remains the initial value). In step S13, the cross-connect function unit 113 (see FIG. 1) of the transponder 110 switches the path to form the loopback path 200 (see FIG. 1). The loopback path 200 forms a loopback path 200 that feeds back the received signal of the Rx 112 to the Tx 111 side.

[0024] In step S14, the electrical signal generator 1111 of the Tx 111 determines the correction value for frequency correction (see the optimization subroutine in FIG. 7). The determined correction value mainly corrects the frequency characteristics of the Tx 111. This allows a signal having an inverse frequency characteristic (see FIG. 4) to be set as the correction value for frequency correction.

[0025] In step S15, the electrical signal transmitting unit 1112 of the Tx 111 transmits the determined frequency correction value to the Rx 112 side via the loopback path 200.

[0026] In step S16, the electrical signal receiving unit 1121 of the Rx 112 receives the frequency correction value determined on the Tx 111 side.

[0027] In step S17, the electrical signal generator 1122 of the Rx 112 determines the correction value for frequency correction (see the optimization subroutine in FIG. 7), and ends the processing of this flow. The determined correction value mainly corrects the frequency characteristics of the Rx 112.

[0028] 7 shows an optimization subroutine for the design process of the optical transmission system 1. It is called and executed in step S14 or step S17 in FIG. First, the frequency characteristics of the individual modules themselves are obtained by offline means and used as initial values ​​(step S101). In step S102, the bit error rate (BER) of the signal is acquired.

[0029] In step S103, it is determined whether the BER has achieved a predetermined reference value (see FIG. 8). If the BER has reached the predetermined reference value (S103: Yes), this routine ends and the process returns to step S14 or step S17 in FIG. If the BER does not reach the predetermined reference value (S103: No), the correction value of the frequency characteristic is changed in step S104, and the process returns to step S102.

[0030] Fig. 8 is a diagram illustrating the relationship between BER and reference value. The horizontal axis represents the correction value of the frequency characteristic, and the vertical axis represents BER. In Fig. 8, symbol a1 indicates the initial value, symbol a2 indicates the state after the frequency characteristic is changed from the initial value, and symbol a3 indicates the minimum value of BER (reference value of BER). As shown in Fig. 8, the server 150 (see Fig. 1) records the BER in several states where the frequency characteristics are changed. The state where the BER is smallest is set as the reference value of the BER that is closest to the optimum.

[0031] As described above, according to this embodiment, in order to individually optimize Tx and Rx, correction is completed within the transponder 110 using loopback. However, in practice, since the transponder will be paired with a transponder located in another station, the Tx / Rx may not be optimized as a whole.

[0032] (Second embodiment) 9 is a configuration diagram showing an optical transmission system according to a second embodiment of the present invention. Components that are the same as those in FIG. 1 are given the same reference numerals, and explanations of overlapping parts will be omitted. As shown in FIG. 9, the optical transmission system 1A includes a station 100A, a path 210 (second path) passing through components 10 of the optical transmission system other than the transponder, a station 100B connected to the station 100A via the path 210, and a feedback path 220 that feeds back BER information from the station 100B to the station 100A.

[0033] A method for designing the optical transmission system 1A configured as described above will now be described. FIG. 10 is a flowchart showing the design process of the optical transmission system 1A. In step S21, it is determined whether or not to optimize the Tx111 side. If optimization of the Tx111 side is not to be performed, the process of this flow ends. When optimizing the Tx 111 side, the function of the electrical signal receiving unit 1121 (see FIG. 9) of the Rx 112 is turned on in step S22 (at this time, the correction value remains the initial value). In step S23, the electrical signal receiving unit 1121 of the Rx 112 in the station 100A receives the BER information fed back from the station 100B to the station 100A via the feedback path 220.

[0034] In step S24, the electrical signal generator 1111 of the Tx 111 in the station 100A determines the correction value for frequency correction (see the optimization subroutine in FIG. 7). The determined correction value mainly corrects the frequency characteristics of the Tx 111. This allows a signal having an inverse frequency characteristic (see FIG. 4) to be set as the correction value for frequency correction. In step S25, the electrical signal transmitting unit 1112 of the Tx 111 in the station 100B transmits the determined frequency correction value to the Rx 112 side via the loopback path 200.

[0035] In step S26, the electrical signal receiving unit 1121 of the Rx 112 in the station 100A receives the frequency correction value determined on the Tx 111 side. In step S27, the electrical signal generator 1122 of the Rx 112 in the station 100B determines the correction value for frequency correction (see the optimization subroutine in FIG. 7). This means that the frequency characteristics of the Rx 112 are mainly corrected. In step S28, the Rx 112 of the station 100A feeds back the BER information to the Tx 111 of the station 100A, and the process of this flow ends.

[0036] As described above, according to the second embodiment, in order to individually optimize Tx and Rx, the transponders 110 between different stations are connected and corrected via components 10 of the optical transmission system other than the transponders 110.

[0037] In the second embodiment, the frequency characteristics inherent in the components 10 of the optical transmission system other than the transponder 110 are also corrected. Therefore, compared to the first embodiment, when the transponders 110 that actually exchange main signals are corrected as a pair, there is an advantage that Tx / Rx are optimized in total.

[0038] (Third embodiment) 11 is a configuration diagram showing an optical transmission system according to a third embodiment of the present invention. The same components as those in FIG. 9 are assigned the same reference numerals, and the description of overlapping parts will be omitted. As shown in FIG. 11, the optical transmission system 1B includes a station 100A, a path 210 passing through components 10 of the optical transmission system other than the transponder, and a station 100B connected to the station 100A via the path 210. The Rx 112 of the transponder 110 in the station 100B is modified to have an electric signal receiving unit 1121A having a DSP instead of the electric signal receiving unit 1121 in FIG. The electrical signal receiving unit 1121A uses the Rx-side DSP to optimize the frequency characteristics of the Tx and Rx sets.

[0039] A method for designing the optical transmission system 1B configured as above will be described below. FIG. 12 is a flowchart showing the design process of the optical transmission system 1B. In step S31, it is determined whether or not to optimize the Tx111 side. If optimization of the Tx111 side is not to be performed, the processing of this flow is terminated.

[0040] In step S32, the electrical signal generator 1111 of the Tx 111 in the station 100A determines the correction value for frequency correction (see the optimization subroutine in FIG. 7). The determined correction value mainly corrects the frequency characteristics of the Tx 111.

[0041] This allows a signal having an inverse frequency characteristic (see FIG. 4) to be set as the correction value for frequency correction.

[0042] In step S33, the electrical signal transmitting unit 1112 of the Tx 111 in the station 100B transmits the determined frequency correction value to the Rx 112 side via the loopback path 200. In step S34, the electrical signal receiving unit 1121A having a DSP in the Rx 112 of the station 100A receives the correction value for frequency correction determined on the Tx 111 side. In step S35, the electrical signal generator 1122 of the Rx 112 in the station 100B determines the correction value for frequency correction, and ends the processing of this flow (see the optimization subroutine in FIG. 7). This means that the frequency characteristics of the Rx 112 are mainly corrected.

[0043] As described above, according to the third embodiment, the frequency characteristics of the Tx and Rx set are optimized by the Rx-side DSP of the electrical signal receiving unit 1121A. In the third embodiment, the processing time can be reduced by approximately half compared to the first and second embodiments because there is no processing flow that fixes either one (for example, the processing of step S22 in FIG. 10). Furthermore, there is an advantage that in the flow of optimizing the frequency characteristics, it is not necessary to feed back the BER to the transmitting side (for example, the process of step S28 in FIG. 10).

[0044] (Fourth embodiment) 13 is a configuration diagram showing an optical transmission system according to a fourth embodiment of the present invention. The same components as those in FIG. 9 are given the same reference numerals, and the description of overlapping parts will be omitted. As shown in Fig. 13, the optical transmission system 1C includes a station building 100A, paths 210 and 230 passing through components 10 of the optical transmission system other than the transponder, and a station building 100B connected to the station building 100A via the paths 210 and 230 (second paths).

[0045] In addition to the transponders 110 and servers 150, the station buildings 100A and 100B further include a reference transponder 120. The reference transponder 120 outputs a frequency signal serving as a frequency-corrected reference.

[0046] Tx111 of the transponder 110 in the station building 100A is connected to Rx122 of the reference transponder 120 via the path 210. Also, Rx112 of the transponder 110 in the station building 100A is connected to Tx121 of the reference transponder 120 via the path 230.

[0047] As described above, according to the fourth embodiment, in order to optimize the Tx and Rx individually, the reference transponder 120 is connected and corrected. It becomes possible to correct the transponder 110 in the station building​​​​​​​​​​​​​​​​​ FIG. 15 is a diagram showing an optical signal spectrum. The horizontal axis represents frequency (Frequency [GHz]), and the vertical axis represents the frequency correction amount. As shown in FIG. 15, for an ideal Tx signal shape, the signal transmitted through the component 10 of the optical transmission system other than the transponder has a Tx signal shape in which components are attenuated more at higher frequencies. As shown by reference sign a in FIG. 15, the Tx high-frequency components are corrected by the DSP.

[0051] As described above, according to the fifth embodiment, in <Tx-side correction>, as a means for correcting the frequency characteristics on the Tx side, instead of the BER, the frequency spectrum measurement result of the spectrum analyzer 130 is utilized. In recent years, a small optical spectrum measurement module for incorporation into an optical transmission system has been realized. The fact that the signal band is attenuated more at higher frequencies means that the optical spectrum of the optical signal becomes non-flat. The degree of non-flatness is measured by the spectrum analyzer 130, and the frequency characteristics on the Tx side are corrected with the goal of making the measurement result of the spectrum analyzer 130 flat. At this time, the data sequence of the optical signal on the transmission side may be changed to a data sequence that makes the optical spectrum flat instead of the actual data.

[0052] <Rx-side correction> FIG. 16 is a configuration diagram showing an optical transmission system according to a sixth embodiment of the present invention. As shown in FIG. 16, the optical transmission system 1E includes a station 100A, a path 210 passing through the component 10 of the optical transmission system other than the transponder, and a station 100B connected to the station 100A via the path 210. The spectrum analyzer 130 that branches the same optical power measures the frequency spectrum of the received signal.

[0053] FIG. 17 is a diagram showing an optical signal spectrum. The horizontal axis represents frequency (Frequency [GHz]), and the vertical axis represents the frequency correction amount. As shown in Fig. 17, when receiving a signal transmitted through the components 10 of the optical transmission system other than the transponder with respect to the ideal Rx signal shape, the received signal has an Rx signal shape with components attenuating more at higher frequencies. As shown by the reference sign b in Fig. 17, the Tx high-frequency components are corrected by the DSP.

[0054] As described above, according to the sixth embodiment, in <correction on the Rx side>, as a correction means for the frequency characteristics on the Rx side, instead of the BER, the frequency spectrum measurement result of the spectrum analyzer 130 is utilized. In recent years, small optical spectrum measurement modules for incorporation into optical transmission systems have been realized. The frequency dependency of the spectrum analyzer 130 is generally sufficiently smaller than the Rx-side frequency characteristics. Correct the frequency characteristics on the Rx side so as to approach the measurement result of the spectrum analyzer 130. At this time, the output of the Tx signal on the transmission side may be stopped and the ASE noise generated in the optical amplification relay section may be utilized (generally, the frequency flatness of the EDFA used in the optical amplification relay section is flatter than the frequency characteristics including the electrical modules of the transceiver).

[0055] [Effect] Hereinafter, the effects of the optical transmission system and the like according to the present invention will be described. The transmission system 1 of the present embodiment is an optical transmission system 1 including a transponder 110 having a transmitter 111 and a receiver 112, and includes a first path (loopback path 200) that directly connects the signal of the receiver 112 to the transmitter 111, and a calculation unit (server 900) that calculates a correction value for correcting the frequency characteristics of the signal transmitted from the transmitter based on the signal transmitted using the first path.

[0056] By doing so, in order to optimize the Tx and Rx individually, the correction is completed with the transponder 110 alone using loopback. Thereby, the frequency correction in the transponder can be optimally designed.

[0057] [[ID=2,3]] The optical transmission system is characterized by comprising a first station (station 100A) on the transmitting side equipped with a transponder 110 and a second station (station 100B) on the receiving side equipped with a transponder 110, and connecting the first station and the second station via a second path (path 210) that passes through components of the optical transmission system other than the transponder, instead of the first path.

[0058] In this way, the transponders 110 between different stations are connected and corrected via the components 10 of the optical transmission system other than the transponders 110. The frequency characteristics inherent in the components 10 of the optical transmission system other than the transponders 110 are also corrected. Therefore, when correction is made for the transponder 110 pair that actually exchanges the main signal, there is an effect of optimizing the Tx / Rx in total.

[0059] Also, in the optical transmission system, the signal from the transmitter of the transponder in the first station is received by the receiver of the transponder in the second station via the second path (path 210), and the signal from the transmitter of the transponder in the second station is received by the receiver of the transponder in the first station via the second path (path 230).

[0060] By doing this, the frequency characteristics inherent in the components 10 of the optical transmission system other than the transponder 110 are also corrected. Therefore, when the transponders 110 that actually exchange the main signal are corrected as a pair, there is an effect that the Tx / Rx are optimized in total. This makes it possible to design frequency correction more optimally.

[0061] The optical transmission system is also characterized by comprising a feedback path 220 for feeding back BER information from the second station to the first station.

[0062] This has the effect of eliminating the need to feed back the BER to the transmitting side during the frequency characteristic optimization flow.

[0063] In addition, the optical transmission system is characterized in that a reference transponder 120 is provided in a second station, and the calculation unit calculates a correction value for correcting the frequency characteristics of the signal transmitted from the transmitter based on the signal of the reference transponder 120.

[0064] In this way, it is possible to design frequency correction more optimally by connecting and correcting the reference transponder 120. It also becomes possible to simultaneously correct the Tx / Rx of the transponder 110 in the station 100A.

[0065] The optical transmission system is also characterized in that a spectrum analyzer 130 is provided in the second station, and the calculation unit calculates a correction value for correcting the frequency characteristics of the signal transmitted from the transmitter based on the measurement results of the spectrum analyzer 130.

[0066] In this way, it is possible to utilize not the BER but the frequency spectrum measurement results of the spectrum analyzer 130. For example, the frequency characteristics on the Rx side are corrected so as to approach the measurement results of the spectrum analyzer 130.

[0067] In the above embodiments, the optical TDM technology has been described as being applied to optical transmission equipment and optical transmission systems that utilize communication devices and equipment, such as PON, as a network using the technology. However, the present invention can also be applied to any network system or optical transmission equipment in which a first optical transmission equipment having an OLT as an optical line terminal that terminates signals sent and received between external equipment and serves as the controlling entity, and a plurality of second optical transmission equipment having ONUs as optical line terminals that serve as objects to the controlling entity, are connected in a ring shape by at least two optical transmission paths, and the same two data pass through the two optical transmission paths in opposite directions.

[0068] Furthermore, among the processes described in the above embodiments, all or part of the processes described as being performed automatically can be performed manually, or all or part of the processes described as being performed manually can be performed automatically using a known method.In addition, the information including the processing procedures, control procedures, specific names, various data, and parameters shown in the above documents and drawings can be changed as desired unless otherwise specified. Furthermore, the components of each device shown in the figure are conceptual functional components and do not necessarily have to be physically configured as shown in the figure. In other words, the specific form of distribution and integration of each device is not limited to that shown in the figure, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc.

[0069] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. The above-described configurations, functions, etc. may also be implemented by software that causes a processor to interpret and execute programs that implement the respective functions. Information such as programs, tables, and files that implement the respective functions may be stored in a memory, a recording device such as a hard disk or a solid-state drive (SSD), or a recording medium such as an integrated circuit (IC) card, a secure digital (SD) card, or an optical disc. [Explanation of symbols]

[0070] 1A, 1B, 1C, 1D, 1E Optical Transmission System 10 Components of optical transmission systems other than transponders 100A Station Building A (1st Station Building) 100B Station building B (second station building) 110 Transponder 111 Transmitter (Tx) 112 Receiver (Rx) 113 Cross-connect function unit 120 Reference Transponder 130 Spectrum Analyzer 150 Server (calculation unit) 200 Loopback route (first route) 210, 230 Path through components of optical transmission system other than transponder (second path) 220 Feedback Path 1111 Electrical signal generation unit 1112 Electrical signal transmitter 1121, 1121A Electrical signal receiving unit 1122 Electrical signal generation unit

Claims

1. 1. An optical transmission system comprising a transponder having a transmitter and a receiver, a first station on the transmitting side that includes the transponder; a second station on the receiving side, which includes the transponder, a spectrum analyzer, and a calculation unit; a first path connecting the first station and the receiver of the second station; a second path branching from the first path and connecting the first station and the spectrum analyzer in the second station; The calculation unit calculates a correction value for correcting the frequency characteristics of the signal transmitted from the transmitter in the first station via the first path at the receiver side of the second station so that the frequency characteristics of the signal transmitted from the transmitter in the first station via the second path approach the frequency characteristics of the result of measurement by the spectrum analyzer. An optical transmission system comprising:

2. A method for designing an optical transmission system including a transponder having a transmitter and a receiver, comprising: a first station on the transmitting side that includes the transponder; a second station on the receiving side, which includes the transponder, a spectrum analyzer, and a calculation unit; a first path connecting the first station and the receiver of the second station; a second path branching from the first path and connecting the first station and the spectrum analyzer in the second station; The calculation unit includes a step of calculating a correction value for correcting a frequency characteristic at a receiver side of the second station of a signal transmitted from a transmitter of the first station via the first path so that the frequency characteristic of the signal transmitted from the transmitter of the first station via the second path approaches a frequency characteristic obtained as a result of measurement by the spectrum analyzer. A method for designing an optical transmission system.

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