Optical transmitter, optical transmission system, and optical transmission method

Abstract

One embodiment of the present invention is an optical transmitter comprising a transmission digital signal processing unit that performs digital processing on a transmission signal. The transmission digital signal processing unit changes a signal pattern of the transmission signal to a signal pattern different from the signal pattern before the change a plurality of times, and transmits each of the plurality of changed signal patterns as an optical transmission signal.

Description

Optical Transmitter, Optical Transmission System, and Optical Transmission Method

[0001] The present invention relates to technologies of an optical transmitter, an optical transmission system, and an optical transmission method.

[0002] In an optical fiber transmission system, the transmission performance is greatly affected by the characteristics of optical components in the optical transmission path. Therefore, development has been underway regarding DLM (Digital Longitudinal Monitoring) for estimating the characteristics of various components distributed in the longitudinal direction of an optical fiber using only digital signal processing in an optical receiver (see, for example, Non-Patent Documents 1 and 2). Note that averaging the estimation results multiple times is effective for improving the accuracy of DLM estimation results.

[0003] Takahito Tanimura, Setsuo Yoshida, et al., “Fiber-Longitudinal Anomaly Position Identification Over Multi-Span Transmission Link Out of Receiver-end Signals”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 38, NO. 9, MAY 2020, p2726-2733, IEEE, 2020Takeo Sasai, Masanori Nakamura, et al., “Digital Longitudinal Monitoring of Optical Fiber Communication Link”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 40, NO. 8, APRIL 15, p2390-2408, IEEE, 2022

[0004] However, in the prior art, there is a problem that it is difficult to improve the accuracy of DLM estimation results because there is an upper limit to the effect of reducing distortion by simple averaging. In view of the above circumstances, an object of the present invention is to provide a technology capable of improving the accuracy of DLM estimation results.

[0005] One aspect of the present invention is an optical transmitter comprising a transmission digital signal processing unit that performs digital processing on a transmission signal, wherein the transmission digital signal processing unit changes the signal pattern multiple times to a different signal pattern from the original, and transmits each of the multiple changed signal patterns as an optical transmission signal.

[0006] One aspect of the present invention is an optical transmission system comprising: an optical transmitter that changes a signal pattern multiple times to a signal pattern different from the original and transmits each of the multiple changed signal patterns as an optical signal; an optical transmission path that connects the optical transmitter and an optical receiver and includes an amplifier; an optical receiver that receives the optical signals of the multiple signal patterns transmitted by the optical transmitter; and an optical transmission path characteristic estimation unit that estimates the physical characteristics of the optical transmission path by averaging the physical characteristics of the optical transmission path with respect to the optical signals of the multiple signal patterns received by the optical receiver.

[0007] One aspect of the present invention is an optical transmission method in which an optical transmission unit changes the signal pattern multiple times to a different signal pattern from the original, and transmits each of the multiple changed signal patterns as an optical transmission signal.

[0008] This invention makes it possible to improve the accuracy of DLM estimation results.

[0009] This figure shows an example system configuration of an optical transmission system according to the embodiment. This figure shows an example configuration of an optical transmitter according to the embodiment. This figure shows a schematic of an example hardware configuration of a transmission digital signal processing unit applied to the embodiment. This figure shows an example of averaging when the same signal pattern is used in the prior art and an example of averaging when different signal patterns are used according to the method of this embodiment. This is a flowchart of the processing procedure performed by the optical transmission system according to the embodiment. This is a flowchart of the processing procedure performed by the transmission digital signal processing unit of the embodiment. This figure shows an example configuration of an optical transmission system when the optical receiver has the functions of an optical transmission path characteristic estimation unit and a network controller. This is an example configuration when the signal pattern generation unit or signal pattern change instruction unit is connected to the outside of the optical transmitter.

[0010] Embodiments of the present invention will be described in detail with reference to the drawings. Figure 1 is a diagram showing an example of the system configuration of the optical transmission system of this embodiment. As shown in Figure 1, the optical transmission system 1 includes, for example, an optical transmitter 2, an optical transmission path 3, an optical receiver 4, an optical transmission path characteristic estimation unit 5, and a network controller 6. The optical transmission path characteristic estimation unit 5 includes, for example, a storage unit 51.

[0011] The optical transmitter 2 transmits multiple random pattern optical signals to the optical receiver 4 via the optical transmission path 3. The configuration and processing of the optical transmitter 2 will be explained in detail with reference to Figure 2.

[0012] The optical transmission path 3 is, for example, an optical fiber transmission path. The optical transmission path 3 includes, for example, an optical amplifier.

[0013] The optical receiver 4 receives multiple random pattern optical signals output by the optical transmitter 2 and outputs the received optical signals to the optical transmission path characteristic estimation unit 5.

[0014] The optical transmission path characteristic estimation unit 5 estimates, for example, the longitudinal physical characteristics of the optical fiber from the optical signal (received signal) output by the optical receiver 4, using a method described in Non-Patent Document 2 or other well-known methods, and stores the estimated results in the storage unit 51. The optical transmission path characteristic estimation unit 5 averages the DLM results obtained using multiple transmission signal patterns. This improves the accuracy of the DLM estimation results according to this embodiment. The optical transmission path characteristic estimation unit 5 also performs, for example, estimation of the optical power distribution in the longitudinal direction of the optical fiber, estimation of the gain spectrum of the optical amplifier, estimation of the response of individual optical filters, etc. (see, for example, Non-Patent Document 2). In this way, the optical transmission path characteristic estimation unit 5 measures the entire length of the optical transmission path at once by analyzing the received signal. Based on the analysis results, for example, abnormal loss locations and abnormal gain locations in the optical fiber transmission path can be estimated. The DLM method performed by the optical transmission path characteristic estimation unit 5 visualizes the optical power distributed in the longitudinal direction of the optical fiber transmission path by applying digital signal processing to the received signal waveform that reaches the optical receiver 4. Furthermore, the optical transmission path characteristic estimation unit 5 may perform four-dimensional optical power visualization extended to the polarization, frequency, and time directions, in addition to measuring the optical signal power distributed in the distance direction within the optical fiber transmission path (see, for example, Reference 1). Also, when the optical transmission path characteristic estimation unit 5 has finished acquiring the optical signal from the optical receiver 4, it outputs a waveform acquisition completion notification g1 to the network controller 6.

[0015] Reference 1: Takeo Sasai, Giacomo Borraccini, et al., “4D Optical Link Tomography: First Field Demonstration of Autonomous Transponder Capable of Distance, Time, Frequency, and Polarization Resolved Monitoring”, 2024 Optical Fiber Communications Conference and Exhibition (OFC), Th4B.7, 2024

[0016] The storage unit 51 stores the results obtained by the optical transmission path characteristic estimation unit 5 performing DLM. Note that the storage unit 51 does not necessarily have to be provided by the optical transmission path characteristic estimation unit 5, or it may be connected to the optical transmission path characteristic estimation unit 5.

[0017] The network controller 6 receives the waveform acquisition completion notification g1 output by the optical transmission path characteristic estimation unit 5, and outputs a signal pattern change notification g2 to the optical transmitter 2 in accordance with the acquired waveform acquisition completion notification g1. The network controller 6 controls the network in the optical transmission system 1.

[0018] In the example described above, the optical transmission path characteristic estimation unit 5 performs DLM processing, but this is not the only example. DLM may be performed, for example, inside the optical receiver 4, outside the optical receiver 4, by the network controller 6, or by an external device (such as a personal computer or server).

[0019] Figure 2 shows an example configuration of the optical transmitter in this embodiment. As shown in Figure 2, the optical transmitter 2 includes, for example, a transmission digital signal processing unit 21 and an optical front end 22. The transmission digital signal processing unit 21 includes, for example, a pseudo-random bit sequence generation unit 211, a symbol mapping unit 212, a waveform shaping unit 213, a digital-to-analog conversion unit 214, and a signal pattern generation unit 215. The transmission digital signal processing unit 21 may also include a storage unit, or a storage unit may be connected to it.

[0020] The pseudo-random bit sequence generation unit 211 generates, for example, a pseudo-random number transmission bit sequence and outputs the generated pseudo-random number transmission bit sequence to the symbol mapping unit 212.

[0021] The symbol mapping unit 212 encodes the transmission bit sequence output by the pseudo-random bit sequence generation unit 211 to generate a transmission signal. The symbol mapping unit 212 maps the generated transmission signal to symbols.

[0022] The waveform shaping unit 213 shapes the spectrum (waveform) of the transmitted signal by sampling the symbol-mapped transmitted signal.

[0023] The digital-to-analog conversion unit 214 converts the digital signal transmission signal output by the waveform shaping unit 213 into an analog signal, and outputs the converted analog signal transmission signal to the optical front end 22.

[0024] The signal pattern generation unit 215 generates a random signal pattern different from the previous one (before modification), and inserts the generated random signal pattern after one of the pseudo-random bit sequence generation unit 211, the symbol mapping unit 212, and the waveform shaping unit 213. If the generated random signal pattern is inserted after the pseudo-random bit sequence generation unit 211, the signal pattern generation unit 215 inserts a bit sequence different from the previous one. If the generated random signal pattern is inserted after the symbol mapping, the signal pattern generation unit 215 inserts a symbol sequence different from the previous one. If the generated random signal pattern is inserted after the waveform shaping unit 213, the signal pattern generation unit 215 inserts a signal sample sequence different from the previous one.

[0025] The signal pattern to be inserted can be any signal pattern, as long as it yields DLM results and is different from any signal pattern already used. For example, when inserting a sequence of symbols, it could be a sequence of symbols composed of QPSK (Quadrature Phase Shift Keying), 16QAM, or a stochastically shaped QAM (Quadrature Amplitude Modulation), or it could be a sequence of symbols following a simple Gaussian distribution.

[0026] The signal pattern generation unit 215 may be located inside or outside the transmitted digital signal processing unit 21. The signal pattern generation unit 215 may also be provided by, for example, the network controller 6.

[0027] The optical front-end 22 converts the analog transmission signal output by the digital-to-analog conversion unit 214 from an electrical signal to an optical signal, and transmits the converted optical transmission signal via the optical transmission path 3. For example, the optical front-end 22 includes, for example, an amplifier and an optical modulator. The amplifier amplifies the transmission signal output by the digital-to-analog conversion unit 214, and the amplified transmission signal drives the optical modulator. The optical modulator generates an optical signal by converting the analog transmission signal into an optical signal.

[0028] All or part of the functions of the Transmit Digital Signal Processing Unit 21 are configured using a processor such as a CPU (Central Processing Unit) and memory. The Transmit Digital Signal Processing Unit 21 functions as part of the pseudo-random bit sequence generation unit 211, the symbol mapping unit 212, and the waveform shaping unit 213 when the processor executes a program. Note that all or part of the functions of the Transmit Digital Signal Processing Unit 21 may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The above program may be recorded on a computer-readable recording medium. Computer-readable recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and semiconductor memory devices (e.g., SSDs: Solid State Drives), as well as storage devices such as hard disks and semiconductor memory devices built into computer systems. The above program may be transmitted via a telecommunications line.

[0029] Figure 3 is a schematic diagram of an example hardware configuration of a transmission digital signal processing unit applied to this embodiment. The transmission digital signal processing unit 21 includes a processor 201, a main memory 202, a communication interface 203, an auxiliary storage device 204, an input / output interface 205, and an internal bus 206. The processor 201, the main memory 202, the communication interface 203, the auxiliary storage device 204, and the input / output interface 205 are connected to each other via the internal bus 206 so as to be able to communicate with each other. Furthermore, the storage unit included in or connected to the transmission digital signal processing unit 21 may be configured using the main memory 202 or the auxiliary storage device 204. Alternatively, the transmission digital signal processing unit 21 may be configured using the processor 201 and the main memory 202.

[0030] Next, we will explain the averaging of DLM estimation results using the same signal pattern in the conventional technology and the averaging of DLM estimation results between different signal patterns using the method of this embodiment. Figure 4 shows an example of averaging using the same signal pattern in the conventional technology and an example of averaging using different signal patterns using the method of this embodiment.

[0031] The graph labeled g100 shows an example of signal pattern averaging in the conventional technology. The horizontal axis represents distance (km), and the vertical axis represents optical power (dBm). Line g101 shows the distribution average of optical power using only the same signal pattern (patterns 1 to 24). Line g102 shows the optical power average after convergence (average of 25 power distributions).

[0032] The graph labeled g200 shows an example of averaging between different signal patterns using the method of this embodiment. The horizontal axis represents distance (km), and the vertical axis represents optical power (dBm). The dashed line g201 shows the results measured by the measuring instrument. Line g202 shows an example of the average distribution of optical power averaged using only one pattern. Line g203 shows an example of the distribution of optical power averaged using multiple patterns (13 patterns) of different signal patterns.

[0033] As shown in the graph of code g100, the conventional technique has limitations in reducing distortion through simple averaging using the same signal pattern. On the other hand, as shown in the graph of code g200, according to this embodiment, accuracy is improved by averaging across different signal patterns.

[0034] Although Figure 4 illustrates an example of estimating the distribution of optical power, the optical transmission path characteristic estimation unit 5 is not limited to this. As described above, the optical transmission path characteristic estimation unit 5 may also perform tasks such as estimating the distribution of optical power in the longitudinal direction of the optical fiber, estimating the gain spectrum of the optical amplifier, and estimating the response of individual optical filters.

[0035] Next, an example of the processing procedure performed by the optical transmission system 1 will be described. Figure 5 is a flowchart of the processing procedure performed by the optical transmission system in this embodiment.

[0036] (Step S1) The optical transmitter 2 generates an optical transmission signal to be transmitted by changing the signal pattern in response to a signal pattern change notification from the network controller 6. As described above, the functional units in the transmission digital signal processing unit 21 in which the optical transmitter 2 changes the signal pattern are arbitrary.

[0037] (Step S2) The optical transmitter 2 transmits the generated optical transmission signal to the optical receiver 4 via the optical transmission path 3.

[0038] (Step S3) The optical receiver 4 receives the optical transmission signal transmitted by the optical transmitter 2.

[0039] (Step S4) The optical transmission path characteristic estimation unit 5 performs DLM on the optical signal output from the optical receiver 4 to estimate, for example, the physical characteristics in the longitudinal direction of the optical fiber.

[0040] (Step S5) The optical transmission path characteristic estimation unit 5 stores the estimated result in the storage unit 51. The processing in steps S1 to S5 is repeated a predetermined number of times for multiple signal patterns.

[0041] (Step S6) The optical transmission path characteristic estimation unit 5 averages the results of multiple DLMs obtained using different patterns.

[0042] Note that the timing for averaging is arbitrary. The timing for averaging may be to wait until all the results of multiple times are obtained and then perform averaging, or it may be to perform averaging each time a result is obtained.

[0043] Also, in the process of step S6, the optical transmission path characteristic estimation unit 5 may average the final result (such as power distribution) of the DLM, or may average the intermediate result (such as matrix or vector) of the DLM process.

[0044] Next, a processing procedure example performed by the transmission digital signal processing unit 21 of the optical transmitter 2 will be described. FIG. 6 is a flowchart of the processing procedure performed by the transmission digital signal processing unit of the present embodiment. Note that the processing example in FIG, 6 is a processing procedure when the signal pattern generation unit 215 inserts the generated random signal pattern after the pseudo-random bit sequence generation unit 211.

[0045] (Step S11) The signal pattern generation unit 215 acquires a signal pattern change notification output by the network controller 6.

[0046] (Step S12) The signal pattern generation unit 215 generates a random signal pattern different from the previous time according to the acquired signal pattern change notification.

[0047] (Step S13) The signal pattern generation unit 215 inserts the generated random signal pattern (bit sequence) different from the previous time after the pseudo-random bit sequence generation unit 211 generates the transmission bit sequence of the pseudo-random number.

[0048] (Step S14) The symbol mapping unit 212 encodes the transmission bit sequence output by the pseudo-random bit sequence generation unit 211 to generate a transmission signal, and maps the generated transmission signal to a symbol.

[0049] (Step S15) The waveform shaping unit 213 shapes the spectrum (waveform) of the transmission signal by sampling the symbol-mapped transmission signal.

[0050] (Step S16), the digital-to-analog conversion unit 214 converts the transmission signal of the digital signal output by the waveform shaping unit 213 into an analog signal.

[0051] (Step S17) The optical front end 22 converts the analog signal output by the digital-to-analog conversion unit 214 from an electrical signal to an optical signal, and transmits the converted optical transmission signal via the optical transmission path 3.

[0052] As described above, in this embodiment, the DLM results obtained using multiple random transmission signal patterns are averaged. As a result, according to this embodiment, the accuracy of the DLM estimation results is improved.

[0053] <Other Embodiments> In the above-described example, the signal pattern generation unit 215 of the transmitting digital signal processing unit 21 inserts a random signal pattern different from the previous one, generated in response to a signal pattern change notification. However, the embodiment is not limited to this. In this embodiment, an example is described in which the transmitting digital signal processing unit gives a waveform change instruction in response to a signal pattern change notification.

[0054] Figure 7 shows an example of the configuration of an optical transmitter in another embodiment. As shown in Figure 7, the optical transmitter 2A includes, for example, a transmission digital signal processing unit 21A and an optical front end 22. The transmission digital signal processing unit 21A includes, for example, a pseudo-random bit sequence generation unit 211A, a symbol mapping unit 212A, a waveform shaping unit 213A, a digital-to-analog conversion unit 214, and a signal pattern change instruction unit 216.

[0055] The signal pattern change instruction unit 216 outputs a waveform change instruction to at least one of the pseudo-random bit sequence generation unit 211A, the symbol mapping unit 212, and the waveform shaping unit 213A. The signal pattern change instruction unit 216 outputs a seed or a seed change instruction for generating pseudo-random bit sequences to the pseudo-random bit sequence generation unit 211A. The seed is the initial bit sequence. The signal pattern change instruction unit 216 outputs a change instruction for the mapping method of the bit sequence output by the pseudo-random bit sequence generation unit 211 to the symbol mapping unit 212A. The signal pattern change instruction unit 216 outputs a change instruction for the waveform shaping method to the waveform shaping unit 213A.

[0056] When the pseudo-random bit sequence generation unit 211A receives a change instruction, it changes the signal pattern by changing the generation seed of the pseudo-random bit sequence according to the change instruction.

[0057] When the symbol mapping unit 212A receives a change instruction, it changes the signal pattern by changing the bit sequence mapping method according to the change instruction.

[0058] When the waveform shaping unit 213A receives a change instruction, it modifies the signal pattern according to the instruction, for example, by a process that pre-applies wavelength dispersion.

[0059] Next, an example of the processing procedure performed by the transmitting digital signal processing unit 21A of the optical transmitter 2 will be described. Figure 8 is a flowchart of the processing procedure performed by the transmitting digital signal processing unit of another embodiment. Note that the processing example in Figure 8 is the processing procedure when the signal pattern change instruction unit 216 outputs a change instruction to the symbol mapping unit 212A.

[0060] (Step S21) The signal pattern change instruction unit 216 acquires the signal pattern change notification output by the network controller 6.

[0061] (Step S22) The signal pattern change instruction unit 216 outputs an instruction to the symbol mapping unit 212A to change the mapping method of the bit sequence output by the pseudo-random bit sequence generation unit 211A, in response to the acquired signal pattern change notification.

[0062] (Step S23) The pseudo-random bit sequence generation unit 211A generates a pseudo-random bit sequence for transmission.

[0063] (Step S24) The symbol mapping unit 212A changes the bit sequence mapping method in response to the change instruction.

[0064] (Step S25) The symbol mapping unit 212A encodes the transmission bit sequence output by the pseudo-random bit sequence generation unit 211A to generate a transmission signal, and maps the generated transmission signal to symbols using a modified mapping method.

[0065] (Step S26) The waveform shaping unit 213A shapes the spectrum (waveform) of the transmitted signal by sampling the symbol-mapped transmitted signal.

[0066] (Step S17) The digital-to-analog conversion unit 214 converts the digital signal output by the waveform shaping unit 213A into an analog signal.

[0067] (Step S28) The optical front end 22 converts the analog signal output by the digital-to-analog conversion unit 214 from an electrical signal to an optical signal, and transmits the converted optical transmission signal via the optical transmission path 3.

[0068] In other embodiments, the signal pattern is modified in each functional block within the transmitted digital signal processing unit 21A. In other embodiments, the optical transfer characteristics are estimated for the transmitted signal of the modified signal pattern, thereby averaging the DLM results obtained using multiple different transmitted signal patterns. As a result, according to other embodiments, the accuracy of the DLM estimation results is improved.

[0069] (Modification) In the above example, for example, all or some of the functions of the optical transmission path characteristic estimation unit 5 and the network controller 6 may be provided by, for example, an optical receiver. Figure 9 is a diagram showing an example of the configuration of an optical transmission system when the optical receiver is equipped with the functions of the optical transmission path characteristic estimation unit and the network controller. As shown in Figure 9, the optical receiver 4A may be equipped with all or some of the functions of the optical transmission path characteristic estimation unit 5 and the network controller 6. The receiving unit 41 is the functional unit of the optical receiver 4 in Figure 1. In such a configuration, the optical receiver 4A may, after receiving the transmission signal, perform optical transmission path characteristic estimation processing and further output a signal pattern change notification to the optical transmitter 2.

[0070] Figure 10 shows an example configuration when a signal pattern generation unit or a signal pattern change instruction unit is connected to the outside of the optical transmitter. In the configuration example of Figure 10, the optical transmission system 1B includes, for example, an optical transmitter 2B, an optical transmission path 3, an optical receiver 4, an optical transmission path characteristic estimation unit 5, a network controller 6, and a signal pattern change unit 7. The optical transmitter 2B includes, for example, a transmission digital signal processing unit 21B and an optical front end 22. The transmission digital signal processing unit 21B includes, for example, a pseudo-random bit sequence generation unit 211 (or 211A), a symbol mapping unit 212 (or 212A), a waveform shaping unit 213 (or 213A), and a digital-to-analog conversion unit 214 (or 214A).

[0071] The signal pattern modification unit 7 is either the signal pattern generation unit 215 or the signal pattern modification instruction unit 216 described above. When the signal pattern modification unit 7 receives a signal pattern modification instruction from the network controller 6, it inserts a different signal pattern before and after each block in the transmitted digital signal processing unit 21B, or modifies the signal pattern in each functional block within the transmitted digital signal processing unit 21B.

[0072] When the signal pattern modification unit 7 is a signal pattern generation unit 215, the transmitted digital signal processing unit 21B includes a pseudo-random bit sequence generation unit 211, a symbol mapping unit 212, a waveform shaping unit 213, and a digital-to-analog conversion unit 214. When the signal pattern modification unit 7 is a signal pattern modification instruction unit 216, the transmitted digital signal processing unit 21B includes, for example, a pseudo-random bit sequence generation unit 211A, a symbol mapping unit 212A, a waveform shaping unit 213A, and a digital-to-analog conversion unit 214A.

[0073] Furthermore, the network controller 6 may also include the function of the signal pattern modification unit 7. In addition, even in the configuration of Figure 10, as explained using Figure 9, the optical receiver 4 may include all or some of the functions of the optical transmission path characteristic estimation unit 5 and the network controller 6.

[0074] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0075] The present invention is applicable to optical transmission systems, optical communication systems, optical transmitting devices, optical communication devices, and the like.

[0076] 1...Optical transmission system, 2...Optical transmitter, 3...Optical transmission path, 4...Optical receiver, 5...Optical transmission path characteristic estimation unit, 6...Network controller, 21, 21A...Transmit digital signal processing unit, 22...Optical front end, 51...Storage unit, 211, 211A...Pseudo-random bit sequence generation unit, 212, 212A...Symbol mapping unit, 213, 213A...Waveform shaping unit, 214...Digital-to-analog conversion unit, 215...Signal pattern generation unit, 216...Signal pattern change instruction unit, 201...Processor, 202...Main memory, 203...Communication interface, 204...Auxiliary memory, 205...Input / output interface, 206...Internal bus

Claims

1. An optical transmitter comprising a transmission digital signal processing unit that performs digital processing on a transmission signal, wherein the transmission digital signal processing unit changes the signal pattern multiple times to a different signal pattern from the original, and transmits each of the multiple changed signal patterns as an optical transmission signal.

2. The optical transmitter according to claim 1, wherein the transmitting digital signal processing unit changes the signal to a different signal pattern from the one before the change by inserting a different signal pattern into the signal during processing.

3. The optical transmitter according to claim 1, wherein the transmitting digital signal processing unit changes the signal during processing to a different waveform from the original, thereby changing the signal pattern to one different from the original.

4. The optical transmitter according to claim 2, wherein the transmitting digital signal processing unit changes the signal pattern to one different from the original by inserting one of the following into the signal during processing: a bit sequence different from the original, a symbol sequence different from the original, and a signal sample sequence different from the original.

5. The optical transmitter according to claim 1 or claim 2, wherein the optical transmitter generates a signal pattern different from the original signal pattern by inserting a bit sequence different from the original into the output of the pseudo-random bit sequence generation unit, inserting a symbol sequence different from the original into the output of the symbol mapping unit, and inserting a signal sample sequence different from the original into the output of the waveform shaping unit.

6. The optical transmitter according to claim 1 or claim 3, wherein the transmitting digital signal processing unit comprises: a pseudo-random bit sequence generation unit that generates a pseudo-random number transmission bit sequence; a symbol mapping unit that encodes the transmission bit sequence output by the pseudo-random number bit sequence generation unit to generate a transmission signal and maps the encoded transmission signal to symbols; a waveform shaping unit that shapes the spectrum of the transmission signal mapped to symbols by sampling the transmission signal mapped to the symbols; and the optical transmitter modifies the waveform by performing at least one of the following: changing the pseudo-random number bit sequence generation sheet in the pseudo-random number bit sequence generation unit, changing the mapping method in the symbol mapping unit, and changing the waveform shaping method in the waveform shaping unit.

7. An optical transmission system comprising: an optical transmitter that changes to a signal pattern different from the original multiple times and transmits each of the multiple changed signal patterns as an optical signal; an optical transmission path that connects the optical transmitter and an optical receiver and includes an amplifier; an optical receiver that receives the optical signals of the multiple signal patterns transmitted by the optical transmitter; and an optical transmission path characteristic estimation unit that estimates the physical characteristics of the optical transmission path by averaging the physical characteristics of the optical transmission path with respect to the optical signals of the multiple signal patterns received by the optical receiver.

8. An optical transmission method in which an optical transmission unit changes the signal pattern multiple times to a different signal pattern than the one before the change, and transmits each of the multiple changed signal patterns as an optical transmission signal.

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