Control device, optical transmission system, and control method

Abstract

The present invention provides a control device capable of controlling the signal quality to a desired level. [Solution] The control device controls an optical transmission system comprising: a plurality of transmitters each transmitting a plurality of optical signals; a plurality of transmission paths each transmitting the plurality of transmitted optical signals; a multiplexing unit that combines the transmitted plurality of optical signals; an adjustment unit that adjusts the combined optical signals to a certain optical power; and a receiver that receives the adjusted optical signals as a plurality of electrical signals corresponding to the plurality of optical signals, and further comprises: an acquisition unit that acquires information on a plurality of losses in each of the plurality of transmission paths; and a control unit that, based on the acquired information on the plurality of losses, controls the power of each of the plurality of optical signals before inputting them to each of the plurality of transmission paths so that the signal quality of each of the plurality of electrical signals becomes a desired quality.

Description

[Technical Field]

[0001] The present invention relates to a control device, an optical transmission system, and a control method. [Background technology]

[0002] Optical transmission systems that perform one-point to multi-point optical transmission and reception using optical subcarrier multiplexing technology are known (e.g., Non-Patent Document 1). Methods are known for controlling the modulation level and error correction code conditions for each distance when the distance between the transceiver and the aggregater is different (e.g., Non-Patent Document 2). Methods are known for controlling optical power to compensate for loss differences between optical transceivers (e.g., Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-178376 [Non-patent literature]

[0004] [Non-Patent Document 1] D. Welch et al., "Point-to-Multipoint Optical Networks Using Coherent Digital Subcarriers," IEEE / OSA Journal of Lightwave Technology, vol. 39, no. 16, pp. 5232-5247, 2021. [Non-Patent Document 2] R. Borkowski et al., "FLCS-PON-An Opportunistic 100 Gbit / s Flexible PON Prototype with Probabilistic Shaping and Soft-Input FEC: Operator Trial and ODN Case Studies," Journal of Optical Communications and Networking, vol. 14, no. 6, pp. C82-C91, 2022. [Overview of the project] [Problems that the invention aims to solve]

[0005] In optical transmission systems that combine multiple optical signals transmitted from multiple transmitters and receive the resulting multiplexed optical signal collectively, or in optical transmission systems that separate multiplexed optical signals so that multiple receivers receive each signal individually, there may be constraints that keep the optical power of the multiplexed optical signal constant. In this case, if the optical power of one optical signal in the multiple optical signals is attenuated, the power of another optical signal increases. This makes it difficult to control the signal quality, such as the bit error rate (BER), of the multiple optical signals to the desired quality (e.g., the same quality).

[0006] This disclosure aims to provide a control device, an optical transmission system, and an optical transmission system that can be controlled to a desired signal quality. [Means for solving the problem]

[0007] Embodiments of the present disclosure are control devices for controlling an optical transmission system comprising: a plurality of transmitters each transmitting a plurality of optical signals; a plurality of transmission paths each transmitting the plurality of transmitted optical signals; a multiplexing unit for combining the transmitted plurality of optical signals; an adjustment unit for adjusting the combined optical signals to a constant optical power; and a receiver for receiving the adjusted optical signals as a plurality of electrical signals corresponding to the plurality of optical signals, the control device comprising: an acquisition unit for acquiring information on a plurality of losses in each of the plurality of transmission paths; and a control unit that, based on the acquired information on the plurality of losses, controls the power of each of the plurality of optical signals before inputting them to each of the plurality of transmission paths so that the signal quality of each of the plurality of electrical signals becomes a desired quality.

[0008] Embodiments of the present disclosure are control devices for controlling an optical transmission system comprising: a transmitter that transmits an optical signal obtained by synthesizing a plurality of electrical signals; an adjustment unit that adjusts the transmitted optical signal to a constant optical power; a demultiplexing unit that demultiplexes the adjusted optical signal into a plurality of optical signals corresponding to the plurality of electrical signals; a plurality of transmission paths that transmit the demultiplexed plurality of optical signals; and a plurality of receivers that receive the transmitted plurality of optical signals, the control device comprising: an acquisition unit that acquires information on a plurality of losses in each of the plurality of transmission paths; and a control unit that, based on the acquired information on a plurality of losses, controls the power of a plurality of signals corresponding to the plurality of electrical signals in the transmitter so that the signal quality in each of the plurality of receivers becomes a desired quality.

[0009] Embodiments of this disclosure are optical transmission systems comprising the plurality of transmitters, the plurality of transmission lines, the multiplexing unit, the adjustment unit, the receiver, and the control device.

[0010] An embodiment of the present disclosure is an optical transmission system comprising the transmitter, the adjustment unit, the demultiplexer, the plurality of transmission lines, the plurality of receivers, and the control device.

[0011] Embodiments of the present disclosure are control methods for controlling an optical transmission system comprising: a plurality of transmitters each transmitting a plurality of optical signals; a plurality of transmission paths each transmitting the transmitted plurality of optical signals; a multiplexing unit for combining the transmitted plurality of optical signals; an adjustment unit for adjusting the combined optical signals to a constant optical power; and a receiver for receiving the adjusted optical signals as a plurality of electrical signals corresponding to the plurality of optical signals, the control method comprising: acquiring information on a plurality of losses in each of the plurality of transmission paths; and, based on the acquired information on the plurality of losses, controlling the respective powers of the plurality of optical signals before inputting them to each of the plurality of transmission paths so that the respective signal quality of the plurality of electrical signals is of a desired quality.

[0012] Embodiments of the present disclosure are control methods for controlling an optical transmission system comprising: a transmitter that transmits an optical signal obtained by synthesizing a plurality of electrical signals; an adjustment unit that adjusts the transmitted optical signal to a constant optical power; a demultiplexing unit that demultiplexes the adjusted optical signal into a plurality of optical signals corresponding to the plurality of electrical signals; a plurality of transmission paths that transmit the demultiplexed plurality of optical signals; and a plurality of receivers that receive the transmitted plurality of optical signals, the control method comprising: acquiring information on a plurality of losses in each of the plurality of transmission paths; and, based on the acquired information on the plurality of losses, controlling the power of each of the plurality of signals corresponding to the plurality of electrical signals in the transmitter so that the signal quality in each of the plurality of receivers becomes a desired quality. [Effects of the Invention]

[0013] According to the disclosed technology, the desired signal quality can be controlled. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a block diagram of the optical transmission system according to the first embodiment. [Figure 2]Figure 2 is a block diagram of the transmitter in the first embodiment. [Figure 3] Figure 3 is a block diagram of the receiver in the first embodiment. [Figure 4] Figure 4 is a block diagram showing a hypothetical example of the first embodiment. [Figure 5] Figure 5 is a block diagram showing a hypothetical example of a comparative form. [Figure 6] Figure 6 shows the bit error rate BER (Bit Error Rate) against the unadjusted transmitted optical power PT in a hypothetical example of the comparison configuration. [Figure 7] Figure 7 shows the bit error rate BER (Bit Error Rate) against the adjusted transmitted optical power PT in a hypothetical example of the comparison configuration. [Figure 8] Figure 8 shows the bit error rate BER (Between Bit Error Rate and Bit Error Rate) before and after adjustment with respect to the received optical power Pr in a hypothetical example of the first embodiment. [Figure 9] Figures 9(A) and 9(B) show the light intensity as a function of wavelength in hypothetical comparative configurations. [Figure 10] Figures 10(A) and 10(B) show the light intensity as a function of wavelength in a hypothetical example of the first embodiment. [Figure 11] Figure 11 shows the bit error rate BER as a function of received optical power Pr in a hypothetical example of the first embodiment. [Figure 12] Figure 12 shows the receiving sensitivity for αQPSK and αBPSK in a hypothetical example of the first embodiment. [Figure 13] Figure 13 shows the received sensitivity for αQPSK and αBPSK when the transmission loss of QPSK, BPSK, and OOK is 0 dB in a hypothetical example. [Figure 14] Figure 14 shows the receiving sensitivity for αQPSK and αBPSK in a hypothetical example where the transmission loss of QPSK and BPSK is 0 dB and the transmission loss of OOK is -3 dB. [Figure 15] Figure 15 is a functional block diagram of the control device in the first embodiment. [Figure 16]Figure 16 is a flowchart showing the processing of the control device in the first embodiment. [Figure 17] Figure 17 is a flowchart showing another example of the processing of the control device in the first embodiment. [Figure 18] Figure 18 shows the bit error rate BER as a function of received optical power Pr in a hypothetical example of Modification 1 of the first embodiment. [Figure 19] Figure 19 shows the bit error rate BER as a function of received optical power Pr in a hypothetical example of Modification 1 of the first embodiment. [Figure 20] Figure 20 shows the bit error rate BER as a function of received optical power Pr in a hypothetical example of Modification 1 of the first embodiment. [Figure 21] Figure 21 is a flowchart showing the processing of the acquisition unit in a modified example 1 of the first embodiment. [Figure 22] Figure 22 is a block diagram showing the optical transmission system according to the second embodiment. [Figure 23] Figure 23 is a block diagram showing the optical transmission system according to the third embodiment. [Figure 24] Figure 24 is a block diagram of the transmitter in the third embodiment. [Figure 25] Figure 25 is a block diagram showing the optical transmission system according to the fourth embodiment. [Modes for carrying out the invention]

[0015] The embodiments for implementing this disclosure will be described in detail below with reference to the drawings. The embodiments described below are examples for realizing the technical concept of the invention and do not limit this disclosure to the configurations and numerical values ​​described. In each drawing, the same components are denoted by the same reference numerals, and redundant explanations may be omitted as appropriate.

[0016] In the following embodiments, the signal quality of multiple optical signals is set to a desired quality (e.g., the same quality) by controlling the power, modulation bandwidth, and / or modulation scheme of multiple optical signals based on the transmission path loss between multiple transmitters and multiplexers, or the transmission path loss between multiple receivers and demultiplexers.

[0017] (First Embodiment) The first embodiment is an example in which optical signals transmitted from multiple transmitters are combined, the optical power of the combined optical signals is adjusted to a constant level, and then they are converted into an electrical signal all at once. Figure 1 is a block diagram of the optical transmission system according to the first embodiment. As shown in Figure 1, the optical transmission system 100 according to the first embodiment includes multiple paths PA1~PAi~PAn, a multiplexing unit 13A, a transmission line 14A, an adjustment unit 15A, a receiver 16A, and a control device 20A. The number of paths PA1~PAi~PAn is n (where n is an integer of 2 or more), and i is an integer between 1 and n.

[0018] Each path PA1~PAi~PAn comprises transmitters 10A1~10Ai~10An, adjustment units 11A1~11Ai~11An, and transmission lines 12A1~12Ai~12An. The multiple transmitters 10A1~10Ai~10An each convert electrical signals Et1~Eti~Etn into optical signals O1A1~O1Ai~O1An, and each transmits the converted optical signals O1A1~O1Ai~O1An. The wavelengths of the optical signals O1A1~O1Ai~O1An are different from each other, and each may be a single-carrier signal or a group of subcarriers. Furthermore, the modulation schemes of the optical signals O1A1~O1Ai~O1An may be the same or different. The modulation scheme for optical signals O1A1~O1Ai~O1An is, for example, M-phase PSK (Phase Shift Keying), M-phase PAM (Pulse Amplitude Modulation), or M-phase QAM (Quadrature Amplitude Modulation). M is generally a power of 2 greater than or equal to 2. BPSK (Binary PSK) is PSK with M=2, and QPSK (Quadrature PSK) is PSK with M=4. OOK (On Off Keying) is PAM with M=2.

[0019] The multiple adjustment units 11A1~11Ai~11An are, for example, variable optical attenuators, and based on the signal output by the control device 20A, they adjust the optical power of the multiple optical signals O1A1~O1Ai~O1An and output the adjusted optical signals O2A1~O2Ai~O2An, respectively. The adjustment units 11A1~11Ai~11An may be provided within the transmitters 10A1~10Ai~10An.

[0020] Multiple transmission lines 12A1~12Ai~12An are, for example, optical fibers, which transmit optical signals O2A1~O2Ai~O2An and output them as optical signals O3A1~O3Ai~O3An. The length of the transmission lines 12A1~12Ai~12An varies depending on the distance between the transmitters 10A1~10Ai~10An and the multiplexer 13A.

[0021] The multiplexer 13A is, for example, an optical splitter / coupler, an array-type optical waveguide, or an optical wavelength selector switch, which combines the optical signals O3A1, O3Ai, and O3An on the frequency axis and outputs the combined optical signal O4A. The optical signal O4A is, for example, a frequency multiplexed signal.

[0022] The transmission path 14A is, for example, an optical fiber, which transmits the optical signal O4A and outputs the transmitted optical signal O5A.

[0023] The adjustment unit 15A is, for example, a variable optical attenuator, which adjusts the combined optical signal O4A to a constant optical power and outputs the adjusted optical signal O6A. The adjustment unit 15A keeps the overall optical power of the optical signal O5A constant for collective reception, and does not individually adjust the optical power of the optical signals corresponding to paths PA1 to PAn.

[0024] Receiver 16A receives the optical signal O6A as multiple electrical signals Er1, Eri, and Ern corresponding to multiple optical signals O1A1, O1Ai, and O1An, and outputs the received electrical signals Er1, Eri, and Ern.

[0025] The control device 20A acquires information from the transmitters 10A1 to 10An, the adjustment units 11A1 to 11An and 15A, and the receiver 16A, and controls the transmitters 10A1 to 10An, the adjustment units 11A1 to 11An and 15A, and the receiver 16A.

[0026] A transmitter control unit for controlling transmitters 10A1 to 10An, a transmission line control unit for controlling transmission lines 12A1 to 12An, and a receiver control unit for controlling receiver 16A may be provided. In this case, the control device 20A controls transmitters 10A1 to 10An via the transmitter control unit. The control device 20A controls receiver 16A via the receiver control unit. The control device 20A controls adjustment units 11A1 to 11An via the transmitter control unit or the transmission line control unit, and controls adjustment unit 15A via the receiver control unit or the transmission line control unit.

[0027] Figure 2 is a block diagram of the transmitter in the first embodiment. Transmitters 10A1~10Ai~10An will be explained using transmitter 10Ai as an example. The configurations of the other transmitters 10A1~10An are the same as transmitter 10Ai and will not be explained.

[0028] As shown in Figure 2, the transmitter 10Ai comprises an electrical signal generation unit 26A, a light source 27A, and an optical modulator 28A. The electrical signal generation unit 26A generates an electrical signal E7A having a predetermined power, modulation scheme, and modulation bandwidth from the electrical signal Eti to be transmitted. The electrical signal Eti is a digital signal in the form of a bit sequence, and the electrical signal E7A is an analog signal. The electrical signal generation unit 26A includes a circuit formed by, for example, an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) and a digital-to-analog converter. The electrical signal generation unit 26A may adjust the optical power of the optical signal O2Ai in addition to, or instead of, the adjustment unit 11Ai by amplifying or attenuating the generated electrical signal.

[0029] The light source 27A is, for example, a semiconductor laser element, and outputs laser light LO1 having a predetermined wavelength. The optical modulator 28A modulates the laser light LO1 using an electrical signal E7A. This generates an optical signal O1Ai having a predetermined modulation scheme and modulation bandwidth.

[0030] Figure 3 is a block diagram of the receiver in the first embodiment. As shown in Figure 3, the receiver 16A includes a power detection unit 21A, a local oscillator light source 22A, a photoelectric conversion unit 23A, a separation unit 24A, and demodulation units 25A1 to 25Ai to 25An.

[0031] The power detection unit 21A detects the optical power of the optical signal O6A and outputs it to the control device 20A. The local oscillator light source 22A is, for example, a semiconductor laser element and outputs laser light LO2 having a predetermined wavelength. The photoelectric conversion unit 23A uses the laser light LO2 to convert the optical signal O6A into an electrical signal E1A and outputs the electrical signal E1A.

[0032] The separation unit 24A separates the electrical signal E1A into electrical signals E2A1, E2Ai, and E2An, corresponding to the optical signals O1A1, O1Ai, and O1An, on the frequency axis, and outputs the electrical signals E2A1, E2Ai, and E2An. The electrical signal E2Ai is an analog or digital signal modulated using the same modulation scheme as the electrical signal E7A generated in the electrical signal generation unit 26A of the transmitter 10Ai.

[0033] The demodulation units 25A1, 25Ai, and 25An demodulate the electrical signals E2A1, E2Ai, and E2An and output the demodulated electrical signals Er1, Eri, and Ern, respectively. The electrical signals Er1, Eri, and Ern are digital signals in the form of bit sequences. The demodulation units 25A1, 25Ai, and 25An may also output information regarding signal quality to the control device 20A.

[0034] (Hypothetical example) (Block diagram of a hypothetical example of the first embodiment) To explain the principle of the first embodiment, a hypothetical example of the first embodiment and a comparative embodiment will be described. Figure 4 is a block diagram of a hypothetical example of the first embodiment. As shown in Figure 4, the optical transmission system 100A in the hypothetical example of the first embodiment has three paths PA1 to PA3. Transmitter 10A1 performs QPSK modulation on the digital electrical signal Et1 and outputs the optical signal O1A1. Transmitter 10A2 performs BPSK modulation on the digital electrical signal Et2 and outputs the optical signal O1A2. Transmitter 10A3 performs OOK modulation on the digital signal Et3 and outputs the optical signal O1A3. The optical power of optical signals O1A1 to O1A3 is P T Let's assume that each P T We assume they are the same.

[0035] Adjustment units 11A1 to 11A3 are attenuators that attenuate optical signals O1A1 to O1A3, respectively, to output optical signals O2A1 to O2A3, respectively. Transmission line 12A1 is an optical fiber with a length L1 of approximately 0 km and is not shown. Transmission line 12A2 is an optical fiber with a length L2 of 20 km. Transmission line 12A3 is an optical fiber with a length L3 of 40 km.

[0036] The combined wave section 13A combines optical signals O3A1 to O3A3 and outputs optical signal O4A. The transmission line 14A is an optical fiber with a length L0 of 10 km. The adjustment section 15A is an attenuator that attenuates optical signal O5A and outputs optical signal O6A. The optical power of optical signal O6A is P r The receiver 16A processes the optical signal O6A and outputs electrical signals Er1 to Er3, which correspond to the optical signals O1A1 to O1A3, respectively.

[0037] The combined frequency unit 13A corresponds to a cluster station located in an urban area. In areas far from urban areas and with low traffic demand, such as mountainous regions, inexpensive OOK transmitters are placed. In areas with high traffic demand and close to the cluster station in urban areas, high-performance and efficient QPSK transmitters are placed. For this reason, the distances L1 to L3 of the transmission lines 12A1 to 12A3 are assumed to be 0 km, 20 km, and 40 km, respectively.

[0038] (Block diagram of a hypothetical example of a comparative configuration) Figure 5 is a block diagram showing a hypothetical example of a comparative configuration. As shown in Figure 5, the optical transmission system 110A in the hypothetical example of the comparative configuration does not have an adjustment unit 15A. The demultiplexer 17A demultiplexes the optical signal O6A transmitted through the transmission line 14A. The adjustment units 19A1 to 19A3 adjust the optical power of the demultiplexed optical signals O8A1 to O8A3 and output the adjusted optical signals O8A1 to O8A3 to the receivers 18A1 to 18A3. The receivers 18A1 to 18A3 perform photoelectric conversion on the optical signals O8A1 to O8A3, respectively, decode the QPSK signal, BPSK signal, and OOK signal, respectively, and output the bit-sequence digital electrical signals Er1 to Er3, respectively.

[0039] In the optical transmission system 100A of the first embodiment, the adjustment unit 15A adjusts the combined optical signal O5A to a constant optical power. The receiver 16A generates electrical signals Er1 to Er3 from the adjusted optical signal O6A. This is because, as shown in Figure 3, the receiver 16A is a so-called coherent receiver, which converts the optical signal O6A into electrical signals in one unit and separates the electrical signal E1A.

[0040] On the other hand, in the comparative optical transmission system 110A, the adjustment units 19A1 to 19A3 individually adjust the optical power of the optical signals O7A1 to O7A, which are obtained by demultiplexing the optical signal O5A.

[0041] (Calculation example in a hypothetical comparative example) First, in a hypothetical example of the comparison configuration, we consider adjusting the adjustment units 11A1 to 11A3 to make the signal quality of electrical signals Er1 to Er3 equivalent. BER is used as the signal quality.

[0042] BER of BPSK signal BPSK γ is represented by the number 1. Here, γ S This is the ratio of noise to signal, or the signal-to-noise ratio (S / N ratio).

[0043]

number

[0044] erfc(x) is the error complement function and is expressed in Mathematics 2.

number

[0045] Similarly, the BER of an M (M≧4) phase PSK signal M-PSK It can be expressed using the mathematical formula 3.

[0046]

number

[0047] From Math 3, the BER of the QPSK signal QPSK It can be represented by the number 4.

[0048]

number

[0049] OOK signal BEROOK It is represented by Equation (5).

[0050]

Equation

[0051] BER of M (M≧4)-phase PAM signal M-PAM It is represented by Equation (6).

[0052]

Equation

[0053] BER of M (M≧4)-phase QAM signal M-QAM It is represented by Equation (7).

[0054]

Equation

[0055] When shot noise is considered as noise, γ S =2R·P T / qB. Here, R is the conversion efficiency, q is the charge amount, and B is the modulation bandwidth. For QPSK and BPSK, Nyquist waveform shaping is assumed, and for OOK, NRZ (Non-Return-Zero) waveform shaping is assumed. Therefore, the modulation bandwidth 2B of OOK is assumed to be twice the modulation bandwidth B of QPSK and BPSK. The receivers 16A, 18A1 to 18A3 perform coherent reception, and the noise is mainly assumed to be shot noise. When the receivers 16A, etc. directly detect and include noise other than shot noise, the total amount of noise may be changed. The following Equations (8), (9), and (10) are derived from Equation (4), Equation (1), and Equation (5), respectively.

[0056]

Equation

[0057]

Equation

[0058]

number

[0059] The losses in transmission lines 12A2, 12A3, and 14A are L, respectively. SMF,20km , L SMF,40km and L SMF,10km Assuming this, the damping amounts of adjustment units 11A1 to 11A3 are α QPSK , α BPSK and α OOK Let's assume that numbers 8 through 10 can be represented by numbers 11 through 13, respectively.

[0060]

number

[0061]

number

[0062]

number

[0063] Using equations 11-13, assuming a conversion efficiency R of 0.14, a modulation bandwidth B of 10 GHz, and a transmission loss of 0.35 dB / km for the optical fiber, the transmitted optical power P T The bit error rate BER was calculated for α. First, without adjusting the adjustment units 11A1 to 11A3, QPSK , α BPSK and α OOK We assumed it to be 0 dB.

[0064] Figure 6 shows the unadjusted transmitted optical power P in a hypothetical example of the comparison configuration. T This figure shows the bit error rate BER for . The numbers in parentheses in the labels represent α. QPSK , α BPSK and α OOKThis shows that the dots are calculation points, and the curves are the lines connecting the dots. As shown in Figure 6, in OOK, the transmission loss is large, so P T The BER will not improve unless the value is increased. In QPSK, there is almost no transmission loss, so P T Even if the BER is small, it is good. In QPSK, BPSK, and OOK, the BER is the reference BER (e.g., 1 × 10⁻¹⁰). -3 P for ) T The difference is 17 dB between QPSK and OOK, and 13 dB between BPSK and OOK. Transmit optical power P to obtain the reference BER. T A large value indicates a poor BER, and P is needed to obtain the baseline BER. T A small value indicates a good BER.

[0065] Next, assuming that adjustments will be made to the adjustment sections 11A1 to 11A3, α QPSK , = -17dB, α BPSK = -13dB and α OOK It was assumed to be =0dB.

[0066] Figure 7 shows the adjusted transmitted optical power P in a hypothetical example of the comparison configuration. T This figure shows the bit error rate BER for α. As shown in Figure 7, QPSK If we set it to -17dB, then the adjustment unit 11A1 will be the optical power P T To attenuate the optical signal O1A1, QPSK's P T - The BER curve shifts 17 dB to the right. Similarly, the P of BPSK T - The BER curve shifts 13 dB to the right. As a result, the QPSK, BPSK, and OOK curves are nearly identical. This allows for nearly equivalent signal quality in QPSK, BPSK, and OOK.

[0067] In Figures 6 and 7, the horizontal axis represents the transmitted optical power P, for comparison with equations 11 to 13. T Assuming no loss in the transmission path, the transmitted optical power P T The received optical power P r It is the same as this.

[0068] (Calculation example in a hypothetical example of the first embodiment) (Description of the assignment) Next, in a hypothetical example of the first embodiment, we consider adjusting the adjustment units 11A1 to 11A3 to make the BER, which is the signal quality of the electrical signals Er1 to Er3, equal to each other. In the first embodiment, the receiver 16A processes all optical signals together as optical signal O6A. Therefore, the optical power P of the optical signal O6A input to the receiver 16A r It is represented by the number 14. α C This is the loss of the adjustment unit 15A, and α C The sign is negative in dB. When an optical amplifier is used as the adjustment unit 15A, α C The sign of is considered positive in dB. As mentioned above, the optical power of the optical signals O1A1 to O1A3 output by transmitters 10A1 to 10A3 is the same P. T This is an assumption.

[0069]

number

[0070] P r When a value is fixed, the BER values ​​corresponding to numbers 11-13 are expressed by numbers 15-17.

[0071]

number

[0072]

number

[0073]

number

[0074] In Math 15-17, C r It is represented by the number 18.

[0075]

number

[0076] In Math 15-17, each formula contains the C from Math 18. r This is introduced. Therefore, BER is 15 QPSK α BPSK and α OOK This has an effect. P r =α C ·C r And in numbers 15 to 17, P r and C r It is also possible to exclude P. r To keep α constant C This will change alpha C Changes include α BPSK and α OOK This also has an effect. For this reason, we used the expressions from numbers 15 to 17.

[0077] From equations 15 to 17, as in the hypothetical example of the comparison form, α corresponds to the BER difference in Figure 6. QPSK , α BPSK and α OOK Even if you set it, the BER will not be the same. For example, α QPSK and α BPSK We will now explain the cases where the values ​​are set to -5dB and -3dB.

[0078] Figure 8 shows the received optical power P before and after adjustment in a hypothetical example of the first embodiment. r This figure shows the bit error rate BER for α. As shown in Figure 8, before adjustment, α QPSK , α BPSK and α OOK It is 0 dB. After adjustment, α QPSK , α BPSK and α OOK These are set to -5dB, -3dB, and 0dB respectively. In QPSK, even if the optical signal is attenuated by -5dB, the reference BER (e.g., 1 × 10⁻¹⁰) -3 P in ) T This only degrades by 0.5dB. In BPSK, attenuating the optical signal by -3dB results in a decrease in P at the reference BER. TThis improves by 1.5 dB. In OOK, the optical signal is not attenuated, but the P in the reference BER is lower. T This improves by 3.5 dB. In this way, the received optical power P r To keep it constant, when adjustment units 11A1 and 11A2 attenuate the optical power in QPSK and BPSK, adjustment unit 15A increases the optical power. As a result, the optical power corresponding to OOK in the optical signal O6A increases. Therefore, in QPSK, BPSK and OOK, the P in the reference BER T Controlling the adjustment units 11A1 to 11A3 to make them equivalent, that is, to make the signal quality equivalent, is complex.

[0079] The above-mentioned problems of the first embodiment will be explained with reference to the figures. Figures 9(A) and 9(B) show the optical intensity against wavelength in a hypothetical example of a comparative configuration. Figure 9(A) shows the state before adjustment using adjustment units 11A1 to 11A3, and Figure 9(B) shows the state after adjustment using adjustment units 11A1 to 11A3. The horizontal axis represents the wavelength of the optical signal O6A. λ1, λ2, and λ3 are the center wavelengths of the QPSK signal, BPSK signal, and OKK signal in the optical signal O6A, respectively. The area of ​​the crosshatch corresponds to the optical power of the QPSK signal, BPSK signal, and OKK signal. The sum of the areas of the crosshatch corresponds to the total optical power of the optical signal O6A.

[0080] In Figure 9(A), the optical power of the QPSK and BPSK signals is reduced. Therefore, the optical power of optical signals O2A1 and O2A2 is reduced using adjustment units 11A1 and 11A2. As shown by arrow 50A in Figure 9(B), the optical power of the QPSK and BPSK signals in optical signal O6A decreases. As a result, as shown in Figure 7, the P in QPSK, BPSK, and OOK decreases. T - The BER curve can be made almost identical.

[0081] Figures 10(A) and 10(B) show the light intensity against wavelength in a hypothetical example of the first embodiment. Figure 10(A) shows the light intensity before adjustment using adjustment units 11A1 to 11A3, and Figure 10(B) shows the light intensity after adjustment using adjustment units 11A1 to 11A3.

[0082] In FIG. 10(A), similar to FIG. 9(A), reduce the optical power of the QPSK signal and the BPSK signal. As shown by arrow 50A in FIG. 10(B), the optical powers of the QPSK signal and the BPSK signal in the optical signal O6A decrease. At this time, in order to keep the total optical power P r constant, the adjustment unit 15A increases the optical power of the optical signal O6A. For this reason, as shown by arrow 50B, the optical power of the OOK signal increases. Thus,

[0083] In the assumed example of the first embodiment, because there is a premise that the total optical power P r is constant, other BPSK signals and OOK signals affect the BER QPSK , so the optimization of the BER QPSK , BER BPSK and BER OOK becomes complicated. Such a problem occurs not only when the BER QPSK , BER BPSK and BER OOK are equally controlled, but also when the BER QPSK , BER BPSK and BER OOK are controlled to desired values.

[0084] (Method for calculating α QPSK and α BPSK ) To solve the problems described from FIG. 9(A) to FIG. 10(B), a method for calculating the attenuation amounts α QPSK , α BPSK and α OOK of the adjustment units 11A1 to 11A3 for making the BER QPSK、 α BPSK and αOKK equal will be described.

[0085] In equations 15 to 17, consider making the BER QPSK , BER BPSK and BER OOK equal. For simplicity, hereinafter, it is assumed that α OKK = 1 (i.e., 0 dB). BER QPSK = BER OOKTo achieve this, the number 19 must be derived from the numbers 15 and 17.

[0086]

number

[0087] BER BPSK =BER OOK To achieve this, the number 20 must be derived from numbers 16 and 17.

[0088]

number

[0089] From number 19, α QPSK It is represented by the number 21.

[0090]

number

[0091] From number 20, α BPSK It is represented by the number 22.

number

[0092] As in numbers 21 and 22, L SMF,20km and L SMF,40km If you can obtain BER QPSK ,BER BPSK and BER OOK α that makes equal QPSK and α BPSK It is possible to find this.

[0093] α C α obtained when = 1 QPSK and α BPSK And from number 14, adjustment parts 11A2 and 11A3 are α QPSK and α BPSK C after setting r It is represented by the number 23.

[0094]

number

[0095] (α QPSK and α BPSK (Calculation of BER using) Substituting number 23 into numbers 15 through 18 yields numbers 24 through 26.

[0096]

number

[0097]

number

[0098]

number

[0099] If the distances L1 to L3 of transmission lines 12A1 to 12A3 are equal, then from equation 18, C r =3P T Therefore, the terms after the multiplication sign in numbers 24 to 26 become 1 / 3. To correct this relative power, we multiply the square roots in numbers 22 to 24 by 3.

[0100] As shown in numbers 24-26, α was found using numbers 21 and 22. QPSK and α BPSK By using this to control the adjustment units 11A2 and 11A3, BER QPSK ,BER BPSK and BER OOK They are equal to each other. In this way, L SMF,20km and L SMF,40km If we can obtain this, we can also calculate the target BER.

[0101] Assuming the transmission loss of optical fiber is 0.35 dB / km, then from equations 20 and 21, α QPSK = -17 dB and αBPSK = -13dB. At this time, using equations 15 to 17, assuming that the conversion efficiency R is 0.14 and the modulation bandwidth B is 10 GHz, P r The bit error rate (BER) was calculated for this value.

[0102] Figure 11 shows the received optical power P in a hypothetical example of the first embodiment. r This figure shows the bit error rate BER for P before adjustment. r - The BER curve is the unadjusted P in Figure 8. T - It is the same as the BER curve. α QPSK = -17 dB and α BPSK =-13dB and the adjusted P of QPSK, BPSK, and OOK r - The BER curves are almost identical, based on the reference BER (e.g., 1 × 10⁻⁶). -3 P in ) r In OKK, where the value was largest, P in the reference BER r This has improved by 12 dB. In the hypothetical example, as a result, both the comparative form and the first embodiment show α QPSK = -17 dB and α BPSK = -13dB. However, in the comparison configuration, as shown in Figure 7, the BER of QPSK and BPSK is matched to OKK, which has a poor BER. In contrast, in the first embodiment, as shown in Figure 11, the P of QPSK, BPSK and OOK r This represents a 12dB improvement over the comparison configuration.

[0103] (α QPSK and α BPSK (Calculation of BER without using) Of the optical signals O6A, the optical power corresponding to optical signals O1A1 to O1A3 is P r,QPSK , P r,BPSK and P r,OOK If we assume that, then from numbers 8 to 10, BER QPSK ,BER BPSK and BER OOK These are represented by the numbers 27, 28, and 29, respectively.

[0104]

number

[0105]

Number

[0106]

Number

[0107] Assuming that there is no loss in transmission paths 12A1 to 12A3 and 14A, from Equations 27 to 29, P r,QPSK / 2 + P r,BPSK / 4 + P r,OOK = 3P r when BER QPSK BER BPSK and BER OOK are equal. The 3 multiplied by P r is a coefficient for correcting the relative power, similar to Equations 24 to 26. When there is no loss in transmission paths 12A1 to 12A3 and 14A, P r,QPSK P r,BPSK and P r,OOK are equal to the optical powers P T of the optical signals O1A1 to O1A3. Therefore, P r,QPSK = P r,BPSK = P r,OOK = P T and P T / 2 + P T / 4 + 1 = 3P r that is, P T = 12P r / 7. For this reason, P r,QPSK = P T / 2, P r,BPSK = P T / 2 and P r,OOK = P T and under the condition that P r is constant, BER BPSK and BER OOK are represented by Equations 30, 31 and 32 respectively.

[0108]

Number

[0109]

number

[0110]

number

[0111] As described above, α QPSK and α BPSK Without using BER QPSK ,BER BPSK and BER OOK It is also possible to calculate the values ​​that are equal.

[0112] (α QPSK and α BPSK (Receiving sensitivity to) α OOk Assuming =0dB, α QPSK and α BPSK The receiving sensitivity was graphed when the value was changed while keeping it equal to the same value. Figure 12 shows the α in a hypothetical example of the first embodiment. QPSK and α BPSK This figure shows the receiving sensitivity for [a specific value]. The receiving sensitivity is 1 × 10⁻¹⁰ with a reference BER. -3 The optical power P of the optical signal O6A at that time r It is. α QPSK and α BPSK When the value is set to a certain value (for example, -16dB), the BER of QPSK QPSK is 1 x 10 -3 P such that r (For example, -42 dBm) is α QPSK and α BPSK This is the QPSK receiver sensitivity at a certain value (e.g., -16dB). BPSK BER BPSK is 1 x 10 -3 P such that r is, α QPSK and α BPSK The BPSK receiving sensitivity is a value of a certain value. OOK's BER OOK is 1 x 10 -3 P such that r is, αQPSK and α BPSK This represents the OOK receiving sensitivity for a given value. A lower receiving sensitivity indicates an improvement in BER.

[0113] As shown in Figure 12, α QPSK and α BPSK Making the value of α significantly negative, i.e., increasing the attenuation, worsens the reception sensitivity of QPSK and BPSK, but improves the reception sensitivity of OOK. QPSK and α BPSK The relationship between α and receiving sensitivity is nonlinear. QPSK and α BPSK When the signal strength is -17dB, QPSK and OKK intersect at intersection point 52A, and the receiving sensitivities of QPSK and OOK are the same. α QPSK and α BPSK When the signal strength is -13dB, BPSK and OKK intersect at intersection point 52B, and the receiving sensitivities of BPSK and OOK are the same. As a result, α QPSK If we set it to =-17dB, then BER QPSK and BER OKK This is equal to α BPSK If we set it to =-13dB, then BER BPSK and BER OKK This is equal to QPSK and OOK are nonlinear near intersection 52A, and BPSK and OOK are nonlinear near intersection 52B. Therefore, as explained in Figure 8, α QPSK and α BPSK Controlling it becomes more complex.

[0114] (Investigation of the impact on transmission lines) We investigated the extent to which the difference in losses between transmission lines 12A1 to 12A3 becomes complex in order to maintain equivalent BER. We calculated the receiving sensitivity against attenuation in two cases: when the losses of transmission lines 12A1 to 12A3 are 0 dB, and when the losses of transmission lines 12A1 and 12A2 are 0 dB and the loss of transmission line 12A3 is -3 dB.

[0115] Figure 13 shows the α when the transmission loss of QPSK, BPSK, and OOK is 0 dB in a hypothetical example. QPSK and α BPSKThis figure shows the receiving sensitivity for α. QPSK and α BPSK α is near 0dB (for example, in the range of 0dB to -4dB) BPSK and α QPSK The curve between the signal strength and the receiving sensitivity was extended with a dashed straight line. As shown in Figure 13, near the intersection of QPSK and OKK 52A, and the intersection of BPSK and OKK 52B, α BPSK and α QPSK The relationship between α and reception sensitivity is approximately within the range of the dashed straight line. Therefore, intersections 52A and 52B are α BPSK and α QPSK It lies within the range where the line between and the receiving sensitivity is a straight line. Therefore, as explained in Figure 12, α QPSK and α BPSK Controlling it is unlikely to be complex.

[0116] Figure 14 shows the α in a hypothetical example where the transmission loss of QPSK and BPSK is 0 dB and the transmission loss of OOK is -3 dB. QPSK and α BPSK This figure shows the receiving sensitivity for α. As shown in Figure 14, near the intersection of QPSK and OKK 52A, and the intersection of BPSK and OKK 52B, α BPSK and α QPSK The relationship between α and reception sensitivity does not fall within the range of the dashed straight line. Therefore, intersections 52A and 52B are α BPSK and α QPSK The line between and the receiving sensitivity is not within the range where it is a straight line. Therefore, as explained in Figure 12, α QPSK and α BPSK Controlling it becomes complex.

[0117] As described above, in Figure 1, when there is no difference in loss between transmission lines 12A1 and 12An, the control of adjustment units 11A1 to 11An is easy. When the difference in loss between transmission lines 12A1 and 12An is large, the control of adjustment units 11A1 to 11An becomes complex. For this reason, for example, when the difference between the maximum and minimum loss values ​​of transmission lines 12A1 to 12An is 3 dB or more, the adjustment units 11A1 to 11An are controlled based on the loss values ​​of transmission lines 12A1 to 12An.

[0118] (Control by Modulation Bandwidth) As described above, the method of adjusting the BER by controlling the optical power using the adjustment units 11A1 to 11A3 has been explained. However, the BER can also be controlled using the modulation bandwidth and modulation method. Define the modulation bandwidths of QPSK, BPSK, and OOK as B q , B b and B o respectively.

[0119] BER QPSK =BER OOK In order to obtain this, Equation 33 is derived from Equations 15 and 17 in the same way as the derivation of Equation 19.

[0120]

Equation

[0121] BER BPSK =BER OOK In order to obtain this, Equation 34 is derived from Equations 16 and 17 in the same way as the derivation of Equation 20.

[0122]

Equation

[0123] From Equation 33, α QPSK is represented by Equation 35.

[0124]

Equation

[0125] From Equation 34, α BPSK is represented by Equation 36.

Equation

[0126] As in Equations 35 and 36, in addition to the optical power, the BER can be controlled using the modulation bandwidth.

[0127] (Control using modulation scheme) Assuming that modulation to PSK is possible in the BPSK transmitter 10A2, the BER of OOK OOK and the BER of M-phase PSK MSPK These are represented by equations 37 and 38, respectively. Here, the modulation bandwidth of the M-phase PSK is B. M , the damping amount by the adjustment unit 11A2 is α MPSK Let's assume that.

[0128]

number

[0129]

number

[0130] From equations 37 and 38, α MPSK It is represented by the number 39.

number

[0131] In equation 39, if M=4, it corresponds to switching the modulation scheme from BPSK to QPSK, and α QPSK It is represented by the number 40.

[0132]

number

[0133] This corresponds to equation 36. However, due to the switch from BPSK to QPSK, equation 40 is twice as complex as equation 36.

[0134] (Control method 1) As shown in the hypothetical example above, if the losses of the transmission lines 12A1 to 12An and transmission line 14A in Figure 1 of the first embodiment are known, the BER can be controlled to a desired value by controlling the attenuation amount of the adjustment units 11A1 to 11An. In addition, the BER can be controlled to a desired value by instructing the transmitters 10A1 to 10An to control the modulation bandwidth and / or modulation scheme of at least one of the optical signals O1A1 to O1An.

[0135] The control method performed by the control device 20A will be described below. Figure 15 is a functional block diagram of the control device in the first embodiment. The control device 20A includes an acquisition unit 30, a control unit 31, and a storage unit 32.

[0136] The storage unit 32 stores information. The acquisition unit 30 acquires information from the storage unit 32 or an external device. The external device is, for example, a transmitter 10A1 to 10An, adjustment units 11A1 to 11An, 14A and a receiver 16A. The external device may also be a device outside the optical transmission system 100. The control unit 31 controls the transmitter 10A1 to 10An, adjustment units 11A1 to 11An, 14A and the receiver 16A based on the information acquired by the acquisition unit 30.

[0137] The storage unit 32 is, for example, a semiconductor memory device, an optical memory device, or a magnetic memory device. The processor may work in cooperation with software to function as at least part of the acquisition unit 30 and the control unit 31. Dedicated hardware may function as at least part of the acquisition unit 30 and the control unit 31.

[0138] Figure 16 is a flowchart showing the processing of the control device in the first embodiment. As shown in Figure 16, the acquisition unit 30 acquires information regarding the losses of the transmission lines 12A1 to 12An and 14A (step S10). The storage unit 32 may have information regarding the losses of the transmission lines 12A1 to 12An and 14A stored in advance, and the acquisition unit 30 may acquire the information regarding the losses of the transmission lines 12A1 to 12An and 14A from the storage unit 32. The acquisition unit 30 may also acquire information regarding the losses of the transmission lines 12A1 to 12An and 14A from an external device.

[0139] Next, the control unit 31 controls the optical power of the optical signals O2A1 to O2An before they are transmitted to the transmission lines 12A1 to 12An, based on information regarding the losses of the transmission lines 12A1 to 12An and 14A (step S11). For example, the control unit 31 uses mathematical formulas such as equations 21 and 22 to calculate the attenuation of the adjustment units 11A1 to 11An from the losses of the transmission lines 12A1 to 12An and 14A, and controls the adjustment units 11A1 to 11An so that their attenuation becomes the calculated attenuation.

[0140] In step S11, the control unit 31 may use formulas such as equations 35, 36, and 40 to calculate the modulation bandwidth and / or modulation scheme of at least one optical signal O1A1 to O1An from the losses of the transmission lines 12A1 to 12An and 14A, and then control the transmitters 10A1 to 10An. The process then terminates.

[0141] (Control method 2) Figure 17 is a flowchart showing another example of the processing of the control device in the first embodiment. As shown in Figure 17, the acquisition unit 30 acquires information regarding the losses of the transmission lines 12A1 to 12An and 14A (step S10).

[0142] Next, the control unit 31 calculates the target signal quality based on information regarding the losses in the transmission lines 12A1-12An and 14A (step S13). Signal quality is, for example, the BER or reception sensitivity of the electrical signals Er1-Ern. For example, the control unit 31 uses formulas such as equations 15-17 to calculate the BER that makes the BERs of the electrical signals Er1-Ern equal from the losses in the transmission lines 12A1-12An and 14A.

[0143] Next, the control unit 31 controls the optical power of the optical signals O2A1 to O2An before they are transmitted to the transmission lines 12A1 to 12An (step S14). For example, the control unit 31 calculates the attenuation of the adjustment units 11A1 to 11An, similar to S11 in Figure 16, and controls the adjustment units 11A1 to 11An so that their attenuation is equal to the calculated attenuation. The control unit 31 may use the same method as in S11 in Figure 16, or it may use a different method to control the adjustment units 11A1 to 11An.

[0144] Next, the acquisition unit 30 acquires the signal quality (step S15). The acquisition unit 30 acquires information about the signal quality from the demodulation units 25A1 to 25An. For example, if the signal quality is BER, BER can be calculated by comparing the bit sequence demodulated by the demodulation units 25A1 to 25An with the bit sequence of the electrical signals Et1 to Etn. In this case, the acquisition unit 30 acquires the bit sequence of Et1 to Etn from the transmitters 10A1 to 10An and the bit sequence demodulated by the demodulation units 25A1 to 25An from the receiver 16A. The control unit 31 acquires the BER by comparing the transmitted bit sequence with the received bit sequence. If the demodulation units 25A1 to 25An perform error correction, BER can be calculated by comparing the bit sequence before error correction with the bit sequence after error correction. In this case, the acquisition unit 30 acquires the BER from the receiver 16A.

[0145] Next, the control unit 31 determines whether the difference between the target signal quality calculated in step S13 and the signal quality acquired in step S15 is within a predetermined range (step S16). For example, the control unit 31 determines whether the difference between the target BER calculated in step S13 and the BER acquired in step S14 is less than or equal to a predetermined value. The control unit 31 determines Yes if the BER difference is within the predetermined value, and No if the BER difference is greater than the predetermined value. The control unit 31 may determine Yes if the difference between the acquired BER and the target BER is within a predetermined range for all BERs corresponding to electrical signals Er1 to Ern, and No in other cases. The control unit 31 may determine Yes if the average value or standard deviation of the difference between the acquired BER and the target BER for BERs corresponding to electrical signals Er1 to Ern is within a predetermined range, and No in other cases.

[0146] The predetermined value of the difference between the target BER and the acquired BER may be, for example, 5 times or less and 0.1 times or more the target BER, or 2 times or less and 0.5 times or more the target BER.

[0147] If the answer in step S16 is Yes, the signal quality of electrical signals Er1 to Ern is approximately the target quality (for example, the signal quality of electrical signals Er1 to Ern is approximately equivalent). Then the process terminates.

[0148] If the answer in step S16 is No, the signal quality of the electrical signals Er1 to Ern is not the target quality (for example, the signal quality of the electrical signals Er1 to Ern is not equivalent). Therefore, the control unit 31 controls the optical power of the optical signals O2A1 to O2An before they are transmitted to the transmission lines 12A1 to 12An (step S17). For example, the control unit 31 calculates the attenuation amount of the adjustment units 11A1 to 11An so that the difference between the target signal quality and the signal quality obtained in step S14 is reduced, and controls the adjustment units 11A1 to 11An so that their attenuation amounts become the calculated attenuation amounts. For example, to improve the BER, the attenuation amount of the corresponding adjustment units 11A1 to 11An is reduced, and to degrade the BER, the attenuation amount of the corresponding adjustment units 11A1 to 11An is increased. Formulas such as equations 21 and 22 may be used to calculate the attenuation amount of the adjustment units 11A1 to 11An. In this case, the number of feedback cycles can be reduced. Then, return to step S17.

[0149] If the result in step S15 is "Yes," it means that the difference between the target signal quality calculated in step S13 and the signal quality obtained in step S15 is within a predetermined range. In this case, the process terminates.

[0150] The determination in step S16 may also be made using the receiving sensitivity as follows. In step S15 in Figure 17, the acquisition unit 30 acquires the receiving sensitivity corresponding to each of the electrical signals Er1 to Ern as signal quality. The receiving sensitivity is the optical power of the optical signal O6A such that the BER becomes the reference BER. In step S16, the control unit 31 determines whether the difference in the receiving sensitivity corresponding to each of the electrical signals Er1 to Ern is within a predetermined range.

[0151] In steps S14 and S17, the control unit 31 may calculate the modulation bandwidth and / or modulation scheme of at least one of the optical signals O1A1 to O1An and control the transmitters 10A1 to 10An. For example, to improve the BER, the modulation bandwidth and / or number of modulation phases of the corresponding optical signals O1A1 to O1An are reduced, and to degrade the BER, the modulation bandwidth and / or number of modulation phases of the corresponding optical signals O1A1 to O1An are increased.

[0152] In the first embodiment, based on the losses in the transmission lines 12A1 to 12An, the power levels of the multiple optical signals O2A1 to O2An, before they are input to the multiple transmission lines 12A1 to 12An, are controlled so that the signal quality of each of the multiple electrical signals Er1 to Ern is of a desired quality. This makes it easy to control the desired signal quality.

[0153] (Modification 1 of the first embodiment) Modification 1 of the first embodiment includes a method for measuring or estimating the losses of transmission lines 12A1 to 12An when the losses of transmission lines 12A1 to 12An are unknown.

[0154] (Hypothetical example) (Method 1 for estimating transmission line losses) This is the same hypothetical example as in the first embodiment. Method 1 for estimating transmission line loss is P in the reference BER. r This is a method for estimating transmission line loss when the signal strength is known. Figure 18 shows the received optical power P in a hypothetical example of Modification 1 of the first embodiment. r This figure shows the bit error rate BER for α. QPSK , α BPSK and α OOK Assume 0 dB. BER = 1 × 10⁻¹⁰ in QPSK, BPSK, and OOK. -3 The received optical power Pr (reference BER is 1 × 10) is then -3 The corresponding receiving sensitivities are -46 dBm (QPSK), -42 dBm (BPSK), and -29 dBm (OOK), respectively, and are known values.

[0155] If there is no loss in transmission lines 12A1 to 12A3 and 14A, P T =P r Therefore, from a comparison of numbers 11 and 12, BER QPSK and BER BPSK The two are equal when -46 dBm (QPSK) = 2 × L SMF,20km This is when the signal strength is ×-42dBm(BPSK). Therefore, L SMF,20km =7dB. From the comparison of equations 11 and 13, BER QPSK and BER OOK The two are equal when -46dBm(QPSK) = 1 / 2 × L SMF,40km This is when the value is ×-29dBm(OOK). Therefore, L SMF,40km This equals 14 dB. This matches the loss assumed in the hypothetical example, where the transmission loss was 0.35 dB / km.

[0156] As described above, if the Pr value at the reference BER is known, it is possible to estimate the losses in transmission lines 12A1 to 12A3.

[0157] (Method 2 for estimating transmission line loss) Method 2 for estimating transmission line loss is a method for estimating transmission line loss when the BER is known and the value of Pr is the same. Figure 19 shows the received optical power P in a hypothetical example of Modification 1 of the first embodiment. r This figure shows the bit error rate (BER) relative to the received optical power P in QPSK, BPSK, and OOK. r BER is -45dBm QPSK ,BER BPSK and BER OOK These are 3.42 × 10 -4 , 1.59 × 10 -2 and 3.16 × 10 -1 It is known.

[0158] For simplification, L SMF,10km =0dB and α OOK Let = 0 dB. In this case, equations 41 to 43 can be derived from equations 11 to 13, respectively.

[0159]

number

[0160]

number

[0161]

number

[0162] First, BER QPSK = 3.42 × 10 -4 In P r =P T Since it is -45 dBm, from equation 41, qB / R = 1.14 × 10 -8 Next, we obtain L from the calculated qB / R and equation 42. SMF,20km Calculate BER. BPSK = 1.59 × 10 -2 From equation 42, the right-hand side is -52 dBm. Therefore, from equation 42, L SMF,20km ·P r = -52 dBm. BER BPSK = 1.59 × 10 -2 In P r =P T Since L = -45 dBm, SMF,20km = -7 dB is obtained. Finally, L is obtained from the calculated qB / R and equation 43. SMF,40km Calculate BER. OOK = 3.16 × 10 -1 From equation 43, the right-hand side is -59 dBm. From equation 43, L SMF,40km ·P r = -59 dBm. BER OOK = 3.16 × 10 -1 In P r Since L = -45 dBm, SMF,40km = -14dB is calculated.

[0163] As described above, the received optical power P r If the BER is known when the same value is obtained, it is possible to estimate the transmission lines 12A1 to 12A3. In practice, the received optical power P rTo keep this constant, estimating the transmission lines 12A1 to 12A3 at this time is the easiest method.

[0164] (Method 3 for estimating transmission line loss) Method 3 for estimating transmission line loss involves arbitrary BER and P r This is a method for estimating transmission line loss when the signal strength is known. Figure 20 shows a hypothetical example of a modification 1 of the first embodiment in which the received optical power P r This figure shows the bit error rate BER for QPSK. r When the BER is -44dBm QPSK = 2.03 × 10 -5 In BPSK, P r When the BER is -42dBm BPSK = 5.50 × 10 -4 In OOK, P r When the BER is -34dBm OOK = 3.36 × 10 -2 That is the case.

[0165] First, similar to Method 2 for estimating transmission line loss, we can use equation 41 to calculate qB / R = 1.14 × 10⁻⁶. -8 Next, we calculate the P between QPSK and BPSK. T The ratio of ΔP T1 =P r,QPSK / P r,BPSK Let's assume that BER BPSK = 5.50 × 10 -4 From equation 42, the right-hand side is -49 dBm. Therefore, from equation 42, L SMF,20km ·P r,QPSK / ΔP T1 = -49 dBm. Therefore, in dB notation, L SMF,20km = -49 dBm - (-44 dBm) - ΔP T1 = -5dB - (P r,BPSK -P r,QPSK ) = -7dB. Finally, the P between QPSK and OOK T The ratio of ΔP r2 =P r,QPSK / P T,OOK Let's assume that BER OOK = 3.36 × 10 -2 From equation 43, the right-hand side is -48 dBm. Therefore, from equation 43, LSMF,40km ·P T,QPSK / ΔP T2 = -48 dBm. Therefore, in dB notation, L SMF,40km = -48dBm - (-44dBm) - ΔP T2 =-4dB-(P T,OOK -P T,QPSK ) = -14dB.

[0166] As described above, any BER and P r If this is known, it is possible to estimate the transmission lines 12A1 to 12A3.

[0167] (Method for obtaining transmission line losses) As shown in the hypothetical example above, even if the losses of transmission lines 12A1 to 12An are unknown, the losses of transmission lines 12A1 to 12An can be estimated if the received optical power Pr and BER are known. Therefore, the processing of the acquisition unit 30 in step S11 of Figures 16 and 17 will be explained.

[0168] Figure 21 is a flowchart showing the processing of the acquisition unit in Modification 1 of the First Embodiment. As shown in Figure 21, in step S10 of Figure 16 or Figure 17, the acquisition unit 30 determines whether the losses of the transmission lines 12A1 to 12An are known (step S20). For example, if the losses of the transmission lines 12A1 to 12An are stored in the storage unit 32, the acquisition unit 30 determines Yes, and in other cases determines No.

[0169] If the answer is Yes, the acquisition unit 30 outputs information regarding the loss of transmission lines 12A1 to 12An stored in the storage unit 32 to the control unit 31 (step S28). The process then terminates.

[0170] If the answer in step S20 is No, the acquisition unit 30 determines whether or not to measure the loss of the transmission lines 12A1 to 12An (step S22). For example, if it is easy to measure the loss of the transmission lines 12A1 to 12An, the acquisition unit 30 determines Yes, and in other cases, it determines No.

[0171] If the answer is Yes, the acquisition unit 30 measures the loss of the transmission lines 12A1 to 12An (step S26). For example, the acquisition unit 30 measures the optical power of optical signals O1A1 to O1An and the optical power of optical signal O6A. The acquisition unit 30 measures the loss of the transmission lines 12A1 to 12An from the difference between the optical power of optical signals O1A1 to O1An and optical signal O6A. After that, the acquisition unit 30 outputs information regarding the measured loss of the transmission lines 12A1 to 12An to the control unit 31 (step S28). Then the process ends.

[0172] If the answer in step S22 is No, the acquisition unit 30 estimates the loss of the transmission lines 12A1 to 12An (step S24). For example, as shown in Figure 18, if the information of the receiving sensitivity at the reference BER is stored in the storage unit 32, the loss of the transmission lines 12A1 to 12An is estimated using method 1 for estimating the loss of the transmission line from the reference BER and the receiving sensitivity. As shown in Figures 19 and 20, BER and P r The loss of transmission lines 12A1 to 12An is estimated using method 2 or 3, which involves measuring the transmission line loss. Subsequently, the acquisition unit 30 outputs information regarding the measured loss of transmission lines 12A1 to 12An to the control unit 31 (step S28). The process then terminates.

[0173] The judgment in step S22 may be omitted, and either step S24 or S26 may be omitted. Also, the judgment in step S20 may be omitted.

[0174] As shown in Modification 1 of the First Embodiment, the acquisition unit 30 may measure or estimate the loss of the transmission lines 12A1 to 12An.

[0175] (Second Embodiment) The second embodiment is an example in which optical signals transmitted from multiple transmitters are combined, the optical power of the combined optical signal is adjusted to a constant level, and then the combined optical signal is split into multiple optical signals, and each of the split optical signals is converted into multiple electrical signals. Figure 22 is a block diagram of the optical transmission system according to the second embodiment. The optical transmission system according to the second embodiment is, for example, a WDM (Wavelength Division Multiplexing)-PON (Passive Optical Network) system. As shown in Figure 22, the optical transmission system 102 according to the second embodiment includes a receiving unit 16C instead of the receiver 16A of the first embodiment. The receiving unit 16C includes a demultiplexing unit 17A and receivers 18A1~18Ai~18An.

[0176] The demultiplexer 17A demultiplexes the optical signal O6A, which has been adjusted by the adjustment unit 15A, into optical signals O7A1, O7Ai, and O7An, which correspond to the optical signals O1A1, O1Ai, and O1An, respectively. The receivers 18A1, 18Ai, and 18An perform photoelectric conversion of the optical signals O7A1, O7Ai, and O7An, decode the resulting electrical signals, and output electrical signals Er1, Eri, and Ern, respectively. The other configurations are the same as in the first embodiment.

[0177] As in the second embodiment, the decoupled optical signals O7A1~O7Ai~O7An may be photoelectrically converted and decoded. Even in this case, the same problems as in the first embodiment will arise unless the adjustment unit 15A controls the optical power of optical signal O6A to a constant level and an adjustment unit is provided between the decoupler 17A and the receivers 18A1~18An to individually adjust the optical power of optical signals O7A1~O7An. Therefore, the adjustment units 11A1~11An, the modulation bandwidth and modulation scheme are controlled using control methods 1 and 2, as in the first embodiment. This makes it possible to easily control the desired signal quality.

[0178] (Third embodiment) The third embodiment is an example in which multiple electrical signals are converted into optical signals collectively, the power of the optical signals is adjusted to a constant level, and then the signals are split into multiple optical signals, which are then received by multiple receivers. Figure 23 is a block diagram of the optical transmission system according to the third embodiment. As shown in Figure 23, the optical transmission system 104 according to the third embodiment includes multiple paths PB1~PBi~PBn, a demultiplexer 13B, a transmission line 14B, an adjustment unit 15B, a transmitter 16B, and a control device 20B.

[0179] Transmitter 16B combines the electrical signals Er1, Eri, and Ern, converts the combined electrical signal into an optical signal, and outputs the converted optical signal O6B. The optical signal O6A is, for example, a frequency multiplexed signal, in which optical signals corresponding to the electrical signals Et1, Eti, and Etn are combined on the frequency axis.

[0180] The adjustment unit 15B is, for example, a variable optical attenuator, which adjusts the optical signal O6A to the desired optical power and outputs the adjusted optical signal O5B. The adjustment unit 15B keeps the overall optical power of the optical signal O5B constant for simultaneous transmission. The optical power of the optical signals corresponding to paths PB1 to PBn is not adjusted individually.

[0181] The transmission path 14B is, for example, an optical fiber, which transmits the optical signal O5B and outputs the transmitted optical signal O4B.

[0182] The demultiplexer 13B is, for example, an optical splitter / coupler, an array-type optical waveguide, or an optical wavelength selector switch, and demultiplexes the optical signal O4A into optical signals O3B1~O3Bi~O3Bn corresponding to the electrical signals Et1~Etn. The demultiplexed optical signals O3B1~O3Bi~O3Bn are output to paths PB1~PBi~PBn, respectively.

[0183] Each path PB1~PBi~PBn is equipped with receivers 10B1~10Bi~10Bn and transmission lines 12B1~12Bi~12Bn, respectively.

[0184] Multiple transmission lines 12B1~12Bi~12Bn are, for example, optical fibers, which transmit optical signals O3B1~O3Bi~O3Bn and output the transmitted optical signals O1B1~O1Bi~O1Bn. The length of the transmission lines 12B1~12Bi~12Bn varies depending on the distance between the receivers 10B1~10Bi~10Bn and the demultiplexer 13B.

[0185] Multiple receivers 10B1~10Bi~10Bn receive optical signals O1B1~O1Bi~O1Bn, convert them into electrical signals Er1~Eri~Ern respectively, and output the converted electrical signals Er1~Eri~Ern. Receivers 10B1~10Bi~10Bn detect the optical power of the received optical signals O1B1~O1Bi~O1Bn and the signal quality of the electrical signals Er1~Eri~Ern.

[0186] The control device 20B acquires information from the receivers 10B1 to 10Bn, the adjustment unit 15B, and the transmitter 16B, and controls the receivers 10B1 to 10Bn, the adjustment unit 15B, and the transmitter 16B. The functional block diagram of the control device 20B is the same as in Figure 15.

[0187] Figure 24 is a block diagram of the transmitter in the third embodiment. As shown in Figure 24, the transmitter 16B comprises transmitters 25B1 to 25Bi to 25Bn, adjustment units 11B1 to 11Bi to 11Bn, an adder 24B, a light source 22B, and an optical modulator 23B. Transmitters 25B1 to 25Bi to 25Bn each generate electrical signals E3B1 to 3Bi to 3Bn, having predetermined power, modulation scheme, and modulation bandwidth, from the electrical signals Et1 to 1ti to 25Bn to be transmitted. An example of the modulation scheme is the same as the example of the modulation scheme of the electrical signal generation unit 26A in the first embodiment. Electrical signals Et1 to 1tn are digital signals in bit sequence form, and electrical signals E3B1 to 3Bn are analog signals.

[0188] Multiple adjustment units 11B1~11Bi~11Bn each adjust the power of electrical signals E3B1~E3Bi~E3Bn and output the adjusted electrical signals E2B1~E2Bi~E2Bn. Transmitters 25B1~25Bn may adjust the power of electrical signals E3B1~E3Bn in addition to, or instead of, the adjustment units 11B1~11Bn by amplifying or attenuating the electrical signals they generate.

[0189] The summing unit 24B adds the electrical signals E2B1, E2Bi, and E2Bn on the frequency axis and outputs the electrical signal E1B. The light source 22B is, for example, a semiconductor laser element and outputs laser light LO3 having a predetermined wavelength. The optical modulator 23B modulates the laser light LO3 using the electrical signal E1B. This generates an optical signal O6B having a predetermined modulation scheme and modulation bandwidth.

[0190] The optical transmission system 100 of the first embodiment and the optical transmission system 104 of the third embodiment may be an integrated optical transmission system. In this case, the transmitters 10A1 to 10An and the corresponding receivers 10B1 to 10Bn each form a transponder, and the receiver 16A and transmitter 16B form a transponder.

[0191] The results of the hypothetical examples in the first embodiment and its modifications are also applicable to the third embodiment. In the third embodiment, the adjustment unit 15B adjusts the optical signal O6B to a constant optical power, and the optical power of the optical signals O3B1 to O3Bn is not individually adjusted between the demultiplexer 13B and the transmission lines 12B1 to 12Bn. The control unit 31 controls the power of each of the signals before they are input to the multiple transmission lines 12B1 to 12Bn, based on the losses in the transmission lines 12B1 to 12Bn, so that the respective signal quality of each of the multiple signals in the multiple receivers 10B1 to 10Bn is of the desired quality. For example, the control unit 31 controls the power of the electrical signals E3B1 to E3Bn by controlling the adjustment units 11B1 to 11Bn. This makes it easy to control the desired signal quality. The control unit 31 may also control the modulation bandwidth and / or modulation scheme of the electrical signals E2B1 to E2Bn by the transmitters 25B1 to 25Bn.

[0192] (Fourth Embodiment) The fourth embodiment is an example in which multiple electrical signals are each converted into multiple optical signals, then combined, the optical power of the combined optical signals is adjusted to a constant level, then the signals are separated into multiple optical signals, and the separated optical signals are received by multiple receivers. Figure 25 is a block diagram of the optical transmission system according to the fourth embodiment. As shown in Figure 25, the optical transmission system 106 according to the fourth embodiment includes a transmitting unit 16D instead of the transmitter 16B of the second embodiment. The transmitting unit 16D includes a multiplexing unit 17B, adjustment units 11B1~11Bi~11Bn and transmitters 18B1~18Bi~18Bn.

[0193] Transmitters 18B1, 18Bi, and 18Bn convert electrical signals Et1, Eti, and Etn into optical signals O8B1, O8Bi, and O8Bn modulated according to a desired modulation scheme, and output the optical signals O8B1, O8Bi, and O8Bn respectively.

[0194] Multiple adjustment units 11B1~11Bi~11Bn each adjust the power of the optical signals O8B1~O8Bi~O81Bn and output the adjusted optical signals O7B1~O7Bi~O8Bn. Transmitters 18B1~18Bn may adjust the power of the optical signals O8B1~O8Bn in addition to, or instead of, the adjustment units 11B1~11Bn by amplifying or attenuating the electrical signals they generate.

[0195] The combined optical signal unit 17B combines the optical signals O7B1~O7Bi~O7Bn, which have been adjusted by the adjustment unit 15A, onto the frequency axis and outputs the combined optical signal O6B. The other configurations are the same as in the third embodiment.

[0196] As in the fourth embodiment, the optical signals O7B1~O7Bi~O7Bn output by transmitters 18B1~18Bn may be combined. In this case as well, the same problems as in the third embodiment arise. Therefore, as in the third embodiment, the adjustment units 11B1~11Bn, the modulation bandwidth and modulation method are controlled. This makes it possible to obtain the desired signal quality.

[0197] (Summary of the first to fourth embodiments) In the first and second embodiments, as shown in Figures 1 and 22, the adjustment unit 15A adjusts the optical signal O5A to a constant optical power. The receiver 16A or receiving unit 16C receives the adjusted optical signal O6A as a plurality of electrical signals Er1 to Ern corresponding to a plurality of optical signals O1A1 to O1An. In such an optical transmission system 100 or 102, the control device 20A has an acquisition unit 30 and a control unit 31, as shown in Figure 15. As shown in step S10 of Figures 16 and 17, the acquisition unit 30 acquires information on each of the plurality of losses in the plurality of transmission lines 12A1 to 12An. As shown in step S11 of Figure 16 and step S17 of Figure 17, the control unit 31 controls the respective powers of the plurality of optical signals O2A1 to O2An before inputting them to the plurality of transmission lines 12Ai to 12An, respectively, so that the respective signal quality of each of the plurality of electrical signals Er1 to Ern is of a desired quality, based on the acquired information on the plurality of losses. This allows for control to achieve the desired signal quality.

[0198] In the third and fourth embodiments, as shown in Figures 23 and 25, the transmitter 16B or transmitting unit 16D transmits an optical signal O6A which is a composite of multiple electrical signals Et1 to Etn. The adjustment unit 15B adjusts the transmitted optical signal O6B to a constant optical power. In such an optical transmission system 104 or 106, the control device 20B has an acquisition unit 30 and a control unit 31, as shown in Figure 15. As shown in step S10 of Figures 16 and 17, the acquisition unit 30 acquires information on the multiple losses in each of the multiple transmission lines 12B1 to 12Bn. As shown in step S11 of Figure 16 and step S17 of Figure 17, the control unit 31 controls the power of each of the multiple optical signals O3B1 to O3Bn before inputting them into the multiple transmission lines 12Bi to 12Bn, based on the acquired information on the multiple losses, so that the signal quality of each of the multiple electrical signals Er1 to Ern is of a desired quality. This allows control to be made to the desired signal quality.

[0199] Here, the adjustment unit 15A (or 15B) adjusts the optical signal O5A (or O6B) to a constant optical power, which means that when the device is in operation and transmitting information from the transmitter or transmitting unit to the receiver or receiving unit, it adjusts the optical signal O5A (or O6B) to a constant optical power. For example, when measuring signal quality, the adjustment unit 15A (or 15B) may change the power of the optical signal O5A (or O6B). Also, "constant" does not mean that the optical power is strictly fixed. A constant optical power means that, in operation, the range of optical power adjusted by the adjustment unit 15A (or 15B) (for example, the difference between the maximum and minimum values) is, for example, 3 dB or less, but may also be 2 dB or less.

[0200] More precisely, transmission loss also includes the loss in the paths through which optical signals are transmitted within each device other than the transmission lines 12A1-12An (or 12B1-12Bn). Generally, the paths through which optical signals are transmitted in devices other than the transmission lines 12A1-12An (or 12B1-12Bn) are shorter than those of the transmission lines 12A1-12An (or 12B1-12Bn). For example, the length of the paths through which optical signals are transmitted in devices other than the transmission lines 12A1-12An (or 12B1-12Bn) is less than or equal to 1 / 10 of the length of the transmission lines 12A1-12An (or 12B1-12Bn). Therefore, the loss of the transmission lines 12A1-12An (or 12B1-12Bn) should be used as the transmission loss. If the loss in the paths through which optical signals are transmitted within each device other than the transmission lines 12A1 to 12An (or 12B1 to 12Bn) is not negligible compared to the loss in the transmission lines 12A1 to 12An (or 12B1 to 12Bn), then the loss in the paths other than the transmission lines may be included in the loss of the transmission lines 12A1 to 12An (or 12B1 to 12Bn).

[0201] In the first to fourth embodiments, as shown in Figure 17, the control unit 31 controls the adjustment unit 15A or 15B so that the difference between the maximum and minimum values ​​of the signal quality is reduced. This makes it possible to make the signal quality of the electrical signals Er1 to Ern nearly uniform. When the signal quality is BER, the maximum value of BER is preferably 5 times or less the minimum value of BER, more preferably 3 times or less, and even more preferably 2 times or less.

[0202] The first optical modulation scheme in at least one of the optical signals O1A1~O1An (or O1B~O1Bn) is different from the second optical modulation scheme in the other optical signals. For example, the first optical modulation scheme is a modulation scheme that performs phase modulation and amplitude modulation, while the second optical modulation scheme is a modulation scheme that does not perform phase modulation. When the modulation schemes of the optical signals O1A1~O1An (or O1B1~O1Bn) are different in this way, controlling the signal quality becomes complex. Therefore, it is preferable to adjust the adjustment section 11A1~11An (or 11B1~11Bn) using the loss of the transmission line 12A1~12An (or 12B1~12Bn).

[0203] In Figures 12 and 14, α corresponds to the control amount of multiple optical signals O2A1~O2An (or O3B1~O3Bn). BPSK and α QPSK At a point where at least two of the lines indicating the receiving sensitivity (signal quality) intersect (for example, intersections 52A and 52B), at least one of the two lines is not a straight line. In such cases, controlling the signal quality becomes complex. Therefore, it is preferable to adjust the adjustment section 11A1 to 11An (or 11B1 to 11Bn) using the loss of the transmission line 12A1 to 12An (or 12B1 to 12Bn).

[0204] Note that the straight line does not have to be a geometric straight line. For example, in Figures 12 to 14, the control amount of the power at intersections 52A and 52B (i.e., α) BPSK and α QPSK Controllable quantity and signal quality (i.e., α) within the range of ) BPSK and α QPSK When the correlation coefficient R2 between the signal and the receiving sensitivity is 0.98 or less, the intersection points 52A and 52B are not a straight line.

[0205] As shown in Figure 14, the maximum loss in the transmission path 12A1~12An (or 12B1~12Bn) is at least twice (3 dB or more) the minimum loss in the transmission path 12A1~12An (or 12B1~12Bn). In this case, the receiving sensitivity for optical power and optical signals O2A1~O2An (or O3B1~O3Bn) becomes nonlinear. Therefore, it is preferable to adjust the adjustment section 11A1~11An (or 11B1~11Bn) using the loss in the transmission path 12A1~12An (or 12B1~12Bn). The maximum loss in the transmission path 12A1~12An (or 12B1~12Bn) may be at least five times, or even ten times, the minimum loss in the transmission path 12A1~12An (or 12B1~12Bn).

[0206] As shown in step S26 of Figure 21, the acquisition unit 30 measures the losses of multiple transmission lines 12A1 to 12An (or 12B1 to 12Bn). In step S11 of Figure 16 and step S17 of Figure 17, the control unit 31 adjusts the adjustment units 11A1 to 11An (or 11B1 to 11Bn) based on the measured losses of the multiple transmission lines 12A1 to 12An (or 12B1 to 12Bn). This allows the adjustment units 11A1 to 11An (or 11B1 to 11Bn) to be adjusted even when the losses of the multiple transmission lines 12A1 to 12An (or 12B1 to 12Bn) are unknown.

[0207] As shown in step S24 of Figure 21, the acquisition unit 30 estimates the losses of multiple transmission lines 12A1 to 12An (or 12B1 to 12Bn) based on the multiple signal quality. In step S11 of Figure 16 and step S17 of Figure 17, the control unit 31 adjusts the adjustment units 11A1 to 11An (or 11B1 to 11Bn) based on the estimated losses of the multiple transmission lines 12A1 to 12An (or 12B1 to 12Bn). This allows the adjustment units 11A1 to 11An (or 11B1 to 11Bn) to be adjusted even when the losses of the multiple transmission lines 12A1 to 12An (or 12B1 to 12Bn) are unknown.

[0208] In addition to adjusting the adjustment units 11A1 to 11An (or 11B1 to 11Bn), the control unit 31 controls the modulation bandwidth and / or modulation scheme of at least one of the optical signals O1A1 to O1An (or O1B to O1Bn). This allows for broader control of signal quality.

[0209] While BER and receiver sensitivity were used as examples to explain signal quality, signal quality can also be expressed as the signal-to-noise ratio (SNR) or the optical signal-to-noise ratio (OSNR). SNR is, for example, the signal-to-noise ratio per 1 Hz of bandwidth. OSNR is, for example, the bandwidth noise per 12.5 GHz obtained by multiplying the SNR by an appropriate coefficient.

[0210] In the first and second embodiments, the number of transmitters 10A1 to 10An is n, and i is an integer between 1 and n. The power of the optical signal O1Ai transmitted by the i-th transmitter 10Ai is P i α i The loss of the i-th transmission line 12Ai is L i The loss occurring from the combined wave section 13A to the adjustment section 15A is α c Let's assume that.

[0211] At this time, the optical power P of the optical signal O6A r It is represented by the number 44.

[0212]

number

[0213] The noise power from the i-th transmitter 10Ai to the receiver 16A or the receiving unit 16C is σ i Let's assume that.

[0214] In this case, when the modulation scheme of the i-th transmitter 10A1 is M-phase PSK, the i-th BER is represented by the number 45.

[0215]

number

[0216] When the modulation scheme of the i-th transmitter 10A1 is M-phase PAM, the i-th BER is represented by the number 46.

[0217]

number

[0218] When the modulation scheme of the i-th transmitter 10A1 is M-phase QSK, the i-th BER is represented by the number 47.

[0219]

number

[0220] When the modulation scheme of the i-th transmitter 10Ai is BPSK, the i-th BER is represented by the number 48.

[0221]

number

[0222] When the modulation scheme of the i-th transmitter 10Ai is OOK, the i-th BER is represented by the number 49.

[0223]

number

[0224] The control unit 31 may adjust the adjustment units 11A1 to 11An using at least one of the formulas 45 to 49 so that the difference between the maximum and minimum values ​​of the BER for i from 1 to n becomes small. The control unit 31 may also control the modulation bandwidth and / or modulation scheme of at least one of the optical signals O1A1 to O1An using at least one of the formulas 45 to 49.

[0225] In the third and fourth embodiments, the number of receivers 10B1 to 10Bn is n, and i is an integer between 1 and n. The attenuation of the electrical signal Eti corresponding to the optical signal O1Bi received by the i-th receiver 10Bi in transmitter 16B is α. i , damping amount α i When the value is set to 0 dB, the optical power of the optical signal of the channel corresponding to the i-th optical signal received by the receiver 10Bi among the optical signals O6B output by the transmitter 16B is P. i ,

[0226] At this time, the optical power P of the optical signal O6B tx It is represented by the number 50.

[0227]

number

[0228] The loss of the i-th transmission line 12Bi is L i The loss occurring from transmitter 16B to demultiplexer 13B is α c In this case, the noise power from transmitter 16B to the i-th receiver 10Bi is σ i In this case, the control unit 31 may adjust the adjustment units 11B1 to 11Bn using at least one of the formulas 45 to 49 such that the difference between the maximum and minimum values ​​of the BER for i from 1 to n becomes small. Alternatively, the control unit 31 may control the modulation bandwidth and / or modulation scheme of at least one of the optical signals O1B1 to O1Bn using at least one of the formulas 45 to 49.

[0229] Although the present invention has been described above based on various embodiments, the present invention is not limited to the requirements shown in the above embodiments. These points can be modified as long as they do not impair the spirit of the present invention, and can be appropriately determined according to their application. [Explanation of Symbols]

[0230] 10A1, 10A2, 10A3, 10Ai, 10An, 16B, 18B1, 18Bi, 18Bn, 25B1, 25Bi, 25Bn Transmitters 10B1, 10Bi, 10Bn, 16A, 18A1, 18A2, 18A3, 18Ai, 18An receivers 11A1, 11A2, 11A3, 11Ai, 11An, 11B1, 11Bi, 11Bn, 15A, 15B, 19A1, 19A2, 19A3 Adjustment section 12A1, 12A2, 12A3, 12Ai, 12An, 12B1, 12Bi, 12Bn, 14A, 14B transmission lines 13A, 17B Multiplexing section 13B, 17A branching section 16C Receiver 16D Transmitter 20A, 20B control devices 21A Power detection unit 22A Local Oscillator 22B, 27A 23A Photoelectric conversion unit 23B, 28A Optical modulators 24A Separation part 24B Addition section 25A1, 25Ai, 25An Demodulation Unit 26A Electrical signal generation unit 30 Acquisition Department 31 Control Unit 32 Storage section

Claims

1. Multiple transmitters, each transmitting multiple optical signals, Multiple transmission paths for transmitting the multiple optical signals that have been transmitted, A multiplexer that combines the multiple optical signals that have been transmitted, An adjustment unit that adjusts the combined optical signal to a constant optical power, A control device for controlling an optical transmission system comprising: a receiver that receives the adjusted optical signal as a plurality of electrical signals corresponding to the plurality of optical signals; An acquisition unit that acquires information on each of the multiple losses in the aforementioned multiple transmission lines, A control unit that controls the power of each of the multiple optical signals before inputting them into each of the multiple transmission paths, based on the acquired information on the multiple losses, so that the signal quality of each of the multiple electrical signals is of a desired quality, A control device equipped with the following features.

2. A transmitter that transmits an optical signal formed by combining multiple electrical signals, An adjustment unit that adjusts the transmitted optical signal to a constant optical power, A dewave splitter that splits the adjusted optical signal into multiple optical signals corresponding to the multiple electrical signals, Multiple transmission paths for transmitting each of the multiple separated optical signals, A control device for controlling an optical transmission system comprising a plurality of receivers, each receiving a plurality of transmitted optical signals, An acquisition unit that acquires information on each of the multiple losses in the aforementioned multiple transmission lines, Based on the acquired information on the plurality of losses, a control unit controls the power of each of the plurality of signals corresponding to the plurality of electrical signals in the transmitter so that the signal quality of each of the plurality of signals in the plurality of receivers becomes the desired quality, A control device equipped with the following features.

3. The control device according to claim 1 or 2, wherein the control unit controls the plurality of powers such that the difference between the maximum and minimum values ​​of the plurality of signal quality is reduced.

4. The control device according to claim 1 or 2, wherein the first optical modulation scheme in at least one of the plurality of optical signals is different from the second optical modulation scheme in the plurality of optical signals.

5. The control device according to claim 1 or 2, wherein at a point where at least two of the lines indicating the signal quality for the control amounts of the plurality of powers intersect, at least one of the two lines is not a straight line.

6. The control device according to claim 1 or 2, wherein the maximum value of the plurality of losses is at least twice the minimum value of the plurality of losses.

7. The acquisition unit measures the plurality of losses, The control device according to claim 1 or 2, wherein the control unit controls the plurality of powers based on the measured plurality of losses.

8. The acquisition unit estimates the plurality of losses based on the plurality of signal quality, The control device according to claim 1 or 2, wherein the control unit controls the plurality of powers based on the estimated plurality of losses.

9. The control device according to claim 1 or 2, wherein the control unit controls, based on the acquired information regarding the loss, the respective powers of the plurality of optical signals before they are input to the plurality of transmission lines, and the modulation bandwidth and / or modulation scheme of at least one of the plurality of optical signals, so that the respective signal quality of the plurality of electrical signals becomes a desired quality.

10. The control device according to claim 1 or 2, wherein the plurality of signal quality parameters are BER or receiving sensitivity.

11. The aforementioned plurality of transmitters are n transmitters, which are integers greater than or equal to 2. When i is an integer between 1 and n, P is the power of the optical signal output by the i-th transmitter. ｉ α ｉ , the loss of the i-th transmission line is L ｉ The loss that occurs from the wave combining section to the adjustment section is α ｃ , the aforementioned constant light power P ｒ In that case, P ｒ It is represented by the number 1, [Math 1] It is expressed as, The noise power from the i-th transmitter to the receiver is σ ｉ In that case, When the modulation scheme of the i-th transmitter is M-phase PSK, the i-th BER is represented as the number 2. [Math 2] When the modulation scheme of the i-th transmitter is M-phase PAM, the i-th BER is represented as the number 3. [Math 3] When the modulation scheme of the i-th transmitter is M-phase QAM, the i-th BER is represented as the number 4. [Math 4] When the modulation scheme of the i-th transmitter is BPSK, the i-th BER is represented as the number 5. [Math 5] When the modulation scheme of the i-th transmitter is OOK, the i-th BER is represented as the number 6. [Math 6] The control device according to claim 1, which controls the plurality of powers using at least one of the formulas from number 2 to number 6 such that the difference between the maximum and minimum values ​​of BER for i from 1 to n becomes small.

12. The aforementioned plurality of receivers are n receivers, which are integers of 2 or more. When an integer from 1 to n is defined as i, the attenuation amount of the electrical signal corresponding to the optical signal received by the i-th receiver in the transmitter is α ｉ , α ｉ When it is set to 0 dB, the optical power of the optical signal of the channel corresponding to the optical signal received by the i-th receiver among the optical signals output by the transmitter is P ｉ , the constant optical power is P ｔｘ When it is set as, P ｔｘ is represented by Equation (7), [Number 7] It is expressed as, The loss in the i-th transmission line is L ｉ The loss occurring from the transmitter to the demultiplexer is α ｃ In this case, the noise power from the transmitter to the i-th receiver is σ ｉ In that case, When the modulation scheme of the i-th receiver is PSK in M ​​phase, the i-th BER is represented as the number 8. [Number 8] When the modulation scheme of the i-th receiver is M-phase PAM, the i-th BER is represented as the number 9. [Number 9] When the modulation scheme of the i-th receiver is M-phase QAM, the i-th BER is represented as the number 10. [Number 10] When the modulation scheme of the i-th receiver is BPSK, the i-th BER is represented as the number 11. [Math 11] When the modulation scheme of the i-th receiver is OOK, the i-th BER is represented as the number 12. [Math 12] The control device according to claim 2, which controls the plurality of powers using at least one of the formulas from number 8 to number 12 such that the difference between the maximum and minimum values ​​of BER for i from 1 to n becomes small.

13. An optical transmission system comprising the plurality of transmitters, the plurality of transmission lines, the multiplexing unit, the adjustment unit, the receiver, and the control device according to claim 1.

14. An optical transmission system comprising the transmitter, the adjustment unit, the demultiplexer, the plurality of transmission lines, the plurality of receivers, and the control device according to claim 2.

15. Multiple transmitters, each transmitting multiple optical signals, Multiple transmission paths for transmitting the multiple optical signals that have been transmitted, A multiplexer that combines the multiple optical signals that have been transmitted, An adjustment unit that adjusts the combined optical signal to a constant optical power, A control method for controlling an optical transmission system comprising: a receiver that receives the adjusted optical signal as a plurality of electrical signals corresponding to the plurality of optical signals; The steps include: obtaining information on each of the multiple losses in the multiple transmission lines; A step of controlling the power of each of the multiple optical signals before inputting them into each of the multiple transmission paths, based on the acquired information on the multiple losses, so that the respective multiple signal quality of each of the multiple electrical signals is of a desired quality; A control method including

16. A transmitter that transmits an optical signal formed by combining multiple electrical signals, An adjustment unit that adjusts the transmitted optical signal to a constant optical power, A dewave splitter that splits the adjusted optical signal into multiple optical signals corresponding to the multiple electrical signals, Multiple transmission paths for transmitting each of the multiple separated optical signals, Multiple receivers, each receiving the transmitted multiple optical signals, A control method for controlling an optical transmission system comprising: The steps include: obtaining information on each of the multiple losses in the multiple transmission lines; Based on the acquired information on the plurality of losses, the transmitter controls the power of each of the plurality of signals corresponding to the plurality of electrical signals so that the respective signal quality of each of the plurality of receivers becomes a desired quality. A control method including

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