Low power optical information transmission system

Abstract

To provide a low-power optical information transmission system in which communication capacity is assumed and power consumption is reduced in a future large-capacity optical access network system.SOLUTION: The communication of the low-power optical information transmission system includes an optical signal transmitting device, an optical signal receiving device, and a monitoring function unit, wherein the monitoring function unit notifies which of the M-phase amplitude optical modulation signal and the polarization time domain multi-dimensional index optical modulation signal is to be operated, and the optical signal transmitting device includes a channel coding unit 1a that processes original information into channel coding index bits and amplitude phase modulation bits and outputs the bits, and a transmitting unit TX that transmits the polarization time domain multi-dimensional index optical modulation signal and the M-phase amplitude optical modulation signal from the bits. The optical signal receiver is provided with a local oscillation light source, a polarized wave phase diversity detector RX and a demodulation section 6, demodulates the M-phase phase amplitude optical modulation signal and the polarized wave time domain multi-dimensional index optical modulation signal and reduces the power of the local oscillation light source in the case of the operation with the polarized wave time domain multi-dimensional index optical modulation signal.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an optical information transmission system that is applied to optical fiber transmission networks, particularly optical access networks. The present invention provides a system that can construct an optical communication line with lower power consumption than conventional technologies, and realizes a low-power optical information transmission system by enabling multimode operation of a conventional multilevel optical modulation method and a low-power time-domain index optical modulation method to be switched according to the state of communication traffic.

[0002] The low-power optical data transmission system of the present invention has a function of selecting an optical modulation method to be applied to optical data transmission by a control device provided on the transmitting side in response to instructions from a monitoring function unit that monitors the entire system, and notifying an optical signal receiving device at the other end of the transmission of the selected optical modulation method. The optical signal transmitting device switches the operating mode of its built-in coding and modulation circuit using the control device, and in the low-power operating mode, transmits a time-domain index optically modulated signal while directly modulating the laser diode of the signal light source.

[0003] In addition, the optical signal receiving device also selects an optical modulation method to be applied to the operation mode selected by the control device of the optical signal transmitting device, and switches the operation mode of the built-in local oscillator light source driver. In addition, in the low power operation mode, the time domain index optically modulated signal is received while suppressing the laser diode drive current of the local oscillator light source. [Background technology]

[0004] Optical access networks have spread to approximately 30 million households in Japan and have become an essential social infrastructure system in an advanced information society.

[0005] In particular, in recent years, optical access network services that achieve a maximum transmission rate of 10 Gbit / s in each household are being developed in accordance with the IEEE 802.3av (10GE-PON) standard (Non-Patent Document 1). In many cases, this system employs a configuration in which optical fiber lines are branched in a tree shape from an optical line terminal (OLT) installed in a communication station in each local city, and connected to multiple (maximum 32) optical network units (ONUs) installed in each household (Figure 19).

[0006] Due to the large number of these systems, it is estimated that they consume 0.1% of the total annual power consumption in Japan. Furthermore, due to the large number of ONUs installed, it has been shown that they account for more than 70% of the power consumption of the entire system (Non-Patent Document 2).

[0007] It has been demonstrated that the power efficiency of optical information transmission, i.e., the ratio of the amount of transmitted information to the average optical signal power, can be improved by as much as 3 dB when a time-domain index modulation method based on binary phase shift keying is used (Non-Patent Document 3). When the amount of communication traffic is low, the optical information transmission system applies the time-domain index modulation method to reduce the power consumption of the optical signal transmitter and optical signal receiver inside the ONU.

[0008] In the time-domain index optical modulation method, the optical signal transmitter of the ONU reduces power consumption by directly modulating the laser diode of the signal light source, and the optical signal receiver reduces the drive current of the laser diode of the local light source. Either or both of these operations reduce the power consumption of the entire optical information transmission system. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-100734 [Patent Document 2] Multidimensionally modulated optical signal demodulator and demodulation method (Patent Application No. 2023-215632) [Non-patent literature]

[0010] [Non-Patent Document 1] IEEE Std 802.3av-2009, IEEE Standard for Ethernet-Physical Layer Specifications and Management Parameters for 10Gb / s Passive Optical Networks. [Non-patent document 2] A.Otaka, “Power saving ad-hoc report” Retrieved 2 2012, from IEEE 802.3av: http: / / www.ieee802.org / 3 / av / public / 2008_09 / 3av_809_otaka_1.pdf [Non-patent document 3] W. Imajuku, D. Aoki, Y. Yamaga, K. Yamamloto and S. Takahashi, “Time-Domain Single Carrier Index Modulation for Elastic Optical Access Links,” Journal of Lightwave Technology, vol. 42, no. 6, pp. 18539-1860, March 2014. [Non-patent document 4] Ryo Kuma, Junichi Kani, Kota Asaka, and Kenichi Suzuki, "Standardization Trends for Further Speed ​​Improvement of PON Systems," NTT Technical Journal, vol. 29, no. 8, pp. 51–53, August 2017. [Non-Patent Document 5] Senta Suzuki, Yutaka Miyamoto, Masato Tomizawa, Hisakazu Sakano, Koichi Murata, Shinji Mino, Mitsufumi Shibayama, Masamasa Shibuya, Kiyoshi Fukuchi, Hiroshi Onaka, Takeshi Hoshida, Kosuke Komaki, Takashi Mizuochi, Kazuo Kubo, Yoshikuni Miyata, and Toru Kamio, "Research and Development of Digital Coherent Signal Processing Technology for Increasing the Capacity of Optical Communication Networks," Journal of the Institute of Electronics, Information and Communication Engineers, vol. 95, no. 12, pp. 1100-1116, December 2012. Summary of the Invention [Problem to be solved by the invention]

[0011] Future large-capacity optical access network systems, which have evolved from the IEEE 802.3av (10GE-PON) standard (Non-Patent Document 1), are expected to be based on the time-wavelength division multiplexing passive optical network system (Non-Patent Document 4) and the polarization phase diversity coherent optical communication system (Non-Patent Document 5). However, there are concerns that the increase in communication capacity will lead to a further increase in power consumption.

[0012] An object of the present invention is to provide an optical information transmission system incorporating an optical signal transmitter or an optical signal receiver, or both, which normally transmits and receives optical signals using M-phase quadrature phase amplitude modulation signals and which can switch to optical information transmission using a time domain index optical modulation method that has high power efficiency in optical information transmission, i.e., high transmitted information volume / average optical signal power, depending on the communication traffic state of an optical access network.

[0013] In addition, in order to achieve the above object, the present invention has the problem that it is necessary to be able to control the driving of the signal light source of the optical signal transmitting device or the local light source of the optical signal receiving device in accordance with the system operation policy or the state of communication traffic. [Means for solving the problem]

[0014] In view of the above problems, the present invention provides a demodulation device and method for optical communications that provides best-effort optical access services in accordance with communication traffic conditions and transmission path conditions even when the optical loss budget exceeds 29 dB.

[0015] To this end, the optical signal transmitting device has a control device that selects an optical modulation method to be applied to optical information transmission and notifies the receiving device on the opposite side of the selected optical modulation method. The optical signal transmitting device switches the operating mode of its built-in encoding and modulation circuit in accordance with the control device, and in low-power operating mode, transmits a time-domain index optically modulated signal while directly modulating the laser diode of the signal light source. The optical signal receiving device also selects the optical modulation method to be applied to optical information transmission selected by the control device of the optical signal transmitting device, switches the operating mode of its built-in local oscillator light source drive circuit, and in low-power operating mode, receives the time-domain index optically modulated signal while suppressing the drive current of the laser diode of the local oscillator light source.

[0016] More specifically, the low-power optical information transmission system according to the present invention comprises: A low-power optical information transmission system including an optical signal transmitting device, an optical signal receiving device, and a monitoring function unit, The monitoring function unit An optical signal transmitting device, M-phase quadrature amplitude modulation signal, transmitting an operation mode notification signal to the optical signal transmitter, notifying the optical signal transmitter of whether it will operate using a polarization time domain multidimensional (N-, K-, or M-QAM) index optical modulation signal; The optical signal transmitting device includes: a channel coding unit that separates original information into index bits to be transmitted by the polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal and amplitude phase modulation bits to be transmitted by the M-phase quadrature phase amplitude modulation signal, processes the index bits into channel coded index bits and channel coded amplitude phase modulation bits, and outputs the processed bits; a transmitter that transmits either the polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal or the M-phase quadrature phase optical amplitude modulation signal, and the operation mode notification signal to the optical signal receiving device from the channel-coded index bits and the channel-coded amplitude and phase modulation bits based on the operation mode notification signal, The optical signal receiving device includes: The device comprises a local light source, a polarization phase diversity detector, and a demodulator. demodulating the M-phase quadrature amplitude modulation signal and the polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal sent from the optical signal transmission device in accordance with the operation mode notification signal from the optical signal transmission device; The optical signal demodulator is characterized in that, when receiving the operation mode notification signal that operates with the polarization time domain multidimensional (N, K, M-QAM) index optical modulated signal, the power of the local oscillator light source is made lower than the power of the local oscillator light source when receiving the M-phase quadrature phase amplitude modulated signal.

[0017] The low-power optical information transmission system of the present invention may be adapted to transmit a time-domain (N, K, M-Stokes Vector Modulation) index optical modulation signal instead of a polarization time-domain multidimensional (N, K, M-QAM) index optical modulation signal. [Effects of the Invention]

[0018] According to the low-power optical information transmission system of the present invention, in low-power operation mode, the effective current value of the signal light source of the optical signal transmitting device can be reduced to approximately 1 / 8, and the effective current value of the local light source of the optical signal receiving device can be reduced to approximately 1 / 4. In theory, the power consumed by the light source can be reduced to approximately 1 / 64 in the optical signal transmitting device and 1 / 16 in the optical signal receiving device.

[0019] Furthermore, the low-power optical information transmission system of the present invention can be applied to future optical access network systems. By controlling the signal light source wavelength of the ONU device installed on the subscriber side of the system, the communication capacity required by the user can be secured by selecting a wavelength channel that realizes information transmission using M-phase quadrature amplitude modulation signals in normal operation mode. On the other hand, in low-power operation mode, by selecting a wavelength channel that realizes information transmission using time-domain index modulation signals, power consumption can be reduced although communication capacity is small.

[0020] The traffic volume sent and received by subscribers of current optical access network systems shows a wide distribution (Fig. 20) (Non-Patent Document 5). In Fig. 20, "In" represents the upstream line, and "Out" represents the downstream line. The ratio of communication traffic volume to the communication capacity of the current optical access network can be defined as traffic volume. Taking into account the distribution of traffic volume, Fig. 20 makes clear that 94% of the time is spent with a traffic volume of 0.25 or less.

[0021] If the low-power optical data transmission system of the present invention is deployed and communication demand continues to occur with a similar traffic distribution in the future, it is estimated that the low-power optical data transmission system of the present invention will operate in low-power operation mode for approximately 90% of its total operating time. The reduction in power consumption of the ONU equipment for 30 million subscribers is expected to be approximately 0.1 trillion watt-hours compared to the current situation, which is a significant power reduction effect. [Brief explanation of the drawings]

[0022] [Figure 1] An example of modulation rules in an M-phase quadrature amplitude modulation system is shown below. [Figure 2] 1 shows an example of a modulation rule in a time domain index optical modulation method. [Figure 3] 1 shows an example of an amplitude and phase modulation rule for ON symbols in a time-domain index optical modulation system. [Figure 4] FIG. 1 is a diagram showing a frame structure of polarization time domain multidimensional index optical modulation according to the present invention. [Figure 5] 1 shows a logical model diagram of a time domain index optical modulation method to be realized in the present invention. [Figure 6] FIG. 10 is a diagram illustrating the communication capacity of a time-domain index optical modulation method. [Figure 7] 1A and 1B are diagrams showing the change in bit error rate characteristics of time-domain index optically modulated signals relative to the local light power. (a) Time-domain (8,1,BPSK) index optically modulated signal, (b) Time-domain (8,2,BPSK) index optically modulated signal [Figure 8] FIG. 1 is a diagram illustrating a configuration of a first embodiment. [Figure 9] FIG. 2 is a diagram illustrating a configuration of a coding and modulation circuit according to the first embodiment. [Figure 10] 3 is a diagram illustrating an example of a polarization time domain multidimensional index optical modulation signal output from a transmitting device of the first embodiment. FIG. [Figure 11] FIG. 10 is a diagram illustrating a configuration of a second embodiment. [Figure 12] FIG. 10 is a diagram illustrating a configuration of a coding and modulation circuit according to a second embodiment. [Figure 13] FIG. 10 is a diagram illustrating a configuration of a third embodiment. [Figure 14] FIG. 10 is a diagram illustrating a configuration of a fourth embodiment. [Figure 15] 1A and 1B are diagrams illustrating signals of another modulation format of polarization time domain multidimensional (4,1,QPSK) index optical modulation signals, (a) an example of system configuration, and (b) an example of wavelength allocation. [Figure 16] FIG. 10 is a diagram illustrating a subframe configuration using 4-SVM. [Figure 17] 1 is a diagram showing an example of the configuration of a system incorporating a low-power optical information transmission system according to the present invention; [Figure 18] FIG. 10 is a diagram illustrating how the operation mode selected by each OSU changes according to the amount of communication traffic requested by a subscriber. [Figure 19] This figure shows the basic configuration of an optical access network service that is currently being rolled out, which will achieve a maximum transmission rate of 10 Gbit / s for each household. [Figure 20] FIG. 1 is a distribution diagram of communication traffic volume of access network subscribers. DETAILED DESCRIPTION OF THE INVENTION

[0023] The configuration and operation of an optical signal demodulation device according to the present invention will be described below with reference to the drawings. Note that the following description exemplifies one embodiment and one example of the present invention, and the present invention is not limited to the following description. The following description can be modified within the scope of the present invention. Furthermore, parts referred to as "parts" in the following embodiments can be realized with either hardware or software configurations. Furthermore, parts referred to as "parts" may also be referred to as "processes" having the functions they perform.

[0024] The principle of the M-ary quadrature amplitude modulation method, which is the premise of this invention, is as follows. M-ary quadrature amplitude modulation is a method in which the amplitude and phase of an optical symbol are changed in accordance with the signal to be transmitted. Hereinafter, M-ary quadrature amplitude modulation will also be referred to as M-QAM method, and the signal will also be referred to as M-QAM signal. M-ary pulse amplitude modulation (M-PAM) can also be used.

[0025] An example is shown in Figure 1. The QPSK method in Figure 1(a) is a modulation method that defines four signal points. Because four types of signal points are defined, a two-bit code can be assigned to each signal point. In other words, two bits of information can be transmitted with one optical symbol. Similarly, the 16-QAM method in Figure 1(b) is a modulation method that defines 16 signal points. Because 16 types of signal points are defined, a four-bit code can be assigned to each signal point.

[0026] The principle of time-domain index optical modulation, another modulation method that forms the premise of this invention, is as follows: In time-domain index optical modulation, an index optical modulation signal frame (hereinafter simply referred to as a "frame") is composed of multiple time slots. Optical signals are transmitted and received using this frame as a single unit. A time slot has a predetermined time width. There is a time gap between one time slot and the next. However, if the sending and receiving sides are completely synchronized, there is no need for a time gap. The time width of a time slot, including the time gap, is represented by "Ts."

[0027] Under these conditions, we consider a case where the average optical signal power of each frame is set to a constant value near the upper limit of the output of the laser light source of the optical signal transmitter. In this case, by thinning out a fixed number of optical symbols in each frame, the amplitude of the optical symbols and, therefore, the signal-to-noise ratio of the optical symbols increases. In addition, by changing the transmission and reception time slots of the thinned optical symbols in accordance with the time-domain index modulation rule, it becomes possible to transmit and receive codes.

[0028] Figure 2 shows an example of a transmit / receive time slot. The top represents X polarization and the bottom represents Y polarization. Here, a symbol refers to the light (optical symbol carrier: hereafter simply referred to as "optical signal LS") that carries information from the sender during the time slot. Symbol thinning refers to a state in which there is no light or the intensity is low (dark) during the time slot. Changing the time slot includes changing the time of the time slot or changing the intensity of the symbol during the time slot.

[0029] Figure 2 shows eight frames. Each frame consists of eight time slots. The black time slots in each time slot carry optical symbols. The optical symbols carry information using an M-QAM (M-Quadrature Amplitude Modulation) method such as QPSK (Quadrature Phase Shift Keying). For example, the third frame shows that an optical symbol is carried in the third time slot. The white time slots are time slots that do not carry optical symbols.

[0030] Figure 2 shows a case where an optical symbol is placed in one of eight time slots. Eight activation patterns are possible depending on the position of the optical time slot in which the optical symbol is placed. By assigning an index bit to each activation pattern, three bits of information can be specified.

[0031] Note that Figure 2 shows two systems: 8 time slots on the X polarization plane and 8 time slots on the Y polarization plane. In this case, the frames on the X polarization plane and the Y polarization plane are unrelated. In other words, the time slots on the X polarization plane and the time slots on the Y polarization plane at the same time are not the same frame.

[0032] On the other hand, in the low-power optical information transmission system according to the present invention, index optical modulation is performed that includes not only the time domain but also polarization. Figure 3 shows an example of a frame configuration according to the present invention. One frame uses the time domain in the X polarization plane (time slots 1 to 4) and the time domain in the Y polarization plane (time slots 5 to 8) as one frame. Figure 3 shows a case where a symbol is carried in the second slot in the X polarization plane. When index optical modulation that includes polarization plane is performed in this way, one slot is also called a "polarization-time slot."

[0033] Each polarization time slot can carry three bits of information ranging from "000" to "111." Figure 3 shows that in the low-power operation mode of the low-power optical information transmission system according to the present invention, the polarization time slot on the X polarization plane and the polarization time slot on the Y polarization plane at the same time constitute the same frame. For example, the polarization time slots of "000" and "100" are polarization time slots at the same time and belong to the same frame. Note that, physically, time-domain index optical modulation is performed on the same polarization plane.

[0034] Furthermore, by simultaneously coherently detecting the optical symbols, it becomes possible to transmit and receive codes using M-QAM optical modulation symbols, similar to conventional digital coherent optical signal receivers. Figure 4 shows an example of the signal points of optical symbols sent in a time slot. Figure 4(a) is a QPSK signal, and Figure 4(b) is a 4PAM (4 Pulse Amplitude Modulation) signal.

[0035] In the present invention, M-phase quadrature amplitude modulation (M-QAM optical modulation) and M-phase pulse amplitude modulation (M-PAM optical modulation) can be suitably used as modulation methods for symbols. Although the following explanation will be given using M-QAM optical modulation as an example, M-PAM optical modulation may also be used.

[0036] Furthermore, index modulation performed using the time domain and polarization plane as described above is called polarization time domain multidimensional (N,K,M-QAM) index optical modulation. The part in parentheses indicates the attributes of the optical symbols, meaning that there are N time slots in one frame, of which there are K optical symbols, and that the optical symbols are optically modulated using the M-QAM method. Since there are N time slots for the X polarization plane and the Y polarization plane, one frame has 2N polarizations and time slots.

[0037] The communication path realized by the polarization time domain multidimensional index optical modulation method is logically a communication path consisting of a parallel index channel (Index_ch) that transmits and receives codes (index bits, also written as "Index bits") by changing the symbol position within one frame of the transmission and reception polarization and time slot of optical symbols in accordance with the polarization time domain multidimensional index modulation rules, and an amplitude phase modulation channel (APM_ch) that transmits and receives codes (amplitude phase modulation bits, also written as "APM bits") using M-QAM optical modulation.

[0038] Figure 5 is a conceptual diagram of the overall configuration of a communication system in a low-power optical information transmission system that transmits and receives index bits and APM bits. The overall system consists of a transmitting side (optical signal transmitter 1), a receiving side (optical signal receiver 3), a transmission path 2, and a monitoring function unit 4. The monitoring function unit 4 determines the operating mode based on the traffic on the transmission path 2 or a power-saving policy, and notifies the transmitting side (transmitter TX) of this decision using an instruction signal 4c. Here, the operating mode refers to either the use of polarization time-domain multidimensional index optical modulation (low-power operating mode) or the use of M-phase quadrature amplitude modulation (normal operating mode).

[0039] The monitoring function unit 4 may be set independently on the transmitting side (optical signal transmitting device 1) and the receiving side (optical signal receiving device 3) without belonging to the transmission path 2, or may be set within the transmitting side or the receiving side.

[0040] On the transmitting side (optical signal transmitter 1), the original information INF is separated by a serial / parallel converter (S / P) into index bits transmitted as a polarization-time-domain multidimensional (N, K, M-QAM) index optical modulation signal and amplitude-phase modulation bits (APM bits) transmitted as an M-phase quadrature phase optical modulation signal. An error correction code is added to each signal by an error correction coder (FEC_Enc.), and the signals are mapped (MAP) and processed into channel-coded index bits and channel-coded APM bits. The channel-coded index bits and channel-coded APM bits are sent to the transmitter TX.

[0041] In the transmitter (TX), a polarization time-domain multidimensional (N, K, M-QAM) index optical modulation signal or an M-phase quadrature amplitude modulation signal is generated using the channel-coded index bits and the channel-coded APM bits, and transmitted as an optical signal LS.

[0042] The components from the serial / parallel conversion unit (S / P) to the mapping (MAP) are called the channel coding unit 1a. The original information INF may include not only the information that the transmitting side wants to send to the receiving side, but also an operation mode notification signal Snm that indicates in what operation mode the optical signal transmitting device 1 will operate.

[0043] The transmitter TX determines the operation mode based on the operation mode instruction signal 4c sent from the monitoring function unit 4. Depending on the operation mode, power control of the signal light source may be performed. The transmitter TX also sends an operation mode notification signal Snm to the receiver. Note that the index bits may include a training sequence for synchronization on the receiver at regular intervals.

[0044] The training sequence is a signal sequence that transmits a predetermined number of frames in succession at regular intervals, each frame carrying a symbol in a specific polarization and time slot. The receiving side uses this training sequence to establish synchronization with the optical signal receiving device 3.

[0045] Logically, an index channel (Index_ch) and an amplitude-phase modulation channel (APM_ch) are transmitted on transmission path 2. Physically, an optical signal LS is transmitted in which an M-QAM modulated optical signal is carried as an optical symbol in the polarization and time slot as explained in Figures 2 and 3.

[0046] Referring again to Figure 5, on the receiving side (optical signal receiving device 3), the receiving unit RX controls the power consumption of the local light source (see Figures 13 and 14) based on the operation mode notification signal Snm received from the transmitting side. The signal received by the receiving unit RX is separated after at least polarization rotation compensation by a polarization rotation compensation unit RXe, and a timing channel determination unit RXf determines the training sequence from this output signal, and determines the start timing of the frame and subframe, as well as the polarization plane of the received signal.

[0047] It also generates a timing signal to determine the IQ axes of the received signal. It also performs receiving operations according to the signal from the transmitter based on the operation mode notification signal Snm received from the transmitter. As a result, the receiver RX obtains the IQ components of the X polarization plane and the IQ components of the Y polarization plane, i.e., the M-QAM modulation code.

[0048] Next, the demodulation unit 6 includes an index demodulation unit 10 that demodulates the channel-coded Index bits from the IQ components of the X polarization plane and the IQ components of the Y polarization plane, and a symbol demodulation unit 20 that demodulates the channel-coded APM bits. In the index demodulation unit 10, an index demapping unit (DMAP) and a subsequent error correction unit (FEC Dec.) perform error correction, and the Index bits are decoded from the channel-coded Index bits.

[0049] In the symbol demodulation unit 20, the M-QAM modulation code is frequency offset compensated by the frequency offset compensation unit (FC), and phase shift compensated by the phase shift compensation unit (PC).The code is then channel coded by the demapping unit (DMAP) and returned to APM bits, and further error correction is performed by the error correction unit (FEC Dec.) before being decoded into APM bits.

[0050] In the optical signal receiving device 3 according to the present invention, the activation pattern signal AP is transmitted from the index demodulator 10 to the symbol demodulator 20. CS This activation pattern signal AP CS specifies the timing and polarization plane at which the M-QAM modulation code should be demodulated. In other words, AP CS The signal specifies the polarization and time slot to be demodulated.

[0051] In this way, the index bits and APM bits are decoded. These codes are converted back to serial codes by the parallel / serial converter 29, and decoded information DE(INFO) corresponding to the original information INF is obtained. The overall communication capacity C (bit / sec) of these is given by equation (1).

[0052]

number

[0053] In equation (1), N is the number of symbols per frame of the time-domain index optical modulation signal, K is the number of symbols to insert optical symbols into (the lower brackets are Gaussian symbols), and M is the number of signal points defined for M-QAM modulated optical symbols. The first term on the right-hand side corresponds to the communication capacity of Index_ch, and the second term corresponds to the communication capacity of APM_ch.

[0054] Figure 6 shows the relationship between the number of optical symbols per frame (K / N) (horizontal axis) and the transmission data rate B (bits / symbol) (vertical axis). The open symbols indicate the case where only amplitude-phase modulation bits (APMbits) are used, and the solid symbols indicate the case where index bits are also used. The APMbits in each case are QPSK. The square symbols indicate the case where one frame has 16 time slots, the circle symbols indicate the case where one frame has 8 time slots, and the triangle symbols indicate the case where one frame has 4 time slots.

[0055] Here, methods for transmitting codes under low average optical signal power conditions, in which the average number of optical symbols is reduced to 1 / 16 to 1 / 4, include a method for allocating optical symbols to fixed time slots (referred to as FIM in Fig. 6) and a time-domain (N, K, QPSK) index optical modulation method (referred to as IM in Fig. 6). In the method for allocating optical symbols to fixed time slots, the position of the time slot within a frame does not carry any information content.

[0056] For example, in the time-domain (8,1,QPSK) index optical modulation transmission method (in Figure 6, when K is 1, as indicated by a circle: K / N=0.125), which transmits codes under low average optical signal power conditions with the average number of optical symbols narrowed to 1 / 8, the bit rate is 0.625 bits / symbol, which enables a communication capacity increase of 2.5 times compared to the 1 / 8 rate QPSK modulation transmission method (0.25 bits / symbol) in which the number of optical symbols is narrowed to 1 / 8.

[0057] Furthermore, the condition K / N=1 corresponds to the QPSK modulation transmission method itself, i.e., the M-ary quadrature phase amplitude modulation method itself in the normal operating mode. The communication capacity (0.625 bits / symbol) of time-domain (8,1,QPSK) index optical modulation transmission is 5 / 16 of the communication capacity (2 bits / symbol) of QPSK modulation transmission under the condition K / N=1. However, the average optical signal power is reduced by a large factor of 1 / 8, so the power efficiency of optical information transmission, i.e., the amount of transmitted information / average optical signal power, is increased by 5 / 2 times.

[0058] Therefore, the minimum receiving sensitivity of the time-domain index optical modulation transmission method exhibits excellent performance, as shown in Figure 7. Figure 7 shows the experimental evaluation results of the dependence of the received bit error rate on the received optical power for a time-domain (8,1,BPSK) index optical modulation signal and a time-domain (8,2,BPSK) index optical modulation signal. In both Figures 7(a) and 7(b), the horizontal axis represents the received optical power (dBm), and the vertical axis represents the received bit error rate (BER). Note that the vertical axis is expressed logarithmically. For both modulation methods, a comparison is made with that of a BPSK modulation signal.

[0059] Figure 7(a) shows the received bit error rate for a time-domain (8,1,BPSK) optical modulated signal, compared with that for a BPSK modulated signal. LO ) is for 11.6 dBm. The time-domain (8,1,BPSK) optical modulated signal had a 6 dB higher receiving sensitivity than the BPSK optical modulated signal. Therefore, this margin can be used to reduce the local oscillator power.

[0060] Therefore, the local light power (P LO ) was reduced to 9.7 dBm and 7.7 dBm, and the bit error rate was evaluated. LO ) obtained a lower received bit error rate than the BPSK optical modulated signal received at 11.6 dBm. Furthermore, when the local oscillator power was increased to 14.0 dBm, a lower received bit error rate was obtained even at a lower received optical power.

[0061] Figure 7(b) shows the same experiment evaluated for the time domain (8,2,BPSK) optical modulation signal. LO It was confirmed that even if the local oscillator power (P LOIt was experimentally confirmed that sufficient signal quality can be ensured (high reliability of data communication) even when the above-mentioned noise level is suppressed.

[0062] The low-power optical information transmission system of the present invention provides a means for converting the high communication reliability achieved by the time-domain index optical modulation method into a reduction in the power consumption of an actual system, and it is necessary to provide a means that can accommodate modulation signals using both the M-phase quadrature phase optical amplitude modulation method in normal operation mode and the time-domain index optical modulation method in low-power operation mode.

[0063] Specifically, the following requirements must be satisfied. First, the transmitter must have a coding and modulation circuit that can support both M-ary quadrature phase optical amplitude modulation and time-domain optical index modulation, and must have a means for reducing the drive power of the signal light source in low-power operation mode. In particular, from the perspective of improving frequency efficiency, a method is needed to achieve polarization multiplexing transmission that ensures frequency utilization efficiency while reducing the drive power of the signal light source.

[0064] Second, the receiver must be able to support both M-ary quadrature phase amplitude modulation and time-domain index modulation, and must be able to reduce the driving power of the local oscillator in low-power operation mode.

[0065] The first requirement is an inevitable requirement if one wishes to support both M-ary quadrature amplitude modulation and time-domain index modulation while reducing the power consumption of the signal light source. The optical signal transmitter 1 requires IQ vector optical modulation when outputting an optical signal using M-ary quadrature amplitude modulation, and it is necessary to generate a polarization multiplexed optical signal while reducing power consumption by directly modulating the signal light source when outputting an optical signal using time-domain index modulation. However, it is difficult to directly generate a polarization multiplexed optical signal from a single directly modulated signal light source.

[0066] The second requirement is that a means be provided for controlling the drive power of the local light source in accordance with the arrival timing of the optical signal to be received. A mode for satisfying these requirements will be described below.

[0067] The present invention addresses the first requirement by adopting polarization time-domain multidimensional index optical modulation that simultaneously uses either X polarization or Y polarization, thereby avoiding the difficulty of directly generating a polarization multiplexed optical signal from a single directly modulated signal light source. Furthermore, the present invention addresses the second requirement by providing a configuration that controls the driving power of a local light source using an operation mode notification signal.

[0068] As described above, the present invention builds a low-power optical information transmission system by combining polarization time-domain multidimensional index modulation and M-ary quadrature amplitude modulation. However, Stokes vector modulation can also be used instead of M-ary quadrature amplitude modulation or pulse amplitude modulation. This is because polarized light using the Stokes vector can also be generated from a directly modulated signal light source. However, because the polarized light itself is used as the signal point, polarization time-domain multidimensional index modulation cannot be performed. Therefore, it is possible to combine it with time-domain index modulation.

[0069] Therefore, the present invention can provide a combination of polarization time-domain multidimensional (N,K,M-QAM) index optical modulation (or polarization time-domain multidimensional (N,K,M-PAM) index optical modulation) and M-phase quadrature amplitude modulation, or a combination of time-domain (N,K,M-Stokes Vector Modulation) index optical modulation and M-phase quadrature amplitude modulation.

[0070] (First embodiment) Fig. 8 shows a configuration diagram of the transmitter TX of the optical signal transmitter 1 in the low-power optical information transmission system of the present invention shown in Fig. 5. The transmitter TX includes a coding and modulation unit TX1, an operation mode control unit TX2, a polarization multiplexed IQ optical modulation unit TX3, a signal light source driver TX4, a bias T circuit TX5, and a signal light source TX6.

[0071] The input original information INF is input to the channel coding unit 1a (see FIG. 5). As shown in FIG. 5, the channel coding unit 1a encodes the original information INF, and further performs a channel coding process on the optical signal receiving device 3 side so that error correction is possible.

[0072] The output of the channel coding unit 1a is a channel-coded index bit and a channel-coded amplitude and phase modulation bit. From these, a polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal or an M-phase quadrature phase modulation optical signal is generated. These codes are output via wiring corresponding to the index channel (Index_ch) and the amplitude and phase modulation channel (APM_ch), respectively, and input to the coding and modulation unit TX1. Note that the APM_ch is wired for the X polarization plane (APM_chX) and the Y polarization plane (APM_chY).

[0073] In Figure 8, they are simply written as "X" and "Y." The Index_ch wiring transmits channel-encoded Index bits, and the APM_ch wiring transmits channel-encoded APMbitsX and APMbitsY.

[0074] In normal operation mode, in which an M-phase quadrature amplitude modulation signal is output from the optical signal transmitter 1, the signal light source emits light in all time slots. In other words, no time slots are thinned out. On the other hand, in low-power operation mode, in which a polarization time-domain multidimensional index optical modulation signal is output, Index_ch (index channel) is driven. The APM_ch (amplitude-phase modulation channel) is driven regardless of the operation mode, but in low-power operation mode, either the X channel (APM_chX) or the Y channel (APM_chY) is driven.

[0075] Here, the operation mode of the communication channel coding unit 1a is set in accordance with an operation mode notification signal Snm from the operation mode control unit TX2. The operation mode control unit TX2 receives an operation mode instruction signal 4c from the monitoring function unit 4 (see FIG. 5) and determines the operation mode based on that signal.

[0076] In this embodiment, it is assumed that the monitoring function unit 4 is installed outside the low-power optical information transmission system. The monitoring function unit 4 transmits an operation mode instruction signal 4c to the operation mode control unit TX2, which changes the operation mode based on either policy-driven, which changes the operation mode according to a predetermined policy, or traffic-driven, which monitors the amount of information to be transmitted.

[0077] The operation mode control unit TX2 includes a function of transmitting an operation mode notification signal Snm that notifies the optical signal receiving device 3 of the operation mode set in the optical signal transmitting device 1. In this embodiment, a case will be described in which the operation mode control unit TX2 notifies the receiving side of the operation mode notification signal Snm via a so-called out-band control line that is separate from the main signal line ML. The operation mode control unit TX2 also notifies the coding and modulation unit TX1 of the operation mode notification signal Snm.

[0078] Next, the channel-coded index bits and channel-coded amplitude-phase modulation bits output from the channel coding unit 1a are converted into modulation codes by the coding and modulation unit TX1. The channel-coded index bits are converted into activation pattern modulation codes of a polarization time-domain multidimensional index optical modulation signal. Meanwhile, the amplitude-phase modulation bits are converted into M-ary quadrature phase amplitude modulation codes of an M-ary quadrature phase optical amplitude modulation signal.

[0079] Here, the operation of the coding and modulation unit TX1 changes depending on the operation mode notification signal Snm from the operation mode control unit TX2. Fig. 9 shows an example of the configuration of the coding and modulation unit TX1. The operation mode control unit TX2 includes an activation pattern mapper Mact, an M-phase quadrature amplitude signal mapper MmpX for X polarization, and an M-phase quadrature amplitude signal mapper MmpY for Y polarization.

[0080] The activation pattern mapper Mact receives the channel-coded index bits from the index channel Index_ch and generates activation pattern modulation codes S for the X and Y polarizations. APX , S APYThe X-polarized M-phase quadrature amplitude signal mapper MmpX and the Y-polarized M-phase quadrature amplitude signal mapper MmpY receive the channel-coded amplitude-phase modulation bits for the X-polarized wave and the channel-coded amplitude-phase modulation bits for the Y-polarized wave, respectively, and place the information on the IQ components to generate the M-phase quadrature amplitude modulation codes S for the X-polarized I component, X-polarized Q component, Y-polarized I component, Y-polarized Q component. MQ Generate.

[0081] The activation pattern generated by the activation pattern mapper Mact is sent to the M-phase quadrature amplitude signal mapper MmpX for the X polarization and the M-phase quadrature amplitude signal mapper MmpY for the Y polarization via the selector APM-SEL. The activation pattern modulation code for the X polarization SAP X are multiplied by the I and Q components of the X polarization in multipliers TX100 and TX102, respectively. Also, the activation pattern modulation code SAP for the Y component Y are multiplied by the I and Q components of the Y polarization in multipliers TX104 and TX106, respectively.

[0082] In addition, the activation pattern modulation code SAP for X polarization generated by the activation pattern mapper Mact X and Y-polarized activation pattern modulation code SAP Y are added by the adder TX108 and then sent as the activation pattern modulation code SAP to the bias T circuit (see FIG. 8) via the selector IND-SEL. In other words, the output of the selector IND-SEL is the activation pattern modulation code S AP is.

[0083] Furthermore, the operation mode notification signal Snm sent to the coding / modulation unit TX1 controls the selector IND-SEL and the selector APM-SEL. When the normal operation mode is set as the operation mode, the selector IND-SEL selects 0 and the selector APM-SEL selects 1.

[0084] When the selector IND-SEL selects 0, the activation pattern modulation code S emitted by the signal light source TX6 is used for all polarizations and time slots. AP is output from the coding / modulation unit TX1 to the bias T circuit TX5. When the selector APM-SEL selects 1, both the IQ components of the X polarization and the IQ components of the Y polarization are output. MQ is output from the encoding / modulation unit TX1 to the polarization multiplexed IQ optical modulation unit TX3.

[0085] On the other hand, when the low power operation mode is set, the selector IND-SEL selects a value other than 0 according to the operation mode notification signal Snm, and the selector APM-SEL selects a value other than 1. When the selector IND-SEL selects a value other than 0, the coding and modulation unit TX1 outputs to the bias T circuit TX5 the activation pattern modulation code S converted based on the input from Index_ch (the channel-coded index bit). AP More specifically, the activation pattern modulation code S for X polarization generated by the activation pattern mapper Mact is output. APX and Y-polarized activation pattern modulation code S APY are added in the selector IND-SEL to generate the activation pattern modulation code S AP to the bias T circuit TX5, causing the signal light source TX6 to emit light.

[0086] Also, if the selector APM-SEL selects a value other than 1, the activation pattern modulation code S for X polarization generated by the activation pattern mapper Mact is APX and Y-polarized activation pattern modulation code S APY is passed through selector APM-SEL and multiplied by the IQ components of the X polarization plane in multipliers TX100 and TX102, and is multiplied by the IQ components of the Y polarization plane in multipliers TX104 and TX106.

[0087] The IQ signal components for the X polarization and Y polarization are obtained by converting the APM_ch codes (channel-coded APMbitsX and channel-coded APMbitsY) into M-phase quadrature amplitude modulation codes in an X polarization M-phase quadrature amplitude signal mapper MmpX and a Y polarization M-phase quadrature amplitude signal mapper MmpY. These multiplied values ​​are output to the polarization multiplexed IQ optical modulator TX3.

[0088] Returning to FIG. 8 again, the signal light source TX6 is a bias T circuit TX5 that combines the output from the signal light source driver TX4 and the activation pattern modulation code S output from the coding and modulation circuit TX1. AP The light is emitted by the electrical signal on which the light is superimposed.

[0089] Next, the operation of the polarization multiplexing IQ optical modulator TX3 will be explained. In normal operation mode, the input light from the signal light source TX6 is laser-oscillated light in all time slots except for the training sequence. Therefore, signals carrying M-phase quadrature amplitude modulated signals are transmitted in all time slots, including the X and Y polarization planes, simply by the modulation operation of the polarization multiplexing IQ optical modulator.

[0090] On the other hand, in the low-power operation mode, the input light from the signal light source TX6 is an activation pattern modulation code S AP This is light based on the above. More specifically, it is light for which the time slot and polarization plane for carrying the symbol are specified. The polarization multiplexed IQ optical modulator TX3 then performs M-phase quadrature amplitude modulation in the time slot (polarization-time slot) of the polarization plane for carrying the symbol. This means that when the time comes to carry the symbol, it switches to the specified polarization plane and performs M-phase quadrature amplitude modulation on the channel-encoded APMbits.

[0091] In low-power operation mode, index modulation in both the polarization plane and the time axis is achieved by performing optical modulation according to the above procedure, and a polarization-time-domain multidimensional (N, K, M-QAM) optical index modulated signal or an M-phase quadrature amplitude modulated signal is output as the optical signal LS.

[0092] FIG. 10 shows an example of a polarization time-domain multidimensional (N, K, M-QAM) index optically modulated signal output from the optical signal transmitter 1 of the low-power optical information transmission system of the present invention. The optical signal LS is divided into a training sequence portion and a payload portion, which are repeated as a single unit. When the optical signal LS is configured in this manner, the frame shown in FIG. 2 or 3 may be called a subframe. Here, a comparison is made between a polarization time-domain multidimensional index optically modulated signal and a time-domain index optically modulated signal. More specifically, as an example, a comparison is made between a polarization time-domain multidimensional (4, 1, QPSK) index optically modulated signal and a polarization multiplexed time-domain (8, 1, QPSK) index optically modulated signal.

[0093] Polarization time-domain multidimensional (4,1, QPSK) index optical modulation signals use both polarization planes and time slots for mapping. Therefore, one frame consists of four time slots in the X and Y polarization planes (a total of eight polarizations and time slots). On the other hand, polarization multiplexed time-domain (8,1, QPSK) index optical modulation signals consist of eight time slots in one polarization plane, and then polarization planes are multiplexed.

[0094] Both the polarization time-domain multidimensional (4,1,QPSK) index optical modulation signal and the polarization multiplexed time-domain (8,1,QPSK) index optical modulation signal are index optical modulation signals in which a frame consists of a total of eight slots and an optical symbol is inserted into one of those eight slots. Therefore, the communication capacity achieved by these optical modulation signals is the same. In other words, even if a transmitter that cannot generate polarization multiplexed optical signals is used, the same communication capacity can be achieved.

[0095] When the optical signal transmitter 1 of the present invention is operated in low-power operation mode, the signal light source TX6 is directly modulated, making it impossible to adopt a polarization multiplexing transmission method. Instead, by applying the coding and modulation unit TX1 circuit of the present invention, it is possible to realize polarization time-domain multidimensional index optical modulation as shown in Figure 10. This makes effective use of the polarization plane and avoids a significant decrease in the frequency utilization efficiency of the optical signal LS. This makes it possible to provide a system that meets the first requirement above.

[0096] In the normal operation mode of the present invention, in the polarization time domain multidimensional (4,1,M-QAM) index optical modulation signal of FIG. 10, M-phase quadrature amplitude modulation signals are carried as symbols in all polarization time slots 1 to 8. Even in this case, the training sequence portion is maintained for synchronization on the receiving side. Also, although the normal operation mode is described as an M-phase quadrature amplitude modulation signal, an M-phase pulse amplitude modulation signal (M-PAM) may also be selected. Similarly, in the low power operation mode, a polarization time domain multidimensional (N,K,M-PAM) index optical modulation signal may also be selected instead of the polarization time domain multidimensional (N,K,M-QAM) index optical modulation signal.

[0097] (Second embodiment) 11 shows the transmitter TX2 of the optical signal transmitter 1 in the low-power optical information transmission system of the present invention. The invention according to this embodiment is basically the same as that of the first embodiment. However, unlike the first embodiment, the operation mode notification signal Snm notified from the operation mode controller TX2 to the optical signal receiver 3 is not transmitted via a separate line but via in-band notification transmitted from the transmitter TX.

[0098] In the transmitter TX2, the polarization multiplexed IQ optical modulator TX3, signal light source driver TX4, bias T circuit TX5, and signal light source TX6 are the same as those in the first embodiment, and therefore their explanations will be omitted. In this embodiment, the operation mode controller TX22 and coding modulator TX21 are different from those in the first embodiment.

[0099] The operation mode control unit TX22 receives an operation mode instruction signal 4c from the monitoring function unit 4 and notifies the communication path coding unit 1a and the coding and modulation unit TX21 of an operation mode notification signal Snm. However, unlike the first embodiment, the operation mode notification signal Snm is not transmitted out-of-band to the optical signal receiving device 3.

[0100] 12 shows the coding and modulation unit TX21 of the present invention. The coding and modulation unit TX21 includes an activation pattern mapper Mact, an X-polarized M-phase quadrature amplitude signal mapper MmpX, a Y-polarized M-phase quadrature amplitude signal mapper MmpY, a selector APM-SEL, a selector IND-SEL, multipliers TX100, TX102, TX104, TX106, and an adder TX108, as well as an operation mode notification pattern signal generator GSnm, an insert switch TX120, an insert switch TX122, an insert switch TX124, an insert switch TX126, and an insert switch TX128.

[0101] The operation mode notification signal Snm is supplied to the selector APM-SEL, the selector IND-SEL, and also to the operation mode notification pattern signal generator GSnm.

[0102] The operation mode notification signal Snm notified from the operation mode control unit TX2 operates the selector APM-SEL and the selector IND-SEL to select whether the output optical signal LS is an M-phase quadrature phase amplitude modulation signal in the normal operation mode or a polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal in the low power operation mode.

[0103] In addition, an operation mode notification pattern signal generator GSnm outputs a specific pulse pattern PSnm in order to transmit an operation mode notification signal Snm from the optical signal transmitter 1 to the optical signal receiver 3. This specific pulse pattern PSnm is added to the optical signal LS output from the optical signal transmitter 1 through the add switches (TX120 to TX126).

[0104] At this time, since the channel coding unit 1a supplying the code to the coding / modulation unit TX21 also receives the operation mode notification signal Snm, the signals of the index channels Index_ch and APM_ch (channel-coded index bits and channel-coded amplitude-phase modulation bits) may be stopped while the operation mode notification pattern signal generation unit GSnm outputs the specific pulse pattern PSnm.

[0105] (Third embodiment) 13 shows an example of an optical signal receiving device 3 in a low-power optical information transmission system according to the present invention. This embodiment is an optical signal receiving device 3 corresponding to the first example. The receiving unit RX (see FIG. 5) includes an operation mode receiving unit RX1, a receiving operation mode control unit RX2, a local oscillator light source driving unit RX3, a local oscillator light source RX4, a polarization phase diversity detector RX5, and an analog-to-digital conversion unit RX6. A demodulation unit 6 is disposed downstream of the receiving unit RX. The output of the demodulation unit 6 is decoded information DE(INFO).

[0106] The operation mode receiver RX1 terminates the optical signal LS and an out-band control line that is a separate line. The operation mode receiver RX1 also acquires the operation mode notification signal Snm notified from the transmitter TX of the optical signal transmitter 1. This information is notified to the reception operation mode controller RX2. The reception operation mode controller RX2 controls the local light source driver RX3 to set a predetermined drive power P according to the operation mode. LO The local light source driver RX3 sets the drive power P LO This makes it possible to provide a system that meets the second requirement above. That is, in the low power operation mode, the drive power P LO can be lowered.

[0107] Here, the driving power P LOIn the normal operation mode, the drive power P is set high so that the receiving sensitivity of the optical signal receiving device 3 is high. For example, it is 14.0 dBm as shown in FIG. 7(a). On the other hand, in the low power operation mode, it is set low. For example, it is 7.7 dBm as shown in FIG. 7(a). In other words, in the low power operation mode, the drive power P LO In the normal operating mode, the drive power P LO If it is high, it is enough.

[0108] In the low power operation mode, the receiving sensitivity of the optical signal receiving device 3 is lowered, but the driving power P LO In the low-power operation mode, the optical signal LS is transmitted using an index optical modulation signal, so the driving power P LO Even if the signal is reduced, the reception performance is ensured as explained in FIG.

[0109] The local light output from the local light source RX4 is input to the polarization phase diversity detector RX5 together with the optical signal LS received by the optical signal receiving device 3, where they are coherently detected. Here, the optical signal LS is converted into four detection currents. The four detection currents are the I and Q components of the X polarization and the I and Q components of the Y polarization. These are converted into four digital signals by the analog-to-digital converter RX6. These are input to the demodulator 6, where the decoding information DE(INFO) is decoded as described in FIG. 5. For more details, see Patent Document 1 or Patent Document 2.

[0110] (Fourth embodiment) FIG. 14 shows another example of an optical signal receiving device 3 in a low-power optical information transmission system according to the present invention. This embodiment is the optical signal receiving device 3 of the second embodiment. It is basically the same as that of the third embodiment. However, unlike the third embodiment, the operation mode notification signal Snm is not transmitted via a separate line but is transmitted by in-band notification of the optical signal LS transmitted from the transmitting device of the present invention. The receiving unit RX is the same as the receiving unit RX of the third embodiment, except that the operation mode receiving unit RX1 receives the operation mode notification signal Snm from a specific pulse separating unit DSnm, which will be described later. The optical signal receiving device 3 differs from the third embodiment in that a specific pulse pattern separating unit DSnm, which will be described later, is provided subsequent to the demodulating unit 6.

[0111] The operation mode notification signal Snm notified to the operation mode receiver RX1 is inserted as a specific pulse pattern PSnm into the optical signal LS by the optical signal transmitter 1. In this embodiment, the operation mode notification signal Snm is separated from this specific pulse pattern PSnm and input to the operation mode receiver RX1. Here, the specific pulse pattern PSnm indicating the operation mode is provided on the output side of the symbol demodulator 20 of the demodulator 6. This is due to the constraints of the demodulation process performed by the demodulator 6.

[0112] That is, if the specific pulse pattern PSnm indicating the operating mode inserted into the optical signal LS is separated before the demodulation unit 6, it becomes difficult to compensate for the frequency and phase offsets between the optical signal LS and the local light. If the optical signal LS is removed before these processes are performed, errors in the frequency offset compensation and phase offset compensation will increase. Therefore, these processes are performed first, and then the specific pulse pattern PSnm is separated from the main signal ML at a later stage. After that, it is input to the operating mode receiver RX1. The subsequent operations are the same as those in the third embodiment.

[0113] (Fifth embodiment) Figure 15 is a diagram illustrating another modulation form of the polarization time domain multidimensional (4,1,QPSK) index optical modulated signal transmitted by the optical signal transmitter 1 and the optical signal receiver 3 of the low-power optical information transmission system of the present invention.

[0114] In the first to fourth embodiments, a polarization time domain multidimensional (4,1,QPSK) index optical modulation signal transmitted by the QPSK optical modulation signal of FIG. 15(a) is applied in the low power operation mode. However, in place of this, this embodiment applies a 4-Stokes Vector Modulation (hereinafter referred to as "4-SVM") optical signal of FIG. 15(b).

[0115] This method defines signal points on a two-dimensional plane consisting of X and Y polarization planes, instead of the M-QAM method which defines signal points on the IQ plane. Unlike the first to fourth embodiments, the polarization planes are used to represent optical symbols, not to assign indexes. Therefore, from the perspective of index modulation, this method is applied in combination with time-domain index modulation, not with polarization-time multidimensional index modulation.

[0116] Figure 16 shows the subframe structure shown in this embodiment. Figure 16(a) shows the subframe configuration in low power operation mode, and Figure 16(b) shows the subframe configuration in normal operation mode. Referring to Figure 16(a), subframe #1 and subframe #2 have four time slots per subframe, and each symbol has two bits of information ranging from 00 to 11 depending on the polarization state.

[0117] Here, symbols with index bits "00" and "10" are superimposed in the second time slot of subframe #1 and the third time slot of subframe #2. In other words, light with polarization states corresponding to index bits "00" and "10" is used as the symbol.

[0118] In addition to the X and Y polarization planes, two index bits can be transmitted in four polarization planes: an elliptical polarization plane (01) with its major axis in the X polarization plane and an elliptical polarization plane (01) with its major axis in the Y polarization plane. In other words, this index bit can transmit two bits of information in four polarization planes. In other words, it is possible to transmit the same amount of information as polarization time-domain multidimensional (4,1,QPSK) index optical modulation.

[0119] 16(b), in the normal operation mode, symbols are superimposed on all time slots, and all symbols are M-phase amplitude-phase optical modulation signals.

[0120] In this embodiment, an example is shown in which this modulation method is used to configure a subframe with a length of four time slots, similar to the polarization time domain multidimensional (4,1,QPSK) applied in the first to fourth embodiments. That is, a time domain (4,1,4-SVM) index optical modulation signal is generated.

[0121] The block configuration of the transceiver that realizes this method is the same as that of the first to fourth embodiments. However, in the low-power operation mode, the optical signal transmission device is driven to generate signal light having the polarization plane shown in Fig. 15(b) by using different operation algorithms for the activation pattern mapper Mact in Fig. 12, the X-polarized M-phase quadrature amplitude signal mapper MmpX, and the Y-polarized M-phase quadrature amplitude signal mapper MmpY. That is, the activation pattern mapper Mact generates an activation pattern corresponding to a time-domain index modulation signal, rather than an activation pattern corresponding to a polarization time-domain multidimensional index modulation signal.

[0122] Furthermore, the X-polarized M-phase quadrature amplitude signal mapper MmpX and the Y-polarized M-phase quadrature amplitude signal mapper MmpY are driven to generate a 4-SVM optical signal, but the Index bits and APM bits output from the channel coding unit 1a remain unchanged.

[0123] In the receiving device, the demodulator 6 in FIG. 13 is driven to demodulate the time domain index modulated signal and the 4-SVM optical signal.

[0124] On the other hand, in normal operation mode, as shown in FIG. 9, the selector IND-SEL outputs zero, and symbols are loaded onto all time slots. These symbols then become M-phase quadrature amplitude modulated signals. That is, the X-polarized M-phase quadrature amplitude signal mapper MmpX and the Y-polarized M-phase quadrature amplitude signal mapper MmpY, to which the channel-coded APMbitsX and channel-coded APMbitsY are input via APM_chX and APM_chY, respectively, output the IQ components of the X-polarized wave and the IQ components of the Y-polarized wave for M-phase quadrature amplitude modulation. Therefore, in this embodiment, a time-domain (N, K, M-SVM) index optical modulated signal is output in low-power operation mode, and an M-phase quadrature amplitude modulated signal is output in normal operation mode.

[0125] In the low-power operation mode, activation patterns are generated by directly modulating laser light. However, when a laser light source is directly modulated, the continuity (coherence) of the optical phase deteriorates. This embodiment is effective in that it realizes optical index modulation even for directly modulated optical pulse trains with deteriorated coherence, and can achieve the same communication capacity as polarization time-domain multidimensional (4,1,QPSK) modulation while using low power.

[0126] (Sixth embodiment) FIG. 17 shows an example of the configuration of a system incorporating the low-power optical information transmission system of the present invention. The embodiment is a TWDM-PON system configuration. Information devices of system subscribers are connected on the ONU device side. An optical signal transmitter 1 and an optical signal receiver 3 of the present invention are incorporated into the ONU and an Optical Service Unit (OSU). The ONU incorporates the optical signal transmitter 1 of the low-power optical information transmission system of the present invention for transmitting on the upstream line to the OSU. The ONU also incorporates the optical signal receiver 3 of the low-power optical information transmission system of the present invention for receiving on the downstream line. During low-power operation, this ONU transmits a polarization time-domain index optically modulated signal to the OSU as a transmit signal, and receives a time-domain index optically modulated signal from the OSU.

[0127] In the OSU equipment on the carrier side, optical signal transmitter 1 transmits a time-domain index modulated signal, and optical signal receiver 3 receives a polarization-time-domain multidimensional index modulated signal. An optical coupler or optical switch called a Photonics Aggregator is installed between the ONU and OSU. An Edge Router is installed beyond the OSU equipment, where forwarding processing at the Ethernet or IP level is performed, and communication traffic is distributed to the relay network side.

[0128] As shown in Figure 17, the wavelengths of each OSU are different from each other. The operating mode selected by each OSU changes depending on the amount of communication traffic required by the subscriber. Figure 18 shows this situation. For example, an ONU accommodating a subscriber user requiring a large amount of communication traffic selects a wavelength channel that operates in the normal operation mode. On the other hand, an ONU accommodating a subscriber user requiring a small amount of communication traffic selects a wavelength channel that operates in the low-power operation mode.

[0129] The ONU can change the laser oscillation optical frequency of the signal light source and the local light source by switching the operating mode. The change in the laser oscillation optical frequency is achieved by changing the driving temperature of the light source.

[0130] In this embodiment, the signal transmitted from the ONU to the OSU may be a time-domain (N, K, M-SVM) index optical modulation signal described in the fifth embodiment instead of a polarization time-domain index optical modulation signal. [Industrial Applicability]

[0131] The present invention is applied to optical access networks, which are essential social infrastructure systems in an advanced information society. Conventional optical access networks operate continuously regardless of the state of communication traffic, and measures to reduce power consumption are insufficient.

[0132] This invention enables switching of operating modes according to the optical access network's operational policy and communication traffic conditions. The low-power operating mode utilizes a time-domain index optical modulation scheme, which thins out optical symbols and utilizes an activation pattern, which reduces the transmission rate, thereby enabling highly power-efficient optical information transmission. This characteristic is utilized to reduce the signal light driving power of the transmitter and the local oscillator power of the receiver. If communication traffic demand continues to occur with a similar traffic distribution to the current situation, it is estimated that the low-power optical information transmission system of this invention will operate in low-power operating mode for approximately 90% of its total operating time. The overall power consumption reduction for ONU equipment for 30 million subscribers is expected to be approximately 0.1 trillion watt-hours compared to the current situation, resulting in significant power savings. [Explanation of symbols]

[0133] 1 Optical signal transmitter 1a Communication path encoder 2 Transmission Path 3 Optical signal receiving device 4 Monitoring function section 4c instruction signal 6 Demodulation section 10 Index demodulation section 20 Symbol demodulation section TX transmitter INF original information (S / P) Serial / Parallel Conversion Section (MAP) Mapping RXe Receiver RX Polarization Rotation Compensation Unit RXf timing channel determination section (DMAP) Index Demapping (FEC Dec.) Error Correction Section (FC) Frequency offset compensation section (PC) Phase Shift Compensation Unit (DMAP) Demap section 29 Parallel / Serial Conversion Unit LS optical signal Snm Operation mode notification signal AP CS Activation Pattern Signal DE(INFO) Decryption information TX1 coding and modulation section TX2 operation mode control section IQ polarization multiplexing TX3 optical modulation section TX4 signal light source driver TX5 Bias Tee Circuit TX6 signal light source TX21 coding and modulation section TX22 operation mode control unit Mact Activation Pattern Mapper Mapper MmpX: M-phase quadrature amplitude signal of X-polarized wave Mapper MmpY Y-polarized M-phase quadrature amplitude signal S AP Activation Pattern Modulation Codes S APX Activation pattern modulation code for X polarization S APY Activation pattern modulation code for Y polarization S MQ M-ary quadrature amplitude modulation code APM-SEL selector IND-SEL selector TX108 Adder TX100 Multiplier TX102 multiplier TX104 multiplier TX106 multiplier ML Main signal line GSnm Operation mode notification pattern signal generator PSnm specific pulse pattern TX120 Insertion Switch TX122 Insertion Switch TX124 Insertion Switch TX126 Insertion Switch TX128 Insertion Switch RX1 Operation Mode Receiver RX2 Reception operation mode control section RX3 local oscillator driver RX4 local light source RX5 Polarization Phase Diversity Detector RX6 Analog-to-Digital Converter P LO Drive Power DSnm specific pulse separation unit DSnm specific pulse pattern separation unit

Claims

1. The optical signal transmitting device has an optical signal receiving device, and the optical signal transmitting device has: M-phase quadrature amplitude modulation signal, The optical signal transmitter in a low-power optical information transmission system has a monitoring function unit that transmits an operation mode notification signal that notifies whether the optical signal transmitter operates using a polarization time domain multidimensional (N-QAM), K-QAM, or M-QAM index optical modulation signal, a channel coding unit that separates original information into index bits to be transmitted by the polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal and amplitude phase modulation bits to be transmitted by the M-phase quadrature phase amplitude modulation signal, processes the index bits and amplitude phase modulation bits into channel coded index bits and channel coded amplitude phase modulation bits, and outputs the processed bits; an optical signal transmitting device having a transmitting unit that transmits, based on the channel-coded index bits and the channel-coded amplitude-phase modulation bits, either the polarization time-domain multidimensional (N, K, M-QAM) index optical modulation signal or the M-phase quadrature-phase amplitude modulation signal, and the operation mode notification signal, to the optical signal receiving device.

2. The optical signal transmitting device has an optical signal receiving device, and the optical signal transmitting device has: M-phase quadrature amplitude modulation signal, The optical signal transmitter in a low-power optical information transmission system has a monitoring function unit that transmits an operation mode notification signal that notifies whether the optical signal transmitter operates using a time domain (N-, K-, or M-Stokes Vector Modulation) index optical modulation signal, a channel coding unit that separates original information into index bits transmitted by the time domain (N, K, M-Stokes Vector Modulation) index optical modulation signal and amplitude phase modulation bits transmitted by the M-phase quadrature phase amplitude modulation signal, processes the index bits into channel coded index bits and channel coded amplitude phase modulation bits, and outputs the processed bits; an optical signal transmitting device having a transmitting unit that transmits the channel-coded index bits, one of the time-domain (N, K, M-Stokes Vector Modulation) index optical modulated signal and the M-phase quadrature phase optical amplitude modulated signal from the channel-coded amplitude phase modulated bits, and the operation mode notification signal to the optical signal receiving device.

3. The optical signal transmitting device has an optical signal receiving device, and the optical signal transmitting device has: Operates on M-phase quadrature amplitude modulated optical signals, or The optical signal receiving device in a low-power optical information transmission system has a monitoring function unit that transmits an operation mode notification signal that notifies whether the optical signal receiving device operates using a polarization time domain multidimensional (N-QAM), K-QAM, or M-QAM index optical modulation signal, The device has a local light source, a polarization phase diversity detector, and a demodulator. an optical signal receiving device that demodulates the M-phase quadrature amplitude modulation signal and the polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal sent from the optical signal transmitting device in accordance with the operation mode notification signal from the optical signal transmitting device.

4. The optical signal transmitting device has an optical signal receiving device, and the optical signal transmitting device has: Operates on M-phase quadrature amplitude modulated optical signals, or The optical signal receiving device in a low-power optical information transmission system has a monitoring function unit that transmits an operation mode notification signal that notifies whether the optical signal receiving device operates using a time domain (N-, K-, or M-Stokes Vector Modulation) index optical modulation signal, The device has a local light source, a polarization phase diversity detector, and a demodulator. an optical signal receiving device that demodulates the M-phase quadrature amplitude modulated signal and the time domain (N, K, M-Stokes Vector Modulation) index optical modulated signal sent from the optical signal transmitting device in accordance with the operation mode notification signal from the optical signal transmitting device.

5. A low-power optical information transmission system including an optical signal transmitting device, an optical signal receiving device, and a monitoring function unit, The monitoring function unit An optical signal transmitting device, M-phase quadrature amplitude modulation signal, transmitting an operation mode notification signal to the optical signal transmitter, notifying the optical signal transmitter whether it will operate using a polarization time domain multidimensional (N-QAM), K-QAM, or M-QAM index optical modulation signal; The optical signal transmitting device includes: a channel coding unit that separates original information into index bits to be transmitted by the polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal and amplitude phase modulation bits to be transmitted by the M-phase quadrature phase amplitude modulation signal, processes the index bits and amplitude phase modulation bits into channel coded index bits and channel coded amplitude phase modulation bits, and outputs the processed bits; a transmitter that transmits, to the optical signal receiving device, either the polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal or the M-phase quadrature phase amplitude modulation signal, and the operation mode notification signal from the channel-coded index bits and the channel-coded amplitude and phase modulation bits, based on the operation mode notification signal; The optical signal receiving device includes: The device comprises a local light source, a polarization phase diversity detector, and a demodulator. demodulating the M-phase quadrature amplitude modulated signal and the polarization time domain multidimensional (N, K, M-QAM) index optical modulated signal sent from the optical signal transmitter in accordance with the operation mode notification signal from the optical signal transmitter; A low-power optical information transmission system in which, when the optical signal demodulation device receives the operation mode notification signal that operates with the polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal, the power of the local oscillator light source is made lower than the power of the local oscillator light source when receiving the M-phase quadrature phase amplitude modulation signal.

6. A low-power optical information transmission system including an optical signal transmitting device, an optical signal receiving device, and a monitoring function unit, The monitoring function unit An optical signal transmitting device, M-phase quadrature amplitude modulation signal, Transmitting an operation mode notification signal to the optical signal transmitter, which notifies the optical signal transmitter which of a time domain (N-, K-, M-Stokes Vector Modulation) index optical modulation signal to operate with, The optical signal transmitting device includes: a channel coding unit that separates original information into index bits transmitted by the time domain (N, K, M-Stokes Vector Modulation) index optical modulation signal and amplitude phase modulation bits transmitted by the M-phase quadrature phase amplitude modulation signal, processes them into channel coded index bits and channel coded amplitude phase modulation bits, and outputs them; a transmitter that transmits, from the channel-coded index bits and the channel-coded amplitude-phase modulation bits based on the operation mode notification signal, either the time-domain (N, K, M-Stokes Vector Modulation) index optical modulation signal or the M-phase quadrature phase optical amplitude modulation signal, and the operation mode notification signal to the optical signal receiving device; The optical signal receiving device includes: The device comprises a local light source, a polarization phase diversity detector, and a demodulator. demodulating the M-phase quadrature amplitude modulated signal and the time domain (N, K, M-Stokes Vector Modulation) index optical modulated signal sent from the optical signal transmitter in accordance with the operation mode notification signal from the optical signal transmitter; A low-power optical information transmission system in which, when the optical signal demodulation device receives the operation mode notification signal that operates with the polarization time domain multidimensional (N, K, M-QAM) index optical modulation signal, the power of the local oscillator light source is made lower than the power of the local oscillator light source when receiving the M-phase quadrature phase amplitude modulation signal.

7. 7. A low-power optical data transmission system according to claim 5, wherein said operation mode notification signal is transmitted to said optical signal receiving device as an out-of-band signal.

8. 7. A low-power optical data transmission system according to claim 5, wherein said operation mode notification signal is transmitted to said optical signal receiving device as an inbound signal.

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