Abstract: An input bit error ratio estimating method executed by a communication control unit includes a computing, a condition determining, a first input BER estimating, a second input BER estimating, a third input BER estimating, and an input BER estimation result outputting. In the condition determining, the communication control unit determines which of a plurality of conditions set in advance to be narrowed down to one has been established, based on a post-internal decoding residual error detection ratio. Based on the condition that is determined in the condition determining as one that has been established, the communication control unit selects one out of a plurality of processing procedures for estimating the input BER, namely, selects one of the first input BER estimating to the third input BER estimating and executes the selected processing.

Abstract: An optical communication system includes an optical-signal transmission unit transmitting an existing optical signal and a low-rate-signal superimposition unit superimposing a low-rate signal on the existing optical signal by intensity modulation. It further includes: a low-rate-signal extraction unit that extracts the low-rate signal from the existing optical signal on which the low-rate signal is superimposed and converts the extracted low-rate signal into a low-rate electric signal; an add-on optical-signal transmission unit that transmits an add-on optical signal; a low-rate-signal superimposition unit that superimposes a low-rate signal on the add-on optical signal by the intensity modulation based on the low-rate electric signal; and a repeater that repeats the add-on optical signal on which the low-rate signal is superimposed, to a transmission destination.

Abstract: An error-correction coding method that includes outer coding of performing a coding process for an outer code; and inner coding of performing a coding process for an inner code that has an error correction capability adjusted based on an error correction capability of the outer code.

Abstract: In an optical transfer system, an optical transmission unit generates an optical signal in which respective polarization components are alternately present on a time axis, a time period during which the respective polarization components are simultaneously present on the time axis is substantially zero, and a symbol repetition cycle of optical signals of the respective polarization components becomes Ts, an optical reception unit causes an interference between local oscillation light and a received optical signal and converts an interfered optical signal to an electric signal, and a received electric-signal processing unit performs analog-digital conversion of an electric signal, elimination of a delay difference of Ts/2 between the respective polarized signal components, and adaptive equalization of a distortion other than the delay difference.

Abstract: An optical transmission and reception system in which a plurality of tributary signals are converted into multilevel modulated light for transmission and reception. An apparatus for transmitting multilevel modulated light includes: FECs which perform error correction processing including addition of a tributary identifier; and a GEAR BOX which performs rate conversion on the processed signals.

Abstract: An optical transmitter for converting an input data series into an optical multi-level signal and for outputting the same, includes an LUT in which data for executing optical multi-level modulation is stored and from which first modulation data and second modulation data are output based on the input data series. A DAC converts the first modulation data by D/A conversion to generate a first multi-level signal. A DAC converts the second modulation data by D/A conversion to generate a second multi-level signal. A dual-electrode MZ modulator includes a first phase modulator for modulating light from a light source in accordance with the first multi-level signal and a second phase modulator for modulating light from the light source in accordance with the second multi-level signal, and combines an optical signal from the first phase modulator and an optical signal from the second phase modulator to output the optical multi-level signal.

Abstract: An optical network system includes a first node that converts input signals of n systems into optical signals having wavelengths different for each of the systems and wavelength-multiplexes and transmits the optical signals and a second node that selects signals of n systems from the wavelength-multiplexed signals and outputs the signals. The first node includes an optical coupler that divides the input signals into operating system signals and redundant signals, TPNDs that convert the operating systems into optical signals, an optical switch that selects standby system signals from the redundant signals, and a TPND that converts the standby system signals into optical signals in a storage mode corresponding to a type of the standby system signals.

Abstract: An optical receiving apparatus includes: an A/D converting circuit; a received-signal demodulating circuit that demodulates a received digital signal from the A/D converting circuit into an m-bit received signal; a soft-decision-data generating circuit that generates n-bit (n?m) soft-decision data based on the m-bit received signal; and an error correcting circuit that performs error correction based on the n-bit soft-decision data and outputs an error-corrected received signal. The soft-decision-data generating circuit generates soft-decision data of n bits (n=p+1) that corresponds to a determination result according to 2n?1 soft-decision thresholds, by using an MSB of the m-bit received signal as hard-decision data, and by using, as reliability information, a result of comparison between a plurality of bits (k bits, where k?m) on an MSB side of the m-bit received signal and a fixed threshold, or p bits (p?m?k) selected from (m?k) bits on an LSB side of the m-bit received signal.

Abstract: An error correction encoding device includes an outer encoding circuit that performs encoding processing for an outer code and an inner encoding circuit that performs encoding processing for an inner code. The inner encoding circuit includes an inner-encoding input circuit that performs interleaving processing in which a parallel input sequence is divided into lanes and in which a barrel shift is performed for each inner frame in the lanes. Thus, allocation ratios between an information sequence area and a parity sequence area are made uniform.

Abstract: An input bit error ratio estimating method executed by a communication control unit includes a computing, a condition determining, a first input BER estimating, a second input BER estimating, a third input BER estimating, and an input BER estimation result outputting. In the condition determining, the communication control unit determines which of a plurality of conditions set in advance to be narrowed down to one has been established, based on a post-internal decoding residual error detection ratio. Based on the condition that is determined in the condition determining as one that has been established, the communication control unit selects one out of a plurality of processing procedures for estimating the input BER, namely, selects one of the first input BER estimating to the third input BER estimating and executes the selected processing.

Abstract: An FEC frame structuring device includes a multi-lane distributing unit that distributes a data frame to be transmitted to n lanes, FEC coding units each performs FEC coding of the distributed data frame independently for each of the n lanes to generate an FEC frame, a multiplexing unit that multiplexes the FEC frame from the FEC coding units by relating to m channels of an optical signal, a demultiplexing unit that demultiplexes the m channels of the received optical signal by relating to the n lanes, FEC decoding units each performs FEC decoding of the demultiplexed FEC frame independently for each of the n lanes, and a multi-lane synchronizing unit that synchronizes the n lanes with each other after the FEC decoding performed by the FEC decoding units to reconstruct the original data frame.

Abstract: An optical switch according to the present invention includes a multiple-stage optical-switch unit that includes one input port and a plurality of output ports that are configured by connecting multiple stages of optical switching elements each of which includes three or more optical input-output ports; and a switching control circuit that, when receiving a switching instruction to switch an output destination of light input from the input port, executes at first a first control that changes setting of an optical switching element that is included in part not overlapping with an optical transmission channel reaching an optical output port before switching in an optical transmission channel reaching an optical output port after switching and is positioned at a point other than a branch point from an overlapping part, and then executes a second control that changes setting of an optical switching element that is positioned at the branch point.

Abstract: Provided is a multi-value optical transmitter in which a DC bias may be controlled to be stabilized so as to obtain stable optical transmission signal quality in multi-value modulation using a dual-electrode MZ modulator. The multi-value optical transmitter includes: D/A converters for performing D/A conversion on first and second modulation data which are set based on an input data series, so as to generate a first and a second multi-value signal, respectively; a dual-electrode MZ modulator including phase modulators for modulating light from a light source based on the first multi-value signal and the second multi-value signal, so as to combine optical signals from the phase modulators to output the optical multi-value signal; an optical output power monitor for detecting average power of the optical multi-value signal; and a DC bias control unit for controlling a DC bias for the dual-electrode MZ modulator, so as to maximize the average power.

Abstract: In an optical transfer system, an optical transmission unit generates an optical signal in which respective polarization components are alternately present on a time axis, a time period during which the respective polarization components are simultaneously present on the time axis is substantially zero, and a symbol repetition cycle of optical signals of the respective polarization components becomes Ts, an optical reception unit causes an interference between local oscillation light and a received optical signal and converts an interfered optical signal to an electric signal, and a received electric-signal processing unit performs analog-digital conversion of an electric signal, elimination of a delay difference of Ts/2 between the respective polarized signal components, and adaptive equalization of a distortion other than the delay difference.

Abstract: An optical communication system includes an optical-signal transmission unit transmitting an existing optical signal and a low-rate-signal superimposition unit superimposing a low-rate signal on the existing optical signal by intensity modulation. It further includes: a low-rate-signal extraction unit that extracts the low-rate signal from the existing optical signal on which the low-rate signal is superimposed and converts the extracted low-rate signal into a low-rate electric signal; an add-on optical-signal transmission unit that transmits an add-on optical signal; a low-rate-signal superimposition unit that superimposes a low-rate signal on the add-on optical signal by the intensity modulation based on the low-rate electric signal; and a repeater that repeats the add-on optical signal on which the low-rate signal is superimposed, to a transmission destination.

Abstract: An error correcting device in an optical communication system that transmits a transmission frame formed by adding an overhead and an error correction code to information data uses a concatenated code or an iterated code of at least two error correction codes as an outer code and an error correction code for soft-decision decoding as an inner code.

Abstract: In a digital signal processing optical transmission apparatus such as a predistortion or OFDM type one, optical transmission at a stable S/N ratio is intended to be able to be made by controlling an output of an optical transmission signal with fixed average power, even if a peak to average power ratio of the optical transmission signal changes. The apparatus is provided with an average power calculation unit (30) that calculates the average power of a digital signal outputted from a digital signal processing circuit (2), and an optical power variable unit (31) that serves to make constant the average power of an optical transmission signal outputted from an optical vector modulator (5).

Abstract: An optical communication system including optical transmission systems each includes a transmission processing unit and a receiving processing unit, wherein the transmission processing unit includes an optical transmission unit that converts electric signals into optical signals, an auxiliary optical transmission unit that converts a part of the electric signals into an optical signal having a wavelength other than wavelengths of the optical signals generated by the optical transmission unit, and outputs the generated optical signal to a different transmission processing unit, and a wavelength multiplexing unit, and the receiving processing unit includes a wavelength demultiplexing unit, an optical receiving unit that converts the optical signals having the wavelengths of the optical signals generated by the optical transmission unit into electric signals, respectively, and an auxiliary optical receiving unit that converts the optical signal having the wavelength of the optical signal generated by the auxilia

Abstract: Provided is an error correction method for an optical communication system that transmits a transmission frame formed of information data added with an overhead and an error correction code, the error correction method including adjusting a size of an FEC redundant area of an FEC frame for storing client signals of different signal types in accordance with the client signals so that transmission rates of the FEC frame for the respective client signals have an approximately N-multiple relationship (N is a positive natural number). With this, it is possible to obtain an error correction method and device capable of providing a high-quality and high-speed optical communication system without performance degradation caused by jitter or the like and with the common use of circuits having a reduced circuit scale.

Abstract: A pre-equalization optical transmitter includes: an RZ conversion circuit for generating an RZ-type input data sequence based on an NRZ-type input data sequence and a clock that is twice the speed of the NRZ-type input data sequence; a digital filter for generating pre-equalized data by a convolution operation between the RZ-type input data sequence and a desired transfer function corresponding to the wavelength dispersion of an optical fiber transmission path; D/A converters for performing D/A conversion on the pre-equalized data to output analog pre-equalized data; and a vector modulator for modulating light from a laser light source based on the analog pre-equalized data to output an RZ-type optical signal.