Nippon Telegraph and Telephone Corporation

Nippon Steel Sumitomo Metal Corporation

Akihide Sano

Yutaka Miyamoto

Takayuki Kobayashi

Koichi Ishihara

Riichi Kudo

Yasushi Takatori

Masato Mizoguchi

Etsushi Yamazaki

Munehiro Matsui

Eiji Yoshida

Tadao Nakagawa

Shogo Yamanaka

Hideyuki Nosaka

Masahito Tomizawa

Akira Hirano

Kazushige Yonenaga

Shoichiro Kuwahara

Tomoyoshi Kataoka

Gentaro Funatsu

Eiichi Yamada

Mikio Yoneyama

Koichi Fukuda

Munehiko Nagatani

Hiroshi Yamazaki

Masato Sugiura

Michitaka Sakaida

Tomoyuki Nakagawa

Yoshifumi Morizane

Keisuke Irie

In the conventional technique, only an output having a bandwidth identical to the bandwidth of individual DACs has been obtained even by using a plurality of DACs. Also, even when the output of a bandwidth broader than the individual DAC is obtained, there has been a problem associated with asymmetricity of a circuit configuration. In a signal generating device of the present invention, a plurality of normal DACs are combined to realize an analog output of a broader bandwidth beyond the output bandwidth of the individual DACs, and the problem of the asymmetricity of the circuit configuration is also resolved. A desired signal is separated into a low-frequency signal and a high-frequency signal in a frequency domain, and a series of operation of constant (r)-folding the amplitude of the high-frequency signal and shifting it on the frequency axis to superimpose it on the low-frequency signal are made in a digital domain. The output of each DAC is switched by an analog multiplexer.

Signal generating device

To enable signal position detection, frequency offset compensation, clock offset compensation, and chromatic dispersion amount estimation in a communication system based on coherent detection using an optical signal, even on a signal having a great offset in an arrival time depending on a frequency due to chromatic dispersion. An optical signal transmitting apparatus generates specific frequency band signals having power concentrated on two or more specific frequencies and transmits a signal including the specific frequency band signals. An optical signal receiving apparatus converts a received signal into a digital signal, detects positions of the specific frequency band signals from the converted digital signal, estimates frequency positions of the detected specific frequency band signals, and detects a frequency offset between an optical signal receiving apparatus and an optical signal transmitting apparatus. Moreover, the optical signal receiving apparatus detects a clock offset between the optical signal receiving apparatus and the optical signal transmitting apparatus from an interval between the estimated frequency positions of the specific frequency band signals. Furthermore, the optical signal receiving apparatus estimates temporal positions of the detected specific frequency band signals and detects a chromatic dispersion amount from a difference between the temporal positions of the specific frequency band signals corresponding to different frequencies.

Signal generating circuit, optical signal transmitting apparatus, signal receiving circuit, method for establishing optical signal synchronization, and optical signal synchronization system

A frequency domain multiplexed signal receiving method which decodes received signals that are multiplexed in a frequency domain, includes: a digital signal acquisition step of acquiring digital signals from the received signals that are multiplexed in the frequency domain; an offset discrete Fourier transform step of applying an offset discrete Fourier transform to odd discrete point numbers based on the acquired digital signals; and a decode step of decoding frequency domain digital signals in the frequency domain obtained by the offset discrete Fourier transform, and that are the frequency domain digital signals of one or more frequency channels.

Method for receiving frequency domain multiplexed signal and device for receiving frequency domain multiplexed signal

A polarization state of a transmission signal can be changed at a high speed based on a symbol-rate By switching a first switch, a second switch, and a third switch with time, one of an X-polarized wave_I-signal as a Y-polarized wave_I-signal, a signal caused by performing logical inversion for an X-polarized wave_I-signal, an X-polarized wave_Q-signal and a signal caused by logical inversion for an X-polarized wave_Q-signal is input to a second modulator. Further, by switching the first switch, the second switch and the third switch with time, the second modulator is input one of the X-polarized wave_I-signal as the Y-polarized wave_Q-signal, the X-polarized wave_I-signal, the signal caused by performing logical inversion for the X-polarized wave_I-signal, the X-polarized wave_Q-signal and the signal caused by performing logical inversion for the X-polarized wave_Q-signal. Thereby, a polarization state of a transmission signal can be changed at high speed based on a symbol-rate speed.

Transmission method, reception method, transmitter apparatus, and receiver device

When a circuit that calculates a frequency offset using a shape of a frequency spectrum is implemented by hardware, the circuit size can be reduced. A frequency offset estimating method for estimating the difference between a carrier frequency of a reception signal and the frequency of an output signal of a local oscillator includes performing a discrete Fourier transform on a reception signal previously sampled at a predetermined sampling frequency and outputting a frequency spectrum with a plurality of frequency components, calculating an average power of the frequency spectrum, calculating a threshold by adding a predetermined value to the average power or power obtained by multiplying the average power by a constant, performing 1-bit quantization on powers of the frequency components of the frequency spectrum based on the threshold, and calculating a centroid frequency by multiplying frequencies of the frequency components by powers of 1-bit quantized frequency components, calculating the sum of multiplied products, and dividing the sum of the products by the sum of the powers of the 1-bit quantized frequency components of the frequency spectrum.

Frequency offset estimating method and frequency offset estimating apparatus

In order to compensate for chromatic dispersion caused by optical fiber transmission in a communication system with coherent detection using optical signals, specific frequency band signals are used to enable estimation of a chromatic dispersion value. The chromatic dispersion value calculating apparatus is provided with: a signal distributing circuit which distributes, into a plurality of signal sequences, an electrical digital signal converted from received optical signals of an optical signal transmitted by an optical signal transmitting apparatus, in which a known signal with concentrated frequency components of a plurality of specific frequencies is appended to a signal generated from a transmission data sequence; a plurality of frequency band pass filter circuits, each of which separating only each of a plurality of specific frequency components in which the known signal is included from each of the signal sequences distributed by the signal distributing circuit, and passing each of the specific frequency components therethrough; a plurality of power calculating circuits which are provided so as to correspond respectively to the plurality of frequency band pass filter circuits and which calculate power values of signals output from the corresponding frequency band pass filter circuits; a delay time calculating circuit which detects times at which power has the maximum value or times at which the power exceeds a predetermined threshold value, respectively from signal sequences of the power values output from the plurality of power calculating circuits, and which compares the detected times; and a chromatic dispersion value calculating circuit which calculates a chromatic dispersion value based on a comparison result of the times by the delay time calculating circuit.

Chromatic dispersion value calculating apparatus, optical signal receiving apparatus, optical signal transmitting apparatus, and chromatic dispersion value calculation method

Provided is a frequency offset estimation apparatus that appropriately estimates and compensates for a frequency offset of a received signal when estimating the frequency offset which is the difference between a carrier frequency of the received signal and the frequency of an output signal of a local oscillator. The frequency offset estimation apparatus converts the received signal sampled in advance with a predetermined sampling frequency into a frequency spectrum having N frequency components, limits a frequency band of negative frequency components from 1 to N/2 of the frequency spectrum and a frequency band of positive frequency components from N/2+1 to N of the frequency spectrum, calculates the sum of the squares of the positive frequency components of the frequency spectrum that have been subjected to frequency band limitation and the sum of the squares of the negative frequency components of the frequency spectrum that have been subjected to frequency band limitation to calculate power of the positive frequency components and power of the negative frequency components, and cyclically shifts all frequency components of the frequency spectrum in a frequency domain until the absolute value of a power difference between the power of the positive frequency components and the power of the negative frequency components is less than or equal to a predetermined threshold value, and estimates the frequency offset based on a shift amount until the absolute value is less than or equal to the threshold value.

Frequency offset estimation apparatus, reception apparatus, frequency offset estimation method, and reception method

A receiver device receives a signal inputted to one or a plurality of ports as a plurality of received signals, and includes: a phase offset estimating unit that, on the basis of a unique word of each signal block contained in said received signal, estimates the phase offset, and a phase offset compensating unit that, on the basis of a phase offset estimated by said phase offset estimating unit, compensates the phase offset; the receiver device uses a known signal component (unique word) contained in a frequency-domain equalized signal to compensate the phase offset, whereby it compensates complex phase offset fluctuation, and estimates the phase offset of a signal obtained at each port.

Receiver device, communication system and receiving method

An optical modulator and an optical transmission system convert continuous light of a multiple wavelength light source, which generates the continuous light with a fixed and complete phase but different frequencies, to a modulator driving signal so as to generate a light subcarrier with each frequency at the center and modulate the continuous light to the light subcarrier by using the modulator driving signal. In the case where an optical modulation is carried out by an optical IQ-modulator, transmitting data, for example, is converted to two parallel data A(t) and B(t), an I phase signal, in which the data A(t)+B(t) are modulated with a clock signal with a frequency &#x3c9;, and a Q phase signal, in which the data A(t)&#x2212;B(t) are modulated with a clock signal with a &#x3c0;/2 phase shifted, are generated, and the I phase signal and the Q phase signal are applied to electrodes of the optical IQ-modulator, respectively.

Optical modulation circuit and optical transmission system

A high-performance optical OFDM receiver is realized. A subcarrier separation circuit receives an optical OFDM signal consisting of two subcarriers A and B and separates a subcarrier component, signal light and first local oscillator light are input to the subcarrier separation circuit, the subcarrier separation circuit converts the signal light and the first local oscillator into a baseband electrical signal, the subcarrier separation circuit converts the baseband electrical signal into a digital signal, the subcarrier separation circuit shifts the frequency of the converted digital signal so that a center frequency of the subcarrier A becomes zero, and the subcarrier separation circuit adds a frequency shifted signal to a signal obtained by delaying the frequency shifted signal by &#xbd; of a symbol time to separate a component of the subcarrier A.

Optical OFDM receiver, optical transmission system, subcarrier separation circuit, and subcarrier separation method

An optical transmission system is provided in which the optimum operating point of a Mach-Zehnder interferometer, matched to the optical frequency of the light source on the transmitting side, can be set. The optical receiver () has an infinitesimal-modulated signal component detection circuit (), which uses the signal train output from a balanced detection circuit () to detect the infinitesimal-modulated signal component applied to the phase adjustment terminal () of an MZI () by an infinitesimal-modulated signal oscillation circuit (); a synchronous detection circuit (), which synchronously detects the infinitesimal-modulated signals output from the infinitesimal-modulated signal component detection circuit () and infinitesimal-modulated signal oscillation circuit () and detects the error signal component arising from the shift between the optical signal carrier frequency and the optical frequency characteristic of the MZI (); and a controller (), which outputs a control signal to adjust the phase difference between two split optical signals output from the MZI () so as to correct the shift amount.

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Yokosuka, Japan

Akihide Sano