Abstract: The present invention aims at providing a control technique for an optical modulator, which can accurately detect a phase shift between signals of a drive system of an optical modulator, to feedback control. To this end, a control apparatus of the present invention comprises, for example, in an optical modulator which generates a signal light corresponding to the CS-RZ modulation method by two LN modulators connected in series: a monitor section that extracts a specific frequency component from a spectrum of the CS-RZ signal light output from a latter LN modulator to detect the optical intensity thereof, and a control CPU that determines a phase shift between first and second drive signals corresponding to a clock signal supplied to the latter LN modulator based on the optical intensity detected by the monitor section, and controls a phase difference between the drive signals so that the phase shift is minimized.

Abstract: A repeating apparatus disposed at an end point of each divisional repeating interval of a light transmission line performs a first dispersion compensation step, an optical add/drop multiplexing step and a second dispersion compensation step to perform repeating transmission. The ratio of an over compensation amount at the second dispersion compensation step to the sum of dispersion compensation amounts at the first and second dispersion compensation steps is set so as to gradually vary together with the transmission distance from the terminal apparatus for transmission at which the repeating apparatus is disposed on the light transmission line so that degradation of wavelengths to be received by the terminal apparatus for reception is suppressed while dispersion compensation is performed with a high degree of accuracy at each optical add/drop multiplexing point on the transmission line.

Abstract: A dispersion compensation controlling apparatus used in a very high-speed optical communication system adopting optical time division multiplexing system comprises a first specific frequency component detecting unit (2a) detecting a first specific frequency-component in a baseband spectrum in a transmission optical signal inputted to a receiving side over a transmission fiber as a transmission line (6a), a first intensity detecting unit (3a) detecting information on an intensity of the first specific frequency component detected by the first specific frequency component detecting unit (2a and a polarization-mode dispersion controlling unit (220a) con trolling a polarization-mode dispersion quantity of the transmission line (6a) such that the intensity of the first specific frequency component detected by the first intensity detecting unit. (3a) becomes the maximum, thereby easily detecting and compensating polarization-mode dispersion generated in a high-speed optical signal.

Abstract: A polarization converter followed by two PMFs adjusts principal states of polarization (PSP) of a PMD compensator against PSP of an optical transmission line, and a mode-coupling adjuster between the PMFs adjusts a differential group delay and a PSP rotation rate of the PMFs.

Abstract: The degree of polarization of an optical signal is measured by a polarimeter and used for providing a feedback signal to adjust adaptive optics of a polarization mode dispersion compensator. The polarization properties of the polarimeter are determined with high accuracy to match the polarimeter through calibration and used to produce the feedback signal.

Abstract: A dispersion compensation controlling apparatus used in a very high-speed optical communication system adopting optical time division multiplexing system comprises a first specific frequency component detecting unit (2a) detecting a first specific frequency component in a baseband spectrum in a transmission optical signal inputted to a receiving side over a transmission fiber as a transmission line (6a), a first intensity detecting unit (3a) detecting information on an intensity of the first specific frequency component detected by the first specific frequency component detecting unit (2a), and a polarization-mode dispersion controlling unit (220a) controlling a polarization-mode dispersion quantity of the transmission line (6a) such that the intensity of the first specific frequency component detected by the first intensity detecting unit (3a) becomes the maximum, thereby easily detecting and compensating polarization-mode dispersion generated in a high-speed optical signal.

Abstract: An optical transmitter having a function which compensates for wavelength dispersion is provided with a plurality of light sources for outputting light having wavelengths that differ from one another. Before the optical transmission system begins operating, the wavelength of light output to an optical transmission line is varied by changing over the light sources in order to detect a wavelength whose transmission characteristic is optimum with regard to wavelength dispersion exhibited by this optical transmission line. During system operation, the light having the detected optimum wavelength is output to the optical transmission line.

Abstract: The automatic dispersion compensation device of the present invention comprises a unit measuring the transmission quality of incoming optical signals for one or more channels input from a transmission line and a unit separating and detecting the transmission quality degradation due to chromatic dispersion, in the measurement result of the unit from degradation due to other factors and controlling a variable chromatic dispersion compensator (VDC) in such a way as to compensate for that degradation.

Abstract: In order to compensate for chromatic dispersion ad dispersion slope over an entire wavelength band of the optical signal, the wavelength band is split into a plurality of bands, and chromatic dispersion compensation is made to make chromatic dispersion in a central wavelength of each of the bands zero.

Abstract: The present invention aims at providing a control technique for an optical modulator, which can accurately detect a phase shift between signals of a drive system of an optical modulator, to feedback control. To this end, a control apparatus of the present invention comprises, for example, in an optical modulator which generates a signal light corresponding to the CS-RZ modulation method by two LN modulators connected in series: a monitor section that extracts a specific frequency component from a spectrum of the CS-RZ signal light output from a latter LN modulator to detect the optical intensity thereof, and a control CPU that determines a phase shift between first and second drive signals corresponding to a clock signal supplied to the latter LN modulator based on the optical intensity detected by the monitor section, and controls a phase difference between the drive signals so that the phase shift is minimized.

Abstract: In the case in which independent driving voltages are applied to electrodes that are provided in waveguides #1 and #2 of a Mach-Zehnder optical modulator, light passing through the waveguide #1 and light passing through the waveguide #2 undergo the same amount of phase modulation of opposite signs (positive and negative) while a driving voltage E1 is applied. Similarly, the Mach-Zehnder optical modulator is configured so that when a driving voltage E2 is applied, phase modulation provided to the light passing through the waveguide #1 and phase modulation provided to the light passing through the waveguide #2 are offset after these lights are coupled. With this configuration, the amount of phase modulation provided by the Mach-Zehnder optical modulator is always kept at “0”, resulting in that chirping, which is defined as the differentiation of a phase modulation amount with respect to time, does not occur.

Abstract: A signal having a low frequency fm is superposed on a signal having a high frequency f1. The light having the frequency fs is modulated and transmitted to a transmission line as a wavelength dispersion measurement light. A local oscillation light is multiplexed with the wavelength dispersion measurement light, and heterodyne-detected on a receiving side. Sideband components generated by modulating the frequency fs within the heterodyne-detected wavelength dispersion measurement light are extracted by bandpass filters, and the wavelength dispersion value of the transmission line is calculated by detecting the phase difference between the sideband components.

Abstract: In the case in which independent driving voltages are applied to electrodes that are provided in waveguides #1 and #2 of a Mach-Zehnder optical modulator, light passing through the waveguide #1 and light passing through the waveguide #2 undergo the same amount of phase modulation of opposite signs (positive and negative) while a driving voltage E1 is applied. Similarly, the Mach-Zehnder optical modulator is configured so that when a driving voltage E2 is applied, phase modulation provided to the light passing through the waveguide #1 and phase modulation provided to the light passing through the waveguide #2 are offset after these lights are coupled. With this configuration, the amount of phase modulation provided by the Mach-Zehnder optical modulator is always kept at “0”, resulting in that chirping, which is defined as the differentiation of a phase modulation amount with respect to time, does not occur.

Abstract: A method and apparatus for optimizing dispersion in an optical fiber transmission line. The method and apparatus (a) determine an optimum amount of total dispersion of an optical transmission line corresponding to a power level of an optical signal transmitted through the optical transmission line; (b) control dispersion of the optical transmission line so that the total dispersion up to a specific point along the optical transmission line becomes approximately zero; and (c) add dispersion to the optical transmission line downstream of the specific point, to obtain the determined optimum amount of total dispersion. The control of dispersion in (b), above, can be performed in several different manners. For example, the control of dispersion can include (i) detecting the intensity of a specific frequency component of the optical signal, the optical signal having an intensity v.

Abstract: Signal wavelength in an optical transmission system is optimally set. Before operation of the system is started, the intensity of a particular frequency component is measured by a dispersion monitor while sweeping the wavelength of a tunable light source over a wide range, to determine an optimum wavelength. Once operation of the system is started, the wavelength is swept over a narrower range containing the optimum wavelength, and the optimum wavelength is updated with a wavelength determined based on the result of the sweeping.

Abstract: An optical transmission system in which a wavelength-division-multplexed (WDM) optical signal including a plurality of optical signals having different wavelengths is demultiplexed into first optical signals and second optical signals. The second optical signals have wavelengths longer than wavelengths of the first optical signals. A first dispersion compensator compensates dispersion of the first optical signals. A second dispersion compensator compensates dispersion of the second optical signals. The dispersion compensated first and second optical signals are then multiplexed together.

Abstract: A method and apparatus for minimizing the intensity of a specific frequency component of an optical signal travelling through an optical fiber transmission line, to thereby minimize the total dispersion in the transmission line. More specifically, the intensity of a specific frequency component of an optical signal transmitted through the transmission line is detected. The optical signal has an intensity v. total dispersion characteristic curve with a corresponding eye opening. The total dispersion is controlled to minimize the intensity of the specific frequency component in the eye opening, thereby minimizing the total dispersion.

Abstract: An optical transmission system in which a wavelength-division-multiplexed (WDM) optical signal including a plurality of optical signals having different wavelengths is demultiplexed into first optical signals and second optical signals. The second optical signals have wavelengths longer than wavelengths of the first optical signals. A first dispersion compensator compensates dispersion of the first optical signals. A second dispersion compensator compensates dispersion of the second optical signals. The dispersion compensated first and second optical signals are then multiplied together.

Abstract: An optical modulator having a voltage-optical output characteristic in which optical output varies periodically with respect to a voltage value of an electrical drive signal is driven by a modulator driving voltage signal, which has an amplitude of 2·V&pgr; between two light-emission culminations or two light extinction culminations of the voltage-optical output characteristic. A low-frequency superimposing unit superimposes a prescribed low-frequency signal on the modulator driving voltage signal, and an operating-point controller controls the operating point of the optical modulator by detecting operating-point drift of the optical modulator based upon the low-frequency signal component contained in an optical signal output from the optical modulator and controlling the bias voltage of the optical modulator in dependence upon the drift of the operating point of the optical modulator.

Abstract: A signal having a low frequency fm is superposed on a signal having a high frequency f1. The light having the frequency fs is modulated and transmitted to a transmission line as a wavelength dispersion measurement light. A local oscillation light is multiplexed with the wavelength dispersion measurement light, and heterodyne-detected on a receiving side. Sideband components generated by modulating the frequency fs within the heterodyne-detected wavelength dispersion measurement light are extracted by bandpass filters, and the wavelength dispersion value of the transmission line is calculated by detecting the phase difference between the sideband components.