Abstract: The scale and complexity of an apparatus is reduced by omitting a clock extraction section. The apparatus includes: a sampling pulse train generation device which generates an optical or electrical sampling pulse train, independently of an input optical or electrical data signal with a bit rate f0 (bit/s), and which has a repetition frequency f1 (Hz); a data signal sampling device which samples the data signal in accordance with the sampling pulse train to obtain a sampled signal; a voltage retaining device which converts the sampled signal, and stores pieces of electrical digital data; an electrical signal processing device which reads the digital data at once or sequentially to obtain a signal eye-diagram and evaluates optical data signal quality parameters; and a trigger signal generation device which applies triggers indicating the start/finish of data acquisition and data read to the voltage retaining device and the electrical signal processing device. respectively.

Abstract: An optical modulation/multiplexing circuit can fabricate a plurality of nonlinear optical waveguide devices and silica optical waveguides through a small number of processes, and achieve the simplification of the fabrication process and stabilization of the operation by hybrid integration with reduced connection loss. It employs lithium niobate domain inversion optical waveguides as nonlinear optical switches, and implements functions necessary for modulation and multiplexing such as input, splitting, multiplexing and timing adjustment of optical modulation signals and an optical clock signal by connecting glass waveguides to the input and output terminals of the domain inversion optical waveguides. Nonlinear optical media generate a second harmonic light beam of the optical clock signal, and at the same time produces a light beam with a frequency corresponding to the difference frequency of the two high frequency signals, the second harmonic light beam and the signal pulses.

Abstract: It is the object of the present invention to provide a transmission system that transmits a control signal corresponding to the overhead accommodating time division multiplexing information at a frequency that is the same (or nearly the same) as that of the main signal. In order to attain this object, an optical transmitter broadens in a time range the optical waveform of the OTDM signal having a wavelength &lgr;0 and the control light having a wavelength &lgr;1(≈&lgr;0), and multiplexes the signal light having an optical peak intensity set low compared to the OTDM signal peak intensity and sending this to an optical transmission fiber.

Abstract: A monitoring system includes first and second evaluation sections for obtaining an averaged Q-factor parameter and a waveform distortion parameter from an optical signal amplitude histogram collected from optical signals under measurement. The monitoring system further includes a third evaluation section for determining both averaged Q-factor parameter and waveform distortion parameter, and for making a decision as to whether the main factor of the optical signal quality degradation is waveform distortion or not by comparing the averaged Q-factor parameter and waveform distortion parameter with their initial values or initial characteristics which are obtained when no optical signal quality degradation is present.

Abstract: A nonlinear optical crystal allowing type 2 phase matching multiplexes a fixed wavelength light having an angular frequency &ohgr;D and a variable wavelength light having an angular frequency &ohgr;S, with the polarization directions thereof being perpendicular to each other, so as to produce a sum frequency light having an angular frequency &ohgr;D+&ohgr;S. When multiplexing the fixed wavelength light and the variable wavelength light through the nonlinear optical crystal, a controlling section controls the polarization direction of the fixed wavelength light so as to be parallel to a predetermined reference axis within a plane vertical to a phase matching direction of the nonlinear optical crystal. Even when the wavelength of inputted light is changed, the predetermined reference axis is a single axis which maintains parallelism with the crystal axis of the nonlinear optical crystal.

Abstract: A nonlinear optical crystal is composed of 2-adamantyl-5-nitorpyridine (AANP) allowing the type 2 phase matching to the sampling light and a measuring object light, emitting a sum frequency light of the measuring object light and the sampling light, with the polarization directions thereof being perpendicular to each other, when the sampling light and measuring object light multiplexed by a multiplexer are entered. When the sum frequency light is emitted through the nonlinear optical crystal, a control portion controls the polarization direction of the sampling light so as to be parallel to a predetermined reference axis located within a plane perpendicular to a phase matching direction of the nonlinear optical crystal. The predetermined reference axis is a single axis maintaining parallelism with the crystal axis of the nonlinear optical crystal even if the wavelength of the inputted light is changed.

Abstract: An optical signal quality degradation monitoring apparatus for monitoring an optical wavelength division multiplex signal is implemented in a small size. To monitor the optical signal quality degradation in the optical wavelength division multiplex signal by a configuration as simple as possible, the following configurations are used: A configuration using an optical wavelength division demultiplexer and a sampling clock generator to make one an electric signal processor; A configuration using an optical sampling pulse train generator, an optical multiplexer, a nonlinear optical medium, and an optical wavelength division demultiplexer to make one an electric signal processor; or a configuration using a selection wavelength control section, an optical wavelength selecting section, and a sampling clock generator to make one electric signal.

Abstract: An optical signal quality monitoring system is provided, by which the quality of optical signals can be examined using a single monitoring system, not depending on the bit rate of each signal. In the system, an optical signal having a bit rate N·f0, that is, N times as much as basic clock frequency f0, is sampled by using a pulse repetition frequency f0/n1−&Dgr;f or f0/n1+&Dgr;f where n1 is a predetermined natural number and the pulse repetition frequency slightly differs from f0/n1 by &Dgr;f, and an amplitude histogram of the optical signal is determined based on results of the sampling.