Disclosed are an apparatus and method for converting the wavelength of an optical signal using a multi-mode Fabry-Perot laser diode. The apparatus controls polarization of an external pump optical signal to output a TE polarized pump optical signal, and controls polarization of a probe optical signal to output a TM polarized probe optical signal. The apparatus couples the TM polarized probe optical signal and TE polarized pump optical signal irrespective of the polarization of the optical signals. The apparatus finely controls the polarization of the pump optical signal and the polarization of the probe optical signal such that they conform to TE and TM modes of the Fabry-Perot laser diode, respectively. The Fabry-Perot laser diode injection-locks the TE polarized pump optical signal of the coupled signal to change the position of a TM mode absorption null (a point at which an output optical signal has the minimum intensity), to thereby convert the wavelength of the TE polarized pump optical signal to the wavelength of the TM polarized probe optical signal. Accordingly, a wide wavelength conversion band is provided, and inverting and non-inverting wavelength conversions are easily carried out.

The present invention discloses an all-optical wavelength converter using a semiconductor optical amplifier and a polarization interferometer. The all-optical wavelength converter using a semiconductor optical amplifier and a polarization interferometer including a wavelength converter which modulates a probe light into a inverting waveform to a signal light and outputs the modulated light by using cross gain modulation, a phenomenon that occurs while the signal light and the probe light pass together through an optical splitter/combiner, a semiconductor optical amplifier and a filter at the same time, a polarization interferometer which makes the probe light outputted from the wavelength converter and having the inverting waveform to the signal light undergo a double-refraction so that a predetermined time split occurs on it and provides a non-inverting wavelength conversion and suppresses the slow XGM components in the converted outputs due to the slow carrier recombination time.

In an optical fiber transmission line between two terminal stations, an input side wavelength converter for up-shifting a wavelength of a signal light is inserted at a front part of each of the optical amplifiers and an output side wavelength converter for down-shifting a wavelength of a signal light is inserted at a rear step of the optical amplifiers. Signal lights transmit in a wavelength band shorter or longer than the zero dispersion wavelength of the transmission optical fiber on said transmission optical fibers. The input side wavelength converter converts the wavelength of the signal lights from the transmission optical fibers within the amplifying bandwidth of the optical amplifiers and the output side wavelength converter returns the wavelength of the signal lights optically amplified by the optical amplifiers.

An optical digital regenerator for digitally regenerating an input signal in an intact optical state. A first operating unit has a first probe light generator for generating a first probe light and a first optical operator for converting a waveform of the first probe light output from a first probe light generator according to an optical intensity waveform of the input signal light. A clock extractor extracts a clock component of the input signal light from a photocurrent generated by the first optical operator. A second optical operating unit has a second probe light generator for generating a second probe light pulsed in accordance with the clock output from the clock extractor and a second optical operator for sampling the second probe pulse light output from the second probe light generator.

An optical function device capable of controlling an optical signal with another optical signal, wherein a modulated input light I.sub.in of a wavelength .lamda..sub.1 is coupled with a bias light I.sub.bias of a wavelength .lamda..sub.2, and the thus coupled input and bias lights are input to a first semiconductor optical amplifying element 48, so that the bias light Ibias is intensity-modulated in a phase reversed with respect to the input light I.sub.in, while the input light I.sub.in is cut by a first wavelength extracting element 56. A control light I.sub.c of the wavelength .lamda..sub.1 is coupled with the intensity-modulated bias light I.sub.bias of the wavelength .lamda..sub.2, and the thus coupled control and bias lights are input to a second optical amplifying element 50, so that the once reversed bias light I.sub.bias of the wavelength .lamda..sub.2 is intensity-modulated with respect to the control light I.sub.c of the wavelength .lamda..sub.1, and is extracted as an output light by a second wave extracting element 50. The optical function device functions as a three-terminal optical computing and amplifying device, a three-terminal optical switching device or an optical DEMUX device, which is capable of controlling an optical intensity by using one wavelength and which permits multi-stage connection.