Japan Science and Technology Agency

Toshihiko Hirooka

Masataka Nakazawa

To compensate a waveform distortion by using a nature that a spectral shape is perfectly retained even if all the linear distortions occur on a time-axis. An optical pulse transmitted from an optical pulse transmitter () via an optical fiber transmission line () is transmitted. An optical Fourier transformer () receives an optical pulse, and optically Fourier-transforms an optical pulse on a time-axis onto a frequency-axis to reproduce the frequency spectrum of an optical pulse on a time-axis be effecting switching between frequency and time, thereby compensating a waveform distortion by a linear effect on the optical fiber transmission line (). A photodetector () receives an optical pulse from the optical Fourier transformer () and transforms this into an electrical signal to thereby obtain a pulse waveform before a transmission over the optical fiber transmission line ().

Optical transmission method and optical transmission apparatus

An OTDM transmitting method and transmitter realizing an OTDM distortion-free transmission substantially not relying upon dispersion. A time division multiplexed OTDM signal from an OTDM signal transmitter () enters an optical Fourier transform unit (). Optical Fourier transform can be carried out most accurately so long as the optical pulse is a chirp-free Fourier transform limit pulse. The optical Fourier transform unit () converts the time waveform of the pulse into a signal on the frequency axis, and an optical inverse Fourier transform unit (') converts a spectral shape on the frequency axis into a time waveform (pulse). An optical fiber transmission line () is a transmission line having an arbitrary dispersion and a polarization mode dispersion. These dispersions may involve a time variation. An OTDM signal receiver () demultiplexes a transmission signal into low-speed optical signals, in a light region, receives optical pulses for respective channels and converts them into electric signals.

OTDM transmission method and apparatus

A small-sized, high-functionality optical pulse compressor capable of generating a low-power, high-repetition-frequency ultrashort pulse train used for ultrafast optical communication and photometry, and a simple-structure optical function generator for realizing an arbitrary time waveform. The optical pulse compressor comprises and optical Fourier transform device (F) having an optical phase modulator () driven by the repetition-frequency of an input optical pulse train and a dispersive medium (), for converting the shape of an input optical pulse frequency spectrum into its time waveform, and an optical filter () inserted ahead of the optical Fourier transform device (F), for reducing the spectrum width of an input optical pulse, wherein the optical Fourier transform device (F) converts a small-spectrum-width optical pulse output from the optical function generator generates an optical pulse. The optical function generator generates an optical pulse having an arbitrary time waveform by reproducing, as it is, a spectrum waveform-shaped arbitrarily by an optical filter on a time-axis by the optical Fourier transform device (F).

Optical pulse compressor, optical function generator, optical pulse compression method, and optical function generation method

Optical Fourier transform is executed over a wide time range. A quadratic function type optical pulse generator () generates a control light pulse of a shape expressed by a quadratic function or a parabola according to a clock signal based on a signal light pulse from an optical coupler (). The signal light pulse inputted is multiplexed by a multiplexer () with the control light pulse optically delayed by an optical delay element () so that the timing is matched with the signal light pulse, and introduced into an optical Kerr medium (). In the optical Kerr medium (), the signal light pulse inputted by the mutual phase modulation between the signal light pulse and the control light pulse is subjected to a linear phase modulation (frequency chirp) over the entire pulse or a wide time range. After that, the signal light pulse isolated by an optical filter () is introduced into the dispersion medium () having a group velocity dispersion (secondary dispersion), thereby converting the time waveform of the inputted signal light pulse into the shape of the frequency spectrum.

Growing community of inventors

Sendai, Japan

Toshihiko Hirooka