Study on ultra-fast nonlinear optical functional devices

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We have investigated mainly the following four topics to create new nonlinear optical functional devices.(1) Highly nondegenerate four-wave mixing in a semiconductor optical amplidierWe have demonstrated the highly nonfegenerate four-wave mixing (FWM) among subpicosecond optical pulses in a 1.3-mum multiple-quantum-well (MQW) semiconductor optical amplifier (SOA). We could directly measure the FWM signal in the output spectrum by current pulse pumping of the device. We achieved a high conversion efficiency of over 10% at a frequency conversion range of less than 1 TH_z.(2) Optical sampling using FWM in a SOAWe have demonstrated ultra-fast optical sampling using the FWM process in an SOA.A signal light and a sampling light are injected into an SOA as a probe light and a pump light, respectively. We can measure the sampling waveform as the envelope of the FWM signal. The result shows good linear relation between the FWM intensity and input probe energy for an input energy of 1 fJ to 0.1 pJ.(3) Suppression of multiple pulse formation in mode-locked laser diodesWe have proposed a new method for obtaining short optical pulses without trailing pulses from an actively mode-locked laser diode. A part of the output is reflected back into the laser diode with an orthogonal polarization. The trailing pulses caused both by the excess gain and the residual reflection at the laser diode facet are drastically suppressed. We experimentally demonstrated the reduction of the trailing pulses caused by the excess gain using 1.55mum In G_aA_sP laser diodes.(4) Sub-picosecond optical pulse generation from a mode-locked laser diodeWe have generated short optical pulses (1-2ps) by hibrid mode-locking of a laser diode with a fast saturable absorber. The wavelength could be changed in the range between 1.49mum and 1.54mum. The pulse width was shortened to 800fs using the fiber compression.