A new quantum well intermixing technique, which involves irradiating multiple quantum well material with high energy laser pulses and producing transient heating, has been developed. A Q-switched Nd:YAG laser with pulse length of -7 ns, repetition rate of 10 Hz and pulse energy density -5 mJ mm-2 is used to generate a localised increase in the density of point defects. After subsequent annealing in a rapid thermal processor bandgap shifts of over 100 nm were observed. The spatial resolution was investigated by masking the sample with a metal mask. Spatially resolved photoluminescence measurements showed that the resolution of the process was 25 pm or better, this measurement being limited by the resolution of the photoluminescence set up. Gratings, with a pitch of 2.5 pm, were wet-etched into the back of waveguide samples, and the samples were irradiated through the grating and annealed as before. Waveguide transmission spectra showed a dip in the transmitted intensity around a wavelength of 1.525 pm indicating that a grating had been formed.
Optoelectronic down-conversion of very high-frequency amplitude-modulated signals using a semiconductor laser simultaneously as a local oscillator and a mixer is proposed. Three possible constructions of a monolithically integrated down-converter are considered theoretically: a four-terminal semiconductor laser with dual pumping current/modal gain control, and both a passively mode-locked and a passively Q-switched semiconductor laser monolithically integrated with an electroabsorption or pumping current modulator. Experimental verification of the feasibility of the concept of down conversion in a laser diode is presented.
Generation and detection of high power short optical pulses are of interest for applications such as high speed switching and optically controlled microwave generation. Such systems based entirely on semiconductor technology are highly desirable. In our experiments significant enhancement in the response of metal-semiconductor-metal photoconductive switches fabricated on Fe doped semi-insulating InP with heavy ion N implantation has been observed. The response tail of the devices was effectively eliminated, resulting in FWHM pulse widths reduction from 200 ps (when unimplanted) to less than 40 Ps for 4.5 m gap device. No appreciable decrease in the breakdown field was observed. The dependence of spectral sensitivity on implantation dose was also studied. By proper optimization of the detector circuit, and use of high power semiconductor lasers with saturable absorber, generation of microwave signals in excess of 25GHz and several volts could be achieved.
Cross-correlation method of measuring the optical and electrical waveforms with picosecond time resolution is reported. Sampling pulses (duration 5 -15 ps) were generated by injection AlGaAs laser. Electrooptical Pockels effect were used for electrical measurements, and sum-frequency generation was used for optical measurements.
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