Direct writing of gratings in GaInAs/GaInAsP quantum wells using pulsed laser irradiation

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 μm or better, this measurement being limited by the resolution of the photoluminescence set up. Gratings, with a pitch of 2.5 μm, 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 μm indicating that a grating had been formed