Optical studies of A1GaAs photonic crystal waveguides
This thesis describes a number of optical spectroscopic measurements in novel one and two dimensional photonic crystals patterned in a slab waveguide. Two dimensional photonic crystals have also been embedded in a ridge waveguide to confine light to the plane containing the photonic crystal. Linear characterization of these structures revealed a photonic band gap. Non linear measurements revealed pulse· compression, negative differential transmission and showed that the ridge waveguide nonlinear response dwarfs that of the photonic crystal. Pump-probe spectroscopy is used to study the nonlinear response of AlGaAsllnAlGaAs MQW one dimensional photonic crystals. The modulation of the reflectivity spectra due to the refractive index change produced by two and three photon induced free-carriers was measured. Pump-induced blue-shifts in the wavelength of photonic resonances were measured. These were followed by rapid decay - 25 ps. The blue-shifts in the photonic resonances were as large as 15 nm. The lifetime of free-carrier nonlinearities in one dimensional photonic crystals was found to depend on the photonic crystal parameters, i.e. period, air fill factor and etch depth. It was found that the free-carrier nonlinearities lifetime varied from 8 to 33.5 ps. Ultrafast tuning of the photonic resonances was obtained via the optical Kerr effect and the optical (AC) Stark effect. Decay-less tuning was observed. The response time was measured to be at FWHM - 300-400 fs.