A photonic integrated circuit is designed containing a long grating with spiral geometry. Waveguide width and index
modulation are studied as methods to form the grating structure. Both methods require an initial mask step for
waveguide formation. In the case of width modulation the grating is formed in the same step as the waveguide, whereas
a second mask step is required for index modulation. Thus width modulation removes the alignment tolerances
associated with a two step process. The spiral geometry enables a long grating (~1 m) to be realized in a small area (1
cm2). The ability to form the grating in such a small area enables the use of current lithography mask / projection
equipment. Thus, the requirements for mechanical/optical precision in a customized long fiber Bragg grating fabrication
system is transferred to the precision of commercial lithography mask fabrication and projection equipment.
Photonic crystals have a great deal of potential in the area of integrated optics. Waveguides with small bends may be formed allowing compact integrated photonic circuits to be formed. Two-dimensional planar photonic crystals are examined for use as integrated photonic circuits. They, however, possess an inherent loss associated with coupling to radiation modes in the surrounding media. Thus, three-dimensional photonic circuits are required in order to realize very low loss integrated photonic crystal circuits. A three-dimensional photonic crystal that is only a few periods thick, quasi-3-D, and can support low loss waveguides embedded in it needs to be identified. We examine several candidate 3-D photonic crystal structures to determine a suitable structure for the fabrication of quasi-3-D photonic crystals.
The ability to engineer the free carrier lifetime of epitaxially grown semiconductors without significantly affecting the desirable nonlinear optical properties would allow the development of an entire new class of high-speed photonic devices. The primary method of achieving this is the controlled introduction of mid-gap defects via a variety of techniques including low temperature growth. We report on a systematic investigation of low-temperature-grown materials including bulk GaAs and Be-doped In0.53Ga0.47As/In0.52Al0.48As multiple quantum wells. Using both wavelength-dependent time-resolved nonlinear bandedge absorption spectroscopy and far infrared Terahertz spectroscopy, we unambiguously discriminate between recombination and trapping events and determine the carrier lifetime and mobility in a contactless fashion. We correlate the far infrared response and the bandedge response and thereby explain the apparent discrepancies with previous measurements and clarify the physical origin of the optical nonlinearity as well as the defect densities, carrier lifetimes and mobility.