Amir A. Jalali

Band structure and Bloch states in birefringent one-dimensional magnetophotonic crystals: an analytical approach

An analytical formulation for the band structure and Bloch modes in elliptically birefringent magnetophotonic crystals is presented. The model incorporates both the effects of gyrotropy and linear birefringence generally present in magneto-optic thin-film devices. Full analytical expressions are obtained for the dispersion relation and Bloch modes in a layered-stack photonic crystal, and their properties are analyzed. It is shown that other models recently discussed in the literature are contained as special limiting cases of the formulation presented herein.

Local normal-mode coupling and energy band splitting in elliptically birefringent one-dimensional magnetophotonic crystals

An analysis is presented of wave-vector dispersion in elliptically birefringent stratified magneto-optic media having one-dimensional periodicity. It is found that local normal-mode polarization-state differences between adjacent layers lead to mode coupling and affect the wave-vector dispersion and the character of the Bloch states of the system. This coupling produces extra terms in the dispersion relation not present in uniform circularly birefringent magneto-optic stratified media. Normal-mode coupling lifts the degeneracy at frequency band crossover points under certain conditions and induces a magnetization-dependent optical bandgap. This study examines the conditions for bandgap formation in the system. It shows that such a frequency split can be characterized by a simple coupling parameter that depends on the relation between polarization states of local normal modes in adjacent layers. The character of the Bloch states and conditions for maximizing the strength of the band splitting in these systems are analyzed.

Gyrotropic band gap optical sensors

Faraday-effect-active photonic band gap structures fabricated in iron garnet films are shown to provide a platform for optical sensing based on refractive index detection. Strong near-band gap-edge polarization rotations serve as a sensitive probe to cover-index changes in birefringent magneto-optic waveguides. A wide index range from air to n=1.6 is explored. Device sensitivity is found to improve with cover index increase. Theoretical analysis of Bloch modes polarization state shows large near stop-band edge rotations and strong sensitivity to cover index. The combined effects of geometrical waveguide birefringence and Faraday rotation contribute to the strength of the sensor response.

Bandgap formation and selective suppression of Bloch states in birefringent gyrotropic Bragg waveguides

Birefringent magnetophotonic crystals are found to exhibit degeneracy breaking for asymmetric contradirectional coupling in planar waveguides. Fundamental to high-order local normal mode coupling leads to partially overlapping gyrotropic bandgaps inside the Brillouin zone and partial suppression of Bloch mode propagation. A large magneto-optically active reorientation in polarization state is found for allowed Bloch modes at bandgap edges.

Thermal lensing analysis of TGG and its effect on beam quality.

An analysis is presented of a TGG crystal rod under high power laser operation. A semianalytical thermal analysis is investigated to obtain the temperature profile and thermal lensing effect in a TGG crystal upon incidence of a high power laser light. By solving the heat transfer equation for the TGG crystal and taking the Gaussian beam transverse intensity profile as the heat source, the optical path difference due to induced thermal effects was obtained. Moreover, a detailed model for the dependence of thermal lensing and beam degradation which takes into account up to the fifth-order spherical aberration is presented. Based on this model, it is shown that up to a critical value of the beam power the degradation of the beam is not significant. The experimental results on thermal lensing and degradation on beam quality of a high power laser passing through a TGG crystal rod are in agreement with the main results from our model.

Polarization rotation enhancement and gyrotropic photonic bandgaps in birefringent magneto-photonic crystals

We present a study of polarization rotation enhancement in birefringent magneto-optic photonic crystal waveguides and provide theoretical and experimental support for a novel type of photonic bandgap. The coupling between counter-propagating elliptically birefringent local normal modes of different order results in the formation of partially overlapping bandgaps and selective suppression of Bloch state propagation near the band edges. We use a bilayer unit cell stack model with an alternating system of birefringent states in adjacent layers. A magnetically tunable and large polarization rotation of the allowed Bloch modes near the band edges is computed theoretically and observed experimentally.