Pochi Yeh

A new optical model for wire grid polarizers

Abstract A new and simple optical model for wire grid polarizers is presented. We have shown that a wire grid polarizer is optically equivalent to a thin birefringent film with complex refractive indices.

Contra-directional two-wave mixing in photorefractive media

Abstract The energy transfer between two counter-propagating beams in photorefractive media is analyzed. A solution of a non-linear model of holographic two-wave mixing is presented. Expressions for the transmissivity are obtained and discussed.

Frequency shift and cavity length in photorefractive resonators.

Photorefractive resonators exhibit an extremely small frequency difference (Deltaomega/omega~10(-15)) between the oscillating and pumping beams. The observed frequency difference is proportional to cavity-length detuning. This dependence is explained by a photorefractive phase shift that is due to slightly nondegenerate two-wave mixing that compensates for cavity detuning and satisfies the round-trip phase condition for steady-state oscillation. The measured onset or threshold of oscillation as a function of photorefractive gain and intensity agrees with theory.

Photorefractive conical diffraction in BaTiO3

Abstract A laser beam incident on BaTiO 3 can cause a cone of light to exit the crystal. If the incident beam is polarized as an extraordinary ray, the cone of light is formed by ordinary rays. The cone angle is fixed by a phase-matching condition for the incident and cone beams. Measurement of this cone angle as a function of the incident angle is a simple and sensitive method for determining the birefringence of a BaTiO 3 crystal over the entire range of wavelengths where the sample is photorefractive.

Time reversal by an interferometer with coupled phase-conjugate reflectors

A new type of interferometer has been constructed that uses a beam splitter and two self-pumped BaTiO(3) crystals as phase-conjugate reflectors in place of the usual interferometer mirrors. Counterpropagating beams of light are spontaneously generated between the two crystals, coupling the pair of phase conjugators. This optical oscillation locks the relative phase of the two phase-conjugate reflections such that they recombine at the beam splitter to form only a single beam as though they were truly time-reversed waves.

Scalar phase conjugator for polarization correction

Abstract The concept of a scalar phase-conjugator is proposed and investigated. It is shown that only a scalar phase-conjugator can correct for polarization distortion and restore the original polarization state. The tensor property of a phase-conjugate reflector is investigated. An example to achieve such a scalar phase conjugation is discussed.

Zero crossing birefringent filters

Abstract A new type of narrowband and wide field-of-view filters is proposed and analyzed. This filter consists of a birefringent network such as that of Lyot-Ohman or Solc filters using crystals with a zero birefringence crossing. The results arre presented and discussed.

Christiansen-Bragg filters

Abstract A new type of wide field-of-view filter is proposed and analyzed. Coupled mode theory and matrix methods are applied to investigate the transmission characteristics of the Christiansen-Bragg filter. This filter consists of a multilayer stack of two dielectric media such that the dispersion curves of these two media intersect at a particular wavelength. The results are presented and discussed.

Dispersive birefringent filters

Abstract Polarization interference filters that employ crystals with a strong dispersion of birefringence as the wave plates can accomodate a very wide field-of-view while at the same time maintaining a very narrow bandwidth. It is noted, in particular, that CdS exhibits a strong dispersion in the spectral regime between 5200 A and 5400 A, with a rate of dispersion that could provide a passband of only 1 A with a filter structure of several millimeters thick. This paper investigates the properties of these filters. The results are presented and discussed.

Transmission spectrum of a Solc filter

Abstract This paper considers the transmission of light through a stack of alternating birefringent plates. Coupled mode theory, Jones calculus and a recently developed coherent matrix method are employed to calculate the transmission spectrum of a Solc filter. The results are compared and discussed.