Abstract
The performance of an acousto-optic deflector is studied for two-dimensional refractive index that varies as periodic and sinc functions in the transverse and longitudinal directions, respectively, with respect to the direction of light propagation. Phased array piezoelectric transducers can be operated at different phase shifts to produce a two-dimensionally inhomogeneous domain of phase grating in the acousto-optic media. Also this domain can be steered at different angles by selecting the phase shift appropriately. This mechanism of dynamically tilting the refractive index-modulated domain enables adjusting the incident angle of light on the phase grating plane without moving the light source. So the Bragg angle of incidence can be always achieved at any acoustic frequency, and consequently, the deflector can operate under the Bragg diffraction condition at the optimum diffraction efficiency. Analytic solutions are obtained for the Bragg diffraction of plane waves based on the second order coupled mode theory, and the diffraction efficiency is found to be unity for optimal index modulations at certain acoustic parameters.
Highlights
The light diffraction by bulk acoustic waves is a subject of considerable interest due to the wide variety of important applications
The frequency of the acoustic waves emitted by the transducers can be adjusted to achieve the Bragg angle of incidence, i.e., θin = θB for each lobe, which ensures large deflection angle given by θin and large diffraction efficiency given by the Bragg diffraction condition
A two-dimensional refractive index model has been presented to modulate the refractive index in two dimensions for improved performance of acousto-optic deflectors (AODs)
Summary
The light diffraction by bulk acoustic waves is a subject of considerable interest due to the wide variety of important applications. Gaylord and Magnusson [12] studied the diffraction of Gaussian beams in acousto-optic media using a modified version of the coupled wave theory, yielding two coupled first order partial differential equations. Chu and Tamir [3,9,10] simplified the coupled mode equations under the assumption of slowly-varying electric field, E ( x) , such that d 2E ( x) / dx k0xdE ( x) / dx where kx is the angular wavevector in the direction, x, of the light propagation This approximation, which is generally applicable to weakly-modulated media, yielded two coupled first order ordinary differential equations. Later Kong [14] presented a simplified second order coupled mode approach for both weakly and strongly modulated media and provided analytic solutions for the reflection and transmission coefficients, accounting for the effects at both boundaries of an AOD. The diffraction efficiency of this twodimensional refractive index model is compared to the results of others’ one-dimensional refractive index models
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