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Abstract

Wavelength diversity coupled with fiber-based time delay, optical energy delivery, and ultrasonic energy sensing, are proposed to form a novel, rapidly tunable (e.g., 1 Khz-100 Mhz) and wide instantaneous bandwidth (e.g., >50% bandwidth at center carrier), ultrasonic probe system for therapy, diagnostics, and non-invasive surgery, particularly for intracavity operation with a typical 100 channel/transducer element count. This ultrasonic system architecture is a multi-wavelength optical delay line module using two high speed (i.e., <10 microseconds wavelength switching time), bulk acousto-optic tunable filters, that provide collinear, high power, multi-wavelength optical input and output beams. This wavelength selection module also provides high optical throughput (e.g., 90% efficiency) and excellent (e.g., -30 db) optical blockage of the unwanted leakage (undiffracted) light, preventing noise propagation when such modules are cascaded to provide many variable signal time delays. The overall system also uses another multi-wavelength module that adjusts the optical polarization of the optical beams at various critical stages of the proposed polarization sensitive ultrasonic control system. This polarization controller is based on an interferometric design using a variety of low loss two dimensional pixelated thin-film device arrays of various types of liquid crystals such as twisted nematic, parallel-rub birefringent-mode, and ferroelectric. These liquid crystal devices form the required polarization mode converters, phase shifters and half-wave plates required to form our novel polarization control module.

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