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.

A true time delay phased array is provided which includes a digital subarray interface in the transmit signal path. The digital transmit signal path interface includes a digital reference signal generation means and digital signal propagation means for supplying the digital reference signal to the subarray. Each subarray includes RF carrier signal generating means for generating an RF carrier signal phase coherent with the reference signal, a fiber optic true time delay circuit for applying an appropriate phase delay to the RF carrier and an appropriate true time delay to the modulation signal, and a waveform modulator for modulating the modulating signal onto the phase locked RF carrier signal to provide the transmit signal for the subarray. The present invention can be used in conjunction with existing digital interface technology for receive and control signal paths to provide an entirely digital subarray signal path interface.

A compact optical switching unit includes a polarization independent beamsplitter switch (PIBS) coupled to a delay path apparatus such that incident light beams are respectively selectively directed along either a direct path or a delay path dependent on the the manipulation of the polarization of polarized constituent light beams in the PIBS. The delay path apparatus is typically a mirror prism or fiber optic cable disposed such that light deflected onto the delay path traverses a longer distance than light passing along the direct path and thus a particular light beam can be selectively time delayed by controlling the PIBS to direct the beam into desired delay paths in a cascade of optical signal switching units. A compact and readily fabricated cascade of optical switching units includes PIBS blocks, a portion of which constitutes the PIBS in respective optical switching units sequentially optically coupled. Delay path apparatuses disposed along an axis orthogonal to both the axis of beams passing along a direct path through polarizing beam splitter switches on the direct path and the axis between respective optical switching units result in a compact optical architecture.

A compact optical switching unit includes a spatial light modulator coupled to a delay assembly such that incident light beams are respectively selectively directed along either a direct path or a delay path dependent on the linear polarization of the light beam. The delay assembly includes a light deflection device, such as a polarizing beam splitter, coupled to a delay path apparatus, such as mirror prisms or fiber optic cable. A compact and readily fabricated cascade of optical switching units includes polarizing beam splitter blocks and polarization rotation switch blocks, a portion of which constitutes the polarizing beamsplitters and spatial light modulators in respective optical switching units sequentially optically coupled. Delay path apparatuses disposed along an axis orthogonal to both the axis of beams passing along a direct path through polarizing beam splitter switches on the direct path and the axis between respective optical switching units result in a compact optical architecture.

An optical beamsteering system for providing a plurality of respectively time-delayed optical signals to control a phased array of transducer elements or the like includes an optical signal processing system having a plurality of optical time delay units optically coupled together in a cascade. In each optical time delay unit includes a respective multiple-pass optical delay path apparatus in which respective optical signals passing through the delay path apparatus pass along either a direct path or a delay path dependent upon the polarization orientation of the light. The delay path apparatus includes optical components disposed such that optical signals passing along the delay path pass through a given fiber delay line twice before passing from the multiple-pass optical time delay unit so as to cancel out any uncommanded polarization shifts resulting from passage of the optical signal through the fiber.