Photorefractive adaptive filter structure with 40-dB interference rejection

Abstract

A new architecture for photorefractive adaptive filtering is introduced. This architecture is based on the principle of time-integrating correlator with a photorefractive material as the time-integrating photosensor. A compact and rugged system is achieved by using the same Bragg cell as both the delay line for computing correlation values and the delay to which the tap weights are applied. In this way a self-aligning structure is achieved. Semiconductor photorefractive materials are used with 1.2-1.3-microm wavelength injection lasers to achieve fast response, low power, and a compact structure. Tests of an experimental system demonstrated >40-dB rejection of narrow-band interference with a transient response time constant of 70micros.

Optical architectures for programmable filtering and correlation of microwave signals

“…For a given frequency , corresponding to , this modulated photocurrent vanishes, which means that a rejection filter canceling the frequency of the signal is obtained. The power transmission (in decibels) of the synthesized filter at frequency is proportional to (10) assuming second-order Taylor expansion for . Therefore, with a SLM providing a contrast ratio it is possible to implement a filter at with a rejection of about 50 dB.…”

Experimental demonstration of a broadband adaptive processor for phased-array antennas

“…Applications include the bias-free, timeintegrating correlator, 1 adaptive signal processing, and jammer excision. 2,3 Photorefractive processing of signals from RF antenna arrays is especially appropriate because of the massive parallelism that is readily achievable in a photorefractive crystal (in which many resolvable beams can be incident on a single crystal simultaneously-each coming from a separate RF antenna element), and because a number of approaches for adaptive array processing using photorefractive crystals have been successfully investigated (in which the adaptive weight coefficients are represented by the amplitude and phase of the holographic gratings 4,5 ). In these types of applications, RF modulated optical signals from each array element are diffracted from the adaptively recorded photorefractive gratings (which can be multiplexed either angularly or spatially), and are then coherently combined with the appropriate amplitude weights and phase shifts to effectively steer the angular receptivity pattern of the antenna array toward the desired arriving signal.…”

<title>Acousto-optic null-steering adaptive photonic processor architectures for phased arrays</title>

“…The key benefit of an all-optical adaptive processor is the simultaneous wide instantaneous bandwidth correlation operation of the multipath signals with the direct signals, resulting in high cancellation ratios for a moderate number (e.g., 64) of auxiliary channels. Over the years, several adaptive optical processors of a varying degree of complexity and performance have been proposed and demonstrated, both for narrowband and widebandjammers [2][3][4][5][6][7][8][9][10][11][12].…”

“…The key benefit of an all-optical adaptive processor is the simultaneous wide instantaneous bandwidth correlation operation of the multipath signals with the direct signals, resulting in high cancellation ratios for a moderate number (e.g., 64) of auxiliary channels. Over the years, several adaptive optical processors of a varying degree of complexity and performance have been proposed and demonstrated, both for narrowband and widebandjammers [2][3][4][5][6][7][8][9][10][11][12].In this paper, we propose two novel all-optical adaptive photonic processor architectures that have a high interferometric stability almost common-path in-line design with simultaneous read and write capabilities required for all-optical processing. These adaptive processors rely on a holographic time integrating detector, e.g., a photorefractive (PR) crystal or a polmer dispersed liquid crystal material (PDLC), to provide all-optical adaptive processing.…”