Recirculating Photonic Filter (RPF): A Wavelength Selective True Time Delay for Optically Controlled Phased Array Sensors

摘要

This report describes our theoretical investigation into the nature of the experimentally observed loss and crosstalk in the RPF. The study shows that the loss of the RPF can be reduced to around 2dB through optimum design of the diffraction grating and waveguide. Phase linearity and measurements and temperature sensitivity of the RPF are also presented. We then describe optically controlled two dimensional beam steering systems wherein the signal is transferred between the delay states all optically be employing wavelength conversion in a semiconductor optical amplifier (SOA). We describe the concept and demonstrate experimentally this scheme to achieve independent control of azimuth and elevation beam steering. Applications of this technique include the ability to extend the total number of discrete time delays. In any wavelength selective time delay technique the spectral tuning range of the tunable laser source limits the number of different delays that can be obtained. However, by cascading two N channel time delay stages with wavelength conversion, we now obtain N2 different delays. Another application is the ability to realize digitally controlled time delays. An m stage cascade, with m independently tuned lasers, can be used to realize the most significant bit (MSB) while the successive time delay stages will represent the less significant bits.