Recirculating photonic filter: A wavelength-selective true-time-delay device for optically controlled phased array sensors and wavelength code-division multiple access.

摘要

In this dissertation we propose a novel wavelength-selective photonic time-delay filter. This device consists of an optical phased-array waveguide grating in a recirculating feedback configuration: This all-optical tunable optical delay line device permits several novel applications in the optical processing of high frequency signals.; The first application is as a true-time-delay generator for squint-free beam steering in optically-controlled microwave phased-array antennas where the optical carrier wavelength is used to select a desired time delay for the microwave signal. Time-delay beam steering ensure wide instantaneous bandwidth operation. The mapping of optical wavelength to the microwave beam direction permits a hardware compressive architecture for the optical control unit that can easily scale to large aperture antenna arrays. Prototype integrated optical chips consisting of optical filters and precision delay lines have demonstrated picosecond resolution time delays. Hybrid devices permit longer time-delays of several tens of nanoseconds through external fiber delay lines. Extension to optically controlled two-dimensional array beam steering using optical wavelength conversion between azimuth and elevation beam steering units is also explored. This overcomes optical/electrical/optical conversion losses in cascading individual beam steering units. A 2-element X-band optically controlled phased array transmitter is assembled in a compact test range to verify the wide bandwidth beam steering system.; Such wavelength selective time delay filter devices can also transform optical pulses with wide spectral bandwidth into simultaneous wavelength and time coded waveforms. One application of such hybrid coded waveforms is in optical code-division multiple access (CDMA) communication. Their perfect delta-function autocorrelation and small cross-correlation properties result in significant improvements in the number of orthogonal codes and the number of simultaneous users compared to traditional incoherent CDMA. We demonstrate such hybrid encoding of picosecond pulses from a modelocked laser. The superior correlation properties of such encoded pulses have also been verified. Digital data transmission over a CDMA fiber link with matched filter decoding at the receiver is shown.; Finally, we discuss the silicon-on-insulator (SOI) integrated optical technology for realizing passive and active devices such as discussed in this dissertation. This planar waveguide technology is attractive for the potential low cost silicon IC compatible fabrication and low waveguide losses above 1.2 mum. This approach could transform the optical processing functions such as discussed here into real world application specific optical circuits. We present the design, fabrication and demonstration of filter devices in the silicon-on-insulator integrated optical waveguide technology wherein the filter can be actively controlled through free-carrier electro-optic tuning.; Following the rapid progress in recent years in multiwavelength pulsed sources, optical filter components and high-speed high linearity photodetectors, optical processing devices such as discussed in this thesis could form the building block of systems performing complex signal processing functions such as sampling, synthesis and filtering of high-speed signals.