Microwave fiber delay line performance simulation research

ABSTRACT The design, component selection, fabrication, testing, and evaluation of an optically-switched, binary, fiber optic programmable delay line are discussed. The basic building blocks, including laser diode which is based on a rate equation model, external modulated transmitter, transmission fiber and receiver, are explained. The system comprises eight delay stages, has a maximum delay of 6.4µs with a 100ps step and operates over the 1-18 GHz band. This computer controlled prototype used low-cost commercially available components in conjunction with graded-index, single-mode fiber. Its overall performance is sa tisfied with the simulation result. Keywords: external modulation, fiber delay line, delay stages, dynamic range 1. INTRODUCTION Recently, there has been increasing interest in optical true-t ime delay (OTTD). OTTD can be used in wideband photonic phased-array antennas (PAA), which have the advantage of controllable beam steering without physically repositioning the antenna aperture. Comparing with electrical TTD, OTTD techniques offer unique features for high performance antenna systems, such as wide bandwi dth, compact size, reduced weights and low electromagnetic interference. Delays, instead of phase shifts, are needed to ensure frequency-indepe ndent beam steering. Usually, true time delays are obtained by the use of coaxial links or micro-strip lines. In this case, the limitations are antenna dimensions and instantaneous bandwidth. Programmable optical delay is critical for optical communication, telecommunication routing, radar applications and RF communication system. True time delay is needed for signal buffering and address-recognition in packet switched signal processing and for the synchronization of data bits between different channels of a single high bit rate data stream to compensate for differential dispersion an d delay between the different optical paths. For any of these applications, it is advantageous to develop a programmable optical delay system, where true time delay can be varied over a large range of delay. This is potentially realized by inte grating coarse delay steps with a device that can be used to tune continuously between steps. True time delay could be optically obtained by associating switching matrixes with fibers of different lengths. Architecture properties are characterized by both temporal dynamic and resolution.