Reduced Insertion Loss Of X-Band RF Fiber Optic Links

Fiber optic (FO) links offer the promise of providing the microwave system designer with new flexibility and capabilities for use in radar and avionics systems. Results presented in this paper show a significant reduction in link RF insertion loss from the typical 40 dB at X-band (9 GHz) to 7 dB over a 3 dB bandwidth of 800 MHz, while maintaining a signal-to-noise ratio (SNR) of greater than 125 dBc/Hz. This 33 dB improvement can lead the way to many uses of fiber optics in microwave designs, especially for short distance applications, where currently used waveguide or coax cables have low insertion loss. The improved link insertion loss was obtained in a joint internal research and development (IR&D) project of the Ortel Corporation and Hughes Aircraft Company, in which both optical performance and RF narrow bandwidth passive reactive matching improvements were made on the typical Ortel high frequency laser transmitter and photodiode detector receiver units.