Broadband microwave fiber-optic links with RF phase control for phased-array antennas

The authors report the use of injection-locked self-pulsing laser diodes as optical transmitters in RF fiber-optic links, in which the RF phase of the transmitted signal can be continuously adjusted by simply varying the bias current into the laser. These devices are intended for use in optically-controlled phased-array antenna systems or in optical networks for the remote synchronization of antenna stations. It is demonstrated that by using a commercial, low-cost, compact-disk self-pulsing laser diode, phase shifting over a range of 180 degrees is possible over a broad operational frequency band of 1-7 GHz, with a switching time of <5 ns and a phase resolution of <1 degrees . This phase shifter/optical link can also exhibit inherent electrical gain of up to 10 dB and an RF isolation of >80 dB with proper impedance matching of the laser and photodetector.<>