In addition to the possibility of enhancing receiver sensitivity1,2 heterodyne detection allows the separation of narrow spaced optical channels in the receiver.3,4 Figure 1 shows schematically (the fiber-optic elements are emphasized) our experimental setup for two channels at λ = 830 nm. The signals of the semiconductor lasers 1 and 2 are coupled into the polarization-maintaining single-mode fiber (PMF) link and alternatively detected by the tunable heterodyne receiver. The light frequency of laser 1 is absolutely stabilized by a fiber ring resonator; the frequency of laser 2 is held 2 GHz apart with a difference-frequency tracking loop. The frequency of the local laser is tuned to a received signal by stabilizing the intermediate frequency to 1.5 GHz. We report the requirements and features of the fiber-optic components developed for this heterodyne system.
© 1985 Optical Society of AmericaPDF Article