Incrementally lossless, broad-bandwidth analog fiber-optic link

Operation of a broadband, incrementally lossless, fiber-optic link is reported. By using a solid-state laser as the CW source, a dynamic range for this externally modulated link was measured and shown to exceed that of a directly modulated link. The modulator was a conventional Mach-Zehnder design. The average optical power on the detector was 20 mW. The modulator input and detector output are resistively terminated with 50 Omega , and the link RF-to-RF insertion loss vs. frequency is measured using an RF network analyzer. The maximum intermodulation-free (IM-free) dynamic range occurs at the optical modulation depth (OMD) for which the output intermodulation power equals the link output noise power. Consequently, the maximum IM-free dynamic range depends not only on the linearity of the modulating device, but also on the sources of noise in the link.<>