Spectrum of the intensity of modulated noisy light after propagation in dispersive fiber

The spectral density of the optical intensity which results after modulated noisy light is propagated in dispersive single-mode fiber is investigated theoretically and experimentally. An exact general result is obtained for the case of lowest-order-only group velocity dispersion and is applied to light from a 1550-nm distributed-feedback semiconductor laser which is large-signal phase modulated and then propagated through 50 km of standard single-mode fiber. Experimental results demonstrate the effect of dispersion on the intensity spectrum (and thus, on lightwave system characteristics such as modulation response, relative intensity noise, carrier-to-noise ratio, and harmonic distortion) in this situation and provide confirmation of the theoretical results.