Observation of a dip in the spectrum of noise after propagation in an optical fiber

Summary form only given. We report on the observation of a dip in the optical noise spectrum induced by a laser (frequency /spl omega//sub 1/). The dip occurs always at the frequency /spl omega//sub d/=2/spl omega//sub 0/-/spl omega//sub 1/, where /spl omega//sub 0/=2/spl pi/c//spl lambda//sub 0/ and /spl lambda//sub 0/ is the zero dispersion wavelength of the fiber, whenever the input noise power is high. For these measurements we used a tunable laser diode amplified by an erbium amplifier to 17.5 dBm and a 25 ion long dispersion shifted fiber (DSF) with measured /spl lambda//sub 0/=1551.3 nm. We show the input and output spectra with the laser tuned to four different wavelengths (the side lobes around the laser spectrum are due to the modulation instability effect). Since /spl omega//sub d/ mirrors the laser frequency relative to /spl omega//sub 0/, i.e., /spl omega//sub 0/=(/spl omega//sub d/+/spl omega//sub 1/)/2, one can use this effect as a fast and simple method to determine /spl lambda//sub 0/. We observed a dip in the noise spectrum and explained it as a FWM process involving annihilation of two input photons from noise. This effect can be used as a simple method to determine the zero-dispersion wavelength of optical fibers.