Abstract

We report on the observation of a dip in the optical noise spectrum induced by a laser (frequency ω₁). The dip occurs always at the frequency (ω_d = 2ω₀ - ω₁, where ω₀ = 2πc/λ₀ and λ₀ is the zero dispersion wavelength of the fiber, whenever the input noise power is high, as shown in Figure 1 (a, b, c). For these measurements we used a tunable laser diode amplified by an erbium amplifier to 17.5 dBm and a 25 km long dispersion shifted fiber (DSF) with measured λ₀ = 1551.3 nm. In Fig. 1 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 ω_d mirrors the laser frequency relative to ω₀, i.e., (ω₀ =(ω_d + ω₁)/2, one can use this effect as a fast and simple method to determine λ₀. In Fig. 1(d) the laser was tuned so that the dip should occur in a region of low input noise power and the dip is not observed.

© 2000 IEEE