Recently there is a growing interest in developing few-mode fiber (FMF) based distributed sensors, which can attain higher spatial resolution and sensitivity compared with the conventional single-mode approaches. However, current techniques require two lightwaves injected into both ends of FMF, resulting in their complicated setup and high cost, which causes a big issue for geotechnical and petroleum applications. In this paper, we present a single-end FMF-based distributed sensing system that allows simultaneous temperature and strain measurement by Brillouin optical time-domain reflectometry (BOTDR) and heterodyne detection. Theoretical analysis and experimental assessment of multi-parameter discriminative measurement techniques applied to distributed FMF sensors are presented. Experimental results confirm that FM-BOTDR has similar performance with two-end methods such as FM-BOTDA, but with simpler setup and lower cost. The temperature-induced expansion strain (TIES) in response to different modes is discussed as well. Furthermore, we optimized the FMF design by exploiting modal profile and doping concentration, which indicates up to fivefold enhancement in measurement accuracy. This novel distributed FM-sensing system endows with good sensitivity characteristics and can prevent catastrophic failure in many applications.

In this letter, we demonstrate a simple technique for dispersion monitoring by adding a single inband subcarrier tone to the transmitted data signal. A measurable dispersion of up to 1200 ps/nm is demonstrated in a 10-Gb/s channel using a 7-9 GHz subcarrier and the addition of the subcarrier induced a power penalty of <0.5 dB. Dynamic ranges exceeding 20 dB and resolution sensitivities better than 10 (ps/nm)/dB are shown. With an 8-GHz tone and a 15% modulation depth for 10-Gb/s signals, we show a measurement range of 975 ps/nm with a 22-dB dynamic range. We used the monitor output signal to achieve accurate tunable dispersion compensation.

We show that the clock tone will be regenerated in the presence of higher order fiber-based polarization-mode dispersion (PMD) in nonreturn-to-zero systems. Due to the frequency-dependent optical propagation induced by higher order PMD, the extracted clock-tone power of the received data correlates with higher order PMD and is independent of first-order PMD.

All-optical wavelength conversion and multicasting with input and output wavelength tunability is a desired component for reconfigurable wavelength-division-multiplexed (WDM) networks for improving the efficiency and performance. In this paper, we propose a novel tunable all-optical wavelength-conversion-and-wavelength-multicasting schemes by using orthogonally polarized nondegenerate four-wave mixing (FWM) in highly nonlinear fiber. The input signal is amplified and serves as one of the two pumps. Wide tunability is obtained by placing a dummy pump and dummy signals at appropriate wavelengths with respect to the input wavelength and desired output wavelengths. For a 10-Gb/s NRZ system, 1:3 multicasting is demonstrated with a less than 0.6-dB power penalty, over a 25-nm tuning range for both input and output signals.

We demonstrate a 10-Gb/s all-optical XOR gate based on polarization rotation induced by Kerr effect in a single highly nonlinear fiber (HNLF). Using 2 km of HNLF with a nonlinear coefficient of 9.1 W/sup -1//spl middot/km/sup -1/, we obtain a 25-dB extinction ratio at the XOR output.