We present a new simultaneous differential phase-shift keying (DPSK) payload and subcarrier-multiplexed (SCM) label generation technique using a single dual-electrode Mach-Zehnder modulator (DE-MZM). We conduct simulations to verify the feasibility of the new SCM labeling scheme and examine the mutual interference between the DPSK payload and the SCM label. By selecting the subcarrier at half of the payload bit-rate frequency, we can significantly suppress the SCM label induced-power penalty to the DPSK payload. Moreover, we apply the SCM label generated by the proposed labeling technique to chromatic dispersion monitoring for DPSK systems. Simulation results show that by detecting radio frequency power of both the clock tone and the SCM label, the monitoring range is greatly improved.
In today's high-bit-rate WDM systems, it is essential to monitor the residual chromatic dispersion (CD) to ensure that it does not exceed the designed tolerance. Among the schemes for CD monitoring reported so far, inband subcarrier tone method is relatively simple and effective for CD monitoring. However, this technique may be influenced by both polarization mode dispersion (PMD) and the chirp fluctuation of the external modulator. In this paper, we investigate the effect of PMD and chirp on CD monitoring and show that the presence of PMD and chirp induces significant CD monitoring errors. To tackle this problem, we propose a CD monitoring technique to
suppress the influence caused by PMD and chirp fluctuation. In the proposed CD monitoring scheme, two RF tones are added at the transmitter. The light is coupled into an apriori known dispersion offset and then split into two branches in the monitoring module. A fiber Bragg grating filter which can remove one sideband is inserted before the photodetector of one branch. The PMD effect is eliminated by optically sideband filtering and RF power ratio detection, and the monitoring error induced by the small chirp fluctuation can be suppressed using two RF tones and a dispersion offset. The operational principle is analyzed and the experimental investigation is presented. Experimental results show that this technique can accurately monitor the accumulated CD without being affected by the PMD and small chirp fluctuation.
Despite advantages of distributed fiber optic sensor systems, the stability, reliability and limitation of physical parameters detected by the systems are still the bottlenecks of the applications in industrial control fields. In this paper, we compare different structures of fiber optic sensor networks based on special needs for manufacturing control and monitoring. A double-bus fiber optic sensor network directly used in industrial scene is presented. The multiplexing methods, such as time division multiplexing, frequency division multiplexing and code division multiplexing are analyzed. The result demonstrates that the double-bus fiber optic sensor network is adapted to use as manufacturing control systems in industrial environment, which offer low crosstalk levels, high signal to noise ratio and low optical path loss.
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