Recently pilot tones have been widely deployed as a path supervisory method for optical crossconnects (OXCs). In this work we present a wavelength-routing fault detection scheme for concatenated OXCs in an all-optical network (AON) testbed, in which pilot tones are added to wavelength channels as channel identifiers (CIDs) at input ports. OXC routing errors then can be detected by comparing the CIDs at output ports with the stored routing information.
The AON testbed is based on commercially available photonic switches, which support dynamic wavelength switching. At each input port of an OXC, a unique frequency tone is added. We compare the performance of two sets of candidacy pilot frequencies, 101 kHz ~ 117 kHz and 1.01 MHz ~ 1.17 MHz (with 2 kHz and 20 kHz separation respectively). The modulation index is set to 10%. On the output side of each OXC, a modulator is inserted after each output port. We detect the tone after the modulator and feed the amplified, filtered, and inverted signal back to the modulator, for removing the tone.
The pilot tones added to all OXCs construct the concatenated wavelength-routing fault detection scheme. This work numerically evaluates the effects of concatenated pilot tones and different pilot frequencies on the overall system performance, e.g., bit error rate or Q-factor. The simulation results show that the proposed scheme is feasible and the degradation of system performance due to pilot tones is negligible.