Optical routing typically makes use of nodes located at various places around the optical network. However, many locations can be vulnerable to failure due to the potential for power to be interrupted at optical networks, leading to performance degradation, because the network routing node itself typically requires an electrical DC bias voltage and a control signal. In addition, another key challenge is monitoring the state of the node, especially due to bias and temperature drifts that are common in typical Mach–Zehnder interferometers (MZIs) or nonlinear waveguides such as periodicallypoled- lithium-niobate (PPLN) waveguides.

One approach could be to use bidirectional transmission of multiple laser sources over an optical link. Subsequently, (i) arrays of photodiodes that are driven from remote laser sources are used to enable biasing and controlling; (ii) pilot tones are transmitted and their ratios after backpropagation are observed in the transmitter side to monitor the state of operation and adjust the optical powers accordingly.

This paper highlights certain architectures for remotely biasing, controlling, and monitoring a network node that lacks local power, which might enable flexible optical networking. These architectures include: (i) an MZI-based optical switch with optically delivered control and data signals as well as a remotely controlled and monitored optical correlator based on either (ii) delay line interferometer (DLI) or (iii) nonlinear wave-mixing in a PPLN waveguide for a QPSK data.