We experimentally demonstrated two enabling architectures for remotely controlled optical quadrature-phase-shift-keying (QPSK) correlators based on both linear and nonlinear elements. The correlator site was located far from the transmitter site and had no access to the local optical power. In the first demonstration, a remote correlator based on a cascade of Mach–Zehnder interferometers (MZIs) was phase-controlled through optical power sent from the transmitter via an optical fiber link. The issue of power loss because of fiber nonlinearities was further addressed by monitoring and managing the backscattered power. In this manner, the power delivered through the link was boosted by ∼13 dB. Another ∼6 dB gain in the delivered power was obtained by adding a second source of light power. The correlator was shown to be able to identify different target patterns within incoming QPSK signals at different baud rates from 10 to 50 Gbaud. In the second architecture, we experimentally demonstrated a tunable optical correlator for a 10/15-Gbaud QPSK data signal using temperature-controlled nonlinear wave mixing at a remote node. A high-power pump was phase-modulated to overcome the link backscattering effect and was sent along with the signal copies to a remote correlator node through an optical fiber link. The waves generated at the output of the correlator were sent back to the transmitter for the monitoring of the operation. We showed a power boost of more than 3 dB for the correlated signal at a temperature drift of 2 °C. Using remote control and monitoring, improved constellation diagrams with lower error vector magnitudes (EVMs) for a temperature drift range of < 2 °C were obtained.
- Mach Zehnder Interferometer (MZI)
- Nonlinear wave mixing
- Optical correlator
- Optical signal processing
- Periodically-poled Lithium- Niobate (PPLN) waveguide