Phase Conjugated Mode Conversion Enabled by Two-Stage Cascaded Four-Wave Mixing Processes

Optical phase conjugation and mode selective conversion are indispensable for all-optical signal processing in mode-division multiplexing (MDM) transmission systems. However, manipulation in spatial mode domain based on a single-stage four-wave mixing (FWM) usually varies the operation wavelength. In this letter, we present a phase conjugated mode conversion scheme, without the parasitic wavelength conversion, enabled by two-stage cascaded FWMs. By properly incorporating the intra-modal and inter-modal FWMs, we experimentally demonstrate the phase-conjugated mode conversion between LP01 and LP11 modes at the signal wavelength of 1555.75 nm and 1541.25 nm, with a pump-signal detuning of 2.5 nm. The proposed phase conjugated mode conversion is promising to enhance the robustness and flexibility of MDM transmission systems.