Demonstration of recovering orbital-Angular-momentum multiplexed channels using a tunable, broadband pixel-Array-based photonic-integrated-circuit receiver

We experimentally utilize a tunable, broadband pixel-Array-based integrated receiver for recovering orbital-Angular-momentum (OAM) multiplexed channels. The OAM receiver comprises a pixel-Array-based mode converter, four phase controllers, and a pixel-Array-based 4-To-3 coupler. Utilizing the mode converter, a free-space data-carrying OAM beam (ℓ =-1 or ℓ = + 1) is vertically coupled into four waveguides. The resulting waveguide modes carry an OAM-order-dependent phase delay between each other. Subsequently, a 4-To-3 coupler coherently combines four waveguide inputs with the specific phase delay into a specific output port. By further tuning the relative phase delay of the waveguides using the phase controllers, the data channel carried by a specific OAM beam (ℓ =-1 or ℓ = + 1) could be routed to different ports. As there is no specific resonant wavelength, the OAM receiver could be operated with a relatively broad bandwidth. The experimental results show that: (a) the target OAM mode to be received by the OAM receiver could be tuned from (ℓ =-1 or ℓ = + 1) with a <-14-dB inter-modal power coupling; (b) in a wavelength range of ∼6 nm, two OAM-carried 50-Gbaud quadrature-phase-shift-keying (QPSK) data channels (ℓ =-1 or ℓ = + 1) could be recovered by the tunable OAM receiver with a bit error rate (BER) performance below the 7% forward error correction threshold; and (c) a 400-Gbit/s OAM-multiplexed and wavelength-division-multiplexed (WDM) QPSK link is demonstrated with a <2-dB optical signal-To-noise ratio (OSNR) penalty compared to that of a single-beam link.