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 (
$\ell \ = \ - 1$
or
$\ell \ = \ + 1$
) 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 (
$\ell \ = \ - 1$
or
$\ell \ = \ + 1$
)) 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 (
$\ell \ = \ - 1$
to
$\ell \ = \ + 1$
) 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 (
$\ell \ = \ - 1$
and
$\ell \ = \ + 1$
) 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.