A THz Integrated Circuit Based on a Pixel Array to Mode Multiplex Two 10-Gbit/s QPSK Channels Each on a Different OAM Beam

We experimentally demonstrate a THz integrated circuit with a pixel-array-based orbital-angular-momentum (OAM) mode converter for the generation and multiplexing of multiple data-carrying OAM beams. The integrated device consists of (i) two coupling spikes, which serve as inputs and can couple THz signals from hollow metallic waveguides to the device; (ii) two mode expansion structures, which expand the mode profiles from the waveguide inputs to match the OAM mode converter; and (iii) a 3.6 × 3.6 mm
²
pixel-array-based OAM mode converter, which vertically emits and multiplexes two free-space THz data-carrying OAM beams with different mode orders. The generated OAM order depends on the corresponding input port. Two different designs of the integrated OAM emitters show the generation and multiplexing of (a) OAM +1 and –1, and (b) OAM +1 and –2 at the center frequency of ∼ 0.317 THz. Crosstalk lower than –15 dB between the OAM modes can be achieved. Specifically, the OAM +1/–1 emitter has a 3-dB power bandwidth of ∼15 GHz. Using the OAM +1/–1 emitter for a free-space link at a 0.317-THz carrier frequency, we experimentally demonstrate 20-Gbit/s quadrature-phase-shift-keying (QPSK) transmission by multiplexing OAM +1 and –1. Compared to a single-beam transmission, the multiplexed link induces a ∼1-dB signal-to-noise ratio (SNR) penalty at the bit error rate (BER) of 3.8×10
⁻³
.