Photonic-enabled beam steering at 300†GHz using a photodiode-based antenna array and a polymer-based optical phased array.

For wireless networks beyond 5G, directivity and reconfigurability of antennas are highly relevant. Therefore, we propose a linear antenna array based on photodiodes operating at 300 GHz, and an optical phased array based on polymer waveguides to orchestrate the antennas. Due to its low thermal conductivity and high thermo-optical coefficient, the polymer chip enables highly efficient and crosstalk-free phase shifting. With these, we demonstrate purely photonic-controlled beam steering across 20°. Compared to a single emitter, the 3-dB beam width is reduced by 8.5° to 22.5° and the output power is >10 dB higher. Employing Snell's law for coupling into air, we can precisely predict the radiation patterns.

Photonic integrated circuit with sampled grating lasers fabricated on a generic foundry platform for broadband terahertz generation.

We demonstrate a monolithically integrated photonic integrated circuit (PIC) for terahertz spectroscopy with wide spectral bandwidth. The PIC includes two widely tunable sampled grating DBR (SG DBR) lasers, semiconductor optical amplifiers (SOAs), and passive components to combine signals. The SG DBR lasers cover 22 nm and 24 nm tuning range, respectively, with 4 nm overlap in the C band. The side mode suppression ratio (SMSR) exceeds 37 dB with a linewidth below 4.3 MHz. We used the PIC to generate THz radiation with a state-of-the-art photodiode emitter. The measured THz power spectrum between 0.03 and 1 THz compares well with the spectrum generated with commercial tunable laser sources. This demonstrates the suitability of our PIC for future miniaturized continuous wave (cw) THz systems.

Radiation pattern of planar optoelectronic antennas for broadband continuous-wave terahertz emission.

In future wireless communication networks at terahertz frequencies, the directivity and the beam profile of the emitters are highly relevant since no additional beam forming optics can be placed in free-space between the emitter and receiver. We investigated the radiation pattern and the polarization of broadband continuous-wave (cw) terahertz emitters experimentally and by numerical simulations between 100 GHz and 500 GHz. The emitters are indium phosphide (InP) photodiodes with attached planar antenna, mounted on a hyper-hemispherical silicon lens and integrated into a fiber-pigtailed module. As both packaging and material of the emitter was identical for all devices, similarities and differences can be directly linked to the antenna structure. We found that the feeding point structure that connects photodiode and antenna has a large influence on the radiation pattern. By optimizing the feeding point, we could reduce side lobes from -2 dB to -13 dB and narrow the 6dB beam angle from ±14° to ±9° at 300 GHz.