We propose a broadband end-fire antenna for continuous-wave terahertz (THz) photomixing-based devices working in the frequency range of 0.5-1 THz. A compact Vivaldi antenna is presented that does not require any hyper-hemispherical silicon lens to collect and collimate THz radiation unlike the conventionally used broadside antennas. The antenna is tailored to radiate THz into or receive radiation from a dielectric waveguide placed in close vicinity of it. The antenna is fabricated on an indium phosphide (InP) substrate. A silicon (Si) superstrate is used to improve the directionality of the radiated beam. THz power coupled into Si waveguides is measured using two different techniques between 0.1 and 1.15 THz. Firstly, the waveguide is placed in the optical path of a 1550 nm based continuous-wave THz setup with a commercial broadside emitter, focusing optics, and a detector fabricated on the InP substrate with log-periodic broadside antenna. Secondly, the waveguide is placed in direct contact with the designed Vivaldi antenna-based THz receiver and using the commercial broadside emitter as a source. It is observed that the direct coupling technique using the Vivaldi end-fire antenna outperforms the optically coupled approach at frequencies higher than 668 GHz. Efficient THz photoconductive sources and receivers based on the designed compact Vivaldi end-fire antenna will be suitable for launching THz power into on-chip THz circuitry and for compact THz systems.

We report thorough investigations of a photonic memory with phase change material embedded in a partially etched silicon waveguide, for operation at 1550 nm wavelength. Optical and thermal analyses are performed to study the performance of memory and the effect of deformity in G e 2 S b 2 T e 5 (GST) cells due to volume contraction upon crystallization. The presented approach has better performance than other approaches with GST integrated on top of or filled in a fully etched waveguide. It is shown that a high readout contrast of ∼ 33 d B with a low insertion loss of 0.79 dB is possible using an active volume of only 0.0079 µ m 3 . The photonic memory presented shows a low power consumption of 0.66 mW and 3.71 mW for switching the memory state from high to low and vice versa, respectively, with zero static power consumption. Using 100 ns and 10 ns pulses for phase transformation from amorphous to crystalline and that from crystalline to amorphous, the energy consumption is 82 pJ and 44.1 pJ, respectively.

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