Vivaldi End-Fire Antenna for THz Photomixers

Abstract

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.

Broadband Dielectric Waveguides for 0.5–1.1 THz Operation

“…As losses of metallic hollow core waveguides increase with increasing frequency, it is expected that optimized dielectric waveguides outperform metal waveguides at frequencies above 1 THz. Furthermore, coupling losses in silicon WGs can be drastically reduced by nearfield coupling to appropriately designed THz emitters and receivers as proposed in [9].…”

A Photonic Spectrum Analyzer for Waveguide-Coupled Sources in the Terahertz Range

“…The difference to the PSA version in [4] is the PCA. The logarithmic-periodic antenna and the silicon lens are replaced by a broadband planar end-fire Vivaldi antenna (VA) [8], similar to the one shown in [9], coupled to a dielectric waveguide [9], [10]. Both are designed to enable planar PSAs and photonic VNAs and operate between 450 GHz and 1.05 THz [9]- [11].…”

“…The ACQC is an Advantech PCIE-1840L, set to an acquisition rate of 5 MSa/s and an acquisition range of ±0.1 V. The intermediate frequency range is limited by the TIA to 220 kHz. The PCA consists of an ErAs:In(Al)GaAs photomixer with a Vivaldi antenna on an InP-substrate [8]. The Vivaldi antenna is connected to a Si waveguide with the dimensions of 200 µm × 50 µm.…”

Broadband Terahertz Photonic Integrated Circuit with Integrated Active Photonic Devices

“…Further details on the material and a theoretical description of the receiving process can be found elsewhere [55]. The shown VA is a modification of antennas proposed by Abdullah et al [56], where instead of having a superstrate atop the antenna, we thin the InP substrate supporting the active ErAs:InGaAs device [40] down to h = 32 µm to increase the antenna directivity in end-fire direction (θ = 90 • , φ = 0) and to reduce squinting into the high index InP substrate (n InP ≈ 3.48). A substrate thickness h fulfilling 0.005λ 0 ≤ (n InP − 1) × h ≤ 0.03λ 0 is desired for improved impedance matching between the antenna and the radiated THz wave at the point of radiation [57].…”