An Integrated Germanium-Based THz Impulse Radiator with an Optical Waveguide Coupled Photoconductive Switch in Silicon

• Published in: Micromachines (Basel) Vol. 10; no. 6; p. 367
• Main Authors: Chen, Peiyu, Hosseini, Mostafa, Babakhani, Aydin
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 31.05.2019; MDPI
• Subjects: Antennas; Bandwidths; Beam steering; Carrier lifetime; Design techniques; Electrodes; Emitters; Excitation; Femtosecond pulsed lasers; Germanium; Impulses; integrated optics; Lasers; Low cost; Optical communication; Optical waveguides; optoelectronics; Phosphorus; photoconductivity; Photonics; Radiation; Radiators; Semiconductors; Silicon; silicon photonics; Systems stability; terahertz; Thin films; Transient response; photoconductivity; germanium; integrated optics; silicon photonics; terahertz; optoelectronics
• ISSN: 2072-666X; 2072-666X
• DOI: 10.3390/mi10060367

This paper presents an integrated germanium (Ge)-based THz impulse radiator with an optical waveguide coupled photoconductive switch in a low-cost silicon-on-insulator (SOI) process. This process provides a Ge thin film, which is used as photoconductive material. To generate short THz impulses, N++ implant is added to the Ge thin film to reduce its photo-carrier lifetime to sub-picosecond for faster transient response. A bow-tie antenna is designed and connected to the photoconductive switch for radiation. To improve radiation efficiency, a silicon lens is attached to the substrate-side of the chip. This design features an optical-waveguide-enabled "horizontal" coupling mechanism between the optical excitation signal and the photoconductive switch. The THz emitter prototype works with 1550 nm femtosecond lasers. The radiated THz impulses achieve a full-width at half maximum (FWHM) of 1.14 ps and a bandwidth of 1.5 THz. The average radiated power is 0.337 μ W. Compared with conventional THz photoconductive antennas (PCAs), this design exhibits several advantages: First, it uses silicon-based technology, which reduces the fabrication cost; second, the excitation wavelength is 1550 nm, at which various low-cost laser sources operate; and third, in this design, the monolithic excitation mechanism between the excitation laser and the photoconductive switch enables on-chip programmable control of excitation signals for THz beam-steering.