Abstract-Navigating Terahertz Spectrum via Photomixing

Shang-Hua Yang and Mona Jarrahi

https://www.osapublishing.org/opn/abstract.cfm?uri=opn-31-7-36

Photomixers, including recent designs based on plasmonics, can combine tunability, power and room-temperature operation in both THz transmitters and receivers, for applications in 5G communications, astronomy and more.

© 2020 Optical Society of America

Abstract-Enhancing THz generation in photomixers using a metamaterial approach

Daniel J. Ironside, Rodolfo Salas, Pai-Yen Chen, Khai Q. Le, Andrea Alú, and Seth R. Bank

Fig. 1 As illustration depicting key photomixer design features between (a) the conventional photomixer design and (b) the proposed enhanced metamaterial design.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-7-9481

Photomixers at THz frequencies offer an attractive solution to fill the THz gap; however, conventional photomixer designs result in low output powers, on the order of microwatts, before thermal failure. We propose an alternative photomixer design capable of orders of magnitude enhancement of continuous-wave THz generation using a metamaterial approach. By forming a metal-semiconductor-metal (MSM) cavity through layering an ultrafast semiconductor material between subwavelength metal-dielectric gratings, tailored resonance can achieve ultrathin absorbing regions and efficient heat sinking. When mounted to a tunable E-patch antenna, gratings also act as vertically biased electrodes, further enhancing photoconductive gain by reducing the carrier path length to nanoscales. Thus, through these multiplicative enhancements, the metamaterial-enhanced photomixer is projected to generate THz powers in the milliwatt range and exceed the Manley-Rowe limit for frequencies less than 2 THz.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Dielectric Antenna Adds Photomixer for Terahertz Emissions

Jack Browne 

http://mwrf.com/passive-components/dielectric-antenna-adds-photomixer-terahertz-emissions

The use of terahertz EM energy in combination with optoelectronics technology offers great promise for short-range, high-data-rate communications, which will likely be needed in Fifth-Generation (5G) wireless-communications networks and to appease the general public’s growing obsession with having more data available on mobile wireless devices. To facilitate such communications, photomixing has been performed to achieve carrier waves at terahertz frequencies. Accordingly, researchers from sites in Spain, Finland, and Germany have developed a dielectric rod waveguide (DRW) antenna with integrated photomixer.

Classic generation of terahertz signals involves the photomixing of two heterodyne laser beams in a semiconductor device with signals emitted by a suitable antenna for the wavelength of interest. Since power from available semiconductor devices is quite limited at terahertz frequencies, the design of the antenna is critical for achieving a usable radiation pattern.

The researchers chose to integrate the photomixer with a planar DRW antenna for its low cost and ease of fabrication on commonly available substrate materials, such as silicon or GaAs semiconductor wafers. A prototype was manufactured on 500-μm-thick GaAs; the antenna has a cross section of 1.0 × 0.5 mm². It can be fed by rectangular metal waveguide for ease of installation, and produced consistent radiation patterns at 137 GHz.

See: “Dielectric Rod Waveguide Antenna as THz Emitter for Photomixing Devices,” IEEE Transactions on Antennas and Propagation, Vol. 63, No. 3, March 2015, p. 882.

Abstract-Branchlike nano-electrodes for enhanced terahertz emission in photomixers

Qing Yang Steve Wu1, Hendrix Tanoto1, Lu Ding1, Chan Choy Chum1, Bing Wang2, Ah Bian Chew1, Agnieszka Banas3, Krzysztof Banas3, Soo Jin Chua4,5 and Jinghua Teng1,5

http://iopscience.iop.org/0957-4484/26/25/255201

elecsj@nus.edu.sg jh-teng@imre.a-star.edu.sg

1 Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore 117602, Singapore
2 School of Physics, Huazhong University of Science and Technology, Wuhan, People's Republic of China
3 Singapore Synchrotron Light Source, National University of Singapore, Singapore 117576, Singapore
4 Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Singapore
5 Authors to whom any correspondence should be addressed. 

Branchlike nano-electrode structures were found to improve the THz emission intensity of a photomixer by approximately one order of magnitude higher than that of a photomixer with one row of nano-electrodes separated by the same 100 nm gap. The enhancement is attributed to a more efficient collection of generated carriers, which is in turn due to a more intense electric field under the branchlike nano-electrodes' structures. This is coupled with an increased number of effective areas where strong tip-to-tip THz field enhancements were observed. The optical-to-THz conversion efficiency of the photomixers with the new branchlike nano-electrodes was found to be 10 times higher. The more efficient THz photomixer will greatly benefit the development of continuous-wave THz imaging and spectroscopy systems.