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Beam steering, frequency reconfigurable terahertz photomixer array using nano-actuators

Periodic Reporting for period 1 - TERA-NANO (Beam steering, frequency reconfigurable terahertz photomixer array using nano-actuators)

Reporting period: 2015-04-01 to 2017-03-31

The research on terahertz technology has become one of the emerging fields due to the unique properties that it offers, presenting enabling alternatives in imaging, spectroscopy, and communication applications. Increasing research activities in the field also brings the need for high performance components that operate in the terahertz regime, the most important of which are the high performance sources and detectors. Photomixing is one of the most commonly used methods for terahertz generation and detection, which employs an ultrafast semiconductor substrate integrated with an antenna. The state-of-the-art photomixer antennas have either a low radiation resistance in a wide band or a high radiation resistance in a narrow band, both of which introduce a significant reduction in the amount of terahertz power generated or detected. Possible antenna reconfigurability options to overcome these issues have not been investigated so far due to the lack of high performance switching elements in the terahertz band, which could boost the antenna, and hence, photomixer performance significantly. Moreover, electronically controlled beam steering possibilities, which could enhance the system performance radically in terahertz imaging and communication applications, have not been studied to date, which also requires high performance switching elements.
In this project, we aim to develop, for the first time, beam steerable and frequency reconfigurable photomixer antenna array for terahertz generation and detection. Beam steering and frequency reconfiguration will be achieved by means of nano-actuators, which is expected to provide high performance switching at terahertz frequencies. The nano-actuators that we target to develop will be the smallest ones reported up to date, which is mandatory to integrate them into the very small antenna dimensions. The proposed project will be a high level of interdisciplinary research between optics, electronics, and mechanical engineering.

The achievements of the Tera-Nano project can be summarized as follows:
• We successfully designed a nano actuator having less than 20 um length as a switching element in photomixers antennas for the first time in the literatures. The electromechanical and electromagnetic performance of the nano actutator is better than its rivals to the best of our knowledge.
• We successfully demonstrated, for the first time, a triple stub phase shifting impedance tuner circuit that is used for controlling the insertion phase and input impedance of the photomixer antenna. The simultaneous phase and impedance control improves the photomixer efficiency significantly due to the reduces mismatch between the high photoconductor impedance (~1-10 k) and low antenna impedance (70-100 ).
• We successfully demonstrated, for the first time, the concept of electronic beam steering for photomixers using nano actuators.
• We developed a fabrication process for nano actuators having dimensions less than 20 m for terahertz signal switching (to the best of our knowledge) first time in Europe.
• We developed a fabrication process on LT-GaAs for photoconductive antennas and photomixers for the first time in Turkey.
• We developed a novel time-domain spectroscopy setup for the radiation pattern measurements of the reconfigurable terahertz antennas and antenna arrays.
• Dr. Unlu has set up several collaborations inside and outside Europe for the fabrication and characterization of terahertz reconfigurable components. He has started two new projects, has co-authored several publications, and given several talks following the outcomes of Tera-Nano.
The Tera-Nano project has come up with more fruitful than expected in terms of the dissemination of the results. Dr. Unlu had several chances in different environments not only to exploitation of the results of the project, but also train and encourage people ranging from 7 to 70. The details of the project outcomes are listed below:

Conference publications: 11 (2 targeted in DoA) Dr. Unlu has co-authored 7 international (6 oral, 1 poster) and 4 national conference papers as the outcomes of the research of Tera-Nano, which are listed below:
Journal publications: 4 (in preparation) (2 targeted in DoA) We are in the preparation phase of 4 journal papers for the design of the frequency reconfigurable photomixers and beam-steering photomixer arrays. These papers will be detailed versions of the conference papers that were accepted for oral presentation recently, which are listed below:
Invited talk: 2 (none targeted in DoA) Dr. Unlu has given 2 invited talks about the reconfigurable terahertz components at TOBB University of Economics and Technology on 06/03/2107 and at Abdullah Gul University, Kayseri, on 16/05/16.
Professional seminar: 2 (none targeted in DoA) Dr. Unlu was invited by TUBITAK to give 2 invited talks on the success story of the Tera-Nano project on 2016 and 05/06/2017
Public seminar/interview: 1 (1 targeted in DoA) An interview with Dr. Unlu was published on terahertz technology in 11/05/2016 (
Seminar for high school students: 2 (1 targeted in DoA) Dr. Unlu was invited by TUBITAK to give talks to gifted primary, secondary, and high-school students in the ages between 10 and 17 about terahertz technology and nanotechnology on the eastern parts of Turkey (04/05/2016, Kahramanmaras and 16/05/16, Kayseri).
Seminar for undergraduate and graduate students: 1 (1 targeted in DoA) A seminar was given by Dr. Unlu at Ankara Yildirim Beyazit University on reconfigurable terahertz components on 06/04/2017.
Technical visit to METU MEMS Center: 1 (1 targeted in DoA) A technical visit was made to METU MEMS Center to discover the micro/nano fabrication facilities on 18/05/2017 for undergraduate, graduate students and faculty members.
The Tera-Nano has come up with greater potential than it was expected in the project proposal. First of all, the proof-of-concept demonstration of electronically controlled beam-scanning and frequency reconfigurable operation for the terahertz photomixers has attracted the attention of the terahertz community significantly. The presentation of the designs were even accepted for five oral presentations in the IEEE AP-S conference. Secondly, the electromechanical investigation has also brought some new collaborations. The theoretical background of the behavior of the nano beams has a strong potential for ground breaking research. The idea has also attracted the attention of the micromechanics community.
The outcomes of the Tera-Nano has great potential on indoor communications, especially for 5G systems, and high-speed terahertz security imaging systems. With the increase of the array size and decrease of the beam width and beam size, the beam steering photomixers is prone to unprecedented applications for the above mentioned applications.
The SEM of the nano actuator developed within the frame of Tera-Nano