THz communications based on spatio-temporal light modulation

About This Grant

In the current world, there is an ever-growing need for data transmission: not only does more information need to be transmitted, but also more devices are transmitting data: from electric grid infrastructure to traffic signals, more efficiency can be achieved if all equipment is communicating with each other. Wireless communications are simple and easily deployable; however, the range of frequencies available for existing techniques is currently limited to below 300 GHz, thereby not accommodating future growth as devices using the same frequency may be talking over each other. The terahertz (THz) frequency region (from 300 GHz to beyond 1 THz) is located beyond where typical radio equipment typically operates and such high frequencies are particularly suited for these challenges as it not only offers more bandwidth but a larger usable frequency range. Because the wavelength of THz waves is shorter than that of lower frequency radio waves, highly directive beams that are less sensitive to obstacles can be obtained. The aim of this project is therefore to develop new technologies utilizing the terahertz frequency region to obtain high speed and highly directive data transmission between a transmitter and a receiver, using dynamic obstacle avoidance. In addition, water vapor from the atmosphere absorbs light at certain THz frequencies; the use of a widely tunable source of THz will enable the choice of a specific propagation range. The low divergence of THz beams, combined with this tunable propagation range, can drastically limit the eavesdropping and detection probability therefore creating very private communications links. In addition, these techniques would also enable high-speed wireless connections across challenging terrains and into remote areas. The primary goal of this project is to develop two key devices that allow efficient and reconfigurable THz communication links: an amplitude modulator and a spatial light modulator. An amplitude modulator operating at THz frequency is critical to obtaining any sort of data transmission; however, the use of a spatial light modulator is only necessary if one wants to achieve reconfigurable beams (i.e., dynamic beam steering for tracking the detector, or obstacle avoidance). By combining these two devices with state-of-the-art THz sources and detectors, communication links at high data-rate with an intrinsically limited range will be demonstrated. To achieve high speed modulation of a THz field, the free carrier concentration in a low doped (and highly transparent in the THz) semi-conductor such as high-resistivity silicon, will be electrically modulated. The fabrication of such a modulator will require the use of conductive and THz-transparent electrodes using materials such as graphene. The spatial light modulator will be designed using micro-electro-mechanical system (MEMS), where wavelength scale movable mirrors will allow for a full phase front control of the THz beam, thereby allowing the dynamic shaping of the transmitted THz light to avoid obstacles (e.g., using bottle beams). Finally, the two devices will be combined to demonstrate two communication datalinks: an indoor link with obstacle avoidance (<10m) and an outdoor link with high directivity (>100m). These two demonstrations will show the relevance of THz technologies for the future of wireless communications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.