PI Mittleman has also been involved in a collaboration with researchers at UESTC in China, working to develop high-precision phase modulators for the terahertz range. Because of covid, this collaboration has been limited entirely to online interactions. However, after many zoom calls, this work has now resulted in a publication describing a device which can implement a remarkably precise phase modulation of a THz carrier wave. For example, at 265 GHz, a phase modulation with a precision of 4 degrees and a phase error of less than 1 degree, over a range of about 60 degrees, has been experimentally demonstrated. The implementation involves a very creative design in which a number of independently controllable modulation taps impose a nonlinear superposition of phase variation on a THz guided wave. The nonlinearity vastly broadens the range of possible output phase values, and enables the device to be operated with digital inputs and extraordinary precision (on the order of a few femtoseconds of temporal phase uncertainty). The amplitude insertion loss is around 6 dB, and varies by less than 0.5 dB over the entire range of phase modulation, making this nearly an ideal phase-only modulator. This work is soon to appear in Nature Photonics.
Publications:
Hongxin Zeng, Huajie Liang, Yaxin Zhang, Lan Wang, Shixiong Liang, Sen Gong, Zheng Li, Ziqiang Yang, Xilin Zhang, Feng Lan, Zhihong Feng, Yubin Gong, Ziqiang Yang and Daniel M. Mittleman, “High-precision digital terahertz phase manipulation within a multichannel field perturbation coding chip,” Nature Photonics, in press (2021)