Research Topics

I started to study the underlying physics of superluminality (faster-than-light phenomena) since my senior undergraduate life under the supervision of Prof. Tsun-Hsu Chang (National Tsing Hua University, Taiwan). In 2009-2011, we developed two microwave rectangular waveguide systems to experimentally demonstrate the time-domain superluminal effect. We found that such effect can be observed in not only tunneling system (with cutoff waveguide junction) but also Fabry-Pérot (FP) interferometer (with E-plane waveguide discontinuities). Those works have been published in “Progress in Electromagnetics Research” (Prog. Electromagn. Res. 122, 1 (2012) and 101, 291 (2010)). To investigate the underlying physics, in 2012, we cooperated with a prestigious theorist—Prof. Herbert Winful (University of Michigan, USA). We discovered that the group delay for signal passing through a FP cavity is strongly frequency dependent. The total group delay is composed of multiple terms, including the dwell time for signal staying within the cavity, the scattering times at the cavity’s boundaries, and the dispersive time. This work has been published in “Physical Review A” (Phys. Rev. A 86, 053832 (2012)). In 2013-2016, we kept cooperating with Prof. Winful and demonstrated the negative superluminality by a birefringent waveguide system. What interesting is that the peak of wave packet can just leave the system even before the time when it enters. The underlying mechanism can be clearly explained by the interference between two-polarization channels of the birefringence. In 2016, we published both the experimental and theoretical results in “IEEE Transection on Microwave theory and Techniques” (IEEE Trans. Microw. Theory Techn. 64, 3121 (2016)). As the previous research usually based on the frequency domain, in 2019-2020, we tried to make an alternative interpretation on positive superluminality from the time domain. We discovered that the destructive (constructive) interference can effectively speedup (retarding) the wave packet, which serves as the major mechanism of positive superluminality in a FP system. This work has been recently published in “Chinese Journal of Physics” (Chin. J. Phys. 67, 657 (2020)). After about ten-year theoretical and experimental efforts, we believe those group-delay control techniques can facilitate the efficient signal processing, high signal integrity, and devices miniaturization.