Frozen mode in an asymmetric serpentine optical waveguide

Abstract

We show the existence of a frozen mode in a periodic serpentine waveguide with broken longitudinal symmetry. The frozen mode is associated with a stationary inflection point (SIP) of the Bloch dispersion relation, where three Bloch eigenmodes collapse on each other. Indeed, we show that the SIP is an exceptional point of degeneracy of order three. The frozen mode regime is characterized by vanishing group velocity and enhanced field amplitude, which can be very attractive in various applications including dispersion egineering, lasers, and delay lines. We show the trend in group delay and quality factor with waveguide length that is peculiar of the frozen mode. In a finite length waveguide, full transmission occurs at the resonance frequency very close to the SIP frequency.

Photonic Beamforming for 5G and Beyond: A Review of True Time Delay Devices Enabling Ultra-Wideband Beamforming for mmWave Communications

“…Recently, Yada and Capolino proposed that a slight variation and proper parameter tuning of the CROW structure can result in a unique slow wave device by utilizing an EPD at which two or more system eigenmodes coalesce in both eigenvalues and eigenvectors [144]- [146]. The proposed CROW is shown in Figure 10 coupling to an adjacent uniform optical waveguide gives rise to these EPDs leading to unique modal characteristics otherwise unavailable in regular CROW [144].…”

“…More recently, a periodic asymmetric serpentine optical waveguide (ASOW) with broken longitudinal symmetry was also proposed as shown in Fig. 10(c) due to different coupling among forward and backward propagating waves within the unit cell [146]. At the EPDs, group velocity is δω/δk = 0, with significantly reduced group velocity in the vicinity which could be utilized for efficient true time delay engines.…”