Low-Threshold Lasing with Frozen Mode Regime and Stationary Inflection Point in Three Coupled Waveguide Structure

TL;DR

This paper introduces a novel three-waveguide structure exhibiting frozen mode regime and stationary inflection points, enabling low-threshold lasing with enhanced optical properties for integrated photonic devices.

Contribution

It presents a new design of coupled waveguides with micro-cavities that achieves third order stationary inflection points and demonstrates improved lasing performance over traditional band edge lasers.

Findings

Realization of third order stationary inflection points in the structure

Demonstration of two overlapping SIPs at the Brillouin Zone center

Finite structure lasing thresholds outperform conventional DFB lasers

Abstract

The frozen mode regime is a unique slow-light scenario in periodic structures, where the flat-bands (zero group velocity) are associated with the formation of high-order stationary points (aka exceptional points). The formation of exceptional points is accompanied by enhancement of various optical properties such as gain, Q-factor and absorption, which are key properties for the realization of wide variety of devices such as switches, modulators and lasers. Here we present and study a new integrated optical periodic structure consisting of three waveguides coupled via micro-cavities and directional coupler. We study this design theoretically, demonstrating that a proper choice of parameters yields a third order stationary inflection point (SIP). We also show that the structure can be designed to exhibit two almost-overlapping SIPs at the center of the Brillouin Zone. We study the transmission and reflection of light propagating through realistic devices comprising a finite number of unit-cells and investigate their spectral properties in the vicinity of the stationary points. Finally, we analyze the lasing frequencies and threshold level of finite structures (as a function of the number of unit-cells) and show that it outperforms conventional lasers utilizing regular band edge lasing (such as DFB lasers).