Zero-coupling-gap degenerate band edge resonators in silicon photonics

Abstract

Resonances near regular photonic band edges are limited by quality factors that scale only to the third power of the number of periods. In contrast, resonances near degenerate photonic band edges can scale to the fifth power of the number periods, yielding a route to significant device miniaturization. For applications in silicon integrated photonics, we present the design and analysis of zero-coupling-gap degenerate band edge resonators. Complex band diagrams are computed for the unit cell with periodic boundary conditions that convey characteristics of propagating and evanescent modes. Dispersion features of the band diagram are used to describe changes in resonance scaling in finite length resonators. Resonators with non-zero and zero coupling gap are compared. Analysis of quality factor and resonance frequency indicates significant reduction in the number of periods required to observe fifth power scaling when degenerate band edge resonators are realized with zero-coupling-gap. High transmission is achieved by optimizing the waveguide feed to the resonator. Compact band edge cavities with large optical field distribution are envisioned for light emitters, switches, and sensors.

Experimental Demonstration of Degenerate Band Edge in Metallic Periodically Loaded Circular Waveguide

“…4(c). Furthermore, as discussed in [19], [38], the Q factor grows linearly in the log(Q)-log(N) plot in Fig. 6 even for small values of N when the DBE feature is not yet evident.…”

High-Q Localized States in Finite Arrays of Subwavelength Resonators

“…Decrease of the period leads to modification of the dispersion curve and, for a specific value of the period (see an analytical expression in Supporting Information) the group velocity dispersion vanishes and the dispersion curve becomes quartic. Such a type of dispersion is known to exist in different systems, for example, in anisotropic crystals 37 or coupled waveguides, 18,38,39 and it leads to a faster growth of Q-factor as Q ∝ N 5 . 36,37 Interestingly, an even further decrease of the period results in a change of the sign of the group velocity dispersion, as shown schematically in Figure 1.…”

Degenerate band edge laser

“…However, it is important to stress that the DBE, which is a fourth order EPD, occurs in a passive and lossless system, i.e., without the need of gain or loss. Some DBE characteristics have been shown to occur at optical frequencies using perturbed coupled silicon waveguides [48,49], or a chain of ring resonators coupled to a waveguide [50]; as well as in metallic waveguides at microwaves [39]. There have been also significant efforts in analysis, design, and experimental realization of the DBE structures and its slow-wave properties at both microwave [51][52][53] and optical frequencies [54,55].…”