Designing coupled microcavity lasers for high-Q modes with unidirectional light emission

Abstract

We design coupled optical microcavities and report directional light emission from high-Q modes for a broad range of refractive indices. The system consists of a circular cavity that provides a high-Q mode in form of a whispering gallery mode, whereas an adjacent deformed microcavity plays the role of a waveguide or collimator of the light transmitted from the circular cavity. As a result of this very simple, yet robust, concept we obtain high-Q modes with promising directional emission characteristics. No information about phase space is required, and the proposed scheme can be easily realized in experiments. c 2018 Optical Society of America OCIS codes: 130.3120, 140.3410, 140.3945, 140.4780. Microcavity lasers have attracted much attention because of their high potential in a number of applications related to high-density optoelectric integration [1,2]. An important objective is the design of microlasers with unidirectional emission properties. One promising route to achieve this was the modification of the original circular boundary that, due to the inherent rotational symmetry, yields a uniform far field. Spiral-shaped microcavity laser [3] were one of the first geometries successfully tested in many experiments [4][5][6][7][8], and conditions for unidirectional light emission from spiral-shaped microcavities were studied in detail [9][10][11]. A triangular shape has been proposed especially for small lasers [12,13]. In annular microcavities, high-Q modes with unidirectional light emission were achieved through a mechanism that couples a uniform emitting high-Q whispering gallery mode (WGM) to a directional emitting low-Q mode by means of mode hybridization near avoided resonance crossings [14]. Recently, Limaçon-shaped microcavity lasers were proposed [15] as source for high-Q modes with unidirectional light emission working for a substantial range of geometries and material parameters, and many experimental demonstrations of unidirectional light emission from those lasers were reported soon after [16][17][18][19]. Optimization of the system geometry involved the study of the so-called unstable manifold that governs the chaotic ray dynamics [20][21][22][23].Besides the single chaotic microcavity lasers with geometry controlled far-field characteristics, two-disk microcavity lasers have been shown to also produce high-Q modes with unidirectional light emission [24]. These lasers are not practical because there are many nearly degenerate modes with, however, opposite directions of light emission, and moreover, the emission directions depend sensitively on the material parameters such as small variations in the refractive indices.In this Letter we report a scheme that overcomes the drawbacks of two-disk microcavities and the limited range of working refractive indices for Limaçon-shaped devices, yet keeping their robustness. Our design couples a circular cavity with a deformed disk, cf. Figure 1(a) shows our system which consists of two cavities with different boundary shapes: a circular cavity of radius ...

Abnormal high-Q modes of coupled stadium-shaped microcavities

“…In this case, there is no dramatic enhancement of Q-factors. Similar lens effects by the circular boundary have been reported in relation to the emission directionality [21][22][23][24][25][26].…”

Dielectric microcavities: Model systems for wave chaos and non-Hermitian physics

“…Recently, the collimation effect has been exploited in numerical simulations by coupling a microdisk to a lens-shaped cavity nearby (Ryu and Hentschel, 2011). By a proper choice of parameters unidirectional light emission from high-quality modes is possible even in the low-index regime.…”

Microcavity lasers on polymer materials: Boundary integral equation modeling and experiments

“…For instance, all the works [7,[9][10][11][12]18,19] dealt with such IE although this fact was fully acknowledged only in the paper [10]. The spurious eigenvalues are the real frequencies (zero-threshold values, in LEP) that are the eigenvalues of the interior electromagnetic problem where the boundary is assumed perfectly electrically conducting and the inside filling is free space.…”

“…This included fully convex contours like ellipse, stadium, cut circle, various regular polygons, and others, and also partially concave "notched" contours" [7][8][9][10][11][12][13][14][15][16]. Particularly high expectations had been associated with a resonator having in-plane contour given by an Archimedean spiral with a small step [17][18][19][20].…”