Manipulation of High-Order Scattering Processes in Ultrasmall Optical Resonators to Control Far-Field Emission

Abstract

By imposing a set of harmonic perturbations to a microcavity boundary, we induce conversion and mixing of orbital angular momentum of light via surface scattering. Multiple scattering paths are available due to high-order scattering, which can be greatly enhanced by quasidegenerate resonances. By manipulating the relative strengths of these scattering processes, we theoretically synthesize the angular momentum spectra of individual modes so as to control their far-field patterns. We demonstrate experimentally that in wavelength-scale cavities of a fixed shape, the neighboring modes can have dramatically different emission directionality. This phenomenon is robust against slight shape deviation and surface roughness, and provides a general mechanism to control the emission direction of ultrasmall resonators.

Pump-controlled modal interactions in microdisk lasers

“…has additional WG waves of higher radial order number 7 and azimuthal number 34. This is attributed to the mixing of WG modes with different order via wave scattering by the rough boundary of the microdisk [32][33][34].…”

“…In practice, there is always inherent cavity surface roughness introduced unintentionally during the fabrication process. The coupling between high-Q WG modes of low radial numbers and lower-Q WG modes of higher radial numbers, caused by the surface roughness [32][33][34], enhances the spatial diversity of the lasing WG modes, which plays a critical role to differentiate the WG modes by adaptive pumping.…”

Generalized Perturbation Theory for Weakly Deformed Microdisk Cavities

“…For instance, the underlying mechanism of the coupling of modes with different angular momenta in a weakly deformed microdisk cavity is ascribed to the surface scattering processes of light at the microcavity sidewall, of which the strengths can be individually evaluated for different scattering paths by the perturbation theory. [64,65] In fact, the scattering processes are not limited to weakly deformed microdisk cavities, i.e., the formation and characteristics of modes in strongly deformed microdisk cavities are also governed by the scattering. [10] The scattering processes can be manipulated by imposing specific cavity shape deformation to achieve unidirectional light emission for weakly deformed microdisk cavities, according to the perturbation theory.…”

“…[10] The scattering processes can be manipulated by imposing specific cavity shape deformation to achieve unidirectional light emission for weakly deformed microdisk cavities, according to the perturbation theory. [55,65] In general, the coupling of modes with different angular momenta via surface scattering processes is in the weak coupling regime for weakly deformed microdisk cavities, as the scattering processes are trivial non-resonant scattering. [55,64] However, the coupling of modes is radically altered in quasi-degenerate cases, where resonant scattering processes occur.…”

Threshold current reduction and directional emission of deformed microdisk lasers via spatially selective electrical pumping

“…6,7 It has been shown that a smooth deformation from circular symmetry produces directional light output. [8][9][10][11][12][13][14][15] Usually, these cavities are pumped uniformly, and lasing occurs in the modes with the highest-Q values. These modes are generally whisperinggallery like and reside close to the cavity boundary.…”