Polymeric photonic molecule super-mode lasers on silicon

Abstract

Optically coupled microcavities have emerged as photonic structures with promising properties for investigation of fundamental science as well as for applications. We report on the fabrication and spatially resolved spectroscopy of on-chip photonic molecule (PM) lasers consisting of two coupled, dye-doped polymeric microdisks on a silicon substrate. We investigate the fundamental lasing properties with focus on the spatial distribution of modes, the coupling dependent suppression of lasing modes, and in particular the application-oriented operation of these devices in aqueous environments. By depositing an additional polymer layer onto the lithographically structured cavities made of dye-doped poly(methyl methacrylate), coupling-gap widths below 150 nm with aspect ratios of the micro-/nanostructure exceeding 9 : 1 are achieved. This enables strong optical coupling at visible wavelengths despite relatively small resonator radii of 25 mm. The lasing properties of dye-doped PMs are investigated using spatially resolved micro-photoluminescence (m-PL) spectroscopy. This technique allows for the direct imaging of whispering-gallery modes (WGMs) in the photonics molecules. For subwavelength coupling gaps, we observe lasing from delocalized eigenstates of the PMs (termed in the following as super-modes). Using size-mismatched cavities, the lasing mode suppression for different coupling-gap widths is investigated. We further demonstrate single-mode lasing operation in aqueous environments with PMs, which are realized on a low-cost, polymer-on-silicon platform.

Strong Coupling in a Photonic Molecule Formed by Trapping a Microsphere in a Microtube Cavity

“…When some discrete resonant modes in each resonant spec trum overlap (or close to each other), optical coherent coupling occurs between the two cavities, which results in delocalized eigenmodes (also termed as "supermodes"). [12,18] As such, in the microspheretube system the resonant modes of microtube are coupled to microsphere with a periodicity of N = [FSR S /FSR T ] ("[]" stands for the nearest integer), i.e., the resonant modes are selectively coupled with an interval of N modes in the resonant spectrum. For instance, in the optical coupling at mode M, the optical field can be efficiently coupled into the microsphere, which can be evidenced by the variation of mode intensity and the occurrence of mode splitting.…”

“…As such, one needs a deliberate control on both the cavity geometries and the intercavity coupling gap to ensure a good spectral match and efficient evanescent coupling between the coupled cavities. [18] Moreover, dynamic tuning of the intercavity coupling strength has been investigated in recent years, which were carried out by advanced and sophisticated techniques such as strain tuning, [21,22] acoustooptic control, [23] and precise micromanipulation techniques. [3] To extend and promote the research in the field of photonic molecules, it is of high interest to design novel photonic molecules extending from adjacent solid microcavities to thinwalled hollow cavities which possess intense evanescent field facilitating intercavity coupling and provide novel strategy for tuning of the coupling strength.…”

“…However, the evanescent field is relatively weak in the reported photonic mole cules because most of the optical field is strongly confined within the coupled cavities (e.g., microdisks, [4,8,11,18] micro toroids, [19] microspheres, [3] microrods, [5,20] and microfibers [7] ). As such, one needs a deliberate control on both the cavity geometries and the intercavity coupling gap to ensure a good spectral match and efficient evanescent coupling between the coupled cavities.…”

“…We focus on studying the WGM coupling between the trapped microsphere and microtube cavity with a significant difference of cavity sizes, which is in contrast to pre vious reports where the two externally adjacent microcavities possess highly similar sizes [11,12,41] or slightly mismatched sizes (less than two times). [4][5][6][7]18,[42][43][44] Periodic modulations on A photonic molecule formed by trapping a microsphere cavity into a hollow microtube cavity is demonstrated, which provides a novel design over conventional photonic molecules comprised of solid-core whispering gallery mode microcavities with externally tangent configuration. Periodic spectral modulations of mode intensity, resonant mode shift, and quality factor are observed owing to the largely mismatched cavity sizes.…”

Optically controlled elastic microcavities

“…Besides their excellent sensing capabilities they can also be turned into micro-lasers when incorporating laser dyes 12 or quantum dots 13 or be coupled to form photonic molecules. 14 But an obstacle effectively hindering some applications of these cavities is the limited tunability of these cavities. This is different for semiconductorbased WGM cavities where tuning of the cavity resonances is achievable by temperature-, field-or carrier-induced changes of the optical properties.…”