Abstract
Optical micro-cavities of various types have emerged as promising photonic structures, for both the investigation of fundamental science in cavity quantum electrodynamics and simultaneously for various applications, e.g., lasers, filters, or modulators. In either branch a demand for adjustable and tunable photonic devices becomes apparent, which has been mainly based on the modification of the refractive index of the micro-resonators so far. In this paper, we report on a novel type of whispering gallery mode resonator where resonance tuning is achieved by modification of the configuration. This is realized by polymeric split-disks consisting of opposing half-disks with an intermediate air gap. Functionality of the split-disk concept and its figures of merit like low-threshold lasing are demonstrated for laser dye-doped split-disks fabricated by electron beam lithography on Si substrates. Reversible resonance tuning is achieved for split-disks structured onto elastomeric substrates by direct laser writing. The gap width and hence the resonance wavelength can be well-controlled by mechanically stretching the elastomer and exploiting the lateral shrinkage of the substrate. We demonstrate a broad spectral tunability of laser modes by more than three times the free spectral range. These cavities have the potential to form a key element of flexible and tunable photonic circuits based on polymers.
Highlights
Optical micro-cavities have enormously promoted research progress in optics in recent years
We report on the influence of splitting disks into two parts on the lasing threshold and quality factor for the devices with fixed gap; afterwards, we focus on resonance tuning of split-disks patterned on elastomeric PDMS substrates
Laser emission from fixed-gap split-disks made by electron beam lithography is used to characterize the resonator properties
Summary
Optical micro-cavities have enormously promoted research progress in optics in recent years. A mechanical substrate deformation[34,35,36] is applied; for electroactive materials an electrical tuning has been achieved.[37] Tunable elastomer DFB lasers are realized in combination with liquid active materials, e.g., with the aid of dye solutions,[34] and in solid-state polymeric devices with embedded emitters.[35,37] In this context, the trendsetting concept of using polymers and elastomers for photonic devices becomes apparent as they provide an alternative approach to tunability. Up to the coupling of two resonators, this is feasible by using nano-positioning systems.[21,38] For such tuning in larger cavity arrays, we have established an alternative platform by structuring the cavity arrays onto elastomeric substrates.[39] Elaborating this approach, we present here a novel type of a WGM micro-resonator with a wide tuning range and with the prospect of easy integration into cavity arrays: Polymeric splitdisk resonators. We first focus on the demonstration of the functionality of split-disk micro-resonators and prove resonance tuning over a broad spectral range
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