Electrically tunable microcavities are essential elements for tunable laser sources indispensable for modern telecommunication and spectroscopy. However, most device concepts suffer from extensive lithography or etching for membrane processing. Here, we present an electrically and continuously tunable, multi-half-wavelength microcavity with a quality factor > 1000 as an easy-to-fabricate platform with potential use for vertical-cavity surface-emitting lasers. The microcavity has a Fabry-Pérot structure consisting of ultrasoft PDMS gel with a thickness of 14-15 μm and capped by a distributed Bragg reflector on the bottom end and a silver layer serving as top mirror and electrode. Additionally, we have embedded a pyrromethene dye into the PDMS matrix to prove efficient gain medium integration. By means of an integrated dielectric elastomer actuator, the microcavity thickness is varied 1.3 μm (9%) with a driving voltage of 70 V. The subsequent silver mirror deflection achieves a reversible 40 nm tuning of the cavity resonance wavelength. The tuning range is limited by the lateral bending of the electrodes for increasing voltages. This characteristic bending is confirmed by simulations with finite elements method. The dynamic behavior of the microcavity is characterized by capacitance measurements and modeled by viscoelastic theory. Our research provides in-depth examinations of electrically tunable, PDMS gel-based microcavities with the future goal of building simple, miniaturized, and cost-efficient laser sources with high tuning range.
Keywords: PDMS gel; dielectric elastomer actuator; flexible mirror; optical microcavity; polymer metallization; tunable dye emission; vertical-cavity surface-emitting laser.