Evanescent coupling between refillable ring resonators and laser-inscribed optical waveguides.

We investigated theoretically and experimentally the evanescent coupling between photonic waveguides of arbitrary shapes and refillable optical ring resonators on the same chip. The resonator hosts were designed to facilitate whispering gallery modes and etched by using a single-mask standard lithography process, whereas the waveguides were imprinted in the proximity of the ring resonator by using 3D ultrafast laser-writing technology. Finite element analysis in conjunction with coupled-mode theory revealed a coupling Q-factor (Q) of approximately 10. The polymer core ring resonator exhibited a loaded Q-factor (Q) as high as 5.4×10 and a free spectral range (FSR) of 406 pm at a center wavelength of 775 nm. Long-term stability of the ring resonator was repeatedly tested by examining the spectral location of optical resonances and the constancy of Q-factors and FSRs under ambient laboratory conditions for 1 month. We recorded consistent Q-factors and repeatable FSRs for all measurements. Renewability of the polymer core was demonstrated by removing and redepositing the polymer in the cavity, followed by measurements of Q-factors and FSRs. This work promises to enable reconfigurable and renewable photonic devices for on-chip lasers, 3D integrated optical signal processing, chip-scale molecular sensing, and the investigation of new optical phenomena.