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

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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 (QC) of approximately 106. The polymer core ring resonator exhibited a loaded Q-factor (QT) as high as 5.4 x 104 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.


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Applied Optics