Microresonators and Frequency-Selective Optical Components Made by Photopolymerisation: Quality Factor, Surface and Drift

Photopolymerisation can directly fabricate three-dimensional optical microresonators and other frequency-selective structures, including whispering-gallery microcavities and microrings. Their performance is unusually sensitive to the interaction of material absorption, surface roughness, geometric error and environmental drift. High quality factor is therefore not a simple printing-resolution metric. Two-photon-polymerised hybrid microcavities have demonstrated quality factors above 10⁵, while subsequent work has explored asymmetric cavities, multiphoton-written microrings and polymer resonators for sensing. These results show that direct writing can produce functional resonators but also that Q, free spectral range and resonance wavelength are coupled to the exact fabrication and measurement state. This review separates intrinsic material loss, scattering, radiation loss and coupling loss; treats surface and geometry as optical boundary conditions; and defines drift, hysteresis and ageing as part of qualification. A minimum evidence framework is proposed around spectral measurement, coupling method, surface/dimensional metrology, thermal and humidity response, and repeat testing over time. ER-428.