  Photonic integration on plastic substrates enables emerging applications
ranging from flexible interconnects to conformal sensors on biological tissues.
Such devices are traditionally fabricated using pattern transfer, which is
complicated and has limited integration capacity. Here we pioneered a
monolithic approach to realize flexible, high-index-contrast glass photonics
with significantly improved processing throughput and yield. Noting that the
conventional multilayer bending theory fails when laminates have large elastic
mismatch, we derived a mechanics theory accounting for multiple neutral axes in
one laminated structure to accurately predict its strain-optical coupling
behavior. Through combining monolithic fabrication and local neutral axis
designs, we fabricated devices that boast record optical performance
(Q=460,000) and excellent mechanical flexibility enabling repeated bending down
to sub-millimeter radius without measurable performance degradation, both of
which represent major improvements over state-of-the-art. Further, we
demonstrate that our technology offers a facile fabrication route for 3-D
high-index-contrast photonics difficult to process using traditional methods.
