  Flexible microelectronics has shown tremendous promise in a broad spectrum of
applications, especially those that cannot be addressed by conventional
microelectronics in rigid materials and constructions1-3. These unconventional
yet important applications range from flexible consumer electronics to
conformal sensor arrays and biomedical devices. A recent successful paradigm
shift in implementing flexible electronics is to physically transfer and bond
highly integrated devices made in high-quality, crystalline semiconductor
materials on to plastic materials4-8. Here we demonstrate a flexible form of
silicon photonics on plastic substrates using the transfer-and-bond fabrication
method. Photonic circuits including interferometers and resonators have been
transferred onto flexible plastic substrates with preserved functionalities and
performance. By mechanically deforming the flexible substrates, the optical
characteristics of the devices can be tuned reversibly over a remarkably large
range. The demonstration of the new flexible photonic system based on the
silicon-on-plastic (SOP) material platform could open the door to a plethora of
novel applications, including tunable photonics, optomechanical sensors and
bio-mechanical and bio-photonic probes.
