Fig. 1. Flexible photonic devices based on different materials. (a) Flexible polymer waveguide cladded in PDMS^[25]; (b) flexible optical waveguide cladded in PI^[26]; (c) flexible Si NM phototransistor^[34]; (d) array of Ge NM MSM photodiodes on PET substrate^[75]; (e) 8 × 100 thin-film InGaAs p-i-n photodiode

Fig. 2. Design of multi-neutral plane structure. (a) Pure bending of multi-layer structure, whose top and bottom surfaces undergo tensile and compressive strain, respectively. The neutral plane position is specified by Equation (1)^[85]; (b) finite element simulation results of strain distribution in two thin-film structures with bending radius of 1 mm. The blue curve corresponds to strain in a polyimide (10 μm)-silicone (50 μm)-polyimide (10 μm) tri-laye

Fig. 3. Meandering and isolated structure based stretchable devices. (a) Procedures for the fabrication of honeycomb metamaterial with wrinkled layouts^[91]; (b) schematic of integrated stretchable photonic device based on the design of meandering waveguide and local hardening^[96]; (c) optical micrographs of waveguide coupled microring resonator without tensile strain and with 36% tensile strain[

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Fig. 4. General process illustration for semiconductor membrane release, transfer, and stacking^[85]

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Fig. 5. Fabrication process of monolithic integration of flexible photonic devices^[87]

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Fig. 6. Hybrid integration technology for flexible photonic devices. (a) Schematic of fabrication process of flexible waveguide-integrated detector^[88]; (b) optical micrograph of flexible waveguide integrated detector^[88]

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Fig. 7. Applications of flexible photonic devices in sensing field. (a) Flexible fibers for monitoring knees' weight bearing^[127]; (b) eye pressure sensor based on deformation of periodically nanostructured Bragg grating^[126]; (c) stretchable optical waveguides based on soft robotic hand for optoelectronic strain sensing^[123]; (d) polymer waveguide base

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Fig. 8. Flexible photonic devices for optical interconnect. (a) Diagram and (b) photo of flexible optical interconnection scheme using fully embedded optical link with polymer waveguides, mirrors, and optoelectronic components^[151];(c) stretchable optical link including integrated light sources, detectors, and polymer waveguide^[146]; (d) schematic of high-density integration optical interconnect based o

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Fig. 9. Applications of flexible photonic devices in new optical field manipulation. (a) Continuous reconfigurable switching of multiple holograms based on stretchable metasurface structure^[156]; (b) flexible Bragg grating based tunable organic DFB lasers^[158]; (c) schematic of dielectric metasurface layer conformed to the surface of transparent object with arbitrary geometry[

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