From Rigidity to Flexibility: Patterning Stripping Unlocks Flexibility of Crystals for Flexible Photonics

ABSTRACT The development of flexible photonics is fundamentally limited by the scarcity of functional, flexible optical materials. While conventional materials such as rare‐earth‐doped yttrium aluminum garnet (YAG) crystals offer superior optical properties, their inherent rigidity precludes their use in flexible devices. Here, a corrosion‐assisted patterned stripping (CAPS) technique is reported to directly fabricate flexible, microscale bi‐spiral Er:YAG filaments from bulk crystals, significantly expanding the material options for flexible photonics. These filaments exhibit remarkable mechanical compliance, enduring the degree of stretching up to 300% with full recovery after thousands of stretching cycles. Integrated onto elastomeric substrates, the filaments act as low‐loss optical waveguides exhibiting stable light transmission during deformation. As a proof of concept, a flexible optical waveguide amplifier operating in the telecommunication band is demonstrated, achieving a net gain of 10 dB, comparable to devices on rigid substrates. This direct conversion of rigid optical crystals into compliant components provides new design paradigms for flexible optoelectronic systems, addressing a critical materials challenge in the field.