Flexible bragg reflection waveguide devices fabricated by post-lift-off process

Bragg reflection waveguide devices are fabricated on a flexible substrate by using a post-lift-off process in order to obtain highly uniform grating patterns on a wide range. In this process, the flexible substrate formed by spin-coating on a silicon wafer is lifted-off at the end of fabrication procedures. The flexible Bragg reflector exhibits very sharp transmission spectrum with a 3-dB bandwidth of 0.1 nm and a 10-dB bandwidth of 0.4 nm, which is provided by the grating pattern with excellent uniformity. Athermal operation of the flexible Bragg reflector is also demonstrated through the optimization of thermal expansion property of the plastic substrate by controlling the thickness of two polymer substrate materials. The flexible substrate made of 0.7-mu m SU-8 layers sandwiching 100-mu m NOA61 film provides an optimized thermal expansion property compensating the thermooptic effect of the polymer waveguide. The temperature dependence of the Bragg reflector is reduced to -0.011 nm/degrees C by the plastic substrate.