Thermally induced birefringence and stress in poly(methyl methacrylate) waveguides on oxidized silicon substrates

A thermally induced birefringence in a poly(methyl methacrylate) waveguide has been observed. From polarization measurements made at the output of a waveguide in the range 20-60 degrees C, a value for Delta(n(TE) - n(TM))/DeltaT of 1.1 x 10(-6) degrees C(-1) has been calculated. After waveguide preparation the underlying substrate was found to have a bow. By measuring changes in the bow caused by temperature in the range 20-60 degrees , we have calculated a value for the change in stress in the polymethyl methacrylate film of 0.18 MPa/ degrees C. By relating polarization to stress, changes in stress as small as 90 kPa can be measured.