Investigation of birefringence in PMMA channel waveguides inscribed with DUV radiation

We studied both experimentally and numerically the spectral behavior of modal birefringence in channel waveguides inscribed in PMMA by DUV illumination. The measurements of birefringence were carried out using a spectral interference method for different waveguide widths, respectively 2, 3, 4, 5, 6 µm, which were inscribed using 2 J cm−2 and 3 J cm−2 irradiation doses. We have also modeled the spectral dependence of birefringence related only to waveguide geometry using the finite element method. High discrepancy was observed between measured and calculated birefringence. This is related to the fact that numerical analysis accounts only for the so-called geometrical birefringence induced by an asymmetry of the waveguide, while in measurements the overall modal birefringence relates to both the geometrical and the material effect. Our measurement results indicate that the contribution of the material birefringence in the analyzed waveguides may reach up to 3 × 10−4 in a short wavelength range