Silicon-on-insulator interferometric strain sensor

An integrated optical strain sensor was fabricated in silicon-on-insulator. The sensor utilizes a novel Mach-Zehnder interferometer with arms of equal length having mutually perpendicular waveguide elements. When the applied strain in these two orthogonal directions is different, the symmetry of the device is broken, and this modifies the optical power output. Isotropic external influences like temperature, however, influence both arms equally and therefore have no effect on the optical output. For the sensor studied, observed phase sensitivity of the TM mode is 13.3degrees/muepsilon while that of the TE mode is lower at 6.7degrees/muepsilon. The TM mode's strain resolution in the linear response region is 0:05 muepsilon. The sensor exhibited drift of less than 0.5 muepsilon when monitored over a 24 hour period. Preliminary experimental results indicated a thermal apparent strain sensitivity of 1.0 muepsilon/degreesC, possibly related to adhesive layer non-uniformity.