Birefringence compensation, improved fringe contrast and trimming in an integrated asymmetric Mach–Zehnder interferometer using mid-IR laser processing

Abstract Tuning of an asymmetric Mach–Zehnder interferometer using mid-IR laser radiation is demonstrated. The device birefringence is compensated for by processing at the surface above one of the arms with 10.6 μm light from a CO 2 laser. The spectral contrast of the component is improved from ∼7 to ∼12 dB for the TE and TM eigenstates, respectively to ∼20 dB for both eigenstates by balancing the optical energy in each arm before the output coupler.