A silicon-on-insulator single-arm Mach-Zehnder interferometer (SAMZI) modulator

We demonstrate a single-arm Mach-Zehnder interferometer (SAMZI) modulator based on asymmetric long-period gratings for TE0-TE1 mode conversion integrated with a p-n junction doped waveguide for relative phase modulation between these modes via the electro-optic effect. The device consists of two long-period grating sections, with the active waveguide modulator section in-between, and inverse tapers at the input (to couple in only the TE0 mode), and the output (to filter out the excited TE1 mode). The periodicity dictates a central mode conversion wavelength and thus the region of operation for the modulator. Simulations are performed to investigate passive device properties, such as central wavelength sensitivity, free spectral range, and coupling coefficient, as well as active performance of the modulator. A fabricated device was characterized with a central wavelength of 1490 nm, a free spectral range of 0.975 nm, and a thermal stability of −0.521 rad/K or 42.4 pm/K. By balancing the lengths of each section, the device can be made athermal. Steady-state characterization shows a maximum on-off extinction ratio of 3.96 dB for a voltage difference of −8 V. The total phase-shift of the measured device agrees with simulation, with a phase-shift of 0.34π at −8 V. The VL of the measured device is 2.96 Vcm at −1 V and 6.37 Vcm at −8 V.