Rapidly tunable optical add-drop multiplexer (OADM) using a static-strain-induced grating in LiNbO3

A rapidly tunable, polarization-independent, low-loss optical add-drop multiplexer (OADM) for the 1550-nm wavelength regime is reported. The four-port device consists of two input waveguides, a polarization beam splitter (PBS), two polarization conversion/electrooptic tuning waveguide sections, a second PBS and two output waveguides. The waveguides, which are single mode for both TE and TM polarizations, are fabricated on a LiNbO₃ substrate by Ti diffusion. Spectral selection is based on phase-matched polarization conversion due to shear strain induced by a dielectric grating overlay film. An applied voltage tunes the device by changing the waveguide birefringence and hence the optical wavelength at which most efficient polarization conversion occurs. Tuning of 0.1 nm/V with a maximum range of 24 nm has been obtained. A tuning speed of 50 ns, corresponding to a rate of 0.128 nm/ns, has been achieved. Channel isolation is better than 24 dB. Fiber-to-fiber insertion loss <5.4 dB has been obtained and polarization independent loss (PDL) of 0.24 dB for both drop and through ports have been realized over the tuning range. Thermal tuning has also been demonstrated.