Investigation of a Polarization Controller in Titanium Diffused Lithium Niobate Waveguide near 1530 nm Wavelength

Abstract

Optical polarization control in Ti diffused channel waveguides onto LiNbO_(3) substrates have been investigated near 1530 nm wavelength regime by utilizing electro-optic effects of the substrate material. A device configuration composed of two polarization converters with a phase shifter centered between them and all integrated on a single optical channel waveguide was used. The polarization converters provided a means to control the polarization, and the phase shifter offered a tool to maintain the required phase condition between them. Single mode channel waveguides were fabricated by diffusing 7μm-wide Ti stripes into the LiNbO_(3) substrate. The polarization converters and phase shifter were formed by patterning aluminum surface electrodes on top of a SiO_(2) buffer layer. The polarization converters were produced in an interdigitated electrode form with a spatial period of 21 μm, over 10.5 mm coupling length. The phase shifter was implemented in the form of a 6,000 μm long electrode with 17 μm gap. The characteristics of each electro-optic element in the integrated configuration were individually evaluated first, and then the behavior of the overall device as a polarization controller was investigated. Polarization conversion efficiency of 99.5% between TE and TM orthogonal modes was realized for the converters, and π-radian phase shift between orthogonal modes was achieved with 40 V on the phase shifter. Using an optical vector analyzer (OVA) for characterizing the output, transformation of orthogonal or arbitrary incident polarization to either TE or TM polarization at the output was successfully realized. Suppression for the unwanted polarization at the output of approximately -40 dB near 1529.4 nm wavelength was obtained with voltages on both converters for TETM transformation, as well as 45o and 56^(o) incident polarization. For the incident orthogonal polarization case the transformation was realized without a voltage on the phase shifter supporting the implemented design parameters, and transformation of the obtained output back to its incident polarization through an induced -radian retardation was confirmed by applying 40 V on the phase shifter.