陳彥宏

In recent years, the growth of digital communications devices using optical systems, especially with Integrated Circuits (IC), has become the main interest. To create fast, broadband, and tunable optical switch in a photonic circuit chip, the research to integrate the “broadband passive elements of Adiabatic Coupler” and the “active narrowband EOPMC” has been studied. Using the broadband polarization beam splitter of the adiabatic light transfer of TE- and TM-polarized fundamental modes in Ti: In diffused (LiNbO3) waveguides and narrowband but tunable active electro-optical polarization mode conversion based on a Ti:PPLN waveguide will lead to tunable broadband active mode polarization mode switch on a single chip. In this study, the broadband tunable EO switch device is fabricated in a 50-mm long, 20-mm wide, and 1-mm thick z-cut LiNbO3 chip using the thermal in: diffusion method and electric-field poling technique with a 23 µm grating period. The AAC part is designed to work as a wavelength-independent and high polarization-extinction-ratio (PER) polarization beam splitter (PBS), then EOPMC could convert between TE and TM-Polarized modes when an external electric field is applied along the crystallographic y-axis of the Ti:PPLN at EO coefficient r51. Our goal is to achieve the broadband polarization mode switches by actively tuning the input polarization wave for either polarization so that the output polarization wave could be determined as a result of the high coupling efficiency of adiabatic couplers. The experiment also has been done in broad temperature and wavelength. The measurement result of the active switch had a good-fitting result with the simulation process. The conversion efficiency/coupling efficiency also can reach as high as 96% with ~2.6 nm bandwidth which is close to the passive switch’s result (98%). This unique device works at a low driving voltage of 20 V and also shows a broad temperature range with tuning rate dλ/ dT = -1 nm over broad wavelength for both TE and TM polarization.