Temperature-insensitive polarization mode converter based on thin-film periodically-poled lithium niobate

Periodically poled lithium niobate (PPLN) is a promising platform for realizing high-speed active polarization mode conversion. Especially, the development of thin-film PPLN techniques drives related devices to lower power consumption, higher performance and more integration. However, the wavelength shifting with the temperature variation is still a problem that brings instability and impedes modulation efficiency. In this paper, we first analyzed the temperature characteristics of a well-designed z-cut polarization mode converter based on thin-film PPLN. The simulated modulation voltage is smaller than 5V. Then a temperature-insensitive device was proposed with different coating materials of negative thermo-optic coefficients. Compared to the structure without coating, the wavelength shifting decreases from 0.25nm/°C to 0.07nm/°C, in the meantime, the modulation voltage can still be kept smaller than 5V or even be reduced slightly.