Optical circulators enable bidirectional transmission of light and play an important role in data centers, communication networks and LIDAR. The integration of optical circulators is currently one of the thorny issues limiting the full integration of optical systems, and the usual schemes require hybrid integration of magneto-optical materials to break the optical reciprocity. In this work, we propose a thin-film lithium niobate (TFLN) optical circulator consisting of a traveling-wave electrode modulator (TWEM) and micro-ring resonators (MRRs). It realizes optical non-reciprocity based on the phase accumulation asymmetry of forward and backward traveling wave modulation, and adjusts the path of light with the help of the MRRs. The circulator has four optical channels to realize the light propagation along the 1-2-3-4-1 spatial sequence. The calculated isolation of each channel is greater than 20 dB, and the channel loss is less than 3 dB. Our scheme is wavelength-tunable, scalable, and process-friendly, and provides a promising implementation route for all-optical integration.
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.
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