Athermal lithium niobate microresonator

Lithium niobate (LN), possessing wide transparent window, strong electro-optic effect, and large optical nonlinearity, is an ideal material platform for integrated photonics application. Microring resonators are particularly suitable as integrated photonic components, given their flexibility of device engineering and their potential for large-scale integration. However, the susceptibility to temperature fluctuation has become a major challenge for their implementation in a practical environment. Here, we demonstrate an athermal LN microring resonator. By cladding an x-cut LN microring resonator with a thin layer of titanium oxide, we are able to completely eliminate the first-order thermo-optic coefficient (TOC) of cavity resonance right at room temperature (20°C), leaving only a small residual quadratic temperature dependence with a second-order TOC of only 0.37 pm/K2. It corresponds to a temperature-induced resonance wavelength shift within 0.33 nm over a large operating temperature range of (−10 – 50)°C that is one order of magnitude smaller than a bare LN microring resonator. Moreover, the TiO2-cladded LN microring resonator is able to preserve high optical quality, with an intrinsic optical Q of 5.8 × 105that is only about 11% smaller than that of a bare LN resonator. The flexibility of thermo-optic engineering, high optical quality, and device fabrication compatibility show great promise more »

Authors:
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Publication Date:
NSF-PAR ID:
10371328
Journal Name:
Optics Express
Volume:
28
Issue:
15
Page Range or eLocation-ID:
Article No. 21682
ISSN:
1094-4087; OPEXFF
Publisher:
Optical Society of America
1. Materials with strong second-order ($χ<#comment/>(2)$) optical nonlinearity, especially lithium niobate, play a critical role in building optical parametric oscillators (OPOs). However, chip-scale integration of low-loss$χ<#comment/>(2)$materials remains challenging and limits the threshold power of on-chip$χ<#comment/>(2)$OPO. Here we report an on-chip lithium niobate optical parametric oscillator at the telecom wavelengths using a quasi-phase-matched, high-quality microring resonator, whose threshold power ($∼<#comment/>30µ<#comment/>W$) is 400 times lower than that in previous$χ<#comment/>(2)$integrated photonics platforms. An on-chip power conversion efficiency of 11% is obtained from pump to signal and idler fields at a pump power of 93 µW. The OPO wavelength tuning is achieved by varying the pump frequency and chip temperature. With the lowest power threshold among all on-chip OPOs demonstrated so far, as well as advantages including high conversion efficiency, flexibility in quasi-phase-matching, and device scalability, the thin-film lithium niobate OPO opens new opportunities for chip-based tunable classical and quantum light sources and provides a potential platform for realizing photonic neural networks.