Cai Lutong, Han Shuang Li Huangpu, Hu Hui
Opt Express. 2015 Jan 26;23(2):1240-8. doi: 10.1364/OE.23.001240.
The proton exchanged (PE) planar and channel waveguides in a 500 nm thick single-crystal lithium niobate thin film (lithium niobate on insulator, LNOI) were studied. The mature PE technique and strong confinement of light in the LN single-crystal thin film were used. The single mode and cut-off conditions of the channel waveguides were obtained by finite difference simulation. The results showed that the single mode channel waveguide would form if the width of the PE region was between 0.75 μm and 2.1 μm in the β(4) phase. The channel waveguide in LNOI had a much smaller mode size than that in the bulk material due to the high-refractive-index contrast. The mode size reached as small as 0.6 μm(2). in simulation. In the experiment, the refractive index and phase transition after PE in LNOI were analyzed using the prism coupling method and X-ray diffraction. Three different width waveguides (5 μm, 7 μm and 11 μm) were optically characterized. Near-field intensity distribution showed that their mode sizes were 3.3 μm(2).,5 μm(2). and 7 μm(2). The propagation losses were evaluated to be about 16 dB/cm, 12 dB/cm and 11 dB/cm, respectively. The results indicate that PE is a promising method for building more complicated photonic integrated circuits in single-crystal LN thin film.
研究了500nm厚的单晶铌酸锂薄膜（绝缘体上铌酸锂，LNOI）中的质子交换（PE）平面波导和通道波导。采用了成熟的PE技术以及铌酸锂单晶薄膜中光的强限制特性。通过有限差分模拟获得了通道波导的单模和截止条件。结果表明，在β(4)相中，当PE区域的宽度在0.75μm至2.1μm之间时，将形成单模通道波导。由于高折射率对比度，LNOI中的通道波导的模尺寸比块状材料中的小得多。在模拟中，模尺寸小至0.6μm²。在实验中，使用棱镜耦合方法和X射线衍射分析了LNOI中PE后的折射率和相变。对三种不同宽度的波导（5μm、7μm和11μm）进行了光学表征。近场强度分布表明，它们的模尺寸分别为3.3μm²、5μm²和7μm²。评估得到的传播损耗分别约为16dB/cm、12dB/cm和11dB/cm。结果表明，质子交换是在单晶铌酸锂薄膜中构建更复杂光子集成电路的一种有前景的方法。
