利用鎳擴散製程於週期性極化反轉鉭酸鋰垂直調制準相位匹配結構

Vertically Spatial Modulation of Quasi-Phase-Matching Structures on Periodically-Poled Lithium Tantalate Using Nickel-Diffused Process

韓志勇(Jhih-Yong Han)

指導教授 ： 彭隆瀚

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802718

摘要

本論文主要分為三部分:(1)三波混合與準相位匹配之理論之介紹及數值模擬，(2)週期性極化反轉鉭酸鋰之設計與製作，(3)進行折射率差模型以及樣品之光學量測。
本論文利用鎳擴散製程來對鐵電極化反轉區域進行定義，以製作週期性極化反轉鉭酸鋰，分別在週期性極化反轉鉭酸鋰晶片之+z面以及-z面濺鍍20 nm之金屬鎳薄膜，以略低於鉭酸鋰之居禮溫度條件下進行高溫585 ◦C鎳擴散使其表面區域產生折射率之梯度，藉此對準相位匹配所需補償之晶格動量進行縱向空間調制，以此得到更具可調性之寬頻光源。
光學量測部分，利用532 nm綠光雷射作為泵浦光源，對週期為7.63 µm 之極化反轉鉭酸鋰，進行光學參量產生以及光學參量震盪之量測。吾人在對樣品的深度掃描中，將泵浦光源焦點由距離+z面100 µm掃描至20 µm，發現對1020 nm附近之信號光而言，鎳擴散效應對光學參量產生過程可達到8.91 nm之光頻譜位移，而對光學參量震盪過程，則可造成3.27 nm信號光頻譜位移。
此外，在本篇論文利用動量守恆以及能量守恆建立出造成頻譜位移所對應到折射率差解之模型。

關鍵字

鉭酸鋰 ； 週期性極化反轉鉭酸鋰 ； 鐵電材料 ； 鐵電疇 ； 非線性光學 ； 準相位匹配 ； 三波混合 ； 光學參量震盪器

並列摘要

This thesis is composed of three parts: (1) theory of three-wave mixing and mechanism of quasi-phase-matching (QPM), (2) design and fabrication of periodically poled lithium tantalate, (3) implementation of a numerical model for analyzing the changes in refractive indices, and comparison with the optical measurements.
The patterning of periodic ferroelectric structures with designated and inverted domains is defined by shallow nickel (Ni)-diffusion process followed by pulse electric poling to fabricate periodically poled lithium tantalate (PPLT). To generate a gradient distribution of refractive indices along the depth directions beneath the surfaces, the samples were annealed at a temperature around 585 ◦C, which is slightly below the Curie temperature of the crystal, with 20 nm-thick nickel films deposited on the crystal’s +/-z faces. The latter provides a mechanism to establish effective modulation of the crystal momentum, along the vertical direction, for QPM-parametric generation to obtain a broadband light source.
Effective variation in the crystal momentum is confirmed by spectral analysis taken from measurements of optical parametric oscillation (OPO) and optical parametric generation (OPG) with 532 nm wavelength pump to the PPLT crystals with QPM periodicity of 7.63 µm. These optical experiments were taken with the pump laser beam scanned at a distance between 20 to 100 µm beneath the +z face of PPLT. We thereby resolved an 8.91 and 3.27 nm wavelength shift, respectively, for the 1020 nm signal wave from the OPG and the OPO spectra.
Moreover, the implementation of a numerical model for analyzing the changes in refractive indices was constructed by considering the laws of momentum and energy conservation for QPM processes in this thesis.

並列關鍵字

Lithium tantalate ； PPLT ； Ferroelectric material ； Ferroelectric domain ； Nonlinear optics ； Quasi-Phase-Matching ； Three-wave mixing ； Optical parametric oscillator

參考文獻

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