摘要
随着光纤通信与光纤传感的发展,以LiNbO_3为衬底材料、以M-Z干涉仪为光波导结构、采用共面行波电极(CPW)为调制电极的集成光学强度调制器得到了越来越广泛的应用。采用行波电极的M-Z型外调制器调制速率高,波长的啁啾噪声理论上为零,几乎不受光纤色散的限制,已成为高速长距离光纤传输系统必不可少的器件。又由于LiNbO_3材料具有良好的电光效应、很短的电光响应时间、较宽的透明波长范围,因而适合用于制作低损耗、低电压、高速宽带强度调制器。光纤通信向着大容量、高速宽带方向发展,光纤延迟线系统要求强度调制器具有高速信号传输、快速响应的特点,因此以LiNbO_3为衬底材料的集成光学强度调制器具有十分良好的应用前景。
本课题旨在研究以LiNbO_3为衬底材料、以M-Z干涉型光波导结构为基础、以CPW行波电极为调制电极的集成光学强度调制器。该强度调制器工作于1.3μm,具有大于25dB的消光比、低驱动电压、宽工作带宽的特点。
研究内容包括光波导理论、电光效应等基本理论研究,强度调制器结构的设计、工艺技术研究与设计、测试技术研究等几个方面。
光波导理论研究从波动方程与射线光学的角度入手,得出模式方程,并分析了波导模式、波导的截止条件。
电光效应理论是从双折射晶体的折射率椭球出发,分析外加调制电场通过晶体电光张量对折射率椭球的影响,从而分析电光效应的机理。
调制器的结构设计从M-Z干涉型光波导的结构出发,分析了M-Z干涉型光波导的工作原理,调制电极的工作原理,从而设计出了工作于1.3μm的M-Z干涉型光波导、采用行波电极的LiNbO_3强度调制器的结构参数。
通过对器件结构的研究,合理设计出工艺参数,制作出工作于1.3μm,带宽2GHz,消光比优于25dB的强度调制器,并对该调制器的各项参数进行测试,使理论设计得到了很好的验证,也为以后研制其它1.3μm的波导调制器件以及宽带行波电极强度调制器提供了很好的理论技术基础。
With the development of fiber-optic communication systems and fiber-optic sensors, the LiNbO_3 integrated optical intensity modulators consisting of M-Z optical waveguide and CPW modulation electrode structure get an extensively application. Especially, LiNbO_3 optical modulators, using M-Z waveguides and traveling-wave electrodes, are essential for high-speed and long-haul optical fiber transmission systems since the wavelength chirp is very small and the effect of the fiber dispersion is minimized. Because of its excellent electro-optic effect, very short electro-optical response time, and wide transparent wavelength range, LiNbO_3 material meet the demands of low-loss, low drive voltage, high-speed and wide-band intensity modulator. As far the trend of fiber-optic communication systems is to obtain higher capacity, and higher transmission speed. The intensity modulator is widely applied to a lot of fields. It is necessary for the intensity modulator subject to the laser pulse rectification systems that should be provided with following performances as high speed signal transmission and quick response and so on. So the application prospects of LiNbO_3 integrated optic intensity modulators are getting better.
The LiNbO_3 integrated optical intensity modulators consisting of M-Z optical waveguide and CPW modulation electrode structure is presented in this thesis. The specifications of the intensity modulator at 1.3μm involved with extinction ratio better than 25 dB, and low drive voltage, and wide operation band width and so on.
Based on optical waveguide theory and electro-optic effect, the structure of the intensity modulator, fabrication technique, and measurement technology are studied intensively.
The optical waveguide characteristics such as waveguide mode field profile, and the mode cut-off conditions, and the waveguide dispersion are analyzed with the solution of a certain wave equation.
The mechanism of index ellipsoid of LiNbO_3 crystal distorted with an external applied electric field by means of the electro-optic tensor as investigated.
Based on the operation principle of M-Z waveguide, the operation mechanism of
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