RIA: Spatial Coherence for Determining Mode Structure in Optoelectronic Devices

虽然直接观测光波导器件的光场分布通常是不可能的，但检测发射光束的空间相干函数（SCF）是获得信息的一种方法。由于通常的测量技术（即杨氏双缝）的繁琐性质以及这些器件中相对较低的光功率，关于光电器件的空间相干性的信息很少发表。研究人员开发了一种基于光纤的干涉测量技术，首次实现了对低功率光束空间相干性的直接、可重复测量。本研究启动奖计划使用测量的SCF来确定激光二极管腔内的模式分布。提出了三种可能的方法：1)基于Van Cittert- Zernike定理的非严格一阶分析（不严格适用于相干源，如激光，但相干效应可以通过时间平均去除）；2)采用Spano的方法，即写出光腔中前几个模的表达式，预测光腔中光场的光场密度，然后利用测量到的光场密度提取每个模的权值；3)将Tervonen等人提出的计算Hermite-Gaussian模式（光纤）的SCF模式分布的算法应用于平面波导，例如用于激光二极管和光电集成电路的波导。

Although it is not generally possible to observe directly the optical field distribution in optical waveguiding devices, one approach to obtaining the information is to examine the spatial coherence function (SCF) of the emitted beam. Very little information has been published on the spatial coherence of optoelectronic devices due to the cumbersome nature of the usual measurement technique (i.e. Young's double slit), and the relatively low optical powers in these devices. A new fiber- based interferometric technique has been developed by the principal investigator, which, for the first time, allows the direct and repeatable measurement of spatial coherence of low-power light beams. It is planned in this Research Initiation Award to use the measured SCF to determine the mode distribution in the cavities of laser diodes. Three possible approaches are proposed: 1) a non-rigorous first order analysis based on invoking the Van Cittert- Zernike Theorem (not strictly applicable to coherent sources such as lasers, but coherence effects can be removed by time-averaging); 2) an approach following that of Spano, i.e. writing down expressions for the first few modes in an optical cavity and predicting the SCF, then using the measured SCF to extract the weight for each mode; and 3) adapting the algorithm of Tervonen et al, who presents a method for computing the mode distribution from the SCF for Hermite-Gaussian modes (fiber), to planar waveguides such as those used in laser diodes and optoelectronic integrated circuits.