RIA: Spatial Coherence for Determining Mode Structure in Optoelectronic Devices

虽然通常不可能直接观察光波导器件中的光场分布，但获得信息的一种方法是检查发射光束的空间相干函数(SCF)。由于通常的测量技术(即杨氏双缝)的繁琐性质，以及这些器件中的光学功率相对较低，关于光电子器件的空间相干性的信息发表得很少。首席研究员开发了一种新的基于光纤的干涉测量技术，首次允许直接和可重复地测量小功率光束的空间相干性。在这个研究启动奖中，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(不严格地适用于激光等相干源，但相干效应可以通过时间平均来消除)；2)遵循SPANO的方法，即写下光腔中前几个模式的表达式并预测SCF，然后用测得的SCF来提取每个模式的权重；3)采用Tervonen等人的算法，给出了计算厄米-高斯模(光纤)SCF的模式分布的方法，并将其应用于激光二极管和光电子集成电路等平面波导。

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.