Using software to model, analyze, and determine manufacturing tolerances for coherent optical systems

Abstract

There is a long tradition of analyzing lens designs and establishing their manufacturing tolerances in software. The lens-design codes used for this process are based on sequential, geometric ray tracing techniques and the tolerances are based on geometric image quality as determined by system aberration content. More recently, largely due to the rapid expansion of optical telecom applications, there has been increased interest in the non-sequential propagation of complex optical fields, rather than geometric rays, through optical systems. Starting with sources of varying degrees of coherence or from the output from fibers or waveguides, fields can be non-sequentially propagated through optical systems, and the amplitude and phase of these fields can be examined at any position in space. This has enabled an enormous increase in the ability to analyze and tolerance coherent optical systems used in two main categories of optical systems: (1) measurement systems and (2) systems used to propagate coherent optical signals. This paper addresses the methodology involved in modeling, analyzing, and tolerancing coherent systems and highlights the main differences between the methods used with coherent systems and traditional lens designs. Coherent systems models include components that require modeling diffraction and interference effects. They typically extend the path length of the model, beginning at the source and continuing through to a detailed description of the detector or a coupling into an output waveguide. They may even include a measurement algorithm within the system model. Additionally, unlike the traditional lens-design models, the performance parameters used in establishing the manufacturing tolerances of these coherent systems, are not necessarily based on the image quality of the system. Instead, tolerancing of coherent systems is usually more directly related to the functionality of that system. To further demonstrate the methodology of modeling, analyzing, and tolerancing coherent systems in software, two examples of coherent system models, an interferometer and a telecom component, are presented. Some of the tolerancing results from these systems are presented.