Method designs free-form optical devices

Abstract

The simultaneous multiple surfaces (SMS) method was developed to calculate the surfaces of increasingly complex optical devices in nonimaging applications where the goal is efficient light transfer from a source to a target. It is primarily concerned with the design of devices such as waveguides, reflectors, and lenses. The method calculates all the optical surfaces (top, bottom, internal) of the lens or reflector simultaneously, starting from an initial area which has been pre-defined. Details of the early development of the method have been presented elsewhere.1–6 In this article, we give examples of our successful design solutions using SMS and outline the procedure by which subsequent parts of a device or optical system are calculated so that they meet the requirements of the application. The first applications of the SMS method were devoted to the problem of coupling two input sets of rays with two output sets of rays. The simplest design case is a lens that perfectly focuses two source points, P and P’, onto two image points, Q and Q’ (see Figure 1). Only when the distances PP’ and QQ’ approach zero does the lens tend to the aplanatic case (where the system is free of spherical aberrations and circular coma of all orders). The goal in the SMS method is to design a system that generates a sharp image over as broad a plane of incidence as possible (i.e., when the distances PP’ and QQ’ are not negligible).7 So while the aplanatic strategy is to improve the optical quality near the axis, the SMS strategy looks at improving image quality more evenly across the whole field. The result is that there is always a segment of design points such that the maximum spot size for any point in the field is smaller in the SMS case than the aplanatic one. In other words, the SMS case is better. For example, for a given maximum rms spot size (for instance 25a.u.), the SMS design will have a wider useful field (4.4 degrees versus 3.1 degrees) than the aplanatic case (see Figure 2). Figure 1. An SMS construction. The entire lens (right) is calculated from an initial pre-defined portion of the lens (left). With the SMS method, both surfaces of the lens are calculated simultaneously. P, P’: source points for optical rays. Q, Q’: image points.