Autostigmatic far field simulator

Abstract

A far-field simulator (FFS) which can be accurately calibrated and verified to sub-wavelength optical precision under any applicable test conditions is described. The FFS can be used over a tremendous range of ambient temperatures, and other conditions without detriment to its inherent accuracy. The accuracy is provided by means of interferometric self-reference capability rather than by complex, delicate, and/or extremely expensive metering structures. As such, the described approach provides a test instrument that is highly insensitive to packing, shipping, and other sources of system misalignment, and yet provides alignment accuracy to the extent practically achievable by comparable systems. These preferred embodiments include an FFS with an autostigmatic cube an objective mirror and interferometer optics for calibrating the FFS with precision. The autostigmatic cube provides an image plane and includes a beam splitter, a pinhole and an optic defining a reference sphere having, by reason of the beam splitter, two optical centers of curvature. A first optical center of curvature is located at, or approximately at the image plane and a second optical center of curvature is located at the pinhole. The objective mirror has (also by reason of the beam splitter) a first focus and a second focus. It is positionable in tilt, tip and piston such that the first focus is located at the first optical center of curvature (i.e., at the image plane) of the autostigmatic cube and the second focus is located at the cube's second center of curvature (i.e., the pinhole). An imaging microscope objective is provided which magnifies the image plane and relays it to a view plane where a CCD is located. The FFS is calibrated by adjusting the objective mirror to null out interference fringes at the image and view planes.