A tolerance analysis of an illumination system is an iterative process used to determine the bounds on the tolerances which result in an acceptable range of performance measures. Tolerances are parameters in an optical system that could deviate from their nominal value during manufacturing and assembly of optical systems (eg. curvature, conic constant, aspheric coefficients, the position or alignment of an optical element, surface roughness etc). Performance measures are properties of an optical system that encapsulate requirements like total power, or uniformity of illuminance, manufacturing cost etc.
Modern optical systems for illumination use Monte-Carlo simulations for design and analysis . Often, these optical Monte-Carlo simulations for illumination systems are computationally expensive and could take multiple hours to complete. A tolerance analysis can require multiple optical Monte-Carlo simulations, which can then take days to complete.
To reduce the time to perform a tolerancing analysis, we used a multidimensional fit. This fit allows us to modify the tolerance distributions and estimate the resulting performance measures without having to rerun lengthy ray trace simulations. Two illumination examples, one with color analysis and the other with a TIR lens are used to illustrate the advantages and limitations of this approach.
 Koshel, R.J., ed. [Illumination Engineering: Design with Nonimaging optics], Wiley-IEEE Press, New York (2013).
We are developing a stable and precise spectrograph for the Large Binocular Telescope (LBT) named “iLocater.” The instrument comprises three principal components: a cross-dispersed echelle spectrograph that operates in the YJ-bands (0.97-1.30 μm), a fiber-injection acquisition camera system, and a wavelength calibration unit. iLocater will deliver high spectral resolution (R~150,000-240,000) measurements that permit novel studies of stellar and substellar objects in the solar neighborhood including extrasolar planets. Unlike previous planet-finding instruments, which are seeing-limited, iLocater operates at the diffraction limit and uses single mode fibers to eliminate the effects of modal noise entirely. By receiving starlight from two 8.4m diameter telescopes that each use “extreme” adaptive optics (AO), iLocater shows promise to overcome the limitations that prevent existing instruments from generating sub-meter-per-second radial velocity (RV) precision. Although optimized for the characterization of low-mass planets using the Doppler technique, iLocater will also advance areas of research that involve crowded fields, line-blanketing, and weak absorption lines.