Design and analysis of a strip-coated parallel-slab beamsplitter for the equipartition of infrared input power

Abstract

Several recent applications in ellipsometry, spectropolarim- etry, and multiplexed galvanometric scanners require a single compact beamsplitter capable of splitting an input beam of light into four or more components. Of special interest is the design of a single beam splitter to produce multiple components of equal power for incident unpolarized or circularly polarized light. We present a specific infrared design of a parallel-slab beamsplitter that uses a fused silica, which is strip-coated with a Ge thin film on the front and a uniform Ag coating on the back. Equal powers among the first four components can be achieved when the unpolarized reflectance levels on the first, second, third, and fourth strip are ?20, 68, 54, and 18%, respectively. Specific designs at wavelengths of 1.55, 2.02, and 5.0 ?m are presented. At a wavelength of 5.0 ?m, glass shows some absorption and is replaced by another transparent slab material. The choice of optical materials and thicknesses of the strips provide sufficient flexibility in the design and operation of the beamsplitter.