Past research on all-dielectric nonpolarizing beam splitters is reviewed. It is shown that, for a 50-nm spectral region, it is possible to design and manufacture a two-material nonpolarizing plate beam splitter for use at an angle of 45° (with a measured rms reflectance of 0.50 ± 0.01 for both s- and p-polarized incident light).

Design and manufacture of all-dielectric nonpolarizing beam splitters

A three-step design procedure is developed for dielectric stacks which are required to be nonpolarizing for a given wavelength λr and angle of incidence θ0,r, at which the reflectance Rr is prescribed. The method leads to solutions in which only three layer materials occur and can be applied for a wide range of values of θ0,r and Rr. The media can be chosen from the available coating materials. Furthermore, the procedure offers the possibility of optimizing with respect to the behavior of the reflectance in the neighborhood of λr and θ0,r. An example is elaborated, and its results are compared with an actually produced coating.

Nonpolarizing beam splitter design

Truly polarization-independent beam splitters for 0.6328- and 10.6-microm (He-Ne and CO(2)) laser radiation are designed using single-layer-coated (Cleartran) ZnS and Ge prisms. These devices are found to be reasonably achromatic, their reflectance (beam-splitting ratio) can be varied over a wide range with little accompanying polarization error, and they are tolerent to small film-thickness and film refractive-index errors.

Variable-reflectance thin-film polarization-independent beam splitters for 0.6328- and 10.6-microm laser light.

Some properties of the reflectivity and transmissivity of multilayer dielectric optical coatings are derived from energy conservation applied to a beam splitter acting as a beam combiner. It is shown that dispersion in the phase shifts of the beam splitter coatings influences which quadrature amplitude is measured in a homodyne detector, and, in a Michelson interferometer, how the white-light fringe pattern is disposed about the zero-path-difference condition. The functions of reflectivity and transmissivity that determine these properties are shown to be not completely constrained by considerations of energy conservation and time reversibility, in contrast to commonly employed models for beam splitter reflectivity and transmissivity. Some representative beam splitter coating designs are used to illustrate this point.

Phase shifts in multilayer dielectric beam splitters

The design and construction of a hexagonal interferometer beam splitting prism is described in which the light falls onto the all-dielectric partially reflecting coating at an angle of 30° with respect to the normal. For a beam that undergoes one transmission and one reflection by the device, the average effective transmittance ½(T‖R‖ +T⊥R⊥) in the 0.55–0.75-μm spectral region is ∼0.23. This quantity is not strongly dependent on the plane of polarization of the incident light, nor on small changes of the angle of incidence from the design angle of 30°. Ways to improve further the performance of the beam splitter are indicated. Coating designs for other angles of incidence are also given.

M. Vampouille

Papers

Non-polarizing Beam Splitters