Thin-film PBS has large spectral and angular ranges

Polarizing beamsplitters (PBSs) are widely used in optical systems for data storage, scientific measurement, lasers, and other applications. Conventional PBSs based on enhancement of Brewster-angle effects work well only over narrow spectral or angular ranges; although achromaticity can be gained by the use of birefringent devices such as Wollaston prisms, the property comes at the cost of a further narrowing of angular range. Researchers at the National Research Council of Canada (Ottawa, Ontario, Canada) have designed and built a PBS that operates using frustrated total internal reflection, in which internal thin films placed at greater than the critical angle transmit light as a result of evanescent coupling. Because the design is relatively insensitive to thin-film thickness variations, the PBS is easy to fabricate.

The device is hexagonal in shape to allow high internal-incidence angles. A simple prototype containing 27 thin-film layers was built to test the concept. Transmittance of s-polarization was close to 100% across much of the visible spectrum, while p-polarization transmittance reached to between 10-2 and 10-4 for an angular range of a few degrees. Calculations show that such PBSs built with additional thin-film layers can attain either angular fields as high as ±15.8° in the visible and ±60° in the infrared, or a wavelength range of 0.33-2.0 µm. Contact Li Li at [email protected].