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].