New Thin Film Polarizing Beamsplitter
In the paper*,
given at the Optical Interference Coatings conference in June 1998, the authors discuss a new design for a high-performance polarizing beamsplitter based on frustrated total internal reflection. This polarizer has the following advantages: non-absorbing, broad band, wide-angle, and high extinction ratios (Ts/Tp and Rp/Rs). The diagram below illustrates the operation of this polarizer.
The coating is sandwiched between two prisms. Note that S polarized light is transmitted, which is the opposite of other designs. Also, note that light strikes the coating at a very high angle.
Although the authors do not give the exact details of the coating design, it is possible to use TFCalc to create such a polarizer. Here we design a polarizer for 400-700 nm to operate for the angles 65-75 degrees in the prism. This design requires a high-index glass prism. An index of 1.85 is used in this design. This means that the range of angles in air is ±9.28, which is considered wide-angle. We use the following 22 continuous optimization targets:
Here is the design, with the first layer closest to the substrate and
thickness given in nm:
H 11.16 L 48.87 H 35.94 L 68.58 H 39.50 L 79.77 H 46.20 L 96.61 H 49.71 L 102.74 H 50.49 L 102.74 H 49.71 L 96.61 H 46.20 L 79.77 H 39.50 L 68.58 H 35.94 L 48.87 H 11.16
Note, curiously, that optimization preserved the symmetry of the original design (i.e., layers 1 and 21, 2 and 20, 3 and 19, etc., have the same thickness).
The authors are commended for this ingenious polarizer, which is the subject of a patent application. However, it seems that this polarizer has two drawbacks: (1) the dimensions of the prisms may prevent its use in some applications and (2) the prisms seem to require a high-index glass, which presents other problems.
*Recently, a paper was published that gives much more detail about this polarizer. See
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