Alignment method for optimizing extinction ratios of coated polarizing beam splitters
View Patent ↗An optical element such as a beam splitter for interferometer separates a heterodyne beam from the laser into separate beams having different the frequencies and orthogonal polarizations. Optical fibers can conduct the separate beams to a beam combiner for interferometer optics. The PBS and/or the beam combiner can use a coating to reflect one linear polarization and transmit an orthogonal linear polarization. To improve extinction ratios in the PBS or the beam combiner, a yaw angle for an input beam is non-zero and corresponds to a peak in the extinction ratio of a reflected beam.
1. A method for aligning an optical element containing a polarizing beam splitter coating, comprising:
directing an input beam along a first axis into the optical element;
rotating the optical element to change an angle of incidence of the input beam on the polarizing beam splitter coating;
observing an output beam from the polarizing beam splitter coating; and
mounting the optical element at the angle that the observing indicates provides a best extinction ratio for the output beam.
2. The method of claim 1 , wherein the angle changed by rotating the optical element is a yaw angle of the incidence of the input beam.
3. The method of claim 2 , further comprising rotating the optical element to change a pitch angle of incidence of the input beam and adjust a path of a beam resulting from a portion of the input beam reflected by the polarizing beam splitter coating.
4. The method of claim 2 , wherein the output beam comprises a reflected beam resulting from reflection of a portion of the input beam from the polarizing beam splitter coating.
5. The method of claim 3 , further comprising:
rotating the optical element to change a roll angle of incidence of the input beam;
observing a transmitted beam resulting from a portion of the input beam passing through the polarizing beam splitter coating; and
mounting the optical element at the roll angle that the observing of the transmitted beam indicates minimizes presence of a first frequency in the transmitted beam.
6. The method of claim 1 , wherein the optical element comprises a polarizing beam splitter.
7. The method of claim 1 , wherein the optical element comprises a beam combiner.
8. The method of claim 1 , wherein observing the output beam comprises:
placing in a path of the output beam a polarizer having a polarization axis orthogonal to a desired polarization of the output beam; and
measuring light intensity passing through the polarizer.