Non-polarization and non-absorbing beamsplitters for laser communications

We report the most recent advances of optical beamsplitters for laser communications developed at Barr Associates. The challenges for meeting the two key requirements, polarization control and wavefront control, of the lasercom beamsplitters are discussed. It is demonstrated that in order to meet the two key requirements, the repeatability of the refractive indices and the thickness of the coatings need to be controlled within 0.3% and 0.1% respectively from run to run, and the coating stress need to be controlled to less than 25 MPa. The latest result of various lasercom beamsplitters will be presented. For a typical 50% reflection and 50% transmission beamsplitter at 22.5 degree angle of incidence, the s and p polarization split is less than 0.2% from 1540nm to 1575nm and the surface flatness of the beamsplitter after coating is less than 1/40 th waves peak to valley at 632.8nm.