Fiber-connectorized ultrafast-laser-inscribed K-band integrated optics beam combiner for the CHARA telescope array

A fiber-connectorized K -band integrated -optics two -telescope beam combiner was developed for long -baseline interferometry at the CHARA telescope array utilizing the ultrafast laser inscription (ULI) technique. Singlemode waveguide insertion losses were measured to be similar to 1.1 dB over the 2-2.3 mu m window. The development of asymmetric directional couplers enabled the construction of a beam combiner that includes a 50:50 coupler for interferometric combination and two similar to 75 : 25 couplers for photometric calibration. The visibility of the bare beam combiner was measured at 87% and then at 82% after fiber-connectorization by optimizing the input polarization. These results indicate that ULI technique can fabricate efficient fiber-connectorized K -band beam combiners for astronomical purposes.