We used ultrafast laser inscription to fabricate three-dimensional integrated optical transitions that efficiently couple light from a multimode waveguide to a two-dimensional array of single mode waveguides and back. Although the entire device has an average insertion loss of 5.7 dB at 1539 nm, only 0.7 dB is due to mode coupling losses. Based on an analysis which is presented in the paper, we expect that our device should convert a multimode input into an array of single modes with a loss of 2.0 dB, assuming the input coupling losses are zero. Such devices have applications in astrophotonics and remote sensing.
Thomson, R. R., Birks, T. A., Leon-Saval, S. G., Kar, A. K., & Bland-Hawthorn, J. (2011). Ultrafast laser inscription of an integrated photonic lantern. Optics Express, 19(6), 5698-5705. https://doi.org/10.1364/OE.19.005698