Enabling photonic technologies for seeing-limited telescopes: fabrication of integrated photonic lanterns on a chip

In this paper we present theoretical and laboratory results on integrated directly-written photonic lanterns with varying taper lengths. These lanterns convert seeing-limited light into multiple diffraction limited signals, in other words, a multimode signal into multiple single-mode signals. We investigated 19-channel structures which were written within a 30-mm-long glass block and designed to operate at 1550 nm. A single structure consisted of a multimode waveguide which transitioned into an array of single-mode waveguides and then back to a multimode waveguide utilizing cosine taper transitions. Based on simulations we found that transition lengths of 6 mm were sufficient to obtain throughput at a level of ~95%. Fabricated devices showed losses (coupling and transition losses) at the level of 30% for injection F/# < 5 and taper lengths < 5 mm. We believe that such devices show great promise for future use in astronomy.