Towards efficient mid-infrared integrated photonic-lanterns

We report the fabrication and characterization of a prototype integrated photonic-lantern for operation in the mid-IR (λ = 3.39 μm). The device was fabricated in a commercial gallium lanthanum sulphide chalcogenide glass substrate using ultrafast laser inscription. It was formed by inscribing a two-dimensional array of single-mode waveguides, which were then brought increasingly close together to form a single multimode waveguide. We demonstrate that the lantern successfully transforms particular single-mode states into well-defined coherent multimode states, with a loss comparable to that of a straight single-mode waveguide of the same length as the lantern (∼1.6 dB). We conclude, therefore, that the device should also work equally well in the reverse direction, thus enabling the low-loss conversion of mid-IR multimode states of light into discrete single-modes. This technology may be useful in a variety of emerging areas, including free-space laser communications and mid-infrared heterodyne spectroscopy.