Mode-Group Selective Photonic Lantern Based on Indium Fluoride Optical Fibers for Mid-Infrared

This manuscript illustrates the design and characterization of the first fiber-based photonic lantern, tailored for an efficient operation in the Mid-Infrared spectral range. The design and fabrication of the proposed device involve the use of three distinct indium fluoride optical fibers into a surrounding low refractive index glass capillary. An adiabatic transition is achieved through a controlled manufacturing process based on heating and drawing. The modal behavior of the photonic lantern is investigated along the transition via electromagnetic modal analysis, at the wavelength <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\bm{\lambda}} \ = \ \text{3.34}\ {\bm{\mu} \mathbf{m}}$</tex-math></inline-formula>. Mode-group selectivity is obtained through the use of optical fibers with different characteristics. This implies that the light launched into a particular optical fiber evolves into specific mode groups at the photonic lantern multi-mode end. Experimental results demonstrate the possibility to excite the LP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode and two, odd and even, LP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> propagation modes, with losses below 1.3 dB and 1.7 dB, respectively. These results emphasize the feasibility of the proposed photonic lantern based on indium fluoride glass, with potentials for diverse applications, e.g., in communications, astrophotonics, remote sensing and spectroscopy.