Guided-wave infrared/visible coupler and its incorporation into a miniature beam transmitter

Abstract

A guided-wave coupler based on silica waveguides, which enables an infrared (IR) light beam at λ=905nm to be integrated with a visible beam at λ=650nm, was designed and realized, where both the IR and visible guided modes are simultaneously available from the same port. The coupling length was set to 1240μm, in order to guarantee the nearly complete transfer of the visible beam power to the IR channel, for a channel waveguide in silica, with a core-cladding index contrast of 0.34% and a dimension of 5×5μm2. A miniature light beam transmitter was then built by taking advantage of the IR/visible coupler, which was fiber-pigtailed to the corresponding laser diodes, in conjunction with a collimating lens. The presented transmitter is predicted to potentially feature flexible beam shaping, a compact size, and cost effective fabrication. For the embodied IR/visible transmitter, the collimated IR beam acts as a long-range projectile, while the visible beam is useful for tracking the IR beam. The generated IR beam exhibited Gaussian-like profiles with a divergence angle of 0.2°, and was precisely aligned with the visible monitoring beam with an angular accuracy of 0.0002°. Finally, the effective trajectory was observed by the receiver over a distance of 600m along the propagation direction.