Optical Combining in Medium Infrared Wavelength Range and Its Applications

A review on the optical combining in medium infrared wavelength range is illustrated. Moreover, details on the design, fabrication and characterization of novel combiners based on multimode step-index fluoroindate optical fibers (InF3) are given. The electromagnetic design of the combiner is carried out through modal investigation and the beam propagation method is exploited to evaluate the transmission efficiency. In the fabrication process, including the normalization procedure, the low melting temperature and the mechanical properties of fluoroindate glasses are taken into account. The repeatability and absence of crystallization are verified. The experimental results agree with the simulation and pave the way for a number of applications in the mid-infrared spectral range.

1. INTRODUCTION

The mid-infrared (Mid-IR) wavelength range exploitation is promising intriguing applications in several scientific fields including light sources, environmental sensing, medical surgery and comb generation [1] - [5]. Mid-IR is also attracting the research interest in spectroscopy, since the absorption bands of numerous biological substances lies within the wavelengths range λ = 2 – 20 μm. The demand for Mid-IR optical sources and systems is increasing the need of optical fiber devices, feasible also thank to the development of novel materials [6], [7]. Commercial optical fiber components are typically made of silica glass and their use is limited up to the wavelength λ = 2 μm. As an alternative to silica glasses, chalcogenide and fluoride ones, including heavy metal fluoride and halide polycrystals, show a wider transmission window, resulting excellent candidates for Mid-IR applications [8] - [10].