Figure 2: Using MMI in a tapered fibre for optical spectroscopy.
From: High-resolution optical spectroscopy using multimode interference in a compact tapered fibre
(a) Imaging set-up used in the experiment. The device is mounted securely in an acrylic holder using optical adhesives and is imaged through a cover glass. MMF, multimode fibre; PMF, polarization-maintaining fibre; SMF, single-mode fibre. (b) Isoplanes of propagation constants at four frequencies corresponding to λ=450, 532, 595 and 638nm for a silica fiber of core radius 30μm. Inset: propagation constant as a function of mode order. (c) Schematic of the TFMMI spectrometer, consisting of a tapered fibre imaged on a commercial camera. The optical image shows the device when a 638-nm laser was directed through the tapered fibre. The intensity distribution is extracted from one MMI section for the purpose of illustration, showing qualitative agreement between experiment and model. (d) Monochrome and optical images show the spatial intensity distribution for wavelengths of 1,550, 1,530, 638, 595, 532 and 450 nm monochromatic fields through the tapered fibre. Scale bar, 50 μm. (e) Imaging the fibre using a smartphone camera shows a potential for portable and field applications.
