Proceedings Article | 29 April 2009
Proc. SPIE. 7339, Enabling Photonics Technologies for Defense, Security, and Aerospace Applications V
KEYWORDS: Multimode fibers, Optical filters, Refractive index, Tunable lasers, Single mode fibers, Wavelength tuning, Brain-machine interfaces, Tunable filters, Multimode interference devices, Liquids
We report on the optofluidic tuning of MMI-based bandpass filters. It is well known that MMI devices exhibit their
highest sensitivity when their diameter (D) is modified, since they have a D2 wavelength dependence. In order to
increase the MMF diameter we use a special fiber, called No-Core fiber, which is basically a MMF with a diameter of
125 μm with air as the cover. Therefore, when this No-Core fiber is immersed in liquids with different refractive indexes,
as a result of the Goes-Hänchen shift the effective width (fundamental mode width) of the No-Core fiber is increased,
and thus the peak wavelength is tuned. A tunability of almost 40 nm in going from air (n=1.333) to ethylene glycol
(n=1.434) was easily obtained, with a minimum change in peak transmission, contrast, and bandwidth. Moreover, since
replacing the entire liquid can be difficult, the device was placed vertically and the liquid was covering the No-Core fiber
in small steps. This provided similar amount of tuning as before, but a more controllable tuning mechanism.
