Wavelength tuning of multimode interference bandpass filters by mechanical bending: Experiment and theory in comparison

Walbaum T., Fallnich C.

Abstract

We present the tuning of multimode interferencebandpass filters made of standard fibers by mechanicalbending. Our setup allows continuous adjustment of thebending radius from infinity down to about 5 cm. The impactof bending on the transmission spectrum and on polarizationis investigated experimentally, and a filter with a continuoustuning range of 13.6 nm and 86 % peak transmission was realized.By use of numerical simulations employing a semianalyticalmode expansion approach, we obtain quantitativeunderstanding of the underlying physics. Further breakdownof the governing equations enables us to identify the fiberparameters that are relevant for the design of customized filters.