Narrow-band an Low Sidelobes Spectral Filter with Weighted Coupling

Abstract

The paper discusses the narrow-band and low sidelobes spectral filter achievable with directional coupler constructed with a W-index and a step-index fibers. By properly weighting the coupling strength along the device, the sidelobe levels can be reduced significantly. With a Gaussian function weighting, -39.6 dB transfer response sidelobes have been obtained, more than 30 dB reduction over the uniform coupling case. Besides, the implict relations between the coupling length and the required bending radius can be found.