A tunable microwave photonic filter based on hole-assisted graded-index few mode fiber with uniform differential modal group delay

Abstract

A tunable delay-line microwave photonic filter (MPF) based on hole-assisted graded index few mode fiber (HGI-FMF) is proposed. The HGI-FMF is designed with low mode crosstalk, low nonlinear effect and multiple modal groups. In particular, the designed HGI-FMF shows uniform differential modal group delay (MGD) to form finite impulse response (FIR) MPF. The uniform differential MGD is tunable with wavelength, which results in tunable MPF response. The free spectrum range (FSR) of MPF is continuously tunable from 11.73 GHz down to 10.84 GHz with 120 m designed HGI-FMF as the optical source is tuned from 1530 nm up to 1630 nm. The main sidelobe suppression ratio (MSSR) of the 4-taps filter is larger than 9.93 dB, and the 3 dB bandwidth is around 2.62 GHz.