Room-temperature operation of widely tunable loss filter

A widely tunable and room-temperature operationable loss filter based on a long-period fibre grating (LPFG) fabricated in a B/Ge codoped fibre is repo rted. The filter exhibits extremely high temperature sensitivity. A maximum spectral shift of -48.1 nm from 10 to 40 degreesC is achieved, correspondi ng to a thermal tuning efficiency of 1.6nm/degreesC. This value is increase d by more than one order of magnitude compared with the LPFGs fabricated in standard telecom fibre, and even twice that of a LPFG with sensitivity enh anced by a special polymer.