Compact all-fibre wavelength drop and insert filter

A compact all-fibre design, comprising two identical Bragg gratings written on to the arms of a fused fibre Mach-Zehnder interferometer, has been used to produce a low-loss wavelength drop and insert filter for wavelength division multiplexing/demultiplexing applications in optical fibre communication systems. A prototype device has been produced which can multiplex/demultiplex a signal centred on 1558.7 nm with any other wavelength in the 1550 nm transmission window with a maximum insertion loss of 1.0 dB.