A thin-film filter-based 1×2 reconfigurable fiber-optic add-drop module with a quadruple fiber-optic collimator

Due to a limited optical crosstalk in most thin-film filter (TF)-based fiber-optic modules, we propose and experimentally verify a low optical crosstalk TF-based 1×2 reconfigurable fiber-optic add-drop structure. Our key idea is to employ a passive noise rejection scheme by introducing a double reflection on the TF as well as a spatial separation through a combination of a quadruple and a single fiber-optic collimators. Our experimental results show a much improved <-39.1-dB optical crosstalk at the Thru port. In addition, the measured average optical losses at the Drop and the Thru ports are 1.40 and 1.23 dB, respectively, when the TF is in the optical path. When the mirror is in the optical path, all wavelength optical beams are directed to the Thru port with a measured average 2.50-dB optical loss. A low polarization-dependent loss of <0.17 dB is also determined. Furthermore, our design concept can be used to form a low optical crosstalk fixed three-port add-drop filter and a high dynamic-range wavelength-sensitive variable fiber-optic attenuator.