Abstract: A fused-fiber multi-window wavelength filter (MWF) is constructed with an unbalanced Michelson Interferometer, in which input light passing through the fused coupling region is decoupled and travels along two fibers of different optical path lengths. The two light signals travel to the end of the two fibers, where a highly reflective coating reflects the light back toward the coupling region, where the signals are coupled again and then decoupled after exiting the coupling region. By adjusting the optical path length difference, either by changing the length or refractive index, a signal at a desired wavelength can be obtained at the filter output. The MWF can be combined with other MWFs to form more compact sized multi-window wavelength division multiplexers (MWDMs) and dense WDMs. Passive thermal compensation techniques can be applied to one or both of the reflecting fibers to maintain the desired optical path length difference.

Abstract: An optical add/drop filter (OADF) module is provided that is capable of only utilizing one filter to drop and add multiple channels from a multiplexed signal. In one embodiment, a demultiplexer separates the input signal into groups of signals or channels to be dropped. This group of channels is coupled to one input of a 2×2 interleaving OADF, which in one embodiment is an unbalanced Mach-Zehnder Interferometer, while another group of channels to be added back to the multiplexed signal is coupled to the other input. One output of the OADF drops one group of channels, while the other output transmits the added group of channels to an input of a multiplexer, which combines the group of added channels with the other groups of channels from the outputs of the demultiplexer. In another embodiment, a multi-window filter formed from an unbalanced Michelson Interferometer outputs two signals, each having either odd or even wavelength signal components.