The TFT filter device is a dielectric component that consists of multiple cavities, each of which is bounded by alternating thin film layers of high and low index refractive materials. The filter with a certain angle of incident light can be designed to pass a specific band of wavelengths while the remaining input wavelengths are reflected. The fiber coupled three-port TFF device consists of an input port, a transmitted port, and a reflected port. The use of dual and single-fiber collimators allows the light to be coupled from the fiber to the free space and vice versa. The insertion loss of this device is a function of the alignment of the micro-optic component, whereas the spectral properties, such as bandwidth and isolation, are determined by the construction of the filter element.

TFF Mux/DeMux modules are typically assembled using multiple three-port devices concatenated in a certain sequence.  

The multi channel Mux/DeMux can be implemented by concatenating multiple three-port devices with different passbands. The first device removes the first channel in transmission and reflects all other channels. The reflected port from this device is spliced to the input port of the second device that transmits only the second channel. This DeMux chain continues until all channels are separated.  Low loss and even channel insertion loss can be achieved by arranging the filters in the Mux in an order that offsets the channel-to-channel insertion loss variation introduced by the DeMux. This can be done by concatenating the TFF devices arranging channel 1 to channel N in the Mux module while DeMux is arranged the insertion loss increases from channel N to channel 1 in reverse order.