*2.3.6 Spectral filter-based devices*

A spectral filter inserted in the optical path can be used to sort out wavelengths and hence can be used as DeMux. These devices can be implemented in different configurations, a couple of which are shown in **Figure 8**.

The first one is a fiber sandwiched at the cleaved surface of a fiber. The incident ray with two wavelengths is incident on the filter, which passes one and reflects the other. The reflected one is collected through another fiber achieving DeMux operation. Another form of filter can be implemented in a graded-index (GRIN) rod.
