10.4 WDM Devices Based on Grating Principles
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Circulator
rules
Fig. 10.21 Simple concept of a demultiplexing function using a fiber grating and an optical
circulator
Fig. 10.22 Multiplexing of four wavelengths using three FBG devices and three circulators
and FBG 4 are constructed to reflect wavelengths λ 2 , λ 3 , and λ 4 , respectively, and to
pass all others.
The following steps show the multiplexer functions:
(a) First consider the combination of circulator C 2 and fiber Bragg filter FBG 2 .
Here filter FBG 2 is designed to reflect wavelength λ 2 and allow wavelength λ 1
to pass through.
(b) After the incoming wavelength λ 1 passes through FBG 2 it enters port 2 of
circulator C 2 and exits from port 3. The incoming wavelength λ 2 enters port
1 of circulator C 2 and exits from port 2. After being reflected from FBG 2 it
enters port 2 of circulator C 2 and exits from port 3 together with wavelength λ 1 .
These two wavelengths then continue passing through the next four elements to
emerge from port 2 of circulator C 4 .