Wavelength division multiplexing (WDM) technique, which is employed for transmission of optical signals at different wavelengths can multiply the capacity of optical fiber transmission systems. There are several optical methods in WDM i.e., prism type, diffraction grating type and interference filter type. Interference filter type is the method using dichroic filter and is superior to the other types because of the higher coupling efficiency and convenience.
The purpose of present research is to analyze and design a two channel wavelength division multiplexer using dichroic filter. In the design of the complete system, we have the criterion of 8 dB and 20 dB for the coupling loss and cross talk respectively, and particular efforts are made by designing the dichroic filter.
Extensive computer calculations are carried out in the design of the filter for R=100% (atλ=0.85㎛) and R=0% (atλ=1.3㎛) both for the incident angle of 45℃ The optimum design gives R=99.1% (atλ=0.85㎛) and R=0.83% (atλ=1.3㎛). In the dichroic filter prepared by vacuum deposition technique the reflectances are measured and they are found to be 97% and 10% respectively at the two wavelengths.
The whole WDM system is finally tested and is found that the coupling losses are 8 dB (atλ=0.85㎛) and 12 dB (atλ=1.3㎛) and the cross talk is nearly 10 dB.
