Optical Equalizer basics
As we know equalizer is the name referred to the device which equalizes the input signal over the range. In the optical domain, equalizer refers to the device which equalizes the gain response over the wavelength range. The main reason for this equalization is to make cascading of amplifiers possible so that signal can be transmitted over long distances without distorting the envelope. Optical amplifier gain varies at different wavelengths and hence small variable between two wavelength channels result into large variation after few stages of amplification in the optical chain. In order to avoid this situation equalization is carried out at regular stages. The best way is to equalize after each amplifier device as shown in the figure.
In WDM systems after each EDFA device optical equalizers with multi channel options are incorporated to help cascade the EDFA chain to achieve the goal of optical signal transmission. The WDM channel equalizers in 8 -channel and 16-channel options are available. Filtering is incorporated inside the equalizer to filter out the un-wanted and segregate the wanted wavelengths.
Following is the typical specifications of dynamic gain equalizer used for 10Gbps and 40 Gbps optical networks (in DWDM systems). This makes it possible to cascade about 50 optical amplifiers which helps in extending the range of optical fiber to a distance of about 5000 Km.
Optical Equalizer specifications
• Band of operation: L band, C band or any other band
• Insertion loss: Around 5.5 dB
• Resolution (nm): less than 2.6 nm
• Polarization dependent loss (PDL) in dB: less than 0.3 dB
• Polarization mode dispersion (in ps): less than 0.3 ps
• Dynamic range: 15 dB
• Optical response time: max. 30 ms