Optical transmission system including optical repeaters with selectively enabled gain equalizers contained therein and including an add/drop apparatus with a plurality of individually selectable filters

An optical transmission system including a plurality of optical repeaters arranged along a transmission line. A respective gain equalizer is arranged along the transmission line after an integer number of optical repeaters. Further, each optical repeater can include an optical amplifier, a gain equalizer and a connection mechanism. The connection mechanism has a first state and a second state so that (a) when the connection mechanism is in the first state, the gain equalizer of the optical repeater performs an equalization process on the light signal, and (b) when the connection mechanism is in the second state, the gain equalizer of the optical repeater does not perform an equalization process on the light signal. An add/drop apparatus is also provided for adding/dropping an individual wavelength signal from a wavelength division multiplexed (WDM) signal travelling through the optical communication system. The add/drop apparatus includes a plurality of filters, and a selection mechanism. Each filter affects a different wavelength. The plurality of filters includes at least one filter affecting a wavelength corresponding to a wavelength signal in the WDM signal. The selection mechanism selects a respective filter of the at least one filter to allow the apparatus to add/drop the wavelength signal in the WDM signal corresponding to the wavelength of the selected filter.