Components of a WDM system that multiplexes N wavelengths:
pOptical Transponder Unit (OTU)
pOptical Multiplexer Unit/Optical Demultiplexer Unit (OMU/ODU)
pOptical Amplifier (OA. BA is short for booster amplifier, LA for line amplifier, and PA for pre-amplifier.)
p Optical Supervisory Channel/Electrical Supervisory Channel (OSC/ESC
lAn OTU converts diverse wavelengths to standard wavelengths specified by ITU-T using the optical to electrical to optical (O/E/O) scheme. That is, a positive-intrinsic-negative (PIN) photodiode or an avalanche photodiode (APD) converts the received optical signals to electrical signals, and the electrical signals modulate the standard-wavelength laser to obtain new optical signals over ITU-T-compliant WDM wavelengths.
lAn OMU, located at the transmit end, is a component that has several input ports and one output ports. Each input port receives one optical signal. These signals are transmitted together through one output port. An ODU, located at the receive end, has one input port and several output ports and separates signals at multiple wavelengths.
lAn OA (such as BA/LA/PA) amplifies optical signals. An all-optical amplifier features real-time, high gain, broad width, on-line, low noise, and low attenuation. It is an essential component in a new-generation optical fiber communication system. Erbium-doped fiber amplifiers (EDFAs) and fiber Raman amplifiers (FRAs) are commonly used in practice. Particularly, EDFAs have outstanding performance and are extensively used as BAs, LAs, or PAs in optical fiber communication systems that support long-haul, large-capacity, and high-speed transmission.
lAn OSC is set up to monitor WDM optical transmission systems. ITU-T recommends the preferential use of 1510 nm wavelength at 2 Mbit/s. The OSC can work properly at low rates based on high receiver sensibility (greater than –48 dBm). However, it must be dropped before reaching an EDFA and be added after reaching the EDFA.
