A
ALC Automatic Level Control. It supports the adjustment of optical power aimed to restrain the output power to be inferior on the downstream and keep the optical power to be within a certain working range.
APD Avalanche Photodiode. A semiconductor photodetector with integral detection and amplification stages. Electrons generated at a p/n junction are accelerated in a region where they free an avalanche of other electrons. APDs can detect faint signals but require higher voltages than other semiconductor electronics.

C
CWDM Coarse Wavelength Division Multiplexing. Transmitting signals at multiple wavelengths through the same fiber with wide spacing between optical channels. Typical spacing is several nanometers or more.

D
DWDM Dense Wavelength Division Multiplexing. DWDM technology utilizes the characteristics of broad bandwidth and low attenuation of single mode optical fiber, employs multiple wavelengths with spacing of 100GHz or 50GHz as carriers, and allows multiple channels to transmit simultaneously in the same
fiber.

E
ECC Embedded Control Channel. An ECC provides a logical operations channel between SDH NEs, utilizing a data communications channel (DCC) as its physical layer.
ESC Electric Supervisory Channel. It owns the same function with OSC to realize the communication among all the nodes and transmit the monitoring data in the optical transmission network. The difference is monitoring data of ESC is introduced into DCC service overhead and is transmitted with service signals.
ESD Electrostatic Discharge. The phenomena the energy being produced by electrostatic resource discharge instantly.

N
NE Network Element. A stand-alone physical entity that supports at least network element functions and may also support operations system function or mediation functions. It contains managed objects, a message communication function and a management applications function.
NM Network Management. Any aspect of monitoring or controlling a network, including all administration details.

O
OADM Optical Add/Drop Multiplexer. A device that drops and/or adds one or more optical channels to a signal.
OLA Optical Line Amplifier. A device that amplifies an input optical signal without converting it into electrical form. The best developed are optical fiber doped with the rare-earth element erbium.
OLP Optical Line Protection. With the way to back up the working link, it supports primary optical transmitting link with multiple wavelengths and standby one in order to be against the situation that there is any fault in the primary link.
ONE Optical Network Element. A stand-alone physical entity in a optical transmission network that supports at least network element functions and may also support operations system function or mediation functions.
Optical demultiplexer A device which performs the inverse operation of a wavelength multiplexer, where the input is an optical signal comprising two or more wavelength ranges and the output of each port is a different preselected wavelength range.
Optical multiplexer A branching device with two or more input ports and one output port where the light in each input port is restricted to a preselected wavelength range and the output is the combination of the light from the input ports.
OSC Optical Supervisory Channel. It realizes the communication among the nodes in the optical transmission network and transmits the monitoring data in the certain channel (the wavelength of the working channel for it is 1510nm and that of the corresponding protection one is 1625nm).
OTU Optical Transponder Unit. A device that access service signals compliant with standards at the client side and convert them into standard DWDM wavelength.
OWSP Optical Wavelength Shared Protection. It is just configured in the ring network with distributed service and protects one service channel among all nodes with only two wavelengths.

V
VOA Variable Optical Attenuator. An attenuator in which the attenuation can be varied.

W
WDM Wavelength-Division Multiplexing. WDM technology utilizes the characteristics of broad bandwidth and low attenuation of single mode optical fiber, employs multiple wavelengths as carriers, and allows multiple channels to transmit simultaneously in a single fiber.