Hello everyone!
Now, I share an article about colored light and grey Light, I hope you like it.
About Light
The light in WDM systems is in the near-infrared region and is invisible. The wavelengths range from 1260 nm to 1611 nm.
Avoid direct eye exposure to the optical ports, preventing the laser from hurting your eyes. 
Colored Light & Grey Light
The light in WDM systems is carried over different wavelengths compliant with specific standards.
To distinguish wavelengths in different systems, the wavelengths in WDM systems are called colored light whereas the wavelengths in common optical systems are called grey light.
Wavelength Difference
1. Grey light is within a certain wavelength range and does not have a standard wavelength, for example, the light at client-side optical ports of WDM devices.
2. Colored light is WDM-side optical signals of the OTN or line boards in a WDM system. The signals can be directly transmitted to multiplexer devices and have standard wavelengths. Colored light is divided into CWDM and DWDM light, depending on wavelength division standards.
Standards compliance
Colored light: ITU-T G.694.1 (DWDM) and ITU-T G.694.2 (CWDM).
Grey light: ITU-T G.957, ITU-T G.959.1, and IEEE 802.3
Application Scenario
Typical scenario
Client-side optical modules provide grey optical ports while WDM-side optical modules provide colored optical ports.
Client-side colored light
The client-side optical module of the tributary board provides colored optical ports, which can be used to connect to a multiplexer board. The major application scenarios are as follows:
1. The client-side device interconnected with the WDM device has colored optical ports.
2. The 10GE ports of the packet board are colored optical ports, which can be directly connected to the multiplexer board. In this situation, services do not need to be processed on the universal line board. See the figure on the right.
WDM-side grey light
A Huawei WDM device is interconnected with a third-party WDM device. The third-party WDM device, however, does not support the tributary/line separation mode. If service grooming is required, the line boards (grey light on the WDM side) of Huawei WDM device can be used to receive services, implementing service adding/dropping or grooming on Huawei WDM device.
How to Distinguish Colored and Grey Optical Modules?
They can be distinguished by whether their specifications contain center wavelengths.
1. The transmit and receive wavelengths of colored optical modules have a nominal center frequency and center wavelength.
2. The transmit and receive wavelengths of grey optical modules have a wide range and do not have a center wavelength.
Thank you!
