Passive wavelength division multiplexing technology for 5G fronthaul

Nowadays, the optical fiber access technology mainly based on passive optical network technology has been widely used in various forms around the world. In order to meet the development needs of higher speed, more transmission wavelengths, and wider coverage of optical access networks in the future, new FTTx (Fiber To The X: Optical Fiber Access) technologies emerge one after another, and WDM-PON is also one of the key technologies. Next, let's follow ETU-LINK to see the WDM-PON passive wavelength division multiplexing technology.

First, what are PON and WDM technologies? PON (Passive Optical Network) is a passive optical network. Optical distribution network (ODN) connected network composed of devices, etc. At present, the PON technologies used for broadband access mainly include EPON and GPON. WDM (Wavelength Division Multiplexing) is a wavelength division multiplexing technology that uses multiple lasers to transmit multiple lasers of different wavelengths simultaneously on a single fiber. As an important supplement to the 5G fronthaul solution, the basic idea is to save optical fiber, which is the main way to expand optical fiber transmission capacity and increase speed.

WDM-PON is a point-to-point passive optical network that uses wavelength division multiplexing technology, that is, in the same fiber, the number of wavelengths used in both directions is more than 3. Using wavelength division multiplexing technology to achieve uplink access, you can Increase users' access to broadband several times or even dozens of times to meet the ultimate needs of users. A typical WDM PON system consists of three parts: Optical Line Terminal (OLT), Optical Wavelength Distribution Network (OWDN) and Optical Network Unit (ONU). The most direct WDM-PON solution is that there are multiple light sources of different wavelengths in the OLT, each ONU also uses a light source of a specific wavelength, and each point-to-point connection is configured and operated according to the pre-designed wavelength.

The biggest feature of WDM-PON is that ODN (Optical Distribution Network) is composed of passive devices such as optical splitters (Splitter), and does not contain any active electronic devices and electronic power supplies. Why WDM-PON can become a 5G fronthaul solution is related to its technical characteristics, as follows:

1. Long transmission distance: The insertion loss is smaller than that of the optical power splitter in the traditional TDM PON system, and the network coverage is larger.

2. High transmission rate: Each ONU uses an independent and different wavelength channel, no special MAC protocol is required, and the system complexity is reduced.

3. High bandwidth: Each user exclusively enjoys the bandwidth of one wavelength channel, and does not require dynamic bandwidth allocation, meeting the bandwidth requirements of 25G eCPRI fronthaul signals.

4. High security: All ONUs are physically isolated and will not affect each other.

5. Low cost: The optical modules used in the ONU are exactly the same, which solves the problem of device storage, and the single fiber 32-40 wavelengths can be extended to 80 wavelengths, saving the cost of the backbone fiber and OSP.

6. Easy maintenance: due to the application of colorless technology in WDM PON, maintenance is more convenient.