The Basic Principle and Main Characteristics of WDM PON

WDM PON is a point to pint passive optical networking WDM technology. That is, in the same optical fiber, the number of bidirectional wavelengths is more than three, we use WDM technology to achieve the uplink access can provide large working bandwidth at a lower cost, which is an important development direction of optical fiber access in the future. Typical WDM PON system 

consists of three parts: OLT ( Optical Line Terminal), OWDN ( Optical Wavelength Distribution Network) And ONU( Optical  Network Unit). OLT is the local device, including optical wavelength division multiplexer/demultiplexer ( OM/OD). Generally with control, exchange, management and other functions. The OM/OD of the site can be physically 

separated from the OLT device. OWDM refers to an optical network between OLT and ONU that implements wavelength-based distribution from OLT to ONU or from ONU to OLT. A physical link consists of feeder optical and 

Passive Remote Node ( PRN). PRN mainly includes thermal insensitive Array Wave-guide Grating(AAWG). AAWG is a wavelength sensitive passive optical device, which completes wavelength multiplexing and demultiplexing functions. The ONU is an optical terminal device on the user side.

Downlink direction,multiple different wavelengths LD1... The LDN is transmitted to the OWDN after the OM/OD wave combination at the office and is allocated to each ONU based on different wavelengths. In the uplink direction, different user ONU emits different light wavelength LU1......, Luns are added to the OWDN, combined at the PRN of the OWDN, and then sent to the OLT. Complete the uplink and downlink transmission of optical signals. The downlink wavelength LDN and uplink wavelength LUN can work in the same band or in different bands. 

The main characteristics of PON Technology using WDM are as follows:

Longer transmission distance. Because the insertion loss of AAWG in WDM PON is smaller than that of optical power splitters in traditional TDM PON system, WDM PON can transmit longer distance and cover larger network when the output power of OLT or ONU optical is equal. 

Higher transmission efficiency. For Uplink transmission in WDM PON, each ONU uses independent and different wavelength channels without special MA protocol, so the complexity of the system is greatly reduced and the transmission efficiency is greatly improved.

Higher bandwidth. WDM PON is a typical point to point network architecture. Each user has a unique wavelength channel bandwidth and does not need dynamic bandwidth allocation. It can provide higher bandwidth for each user at a relatively lo rate.

More Security. Each ONU has its own wavelength channel bandwidth. All ONUs are physically isolated and do not affect each other, so they are more secure.

Be completely transparent about business and rate. Because the electrical signal does not do any processing in the physical layer optical path, no encapsulation protocol is required.

Lower costs. Due to the application of colorless light source technology in WDM PON, the optical modules of ONU are exactly the same, which solves the storage problem of devices and reduces OPEX and CAPEX. And the single fiber 32-40 wave, can be extended to 80 wave, save the backbone fiber and OSP costs.

measurement limitation such as optical fiber lines due to high insertion losses. In addition, the application of color less light source technology makes maintenance more convenient.