Central office has a lot of equipment installed. Most significant part of PON is the OLT (Optical Line Termination) – service provider endpoint. OLT is using 1490 nm and 1550 nm laser transmitters for digital data and voice, and analog video data transmission, respectively. 1310 nm laser detector is performing  digital data and voice reception.

 

In the GEPON OLT 1490 nm transmitting laser is the distributed feedback (DFB) laser. If the video signal should be amplified – it is done with an erbium-doped fiber amplifier (EDFA). Figure 1 shows commercial example of OLT and GEPON ONU manufactured by AD-net Technology.

 

 

 

Figure 1. AN-2000 OLT and AN-E-ONU-FTTH03 by AD-net

 

Another endpoint in PON is the ONU/ONT shown in Figure 2. This users endpoint is located in subscriber premises or around them. ONT is a simple termination point, while ONU is a field unit that might be a termination point for multiple networks. ONU/ONT receives digital data and voice, and analog video through the 1490 nm detector receiver and 1550 nm detector, respectively. At the same time ONT/ONU transmits data and voice from 1310 nm laser transmitter. It is using directly modulated uncoded Fabry-Perot laser.

 

PON standards specify many characteristics for GEPON OLT and ONT/ONU. Table 1 shows main characteristics for active equipment in PON.

 

Table 1. Active Equipment Characteristics

 

Equipment	Service	Laser	Wavelength (nm)
OLT	Data and voice (downstream)Analog video (downstream)	DFBDFB	1480-1500 (typical: 1490)1550-1560 (typical: 1550)
ONU/ONT	Data and voice (upstream)	Fabry-Perot	1260-1360 (typical: 1310