EDFA & 1550 nm Transmitter

1550 nm transport is how a CATV signal or a long-haul data link shares the same fibre plant as a PON. The 1550 nm window has lower fibre loss than 1310 nm and supports erbium-doped fibre amplification, so one transmitter can feed a passive split and an EDFA chain without regenerating the RF signal. On a hotel or campus, the CATV headend sits beside the OLT; a WDM coupler combines 1550 nm CATV with 1490/1310 nm PON, and an ONU with a CATV port separates it at the room.

The transmitter choice is direct-modulated or externally modulated. A direct-modulated 10 dBm unit is the economical choice for a small headend and a short span; an externally modulated 7/9 dBm unit avoids the chirp and SBS limits of direct modulation and is preferred when the signal must travel farther or pass a high-power EDFA. The EDFA family covers 4, 8, 16 and 32 output ports at 19 or 22 dBm, so the split can be sized to the number of buildings or floors.

At the subscriber end, a CATV optical receiver takes +2 to −18 dBm at 1550 nm and delivers 47–1000 MHz at 75 Ω with AGC, maintaining ≥81 ± 2 dBµV in the AGC window. Plan the RF level and the optical input together: too high an optical input saturates the receiver, too low degrades MER. The link budget, not the amplifier’s headline power, decides how many splits are possible.