Experimental PDFA and its application on the CATV system

Because many existing fiber optical communication systems operate at 1.3 /spl mu/m, the praseodymium-doped fluoride fiber amplifier (PDFA) is attractive for application on these systems. A 12.8 meters PDFA with doping concentration of 1000 ppm and a Nd:YLF laser operating around 1.047 /spl mu/m are used to experimentally implement the PDFA. In order to have maximum gain, the PDFA is modeled and the optimum pumping power is set accordingly. The PDFA can achieve small signal gain of 15 dB, operating bandwidth of 27 nm, noise figure (NF) less than 7.5 dB, and ASE noise less than -33 dBm. Most CATV systems have the hybrid fiber/coaxial architecture. In order to have large coverage, optical splitters may be used to form a passive optical network for the main distribution paths. A PDFA is an ideal candidate to amplify the signals along the transmission. A laser source at 1300 nm is connected with an external modulator. The output power of the laser source is set to 12 dBm. At the headend the AM-VSB channels are multiplexed and allocated from 55.25 MHz to 83.25 MHz and from 163.25 MHz to 547.25 MHz with 6 MHz channel spacing. Then the signals are fed into the external modulator. The optimum receiving range of optical power of the receiver is from -7 dBm to 0 dBm. The optical signal transmits through 70 km single mode fiber and is fed into the input of the PDFA, where the fiber is 12.8 meters long and the pumping power is 650 mW at 1047 nm. After the filter, an optical receiver is used to convert the optical signals to the electrical signals. The PDFA with small signal gain about 15 dB and low noise characteristics (NF<7.5 dB, ASE<-33 dBm) can successfully amplify the CATV signal to meet the system required levels.