587Km pure digital TV 1550nm overlength optical trunk application Cases
1. Demand of the solution design
The farthest distance of the main line is 587Km, transmit 80QAM
587Km sub-head-end: MER≥33dB; 587Km sub-head-end user: MER≥27dB
2. This solution adopts 1550nm full optical relay, mainly adopt EM-TX, EDFA, RFA and DCM. Comparing with SDH, it needs an absolutely low cost including operation cost. It is convenient to add network management function and update.
3. 1550nm over-length trunk, the SBS set of EM-TX is a sticking point. SBS too high will affect the transmit distance, if too low it will affect the optical power into the fiber. This solution is adopting SBS 15.5dBm.
4. All-optical relay dispersion is accumulated. G.652standard single mode dispersion accumulated value of over 100Km (1700ps/nm), will lead to bit error rate surge, so it must use dispersion compensation. In this solution the longest sub head end to the head end is 587km, and the total dispersion compensation here is 490km, adopt Huatai HDCM-F.
5. There are many ways to realize dispersion compensation, practice proves that it is the most easy, economical and effective method to adopt dispersion compensation optical module (DCF and DCM). In practice, it is necessary to optimize the dispersion value of the system needed to compensate and the location of the dispersion compensation in the system install.
6. DCF exist a larger loss, adopt Mid-Stage Access（MSA）EDFA is an easy and convenient way. In this case, we adopt Huatai HA5700 series MSA EDFA. HA5212+HA5100 (or HA5212+HA5400) can be instead of using HA5700.
7. DCM has short MFD (mode field diameter); too high input power will lead to serious distortion of the system. Input power should be 2~3dB less than the system SBS threshold value. For this application, it should be ≤12dBm. Optical input power to the DCM should be optimized during system adjustment.
8. The effect of dispersion in 1550nm over-length truck will be eliminated after adopting DCM, the main problem concerned is CNR (MER) deterioration. MER deterioration is related to optical input power to EDFA and cascade connection, relay of DTV is 100km, of AM TV is 70km, RFA (Fiber Raman Amplifier) should be applied to increase the optical input power of EDFA.
9. Optical input power to the HA5100, HA5700 should be determined by the service radius of the head-end and numbers of subscribers.