Research On The Multiple-Path Interference In Fiber Raman Amplifier

As the demand for higher transmission capacity in dense wavelength division multiplexing (DWDM) systems increases, channel speed, channel number, and spectral efficiency need to be upgraded. As a result, fiber Raman amplifiers (FRA) have become essential in overcoming the limitation of bandwidth and noise figure. FRA can work on the whole wave band from1270nm to1670nm.It is increasingly becoming the research hotspot of optical fiber communications systems. It is essential to improve the efficiency and quality of signal amplification by studying their performance. The followings are the main aspects of this thesis:First of all, based on the simplified SRS power transfer equation, an average power method is used to solve the FRA power coupled equations, thus the output power of FRA is gotten. The results of signal power and pump power along SMF and NZDSF FRA when using co-pumped, counter-pumped, co and counter-pumped FRA are reached, and Raman gain spectra on various signal wavelengths as well.Secondly, the ASE and DRB noise properties of SMF and NZDSF FRA have been studied on. Using the result of the stimulation, we can get the NF with DRB included and not included, as well as the OSNR of DRB noise. The research results show that when using the same pump method, with the increase of Raman gain, the function that fiber Raman amplifiers have on improving the OSNR property of FRA system has been seriously restricted.Last but not least, by putting an isolator in FRA system is a very effective way to reduce DRB power and noise figured. Using the same average power and fiber division method, we have analysis the relationships between the NF and OSNR at receiver of100km SMF FRA and the position where the isolator is placed. It is shown that the best position is15km from input. What’s more, we have compared the result of NF and OSNR at various signal wavelengths when isolators aren’t used or are placed in the best position. The validity that the isolator can reduce the NF by2dB and increase the OSNR by4dB is strongly proved.