Dawei Fang

Forward cascaded stimulated Brillouin scattering (SBS) in an S-band distributed G652 fiber Raman amplifier

The cascaded forward stimulated Brillouin scattering (SBS) in the S band distributed G652 fiber Raman amplifier forward pumped and backward pumped by the tunable power fiber laser and signal source is a tunable narrow spectral bandwidth(<100MHz)ECL have been studied. Forward SBS does not obey the common theory, that only weaken backward-SBS lines existed, according to conservation of energy and momentum and wave vector selected rule. Because the wave-guide character weaken the wave vector rule. The forward transmit sound wave-guide Brillouin scattering lines are generated and amplified in FRA. Forward SBS that is amplified phenomena of transmit sound wave Brillouin scattering in the FRA, during pump power is larger than the threshold value of SBS in a S band G652 FRA. The 2 orders Stokes forward Brillouin lines are present during forward pump power of FRA is 920mW, the pump power of BP line is 7.7dBm and the FRA gain is 15.05dB, the power of first order Brillouin lines is smaller than the second Brillouin scattering line. When pump power is further increased, cascaded SBS lines and comb profile are observed. The even order SBS lines is stronger than odd order SBS lines, The odd order SBS lines are named Brillouin- Rayleigh scattering lines.

Forward and backward cascaded stimulated Brillouin scattering in a S band distributed G652 fiber Raman amplifier

The forward and backward cascaded stimulated Brillouin scattering (SBS) in the backward pumped S band distributed G652 fiber Raman amplifier have been researched, pumped by the tunable power 1428nm fiber Raman laser and signal source is a tunable narrow spectral bandwidth (<100MHz)ECL. The forward SBS does not obey the common theory, that only weaken backward-SBS lines existed, according to conservation of energy and momentum and wave vector selected rule. Because the wave-guide character weaken the wave vector rule, the forward transmit sound wave-guide forward Brillouin scattering lines are generated and amplified in S band G652 FRA. Forward SBS that is amplified phenomena of transmit sound wave Brillouin scattering in the G652 FRA, during pump power is larger than the threshold value of SBS in a S band G652 FRA. Two-order SBS in the Stokes region is observed during the pump power is increased. When the FRA pump power is further increased, Cascaded SBS lines and comb profile are observed.

Dependence of Raman gain and Raman gain coefficients on GeO2 concentration for different silica fibers

A method to predict the Raman gain and Raman gain coefficient of some fibre types is developed by analyzing the relationship between stimulated Raman scattering and the doping constituents. The calculated results were compared with measurement results on dispersion-shift fibre(DSF)and dispersion compensating fibre(DCF). Agreement between the calculated and measured data on DCF is quiet well.

Phonon modes structure spectrum research in DCF optical fiber Stokes Raman scattering gain spectrum

DCF optical fiber Stokes Raman forwrad scattering and backward scattering gain spectrum have been measured by Raman laser as a pump source and high spectral resolution four grating spectrometer. There are 15 phonon modes in the Stokes forward scattering region and 18 phonon modes in the Stokes backward scattering region. In the low frequency region, there are 3 characteristic phonon modes they are 41.4 cm-1, 68.0 cm-1 and 96.7 cm-1. The characteristic Raman peaks of DCF fiber is 434.7 cm-1 and 455.4 cm-1 that are correspond to 440 cm-1 and 490 cm of normal single mode fiber as a function of pump power has been measured. Measured DCF Raman gain spectrum is different from that in common reference and books. The reasons are the high Ge02 concentration in DCF fiber and the developing of measuring technology.

Optimal design scheme for multiwavelength backward-pumped Raman amplifiers

A new and practically applicable scheme of optimally configuring backward multiple pumps in optical fiber Raman amplifiers is presented based on the characteristics of Raman gain spectra and the fact that different pump powers and wavelengths have different impact on the gain slope by using Optiamplifier 4.0 simulating software, which is made in Optiwave Corporation, Canada. We use the idea to optimize a distributed Raman amplifier pumped by 2-walvelength sources. The optimized design contained signal channels between 1490 and 1530 nm with 4-nm separations. The fiber used as the gain medium was a 50-km single-mode fiber (SMF) with 9.9e-14m/W peak Raman-gain coefficient. After calculating 11 times optimum pump wavelengths 1390nm, 1427nm are obtained. The achieved gain flatness is 1.46dB and the maximum forward on/off gain is 10.43 dB, which is much better than initial un-optimized gain flatness 5 dB. Then after 24 calculations we get the optimum pump powers. The final optimized pump sources are 1390nm 300mW, 1427nm 290mw. Gain ripple less than 1.2 dB in 40nm and maximum Raman on/off gain about 10.1 dB are obtained. Finally the factors of the noise figure are analyzed and ASE is found to be the main noise source.