Bizhi Dai

Experimental study of Raman amplification on stimulated Brillouin scattering in the G652 fibers at 1520nm

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 at 1428nm fiber Raman laser and signal source is a tunable power external cavity laser (ECL) with narrow spectral bandwidth (<100MHz). The threshold power of backward Stokes the first and second stimulated Brillouin scattering SB1- and SB2- in the backward pumped S band distributed fiber Raman amplifier is 5mW and 67.6mW, respectively. The Stokes stimulated Brillouin scattering lines is amplified by fiber Raman amplifier and fiber Brillouin amplifier. The total GA is production of the gain of Raman GR and the gain of Brillouin amplifier GB. GA=GR×GB. In experimental work, the saturation gain of SB1- and SB2- is about 50dB and 65dB respectively and the saturation gain of 25km G652 backward FRA is about 25dB, so the gain of backward fiber Brillouin amplifier SB1- and SB2- are about 25dB and 40dB, respectively. The forward SBS does not obey the common theory that only weakening backward-SBS lines existed, according to conservation of energy and momentum and wave vector selected rule. Because the wave-guide characters weaken the wave vector rule, but the forward transmit sound wave-guide forward Brillouin scattering lines are generated and amplified in S band G652 FRA. The stimulated threshold power of the forward first Stokes SBS (SB1- ) in the backward pumped FRA is 6.6mW. In experimental work, the saturation gain of SB1- is about 49dB and the saturation gain of 25km G652 backward FRA is about 10dB, so the gain of SB1- in the forward fiber Brillouin amplifier is about 39dB.

Threshold level and gain of forward stimulated Brillouin scattering in a forward pumped s-band discrete DCF fibers Raman amplifier

Amplification effect of forward stimulated Brillouin scattering (SBS) lines on the forward pumped s-band discrete DCF fiber Raman amplifier (FRA) has been studied. Pump threshold power of the forward first order Stokes SBS (FSB1-), second order Stokes SBS (FSB2-) and third order SBS (FSB3-) in the forward pumped FRA are 1.5 mW, 1.4 mW and 1.7 mW, respectively. The Stokes SBS lines are amplified by FRA and fiber Brillouin amplifier (FBA) at the same time. Gain of amplification is given as GA=GR · GB, where GR is Raman gain and GB is Brillouin gain. Saturation gain of FSB1-, FSB2- and FSB3- are about 52 dB, 65 dB and 65 dB, respectively. The saturation Raman gain of 10 km DCF forward FRA is about 14 dB, so Brillouin gain of FSB1-, FSB2- and FSB3- are about 38 dB, 51 dB and 51 dB, respectively. The forward cascaded SBS lines have been observed.

Study and manufacture of gain flattened S-band distributed dispersion compensation fiber Raman amplifier

Now the communication band of fiber focuses on C-band, but with increasing demand of fiber communication capacity, the communication band will extend to the S-band and L-band and fiber Raman amplifier will play a very important role in this process. In this paper, actual fiber Raman gain spectrum using single high power fiber Raman laser as pump was tested and the proper chirped Bragg fiber grating as gain flattening filter was designed to flatten actually tested gain spectrum. Besides, FWDM (film wavelength division multiplexer) is used as the multiplexer of signals and 1427nm/1505nm CWDM (coarse wavelength division multiplexer) is used as pump-signal coupler. The gain media are 50 km G652 fiber and 5km DCF (dispersion compensation fiber). The gain is 10dB of S-band fiber dispersion compensation Raman amplifier from1487.88nm~1541.88nm (total 53nm bandwidth) with gain ripple ± 0.6dB was successfully obtained. Besides, the effect caused by different location ways of different type fibers was also discussed. It is very significant for extending range of communication band of fiber and increasing the capacity of fiber communication especially for ultra-long haul and ultra-high capacity communication system.

Broadband distributed Raman amplifier using single pump

A simple method of broadband distributed Raman amplifier is presented based on Chirped Fiber Bragg Grating Filter. C+L band gain flattened distributed fiber Raman amplifier with bandwidth of 50nm (1520nm~1570nm) and 15 dB averaged gain and ± 0.6dB gain ripple using single pump has been demonstrated. Compared to design methods of other existing Raman amplifier, our method has a substantial improvement in simplifying system.

Amplification effect on stimulated brillouin scattering in the forward pumped S band discrete DCF fibers Raman amplifier

The amplification effect on forward and backward stimulated Brillouin scattering lines in the forward pumped S band discrete DCF fiber Raman amplifier (FRA) has been studied. The pumped threshold power of the forward first order Stokes SBS (FSB1- ), second order Stokes SBS (FSB2-) and third order SBS (FSB3-) in the forward pumped FRA are 1.5 mW, 1.4 mW and 1.7 mW respectively. The Stokes SBS lines are amplified by FRA and fiber Brillouin amplifier (FBA) at the same time. The gain of amplification is given as GA=GR multiplied by GB where GR is Raman gain and GB is Brillouin gain. In the experiments, the saturation gain of FSB1-, FSB2- and FSB3- are about 52dB, 65dB and 65dB respectively. The saturation Raman gain of 10km DCF forward FRA is about 14dB, so the Brillouin gain of FSB1- , FSB2- and FSB3- are about 38dB, 51dB and 51dBrespectively. There are pumped threshold power of the first order, second order and third order Stokes backward SBS (B-SBS) line BSB1-, BSB2- and BSB3- in the forward pumped discrete DCF FRA, and they are about 4.7mW, 17.1mW and 67mW respectively. The saturation gain of the first order, second and third Stokes backward SBS line BSB1-, BSB2-and BSB3- are about 60dB and the saturation gain of 10km DCF forward pumped FRA is about 27dB, so the gain of FBA is about 33dB. The forward and backward cascaded SBS lines have been observed.

Manufacture and test of C-band and S-band gain flatness dispersion compensation fiber Raman amplifier

C-band and S-band fiber Raman gain spectrum pumped by single wavelength high power fiber Raman laser were tested and the proper chirped Bragg fiber grating as gain flattening filter was designed to flatten actually tested gain spectrum. Besides, FWDM (filter wavelength division multiplexer) and 1427nm/1505nm CWDM (coarse wavelength division multiplexer) are used as C-band and S-band fiber Raman amplifier pump-signal couplers respectively. The gain media are 50 km G652 fiber and 5km DCF (dispersion compensation fiber). C-band fiber dispersion compensation Raman amplifier with bandwidth from 1519nm to 1574nm (55nm) and average gain 15.2dB and ripple ±0.8dB was successfully obtained. S-band fiber dispersion compensation Raman amplifier with bandwidth from 1488nm to 1541nm (53nm) and average gain 10.1dB and ripple ±0.9dB was successfully obtained. During the test of C-band fiber Raman amplifiers, broadband ASE light source and WDM-emulator were used to simulate the DWDM (dense wavelength division multiplexing) signal source that can make the whole test more accurate. It is very significant for extending range of communication band of fiber and increasing the capacity of fiber communication especially for ultra-long haul and ultra-high capacity communication system. At last, the result of experiment using these setup and influence caused by gain flattening filter and different type fibers location arrangements (G652 fiber and DCF) and corresponding solutions were also discussed.

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.