Exact analysis for statistics of gain in counter-pumped Raman amplifier

Jiangming Xu, Leng Jinyong, Han Kai +2 more

Single-frequency fiber Raman amplifier (SF-FRA) is known for the ability of all-band amplification, and it is very attractive for the amplification of single-frequency seed light at a special wavelength, such as 1178nm and 1271nm. The 1080nm single-frequency signal light is amplified by a 1031nm pump source, and the influences of seed power of single-frequency signal light, length of Raman gain fiber, pump scheme are experimentally investigated. The results show that the efficiency of SF-FRA increases with the enhancement of the single-frequency signal power and the length of Raman gain fiber. The efficiency of co-pump SF-FRA is higher than that of the counter-pump SF-FRA. The measure ments show that the linewidth of single-frequency signal light is not broadened obviously in the process of Raman amplification. The visibilities of the rapid-exposure pattern of far-field interference of single-frequency seed light and the amplified light are 0.814 and 0.719, respectively. The results show that the coherence of single-frequency signal light is affected by the SF-FRA more or less. These experimental results can provide a reference for designing other special wavelength SF-FRA.

Po Dong, Weining Man, Jin-Yue Gao

Michael D. Duncan, Rita Mahon, Lawrence L. Tankersley +1 more

We have studied the phase pulling and locking of an injected Stokes pulse in a transient Raman amplifier both experimentally and theoretically. In addition, we have investigated the pulse energy statistics and related spatial modes of a high gain amplified Stokes pulse. Experiments reported here show that in the unsaturated case, the phase of the amplified Stokes is pulled almost instantaneously to that of the pump, as soon as integrated gain levels of slightly greater than unity are reached. For higher input seed-Stokes levels, such that the amplified Stokes energy is saturated, the phase locking is completed early, and the phase of the amplified Stokes then follows the phase excursion of the pump. The phase pulling has been modelled theoretically for the specific parameters of our experiment. We have also used the pulse energy statistics to study the seed-Stokes control of a high gain Raman amplifier. For an input seed-Stokes beam to control a transient, high gain Raman amplifier, operated near threshold, it must dominate the self-generated Raman which builds from quantum noise. For a near-unity-Fresnel-number Raman amplifier we have measured the number of input seed-Stokes photons needed to produce an unchanged statistical signature on the amplified Stokes pulse and have found that a surprisingly large number (109) were needed. For a larger Fresnel number Raman amplifier, a near-field camera was used to study the level at which the seed-Stokes pulse controlled the spatial output of the amplifier. Control of the spatial modes seems to have a sharp threshold with input Stokes energy and was fully established with an input of 2x103 photons per mode.

Daniel J. Gauthier, Michael D. Stenner

M. G. Raymer, Ian A. Walmsley

Marco Santagiustina

Exact integral solutions of forward and backward Raman Stokes-pump interaction are presented. They enable one to determine the gain and depletion characteristics of optical Raman amplifiers, as well as a good approximation of the noise figure, without the need of numerically solving the nonlinear boundary value differential equations governing the Raman interaction.