Gain optimization of germanosilicate fiber Raman amplifier and its applications in the compensation of Raman-induced crosstalk among wavelength division multiplexing channels

Abstract

Spectral characteristics of stimulated Raman scattering (SRS) process were theoretically investigated for step-index silica optical fibers with various GeO 2 concentrations. Optimal-fiber lengths and germanium concentration, where the first Stokes power reaches maximum, were calculated at various pump power levels for application in Raman amplifiers. Based on this analysis, we proposed and experimentally demonstrated a new channel-equalizing technique to simultaneously compensate Raman-induced crosstalk and amplify wavelength-division-multiplexing (WDM) signals using a discrete Raman amplifier in the 1.5m range. As a further application of SRS in germanosilicate glass fibers, we introduce an all-optical variable attenuator for channel equalization that could be used in dynamic optical power tilt control in WDM systems.

Broadband Wavelength-swept Raman Laser for Fourier-domain Mode Locked Swept-source OCT

“…The second terms on the right side are due to the linear absorption in the fiber medium. From a numerical simulation of the cascaded Raman frequency shift [10,11], it was confirmed that a wider distribution of multi-wavelength pumping below 1500 nm will reduce the broader distribution of Raman gain above the 1500 nm region.…”

“…This is the first experimental demonstration of a broadband SS-OCT based on a fiber Raman amplifier as a broad gain medium over 50 nm, compared with the previous report of narrower Raman gain using a single-wavelength optical pumping scheme [6,7]. As high power optical pump sources have become commercially available, a fiber Raman amplification based on stimulated Raman scattering in silica optical fibers has been studied widely, particularly in wavelength-division-multiplexed (WDM) telecommunication system applications [8][9][10][11][12][13]. The fiber Raman amplifier has several advantages, such as low noise, arbitrary gain band determined on the band of the optical pump sources, high temperature stability and instantaneous carrier relaxation times of A novel broadband wavelength-swept Raman laser was used to implement Fourier-domain mode locked (FDML) swept-source optical coherence tomography (SS-OCT).…”

“…Considering the interaction between the pump and Stokes waves to find the Raman threshold, the evolution of the signal and pump power levels can be described using the following coupled equations [11],…”

Wavelength-Swept Cascaded Raman Fiber Laser around 1300 nm for OCT Imaging

“…Considering the interaction between the pump light and Stokes waves, the generation of the instantaneous Stokes intensity is proportional to the optical pumping power and the stimulated Raman gain coefficient [18][19][20][21]. With increase in the length of the HNLF, the stimulated Raman gain coefficient can proportionally increase; however, the increased fiber loss coefficient at the Stokes wavelength suppresses the generation of the instantaneous Stokes intensity.…”

“…Therefore, within the limits of the given length of the HNLF and the limited optical pump power, it is important to increase the path-length efficiency by applying a feedback cavity structure. Since each cavity round-trip across the HNLF is optimally induced from the pairs of the FBG mirrors at 1064, 1117, 1175, and 1240 nm, the required pump power to increase the Stokes intensity can be effectively reduced, as can be inferred from the coupled equations of the cascaded RamanStokes shift [21]. When we remove the coupled FBG mirrors and adopt a ring cavity feedback structure based on the 1064/1310 nm WDM coupler only, a higher pumping power of more than 3 W is required to generate the fourthorder Stokes waves [18].…”