研究目的
To present a division technique for separating stimulated and spontaneous parts of optical noise in fiber Raman amplifiers (FRA) and to experimentally study the maximum power of amplified spontaneous noise as a function of pump power, showing that the real FRA noise figure can be less than 3 dB.
研究成果
The research demonstrates a method to separate stimulated and spontaneous noise in FRAs, showing that the noise figure can be below the quantum limit of 3 dB at practical pump powers. This resolves contradictions in prior noise theories and confirms improved noise properties in distributed FRAs, with implications for high-data-rate optical communications.
研究不足
The study is limited to a specific 50 km SMF segment and pump wavelengths; results may not generalize to other fiber types or configurations. The spectral resolution of 1 nm might not capture finer details, and the assumption of no pump depletion in the model could introduce inaccuracies at higher powers.
1：Experimental Design and Method Selection:
The study uses a backward-pumped scheme for optical noise registration in a 50 km single-mode fiber (SMF) segment in the idle mode of a counter-pumped FRA. The methodology involves measuring amplified spontaneous emission (ASE) spectra using an optical spectrum analyzer (OSA) and analyzing the noise components based on coupled wave equations for Raman gain dynamics.
2：Sample Selection and Data Sources:
A 50 km span of standard single-mode fiber (SMF) is used. Data are acquired from ASE spectra measured with a spectral resolution of 1 nm.
3：List of Experimental Equipment and Materials:
Equipment includes a standard multiwave FRA unit with four laser diodes (LDs) at wavelengths 1425 nm, 1435 nm, 1455 nm, and 1465 nm, each tunable up to 300 mW; an optical spectrum analyzer (OSA); a circulator; a pump combiner; and the SMF segment.
4：Experimental Procedures and Operational Workflow:
The setup involves pumping the fiber with the FRA unit in the backward direction, measuring ASE spectra at different pump powers (e.g., 100 mW and 300 mW), and analyzing the spectra to separate spontaneous and stimulated noise components using a model function.
5：Data Analysis Methods:
Data analysis includes nonlinear fitting of experimental data to a model function, calculation of noise figure and bit error rate (BER) using derived equations, and statistical comparison of noise levels.
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