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Applied Optics

Recovery of population inversion in an erbium-doped fiber amplifier observed by temporally resolving amplified spontaneous emissions

K. Kuroda, Yuzo Yoshikuni

Published May 31, 2012• 12 citations
Publisher

Abstract

We report on the recovery of population inversion in a CW-pumped erbium-doped fiber amplifier. Spontaneous emissions after the input of signal pulses were temporally resolved. The recovery time for population inversion was estimated to be a few hundred microseconds. The pump power and signal width dependences of the recovery were measured. We discuss the dependences by applying an analytical formula derived for the temporal evolution of population inversion.

DOI
10.1364/ao.51.003670

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A method of measuring the local fractional population of the upper state /sup 4/I/sub 13/2/ of an erbium-doped amplifier is investigated. The local fractional population is related theoretically by EDF parameters to the local spontaneous emission (SE) power that leaks laterally from the EDF. The proportional constant between the fractional population and the detected SE power is determined experimentally by measuring saturated spontaneous emission power. The local fractional population of a 19.7 m-long EDF, pumped with a 1.48 mu m light and injected with a 1.552 mu m signal light, was measured by detecting the local SE power with a Ge photodiode having a diameter of 2 mm. The measured fractional population coincides with the calculated value.>

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A theoretical model that allows numerical simulations of optical bistability phenomena in CW-pumped erbium-doped fiber lasers is presented. Results of the simulations match correctly with previous experimental data. In order to simulate this phenomenon, the population inversion and optical powers longitudinal distributions along the active fiber have been considered. If this fiber is long enough, it has been found that the transition between the non-lasing and the lasing states involves a dramatic redistribution of the population inversion along the active medium. This fact makes that non-lasing and lasing states constitute different enough initial conditions which determine different final responses to the same control parameter, that is to say, bistability. On the other hand, a theoretical justification is found for a previous experimental result which pointed out that the bistability range becomes reduced if an external signal is launched to the cavity. Finally, the bistability range width dependence on the active fiber length is analyzed.

Optics Communications•Aug 5, 2022•2 citations
We report on the recovery of population inversion in a CW-pumped erbium-doped fiber amplifier. Spontaneous emissions after the input of signal pulses were temporally resolved. The recovery time for population inversion was estimated to be a few hundred microseconds. The pump power and signal width dependences of the recovery were measured. We discuss the dependences by applying an analytical formula derived for the temporal evolution of population inversion.
We present an analytical solution for the coupled rate and propagation equations for a dynamic two-level homogeneously broadened system interacting with radiation and with constant population inversion along the longitudinal axis of the fiber, z. We derive an analytical solution for the z dependence of these equations, which greatly simplifies the numerical solution for the output powers’ time dependence. Amplified spontaneous emission and background loss influences are considered in the model, in contrast to the previous analytical solution presented by Y. Sun et al. The solution is derived, and the importance of each term for the dynamic modeling of typical erbium-doped fiber amplifiers is analyzed.
A model is presented for erbium-doped fiber amplifiers that operate by an upconversion process in which two pump photons at ~800 nm are absorbed and can provide an inverted population and hence the ability to amplify signal photons at ~850 nm. The most important spectroscopic features of the amplifier are identified and used to formulate a theory that predicts how the amplifier gain varies with fiber length and doping density, as well as with launched pump and signal powers. The limitation that amplified spontaneous emission imposes on the gain is investigated, and useful approximate formulas are derived in the limit where amplified spontaneous emission is negligible.
Some analysis of the transient response of the Yb-doped fiber amplifier are performed by solving a set of time-dependent rate and power transfer equations based on finite-difference method. Meanwhile, the variation of time to reach the steady state for upper level population distribution, the forward and backward amplified spontaneous emissions (ASEs) and stored energy on the system parameters including pump power, fiber length, Yb-doped concentration, and core area are numerically simulated, respectively. The results show that, by optimizing pump pulse width, stored energy can reach or even exceed the steady state value of continuous wave (CW) pump. By increasing Yb-doped concentration and core area, stored energy is increased, the ASE is suppressed and the ASE built-up time is postponed. In addition, the experimental results show the validity of the theoretical ASE built-up time. The obtained results can provide important guiding for the optimization of pump pulse width and fiber parameters.
A method of measuring the local fractional population of the upper state /sup 4/I/sub 13/2/ of an erbium-doped amplifier is investigated. The local fractional population is related theoretically by EDF parameters to the local spontaneous emission (SE) power that leaks laterally from the EDF. The proportional constant between the fractional population and the detected SE power is determined experimentally by measuring saturated spontaneous emission power. The local fractional population of a 19.7 m-long EDF, pumped with a 1.48 mu m light and injected with a 1.552 mu m signal light, was measured by detecting the local SE power with a Ge photodiode having a diameter of 2 mm. The measured fractional population coincides with the calculated value.>
A theoretical model that allows numerical simulations of optical bistability phenomena in CW-pumped erbium-doped fiber lasers is presented. Results of the simulations match correctly with previous experimental data. In order to simulate this phenomenon, the population inversion and optical powers longitudinal distributions along the active fiber have been considered. If this fiber is long enough, it has been found that the transition between the non-lasing and the lasing states involves a dramatic redistribution of the population inversion along the active medium. This fact makes that non-lasing and lasing states constitute different enough initial conditions which determine different final responses to the same control parameter, that is to say, bistability. On the other hand, a theoretical justification is found for a previous experimental result which pointed out that the bistability range becomes reduced if an external signal is launched to the cavity. Finally, the bistability range width dependence on the active fiber length is analyzed.