Konstantin E. Riumkin

Bi-Doped Optical Fibers and Fiber Lasers

The current state of the art in infrared Bi-doped fiber laser research is reviewed. The relevant fiber glass compositions and fiber technologies are introduced. Lasers operating on transitions ranging from 1.15 to 1.55 μm occurring in the bismuth active centers and their energy level schemes are discussed on the basis of the spectroscopic properties of these centers. Continuous-wave fundamental-mode power levels ranging from a few mW near 1.55 μm up to 16 W near 1.16 μm and 22 W near 1.46 μm have been demonstrated in recent years.

Superfluorescent 1.44 μm bismuth-doped fiber source

The first bismuth-doped superfluorescent fiber source operating at 1.44-μm was developed. At pump power of 200 mW and pump wavelength of 1310 nm, its output signal reaches 57 mW with spectrum width of 25 nm.

A 23-dB bismuth-doped optical fiber amplifier for a 1700-nm band

It is now almost twenty-five years since the first Erbium-Doped Fiber Amplifier (EDFA) was demonstrated. Currently, the EDFA is one of the most important elements widely used in different kinds of fiber-optic communication systems. However, driven by a constantly increasing demand, the network traffic, growing exponentially over decades, will lead to the overload of these systems (“capacity crunch”) because the operation of the EDFA is limited to a spectral region of 1530–1610 nm. It will require a search for new technologies and, in this respect, the development of optical amplifiers for new spectral regions can be a promising approach. Most of fiber-optic amplifiers are created using rare-earth-doped materials. As a result, wide bands in shorter (1150–1530 nm) and longer wavelength (1600–1750 nm) regions with respect to the gain band of Er-doped fibers are still uncovered. Here we report on the development of a novel fiber amplifier operating in a spectral region of 1640–1770 nm pumped by commercially available laser diodes at 1550 nm. This amplifier was realized using bismuth-doped high-germania silicate fibers fabricated by MCVD technique.

Watt-level, continuous-wave bismuth-doped all-fiber laser operating at 1.7 μm

A watt-level all-fiber laser radiating at the wavelength of 1.7 μm in a continuous-wave regime was developed by using bismuth-doped high-germania optical fiber. A maximum slope efficiency of 33% with respect to the launched pump power was achieved. The dependencies of the slope efficiencies of bismuth-doped fiber laser versus the length of active fiber and reflectivity of the output mirror were obtained.

Laser-induced bleaching and thermo-stimulated recovery of luminescent centers in bismuth-doped optical fibers

In this paper, we report the detailed study of photobleaching and recovery in bismuth-doped fibers that proved to be a unique laser media for the near IR spectral regions unreachable for rare-earth-doped lasers. The laser-induced bleaching and recovery dynamics of the characteristic absorption and emission bands assigned to different types of the bismuth-related active centers were obtained. By analyzing the Raman-scattering spectra of the bleached bismuth-doped fibers, the intensity-dependence of the photobleaching rate and the experimentally determined activation energy of the recovery process and underlying mechanisms of these phenomena are discussed. Furthermore, a bleaching–recovery cycling and “memory effect” are demonstrated.

Bismuth-doped fibers and fiber lasers for a new spectral range of 1600-1800 nm

For the near IR spectral region from 1150 to 1800 nm, including the ranges from 1250 to 1500 nm and 1600 to 1800 nm where efficient rare-earth-doped fiber lasers don’t exist, bismuth-doped optical fibers are promising active materials. The last two spectral ranges are of great interest for some applications, in particular for optical fiber communication. Earlier, we developed Bi-doped fiber lasers and optical amplifiers operating in the first of these spectral ranges. Here, we report new results on the development of bismuth-doped optical fibers and fiber lasers for a spectral range of 1600-1800 nm.

Recovery of IR luminescence in photobleached bismuth-doped fibers by thermal annealing

The effect of annealing temperature on the luminescent properties of bismuth-doped fibers bleached by 532 nm laser radiation was investigated. The photoluminescence (PL) measurements were performed in pristine and photobleached samples which were thermally annealed at various temperatures ranging from 100 to 900 °C and slowly cooled. We observed that the intensity of the PL band at 1700 nm in the photobleached fibers recovered its pre-bleached level. Moreover, it was shown that a significant increase of the PL level could be achieved using the special annealing regime. Thereby, we obtained the experimental evidence of a thermally activated recovery process of the PL intensity showing that photoinduced changes of PL in bismuth-doped fibers are completely reversible. The mechanism of the thermal recovery of the PL is discussed.

Effect of gamma-irradiation on the optical properties of bismuth-doped germanosilicate fibers

In this paper we present the results on the effect of γ-irradiation on the optical properties of bismuth-doped germanosilicate fibers. It has been revealed that the absorption and emission bands of the bismuth-related active centers are mildly affected by γ-radiation with a dose ranging from 1 to 8 kGy. Experimental data on the radiation-induced absorption (RIA) dynamics of Bi-doped fibers under irradiation and post-irradiation recovery have been obtained. The RIA spectra of the Bi-doped germanosilicate fibers have been measured. The effect of Bi concentration on the RIA level is discussed.

Temperature-dependent characteristics of bismuth-doped fiber amplifier operating in a 1720-nm band

The temperature dependencies of the characteristics of a bismuth-doped fiber amplifier (BDFA) for a 1725-nm band have been studied. The amplifier was backward-pumped with an Er-Yb-codoped fiber laser at 1568 nm. A peak gain of 24 dB, a 3-dB gain bandwidth of 55 nm, a noise figure of 5 dB and slope gain efficiency of 0.17 dB/mW at room temperature have been obtained. It has been shown that peak gain of the BDFA varies by 25 % in the temperature range from −60 to +60 °C while the noise figure remains almost unchanged. Some possible mechanisms responsible for the thermal behavior of the characteristics of the BDFA are considered.

Bismuth-doped optical fiber amplifier and watt-level CW laser for the spectral region 1600–1800 nm

The first bismuth-doped fiber amplifier (BDFA) for 1640-1770-nm region was developed. The BDFA diode-pumped at 1550 nm is characterized by 23-dB peak gain at 1710 nm, noise figure~7 dB, Δλ_1/2=40 nm and g=0.1 dB/mW.