This paper describes a new approach to amplify optical images by using optically pumped doped cores in a multi-core
optical fiber structure. This approach combines the high gain and high efficiency properties of cladding pumped optical
amplifiers with the imaging properties of coherent fiber bundles. The individual cores correspond to the pixels in the image amplifier. We have demonstrated 3x3 arrays in an ytterbium-doped phosphate fiber energized by one multimode
semiconductor diode. Each pixel is capable of high gain (> 20 dB), low noise, and large acceptance angle (>12 degrees).
We expect our glass and preform fabrication method to scale to over 100 pixels. The amplified image can preserve
coherence (phase and wavelength) - or scramble the coherence depending on the design of the cores. This image
amplifier is an enabling technology for any type of imaging system that is photon-starved and requires a compact and
low noise image amplifier.
A model for population dynamics of Er3+ in tellurite glasses with high erbium concentrations is proposed. Luminescence decay curves from transitions of 4I13/2 yields 4I15/2 and 4S3/2 yields 4I15/2 were measured experimentally. Cooperative upconversion coefficients were obtained by numerically solving the rate equations of the model to fit the population dynamics of the 4I13/2 and 4S3/2 levels. The cooperative upconversion coefficient for 4I13/2 + 4I9/2 yields 4I15/2 + 4I15/2 is found to be 2.74 X 10-18 cm3/s and for 4I11/2 + 4I11/2 yields 4I15/2 + 2F7/2 is 1.09 X 10-18 cm3/s. The model provides a god basis for explaining the experiment data as it shows a high sensitivity to the input fitting parameters. This model can be used to analyze spectroscopic properties of Er3+ ions in glass hosts where various energy levels of Er3+ and transitions between them cannot be neglected.
Broadband erbium-doped fiber amplifiers at 1.5 micrometers band, an important communication band, are generating great interest in order to increase the transmission capacity of wavelength-division-multiplexing transmission networks. The host materials for Er3+ doping are very important for obtaining an intrinsically broad amplifier bandwidth. This paper reports the spectral properties of the Er3+ doped lead halotellurite glasses, PbX2-TeO2 (X equals F, Cl, Br). The measured absorption and emission spectra were analyzed by Judd-Ofelt and McCumber theories. It was found that Er3+ doped lead halotellurite glasses have a good glass stability, high refractive indices, high absorption and stimulated emission cross sections, and a very broad bandwidth for 1.5 micrometers absorption and emission. The 1.5 micrometers band, which has a substantial magnetic dipole transition component, is a special band whose bandwidth increases significantly with the refractive index of the host material. It is expected that the halotellurite glasses will be the promising host materials for 1.5 micrometers broadband amplification.
Two erbium doped germanate glass samples prepared by sol-gel process and melting and casting method, respectively, have been characterized. A fluorescence lifetime of 2.5 ms at the 4I13/2 level and a very broad bandwidth (FWHM: 53.7 nm) around 1.55 micrometers have been observed for the sol-gel sample. The fluorescence lifetime and the spectrum bandwidth for 1.535 micrometers transition for the sample fabricated by the melting and casting technique were measured to be 10 ms, and 19 nm (FWHM). The cooperative up-conversion coefficient is measured to be 1.3 X 1018 cm3/s for the sample with an erbium concentration of 2.69 X 1020 ions/cm3.
Decay curves of 1.5 micrometers (4I13/2) and 980 nm (4I11/2) emissions from Er3+ ions in Ga2S3-GeS2-La2S3 glasses were measured by the excitation of 1.5 micrometers laser diode pump. The decay curves were simulated using rate equations for a model consisting of four levels (4I15/2, 4I13/2, 4I11/2, and 4I9/2) of Er3+. A pair of unknown parameters, i.e., an excited state absorption coefficients for 4I13/2 yields 4I9/2, (sigma) esa, and a cooperative upconversion coefficient for (4I13/2, 4I13/2) yields (4I9/2, 4I15/2), C, were included in the rate equations. They were estimated by fitting the simulated curves to the measured ones. The obtained values were 3 X 10-21 cm2 and 1 or 3 X 10-21 cm3/s for the (sigma) esa and C, respectively.
Er$3+) doped tellurite glasses with various Na2O/Li2O, Na2O/K2O and K2O/Li2O ratios were prepared. Absorption and emission spectra, glass transition temperatures, crystallization temperatures, densities, and refractive index of these glass samples were characterized. For all studied glass samples, the highest effective linewidth was obtained with mixed alkali molar ratio of Na2O/Li2O equals 1, Na2O/K2O equals 1 and K2O/Li2O equals 1. The studied glasses have a (Tx- Tg) exceeding 100 degree(s)C, indicating these glass samples are stable against devitrification. In addition, Judd-Ofelt analysis of several glasses was also performed.
Cooperative upconversion and Yb3+-Er3+ energy transfer in newly developed phosphate glasses were studied in this paper. The cooperative upconversion coefficients of 4I13/2 level for different Er3+ concentrations were deduced from the pump intensity- dependent luminescence decay curves. Yb3+-Er3+ energy transfer efficiencies for different Yb3+ concentrations codoped with Er3+ (approximately 2 X 1020 ions/cm3) were estimated from the lifetime measurements of 2F5/2 level of Yb3+ ions. The small cooperative upconversion coefficients and high Yb3+-Er3+ energy transfer efficiencies indicate these newly developed Er3+ and Yb3+/Er3+ doped phosphate glasses are excellent for amplifier and laser applications.
A new strip-loaded structure for ion-exchanged waveguide amplifiers in Er3+-doped glass is suggested. The fabrication of these waveguides lacks steps such as mask deposition and burial process that can be critical for some glasses. A simple numerical modeling shows that similar, or even higher, gain values as in ion-exchanged buried waveguides can be achieved. Preliminary experimental data for the fabrication of the strip-loaded structure are also reported.
A new Er3+ doped phosphate glass exhibiting an excellent durability in both boiling water and NaNO3 molten salt was developed. Ion-exchange process of this glass was investigated by treating glass samples in a variety of salt bathes with various exposure times. Planar waveguide with one mode at 1.54 micrometers and three modes at 632.8 nm was demonstrated. Spectral properties of Er3+ in this glass were characterized by measuring absorption and emission spectra, and fluorescence lifetimes. Emission cross section of Er3+ in this glass was calculated to be 0.76 X 10-20 cm2 using McCumber theory. Our preliminary experimental results indicate this new Er3+ doped glass is an excellent material for ion-exchanged waveguide lasers and amplifiers.
We successfully placed a metal strip along the core of an optical fiber, see Fig. 1. These devices can be used as polarizers. Light polarized parallel to the metal strip is absorbed while light polarized perpendicular to the metal strip is absorbed less. Potentially large ratios of transmitted to absorbed light can be achieved in relatively short pieces of fiber. The Metal Strip Polarizing Fibers (MSPFs) are typically about 5 mm long. We report both on the fabrication process and some preliminary test.
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