Jørn Hedegaard Povlsen

The design of erbium-doped fiber amplifiers

An accurate model for the erbium-doped fiber amplifier is presented. The model is used to design the index profile of the doped fiber, optimizing with regard to efficiency for inline- and preamplifiers as well as for power booster amplifiers. The predicted pump efficiencies (maximum gain to pump power ratios) are in agreement with experimental results presented in the literature. The choice of codopant is shown to be very significant for the pump efficiency when pumping in the 0.98 mu m. The pump efficiency in the 0.98- mu m pump band is shown to be twice the pump efficiency in the 1.48- mu m pump band. >

Emission and absorption cross section of thulium doped silica fibers

A thorough investigation of the emission and absorption spectra of the (3F4,3H6) band in thulium doped silica fibers has been performed. All the basic parameters of thulium in silica have been extracted with the purpose of further analysis in laser and amplifier simulations. The experimental methods used to obtain the scaled cross sections have been carefully selected in order to avoid problems associated with calibrated measurements and knowledge of the radiative lifetime. The values of the absorption cross sections agree well with previously reported values, however the peak emission to peak absorption cross section ratios are found to be significantly below 1. Also confinement factors and thulium concentrations are estimated from the results.

Advances in silica-based integrated optics

Recent advances within the realization of silica-based planar waveguide circuitry are presented. This ranges from the production methods for planar waveguides, including a novel method based on the utilization of focused UV-laser beams for direct waveguide imprinting, to the functionalities that are embedded into the glass materials and waveguide circuitry. Planar waveguide amplifiers, lasers, and the pursuit to obtain highly nonlinear materials to realize purely glass-based switches, modulators, and wavelength converters are also presented. Furthermore, microring resonators are discussed, and finally the latest results within 2-D photonic bandgap structures are reviewed.

Design and performance evaluation of 1-by-64 multimode interference power splitter for optical communications

A 1-by-64 multimode interference power splitter in SiO/sub 2/ has been designed for use in fiber-optics communication systems. The splitter exhibits a minimum loss of 0.5 db and a uniformity of 1.7 dB at a wavelength of 1.55 /spl mu/m. The polarization sensitivity is below 0.14 dB, the reflection level below -55 dB, and the optical bandwidth 30 nm. The fabrication tolerances are /spl plusmn/0.1 mm on the length and /spl plusmn/3.5 /spl mu/m on the width of the multimode section of the splitter. In comparison with a branching-type splitter it is found that the designed device is approximately 30% shorter than the branching-type device for comparable losses. >

Detailed theoretical and experimental investigation of high-gain erbium-doped fiber amplifier

A full-scale numerical model for the erbium-doped fiber amplifier has been developed that incorporates realistic index and erbium-concentration profiles as well as the spectral distribution of amplified spontaneous emission (ASE). The high accuracy of the model is demonstrated by comparison with a comprehensive set of data, including gain, ASE, and pump power, obtained for a well-characterized Er-Al-doped fiber. An absorption-to-emission cross-section ratio of 1.0 was measured at the gain peak. Pumping at 654 nm, the excited state absorption was observed to be insignificant. A high gain of 39.6 dB was achieved in the experiment.<<ETX>>

Optimum position of isolators within erbium-doped fibers

An isolator is used as an amplified spontaneous emission suppressing component within an erbium-doped fiber. The optimum isolator placement is both experimentally and theoretically determined and found to be slightly dependent upon pump power. Improvements of 4 dB in gain and 2 dB in noise figure are measured for the optimum isolator location at 25% of the fiber length when the fiber is pumped with 60 mW of pump power at 1.48 mu m.<<ETX>>

Long distance transmission through distributed erbium-doped fibers

High bit rate, all-optical long-distance transmission could be created through the combined use of loss-compensating gain in erbium-doped fibers and solitons. A detailed analysis of the distributed erbium-doped fiber, including the spectral-gain dependency, is combined with an optimum design of the transmission fiber and general bit-error-rate calculations. Changes in wavenumber, group velocity, and fiber dispersion due to erbium doping in a single-mode fiber are evaluated, and a reduction in bit-error rates due to the erbium spectral-gain profile is shown. Transmission through distributed erbium-doped fiber with 100-km separation between each pump-power station is shown, with a total bit-rate distance product of 55 Gb/s . Mm. >

Analyzing the fundamental properties of Raman amplification in optical fibers

The Raman response of germanosilicate fibers is presented. This includes not only the material dependence but also the relation between the spatial-mode profile of the light and the Raman response in the time and frequency domain. From the Raman-gain spectrum, information is derived related to the nonlinear refractive index due to nuclear motions and the Raman response function in the time domain. It is demonstrated that the Raman-gain coefficient may be reduced up to 60% if the signal propagates in the fundamental mode while the pump alternates between the fundamental mode and a higher order mode. A simple model shows that the time response related to the decay of phonons is significantly larger in germanate glass relative to silica glass. From the Raman gain, it is found that the contribution to the nonlinear refractive index from nuclear motions is reduced by a factor of 2 in germanate relative to silica glass.

Detailed design analysis of erbium-doped fiber amplifiers

When pumping the erbium-doped fiber amplifier at 0.98 and 1.48 mu m, the optimum cutoff wavelength for step profiles with arbitrary numerical aperture is shown to be 0.80 and 0.90 mu m, respectively. The use of a confined erbium profile can improve the gain coefficient up to 45%. The index raising co-dopant is shown to be very significant for the gain coefficient when pumping at 0.98 mu m.<<ETX>>

Detailed comparison of two approximate methods for the solution of the scalar wave equation for a rectangular optical waveguide

Two approximate methods for the determination of the fundamental mode of an optical waveguide with rectangular core cross section and step refractive-index profiles are presented and analyzed thoroughly. Both methods are based on Galerkins method. The first method uses Hermite-Gauss basis functions and the second uses the guided and nonguided slab waveguide solutions as basis functions. The results are compared with results from an accurate circular harmonic analysis. Both methods provide values of the normalized propagation constant with errors less than 0.1% for practical rectangular single-mode waveguides. The slab waveguide method is the fastest, and even when only one slab waveguide mode is used the propagation constant for the fundamental mode can be calculated with an error of less than 1%. The slab waveguide method also gives very accurate results for the propagation constant for higher order modes. >