Joern Hedegaard Povlsen

Noise and gain performance for an Er3+-doped fiber amplifier pumped at 980 nm or 1480 nm

A comprehensive model is used to analyze gain and noise performance for Erbium doped fibre amplifiers pumped at 980 and 1480 nm. A minimum noise figure is shown to be given by emission to absorption cross section ratios at both pump and signal wavelength. The deterioration from the minimum noise figure in each pumpband is shown mainly to be due to the presence of the counter propagating Amplified Spontaneous Emission. It is shown that for the preamplifier the fibrelength for optimum receiver sensitivity is up to 50 % smaller than the maximum gain fibre-length

Demand for accuracy of the attenuation constant in distributed active fibers

Design of a distributed Erbium doped fiber amplifier for a long distance transmission line is investigated, using a very accurate model. The design is evaluated for a bidirectional pumping scheme, taking nonlinearities into account. Bit error rates based on amplified spontaneous emission are calculated. For distances between each pumping station equal to 100km, bit error rates lower than 10-10 at 4GBit/s is found.

Microbending losses in fluoride glass fibres

Abstract Microbending losses of fluoride-glass fibres are calculated using the discrete mode coupling theory, which accurately describes losses of SiO 2 -fibres. Calculations show microbending losses of the same order of magnitude as the intrinsic loss of fluoride-glass.

Polymer-based electro-optic modulator with microwave shield for high-speed applications

The use of a shielded microstrip-configuration for polymer- based electro-optic modulators has the advantage over an open microstrip geometry that the modulator is pacified with respect to environmental conditions. We investigate such a shielded modulator numerically. Employing the Laplace equation the quasi-TEM field distribution is calculated and by employing Wheelers incremental rule we determine the conductor loss due to the skin effect. We demonstrate that the use of a shield in combination with a buffer layer with a low dielectric constant yields the modulator insensitive to geometrical variations. For a modulator with a wide driving electrode the maximum bandwidth may be as high as 90 GHz.

Cross-phase modulation in fiber lasers

A theoretical method is presented for investigation of modelocking in a fiber laser, where the modulation is performed by the cross phase modulation (XPM) from synchronous pumping using an external signal. Using this method, modelocking in a cross phase modulated fiber laser has been investigated.

Long-haul transmission in aluminum- and germanium-codoped distributed erbium-doped fibers

Theoretical limits in noise figures for a long haul transmission line based on lumped amplification are compared with distributed amplification. A reduction of approximately 60% of the required number of pump power stations is achieved. The distributed optical amplification is provided by an erbium doped fiber and comparisons of aluminum and germanium as codopant materials are shown. The pump power consumption and noise figure are analyzed with respect to the background loss.

Experimental investigation of tapered erbium-doped fiber amplifiers

Low noise erbium-doped fiber amplifiers find widespread use in telecommunication systems. Different design ideas have been presented for such amplifiers, including various pump configurations, the use of filters, and advanced active fiber design. In this paper we present an experimental confirmation of a fiber design based on an Er/Al doped untapered fiber. As recently predicted theoretically, a continuous uptapering of the radius of the core of the active fiber from the signal input end to the signal output end improves the population inversion of the erbium in the signal input end of the fiber. This ensures that the generated amplifier spontaneous emission is reduced while the high gain properties are retained. The result is a significant reduction of the noise figure. The active fiber is pumped at 980 nm with the pump power copropagating with the signal. In this way we have demonstrated noise figure improvements in excess of 1.5 dB compared with similar conventional fibers, while still obtaining high gain. To our knowledge, this represents the first experimental verification that tapered fiber amplifiers have considerably improved noise properties. This communication will include a short description of the method used to fabricate the tapered fiber.

Silica waveguide integrated optical isolator

An integrated optical waveguide isolator based on adiabatic polarization splitters in the silica- on-silicon technology and non-reciprocal elements are proposed and investigated with an accurate Finite Difference Beam Propagation Method. Improvements of noise figure of an erbium-doped fiber amplifier by using this type of isolator are calculated and discussed.

Performance improvement of direct detection systems using local and/or long-distance-pumped fiber amplifiers

Erbium doped fiber amplifiers in eight different system configurations are investigated, using a very accurate model. The in-line placement of the amplifier is shown to be optimum. A distributed amplifier is compared to the remote pumping scheme showing no system improvement. By the use of a booster, an inline remote pumped amplifier and a preamplifier up to 180 km of extra transmission fiber can be added.