Thomas P. Rasmussen

Fundamental design of a distributed erbium-doped fiber amplifier for long-distance transmission

Comprehensive theoretical analysis on the design of a distributed erbium-doped fiber amplifier for long-distance transmission has been carried out, using a highly accurate model. The dispersion of the optical fiber as a function of the numerical aperture and the cutoff wavelength is included. Designs based on a bidirectional pumping scheme are evaluated, taking nonlinearities into account. The optimum value of the numerical aperture will be evaluated for cutoff wavelengths where the propagating pump power is single moded. For distances between each pumping station in the region between 10 and 100 km, the optimum ratio of copropagating and counterpropagating pump power will also be evaluated. >

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.

Normalized parameters for integrated optical waveguide components

The design of integrated optical S-bands, power splitters, and directional couplers are described in terms of normalized parameters. These parameters are calculated accurately by a numerical method leading to general design curves for fiber-compatible waveguide devices.

Modeling of integrated erbium doped optical amplifiers: influence of background loss and requirements to process control

An overview of the development on lossless Er-doped Y-branches and high gain Er-doped waveguide amplifiers is given, and their applications in future prospects are reviewed. A comprehensive model is presented for the integrated Er-doped phosphate silica amplifier, that includes high concentration ion-ion interaction. The model is applied to a rigorous design optimization of high gain amplifiers, where the influence of variations in the launched pump power, the core cross-section, the waveguide length, the Er-concentration, and the background loss are evaluated. Optimal design proposals are given and the process reproducibility of the proposed design is examined. Requirements to process parameter control in the fabrication of the Er-doped waveguide are also set up.

Microwave and optical properties of integrated electro-optic devices

A numerical analysis of microwave and optical properties of a polymer-based travelling-wave integrated electro-optic modulator is presented. We propose a new structure with a microwave buffer layer on top of the driving electrode. This buffer layer is added in order to obtain phase velocity matching between the optical field and the microwave modulation field. Employing the Effective Index Method and the 2D Beam Propagation Method the optical properties is investigated and the optical modulation index and the driving voltage is determined. Employing the Spectral Domain Approach we investigate the microwave properties of the new structure in a configuration with a travelling-wave electrode. It is shown that the two characteristics: the microwave mode index and the characteristic impedance, can be varied independently for the proposed structure. From the optical and microwave properties the active characteristics of a Mach-Zehnder interferometer based on the waveguide structure is investigated. We show that with no restrictions on the electrical power consumption, the optical modulation bandwidth can be higher than 100 GHz. This bandwidth will be reduced to 34 GHz, if a restriction on the electrical power from the signal generator is imposed.

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.