Christian Lester

Modeling of Yb/sup 3+/-sensitized Er/sup 3+/-doped silica waveguide amplifiers

A model for Yb/sup 3+/-sensitized Er/sup 3+/-doped silica waveguide amplifiers is described and numerically investigated in the small-signal regime. The amplified spontaneous emission in the ytterbium-band and the quenching process between excited erbium ions are included in the model. For pump wavelengths between 860 and 995 nm, the amplified spontaneous emission in the ytterbium-band is found to reduce both the gain and the optimum length of the amplifier significantly. The achievable gain of the Yb/sup 3+/-sensitized amplifier is found to be higher than in an Er/sup 3+/-doped silica waveguide without Yb/sup 3+/ (18 dB versus 9 dB for a pump power of 100 mW). However, it is important to optimize the Yb-concentration according to the choice of pump wavelength. >

Microwave characteristics of polymer electro-optic modulators

The finite difference method is employed for the Laplace equation to calculate the microwave properties of polymer-based electro-optic modulators. The finite difference scheme uses a nonequidistant grid for fast calculation of the mode index and characteristic impedance of an open micro striplike modulator with a thick electrode as well as for a shielded micro striplike structure. It is demonstrated that the finite thickness of the electrode must be taken into consideration when optimizing the design of an electro-optic modulator. It is shown that by using a shielded microstrip configuration the modulator may be optimized and simultaneously pacified with regard to environmental influence.

91-km attenuation-free transmission with low noise accumulation by use of distributed erbium-doped fiber

Transparency of a 91-km distributed erbium-doped fiber is achieved with 0.46 mW/km of pump power at a signal power of -12 d Bm. The accumulation of amplif ier noise is measured to be smaller than the minimum noise accumulation that can be achieved in a 91-km link with two lumped amplifiers separated by 45 km.

RAMAN EFFECT IN TRANSPARENT DISTRIBUTED ERBIUM-DOPED FIBRE

Abstract Stimulated Raman scattering is examined for a distributed Er-doped fibre. An optimum Er-concentration is found, where the noise figure is minimum. Compared with a distributed Er-doped fibre designed without considering Raman scattering the necessary pump power is reduced 50%, or alternatively the noise figure is improved 2 dB.

Noise optimization of an Er-doped superfluorescent fiber source

A theoretical analysis of the noise properties of an Er-doped superfluorescent fiber source is presented. The optimum fiber design with respect to the signal-to-noise ratio and output power is found.

Soliton Transmission at High Bit Rates through Distributed Erbium-doped Fibres

In ultra-long transmission systems, the combined effects of fibre-dispersion and optical Kerr effect, can be used to transmit soliton pulses well beyond the dispersion limit [1]. To overcome fiber loss in an all-optical soliton link, both lumped and distributed amplification have been used. Excursions in the signal power reduce the stability of the soliton. To sustain stable soliton propagation in a system with lumped amplifiers, the spacing between the amplifiers, Za, has to be much shorter than the soliton period, Z0, i.e. Za/Z0 > 1 [3], when using distributed amplification. Distributed amplification may be realized through the use of the Raman effect [4] or distributed erbium-doped fibres (d-EDFs) [5]. Here we present an experimental characterization of the transmission of solitons over 90 km using d-EDFs. We characterize the performance of the d-EDF according to the relation Za/Z0 and the magnitude of the signal excursion along the d-EDF, and verify experimentally that stable soliton transmission also is achievable when Za/Z0 > 1.

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.