167 W, power scalable ytterbium-doped photonic bandgap fiber amplifier at 1178 nm.

An ytterbium-doped photonic bandgap fiber amplifier operating at the long wavelength edge of the ytterbium gain band is investigated for high power amplification. The spectral filtering effect of the photonic bandgap efficiently suppresses amplified spontaneous emission at the conventional ytterbium gain wavelengths and thus enables high power amplification at 1178 nm. A record output power of 167 W, a slope efficiency of 61% and 15 dB saturated gain at 1178 nm have been demonstrated using the ytterbium-doped photonic bandgap fiber.

Amplification and ASE suppression in a polarization-maintaining ytterbium-doped all-solid photonic bandgap fibre.

We demonstrate suppression of amplified spontaneous emission at the conventional ytterbium gain wavelengths around 1030 nm in a cladding-pumped polarization-maintaining ytterbium-doped all-solid photonic crystal fibre. The fibre works through combined index and bandgap guiding. Furthermore, we show that the peak of the amplified spontaneous emission can be shifted towards longer wavelengths by rescaling the fibre dimensions. Thereby one can obtain lasing or amplification at longer wavelengths (1100 nm - 1200 nm) as the amount of amplification in the fibre is shown to scale with the power of the amplified spontaneous emission.

Confinement loss spectral behavior in hollow-core Bragg fibers.

The influence of each cross-section geometric parameter on hollow-core Bragg fiber guiding properties has been numerically investigated. Fabricated fibers have been modeled, giving insight into the spectral behavior of the confinement loss. It has been verified that, by changing the amount of silica and air in the fiber cladding, it is possible to change the reflection conditions undergone by the field within the core, thus shifting the confinement loss spectrum.

Nonlinear polarization rotation in a dispersion-flattened photonic-crystal fiber for ultrawideband (>100 nm) all-optical wavelength conversion of 10 Gbit/s nonreturn-to-zero signals.

We study the conversion bandwidth of the cross-polarization-modulation (XPoIM)-based wavelength conversion scheme with a dispersion-flattened highly nonlinear photonic-crystal fiber for signals with a nonreturn-to-zero (NRZ) modulation format. Both theoretical and experimental results show that the conversion bandwidth can be extended to cover a very wide band, including S-, C-, and L-bands for 10 Gbit/s NRZ signals (a total bandwidth of 120 nm is experimentally demonstrated). We also study the theoretical bandwidth limit for 40 Gbit/s NRZ signals. A significant extension of the conversion bandwidth using the XPoIM approach compared with the four-wave mixing approach previously reported is demonstrated.

Extinction ratio improvement by pump-modulated four-wave mixing in a dispersion-flattened nonlinear photonic crystal fiber.

We demonstrate extinction ratio improvement by using pump-modulated four-wave mixing in a dispersion-flattened nonlinear photonic crystal fiber. A 6-dB improvement in the extinction ratio of a degraded return-to-zero signal has been achieved. A power penalty improvement of 3 dB at 10(-9) bit-error-rate level is obtained in the 10 Gb/s bit-error-rate measurements.

Photonic crystal fiber based evanescent-wave sensor for detection of biomolecules in aqueous solutions.

We demonstrate highly efficient evanescent-wave detection of fluorophore-labeled biomolecules in aqueous solutions positioned in the air holes of the microstructured part of a photonic crystal fiber. The air-suspended silica structures located between three neighboring air holes in the cladding crystal guide light with a large fraction of the optical field penetrating into the sample even at wavelengths in the visible range. An effective interaction length of several centimeters is obtained when a sample volume of less than 1 microL is used.

Birefringence-induced splitting of the zero-dispersion wavelength in nonlinear photonic crystal fibers.

We investigate how the strongly wavelength-dependent birefringence in nonlinear photonic crystal fibers leads to a splitting in the zero-dispersion wavelength for the two polarizations. We translate the requirements for the maximum splitting of the zero-dispersion wavelength to requirements for transverse structural uniformity by adopting a simple effective-index approach in which the birefringence is calculated in a step-index fiber with an elliptical core. We find that to reduce the splitting to less than 1 nm the birefringence should be less than 2 x 10(-5), resulting in a transverse uniformity requirement of 1-3%, depending on the index step from the core to the cladding.

Bandwidth comparison of photonic crystal fibers and conventional single-mode fibers.

We experimentally compare the optical bandwidth of a conventional single-mode fiber (SMF) with 3 different photonic crystal fibers (PCF) all optimized for visible applications. The spectral attenuation, single-turn bend loss, and mode-field diameters (MFD) are measured and the PCF is found to have a significantly larger bandwidth than the SMF for an identical MFD. It is shown how this advantage can be utilized for realizing a larger MFD for the PCF while maintaining a bending resistant fiber.

Predicting macrobending loss for large-mode area photonic crystal fibers.

We report on an easy-to-evaluate expression for the prediction of the bend-loss for a large mode area photonic crystal fiber (PCF) with a triangular air-hole lattice. The expression is based on a recently proposed formulation of the V-parameter for a PCF and contains no free parameters. The validity of the expression is verified experimentally for varying fiber parameters as well as bend radius. The typical deviation between the position of the measured and the predicted bend loss edge is within measurement uncertainty.

Group-theoretical description of the triangular air-silica photonic crystal -out-of-plane propagation.

The method of assigning irreducible representations to modes in three-dimensional photonic structures is applied to the two-dimensional triangular air-silica lattice with out-of-plane wave propagation. In particular prediction of spatial symmetries of the crystal modes is addressed. We show how the photonic bands are affected by different rod radii and out-of-plane components from a group-theoretical point of view. One particular defect mode is analyzed and the structure which is optimal for air-guidance is found.

Analysis of air-guiding photonic bandgap fibers.

We present what is to our knowledge the first theoretical analysis of air-guiding photonic bandgap fibers. The fibers are characterized by a large hollow core and a microstructured cladding exhibiting photonic bandgap effects. Using an efficient, full-vectorial numerical method, we explain the operational principle of the fibers and obtain detailed information about the properties of the air-guided modes. This information includes accurate determination of the modes' spectral extent, cutoff properties, and mode-field distributions.

Silica-air photonic crystal fiber design that permits waveguiding by a true photonic bandgap effect.

A theoretical investigation of a novel type of optical fiber is presented. The operation of the fiber relies entirely on wave guidance through the photonic bandgap effect and not on total internal reflection, thereby distinguishing that fiber from all other known fibers, including recently studied photonic crystal fibers. The novel fiber has a central low-index core region and a cladding consisting of a silica background material with air holes situated within a honeycomb lattice structure. We show the existence of photonic bandgaps for the silica-air cladding structure and demonstrate how light can be guided at the central low-index core region for a well-defined frequency that falls inside the photonic bandgap region of the cladding structure.

Optical electromagnetic vector-field modeling for the accurate analysis of finite diffractive structures of high complexity.

An electromagnetic vector-field model for design of optical components based on the finite-difference time-domain method and radiation integrals is presented. Its ability to predict the optical electromagnetic dynamics in structures with complex material distributions is demonstrated. Theoretical and numerical investigations of finite-length surface-relief structures embedded in polymer dielectric waveguiding materials are presented. The importance of several geometric parameter dependencies is indicated as far-field power distributions are rearranged between diffraction orders. The influences of the variation in grating period, modulation depth, length, and profile are investigated.

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.

Optimal design of single-cladded dispersion-compensating optical fibers.

Specific and simple design relations are presented for different classes of single-cladded optical fibers designed to obtain maximum dispersion compensation. The performance limitations of the different fibers are compared, and the needs for very high refractive-index differences are evaluated.

Improved two-dimensional beam-propagation method for three-dimensional integrated-optical waveguide structures having rectangular-core cross sections.

An optimized effective index method is combined with a two-dimensional beam-propagation method to form an efficient design tool for integrated-optical waveguide structures with rectangular-core cross sections. The accuracy is evaluated by comparisons with the results from a full three-dimensional beam-propagation method.

Scaling laws for integrated optics waveguides.

The accurate design of integrated optical S bends, power splitters, and directional couplers is described through a minimum number of normalized parameters. General design curves showing these normalized parameters for waveguides with a step refractive index profile and a quadratic core cross section are given. Thus a wide variety of integrated optical components may be designed accurately without the use of time-consuming numerical methods.

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.

Maximum gain in optical amplifier-based systems as determined from reflections and backscattering effects.

A simple method for stability investigations of systems with optical amplifiers is presented. Uppergain limits arepredicted for specified reflections and Rayleigh backscattering.