Ottokar Leminger

Determination of single-mode fiber coupler design parameters from loss measurements

A method is presented for determining the minimum spacing between the fiber core centers in a single-mode fiber coupler which consists of two substrate blocks each provided with a fiber fixed in a curved groove. Immersion liquids with known refractive indices are placed on the top surface of one coupler block and the introduced power loss of the light guided within the fiber is measured. By fitting these results to calculated curves the minimum spacing may be determined with an error of less than 0.2 μm.

Wavelength-selective directional coupler made of nonidentical single-mode fibers

Low-loss asymmetrical single-mode fiber directional couplers applicable to WDM between transmission channels at 1300 and 1500 nm have been constructed. The crossover wavelength of these couplers can be tuned by a suitable intermediate layer. Theoretical calculations show that fiber multiplexers with channel spacings less than 20 nm Can be fabricated.

Determination of the variable core-to-surface spacing of single-mode fiber-coupler blocks.

A description is given of a method for exact determination of the variable core-to-surface spacing along the polished region of single-mode fiber-coupler blocks. It is based on throughput attenuation measurements made while covering the block surface gradually by a liquid with a known refractive index. Examples of the validity of the technique are given.

Narrow-band wavelength-selective directional couplers made of dissimilar single-mode fibers

Asymmetrical wavelength-selective fiber couplers with a bandwidth of 22.5 nm have been constructed and investigated. The special shapes of the measured sidelobes in the power transmission characteristics are explained by the bending profiles of the fibers.

Wave-vector diagrams for two-dimensional photonic crystals

Photonic crystals exhibit band gaps, meaning that electromagnetic fields cannot propagate in them for specific ranges of wavelengths and directions. The calculation of band structure diagrams has been intensively studied and is now well understood. In contrast to that, so-called wave-vector diagrams (i.e. dispersion surfaces, depicting the loci of all relevant wave vectors at a fixed wavelength) are less known and used. In principle, they show how the effective index of the structure depends on the direction of propagation. A method to calculate explicitly wave-vector diagrams for two-dimensional photonic crystals is derived which leads finally to quadratic eigenvalue problems. Results for square and triangular lattices are presented and some applications are discussed.

Narrow-band directional couplers made of dissimilar single-mode fibers with different cladding refractive indexes

A wavelength-selective directional coupler, consisting of two polished single-mode fibers with different cladding refractive indexed, has been fabricated. In contrast to symmetrical couplers, where the power transfer characteristic is a quasiperiodic function of the wavelength, couplers made of dissimilar fibers show a true bandpass-filter characteristic. They consist of two fibers with different core diameters and refractive-index profiles, having the same cladding refractive index. The parameters of the fibers must be chosen in such a way that if their propagation constants beta /sub 1/, beta /sub 2/ are plotted over the wavelength, the curves intersect at a cross-over wavelength lambda /sub 0/ equal to the center wavelength of the filter. The 3-dB bandwidth of the couplers power transfer characteristic is 13.6 nm, the best value achieved up to now. >

Tunable wavelength-selective asymmetrical single-mode fibre directional couplers with an intermediate layer

The power-transfer function of asymmetrical directional couplers consisting of two polished single-mode fibres with different core diameters and refractive-index differences has a band-pass behaviour over the wavelength. The fixed centre wavelength of the bandpass is determined by the fibre parameters only. Theoretical calculations show that, by inserting an intermediate dielectric layer with suitable thickness and shape between the fibres, the centre wavelength can be shifted easily over a range of ±30 nm. Experimental results are in good agreement with theory.

Principles of dispersion engineering in photonic crystal devices

Wave propagation in Photonic Crystal Fibers is known for revealing very strong chromatic dispersion characteristics despite the waves being confined in the direction along the fiber axes. 2D and 3D photonic crystal devices offer even more degrees of freedom, as the angular dispersion of the propagating waves can be additionally included into the design. We present the basic principles which can be used for tailoring the overall dispersion characteristics of a single photonic crystal device and of combinations of different structures. Precise calculations and simulations are required in order to obtain reliable information on the dispersion parameters including also higher-order terms. Thus our calculations are based on the propagation of Gaussian beams.

Narrowband directional couplers made of dissimilar single-mode fibers with different cladding refractive indices

En utilisant des fibres a differents indices de refraction de revetement, on fabrique un coupleur selectif a largeur de bande 13,6 nm a 3 dB

Narrow-Band Optical Grating Filters Made Of Glass Channel Waveguides

ABSTRACTThe performance of optical grating filters, using ion -exchanged channel waveguides inglass covered with a dielectric grating quarter -wave resonator, is investigated theoret- ically and experimentally. For the transmission resonance peak of the filter a bandwidth of about 10 GHz has been obtained. 1. INTRODUCTIONNarrow -band optical filters are key components in closely spaced wavelength- division- multiplexed fibre networks. Grating structures, as for example periodically corrugateddielectric waveguides, have been proposed for that purpose and can act as reflection fil- ters. Their stop -band can be tailored by proper dimensioning of the grating structure. It is often desirable to use filters operating in transmission. In order to achieve this, the grating must consist of two parts with a spatial phase shift of 1C between them (grating resonator filter). Then a narrow transmission peak in the filter frequency re- sponse can be obtained.In this paper, we report on the performance of single -mode ion - exchanged channel wave -