Reinhard Dr. März

Results of benchmark tests for different numerical BPM algorithms

Some key results of a benchmark test, initiated in 1992 by the Working Group 2 of COST Project 240 at a modelling workshop in Teupitz, Germany, are presented. A great number of BPM algorithms, such as the FTBPM, various types of FDBPMs, wide angle approximations and adaptive FE-BPM are compared. The quasi-analytic character of the benchmark tests gains a deeper insight into the absolute accuracy. >

8-channel optical demultiplexer realized as SiO/sub 2//Si flat-field spectrograph

The operation of a flat-field spectrograph in silica on silicon (SiO/sub 2//Si) for 2-nm channel spacing is demonstrated. Crosstalk attenuations of >20 dB and significantly reduced fiber-to-fiber insertion losses of 5 dB could be obtained.<<ETX>>

On the theory of planar spectrographs

The theory of planar spectrographs is presented. It is proven that by no means all aberrations up to the order of x/sup 4/ can be corrected over a finite spectral range. A general procedure to construct gratings with two stigmatic points of (nearly) arbitrary wavelength and location is proposed. Rowland-type and flatfield spectrographs are discussed as numerical examples. >

Wavelength-adaptable optical phased array in SiO/sub 2/-Si

An optical phased array in the silica-on-silicon material system (SiO/sub 2/-Si) with 8-nm channel spacing in the 1.5-/spl mu/m wavelength region is reported. The device exhibits quasi-polarization independent operation with insertion losses of 2.5-3 dB and crosstalk attenuations of >20 dB. It can be adapted to the specified center wavelength simultaneously with the adjustment of the input fiber.<<ETX>>

Bragg gratings on InGaAsP/InP waveguides as polarization independent optical filters

The fabrication and operation of Bragg gratings for future wavelength-division multiplexing (WDM) devices in integrated optical circuits are discussed. Crosstalk attenuation of more than 20 dB with respect to the optical power and spectral bandwidths of up to 2.2 nm were achieved. Polarization-independent operation of the gratings, an important qualification for their operation in fiber optical transmission systems, was demonstrated with a filter bandwidth of 0.2 nm at -10 dB and channel spacings as small as 1 nm. >

Monolithically integrated detector chip for a two-channel unidirectional WDM link at 1.5 mu m

The fabrication and operation of a monolithically integrated InGaASP/InP wavelength division multiplexing (WDM) detector chip is reported. It consists of a Y-branch grating demultiplexer and two p-i-n photodiodes. Polarization-independent operation for two closely spaced channels ( Delta lambda =3.6 nm) at lambda =1.5 mu m was obtained. In polarization-independent operation, 1.3-mm-long Bragg gratings on buried waveguides showed a peak crosstalk attenuation of 15 dB and a stop bandwidth of 0.2 nm at -10 dB. These values show the high potential of Bragg grating devices for dense wavelength division multiplexing applications. The static electrical properties of the monolithically integrated p-i-n photodiodes (dark current of 2-5 nA at -10 V, breakdown voltage of 45-65 at a 10 mu A leakage current) approach the values obtained for discrete devices. The bandwidth of 420 MHz enables operation in the 600-Mbaud region. The external quantum efficiency of the complete detector chip ( eta =0.08) is still rather small. However, it could be considered sufficient for the operation of such devices in local networks with distances of a few kilometers. >

Investigation of Bragg gratings on planar InGaAsP/InP waveguides at normal and oblique incidence

The polarization-dependent mode coupling of Bragg gratings on planar InGaAsP/InP waveguides is investigated by transmittance and reflectance measurements at normal and oblique incidence in the 1.5- mu m wavelength region. Strong coupling between TE (transverse electric) and TM (transverse magnetic) modes is observed at oblique incident, whereas the TE-TE coupling vanishes at an incidence angle of 45 degrees . The behavior of the near field close to the Bragg wavelength and the effects of radiation into the substrate are analyzed. It is experimentally shown that small deformations of the phase fronts on the input side lead to strong interference effects on the output side. >

Yield and cost model for integrated optical chips

A yield and cost model for integrated optical chips is presented on the basis of easily attainable figures. It allows a prediction to be made of yield and cost for complex optical chips on the basis of currently available processing technology. Both yield and cost area of calculated in absolute terms but in comparison with a simple reference chip from the production line. The model can already be applied when a chip is at an early phase of development, i.e., at the planning stage.

On the reference wave vector of paraxial Helmholtz equations

The reference wave vector for both scalar and vectorial formulations of the paraxial Helmholtz equation is determined by using various strategies which aim at the optimization of different features of the approximated solution. It turns out that all optimization schemes yield similar results, i.e., an overall optimization of the paraxial Helmholtz equation. A detailed analysis of a benchmark example shows that the reference wave vector must be adapted continuously during beam propagation. However, the required evaluation is so efficient that the additional numerical effort can be neglected.

A comparison between finite element calculations and experimental results on InGaAsP/InP waveguides

Calculated and measured properties of InGaAsP/InP waveguides are compared. The spectral response of Bragg gratings was used to measure precisely the effective indexes of the guided modes of InGaAsP/InP waveguides. The shape of the near fields and the effective refractive indexes of waveguides, which support more than one guided mode, show an excellent agreement between theory and experiment. It is shown that rigorous calculation methods such as the finite-element method can be used to predict exactly the optical properties of integrated devices. >