Winfried Bernhard

High-performance low-cost fabrication method for integrated polymer optical devices

For all optical path networks there is a need for optical crossconnect systems and switching matrices. Using polymer materials and technologies, not only low cost components but low power consumption devices can be fabricated. We optimize ORMOCERs, a new class of polymer materials, which combine the specific advantages of organic polymers and inorganic glasses, with respect to the need of photonic applications. They exhibit a high thermal stability of up to 250 degrees C and a low optical attenuation of 0.2 dB/cm at 1.3 micrometers and 0.4 dB/cm at 1.55 micrometers .

Cross talk reduction in switching networks by asymmetrical off-on switches

A new off-on switching scheme is introduced which blocks a waveguide path in the passive off-state and transmits the signal in the active on-state. The operating principle is based on the self-diffraction of a narrow guided beam when it escapes from a waveguide with two dimensional confinement into a region of appropriate length with at most one dimensional confinement. In particular a remaining interface of the initial waveguide superimposes reflection, which in sum results in a very efficient asymmetrical blow out of the guided power. In the active on-state, low-loss waveguiding is sustained when an electrode causes an appropriate refractive index change, e.g. due to the thermo-optical effect. Thus the signal is received in the output waveguide, an identical pendant of the input guide. The switching behavior is almost digital, and the wavelength dependence is minimal only. This makes the device useful for switching and modulation in a multi-wavelength optical network. Calculations show on-off signal ratios of better than 30 dB e.g. in polymeric waveguide configuration of 3 mm length. This is nicely adapted to the demands of crosstalk reduction in switching networks. Experimental results from a thermo-optic polymer waveguide device with 32 dB off-state attenuation and 0.8 dB on-state excess loss fit well to the data obtained from the numerical modeling.

Reliability of micromachined membranes under particle impact

We report experimental and numerical results on the mechanical reliability of silicon nitride membranes under particle impact. Over 1000 membranes of various geometries were subjected to controlled particle bombardment leading to their failure. Based on the statistical analysis of the characteristic times to failure /spl tau/ and their dependence on geometry, on the optical failure analysis, and on numerical simulations of impact events, the following conclusions are drawn: failure is due to a singular event as opposed to fatigue, failure is caused by impacts close to the membrane edge, the absolute distance of the impact point to the nearest edge is the dominant factor, the characteristic lifetime /spl tau/ is inversely proportional to the perimeter length, reinforcing the membrane perimeter secures an up to tenfold increase in lifetime.

Optimized design and fabrication of integrated optic 1x32 and 2x32 multifunnel power splitters in polymer

We present the optimized design and the fabrication of an integrated-optic 1 by 32 multifunnel power splitter and the extension to a 2 by 32 splitter of the same type which we are the first to report. This splitter type operates by receiving the radiated input power at the end of a slab waveguide by funnel shaped waveguides of increasing width to compensate for the power decrease towards the outer parts. Using cycle of BPM simulation and adapting the width of the receiver waveguides according to the calculated intensity distribution we achieved a maximum excess loss of 0.5 dB in the simulation. The 2 by 32 splitter was designed using two input waveguides placed symmetrically 8 micrometers off-center and facing the center of the receiver region. Both splitters were fabricated by UV exposure of PMMA with photo initiator BDK. The realized 1 by 32 splitter shows an excess loss of 0.7 dB compared to a reference waveguide and a standard deviation of 0.5 dB with a maximum loss of 1.8 dB at (lambda) equals 1320 nm, the 2 by 32 splitter has 1.3 dB excess loss, 0.8 dB standard deviation and 2.5 dB maximum loss.