Peter Vetter

Control of Liquid Crystal Alignment Using Stamped-Morphology Method

We propose a new method to align liquid crystals using microgrooves that are fabricated by a stamping process. This rubless alignment method has the advantage of accurate control of the pretilt angle and azimuthal surface anchoring energy by means of changing the surface morphology. In this paper we discuss the control of the pretilt angle and the azimuthal surface anchoring energy in detail.

Study of Memory Alignment of Nematic Liquid Crystals on Polyvinyl Alcohol Coatings

Polymer layers can cause memory alignment of nematic liquid crystals. We describe an experimental method to characterize this effect. We studied the temperature dependence of the memory alignment on polyvinyl alcohol coatings. We also investigated the influence of the time span during which the memory alignment is generated. We propose an adsorption-desorption mechanism by which we can explain our observations in a reasonable way.

Orientation of Polymer Molecules in Rubbed Alignment Layer and Surface Anchoring of Liquid Crystals

In order to better understand liquid crystal alignment on a rubbed polymer surface, the authors investigated the relationship between the orientation of polymer molecules and the surface anchoring strength of liquid crystals on a rubbed surface. Measuring the IR-absorption and the optical retardation, it was found that the polymer molecules were oriented parallel to the rubbing direction. The order of molecular orientation in the polymer and the surface anchoring strength of liquid crystal both increased with the rubbing strength.

Determination of Molecular Inclination in Rubbed Polymer for Liquid Crystal Alignment by Measuring Retardation

Liquid crystal molecules on a rubbed polymer alignment layer are aligned at some polar angle away from the surface, but the physical reason for this pretilt is not yet clearly understood. In our research, we have developed a new method to determine the tilted direction of the polymer by a precise measurement of the optical retardation using Senarmont ellipsometry. Using this method, we also studied the tilt angle of the polymer molecules near the surface of a side-chain polymer layer as a function of the rubbing strength and compared the pretilt angle of the liquid crystal to the tilted direction of the polymer.

Architectures for 100-km 2048 split bidirectional SuperPONs from ACTS-PLANET

This paper presents different architectures for high split, wide range bidirectional SuperPONs.One of the ways to achieve such SuperPONs is by the introduction of erbium- doped-fiber-amplifiers or semiconductor optical amplifiers (SOA) in order to overcome the strongly increased power budgets in comparison to conventional PONs. This will however present new challenges in overcoming the noise- funneling effect caused by the parallel amplifiers. Four different approaches are studied: 1) using of on/off switchable semiconductor optical amplifiers, 2) using parallel erbium-doped-fiber amplifiers, 3) using electro- optic regeneration, and 4) using conventional SDH, ATM and APON technology. A description is given of each architecture, including advantages and drawbacks. These architectures serve as input to further studies performed by the ACTS-PLANET consortium. The power-budget studies showed that it is technically feasible to develop a SuperPON with a 2048 split and a 70-100 km range.

Wide-viewing-angle display mode for active-matrix LCDs using a bend-alignment liquid-crystal cell

Abstract— The display quality of active-matrix LCDs has been greatly improved. However, the problem of narrow viewing angle has not yet been sufficiently solved. In order to solve this problem, a new LCD comprised of a bend-alignment LCD cell with an optical compensator was designed. The improvement is shown by theoretical and experimental analysis.

Demonstration of extended split APON

An end-to-end data link was demonstrated on an ATM passive optical networks (APON) with extended splitting factor of 128 and 256. The measurements show that the transparent solution can regroup PONs to a split of 128 and 256 on the condition of the optical network units having a limited maximal distance of, for example, 10 km. This solution reuses the standard APON IT hardware. We have also demonstrated that the hardware upgrade solution achieves PON topologies with an extended split of 128 and 256. The critical required increase in upstream sensitivity is offered by the combination of the APD-based burst mode receiver with the low loss combiner.

Multichannel optical modules compatible with the fiber-in-board technology

Fiber-in-board technology offers a full solution for high-speed parallel interconnections. Packaging techniques compatible with this board technology have been realized. Two different solutions are presented for the fiber alignment in the module. The first technique is based on a silicon board bench with etched V-grooves and thermo compression flip-chip bonding. The second technique is based on a vacuum pick-up tool, capable of handling 16 multimode fibers. A dedicated alignment piece has been developed for interfacing the fibers towards the optical contact in the board. For the realization of electrical interconnections inside the module, three different substrate technologies are evaluated. First, prototypes were elaborated in a thin-film technology. For the electrical interface of the silicon motherboard a standard thick-film technology was used. A novel thick-film technology based on the FODEL/sup TM/ material, which offers high density interconnection capabilities, was used for the development of an alternative packaging technique. The different modules were tested and integrated in a system demonstrator. Four parallel on-board optical links were operational at 311 Mb/s. The speed was limited by the receiver electronics, which were designed for operation at 155 Mb/s.

Parallel optical interconnections for future broad band systems, based on the "fibre in board technology"

A novel interconnection technology based on the integration of glass optical fibres in a standard printed circuit board is presented to overcome the interconnection bottleneck in the nest generation of broad band switching fabrics. Within these systems, the parallel electro-optical modules will be: integrated on the switching board itself which has a switching capacity of 20 Gbit/s. A robust and automated technology is used for the realisation of optical interconnections between these electro-optical (E/O) modules and the off-board connectors at the edge of the board. Dedicated surface optical contacts have been developed, capable of handling 16 parallel channels. These surface optical contacts can be integrated everywhere on the board and can be used for mounting an electro-optical module or a multifibre connector compatible with this technology. Electro-optical modules (8 channel transmitters and 4 channel receivers) and multifibre optical back panel connectors have been integrated on an engineering prototype for the evaluation of the technology. Off-board links, over 200 m MM (graded index) fibre, and on-board links are operational at 622 Mbit/s. The boards have been subjected to reliability tests and preliminary results reveal no degradation of the board after thermal cycling. Precision moulding techniques are presented to make the proposed technology more cost-effective and suitable for volume production.

Efficient control of ATM traffic accessing broadband core networks via SuperPONs

Passive Optical Networks offer quite promising results in terms of cost, robustness, flexibility and traffic concentration. The addition of Optical Amplifiers, overcame the optical budget limitations of fully passive first generation technology, enabling the extension of the PONs to up to 15000 subscribers and a 100 km distance, creating the concept of SuperPONs currently at the development stage. The larger round trip delay, as well as the high number of subscribers, coupled with the strict traffic control dictates of ATM, create very complex traffic control and management problems but at the same time open the prospects of high multiplexing gain by aggregating many relatively small connections on a shared feeder. Novel solutions are required since the tree topology and the shared feeder create new problems not encountered in non-distributed multiplexers/concentrators. Methods to resolve the VPI/VCI conflicts on the shared medium, support OAM, ensure privacy and security, police the entry to the system, and the traffic engineering issues, are the focal points of this paper.