CyberWalk : a web-based distributed virtual walkthrough environment

A distributed virtual walkthrough environment allows users connected to the geometry server to walk through a specific place of interest, without having to travel physically. This place of interest may be a virtual museum, virtual library or virtual university. There are two basic approaches to distribute the virtual environment from the geometry server to the clients, complete replication and on-demand transmission. Although the on-demand transmission approach saves waiting time and optimizes network usage, many technical issues need to be addressed in order for the system to be interactive. CyberWalk is a web-based distributed virtual walkthrough system developed based on the on-demand transmission approach. It achieves the necessary performance with a multiresolution caching mechanism. First, it reduces the model transmission and rendering times by employing a progressive multiresolution modeling technique. Second, it reduces the Internet response time by providing a caching and prefetching mechanism. Third, it allows a client to continue to operate, at least partially, when the Internet is disconnected. The caching mechanism of CyberWalk tries to maintain at least a minimum resolution of the object models in order to provide at least a coarse view of the objects to the viewer. All these features allow CyberWalk to provide sufficient interactivity to the user for virtual walkthrough over the Internet environment. In this paper, we demonstrate the design and implementation of CyberWalk. We investigate the effectiveness of the multiresolution caching mechanism of CyberWalk in supporting virtual walkthrough applications in the Internet environment through numerous experiments, both on the simulation system and on the prototype system

Non-silica microstructured optical fibers for mid-IR supercontinuum generation from 2 µm - 5 µm

We have performed numerical simulations to investigate the optimization of compound glass microstructured optical fibers for mid IR supercontinuum generation beyond the low loss transmission window of silica, using pump wavelengths in the range 1.55-2.25 µm. Large mode area fibers for high powers, and small core fiber designs for low powers, are proposed for a variety of glasses. Modeling results showed that for Bismuth and lead oxide glasses, which have nonlinearities ~10 x that of silica, matching the dispersion profile to the pump wavelength is essential. For chalcogenide glasses, which have much higher nonlinearities, the dispersion profile is less important. The pump pulses have duration of <1 ps, and energy <30 nJ. The fiber lengths required for generating continuum were <40 mm, so the losses of the fibers were not a limiting factor. Compared to planar rib-waveguides or fiber-tapers, microstructured fiber technology has the advantages of greater flexibility for tailoring the dispersion profile over a broad wavelength span, and a much wider possible range of device lengths

A lead silicate holey fiber with γ=1860W^-1km^-1 at 1550nm

We report the fabrication of lead silicate holey fibers with record nonlinearities of up to 1860W-1km-1 at 1.55µm. Broadband supercontinuum generation is obtained in a dispersion optimized fiber variant at ~100pJ pulse energies for 1.06µm pumping