Individual Lightpaths Research Articles

Ray tracing as a supportive tool for interpretation of FBRM signals from spherical particles

Focused beam reflectance measurement (FBRM) is a versatile and frequently used method for in-process particle sizing. The method works with a laser beam eccentrically rotating around a parallel axis, thus describing a circular path which randomly crosses the particles in front of the probe. Chord length distributions (CLDs) are calculated from the durations of the reflected light pulses, which can be related to the particle size. As the reflection signals are strongly biased by the particles' morphology and the optical properties of the particle surface, the obtained distribution profiles are often complex and do not allow direct conclusions on the true particle size. A number of models so far developed for interpretation of CLDs account for the particle shape but they pay little regard to reflective properties. The approach of this study is based on ray tracing, which means that the luminous flux to the particle surface and the light reflected back to the detector is calculated by tracking the individual light paths for several thousand surface elements per particle and iterating this procedure for a huge number of relative detector/particle positions. The model considers three different types of reflection, Lambertian reflection, quasi-specular reflection, and subsurface scattering, which can be combined as required to fit a measured chord length profile. For reasons of simplification the calculations in this study were restricted to spherical particles. The model was shown to be able to simulate the main characteristics of CLDs obtained from three types of monodisperse spheres having different light transmission and surface properties. This simulation helps to explain how the principal features of the complex profiles are co-determined by the three basic types of reflection mentioned above. The model provides a valuable tool particularly for applications in which not only the size of spherical particles but also structural changes with impact on optical properties are monitored by FBRM.

Switching and amplification in disordered lasing resonators

Controlling the flow of energy in a random medium is a research frontier with a wide range of applications. As recently demonstrated, the effect of disorder on the transmission of optical beams may be partially compensated by wavefront shaping, but losing control over individual light paths. Here we demonstrate a novel physical effect whereby energy is spatially and spectrally transferred inside a disordered active medium by the coupling between individual lasing modes. We show that it is possible to transmit an optical resonance to a remote point by employing specific control over optical excitations, obtaining a random lasing system, which acts both as a switch and as an amplifier.

P-Cycle protection at the glass fiber level

The cost and complexity of wavelength assignment, wavelength conversion and wavelength-selective switching are always of primary considerations in the design of survivable optical networks. This proposal recognizes that as long as the loss budgets are adequate, entire DWDM wavebands could be restored with no switching or manipulation of individual lightpaths; so that the DWDM layer would never know the break happened. And environments where fiber switching devices are low cost, and ducts are full of dark fibers provide a very low cost alternative to protect an entire DWDM transport layer (or working capacity envelope) against the single largest cause of outage. Yet, while nodes and single DWDM channels may fail, a pre-dominant source of unavailability is the physical damage of optical cables. Thus, with the objectives of reducing the overall real CapEx costs and removing the complexity due to wavelength assignment and wavelength continuity constraints when configuring p-cycles in a fully transparent network context, this paper addresses the subsequent questions: if it is ultimately glass that fails, what if just the glass is directly replaced? More specifically, what if p-cycles were used to rapidly, simply and efficiently provide for the direct replacement of failed fiber sections with whole replacement fibers?

Density‐based Outlier Rejection in Monte Carlo Rendering

AbstractThe problem of noise in Monte‐Carlo rendering arising from estimator variance is well‐known and well‐studied. In this work, we concentrate on identifying individual light paths as outliers that lead to significant spikes of noise and represent a challenge for existing filtering methods. Most noise‐reduction methods, such as importance sampling and stratification, attempt to generate samples that are expected a priori to have lower variance, but do not take into account actual sample values. While these methods are essential to decrease overall noise, we show that filtering samples a posteriori allows for greater reduction of spiked noise. In particular, given evaluated sample values, outliers can be identified and removed. Conforming with conventions in statistics, we emphasize that the term “outlier” should not be taken as synonymous with “incorrect”, but as referring to samples that distort the empirically‐observed distribution of energy relative to the true underlying distribution. By expressing a path distribution in joint image and color space, we show how outliers can be characterized by their density across the set of all nearby paths in this space. We show that removing these outliers leads to significant improvements in rendering quality.

A Theory of Refractive and Specular 3D Shape by Light-Path Triangulation

We investigate the feasibility of reconstructing an arbitrarily-shaped specular scene (refractive or mirror-like) from one or more viewpoints. By reducing shape recovery to the problem of reconstructing individual 3D light paths that cross the image plane, we obtain three key results. First, we show how to compute the depth map of a specular scene from a single viewpoint, when the scene redirects incoming light just once. Second, for scenes where incoming light undergoes two refractions or reflections, we show that three viewpoints are sufficient to enable reconstruction in the general case. Third, we show that it is impossible to reconstruct individual light paths when light is redirected more than twice. Our analysis assumes that, for every point on the image plane, we know at least one 3D point on its light path. This leads to reconstruction algorithms that rely on an “environment matting” procedure to establish pixel-to-point correspondences along a light path. Preliminary results for a variety of scenes (mirror, glass, etc.) are also presented.

Optical dynamic intelligent network services (ODIN): an experimental control-plane architecture for high-performance distributed environments based on dynamic lightpath provisioning

Currently, many large-scale, resource-intensive applications and services are being developed that can be supported only with high-performance, highly distributed, heterogeneous infrastructures, including grids. This type of infrastructure is particularly effective for supporting applications and services that must quickly adjust to continuously changing conditions. Such processes require the flexibility of highly adaptive, dynamic, and deterministic resource provisioning. One such architecture is described here. To enhance the performance and flexibility of distributed environments, an experimental architecture for optical dynamic intelligent network (ODIN) services has been designed to enable core optical network capabilities to extend to edge processes, including applications. This architecture allows those processes to directly address arid control core network resources, for example, individual lightpaths on demand. This approach supports flexible and deterministic communications by integrating signaled requirements with adjustable network resources. An experimental prototype of ODIN has been designed, developed, and implemented on several optical network testbeds.