375 research outputs found
Optical coupling and optoelectronics integration studied on demonstrator for optical interconnects on board
Towards Low Cost Coupling Structures for Short-Distance Optical Interconnections
The performance of short distance optical interconnections in general relies
very strongly on coupling structures, since they will determine the overall
efficiency of the system to a large extent. Different configurations can be
considered and a variety of manufacturing technologies can be used. We present
two different discrete and two different integrated coupling components which
can be used to deflect the light beam over 90 degrees and can play a crucial
role when integrating optical interconnections in printed circuit boards. The
fabrication process of the different coupling structures is discussed and
experimental results are shown. The main characteristics of the coupling
structures are given. The main advantages and disadvantages of the different
components are discussed
Opto-PCB: Three demonstrators for optical interconnections
We report on a research project targeting optical waveguide integrated PCBs conducted within the European FP6
Network of Excellence on Micro-Optics NEMO. For three identified feature requests we have built three specific demonstrators
respectively addressing the integration of active components, the fabrication of peripheral fibre ribbons and the integration of
multiple layers of waveguides on the board
Determination of the radial profile of the photoelastic coefficient of plastic optical fibers
We developed a measurement method to determine the radial distribution of the photoelastic coefficient C(r) in step-index polymer optical fibers (POFs). The method is based on the measurement of the retardance profile of a transversally illuminated fiber for increasing tensile load. The radial profile C(r) is obtained from the inverse Abel transform of this retardance profile. We measured polymer fibers from different manufacturers. The radial profile of the photoelastic constant can considerable vary depending on the type and treatment of POFs, even when made from similar materials, which leads to the conclusion that the photoelastic constant should be characterized for each different type of POF. The impact of annealing the fiber samples on C(r) is also addressed
Fatigue crack behaviour: comparing three-point bend test and wedge splitting test data on vibrated concrete using Paris' law
The fatigue behaviour of concrete has become more important for the design of constructions due to the desire to build slimmer structures, which are more sensitive to fatigue loading. This article aims to evaluate and compare the fatigue crack propagation rate in vibrated concrete for four different stress ratios using the Paris-Erdogan law. The data evaluation in this article is based on crack mouth opening displacement (CMOD) measurements from cyclic three-point bending tests on single edge notched beams and from wedge splitting tests on notched cubes, obtained from experiments at Ghent University. For this study, finite element analysis is used to obtain a mathematical relationship between the CMOD and the relative crack length a/W, as well as a relationship between the stress intensity ratio ?K and a/W. The obtained mathematical relationships were then combined with the measured CMOD values to correlate the test data to the Paris- Erdogan law. Herein, the crack propagation rate da/dN is plotted against the corresponding stress intensity range ?K in a log-log graph. In a final step, the Paris-Erdogan law parameters C and m were obtained through linear curve fitting on the data points from the obtained graphs. The parameters C and m are then used to compare and evaluate the fatigue crack behavior in vibrated concrete, and the differences between the results from the three-point bend tests and wedge splitting tests
Deterministic polarization chaos from a laser diode
Fifty years after the invention of the laser diode and fourty years after the
report of the butterfly effect - i.e. the unpredictability of deterministic
chaos, it is said that a laser diode behaves like a damped nonlinear
oscillator. Hence no chaos can be generated unless with additional forcing or
parameter modulation. Here we report the first counter-example of a
free-running laser diode generating chaos. The underlying physics is a
nonlinear coupling between two elliptically polarized modes in a
vertical-cavity surface-emitting laser. We identify chaos in experimental
time-series and show theoretically the bifurcations leading to single- and
double-scroll attractors with characteristics similar to Lorenz chaos. The
reported polarization chaos resembles at first sight a noise-driven mode
hopping but shows opposite statistical properties. Our findings open up new
research areas that combine the high speed performances of microcavity lasers
with controllable and integrated sources of optical chaos.Comment: 13 pages, 5 figure
- …