J.H. den Besten

Integrated two-state AWG-based multiwavelength laser

An integrated InP-InGaAsP two-state coupled-laser device for use in optical packet switching and signal processing is presented. The two states are identified by distinct lasing wavelengths. Single-mode lasing occurs in both states and the contrast ratio between the two states is 35 dB. Switching between states with optical pulses is demonstrated. The use of an arrayed waveguide grating (AWG) and ring laser configuration permits monolithic integration without the need for cleaved facets. How the AWG can be used to obtain partial isolation between multiple interconnected devices is also discussed.

Low-loss, compact, and polarization independent PHASAR demultiplexer fabricated by using a double-etch process

A compact low-loss polarization independent 8 /spl times/ 8 PHASAR demultiplexer is presented. Device size is 0.93 /spl times/ 0.75 mm/sup 2/. On-chip losses are less than 4 dB and crosstalk is better than -20 dB. The device is suitable for integration with electro-optical switches for application in integrated optical crossconnects, add-drop multiplexers and multiwavelength lasers.

Coupled Mach–Zehnder interferometer memory element

Two active Mach-Zehnder interferometers are integrated in a monolithic InP/InGaAsP photonic integrated circuit. Together they form a crucial component for optical signal processing: an optical memory element or set-reset flip-flop. The switching time for this initial device is approximately 200 ps. The photonic integrated circuit contains active and passive optical components, including electro-optic phase shifters.

Monolithically integrated 80-gb/s AWG-based all-optical wavelength converter

We present a monolithically integrated all-optical wavelength converter. The converter consists of four semiconductor optical amplifiers for four separate inputs and an arrayed-waveguide grating. Error-free wavelength conversion with reasonable penalties for a 27 -1 pseudorandom binary sequence was shown for a single input 80-Gb/s signal. The device exploits cross-gain/phase modulation in a single amplifier and selects with a filter the blue-chirped spectrum of the new wavelength signal in order to speed up the device response. This device has a dimension of 1.7times3.5 mm2 and it can be operated to convert simultaneously four 80-Gb/s wavelength channels

Ultrafast All-Optical Wavelength Routing of Data Packets Utilizing an SOA-Based Wavelength Converter and a Monolithically Integrated Optical Flip–Flop

We demonstrate all-optical wavelength routing of 80 Gb/s data packets without using electronic control. The system consists of an optical wavelength converter and a monolithically integrated optical flip-flop memory. The integrated optical flip-flop is based on two coupled lasers, exhibiting single-mode operation, having a 35 dB contrast ratio between the states, and switching its state in about 2 ns. The wavelength converter is optically controlled by the optical flip-flop. We show that the optical set and reset pulses can force the optical flip-flop to switch its continuous-wave output light between two specific wavelength positions. The output light feeds the wavelength converter, which, in turn, converts the data packet into the flip-flops output wavelength, causing the data packet to be routed into a specific port.

Validation of the corrected Dang Van multiaxial fatigue criterion applied to turret bearings of FPSO offloading buoys

ABSTRACT In engineering practice, multiaxial fatigue analyses are often avoided due to their complexity and computational intensity. However, damages have been encountered in turret bearings of Floating Production Storage and Offloading vessel (FPSO) offloading buoys which were likely caused by multiaxial fatigue. The Dang Van criterion has often been used to assess problems with multiaxial fatigue in rolling contacts. Therefore, this study set out to validate the application of the Dang Van criterion to turret bearings of FPSO offloading buoys. For this purpose, the criterion was corrected with a horizontal conservative locus for compressive hydrostatic stresses. Three load cases were identified based on the seakeeping analysis of an FPSO offloading buoy equipped with a wheel-rail turret bearing. For each load case, the surface pressure distribution and sub-surface stress states were determined analytically. Staircase tests were used to determine the characteristic parameters (α and β) of the Dang Van curve. Then, the Dang Van criterion was corrected and used to perform a multiaxial fatigue analysis in the critically stressed area of the wheel-rail contact. Finally, full-scale, long-duration fatigue tests were used to validate the results. The corrected Dang Van criterion shows agreement with the experimental results and is not rejected as multiaxial fatigue criterion for application to turret bearings in FPSO offloading buoys.

Comparative study of multiaxial fatigue methods applied to welded joints in marine structures

Marine structures are particularly prone to action of waves, winds and currents with stochastically varying composition, intensities and directions. Therefore, resultant stresses may cause multiaxial fatigue in specific welded structural details. For the assessment of multiaxial fatigue in welded joints, a wide variety of methods have been suggested. However, there is still no consensus on a method which can correctly account for non-proportional and variable amplitude loading. This paper beholds a comparative study of multiaxial fatigue methods applicable for design of marine structures. For the purpose of comparison several load cases were defined including non-proportional and variable amplitude loadings with different normal and shear stress amplitude ratios. Three types of methods are compared: those described by three different codes (i.e. Eurocode 3, IIW and DNV-GL), those described by three different multiaxial fatigue approaches from literature (i.e. Modified Carpinteri-Spagnoli Criterion, Modified Wohler Curve Method and Effective Equivalent Stress Hypothesis) and an approach based on Path-Dependent-Maximum-Range multiaxial cycle counting. From this study it has been concluded that non-proportional variable amplitude loading has a significant negative impact on the fatigue lifetime estimates, and that further research and experimental testing are essential to come to a consensus.

Photonic true-time delay beamformer for broadband wireless access networks at 40 GHz band

The design parameters, sensitivity analysis and time delay measurements of a photonic true-time delay beamformer for broadband adaptive wireless access networks in the 40 GHz band are presented. The beamforming is achieved by using a multiwavelength laser in combination with a digital delay line based on optical switches and dispersive fibers.

All Optical Packet Switching above 80 Gb/s

All-optical packet switching is discussed. In particular, we focus on the utilisation of monolithically integrated building to achieve high-bit-rate operation.

Multiaxial fatigue assessment of welded joints in marine structures

Structural geometry and stochastic loads such as swell and wind seas can typically induce multiaxial stress states in welded details of marine structures. It is known that such complex time varying stress states determine the fatigue resistance of welded steel joints. Therefore, it is of importance to account for them in fatigue lifetime estimation. Over the past few decades a wide variety of design guidelines and methods have been developed for multiaxial fatigue assessment, but so far there does not exist a general hypothesis applicable to all possible load cases. This study provides an overview of the current state-ofthe-art in academia and engineering practice in terms of multiaxial fatigue assessment, and is focusing on the application to welded joints in marine structures. The progress of different approaches and methods is elaborated and commented upon, taking their hypothesis and (physical) basis into consideration. The insights that are provided in this paper form a valuable foundation for future investigations and emphasize the necessity of experimental proofs and model validation.