Pulse trains with only 2 ps in width and low root-mean-square timing jitter of 220 fs are demonstrated from fine tunable monolithic 40-GHz laser integrated circuits on GaInAsP-InP. The repetition rate is tunable within 500 MHz by changing only the gain current and the absorber voltage. Simultaneously, the small pulsewidths are kept constant and the timing jitter remains below 300 fs. The determined time-bandwidth products between 0.37 and 0.5 are close to the transform limit and the fiber coupled optical power is >or=1 mW. The fact that pulsewidth and timing jitter remain small over the whole repetition-rate tuning range constitutes an important step toward economic commercial applications, especially if frequency shifts caused by fabrication tolerances have to be compensated
Articles you may be interested inOptimum phase noise reduction and repetition rate tuning in quantum-dot mode-locked lasers Appl. Phys. Lett.
Urbanization becomes increasingly important in our modern life. This is undoubtedly a huge opportunity and challenge for construction industry. More and more bridges are constructed to improve the infrastructure and develop the economy. For more than a century, reinforced concrete bridges are the most common bridges due to its durability, relatively low maintenance cost and rapid construction. In general, concrete bridges are designed to ensure a service life of at least 100 years. However, mechanical and environmental factors or excessive use accelerate the deterioration of the bridges. Some bridges even failed in their early-life. Thus, we are faced with the necessity to monitor health condition of bridges at every moment during their life which is also the aim of Structure Health Monitoring (SHM). Most deterioration and failure mechanisms are connected to the development of micro-or macro-cracks. Ultrasonic Coda Wave Interferometry (CWI) method using diffuse wave is one of the most promising method to detect subtle changes and cracking in heterogeneous materials such as concrete. Moreover, the data acquisition system has a high portability and the size of data recorded is small. If needed, even real-time assessment can be performed with an optimized algorithm. Embedded ultrasonic sensors can be installed inside the structure to avoid changes in coupling or excess influence of environmental influence factors. The measurements will focus more on the internal of the structure. Research shows that CWI has high sensitivity in detecting temperature change, stress variation and cracks in laboratory size concrete specimens. A young reinforced concrete road bridge in Gliwice, Poland has been monitored in a first step. Results have shown that the bridge is in good condition. However, the method has so far not been implemented on existing middle-aged bridge. In this paper, the monitoring of a 46 years old reinforced concrete road bridge close to Cologne, Germany will be discussed. Multiple sensors (thermocouples, strain gages and embedded ultrasonic sensors) were installed in the bridge. The bridge will be monitored for at least one month and subjected to a load test. As a result, the influence of temperature should be detected and quantified and a diagnosis of the bridge condition (especially changes in cracks) should be established.
Low-frequency ultrasonic testing is a well-established non-destructive testing (NDT) method in civil engineering for material characterization and the localization of cracks, reinforcing bars and delamination. A novel ultrasonic borehole probe is developed for in situ quality assurance of sealing structures in radioactive waste repositories using existing research boreholes. The aim is to examine the sealing structures made of salt concrete for any possible cracks and delamination and to localize built-in components. A prototype has been developed using 12 individual horizontal dry point contact (DPC) shear wave transducers separated by equidistant transmitter/receiver arrays. The probe is equipped with a commercially available portable ultrasonic flaw detector used in the NDT civil engineering industry. To increase the sound pressure generated, the number of transducers in the novel probe is increased to 32 transducers. In addition, the timed excitation of each transducer directs a focused beam of sound to a specific angle and distance based on the previously calculated delay time. This narrows the sensitivity of test volume and improves the signal-to-noise ratio of the received signals. In this paper, the newly designed phased array borehole probe is validated by beam computation in the CIVA software and experimental investigations on a half-cylindrical test specimen to investigate the directional characteristics. In combination with geophysical reconstruction methods, it is expected that an optimised radiation pattern of the probe will improve the signal quality and thus increase the reliability of the imaging results. This is an important consideration for the construction of safe sealing structures for the safe disposal of radioactive or toxic waste.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.