54 research outputs found
Mid-infrared group IV nanowire laser
No full textSemiconductor nanowires have shown great potential for enabling ultracompact lasers for integrated photonics platforms. Despite the impressive progress in developing nanowire lasers, their integration into Si photonics platforms remains challenging largely because of the use of III-V and II-VI semiconductors as gain media. Recently, group IV nanowires, particularly direct bandgap GeSn nanowires capable of emitting above 2 μm, have emerged as promising cost-effective gain media for Si-compatible nanowire lasers, but there has been no successful demonstration of lasing from this seemingly promising nanowire platform. Herein, we report the experimental observation of lasing above 2 μm from a single bottom-up grown GeSn nanowire. By harnessing strain engineering and optimized cavity designs simultaneously, the single GeSn nanowire achieves an amplified material gain that can sufficiently overcome minimized optical losses, resulting in single-mode lasing with an ultralow threshold of ~5.3 kilowatts per square centimeter. Our finding paves the way for all–group IV mid-infrared photonic-integrated circuits with Si-compatible lasers for on-chip classical and quantum applications
Computer simulation of asymmetric microstructured optical fiber
No full textMany high birefringence microstructured optical fibers (MOFs) ate generated by introducing asymmetry with different modifications. Due to the deformations of MOF in transportation and usage, ellipticity is one of the most popular choices.
In this dissertation, a special glass MOF with asymmetric core refion and elliptical-hole cladding is studied and simulated with two simulation software tools. Subsequently, the results are compared which can verify the reliability of the study. With this unique structure of proposed MOF, the field distributions of the first two modes are generated and then the birefringence can be calculated. By doing simulation based on the finite difference (FD) method at THz region, it is found that the birefringence is optimized to 0.089. This value is several magnitudes higher than the ones of conventional MOFs and is beneficial for its properties.
Furthermore, additional researches based on this structure are conducted. In the original solid-core structure, the ellipticity of the air-holes are changed, and the impact of ellipticity as well as the asymmetry of the structure can be observed. In the late hollow-core structure, the core-size is changed, based on which the cladding mode of this MOF is confirmed. And the study about ellipticity and core size on this MOF will provide significant information for the following studies.Master of Science (Precision Engineering
Strain-induced pseudo-magnetic fields in graphene for novel optoelectronic applications
No full textThe research progress toward creating efficient light sources on graphene-based electronic-photonic integrated circuits has been relatively sluggish, mainly because of graphene’s zero-bandgap nature. Recently, strain-induced pseudo-magnetic fields in graphene have attracted particular interest due to their capability to mimic real magnetic fields and create energy gaps, emerging as a promising route to favor the realization of integrated graphene optoelectronic devices.
Theoretical and experimental work on generating strain-induced pseudo-magnetic fields in graphene has been demonstrated. In the meantime, scanning tunneling spectroscopy has repeatedly witnessed the pseudo-Landau levels in strained graphene and verified the existence of pseudo-magnetic fields. However, the effect of pseudo-magnetic fields has been rarely explored in graphene thus far. Moreover, previous attempts to experimentally achieve strain-induced pseudo-magnetic fields have mostly been limited to the nanometer scale, making it challenging to harness them in graphene-based optoelectronic applications.
In this thesis, we focus on investigating strain-induced pseudo-magnetic fields in graphene. Starting from fabricating highly strained graphene on nanopillars, we demonstrate how pseudo-magnetic fields change the optical properties of graphene. In the second part, we experimentally induce quasi- uniform pseudo-magnetic fields over an area that can be at the micrometer scale. The demonstrated platform allows customizing the strain distribution in a simple and reproducible way. Using theoretical simulations, we also present the possibility of creating an efficient graphene-based laser. Lastly, I strive to show that graphene holds the potential to act as a light source material by employing ultrafast photoluminescence measurement. Throughout this thesis, we discuss the realization and effect of strain-induced pseudo-magnetic fields in graphene that will help pave the way towards facilitating graphene-based light sources and completing graphene-based electronic-photonic integrated circuits.Doctor of Philosoph
The study of corrosion on carbon steel and zinc under thin-film electrolyte
No full textAtmospheric corrosion is one of the most widespread types of metal corrosion in the world. Commonly, atmospheric corrosion is affected by the electrochemical properties of the metal and environmental factors, such as humidity, temperature and the properties of the electrolyte on the metal surface. Currently, there still lack of laboratory studies which investigated the effect of changing electrolyte thickness on corrosion behaviours. In this study, a corrosion cell with adjustable electrolyte thickness was used to simulate the atmospheric corrosion process of carbon steel and zinc under thin-film sodium chloride electrolyte conditions. The effects of electrolyte thickness and chloride ion concentration on the atmospheric corrosion of these two metals were investigated by open circuit potential, polarization and galvanic coupling techniques. To perform the experiments under thin-film conditions a novel electrochemical cell was employed. Experiments confirmed the effect of electrolyte thickness on the corrosion rate of the metals. Particularly, it was established the role of oxygen transport in the kinetics of the process. At large electrolyte thickness (several hundred micrometers), oxygen is limited at the proximities of the metal, leading to corrosion rates comparable to the values under bulk electrolyte conditions. With the reduction of the electrolyte thickness, a higher concentration of oxygen is available, due to the faster oxygen equilibrium between air-electrolyte, leading to a substantial increase in both corrosion rate and the diffusion control limiting current. Corrosion current density under approximately 40μm thin-film electrolytes were two orders of magnitude higher than the currents measured for both carbon steel and zinc metals under immersed conditions (bulk electrolyte). The effect of chloride ion concentration on corrosion rate under thin-film electrolytes was also revealed. The higher solubility of oxygen on low chloride-concentration electrolytes showed also an acceleration of the process. Carbon steel and zinc metals presented the highest corrosion rates under 0.01M NaCl electrolyte with 40μm thickness.Materials Science and Engineerin
Stressor for Tensile Strain in GeSn‐on‐Insulator Nanobeam Lasers
No full textTensile strained GeSn alloys are considered a key enabler for the realization of complementary metal-oxide-semiconductor laser sources. However, the tensile strained GeSn lasers reported to date require complex fabrication processes for applying tensile strain in GeSn, preventing tensile GeSn lasers from becoming the mainstream technology for integrated photonics. Here, a unique strain engineering method is presented that can introduce a uniform tensile strain in GeSn lasers by harnessing a widely developed atomic layer deposition (ALD) process. 1D photonic crystal nanobeam lasers under homogenous tensile strain induced by an ALD HfO2 all-around stressor layer show a single-mode lasing peak with a ≈31 nm redshift and ≈2 times intensity increase. The lasing threshold of tensile strained GeSn lasers is ≈12% improved compared to the unstrained GeSn lasers. It is believed that the approach offers a new path toward the realization of practical group-IV laser sources for photonic-integrated circuits.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)National Research Foundation (NRF)The research of the project was in part supported by the Ministry of Education, Singapore, under grant AcRF TIER 1 (RG 115/21). This work was also supported by the National Research Foundation of Singapore through the Competitive Research Program (NRF-CRP19-2017-01). This work was also supported by the iGrant of Singapore A*STAR AME IRG (A2083c0053). This research was also supported by the National Research Foundation, Singapore and A*STAR under its Quantum Engineering Programme (NRF2022-QEP2-02-P13)
Quick PCR to detect M. tuberculosis and M. bovis in swine blood samples
No full textThe disease control strategies in livestock are the key areas to enhance improvement of livestock production and safety of livestock product consumers. Therefore, reliable techniques for quick detection and specific identification of disease causing agents need to be developed. In this study a nested PCR was developed using primer primier 5.0 software for primer design targeting IS1081 gene conserved regions in both M. tuberculosis and M. bovis. Two sets of primers TB-Q1/TB-Q2 and TB-B1/TB-B2, were designed to detect M. tuberculosis and M. bovis DNA extracted from blood samples. The findings were, the assay is sensitive enough to detect up to 1.35fg of the antigen DNA with 100% specificity.</p
Parameters extraction for perovskite solar cells based on Lambert W-function
No full textThe behaviors of the solar cells are decided by the device parameters. Thus, it is necessary to extract these parameters to achieve the optimal working condition. Because the five-parameter model of solar cells has the implicit equation of current-voltage relationship, it is difficult to obtain the parameters with conventional methods. In this work, an optimized method is presented to extract device parameters from the actual test data of photovoltaic cell. Based on Lambert W-function, explicit formulation of the model can be deduced. The proposed technique takes suitable method of selecting sample points, which are used to calculate the values of the model parameters. By comparing with the Quasi-Newton method, the results verify accuracy and reliability of this method
Helmet-Wearing Tracking Detection Based on StrongSORT
No full textObject detection based on deep learning is one of the most important and fundamental tasks of computer vision. High-performance detection algorithms have been widely used in many practical fields. For the management of workers wearing helmets in construction scenarios, this paper proposes a framework model based on the YOLOv5 detection algorithm, combined with multi-object tracking algorithms, to monitor and track whether workers wear safety helmets in real-time video. The improved StrongSORT tracking algorithm of DeepSORT is selected to reduce the loss of the tracked object caused by the occlusion, trajectory blur, and motion scale of the object. The safety helmet dataset is trained with YOLOv5s, and the best result of training is used as the weight model in the StrongSORT tracking algorithm. The experimental results show that the [email protected] of all classes in the YOLOv5s model can reach 95.1% in the validation dataset, [email protected]:0.95 is 62.1%, and the precision of wearing helmet is 95.7%. After the box regression loss function was changed from CIOU to Focal-EIOU, the [email protected] increased to 95.4%, [email protected]:0.95 increased to 62.9%, and the precision of wearing helmet increased to 96.5%, which were increased by 0.3%, 0.8% and 0.8%, respectively. StrongSORT can update object trajectories in video frames at a speed of 0.05 s per frame. Based on the improved YOLOv5s combined with the StrongSORT tracking algorithm, the helmet-wearing tracking detection can achieve better performance
Strained germanium nanowire optoelectronic devices for photonic-integrated circuits
No full textStrained germanium nanowires have recently become an important material of choice for silicon-compatible optoelectronic devices. While the indirect bandgap nature of germanium had long been problematic both in light absorption and emission, recent successful demonstrations of bandstructure engineering by elastic strain have opened up the possibility of achieving direct bandgap in germanium, paving the way towards the realization of various high-performance optical devices integrated on a silicon platform. In particular, the latest demonstration of a low-threshold optically pumped laser in a highly strained germanium nanowire is expected to vitalize the field of silicon photonics further. Here, we review recent advances and challenges in strained germanium nanowires for optoelectronic applications such as photodetectors and lasers. We firstly introduce the theoretical foundation behind strained germanium nanowire optoelectronics. And several practical approaches that have been proposed to apply tensile strain in germanium nanowires are further discussed. Then we address the latest progress in the developments of strained germanium nanowire optoelectronic devices. Finally, we discuss the implications of these experimental achievements and the future outlook in this promising research field.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Accepted versio
Construction and immunogenicity of recombinant adenovirus expressing ORF2 of PCV2 and porcine IFN gamma
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