Silicon Nitride Waveguides for Plasmon Optical Trapping and Sensing Applications

We demonstrate a silicon nitride trench waveguide deposited with bowtie antennas for plasmonic enhanced optical trapping. The sub-micron silicon nitride trench waveguides were fabricated with conventional optical lithography in a low cost manner. The waveguides embrace not only low propagation loss and high nonlinearity, but also the inborn merits of combining micro-fluidic channel and waveguide together. Analyte contained in the trapezoidal trench channel can interact with the evanescent field from the waveguide beneath. The evanescent field can be further enhanced by plasmonic nanostructures. With the help of gold nano bowtie antennas, the studied waveguide shows outstanding trapping capability on 10 nm polystyrene nanoparticles. We show that the bowtie antennas can lead to 60-fold enhancement of electric field in the antenna gap. The optical trapping force on a nanoparticle is boosted by three orders of magnitude. A strong tendency shows the nanoparticle is likely to move to the high field strength region, exhibiting the trapping capability of the antenna. Gradient force in vertical direction is calculation by using a point-like dipole assumption, and the analytical solution matches the full-wave simulation well. The investigation indicates that nanostructure patterned silicon nitride trench waveguide is suitable for optical trapping and nanoparticle sensing applications

Printable surface hologram via nanosecond laser ablation

Holography plays a significant role in applications such as data storage, light trapping, security, and biosensors. However, traditional fabrication methods remain time-consuming, labour-intensive, complex and costly, limiting the extensive and massive production of holograms. In this thesis, a single-pulse laser ablation strategy was used to write surface gratings and zone plates. A 5 ns high-energy green laser pulse was utilized to form interference patterns on ink-based (150 nm thickness) and gold-based (4 nm thickness) substrates. The holographic recording process was completed within seconds. The periodicities for ink-based and gold-based gratings are 2.6 μm and 820 nm, respectively. The optical characteristics of the interference patterns have been computationally modeled, and diffraction patterns were observed from the fabricated grating holograms by different monochromatic wavelengths. In addition, the asymmetric zone plate was fabricated on 4.5 nm gold layer, and a well-ordered rainbow pattern with a significant diffraction angle of 32° was measured from the normal incident. An power meter experiment was also conducted to determine the diffraction efficiency of 0.8% by white light illumination. Handwritten signatures and 3D coin images were demonstrated to support the utilization of single laser ablation approach, and the fabrication methodology holds great potential in applications for optical devices

Electronic control of optical tweezers using space-time-wavelength mapping

We present a new approach for electronic control of optical tweezers by using space-time-wavelength mapping (STWM), a technique that uses time-domain modulation to control local intensity values, and hence the resulting optical force, in space. The proposed technique enables direct control of magnitude, location, and polarity of force hot-spots created by Lorentz force (gradient force). In this paper, we develop an analytical formulation of the proposed STWM technique for optical tweezing. In the case study presented here, we show that 150 fs optical pulses are dispersed in time and space to achieve a focused elliptical beam that is ~20 {\mu}m long and ~2 {\mu}m wide. By choosing the appropriate RF waveform and electro-optic modulator, we can generate multiple hot-spots with >200 pN force per pulse.Comment: 7 pages, 7 figure

Design of Partially Etched GaP-OI Microresonators for Two-Color Kerr Soliton Generation at NIR and MIR

We present and theoretically investigate a dispersion engineered GaP-OI microresonator containing a partially-etched gap of 250 nm x 410 nm in a 600 nm x 2990 nm waveguide. This gap enables a 3.25 {\mu}m wide anomalous dispersion spectral span covering both the near-infrared and the mid-infrared spectra. This anomalous dispersion is manifested by two mechanisms, being the hybridization of the fundamental TE modes around 1550 nm and the geometric dispersion of the higher order TE mode around the 3100 nm wavelengths, respectively. Two Kerr soliton combs can be numerically generated with 101 GHz and 97 GHz teeth spacings at these spectral windows. The proposed structure demonstrates the design flexibility thanks to the partially etched gap and paves the way towards potential coherent multicolor frequency comb generation in the emerging GaP-OI platform

Circulating Monocytes Act as a Common Trigger for the Calcification Paradox of Osteoporosis and Carotid Atherosclerosis via TGFB1-SP1 and TNFSF10-NFKB1 Axis

BackgroundOsteoporosis often occurs with carotid atherosclerosis and causes contradictory calcification across tissue in the same patient, which is called the “calcification paradox”. Circulating monocytes may be responsible for this unbalanced ectopic calcification. Here, we aimed to show how CD14+ monocytes contribute to the pathophysiology of coexisting postmenopausal osteoporosis and carotid atherosclerosis.MethodsWe comprehensively analyzed osteoporosis data from the mRNA array dataset GSE56814 and the scRNA-seq dataset GSM4423510. Carotid atherosclerosis data were obtained from the GSE23746 mRNA dataset and GSM4705591 scRNA-seq dataset. First, osteoblast and vascular SMC lineages were annotated based on their functional expression using gene set enrichment analysis and AUCell scoring. Next, pseudotime analysis was applied to draw their differentiated trajectory and identify the key gene expression changes in crossroads. Then, ligand–receptor interactions between CD14+ monocytes and osteoblast and vascular smooth muscle cell (SMC) lineages were annotated with iTALK. Finally, we selected calcification paradox-related expression in circulating monocytes with LASSO analysis.ResultsFirst, we found a large proportion of delayed premature osteoblasts in osteoporosis and osteogenic SMCs in atherosclerosis. Second, CD14+ monocytes interacted with the intermediate cells of the premature osteoblast and osteogenic SMC lineage by delivering TGFB1 and TNFSF10. This interaction served as a trigger activating the transcription factors (TF) SP1 and NFKB1 to upregulate the inflammatory response and cell senescence and led to a retarded premature state in the osteoblast lineage and osteogenic transition in the SMC lineage. Then, 76.49% of common monocyte markers were upregulated in the circulating monocytes between the two diseases, which were related to chemotaxis and inflammatory responses. Finally, we identified 7 calcification paradox-related genes on circulating monocytes, which were upregulated in aging cells and downregulated in DNA repair cells, indicating that the aging monocytes contributed to the development of the two diseases.ConclusionsOur work provides a perspective for understanding the triggering roles of CD14+ monocytes in the development of the calcification paradox in osteoporosis- and atherosclerosis-related cells based on combined scRNA and mRNA data. This study provided us with an elucidation of the mechanisms underlying the calcification paradox and could help in developing preventive and therapeutic strategies

Integrated Planar Optical Devices Based on Silicon Nitride Waveguides

Silicon nitride is a subject of growing interest with the potential of delivering planar integrated optical devices as a complementary part of silicon photonics. The material has a moderate refractive index, wide optical transparency window, lack of two-photon absorption, and low nonlinear susceptibility. Thanks to its CMOS fabrication compatibility, the freedom of integrating different materials into Si3N4 renders the platform omnipotent. This dissertation is dedicated to developing Si3N4 based optical devices integrated with Si nanowires, fishbone antennas, bowtie antennas and gold nanoparticles to achieve active and passive optical functionalities. To be specific, the thesis covers Si3N4 based optical leaky wave antennas that emit narrow beams towards desired directions in free space, bimetallic fishbone waveguide-based detectors that detect optical radiations plasmonically and thermo-mechanically, and trench waveguides that can be equipped with bowtie antennas for optical trapping or with gold nanoparticles for nonlinearity enhancement.The purpose of the first part of the dissertation is to experimentally demonstrate emission from a leaky wave antenna and to investigate the possible modulation method in tuning the radiation beam. The optical leaky wave antenna is composed of a Si3N4 waveguide and periodic Si nanowires. The antenna has a single directive radiation peak at the angle of 85.1° in the measured range from 65° to 112° at the wavelength of 1550 nm. The side lobes are at least 7 dB lower than the main peak. The peak radiation angle moves to the broad side as the wavelength increases. The device can find promising applications in optical communications, especially for multi-wavelength space division multiplexing owing to its capability of beam scanning with frequency. The study on the optical leaky wave antenna proves the functionality of off-plane emission from a waveguide and explores the potential electronic modulation methods.The second part of the dissertation presents a plasmo-thermomechanical radiation detector. The goal of the second work is to investigate if thermomechanical vibrations can be detected in an on-chip optical readout system. To study the problem, I designed a device that is composed of a Si3N4 waveguide and 13 fishbone nanowires suspended above the waveguide. Each wire is 12.54 µm long and consists of 16 nanoantennas with a period of 660 nm. Under the illumination of 660 nm light, the detector shows a responsivity of 3.954×10-3 µm2/µW. The noise equivalent power, dominated by the waveguide coupling instability, is 3.01 µW/√Hz. The 3dB bandwidth of the device is 9.6 Hz corresponding to a time constant of 16.6 ms. Besides the demonstrated radiation detector for visible wavelength, another device for mid-infrared wavelength has also been designed and optimized for fabrication. This study verifies the possibility of using on-chip waveguide-based readout system to detect the mechanical vibration that is induced by radiation.The third part of the dissertation focuses on Si3N4 trench waveguides. The objective of this part is to thoroughly explore the optical properties of the trench waveguides and investigate their applications. The trench waveguide shape is determined by the silicon wet etching properties and thus can be controlled in either triangle or trapezoidal shape. Experimental results show that the propagation loss of the TM mode can be as low as 0.8 dB/cm. The nonlinear parameter of the waveguide is measured to be 0.3 W-1/m. Coating gold nanoparticles can enhance the waveguide nonlinearity. The trench waveguide is promising for liquid sensing thanks to its unique structure that can combine fluidic channel and waveguide together. Explorations on the trapezoidal trench waveguide and bowtie antennas also show that the platform is suitable for trapping nanoparticles. Switching between trapping and releasing the particles can be done by changing the mode polarization states from the TE mode to the TM mode. This work provides an in-depth study of the trench waveguides from optical properties, fabrication, to applications.This study expands the knowledge and capabilities of conventional silicon photonics and paves way for novel devices pertinent to communications and sensing. In particular, this thesis shows that the use of Si3N4 based planar optical circuits, the operational bandwidth of silicon photonics can cover wavelengths shorter than 1.1μm for novel applications. The presented work on new optical planar emitters, waveguides, detectors, optical trapping, and microfluidics at wavelengths from visible to mid-wave infrared will be beneficial to both future research and industry applications

Integrated Planar Optical Devices Based on Silicon Nitride Waveguides

Silicon nitride is a subject of growing interest with the potential of delivering planar integrated optical devices as a complementary part of silicon photonics. The material has a moderate refractive index, wide optical transparency window, lack of two-photon absorption, and low nonlinear susceptibility. Thanks to its CMOS fabrication compatibility, the freedom of integrating different materials into Si3N4 renders the platform omnipotent. This dissertation is dedicated to developing Si3N4 based optical devices integrated with Si nanowires, fishbone antennas, bowtie antennas and gold nanoparticles to achieve active and passive optical functionalities. To be specific, the thesis covers Si3N4 based optical leaky wave antennas that emit narrow beams towards desired directions in free space, bimetallic fishbone waveguide-based detectors that detect optical radiations plasmonically and thermo-mechanically, and trench waveguides that can be equipped with bowtie antennas for optical trapping or with gold nanoparticles for nonlinearity enhancement.The purpose of the first part of the dissertation is to experimentally demonstrate emission from a leaky wave antenna and to investigate the possible modulation method in tuning the radiation beam. The optical leaky wave antenna is composed of a Si3N4 waveguide and periodic Si nanowires. The antenna has a single directive radiation peak at the angle of 85.1° in the measured range from 65° to 112° at the wavelength of 1550 nm. The side lobes are at least 7 dB lower than the main peak. The peak radiation angle moves to the broad side as the wavelength increases. The device can find promising applications in optical communications, especially for multi-wavelength space division multiplexing owing to its capability of beam scanning with frequency. The study on the optical leaky wave antenna proves the functionality of off-plane emission from a waveguide and explores the potential electronic modulation methods.The second part of the dissertation presents a plasmo-thermomechanical radiation detector. The goal of the second work is to investigate if thermomechanical vibrations can be detected in an on-chip optical readout system. To study the problem, I designed a device that is composed of a Si3N4 waveguide and 13 fishbone nanowires suspended above the waveguide. Each wire is 12.54 µm long and consists of 16 nanoantennas with a period of 660 nm. Under the illumination of 660 nm light, the detector shows a responsivity of 3.954×10-3 µm2/µW. The noise equivalent power, dominated by the waveguide coupling instability, is 3.01 µW/√Hz. The 3dB bandwidth of the device is 9.6 Hz corresponding to a time constant of 16.6 ms. Besides the demonstrated radiation detector for visible wavelength, another device for mid-infrared wavelength has also been designed and optimized for fabrication. This study verifies the possibility of using on-chip waveguide-based readout system to detect the mechanical vibration that is induced by radiation.The third part of the dissertation focuses on Si3N4 trench waveguides. The objective of this part is to thoroughly explore the optical properties of the trench waveguides and investigate their applications. The trench waveguide shape is determined by the silicon wet etching properties and thus can be controlled in either triangle or trapezoidal shape. Experimental results show that the propagation loss of the TM mode can be as low as 0.8 dB/cm. The nonlinear parameter of the waveguide is measured to be 0.3 W-1/m. Coating gold nanoparticles can enhance the waveguide nonlinearity. The trench waveguide is promising for liquid sensing thanks to its unique structure that can combine fluidic channel and waveguide together. Explorations on the trapezoidal trench waveguide and bowtie antennas also show that the platform is suitable for trapping nanoparticles. Switching between trapping and releasing the particles can be done by changing the mode polarization states from the TE mode to the TM mode. This work provides an in-depth study of the trench waveguides from optical properties, fabrication, to applications.This study expands the knowledge and capabilities of conventional silicon photonics and paves way for novel devices pertinent to communications and sensing. In particular, this thesis shows that the use of Si3N4 based planar optical circuits, the operational bandwidth of silicon photonics can cover wavelengths shorter than 1.1μm for novel applications. The presented work on new optical planar emitters, waveguides, detectors, optical trapping, and microfluidics at wavelengths from visible to mid-wave infrared will be beneficial to both future research and industry applications