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

Silicon on sapphire and SOI photonic devices for mid-infrared and near-IR wavelengths

Conventional SOI waveguide technology, serving as the foundation of near-IR photonics, meets its limitation in mid-IR due to high loss associated with the buried oxide. Silicon-on-sapphire (SOS) waveguides are considered as a good mid-IR alternative, because the transparency window of sapphire is up to 6 μm and SOS waveguides are compatible with SOI technology. We show that properly-designed SOS waveguides can facilitate frequency band conversion between near-IR and mid-IR. An indirect mid-IR detection scheme is proposed and the mid-IR signal is down-converted to telecommunication wavelength (1.55 μm) through SOS waveguides and indirectly detected by near-IR detectors. The performance of the indirect mid-IR detection scheme is discussed. Particularly we model and compare the noise performance of the indirect detection with direct detection using state-of-the-art mid-IR detectors. In addition to advantages of room temperature and high-speed operation, the results show that the proposed indirect detection can improve the electrical signal-to-noise ratio up to 50dB, 23dB and 4dB, compared to direct detection by PbSe, HgCdTe and InSb detectors respectively. The improvement is even more pronounced in detection of weak MWIR signals. In order to further boost the performance, we also investigate mechanisms to increasing the conversion efficiency in SOS waveguide wavelength converters. The conversion efficiency can be improved by periodically cascading SOS waveguide sections with opposite dispersion characteristics to achieve quasi-phase-matching. Conversion efficiency enhancement over 30dB and the conversion bandwidth increased by 2 times are demonstrated, which may facilitate the fabrication of parametric oscillators that can improve the conversion efficiency by 50dB

Experimental demonstration of bandwidth enhancement based on two-pump wavelength conversion in a silicon waveguide

SPARC (osteonectin/BM40) is a secreted protein that modifies the interaction of cells with extracellular matrix (ECM). When we added SPARC to cultured rabbit synovial fibroblasts and analyzed the secreted proteins, we observed an increase in the expression of three metalloproteinases--collagenase, stromelysin, and the 92-kD gelatinase-- that together can degrade both interstitial and basement membrane matrices. We further characterized the regulation of one of these metalloproteinases, collagenase, and showed that both collagenase mRNA and protein are upregulated in fibroblasts treated with SPARC. Experiments with synthetic SPARC peptides indicated that a region in the neutral alpha-helical domain III of the SPARC molecule, which previously had no described function, was involved in the regulation of collagenase expression by SPARC. A sequence in the carboxyl-terminal Ca(2+)-binding domain IV exhibited similar activity, but to a lesser extent. SPARC induced collagenase expression in cells plated on collagen types I, II, III, and V, and vitronectin, but not on collagen type IV. SPARC also increased collagenase expression in fibroblasts plated on ECM produced by smooth muscle cells, but not in fibroblasts plated on a basement membrane-like ECM from Engelbreth-Holm-Swarm sarcoma. Collagenase was induced within 4 h in cells treated with phorbol diesters or plated on fibronectin fragments, but was induced after 8 h in cells treated with SPARC. A number of proteins were transiently secreted by SPARC-treated cells within 6 h of treatment. Conditioned medium that was harvested from cultures 7 h after the addition of SPARC, and depleted of residual SPARC, induced collagenase expression in untreated fibroblasts; thus, part of the regulation of collagenase expression by SPARC appears to be indirect and proceeds through a secreted intermediate. Because the interactions of cells with ECM play an important role in regulation of cell behavior and tissue morphogenesis, these results suggest that molecules like SPARC are important in modulating tissue remodeling and cell-ECM interactions

Experimental demonstration of bandwidth enhancement based on two-pump wavelength conversion in a silicon waveguide

SPARC (osteonectin/BM40) is a secreted protein that modifies the interaction of cells with extracellular matrix (ECM). When we added SPARC to cultured rabbit synovial fibroblasts and analyzed the secreted proteins, we observed an increase in the expression of three metalloproteinases--collagenase, stromelysin, and the 92-kD gelatinase-- that together can degrade both interstitial and basement membrane matrices. We further characterized the regulation of one of these metalloproteinases, collagenase, and showed that both collagenase mRNA and protein are upregulated in fibroblasts treated with SPARC. Experiments with synthetic SPARC peptides indicated that a region in the neutral alpha-helical domain III of the SPARC molecule, which previously had no described function, was involved in the regulation of collagenase expression by SPARC. A sequence in the carboxyl-terminal Ca(2+)-binding domain IV exhibited similar activity, but to a lesser extent. SPARC induced collagenase expression in cells plated on collagen types I, II, III, and V, and vitronectin, but not on collagen type IV. SPARC also increased collagenase expression in fibroblasts plated on ECM produced by smooth muscle cells, but not in fibroblasts plated on a basement membrane-like ECM from Engelbreth-Holm-Swarm sarcoma. Collagenase was induced within 4 h in cells treated with phorbol diesters or plated on fibronectin fragments, but was induced after 8 h in cells treated with SPARC. A number of proteins were transiently secreted by SPARC-treated cells within 6 h of treatment. Conditioned medium that was harvested from cultures 7 h after the addition of SPARC, and depleted of residual SPARC, induced collagenase expression in untreated fibroblasts; thus, part of the regulation of collagenase expression by SPARC appears to be indirect and proceeds through a secreted intermediate. Because the interactions of cells with ECM play an important role in regulation of cell behavior and tissue morphogenesis, these results suggest that molecules like SPARC are important in modulating tissue remodeling and cell-ECM interactions

Analytical study on arbitrary waveform generation by MEMS micro mirror arrays.

We provide analytical modeling and the detailed procedure that is used in recently proposed arbitrary waveform generation technique by using MEMS digital micro-mirror arrays. We estimate the achievable temporal resolution, repetition rate, modulation index and the rise/fall times of the final waveform as figure of merit in the proposed systems. We show that reducing the diffraction limit via increasing the ratio of beam size to lens focal length (>0.075) and the spatial modulation down to single mirror pitch size (10.8μm), waveforms up to 18GHz repetition rates with >90% modulation index and <100ps rise times are achievable. Theoretical calculations are compared with experimental generation of 120MHz square waves and 160MHz sawtooth waves and obtained good agreement

Analytical study on arbitrary waveform generation by MEMS micro mirror arrays.

We provide analytical modeling and the detailed procedure that is used in recently proposed arbitrary waveform generation technique by using MEMS digital micro-mirror arrays. We estimate the achievable temporal resolution, repetition rate, modulation index and the rise/fall times of the final waveform as figure of merit in the proposed systems. We show that reducing the diffraction limit via increasing the ratio of beam size to lens focal length (>0.075) and the spatial modulation down to single mirror pitch size (10.8μm), waveforms up to 18GHz repetition rates with >90% modulation index and <100ps rise times are achievable. Theoretical calculations are compared with experimental generation of 120MHz square waves and 160MHz sawtooth waves and obtained good agreement

Ultra-broadband one-to-two wavelength conversion using low-phase-mismatching four-wave mixing in silicon waveguides

An ultra-broadband wavelength conversion is presented and experimentally demonstrated based on nondegenerate four-wave mixing in silicon waveguides. Two idlers can be generated and their wavelengths can be freely tuned by using two pumps where the first pump is set close to the signal and the second pump is wavelength tunable. Using this scheme, a small phase-mismatch and hence an ultra-broad conversion bandwidth is realized in spite of the waveguide dispersion profile. We show that the experimental demonstrations are consistent with the theoretical estimations. Total conversion bandwidth is estimated to reach > 500 nm and it can provide a feasible approach to realize one-to-two wavelength conversion among different telecommunication bands between 1300 nm and 1800 nm. (C) 2010 Optical Society of Americ

Highly nonlinear sub-micron silicon nitride trench waveguide coated with gold nanoparticles

We demonstrate the fabrication of a highly nonlinear sub-micron silicon nitride trench waveguide coated with gold nanoparticles for plasmonic enhancement. The average enhancement effect is evaluated by measuring the spectral broadening effect caused by self-phase-modulation. The nonlinear refractive index n2 was measured to be 7.0917×10-19 m2/W for a waveguide whose Wopen is 5 μm. Several waveguides at different locations on one wafer were measured in order to take the randomness of the nanoparticle distribution into consideration. The largest enhancement is measured to be as high as 10 times. Fabrication of this waveguide started with a MEMS grade photomask. By using conventional optical lithography, the wide linewidth was transferred to a 100 wafer. Then the wafer was etched anisotropically by potassium hydroxide (KOH) to engrave trapezoidal trenches with an angle of 54.7°. Side wall roughness was mitigated by KOH etching and thermal oxidation that was used to generate a buffer layer for silicon nitride waveguide. The guiding material silicon nitride was then deposited by low pressure chemical vapor deposition. The waveguide was then patterned with a chemical template, with 20 nm gold particles being chemically attached to the functionalized poly (methyl methacrylate) domains. Since the particles attached only to the PMMA domains, they were confined to localized regions, therefore forcing the nanoparticles into clusters of various numbers and geometries. Experiments reveal that the waveguide has negligible nonlinear absorption loss, and its nonlinear refractive index can be greatly enhanced by gold nano clusters. The silicon nitride trench waveguide has large nonlinear refractive index, rendering itself promising for nonlinear applications

Silicon-on-sapphire waveguides design for mid-IR evanescent field absorption gas sensors

Major trace gases have absorption lines in mid-IR. We propose silicon-on-sapphire waveguides at mid-IR for gas sensing based on evanescent field absorption. This can provide a general platform for multipurpose sensing of different types of gases in a reusable fashion. Three types of waveguides (strip, rib and slot) are investigated on their geometrical dependence of evanescent-field ratio (EFR) and propagation loss to serve as the proposed gas sensor. Slot waveguide provides the highest EFR (>25%) in mid-IR with moderate dimension, but its fabrication can be more challenging and its high loss (~10 dB/cm) impairs the sensing resolution and necessitates higher input power in longer waveguides. Strip and rib waveguides can achieve similar EFR with smaller dimensions. We analyze the detection of CO2 in atmosphere based on its mid-IR absorption peak at ~4.23 µm as a case study. Numerical analysis based on up-to-date commercial mid-IR detector parameters shows that a resolution of 2 ppm, 5 ppm and 50 ppm can be achieved in cooled InSb, room-temperature HgCdTe and room-temperature PbSe detectors respectively by using 1 cm waveguides. Effect of waveguide loss also has been investigated