Increased Coupling Efficiency Research Articles

Experimental Demonstration of an Easy-to-Fabricate 1.3-μm Directly Modulated DFB Laser With Improved Beam Profile

The integration of a directly modulated laser with a spot-size-converter can greatly reduce packaging requirements thereby reducing costs and promoting applications of these devices. However, most of the reported spot-size-converters integrated directly modulated laser need complex fabrication process which will increase cost and may degrade modulation bandwidth. We report a 1.3-μm directly modulated laser with ridge waveguide distributed feedback region and buried waveguide spot-size-converter region to improve beam profile and increase coupling efficiency with low fabrication cost. The core layer with high refractive index is simply tapered into a 500-nm-wide waveguide before regrowth and after the regrowth process, the buried heterojunction spot-size-converter is formed. The ridge waveguide distributed feedback with conventional high reflection coating is replaced by active-distributed-reflector is applied to prevent the aluminium-containing multi quantum wells from the risk of oxidation and further reduce fabrication cost. The fabricated device realized a nearly circular beam profile and more than 70% improvement of power coupling into a 5-μm lensed-fiber compared to normal ridge waveguide lasers. The fabricated laser also demonstrated a 3-dB modulation bandwidth of ∼19 GHz with good single mode stability. Key parameters are extracted to prove that integration of this spot-size-converter does not degrade the modulation performance and the modulation bandwidth is limited by the material gain as the estimated D factor of the tested device is 2.32 GHz/mA close to that extracted from the material parameters.

Enhancing the optical path inside a capillary without sacrificing light intensity: application to a compact and highly sensitive photometer.

In order to increase the optical path and related sensitivity of photometers, multiple axial-reflection of parallel light-beam inside a capillary cavity is one of the most effective ways. However, there is a non-optimum trade-off between optical path and light intensity, e.g., smaller aperture on cavity mirror can increase multiple axial-reflection times (i.e., longer optical path) due to the lower cavity-loss, but it would also reduce coupling efficiency, light intensity, and related signal-to-noise ratio. Herein, an optical beam shaper, which is composed of two optical lenses with an apertured mirror, was proposed to focus the light beam (i.e., increasing coupling efficiency) without deteriorating beam parallelism and related multiple axial-reflection. Thus, by combining the optical beam shaper with a capillary cavity, large optical path enhancement (10-fold of capillary length) and high coupling efficiency (>65%) can be realized simultaneously, where the coupling efficiency was improved 50-fold. An optical beam shaper photometer (with a 7 cm long capillary) was fabricated and applied to detect water in ethanol with a detection limit of 12.5 ppm, which is 800-fold and 32∼80 fold lower than that of the commercial spectrometer (1 cm cuvette) and previous reports, respectively.

An Orthogonal Covalent Connector System for the Efficient Assembly of Enzyme Cascades on DNA Nanostructures.

Combining structural DNA nanotechnology with the virtually unlimited variety of enzymes offers unique opportunities for generating novel biocatalytic devices. However, the immobilization of enzymes is still restricted by a lack of efficient covalent coupling techniques. The rational re-engineering of the genetically fusible SNAP-tag linker is reported here. By replacing five amino acids that alter the electrostatic properties of the SNAP_R5 variant, up to 11-fold increased coupling efficiency with benzylguanine-modified oligonucleotides and DNA origami nanostructures (DON) was achieved, resulting in typical occupancy densities of 75%. The novel SNAP_R5 linker can be combined with the equally efficient Halo-based oligonucleotide binding tag (HOB). Since both linkers exhibit neither cross-reactivity nor non-specific binding, they allowed orthogonal assembly of an enzyme cascade consisting of the stereoselective ketoreductase Gre2p and the cofactor-regenerating isocitrate dehydrogenase on DON. The cascade showed approximately 1.6-fold higher activity in a stereoselective cascade reaction than the corresponding free solubilized enzymes. The connector system presented here and the methods used to validate it represent important tools for further development of DON-based multienzyme systems to investigate mechanistic effects of substrate channeling and compartmentalization relevant for exploitation in biosensing and catalysis.

Dual-Wavelength-Band Grating Coupler on 220-nm Silicon-on-Insulator With High Numerical Aperture Fiber Placed Perfectly Vertically

We propose and design a novel dual-wavelength-band grating coupler on 220-nm-thick silicon-on-insulator and experimentally investigate its capability to couple two wavelength bands simultaneously under surface-normal fiber placement. Such dual-wavelength-band operation take advantage of a dual-etch grating design not only with increased directionality but also with unique diffraction angle dispersion characteristics for the two targeted wavelength bands. The role of high numerical aperture fiber is theoretically investigated, leading to reduced angular sensitivity in general and subsequently increased coupling efficiency for our proposed dual-wavelength-band operation scheme. Our device is further fabricated using 248-nm deep-UV lithography on an 8-inch wafer for verification. The peak coupling efficiency is measured to be –5.0 dB at 1275 nm and –5.9 dB at 1519 nm for O-band and S/C-band respectively.

Method for increasing coupling efficiency between helical-core and standard single-mode fibers.

Helical core fibers (HCFs) suffer from low coupling efficiency and unavoidable excitation of higher order modes below the cutoff wavelength because of a core tilt with respect to the symmetry axis of the cladding. We propose an effective way of increasing the coupling efficiency to a HCF by untwisting its beginning section in a hydrogen flame. The proposed solution provides also a control over the excitation of higher order modes in HCFs and can be applied in splicing as well as in a free-space launching configuration. We experimentally demonstrate that by using the proposed method, the coupling efficiency between a SMF-28 and HCF can be increased to the level reachable for straight fibers, which is limited only by a modal fields mismatch. We also present detailed numerical and analytical studies of the coupling efficiency between a HCF and SMF versus the pitch distance in the partially untwisted input section of the HCF, which takes into account fundamental and higher-order modes.

Calculation of electronic and optical properties of 1550 nm VCSEL based on Group IV elements

Si/SiGe quantum well (QW) structures show considerable potential in revolutionising Si photonics. This study proposes a novel 1550 nm vertical cavity surface-emitting laser (VCSEL) that is based on Group IV elements and composed of Si/SiO2 distributed Bragg reflectors and Si/Si0.13Ge0.87 QWs. Material composition and QW width in the active region are optimised. The proposed Group IV-based VCSEL can exhibit epitaxial growth on a vertical binary blazed grating coupler and increase coupling efficiency relative to the traditional Group III–V-based VCSEL with an Si waveguide. The proposed VCSEL on Si based on the Group IV element scheme is a cheap, high-yielding and temperature-insensitive on-chip light source that can be used in large-scale, high-density monolithic integration.

Effects of inflammatory pain on CB1 receptor in the midbrain periaqueductal gray.

The periaqueductal gray (PAG) mediates the antinociceptive properties of analgesics, including opioids and cannabinoids. Administration of either opioids or cannabinoids into the PAG induces antinociception. However, most studies characterizing the antinociceptive properties of cannabinoids in the PAG have been conducted in naive animals. Few studies have reported on the role of CB1 receptors in the PAG during conditions which would prompt the administration of analgesics, namely, during pain states. To examine inflammatory pain-induced changes in CB1 receptor expression and function in the midbrain periaqueductal gray. In this study, we used the Complete Freund Adjuvant model to characterize CB1 receptor expression and G-protein coupling during persistent inflammatory pain. Inflammatory pain induced an upregulation in the expression of synaptic CB1 receptors in the PAG. Despite this pain-induced change in CB1 expression, there was no corresponding upregulation of CB1 mRNA after the induction of inflammatory pain, suggesting a pain-induced recruitment of CB1 receptors to the synaptic sites within PAG neurons or increased coupling efficiency between the receptor and effector systems. Inflammatory pain also enhanced ventrolateral PAG CB1 receptor activity, as there was an increase in CP55,940-stimulated G-protein activation compared with pain-naïve control animals. These findings complement a growing body of evidence which demonstrate pain-induced changes in brain regions that are responsible for both the analgesic and rewarding properties of analgesic pharmacotherapies. Because much of our understanding of the pharmacology of cannabinoids is based on studies which use largely pain-naïve male animals, this work fills in important gaps in the knowledge base by incorporating pain-induced adaptations and cannabinoid pharmacology in females.

Local strain gauge based on the nanowires ring resonator embedded in a flexible substrate

The authors proposed a flexible microresonator based on nanowires composed of Ⅱ–Ⅵ compounds to detect the small strain caused by external motion. The nanowire ring resonator is embedded in polydimethylsiloxane (PDMS) flexibility to improve the coupling efficiency. In this work, CdS nanowire is fabricated onto a PDMS flexible substrate. With the help of a fibre tip, the single nanowire is manipulated under a microscope, allowing the curved line to be a ring and making the litter overlapping. This overlap increases coupling efficiency and sensor performance. The ring cavity has the parameters of diameter 1 µm, length 75 µm and radius ∼10 µm. Experiments demonstrated the process of fabricating a strain sensor and detected peak shifts. This resonant wavelength appeared red-shift and linear tuned when stretching the flexible substrate. The quality factor was about 2000 and the gauge factor was about 80 nm per stretching unit. Being a small structure and high sensitivity, the sensor can be integrated into the chip. This promotes the development of miniaturisation to some extent. As a result, this work is beneficial to optical manipulation, further being extended to the tunable light source.

A biomimetic taste biosensor based on bitter receptors synthesized and purified on chip from a cell-free expression system

The conventional approaches for the preparation of receptor proteins towards chemical sensing are usually based on the expression of receptors in a heterologous cell system, which suffers from time-consuming, low efficiency, and complicated purification process. To address these limitations, in this study, a bitter receptor, T2R4, was synthesized and purified on chip from a cell-free protein expression system, which can be realized within a few hours. The bitter receptors were utilized as sensitive elements of a chemical biosensor for the detection of specific bitter substances. Quartz crystal microbalance (QCM) devices were used as transducers to monitor the process of sensor preparation and responses to different bitter substances by recoding the crystal resonant frequency shifts. The obtained results show that the dose-response curves of denatonium and crystal resonant frequency shifts are established in a wide linear range of 10 nM to 0.1 mM with a lower detection limit of 5 nM, which is superior to previous reports. Nearly 3 times of enhancement in sensitivity were achieved, which is calculated to be 4.96 kHz/mM. Such on-chip rapid synthesis and purification of receptors serve to achieve increased coupling efficiency and improved sensing performances. The combination of simple and rapid cell-free expression technique provides a very promising approach for the rapid and high-efficient development of receptor-based biosensors for chemical sensing.

Scaled experiments on cavity confined explosions in limestone and poly(methyl methacrylate)

A scaled experiment comprising a laser-driven explosion in a cavity is used to characterize the coupling of mechanical energy into the surrounding solid material. Experiments are performed using poly(methyl methacrylate) and dry Salem limestone as the explosion containment blocks materials, in which are milled scaled spherical cavities of various dimensions. Measurements of the coupled shock, taken with fiber optic probes at the cavity wall, show the critical radius where wall deformation transitions from plastic to elastic deformation. These measurements also provide a diagnostic of the air blast, which is validated against GEODYN simulation code. The measurement of the coupled shock amplitude taken farther from the wall in the linear region indicates increased coupling efficiency in small cavities over the range of scaled cavity radii from 6 to 20 m/kt1/3, a phenomenon not previously observed in experiments. A comparison of results taken in this experiment with a parallel experiment using high explosive (HE) as the source shows that coupled shocks generated with HE are characteristically different with much larger amplitude than those produced by a high energy density laser-driven source with the same yield. This experimental technique potentially provides a rapid and cost-effective method to analyze the consequences of a full-scale, low yield, buried explosion.

A self-assembled plasmonic optical fiber nanoprobe for label-free biosensing

The plasmonic optical fiber sensors have attracted wide attention for label-free biosensing application because of their high integration, small footprint and point-of-care measurement. However, the integration of plasmonic nanostructures on optical fiber probes always relies on the top-down nanofabrication approaches, which have several inherent shortcomings, including high cost, time-consuming, and low yields. Here, we develop a plasmonic nanohole-patterned multimode optical fiber probe by self-assembly nanosphere lithography technique with low fabrication cost and high yields. The multimode optical fiber possesses large facet area and high numerical aperture, which not only simplifies fabrication process, but also increases coupling efficiency of incident light. Originating from the resonant coupling of plasmonic modes, the plasmonic fiber nanoprobe has a distinct reflection dip in the spectrum and exhibits strong near-field electromagnetic enhancement. We experimentally investigate the sensing performances of plasmonic fiber nanoprobe, and further demonstrate it in real-time monitoring specific binding of protein molecules. The experimental results imply that the nanohole-patterned multimode optical fiber probe is a good candidate for developing miniaturized and portable biosensing systems.

Reduced mitochondrial response sensitivity is involved in the anti‑apoptotic effect of dexmedetomidine pretreatment in cardiomyocytes.

Dexmedetomidine is a commonly used α2-adreno-ceptor agonist, which affects various organs, including providing beneficial effects on the heart. However, the mechanism underlying the cardiac benefit remains to be fully elucidated. In the present study, it was demonstrated that dexmedetomidine pretreatment on primary cultured rat cardiomyocytes protected against reactive oxygen species (ROS)‑induced apoptosis. In terms of the potential mechanism, it was demonstrated that dexmedetomidine inhibited mitochondrial biogenesis and mitochondrial respiratory complexes, but with increased coupling efficiency. However, dexmedetomidine upregulated mitochondrial membrane potential (Δψm) and resisted against the loss of Δψm induced by carbonilcyanide p‑triflouromethoxyphenylhydrazone. Due to the importance of mitochondria affecting ROS, the present study investigated the dexmedetomidine‑suppressed mitochondrial response to H2O2 stimulation, which was explained by suppressed ROS levels and the suppression of the increased oxygen consumption rate. Results demonstrated for the first time, to the best of our knowledge, a novel protective mechanism for dexmedetomidine on cardiomyocytes through the attenuated response of mitochondria towards H2O2, which had a protective effect against ROS‑induced apoptosis.

Development of optimized conditions for Glaser-Hay bioconjugations

The efficient preparation of protein bioconjugates represents a route to novel materials, diagnostics, and therapeutics. We previously reported a novel bioorthogonal Glaser-Hay reaction for the preparation of covalent linkages between proteins and a reaction partner; however, deleterious protein degradation was observed under extended reaction conditions. Herein, we describe the systematic optimization of the reaction to increase coupling efficiency and decrease protein degradation. Two optimized conditions were identified varying either the pH of the reaction or the bidentate ligand employed, allowing for more rapid conjugations and/or less protein oxidation.

An Enzymatic Route to α-Tocopherol Synthons: Aromatic Hydroxylation of Pseudocumene and Mesitylene with P450 BM3.

Aromatic hydroxylation of pseudocumene (1 a) and mesitylene (1 b) with P450 BM3 yields key phenolic building blocks for α-tocopherol synthesis. The P450 BM3 wild-type (WT) catalyzed selective aromatic hydroxylation of 1 b (94 %), whereas 1 a was hydroxylated to a large extent on benzylic positions (46-64 %). Site-saturation mutagenesis generated a new P450 BM3 mutant, herein named "variant M3" (R47S, Y51W, A330F, I401M), with significantly increased coupling efficiency (3- to 8-fold) and activity (75- to 230-fold) for the conversion of 1 a and 1 b. Additional π-π interactions introduced by mutation A330F improved not only productivity and coupling efficiency, but also selectivity toward aromatic hydroxylation of 1 a (61 to 75 %). Under continuous nicotinamide adenine dinucleotide phosphate recycling, the novel P450 BM3 variant M3 was able to produce the key tocopherol precursor trimethylhydroquinone (3 a; 35 % selectivity; 0.18 mg mL-1 ) directly from 1 a. In the case of 1 b, overoxidation leads to dearomatization and the formation of a valuable p-quinol synthon that can directly serve as an educt for the synthesis of 3 a. Detailed product pattern analysis, substrate docking, and mechanistic considerations support the hypothesis that 1 a binds in an inverted orientation in the active site of P450 BM3 WT, relative to P450 BM3 variant M3, to allow this change in chemoselectivity. This study provides an enzymatic route to key phenolic synthons for α-tocopherols and the first catalytic and mechanistic insights into direct aromatic hydroxylation and dearomatization of trimethylbenzenes with O2 .

Optimization of Ultrathin Backlight Unit by Using a Tapered Light Guide Film Studied by Optical Simulation

Optical structures of a tapered ultra-thin light guide film (LGF) were optimized by optical simulation for increasing coupling efficiency between light sources and the LGF. A serration pattern on the entrance side surface could provide a comparable coupling efficiency to that of the conventional LGF where a linear, asymmetric prism array was formed on the taper surface. Several micro-patterns were applied to the top and/or bottom surface of the LGF for achieving better luminance property, and it was found that an optimized micro-pyramid pattern exhibited the highest average luminance together with satisfactory luminance uniformity.

Engineered P450 biocatalysts show improved activity and regio-promiscuity in aromatic nitration

Nitroaromatics are among the most important and commonly used chemicals but their production often suffers from multiple unsolved challenges. We have previously described the development of biocatalytic nitration processes driven by an engineered P450 TxtE fusion construct. Herein we report the creation of improved nitration biocatalysts through constructing and characterizing fusion proteins of TxtE with the reductase domain of CYP102A1 (P450BM3, BM3R). The majority of constructs contained variable linker length while one was rationally designed for optimizing protein-protein interactions. Detailed biochemical characterization identified multiple active chimeras that showed improved nitration activity, increased coupling efficiency and higher total turnover numbers compared with TxtE. Substrate promiscuity of the most active chimera was further assessed with a substrate library. Finally, a biocatalytic nitration process was developed to nitrate 4-Me-dl-Trp. The production of both 4-Me-5-NO2-l-Trp and 4-Me-7-NO2-l-Trp uncovered remarkable regio-promiscuity of nitration biocatalysts.

Interaction between a bubble and a metal target for underwater laser propulsion.

Optical beam deflection and high-speed photographic methods are employed to investigate the interaction mechanism between a laser-induced bubble and a metal target for underwater laser propulsion. A preliminary theory is proposed to reveal the step increases of the kinetic energy transferred to the target during the process of increasing the incident laser energy. This theory also helps to explain the increasing coupling efficiency with incident laser energy for underwater laser propulsion.

Power optimisation for wearable heart rate measurement device with wireless charging

Continuous measurement of heart rate is necessary for monitoring the patients with heart ailments. A wearable which continuously measures heart rate of an individual by a method called reflectance-based photoplethysmography (PPG) computes the heart rate of an individual according to the volumetric changes in blood flowing through the body is developed. In order to make the device more compact as well as with IP67 and IP68 standard, wireless charging technique is employed because it helps to get rid of wires while charging. Following the Qi standard for designing wireless power receiver circuits makes the device interoperable and work with greater efficiency with reduced losses. Impedance matching and designing the circuit to operate under resonance condition increases coupling efficiency in case of inductive coupling.

Waveguiding characteristics of surface enhanced Raman scattering signals along crystalline organic semiconducting microrod.

The waveguiding of surface enhanced Raman scattering (SERS) signals was demonstrated by using organic semiconducting microrods (MRs) hybridized with functionalized gold nanoparticles (Au-NPs). Organic semiconducting 1,4-bis(3,5-bis(trifluoromethyl) styryl)-2,5-dibromobenzene (TSDB) crystalline MRs were fabricated as active optical waveguiding system using a self-assembly method. The static SERS effect and the enhancement of photoluminescence were simultaneously observed for the TSDB MRs hybridized with Au-NPs. The waveguiding characteristics of the SERS signals through the hybrid MR of TSDB/Au-NPs were investigated using a high-resolution laser confocal microscope (LCM) system. The enhanced output Raman characteristic modes of TSDB molecules were clearly observed along the hybrid MR of TSDB/Au-NPs, which is attributed to stronger scattering of the light and the increased coupling efficiency of waveguiding due to the presence of Au-NPs. The waveguiding of the SERS signals exhibited different decay constants for the corresponding characteristic Raman modes, such as -C = C- aromatic, -CF3, and C-Br stretching modes. The observed waveguiding characteristics of various SERS modes enable multi-modal waveguiding with relatively narrow spectral resolution for nanophotonic information.

A Dual Cylindrical Tunable Laser Based on MEMS

Free space optics is considered the topic of the day and have a large variety of applications which free space separates source from destination such as External cavity tunable laser (ECTL). In ECTL, laser source emits Gaussian beam that propagates in plane with substrate until reach external reflector. The efficiency of these applications depends on the amount of light that coupled back to the laser, called coupling efficiency. Increasing coupling efficiency depends on using assembled lens's or any optical part in the path between laser front facet and external reflector, which result in increasing the cost and integration effort. We innovate here anew configuration of external cavity tunable laser based on cylindrical (curved) Mirrors. The usage of cylindrical mirror affects on the amount of light that coupled back to laser and that decreases the alignment requirement in the laser assembly as compared to another configurations based on flat mirror. The fabrication of cylindrical mirror is simple with respect to spherical mirror so it can be used in batch fabrication. Tuning achieved by using micro electro mechanical system MEMS technology. The system consists of a laser cavity and a two filter cavities for wavelength selection. The formation of cylindrical microstructures were made into the substrate volume. So we report also the micromachining method that used for fabricating the cylindrical mirror. Anisotropic etching and the deep reactive ion etching (DRIE) are especially useful for the batch fabrication of large optical mechanical devices. The characteristics of the laser's spectral response versus laser facet reflectance variations are described via simulations. The diffraction of light in ECTL formed by the laser front facet and the external reflector are taken into account. Here we report all things about the model including the fabrication steps and simulation analysis.