High-speed optical pulse shaping based on programmable lithium niobate spatial light modulators.

Pulse shaping plays a key role in various applications of ultrafast lasers, such as optical communications, laser micromachining, microscopy, and quantum coherent control. Conventional pulse shaping devices based on liquid crystal spatial light modulators (LCSLMs) or digital micromirror devices (DMDs) only have the shaping speed of several hertz to kilohertz, which is not suitable for applications requiring a high-speed response. Here, we demonstrate a high-speed programmable lithium niobate spatial light modulator (LNSLM) with 128 individual modulation channels and a modulation speed that can reach 1 MHz. Then we establish a high-speed LNSLM-based Fourier-transform (FT) pulse shaper to realize high-speed pulse shaping, and the update rate can reach 350 kHz, only limited by the electric circuit. The proposed high-speed pulse shaper scheme opens new avenues for future applications of ultrafast science, such as microscopic imaging, interaction between light and matter, and spectroscopy.

An efficient isoelectric focusing of microcolumn array chip for screening of adult Beta-Thalassemia.

Traditional capillary isoelectric focusing (cIEF), liquid chromatography (LC) and capillary zone electrophoresis (CZE) still suffered from low resolution for hemoglobinopathy screening. Herein, a 30-mm pH 5.2-7.8 microcolumn IEF (mIEF) array chip was developed for hemoglobinopathy screening. As a proof of concept, adult beta-thalassemia was chosen as a model disease. In the method, blood samples were hemolyzed via hemolysin solution and loaded into the microcolumn. The experiments showed that (i) the species of Hb A, F, A2 and variants were clearly separated in the chip, and the resolution was greatly higher than the ones of LC/CZE/cIEF; (ii) up to 24 samples could be simultaneously analyzed in 12-min run; (iii) the intraday and interday RSDs were respectively 3.32-4.91 % and 4.07-5.33 %. The assays of mIEF to total 634 samples were compared with the ones of LC (n = 327) and PCR (n = 307). The cutoff of 3.5 % HbA2 led to the sensitivity of 100 % and specificity of 89.1 % for the mIEF-based screening; and there was 96.7 % coincidence between the methods of mIEF and PCR if refer Hb A2 and F. The method had the merits of facility, efficiency, specificity and sensitivity in contrast to the currently-used methods, implying its potential to screening of beta-thalassemia and hemoglobinopathies.

High-speed programmable lithium niobate thin film spatial light modulator.

High-speed spatial modulation of light is the key technology in various applications, such as optical communications, imaging through scattering media, video projection, pulse shaping, and beam steering, in which spatial light modulators (SLMs) are the underpinning devices. Conventional SLMs, such as liquid crystal (LC), digital micromirror device (DMD), and micro-electro-mechanical system (MEMS) ones, operate at a typical speed on the order of several kilohertz as limited by the slow response of the pixels. Achieving high-speed spatial modulation is still challenging and highly desired. Here, we demonstrate a one-dimensional (1D) high-speed programmable spatial light modulator based on the electro-optic effect in lithium niobate thin film, which achieves a low driving voltage of 10 V and an overall high-speed modulation speed of 5 MHz. Furthermore, we transfer an image by using parallel data transmission based on the proposed lithium niobate SLM as a proof-of-principle demonstration. Our device exhibits improved performance over traditional SLMs and opens new avenues for future high-speed and real-time applications, such as light detection and ranging (LiDAR), pulse shaping, and beam steering.

A facile thermometer-like electrophoresis titration biosensor for alternative miRNA assay via moving reaction boundary chip.

Herein, a facile thermometer-like model of electrophoresis titration (ET) biosensor was proposed as an alternative tool for miRNA assay via moving reaction boundary (MRB) chip. For proof-of-concept demonstration, miRNA-122 and catalyzed hairpin assembly (CHA) were chosen as the model analyte and amplification, respectively. In the developed ET system, miRNA triggered the CHA with two hairpin probes (H1, H2) to yield H1-H2 duplexes with negative charges. Under an electric field, the duplexes moved into ET channel, and neutralized the acidic TAE buffer creating an MRB indicated by SYBR Green I (SGI). The model revealed that the MRB distance was as a function of logarithmic miRNA-122 content, indicating a facile sensing model. The relevant experiments were conducted and systemically validated the model of miRNA ET. Under the optimized conditions, the linear range of ET sensor was from 20 fM to 1 nM and the limit of detection (LOD) was 10 fM, showing a more than 100-fold sensitive increase in contrast to the one with a single CHA amplification. The mechanism of sensitive increase was well unveiled by the designed experiments. In addition, the ET biosensor had good selectivity, stability (less than 5% for intra-day and inter-day) and recovery (96%-110%), and was successfully applied for the assay of miRNA-122 and miRNA let-7a in real bio-fluids of serum and cancer cell lysate. Evidently, the proposed biosensor might be used as an alternative assay tool after nucleic acid amplification due to its high simplicity, sensitivity, specificity, linearity, stability and recovery.

Purification of low-abundance lysozyme in egg white via free-flow electrophoresis with gel-filtration chromatography.

As an effective separation tool, free-flow electrophoresis has not been used for purification of low-abundance protein in complex sample matrix. Herein, lysozyme in complex egg white matrix was chosen as the model protein for demonstrating the purification of low-content peptide via an FFE coupled with gel fitration chromatography (GFC). The crude lysozyme in egg while was first separated via free-flow zone electrophoresis (FFZE). After that, the fractions with lysozyme activity were condensed via lyophilization. Thereafter, the condensed fractions were further purified via a GFC of Sephadex G50. In all of the experiments, a special poly(acrylamide- co-acrylic acid) (P(AM-co-AA)) gel electrophoresis and a mass spectrometry were used for identification of lysozyme. The conditions of FFZE were optimized as follows: 130 µL/min sample flow rate, 4.9 mL/min background buffer of 20 mM pH 5.5 Tris-Acetic acid, 350 V, and 14 °C as well as 2 mg/mL protein content of crude sample. It was found that the purified lysozyme had the purity of 80% and high activity as compared with its crude sample with only 1.4% content and undetectable activity. The recoveries in the first and second separative steps were 65% and 82%, respectively, and the total recovery was about 53.3%. The reasons of low recovery might be induced by diffusion of lysozyme out off P(AM-co-AA) gel and co-removing of high-abundance egg ovalbumin. All these results indicated FFE could be used as alternative tool for purification of target solute with low abundance.

[Identification of the relative age of iron gall ink in handwriting by capillary electrophoresis using the Fe(â ¡)/Fe(â ¢) ratio].

Identifying the relative age of iron gall ink in the handwriting on a questioned file is highly significant for court science, because it serves as important evidence for solving criminal cases and in confirming the authenticity of historical documents. This is because many criminal cases involve analysis of forged documents to conclude whether an entire document is as old as purported, or whether the entire text in the document was written at the same time. In this paper, a novel approach based on capillary electrophoresis (CE) to estimate the relative age of iron gall ink-written texts is discussed. Two kinds of chelating agents, 1,10-phen and CDTA, were used for the simultaneous determination of Fe(Ⅱ) and Fe(Ⅲ) by CE. The stability constants of ï¼»Fe(Ⅱ)-(phen)3ï¼½2+ and ï¼»Fe(Ⅱ)-CDTAï¼½2- complexes are log ß 3=21.3 and log K=18.2, respectively, while the corresponding values of ï¼»Fe(Ⅲ)-(phen)3ï¼½3+ and ï¼»Fe(Ⅲ)-CDTAï¼½- complexes are log ß 3=14.1 and log K=29.3. First, specific binding between the two kinds of chelating agents and the ferrous/ferric ions was investigated. The results confirmed specific binding between Fe(Ⅱ) and 1,10-phen as well as that between Fe(Ⅲ) and CDTA. Preliminary studies also showed that Fe(Ⅱ) in the iron gall ink was relatively stable in the ink tank due to the low pH of commercial inks; hence, the oxidation of Fe(Ⅱ) in the tank was considered to be negligible. However, when the gall ink was exposed on a paper, sulfuric acid in the ink was gradually consumed by the cellulose of paper, thus causing gradual oxidation of Fe(Ⅱ) in the written text. Changes in the peak area ratio of Fe(Ⅱ) and Fe(Ⅲ) with aging were monitored: the older the ink in the writing, the smaller is the Fe(Ⅱ)/Fe(Ⅲ) ratio. Hence, the Fe(Ⅱ)/Fe(Ⅲ) ratio could be used for estimating the relative age of iron gall ink in writing. The Fe(Ⅱ)/Fe(Ⅲ) ratio was determined by CE, and the ratio extracted from the questioned handwriting ink was compared with that extracted from the entire document to confirm whether the entire text written at the same time. The keys to the success of this technique are establishing a suitable procedure for extracting the Fe(Ⅱ) and Fe(Ⅲ) species in the handwriting ink and a CE separation procedure. The optimized sample pretreatment procedure is as follows: (1) an ink-drawn line of 1 cm length was cut and placed in a 2 mL Eppendorf tube; (2) then, 0.5 mL of 5.0 mmol/L 1,10-phen was added to the EP tube for chelation with Fe(Ⅱ), and the mixture was subjected to vibration on a vortex mixer; (3) within 60 s, 0.5 mL of 20 mmol/L CDTA was added to the sample tube for chelation with Fe(Ⅲ); (4) the tube was strongly vibrated for 10 min on a vortex mixer; (5) after centrifugation at 10000 r/min for 15 min, the supernatant was decanted into another tube for CE analysis. The optimized conditions for the CE analysis are as follows: 100 mmol/L of pH 9.2 H3BO3-Na2B4O7 buffer, 20 kV applied voltage, sample injection (1.379 kPa, 5s), fused-silica capillary dimensions 40.2 cm×75 µm i.d. (30 cm to the detector), and 254 nm detection wavelength. Meanwhile, small amounts of 1,10-phen and CDTA were added to the buffer solution to ensure stability of the formed complexes during the CE run in the capillary and to maintain the metal ions in their original oxidation state. Finally, two kinds of iron gall ink samples were tested to evaluate the applicability of the developed method. The Fe(Ⅱ)/Fe(Ⅲ) ratios of ink sample 1 and ink sample 2 changed from 1.79 to 0.45 and from 2.67 to 0.3, respectively, from the 1st day to the 75th day after writing. The results demonstrate that the developed method can be used to highlight fraudulent insertion of information and provide important guidance for the forensic analysis of the relative age of gall ink in handwriting.

Identification of chicken meat quality via rapid array isoelectric focusing with extraction of hemoglobin and myoglobin in meat sample.

Isoelectric focusing (IEF) has been used for determination of meat quality with high stability analysis. However, it still suffered from time-consuming, laborious and cost-effective performances, e.g., 3 h protein extraction, more than 10 h rehydration time, 5-12 h focusing time, and imaging of protein band. To overcome these issues, a speedy extraction of colorful proteins was developed by controlling extraction and centrifugation of 0.2g sample within 10 min and 15 min respectively; a rapid analytical method was designed by using a quick array IEF with 25 min rehydration, 7 min focusing, 2 min online scanning and imaging of focused proteins. The total analytical time was well controlled within 1 h, significantly less than the traditional IEF time of 24 h. To demonstrate the proposed method, 18 chickens were classified into three groups, e.g., the normal slaughtering, death treatment underwater, and death with infection via the New castle disease (NDV) virus. The experiments demonstrated that two Mb bands with pI 6.8 and 7.4 were present in slaughtered chickens, while four other bands with pI 6.83, 6.95, 7.09, and 7.13 were observed in abnormal chicken. The additional four proteins bands were identified by western blot (WB) as hemoglobin proteins. Furthermore, array Immobilized pH Gradient (IPG) has high sensitivity (absolute LOD of Mb and Hb were 1.3 ng and 5.5 ng), fair stability (RSD values of 2.32%, 2.27%, and 1.69%) for slaughtered, drowned, NDV-infected chickens for intra-day and (2.94%, 1.66%, and 1.07%) for inter-days, and good recovery (100%, 98.25% and 99.75%). Finally, the developed method could be used for the identification of chicken meat quality with less time and small volume reagents consuming.

Isoelectric focusing array with immobilized pH gradient and dynamic scanning imaging for diabetes diagnosis.

A traditional immobilized pH gradient (IPG) has a high stability for isoelectric focusing (IEF) but suffers from time-consuming rehydration, focusing and staining-imaging as well as complex performance. To address these issues, an IEF system with an array of 24 IPG columns (10 mm × 600 µm × 50 µm) and dynamic scanning imaging (DSI) was firstly designed for protein focusing. Moreover, two IPG columns (pH 4-9 and pH 6.7-7.7 of 10 mm in length) were firstly synthesized for IEF. A series of experiments were carried out based on the IEF array. In contrast to a traditional IPG IEF with more than 10 h rehydration, 5-14 h IEF and ca 10 h stain-imaging, the IEF array had the following merits: 25 min rehydration for sample loading, 4 min IEF, and 2 min dynamics scanning of 24 columns, well addressing the issues of traditional IEF. Furthermore, the IEF array had fair sensitivity (LOD of 60 ng), good recovery (95%), and high stability (1.02% RSD for intra-day and 2.16% for inter-day). Finally, the developed array was successfully used for separation and determination of HbA1c (a key biomarker for diabetes diagnosis) in blood samples. All these results indicated the applicability of the developed IEF array to diabetes diagnosis.

Universal modeling of second-order nonlinear frequency conversion in three-dimensional nonlinear photonic crystals.

The second-order nonlinear frequency conversion in three-dimensional nonlinear photonic crystals is theoretically studied using coupled wave equations. A universal theoretical model is obtained, with a unified expression combining birefringence phase match, quasi-phase match, nonlinear Raman-Nath diffraction, nonlinear Cerenkov radiation and nonlinear Bragg diffraction. They are demonstrated in the numerical simulation. With the phase-matching conditions in lower dimensions extended to three dimensions, more various phenomena can be seen and corresponding mechanisms can be explained. This research enables the control of second-harmonic generation more efficiently and has potential applications in more complicated nonlinear photonic crystals.

Concentric Circular Grating Generated by the Patterning Trapping of Nanoparticles in an Optofluidic Chip.

Due to the field enhancement effect of the hollow-core metal-cladded optical waveguide chip, massive nanoparticles in a solvent are effectively trapped via exciting ultrahigh order modes. A concentric ring structure of the trapped nanoparticles is obtained since the excited modes are omnidirectional at small incident angle. During the process of solvent evaporation, the nanoparticles remain well trapped since the excitation condition of the optical modes is still valid, and a concentric circular grating consisting of deposited nanoparticles can be produced by this approach. Experiments via scanning electron microscopy, atomic force microscopy and diffraction of a probe laser confirmed the above hypothesis. This technique provides an alternative strategy to enable effective trapping of dielectric particles with low-intensity nonfocused illumination, and a better understanding of the correlation between the guided modes in an optical waveguide and the nanoparticles in a solvent.

Interference-type time lens based on temporal hologram in a loop configuration.

An alternative scheme is proposed for implementing a time lens based on the temporal hologram concept. Instead of using edge-pass filtering, this scheme achieves the keeping of only the time-lens (quadratic phase modulation) term of interest through the interference of two modulated component beams. In this scheme, an additional linear frequency component does not have to be added to the electronic drive signal to avoid the overlapping of the target frequency component and its conjugate of the modulated signal. Thus, the proposed hologram-based time lens is not only able to relax the limitation of the bandwidth and sampling rate of the arbitrary waveform generator on the time-bandwidth product and resolution to some extent, but is also capable of processing shorter input pulse signals. These advantages make the proposed interference-type hologram time lens especially suitable for use in a loop configuration, where it can be reused when the signal pulse circulates in the loop. This promises significantly enhanced time-bandwidth product and resolution, and the temporal aperture size can be designed as large as desired theoretically.

Ultrahigh-order mode-assisted determination of enantiomeric excess in chiral liquids.

A chiral liquid, whose constituent molecules lack mirror symmetry, exhibits a minor differential refractive index (RI) between the two circular polarization components. Theoretical analysis shows that the ultrahigh-order modes excited in a symmetrical metal-cladding waveguide (SMCW) are polarization-independent and have a highly sensitive response to the RI variation. We report the observation of circular differential reflectivity in a chiral liquid-filled SMCW and propose an alternative simple technique capable of determining enantiomeric excess with high sensitivity.

Optical-assembly periodic structure of ferrofluids in a liquid core/metal cladding optical waveguide.

We present a novel and simple mechanism for the fabrication of periodic microstructure based on a ferrofluids core/metal cladding optical waveguide chip. The ultrahigh-order modes excited in the millimeter scale guiding layer lead to the ordered particle aggregates in ferrofluids without applying a magnetic field. Since the absorption of photons by the extremely dilute ferrofluids is extremely small and the Soret effect is not noticeable, a tentative explanation in terms of the optical trapping effect is proposed. Furthermore, this scheme exhibits all-optically tunable reflectivity and lateral Goos-Hänchen shift, which potentially may be for practical use in novel optical devices.

High-sensitivity temperature sensor using the ultrahigh order mode-enhanced Goos-Hänchen effect.

A high-sensitivity temperature sensor based on the enhanced Goos-Hänchen effect in a symmetrical metal-cladding waveguide is theoretically proposed and experimentally demonstrated. Owing to the high sensitivity of the ultrahigh-order modes, any minute variation of the refractive index and thickness in the guiding layer induced by the thermo-optic and thermal expansion effects will easily give rise to a dramatic change in the position of the reflected light. In our experiment, a series of Goos-Hänchen shifts are measured at temperatures varying from 50.0 °C to 51.2 °C with a step of 0.2 °C. The sensor exhibits a good linearity and a high resolution of approximately 5×10(-3) °C. Moreover, there is no need to employ any complicated optical equipment and servo techniques, since our transduction scheme is irrelevant to the light source fluctuation.

Tunable delay slow-light in an active fiber Bragg grating.

We proposed and experimentally demonstrated an extremely simple and feasible slow-light technique to achieve tunable optical delay by using the Er/Yb codoped fiber Bragg grating (FBG). The signal light experiences strong dispersion when it is launched into the reflection edge of FBG, and the group delay value is determined by the signal wavelength and the pump power. In the experiment, a controllable delay of 0.9 ns can be obtained through changing the 980 nm pump power. The group velocity can be slowed down to 5.6x10(7) m/s, which is 19% of the speed of light in free space. It provides a very simple approach to control the light group delay, which is likely to have important implications for practical applications.

Tunable polarization beam splitting based on a symmetrical metal-cladding waveguide structure.

Electrical tuning of polarization beam splitting is demonstrated in the structure of symmetrical metal-cladding waveguide by introducing optically nonlinear material into both the coupling prism and the guiding layer. Due to the anisotropy of the coupling material, different excitation conditions for TE and TM modes are obtained, which results in polarization-dependent reflections and transmissions. And the splitting effect of the two orthogonally polarized beams can be manipulated through an electrical modulation of the guiding layer properties.

Enhancement of the superprism effect based on the strong dispersion effect of ultrahigh-order modes.

It is demonstrated that the superprism effect is greatly enhanced in the configuration of a symmetrical metal-cladding waveguide owing to the strong dispersion effect of ultrahigh-order modes. The experimental result shows that a notable spatial displacement of the reflected beam as large as 0.9 mm is achieved within a variation of 0.15 nm in wavelength.

Oscillating wave displacement sensor using the enhanced Goos-Hänchen effect in a symmetrical metal-cladding optical waveguide.

An oscillating wave displacement sensor based on the enhanced Goos-Hänchen (G-H) effect in a symmetrical metal-cladding optical waveguide is proposed. Since the detected signal is irrelevant to the power fluctuation of the incident light and the magnitude of the G-H shift is enhanced to hundreds of micrometers, a 40 pm resolution is demonstrated in our experiment without employing any complicated optical equipment and servo techniques.

Measurement of the second hyperpolarizability of linear conjugated polymer based on attenuated-total-reflection technique.

Based on the attenuated-total-reflection technique, a new method has been proposed to determine the second hyperpolarizability gamma(-omega(4);omega(3),omega(2),omega(1)) of the linear conjugated polymer in the off-resonant region by means of quadratic electro-optic effect. An important feature of this method is the absence of a high-power pulse laser, resulting in more convenience and cost effectivity than other techniques.

Observation of large positive and negative lateral shifts of a reflected beam from symmetrical metal-cladding waveguides.

Both large positive and negative lateral shifts were observed for the reflected light beam on a symmetrical metal-cladding waveguide. The positive and negative shifts approach about 480 and 180 microm, respectively, which to our knowledge are the largest experimental results ever reported. The experiment also proves that the positive or the negative shift depends on sign of the difference between the intrinsic and radiative damping.