High-precision measurement system based on laser interferometer for determining alcohol concentration of liquid solution

This study develops a high-precision, non-destructive measurement technique based on a laser interferometer for determining the alcohol concentration of a liquid solution from its refractive index. The optical metrology system is employed to measure the refractive indexes of samples with known alcohol concentrations ranging from 5% to 95%. By applying regressional analysis to the experimental results, an analytical expression is derived to describe the quadratic relationship between the refractive index and the alcohol concentration. An excellent agreement is observed between the experimentally determined values of the alcohol concentration and the analytically predicted results. For an assumed laser interferometer resolution of 1 nm, the measurement resolution of the proposed metrology system is found to be at least F = 0.0025%, which is significantly better than that of typical stereometry methods (approximately 1.0%) Furthermore, it is shown that the measurement resolution improves as the alcohol concentration reduces.     

A high-precision optical metrology system for determining the thickness of birefringent wave plates

This study develops a non-destructive measurement system for determining the thickness and refractive indices of birefringent optical wave plates. Compared to previous methods presented in the literature, the proposed metrology system provides the ability to measure the thickness of the birefringent optical plate in high-precision. The results show that for a commercially available birefringent optical wave plate with refractive indices of n_e=1.5518, n₀=1.5427 and a thickness of 452.1428 μm, the experimentally determined value for the error in the wave plate thickness measurement is just 0.046 μm. The measurement resolution of the proposed system exceeds that of the interferometer hardware itself. The proposed method provides a simple yet highly accurate means of measuring the principal optical parameters of birefringent glass wave plates.     

Integrated photonic glucose biosensor using a vertically coupled microring resonator in polymers

A photonic glucose biosensor incorporating a vertically coupled polymeric microring resonator was proposed and accomplished. The concentration of a glucose solution was estimated by observing the shift in the resonant wavelength of the resonator. For achieving higher sensitivity the contrast between the effective refractive index of the polymeric waveguide and that of the analyte was minimized. Actually, the effective refractive index of the polymeric waveguide (n = ∼1.390) was substantially close to that (n = ∼1.333) of the fresh solution with no glucose. The fabricated resonator sensor with the free spectral range of 0.66 nm yielded a sensitivity of ∼280 pm/(g/dL), which corresponds to ∼200 nm/RIU (refractive index units) as a refractometric sensor, and provided a detection limit of refractive index change on the order of 10⁻⁵ RIU.     

Ultrahigh sensitivity polarimetric strain sensor based upon D-shaped optical fiber and surface plasmon resonance technology

An ultrahigh sensitivity polarimetric strain sensor is proposed based upon a four-layer D-shaped optical fiber and surface plasmon resonance (SPR) technology. In contrast to existing SPR-based sensors, which are based on changes in the refractive index of the overlayer, the sensor proposed in this study is based on the change in the refractive index of the fiber core in response to the application of an axial load. Specifically, the phase difference between the P and S waves after passing through the sensor under SPR conditions is measured using a common-path heterodyne interferometer and is used to determine the corresponding change in the refractive index of the core, from which the strain is then inversely derived. The experimental results show that the sensitivity of the proposed sensor is around 2.19×10? deg/ε, i.e., degree/strain. By contrast, that of a conventional (non-SPR) polarimetric fiber sensor is just 5.2×102 deg/ε. To the best of the authors' knowledge, the sensor proposed in this study represents the first reported attempt to exploit the refractive index change of the core of an SPR-based fiber sensor for strain measurement purposes.     

A high-precision measurement technique for evaluating alcohol concentrations using an optical metrology system based on a position sensing detector

This study develops a high-precision, non-destructive optical metrology system based on a position sensing detector for measuring the refractive index of a liquid solution such that its alcohol concentration can be derived. A series of experiments are performed to measure the refractive indices of samples of known alcohol concentrations in the range 0–99.5%. The experimental results indicate that the refractive index and the alcohol concentration are related by a quadratic function. According to this mathematical function, the refractive index of a sample with an alcohol concentration of 95% is n_95%=1.36442. The measured value of the refractive index of the same sample is found to be n_alcohol-95%=1.36587. The deviation of just 0.00145 between the two sets of results confirms the accuracy of the analytical prediction method. For a sample with a known alcohol concentration of 37%, the error between the analytically predicted concentration value and the actual value is found to be less than 0.7%. Overall, the results confirm that the proposed system provides a low-cost, straightforward and highly precise approach for measuring the alcohol concentration of liquid samples.     

Nanometeric plasmonic refractive index senor

A novel surface plasmon-polaritons (SPPs) refractive index sensor based on tooth-shaped metal–insulator–metal structure is proposed and numerically simulated by using the finite difference time domain method with perfectly matched layer absorbing boundary condition. Both analytic and simulated results show that the transmission minima wavelengths in the transmitted spectrum of the sensor have a linear relationship with the refractive index of material under sensing. Based on the relationship, the refractive index of the material can be obtained from the detection of one of the transmission minima wavelengths in the transmitted spectrum. The resolution of refractive index of the nanometeric sensor can reach as high as 10^? 6, given the wavelength resolution of 0.01 nm. It could be applied to high-resolution biological sensing.     

Measurements of the refractive indices and refractive index increment of a synthetic PMMA solutions at 488 nm

We describe a Mach–Zehnder interferometer (MZI) method for measuring the refractive index (RI) of polymethyl-methacrylate (PMMA) solution in both acetone and methyl-ethyl-ketone (MEK). The measurements are made as a function of concentration values 4, 8, 12, 16 and 20 g/l at a wavelength of 488 nm with a high degree of accuracy tends to 1.4×10⁻⁵. The refractive index increments (RIIs) dn/dc of PMMA in both investigated solvents are determined too. In addition, the RIIs Δn as a function of concentration and the RIIs at zero concentration (dn/dc)_c=0 are determined for both solvents accurately. The PMMA solutions in acetone and MEK solvents are chosen for laser light scattering investigations.     

Development of a time-resolved white-light interference microscope for optical phase measurements during fs-laser material processing

A modified Mach–Zehnder interferometer set-up combined with microscope objectives has been developed for the measurement of phase changes in the processed material sample, like modification and melting of glass. The white light is generated by focusing ultrafast laser radiation (t _p=80 fs) in a sapphire crystal using a micro-lens array to minimize temporal and spatial fluctuations in the white-light continuum. Lateral and coaxial pump-probe measurements of the phase changes during material processing are performed using two coupled ultrafast laser sources at different repetition rates (f _rep=1 Hz–1 MHz). The optical phase shift and therefore the refractive index of the material are calculated from the interference images using two approaches. The knowledge of the refractive index during the laser processing with a temporal resolution in the ps-range and a spatial resolution of several microns leads to a better understanding of the initial processes for the permanent material modifications.     

Photonic crystal fiber sensor based on hybrid mechanisms: Plasmonic and directional resonance coupling

We propose a special refractive index sensor design based on a photonic crystal fiber. Two analyte channels are introduced, with one analyte channel coated with gold layer and the other one without gold layer. A hybrid resonance method is used in the sensor to achieve a large dynamic index range, where surface plasmon resonance occurs when the analyte index is lower than that of the fiber material, while the core mode couples with the resonant mode of the adjacent analyte-filled cylinder when the analyte index is larger than the fiber material. When considering fluorinated polymer fibers, a broad index range of analyte refractive index from 1.25 to 1.45 with high sensitivity can be achieved. The maximal sensitivities reach 1.4 × 10⁴ nm/RIU and 2.7 × 10⁴ nm/RIU respectively when refractive index is in the range of 1.25 to 1.383 and 1.383 to 1.45. The sensor characteristics, make this simple sensor very interesting for detecting a wide range of fluid's refractive index or chemical agent concentration.     

High-resolution liquid refractive-index sensor using reflective arrayed-waveguide grating

A high-resolution sensor for measuring the refractive index of liquids using a reflective arrayed-waveguide grating (AWG) is proposed. The refractive index of a liquid placed in the groove of the arrayed region is measured via the shift of the maximum intensity in the imaging plane of the AWG owing to the phase change in the region. The refractive index can be monitored in real time by measuring the power ratio between two output waveguides of the AWG with a narrow-band source. A mathematical model based on Fourier optics and wave optics is established. A fitting formula for the relationship between the power ratio and the refractive index of liquid is derived. The results of the study show that the proposed method can eliminate the effects of instability of the light source and the inner loss of the system and provide a refractive index resolution of 10⁻⁷.     

Broad band antireflection coating on zinc sulphide simultaneously effective in SWIR, MWIR and LWIR regions

In recent years multi-spectral imagery is steadily growing popularity. Multi-channel imaging which includes short-wave infrared (SWIR), mid-wave infrared (MWIR) and long-wave infrared (LWIR) systems are useful for threat detection, tracking, thermal signature detection and terrain analysis. In this paper, a broad band antireflection coating on ZnS substrate, simultaneously effective in SWIR, MWIR and LWIR is reported. The coating design approach was evolved using gradient index concept, where refractive index varies gradually from incident media to the ZnS (n = 2.2) substrate. The gradient index profile depicted by 4th degree polynomial n(t) = −0.45t⁴ + 1.9t³ − 2.7t² + 1.9t + 1,where n(t) is the refractive index at the distance t from ambient, and t is the thickness in micron. The profile is best approximated by eight discrete step index layers, whose first layer is thorium fluoride (n = 1.42; lowest index stable material available). Other seven layers are replaced by two equivalent layer system of real materials thorium fluoride and zinc sulphide. Final 15 layers design is deposited by e-beam evaporation. The maximum layer thickness was restricted around 0.7 μm to overcome the stress problem in the film. This 15 layers coating has shown average transmission 95% in 0.9–10.5 μm spectral band having peak 99% at 9 μm.     

An all-fiber high resolution fiber grating concentration sensor

An all-fiber high resolution optical fiber grating concentration sensor has been studied theoretically and experimentally. A long period grating is used as the sensor head and a wavelength matched fiber Bragg grating is used as an interrogator to convert wavelength into intensity encoded information for interrogation. A concentration resolution of 0.104 g/L for NaCl solution is realized in experiment. The all-fiber sensor system, with the sensor head and the interrogator being all optical fiber components, is suitable for far-distance monitoring. The sensor system is with multifunction and can be used for temperature monitoring. A temperature resolution of 0.013 °C has realized in experiment.     

Photonic Spin Hall Effect as a Highly Sensitive Refractive Index Sensing Platform for Glucose

This study presents an innovative refractive index (RI) sensor that measures glucose concentration by utilizing the photonic spin Hall effect (SHE) in a resonant optical tunneling effect (ROTE) structure. The ROTE structure consists of three InP layers with the high RI and two analyte layers (with a high-low-high-low-high RI distribution), in which glucose solution samples with the low RI are injected. By subjecting the InP layers to external bias-assisted light, the photonic SHE can be flexibly manipulated, enabling the modulation of the sensing performance accordingly. It is found that the transverse shift of photonic SHE presents a large variation in response to the tiny change in glucose concentrations. By optimizing the parameters (i.e., intensity or wavelength) of bias light, the sensitivity of this sensor can reach as high as 735.7 µm RIU⁻¹. Compared to traditional glucose sensors, this original work implements the novel photonic SHE with the superior sensing performance. Therefore, the proposed design shows promising potential for biomedical applications, such as medical diagnoses and drug discovery.     

基于离子交换条波导的生物溶液浓度传感研究

提出并实施了一种实验推定离子交换单模条波导折射率分布的新方法,给出扩散系数可用常量等效的离子交换条件,导出了条波导离子交换制备过程的两维扩散方程的一般解,拟合推定了离子交换条波导的折射率分布.多波长测试的折射率色散通过引入玻璃色散关系解决,样品测试中表征导模吸收损耗的传播常量虚部由KK变换确定.在此基础上,试制了光纤-条波导-光纤一体化传感器结构,验证实测了多种不同浓度的葡萄糖溶液,最低检测限为0.1 μM,实现了低浓度微量测试,验证了条波导传感机制的有效性.     

Stokes-Mueller matrix polarimetry system for glucose sensing

A Stokes-Mueller matrix polarimetry system consisting of a polarization scanning generator (PSG) and a high-accuracy Stokes polarimeter is used to sense the glucose concentration in aqueous solutions with and without scattering effects, respectively. In the proposed system, an electro-optic (EO) modulator driven by a saw-tooth waveform voltage is used to perform full state of polarization (linear/circular) scanning, while a self-built Stokes polarimeter is used to obtain dynamic measurements of the output polarized light intensity. It is shown that the measured output Stokes vectors have an accuracy of 10⁻⁴, i.e., one order higher than that of existing commercial Stokes polarimeters. The experimental results show that the optical rotation angle varies linearly with the glucose concentration over the range of 0-0.5 g/dl. Moreover, glucose sensing is successfully achieved at concentrations as low as 0.02 g/dl with a resolution of 10⁻⁶ deg/mm and an average deviation of 10⁻⁴ deg. In general, the polarimetry system proposed in this study provides a fast and reliable method for measuring the Stokes vectors, and thus has significant potential for biological sensing applications.     

Ultracompact refractive index sensor based on microcavity in the sandwiched photonic crystal waveguide structure

A refractive index (RI) sensor based on the two-dimensional photonic crystal is presented. The sensor is formed by a point-defect resonant cavity in the sandwiched waveguide structure. The transmission spectrums of the sensor with different ambient refractive indices ranging from n = 1.0 to n = 1.6 are calculated. The calculation results show that a change in ambient RI of Δn = 0.001 is apparent, the sensitivity of the sensor (Δλ/Δn) is achieved with 330 nm/RIU (when lattice constant a = 440 nm), where RIU means the refractive index unit; and the transmission efficiency in the RI range of 1.0-1.6 can reach about 40% to 70%, that make the detection of spectrum easy and feasible. The properties of the sensor are analyzed and calculated using the plane-wave expansion (PWE) method and simulated using the finite-difference time-domain (FDTD) method.     

Effects of deposition temperature on the structural and morphological properties of thin ZnO films fabricated by pulsed laser deposition

ZnO thin films were grown on Si(1 0 0) substrates using pulsed laser deposition in O₂ gas ambient (10 Pa) and at different substrate temperatures (25, 150, 300 and 400 °C). The influence of the substrate temperature on the structural and morphological properties of the films was investigated using XRD, AFM and SEM. At substrate temperature of T=150 °C, a good quality ZnO film was fabricated that exhibits an average grain size of 15.1 nm with an average RMS roughness of 3.4 nm. The refractive index and the thickness of the thin films determined by the ellipsometry data are also presented and discussed.     

Investigation on optical properties of Bi<Subscript>2.85</Subscript>La<Subscript>0.15</Subscript>TiNbO<Subscript>9</Subscript> thin films by prism coupling technique

Layered-perovskite ferroelectric Bi_2.85La_0.15TiNbO₉ (LBTN) optical waveguiding thin films were grown on fused silica substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD) revealed that the film is highly (00l) textured. We observed sharp and distinct transverse electric (TE) and transverse magnetic (TM) multimodes and measured the refractive indices of LBTN thin films at 632.8 nm. The ordinary and extraordinary refractive indices were calculated to be n _TE=2.358 and n _TM=2.464, respectively. The film homogeneity and the film-substrate interface were analyzed using an improved version of the inverse Wentzel–Kramer–Brillouin (iWKB) method. The refractive index of the film remains constant at n ₀ within the waveguiding layer. The average transmittance of the film is 70% in the wavelength range of 400–1400 nm and the optical waveguiding properties were evaluated by the optical prism coupling method. Our results showed that the LBTN films are very good electro-optical active material.     

Solutions to Yang-Mills field equations in eight dimensions and the last Hopf map

We will show that the Hopf map admits a sourceless, topologically non-trivial gauge field. This result will be cast in the form of a solution to eight dimensional Euclidean Yang-Mills field equations with topological chargeQ=1. This solution is Spin (9) symmetric and leads to a new generalized duality conditionFF=±(FF)*.     

Investigation on micro/nanofiber Bragg grating for refractive index sensing

We propose a refractometric sensor based on micro/nanofiber Bragg grating (MNFBG). The refractive index (RI) sensing performance dependence on the fiber radius and Bragg grating period of the sensor, as well as the temperature cross-sensitive effect, is investigated theoretically. The simulation results demonstrate that 400 nm-radius MNFBG has a linear response to RI ranging from 1.3 to 1.39 with a sensitivity as high as 992.7 nm/RIU and half temperature cross-sensitivity of normal FBG. A maximum sensitivity of up to 1200 nm/RIU and an outstanding RI resolution of 8.3 × 10^-6 can be achieved. MNFBG has high potential in various types of optical fiber sensor applications.