激光回馈效应及其传感应用研究的进展

对基于激光回馈效应的传感应用研究进展进行了综述。由于激光回馈引起激光器功率波动一个条纹对应外部反射镜移动半个光波波长,功率波动深度与传统双光束干涉系统相当,基于该现象的激光回馈干涉仪与传统的干涉仪相比具有相同的相位灵敏度。但其结构简单、紧凑、易准直的特点,引起了国内外科研者浓厚的兴趣,开发了很多全新概念、经济实用的精密测量仪器。对激光回馈效应在位移测量、速度测量、振动测量、距离测量、角度测量和形貌测量中的原理进行了介绍,同时对各传感应用系统进行了评述。     

Single-waveguide-based microresonators for optical sensing

Optical biosensors with a high sensitivity and a low detection limit play a highly significant role in extensive scenarios related to our daily life. Combined with a specific numerical simulation based on the transfer matrix and resonance condition, the idea of novel single-waveguide-based microresonators with a double-spiral-racetrack(DSR) shape is proposed and their geometry optimizations and sensing characteristics are also investigated based on the Vernier effect. The devices show good sensing performances, such as a high quality factor of1.23 × 105, a wide wavelength range of over 120 nm, a high extinction ratio(ER) over 62.1 d B, a high sensitivity of 698.5 nm/RIU, and a low detection limit of 1.8 × 10-5. Furthermore, single-waveguide-based resonators can also be built by cascading two DSR structures in series, called twin-DSRs, and the results show that the sensing properties are enhanced in terms of quasi free spectral range(FSR) and ER due to the double Vernier effect.Excellent features indicate that our novel single-waveguide-based resonators have the potential for future compact and highly integrated biosensors.     

Photonic sensing components for fiber networks

Photonic sensing technologies are an integral part of Remote Fiber Test Systems used for maintaining optical fiber networks. Optical components used for this purpose such as branching components, filters, switches, water sensors and fiber identifiers are overviewed.     

New lipophilic rhodamines and their application to optical potassium sensing

New lipophilic fluorescent rhodamines were synthesized directly from 3,6-dichlorofluoresceins and the respective long-chain amines with excellent solubility in lipids and lipophilic membranes. Spectrophotometric and luminescent properties of the dyes are reported and discussed with respect to their application in new optical ion sensors. One rhodamine (2a) was applied in a poly(vinyl chloride)-based sensor membrane for continuous and sensitive optical determination of potassium ion, using valinomycin as the neutral ion carrier.     

Grating coupled interferometry for optical sensing

An interferometric sensor based on gratings on a planar waveguide is introduced. The device combines the advantages of known interference-based waveguide sensors with the simplicity of grating couplers. In the presented configuration, two parallel and coherent light beams, laterally separated in the direction of mode propagation, are coupled into a planar waveguide through a grating. One of the coupled beams is phase modulated using a periodically relaxing liquid crystal modulator, resulting in a time varying intensity signal at the end face of the waveguide. Refractive index changes within the waveguide section between the two coupling regions are monitored by observing characteristic changes in the intensity signal.     

Modeling of optical spectroscopy for the crystalline silicon

The paper is aimed at modeling optical spectra of silicon. Optical spectra of silicon are described with the Logistic function. A satisfactory agreement between the measured and the modeled optical spectra are obtained. The minimum magnitude of the correlation coefficient between experiment and theoretical results is 0.994, and the maximum average relative error is 4.21%. Meanwhile, it is found that the band gap of semiconductor may be determined by fitting absorption coefficient as a function of wavelength. Lastly, the mathematical relationships between the parameters, which are used to link the reflectance of silicon and wavelength, and radiation fluency, are obtained. Consequently, the change of reflectance for silicon can be predicted by both wavelength and dose radiation fluency only one function. All results in this paper are of interest from both optics and materials point of view.     

Rapid optical measurement of surface texturing result of crystalline silicon wafers for high efficiency solar cells application

Surface texturing of crystalline silicon (c-Si wafers) wafers is a frequently used technique in high efficiency solar cells processing to reduce the light reflectance. Measuring the surface texturing result is important in the manufacturing process of high efficiency solar cells because the surface texturing of c-Si wafers is sensitive to the performance of reducing front reflection. Traditional approach for measuring surface roughness of texturing of c-Si wafers is atomic force microscopy. The disadvantage of this approach include long lead-time and slow measurement speed. To solve this problem, an optical inspection system for rapid measuring the surface roughness of texturing of c-Si wafers is proposed in this study. It is found that the incident angle of 60° is a good candidate for measuring surface roughness of texturing of c-Si wafers and y = ?188.62x + 70.987 is a trend equation for predicting the surface roughness of texturing of c-Si wafers. Roughness average (Ra) of texturing of c-Si wafers (y) can be directly determined from the peak power density (x) using the optical inspection system developed. The results were verified by atomic force microscopy. The measurement error of the optical inspection system developed is approximately 0.89%. The saving in inspection time of the surface roughness of texturing of c-Si wafers is up to 87.5%.     

Nonlinear planar asymmetrical optical waveguides for sensing applications

This paper provides a theoretical analysis for TE polarized waves guided by a linear film surrounded by two asymmetrical nonlinear media for sensing applications. The sensitivity of the proposed sensor is derived. The conditions required for the sensor to exhibit its maximum sensitivity are presented. This analysis covers the case when the measurand is homogeneously distributed in the covering medium. We show that nonlinear sensors have sensitivities higher than those of linear sensors. The authors believe that optical sensing can be improved by introducing nonlinear waveguides.     

Genetic optical design for a compressive sensing task

We present a sophisticated optical design method for reducing the number of photodetectors for a specific sensing task. The chosen design parameter is the point spread function, and the selected task is object recognition. The point spread function is optimized iteratively with a genetic algorithm for object recognition based on a neural network. In the experimental demonstration, binary classification of face and non-face datasets was performed with a single measurement using two photodetectors. A spatial light modulator operating in the amplitude modulation mode was provided in the imaging optics and was used to modulate the point spread function. In each generation of the genetic algorithm, the classification accuracy with a pattern displayed on the spatial light modulator was fed-back to the next generation to find better patterns. The proposed method increased the accuracy by about 30 % compared with a conventional imaging system in which the point spread function was the delta function. This approach is practically useful for compressing the cost, size, and observation time of optical sensors in specific applications, and robust for imperfections in optical elements.     

Silica-clad crystalline germanium core optical fibers

Silica-clad optical fibers comprising a core of crystalline germanium were drawn using a molten core technique. With respect to previous fibers drawn using a borosilicate cladding, the present fibers exhibit negligible oxygen despite being fabricated at more than twice the melting point of the germanium. The counterintuitive result of less oxygen when the fiber is drawn at a higher temperatures is discussed. The measured propagation loss for the fiber was 0.7?dB/cm at 3.39?μm, which is the lowest loss reported to date.     

Antiresonant guiding microstructured optical fibers for sensing applications

A novel refractometric sensor utilizing unique spectral properties of antiresonant-guiding microstructured optical fibers is proposed. The sensor operation is based on the wavelength shift of the transmission spectrum in response to the refractive index change of a sample loaded in the air-holes of the microstructured optical fiber. Refractive index changes on the order of 0.1% can be detected using less than a nanoliter of a sample.     

Silver nanocrystals modified microstructured polymer optical fibres for chemical and optical sensing

In-fibre chemical and optical sensors based on silver nanocrystals modified microstructured polymer optical fibres (MPOFs) were demonstrated. The silver nanocrystals modified MPOFs were formed by direct chemical reduction of silver ammonia complex ions on the templates of array holes in the microstructure polymer optical fibres. The nanotube-like and nanoisland-like Ag-modified MPOFs could be obtained by adjusting the conditions of Ag-formation in the air holes of MPOFs. SEM images showed that the higher concentration of the reaction solution (silver ammonia 0.5 mol/L, glucose 0.25 mol/L), gave rise to a tubular silver layer in MPOF, while the lower concentration (silver ammonia 0.1 M, glucose 0.05 M) produced an island-like Ag nanocrystal modified MPOF. The tubular Ag-MPOF composite fibre was conductive and could be directly used as array electrodes in electrochemical analyses. It displayed high electrochemical activity on sensing nitrate or nitrite ions. The enhanced fluorescence of dye molecules was observed when the island-like Ag-modified MPOF was inserted into a fluorescent dye solution.     

压缩感知理论在光学成像中的应用

压缩感知以信号的稀疏性或可压缩性为条件,以远低于耐奎斯特采样频率对信号数据进行采样和编码。简要概括了压缩感知的基本理论,它采用非自适应线性投影来保持信号的原始结构, 能通过数值最优化问题精确或高概率地重构原始信号。详细介绍了其在光学成像系统中的应用,主要包括单像素相机、超薄成像、编码孔径成像、多路技术智能成像、多光谱成像和CMOS成像等成像系统。最后对该理论的应用前景进行了阐述。     

Resolving pm wavelength shifts in optical sensing

The reflection or transmission properties of one and two-dimensional photonic crystals are widely used for optical sensing applications. A variety of optical sensors exist that change their optical properties upon receiving a stimulus. A compact wavelength detector capable of resolving very small changes in the spectral output of these sensors is highly desirable. A photodiode array (PDA) or position sensor device (PSD) in combination with a linear variable band-pass filter constitutes a very robust and compact device to detect those changes. The filter converts the wavelength information of the incident light into a spatial intensity distribution that is analyzed by the photodetector. We have investigated the performance of these wavelength detectors depending on the optical properties of the filter. This includes the gradient with which the transmission peak shifts across the filter surface and the spectral width of the transmission function. Also, we point out differences between the PDA and the PSD and analyze the influence of inhomogeneous illumination on the unit. PACS 42.68.Ay; 42.79.-e; 42.81.Pa     

Laser-fabricated dielectric optical components for surface plasmon polaritons

Fabrication of dielectric optical components for surface plasmon polaritons (SPPs) by two-photon polymerization (2PP) is studied. This direct-write femtosecond laser technology provides a low-cost and flexible method for the fabrication and investigation of plasmonic structures and optical components. Using the 2PP technique, we fabricated narrow dielectric ridges with dimensions as small as 150 nm on metal surfaces. SPP excitation with the laser-fabricated structures and guiding along them are demonstrated.     

D-shape polymer optical fibres for surface plasmon resonance sensing

We experimentally studied three different D-shape polymer optical fibres with an exposed core for their applications as surface plasmon resonance sensors. The first one was a conventional D-shape fibre with no microstructure while in two others the fibre core was surrounded by two rings of air holes. In one of the microstructured fibres we introduced special absorbing inclusions placed outside the microstructure to attenuate leaky modes. We compared the performance of the surface plasmon resonance sensors based on the three fibres. We showed that the fibre bending enhances the resonance in all investigated fibres. The measured sensitivity of about 610 nm/RIU for the refractive index of glycerol solution around 1.350 is similar in all fabricated sensors. However, the spectral width of the resonance curve is significantly lower for the fibre with inclusions suppressing the leaky modes.     

Porous silicon layer for optical sensing of organic vapor

The objective of this study is to evaluate the feasibility of porous silicon (PS) layer as a vapor sensor. We prepared three types of PS layer samples - a single layer, distributed Bragg reflector (DBR) layer, and microcavity layer - and examined their reflectance spectra before, during, and after exposure to different concentrations of various organic vapors. When the PS layer samples were exposed to the organic vapors, their reflectance spectra promptly shifted toward longer wavelengths. We determined that this redshift in the reflectance spectra could be attributed to the changes in the refractive index induced by the capillary condensation of organic vapors in the pores of the PS layers. The PS layers showed excellent sensing ability under different concentrations and types of organic vapors. Once the organic vapors were removed, the reflectance spectra of the PS layer samples promptly returned to their original states. In this study, we successfully demonstrated the rapid, sensitive, and reversible sensing of organic vapors using different PS layers.     

Modeling of nanoparticle-induced Rayleigh-Gans scattering for nanofiber optical sensing

Based on Rayleigh-Gans scattering theory of spherical particles and evanescent-wave guiding properties of nanofibers, we calculate the scattered power of nanoparticles in the vicinity of typical waveguiding nanofibers. It shows that, by optimizing the wavelength of the probing light and the diameter of the nanofiber, nanoparticle-induced scattering intensity can reach detectable level with possibilities for single-molecule detection. Results presented in this work suggest a simple approach to high-sensitivity nanofiber optical sensing of nanoparticles in aqueous solutions.     

Improvement for optical mechanics method of coherent gradient sensing

Coherent gradient sensing (CGS) is double grating lateral-shearing interferometric technique with the simplicity of the optical set-up, non-contact, real-time, full-field optical information and variable resolution, which has shown many applications in the study of quasi-static as well as dynamic crack-tip field in both homogeneous and composite materials. It can be used both in a reflection mode (for opaque materials) and in a transmission mode (for transparent materials). The accuracy of the fringe order in the CGS interference image will deeply influence the precision of experimental study. Because of the difference in the optical principle from other optical methods, the fringe order of CGS cannot be obtained through the phase-shift technology. In this paper, a kind of modified CGS method is introduced and analyzed, which can accurately obtain the fringe order of random position in the CGS interference image. This method does not need additional optical set-up and complicated image processing techniques, but only needs several (greater than two) CGS interference images under different loadings. Static fracture experiments show that this method can evidently improve the precision of the CGS method.     

Grating-assisted polarization optical time-domain reflectometry for distributed fiber-optic sensing

We report a novel type of polarization optical time-domain reflectometry (POTDR) for fully distributed fiber-optic sensing, in which the reflected optical signal is from a series of fiber Bragg gratings that are uniformly distributed along the fiber. Compared with a conventional POTDR that uses the Rayleigh backscattering, this grating-assisted POTDR can have a much better signal-to-noise ratio and consequently a better measurement resolution and a larger measurement range of the fiber birefringence. Experimental results have shown that the measurement resolution of the grating-assisted POTDR is almost an order of magnitude better than that of a conventional POTDR.