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Surface-enhanced Raman scattering (SERS), owing to its high sensitivity and rapid response, has been widely used in various fields. However, it is still a challenge to prepare SERS substrates with ...

Recently, more and more attention has been given to a semiconductor oxide-based surface-enhanced Raman spectroscopy substrate for its great stability and biocompatibility. However, its poor SERS sensitivity limits the applications of semiconductor oxide SERS substrates. In this paper, we provide a facile reduction method to modulate oxygen vacancy concentrations in oxide SERS substrates. Using MoO2 as an example, the resonance coupling as well as charge transfer between the semiconductor oxide SERS substrate and the target molecules were promoted for the reason of artificial oxygen vacancy embodied in the Raman signals being improved. By using the TEM, SEM, and XPS measurements, we confirmed that we successfully prepared defective MoO2- x with a polycrystalline surface. MoO2- x modulated oxygen vacancy treated with 6 wt % Li shows a very high detection sensitivity of 10-8 M (4.79 ug/L) for R6G, and the intensity of the Raman signal was highly enhanced. Because of the existence of defective energy levels, resonance coupling, as well as charge transfer between semiconductor and molecules, was obviously promoted. More importantly, the method of modulating oxygen vacancy can be widely used in semiconductor oxide materials for its chemical enhancement capacity can be promoted by artificial oxygen vacancy.

In this paper, a transmissive color filter with an ultra-narrow full width at half of the maximum is proposed. Exploiting a material with a high index of refraction and an extremely low extinction coefficient in the visible range allows the quality factor of the filter to be improved. Three groups of GaP/SiO2 pairs are used to form a Distributed Brag reflector in a symmetrical Fabry-Pérot cavity. A band-pass filter which is composed of ZnS/SiO2 pairs is also introduced to further promote the purity of the transmissive spectrum. The investigation manifests that a series of tuned spectrum with an ultra-narrow full width at half of the maximum in the full visible range can be obtained by adjusting the thickness of the SiO2 interlayer. The full width at half of the maximum of the transmissive spectrum can reach 2.35 nm. Simultaneously, the transmissive efficiency in the full visible range can keep as high as 0.75. Our research provides a feasible and cost-effective way for realizing filters with ultra-narrowed linewidth.

High-speed fringe structured light projection system is one of the key technologies for real-time and efficient measurement of phase three-dimensional topography measurement system. Its function is to generate a modulated fringe pattern for three-dimensional measurement. Digital projectors based on DMD (Digital Mircomirror Device) have been widely used in three-dimensional projection fringe measurement systems due to their advantages such as high contrast, high brightness, high efficiency, and secondary development. This paper designs a high-efficiency and high-uniformity fringe projector illumination system based on DMD, with a light efficiency of 54%, a uniformity of 91.5%, and an illumination beam angle distribution of 10°–38°. The overall system size is 70 mm × 74 mm × 35 mm, which is applied to the phase three-dimensional topography measurement system, has important research significance and practical value.

To obtain 3D information of an object, the object must be measured. As a non-contact and active measurement method, structured light-based 3D measurement technology has a wide range of applications. The image quality of the projection lens determines whether the projection grating can be clearly projected on the detection object in the 3D measurement, which directly affects the detection effect. In this paper, a DMD projection imaging lens suitable for 3D measurement of structured light is designed. The effective focal length is 33.9 mm, F/# is 2.3, and the total length of the optical system is 120 mm. At a lens resolution of 93 lp/mm, the MTF values of all fields of view are greater than 0.5, the maximum distortion of the full field of view is less than 1%, the field curvature is less than 0.05 mm, and the imaging quality is good enough for 3D measurement.

As a new class of two-dimensional material, MXene not only has the unique planar structure, electronic and optical properties, but also has a large surface area and hydrophilicity, which make them to build as potential SERS substrates with good sensitivity and stability. In this work, we reported a modified method by adjusting the ratio of HCl to LiF and reducing sonicate time to form large-sized monolayer Ti3C2Tx nanosheets. SERS performance of Ti3C2Tx was demonstrated by detecting dye molecules such as CV, R6G and MG. A remarkable enhanced effect was obtained, and Raman signals up to 10−8 M could be detected. Furthermore, the relationship between SERS effects and illumination laser wavelengths of different probe molecules has been studied, the results showed the selectivity between dye molecules and the excitation wavelengths. Besides, the uniformity and stability of the substrates have been proved by mapping experiments in a large area (80 × 80 μm2). The results demonstrated that Ti3C2Tx nanosheets can be built as lager-sized, uniform and stable sensor for ultra-sensitive detection of organic dye pollutant molecules.

Pesticide detection is of tremendous importance in agriculture, and Raman spectroscopy/Surface-Enhanced Raman Scattering (SERS) has proven extremely effective as a stand-alone method to detect pesticide residues. Machine learning may be able to automate such detection, but conventional algorithms require a complete database of Raman spectra, which is not feasible. To bypass this problem, the present study describes a transfer learning method that improves the algorithm's accuracy and speed to extract features and classify Raman spectra. The transfer learning model described here was developed through the following steps: (1) the classification model was pre-trained using an open-source Raman spectroscopy database; (2) the feature extraction layer was saved after training; and (3) the training model for the Raman spectroscopy database was re-established while using self-tested pesticides and keeping the feature extraction layer unchanged. Three models were evaluated with or without transfer learning: CNN-1D, Resnet-1D, and Inception-1D, and they have improved the accuracy of spectrum classification by 6%, 2%, and 3%, with reduced training time and increased curve smoothness. These results suggest that transfer learning can improve the feature extraction capability and therefore accuracy of Raman spectroscopy models, expanding the range of Raman-based applications where transfer learning model can be used to identify the spectra of different substances.

The CMOS single photon avalanche photodiode (SPAD) image sensor, as the third-generation solid-state imaging device, features single photon response capability, picosecond magnitude time resolution and micron-scale spatial resolution. The device is currently the mainstream ideal device for single-photon, picosecond time-resolved transient imaging, and is gradually applied to time-resolved spectral measurement, 3D ranging and imaging, fluorescence lifetime imaging, quantum imaging sensing and such low light or even single photon ultrafast imaging. In this paper, we introduce the research progress of the CMOS SPAD image sensor, and the challenges and solutions of the device are analyzed. In the past years, the mainstream CMOS SPAD image sensor features front-illuminated SPAD and the planar-structure pixel. However, for the planar-structure pixel, in order to make the SPAD with higher fill factor, reducing the duty cycle of the readout electronics within the pixel is the usual method, which to some extent sacrifices the function of reading electronics. In addition, the lower process node was used to improve the integration of electronics, but the high dark count rate was easily caused; The integration of micro-lens array in pixels was also used, but limits the flexibility of pixel size and increases the costs. Compared with planar-structure pixel, the pixel scheme of the three dimensional (3D) stacked structure, integrates the SPAD device and the readout electronics in the pixel correspondingly on the vertically coupled two wafers, which eliminates the problem of duty cycle of the readout electronics within the pixel and would be the development direction in the future.

Holographic reconstruction is affected by the phase-conjugate wave arising from the symmetry of the complex field. Compressive sensing (CS) has been used in in-line digital holography (DH) to eliminate noise, especially the interference from twin images. Herein, CS with total variation regularization combining autofocusing is presented. It provides an autofocusing function from a single-exposure hologram and obtains reconstructed objects without twin image noise. A series of images at a fixed interval within a reconstruction distance are processed using a two-step iterative shrinkage/thresholding algorithm in CS. It can calculate the focus distance in a larger range around the focal plane using twin-image-free reconstruction, so it can achieve a higher focusing accuracy than traditional focusing methods, including the Laplace operator, absolute gradient operator, and Tamura coefficient. The proposed method is a simple combination of algorithms and a powerful extension that can effectively improve simulated and experimental image quality and handle difficult datasets, which existing algorithms cannot.

A mode-locked all-fiber laser based on the nonlinear multimode interference (NL-MMI) effect of the graded-index multimode fiber (GIMF) is proposed and demonstrated. The saturable absorber (SA) used in the laser consists of a step-index multimode fiber (SIMF) connected by a GIMF. Compared with the theoretically proposed SMF–GIMF–SMF structure, the introduction of the SIMF eliminates the restriction on the length of the GIMF and provides a more flexible method of making an SA based on the NL-MMI. Through bending the device to a certain state, the modulation depth of the SA was measured to be 3.16%. The mode-locked laser output pulses have the pulsewidth of ∼446 fs, the bandwidth of 4.48 nm, and the fundamental repetition rate of 11.73 MHz. This versatility and simplicity of the SA device combined with the possibility of scaling the pulse energy in the large-mode-area double-clad fiber laser make it highly attractive in ultrafast photonics.

Digital holographic imaging is able to reconstruct phase and three-dimensional (3D) information of an object from a one-shot two-dimensional (2D) lensless hologram. A dense encoder–decoder network, called Dense-U-net, is proposed to realize the reconstruction of a 3D particle field. The radii and 3D coordinates of the particles are encoded into a 2D grayscale image as the ground truth. The 2D hologram was served as the input of the network. A Dense_Block is designed and added to the encoder and decoder of the traditional U-net model. Each layer takes the inputs from all previous layers and passes its own feature map to all subsequent layers. Thus, as the diffraction is distributed throughout the entire hologram, both the features with high signal-to-noise ratio at the center of the particle and the diffraction features with low signal-to-noise ratio around the particle can be learned, thereby facilitating the full characterization of the particles. Using the specially designed dense connection module, network training can be accomplished with fewer parameters and faster speeds.

The research of surface enhanced Raman scattering (SERS) based on semiconductor substrate expends the application field of SERS technology. However, the relatively low enhancement sensitivity of semiconductor materials is still a problem to be solved urgently. Herein, high-performance enhancement of Raman scattering is achieved through hierarchical CuS microflowers. Simultaneously based on electromagnetic near-filed effect and charge transfer effect between the reporter molecule and CuS material system, the enhancement factor can reach 105 and the detection limitation is as low as 10−8 M for MG and 10−7 M for CV and R6G molecules. The enhancement sensitivity is proved to be related to the number and spacing of petals of the CuS flowers, and illumination of the incident wavelength. A finite integration method is conducted to estimate the electromagnetic field around the CuS microflower system. The ground-state properties of the system are calculated by DFT method. The energy level schematic diagram of the probe molecules on CuS system is employed to investigate the charge transfer process between the reporter molecule and CuS microflower system. Due to the unique properties of semiconductors, such as surface functionalization, stable material properties and degradability, CuS microflower can be served as a high-performance SERS platform to expend the application field of SERS, and is a valuable tool for the research of semiconductor surfaces.

The artificial intelligence technology has achieved great progress recently and has potential in the applications of military, intelligent industry, transportation and logistics, intelligent security check, national security, biomedicine, intelligent agriculture, intelligent services, and so on. Human-like sensor and algorithm are two pillars of artificial intelligence technology, corresponding to the ‘senses’ and ‘brains’ of intelligent machines, respectively. Based on traditional sensor technology, the artificial intelligence human-like sensor combines the novel complementary metal oxide semiconductor (CMOS), micro-electro-mechanical systems (MEMS), nanotechnology, big data and cloud computing, Internet technology, and so on, leading to the great improvement of the sensors performance. In this paper, the artificial intelligence human perception is divided into five categories: vision, hearing, smell, taste, and touch, and corresponding research progress and application of the sensors were introduced.

This paper introduces the major Chinese research groups in the fields of biomedicine, food safety, environmental testing, material research, archaeological and cultural relics, gem identification, forensic science, and other research areas of Raman spectroscopy and combined methods spanning the two decades from 1997 to 2017. Briefly summarized are the research directions and contents of the major Chinese Raman spectroscopy research groups, giving researchers engaged in Raman spectroscopy research a more comprehensive understanding of the state of Chinese Raman spectroscopy research and future development trends to further develop Raman spectroscopy and its applications.

A nonlinear interferometer can be constructed by replacing the beam splitter in the Mach-Zehnder interferometer with four-wave mixing (FWM) process. Meanwhile, the conventional surface plasmon resonance (SPR) sensors can be extensively used to infer the information of refractive index of the sample to be measured via either angle demodulation technique or intensity demodulation technique. Combined with a single FWM process, a quantum SPR sensor has been realized, whose noise floor is reduced below standard quantum limit with sensitivity unobtainable with classical SPR sensor. Therefore, in this work we have theoretically proposed a nonlinear interferometric SPR sensor, in which a conventional SPR sensor is placed inside nonlinear interferometer, which is called as I-type nonlinear interferometric SPR sensor. We demonstrate that near resonance angle I-type nonlinear interferometric SPR sensor has the following advantages: its degree of intensity-difference squeezing, estimation precision ratio, and signal-noise-ratio are improved by the factors of 4.6 dB, 2.3 dB, and 4.6 dB respectively than that obtained with a quantum SPR sensor based on a single FWM process. In addition, the theoretical principle of this work can also be expanded to other types of sensing, such as bending, pressure, and temperature sensors based on a nonlinear interferometer.

We present a compact and novel “T” structure optical fiber refractive index sensor proposal based on surface plasmon resonance. “T” structure sensing head consists of a single mode fiber (SMF) with a plasmonic facet and a cladding partly removed single mode fiber (CPR-SMF) with a gap. The gold film is deposited on the end of SMF instead of the side of the CPR-SMF. The simulation results show that the SPR based on the “T” structure can be excited effectively. The SPR transmission spectrum shifts towards longer wavelength with the sensing sample refractive index increasing largely. When we divide the refractive index range of the sensing sample to two parts, the linear relationships between the SPR wavelength and the refractive index can be used. The resolutions can be highly up to 7.115×10 −6 RIU and 3.525×10 −6 RIU for the refractive index ranges of 1.3333–1.36 and 1.37–1.4, respectively. The proposed “T” structure sensor works well for achieving the refractive index measurement with high sensitivity and wide range for samples with a tiny amount.

A simple multipoint volatile organic compounds (VOC) measurement by zeolite thin film-coated Fresnel reflection-based fiber sensor with an Array-Waveguide Grating (AWG) is proposed and demonstrated. The sensor comprise a polycrystalline silicalite thin film grown up on the cleaved end face of single-mode fiber. The chemical vapors concentration is measured by monitoring the reflection intensity, which is a function of the molecular adsorption in the crystalline micro-porous structure. Multipoint measurement is achieved by an AWG with 16 channels. Four of the 16 channels has been connected to the sensing channels as representative. The proposed VOC sensor performed with the sensitivity from 0.015 to 3.9 × 10 −3 dB/ppm in the concentration range from 0 to 550 ppm.

This paper concerns the problem of platform vibration induced band-to-band misregistration with acousto-optic imaging spectrometer in spaceborne application. Registrating images of different bands formed at different time or different position is difficult, especially for hyperspectral images form acousto-optic tunable filter (AOTF) imaging spectrometer. In this study, a motion detection method is presented using the polychromatic undiffracted beam of AOTF. The factors affecting motion detect accuracy are analyzed theoretically, and calculations show that optical distortion is an easily overlooked factor to achieve accurate band-to-band registration. Hence, a reflective dual-path optical system has been proposed for the first time, with reduction of distortion and chromatic aberration, indicating the potential of higher registration accuracy. Consequently, a spectra restoration experiment using additional motion detect channel is presented for the first time, which shows the accurate spectral image registration capability of this technique.

An all fiber real-time laser wavelength measurement method based on Faraday rotation effect is proposed and demonstrated, for correcting the nonlinear tuning of wavelength sweep lasers. The wavelength measurement setup is mainly composed of a specially designed fiber magneto-optic device and a wavelength sensitive filter. When the linearly polarized lights with different wavelengths pass through the magneto-optic crystal, their polarization planes will be rotated at different angles. By taking use of the dispersion effect, the light wavelength can be measured by detecting the rotated angles. In our experiments, the wavelength resolution can reach 2.1 pm with a measurement range from 1520 to 1570 nm. Besides monitoring the wavelength tuning, it should be also useful in laser wavelength calibration and optical fiber sensing.

A novel, simple, and inexpensive flexible surface-enhanced Raman-scattering (SERS) platform based on common laboratory filter paper modified with T i 3 C 2 T x flakes was reported. T i 3 C 2 T x synthesized from a T i 3 A l C 2 phase with a mixture of HCl and LiF and T i 3 C 2 T x nanosheets were characterized by the TEM, XRD, UV–Vis spectrum, and Raman spectrum. Paper-based substrate has been proven to sample on rough and irregular surfaces. Thus, T i 3 C 2 T x was further manufactured as paper substrate by the immersion method to transfer nanosheets to filter paper. SERS activity of prepared substrate was demonstrated using R6G by the same filter paper modified with and without T i 3 C 2 T x , and various concentrations of R6G were tested to prove the sensitivity of the substrates. Further detection of CV and MG certified the universality of paper substrate based on T i 3 C 2 T x nanosheets for detection of organic pollutants. The uniformity and stability were proved by CV and R6G molecules. This SERS platform combines the advantages of 2D material and flexible paper scaffolds, resulting in a highly sensitive, cost-efficient, and easy-to-manufacture large-scale flexible substrate and is expected to be used in practice.

Temperature characteristics of Sensitivity-enhanced Fabry-Perot filled with PDMS temperature sensor based on Vernier effect consisting of two Fabry–Perot interferometers (FPI), one of the FPI’s cavity is internally filled with PDMS, are observed experimentally. Results show that temperature sensitivity of the Sensitivity-enhanced Fabry-Perot sensors is 1.808 nm/°C. It is Vernier effect lead to a double improvement of the temperature sensitivity compared with the sensor with single FPI, of which the cavity is internally populated with PDMS but no Vernier effect. Moreover, the improvement can be enlarged by optimizing the free spectra range of these two FPIs.

A novel mode-locking method based on the nonlinear multimode interference in the stretched graded-index multimode optical fiber (GIMF) is proposed in this Letter. The simple device geometry, where the light is coupled in and out of the stretched GIMF via single-mode fibers, is demonstrated to exhibit the temporal intensity discrimination required for mode locking. The nonlinear saturable absorber (SA) characteristics of the device are controllable by simply adjusting the strength of the stretching applied. The modulation depth of the device, which consists of ∼23.5 cm GIMF, is tuned from 10.37% to 22.27%. Such a simple SA enables the wavelength-switchable mode-locking operation in a ring Er-doped fiber laser, and ultrafast pulses with a pulse width of 506 fs at 1572.5 nm and 416 fs at 1591.4 nm were generated. The versatility and simplicity of the SA device, together with the possibility of scaling the pulse energy, make it highly attractive in ultrafast photonics.

An Er-doped mode-locked fiber laser with a saturable absorber based on single mode - graded index multimode - single mode fiber (SMF-GIMF-SMF) with inner micro-cavity is demonstrated. The modulation depth of the saturable absorber was measured to be 1.9% when the SMF-GIMF-SMF structure is bent to a certain state. Such a simple saturable absorber enables the mode-locking operation in a ring Er-doped fiber laser and ultrafast pulses with pulse energy of 0.026 nJ and pulse width of 528 fs at the fundamental repetition rate of 14.34 MHz can be generated. In addition, the harmonic mode-locking operation can also be achieved.

The platform vibration will cause spectral images blurring when using computed tomographic imaging spectrometer (CTIS) on unstable platform, especially in space-borne or ship-based application. As a result, a phenomenon of blur-induced spectral distortion occurs, which greatly affects the accuracy of classification of target. However, without easy accessibility of the knowledge of image motion kernel, it is difficult to restore the degraded images accurately. With the desire to solve the motion function, this paper has made a breakthrough by proposing a motion detection method using short exposure images from zeroth order beam light of 2D-grating. Contributed by the accurate motion kernel, blurred spectral images could be reliably restored as well as the improvement of spectra accuracy. Laboratory experiment result shows the robust spectra restoration capability of this technique.

Raman spectroscopy is a novel method of food analysis and inspection. It is highly accurate, quick, and noninvasive. The investigation and monitoring of food processing is important because most of the foods humans eat today are processed in various ways. In this article, the use of Raman spectroscopy in food processes, such as fermentation, cooking, processed food manufacturing, and so on, are explored. The characteristics and difficulties of the Raman inspection of these processes are also discussed. According to the various research reports, Raman spectroscopy is a very powerful tool for monitoring these food processes in lab environments and is likely to see usage in situ in the future.

A curvature sensor based on two cascading abrupt-tapers modal interferometer in a single mode fiber (SMF) is proposed and experimentally demonstrated in this paper. The device consists of two cascading abrupt-tapers with different sizes, manufactured by CO2 laser in a standard SMF. The cladding modes will be excited in the first abrupt-taper section, partly coupled with the core mode. After propagation of these coupled modes, they will recombine at the second abrupt-taper section. The experimental results show that the optimum visibility of interference fringe can be got only when the two abrupt-tapers are at different sizes. If we bend the proposed modal interference, part of the cladding modes will be leaked out, making the interference pattern having a shift. Thus it can be used to measure curvature. The experimental results show that the shift of the dip wavelength is almost linearly proportional to the change of curvature, and the curvature sensitivities are −13.176 nm/m−1 in the measurement ranges of 4.8 m−1 to 6.38 m−1. As the curvature continues to increase, ranging from 6.38 m−1 to 7.98 m−1, the sensitivity is doubled to −25.946 nm/m−1. Moreover, this curvature sensor can be seen low sensitive to either the external refractive index or the temperature when employing in a relatively stable environment. The proposed curvature sensor is simple-fabricated and inexpensive, which is very suitable for curvature measurement in practical applications.

A compact chemical vapor sensor based on a fiber loop mirror (FLM) inserted with a high-birefringent photonic crystal fiber (HiBi-PCF) is proposed and experimentally demonstrated. Because the resonant dips of the HiBi-PCF FLM are sensitive to the phase difference between two counter-propagating waves in the FLM, a highly sensitive chemical vapor can be achieved by measuring the resonant dip shifts when chemical vapor diffuses into the air holes of the HiBi-PCF. Experimental results show a high sensitivity of 15.5 pm/ppm for ethanol is obtained when a 5.1 cm long HiBi-PCF is used in the FLM. Three different mechanisms for the high sensitivity of the proposed sensor are discussed. A liquefaction model with a full-vector finite element method is proposed and is regarded as the main contribution.

The orientation of talents cultivation for local colleges is to train engineering application-oriented talents, so the exploration and practice on teaching reform of theory curriculum was carried out. We restructured the knowledge units basing on numerical solution problems, and chose the software to build algorithm models for improving the analytical and designed ability. Relying on micro video lessons platform, the teacher-student interaction was expanded from class to outside. Also, we programmed new experimental homework, which was suited for process evaluation. The new teaching mode has achieved good effect, and the students' application ability was significantly improved.

It is well known that broadband antireflective characteristics are frequently realized by using subwavelength tapered micro- or nanostructures. In this paper, we propose that the triangular grating in the resonance domain with period larger than the incident wavelength can also possesses broadband and wide angle antireflective performance and polarization selection. The diffraction pattern for the external reflection grating and the internal reflection one is demonstrated by the rigorous vector diffraction theory. It is found that the total transmittivity with TE polarized illumination is clearly less than that for TM polarization. The aspect ratio of grating is a significant parameter to broadband antireflection performance. For the external reflection grating, the broadband antireflection function can be achieved with the aspect ratio larger than 1.5 for both polarization modes in the resonant domain. For the internal reflection grating, the narrow band antireflection properties are demonstrated for TE polarization with higher aspect ratio. And the broadband antireflection characteristics can be revealed at the aspect ratio higher than 4.0 in the resonance domain for TM polarization. Besides, in order to determine intuitively diffraction pattern and antireflection performance, the electric field distribution was calculated for both types of triangular profile in the resonant domain, and the aspect ratio of the grating is crucial to the total transmittance.

Gauss simulation is often used to help design new LEDs according to photometric and colorimetric performance requirements. This research investigates an improved Gauss simulation model for simulating YAG-PC LEDs. Three types of PC-LEDs are investigated at commonly used CCT ranges. This research shows that desirable photometric and colorimetric qualities can be achieved. For warm white, pure white and cold white CCT ranges, CRI of 72.1, 79.8 and 84.5 can be achieved, respectively. LEDs with optimal color rendering qualities are designed; packaging and measurement of said LEDs shows that the simulation model is successful.

In this study, a fiber in-line air-gap Fabry–Perot interferometer (FPI) is fabricated by HF acid etching. For a low-cost and higher precise measurement, a demodulation system based on frequency modulated continuous wave (FMCW) technique is build up and demonstrated in this air-gap FPI. In temperature measurements, the temperature sensitivity is about 1.75 rad/°C by phase shift detection. We also test the long term performance of the system and the RMS error is about 0.04 rad, which corresponds to the temperature resolution of ~0.02 °C. It is much higher than the measurement resolution by using the traditional wavelength shift detection method. Our experiments show that the FMCW can provide a low-cost, high resolution and high speed interrogation solution to the fiber FPIs.

In this study, a high birefringence (Hi-Bi) polarization maintaining fiber (PMF) is used as the sensing element for static axis strain and dynamic vibration measurements. This multifunctional fiber sensor adopts the Sagnac loop structure, where the Hi-Bi PMF is incorporated in the fiber loop. The static axis strain measurement is realized by interrogating the broadband transmission spectra and the strain sensitivity of 1.09 pm/µs is achieved. Furthermore, the Sagnac fiber loop is applied in dynamic acoustic vibration measurements. The experimental results show that it can detect the acoustic vibrations over the frequency range of 30 Hz to 22 kHz, and shows signal to noise ratios (SNRs) over 40 dB from 800 Hz to 9000 Hz.

In this work a highly reflective long period fiber grating (RLPG) sensor is proposed. The sensor was fabricated by depositing the silver atom on both surfaces of the flat end-face and the tail profile of long period fiber grating (LPG), which makes the LPG work in high reflection mode without interferometric fringe and enhances the coupling at the resonant wavelength of original LPG. The RI-response characteristic of the RLPG was investigated. The reflection spectrum remains the resonant dip without interference infringe and the resonant wavelength has obvious blue shift with the increase of external RI. By utilizing the above characteristic, we propose an application for long distance RI measurement combining a standard optical time domain reflectometer (OTDR). Preliminary results of using the sensor to measure the refractive index of glycerol/water solutions in a distance of 100 km were successfully demonstrated.

A novel optical fiber sensor for minor chemical vapor content detecting, based on Rayleigh scattering effect in simplified hollow-core photonic crystal fiber (HC-PCF), is proposed in this paper. Both ends of the simplified HC-PCF are aligned with standard single-mode optical fibers without splicing, leaving a very short air gap to allow molecules diffusing. As the concentration of volatile organic compounds (VOCs) in a chamber increases, molecules come into the air holes of the simplified HC-PCF so that the Rayleigh scattering is excited, resulting in an intensity loss of transmission light. We can detect the minor change of VOC content by monitoring the output transmission intensity using an optical power meter. The experimental results show that the ethanol concentration sensitivity is ~0.022 dB/ppm, when a ~5.1 cm long simplified HC-PCF is used. The sensitivity will be further improved when a longer simplified HC-PCF is used. When an optical power meter with 0.01 dBm resolution is used, the ethanol concentration's resolution can reach ~0.45 ppm.

Traditional integral colorimeters use tungsten-halogen or xenon lamps for illumination, as well as correcting filters to make the instrument's spectral response meet the Luther condition. This structure causes the instruments to have relatively higher error and poor repeatability. Thus, this letter proposes a new measurement design that uses compound LEDs as the instrument's measurement light source. The new design adjusts the instrument's spectral response by modifying the spectra of the compound LEDs. A compound LED light source is designed for integral colorimeters, and an experiment is conducted to evaluate the performance of the integral colorimeter. Experiments show that the design effectively reduces the error of integral colorimeters.

A simple, compact, and high sensitive optical fiber Mach-Zehnder interferometer (MZI) based micro-displacement sensor is presented. The MZI is fabricated by a core offset connecting of two single mode fibers and bowknot-type taper. The shifts of the MZI transmission spectrum correspond to the micro-displacements on the cross section of the core offset. For the micro-displacement ranging from 0 to 13 μm, the proposed sensor shows a high sensitivity of -1.89 dB/μm, which is almost 787 times higher than that of the current similar existing micro-displacement sensor. In addition by using the intensity demodulation method, the proposed sensor can overcome the temperature and displacement cross-sensitivity effects.

A high-sensitivity hydraulic pressure sensor is proposed, which consists of a Fabry-Perot interferometer (FPI) filled with a polymer film of polydimethylsiloxane (PDMS). The FPI structure is fabricated by splicing a section of hollow core fiber (HCF) to the end-face of a lead-in single mode fiber (SMF). Then, the PDMS is filled into the HCF which acts as a light reflector and a diaphragm to detect external pressure variation. As a result, the length of the FPI cavity and the thickness of the PDMS are 137.8 µm and 33.8 µm, respectively. Experimental results indicate that the sensor's wavelength exhibits a linear response to the hydraulic pressure, which function is described as y = -7.35 × 10-3x + 1536.395. Here, x and y represent the hydraulic pressure and the wavelength, respectively. The pressure sensitivity is up to -7.35 nm/kPa. Besides, a temperature compensation method based on a fiber Bragg grating is proposed to eliminate the influence of temperature. Experiments show that the scheme can effectively eliminate the influence of temperature and achieve accurate measurement of hydraulic pressure.

In this work, a method of causing solid-phase adhered particles to detach and move via photoacoustic resonance was studied. A laser micro-resonator was designed for excitation of the photoacoustic resonance. Both simulation and experimental results showed that a sound field was formed due to transient photoacoustic interactions between the laser and the resonator. A fundamental resonance was found at 18.9 kHz when the laser harmonized with the Eigen-frequency of the resonator. For the 100 μJ/pulse laser energy, the maximum centrifugal acceleration of 3.6 × 105 m/s2 was acquired by the fundamental photoacoustic resonance. The micro-resonator performed competently for the detachment of adhered particles larger than 5 μm. Particle motion could be controlled with an acceleration or constant speed by manipulating the laser frequency and energy. This photoacoustic manipulation of microscopic objects may have applications in separation and fixation of cells, giant molecules, and dusts in lab-on-a-chip systems.

Numerical investigation on the design of a large-mode-area (LMA) single-mode photonic crystal fiber (PCF) as the sensing fiber for Raman distributed temperature sensor (DTS) is presented. The PCF can enable single-mode operation and have an extremely LMA exceeding 288 lm 2 when kept straight and over 284 lm 2 with a lower bending loss of 0.25 dB/m when bent over a 5 cm radius at a wavelength of 1550 nm. We outline the principles of our fiber design and explore the unique properties of the fiber for Raman DTS. Calculation results show that the Raman DTS system, which used the proposed PCF as the sensing fiber, can improve SNR about 3.4 times by increasing the input power compared with the Raman DTS system with a conventional single-mode fiber, because of the improved LMA, single-mode operation and good bending characteristics of the PCF.

A simple multiplexing method for relative humidity (RH) sensors based on multimode-fiber tapers (MFTs) is proposed and demonstrated. By cascading a polyvinyl alcohol (PVA) coated MFT with every channel of an Arrayed-Waveguide Grating (AWG), multipoint RH measurement is achieved. Experimental results show that the proposed multipoint RH sensor system works well. The output power for every sensor head is almost linearly increased with the RH, and the average sensitivity of the proposed sensor is about 0.23 nW/%RH within the measurement range of 35%RH–90%RH with the taper waist diameter of ∼22 μm.

To accurately utilize the sinusoidal nanopatterning grating structure for greatly improving the light extraction efficiency of light-emitting diodes, the transmittance characteristics of these nanostructures as a function of the normalized period and the normalized depth are investigated quantitatively. It is found that when the normalized period of nanostructure is less than 0.46; in other words, only zeroth order transmission light is propagating, the light extraction efficiency can be enhanced immensely due to the higher transmittance of surface structure. When the period scale of nanostructure is more than the emitted wavelength, the transmittances decrease as the structure height increase. However, as the period dimension is less than the emitted wavelength, the transmittance of surface profile is increased as the depth increases. Besides, in order to easily analyze and effectively design the transmittance characteristics of these nanopatterning structures integrated in LEDs, we propose that the developed scalar method and the effective medium theory can be used accurately. The accuracy of both uncomplicated methods is quantitatively evaluated by the comparison of diffraction efficiencies predicted by the scalar theory and effective medium method, to exact results calculated by the rigorous coupled wave analysis method.

A refractive index and temperature simultaneous measurement sensor based on a partial cone-shaped fiber Bragg grating (FBG) was demonstrated. The bandwidth of the partial cone-shaped FBG is only affected by the surround refractive index (SRI), while the wavelength decided by the un-etched FBG is only sensitive to temperature. Utilizing the obvious difference of the bandwidth and the wavelength on the refractive index and temperature, two parameters can be distinguished and measured simultaneously using one partial cone-shaped FBG. Numerical simulation and experimental results are presented. Experimental results show that the proposed sensor has an average SRI sensitivity of −18.027 nm/RIU in the SRI range of 1.33–1.42 and a temperature sensitivity of 9.8 pm/°C in the range of 20–80 °C.

For night vision devices and other applications, the transmission-mode photocathodes must be sealed to tube by indium seal process (ISP) in practical application. But in early research, the integral sensitivity has large drop to about 30% amplitude after ISP process than after activation process. In order to well study the influence of ISP on surface barriers of activated GaAs photocathodes, we used the comparative research method by surface photovoltage spectroscopy (SPS) and spectral response current (SRC). Through fitting calculation, we can find that the impurity gas sources by micro channel plate and fluorescent screen have deep influence on the amplitude and width of surface barriers which lead to the large drop on SRC curves before and after ISP process. This on-line comparative research method can help to optimize ISP technique and vacuum degree optimization for transmission-mode GaAs photocathodes in the future.

Long-period gratings (LPGs) have been fabricated in a side-hole fiber (SHF) by using a pulsed CO2laser. Sensing characteristics of this SHF-LPG to temperature surrounding refractive index and bend have been investigated. Experimental results show that resonant wavelength of the SHF-LPG has a blue shift with temperature with sensitivity of −0.11 nm/°C, a blue shift with increasing sensitivity with surrounding refractive index ranging from 1.335 to 1.44 (the maximum sensitivity is achieved when the surrounding refractive index reaches the effective index of the fiber cladding), and a red shift with bend-direction-dependent sensitivity up to 9.36 nm/m−1.

The transmission characteristics of an internal reflection grating primarily integrated into light-emitting diodes are numerically calculated and optimized by using rigorous coupled-wave analysis (RCWA). The obvious polarization effect of the near field distribution is demonstrated. To easily analyze the transmittance performance of the internal reflection grating, simple methods involving scalar diffraction theory and effective medium theory are used. The validity of both methods is quantitatively evaluated by comparing the transmittance results obtained using the simple methods and RCWA. The limitation of both simple methods mainly depends on the grating structure parameters, such as the normalized period and normalized groove depth. Generally, when the dimensions of the normalized period is more than twofold wavelengths of incident light, the scalar treatment can be used to calculate precisely the transmittance of the optical element within 5% error. Also, the validity of the scalar theory is slightly ...

A fiber sensor scheme for simultaneous measurement of curvature and temperature is presented. It comprises an optical fiber Mach–Zehnder interferometer (MZI) formed by cascading two waist-enlarged fiber tapers and a fiber Bragg grating (FBG) fabricated in between the two fiber tapers. Simultaneous measurement is realized based on the facts that the MZI is sensitive to both curvature and temperature, while the FBG is only sensitive to the later. Sensitivities of 6.73 nm/m−1 and 54.7 pm/°C are achieved experimentally for curvature and temperature measurements, respectively.

The molecular passivation effect on the doping of InAs nanowires is explored by the first-principles calculation within the density-functional theory. We demonstrate the passivation of two different molecules that is implemented by the adsorption of NH3 and NO2 on the sidewall of InAs nanowire, respectively, but the two molecular passivations indicate different roles in the doping of InAs nanowires. The NH3 adsorption is a physisorption process which makes InAs nanowire with surface dangling bonds (SDBs) stay at n-type, while the adsorption of NO2 molecule is chemisorption that can reactivate the Zn dopant in InAs nanowires and yields a p-type doping characteristic. The difference of molecular passivation effect is attributed to the charge-compensation ability of passivating molecules to the SDBs of nanowires. This mechanism can be applied to explain the experimental observations on the doping of InAs nanowires through the surface passivation.

To improve the poor color rendering index (CRI) of YAG:Ce-based white light-emitting diode (LED) due to the lack of red spectral component, core/shell/shell CdSe/CdS/ZnS quantum dots (QDs) were synthesized and blended into nano-YAG:Ce3+ phosphors. Prominent spectral evolution has been achieved by increasing the content of QDs. A white LED combining a blue LED with the blends of nano-YAG phosphors and orange- and red-emission QDs with a weight ratio of 1:1:1 was obtained. This kind of white LED showed excellent white light with luminescent efficiency, color coordinates, CRI and correlated color temperature (CCT) of 82.5 lm/W, (0.3264, 0.3255), 91 and 4580 K, respectively.