We review the state-of-the-art in photonic crystal fiber (PCF) and microstructured polymer optical fiber (mPOF) based mechanical sensing. We first introduce how the unique properties of PCF can benefit Bragg grating based temperature insensitive pressure and transverse load sensing. Then we describe how the latest developments in mPOF Bragg grating technology can enhance optical fiber pressure sensing. Finally we explain how the integration of specialty fiber sensor technology with bio-compatible polymer based micro-technology provides great opportunities for fiber sensors in the field of healthcare.

Fiber Bragg Gratings have been shown to have a much improved thermal sensitivity when coated by Polymethyle methacrylate (PMMA) at cryogenic regime has been proposed. The PMMA has large thermal expansion coefficients and acts as driving elements. It is coated on the FBG at room temperature and the FBG is under compression at lower temperatures. This allows a much wider tuning of Bragg grating as fiber can stand at more compression than tension. An overall sensitivity of 0.039nm/K in the 1550nm wavelength regime has been achieved and the Bragg wavelength has been tuned upto 8.97nm in the temperature range 77K to 303K.

A fiber Bragg grating (FBG) sensor demodulation scheme based on a multi-wavelength erbium-doped fiber laser (EDFL) with linear cavity configuration is presented and demonstrated. The scheme is one linear fiber laser cavity with two FBG sensors as its filters. One is for strain sensing, and the other one is for temperature compensation. A power-symmetric nonlinear optical loop mirror (NOLM) is utilized in the laser in order to suppress the mode competition and hole-burning effect to lase two wavelengths output that correspond with two FBG sensors. The sensing quantity, which is demodulated by spectrometer, is represented by the output wavelength shift of the EDFL with temperature and strain applying on FBG sensors. In the experiment, strain measurement with a minimize resolution of 0.746με, i.e. 0.9pm and adjustable linear sensitivity are achieved. Due to utilizing the linear cavity multi-wavelength EDFL with a NOLM as the light source, the scheme also exhibits important advantages including obviously high signal and noise ratio (SNR) of 40.467dB and low power consuming comparing with common FBG sensors with broadband light as the light source.

A simple technique to discriminate the Strain and Temperature with a single Fiber Bragg Grating (FBG) at cryogenic regime is presented in this paper. An uniform FBG is divided into two parts, one half is without coating (FBG1) and other half is coated with Cyno-Acrylic Adhesive (FBG2). The measured temperature and strain sensitivities of the FBG1 are 4.05x10-6/K and 2.13x10-6/με and FBG2 are 1.39x10-5/K and 1.72x10-6/με respectively.

Fluorescence molecular tomography (FMT) has been receiving more and more attention for its applications in in vivo small animal imaging. Fluorescent sources to be reconstructed are usually small and sparse, which can be considered as a priori information. The stage-wise orthogonal matching pursuit algorithm (StOMP) with L1 regularization has been applied in FMT problem to get a sparse solution and proved efficient and at least 2 orders of magnitude faster than iterated-shrinkage-based algorithms. A sparsity factor that indicates the number of unknowns is determined by estimation in advance in StOMP. However, different FMT experiments have different sparsity factors and the StOMP algorithm doesn't provide a way to determine a specific sparsity factor accurately. Estimation of sparsity factor empirically in StOMP makes the algorithm not robust and applicable in different FMT experiments, which usually results in unacceptable results. In this paper, we propose a novel approach based on adaptive matching pursuit to make reconstruction results more stable and method easier to use. The proposed algorithm is able to find an optimal sparsity factor and a satisfactory solution always, no matter what value of the initial sparsity factor is estimated. Besides, the proposed algorithm adopts an automatical updating strategy. It ends after only a few iterations and doesn't add extral time burden compared to StOMP. So the proposed algorithm is still as fast as the StOMP algorithm. Comparisons are made between the StOMP algorithm and the proposed algorithm in numerical experiments to show the advantages of our method.

For the optical sensing in random media, an annular beam was used because of its nondiffractive feature. In our previous work, we have confirmed the nondiffractive effect of the annular beam in diluted solution of milk as random media. In the experiment of this study, increment of the nondiffractive effect has been confirmed by using the pulsed annular beam. We have simulated propagation characteristics of the annular beam in random media by wave analysis method. The attenuation rate and the forward scattering pattern of the propagation beam were calculated, and it showed agreement by comparing them with results of the experiment.

A single-mode nonadiabatic tapered optical fiber (NATOF) sensor was utilized for studying of bimolecular interaction including DNA-DNA interaction. This work presents a simple evanescent wave sensing system based on an interferometric approach, suitable to meet the requirements of lable-free sensor systems for detecting biomolecular interactions. Furthermore basic experiments were carried out, for detecting the hybridization of 25-mer DNA with an immobilized counterpart on the surface. The wavelength shifting showed a Longmuir behavior with time and a redshifted after the bending probe single strand DNA (ssDNA) and target ssDNA to the sensor surface. The hybridization response of complementary strands was measured at three concenteration of 200, 500, 1000 nM of ssDNA target solution. In this experiment binding constant or association constants for ssDNA-ssDNA interaction was measured to be 3.58 x 10⁵ M^-1.

A novel temperature compensation method for long-period grating (LPG) based biochemical sensor is proposed and experimentally demonstrated. Special laser-heated fiber (LHF) is used for fabricating LPG sensor whose temperature cross-sensitivity can be compensated by laser heating. Experimental results show that such a method is very promising for biochemical sensing and can be used to compensate temperature variation of ~86°C.

A simple refractive index sensor based on a fat long period fiber grating (FLPFG) in a single-mode fiber is constructed and demonstrated. The sensor consists of periodical fattening region in a short piece of single-mode fiber. In this method, the fiber fattening is realized by applying a standard fusion splicing procedure on single mode optical fiber. The sensitivity of the sensor is 7.5 x 10^-5 which the sensitivity is enhanced to the other kinds of long period fiber grating (LPFG).

A sensitivity-enhanced optical fiber refractive index sensor based on inline Mach-Zehnder interferometer is proposed. The sensor head is formed by splicing a tapered thin-core diameter fiber between two sections of single mode fibers. The taper (less than 1 mm) plays an important role in improving the sensitivity of the sensor. The sensitivity of refractive index is measured to be 0.447 nm for a 1% change of refractive index in the typical refractive index range of 1.333- 1.3725. The whole fabrication process (including splicing and tapering) can be operated by a commercial fiber splicing machine. The proposed sensor also shows the merits of simple structure, low cost, and easy fabrication.

A novel method for trace gas detection is presented and developed. A fiber laser with a gas cell in the loop is constructed, whose output spectrum is changed with the concentration of the gas e.g., acetylene. As the concentration of acetylene changes from 0 to 100% under a standard atmosphere, the peak of output spectrum shifts 0.03nm. It means to our system, a resolution of 3.75 KHz in light frequency change will lead to a sensitivity of ppm in gas concentration measurement, which makes it a economical and promising technique to measure low density gas.

We report the development of a rugged calibration method based on the measurement of the spectral response of a distributed anti-Stokes Raman thermometry (DART) system. Due to the presence of a high level of Rayleigh scattered signal in the Stokes channel, we find that the temperature measurement may be more precise if we use the Rayleigh signal as reference for the anti-Stokes thermometry. Moreover, we find that the temperature measurement needs to be calibrated for the loss spectrum of the optical components used in the system. Based on such an algorithm, we have demonstrated a prototype which is capable of sensing temperatures up to 90 °C with an accuracy of 2 °C over distances up to 6.5 km with 8 m spatial resolution.

Noble metal nanoparticles interacting with electromagnetic waves exhibit the effect of localized surface plasmon resonance (LSPR) based on the collective oscillation of their conduction electrons. Local refractive index changes by a (bio) molecular layer surrounding the nanoparticle are important for a variety of research areas like optics and life sciences. In this work we demonstrate the potential of two applications in the field of molecular plasmonics, single nanoparticle sensors and nanoantennas, situated between plasmonics effects and the molecular world.

Surface enhanced Raman scattering (SERS) has attracted widespread concern in the field of bioassay because it can enhance normally weak Raman signal by several orders of magnitude and facilitate the highly sensitive detection of molecules. Conventional SERS substrates are prepared by placing metal nanoparticles on a planar surface. Here we show a unique SERS substrate stacked by disordered TiO₂ nanowires (TiO₂-NWs) supportig gold nanocrystals. The structure can be easily fabricated by chemical synthesis at low cost. The COMSOL model simulation shows the designed SERS substrate is capable of output high Local Field Enhancement (LFE) in the Near Infrared region (NIR) that is the optimal wavelength in bio-detection because of both the unique coupling enhancement effect amony nearby Au nanocrystals on TiO₂-NWs and the Suface Plasmon Resonance (SPR) effect of TiO₂ -NWs. The as-prepared transparent and freestanding SERS substrate is capable of detecting extremely low concentration R6G molecular, showing much higher Raman signal because of the extremely large surface area and the uniqueTiO₂-NWs self-assemblied by Au nanocrystals. These results provide a new approach to ultrasensitive bioassay device.

To combine fluorescence and surface enhanced Raman spectroscopy (SERS) utilizing the same plasmonic array, a silver deposited micro fabricated quartz grating prepared by electron beam lithography is used. The most efficient Raman signal amplification is achieved for molecules directly adsorbed on the metallic surface, while fluorescence is quenched under these conditions. By careful adjustment, fluorescence is also enhanced which is known as metal enhanced fluorescence. In this contribution, the combined fluorescence and SERS readout is verified by a DNA detection scheme based on the usage of the label molecule ATTO565.

Metallic nanocomposite material is widely used in Surface Plasmon Rsesonance (SPR) due to its high stability and special optical features which enhance the Surface Enhanced Ramon Scattering (SERS) effect. A novel multi-layered Au-dielectric core-shell structural SERS substrate is proposed. Finite Elment Analysis (FEA) simulation shows multi-layer shell-core nanosphere (SiO₂@Au, SiO₂@Au@SiO₂...) can improve Local Field Enhancement (LFE), comparing to Au single-layer nanosphere. That is because multi-layer nanoshpere exists intra-layer coupling besides cavity coupling. Moreover, red-shift can be observed via tuning the thickness of multi-layer nanospheres, which is greatly beneficial to biological detection in near infrared region (NIR). Lastly, these multi-layer nanospheres are synthesised by liquid phase reduction. And high absorbance and red-shift effect are verified with UV-vis absorption spectrum.

We proposed an optimized engineering design of an imaging probe for time-resolved diffuse optical tomography system to increase the sensitivity of signal detection from tested objects. With limited number of sources and detectors, we considered an automatic rotational probe to generate more measurement pairs as well as more detection angles, compared to probes with equal number of sources and detectors. We also considered optimizing the arrangements of sources and detectors on the imaging probe to collect more information from the tested domain than those random arrangements. The method for selecting optimized sources' and detectors' positions is based on Cramer-Rao lower bound. Image reconstruction results of semi-infinite domain using phantom experimental data from different patterns of source and detector arrangements are presented. We demonstrated that the optimized source and detector arrangements chosen based on the reconstruction results match the choices from the optimized selecting methods. Thus we selected the optimized sets for the imaging probe.

We observed recent experimental results in area of photonic crystal fibers appliance. Possibility of creation of fiberbased broadband light sources for high resolution optical coherence tomography is discussed. Using of femtosecond pulse laser allows for generation of optical radiation with large spectral width in highly nonlinear solid core photonic crystal fibers. Concept of exploitation of hollow core photonic crystal fibers in optical sensing is demonstrated. The use of photonic crystal fibers as "smart cuvette" gives rise to efficiency of modern optical biomedical analysis methods.

A simple high temperature fiber sensor is proposed and demonstrated. The sensor head is made of a short section of specialty double cladding fiber (DCF). The DCF consists of a depressed inner cladding which is boron (B)-doped silica. Through an evanescent wave, the cladding mode can be excited, and thus the transmission presents a resonant spectral dip. The high temperature sensing properties was studied according to the shift of the transmission spectrum shifts. With increasing the temperature from 28 °C to 850 °C, the resonant spectrum shifts to longer wavelengths. The sensitivity is 0.112 nm / °C.

A fiber optic vibration sensor is demonstrated using bifurcated bundle fiber based on the principle of extrinsic displacement sensor. An IR source is used along with glass fibers to avoid the effect of stray light in sensing. The encapsulation of the sensor enables easy alignment, flexible handling and usage in harsh environments. The sensor is capable of measuring the frequencies up to 650Hz with vibration amplitude resolution of 10μm, enough to monitor the vibrations generated in heavy machines. The sensor is tested in the field to monitor the health condition of the diesel engine.

In this paper, an active temperature sensor based on beat frequency interrogation of a multilongitudinal-mode fiber laser has been proposed and demonstrated. Temperature measurement has been achieved through beat frequency interrogation of the proposed multilongitudinal mode laser. Experimental results show that the temperature sensing curve has good linearity with a coefficient of determination of 0.996004 for a temperature range of 30°C to 105.3°C. Furthermore, its application in the measurement of temperature dependence of fiber birefringence has been also investigated. And calculation results according to experimental observation of the beat frequency spectrum indicate that as temperature increases intrinsic fiber birefringence also linearly increases with a temperature coefficient of about 4.4x10^-10/°C. The proposed multilongitudinal-mode fiber laser sensor based on beat frequency interrogation has several advantages including compactness, high signal to noise ratio, etc, which is expected to be employed in future sensing applications.

A temperature compensated liquid level sensor using FBGs and a bourdon tube that works on hydrostatic pressure is presented. An FBG (FBG1) is fixed between free end and a fixed end of the bourdon tube. When hydrostatic pressure applied to the bourdon tube FBG1 experience an axial strain due to the movement of free end. Experimental result shows, a good linearity in shift in Bragg wavelength with the applied pressure. The performance of this arrangement is tested for 21metre water column pressure. Another FBG (FBG2) is included for temperature compensation. The design of the sensor head is simple and easy mountable external to any tank for liquid level measurements.

The digital coherent detection method is employed into the φ-OTDR. The heterodyne detection offers very high optical gain while the digital signal processing serves as an effective tool to rebuild the instantaneous electric field of Rayleigh scattering light by analyzing the beating signal. Both amplitude and phase signal are obtained in our experiment. PZT vibration measurement verifies that the phase difference signal well represents the external perturbation signal and also with higher SNR. The proposed newφ-OTDR system shows a good application foreground in the area of distributed vibration measurement.

A relative humidity sensor based on polarization maintaining fiber (PMF) loop mirror is presented. The proposed sensors are created through coating a thin layer of polyvinyl alcohol (PVA), whose refractive index varies as a function of humidity level, onto a polarization maintaining fiber, from which a portion of the cladding is removed. The relative humidity optical fiber sensor is tested with different surrounding humidity level, showing a linear response to parameter. The sensitivity of the relative humidity measurement of 0.98 nm/%RH in the range from 20%-80% RH is experimentally achieved.

A hybrid long period fiber grating (HLPFG) sensor was utilized for sensing the refractive index and pressure for downhole applications. The HLPFG is fabricated by fattening and tapering on a single mode fiber, utilizing a standard fusion splicing and a CO2 laser, respectively. The limit of detection (LOD) of the HLPFG for the RI measurement in the range from 1.3150 to 1.3559 is 4x10^-5 as a refractometer sensor which can be used for analysis of multicomponent in native petroleum. Pressure sensitivity of the HLPFG sensors in the range from 500 to 6000 psi is -0.6 pm/psi. With a 10 pm resolution for the wavelength shift detection our OSA, the LOD of the device at room temperature for pressure measurement is calculated to be 17 psi. This sensor can be used as a high pressure sensor in downhole application.

Based on the measurement of intrinsic fluorescence, a set of bio-aerosol including virus aerosols detection instrument is developed, with which a method of calibration is proposed using tryptophan as the target. The experimental results show a good linear relationship between the fluorescence voltage of the instrument and the concentration of the tryptophan aerosol. An excellent correlation (R²≥0.99) with the sensitivity of 4000PPL is obtained. The research demonstrates the reliability of the bio-aerosol detection by measuring the content of tryptophan. Further more the feasibility of prejudgment to the species of bio-aerosol particles with the multi-channel fluorescence detection technology is discussed.

Dynamic contrast enhanced (DCE) MRI is the method of choice for clinical tumor detection. There are three categories of DCE-MRI analysis methods including qualitative DCE-MRI, semi-quantitative DCE-MRI, and quantitative DCE-MRI. Among these three categories, quantitative DCE-MRI is the only one that could provide pharmacokinetic parameters and directly reveal physiological state of tumor. In this paper, we have made a brief review on quantitative DCE-MRI. Firstly, physiological basis of DCE-MRI was described in details. Then, two kinds of contrast agent, low molecular weighted contrast media (LMCM) and macromolecular contrast media (MMCM), are introduced respectively. After that, several T1 weighted DCE-MRI data analysis methods are introduced, too. At last, possible further developments of DCE-MRI have been discussed.

A simple and robust diode laser system emitting 1.28 W of green light suitable for pumping an ultrafast Ti:sapphire laser is presented. To classify our results, the diode laser is compared to a standard, commercially available diode pumped solid-state (DPSS) laser system pumping the same oscillator. When using our diode laser system, the optical conversion efficiencies from green to near-infrared light reduces to 75 % of the values achieved with the commercial pump laser. Despite this reduction the overall efficiency of the Ti:sapphire laser is still increased by a factor > 2 due to the superior electro-optical efficiency of the diode laser. Autocorrelation measurements show that pulse widths of less than 20 fs can be expected with an average power of 52 mW when using our laser. These results indicate the high potential of direct diode laser pumped Ti:sapphire lasers to be used in applications like retinal optical coherence tomography (OCT) or pumping of photonic crystal fibers for CARS (coherent anti-stokes Raman spectroscopy) microscopy.

We present a method for mitigating space variant blur occurring in the images acquired using Optical coherence tomography (OCT). The effect of Gaussian beam divergence on the image resolution is analyzed mathematically to develop space dependent two dimensional point spread functions that define the blurring kernel. Two standard deconvolution algorithms are used to deblur the images using the space dependent point spread functions. We show that the deconvolution method is effective in improving the transverse resolution of cross sectional OCT images at regions up to several times as deep as the confocal region of the Gaussian beam.

Because of the ability of integrating the strengths of different modalities and providing fully integrated information, multi-modality molecular imaging techniques provide an excellent solution to detecting and diagnosing earlier cancer, which remains difficult to achieve by using the existing techniques. In this paper, we present an overview of our research efforts on the development of the optical imaging-centric multi-modality molecular imaging platform, including the development of the imaging system, reconstruction algorithms and preclinical biomedical applications. Primary biomedical results show that the developed optical imaging-centric multi-modality molecular imaging platform may provide great potential in the preclinical biomedical applications and future clinical translation.

A novel swept-wavelength laser for optical coherence tomography (OCT) using a monolithic semiconductor device with no moving parts is presented. The laser is a Vernier-Tuned Distributed Bragg Reflector (VT-DBR) structure exhibiting a single longitudinal mode. All-electronic wavelength tuning is achieved at a 200 kHz sweep repetition rate, 20 mW output power, over 100 nm sweep width and coherence length longer than 40 mm. OCT point-spread functions with 45- 55 dB dynamic range are demonstrated; lasers at 1550 nm, and now 1310 nm, have been developed. Because the laser's long-term tuning stability allows for electronic sample trigger generation at equal k-space intervals (electronic k-clock), the laser does not need an external optical k-clock for measurement interferometer sampling. The non-resonant, allelectronic tuning allows for continuously adjustable sweep repetition rates from mHz to 100s of kHz. Repetition rate duty cycles are continuously adjustable from single-trigger sweeps to over 99% duty cycle. The source includes a monolithically integrated power leveling feature allowing flat or Gaussian power vs. wavelength profiles. Laser fabrication is based on reliable semiconductor wafer-scale processes, leading to low and rapidly decreasing cost of manufacture.

Breast cancer is the most common cancer in women (about 30% of all cancers); and is also the second common cancer after lung cancer. One woman out of eight develops breast cancer during lifetime. Breast thermography has a unique role in early detection of breast cancer and in this regards none of the other method such as mammography, ultrasound, CT scan and MRI could countervail it. The role of infrared imaging in early detection of breast cancer as an adjunct tool to mammography has been proved. Thermograms are usually provided in gray level images but findings show that gray images are not appropriate for human interpretation. Human beings can only discern a few dozen gray level values while they can distinguish thousands of colors. So in order to help thermologists to find abnormal regions in the thermograms, it's better to color thermograms. So pseudo-coloring of thermograms is one of the important factors for accurate diagnosis. In this research we offer comparing some common pseudo-coloring algorithms. Also a nonlinear function transform for pseudo-coloring of infrared breast images based on physiological properties of human eye is proposed, and its efficiency is shown by experience.

Characterized by wisdom and creativity, human beings are huge, complex, giant systems. Each person's life is experienced the process of birth, growth, aging and death. The genetic stability keeps human beings no change, and the mutation keeps the human beings in progress. The balance between stability and mutation are controlled by the nature laws automatically. But the balance often broken because the body's biochemical processes is out of order in vivo, which is scaled by quantitative concentrations for all molecular in human body. Now day, the biomedical imaging tools can investigate these process quantitatively.

In the last years the identification of microorganisms by means of different IR and Raman spectroscopic techniques has become quite popular. Most of the studies however apply the various vibrational spectroscopic methods to bulk samples which require at least a short cultivation time of several hours. Nevertheless, bulk identification methods achieve high classification rates which enable even the discrimination between closely related strains or the distinction between resistance capabilities. However, applying micro-Raman spectroscopy with visible excitation wavelengths enables for the detection of single microorganisms. Especially for time critical process like the fast diagnosis of severe diseases or the identification of bacterial contamination on food samples or pharmaceuticals, a cultivation-free identification of bacteria is required. In doing so, we established different isolation techniques in combination with Raman spectroscopic identification. Isolating bacteria from different matrixes always has an impact on the Raman spectroscopic identification capability. Therefore, these isolation techniques have to be specially designed to fulfill the spectroscopic requirements. In total the method should enable the identification of pathogens within the first 3 hours.

In recent development of fluorescence microscopy, the out-of-focus fluorescence background that arises when imaging deep inside biological tissues is critical in determining the image quality and penetration depth. Focal Modulation Microscopy [1-3] (FMM) is an emerging single-photon excitation fluorescence microscopy technique that can provide sub-micron spatial resolution for deep imaging of biological tissues mainly by preserving the signal-to-background ratio. Here we report a line-scan FMM that enables line-byline recording [4] at video frame rates (>30 fps) depending on the size of region of interest.

This research purpose is to investigate the changing of teeth color and to study the surface of teeth after treatment by laser diode at different power densities for tooth whitening treatment. In the experiment, human-extracted teeth samples were divided into 7 groups of 6 teeth each. After that laser diode was irradiated to teeth, which were coated by 38% concentration of hydrogen peroxide, during for 20, 30 and 60 seconds at power densities of 10.9 and 52.1 W/cm². The results of teeth color change were described by the CIEL*a*b* systems and the damage of teeth surface were investigated by scanning electron microscopy (SEM). The results showed that the power density of the laser diode could affect the whiteness of teeth. The high power density caused more luminous teeth than the low power density did, but on the other hand the high power density also caused damage to the teeth surface. Therefore, the laser diode at the low power densities has high efficiency for tooth whitening treatment and it has a potential for other clinical applications.

There are large demands to monitor the atmosphere in the closed space (hall, factory and so on), to check vegetation remotely and to detect hazardous gases such as explosive gas and bio terror from explosion-proof distance. On the contrary, traditional lidars have blind area, it is hard to monitor the atmosphere and the gas in the near range. In this study, optical designs and concrete developments for the atmosphere monitoring and the certain gas detection in near range were accomplished. Unique optical designs are introduced and their practical setups are explained.

An optical detecting technique to identify bio-aerosol particles is proposed in this paper by normalized fluorescence value which correlates to its size and intrinsic fluorescence. With the bio-aerosol detecting system developed, we test and analyze three types of aerosols, while each of them contains fluorescent microspheres of a certain size. The result indicates that different fluorescent microspheres containing the same fluorescent substances have the same normalized fluorescence voltage to unit particle size in diameter. The normalized fluorescence value of other species aerosols is tested for comparing. The research results can be applied to identification of bio-aerosols preliminarily.

In this paper, a wearable physiologic monitoring system using FBG sensors is investigated. The FBG sensors with the capability of sensing temperature, movement, and respiration are connected to the wireless transceiver, microcontroller and server for wireless and long distance physiologic monitoring and analysis. Biosignals recorded experimentally are analyzed and compared with the data obtained in the traditional medical data acquisition system. The system investigated in this paper can be used in an m-health shirt, which has the capability to measure and wirelessly transmit electrocardiogram, respiration, movement, and body temperature signal to a remote station, with other plug-in modules.

In this paper the transmission and polarization properties of fiber Bragg gratings with magnetically induced circular birefringence are discussed. The evolutions with wavelength of transmission spectrum and the polarization-dependent parameters for different circular birefringence, grating lengths and input polarizations are analyzed. We demonstrate that the third Stokes parameter and ellipticity evolutions contain the information about the amount of circular birefringence and could thus be used to sensor magnetic field value. Three polarizers are used to detect the absolute values of polarization parameters and hence sense the polarization evolutions.

A local oscillator for coherent detection of backward Brillouin scattering in Brillouin optical time domain reflectometry (BOTDR) has been analyzed. A ring Brillouin fiber laser, whose Brillouin gain media is 70m high-nonlinear-fiber (HNLF), is used as local oscillator of coherent detection. The BFL operates at 1549.06nm red-shifted 0.084nm from the pump laser. As to Brillouin light, The detection frequency is reduced from ~11GHz of direct detection to ~420MHz of heterodyne detection in this paper. Self-lasing cavity-modes of BFL impose the "burr" intervalled at 2.5MHz on the frequency domain analysis of the beat-frequency siganl. Signal-to-noise ratio (SNR) of beat-frequency signal decreases greatly, resulting to Lorentzian fitting with error. By adjusting variable optical attenuator (VOA) to increase the cavity loss in the fiber ring cavity, the self-lasing cavity-modes will be eliminated and a stable Brillouin laser will be obtained. The frequency estimation accuracy is improved greatly.

A highly sensitive fiber-optic interferometric sensor based on an all-solid birefringent hybrid photonic crystal fiber (PCF) is demonstrated for measuring strain and temperature. A strain sensitivity of ~23.8 pm/με and a thermal sensitivity of ~- 1.12 nm/°C are demonstrated in the experiment.

Planar integrated optical biosensors are becoming more and more important as they facilitate label-free and real time monitoring biosensing with high sensitivity. In this paper, the systematic research on one kind of optical biosensor, based on a resonant principle in a polymer ring resonator, will be presented. Reduced footprint and high sensitivity are advantages of this kind of biosensor. Rather than expensive CMOS fabrication, the device with high performance is fabricated through a simple UV based soft imprint technique utilizing self-developed low loss polymer material. The measurement results for the bulk sensing of a NaCl solution and the surface sensing of a minimal amount of avidin molecules in a buffered solution will be presented.

The absorption spectrum and fluorescence spectrum of thylakoid(sample I) and chlorophyll (sample II) extracted from brassica chinensis were studied based on polarization technique. As a result, the absorption peak positions of sample I red shift by more than ten nanometers comparing sample II and the absorption intensities of sample I declined when the polarizer went round from 0° to 90°. It gave detailed explanation why the two absorption spectra feel so different. On the other side, the polarization fluorescence spectra of the two samples excited by 437nm were investigated respectively and the calculation of the fluorescence polarization degree which is determined by the environment of the pigment, the bound state, the effectual energy transfer and the ordered arrangement of the pigment in the two samples showed that the pigment in sample I arrayed regularily. The results of the study would provide powerful reference to the research of the energy transfer and transformation during photosynthesis.

To improve the capability and detection precision of the Fiber Bragg sensing system, the novel interrogation technique and detection algorithm based on the tunable ring laser and multiplexing technology are proposed for the multi-channel Fiber Bragg grating sensing system, which can realize the real-time monitoring of 32 channels more than 1,000 FBG sensors. Here, we use the comb filter as multi-wavelength reference instead of the traditional reference grating array. Moreover, a fast wavelength detection algorithm based on the half-power point is proposed. Compared to the Gaussian fitting algorithm, the interrogation method can be greatly improved in the precision, flexibility and working reliability.

In this paper, the theoretical model of high birefringence photonic crystal fiber(PCF) has proposed by the plane wave expansion method. The temperature impacts of the birefringence and beat length in high birefringence PCF which filled with ethanol were numerical analyzed. The results show the refractive index of filling liquid significantly influence on the birefringence and beat length. When the wavelength increases, the birefringence increases while the beat length decreases, when the temperature increases, the birefringence also increases while the beat length decreases. In addition, the temperature affected the birefringence and beat length. Especially the birefringence of high birefringence PCF is more sensitive to temperature. When the wavelength is longer, these results for design temperature sensors have certain reference significance.

The influence of the fiber length and input power on pulse light stimulated Brillouin scattering effect was investigated. Laser with the wavelength 1550nm emitted a continuous optical input electro-optic modulator, and then is modulated into pulsed light. The pulsed signal is provided by the signal generator, pulse width 200ns, repetition frequency 2 KHz. The results show that the threshold of pulse light stimulated Brillouin scattering is 3.1dBm with the 25 Km single-mode optical fiber, and the light intensity of stimulated Brillouin scattering starts to grow slowly when the pump power is beyond 8.1dBm. It can be seen that Brillouin Stokes power increases with the growth of fiber length, but when the fiber is longer than 31km, the Brillouin Stokes power reaches saturation.

We present a novel FBG moisture sensor system using a SOA-based fiber laser with two FBG sensors as resonator mirrors. Two FBG sensors have same temperature coefficient and one of FBGs is coated by polyamide resin film as moisture sensing material. This system is insensitive to temperature changes and the output power of the system is only dependent on the moisture level to be monitored. The operation principle of the system is introduced and the initial experimental results are demonstrated.

A simple optical fiber relative humidity (RH) sensor was proposed and demonstrated. The humidity sensor was fabricated by coating moisture-sensitive film on the end face of a multi-mode optical fiber. The film was synthesized by doping CoCl₂ into a PVA/SiO₂ composite solution. Based on an optical absorption technique, the sensor head was characterized. From the optical absorption, a relative humidity range of 25%~65% was detected. Furthermore, the sensor has good repetitive response, and the response time was less than 2 min.

A temperature sensor using a single-mode tapered fiber coated by thermo-sensitive material is presented. It works on the multimode interference influenced by the small change of the ambient refractive index. To better understand the tapered optical fiber, simulations that change parameters such as the taper waist diameter and the ambient refractive index are performed using RSOFT BeamPROP. It is illustrated that optical losses vary with the ambient refractive index, and reduce diameter within a certain range can increase the sensitivity. In our experiment, with the high thermo-sensitive coefficient of material, a good temperature sensing result was achieved. The range of temperature measured is from -20°C to 80°C. The results show that the temperature sensor has high temperature sensitivity and good repeatability.

The scale factor of optic-fiber current sensor is nonlinearized because of the linear birefringence and the imperfection of quarter wave plate (QWP). In this paper, we analyze the effects of birefringence and show that modified scale factor performs better by using Faraday rotate mirror (FRM) and harmonic division method. The scale factor error associated with integrating imperfect quarter wave plate is also analyzed. Moreover, a certain linear birefringence may be helpful to compensate for deviation of QWP's alignment.

A simple wireless-fiber laser sensor is proposed base on directly photonic generation of microwave beat signal. In this scheme, a multi-longitudinal modes fiber laser is formed by two fiber Bragg gratings and a section of erbium-doped fiber. Two same 2G-GSM mobile antennas are used as wireless transmitter and receiver. By this method, the real-time monitoring of fiber laser sensors can be achieved through over ultra-long distance. This technique offers a simple, all-electrical and cheap way for fiber sensor information accessing wireless net. The experiment result shows the root mean square deviations of the sensor are about 4.7 με and 6.7 με at 2.38 GHz before and after wireless transmission, respectively.

Principles and application of distributed optical fiber temperature sensor (DTS) are introduced. Applications of DTS in power system in Shanghai World Expo project and Shanghai Caojing thermal power plant are studied as examples. Problems and solutions are researched. Test results of the two examples engineering project are listed.

In order to obtain simultaneously high sample rate and large buffer in data acquisition (DAQ) for a chaos fiber-optic fence system, we developed a double-channel high-speed DAQ application of a digital oscilloscope of PicoScope 5203 based on LabVIEW. We accomplished it by creating call library function (CLF) nodes to call the DAQ functions in the two dynamic link libraries (DLLs) of PS5000.dll and PS5000wrap.dll provided by Pico Technology Company. The maximum real-time sample rate of the DAQ application can reach 1GS/s. We can control the resolutions of the application at the sample time and data amplitudes by changing their units in the block diagram, and also control the start and end times of the sampling operations. The experimental results show that the application has enough high sample rate and large buffer to meet the demanding DAQ requirements of the chaos fiber-optic fence system.

A fiber-optic twist sensor based on a pressure-induced birefringence singlemode fiber loop mirror is proposed. The birefringer SMF is made by applying a transverse force against a short length of singlemode fiber. The sensitivity of the twist angle measurement of 0.19 nm/o is achieved experimentally. The proposed sensor is more convenient and simple than that of standard polarization-maintaining fibers.

In this paper, we fabricated fiber-optic extrinsic Fabry-Perot interferometric (EFPI) sensors with photolithography . The sensor has double-layer SU-8 diaphragm: one is the pressure transduction layer; the other is cavity control layer. Since SU-8 material has a low Young's modulus, high pressure sensitivity can be achieved with SU-8 diaphragm. The EFPI were formed by a single mode fiber and a double-layer SU-8 diaphragm. To improve the fringe contrast, gold mirrors with a reflectivity of 50% were evaporated onto the end face of the single mode fiber and the inner face of the SU-8 diaphragm respectively. Experiments were done to estimate the performance of the sensor for static pressure measurement. The results show that an expected cavity length of the sensor was obtained and the EFPI sensor has a good linearity from 100 to 2500 Pa with 100 Pa resolution and a sensitivity of 154.8 nm/kPa.

Label-free biosensor based on the dynamic distributed feedback (DFB) laser emission is proposed. The sensitivity of the sensor is substantially realized by the refractive index of the cladding layer that influences the effective refractive index (n_eff) of the whole waveguide structure. The designed multilayer structure consists of the substrate (n=1.51), the low refractive index mesoporous silica film (n=1.1~1.3), the dye-doped gain layer (n=1.58) and the high refractive index TiO₂ (n=2.1) thin film. We used the finite difference time domain (FDTD) algorithm to simulate the influence of the mesoporous silica film and the TiO₂ layer to the neff of the fundamental transverse electric (TE0) mode and the sensitivity in the DFB structure. It was found that the increase of refractive index of the mesoporous silica and the thickness of TiO₂ layer can slightly increase the n_eff of the structure. And the sensitivity of the sensor can be enhanced not only by the introduction of mesoporous silica, but also by a thicker TiO₂ layer.

Non-equilibrium interferometric Fiber Bragg Grating (FBG) sensor is suitable for the accurate measurements of high-frequency dynamic stress, vibration, etc because of its high sensitivity and high frequency response compared to other types of FBG sensors. In this paper, a Phase Generation Carrier (PGC) demodulation technique of non-equilibrium interferometric FBG sensor that based on ARCTAN algorithm by using an arctangent algorithm with a simple method, has been investigated ,which can avoid the high-frequency noise increases, the error accumulation, the integrator signal jump of the integrator and other inherent weaknesses in the system. ARCTAN has a better response characteristic of the mutant signals, especially for low-frequency large-signal that can be demodulated with a greater range. The experimental result demonstrate that implementing measured resolution can up to 10nε/√Hz@500Hz in vibration strain, a signal sampling rate to 100 KHz and a frequency response range up to 1 KHz. This method can improve the performance of the system greatly which has potential significance for practical sensor application.

In this paper, tomato epidermis' surface-enhanced Raman scattering spectra were measured on gold and silver active substrates and analyzed. Preparing and using gold sol and silver sol in similar particle diameters (about 50-60nm), three comparable Raman spectra were obtained. Silver sol and gold sol can both increase Raman scattering signal of tomato epidermis. Through the Raman spectra, silver sol has greater enhancement ability than gold sol to tomato epidermis.

In this paper, Raman spectra of hepatocellular carcinoma cells were analyzed using gold and silver nanoparticles as SERS active substrates. The size of gold and silver nanoparticles is about 50-60 nm, and these nanoparticles have enhancement role to the Raman spectrum of hepatocellular carcinoma cells. The results show that the Raman enhancement effects of gold colloid are more sensitive than silver colloid to cells.