Polarization coherency matrix tomography.

In this paper, a polarization-sensitive optical coherence tomography (PS-OCT) based polarization coherency matrix tomography (PCMT) combining polarization coherency matrix with Mueller matrix is proposed for the determination of complete polarization properties of tissue. PCMT measures the Jones matrix of biological sample based on similar transformation, in which four elements have initial random phase from different polarization states based on traditional PS-OCT. The results indicate that PCMT can eliminate the phase difference of incident lights with different polarization states. In addition, the polarization coherency matrix using three polarization states has complete information of the sample Jones matrix. Finally, the 16 elements of the sample Mueller matrix are applied for deriving fully polarized optical properties of the sample based on the elliptical diattenuator and the elliptical retarder. Thus, the method based on the PCM and Mueller matrix has the advantage over the traditional PS-OCT.

Mode coupling characteristics investigation on a tapered seven-core fiber sensor.

In this work, we analytically derive the transmission spectra of the seven-core fiber (SCF) with a phase mismatch between the center core and outer cores based on the mode coupling theory. We also establish the wavelength shift as a function of temperature and ambient refractive index (RI) using approximations and differentiation techniques. Our results reveal the opposite effects of temperature and ambient RI on the wavelength shift of the SCF transmission spectrum. The theoretical conclusions are confirmed by our experiments on the behavior of SCF transmission spectra under various temperature and ambient RI conditions.

Highly sensitive optical fiber curvature sensor based on a seven-core fiber with a twisted structure.

A highly sensitive Mach-Zehnder interferometer based on a twisted structure in seven-core fiber (SCF) for curvature measurement is investigated both theoretically and experimentally. The device is fabricated by splicing a segment of a twisted SCF with single-mode fibers by the over fusion method. An interference pattern of the straight sensor appears in the transmission spectra. When the sensor is bent, the wavelength shift of the interference pattern is induced, which may be used for curvature measurement through wavelength shift. In the experiment, SCFs with and without the twisted structure are tested, and the results are compared with wavelength-based sensitivities. The proposed twisted-SCF sensor offers a maximum curvature sensitivity of $ - {25.16}\,\,{{\rm nm/m}^{ - 1}}$-25.16nm/m-1 within the measurement range of ${0.5201 - 1.0071}\,\,{{\rm m}^{ - 1}}$0.5201-1.0071m-1, which is a 37-fold improvement compared with the previous works. The results also indicate that this highly sensitive all-fiber sensor offers great potential for realization of curvature measurement in the field of structural health monitoring.

Overlap Spectrum Fiber Bragg Grating Sensor Based on Light Power Demodulation.

Demodulation is a bottleneck for applications involving fiber Bragg gratings (FBGs). An overlap spectrum FBG sensor based on a light power demodulation method is presented in this paper. The demodulation method uses two chirp FBGs (cFBGs) of which the reflection spectra partially overlap each other. The light power variation of the overlap spectrum can be linked to changes in the measurand, and the sensor function can be realized via this relationship. A temperature experiment showed that the relationship between the overlap power spectrum of the FBG sensor and temperature had good linearity and agreed with the theoretical analysis.

A Loop All-Fiber Current Sensor Based on Single-Polarization Single-Mode Couplers.

Low current sensitivity and insufficient system stability are two key problems in all-fiber current sensor (AFCS) studies. In order to solve the two problems, a novel AFCS combining single-polarization single-mode (SPSM) couplers and a loop structure is presented in this paper with a design that incorporates the advantages of both SPSM couplers and a loop structure. SPSM couplers are shown to simplify the AFCS system and reduce the risk of interference, and the loop structure can enhance the current sensitivity. Both theory and experiment prove that the new AFCS can simultaneously overcome two prevalent obstacles of low current sensitivity and low stability.

Hybrid Structure Multichannel All-Fiber Current Sensor.

We have experimentally developed a hybrid-structure multi-channel all-fiber current sensor with ordinary silica fiber using fiber loop architecture. According to the rationale of time division multiplexing, the sensor combines parallel and serial structures. The purpose of the hybrid-structure multi-channel all-fiber current sensor is to get more information from the different measured points simultaneously. In addition, the hybrid-structure fiber current sensor exhibited a good linear response for each channel. A three-channel experiment was performed in the study and showed that the system could detect different current positions. Each channel could individually detect the current and needed a separate calibration system. Furthermore, the three channels will not affect each other.

Infrared signature of the early stage microsolvation in the NaSO4⁻(H2O)1₋5 clusters: a simulation study.

Infrared photon dissociation (IRPD) spectra of the NaSO4(-)(H2O)n clusters with up to five water molecules have been studied using quantum chemical calculations. Our calculation reveals that the splitting of the peaks in the ~800-1300 cm(-1) region of the IRPD spectra, which contains the information on S-O bond stretching of the anion, indicates the deviation of the cation from the C(3v) axis as well as the asymmetric distribution of the water molecules. The frequency of the H-bonded O-H stretching peak in the ~2300-3000 cm(-1) window, on the other hand, provides information on the position of the newly added water molecule with respect to the cation. The IRPD technique thus provides abundant structural information on the early stage of the microsolvation and has the potential to become a powerful tool complementary to photoelectron spectroscopy.

Coherence theory of a laser beam passing through a moving diffuser.

We present the general coherence theory for laser beams passing through a moving diffuser. The temporal coherence of laser beams passing through a moving diffuser depends on two characteristic temporal scales: the laser coherence time and the mean time it takes the diffuser to move past a phase correlation area. In most applications, the former is much shorter than the latter. Our theoretical analysis shows the spatial coherence area of light scattered from a moving diffuser decreases while the coherence time remains unchanged. The conclusion has been confirmed by experiments using a Michelson interferometer and it is not in accordance with the original coherence theory in which both the temporal and spatial coherence of light scattered by a moving diffuser decrease. We also developed a method based on the theory of eigenvalues to calculate the speckle contrast on a screen illuminated by light transmitted through a moving diffuser.

High-current-sensitivity all-fiber current sensor based on fiber loop architecture.

In this paper, we demonstrate a novel all-fiber current sensor using ordinary silica fiber. The sensor employs a fiber solenoid as a current sensor head, which improves the current sensitivity by allowing optical signals to traverse the sensor head repeatedly. Theory and experiment prove that the improvement in sensitivity increases periodically with the number of repetitions of optical signals circulating round the loop.

Speckle contrast in near field scattering limited by time coherence.

The relationship between the speckle contrast of scattered light in near field and longitudinal distance that is perpendicular to scattering surface is investigated. The experiment indicates that when using the laser illumination source with proper time coherence length, the curve of speckle contrast vs. longitudinal distance appears minimum turning point. The position and value of minimum point are decided by the coherence of light and scattering matter. It is easy to obtain the correlation area of scattered light by measuring the minimum point position and the illuminated area. Comparing to traditional scattering technique, this method can simultaneously measure the roughness parameters of surface height variance and surface height correlation area.

Power calculation of wavelength tunable Yb3+:LSO laser.

A theoretical model is presented describing continuous-wave operation about wavelength tunable Yb(3+):LSO (Yb(3+):Lu(2)SiO(5)) laser. In LSO host, Yb(3+) ion occupies two different Lu(3+) sites and the spectrum exhibits the inhomogeneously broadened property. Working as a computable model, it takes into account the pump absorption saturation, the re-absorption of laser, and the full spectral information of the laser transition. The calculated results are compared with the experimental results, and it verifies the validity of the model. Then the laser performances for different Yb(3+) concentration, crystal length, and the transmission of the output mirror are predicted.

Polarization-independent Fabry-Perot interferometer in a hole-type silicon photonic crystal.

We propose and numerically demonstrate a polarization-independent Fabry-Perot interferometer (PI-FPI) based on the self-collimation effect in a hole-type silicon photonic crystal (PhC). By use of the polarization peak matching method, a resonance frequency of the transverse-electric modes can equal that of the transverse-magnetic modes in the PI-FPI, although the transmission spectra are quite polarization dependent due to birefringence of the PhC. For the operating wavelength of 1550 nm, the PI free spectral range of the PI-FPI is up to 32.3 nm, which nearly covers the whole optical communication C-band window. With its small dimensions, simple structure, and silicon-based material, this PI-FPI may play an important role in photonic integrated circuits.

Photonic NOT and NOR gates based on a single compact photonic crystal ring resonator.

New all-optical NOT and NOR logic gates based on a single ultracompact photonic crystal ring resonator (PCRR) have been proposed. The PCRR was formed by removing the line defect along the GammaM direction instead of the conventional GammaX direction in a square-pattern cylindrical silicon-rod photonic crystal structure. The behavior of the proposed logic gates is qualitatively analyzed with the theory of beam interference and then numerically investigated by use of the two-dimensional finite-difference time-domain method. No nonlinear material is required with less than a 2.2 microm effective ring radius. The wavelengths of the input signal and the probe signal are the same. This new device can potentially be used in on-chip photonic logic-integrated circuits.

Polarization-independent drop filters based on photonic crystal self-collimation ring resonators.

We report here a polarization-independent drop filter (PIDF) based on a photonic crystal self-collimation ring resonator (SCRR). Despite of the large birefringence associated with the polarization-dependent dispersion properties, we demonstrate a PIDF based on multiple-beam interference theory and polarization peak matching (PPM) technique. The PIDF performance was also investigated based on finite-difference time-domain (FDTD) technique, with excellent agreement between the theory and the simulation. For the designed drop wavelength of 1550 nm, the polarization-independent free spectral range is about 36.1 nm, which covers the whole optical communication C-band window. The proposed PIDFs are highly desirable for applications in photonic integrated circuits (PICs).

Multichannel-fiber ringdown sensor based on time-division multiplexing.

A multichannel-fiber ringdown sensor based on the principle of time-division multiplexing is described. The purpose of multiplexing is to obtain the information of one or more fiber ringdown sensor heads simultaneously under the premise of cost neutrality. To illustrate the principle, we study the typical dual-channel fiber ringdown force sensor in our experiment. It shows that the pressures at two different points can be measured simultaneously. In addition, we find by measurement that our sensors have good linear responses above the response threshold of the applied force.