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In this study, an interferometric method was proposed for the simultaneous measurement of phase retardation and fast-axis azimuth angle of a wave plate by using a Mach–Zehnder interferometer. The w...

Mueller matrix polarimetry is widely used in biomedical studies and applications, for it can provide abundant microstructural information about tissues. Recently, several methods have been proposed to decompose the Mueller matrix into groups of parameters related to specific optical properties which can be used to reveal the microstructural information of tissue samples more clearly and quantitatively. In this study, we thoroughly compare the differences among the parameters derived from the Mueller matrix polar decomposition (MMPD) and Mueller matrix transformation (MMT), which are two popular methods in tissue polarimetry studies and applications, while applying them on different tissue samples for both backscattering and transmission imaging. Based on the Mueller matrix data obtained using the setups, we carry out a comparative analysis of the parameters derived from both methods representing the same polarization properties, namely depolarization, linear retardance, fast axis orientation and diattenuation. IN particular, we propose several modified MMT parameters, whose abilities are also analyzed for revealing the information about the specific type of tissue samples. The results presented in this study evaluate the applicability of the original and modified MMT parameters, then give the suggestions for appropriate parameter selection in tissue polarimetry, which can be helpful for future biomedical and clinical applications.

Beam shaping is required for semiconductor lasers to achieve high optical fiber coupling efficiency in many applications. But the positioning errors on optics may reduce beam shaping effects, and then lead to low optical fiber coupling efficiency. In this work, the positioning errors models for the single emitter laser diode beam shaping system are established. Moreover, the relationships between the errors and the beam shaping effect of each shapers are analysed. Subsequently, the relationship between the errors and the optical fiber coupling efficiency is analysed. The result shows that position errors in the Z axis direction on the fast axis collimator have the greatest influence on the shaping effect, followed by the position errors in the Z axis direction on the converging lens, which should be strictly suppressed in actual operation. Besides, the position errors have a significant influence on the optical fiber coupling efficiency and need to be avoided.

We present a beam combination technique to improve the brightness of diode lasers based on both spectral beam combination and polarization beam combination. We use eight diode laser arrays (DLAs) and two diffraction gratings to construct two independent external cavities by using spectral beam combination, and then combine the outputs of these two cavities by using polarization beam combination. The experiment shows that the total output power can be as high as 310.2 W by using this technique with eight DLAs, which are commercial standard cm-bars, each producing ∼60 W of output power. The beam qualities of the combined beam are M2 = 13.55 and 10.27 in the slow and fast axis, respectively. The brightness of the combined output is as high as 252 MW·cm−2·sr−1.

We present a serpentine-based 16-element dispersive OPA at very near-IR wavelengths that leverages SiN waveguide feeding. 2D beam steering is achieved by wavelength sweep, with tunability of 0.11°/nm on slow and 3.52°/nm on fast axis.

In this paper, the research work of two-dimensional beam shaping and homogenization of high power laser diode (LD) stack by a rectangular waveguide is presented. Both the theoretical simulation and experiment results have shown that the diode stack beam can be shaped into a uniform square spot with a dimension of 10 mm × 10 mm and the non-uniformity less than 5% along both directions of slow axis and fast axis, the shaped beam has a uniform pumping depth over 10 mm, which is well to be used for a rectangular laser medium end pumping.

We propose a two-axis electromagnetic micro scanner with a two-phase current path satisfying three criteria (via less microfabrication, independent biaxial scan with minimization of crosstalk, and no current path on the mirror). In the design of a dual radial magnetic field, current paths are arranged to maximize the torque in the active current that actuates a mirror, while nullifying the torque in the passive current that is not intended to actuate the mirror but rather just to complete an electrical current loop. The use of W-shaped springs for the slow-axis scan considerably reduced the torsional spring constant by 2.7 times, whereas it increased the in-plane sliding spring constant by 2.4 times, compared to conventional I-shaped springs. This indicates that the W-shaped springs effectively increase scan angle and enhance the actuation stability. The scanner with a reflection mirror with 3 mm in diameter was fabricated, and in the raster scan gave a maximum scan angle of 50.6° (resonant) and 9.1° (quasi-static) in fast- and slow-axis scans, respectively, with a power consumption of 28.1 mW. The maximum crosstalk of the slow and fast axis from the other axis were measured as small as 0.45% and 0.43%, respectively.

This work aims to characterize the retardation of birefringent samples such as wave-plates and birefringent wedges where the principal axis is uniform over the sample zone. The in-line procedure described and implemented for the purpose uses four frames of intensity data that are digitally recorded and combined to characterize the sample in terms of its retardance from 0 to 2π as also to uniquely identify the direction of its fast axis. Simulated and experimental results presented are in good agreement with the proposed theory.

By allowing spatial variations in the direction of the anisotropic fast axis, tilted transverse isotropy (TTI) helps to image complex or steeply dipping structures. Without a priori geologic constraints, however, recovery of all the anisotropic parameters can be nontrivial and nonunique. We adopt two methods for TTI inversion with tilt-angle recovery: one based on the familiar Voigt parameters, and another based on the so-called Chen and Tromp parameters known from regional and global seismology. These parameterizations arise naturally in seismic wave propagation and facilitate straightforward recovery of the tilt angle and anisotropic strength. In numerical experiments with vertical transversely isotropic starting models and TTI target models, we find that the Voigt as well as the Chen and Tromp parameters allow quick and robust recovery of steeply dipping anticlinal structures.

A blind-angle calibration method is introduced for self-spectral calibration of a compound zero-order waveplate. By rotating the waveplate at blind detection angles, the wavelength-dependent retardance and the orientation of the effective fast axis can be determined through iterative least-squares calculations of the spectra measured by a multi-channel spectrometer. Excellent agreement between the experimental values and the theoretical values is achieved, indicating that the new method can be used as a reliable way to calibrate compound zero-order wave plates. Using the new method, there is no need to rotate the waveplate at specific detection angles. A high-precision waveplate holder or complex adjustment procedure is not required.

We report the measurement of bending-induced birefringence in the presence of large intrinsic birefringence in a hollow-core photonic crystal fiber (HC-PCF). The fast axis of bending-induced birefringence was found to be normal to the bending plane, in contrast to the conventional fiber case. The dependence of the induced birefringence on the bending radius was also different from the typical inverse square law. Possibilities and design criteria for polarization controllers using bending-induced birefringence in HC-PCFs are presented.

Teleseismic earthquakes data recorded by 8 broadband digital seismic stations deployed in the Kumaun-Garhwal and adjoining area of NW Himalaya are analyzed to investigate the seismic anisotropy in the upper mantle. Shear-wave splitting parameters (ɸ and ∂t) derived from the analysis of core-refracted SKS/SKKS phases provide first hand information about seismic anisotropy and deformation in the upper mantle beneath the region. A total, 209 good measurements of seismic anisotropy have been obtained from the two years of collected high-quality teleseismic data in the study region. The analysis shows considerable strength of anisotropy (delay time(∂t) 0.6–2.8 s) with average ENE–WSW-oriented fast polarization orientation at most of the stations while other one either along with the absolute plate motion (APM) of the Indian plate or parallel to strike of the Himalayan mountain belt. The Fast axis direction observed at stations close to between the MBT and MCT aligns parallel to the strike of local geological faults and orthogonal to absolute plate motion (APM) direction of the Indian plate. The large variation in the splitting strength and fast polarization trends around the Kumaun-Gharwal and adjacent in NW Himalaya have invoked both lithospheric and asthenospheric anisotropy.

In order to solve the problem of low efficiency and low accuracy of manually picked fast shaft collimation lens in actual production, the method of recognition of fast shaft collimation lens based on machine vision is studied. Using industrial camera to achieve image acquisition, using HALCON software to pre-process the image of fast-axis collimated lens, edge detection and other aspects of research, through the platform verification, the results show that the processed image is clear and easy to identify. In the lens placement is not accurate, the background is dirty can still ensure a better positioning effect, This study has some reference significance for visual recognition in the actual production of fast-axis collimation lens.

Optical components with complex surfaces are widely applied. Ultra-precision diamond turning technology can fabricate these complex surfaces efficiently and accurately. Fast axis servo (FAS) system has the characteristics of large stroke and high frequency response. In this paper, Fast axis servo system based on linear rolling guide rail was used to process the complex surface. By the speed/acceleration feedforward and the position PID feedback control algorithm, the precision motion control of the fast axis servo system in large stroke and high frequency was realized. According to the principle of fast axis servo machining, the tool path generating for FAS cutting and machining surface simulation were carried out. The Machining experiments of typical complex surfaces were tested and analyzed, the results show that this method can produce the expected complex surface shape and has preferable servo machining performance.

In this study, an optical scheme based on the measurement of light intensity and a proper orientation of the Fresnel Rhomb is successfully developed for simultaneous determination of the phase retardation and fast axis of a wave plate. The theoretical analysis of the principle of measuring the reflection-induced retardance of the Fresnel Rhomb and the phase retardation of a wave plate is given taking Stokes–Mueller Formalism as a mathematical tool. In this method, the fast axis position of the wave plate need not be determined in advance. In addition, the measured result is free of the intensity fluctuation of light source. An application example is also demonstrated. The measured result of the example is verified with an experiment. Some of the merits of the method, such as, a simple optical set-up, high stability and high accuracy, low cost and easier operation, are presented, and the validity of the method is demonstrated.

It is vitally important to numerically simulate the output power spatial distribution of diode laser stacks when they are used in beam shaping and pumping for other lasers. Here, we propose a numerical simulation technique by considering the discreteness of the propagation angles of individual emitters in diode laser stacks in the fast axis. Using this proposed simulation technique, we calculated the spatial distribution of the outputs of the four diode laser stacks and the total output power of the 3000 W fiber-coupled diode laser. The calculated results agree well with the experimentally measured values. Therefore, when designing a laser, this is a useful way to select diode laser stacks based on specifications.

The smile effect is inevitable during the packaging process of diode laser stacks. Position errors and direction errors are used to describe the smile effect. A theoretical smile model has been built, and a beam propagation model of the external cavity has been further proposed based on the smile model. Beam properties such as spectrum, intensity distribution, and beam quality of combined beams have been simulated and discussed. The results show that position errors have little impact on intensity distribution of combined beams but make spectrum slightly broadened. Direction errors make intensity generate side lobes and degrade beam quality significantly. Compared with position errors, direction errors in both slow axis and fast axis have more detrimental effect on output beams. Thus, it is more important to control angle deflection of beams than positions of emitters during the manufacturing process of DLSs.

High-precision chalcogenide molded freeform micro-lenses were designed and produced to perfectly collimate and circularize mid-infrared Quantum Cascade Lasers (QCLs). The innovative micro-lens has an input surface with freeform contour to simultaneously converge the fast axis and further diverge the slow axis, while the output freeform surface collimates both axes. The 5-mm long freeform lens is such that the collimated output fast- and slow-axis beams are circular. This paper presents recent results on the chalcogenide molded freeform micro-lens prototypes specifically designed to collimate and circularize QCL at 9 micron.

The design and characterization of a two-degree-of-freedom serial kinematic microelectromechanical systems (MEMS) nanopositioner for on-chip atomic force microscopy (AFM) is reported. A novel design is introduced to achieve a serial kinematic mechanism based on a standard silicon-on-insulator MEMS fabrication process. The nanopositioner comprises a slow axis with a resonance frequency of 2.4 kHz and a fast axis with a resonance frequency of above 4.4 kHz, making it ideal for rastering, as required in the AFM. Strokes of 14 and $9\,\, \mu \text{m}$ are experimentally achieved for the fast and slow axes, respectively. The serial kinematic design of the stage enables the cross-coupling between the two axes of motion to be as low as −60 dB. Electrothermal displacement sensors are incorporated in the device, which may be used to enable feedback control as required in high-speed AFM. [2014-0248]

We present a technique and algorithm for measuring the phase retardation of a wave plate based on spectral transmission curve. Through accurately extracting the intersection points' wavelengths from the spectral transmission curve, the effective phase retardation, absolute phase retardation, order, and physical thickness of the wave plate can be measured simultaneously in a wide spectral range. Experimental results show that the proposed technique has many advantages, such as higher data utilization, simpler extraction algorithm, and no strict requirement for the directions of transmission axes of the polarizer and analyzer, and the fast axis of the wave plate.

Author(s): Frost, DA; Romanowicz, B | Abstract: Recent studies of PKPdf travel times suggest strong anisotropy (4% or more) in the quasi-western inner core hemisphere. However, the availability of paths sampling at low angles to the Earth's rotation axis (the fast axis) is limited. To augment this sampling, we collected a travel time data set for the phase P′P′df (PKPPKPdf), for which at least one inner core leg is quasi-polar, at two high latitude seismic arrays. We find that the inferred anisotropy is weak (on the order of 0.5 to 1.5%), confirming previous results based on a much smaller P′P′ data set. While previous models of inner core anisotropy required very strong alignment of anisotropic iron grains, our results are more easily explained by current dynamic models of inner core growth. We observe large travel time anomalies when one leg of P′P′df is along the South Sandwich to Alaska path, consistent with PKPdf observations, and warranting further investigation.

Low SMILE vertically stacked laser bars gold/tin (AuSn) soldered on nearly symmetrical micro channel coolers were designed, built and characterized. 96% of 200 measured SMILE (bowing) values are less than 2 μm. Twenty-one 5×1 vertical stacks have a divergence of 2.03mrad with a standard deviation of 0.19mrad after fast axis collimation. A line laser module was built with twelve 5×1 vertical stacks to produce 6 KW in a line geometry of 0.6 mm@1/e2 by 285 mm @85% and a line uniformity of 86%. Several laser line modules can horizontally be connected to form a wider line for glass surface treatment and thin film solar panel processing.

We show that there are a number of ways to transform an arbitrary polarization state into another with just two quarter wave plates (QWPs). We have verified this geometrically using the trajectories of the initial and final polarization states corresponding to all the fast axis orientations of a QWP on the Poincare sphere. The exact analytical expression for the locus of polarization states has also been given, and describes the trajectory. An analytical treatment of the equations obtained through matrix operations corresponding to the transformation supports the geometrical representation. This knowledge can be used to obtain the Mueller matrix by just using QWPs, which has been shown experimentally by exploiting projections of the output states on the input states.

Mode-locked fiber lasers are the most promising lasers for intracavity phase interferometry, 1 because they offer the possibility to have two orthogonally polarized pulses circulating independently in the cavity. The saturable absorbers based on polarization maintaining tapered fiber coated with carbon nanotubes are developed and analyzed for minimum coupling between the slow and fast axis of the fiber.

The performance of a Ti:sapphire laser pumped by a single 461 nm laser diode is presented for both the continuous-wave and the mode-locked regimes of operation. We introduce a simple astigmatism correction scheme for the laser diode beam consisting of two cylindrical lenses affecting the pump beam along the fast axis of the laser diode, which provides the mode-matching between the nearly square-shaped pump beam and the cavity mode. The resulting efficiency of the suggested Ti:Sapphire oscillator pumped by such a laser diode is analyzed for the Ti:sapphire crystals of 3 mm, 5 mm and 10 mm in length. We demonstrate that such a system provides the generation of ultrashort pulses up to 15 fs in duration with the repetition rate of 87 MHz, the average power being 170 mW.

Regeneration of fibre Bragg gratings under application of a high temperature annealing process in a high birefringent polarisation maintaining fibre of type Panda was investigated. During the annealing process, a distinct nonlinearity and hysteresis of the birefringence with temperature was observed. After the temperature process, the birefringence between slow and fast axis at room temperature was nearly doubled, which is in agreement with observations of other researchers. The hysteresis in birefringence might be explained by the crossing of the transition temperature of the stress applying parts and the relief of in-frozen mechanical and thermal stresses.

We present a method for calibration and data extraction for a nonoptimized Mueller matrix polarimeter. The advantage of this type of method is a reduction in measurement time for multiwavelength systems or in systems with slow response times. The calibration process requires the measurement of four known polarization devices. Here we use free-space transmission, a horizontal and a vertical linear polarizer, and a quarter-wave retarder with its fast axis at 30° to the horizontal. Experimental measurements of rotating quarter-wave and half-wave retarders show that accurate results can be obtained with the proposed method.

Transforming polarization states of light from one to another in a controlled manner can be achieved with a minimal gadget consisting of two-quarter waveplates. Using a geometric approach, we demonstrate this result for transforming any completely polarized states of light (CPSL) to any other CPSL, including the orthogonal states. Furthermore, we describe a working algorithm for identifying the fast axis setting of the two-quarter waveplates essential for the state transformation.

In a recent study we reported on the gradient index (GRIN) lens Stokes polarimeter (GLP) [Opt. Lett.39, 2656 (2014)10.1364/OL.39.002656OPLEDP0146-9592]. With a simple architecture, this polarimeter can measure the state of polarization in a single shot. In this article, we present further studies for improving the performance of the GLP. Detailed discussions are presented on the optimization process of the GLP based on different choices of data from the CCD images. It is pointed out that many optimization techniques, although developed for other types of Stokes polarimeters, can also be applied to the GLP because the GRIN lens can traverse all possible retardance and fast axis modulations.

We exploit the birefringence of cellophane to convert a linearly polarised Gaussian beam into either a radially or azimuthally polarised beam. For that, we fabricated a low-cost polarisation mask consisting of four segments of cellophane. The fast axis of each segment is oriented appropriately in order to rotate the polarisation of the incident linearly polarised beam as desired. To ensure the correct operation of the polarisation mask, we tested the polarisation state of the generated beam by measuring the spatial distribution of the Stokes parameters. Such a device is very cost efficient and allows for the generation of cylindrical vector beams of high quality.