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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.

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.

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.

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.

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.

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.

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.

Intra-cavity phase anisotropy causes each laser longitudinal mode to split into two orthogonally polarized frequencies. When the frequency difference generated by small anisotropy is about 40 MHz or less, only one frequency of the splitting mode oscillates while the other is always in lock-in state due to strong mode competition. In that case the longitudinal mode spacing deviates from its original value. And the spacing of two adjacent longitudinal modes shows differential variations depending on direction of cavity length tuning and mode polarization. In this paper, the relationship between spacing variation and small intra-cavity anisotropy is demonstrated experimentally and theoretically. The equivalent fast axis of anisotropy is determined additionally by its correlation with laser intensity tuning of the two orthogonally polarized components. The novel measurement method is successfully tested in several applications.

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.

An automated Stokes-polarimeter with a rotating phase plate has been developed to measure the polarization characteristics of radiation reflected and scattered by objects at different angles to the surface. An estimate is made of the systematic error due to variation of the initial position of the fast axis of the phase plate and deviation of the phase difference of the λ/4 plate from 90°.

A phase step interferometry system using polarization shifting is described. The device is essentially a Mach-Zehnder interferometer in which the polarization of light travelling through one arm is orthogonal to the polarization of light travelling through the other arm. At the interferometer output we place a quarter-wave plate with its fast axis at with respect to the polarization directions and a polarizer. By rotating the polarizer, the interfering waves acquire an extra phase (of topological origin) to that expected from the calculations of optical path lengths, and thus, arbitrary phase shifts can be induced. Then, from a set of interferograms recorded while the reference phase is changed, the `dynamical' phase difference (e.g. the phase profile of an object placed in one of the interferometer arms) can be reconstructed by using techniques of phase-shifting interferometry.

Real-time measurement of the retardation of the quarter-wave plate (QWP) using a Wollaston prism is presented. The collimated beam passes through a circular polarizer, the quarter-wave plate to be measured, a standard quarter-wave plate and then is split by a Wollaston prism. Two sub-beams are detected by a bi-cell detector. From two detection signals, the retardation of the QWP is obtained in real time and is independent of the fast axis azimuth of QWP. At the same time, the method is easy to expand to measure the retardation of the QWP used in deep ultraviolet band and the retardation distribution of the QWP. In experiments, the average and the standard deviation of the retardation of quarter-wave plate are respectively 89.5o and 0.25o. The usefulness of the method is verified.

A method for simultaneous measurement of the retardance and the fast axis angle of quarter-wave plate using one photoelastic modulator is presented. A laser beam passes through a polarizer, a photoelastic modulator, the quarter-wave plate to be measured, and an analyzer to be detected. Before and after the quarter-wave plate is rotated 45° at any initial fast axis direction, two detection signals are obtained to resolve simultaneously the retardance and the fast axis angle. In experiments, a quarter-wave plate was measured with fast axis angles from −89° to 90°. The average and the standard deviation of the retardances at different fast axis directions are respectively 89.50° and 0.17°. The maximum measurement deviation of the fast axis angle is 0.5°. The usefulness of the method is verified.

A study of photoinduced birefringence in bow-tie (stress-induced) high-birefringence (Hi-Bi) and low-birefringence (Lo-Bi) germanosilicate optical fibers is conducted by using 532-nm light. The study reveals that Hi-Bi fibers are insensitive to light polarized along the fast axis, in contrast to Lo-Bi fibers, which are photosensitive along both axes. The induced birefringence in Lo-Bi fibers is reversible, whereas the change in Hi-Bi fibers is permanent. The sign of the induced birefringence is established experimentally for the first time to our knowledge, and the significance of the results to models based on stress and/or glass defects is briefly discussed.

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.

A new design for the vertical waveguide structure of (AIGaIn)(AsSb)-based diode lasers is presented. The active layers of all investigated samples consist of compressively strained 10 nm wide Ga/sub 0.64/In/sub 0.36/As/sub 0.10/Sb/sub 0.90/-QWs, separated by 20 nm wide lattice matched Al/sub 0.29/Ga/sub 0.71/As/sub 0.02/Sb/sub 0.98/ barriers. The emission wavelength is 2.3 /spl mu/m at room temperature. This new quantum-well diode laser design exhibits reduced beam divergence in the fast axis, while the laser performance is maintained compared to a standard large divergence waveguide design. This strong decrease in the fast axis divergence drastically increases the fiber coupling efficiency of GaSb-based diode lasers.

Summary form only given. We report laser performance of an end pumped 100 /spl mu/m Yb:YAG rectangular waveguide. This configuration offers an excellent confinement of the pump field achieved by waveguiding of the slow axis of the diode pump and nonguiding of the fast axis.

During the last five years, INO has conducted a program to develop high performance diode laser illuminator for ATV (active TV) system. Illuminator made using INO proprietary collimating method, which uses GRIN (mu) -lenses for the fast axis and plano-convex (mu) -lenses for the slow axis, were found to provide uniform and tightly collimated beam, diffraction-limited for the fast axis. Such collimated laser diode arrays were proven to efficiently illuminate non- cooperative scene at 1 km with only 6 W of average power.

The copropagation of two optical pulses of different frequencies in single-mode birefringent fibers is investigated. Various combinations of solitary-wave solutions are obtained. It is shown that a dark pulse on the slow axis and a bright pulse on the fast axis simultaneously propagate without distortion in the presence of a bright pulse of different frequency on the slow or the fast axis.

A source of highly collimated coherent red light is developed by packaging several low cost red DVD diode lasers with first slow and then fast axis collimation optics. The source fits a 10 lumen hand held battery operated projector display and operates at temperatures of up to 50°C.

A phase retardation plate, such as a quarter-wave plate, is able to control the state of polarization. Thus, a precise simultaneous determination of phase delay between two eigen-polarization states and its fast-axis angle is essential to the performance of the phase retardation plate to control the state of polarization. Consequently, the measurement of the two-dimensional spatiotemporal distribution of phase retardation and the fast-axis angle become crucial when a large-area of phase retardation plate, such as that for a liquid crystal display, is characterized, due to the inhomogeneity of the retardation plate. In order to measure the linear birefringence parameters, phase retardation and fast-axis angle at the same time, a novel polarized optical heterodyne interferometer is developed, with which the parameters of a quarter-wave plate are successfully measured and verified. The features of this device are (1) a common-path configuration, (2) measurement independent of laser intensity, and (3) the capability of simultaneously determining the spatiotemporal distributions of phase retardation and fast-axis angle of a retardation plate.

Based on the metals property of modifying the phase of an incident beam, a simple method for identifying the fast axis of a wave plate independent of a standard retarder is demonstrated. © 2002 Society