Mirror Facets Research Articles

Role of the thermal boundary resistance of the quantum well interfaces on the degradation of high power laser diodes

The influence of the quantum well (QW) interfaces with the barrier layers on the rapid degradation of AlGaAs based high power laser bars (808 nm) is investigated. Thermal stresses induced in the device by the local heating produced by nonradiative recombination areas at the facet mirror are calculated by means of a thermomechanical model. Results show that the laser power density threshold necessary to achieve the plastic deformation, leading to the generation of dislocations and to the failure of these devices, is reduced as the quality of the QW interfaces worsens in terms of thermal boundary resistance.

200kW 탑형 태양열발전시스템에서 사용되는 Heliostat의 집열특성 분석

Heliostat in the tower type solar thermal power plant is a sun tracking mirror system to reflect the solar energy to the receiver and the optical performance of it affects to the efficiency of whole power plant most significantly. Thus a solid understanding of heliostat`s energy concentration characteristics is the most important step in designing of the heliostat field and the whole power plant. The work presented here is the analysis of energy concentration characteristics of heliostat used in 200kW solar thermal power plant, where the receiver located at 43m high in tower has m rectangular shape. The heliostat reflective surface is formed by 4 of m flat plate mirror facet and the mirror facet is mounted on the spherical frame. The direct normal incident radiation models in vernal equinox, summer solstice, autumnal equinox and winter solstice are first derived from the actually measured data. Then the intercept ratio, heat flux distribution and total energy collected at the receiver for the heliostats located in the various places of the heliostat field are investigated. Finally the effect of mirror facet installation error on the optical performance of the heliostat is analyzed.

Optimized micromirrors for three-dimensional single-particle tracking in living cells

In this letter we describe and fabricate an optimized version of micromirrors for three-dimensional (3D) single-particle tracking in living cells. Our technology is based on parallel arrays of single facet mirrors, which are introduced into the field of view of an optical microscope to provide one tilted view projected alongside the direct fluorescent sample image. Our method outperforms previously published V-shaped micromirrors technologies, as demonstrated by a ten-fold enhanced 3D positioning accuracy and a 1.7-fold reduced bleaching rate. We envision that our technology will be particularly useful for high-throughput 3D live cell imaging.

200kW 탑형 태양열발전시스템을 위한 Heliostat 반사면 구조 설계

Heliostat in the tower type solar thermal power plant is a sun tracking mirror system to reflect the solar energy to the receiver and the optical performance of it affects to the efficiency of whole power plant most significantly. Thus a proper design of structure of the heliostat reflective surface could be the most important step in the construction of such power plant. The work presented here is a design of structure of optical surface of heliostat, which will be used in 200kW solar thermal power plant. The receiver located at 43(m) high from ground in tower has (m) rectangular shape. We first developed the software tool to simulate the energy concentration characteristics of heliostat using the ray tracing technique. Then, the shape of heliostat reflective surface is designed with the consideration of heliostat`s energy concentration characteristics, production cost and productivity. The designed heliostat`s reflective surface has a structure formed by canting four of (m) rectangular flat plate mirror facet and the center of each mirror facet is located on the spherical surface, where the spherical surface is formulated by the mirror facet mounting frame.

Miniaturization of step mirrors in a static Fourier transform spectrometer: theory and simulation

The diffraction at mirror facets restricts the size of step mirrors for static step-mirror-based Fourier transform spectrometers. This paper discusses the miniaturization of these step mirrors and proposes a quasiperiodic approximation of Fresnel diffraction to analyze the diffraction effect. Noise caused by diffraction is classified into approximation noise and edge noise. The edge-enlarge method is developed to reduce edge noise. This method can reduce mirror facet width to less than 30 times the longest wavelength to be studied. Simulation results are given.

Optical analysis for simplified astigmatic correction of non-imaging focusing heliostat

In the previous work, non-imaging focusing heliostat that consists of m × n facet mirrors can carry out continuous astigmatic correction during sun-tracking with the use of only ( m + n − 2) controllers. For this paper, a simplified astigmatic correction of non-imaging focusing heliostat is proposed for reducing the number of controllers from ( m + n − 2) to only two. Furthermore, a detailed optical analysis of the new proposal has been carried out and the simulated result has shown that the two-controller system can perform comparably well in astigmatic correction with a much simpler and more cost effective design.

Optimization of nonimaging focusing heliostat in dynamic correction of astigmatism for a wide range of incident angles

To overcome astigmatism has always been a great challenge in designing a heliostat capable of focusing the sunlight on a small receiver throughout the year. In this Letter, a nonimaging focusing heliostat with a dynamic adjustment of facet mirrors in a group manner has been analyzed for optimizing the astigmatic correction in a wide range of incident angles. This what is to the author's knowledge a new heliostat is not only designed to serve the purpose of concentrating sunlight to several hundreds of suns, but also to significantly reduce the variation of the solar flux distribution with the incident angle.

Development of image mappers for hyperspectral biomedical imaging applications

A new design and fabrication method is presented for creating large-format (>100 mirror facets) image mappers for a snapshot hyperspectral biomedical imaging system called an image mapping spectrometer (IMS). To verify this approach a 250 facet image mapper with 25 multiple-tilt angles is designed for a compact IMS that groups the 25 subpupils in a 5 x 5 matrix residing within a single collecting objective's pupil. The image mapper is fabricated by precision diamond raster fly cutting using surface-shaped tools. The individual mirror facets have minimal edge eating, tilt errors of <1 mrad, and an average roughness of 5.4 nm.

Optical Characterization of Nonimaging Planar Concentrator for the Application in Concentrator Photovoltaic System

The design and construction of miniature prototype of nonimaging planar concentrator, which is capable of producing much more uniform spatial irradiance and reasonably high concentration ratio, were presented in the previous paper. In this paper, we further explore the optical characteristics of the new concentrator that is specially designed to be incorporated in concentrator photovoltaic systems. For this study, we have carried out a comprehensive analysis via numerical simulation based on all the important design parameters, i.e., array of facet mirrors, f/D ratio, receiver size, and the effect of sun-tracking error, which lead to the overall optical performance of the new concentrator.

Curved facet 90° turning mirrors for integrated optical technologies

A curved total internal reflection facet for use as a 90° turning mirror in integrated optical devices is presented. The design exhibits decreased losses and back-reflections compared to standard plain facet mirror designs. Loss measurements and lasing spectra based on serpentine laser devices are presented and show losses as low as 0.57 dB + 0.02 dB per mirror.

A new mirror alignment system for the VERITAS telescopes

Imaging atmospheric Cherenkov telescopes (IACTs) used for ground-based gamma-ray astronomy at TeV energies use reflectors with areas on the order of 100 m 2 as their primary optic. These tessellated reflectors comprise hundreds of mirror facets mounted on a space frame to achieve this large area at a reasonable cost. To achieve a reflecting surface of sufficient quality one must precisely orient each facet using a procedure known as alignment. We describe here an alignment system which uses a digital (CCD) camera placed at the focus of the optical system, facing the reflector. The camera acquires a series of images of the reflector while the telescope scans a grid of points centred on the direction of a bright star. Correctly aligned facets are brightest when the telescope is pointed directly at the star, while mis-aligned facets are brightest when the angle between the star and the telescope pointing direction is twice the mis-alignment angle of the facet. Data from this scan can be used to calculate the adjustments required to align each facet. We have constructed such a system and have tested it on three of the VERITAS IACTs. Using this system the optical point-spread functions of the telescopes have been narrowed by more than 30%. We present here a description of the system and results from initial use.

Beam-Down Mirror: Thermal and Stress Analyses

The “beam-down” optics or solar tower reflector, developed and demonstrated at the Weizmann Institute of Science during the past 9 years, could be a useful modification of the classic solar tower technology, especially for solar applications where reacting solids are involved or heavy equipment has to be placed on top of a conventional tower. The theory of this optics has been thoroughly studied and reported elsewhere. This paper details the development and experience gained with the mirror facets of the tower reflector. Thermal and stress analyses are presented here, validated by temperature measurements and calculated incident flux map. The projection for a large scale solar plant of about 100 MW at the aperture of the receiver is illustrated. The current basic design of the facet made of a sandwich of mirrors glued back-to-back seems to be a feasible solution for future applications. Aluminum-glass facets failed, and cracks in the glass were observed in the course of time. Years of experience proved that using only natural cooling to the surrounding, for the glass/glass facets, which can reach 130–140°C during operation under average incident solar flux of about 30 kW/m2, is a viable design. Maximum working temperatures of 160°C were experienced without any degradation of the reflectivity and the performance of these facets after several hundreds of operation hours.

Realization of Tip Tilting By 8-Step Line Tilting

By direct calculation of rotation matrices of SO(3), we show how certain specific sequence of eight consecutive rotations of digital angles can yield a tilting of a facet mirror. We also design a detailed program specifically to tilt an array of mirrors from planar orientation to the required focusing orientation. We describe how to use the 8-step to realize the focusing of the mirror array. We have found, in our designed program, an important feature of row-sharing during the rotations for the columns and similarly the column-sharing during the rotations for the row. This feature can save a lot of operating time during the actual realization of the mechanical movements.

DFB Quantum Cascade Laser Arrays

DFB quantum cascade laser (DFB-QCL) arrays operating between 8.7 and 9.4 mum are investigated for their performance characteristics-single-mode selection of the DFB grating, and variability in threshold, slope efficiency, and output power of different lasers in the array. Single-mode selection refers to the ability to choose a desired mode/frequency of laser emission with a DFB grating. We apply a theoretical framework developed for general DFB gratings to analyze DFB-QCL arrays. We calculate how the performance characteristics of DFB-QCLs are affected by the coupling strength kappaL of the grating, and the relative position of the mirror facets at the ends of the laser cavity with respect to the grating. We discuss how single-mode selection can be improved by design. Several DFB-QCL arrays are fabricated and their performance examined. We achieve desired improvements in single-mode selection, and we observe the predicted variability in the threshold, slope efficiency, and output power of the DFB-QCLs. As a demonstration of potential applications, the DFB-QCL arrays are used to perform infrared absorption spectroscopy with fluids.

Comparison and Optimization of Heliostat Canting Methods

Heliostat canting (alignment of mirror facets) is known to have a major influence on the optical efficiency of heliostat fields and therefore on the power output of solar tower plants. In recent years several canting concepts were used, mainly on- and off-axis canting. Several new canting concepts, such as stretched-parabolic or target-aligned canting, were proposed in order to improve the performance of heliostats. As solar power plants become economically more attractive, knowledge about the influence of canting becomes more important. In this context, the influence of several factors on the canting method is discussed and optimal canting strategies are described. The considered factors comprise plant power level, heliostat position in the field, heliostat area, receiver dimension, and site latitude. It is concluded that the target-aligned tracking method is superior to all other variants in the majority of cases. As for the standard azimuth-elevation tracking methods, not one of these exhibits a clear advantage. It is only the on-axis method that performs worst in all cases.

Polymeric Waveguide Film With Embedded Mirror for Multilayer Optical Circuits

A polymeric waveguide film with embedded mirrors is presented for a multilayer optical circuit. For the polymeric waveguide fabrication, arrayed waveguide patterns were directly formed on a metallic master body using ultra-precision machining (UPM) method, and 45deg-angled mirrors as beam reflector were constructed at the master pattern ends. We have achieved excellent surface roughness of the pattern and mirror facet using UPM. The waveguide lines and 45deg-angled mirrors were simultaneously fabricated on an under-clad sheet using an imprint method with a mirror-integrated master. We manufactured polymer waveguide films with embedded beam reflectors and consequently measured the optical characteristics of waveguides.

Embedded Micromirror Inserts for Optical Printed Circuit Boards

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We present the use of an embedded 45<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula> micromirror, which is patterned in polymer photoresist using deep proton writing. The micromirror is metallized and inserted in a laser ablated cavity in the optical layer and in a next step covered with cladding material. Surface roughness measurements confirm the excellent quality of the mirror facet. Loss measurements have been carried out to evaluate the behavior of the embedded micromirror. These measurements indicate an average loss below 0.35 dB, measured in a receiver scheme, which is the most stringent configuration. </para>

Influence of patterned TiO2/SiO2 dielectric multilayers for back and front mirror facets on GaN-based laser diodes

Ridge InGaN multi-quantum-well-structure (MQW) edge-emitting laser diodes (LDs) were grown on (0001) sapphire substrates by low-pressure metal-organic chemical vapour deposition (MOCVD). The dielectric TiO2/SiO2 front and back facet coatings as cavity mirror facets of the LDs have been deposited with electron-beam evaporation method. The reflectivity of the designed front coating is about 50% and that of the back high reflective coating is as high as 99.9%. Under pulsed current injection at room temperature, the influences of the dielectric facets were discussed. The threshold current of the ridge GaN-based LDs was decreased after the deposition of the back high reflective dielectric mirrors and decreased again after the front facets were deposited. Above the threshold, the slope efficiency of the LDs with both reflective facets was larger than those with only back facets and without any reflective facets. It is important to design the reflectivity of the front facets for improving the performance of GaN-based LDs.

Fabrication of blue‐shifted Fabry‐Perot laser diodes for integration with optical passive waveguides

AbstractLaser diodes monolithically integrated with a passive waveguide is fabricated by using a quantum‐well intermixing. This technique first consists of using a photolithography and reactive ion etching process to create a Si3N4 implant mask region on the sample. This is followed by a 1‐MeV phosphorous ion implantation at a dose of 5×1014 P+ ions/cm2 at 200 °C. A subsequent two‐step RTA annealing induces QW intermixing through the diffusion of the point defects. For the integration of a laser diode and a passive waveguide, the mirror facet is formed by creating a deeply‐etched trench between an active and passive region by RIE etching. The lasing operation and shifted lasing wavelengths are measured and compared experimentally. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

First principles jitter characterization of two-axis MEMS mirrors

Recently developed MEMS micromirror technology provides an opportunity to replace macroscale actuators for laser beamsteering in lidar and free-space optical communication systems. Precision modeling of mirror pointing and its dynamics are critical to the design of MEMS beamsteerers. Beam jitter ultimately limits MEMS mirror pointing, with consequences for bit error rate and overall optical system performance. Sources of jitter are platform vibration, control voltage noise, and Brownian motion noise. This work relates the random jitter of the mirror facet to its originating sources via a multidimensional first-order Taylor expansion of a first-principles-derived analytic expression for the actuating torque. The input torque, consisting of deterministic and stochastic components, is related to the 2-D jitter through a pair of coupled damped harmonic oscillator differential equations. The linearized 2-D jitter model for the mirror is simulated using Matlab, while the full nonlinear torque model was simulated using Simulink. The work describes an experimental setup and methodology that is used to make precise micromirror measurements. Experimental measurements are in agreement with the jitter model, i.e., the linearized model is able to predict mirror facet jitter based on the measured power spectral densities for the sources of jitter.