In the last 30 days

• Open/close Design, fabrication and testing of microlens arrays for sensors and microsystems

  Ph Nussbaum et al 1997 Pure Appl. Opt. 6 617 Tag this article

  Article References Full text PDF (1.95 MB)

  We report on our activities in design, fabrication, characterization and system integration of refractive microlens arrays for sensors and microsystems. Examples for chemical analysis systems ( , blood gas sensor), neural networks and multiple pupil imaging systems for photolithography (microlens and smart mask lithography) are presented.

• Open/close Approximate calculation of the reflection coefficient from a stratified medium

  C J R Sheppard 1995 Pure Appl. Opt. 4 665 Tag this article

  Article References Full text PDF (165 KB)

  An approximate method for calculating the reflection coefficient of stratified media is discussed. An analytic expression is given for the reflection coefficient for a multi-layer antireflecting stack, with elements of arbitrary thickness and oblique illumination.

• Open/close Film mode matching: a versatile numerical method for vector mode field calculations in dielectric waveguides

  A Sv Sudbo 1993 Pure Appl. Opt. 2 211 Tag this article

  Article References Full text PDF (1.21 MB)

  The old film mode matching or transverse resonance method for calculating mode fields in dielectric waveguides is given a new formulation that makes it an efficient, accurate, and general numerical method, ready to exploit standard computer libraries for numerical linear algebra. Both the scalar and the vector field cases are treated for a rather general class of waveguide cross sections, where the method (like the method of lines) is more accurate and more efficient than sophisticated finite-element and finite-difference methods.

• Open/close Coupling gratings as waveguide functional elements

  Olivier Parriaux et al 1996 Pure Appl. Opt. 5 453 Tag this article

  Article References Full text PDF (209 KB)

  Waveguide grating couplers allow the essential function of waveguide access to be integrated together with optical processing functions on a monolithic planar substrate. Grating coupling technology is topologically and, to a large extent, technologically compatible with the planar processes which define the optical processing waveguide circuit. Poor coupling efficiency, highly dispersive character, absence of user-friendly modelling tools and fabrication difficulties have long prevented this technology from being implemented into practical sensors and microsystems. This paper makes a review of the points where decisive technological progress has been made, illustrates some useful features of waveguide coupling gratings and underlines some of the difficulties which the designer may encounter.

• Open/close Solid-state coherent laser radar wind field measurement systems

  R Milton Huffaker and Paul A Reveley 1998 Pure Appl. Opt. 7 863 Tag this article

  Article References Full text PDF (1.78 MB)

  Diode-pumped solid-state pulsed coherent laser radar systems have recently been developed at Coherent Technologies, Inc., for the remote measurement of atmospheric wind fields. Flashlamp-pumped systems have been utilized since 1990 for obtaining wind field measurements. These flashlamp-pumped lidar systems have been applied to wind profiling, aircraft-wake vortex measurements, airport wind shear and gust front monitoring, military cargo air drops and many other applications. The diode-pumped coherent lidar systems currently available are capable of near turnkey operation. The Tm:YAG laser transceivers operate at with output pulse energies of 1-10 mJ with PRFs of 1000 to 100 Hz, respectively. Range resolutions of 30-75 m are typical. A real-time lidar signal processor has also been developed for collecting and analysing laser radar (lidar) data. The signal processor is based on a commercial PC architecture and offers a real-time data acquisition, analysis, display, recording and playback environment. Wind measurements and overall system performance results will be presented. Wind measurement performance, for a variety of applications, is presented using the flashlamp- and diode-pumped coherent lidars including measured wind profiles from ground and on aircraft, wake vortex tracking results, and example flows over mountain terrain.

• Open/close Comparison of three transmission methods for integrated optical waveguide propagation loss measurement

  G Tittelbach et al 1993 Pure Appl. Opt. 2 683 Tag this article

  Article References Full text PDF (771 KB)

  Three techniques for the measurement of propagation losses of single mode integrated optical waveguides are compared. The insertion loss measurement technique and the backcoupling method are suitable for the measurement of attenuation values alpha L>or=1. The resonator techniques give small relative mean errors of the attenuation only for high finesse resonators, which can, in principle, be realized by a waveguide Fabry-Perot resonator with high reflecting endfaces. A more convenient solution, however, is an additional ring resonator on the integrated optical chip.

• Open/close On image quality of microlens arrays in diurnal superposition eyes

  Rafael Navarro and Nicolas Franceschini 1998 Pure Appl. Opt. 7 L69 Tag this article

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  High-resolution compound eyes of the superposition type have been found in some diurnal insects, suggesting high-quality optics. Here we study whether a superposition eye could potentially achieve a higher resolution than that of a single, diffraction-limited facet, like in modern optical instruments made of a number of facets. We have developed a schematic diffractional model of the particularly acute superposition eye of the diurnal lepidopteran agaristid moth Phalaenoides Tristifica, and estimated the amount of aberrations required to fit the experimental data. Our results show that if the ommatidia were perfect (aberration-free) and perfectly aligned towards a common centre O, the resolution of the superposition image would be about 10 times higher than that provided by a single facet, and this in spite of the large phase lags between the pencils of light stemming from neighbouring ommatidia, due to the spherical geometry of the eye. In the insect species taken as a model system here, however, retinal sampling is too coarse to take full advantage of the high spatial frequency content of the superposition image. We show that the experimental data can be fitted if aberrations such as misalignment are introduced. A corollary of these results is that a superposition compound eye which was better constructed and avoided misalignment would provide its host with a better resolution than its `apposition eye counterpart'. This might explain why some diurnal compound eyes such as that of the fast-flying lepidopteran Macroglossum can afford sampling the focal image with a number of rhabdom exceeding the number of ommatidia (Warrant et al 1998 J. Exp. Biol. at press).

• Open/close The quantum cascade laser. A device based on two-dimensional electronic subbands

  Carlo Sirtori et al 1998 Pure Appl. Opt. 7 373 Tag this article

  Article References Full text PDF (156 KB)

  This paper reviews the state-of-the-art of quantum cascade lasers. These new light sources are unipolar semiconductor lasers based on electron resonant tunnelling and optical transitions between quantized conduction band states. Quantum engineering of the electronic energy levels and tailoring of the wavefunctions are used to obtain the correct matrix elements and scattering rates which enable population inversion and the optimization of the overall laser performance. The laser wavelength can be selected over a broad range of the infrared spectrum using the same heterostructure material by tailoring the active layer thickness. Using MBE-grown AlInAs-GaInAs heterostructures, room temperature operation at and has been achieved and lasers in the 4- range were demonstrated at a temperature of 200 K.