Entire Optical System Research Articles

Experimental research of temperature influence on retardance in crystal quartz for deep ultraviolet range of wavelength

The retardation change versus temperature was measured for deep UV multiorder crystal quartz wave plates. The influence of temperature on the wave-plate performance is even more significant for the deep UV region due to the shorter wavelength and increased number of wave periods in the retarder for the given thickness and sharp changes of refractive indices versus temperature and wavelength? Precise control of temperature is needed for accurate analysis of the wave-plate optical parameters. The wave plate should be designed for a certain temperature and used within a tightly controlled temperature range; otherwise its performance will be degraded, affecting the entire optical system. A simple laser-based method was exploited and developed for wave-plate performance evaluation versus temperature for the half and quarter wave retardation. All this information needs to be taken into account for deep UV wave-plate design to ensure the best possible performance of the retarder.

Selectivity and tolerance calculations with half-cone-shaped reference beam in volume holographic storage

When developing a compact holographic storage system it is beneficial to use a reflection-type arrangement, where the entire optical system is on the same side of the storage material. For reflection type holographic discs, it is important to use half-cone-shaped spherical reference beams to avoid the ghost images caused by phase conjugate readout. The goal of this paper is to look for appropriate engineering tools to model diffraction efficiency of finite volume holograms created by half-cone-shaped reference beams. Two numerical methods – volume integral and beam propagation – were applied to calculate the shift selectivity curves. Simulation results show significant discrepancies between the shift selectivity curves corresponding to the approximated analytical equation and the numerically calculated shift selectivity curves; there are no Bragg zeros and there are no selective and nonselective directions. Beside the shift selectivity curves, track, focus, tilt and wavelength tolerance values are shown for finite volume holograms.

Fast Optical Ray Tracing Using Multiple DSPs

Optical ray tracing is a computationally intensive operation that is central both to the design of optical systems and to analyzing their performance once built. The authors have previously reported on the use of parallel digital signal processors (DSPs) to reduce the time required to perform ray tracing in analyzing the performance of the moderate resolution imaging spectroradiometer (MODIS), which is presently in orbit on multiple spacecraft. The earlier work was incomplete, providing only a conservative estimate of the performance improvement that could be achieved with one to four DSPs. This paper reports on the completed project and extends the earlier work to eight DSPs. As predicted in the earlier paper, not all rays make it through the entire optical system. Many are lost along the way. This is one factor that led to reduced processing time. Another is the use of an optimizing compiler. In this paper, the authors present results showing the separate effect of each of these two independent factors on the overall processing time. The most significant finding is the extraordinarily linear relationship between the number of DSPs available and the speed of the ray tracing. By using eight DSPs, the processing time is reduced from two weeks to less than one and a half days, an improvement of nearly a whole order of magnitude. Low-cost high-speed ray tracing is now feasible using off-the-shelf plug-in processor boards

Shift Selectivity Calculation for Finite-Volume Holograms with Half-Cone Reference Beams

Analytical shift selectivity equations assume an infinite hologram size. When developing a compact holographic storage system, one uses small holograms. From a practical viewpoint, it is better to use reflection type discs, in which the entire optical system, writing and reading objectives, among others, are on the same side of the disc. For reflection-type holographic discs, it is important to use half-cone-shaped reference beams to avoid generating ghost images caused by phase conjugate readout. Our calculations show significant discrepancy between the shift selectivity curves corresponding to the approximated analytic equation and the numerically calculated shift selectivity curves.

Alternative representation of the linear canonical integral transform

Starting with the Iwasawa-type decomposition of a first-order optical system (or ABCD system) as a cascade of a lens, a magnifier, and an orthosymplectic system (a system that is both symplectic and orthogonal), a further decomposition of the orthosymplectic system in the form of a separable fractional Fourier transformer embedded between two spatial-coordinate rotators is proposed. The resulting decomposition of the entire first-order optical system then shows a physically attractive representation of the linear canonical integral transformation, which, in contrast to Collins integral, is valid for any ray transformation matrix.

A thin-film laser, polymer waveguide, and thin-film photodetector cointegrated onto a silicon substrate

Planar lightwave circuits, which include optical passive and active components, can be integrated with electronics to form planar lightwave integrated (PLICs). Integration of PLICs onto standard electronic substrates (FR-4, Si) is an important step toward optical signal processing and signal distribution at the backplane, board, and chip level for sensing, interconnection, and other systems that utilize both optics and electronics. Further, if the topography of the entire planar optical system can mimic that of interconnection and integrated circuits, then the optics can be confined to the substrate plane, and the optical circuits begin to mimic electrical in format. Additionally, beam turning out of the plane of the system is no longer mandatory. In this letter, the first demonstration of a planar lightwave interconnection consisting of a thin-film InP-based laser, waveguide, and thin-film InGaAs photodetector (PD) heterogeneously integrated onto a SiO/sub 2/-Si substrate is reported. PD currents were measured as a function of laser bias current, and the laser to waveguide coupling efficiency was estimated at 22.6%.

Is “Whole Eye” Wavefront Analysis Helpful to Corneal Refractive Therapy?

To examine how corneal refractive therapy (CRT) affects the balance between corneal surface and whole eye spherical aberration (Z4) and to identify whether corneal aberrations alone can accurately predict optical outcomes of CRT. Whole eye and corneal spherical aberrations were measured at baseline and 1 month after CRT in 12 dilated eyes (baseline myopia range, -2.25 to -6.00 diopters [D]; mean, -3.23 +/- 1.06D). Whole eye aberrations were measured under cycloplegia using a Shack-Hartmann aberrometer, and corneal aberrations were measured using Keratron corneal topography elevation maps converted to wavefront Zernike polynomials using VOL-CT. Whole eye and corneal surface aberrations were scaled for 6-mm pupil diameters. No statistically significant correlation existed between corneal and whole eye spherical aberration at baseline. Corneal and whole eye spherical aberration increased in all eyes after CRT. A statistically significant and moderately positive correlation was found between corneal and whole eye spherical aberration after CRT (R = 0.632, P = 0.004). The linear regression slope was positive (m = +1.449) and indicated that whole eye spherical aberration exceeds corneal spherical aberration after CRT. Whole eye wavefront analysis is essential to methods designed to optimize visual performance with CRT; results indicate that CRT affects the entire optical system and not just the anterior corneal surface. Moreover, because CRT-induced whole eye spherical aberration cannot be explained by corneal aberrations alone, commonly accepted beliefs that the mechanism of action is limited to corneal tissue redistribution may need to be revisited.

Calculation of Coulomb Interaction among Electrons in a High-Current Electron-Beam Exposure System

In the present study, we propose a new calculation method for the Coulomb interaction among electrons in an electron beam running at a given optical system. In the simulation, the interaction is expressed by separating the global and the stochastic mechanisms, and then, they are combined in a Monte Carlo electron trajectory simulation. In the case of the global Coulomb effect, the potential distribution is obtained in the beam, and the electron trajectory deflection due to the distribution is calculated. In the case of the stochastic Coulomb effect, it is assumed that electrons interact with only their nearest neighbor electrons in the beam. All electron trajectories in the entire optical system are traced three-dimensionally. Since the Coulomb interaction is calculated for only one pair of electrons instead of all pairs of other electrons around the electron in the present model, the computation time is markedly reduced. It is found that the results obtained by the present simulation show a fair agreement with that obtained by considering all existent electrons in the beam, as in the conventional Monte Carlo simulation of the Coulomb interaction.

Realizing Integral Field Spectroscopy in the Far‐Infrared

The optical design of an integral field spectrometer for far-infrared observations, the Far-Infrared Field-Imaging Line Spectrometer (FIFI LS), is presented. The instrument will fly on board the joint NASA/DLR airborne observatory SOFIA, observing in two nearly independent wavelength channels simultaneously: a blue channel (40-105 μm) and a red channel (105-210 μm). To achieve instantaneous integral field spectroscopy for the first time in the far-infrared, a novel reflective image slicer system is utilized that slices the 5 × 5 pixel, two-dimensional field of view into a pseudo-long slit of 25 × 1 pixels. The slicer assembly consists of three sets of five mirrors that have optical power, enabling a compact design. After the sky field has been optically rearranged to the pseudoslit, the image is spectrally dispersed in a standard Littrow-mounted reflective grating spectrometer. The practical concerns for the optical design in the far-infrared and, in particular, the significant effect of diffraction in the entire optical system is discussed.

1] Measurement of absolute oxygen levels in cells and tissues using oxygen sensors and 2-nitroimidazole EF5

We have established basic methods, using quantitative measures of EF5 binding, to estimate the actual pO2 of cells and tissues. In situations where the tissue can be dissociated into single cells, or for cell cultures, we can measure the distribution of cellular binding rates using flow cytometry and these can be compared with cells treated under pO2S controlled by the spinner vial or thin-film methods in vitro. The flow cytometer is calibrated by staining V79 cells treated with EF5 under "standard" conditions. For intact tissues treated with EF5 in vivo, we need to correct for possible variations in drug exposure (AUC). Frozen sections are stained for EF5 binding and are analyzed by a sensitive (cooled) CCD camera with linear output vs fluorescence [figure: see text] input. The camera has very consistent sensitivity, but the entire optical system, including the camera, can be calibrated by an absolute fluorescence standard (dye in hemocytometer). This system can also be used to measure the fluorescence of the flow cytometer standards, providing a direct link between the two assays. We can measure the maximum binding rate using the tissue cube method, but need to assume an "average" oxygen dependence of binding for intact tissues. The best-fit approximation for existing data is an inverse relationship between binding and pO2, with binding decreasing 50-fold between 0.1 and 10% oxygen. Using these methods, we routinely estimate the minimum pO2 (maximum binding) in experimental rodent and human tumors. In normal tissue models, an excellent correlation is found between near-maximal binding (severe hypoxia) and apoptosis (heart infarct and ductus arteriosus). Some normal tissues (e.g., skeletal muscle) are refractory to both cellular disaggregation and cube calibration methods. To extend the tissue imaging measurements to a complete two- or three-dimensional analysis of the distribution of tissue pO2s requires a substantial additional investment of imaging methods, which are currently being implemented.

Enhanced Raman sensitivity using an actively stabilized external resonator

An enhancement up to 250-fold in laser Raman signals for real-time gas analysis has been achieved within an actively stabilized external resonator (ASER), whose length is actively matched to the single-frequency excitation laser using the Pound–Drever technique. With the Raman cell present, enhancements up to 50-fold are achieved, and the resulting detection limit for hydrogen in ambient-pressure gas mixtures is about ten parts-per-million in a 1 min analysis period at unity signal-to-noise ratio. Based upon the recent development of a fiber-pumped Nd:YVO4 laser with single-frequency output exceeding 5 W at 532 nm, this highly sensitive instrument is applied to detection of tritiated gases, wherein the compactness and low heat of this laser head permit placing the entire optical system, including laser head, charge coupled Raman detector, and ASER, within the glove box necessary for secondary containment of tritium, thereby accomplishing a robust, highly sensitive Raman analytical system for hazardous substances.

Behavioral modeling for hierarchical simulation of optronic systems

In order to find the optimal design for a given specification of a lightwave communication link, an integrated simulation of electronic, optoelectronic, and optical components of a complete system is required. Models for optoelectronic and optical components written in HDL-A/sup TM/ provide an accurate time-domain simulation of an entire optical communication system in a standard circuit simulator environment. The behavioral modeling approach, demonstrated in our work, can be used for transmission-layer simulations, as well as for co-simulation of control and physical levels of optical communication systems.

Propagation of eigenmodes and transfer amplitudes in optical waveguide structures

A method of transfer amplitudes suitable for modeling and simulation in integrated optical circuits is presented. The method is based on vectorial formulation of electrodynamics: distributions and propagation of electromagnetic fields in optical circuits are described by equivalent surface sources. This approach permits a division of complex optical waveguide structures into sets of primitive blocks and to separately calculate the transfer amplitude for each block. The transfer amplitude of the entire optical system is represented by a convolution of transfer amplitudes of its primitive blocks. Diffraction in slab regions is taken into account using known propagation functions. It is shown that the concept of a normalized transverse eigenfunction of the diffracted field is very useful in calculations of transfer amplitudes. The crucial role of transverse Bloch modes in propagation through multiwaveguide structures is emphasized. With this method, the eigenvalues and eigenfunctions of an arbitrary waveguide structure can be obtained with high accuracy. The general approach is illustrated with the transfer amplitude and efficiency calculations for a star coupler and a waveguide grating router.

Free-Space Integrated Optics Realized by Surface-Micromachining

A surface-micromachined free-space micro-optical bench (FS-MOB) technology has been proposed to monolithically integrate micro-optical elements, optomechanical structures, micropositioners, and microactuators on the same substrate. Novel three-dimensional micro-optical elements have been fabricated by surface-micromachining techniques. The optical axes of these optical elements are parallel to the substrate, which enables the entire free-space optical system to be integrated on a single substrate. Mocro-scale Fresnel lenses, refractive microlenses, mirrors, beam-splitters, gratings, and precision optical mounts have been successfully fabricated and characterized. Integration of micro-optical elements with translation or rotation stages provides on chip optical alignment or optomechanical switching. This new free-space micro-optical bench technology could significantly reduce the size, weight, an cost of most optical systems, and could have a significant impact on optical switching, optical sensing and optical data storage systems as well as packaging of optoelectronic components.

The doppler wind and temperature system of the ALOMAR lidar facility: overview and initial results

The Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) facility is a new and major facility for atmospheric research. It is located at Andøya in Northern Norway. One of the important facilities of ALOMAR is the Doppler Wind and Temperature System (DWTS). The DWTS will determine atmospheric wind and temperature profiles between about 8 and 90 km altitude from the Doppler shift and broadening of the lidar signal Rayleigh back-scattered from the atmosphere. The DWTS uses a double-etalon Fabry-Perot interferometer to perform the high-resolution spectral analysis of the back-scattered lidar signal, and to reject the bright background light from the daytime sky. After spectral analysis, the Fabry-Perot fringes are imaged onto a multi-ring anode imaging photon detector which provides, pulse-by-pulse, time-resolved detection of the spectrum of the laser light back-scattered from the atmosphere. The double-etalon Fabry-Perot interferometer has been designed to detect the returned signal during daytime, and thus summer-time conditions at ALOMAR, as well as during night-time. The entire optical system has been designed to maximise the transmission and detection of light, to make maximum use of the faint signals available from high-altitude regions, up to around 80–90 km. This paper reports on the objectives and design of the ALOMAR DWTS, and presents some initial results obtained during commissioning periods in October 1994 and January 1995.

The Edison international space observatory and the future of infrared space astronomy

Edison is a 1.7 m long-lived radiatively/mechanically-cooled space observatory proposed to operate over λ ∼ 3 – 100 + μm using a suite of imaging and spectroscopic instruments. Thanks to innovative use of radiative cooling and very lightweight optics, the total size and mass of the baseline Edison spacecraft is only modestly larger than that of ESA's ISO mission. Thermal models indicate that the optical system will cool radiatively to about 20 K, while mechanical refrigerators now in advanced laboratory development will be used to cool the detectors to temperatures below 2 K. Continuing design work on this project indicates that these cryo-coolers may in fact be used to lower the entire optical system to temperatures as low as 5 K or below. This would achieve the advantages of purely cryogenic space observatories, while avoiding their limitations. Therefore, within a few years, mixed radiative/mechanical systems may replace cryogenic systems for most cooling applications in space. As this is being written, Edison is under consideration by the European Space Agency as a candidate for a ‘Cornerstone’ mission as part of the “Horizon 2000 Plus” process. As such, it is the only candidate for a future infrared space observatory after about 2005.

Micromachined free-space integrated micro-optics

The surface-micromachining technique has been employed to fabricate novel three-dimensional micro-optical elements for free-space integrated optics. The optical axes of these optical elements are parallel to the substrate, which enables the entire free-space optical system to be integrated on a single substrate. Microscale Fresnel lenses, mirrors, beam splitters, gratings, and precision optical mounts have been successfully fabricated and characterized. In addition, micropositioners such as rotary stages and linear translational stages are monolithically integrated with the optical components using the same surface-micromachining process to provide on-chip optical alignment or optomechanical switching. Self-aligned hybrid integration with semiconductor edge-emitting lasers and vertical cavity surface-emitting lasers are also demonstrated for the first time. This new free-space micro-optical bench (FSMOB) technology could significantly reduce the size, weight, and cost of most optical systems, and could have a significant impact on optical switching, optical sensing and optical data-storage systems as well as on the packaging of optoelectronic components.

Mueller matrix imaging polarimetry

The design and operation of a Mueller matrix imaging polarimeter is presented. The instrument is configurable to make a wide variety of polarimetric measurements of optical systems and samples. In one configuration, it measures the polarization properties of a set of ray paths through a sample. The sample may comprise a single element, such as a lens, polarizer, retarder, spatial light modulator, or beamsplitter, or an entire optical system containing many elements. In a second configuration, it measures an optical system's point spread matrix, a Mueller matrix relating the polarization state of a point object to the distribution of intensity and polarization across the image. The instrument is described and a number of example measurements are provided that demonstrate the Mueller matrix imaging polarimeter's unique measurement capability.

Simple and accurate zero dispersion wavelength measurement for long haul optical amplifier systems using induced phase to amplitude modulation conversion

A simple method which can directly measure the zero dispersion wavelength of a entire optical amplifier transmission system is reported. It is based on dispersion induced phase to amplitude modulation conversion in an optical fibre. The experimental and theoretical results agree for a 2000 km transmission system, and the standard deviation of measured zero dispersion wavelengths is only 0.053 nm.

Raman scattering in air: four-dimensional analysis

Inertial confinement fusion requires propagation of high-intensity, pulse-shaped IR and UV laser beams through long air paths. Such beams are subject to energy losses and decreased beam quality as a result by stimulated rotational Raman scattering (SRRS). In this paper we describe how quantum fluctuations, stimulated Raman amplification, diffraction propagation, and optical aberrations interact during the propagation of short, high-power laser pulses using a four-dimensional (4-D) model of the optical beams and the medium. The 4-D model has been incorporated into a general optical-propagation computer program that allows the entire optical system to be modeled and that is implemented on high-end personal computers, workstations, and supercomputers. The numerical model is used to illustrate important phenomena in the evolution of the optical beams. In addition, the OMEGA Upgrade laser system is used as a design case to illustrate the various considerations for inertial confinement fusion laser design.