Showing papers on "Optical filter published in 1981"

Guided-wave devices for optical communication

Abstract: We review the current status of guided-wave optical communication devices. The operation and presently demonstrated performance characteristics of waveguides switches, modulators, filters, and polarization transforming devices are discussed. Emphasis is given to recent developments with very high speed modulators and polarization insensitive devices.

Acousto-Optic Tunable Filters

Abstract: This paper reviews the theory, techniques, and applications of acousto-optic tunable filters (AOTF). Two basic types of AOTF are described, i.e., the collinear and the noncollinear configurations. The important device characteristics of the AOTF presented include the bandpass response and spectral resolution, angular aperture, and the filter tuning relation. This review concludes with a discussion of various AOTF applications.

Tunable Fabry-Perot Filters

Abstract: The Fabry-Perot interferometer is being applied increasingly as a tunable filter. The theoretical limits to its performance are considered, including the effects of phase change at multilayer reflecting coatings. Various forms of construction are discussed as are several ways of tuning Fabry-Perot filters. The review concludes with a description of a number of practical devices.

Spectrum analysis using optical processing

Abstract: Spectrum analysis is one of the most fundamental tools in science today. Its use in one form or another spans virtually every discipline. It was one of the first recognized applications of optical processing, and the usefulness of optical spectrum analysis has grown remarkably in the past decade. This is due to the fundamental simplicity, parallelism and intrinsic speed of optical spectrum analyzers, the maturity of the components now available, and the remarkable variety and versatility of the processing architectures that have been developed. This paper presents six selected topics on spectrum analysis using optics. The topics were selected because they represent practical techniques with broad applicability and illustrate different aspects of the technology. The topics are grouped by architecture as space integrating and time integrating. The space integrating sections cover radiometry for detecting low-level signals in wide-band noise, programmable filtering of electrical signals for interference rejection applications, and an optical technique that is equivalent to 105-106parallel filters for application where fast response, high resolution, and wide bandwidth of coverage are simultaneously required. The time integrating sections cover the versatile time integrating spectrum analyzer, and its extension to the calculation of ambiguity surfaces which have important application to radar processing problems requiring simultaneous measurement of a radar return's time of arrival and possible Doppler frequency shift. This process also illustrates the parallel nature of optical operations, and introduces a fundamental concept, the use of one-dimensional optical components configured for performing two-dimensional operations. The discussion of this concept continues into two-dimensional time integrating spectrum analyzers that use two time integrating spectrum analyzers, each capable of resolving N elements, and combines them to produce N2resolvable elements in real time.

Tunable birefringent filters

Abstract: This article reviews the types and capabilities of birefringent filters. The general operating principles of Lyot (perfect polarizers), partial polarizing, and Solc (no internal polarizers) filters are introduced. Appropriate techniques for tuning each filter type are presented. Field of view of birefringent filters is discussed and is compared to Fabry-Perot and interference filters. The transmission and throughput advantages of birefringent filters are shown. Finally, the current state of the art in practical filters is reviewed.

Far-infrared bandpass filters from cross-shaped grids.

Abstract: The optical transmission characteristics of electroformed metal grids with inductive and capacitive cross patterns have been investigated in the far-infrared spectral region. The transmission characteristics of one-and two-grid devices are represented by transmission line theory parameters. Results are used to suggest construction guidelines for two-grid bandpass filters.

Holographic filter that transforms a Gaussian into a uniform beam

Abstract: A simple method of constructing a holographic filter is described which transforms a Gaussian into a uniform beam and conserves 30% of the beam power.

Endoscopic television apparatus

Abstract: An optical filter member composed of a plurality of ND filters having different transmission factors and arranged circumferentially at regular intervals is disposed between a light source and a light guide of an endoscope. When the optical filter member is rotated, a light beam with periodically varying luminance is transmitted through the light guide to illuminate an object inside a body cavity. Images of the object corresponding to different luminances are converted severally into video signals by a television camera. A signal component within a given level range is extracted from each of these video signals by a limiter. The signal components of the video signals are composed into video data to be supplied to a display. The display indicates the video data as an image with proper contrast.

Obstacle detector for use in vehicles

Abstract: An obstacle detector mounted on an automotive vehicle includes a light emitting element, which includes a semiconductor infrared laser, which transmits a light signal through an optical transmission system against any obstacle liable to present on the road on which the vehicle runs The light signal has a wavelength which is 65 microns and which is of such a wavelength that solar light energy having the same wavelength as that of the light signal is not present, or is of very low intensity, at the surface of the earth and that the light energy from light sources such as the headlights of vehicles and/or streetlamps having substantially the same wavelength as that of the light signal, when the light energy has passed through the front glass of the headlights or streetlamps is not present or is of very low intensity An optical receiving system receives part of the light reflected by the obstacle and passes it to an optical filter which has a pass band width whose central wavelength is 65 microns The output of the filter is converted by a photodetector to a corresponding electrical signal for processing by a data processor in order to determine the distance from the vehicle to the obstacle, the azimuth of the obstacle, the velocity of the vehicle relative to the obstacle, etc

New fluorescence detection system for x‐ray absorption spectroscopy

Abstract: The design and performance of a 24‐channel fluorescence detection system for use in x‐ray absorption spectroscopy are discussed, and comparisons are drawn with other detection systems currently in use. Each channel of the current system consists of a NaI scintillation detector with a filter and collimator arrangement designed to reduce the scatter and filter fluorescence background. Given a sufficiently intense and stable x‐ray source, this apparatus can record a useful EXAFS spectrum for an element (Z⩾23) at 100 ppm concentration in approximately 30 minutes. The new design permits the study of plate‐like samples (such as molybdenum enzyme solutions) unsuitable for previously described slit assemblies. Breaking the detection system up into discrete elements also allows (1) optimization of filter thickness for each direction, (2) use of a weighting scheme to optimize the total S/N, and (3) operation at high total count rates, while retaining the advantages of pulse counting electronics. The relative merits...

Birefringent optical filters in single-mode fiber.

Abstract: In-line fiber-optic spectral-bandpass filters with one, two, three, and four elements are designed in analogy to the Solc filters of bulk optics by bending the fiber into the form of small coils, which are rotated to suitable angles and arranged between polarizers. One four-element filter has a bandwidth of 3.5% at a center wavelength of 704 nm and a free spectral range of 17%.

Optical multi/demultiplexers for single-mode fiber transmission

Abstract: This paper describes two types of optical multi/demultiplexers using a single-mode fiber for a two-way transmission system. One type, the filter type, consists of four bandpass filters and a short wavelength pass filter or a long wavelength pass filter. The other, the filter-grating type, consists of two bandpass filters and a grating. The present multi/demultiplexers have four channels with 1.05, 1.15, 1.3, and 1.5 μm wavelengths. Total insertion losses are less than 2.3 and 3.2 dB for the filter type and the filter-grating type, respectively. Cross-talk between channels is less than -40 dB.

Coatings with induced transmission

Abstract: A brief review is given of how fundamental concepts of thin film optics (potential transmittance, the two-effective-interfaces theorem, the principle of equivalent layers, matching conditions and absentee layers) are used to design optical coatings with controlled absorptance. The general principles are illustrated by a discussion of interference filters containing both dielectric and metallic layers, including the design and preparation of induced transmission filters. Reference is also made to coatings for optimizing the photon efficiencies of photodetectors. Further insight into how coatings with absorbing layers function is provided by consideration of the electric field distribution of radiation within the coatings.

A Liquid Crystal Tunable Spectral Filter: Visible And Infrared Operation

Abstract: The large optical anisotropy of liquid crystal molecules is employed to realize an efficient, voltage tunable Fabry-Perot filter. Tuning has been demonstrated in both the visible and middle infrared. The small voltages required to tune over one free spectral range (FSR) result in a device having greater potential for designing filters having a larger range of FSRs, and therefore bandpass widths, than is possible for the solid electro-optic Fabry-Perot described in previous work.1 We show that for many commercially available liquid crystal materials, infrared operation is possible over wide regions where molecular absorptions do not occur.

Polarization independent optical filter using interwaveguide TE↔TM conversion

Abstract: We report the first demonstration of a polarization‐independent, integrated‐optic wavelength filter. Polarization‐independent filtering is achieved via wavelength selective TE↔TM conversion between a pair of mismatched Ti‐diffused lithium niobate waveguides. A peak coupling efficiency of ∼75% and 5‐A filter bandwidth have been achieved.

Iso-index birefringent filters

Abstract: Disclosed is an optical filter for selectively transmitting light in a passband at the wavelength λ, including an initial polarizer with a polarization direction perpendicular to a beam path and a final polarizer spaced from the initial polarizer along the path and having the same polarization direction. A birefringent element is positioned between the polarizers with an optic axis perpendicular to the path and rotated with respect to the polarization direction, the element having a birefringence which is zero at the wavelength λ. Lyot-Ohman and Solc embodiments of the filter are also described.

Optical analyzing instrument with equal wavelength increment indexing

Abstract: In an instrument adapted particularly for analyzing agricultural products, such as grain, interference filters are rotated successively through an infrared wide wavelength band beam of light, which irradiates a sample of the product. Each of the interference filters operates to transmit a narrow wavelength band of light, the center frequency of which is scanned through a range of values as the angle of incidence of the beam of light to the interference filter varies as the filter rotates through the beam of light. An optical track is provided which rotates with the assembly of interference filters to generate pulses from index markings in the optical track. The markings in the optical track are spaced so that one pulse is generated for each angstrom of variation of the center frequency transmitted through an interference filter. The pulses are counted in the counter and the counts in the counter are used to control the selection of intensities reflected from the sample to be used in the analysis of the sample.

Narrow-band optical filter through phase conjugation by nondegenerate four-wave mixing in sodium vapor

Abstract: An ultrahigh-Q tunable optical filter with a FWHM bandwidth of 41 MHz is demonstrated. The filtering is produced by nondegenerate phase conjugation through four-wave mixing in atomic-sodium vapor. The filter is observed to have a maximum quantum efficiency of 4 x 10^-3. However, degenerate phase-conjugation experiments in sodium suggest that a quantum efficiency of greater than unity can be attained on a cw basis.

Apparatus for the determination of the position of a surface

Abstract: Apparatus is disclosed for determining the position of a surface in which radiation from an optical radiant source is applied to the surface and, by means of a lens system, an image of the radiation is produced on a photoelectric receiver. A laser serves as the radiant source, and is aimed at an angle of inclination relative to an optical axis of the lens system at a point of a surface which, by virtue of its temperature, emits visible radiation in the same wavelength range as the Laser. The surface extends approximately perpendicularly of the optical axis and is subject to positional variations along the said optical axis. The beam is directed from the irradiated point to the photoelectric receiver through a narrow-band optical filter of which the pass band includes the laser wavelength.

Temperature pattern measuring method and a device therefor

Abstract: A temperature pattern distribution measuring method and apparatus by which portions of light from parts of an area of an object whose temperature distribution pattern is to be measured, and whose parts are in a predetermined pattern, are passed through first and second optical filters which respectively pass different wavelengths of light. The level of engery passed by the respective filters for the respective portions of light are determined by scanning the light from the filters with a pickup device or devices and, by using the determined energy levels, an arithmetic unit carries out a two-color temperature determining operation for the respective parts of the area for determining the temperature on each part of the area of the object. The temperature pattern of the area of the object can thereby be determined from the temperatures of the parts of the area.

Electro-Optically Tuned Spectral Filters: A Review

Abstract: Electro-optically tunable spectral filters have been developed over the years and now include a rather diverse collection of devices. These devices, which are of increased importance for remote sensing applications, employ linear electro-optic (Pockets) materials such that tuning is accomplished via externally controlled voltages. A brief review of the properties of linear electro-optic materials is presented followed by descriptions of tunable birefringence interference filters, Fabry-Perot devices, and other novel filter structures. Recent developments in electro-optic tunable filters are included. Issues relating to the further development of infrared tunable spectral filters are discussed.

New type of rapid scanning circular dichroism spectropolarimeter using an acoustic optical filter

Abstract: A new circular dichroism (CD) and magnetic circular dichroism (MCD) system with narrow bandwidth and high scanning rate has been developed. The versatility of the system for the measurements of transient changes in CD and MCD has been also described. This new CD and MCD system is composed of an acoustic optical (AO) filter of TeO2 as a monochromator, a stress modulator, and a photomultiplier together with their operating devices and a computer system. The linearly polarized light from the AO filter is modulated to left‐ and right‐circularly polarized light by a stress modulator operated at 50 kHz. The absorbance difference of the left‐ and right‐circularly polarized light is detected by a photomultiplier, after passing through the sample. The whole optical system and detector system are matched in time by the same computer system. A rapid scanning was performed successfully at the rate of 50 nm range/10 ms, with better spectral resolution and higher signal‐to‐noise ratio than other commercially available ...

Calibration and testing device for optical, single particle, size spectrometers

Abstract: A device comprising a set of fine, uniform, translucent fibers mounted on a suitable holder. When used in conjunction with appropriate neutral density optical filters, if necessary, on suitable particle sizing instruments, the device can easily and quickly be used to perform three important functions--namely, to accurately check the instrument calibration or response to particle size, to locate the limits of the optical depth of field in the particle illuminating beam, and to test the ability of the instrument to detect and register all validly sampled, single particle events.

Passive CCD resonator filters

Abstract: Novel passive recursive CCD bandpass filters have been realized using standard two-level-polysilicon gate NMOS technology. A Chebyshev bandpass (w/SUB rel,/ /SUB 3/ /SUB dB/=3.1 percent) and a fully integrated CCD signal filter with an extremely narrow 3 dB bandwidth of 97 Hz (Q=1350) at 131.85 kHz center frequency were implemented by means of cascaded CCD resonators. The latter chip contains the necessary clock generation and biasing circuitry realized with dynamic circuit techniques to achieve low power consumption (40 mW per filter). Performing all filtering operations exclusively in the charge domain ensures filter passivity. An extremely stable center frequency and a bandwidth independently controlled by a capacitance ratio are the special advantages of such filters.

Narrow-band tunable optical filter made of a CdGa2S4 single crystal

Abstract: An optical polarization filter was constructed from a CdGa2S4 single crystal. This filter was temperature-tunable in the range 487–580 nm. Its pass band was 2 nm and the transmission at the maximum of the spectral characteristic was 48%. The filter was also capable of withstanding high-power laser radiation (damage threshold 32 MW/cm2).

Mechanical Excitation of a Membrane by an Optical Beam.

Abstract: Mechanical or electromechanical resonators, such as metallic bars or piezoelectric plates, play a major role in telecommunication and instrumentation, particularly in filtering devices. Their success arises from the fact that they are easi ly excited with an electrical signal (directly or with a transducer). Will their role remain essential with the advent of optical communication techniques ? It seems to us that the answer to this question depends partly on the optical methods to be used in exciting these resonators. One solution could be the photoacoustic effect. We have carried out p reliminary experiments with membranes excited by a modulated optical beam. Silicon membranes of thickness about 10 urn, of diameter a few millimeters, were excited by an acoustooptically modulated laser or a directly intensity modulated diode. Their impulse or continuous responses (f 10 kHz) were detected by the deviation of a narrow light beam reflected by the vibrating membrane.