Abstract: The principles of operation and current status of single-mode optical directional coupler switches, modulators, and filters using \Delta \beta reversal techniques are reviewed.

Abstract: A multireflection multi/demultiplexer using interference filters is proposed. Light waves of different wavelengths are combined or separated while they propagate between two filter arrays. The insertion loss of the 6-channel demultiplexer was around 1dB.

Abstract: The construction of optical filters, which are required to have optical properties well defined over wide spectral regions, demands the use of multilayer designs in which there are no simple relationships between the thicknesses of the layers. There are considerable difficulties in the manufacture of such multilayers. First, we must be able to reproduce, sufficiently accurately, the indices of refraction that have been used in the theoretical design. Then we must be able to control the optical thicknesses of each layer, which necessitates measurement of the optical properties of the multilayer during deposition. The apparatus described consists of a minicomputer coupled to a rapid-scanning spectrometer that continuously measures the spectral profile during deposition of each layer. The precise measurement of the evolution of the optical properties during actual construction of a filter allows us to control layer thickness with very good accuracy. The technique is demonstrated in the monitoring of a beam splitter made of a few layers.

Abstract: A new resonance principle in optical filters has been utilized to simultaneously permit realization of wide field‐of‐view (∼2π sr) and very narrow acceptance bandwidths, approaching 0.01 A. A light signal is transmitted through an outer bandpass filter into a resonantly absorbing atomic vapor, resulting in a fluorescence signal at a different wavelength which is transmitted through an inner bandpass filter. The outer and inner bandpass filters have no common transmission band, resulting in complete blockage of all optical signals (background noise) that are not resonantly shifted in wavelength by the intervening atomic vapor. This ’’resonance filter’’ principle is experimentally verified, and system parameters are discussed for filters utilizing potassium, rubidium, or cesium vapor at nine wavelengths between 420 and 532 nm.

Abstract: The invention relates to an optical measuring device for measuring physical magnitudes such as position, speed, acceleration, force, pressure, elongation, temperature, etc., comprising at least one optical fiber for conducting light between an electronic unit and a transducer forming an optical modulator which is directly or indirectly influenced by the quantity being measured and, in dependence thereon, modulates the light emitted to the transducer. The transducer contains at least one optical filter having spectrally varying absorbing and/or transmitting and/or reflecting characteristics within the spectra of the emitted light. The light filter generates one or more stabilizing signals for the fiber optic and optoelectronics, and possibly one or more measurement signals within one or more wavelength ranges.

Abstract: Many spectral filtering problems require assemblies of layers having thicknesses that bear no obvious relationship to one another. After a brief review of the optical methods used to monitor deposition of multilayers containing nonintegral thicknesses, we show that the performance of monitoring systems can be improved further by including the real-time calculation of any necessary layer thickness changes that may be required to compensate any errors that might still occur. The apparatus described consists of a minicomputer coupled to a rapid-scanning spectrometer. Such a procedure working in real time avoids the cumulative effects of successive errors. The technique is demonstrated in the production of a beam splitter.

Abstract: This letter describes a tunable optical filter that couples light energy between ordinary and extraordinary polarizations in a birefringent electro‐optic crystal at the phase‐matched wavelength by means of a spatially periodic dc electric field. The specific embodiment described here is a LiTaO3 platelet operating with transverse electric field and located between cross polarizers. Analogies to both the Solc birefringent filter and the Harris acousto‐optic filter are cited. The electro‐optic filter is tuned by varying the spatial period of the electric field via an array of separately addressable finger electrodes. We have demonstrated tunability from 4700 A to 4.5 μm. Experimental results of transmittance versus applied voltage and of bandwidth versus pass wavelength agree well with theory. The flexibility of this type of electronic filter in allowing synthesis of arbitrary transfer functions through nonperiodic voltage distributions is emphasized.

Abstract: Pattern-recognition systems, techniques, and applications using coherent optical systems are reviewed. Many optical pattern-recognition system architectures exist that include time-domain optical correlators and the optical joint transform correlators and refinements in the original optical matched spatial filter synthesis processor. Advanced optical pattern-recognition systems are also described such as hybrid optical/digital processors and diffraction-pattern sampling systems using specially shaped Fourier plane detector arrays. The optical space-variant pattern-recognition systems described are examples of the growing repertoire of operations now achievable in optical computers.

Abstract: Quantitative data are presented on the effectiveness of interference filters for reduction or elimination of stray light effects in optical spectrometers employed for trace atomic emission analyses Specific attention is focused on those analyte species that contribute significant stray light at wavelengths far removed from the offending radiation For simultaneous multielement determinations with a polychromator, band reflection filters are shown to provide an attractive means of eliminating stray light effects arising from the very intense Ca lines emitted in an inductively coupled plasma For the spectrometers used in the present study, a major fraction of the background shifts caused by changing concentrations of Mg arose from real background contributions rather than from stray light

Abstract: Demonstration of real-time coherent optical correlation for both vehicle tracking and identification has been demonstrated. A reference filter has been constructed that can recognize a vehicle from all orientations. A design of a coherent optical processor is presented using laser diode light sources and having a package size of 50 cm3.

Abstract: A tunable, narrow-band thin-film filter consisting of two uniform grating filter sections separated by a phase-shift section is proposed, and the theoretically predicted performance of these new components is verified experimentally. A straightforward method of calculating the reflection spectrum of these structures is also presented; the technique is particularly well suited to accounting for the effects of parasitics in practical structures. Finally, a qualitative model useful for intuitive analysis of these filters and their spectra is described.

Abstract: Results are presented for a number of window materials, color filter glasses, birefringent crystals, and optical fibers. The transmission loss caused by exposure to Co(60) gamma or 10-MeV electron radiation is tabulated over the 400-900-nm wavelength region. The transmission loss is greatest at the shorter wavelengths, and its rate is maximum for most materials at dosages greater than 10(5) rad (Si).

Abstract: A new optical filter, first demonstrated more than a decade ago and recently extended to other frequencies and materials, is based on the accidental isotropy of refractive indexes that occurs in certain uniaxial semiconductors near the band edge. This paper shows how coupling of light energy can take place between ordinary and extraordinary polarizations at the isotropic point by application of a dc electric field. When placed between crossed polarizers, these materials can thus act as narrow-band filters. The field-of-view characteristics have been analyzed; and it is concluded that this type of filter can, in principle, accommodate a 2π field with less than 20 percent increase in passband over that of the narrow-field condition. It is noted, in particular, that AgGaS 2 exhibits the required change of sign of its birefringence at a wavelength of 4970 A (blue-green), with a rate of change that could provide a passband of only 0.2 A in a 1 cm sample.

Abstract: The heating of a tunable-acoustic optical filter (TAOF) results in a drift in the calibration of the TAOF as the acoustic-optical medium temperature varies. In practicing the invention, the TAOF is periodically locked to a reference wavenumber and a calibration correction is then derived and employed to keep the TAOF consistently accurate.

Abstract: The design and performance of some signal processing devices using fiber and integrated optics are discussed. Analog-todigital (A/D) conversion, logic, and computation are among the signal processing functions which can be performed using integrated optical devices. Optical fibers can be used for signal delay and storage and for implementing transversal filters and delay-matched filters. Some other interesting possibilities make use of both fiber delay line and integrated optical elements. These include variable-length delay lines and programmable transversal filters.

Abstract: Disclosed is an optical filter for transmitting light in a narrow bandwidth centered about the wavelength λ, including a birefringent half-wave crystal defining an optical path through the crystal and normal to the optical axis of the crystal, the thickness of the crystal effecting a 180° phase change between the fast and slow components of light of wavelength λ along the optical path; a first polarizer preceding the crystal in the optical path and having a first polarizing plane rotated 45° about the optical path from the optic axis of the crystal; a first reflective surface preceding the first polarizer in the optical path and normal to the optical path; a second polarizer following the crystal in the optical path and having a second polarizing plane rotated 90° about the optical path from the first polarizing plane; and a second reflective surface following the second polarizer in the optical path and normal to the optical path. The crystal may further be an electro-optic birefringent crystal, the filter then additionally including first and second electrodes affixed to the crystal and adapted to apply an electric potential across the crystal in the direction of the optical path, the transmission wavelength λ thereby being tunable by adjusting the electric potential applied to the crystal.

Abstract: Theoretical and experimental studies of optical filtering which utilize anisotropic and noncollinear acoustooptic interaction in a Y -cut LiNbO 3 waveguide are reported. A guided-light beam from either an He-Ne laser at 6328 A or an argon laser at around 5000 A, propagating at an angle centering around 70° from the Z(c) axis of the LiNbO 3 crystal, was Bragg diffracted by the surface acoustic wave with 500 MHz center frequency and propagating at 16° from the x axis of the crystal. High optical resolving power, large optical angular aperture, and good spatial separation between the filtered light and the unfiltered light have been simultaneously achieved. An optical passband of 16 A and an angular aperture of 9° have been measured for the case in which the undiffracted and diffracted light propagate in TE 0 mode and TM 0 mode, respectively. Furthermore, by varying the acoustic frequency from 350 to 670 MHz, the filtered optical wavelength may be tuned from 8300 to 5000 A.

Abstract: PURPOSE:To eliminate the need for separately connecting the elements having the function of optical filters and optical fibers by packing photosensitive material in the contact portions of the optical fibers and forming a grating directly in the layer by making use of its photosensitive characteristics. CONSTITUTION:At least two optical fibers 8, 9 which are cut and ground of clad parts 6 by a suitable length to exposre core parts 7 are coupled at a coupling length L. A layer 10 formed with optical grating is interposed in the contact portion of the optical fibers 8, 9. In forming the grating in the layer 10, the laser beams 11, 12 which are sensitive to photosensitive material are entered to the layer 10 at 2theta0 in the angle assumed by both beams to sensitize the layer 10. At this time, the bright and dark interference fringe is produced along the lengtwise direction of the optical fibers 8, 9, as a result of which only the bright fringe portions are sensitized and the optical grating is thus made. In this way, the need for separate connection of the elements having the function of optical filters and optical fibers may be eliminated.

Abstract: A study of second- and higher-order waveguide grating filters is considerably complicated by the fact that the coupling between the guided waves and the radiated waves has to be taken into account. In this paper, we review the theoretical calculations of the spectral response of these grating filters that have been reported by several authors and present a new approach based on the use of the Green’s functions of the waveguide structure. Excellent agreement is found between the results of our method of calculation and the results of other, more rigorous but much more complicated, methods. The Green’s function method is thus a reasonably simple but fairly accurate method for calculating the spectral response of grating filters.

Abstract: A modified optical design of the 1:1 Perkin–Elmer printer was evaluated at 3100 A and 4000 A for fine‐line photolithography. Special optical coatings were applied to the reflecting surfaces to optimize overall transmission at a 3100 A exposure wavelength while allowing selection of the exposing wavelength by optical filters. A test mask was designed for this evaluation which consists of an array of meander patterns for imaging onto metallized silicon wafers which can be electrically probed for integrity after etching. The array of 300 sites contains meander patterns with widths and spaces varying from 0.5 μm in 0.25 μm steps to 2.5 μm. A plot of the electrical probe yield of the meander patterns with respect to feature dimension indicates performance of the lithography.

Abstract: The effect of a mode filter using fibre bend has been clearly shown experimentally. The mode filter effectively removes the LP11-mode, and has a negligibly small effect on the attenuation of the LP01-mode. The single-mode propagation was attained at the V-value of 2.8 by using the filter.

Abstract: —A series of transmission curves of liquid and solid sheet filter materials in the 280–400 nm range is presented. These filters may be useful as cut-off filters for the near UV.

Abstract: Single or linearly superimposed square‐wave surface‐relief patterns in a transparent plate yield optical transmission characteristics similar to those of interference filters. Reactive sputter etching of fused quartz in CHF3 using Shipley 1350 H photoresist as an etch mask offers a well‐controlled method to produce these complex structures. Gratings with periodicities of 1–2 μm and depths of up to 3 μm are fabricated with dimensional tolerances of ±0.02 μm using laser interferometric techniques. Superposition is obtained by successive masking and etching operations. The optical transmission characteristics of these diffractive filters are analyzed and compared with rigorous diffraction theory.

Abstract: An ultra-high Q isotropically sensitive optical filter or optical detector employing atomic resonance transitions. More specifically, atomic resonance transitions utilized in conjunction with two optical bandpass filters provide an optical detector having a wide field of view (˜2π steradians) and very narrow acceptance bandwidth approaching 0.01 A. A light signal to be detected is transmitted through an outer bandpass filter into a resonantly absorbing atomic vapor, the excited atomic vapor then providing a fluorescence signal at a different wavelength which is transmitted through an inner bandpass filter. The outer and inner bandpass filters have no common transmission band, thereby resulting in complete blockage of all optical signals that are not resonantly shifted in wavelength by the intervening atomic vapor. Two embodiments are disclosed, one in which the light signal raises atoms contained in the atomic vapor from the ground state to an excited state from which fluorescence occurs, and the other in which a pump laser is used to raise the atoms in the ground state to a first excited state from which the light signal then is resonantly absorbed, thereby raising the atoms to a second excited state from which fluorescence occurs. A specific application is described in which an optical detector according to the present invention can be used as an underwater detector for light from an optical transmitter which could be located in an orbiting satellite.

Abstract: By applying the concept of analogue matched filtering to spatially correlated background scenes and making the assumption that they are characterized by a first order Markov process, a simple but powerful digital filter is derived. Direct inspection of this filter results in some useful insights into the process of spatial filtering. The usefulness of this filter is further demonstrated by showing its clutter reduction capability on a set of five measured infrared scenes representing a wide variety of terrain and weather conditions. Also, matched digital filters are obtained directly for each of the five measured scenes making no assumption about the spectral content of the backgrounds. Although the resulting filters sometimes differ in form from those obtained using the first order Markov process assumption, their performance is shown to be nearly identical, proving that this assumption provides a useful model for IR backgrounds. Finally, a technique is developed to construct matched filters to detect resolved targets whose size and intensity distributions are known only statistically. Examples of such targets are constructed and the clutter reduction properties of these filters are quantitatively evaluated.

Abstract: A narrow-band reflection (stop-band) optical filter has been constructed in a planar optical waveguide made by ion exchange of silver in soda-lime glass. A comparison of the measured and computed performance of this optical filter is given. The filter has a bandwidth of 0.35 nm at a centre wavelength of 611 nm.

Abstract: An incoherent optical method for spatial frequency filtering is considered, based on the principle of diffraction in spatial incoherent monochromatic light. Such a method is shown to be possible in an incoherent diffraction correlator with a holographic filter. This permits substantially lower requirements for the adjustment accuracy of the system, significantly decreased required dynamic range of the holographic filter, and the phase distortion influence on the form of an output correlation function is canceled. It is shown that, for completely incoherent processing, the filtering process is invariant to longitudinal shift of the holographic filter. The influence of incomplete phase modulation on the form of output correlation function is discussed as it is used to distort spatial coherence. This case is shown to be analogous to the processing in partially coherent light. Dependence of SNR on the depth of phase modulation is obtained.