bluuebunny/crossref_metadata_2025 huggingface dataset:
Fourier-transform spectroscopy of atmospheric species
Authors: Burkholder James B. , Howard Carleton J.
Published: February 2023

The application of high-resolution Fourier-transform spectroscopy (FTS) to the measurement of both absorption and emission spectra of radicals has grown greatly over the past 10, years with emphasis on the recording of line positions and the determination molecular parameters. Our primary motivation at the NOAA Aeronomy Laboratory for measuring infrared spectra of radicals by means of Fourier-transform spectroscopy is to obtain information that can be used to monitor these species, either in other laboratory experiments or in the atmosphere. This requires accurate determinations of both line positions and line intensities. Data on absolute line intensities of radicals, however, are limited. This is primarily a result of experimental limitations on our ability to produce radicals with a known concentration over a known path length. Recently developed, infrared spectral analysis methods eliminate the need for quantitative concentration measurements in determining line intensities provided that accurate relative line intensities and the dipole moment as a function of v are known. Fourier-transform spectroscopy is well suited to relative line-intensity measurements because the entire spectrum is recorded simultaneously, therefore minimizing possible systematic errors introduced by measuring a spectrum one line at a time. This talk will discuss the experimental techniques used to record spectra of radicals and will focus on experiments designed to obtain line intensities for radicals of atmospheric interest. Examples to be discussed include CIO, BrO, and OH radicals.
Two-dimensional Fourier-transform spectrometer
Authors: Berlinghieri Joel C. , Hilleke Russell O.
Published: February 2023

A Fourier-transform spectrometer has been built by using a common-path ring design for the as interferometer and a two-dimensional charge-coupled device array for the detector. The detector records the Fourier-Fraunhofer hologram that is produced by the sheared images of the source. The advantages of such a device have been published,1 and initial results have been reported.2 Further results of optical spectra measurements, at medium resolution will be shown. The aliasing problem associated with obtaining higher resolution spectra over a broad band has been solved without the need for narrow-band filters or the use of a cross disperser. A slight rotation of the detector array with respect to the fringe direction, along with the use of a two-dimensional transform, sorts the normally overlapping orders formed when the interference pattern is undersampled.
Composite harmonics joint-transform correlator
Authors: Marom Emanuel , Mendlovic David , Deutsch Meir , Konforti Naim
Published: February 2023

In recent years, the use of joint-transform correlators for pattern recognition has become very popular, particularly because of improvements in spatial-light modulator (SLM) devices. These correlators exhibit shift-invariant pattern recognition but have high sensitivity to other parameters (scale, rotation, etc.). Harmonic expansion is one of the most promising wasy to add another invariant parameter to the already-existing shift invariance. For example, rotation invariance can be added by using a single circular harmonic as the reference object. Previously we presented an elegant way of allowing the use of joint-transform correlators for rotation-invariant pattern recognition. There, we used as reference object a single harmonic from the circular-harmonic decomposition, and we showed how recording of phase as well as amplitude information is achieved by encoding them on a grating (by means of Lohmann's phase-detour model). The input object, placed side by side with this reference, has to be multiplied by a grating too, so that the joint-transform correlation distribution can be obtained at the location of the first diffraction order. In this work we suggest a similar way to achieve projection-invariant (tilt invariant) pattern recognition in joint-transform correlators by using a single logarithmic harmonic as the reference image. In addition, based on the composite filter concept, we now present an equivalent approach, called "composite image," for use with project ion-in variant joint-transform correlators, thus extending the selectivity capabilities of this scheme. Some optical experimental results will also be presented.
Implementation and analysis of optical-disk-based joint-transform correlators
Authors: Hsu Fu Kuo , Tam Eddy C. , Lu Taiwei , Yu Francis T. S. , Nishihara Eiichiro , Nishikawa Takashi
Published: February 2023

We have previously proposed a jointtransform correlator incorporating an optical disk as a reference library, for which the reference image is parallelly read out and directly used to obtain joint transform with the real-time input image. The architecture combines the features of the conventional jointtransform correlator and the compact disk optical head. In this paper we shall propose two joint-transform correlator schemes that use optical disks; namely, the equal-image-dimension (EID) and the direct-joint-transform (DJT) schemes. In both schemes a real-time input image is obtained through a video camera and is displayed on an electrically addressable spatial light modulator (SLM). To alleviate the dimensional mismatch of the input images, the reference image is first magnified and then displayed on an SLM by means of the EID scheme. For the DJT scheme, the Fourier transform of the input image is magnified before being combined with the Fourier spectrum of the reference image. Systems analysis and design of both architectures are presented, and experimental demonstrations of these two techniques are also provided.
Comparison of Er- and Er, Pr-doped YLF 2.8-µm lasers
Authors: Knowles D. S. , Cassanho A. , Jenssen H. P.
Published: February 2023

Development of the 3µm laser based on the4I11/2–4I13/2 transition in Er-doped crystals is proceeding slowly because the up-conversion process used to empty the long-lived terminal laser level causes complicated population dynamics that make it difficult to optimize the performance of the laser. We have found that by co-doping these high-concentration Er crystals with small amounts of Pr, the 4I13/2 lifetime can be drastically reduced through energy transfer to the Pr 3F3,4 levels, which allows this transition to be operated as a quasi-four-level laser. The 4I13/3 lifetime in Er:YLF is approximately 14 ms; with the addition of 0.1% Pr, it is reduced to 750 µs with only a slight decrease in the lifetime of the 4I11/2 level. Experiments are now under way to compare the performance of the up-conversion laser with the co-doped laser, and preliminary measurements using an Ar+ laser pump source indicate that both 10% Er: YLF and 20% Er, 0.1% Pr:YLF can be operated cw, with the co-doped sample having the higher threshold. Both lasers should operate most efficiently by directly pumping the Er 4I11/2 level, which will soon be practical with laser diodes operating at 980 nm. We will present results of pumping both the 4I9/2and 4I11/2 levels with a Ti:Al2O3 source using various concentrations of Er and Er, Pr in YLF.
LCTV-based hybrid optical-digital processor for the measurement of sarcomere dynamics in an isolated cardiac heart cell
Authors: Yelamarty Rao V. , Cheung Joseph Y. , Yu Francis T. S.
Published: February 2023

Isolated cardiac muscle cells exhibit phasic contractions when they are electrically stimulated and they maintain their distinct AûI band striation pattern, like a one-dimensional diffraction grating, during the contraction–relaxation cycle. This paper demonstrates the application of an on-line, hybrid digital–optical processor, with liquid crystal television (LCTV) serving as a spatial light modulator (SLM), to monitor the dynamics of contraction in real time. The processor, which is interfaced with a phase-contrast microscope, performs a Fourier transformation of the striated cell image optically and records the Fourier spectra digitally by means of a charge-coupled-device camera. A series of digitized images of the Fourier spectra, at intervals of 16.67 ms (noninterlaced frames), is captured during muscle contraction. The sarcomere length at each time point is calculated from centroidal positions of the firstorder diffraction spots. Experimental results demonstrate that LCTV has improved the contrast of striated cell images by 300%. These results suggest that the hybrid processor has a great potential for biomedical applications. Finally, the results obtained from normal and hypertensive heart cells (both with and without drug effects) will be presented.
How to combat dispersion in fibers
Authors: Lohmann Adolf W.
Published: February 2023

The phase velocity in fibers varies with frequency due to dispersion. The longer the fiber distance, the more severe the degradation of the signal. Hence the permissible frequency bandwidth is inversely proportional to the repeater distance. Bélanger (IEEE Phot. Technol. Lett. 1989) predicted that periodic signals would be self-restored at specific distances. Indebetouw generalized this prediction to a class of quasiperiodic signals. Both predictions were based on a parabolic model of the dispersion. We generalize these predictions for arbitrary dispersions, and we speculate on the usefulness of these predictions, which are based entirely on linear optics.
Cross-phase modulation between the two modes in a dual-mode fiber
Authors: Oh Minsun , Hong B. J. , Yang C. C.
Published: February 2023

The mutual trapping between the two polarization components through cross-phase modulation in a birefringent fiber is a well-known phenomenon. The cross-phase modulation shifts the frequencies of both components and reduces the relative speed between them. When both modes in a dual-mode fiber are excited by a pulsed signal, the effect of cross-phase modulation between the two modes is weak because the relative group velocity between the two modes is large. However, when two pulsed signals of different central frequencies are launched into the same dual-mode fiber, the relative group velocity between the first-order mode of one signal and the second-order mode of the other signal can be small, so that the effect of cross-phase modulation is prominent. This fact provides a chance for studying the dependence of cross-phase modulation on the transverse profiles of the modes. In this research, a set of coupled nonlinear Schrodinger equations is derived for the two modes of two different frequencies in a dual-mode fiber. These equations include overlapping integrals to account for the Kerr effect. The set of equations is solved by means of the beam-propagation method to observe the effects of cross-phase modulation.
Resonant pumping schemes for the Er3+ 3-μm laser
Authors: Stoneman R. C. , Lynn J. G. , Esterowitz L.
Published: February 2023

The effect of excited state absorption on the threshold and slope efficiency of the 3-μm trivalent erbium laser is investigated. The excited state absorption spectrum is measured directly, and the laser results are compared with a model of the resonantly pumped laser.
Diode-pumped injection-seeded, Q-switched Tm:YAG laser
Authors: Kane Thomas , Kubo Tracy S.
Published: February 2023

Eye-safe coherent lasers with pulse energies of a few millijoules may be useful for Doppler anemometry at ranges of a few kilometers. We will describe the performance of an acousto-optically Q-switched Tm:YAG laser pumped by six 1-W laser diodes, and injection seeded with the output of a monolithic diode-pumped single-frequency laser.
Excited-state absorption effects in Tm3+-activated 2-μm laser crystals
Authors: Rosenblatt G. , Quarles G. J. , Marquardt C. L. , Esterowitz L.
Published: February 2023

Blue and UV fluorescence bands have been observed in Cr:Tm garnet laser materials under cw excitation at 632.8 nm. Previous studies have attributed this anti-Stokes fluorescence to upconversion processes involving Cr-Tm energy transfer. These studies have also suggested that this Cr-Tm upconversion substantially limits the efficiency of flashlamp-pumped Cr:Tm-sensitized 2-μm lasers.1 In the present investigation, by using a cw dye laser tuned over the 610-680 nm range, we have measured relative intensities of emission bands and the corresponding excitation spectra in garnets doped with Tm:Cr and with Tm alone. The results clearly demonstrate that the principal source of the blue and UV fluorescence is not upconversion but is excited-state absorption of Tm3+, which takes place in the 3F4 → 1G4 level and the 3H4 → 1D2 levels, respectively. The blue fluorescence, which peaks at approximately 480 nm, arises through emission from the 1G4 level to the 3H6 ground state of Tm3+, and the UV fluorescence, peaked near 360 nm, is due to the 1D2 → 3H6 transition. The results indicate that these processes have negligible effects on the efficiency of Cr:Tm-sensitized 2-μm lasers.
Polymeric reflection interference modulators
Authors: Knoesen Andre , Eldering Charles E. , Kowel Stephen T.
Published: February 2023

Reflection interference modulators consisting of a highly reflective metal mirror, an electro-optic layer, and a partially reflecting, lossy mirror are analyzed. Analysis of the reflection characteristics of the devices as a function of the angle of incidence predicts that reflectance changes from R = 0.8 to R 0.01 can be achieved in less than a 4° angle of incidence interval for both perpendicular and parallel input polarizations. This resonance can be used to implement a reflection-mode electro-optic modulator. The feasibility of such devices is experimentally demonstrated by using a guest-host poled-polymer system consisting of poly(methylmethacrylate) films doped with an azo dye, 4-[N-ethyl-N-(2-hydroxyethyl)]amino-4′-nitroazobenzene. The devices are characterized by measuring the reflectance and the electrically induced change in reflectance as a function of the angle of incidence and input polarization.
Photometric monitoring and control techniques for manufacture of blended optical thin films
Authors: Rahmlow Thomas D. , Lazo-Wasem Jeanne E. , Tirri Bruce A.
Published: February 2023

Optical thin films generated by the co-deposition of two or more materials exhibit a refractive index proportional to the indices of the components in proportion to the mixing ratio. The coevaporation of Ti2O3 and SiO requires strict control of rates and chamber environmental parameters to maintain proper stoichiometry and film performance. Films are oxidized to TiO2 and SiO2 at the substrate. A broad-band photometer monitors film development in the visible region. Photometer scans are acquired by the control computer every 10 seconds. Film absorption, index, and optical thickness are found to be sensitive to rate as well as trace amounts of water vapor. Absorption is due to unconverted SiO, and although the film will convert on chamber venting or a post bake, absorption inhibits reliable interpretation of photometer results. Reliable results are achieved by using a rule-based computer algorithm during source ramp-up and rate stabilization to verify system readiness. Environmental parameters are compared to a data base of previous runs to verify normal status. Photometer scans and scan-to-scan differences are checked for normal behavior. Computer rules are performance goal-oriented, and system status is weighed against the desired film spectral performance.
Impulse response of two-beam coupling amplifiers
Authors: Hermanns Anno , Lininger Diana M. , Benkert Claus , Anderson Dana Z.
Published: February 2023

We derive the impulse-response function of two-beam coupling amplification in the linear regime. Beam loss from absorption and beam fanning are also included. For gains greater than e4, the impulse time response has a peak. The location of the peak in time and its height are functions of the gain, loss, and time constant. Analytic results are obtained for the case of zero-signal beam loss. The case that includes loss from absorption and beam fanning is somewhat more complex. We have made measurements on barium titanate, both in the time domain and in the frequency domain, to verify the theoretical predictions. Whereas measures of the grating time constant are often focused on the material aspects, the impulse time response provides a good and consistent measure of the time constant that is relevant to the optical circuit performance of the two-beam coupling amplifier.
Dynamics of grating formation in photovoltaic media
Authors: Gu Claire , Hong John , Li Hsin-Yu , Psaltis Demetri , Yeh Pochi
Published: February 2023

The dynamic behavior of grating formation in photovoltaic media is different from that in nonphotovoltaic media. For example, grating formation depends on the initial conditions as well as the boundary conditions. This fact causes a problem when we attempt to find an exposure procedure for the recording of multiple holograms. In this paper, we solve the Kukhtarev equations, taking into account various possible boundary conditions that describe the growth of holograms in photovoltaic media. We then provide theoretical plots, using published values of parameters for LiNbO3, that describe the transient behavior of holograms. The experimental results, which show different dynamic behaviors during grating formation for different boundary conditions, are then compared with the theoretical calculations. Both the experimental results and theoretical simulation show the typical behavior of grating formation that does not occur in nonphotovoltaic media, i.e., when the writing starts from an open-circuited crystal without a nonuniform charge distribution, the diffraction efficiency increases to a maximum and then decreases to its steady state. This occurs because the change in the charge distribution owing to the photovoltaic current occurs on a time scale similar to the photorefractive time constant. The results of this paper also suggest that one simple solution to the recording of multiple holograms might be to short circuit the crystal.
Temporal behavior of space-charge fields in volume holographic interconnects
Authors: Baek Woon Sik , Lee Hyuk
Published: February 2023

A general first-order ordinary differential equation that describes the temporal behaviors of all the Fourier components of the space-charge field due to two noncollinear plane light interference patterns is derived from Kukhtarev's nonlinear differential equations. Temporal behaviors of the second- order as well as fundamental components of the space-charge field are analyzed for both stationary and moving light interference patterns. Two special cases are described in detail. The first case is space-charge field generation the application of two noncollinear plane light interference patterns simultaneously. The second case is for sequential recording of two noncollinear gratings in order to investigate the effect of the second light interference pattern on the existing space-charge field grating. Decaying characteristics of the second-order spacecharge field grating are also observed. Numerical simulations for the photorefractive crystal Bi12SiO2 are utilized for the analysis. Implications of the results on volume holographic interconnections are presented.
UV properties of Y2O3 and ZrO2 films produced under various ion-assisted deposition conditions
Authors: Jin Michael S. , Smith Douglas J. , Schmid A. , Papemov Semyon
Published: February 2023

Optical and physical properties of thin films are intimately related to parameters associated with the applied deposition scheme. For ion-assisted deposition (IAD), controllable changes in parameters such as the ion species, energy, flux, deposition rate, substrate temperature, and back-fill gas pressure can influence, among other properties, the resulting values of refractive index, optical transparency, and laser-induced damage threshold. Dependence of these properties on several IAD parameters is examined for applications in the ultraviolet and visible range for Y2O3 and ZrO2 films. In addition, properties of transparent films produced from metallic starting materials by means of oxygen-ion assist are presented. The index dispersion and transparency, evaluated from spectrophoto- metric measurements with the envelope method, are compared as functions of deposition parameters. High-peak-power ultraviolet laser damage thresholds of Y2O3/SiO2 and ZrO2SiO2 multilayers deposited under parameters selected from preliminary optical performances are also presented. Reproducibility of the obtained properties and application possibilities are discussed.
Thermal deflection measurements for the study of loss mechanisms in a film used as waveguide
Authors: Liu X. , Pelletier E.
Published: February 2023

Reduction of losses in thin films is particularly important because losses limit multilayer performances. In theory, losses can be divided into scattering and absorption. In absorption, the energy lost from the primary beam is dissipated and appears as heat. Absorption is a material property, which can be intrinsic or due to impurities. Scattering is usually caused by volume and surface due to defects in the film. Roughnesses of the substrate and interfaces are the sources of surface scattering losses, and volume defects appear as local variations of optical constants and are usually caused by dust particles or pinholes in the film. In order to separate the different classes of losses, we use thermal deflection measurements to track the losses in a thin film used as a waveguide. If the guide supports more than one mode, the losses in each mode can be tracked. The theoretical study shows that the modes respond differently according to the loss mechanism, and this can be used to separate scattering and absorption losses. As an example, the technique is applied to two Ta2O5 films whose extinction coefficient is about 10−5; we study the consequences of layer annealing by measurements performed before and after the thermal process.
Residual scattering in optical coatings
Authors: Amra C. , Albrand G.
Published: February 2023

Investigation of scattering in optical coatings has been considerably extended in the last several years, and numerous factors (e.g., substrate and residual roughness, correlation and cut-off frequency, autocorrelation length and isotropy degree) have been studied in detail. Previous results have shown that residual roughness owing to TiO2/SiO2 and Ta2O5/SiO2 materials produced by ion-assisted deposition and ion plaitng is negligible compared to the roughness produced by a 0.5 nm substrate defect reproduction. In these conditions, measurement of scattering before coating is sufficient to permit an accurate prediction of angular and total scattering. In calculation, interface roughnesses are identical and are perfectly correlated to the substrate surface. We show that prediction of scattering remains valid over a large spectral range, but the deposition conditions of materials must be carefully defined. For example, one can show how the correlation between interfaces is modified by using an oblique incidence deposition. Moreover, by determining the isotropy degree of scattering, we can point out the consequences of local defects in the multilayers, especially for large scattering angles. For substrate roughnesses less than 0.5 nm, structural information on the coatings can be deduced from the residual scattering and is useful for the study of optimal conditions of deposition by such techniques as ion-assisted deposition and ion plating.
Ion-beam polishing of diamond films using a planarizing technique
Authors: Grogan D. F. , Zhao Tianji , Bovard B. C. , Macleod H.A.
Published: February 2023

Diamond films deposited by microwave-assisted chemical-vapor deposition on silicon substrates have been polished by a beam of 500 eV oxygen ions from a 3 cm Kaufman- type ion gun. Before polishing, the films were planarized by the application of a spin-coated overcoat. The film's surface roughness was reduced from over 1 µm rms and 6µm peak-to-valley to 35 nm rms and 217 nm peak-to- valley. The polished films retained their diamond character, and surface contamination was negligible. The films were characterized by stylus and interferometric profilometry, optical microscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy. The polishing process, although still under development, makes optical applications in the near-infrared region realizable for diamond films.
Novel sub-carrier multiplexing for optical multiple access networks with frequencies beyond 10 GHz
Authors: Ih C. S. , Wang X. L. , Tian R. S. , Gu W. Y.
Published: February 2023

The subcarrier multiplexing (SCM) scheme can be effectively used for optical multiple-access network (OMAN) applications. However, if the conventional direct laser modulation is employed, not only are the modulation frequencies limited by laser, but also the induced fiber dispersion and the laser's own distortion can be serious at high frequencies. Therefore, conventional SCM is not suitable for OMAN. We have recently demonstrated a novel double-beam modulation (DBM) method that uses a frequency- locked laser (FLL). The DBM automatically creates a subcarrier upon detection by a photodetector. Information can be readily modulated onto the subcarrier by simply modulating the laser(s) at the baseband. We have demonstrated information transmission on subcarriers from several gigahertz to 15 GHz. Thus, if we use DBM-FLL to implement the SCM, the frequency limitations and distortion problems are minimized or removed. Because subcarriers in tens of gigahertz can be achieved, the information capacity can be quite large. The network is accessed by means of different subcarrier frequencies. Recent advances in laser-diode technologies have made the realization of DBM-FLL feasible. The frequency-shift-keying digital-modulation characteristics of DBM-FLL and various subcarrier frequency generations and detection schemes are described.
Soliton laser: a nonlinear model
Authors: Bélanger P. A.
Published: February 2023

I derive a nonlinear differential equation for the pulse envelope propagating into a soliton laser in which the output coupling and the coupling of the external nonlinear cavity are distributed along the gain medium of the main cavity. For a mismatch phase angle of π/2 between the two cavities, a stable opical soliton is the solution to the differential equation for negative dispersion (soliton into the fiber), as well as for positive dispersion, of the nonlinear external medium. The predicted width of the soliton pulse is a function of the coupling factor and of the intensity into the optical fiber. I also show that the operation of the soliton laser for this stable regime is similar to passive mode locking by a fast saturable absorber. Dark soliton is another possible regime. However, the gain required io sustain it is always higher than that required for the bright-soliton regime. For a critical value of the gain relative to the dispersion, another short-pulse regime is predicted that is in competition with the soliton regime. Bistable operation of the soliton laser is, therefore, possible at this point.
Serial-to-parallel converter for high-data-rate communication
Authors: Verber Carl M. , Tan Ronson K.
Published: February 2023

It has been shown that counterpropagating guided waves in a planar, nonlinear waveguide will generate second-harmonic light in a direction normal to the waveguide surface. We extend this idea by using it in a channel-waveguide configuration, where one end of the channel is polished and metallized to form a mirror. Based on this, we propose a high-data-rate serial-to-parallel converter whose input is a set of data pulses preceded by a timing pulse. Second-harmonic generation occurs only where two pulses overlap. We can therefore determine the proper detector positions from the data rate and the spacing between the timing pulse and the data pulses. Calculations for the second-harmonic generation power for several material systems will be presented, and applications for the device will be discussed.
Thermal-mechanical stability of ZrO2 thin films
Authors: Mao Yalan , Bovard B. G. , Macleod H. Angus
Published: February 2023

In the research on the thermomechanical stability of ZrO2 evaporated films with and without ion-assisted deposition (IAD), we performed interferometry in a vacuum oven to study the stress in the films as a function of temperature. In thermal cycling, all the plots of stress versus temperature for IAD and non-IAD films exhibit hysteresis. To understand the hysteresis, we studied micro-structure and water effects. The results show that the likely mechanisms are water desorption, recrystallization, and phase transformation, and we believe that a combination of all three occurred. In our presentation, we will emphasize the effect of water adsorption and desorption. In the research, we defined thermomechanical instability as the width of the hysteresis and environmental mechanical instability as the stress change from vacuum to air. These parameters have proven to be good at describing thermomechanical and environmental mechanical stability, respectively. Our results also show that high bombardment (increasing oxygen ion bombardment tends to give more tensile stress) and high deposition temperature (increasing deposition temperature tends to give less tensile stress) result in more stable films, both thermomechanically and optically. It is well known that thermal stress is due to a thermal expansion coefficient mismatch between substrate and film. However, if thermal-expansion coefficients are to be derived from thermal stress, then great care must be taken to eliminate the water effect; otherwise, the results will be totally wrong. Furthermore, it is almost impossible to obtain a correct thermal-expansion coefficient from postdeposition thermal stress measurements because at the temperature and after the time required to eliminate the water, the film under measurement will already have experienced a crystal structure transition. Therefore, in situ thermal stress studies are needed.
Thermal stress measurements in aluminum films by interferometry
Authors: de Lega Xavier Colonna , Bovard Bertrand G. , Macleod H. Angus
Published: February 2023

The interferometer used in this in situ stress-measurement study was built by Optical Coating Laboratory and is based on a cat's-eye lens.1 The film stress is derived from the measurement of the evolution of a circular fringe pattern that is produced between the surface of the lens and the back surface of the reflecting substrate. A study of the stress–strain relationship is presented in the case of thin films of aluminum (0.1μm) grown on a thin glass substrate (250μm). The interferometer is positioned inside a low-pressure oven (1 mbar) in order to minimize the combined effects of water desorption and oxidation during heating. The samples are subjected to heat cycles between 20°C and 270°C. Because the thermal coefficient of expansion of glass is smaller than that of aluminum, the film is under compressive stress as the temperature is increased. Experimental results are presented that show that the sample undergoes both a reversible thermal stress and a plastic yield during each temperature cycle.
Integrated optics for signal processing in optical recording heads
Authors: Brazas John C.
Published: February 2023

One avenue for reducing the mass and volume of optical recording heads is the use of integrated optical systems, completely integrated or hybrid with bulk optical components. The principles of design and the difficulties of implementing optical signal processing schemes in waveguides will be discussed with specific examples of grating and mode-index lens use.
Optically induced variability of strain-induced electric fields and band structure in (111) GaSb/AISb quantum wells
Authors: Shanabrook Benjamin V. , Wang Wen I.
Published: February 2023

As a consequence of the piezoelectric effect and the strain induced from pseudomorphic growth, quantum wells grown in the (111) direction from III-V materials are expected to exhibit large built-in electric fields. We show that these built-in fields can be reduced or screened by the optical generation of electon-hole pairs.
Fabrication of quantum-wire arrays on patterned substrate
Authors: Yang S. L. , Liu P. L. , Chen J. C.
Published: February 2023

Progress ip epitaxial growth techniques has enabled us to explore low-dimensional quantum-confined structures. Because of the nature of epitaxy, such growth techniques can directly produce only quantum-well structures on flat surfaces. Other techniques are used to define confinement structures normal to the growth direction, which leads to quantum wires and dots. A high-quality interface is crucial to the realization of such low-dimensional quantum-confined structures. In this paper we present an in situ thermal-etch and regrowth process that is used to fabricate quantum wire arrays. Forty periods of 60 nm AlAs and 30 nm GaAs layers were grown on 100 GaAs. Stripes 10 μm and parallel to [011] were defined by photolithography. V-grooves were formed by a facet-exposing wet etching process. Selective thermal etching was then performed in the growth chamber. After thermal etching, 20 nm AlAs, 20 nm GaAs, 200 nm AlAs, and 100 nm GaAs layers were grown. Quantum wire arrays were formed in the regrown 20 nm GaAs. The quantum wire is triangular because of orientational preferential growth. In this process, all dimensions are determined solely by the thickness of the epitaxial layers. Details of the optical properties of the quantum wire array will be reported.
Near-field diffraction of Gaussian beams by rectangular apertures
Authors: Farrukh Usamah O.
Published: February 2023

Gaussian beam propagation will show axial oscillations if the Gaussian beamwidth is comparable to the dimensions of the aperture. This effect is present whenever an optical element has a rectangular boundary, such as an aperture in a screen, a lens element, or a surface of a laser crystal. These oscillations are similar, but are not identical, to diffractions by circular apertures. Rectangular apertures could be characterized by an equivalent radius and an aspect ratio. Diffraction calculations on the severity of the axial oscillations will be presented. These axial oscillations are present over a specific range of the ratio of the Gaussian width to the equivalent radius of the aperture.
Geometrical and physical modeling and design of the extended cavity optical head
Authors: Lawrence George , Partow Tony
Published: February 2023

The "Extended Cavity Integrated Optical Head" uses a semiconductor amplifier and lases off the optical data storage surface. The device takes advantage of the high dispersion associated with Holographic Optical Elements (HOE's) to self-focus on the moving optical data storage surface, eliminating the need for mechanical focussing schemes. Passive operation of the device was studied through geometrical modeling using a geometrical ray tracing code (CODEV). The results were then verified by setting up a "Passive Cavity Experiment" which demonstrated the self-focussing effect of the device in close agreement with the geometrical model. Active operation of the device was studied by coding a numerical model based on the rate-equation approximation of the semiconductor gain medium to simulate transient laser response to a moving reflecting surface. The results of the model and simulations were then integrated in an attempt to determine suitable design parameters for the device.
Status and prospects of optical data storage
Authors: Bell Alan
Published: February 2023

After more than a decade of intensive research and development, optical data storage products are now becoming available. This talk will review some of the key aspects of current drive media technology and will also examine the research directions that promise enhanced performance for these devices in the future.
Rotationally invariant Fresnel lens-encoded circular-harmonic binary phase-only filters
Authors: Davis Jeffrey A. , Cottrell Don M. , York Linnea R.
Published: February 2023

Rotation-invariant pattern recognition can be performed by encoding the Fourier transform of a circular-harmonic (CH) component of the reference pattern. This technique has recently been applied to a binary phase-only version of the filter (BPOF). However, the recording medium is not capable of recording the complex Fourier transform. A cosine CH BPOF is obtained by encoding binary versions of the real part of the CH filter and a sine CH BPOF is obtained by encoding binary versions of the imaginary part. Rotation invariance is lost when either of these filters is used alone. However, by successively applying the filters and summing the successive output intensities, full rotational invariance can be recovered. The disadvantage of this method is that two separate filters are required. Full rotational invariance can be obtained in a single filter by multiplying the complex Fourier transform by a Fresnel lens. In the binarization process, the desired CH filter is encoded onto a converging lens, and the undesired complex conjugate of the CH filter is encoded onto a diverging lens. This process can be successfully integrated into the short version of the correlator. Computer simulations and experimental results using the MOSLM show that this single filter has full rotational invariance.
Closed orbits and spectral oscillations
Authors: Delos J. B.
Published: February 2023

Closed orbits lead to oscillations in the average absorption rate as a function of energy. Theory nd experiment will be compared.
Optical microcavity experiments using high dielectric contrast mirrors
Authors: Ho S. T. , McCall S. L. , Slusher R. E.
Published: February 2023

An ideal laser has near-zero threshold, unity quantum efficiency, narrow spectral linewidth, high modulation rate, and controllable photon statistics. It can be realized with use of microresonators whose optical cavity lengths are on the order of a wavelength. Laser optical microresonators are now made with more than 10 alternating layers of two materials, which have an optical reflective index ratio of 3.5/3.0. Because of the many layers required, these resonators have long effective cavity lengths. To obtain shorter cavity lengths, high index contrast materials must be used. This is currently achieved by deposition of nonepitaxial layered materials (e.g., ZnS and SiO2). Such techniques can be used for the top mirror of an optical cavity enclosing an active layer grown by molecular beam epitaxy (MBE) but not for the bottom mirror. Here, we report new fabrication techniques that are compatible with the MBE method. The techniques involve selectively etching layered AlxGa1−xAs materials grown by MBE and then replacing the etched regions with acrylic polymers or air. The replacement techniques involve the use of a low-viscosity acrylic and carbon-dioxide critical-point drying apparatus that is commonly used in histological studies. The resulting mirror structures have index contrast ratios of 3.5/1.5 and 3.5/1.0, respectively. Related experiments on controlled spontaneous emission and low laser thresholds will also be reported.
Integrated optical receivers using MSM detectors
Authors: Rogers D. L.
Published: February 2023

The MSM detector's high speed, low capacitance, and FET compatability have resulted in many recent OEIC demonstrations. Some recent results along with tradeoffs in low noise preamplifier design will be discussed indicating that high speed, high sensitivity integrated receivers are possible with high wafer yield and low cost packaging potential.
Design and performance of InGaAs metal-semiconductor-metal photodetectors
Authors: Soole J. B. D.
Published: February 2023

Metal-semiconductor-metal (MSM) photodetectors based on the InGaAs/InP material system are an emerging technology for use in the long wavelength 1.3 µm and 1.55 µm fiber bands. In this talk I give results for InGaAs MSM detectors recently fabricated at Bellcore and discuss the performance characteristics and issues for this type of photodetector.
Data-association multiple-target tracking using a phase-mostly LCTV
Authors: Tam Eddy C. , Yu Francis T. S. , Tanone Aris , Gregory Don A. , Judayt Richard D.
Published: February 2023

We present a technique that uses data-association target tracking in a sequence of images by means of an adaptive joint-transform correlator. The correlator is made to adapt to the input scene that contains the targets by updating the reference image of the correlator with the previous frame of the input scene. The targets in the current frame will then have high correlation with the reference images, and the massive data in the field of view can be reduced into a few correlation peaks. The average velocity of a target during the tracking cycle is then determined from the location of the correlation peaks. We have used a data association algorithm for the analysis of these correlation signals, for which multiple targets can be tracked. A phase-mostly liquid crystal television is used in this hybrid joint-transform correlator system, and simultaneous tracking of three targets is demonstrated.
Optical pattern recognition and the genetic code
Authors: Christens-Barry William A. , Brasher Larry D. , Martin James C.
Published: February 2023

The analysis of genetic-sequence data bases is a pattern recognition problem containing several novel features. The constrained nature of images used as inputs can be exploited to achieve quantitative correlation-plane results not possible for more general images. We have developed several symbolic representations of DNA-sequence data that address particular goals of sequence analysis. Important considerations in the design of appropriate representations are discussed. We present the results of optical correlator experiments that employ matched spatial filtering in a Vander Lugt correlator architecture. Experiments include searches for specific substrings within a larger string of sequence data, searches for unspecified substrings based on structural motifs, and searches for substrings in the presence of noise. A potential architecture for a real-time interactive optical correlatoris also examined.
Holographic microbes identification using dynamic speckle graphs
Authors: Zheng B. , Ih C. S. , Pleass C. M. , Dey N. D.
Published: February 2023

Identifying microbes in real time has a great significance in biological, medical, and environmental research and applications. New techniques are needed to develop a practical method for continuously monitoring the growth, motion, and content of microbes. The holographic filtering technique has been used for this purpose. However, since living microbes are mainly phase objects, varying in size and shape and also moving randomly, it is difficult to recognize them by holographic filtering that is based on their bodies. In our research we found that when a divergent laser beam passes through a culture of microbes, the dynamic-speckle graphs or patterns that are produced are unique to that particular culture. Information related to microbe size, orientation, concentration, and motion is transferred into these speckle graphs. We use the graphs as recognition targets to make an averaged holographic matched spatial filter (MSF). Theoretical analysis and experimental results have shown that MSF, combined with digital information processing, has many advantages over previous techniques. Our experiments support the hypothesis that it will eventually be possible to identify microbes in real time.
Silica-based integrated optical hybrid on silicon for phase diversity coherent receiver
Authors: Barbarossa G. , McGoldrick E.
Published: February 2023

We report the realization of a high silica, fiber compatible, low-loss, integrated optical hybrid on silicon based on a three waveguide directional coupler. The beam propagation method has been used for the simulation of the device, which has been fabricated by a combination of flame hydrolysis deposition and reactive ion etching.
Observation of quantized energy levels in molecular beam epitaxially grown ZnSe/ZnS single quantum wells
Authors: Yang X. H. , Zhou J. F. , Song J. J. , Yao T.
Published: February 2023

Photoluminescence-excitation spectroscopy was performed on a series of wide-gap ZnSe/ZnS single-quantum-well-structure samples grown by molecular-beam epitaxy (MBE) to study quantum confinement effects. Both tunable cw and nanosecond pulsed light sources were used. Single sharp photoluminescence peaks were observed in the range of 2.9-3.2 eV. The half widths of these photoluminescence peaks were much smaller than those reported in samples grown by low-pressure, metal-organic chemicalvapor deposition. This reflects the high quality of these MBE samples. As expected, the photoluminescence peak position increases with decreasing ZnSe well widths. A group of peaks and bumps observed in the photoluminescence excitation spectra will be compared with theoretically calculated energies associated with light-hole and heavy-hole transitions. Experimental data taken from the bulk ZnSe and from MBE ZnSe grown on GaAs substrate will also be presented for comparison.
Picosecond photocurrent anisotropy in stretched trans-polyacetylene with below- and above-gap excitation
Authors: Walser A. D. , Dorsinville R. , Tubino R. , Alfano R. R.
Published: February 2023

The picosecond photoconductivity of highly oriented polymer stretched transpolyacetylene was measured in the one-dimensional configuration (applied electric field parallel to the polymer chain) with respect to the polarization of the incident above- and below-gap excitations. The abovegap excitation was produced by 0.532 mm (2.4 eV), 25 ps pulses from a frequency-doubled YAG laser. For below-gap photoexcitation the fundamental frequency of the YAG at 1.06 mm (1.17 eV) was used. In each case the picosecond photoconductive response was maximum when the polarization of the incident optical pulse was perpendicular to the polymer chain. The anisotropy ratio (defined as the ratio of the photocurrent with perpendicular excitation to that with parallel excitation) for below-gap excitation was approximately 2.4 and was independent of intensity. The anisotropy for both excitations was normalized with respect to the number of absorbed photons. The above-gap anisotropy varied from 7.4 to 4.5 with respect to increasing intensity; and the photocurrent was greatest for below-gap excitation, independent of the optical field polarization. These results are accounted for in the soliton/polaron model.
Simulation and experimental study of Ti:LiNbO3 waveguides
Authors: Chu F. S. , Liu P. L. , Jia S. L. , Cressman P. J.
Published: February 2023

A waveguide-simulation program based on the beam-propagation method has been used to study Ti-indiffused LiNbO3 waveguide structures. By modifying the double-moded branching structure of the conventional Y-junction design, the loss of the branching structure can be substantially reduced. For a 1° half-branching angle, the loss can be lowered from –1.2 dB to 0.2 dB. Experimental data confirm that the modified design indeed has a lower loss. In addition to the branching structure, waveguide bends are also needed to complete a Y-junction. Low-loss coherent coupling bends are simulated and measured. From the measured mode profile, the waveguide simulation program is used to obtain the diffusion parameters for the Y-cut, X- or Z-propagating waveguides. The coupling lengths of directional couplers fabricated on such substrates are calculated and compared with experimental measurements. Coupling between adjacent waveguide bends is simulated. Mismatched waveguides, as well as ion milling, are used to decouple adjacent waveguides. Results of simulation are compared with experimental data.