bluuebunny/crossref_metadata_2025 huggingface dataset:
Photon noise-limited model of threshold-versus-intensity curves
Authors: Rudd Michael
Published: February 2023

On the basis of the work by Rose, de Vries, Barlow, and others, it is generally believed that visual detection at low background illuminances is limited by both photon and neural noise. At high background illuminances, observers are often said to depart from "ideal" performance by following Weber's law rather than the de Vries-Rose Law. This departure is sometimes ascribed to photochemical adaptation. A model is presented here in which performance is assumed to be noise-limited at all background illuminances. No photochemical adaptation is assumed. According to this model, the transition from the de Vries-Rose law to Weber's law, as background illuminance is increased, arises from stimulus-scale and intensity-dependent adjustments in visual integration time. These adjustments occur naturally as a result of the modeling of subthreshold photon summation as a random walk with drift to a fixed weighted energy threshold. The model qualitatively predicts the observed dependence of the threshold-versus-intensity curves on stimulus area and duration. The model is more consistent with the known dependence of visual-system integration time on intensity and scale than is the classical de Vries-Rose assumption of a fixed, stimulus-independent visual integration time.
Sensitivity of optical synthesis imaging through direct photodection
Authors: Prasad Sudhakar
Published: February 2023

All interferometric imaging is based on a direct application of the Van Cittert-Zernike theorem. Because of the existence of cooled solid-state photodetectors with hardly any readout noise, the sensitivity of optical interferometric imaging is limited almost exclusively by the Poissonian shot noise of photoelectron counting. We shall derive the signal-to-noise ratios (SNRs) in the reconstructed image, both for ideal imaging, which is possible for space-based arrays, and for bispectral (or closure-phase) imaging, which is necessary for ground-based arrays. We shall show1 that the beam combination geometry plays no essential role in determining SNR. Also, at high photon rates, the image SNR is the same for ideal arrays as it is for ground-based arrays. However, the sensitivity of ground-based imaging is severely degraded for faint objects that produce less than about 0.3 photon per spatial coherence area per coherence time. I shall compare bispectral imaging with self-calibration and discuss the tradeoff between sensitivity and resolution.
Microspacecraft cameras in exploration of the Solar System
Authors: MeinelMarjorie P. Meinel Aden B.
Published: February 2023

Microspacecraft may have an important role in low-cost exploration of the solar system. Designs for cameras having masses from a few tens of grams to a few kilograms and with effective focal lengths of many times their clear apertures are being explored. Typical missions include high-G situations such as when the camera is attached to an asteroid or comet nucleus penetrator or when the camera is launched by an electromagnetic rail gun. High-G requirements are satisfied by beryllium or aluminum monolithic construction. Single-point diamond turning is a key technology element in the construction of such cameras.
Design overview of the atmospheric IR sounder
Authors: Pagano Robert , Morse Paul , Miller Chris
Published: February 2023

The AIRS instrument, scheduled for launch in 1997, is designed to provide new and more accurate data about the atmosphere, land, and oceans for application to climate studies and weather prediction. Loral Infrared and Imaging Systems, Inc. (LIRIS) is currently under contract to the Jet Propulsion Laboratory (JPL) for the concept definition of the AIRS instrument. To meet the National Weather Service's temperature measurement goal, the next generation infrared sounder must have a spectral resolving power of 1200 over the spectral range 3.4–15.4 µm.1 AIRS employs two multiple-aperture echelle-array spectrometers, each using several grating orders to obtain the desired spectral resolution. Spectral-order separation is accomplished by subdividing the telescope entrance pupil into several apertures, each with its own out-of-band rejection filter. The radiation passing through these apertures is dispersed by the echelle grating before the apertures are reimaged onto a series 2 × n arrays. The focal plane arrays are made of photovoltaic and photoconductive mercury cadmium telluride. To maximize performance all spectrometer components are cooled to 155 K, and the arrays are cooled to 60 K. Systems modeling at LIRIS and JPL indicates that the instrument will achieve the 0.2 K noise-equivalent-delta-temperature goal over most of the spectral bandpass. AIRS will provide global coverage twice per day with a continuous downlink data rate of 1.85 Mbps. The design and development phase of the AIRS program will begin in October 1990.
Ground station for space optical communication experiments
Authors: Toyoda M. , Greenwald D. , McLaughlin C. , LaSala P. , Duggins D. , Yoshikado S. , Araki K. , Arimoto Y. , Shikatani M. , Hiromoto N. , Itabe T. , Aruga T.
Published: February 2023

The Communications Research Laboratory is planning a laser optical communication project to establish the basic technology of optical communications in space. The most important part of the experiment is maintaining the laser link between the satellite and the ground station by means of on-board laser communication equipment. The satellite will be launched in the summer of 1993. In this study of optical communication in space, several experiments are planned. The first is the acquisition and tracking of the satellite by using the point-ahead technique, which is the key to keeping the laser link. The second experiment is to measure the propagation characteristics of the laser beam through the atmosphere and to measure the beam pattern of the on-board laser diode. The third experiment is the high-accuracy attitude determination of the satellite by a controlled, polarized laser beam. The fourth and primary goal of the study is the dual-link optical communication experiment. The ground station includes a transmitting telescope with a fine pointing mechanism, a main telescope for receiving the signal from the satellite, and optics to modulate the Ar laser located in the Coude room under the telescope. In this paper, we will present the specifications of the ground equipment and some preliminary results of experiments that used the ground station.
Multiple-wavelength, mid-IR, cascade laser operation in Tm:LiYF4
Authors: Grasso Robert J.
Published: February 2023

We report multiple wavelength cascade laser operation of Tm3+YF4 at room temperature. The laser operated continuously at 1.88 and 2.31µm from the 3H4 Ä 3H5 and3F4→3H6 transitions, respectively. Pumping was performed longitudinally by a CW Ti:Al2O3 laser tuned to the 0.786µm Tm3+ absorption peak. Lasing has been previously reported as 2.31 µm and at 1.88µm from Tm3+:LiYF4 under pulse pumped conditions.1 The laser consisted of a 1.5% Tm3+:LiYF4 crystal and a 10 cm radius of curvature, 99% reflectivity output coupler. The Ti:Al2O3 laser pumps the 3H4 level which decays to the 3H5 level for output at 2.31 µm. Next, the energy decays via non- radiative multi-phonon processes between the 3H5 3F4 levels. Finally, the 3F4 level is populated and decays to the 3H6 level for output at 1.88 µm. We report a 3% slope efficiency and a 2% conversion efficiency for both wavelengths operating simultaneously.
Theory of the binary phase-only filters for optical pattern recognition
Authors: Horner Joseph L. , Javidi Bahram
Published: February 2023

In this paper, we presentan analysis of the binary phase-only filter (BPOF).1,2 The linear filter function is expressed as the real part of the conventional matched filter, which contains the amplitude and phase of the Fourier transform of the reference signal. The linear filter function is then applied to a binary nonlinear device to produce the BPOF function. Our paper provides analytical expressions for the correlation signals produced by the BPOF. An expression for the BPOF can be obtained by an approach similar to that used in the analysis of nonlinearly transformed filters by the transform method.3 We have investigated the effects of the binary nonlinear transformation on the correlation signals at the output plane. We show that the BPOF results in an infinite sum of harmonic terms. Each harmonic term is phase-modulated by m times the phase modulation of the linear filter function. The amplitude modulation of the harmonic terms is removed in the binary nonlinear transformation. We show that for the first-order harmonic term, the nonlinear transformation preserves the phase of the matched filter. The higher-order terms are added to the first-order term and may be considered as degradation of the filter. The intensity of the higher order terms is less than that of the first-order signal. One component of the first-order term is identical to the continuous phase-only filter. However, the firstorder phase-only filter is degraded by the higher-order intermodulation terms. This explains why the performance of the binary phase-only filter is similar to that of the continuous phase-only filter.
Fisher information as the basis for Maxwell's equations
Authors: Frieden B. Roy
Published: February 2023

Maxwell's equations maybe derived on an information-theoretic basis. Consider a gedanken experiment whereby the space–time coordinate. An efficient (optimum) estimate obeys a condition of minimum Fisher information, or of minimum precision, according to the second law of thermodynamics. The Fisher information is a simple functional of the probability law governing the space–time coordinates of the photons in the field. This probability law is taken to be the local intensity in the optical sense, i.e., the square of the four-vector potential. The principle of minimum Fisher information states that the correct probability law results from minimizing the information subject to a constraint in the mean kinetic energy of the particles of the field. In the electromagnetic field, the closest concept to kinetic energy is the free energy, i.e., the energy available for kinetic energy were a particle of finite mass to enter the field. When the Fisher information is minimized subject to a constraint on mean free energy, Maxwell's equations result.
Properties of mixed composition IR optical thin films
Authors: Gluck Natalie S. , Heuer James P.
Published: February 2023

Mixing two optical materials greatly increases the range of properties that are available from a finite number of discrete materials. The properties of composite films are often unique and unobtainable from any single material. Composition-dependent structural, optical, and mechanical properties of co-deposited and layered infrared optical thin-film materials were investigated. The material pairs studied were Si/ZnSe, Si/AlF3, LaF3/ZnSe, and YF3/ZnSe. Information will be presented on stress, optical properties, scatter and morphology, microhardness, and crystallization behavior and microstructural development upon annealing.
Direct measurement of the amplitude and phase of photorefractive fields
Authors: Sherman Christopher J. , Lawler William B. , Moharam M. G.
Published: February 2023

The properties of the photorefractive periodic space-charge fields are traditionally investigated by measuring the diffraction efficiency of the induced phase gratings and by measuring the beam coupling and energy exchange between the two recording beams. The amplitude of the photorefractive induced space-charge field is then estimated by using involved analytical models. These methods, are in general, not particularly sensitive, and they depend on good assumed values for several material properties. In this work, we present a technique for real-time direct measurement of both the amplitude and the phase of the photorefractive space-charge fields during grating formation. The system utilizes the Doppler frequency-shifting properties of acousto-optic cells to enable the use of heterodyne detection. A network analysis is used to monitor the time development of both the amplitude and the phase of the photorefractive grating. This technique provides substantial dynamic range, and it also provides the necessary sensitivity for the detection of refractive-index changes as small as 10−8 and phase changes as small as 1°. This system has been used to characterize the photorefractive properties of LiNbO3:Fe, KNbO3:Fe, KNbO3:Ta, KNSBN:Fe, and BaTiO3. Data are presented for the buildup of the amplitude and the phase of the photorefractive space-charge fields.
Simple optical switch based on a nonlinear interface
Authors: Strobl. Karlheinz , Golub Ilya
Published: February 2023

The nonlinear interface (NI) has been proposed for ultrafast all-optical switching, pulse shaping, and energy limiting. These potential applications notwithstanding, only a few experimental realizations of NTs have been published. Reasons for this lack include the unavailability of a suitable model in which the effects of various parameters on the switching behavior could be simply explored, and the discouraging results of early (nonsaturating NI) experiments.1 The material combinations in earlier studies used1,2 required special NI preparation that introduced uncontrollable parameters. We present a simple NI that uses a thermal nonlinearity and requires a shorter learning time for its setup; it allows the study of both the reflected and transmitted beams. Although the response time of such a thermal NI is on the order of milliseconds, it can serve as a model system for studies of ultrafast NI applications. Depending on the ratio of pulse length to the response time of the system (formation and relaxation time of the nonlinearity), various operating modes can be observed.
Optical clock recovery circuit using periodic oscillations of a Mach-Zehnder interferometer with delayed feedback
Authors: Chbat M. W. , Iannone P. P. , Perrier P. A. , Prucnal P. R.
Published: February 2023

With the development of high-data-rate optical communication networks, there is a growing interest in processing some highspeed operations optically. Among these, clock extraction is critical because of its function in more complex operations, such as signal regeneration. A novel optical clock recovery circuit is demonstrated that uses the periodic oscillations resulting from the astable behavior of a bistable optical device with finite feedback delay.1 The novel optical clock recovery circuit is based on a hybrid electrooptic bistable system and consists of an integrated-optic Mach-Zehnder interferometer with a feedback loop that introduces a time delay τ. We consider a return-to-zero (RZ) optical data signal with a bit rate I/(2τ) and a pulse width τP (τP ≤ τ), which rides on an optical bias. We show that when this signal enters the clock recovery circuit, the optical signal at the modulator output is a continuous square-wave pattern with a period of 2τ. This signal corresponds to the clock of the incoming optical data signal. The time-dependent behavior of the modulator output intensity arises from the periodic instabilities in bistable systems, which are caused by a finite feedback time delay.2 Clock extraction from an intensity-modulated, 13.6 Mbit/s, 223-1 pseudorandom RZ bit sequence is demonstrated. Jitter performance of the recovered clock for various input data patterns, the effect of long strings of data-bit 0s, and the speed limitations of the circuit are investigated. The inclusion of this clock recovery circuit into an optical regenerator is also discussed.
Effect of phase-conjugate feedback on semiconductor laser dynamics
Authors: Agrawal Govind P. , Klaus Jeffrey T.
Published: February 2023

The sensitivity of semiconductor lasers to the external feedback is well known.1,2 Even a relatively small amount of feedback can destabilize the steady state and lead to nonlinear phenomena, such as coherence collapse, period doubling, and optical chaos. The phase of the feedback signal is important in the nonlinear dynamics. This dependence on the feedback phase can be eliminated if the feedback is produced by using a phase-conjugate mirror. This paper considers the effect of phase-conjugate feedback on semiconductor-laser dynamics by using the appropriate differential–difference rate equations. The steady-state solution of these equations shows that the effect of phase-conjugate feedback is to pin down the phase of the intracavity field. Another difference from the case of ordinary feedback is that the phase equation has only a single solution, so multiple external-cavity modes are never excited. The stability of the steady-state solutions is examined through a linear stability analysis. The results show that the steady state can become unstable not only through a Hopf bifurcation (similar to the case of ordinary feedback) but also through a fold bifurcation. The dynamic behavior beyond the linear stability analysis is studied by solving the differential–difference rate equations numerically.
Defect-mediated turbulence in lasers: experiment and theory
Authors: Green C. , D’Angelo E. , Ocola M. , Gil L. , Narducci L. M. , Oppo G. L. , Tredicce J. R.
Published: February 2023

It was shown that the inclusion of diffraction terms into the usual Maxwell–Bloch equations lead to the appearance of "optical vortices"1 and in the limit of small field amplitudes and large decay rates for the atomic variables, those equations are isomorphic to the Guinzburg–Landau one with constant complex parameters. However, in the case of the "longitudinal" boundary conditions for a real laser, the equations have parameters that depend on the spatial coordinates.2 Here we show that the inclusion of those terms leads also to the appearance of defects, a decay in the spatial correlation function, and therefore to defect-mediated turbulence. In particular, this system does not require the conservation of the topological charge. We analyzed the motion of defects, their interaction, and their influence on the temporal dynamics. The numerical results are compared with experimental data obtained from a CO2 laser with a large Fresnel number.
Laser-beam diameter measurement by using a periodic exponential grating
Authors: Awwal Abdul Ahad S. , Smith Jeanne A. , Belloto Jim , Bharatram Geetha
Published: February 2023

Measurement of laser-beam diameter is essential for the estimation of beam divergence, for laser applications in optical disks, and for metrology applications that use laser sensors. Although the rectangular (Ronchi) ruling of a particular period (L) is capable of estimating the beam radius (r0) for r0/L of 0.2–1.2, triangular and sinusoid gratings1 extend the range to a much smaller radius compared to the grating period. The upper limit of beam diameter measurement has recently been improved by formulation of an aperiodic ruling2 that, for a certain aperiodicity, can extend the measurement range up to an r0/L of 10. However, because of the rectangular (discontinuous) nature of the grating, the lower values of the beam radius can not be measured. In this work, we propose a novel grating with periodic, exponential transmission characteristics that is capable of extending the range to both higher and lower values of the beam radius. Our proposed exponential periodic grating provides a linear variation of k between r0/L of 0–1.2.
Recent advances in holographic storage
Authors: Hesselink Lambertus
Published: February 2023

This paper discusses recent advances in the understanding of holographic data storage in photorefractive SBN. The implications of electrical fixing procedures on the storage architecture will be treated by using a systems approach.
He implantation effects in the 13–55-keV range on the optical recording properties of Te thin films
Authors: Beauvais Jacques , Galarneau Pierre , Lessard Roger A. , Knystautas Emile J.
Published: February 2023

The behavior of the optical recording properties of 55 nm Te thin films on glass substrates has been investigated as a function of singly ionized He beam energies, with an observed decrease of the writing threshold of the thin films in the 23–45 keV range. However, the implanted dose within the Te thin films was always maintained at a fixed value, requiring the total implanted dose for the film–substrate system to increase at higher energies. The results of our study, which investigated implantations at various ion doses and beam energies in the 13–55 keV range, show that the total implanted dose within the film–substrate system is important in the observed decrease of the writing threshold of the thin films. Increases of the ion-beam energy at a fixed total dose produce no decrease in the writing threshold. Furthermore, measurements carried out as a function of planted doses at two fixed energies of 13 and 32 keV confirm that the total implanted dose for the film–substrate system is also important in the determination of a critical dose above which the writing threshold decreases.
Phase-extraction pattern recognition
Authors: Kotzer Tuvia , Rosen Joseph , Shamir Joseph
Published: February 2023

Our novel nonlinear detection system is based on a pseudocorrelator. The basic operation of the system is as follows. A transparency containing a multitude of objects to be detected/discriminated against is placed at the input plane. After a plane wave is superimposed on the Fourier transform, the interference pattern is recorded by a television camera. Then, after some nonlinear operations on the above-mentioned pattern are performed, an appropriately real coded, phase-only filter is displayed on an spatial light modulator (SLM). Illumination by a plane wave of the SLM and multiplication by a spatial filter leads, after a Fourier transform, to the required correlation plane. Simulations and theoretical investigations of the above method indeed show promising results in terms of both detection and discrimination capability. We believe that we have an approach to pattern recognition that yields superior results. This system should provide an attractive detection system.
Experimental observations of atoms in fields
Authors: Kleppner Daniel
Published: February 2023

The nature of a simple atomic system can profoundly alter in the presence of an external electric or magnetic field. The study of such systems can provide unique insights into problems such as correlated motion, the behavior of non-separable systems, and quantum structure in regimes of irregular classical motion ("quantum chaos"). We have carried out a study of the spectrum of the lithium atom in magnetic fields in the vicinity of 6 T, at energies close to and above the ionization limit. By using cw lasers we have been able to obtain a resolution of 0.001 cm, low by current standards, but much higher than previously obtained. General quantum solutions to the problem are lacking but numerical solutions have been able to account for the spectrum in regions up to the zero-field ionization limit. Studies of the classical motion reveal an essentially textbook transition from orderly to disorderly motion as the energy increases. Although spectra at a given field appear similar to other spectra whose statistics display the expected behavior, when the spectra are compared at different fields, forming an energy level "map," we observe regularities that can be described by simple quantum numbers. Such behavior is unexpected and suggests that a regime that is believed to be one of total disorder actually encompasses periodic motion.
CVD silicon carbide—a promising material for low-scatter mirrors
Authors: Bennett Jean M. , Archibald Phillip C. , De’wees Randle V. , Donovan Terence M. , Pickering Michael A. , Scribner Kenneth , Beecroft Michael , Dummer Richard S. , Stover John C.
Published: February 2023

Silicon carbide formed by chemical vapor deposition is a promising material to use for lightweight, low-scatter mirrors. It can be made optically dense with a minimum of growth defects and stress birefringence, and it can be polished to a low-scatter finish that is comparable to the best high-quality fused-silica optics. Roughness values of 0.3 Å rms have been measured on a Zygo heterodyne profiler and under 1 Å rms on a Talystep mechanical-contact profiler. The optical constants measured in the wavelength range from 1.6–25 μm show that there is a reststrahlen band in the 10–13μm region and that the reflectance exceeds 94% at 12 μm. Total integrated scattering (TTS) at 0.647 μm can be as low as 1 × 10−6, corresponding to an rms roughness of 5.2 Å. Bidirectional-reflectance distribution function (BRDF) values of less than 5 × 10−6 at a scattering angle of 10 from the specular direction and approximately 3 × 10−6 at 25–80° from the specular direction have been measured at 0.633 μm. The integrated BRDF values yield a roughness in good agreement with that measured by TIS. These BRDF values are approximately 11 orders of magnitude down from the intensity of the specular beam. Data measured on silicon carbide samples from different sources and polished by different companies will be shown.
Computer-controlled optical surfacing of seven large aspheric optics
Authors: Jones Robert A. , Plante Roland L.
Published: February 2023

Itek Optical Systems has developed computer-controlled optical surfacing (CCOS) processes and equipment for the rapid fabrication of large aspheric optics. An orbiting tool, considerably smaller than the optic, is moved across the optic surface under computer control. Low-spatial-frequency errors are corrected by varying the velocity of the tool over the optic surface to accurately control material removal. High-spatial-frequency errors are eradicated by the pad as it compresses to fit the surface, producing greater pressure and more removal at the higher surface regions under the pad. CCOS was used to fabricate seven 2 m off-axis aspheric optics. These thin facesheets were worked close to their actual edges during both grinding and polishing so that they could be used in a segmented mirror. Excellent grinding and polishing results were achieved for all facesheets. Also, the figure convergence was improved during the operation; the last facesheet was polished in only 11 weeks. The CCOS operation provides efficient automated fabrication. With a number of stations operating on multiple shifts, the intensive optical fabrication needs of the next decade can be met.
Materials and devices technologies for HBT-based long-wavelength OEIC photoreceivers
Authors: Pollack M. A.
Published: February 2023

Advances in material growth and device technologies have permitted the demonstration of ultra-high-speed InP/InGaAs heterojunction bipolar transistors (HBTs), as well as integrated circuits based on these high performance devices. In this talk, progress in the extension of these technologies to HBT-based, monolithic optoelectronic integrated circuit (OEIC) phototreceivers for the long-wavelength (1.3-1.6 µm) region will be described.
Image preprocessing for pattern detection and recognition in the presence of signal-dependent noise
Authors: Terrillon Jean-Christophe , Arsenault Henri H.
Published: February 2023

We have demonstrated that image restoration used as a preprocessing tool can improve pattern recognition and detection. The effects of signal-dependent random noise on digital pattern detection and recognition by matched filtering are investigated. Computer simulations performed on 10 000 noisy realizations of each member of a set of binary and grey-level images by means of phase-only and binary phase-only filters have shown that the signal-to-noise ratio (SNR) in the correlation plane drops by an average amount of 40% with respect to the original correlation SNR. False alarms have been observed in some extreme cases, but the noisy images that give rise to false alarms were restored by locally adaptive filters. We show that, as a result, the SNR increases by a factor of 2-3 with respect to the noisy correlation SNR, and false alarms are eliminated.
Multicategory image classification by the optical implementation of the Kittler-Young transform
Authors: Li John X. , Yu Francis T. S. , Gregory Don A.
Published: February 2023

The Kittler-Young (KY) transform is a feature-extraction linear algorithm. The information of the class means and the class variances are optimally utilized in the KY transform, such that high space-bandwidth product pattern recognition can be performed. Another important feature of the KY transform is the capability to perform multiple-category pattern recognition. A three-category image classification is performed on an optical-matrix multiplication system by using the KY transform. The first three basis KY basis images, which are the column vectors of the KY transform matrix, are written onto the first liquid-crystal television (LCTV), while a target image is displayed on the second LCTV. After the optical inner-product and addition operations, the first three KY features of the target image are present at the output plane. These KY features are detected by a charge-coupled device camera and are fed to a pseudoinverse classifier.
Glass waveguide devices on silicon
Authors: Henry C. H.
Published: February 2023

We have developed two waveguides made with conventional silicon technology: one matching an optical fiber and one matching a semiconductor laser. We will discuss the following devices: a hybrid laser chip with 7 KHz linewidth; a 19 × 19 star coupler; an adiabatic polarization splitter; and a 4 channel multiplexer with elliptical Bragg reflectors.
Sensitivity of guided wave techniques to photo induced refractive-index disturbations in thin films
Authors: Flory F. , Maythaveekulchai N.
Published: February 2023

We have developed the formalism based on the Goss-Hânchen shift to calculate the m-line profiles of the reflected light from a coupling prism pressed on a multilayer guide. The m-line profiles correspond to the coupling and decoupling energy in and out of the guide. If the light intensity is high enough, it will disturb guide index, and two phenomena can be involved: thermal and photorefractive effects. Due to the rather large thermal diffusion length, the thermal effect gives mostly a shift to the considered m-lines. The photorefractive effect is proportional to the local intensity. We compute the energy distribution under the prism, in the guide, both in the propagating direction and in the direction perpendicular to dioptres. Then we introduce non linear coefficient value for each layer of the guide to obtain the refractive index profile from energy distribution. After sampling it in 2 dimensions, we are able to calculate the modification of the m-line profile induced by this third order nonlinearity. Our results show that this m-line profile is then distorted from the linear one. Thus, thermal effect appears to be easily distinguishable from that of photorefractive effect and this method must be useful to measure very weak non linear coefficients which we expect to have with dielectric thin films.
Quantum-confinement and electrostriction effects for optical beam modulation
Authors: Leon R. , Lai H.-S. , Lin F. C. , Fiddy Y. A.
Published: February 2023

Our interest is in the bulk nonlinear optical properties associated with suspensions of conducting particles. These particles can exhibit a discrete line spectrum if they are smaller than the Bohr radius of the free carrier. In principle, the band gap can be engineered to lie in the visible region and, as a result of local field effects, distributions of such particles can possess large optical nonlinearities and can exhibit bistability, making them suitable for optical switching and storage applications. Several physical mechanisms contribute to the nonlinearity, each having different characteristics with respect to wavelength sensitivity and response time. These mechanisms include quantum confinement effects, thermal nonlinearities, and electrostrictive forces. We present results on the scattering and modulation of light from colloidal gold. Two application areas are largearea switching of optical transmission and high-density pixelation of switching elements, both of which are ideal for low-power narrowband optical interconnects.
Excited-state absorption in solid-state molecular complexes
Authors: Koepke Cz. , Lempicki A.
Published: February 2023

Molecular complexes in solids have never been treated as possible laser materials. Among them are known luminophors and scintillators of pronounced luminescence over the range of some 150 nm and thus being potential candidates for tunable laser media (acting in blue-green region). In the few cases studied so far distinct excited state absorption (ESA), usually overlapping the luminescence and spreading even further, was observed. We have investigated CaMoC4, CaWO4 (of nd0 electronic configuration) and Bi4Ge3O12 (BGO) (ns2 configuration). Interesting properties are displayed by BGO, where ESA increases with probe-beam intensity, the phenomenon being a sort of excited-state photochromism (ESP), possibly involving some trap levels in its mechanism. BGO has the best (smallest) ratio of ESA to stimulated emission crossections (σESA/σe) of about one order of magnitude (e.g., for 632.8nmσESA ~ 4×10–19cm2σe ~ 2×10–20 cm2), which precludes a chance for lasing in this crystal. The two other crystals reveal rather "standard", broad ESA spectra of absorption crossections σESA of the order of 10–19, 10–18 cm2 whereas emission cross sections are ~ 10–21, 10–20 cm2. The results, though precluding laser action in these materials, provide spectroscopic data, which, we believe, are new in the field of solid state optics.
Photorefractive mode coupling between two unidirectional ring oscillators
Authors: Dai Li-Xuo , Gou Yih-Shun , Yeh Pochi , Gu Claire
Published: February 2023

Photorefractive mode coupling between resonators provides a simple model for self-pumped phase conjugators,1 in which instability may occur because of energy transfer among different oscillation modes inside the crystal. In this paper, we consider the coupling between two unidirectional ring resonators.2 The first resonator is driven by an external laser beam by means of photorefractive two-wave mixing. The internal oscillating beam is then employed to drive the second ring resonator by the same mechanism. We find that with proper choice of resonator parameters, two type of oscillations may occur. In the first type the primary resonator, which is driven by the external laser, oscillates, but the secondary resonator, which is driven by the primary resonator, does not oscillate. In the second type the primary and secondary resonators oscillate simultaneously, and the oscillation of one resonator affects that of the other. We also find that even though the two resonators can oscillate separately, they may not perform steady-state oscillation when they are coupled. In this case the coupled system is not stable, which may result in temporal instability similar to that which occurs in self-pumped phase conjugators. Our results include the conditions for each of the above operation modes, the intensities and frequencies for steady-state oscillations, and the change of oscillation in one resonator that is brought about by detuning the other one.
Effects of a pulsed Gaussian beam on photorefractive materials
Authors: Xu Chibing , McIver John K. , Statman David
Published: February 2023

The band-transport model is used to study the effects of a pulsed Gaussian laser beam on photorefractive materials. Attention is paid to the relaxation of the polarization of the materials. When the relaxation time of the polarization is much shorter than the pulse length, the results differ little from those obtained when the relaxation is omitted. The induced electrical field in the illuminated area reaches its steady-state value much faster than in the dark area because there are many more photocarriers in the illuminated area. Although electron density and ionized-donor density decrease rapidly because of recombination when the light is turned off, the total charge density, which determines the induced field, keeps growing as a result of a nonzero electrical current. After the initial growth, the field remains unchanged for a long time, i.e., there is long-term storage of the induced field. When the relaxation time is longer than the pulse length, then the longer the relaxation time, the faster the induced field grows when the light is on, but the slower it reaches steady state when the light is off. This occurs because the polarization slowly follows the change in the field.
Determination of the surface nonlinear susceptibility by noncollinear reflected SHG
Authors: Provencher Pierre , Denariez-Roberge Marguerite Marie
Published: February 2023

The use of SHG for probing monolayers of absorbed molecules has been developed recently and has shown its ability to give the molecular orientation of absorbed speciesbut with some restrictions. In this paper we will present a new method that allows us to obtain all elements of the surface optical susceptibility χ(2). By using two noncollinear beams of different polarizations and by rotating independently the polarization of the two beams, we obtain minima and maxima of the signal generated that give the ratios between all independent elements of the tensor χ(2) (which gives the molecular orientation). Theoretical results obtained by this method will also be given for samples of Rhodamine 6G absorbed on fused silica.
Photonic Batcher-Banyan switch architecture with optical control
Authors: Blumenthal Daniel J.
Published: February 2023

Self-routing is employed in fast packet switching systems to increase throughput, which in general is limited by speed of the switch control technology. Optical processing has successfully improved throughput by increasing the processing rate of header information.1 In this paper an architecture is proposed whereby optical processing controls a photonic Batcher-Banyan network. Both switch and control architectures are compatible with current integrated-optic devices. Routing information is coded by wavelength-division multiplexing and processed at the switch in real time with bandpass filters.2 In the sort stage, filters remove routing information, and the weighted sums of routing channels are compared to produce the sort function. The permutation stage consists of crosspoints with prefilters that remove a specific wavelength, analogous to bits in a serial header. Synchronization based on switch setup time and group delay between control signals and data are important issues in this scheme. Channel utilization is calculated to be better than 98% for 155 Mbit/s, 43 byte cells transmitted through a 32 × 32 switch up to 100 km. The number of cross-points is 3/2(N log2 N) for the Banyan switch and 1/2[(log2 N)3 + (log2 N)2] for the Batcher sorter.
Effects of an aperture in the Fourier-transform plane of Fourier-transform imaging systems
Authors: Gallo John T. , Jones Mark L. , Verber Carl M.
Published: February 2023

Fourier-transform holograms are attractive for high-storage-density holographic memories. One of the major drawbacks of storing the Fourier transform of the image is that to get an exact reconstruction of the object it is necessary to record the entire Fourier transform, which may have infinite spatial extent. Because this is not feasible, it is necessary to determine how much of the Fourier transform must be recorded to allow an adequate reconstruction of the image. We present a model that predicts the effect of an aperture placed in the Fourier-transform plane of a Fourier-transform imaging system. Changing the size of the aperture is equivalent to changing the amount of the Fourier transform that is recorded. Our model uses a conventional 4-F geometry as well as the more compact geometry commonly used in Fourier-transform holography. The accuracy of the model was verified by comparing its predictions to experimental results.
Pulse propagation in passive-resonant-doped fibers
Authors: Torres-Cisneros G. E. , Sánchez-Mondragón J. J.
Published: February 2023

Optical solitons are expected to play a key role in single-mode optical-fiber communication systems. However, they are still degraded by the linear fiber loss. Therefore, in order to be realistically feasible, soliton-based systems will need repeaters to enhance the signal, and, from a practical point of view, optical amplifiers are preferable to electro-optical ones. The use of Raman nonlinearity,1 and, more recently, the use of rare-earth-doped fibers,2 have been proposed for such optical amplification. We have numerically simulated pulse propagation through singlemode silica fibers doped with passive two-level atoms in an attempt to cancel the linear fiber loss by the well known doping resonant nonlinearities. Our first results, from experiments carried out in a variety of circum-stances, indicate that the linear rate of loss may be diminished with a proper choice of parameters but that the doped fiber by itself is unable to support steady propagation.
Ultrashort pulse generation in lasers containing an antiresonant ring
Authors: Yakymyshyn Christopher P. , Lotshaw William T.
Published: February 2023

Mode locking with an antiresonant ring is a powerful technique for producing stable trains of ultrashort pulses. This structure1 was first applied to visible dye lasers by placing a saturable absorber within an antiresonant ring that forms the high-reflectivity end mirror of a linear laser cavity. Nearly transform-limited 65 fs pulses have been generated with enhanced pulse stability.2 By using the additive pulse mode-locking (APM) representation, we describe the antiresonant ring (ARR) as a pulse-shaping reflector, which returns a temporally narrowed pulse to the main laser cavity. When a nonlinear element is incorporated within the ARR, an intensity-dependent reflectivity is predicted. A nonlinear element introduces temporal or spectral pulse shaping of the two counterpropagating fields within the ring. If the pulse shaping is unbalanced for the two fields, then preferential reflection of the high-intensity portions of the incident pulse can occur, resulting in a temporally narrowed pulse being returned to the laser gain medium. Results will be presented for a saturable absorber, a saturable amplifier, and a Kerr-type nonlinearity, such as an optical fiber.
Fiber data communication network for tropical environments
Authors: Grochowski Lucjan
Published: February 2023

Fiber-optical local area networks (FO LANs) are attractive for implementation in a tropical environment. This environment is characterized by high humidity and high, varying temperatures, factors that affect the quality of data transmission. Additional investigations are required if FO LANs are to be implemented under such conditions. In this paper, such investigations will be presented by means of implementation studies of FO LANs for computerization of the newly established campus of Moi University. I investigated the costs, the needs of the campus, and the performance of traditional copper connection devices; FO LAN connectors are greatly influenced by high humidity and widely varying daytime and nighttime temperatures. Other factors considered were the available space and the data communication facilities already on campus. The results will be categorized as (1) hardware optimization issues, and (2) access protocols. I will assess the performance of drop/insert devices, the reliability of electro-optic conversion, and the loss budget between transmitter and receivers under specific campus conditions.
Characteristics of proton-exchanged lithium tantalate waveguides
Authors: Matthews Paul J. , Surette Marc , Mickelson Alan R.
Published: February 2023

The use of lithium tantalate for integrated optics offers an attractive alternative to lithium niobate because of its higher stability, smaller birefringence, and greatly reduced susceptibility to optical damage (one to two orders of magnitude). Because lithium tantalate has such a low Curie temperature (610°C), the fabrication of waveguides by the traditional high-temperature indiffusion of various elements presents many difficulties. The use of the low-temperature proton-exchange process alleviates many of these problems and allows the fabrication of efficient, low-loss waveguides. This talk will discuss the efforts underway in our laboratory, to understand and model the mechanisms involved in the proton-exchange process in lithium tantalate. Optical characterization of z-cut slab and channel waveguides, including m-line measurements and near-field mode sizes, will be presented. We have performed parameter-space study to determine the regions of single-mode operation in channel waveguides. The performance of fabricated directional couplers and the effects of annealing on the coupling length and the results of studies of the microscopic aspects of the proton-exchange process, obtained through the use of secondary ion mass spectrometry, will also be presented.
Negative photoconductivity in double-barrier resonant tunneling diode
Authors: Kan S. C. , Wu S. W. , Sanders S. , Griffel G. , Yariv A.
Published: February 2023

We have used double-barrier, resonant tunneling diode to demonstrate a new bistable device that has both positive and negative photoconductive states. This bistable photoconductivity is brought about by the enhancement of the resonant tunneling effect in a double-barrier diode by light. Our double-barrier diode has only partial lateral current confinement, and, hence, the voltage across the double barrier varies laterally along the barrier plane. Because of this variation, the tunneling process is not simultaneously resonant across the entire double-barrier plane, leading to an increase in the valley current. By using light to increase the conductivity of the cap layer of the device, we can decrease the lateral voltage difference along the double-barrier plane and enhance the resonant tunneling effect. This enhancement leads to increased peak current and decreased valley current, thus achieving the bistable (positive and negative) photo-conductivity. Our theoretical model, which considers the partial lateral current confinement of the device, explains our experimental results.
Novel mirror arrangement enhances x-ray stepper beam line at Center for X-Ray Lithography
Authors: Cole R. K. , Cerrina F.
Published: February 2023

For 0.25-μm lithography, the beam of x rays must display high spectral and spacial uniformity at the wafer plane. Synchrotrons provide a very stable and very well defined source of x rays. The small width of the electron beam (σ
x
= 675μm and σ
y
= 175μm —for ALADDIN operating at 800 MeV) acts as a point source, providing crisp images at the exposure plane roughly 2 m away. However, at a distance of 12 m a 1-in.-wide exposure field collects only 2.1 millirad of the available radiation. There are two ways to improve the incident power at the photoresist: shorten the line or install focusing elements. Installing focusing elements has the potential advantage of collecting x rays from a very wide aperture and providing an image that can be matched to the requirements of the exposure system. We will review the different types of beamlines proposed to date and discuss the advantages of this new design. The current status of the beam line being constructed at CXrL by using these optics will also be presented.
How to become a CD-ROM publisher
Authors: Meyer Jane
Published: February 2023

The U.S. Patent and Trademark Office (PTO) provides patent information to a variety of public users through a newwork of 69 Patent Depository Libraries (PDLs) located throughout the United States. In order to improve its patent information dissemination activities, the PTO in 1987 turned to the new technology of compact disc-read only memory (CD-ROM). Since that time, the PTO has mastered over 20 CD-ROM discs and turned a pilot project into a successful and expanding program. The use of CD-ROM has enabled the PTO to replace its more costly on-line system of CASSIS (Classification and Search Support Information System). Additionally, the PTO has developed other CD-ROM applications which provide, in electronic form, information that was previously available to the PDLs only in paper or not at all. This presentation describes the background and development of the PTO's CD-ROM products, briefly demonstrates current products, and discusses future plans.