bluuebunny/crossref_metadata_2025 huggingface dataset:
Photon noise plus dc suppression compared to gain control as a model of threshold vision
Authors: Rudd Michael E.
Published: February 2023

At the 1991 OSA Annual Meeting, I described a model of TVI curves based on the assumption that vision is limited by photon fluctuations at high background levels.1 The theory predicts that a de Vries-Rose region or an asymptotic Weber region—or both—may be observed, depending on the area (or spatial frequency) and the duration of the test stimulus. The model accounts for changes in the slopes of TVI curves as a function of background illuminance without the need for postulating a gain control mechanism. However, certain types of gain control are allowed within the model. Many aspects of the time course of visual response are also accounted for by the model. To account for these latter data, a gain control mechanism (response compression of the output of a dc-suppressing receptive field mechanism) must be assumed. Many alternative models that account for TVI curve shape entirely on the basis of gain control assume that response compression depends on the background, as well as the incremental, intensity. Predictions of the two classes of models will be compared to psychophysical data.
Measurements of tunneling times and enhanced diffusion in strained-layer InGaAs quantum well diodes
Authors: Mahgerefteh Daniel , Yang Ching-Mei , Chen Li , Hu Kezhong , Garmire E. , Madhukar A.
Published: February 2023

We report the first measurements of picosecond carrier transport in InGaAs/GaAs multiple quantum wells (MQWs) in the i region of a reverse biased p-i-n diode. A 1 ps laser pulse operating near the exciton resonance at 950 nm excites electrons and holes, which tunnel out of the wells and screen the field. This changes the transmission of a time delayed probe pulse through the quantum-confined Stark effect. Strained InGaAs/GaAs MQWs grown via MBE within the i layer of a p-i-n diode varied in number from 20 to 50, well width from 45 Å to 100 Å, and barrier width from 125 Å to 200 Å; indium concentration was either 0.13 or 0.18. Mesas of 250 μm were fabricated and contacted by 125 μm off-centered dots. The 36 μm diameter pump and probe overlapped in the center of the non-contacted region. At room temperature a MQW with 13% In, 100 Å wells, and 200 Å barrier widths, using 0.94 pJ/pulse yielded a rise time of 10 ±2 ps and enhanced diffusion times ranging from 20 to 70 ps with applied voltages varying from 0 to 12 V. We believe the rise time is limited by the transit time of carriers to the doped region. Faster times in InGaAs are expected because of the lower electron effective mass.
Subpicosecond degenerate four wave mixing in sol–gel prepared CdS microcrystallites
Authors: Reeves R. J. , Powell R. C. , Knobbe E. T. , Mackenzie J. D. , Li C. , Yamane M.
Published: February 2023

Quantum dots of CdS prepared in silicate glass hosts by sol–gel techniques have been studied by using subpicosecond degenerate four-wave mixing. TEM analysis of the samples shows particle sizes in the range of 34 to 53 Å. The four-wave mixing experiments were conducted off-resonance, and the signals exhibited intensities and decay times that varied with microcrystallite size. In general, biexponential decays were observed with faster decay times recorded for the smaller sizes. Self diffraction arising from the interaction between any two input laser beams was also observed. Relative measurements of the intensity in adjacent orders establish χ(3) values in the range of 10−10 esu for laser pulses of subpicosecond duration.
A 128 fully interconnected optoelectronic neural network
Authors: Zhang Lin , Johnson Kristina M.
Published: February 2023

An optical neural network with 128 input and 128 output units is successfully implemented. This system consists of a 128 two-dimensional ferroelectric liquid crystal (FLC) spatial light modulator (SLM) used to present one-dimensional input patterns, a 240 × 220 LCTV to form the interconnections, a CCD camera to detect the output of the optical system, and a personal computer for updating the interconnections and controlling the CCD and SLMs. The algorithm used to train the network is Delta Rule. The size of the network allows us to test its operation on solving practical problems. We trained the system on samples of handwritten Arabic figures and tested with another set of samples. Laboratory results show that this network recognizes these characters with less than 10% error. In the conference we will present details about this network and further results. We will also present a second generation of optoelectronic neural network architecture utilizing semiconductor diode laser and VLSI/FLC modulators to speed up the training and testing cycles of the Delta Rule algorithm.
Is an empty de Broglie pilot wave capable of inducing coherence?
Authors: Zou X. Y. , Grayson T. , Wang L. J. , Mandel L.
Published: February 2023

The de Broglie pilot wave theory is a hybrid of quantum and classical concepts that was introduced in order to avoid the conceptual difficulties of the Copenhagen interpretation. According to some versions of this theory, there exist both photons and electromagnetic waves, and the waves are supposed not only to yield probabilities for the photons, but also to have a physical reality. Even an ″empty″ wave, which cannot give rise to photoelectric detection, is supposed to be capable of inducing observable effects. We have tested this theory in an experiment with two cascaded parametric down-converter crystals, in which the idler beam from the first crystal has been shown to induce coherence between the signal beams from the two crystals without inducing any emission. When the photon is removed from the first idler with the help of a beam splitter, the remaining empty wave is found not to induce coherence.
Submicrometer displacement sensing based on multimode fiber speckle field
Authors: Yu Francis T. S. , Wen Meiyuan , Yin Shizhuo , Uang Chii-Maw
Published: February 2023

It is well known that by perturbing a multimode fiber, a complicated speckle pattern can be observed in the far field. The speckle field is highly sensitive to the fiber status changes, and this sensitivity is caused by the surrounding sensing environment. The proposed technique is based on the fact that taking the intensity inner product of two speckle fields, for example, before and after the perturbation, represents the similarity between the two speckle patterns that is related to the external changes (such as strain or displacement). Preliminary analysis and experimental demonstrations are provided, in which we have shown that the sensitivity of the proposed multimode fiber sensor can be as high as 0.1 μm.
High frequency models for travelling wave optical fiber current sensors
Authors: Cernosek Richard W.
Published: February 2023

Recently, a travelling wave Faraday effect fiber current sensor was demonstrated that has increased bandwidth without a loss in detection sensitivity.1 This device consists of a helically shaped coil of single-mode optical fiber immersed in the dielectric of a coaxial transmission line. Attempts are made to phase match the velocity of the light propagating in the fiber with the relative velocity of the magnetic wave propagating along with the conducted current by increasing the pitch of the fiber helix and increasing the relative permittivity of the dielectric material. Ideally, an infinite bandwidth is possible, but practically, bandwidth is limited by the frequency- dependent properties of the dielectric and the transmission line. Mathematical models of the frequency-dependent Faraday rotation in a travelling wave sensor system have been developed that account for the modal structure of the coaxial line electromagnetic fields, the dispersion of the relative permittivity of the dielectric, and the effects of the optical fiber leads that carry light to and from the fiber coil. Model results are in good agreement with experimental measurements made on several configurations of current sensors. These include systems using high dielectric constant liquids where large absorption occurs at frequencies above a few hundred megahertz. Predictions based on the models indicate that current sensing well beyond 1 GHz is possible by using travelling wave Faraday effect fiber devices.
Mode discrimination in resonant optical waveguides
Authors: Shakir Sami A. , Salvi Theodore C.
Published: February 2023

Recently, there has been considerable interest in resonant optical waveguide (ROW) arrays.1 These phase-locked arrays have shown the ability to operate coherently with diffraction-limited output power both in the cw and pulsed modes. The strong optical mode confinement within each element provides a mechanism for strong mode discrimination by introducing losses in the cladding layers to favor the resonant mode and improve mode discrimination. We treat the ROW array as a stack of reflectors to compute the array modes and their corresponding losses. In particular, the effect of the right and left bounding mediums on the performance of the array is studied. We show that when the effective index of the bounding mediums approaches the effective index of the antiguiding layer or the cladding layer, mode discrimination deteriorates and disappears when the effective indices are equal. This phenomenon is primarily due to the high radiation losses at both ends of the array by the resonant mode.
Gaussian approximations of the fundamental modes of dielectric waveguides using the vector wave equation
Authors: Erteza Ireena A. , Goodman Joseph W.
Published: February 2023

Previously, we have presented a variational analysis method for the study of rectangular channel dielectric waveguides.1 The previous method determines the value of the propagation constant for the fundamental mode by using variational arguments based on the scalar wave equation, along with a Gaussian wave-field approximation. In this paper, we present the extension of the previous analysis method. The extension is based on the incorporation of the vector wave equation into the variational arguments used. A Gaussian field distribution is still assumed. By using the vector wave equation, instead of the scalar wave equation, the effects of polarization are included. Extensions of the analysis method to include material anisotropies are also discussed.
Multiple pulse gain switched operation of surface-emitting semiconductor lasers
Authors: Mahbobzadeh M. , Mukherjee A. , Brueck S. R. J.
Published: February 2023

Surface-emitting semiconductor lasers are attractive for applications in optical computing, coherent communications, high-power two dimensional arrays, and integrated optoelectronics. For applications involving information processing, high speed pulsed operation of these lasers is necessary. The very short cavity length (~2–5 μm) results in a very short transit time; however, the required high-Q resonator substantially lengthens the cavity lifetime, and hence the gain-switched pulsewidth. Recent optical pumping experiments have demonstrated ultrafast gain-switched operation with pulse widths as short as 3.9 ps. In this report, we present the first results on optically pumped double-pulse excitation with pulse delays as short as 10 ps. Independently switched high-bit-rate multiple pulse trains are required for transmitting information. For pumping with a pair of time delayed pulses, we observe output pulse separations shorter than the input pulse separation. This suggests the use of SELs for optical multiplexing and signal processing. Output pulse separation and pulse width as a function of the input pulse separation at a constant pump power show good agreement with the theoretical simulation. For large pulse separations, the input and output pulse separations are identical. The shortest output pulse separation having a 7:1 peak to background ratio, for a BER of <10−9, was about 35 ps for an input pulse separation of 50 ps. This is readily extendable to smaller pulse separations for higher speed pulses by using lower-Q resonator structures.
Simple model for carrier spill-over in quantum-well lasers consistent with local charge neutrality
Authors: Cai Y. , Engelmann R. , Raghuraman R.
Published: February 2023

For separate confinement heterostructure (SCH) quantum well (QW) lasers, carrier injection levels can be controlled by changing cavity losses. In the low injection case, carriers are confined within the QW, and spill-over into the barrier can be neglected. In the very high injection case, on the other hand, carriers in the barrier are dominant, and the QW contribution becomes insignificant. In the intermediate injection range, carrier distribution in both QW and barrier need to be taken into account. A simplified band filling model is developed for this case, in which charge neutrality condition plays a very important role with the band-offset ratio used as an adjustable parameter. Because of the structural difference between conduction and valence bands, the band offset ratio may be very sensitive to the charge neutrality criterion in both QW and barrier. For a particular SCH InGaAs/GaAs QW device (7.5 nm QW, 250 nm barrier) that we have studied in detail, local charge neutrality forces the conduction band offset ratio, Qc, to change from 0.60 to 0.63, for injection levels (described by total number of carriers) ranging from 0.2 × 1013 to 8.5 × 1013 (cm−2). Gain spectra are calculated based on the model including QW and barrier transitions.
Polarization-selective computer-generated holograms in birefringent media
Authors: Ford Joseph Earl , Xu Fang , Urquhart Kristopher , Fainman Yeshayanu
Published: February 2023

Computer-generated holograms with arbitrary function for the two linear polarizations are demonstrated using surface relief etched birefringent substrates joined face-to-face.
Observation of adiabatic compression of fundamental solitons in optical fibers with higher-order dispersion
Authors: Mamyshev Pavel V. , Wigley Peter G. J. , Wilson James , Stegeman George I. , Semeonov V. A. , Dianov Evgeny M.
Published: February 2023

We demonstrate the compression of a fundamental soliton down to 55 fsec based on a combination of higher order dispersive effects and the soliton self-frequency shift.
Quantum trajectory theory for cascaded open systems
Authors: Carmichael Howard J.
Published: February 2023

The theory of open systems is used in quantum optics in two distinct ways: to model sources of light such as lasers and parametric oscillators, and to describe the response of irradiated cavities and atoms. Sometimes the two applications are used in combination; first, statistical properties of the field radiated by a source are calculated, and these are then used in a separate calculation to determine the response of a system that is irradiated by the source. But the usefulness of this approach is quite hunted. It is essentially limited to coherent sources and certain broadband sources such as broadband squeezed or chaotic light. There exists no general theory for cascaded open systems - a theory that gives the response of system B to radiation emitted by system A when there exists an open-systems treatment for A and B separately. In this paper I develop such a theory using the quantum trajectory formulation of open systems. The source A and irradiated system B are described by a single stochastic wave-function. Generally the wavefunction describes an entangled state of the A and B subsystems. In the quantum trajectory formalism the wavefunction undergoes a coherent evolution governed by a nonunitary Schrödinger equation, interrupted at random times by wavefunction collapses. I derive the nonunitary Schrödinger equation and the form of the collapses. I illustrate the theory with some simple examples and discuss potential applications to problems involving the interaction of atoms with nonclassical light.
A new E-O focusing lens for higher-density optical disks
Authors: Osato Kiyoshi , Kino Gordon S. , Kubota Shigeo
Published: February 2023

We describe a new electro-optic focusing lens using PLZT as a fine focus adjustment for an SHG green laser optical disk pickup system.
Photoemission studies of semiconductor clusters
Authors: Colvin Vicki , Wadill G. D. , Tobin J. G. , Alivisatos A. P.
Published: February 2023

The valence band maximum of semiconductor clusters shifts with size. We attribute this phenomenon to both quantum confinement and dielectric solvation effects.
Multi-target tracking system based on a joint transform correlator and a neural network algorithm
Authors: Kim Eun-Soo , Yi Sang-Yi , Yoon Sang-Ro
Published: February 2023

Multi-target tracking systems have been under intensive study and in use for many years for a number of applications. More recently, emphasis has been placed on the application of real-time multi-target tracking procedures to situations involving large number of targets. In this paper, we describe a hybrid optoneural system to tackle real-time multi-target tracking. In our system, an optical joint transform correlator is used for real-time adaptive target tracking. But, because of many correlation signals in multi-target tracking problem, a data association algorithm can be used to associate each of the peak's correlation signals to the correct trajectories of the target's motion. Since the computational load on the conventional tracking algorithms increases rapidly with the number of targets tracked, in this paper, a new simple Hebbian learning algorithm is introduced to obtain the respective moving probabilities of the multi-target in real-time, and the data association is achieved in Hopfield optimization neural networks.
Intensity autocorrelation measurements of an AlGaAs diode laser
Authors: Westling L. A. , Lopes W. A.
Published: February 2023

We present measurements of the intensity autocorrelation function of the output of a free-running GaAlAs diode laser. To our knowledge these are the first such measurements performed on the output of semiconductor lasers. Our data displays large structure at the relaxation oscillation frequency and shows that the presence of many small secondary modes that accompany the predominant mode in so-called single-mode diode lasers have a significant effect on the fluctuations of the total output of the laser. The autocorrelation function reveals features that depend on the number of secondary modes lasing and, in fact, could be used to measure how many contribute to the fluctuating intensity. The correlations of these features damp away faster than the relaxation-oscillation features. The damping can be modelled by a simple multimode phase diffusion model. Our measurements also show that measurements of the intensity autocorrelation function of the output of a diode laser are a sensitive indicator of the presence and magnitude of external optical feedback.
Random walk point spread functions—characteristics and applications
Authors: Stossel Bryan J. , George Nicholas
Published: February 2023

Characteristics of the random walk point spread function (psf) consisting of a set of N impulses randomly distributed within a pre scribed region in space and the associated transfer function are presented. We show that the effect of the multiple point psf is similar to that of a low pass filter having a peak value proportional to N
2
and an asymptotic value proportional to N at high spatial frequencies. The occurrence of zeros in the transfer function is also considered. A statistical argument is used to demonstrate that the zeros for this special transfer function present little difficulty in recovering images blurred by the random walk psf. This result is verified numerically, and we present a table summarizing the number of zeros per unit area for several common blur functions. The effects of the number of impulses and their spatial distributions on the occurrence of zeros is also considered. The relatively few number of zeros in the transfer function permits high fidelity reconstructions to be obtained by using a modified inverse filter. Several images are coded and recovered to show the general applicability of the method. Additionally, the low pass nature of the blur function allows improved compression ratios to be achieved by using the coded image, as compared to the original scene. We describe the noise using a quality factor to characterize the decompressed and decoded images. Excellent recovery is obtained.
Optical neurodevices using a smart detector array
Authors: Kyuma K. , Ohta J.
Published: February 2023

A smart detector of GaAs-based MSM structure that has the functions of variable sensitivity and analog memory has been developed. The variable sensitivity is based on the phenomenon that the photocurrent is proportional to the electric field applied to the electrodes. The analog memory is based on the optical properties of impurities in the GaAs film. This detector is quite useful as an optical synapse because of the analog operation, memory function, and simple structure for a 2-D integration. Two kinds of novel neurodevices are introduced. The first device is an optical learning chip with analog memory. Its functions are to acquire the knowledge, to store it as the synaptic weights at learning phase, and to perform the vector-matrix multiplication at retrieval phase. The optical learning chip consisting of a 32 × 32 smart detector array and a line-shaped LED array with 32 elements, which are monolithically integrated on a GaAs substrate, was fabricated. The pattern classification experiment was successfully performed. The second device is an artificial retina for direct image processing. The input image is projected on the 2-D smart detector array as the synaptic matrix. The function of the retina can be chosen by an electric control signal as an input vector. Edge detection was successfully made by using the artificial retina with 64 × 64 elements.
Silicon smart spatial light modulators for optical computing
Authors: Neifeld Mark A. , Tabib-Azar M. , Hsiang Pin-Ju , Garcia-Valenzuela Augusto
Published: February 2023

We have investigated two novel techniques for the realization of smart SLMs in silicon. In this paper we discuss an array of electrostatically driven tortional mirror micro-machines. Since these devices are fabricated in silicon, it is natural to integrate photodetectors and processing electronics with the mirror arrays. In the simplest such smart SLM the deflection of each mirror is determined by the intensity of the light incident on an associated photodetector. In more sophisticated designs neighboring pixels may be connected through simple processing electronics to produce mirror deflections in response to local image characteristics such as gradients or averages. This class of device will find application in many areas of optical processing including optical interconnects, optical switching, optical image analysis, and optical neural networks. We will discuss the fabrication of mirror arrays and the electrode strips that are used to actuate them. It is expected that two-dimensional arrays with pixels of 50 μm × 50 μm can be easily fabricated and will yield operating frequencies up to a few kilohertz; however, the results presented here concern the fabrication of eight-element, one-dimensional devices with pixels of 50 μm × 750 μm. The resonant frequency and deflection vs. applied voltage of the fabricated devices are measured and compared with theoretical predictions.
Nonlinear dynamic effects from TE-TM coupling in periodic waveguides
Authors: Sankey Norris D. , Brown Thomas G.
Published: February 2023

The free carrier dynamics and all-optical switching effects in a periodic waveguide were studied in a pump-probe arrangement. A Bragg reflector resonant with the TE0 mode of the waveguide was fabricated to provide the periodicity of the structure. Two couplers were fabricated on either side of the Bragg grating to accommodate efficient coupling for a TM pump signal and TE probe signal. Nd:YAG pulsed and cw lasers at λ =1.064 μm are used as the pump and probe beams, respectively. The reflected signal from the TE0 mode was monitored to study the nonlinear dynamical effects and the free carrier dynamics in the silicon-on-insulator structure. Measurements from Bragg reflectors ranging in periods from 0.16 to 0.1625 μm at various pulse energies will be presented.
Optical instabilities in doped fiber amplifiers
Authors: Liou Lisa W. , Agrawal Govind P.
Published: February 2023

Optical fibers doped with rare-earth ions, such as erbium and neodymium, have attracted considerable attention in view of their applications in light-wave communications and mode-locked lasers. Such doped fibers can be modeled by the Maxwell-Bloch equations, commonly used for two-level atoms, generalized to include the effects of group-velocity dispersion and self-phase modulation induced by the host fiber. This paper discusses optical instabilities inherent in doped fiber amplifiers by considering the steady state solution of the Maxwell-Bloch equations and investigating its stability through a linear stability analysis. Particular attention is paid to the modulation instability occurring even in undoped fibers. Numerical simulations are used to study the growth of perturbations in the nonlinear regime, where the linear stability analysis becomes invalid. The results have implications for mode-locked fiber lasers.
Optical design of a light-tunnel illumination system for a 193-nm photolithographic projector
Authors: Gortych J. E. , Progler C. J. , Hibbs M. , Goodman D. S.
Published: February 2023

The optical design of a light-tunnel illumination system for a prototype 193-nm excimer-laser-based photolithographic stepper is presented. We discuss the system design requirements and establish the first-order layout using paraxial matrix methods. We also discuss the aberrations that have the most impact on image formation and point out the key tolerance considerations. Throughput concerns relating to the laser relay optics, the illuminator, and the projection lens are also addressed. The condenser is installed on a stepper, whose I-line lens was replaced by a one-of-a-kind 10 × 193-nm refractive lens with N.A. = 0.35 and a field size of 10 mm2. Measurements of uniformity, as well as lithographic results from the system, are presented.
The angle eikonal of a diffractive optical element
Authors: Walther Adriaan
Published: February 2023

A curved refractive or reflective interface coated with a diffractive optical element can be characterized by two properties: it forms a perfect image of itself, and rays traversing the surface incur a discontinuous change in optical path length. I show how these two properties can be used to construct the angle eikonal of the surface in a simple, straightforward manner. The technique presented will be used to derive several theorems concerning the system corrected for spherical aberration for all conjugates that was discussed by David Shafer at last year's conference.
Planar Paul traps and trap arrays
Authors: Devoe R. G. , Brewer R. G.
Published: February 2023

We report the laser cooling and trapping of barium ions in a novel planar Paul trap. Unlike other rf quadrupole traps, the electrodes of a planar Paul trap are confined to one or more parallel planes. They may therefore be constructed on a micrometer scale by the same photolithographic techniques used for semiconductor devices. Such devices are under construction in our laboratory. Micro-traps permit entirely new studies, for example, superradiance of a few ions, which occurs as ion-ion distances approach one wavelength of light. Photolithography can also generate an array of traps on a single substrate for an atomic clock. Our traps consist of one or more parallel planes, one above the other, each plane having either a conducting ring or a hole in a conducting sheet. Thus, a ring or a hole results in a potential well for trapping. A three-ring design produces a quadrupole potential that is harmonic up to eighth-order for a particular choice of ring diameters and spacings. Three-hole traps have been constructed with inner hole radii ranging from 50 to 400 μm, and both single barium ions and clouds have been observed.
InP based transceiver modules for optical subscriber networks
Authors: Carter A. C. , Williams P. J.
Published: February 2023

The development of a range of subcomponents and a common integration technology for preparing InP based OEICs for subscriber access systems is described. The development of suitable packaging techniques for incorporating these devices in transceiver modules is also discussed. OEICs are seen as an advantageous route for achieving the type of high functionality devices that are required in these systems, offering the potential of low cost and high reliability. Device functionalities include lasers, waveguides, broad and narrow band WDM, power monitoring, and signal detection. To this end, we have prepared OEICs incorporating DFB and DBR lasers, waveguides, process tolerant couplers, wavelength duplexers, add-drop narrow band WDM components, optical filters, and monitor diodes. Laser-waveguide integration is achieved by a butt coupled approach using low pressure MOVPE. The process is designed to be high yielding and is suitable for high volume OEIC fabrication in future manufacture. OEICs so far developed include those incorporating lasers with wavelength duplexers for 1300/1530 nm bidirectional links, lasers with wavelength duplexers and an additional coupler for bidirectional telephony (1300 nm) and broadband (1530 nm) services, and lasers with narrow band WDM components providing add-drop optical multiplexing facilities.
A photonic integrated circuit technology for coherent optical processing
Authors: Vawter G. A. , Hietala V. M. , Kravitz S. H. , Carson R. F. , Armendariz M. G. , Hadley G. R.
Published: February 2023

A complete photonic integrated circuit (PIC) technology for coherent homodyne and heterodyne optical signal processing is presented. The GaAs/AlGaAs PIC is based exclusively on integration of waveguide phase modulators with interconnecting waveguides, directional couplers, turning mirrors, and gratings. Emphasis is on simplicity of fabrication and high yield of complex PIC designs achieved through the use of only one or two etch steps to define the PIC followed by conventional isolation and metalization steps. Current progress on critical device and fabrication technologies will be discussed. These include high resolution ridge-waveguide etching for definition of directional coupler waveguide power splitters, fabrication of ridge-waveguide phase modulators, without significant bias-dependent absorption modulation, as well as alignment and etch issues for turning-mirrors and gratings. Finally, all of these elements are designed for integration into a single PIC without epitaxial regrowth. Fully integrated Mach-Zehnder amplitude modulators are demonstrated. Systems applications of this PIC technology, including optical frequency modulation of an input single-frequency source, tunable bandpass optical filters, and complete control of frequency and far field of a phased-array radar antenna, will be presented.
Structure and dynamics of OH/D-Rg complexes
Authors: Heaven Michael C.
Published: February 2023

The open-shell van der Waals complexes OH/D-Rg (Rg = Ne, Ar, Kr) have attracted much experimental and theoretical attention during the past few years. These complexes are easily detected and small enough for rigorous theoretical treatment. Large differences in the intermolecular potential energy surfaces for the ground (X2∏) and electronically excited (A2∑+) states permit the observation of progressions of intermolecular vibrational modes. Potential energy surfaces have been derived from analyses of the ro-vibronic level structures. Dissociation energies of the OH/D(A)-Rg bonds were found to be 160 (Ne), 1062 (Ar), and 1840 (Kr) cm−1.
Analysis of single-frequency linear cavity fiber lasers that utilize intra-core Bragg gratings
Authors: Ball G. A. , Glenn W. H.
Published: February 2023

Continuous wave single-frequency lasers are required in a wide range of communication, sensor, and spectroscopic applications. Typically, linear resonators are not used in single frequency laser design because of the detrimental effects of spatial hole burning. This paper will focus on linear fiber lasers that utilize intra-core Bragg reflectors for cavity feedback and mode discrimination. In particular, the design constraints required to achieve single longitudinal mode operation from a standing-wave, homogeneously broadened, three- or four-level, fiber laser that utilizes intra-core Bragg reflectors for cavity feedback will be presented. Given the rare-earth doped fiber and Bragg reflector characteristics, a closed form solution describing the single-frequency operation regime, relative slope efficiency, and relative fiber laser stability is determined. Analytical and experimental results will be presented.
Dynamics of structure formation and optical vortices in nonlinear resonators
Authors: Kreuzer M. , Neubecker R. , Schierhorn R. , Tschudi T.
Published: February 2023

Structure formation, symmetry breaking, and optical vortices are typical spatial phenomena in NLO feedback systems, which have found growing interest in the last decade. The system we investigate consists of a Fabry–Perot resonator with planar mirrors spaced from 50 μm to some centimeters and an intracavity NLC film as an optically nonlinear medium. In our studies we use the optically induced reorientation of the molecules as the optical nonlinearity. As long as the diameter of the input beam does not exceed the spatial resolution of the NLC we observe optical bistability. Using larger beam sizes leads to complex dynamic behavior accompanied by the formation of spatial structures with broken symmetry. The Gaussian input beam decays into a number of spots with a certain diameter trying to form a maximum packing density inside the illuminated area. Observing the phase of transmitted light holographically, we found phase singularities (from their helixlike structure) in the area between such spots. It seems that the appearance of these phase singularities are concomitant phenomena of competition effects between neighboring spots during the self-organizing process of structure formation.
High sensitivity second harmonic imaging method
Authors: Yan C. , Diels J. C.
Published: February 2023

Using high intensity femtosecond laser pulses (>40 MW peak power), we have successfully performed second harmonic imaging through strongly scattering material. An object is illuminated by femtosecond pulses, and the back-scattered and reflected light from a different part of the object is gated by a femtosecond reference pulse through the second harmonic crystal. Three-dimensional images with high depth resolution are obtained by this range gating method. Very low reflecting surfaces, such as soft contact lenses merged in water solutions (normal surface intensity reflectivity is less than 1%), are also being detected by this imaging method. Different imaging objects have been tested. Results show a good signal to noise ratio by using a type II phase matching crystal. This new imaging method can be applied to medical diagnostics, such as imaging an object through human tissue or the low reflectivity fine structure of an eye. It is also an extension of conventional microwave image radar to the optical range with a much higher resolution.
Fluorescent imaging approach to the automatic determination of chromosome damage
Authors: Smith Warren E. , Maislin Seth A.
Published: February 2023

Chromosome damage is produced by several types of agents, including ionizing radiation. There is a need for rapid measurement of such damage in the event of an accident to assist in the determination of the extent of exposure and the planning of consequent therapy. In current practice, radiation damage is measured by operator-intensive analysis of microscope images of suitably prepared lymphocyte chromosomes from the exposed individual. Some of the features looked for are chromosome breakage, dicentrics (chromosomes with two centromeres), and chromosome translocations (unnatural joining of chromosomes).
The effect of aberrations on bispectral imaging
Authors: Zhang J.-Y. , Dainty J. C.
Published: February 2023

Bispectral imaging is one of the most promising methods for high angular resolution imaging through turbulence. On astronomical objects, crowded star fields with individual stars as faint as 16th magnitude have been imaged by Weigelt et al. with a 1.5 m telescope in a few minutes of observing time. One virtue of the technique is its claimed insensitivity to telescope aberrations. In this paper we present a computer study of the effects of aberrations (including de-focus) on the bispectral transfer function. Two major conclusions can be drawn: (i) as the seeing deteriorates, the bispectral transfer function becomes less sensitive to telescope aberrations, and (ii) the average phase of the bispectral transfer function is not exactly zero for a finite number of images, and its departure from zero (for a fixed number of images) increases as the aberration increases.
Performance limitation of optical shadow casting correlator for image morphology
Authors: Raj K. , Prather D. W. , Athale R. A. , Mait J. N.
Published: February 2023

A shadow casting correlator is an incoherent optical image correlator in which the point spread function (PSF) is encoded via a 2-D source (LED/laser diode) array. The shadow casting correlator is well suited for implementing image morphology where the structuring element (realized via the PSF) is binary and needs to be updated rapidly to realize complex algorithms. In this paper we analyze the performance limitations of optical shadow casting correlators in implementing image morphology in the light of the geometrical optics approximation inherent in shadow casting systems. The analysis of the optical systems suggests that the angular divergence of the sources is the crucial parameter in determining the maximum space-bandwidth products of the image and structuring element achievable with the shadow casting correlator. The angular divergence constraint is overcome by steering the different source elements. Analytical results are presented that identify a set of values for the system parameters capable of handling a 512 x 512 image and a 32 x 32 structuring element. Experimental results verifying the analytical model will also be presented.
Gain modulation of a two-mode laser
Authors: Georgiou M. , Mandel P. , Otsuka K.
Published: February 2023

We report on the bifurcation structure of a gain modulated two-mode solid state laser in a Fabry-Perot configuration. We concentrate on the good cavity limit, and we use the rate equations that describe the interaction between the population inversion (including the influence of hole burning) and the photon dynamics. The unforced problem allows in its transient behavior for a new oscillation frequency that is much lower than the relaxation oscillation frequency. Our aim is to explain the lasing mode dynamics through the interplay between these two frequencies. We analyze the response of the laser as a function of the modulation frequency. We differentiate between the cases of small and deep modulation. In the former case, the bifurcation diagram exhibits resonance behavior in the vicinity of the two internal frequencies as well as regions of multistability. In the latter case, where the modulation brings the laser below the second threshold (the one that signifies the onset of the two-mode solution) for part of the cycle, a rich bifurcation structure has been found with regions of multistability, period doublings, bifurcations to torus, and chaos. In the case of multistability, the fine structure for each branch of periodic solutions can be related to the two frequencies.
A broadband SCM communication system using multiple beam modulation
Authors: Tian R.S. , Xia X. Q. , Ih C. S.
Published: February 2023

The characteristics and performance of a light-wave SCM system with multiple beam modulation is described. The microwave sub-carriers are formed automatically by heterodyne transmitters employing multiple laser beams. A 10-channel SCM can be easily fit into a WDM division of 1 nm. Phase-locked loops are used to lock the frequencies of the beams. The relative frequencies of beams, which are locked by monitoring the beat frequencies, are in the tens-of-gigahertz range. They can remain stable within the megahertz range. These SCM channels are identified and demultiplexed by microwave sub-carrier frequencies but not directly by optical wavelengths, thus their exact wavelengths and their stability are less important. A heterodyne transmitter with three frequency-locked beams at sub-carrier frequencies of 21 GHz and 17 GHz and modulation/demodulation of these sub-carrier frequencies with a 1 Gb/s signal have been demonstrated. The sub-carrier frequency can be easily tuned from 3 to 21 GHz. The sub-carrier can be readily extended to higher frequencies by using faster photodetectors. By incorporating SCM within WDM, the capacity can be greatly increased without requiring super stable lasers and high resolution optical filters.
Spatial filtering of atmospheric decorrelations and its application to interferometry
Authors: Prasad S. , Loos G.
Published: February 2023

Interferometric, or aperture synthesis, imaging of faint astronomical objects requires large collecting aperture diameters. For ground-based imaging, the presence of the atmosphere serves to limit the aperture diameters to values no greater than r
o
, the atmospheric spatial coherence scale, unless the star wave front is processed adaptively or otherwise. We present here an application of low-pass spatial filtering as a technique of enhancing the spatial coherence in each aperture beyond r
o
by eliminating the high spatial frequencies of the atmospherically induced wave-front aberrations. We shall show that although spatial filtering of a wave front reduces the signal power throughput, reduction is more than compensated for by the increased spatial coherence in each aperture. By analyzing the coherence loss factor in a two-aperture Michelson stellar interferometer, we demonstrate a clear improvement of the sensitivity of the interferometer when a spatial filter is used in each arm. A possible implementation of spatial filters in an adaptive optics setup will also be discussed.
Observation of quantized motion in optical potential wells in 1-D optical molasses
Authors: Jessen P. , Speeuw R. J. C. , Westbrook C. I. , Gerz C. , Phillips W. D.
Published: February 2023

We have measured the spectrum of fluorescence from 85Rb in 1-D optical molasses. The spectrum consists of a central peak and one set of sidebands characteristic of quantized atomic motion. In a 1-D molasses consisting of two counterpropagating, linear, and orthogonally polarized laser beams, optical potential wells are spaced λ/4 apart where the polarization is circular. Polarization gradient cooling reduces the temperature to a point where the atoms are trapped in these wells. The atomic motion is approximated by a quantum mechanical harmonic oscillator. We interpret the central peak as transitions beginning and ending in the same bound level and the sidebands as Raman transitions changing the vibrational quantum number by ±1. The observed level spacing in the well is proportional to the square root of the light shift. The relative strength of the blue and red sideband is given by a Boltzman factor, allowing us to determine the temperature. As expected, the temperature increases linearly with the light shift.
Multichannel optical system for a medical diagnostic analyzer
Authors: Swope C. H. , Link J. G. , Haugen D. G.
Published: February 2023

An optical analyzer has been developed to monitor biochemical reactions that are used in diagnostic tests, which are typically conducted in clinical hemostasis–thrombosis laboratories. The module measures changes in the optical transmission of up to 15 samples simultaneously at 35 wavelength bands from 395 to 710 nm. The full spectrum transmission data for all samples are collected five times per second. This is accomplished with the use of a 50 W tungsten halogen lamp and holographic diffraction gratings that produce a first order transmission spectrum across a 40 element linear array of Si detectors. A rotating shutter device makes it possible to use only five detector arrays for monitoring all 15 samples. The arrays are scanned synchronously with the rotating shutter. Signals from the diodes are integrated over time through a charge coupled amplifier. The gratings are used under the Bragg condition with an angular dispersion of 0.07°/nm in the first order and with peak efficiencies exceeding 50% at 475 nm. A digital to analog converter is used with the amplifiers to provide a variable gain for each detector element. This feature is used to normalize and optimize the detectors’ output signals.
Study of periodically modulated light beams by means of the moment generating function of the number of photo-pulses
Authors: Saiz J. M. , González F. , Moreno F. , Valle P. J.
Published: February 2023

The study of periodic signals is of great interest in many fields in physics: spectroscopy, optical communications, laser Doppler velocimetry, etc. The aim of the present work is to show a method that allows us to characterize this type of signal when the light intensity level is low (1–10 photoelectrons per period). In these situations, conventional techniques, such as multichannel analysis and measurement of the second normalized factorial moment, n(2)(T), would require a long measurement time to obtain the characteristic parameters with a satisfactory accuracy. The proposed method is based on the measurement of the moment generating function of the number of photopulses, Q
n
(s,T). For the sake of simplicity and in order to check the goodness of the method, a square wave modulated light beam of period P and modulation factor 2A was chosen. The behavior of the experimental errors in the determination of P and A was studied by means of a theoretical error model. Then, a set of experimental measurements was carried out for different situations. From the obtained results we can conclude that the Q
n
(s,T) measurement has two advantages compared with n(2)(T): the signal-to-noise ratio is greater, and the characteristic parameters of the signal can be obtained with less error in the same experimental conditions. These advantages are particularly enhanced when the fluctuating part of the signal is small and the light intensity is low.
VO2-V2O5 films for optical switching
Authors: Picard F. , Jerominek H. , Pan J. , Vincent D.
Published: February 2023

VO2 exhibits a reversible semiconductorto- metal phase transition at a temperature of about 341 K, accompanied by significant changes in its electrical and optical properties. Suggested applications of VO2 include optical switching and storage. Fabrication of the pure VO2 films and the films composed of a mixture of VO2 and V2O5 by the reactive dc magnetron sputtering technique is reported. The fabricated VO2 films exhibit a resistivity change up to 103 during the phase transition. Optical transmittance of these films changes from over 70% to below 1 % at wavelengths longer than 1 pm. Optical transmittance and contrast in the visible and near infrared parts of the spectrum are much lower. V2O5 does not exhibit a semiconductor-metal phase transition. Films composed of a mixture of VO2 and V2O5 retain some of the phase switching properties of vanadium dioxide. Moreover, their transmittance and contrast in the near infrared are increased, which makes these films more suitable for switching applications in this part of the spectrum.