bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-resolved measurements of modal spatial profiles in optical fibers
Authors: Painchaud Yves , LeBel Paul , Duguay Michel A. , Black Richard J.
Published: February 2023

Picosecond pulses of visible light from a mode-locked dye laser are injected into a 600-m fiber designed to be monomode at 1300 nm. Up to seven modes are excited and can be time resolved at the fiber output by an ultrafast photodiode and a sampling oscilloscope. A computer-controlled XY micropositioner is used to make the photodiode scan the far field spatial power profile of each time-resolved mode. The photodiode has a sensitive area that is small compared to the mode size. By plotting the peak power of each time-resolved mode as a function of x and y, we obtain a picture of a mode in flight. This permits unambiguous identification of each mode. The time position of each mode is measured relative to the fundamental mode as the dye laser is tuned over the 560–605 nm spectral range. The group-velocity dispersion curves thus obtained are used to model the refractive- index profile of the optical fiber through its effect on waveguide dispersion. The method is sensitive enough to show the presence of a dip at core center for one of the fibers studied and to pin down the core diameter with submicrometer accuracy.
Solitary waves consisting of bright and dark pulses in optical fibers
Authors: Hong B. J. , Yang C. C. , Wang L. K.
Published: February 2023

It has been discovered that a bright pulse in the anomalous-dispersion (AD) range and a dark pulse in the normal-dispersion (ND) range can support each other through cross-phase modulation to form a solitary wave when they copropagate at the same speed in an optical fiber. Such a solitary wave can be generated by launchinga bright soliton in the AD range and a long pulse of the same speed in the ND range into the fiber. The bright soliton is slightly modified, and a stationary dark pulse is generated on the long pulse. This dark pulse has a shape and phase profile quite different from that of any dark soliton. When a fundamental bright soliton is used for generating such a solitary wave, the soliton must be sharp (the normalized peak amplitude must be larger than 2.5). When a higher-order bright soliton is used, this bright soliton evolves into a pulse close to a soliton of a lower order. The results of this evolution depend on the energy of the input higher-order solitons. For example, a 3- soliton may evolve into a pulse close to a 2-soliton or a fundamental soliton.
Diode-pumped 2-μm lasers for the microjoule-per-pulse regime and beyond
Authors: Suni Paul J. , Henderson Sammy W.
Published: February 2023

Coherent laser radars require transmitters with pulse energies >1 mJ. We discuss the feasibility of building efficient diode-pumped 2-μm Tm and/or Ho lasers for such applications. Experiments and theory indicate that reaching 10-20 mJ/pulse at repetition rates >100Hz should be possible. Significant thermal problems are expected at higher energies.
Performance of a 2-μm laser in Tm:YAG grown by a laser-heated pedestal growth technique
Authors: Chang R. S. F. , Chaddha S. , Sengupta S. , Djeu N.
Published: February 2023

The laser-heated pedestal growth (LHPG) technique for rapid growth of laser crystals can provide small crystal rods at a lower cost than can bulk-growth methods. We have been able to grow a variety of rare-earth-doped garnets and fluorides. Controlled doping was achieved by mixing powdered dopant and host materials in our feedstock preparation. In this paper we report laser performance in Tm:YAG with a sample grown at our facility. The 3% doped sample was 1 mm in diameter and 3 mm long. The minirod had flat and parallel surfaces with an antireflection coating at 2 μm. An argon-pumped Ti:sapphire laser operating at 785 nm was used to end-pump the laser crystal, which was placed in a piano-concave resonator. With 6% output coupling, room temperature operation of this cw laser was observed at a threshold of 75 mw of absorbed pump power at a slope efficiency of 51%. This performance compared favorably with the performance of lasers using bulk-grown Tm:YAG crystals. We have shown that laser-quality crystals can be obtained with this growth method, which will allow us to rapidly study new laser host/dopant/codopant combinations.
Erbium and holmium lasers pumped with Nd:YAG
Authors: Anthon D. W. , Pier T. J. , Leilabady P. A.
Published: February 2023

Diode-pumped neodymium lasers can be used to efficiently pump other rare earth lasers. Intracavity pumping of the ytterbium-sensitized erbium phosphate glass laser gave 6% conversion of 800 nm laser diode arrays to 1.54 μm. Techniques used for pumping 2.9-μm Ho:GGG lasers are also discussed.
Organic materials for electro-optic and parametric devices
Authors: Khanarian Garo
Published: February 2023

Organic and polymeric nonlinear optical materials constitute a new class of materials for device applications. One of their unique features is the diversity of different molecular compounds that can be synthesized with differing nonlinear optical activities and transparencies. The molecules can be packed in a variety of noncentrosymmetric structures, such as crystals, poled polymers, and Langmuir-Blodgett films. They are also potentially more advantageous than inorganic materials because of their high nonresonant optical susceptibilities and low dielectric constants. Recent advances have been made in organic-based devices with glassy poled polymer films owing to their relative ease of fabrication by spin coating. Electro-optic Mach-Zehnder modulators and directional couplers with low switching voltages have been fabricated. Phase-matched second-harmonic generation in polymer waveguides has also been demonstrated. New organic crystals with very high nonlinear susceptibilities have also been reported for frequency doubling. Some of the key issues that will determine the future usefulness of these new materials is their environmental stability in the presence of light and high temperature; the integrability of organic materials with inorganic-based components, such as glass optical fiber, wafer substrates, lasers, and detectors; and finally, the development of a manufacturing technology that is both highly precise and relatively inexpensive.
In situ observation of compositional gradients during OM-VPE growth of AlxGa1-xAs
Authors: Sankur Haluk O. , Southwell William H. , Hall Randolph L.
Published: February 2023

Many optical and optoelectronic device properties depend on the precise control of the composition and thickness of the layers and on the abruptness of compositional steps. Properly designed gas delivery systems in OM-VPE reactors can achieve abrupt steps in gas composition, but not necessarily in the solid material of the epilayers. We have observed composition gradients at the interfaces, during OM-VPE deposition of AlxGa1-xAs, by in situ optical reflection and postdeposition spectrophotometry. A depth profile of the composition was measured by sputtering SIMS and it was compared to the profile obtained by the analysis of in situ reflectance and spectral data. This work demonstrates the presence of compositional gradients in OM-VPE-grown materials, even when the gas-delivery system is designed to achieve abrupt steps in gas composition. Possible mechanisms for the formation of gradients, techniques to achieve abrupt composition steps in the layers, and the usefulness of in situ techniques to characterize the OM-VPE deposition of semiconductors will be discussed.
Finite-element approach to modeling photorefractive grating formations
Authors: Brost George A.
Published: February 2023

We describe a computer modeling technique for calculating photorefractive grating formations in which the chage redistribution and grating formations are calculated by means of a finite-element approach. This method provides time-dependent field and charge distribution characteristics without requiring the small-modulation-index approximation. This approach can be applied to both cw and pulsed laser interactions. The computational time required to model picosecond and nanosecond grating formations is minimal, but the computational time to model cw laser interactions is usually substantial. However, a "quasi-steady-state" approximation can often be applied, which reduces the computational time significantly. This approximation allows the calculation of the steady-state field and charge distributions and in many cases still provides useful time- dependent information.
Spatial self-action effects: self-bending and dark solitons
Authors: Swartzlander G. A. , Andersen D.R. , Kaplan A. E.
Published: February 2023

The self-bending effect (i.e., the deflection of the trajectory of a laser beam in a third-order nonlinear material) is a fundamental phenomenon associated with the propagation of a beam with an asymmetrical intensity profile that forms a self-induced prism in a nonlinear refractive medium. This effect was predicted more than 20 years ago, and a few experimental pulsed-laser observations have been made. Recently we made the first cw observation and detailed measurement of self-bending by using sodium vapor and materials with a thermal nonlinearity (e.g., gasoline). We also used this effect for spectroscopic measurements of the nonlinear refractive index in sodium vapor and semiconductors (ZnSe) by measuring the self-deflection at various frequencies. Possible applications of self-bending include radiation protection and optical limiting, optical bistability and interconnecting, nonlinear coupling, and ultrafast beam scanning. Various incident-beam intensity profiles may result in other spatial self-action effects. In particular, by using these same materials and an amplitude grating (a wire mesh) as a mask for the incident beam, we made the first observation of spatial dark solitons. The formation of a stable grid of dark soliton stripes inside a nonlinear (defocusing) material and remarkably tightly organized nonlinear diffraction patterns in the far-field area behind the nonlinear sample were demonstrated. Our computer simulation and analytical calculations verified the soliton nature of the observed phenomena.
Optical resonators as waveguides for self-phase modulation in intercavity bulk media
Authors: Lee Chi H.
Published: February 2023

Self-phase modulation (SPM) in a Kerr medium has been widely used to spectrally chirp and broaden an optical pulse for pulse compression.1 To compress a high-energy pulse directly, spectrally broadening and chirping the pulse by SPM in a bulk material is necessary. However, the nonuniform beam's spatial profile results in the spatial chirping effect. A stable optical resonator can be used as a large-scale, periodic waveguide for multipass SPM in a bulk medium. We show that a resonator can tolerate a round-trip B integral (maximum on axial, nonlinear phase shift) of 3.6 and still be stable. The calculated results show that the temporal SPM is able to accumulate through multiple passes while the growth of the spatial chirping is restrained. In 10 round trips, the total B integral that is useful for SPM can be as high as ~36, but the effective B integral associated with spatial chirping remains at 1.13. Experimental results of multipass SPM in a Nd-glass regenerative amplifier2 confirm the calculations. The total B integral useful for SPM is found to be ~30. We have studied the switched-outbeam sizes of amplified pulses of short and long durations, which correspond to the cases with and without the self-focusing effect, respectively. We have deduced the effective B integral associated with spatial chirping tobe <1. Such multipass self-phase modulation in an intracavity bulk medium combines the advantages of the confinement characteristics of waveguides and the high power-handling capabilities of bulk media.
Titanium oxide films of various stoichiometries: optical properties
Authors: Chiao Shuchung , Bovard Bertrand G. , Macleod H. Angus
Published: February 2023

The oxygen content of titanium oxide films determines their optical properties. It is well known that temperature, deposition rate, and oxygen partial pressureare the three major parameters in reactive evaporation. Based on this information, with a fixed substrate temperature and deposition rate, we should be able to control the stoichiometry by varying the O2 pressure. This was done in our Balzers 760 high-vacuum chamber. The starting material was Ti2O3. Films 100 nm thick were deposited on carbon substrates. Ti/O ratios were examined by Rutherford backscattering spectrometry (RBS), and the relationship between Ti/O ratios and O2 pressures was established. We were able to determine different stoichiometries in titanium oxide films with reasonable reproducibility. Optical properties of thin films of TiOx are presented along with RBS results.
Reactive ion-assisted deposition of boron nitride and aluminum nitride
Authors: Olinger Dale Kent , Bovard Bertrand G. , Macleod H. Angus
Published: February 2023

Vacuum deposition techniques for boron nitride, aluminum nitride, and mixtures of the two materials have been developed. Starting materials of the pure metal or nitrides are electron-beam evaporated. The films are grown on glass, fused silica, and silicon substrates by reactive nitrogen ion-assisted deposition. A large 12 cm Kaufman-type ion source was used in this work. The goals of the study included development of these materials for visible-wa velength coatings and examination of the potential for Restrahlen mirrors in the infrared region. Matching deposition parameters that gave acceptable transmission characteristics in the visible spectrum for each material were developed. A technique was then developed to accomplish simultaneous codeposition of the two materials. Analysis of the films has been accomplished through both visible and infrared spectrophotometry. Results for boron nitride, aluminum nitride, and mixtures of the two are presented. Continuation work is planned to further develop these materials and expand the analysis techniques employed.
Spectrally opponent central mechanism of chromatic adaptation
Authors: Humanski Richard A. , Shevell Steven K.
Published: February 2023

Under haploscopic viewing conditions, long-wavelength adaptation of one eye changes the perceived redness/greenness of a test presented to only the opposite, dark- adapted eye. We demonstrate that this central mechanism of chromatic adaptation depends on the wavelength of the adapting light presented to the test eye in a manner characteristic of a chromatically opponent process. Perceived redness/greenness was quantified by measuring red/green (r/g) equilibria over a 2 log unit range of test-field levels. The effect of the central mechanism was mea sured by the change in the spectral composition of the test field caused by raising the level of a 660 nm non-test-eye adapting light from 0.5 to 2.0 log td. The dependence of the central effect on test-eye wavelength was determined by varying the wavelength of a 0.5 log td, test-eye adapting field over 540-660 nm. The results demonstrate that with middle- wavelength (540 nm) test-eye adaptation the effect of the central mechanism is exaggerated, whereas with long-wavelength (660 nm) test-eye adaptation the effect is reduced in comparison to non-test-eye (i.e., dark) adaptation. Furthermore, a range of test-eye wavelengths near 580 nm mimic test-eye dark adaptation.
Spatial factors determining field additivity of the middle-wavelength cone pathway
Authors: Schirillo James , Reeves Adam
Published: February 2023

Field additivity depends on the spatial relations between test and field. By means of a 2AFC method, 20% subadditivity was found in detecting a 1° test flashed for 200 ms on one degree fields. This held for a 530 nm test (at one log unit above absolute threshold) on fields of 481 nm, 622 nm, and a mixture of the two. It also held for a 500 nm test on fields of 530 nm, 610 nm, and their mixture. This agrees with Foster's (1981) hypothesis that coincident edges elicit processing at opponent sites ("spectral sharpening"). Additivity was found with 1° tests on 10° backgrounds (Stiles' conditions), and 3.6' arc tests on both 8.6' arc and 10° backgrounds. In the spatially coincident, subadditive conditions, the variance of the threshold was greater on the mixed than on the pure fields. Correspondingly, the psychometric function was shallower on the mixed than on either pure field. The 530 nm 3.6' arc test flashed on its 10° background(s) produced additivity, but it also produced a shallower slope on the mixed field. This implies that under some spatial configurations the psychometric curve is only additive over a limited range.
Temporal tuning of Fechner–Benham subjective color
Authors: Billock Vincent A.
Published: February 2023

Saturation of Fechner–Benham subjective colors depends on the spatiotemporal properties of the inducing stimulus. This dependence can be explained by the properties of the Type I cell signal. Type I cells multiplex hue and luminance by adding and subtracting the center and surround spatiotemporal filters. Because the resulting color and luminance filters overlap in both frequency and phase space, the results of any demultiplexing process are ambiguous for some spatiotemporal stimuli. Therefore, according to signal detection theory, the saturation of an illusory color inferred from that ambiguity should be proportional to the degree of overlap between the encoding filters. Assuming equal sensitivity for color and luminance at the decoder, Billock (1989) used Kelly's (1983) color and luminance CSFs to predict the temporal-saturation tuning of subjective red. These results are improved for subjective red and extended to green and blue by using Grigsby and Ingling's (1989) and Kelly's (1974) estimates of R, G, and B Type I-like lateral inhibitory mechanisms. With no free parameters, the quality of the fit provides further evidence that the Type I hue and luminance multiplexing/demultiplexing operation is the locus of Fechner–Benham subjective color.
Steady state of a single longitudinal mode laser with inhomogeneous broadening and transverse effects
Authors: Hunter L. W. , Bandy D. K.
Published: February 2023

We consider an inhomogeneously broadened, unidirectional ring laser formulated in the traditional Maxwell–Bloch configuration of a two-level atom with transverse modes. We numerically analyze the steady state for a single longitudinal mode in the paraxial approximation, using the uniform-field limit with cylindrical symmetry and Gaussian profile for inhomogeneous broadening. Several domains of steady-state solutions are found for the resonant case in the good-cavity limit. Both single- and multiple-transverse mode solutions are observed; the expected TEM00 mode is seen in the limit of single-mode operation. The laser threshold is found to depend on the mode spacing (A1) as well as on the gain (2C) and the scaled Doppler broadening (σD). This means that as A1 is increased, the laser requires a larger gain to operate, up to a critical gain; beyond this critical gain, the laser threshold is independent of A1. Hysteresis between zero- and nonzero-intensity solutions at the laser threshold is obtained under realistic operating conditions for both increasing and decreasing 2C and A1 (i.e., for changes in the initial conditions). These distinct, but overlapping, domains of parameter space where both single- and multiple-mode steady states exist are qualitatively the same for increasing values of σD ≥ 1 and may indicate the presence of competing attractors.
Integrated optic tapped delay line
Authors: Hartman Nile F. , Corey Larry P. , Kenan Richard P.
Published: February 2023

An integrated-optic tapped delay line has been designed and tested. Potential applications include electro-optic time delay networks for beam forming and beam steering in phased-array antennas. In the latter, the delay line is used to deliver an optical signal that is intensity modulated at an rf frequency. Delays of a few nanoseconds are achievable; actual time delays are selected by electronically addressing grating-based switches integrated with optical waveguides. The integrated-optic device consists of a folded-path optical waveguide that provides long path lengths in a small, compact structure. Thick phase-reflective gratings are used as the reflective elements to achieve the folded configuration. The thick phase gratings also function as electronically addressable taps to provide time-delay selection. The taps offer the additional advantage that their transmittance is controllable by a dc bias field. This ensures a switching network capable of delivering a constant optical power to the detector which is used to convert the optical signal to an rf electronic signal. The delay line described in this paper is based on LiNbO3 waveguides.
Analysis of a high-power beam control system
Authors: Yee C. L. , Ferguson T. , Huang C. C. , Cuneo P. J. , Williams S. G.
Published: February 2023

The Alpha LAMP Integration (ALI) experiment combines the elements of a high power laser and a large segmented primary mirror. The purpose of the ALI experiment is to demonstrate beam control of a high power laser using Holographic Optical Elements on a large primary mirror. We present an optical propagation analysis of the ALI experiment. The simulation includes a physical optics description for beam propagation using standard Fourier methods with a realistic thermal distortion model for the mirrors. Also included in the optical simulation are realistic models for the wavefront correction and out-going wavefront sensor. In this paper, we show results quantifying the ALI performance and identify areas which can critically impact the performance of the ALI experiment.
An energetic requirement for photon-gated photochemical hole burning
Authors: Tamura S. , Kishii N. , Asai N. , Seto J.
Published: February 2023

Photochemical hole burning (PHB) is a promising recording technology for ultra-high-density, wavelength-multiplexed optical data storage. In this paper we report the influence of the free energy change of the electron-transfer reaction on the reactivity of photon-gated PHB. The PHB is induced by an electron-transfer reaction using zinc tetraphenylporphine (ZnTPP) in the higher triplet state as a donor and a series of acceptors with various reduction potentials. We obtained a preliminary energy requirement for PHB. The wavelength-selective light was from a dye laser tuned around 590 nm. The gating light was a 465 nm line of an argon-ion laser in accordance with the triplet–triplet absorption band of ZnTPP. For benzylbromide (−2.34 eV) and chloroform (−1.89 eV), neither single-photon nor photon-gated PHB occurred; the parenthesized values are the calculated free-energy changes for the electron-transfer reactions. However, photongated PHB was observed for ethylbromide (−1.43 eV) and amylbromide (1.30 eV). These results indicate that the reactivity of photongated PHB depends on the free-energy change, and PHB does not occur in the highly exothermic region.
AlGaAs photonic integrated circuits fabricated using chemically assisted ion beam etching
Authors: Grande W. J. , Johnson John E. , Tang C. L.
Published: February 2023

Photonic integrated circuits with a complete set of active and passive devices have been fabricated using a novel dry etching process in AlGaAs. Devices integrating lasers, waveguides, beamsplitters, 90° bends, and photodetectors are demonstrated.
Optoelectronic packaging for telecommunications
Authors: Boudreau R. A.
Published: February 2023

It has been estimated that optoelectronic packaging currently represents between 65 to 75% of the cost of fiber optic components. There have been rapid improvements in the area of semiconductor device performance, but the packaging of the devices remains a major bottleneck. This paper examines key packaging efforts that are defining future telecommunications packaging.
Anisotropy in laser forming of cold-rolled stainless steel
Authors: Namba Yoshiharu
Published: February 2023

Laser forming is a new metal-forming process that makes shapes by using laser irradiation. Cold-rolled AISI 304 stainless steel sheets have been cut into square samples and tensile-test samples. The former samples, which are 0.3 mm thick, have been irradiated with the defocused beam of a 100 W carbon dioxide laser. The samples were bent into a V-shape by repeated beam scans without the application of external force to the samples. The final bending angle of the irradiated samples was almost in proportion to the number of laser beam scans. This bending is caused by the thermal stresses that occur during the extremely rapid heating and cooling brought about by laser irradiation. The bending angle depends on the angle between the laser scan and the rolling direction because there is an anisotropy in the mechanical properties of cold-rolled samples.
Efficient mask pattern design for photonic circuitry
Authors: Liu P. L.
Published: February 2023

Mask patterns are typically designed by using computer-aided design (CaliforniaD) tools. They support such features as line, rectangle, circle, and arc generation. The mask pattern is composed of enclosed areas defined by these line-drawing features. For photonic devices such as optical waveguides, patterns are fractured into rectangles. A complete mask pattern may contain tens of thousands of rectangles. It may take 20 min for a computer to display the entire mask pattern. We have developed an efficient approach. The waveguide patterns are fractured into two files. One data file contains detailed data, and the other data file contains simplified data for display. For example, in the case of an S-shaped bend, every 10 rectangles can be lumped together to form a parallelogram for display. For a circular contact pad, the simplified data file contains only the coordinates of the center and the radius. In this way, the display speed can be increased by one to two orders of magnitude. After the mask pattern is completed, a program is used to insert detailed data into the data base that describes the mask pattern. Such an approach has been successfully incorporated into the Opto-MASK program.
Multigrid phase retrieval
Authors: Garnaoui H. , Tewfik A. H.
Published: February 2023

The problem of reconstructing an object function from the modulus of its Fourier transform arises in many disciplines. Several algorithms have been proposed to solve this problem. One of the most successful of those algorithms is the iterative transform algorithm, but is has a disadvantage in that it stagnates before it reaches a solution in some cases. Here, we propose a multigrid adaptation of this algorithm to speed up convergence. We also propose a second algorithm that attempts to solve the problem entirely in the space domain by using the support constraint and the nonlinear correlation equations. This algorithm is based on an iterative global linearization of the correlation equations. For both algorithms, several cycles of the basic iterative procedure are performed until stagnation is detected or until the number of cycles reaches a predetermined upper limit. At this point, the error and the current object-function estimate are transferred to a coarser grid, and the same basic iterative algorithm is then used to compute a grid correction to the last estimate that was computed on the fine grid. We show that a multigrid generalization of this two-grid procedure greatly improves the convergence of both algorithms.
Photoluminescence in heavily doped AlGaAs/GaAs heterojunction bipolar transistors
Authors: Hwang S. J. , Zhou J. F. , Song J. J. , Pawlowicz L. , Kim M. E.
Published: February 2023

Low-temperature (15 K) photoluminescence (PL) in molecular-beam epitaxy-grown AlGaAs/GaAs heterojunction bipolar transistors (HBTs) has been studied. Both cw and pulsed lasers were used as excitation sources. These HBT samples are heavily doped with Si and Be in the n+-GaAs and p+-GaAs layers, respectively. The origin of each PL signal is identified by removing each layer. Three PL peaks from the n-AlGaAs layer were observed. We found a direct correlation between height of PL peaks in the n-AlGaAs layer and device performance (current gain). We have also studied the correlation between PL in the n-AlGaAs layer and the current gain and Be redistribution from the p+-GaAs base layer into emitter layers while these layers were being grown. Poor current gain was observed as the Be diffusion depth into the emitter layers became large. The Be diffusion depth was measured by means of secondary ion mass spectroscopy. A sharp Be-related peak in the PL spectra from the n-AlGaAs layer clearly indicates Be diffusion into the emitter layers.
Mercurous bromide Bragg cell development
Authors: Brandt Gerald B. , Singh N. B. , Gottlieb M. , Davis J. , Hendrickson B. M.
Published: February 2023

Our overall goal is development of Bragg cells with 200-µs delay and reasonable bandwidth. Mercurous bromide has an extremely low acoustic velocity, 273 m/s, which allows construction of a 200-µs cell with an acoustic path of only 5.5 cm. To exploit this slow acoustic velocity, the acoustic energy must be launched as slow shear wave propagating accurately along a n direction with the shear polarization in the n direction. From our measurements, a 3 dB attenuation is achieved in the 200-µs delay at an operating frequency of 36 MHz. Because mercurous bromide crystals are not readily available in the sizes needed, much of the program effort involved perfection of growth methods for optical-quality crystals of the required size. We were able to grow material that showed adequate optical quality and low scatter. Two Hg2Br2 Bragg cells were fabricated with lengths corresponding to approximately 180-µs delay. Lithium niobate transducers were mounted with a UV-cured polymer and were ground to thickness. Mercurous bromide has been shown to be a practical material for long-delay Bragg cells.
S-SEED-based photonic switching network demonstration
Authors: McCormick F. B. , Tooley F. A. P. , Cloonan T. J. , Brubaker J. L. , Lentine A. L. , Morrison R. L. , Walker S. L. , Hinterlong S. J. , Herron M. J.
Published: February 2023

We implemented part of a multistage switching networkby optically interconnecting three 16 × 8 symmetric-self-electro-opticeffect-device (S-SEED) arrays. The inputs consisted of 64 data and 64 control signals, which were first converted to differential format, fanned out by 2, and then switched through an array of 64, 2×1 switching nodes. The data inputs were generated by a matrix of 64 fibers and identical control signals were sent to all 64 switch nodes by a control laser and an 8 × 8 binary-phase grating. The S-SEEDs have 5×10µm windows on a 20µm pitch, and they were operated as arrays of NAND and NOR gates. Crossover interconnections were used both between and within switch node stages. Logic-level nonuniformity and noise-margin difficulties that were present in an earlier experiment1 have been reduced, and fully functional, relatively stable operation has been achieved. Details of the architecture, optical hardware, and system performance will be presented.
Tunable nanosecond-laser-induced stimulated emission studies in molecular beam epitaxially grown cadmium telluride
Authors: Hays J. M. , Zhou J. F. , Song J. J. , Wu O. K.
Published: February 2023

Cadmium telluride films (~2µm) homo-epitaxially grown by molecular beam epitaxy (MBE) have been observed to undergo stimulated emission (SE) at 10 K. The samples were photoexcited using a 8 ns, 10-Hz pulsed dye laser, using both side-pumping and backscattering geometries. Stimulated emission occurred at the low energy edge and just below the exciton band in the region from 1.570 to 1.590 eV. The effect of the pump power density on the evolution of the SE was studied, including threshold, gain, and saturation behavior. The samples showed competition among the stimulated peaks, with a lower energy peak arising and superceding the higher energy emission in some samples with an increase in the excitation power density. Red-shifting of this lower energy SE peak was observed, while broadening was seen in all samples at high pump densities. The differing behavior between samples has been ascribed to the differences in the details of the impurity states in the samples. All samples showed stimulated emission at ~1.580 eV, which suggests an intrinsic defect related transition. The excitation wavelength dependence was studied using high power photoluminescence excitation near the bandgap. Resonances between multiple LO phonons, the excitons, and bandgap were observed.
Signal-to-noise ratio analyses for FM double-beam modulation systems
Authors: Cu W. Y. , Ih C. S. , Tian R. S. , Wang X. L.
Published: February 2023

We have recently suggested a double-beam modulation (DBM) method for broadband optical communications. A new DBM using frequency locked lasers (FLL) has been recently demonstrated. The DBM automatically creates a subcarrier upon detection by a photo detector. The new DBM-FLL can generate very high subcarrier frequencies that can also be easily tuned. So far we have been able to tune the frequency from several gigahertz to 15 GHz; the frequency range is currently limited by the detector and electronics.
Accurate field propagation procedures
Authors: Hermansson Bjorn , Yevick David
Published: February 2023

Standard beam-propagation methods such as the split-step fast Fourier transform, the split-operator finite difference methods, finite element methods, and the real-space technique are generally based on a second-order formula for the exponentiated sum of two non-commuting operators expressed in terms of the products of the exponents of the individual operators. In this presentation, we introduce an accurate analogous fourth-order formula. The increased and speed of the associated field propagation techniques over standard methods is verified by explicit computations on smoothly varying one-dimensional lens profiles.
Information from data—it’s really there
Authors: Yuen Michael
Published: February 2023

More than 3,000 machine-readable data bases exist and are available to the public through microcomputer and modem. Data bases are topical in nature. For the optical engineer and his or her company, information needs fall into one of three categories: technology, products, and company/industry data. Each category is examined, and examples of what can be obtained are shown. Machine-readable (online) data-base use offers two principal benefits; one benefit is the selection of information that can be found in a single library. Second, computer searching provides precision and speed that is not possible manually. The use of online data bases has long been the domain of the corporate or research librarian, but engineers are among the largest population of new users. New methods and technologies, including artificial intelligence, are being created to accommodate the influx of new users. This paper examines some of the changes in methodology.
Effects of masking on spatial-frequency discrimination
Authors: Morris Robert A. , Wilson Hugh R.
Published: February 2023

Masking by cosine gratings has been previously used to study spatial-frequency tuning of spatial mechanisms in human vision. Here we report on effects of masking on foveal spatial-frequency discrimination. Un-masked discrimination was first measured with vertically oriented stimuli of 50% contrast and localized in space and spatial frequency. The test stimuli were flashed for 30 ms. Then discrimination thresholds were measured in the presence of a 25% contrast cosine mask and at various stimulus onset asynchronies (SOAs). Measurements were made for each combination of test and mask at spatial frequencies of 3.0 and 8.0 cpd. Discrimination threshold elevations averaged 2.5 times at zero SOA but are virtually absent by 200 ms. We hypothesized that the discrimination-threshold elevation was the result of the increased contrast-threshold for the test patterns. Therefore, we measured the contrast threshold elevation due to masking at zero SOA. Unmasked spatial frequency discrimination was remeasured with the patterns adjusted to the appropriate multiple of threshold contrast. Under these conditions, unmasked spatial frequency-discrimination thresholds were the same as the unmasked thresholds using 50% contrast patterns. Thus, interference with spatial frequency discrimination can be accounted for by the elevation in contrast thresholds due to masking.
Coherence properties of fields produced by Lambertian sources
Authors: Wolf Emil , Gamliel Avshalom , Carter William H.
Published: February 2023

Until now, spatial coherence properties of fields generated by partially coherent sources have mainly been studied in the far zone of the sources. This is largely because of the complexities of the calculations that are required when the points of observation are at finite distances from the source. Recently it has been noted that considerable simplification occurs when the field is statistically homogeneous, and this fact has been used to provide contours showing the spatial distribution of the degree of coherence throughout a field of this class. In our paper another statistically homogeneous field is considered, namely a field produced by a large, planar, secondary, Lambertian source. An expression is derived for the degree of spatial coherence of the field at all pairs of points in the half-space into which the source radiates. The results are illustrated by contour diagrams, which show the behavior of the modulus and of the phase of the degree of spatial coherence.
Designing with fiber-array optics
Authors: Burger Robert J. , Greenberg David A.
Published: February 2023

Fiber-array optic composites combine fiber-optic, microlens array, and Fourier-optic properties and allow for many novel, manufacturable, cost-effective designs. Optical elements include fiber-optic faceplates, couplers, inverters, tapers, concentrators, reformatters, field limiters, and resolution filters. Faceplates with high numerical aperture provide substrates for phosphor screens and other energy-conversion devices. Fiber array field flatteners and couplers reduce the size, cost, and weight of optical designs. Inverters with concave surfaces provide on-axis, unobstructed field flattening and image erection in a compact package unparalleled by classical optics. Tapers offer magnification or minification with aspect ratios less than unity and also have the unique capability to illuminate and observe from one face. Fiber-array optics have extraordinary potential in the areas of photonics and integrated optics because they combine optical, mechanical, and electronic properties into one composite. Examples include digital cameras with circuit patterns and active devices on one side that transmit to circuits, devices, or a film imaging medium on the opposite side. New opportunities in optical computing and switching are suggested by the realization of the fractal dimension of array architectures. The design flexibility of fiber-array optics provides designers with tools to create many unique, manufacturable, low-cost optical and photonic systems.
Dual-scale topology optoelectronic processor
Authors: Marsden Gary C. , Krishnamoorthy Ashok , Esener Sadik , Lee Sing H.
Published: February 2023

D-STOP is a parallel, scalable, fully connected optoelectronic computing architecture suitable for applications in interconnection networks, numerical processing, neural networks, and artificial intelligence. The architecture consists of an array of N optoelectronic processing elements arranged in a 2-D topology. Each processing element consists of N electronic processing sub-units having detectors. These detector sub-units are electronically connected by an H-tree interconnection. At each node of the H-tree are additional fan-in processing sub-units. At the center of the H-tree is a single processing sub-unit having an optical modulator. Fully connected interprocessor communication is achieved through space-invariant optical interconnections, leading to a scalable architecture. The architecture can be used to perform outer product and inner product operations. Since all mathematical operations are performed electronically, the products can be generalized. Additional processing is available during fan-in, generalizing the conventional summation of inner products. This feature is particularly useful in neural network applications, including backpropagation networks. The key to the architecture is the dual scale of processing: detector and fan-in sub-units at the lower level and composite processing elements at the higher level. We will present the architecture, its functionality, applications, and optoelectronic design considerations.
Motionless parallel readout system for optical disks
Authors: Marchand P. , Krishnamoorthy A. , Ambs P. , Esener S. , Lee S. H.
Published: February 2023

We present a theoretical and experimental investigation of a novel optical-disk memory. The system is designed to read data blocks that distributed radially on the disk's active surface. These data blocks are one-dimensional Fourier-transform computer-generated holograms, each reconstructing one column of a two-dimensional output image. Owing to the properties of Fourier transform holograms (information redundancy and shift invariance), no tracking or focusing servomechanisms are required. An area whose length is equal to an entire radial line of the disk's active surface is retrieved at once. In this way data are accessed through disk rotation only, with no mechanical motion of the head. Therefore, the entire disk content can be retrieved in a single rotation (25 ms), making this system very suitable for high-speed optoelectronic associative memory applications.
Diode-pumped rod lasers
Authors: Knight M. G.
Published: February 2023

No summary was available at press time.
Beam quality improvements in surface-emitting distributed feedback lasers
Authors: Macomber S. H. , Mott J. S. , Schwartz B. D. , Setzko R. S.
Published: February 2023

Recent work on surface-emitting distributed feedback laser devices is reported. New developments include the incorporation of index guides for a more stable lateral mode and higher efficiency as well as tailored gratings for improved beam quality.
Grating coupled surface emitters
Authors: Streifer W.
Published: February 2023

Summary not available at press time.
High-speed optoelectronics
Authors: Suematsu Y. , Arai Shigehisa
Published: February 2023

Optoelectronic technology has the potential for high-density information transmission and storage, both in time and space. However, the ultimate speed of information transmission-storage systems is believed to be limited mainly by the performance of photonic and electronic devices. The smaller optical loss against the gain is required for high efficiency and stable operation of semiconductor lasers, and larger field-induced refractive-index variation is required for high-speed optical switches, but these optical properties are limited by the nature of carriers in bulk crystals. Thus, some effort has been made to attain superior device performance with novel material systems by using the quantum-size effect. In this paper recent research on lasers and photonic switches based on the quantum size effect are reviewed relative to high-speed information systems. First, the theoretical background of optical properties in quantum size structures is reviewed, and expected improvements in device performance caused by the increase of the dimension of quantization from quantum-film to quantum-box structure will be discussed fsom the aspect of high-speed systems. Second, experiments toward the quantum-wire and quantum-box lasers and optical waveguide switch/modulators utilizing quantum size effects are reviewed. Finally, some basic studies on electronic devices that use quantum size effects are reviewed in relation to highspeed electronics.
UV-fluorescence spectroscopy distinguishes breast cancer from benign tumors
Authors: Das B. B. , Alfano R. R. , Cleary J. , Prudente R. , Celmer E.
Published: February 2023

Breast cancer has one of the highest incidence and mortality rates in the U.S. X-ray mammography is one of the most common tools to diagnose breast cancer. Because of the effects of ionizing radiation and difficulty in differentiating benign from malignant tumors, there is a need for new methods. Fluorescence spectroscopy is a possible modality. We tested over 40 samples of cancerous and noncancerous breast tissues by means of UV-fluorescence spectroscopy. Each sample was excited in the UV, and the ratio of fluorescence intensities at different emission wavelengths were calculated. The ratio of intensities at different wavelengths allowed us to differentiate between malignant tumors and benign tumors and between tumors and normal tissues. The average ratio for 19 malignant samples was 15.7, and for 20 benign tissues and (fibroadenoma) tumors it was 4.7. Pathological diagnosis of each sample was known before the experiment was performed, and the results were used to build up a ratio histogram. Later blind samples were tested, and the results were in 99% agreement with the diagnoses made by pathologists. A spectral study indicates that tryptophan, tyrosine, and NADPH may be among the fluorophors causing the fingerprint of cancer.
Dynamic effects of nonuniqueness of cavity loss
Authors: Rosenberger A. T.
Published: February 2023

Optical resonators, usually in the form of spherical-mirror interferometers, are employed in a wide variety of experiments, including studies of steady-state and dynamic behavior in lasers and optical bistability. To make meaningful comparisons between experiment and theory, a resonator must be characterized in terms of its losses; that is, the behavior of the empty, or linear, resonator must be well understood if one wishes to understand the behavior of the filled, nonlinear resonator. In general, however, it is not possible to characterize an optical cavity in terms of a single loss parameter. Doing so results, for example, in a different state equation for optical bistability.
General method for separation of the nuclear and electronic contributions to femtosecond four-wave mixing transients
Authors: McMorrow Dale , Lotshaw William T.
Published: February 2023

We describe a novel, time-domain, Fourier-transform technique that separates uniquely the nuclear and (nonresonant) electronic contributions to x, that is generally applicable to most femtosecond four-wave mixing experimentson transparent media when optical heterodyn detection techniques are used. This separation is obtained with no curve-fitting or pulse-shape approximations, and reveals directly the impulse response function for nuclear motion with no assumed models being necessary. The general method, which we refer to as Fourier-transform four-wave mixing (FT 4WM) spectroscopy, can be applied to two-beam (stimulated Raman gain, optical Kerr effect) or three-beam (transient grating) femtosecond experiments for any polarization configuration and thus, determine directly the relative magnitude and dynamics of the nonresonant electronic and nuclear contributions for each of the different nonvanishing x matrix elements. Results will be presented for a variety of molecular liquids, illustrating the general utility of the FT 4WM method for investigation of the complex dynamics of molecular motion in condensed-phase media.