bluuebunny/crossref_metadata_2025 huggingface dataset:
Signal fidelity in optical distribution with fiber amplifiers
Authors: Kuo C. Y.
Published: February 2023

The signal fidelity in optical distribution with fiber amplifiers is measured by its ability to retain its signal to noise ratio and amplification linearity. Because of the strong dependence of the optical noise on the pump power, input power, and optical filter, each individual distribution system must be configured according to the specific signal to noise requirements. On the other hand, the slow amplifier gain dynamics ensure amplification linearity in high speed digital and subcarrier multiplexed analog video distribution systems.
ELED based fiber optic wavelength-sampling LAN
Authors: Sun Z. , Jannson T. , Hirsh J. , Savant G.
Published: February 2023

The development of a fiber optic LAN based on wavelength-sampling multiplexing (WSM) techniques has been investigated. WSM techniques, suggested a few years ago for fly-by-light system applications, never achieved practical feasibility because of poor power budgets and their immaturity on a physical (hardware) layer level. Our approach is based on a novel WSM device design and a new generation of non-Lambertian second-window light sources, called ELEDs (edge light emitting diodes), which have excellent power budgets. Our LAN is fully transparent to the type of signal transmitted (voice, data, video). ELED response, channel insertion loss, channel uniformity, and cross-talk characteristics of the WSM device have been measured.
Stability of periodic and almost periodic nonlinear structures
Authors: de Sterke Martijn
Published: February 2023

Results of a stability analysis for periodic and almost periodic structures are presented, showing the required incoming intensity for side band instability to occur. This work is motivated by the fact the instability results in gap solitons; lowering the instability threshold, therefore, leads to a lowering of the threshold for the formation of gap solitons as well. The work shows that the threshold for a structure with a suitably chosen chirp can be lower than that for a periodic medium.
Reflecting coronagraph designs with specialized applications
Authors: Smartt Raymond N. , Koutchmy Serge , Cross Eugene W.
Published: February 2023

With improvements in super-polished mirror technology, coronagraphs can be designed based on mirror objectives. Reflecting coronagraphs provide superior performance capabilities compared with classical singlet-lens-objective Lyot coronagraphs. Specifically, an all-reflecting design has the advantage of full achromaticity; wavelength coverage is limited only by atmospheric spectral transmittance, mirror reflectance, and detector response, and simple heat-flux rejection is inherent in the design. Further, large-aperture systems can be designed to be capable of producing high-angular-resolution imaging. A program to develop reflecting coronagraphs at NSO/SP is described, including the construction of two prototype instruments, of 5-cm and 15-cm apertures, respectively. In particular, applications in the infrared are emphasized; since strong spectral lines are available, the sky brightness is reduced, as are the scattering properties of super-polished surfaces. The advantages of some designs for certain nighttime applications, using either ground- or space-based systems, are discussed.
Operational convergence of estimates in phase diversity
Authors: Paxman Richard G. , Seldin John H.
Published: February 2023

A phased-array telescope will suffer from phase errors unless the subtelescopes are mutually aligned to within a small fraction of a wavelength. In this presentation we describe the use of Gonsalves' phase-diversity method to sense misalignments in a phased-array telescope. The technique requires the simultaneous collection of two images. The first is the conventional focal-plane image that has been degraded by the unknown misalignments. The second image is collected in an out-of-focus plane so that there is an additional (known) degradation due to defocus. Conventional nonlinear optimization methods are employed to estimate misalignment parameters that are consistent with both degraded images. One of the dangers of nonlinear optimization is the possibility of entrapment by local minima, which are known to exist in the phase-diversity objective function. An extensive Monte Carlo simulation was performed to quantify the probability of undesirable entrapment for a particular phased-array telescope. The results suggest that the probability of convergence to within a prescribed tolerance is large.
Radiation characteristics of concentric-circle grating, surface-emitting, semiconductor lasers
Authors: Jordan Rebecca H. , Erdogan Turan , Hall Dennis. G.
Published: February 2023

Coupled-mode analyses of surface-emitting, distributed-feedback lasers with concentric-circle diffraction gratings have described coupling between the waveguide modes, neglecting radiation.1 In this paper we discuss a model of the radiation characteristics of the concentric-circle grating. A boundary perturbation technique is applied to describe the interaction of the waveguide modes with the radiation field. A radiation coupling coefficient describes this interaction and relates the strength and shape of the radiated fields to those of the guided modes. The perturbation technique also predicts the far-field radiation patterns. We explore issues such as the effect of the additional radiative coupling on mode frequencies, threshold gain, and longitudinal mode profiles. An understanding of these radiation field effects is crucial for interpreting the relationship of beam quality to grating parameters such as period, depth of grating, and grating shape.
Dynamics and spatial order of cold cesium atoms in a periodic optical potential
Authors: Grynberg G. , Verkerk P. , Courtois J. Y. , Lounis B. , Salomon C. , Cohen-Tannoudji C.
Published: February 2023

The spatial distribution of cesium atoms in a 1D optical molasses are probed by measuring the absorption (or amplification) of a weak laser beam. Very narrow stimulated Raman and Rayleigh resonances are observed. The position of the Raman resonance gives access to the oscillation frequency of the atoms in the wavelength-scale optical potential. From the width of the Raman lines (~35 kHz), we deduce the damping time of this oscillation, which exhibits a dramatic lengthening due to the spatial confinement of atoms to a fraction of optical wavelength (Lamb–Dicke effect). Furthermore, the narrow stimulated Rayleigh signals (8 kHz) give experimental evidence for a large scale spatial order of the atomic gas presenting some analogy with an antiferromagnetic medium.
Solar-blind imaging radiometer
Authors: Sweatt William C. , Phipps Gary S.
Published: February 2023

We have built an imaging radiometer for mapping temperature variations on the face of solar receivers. It is designed to image a 700-sun, 600-mm square solar receiver that operates between 400°C and 900°C. The imager is located 5 m from the receiver; this allows it to operate in a moderately absorbing spectral band near 1.9 μm. Over the 5-m path, the in-band transmission is about 80%, while the whole atmosphere absorbs nearly all of the sunlight; thus, the system is nearly solar-blind. We are using a 512 × 512 pixel, PbO–PbS vidicon that has a calculated signal-to-noise ratio of S/N = 9 for a 400°C receiver temperature. For temperatures over 500°C, the camera limits us to S / N = 100. The spatial resolution of the camera lens is good enough to fully resolve the temperature in each pixel. The camera mates to standard video equipment. All of the commonly used imaging radiometers either have much poorer resolution or are not solar-blind.
Nanometer resolution optical position sensors based on Ni—Si—Ni photodiodes
Authors: Scott K. A. M. , Wilson C. M. , Sharma A. K. , Brueck S. R. J.
Published: February 2023

Ultra-high-resolution optical position sensing is important for applications ranging from lithographic alignment to complex optical systems. Traditionally, large area position sensors based on the lateral photovoltaic effect have been developed for long distance (several centimeters) applications. Relatively few results have been reported on ultra-high-resolution applications with resolution better than the optical spot size. Here, we report on nanometer scale position sensing using back-to-back Ni–Si–Ni Schottky diode structures. One- and two-dimensional structures with gap dimensions ranging from 3 to 100 μm have been fabricated with a simple, three level, lithographic process and lift-off metalization techniques on bulk Si wafers. The short-circuit photocurrent is monitored as these sensors are scanned under a focused (~4 μm FWHM) laser beam (λ = 334 and 633 nm). The photoresponse is linear across the gap width, and resolution to ±6 nm is demonstrated, limited by vibrational stability. Substantially improved resolutions are possible based on the electronic noise sources. The maximum position sensitivity is 8.5 μA/μm (1 mW incident power) for laser spot sizes on the order of the gap dimensions. A simple model based on the device symmetry and built-in junction fields is presented.
Pyrolysis jet spectroscopy of carbenes, silylenes, and germylenes
Authors: Karolczak J. , Clouthier Dennis J.
Published: February 2023

The spectra of a number of carbenes, silylenes, and germylenes have been recorded under jet-cooled conditions by pyrolysis of stable precursors in the throat of a supersonic nozzle. The strong S1–S0 transitions can be rotationally resolved in some cases, providing detailed information on the ground and excited state molecular structure. In the heavier species, only the vibronic structure is resolvable, yielding ground and excited state vibrational frequencies and band origins. In the case of GeCl2, we have also been able to obtain a jet-cooled phosphorescence excitation spectrum of the T1–S0 transition at 440 nm, providing, to our knowledge, the first direct lase excited detection of the triplet state of any of the carbene or carbene-like species. Ab initio predictions of the excited state energies and vibrational frequencies have been used to provide a consistent picture of the excited states of the germylenes, clearing up a lot of confusion in previous literature assignments. These studies provide the basis for sensitive spectroscopic detection of the carbene analogs, many of which are important in semiconductor growth processes.
Trace gas monitoring by CO2 laser-photoacoustic spectroscopy
Authors: Sigrist M. W. , Thöny A.
Published: February 2023

A computer-controlled, mobile CO2 laser photo-acoustic system has been developed and applied to the in situ monitoring of atmospheric trace gases in urban and rural environments. A line-tunable sealed-off CO2 laser with 12C16O2 and 13C16O2 isotopes is used as radiation source. The special design of the resonant photoacoustic cell permits measurements on flowing air. Emphasis is put on high sensitivity, selectivity, and temporal resolution of the detection. For this purpose, the laser is repetitively tuned to preselected laser transitions chosen on the basis of the characteristic absorption by the molecules to be detected and potential absorption interferences. The minimum detectable absorption coefficient amounts to 10−8 cm−1, which for many components corresponds to parts in 10−9 concentrations. Field studies concern measurements on industrial exhausts in multicomponent mixtures and on ambient air. In a recent measurement campaign we successfully montitored in situ five different types of compounds in rural air. The concentrations of water vapor, CO2′ ammonia (NH3), ozone (O3), and ethene (C2H4) were recorded simultaneously during a 6-day period with a temporal resolution of 10 min. Further results and new developments that demonstrate the great potential of this technique will be discussed.
X-ray laser gain studies using a glass slab driver laser
Authors: Muendel M. H. , Basu S. , Goodberlet J. G. , Hagelstein P. L.
Published: February 2023

We have constructed and tested an Nd:glass slab-based laser system for pumping x-ray laser plasmas and have used this system to commence spectroscopy and gain studies around 190 Å in Ni-like species around Z = 42. The Nd:laser system consists of a commercial mode-locked, Q-switched Nd:YLF oscillator, a double-pass Nd:YLF rod amplifier, and the 30 cm × 20 cm × 1 cm Nd:phosphate glass zig-zag slab; it generates 10 J at 0.3 Hz in 100-ps pulses. Output of this system is focused by using a cylindrical lens doublet into a 1 cm × 30 μm line focus. We are performing gain measurements by using this source on solid Mo targets that are rapidly positioned between shots with an automated alignment system. Recent results of these studies will be discussed, together with future plans, including higher peak power zig-zag slab systems and end-pumped XRL schemes.
Multiphoton interaction or squeezed light with a phased atom
Authors: Wang Changxin , Vyas Reeta
Published: February 2023

Evolution of the squeezed state in a multiphoton Jaynes–Cummings model (JCM) when the field is interacting with an atom prepared initially in a coherent superposition of the ground state and the excited state is studied. Long time and short time evolution of field statistics are discussed and compared with the standard JCM. These properties are found to be sensitive to the initial phase of the atom. For a phased atom, squeezing at later times can be larger than the initial squeezing. It is found that two-photon interaction of a suitably prepared phased atom with the initial vacuum state can yield 45% squeezing below the vacuum noise limit. Multiphoton interaction of a phased atom with the initial vacuum state of the field leads periodically to a pure field state that is a coherent superposition of the vacuum state and the n-photon Fock state.
In situ laser propagation in fresh water ice
Authors: Longacre Jacob M. , Landry Mark A. , Snow Judith B.
Published: February 2023

Because of difficulties associated with field experiments, reported results on laser propagation in ice have been obtained primarily in the laboratory. To avoid changes that occur in optical characteristics of inhomogeneous natural ice when removed from its environment, we conducted laser propagation experiments in situ. We constructed an optical rail to allow a device (either an underwater laser or an underwater detector) to be positioned horizontally at known locations under the ice cover of a frozen lake. By mounting a picowatt detector on the rail, we mapped spatial profiles of a surface-mounted 2XNd:YAG laser beam pointing vertically down through the ice. Profiles were measured as a function of both detector depth and detector angle of view. After stripping layers from the ice surface, we measured additional spatial profiles of the downward-looking laser beam. By mounting an underwater 2XNd:YAG laser on the rail under the ice, we also mapped the spatial profile of an upward-looking laser. At the conclusion of the mapping experiments, blocks of ice near the test region were removed and studied to identify structural features in the ice that affect laser scattering. Spatial profiling results were analyzed to determine the optical properties of specific ice features.
Computer generated planar holograms for optical neural network implementations
Authors: Keller Paul E. , Gmitro Arthur F.
Published: February 2023

While there are several ways to implement the interconnections in an optical neural network, we have concentrated on the use of multifaceted planar holograms. Each facet or subhologram produces the synaptic connections from a single neuron output (optical emitter or modulator) to an array of neuron inputs (detectors). The hologram must accurately encode synaptic weights, have a high diffraction efficiency, utilize the least space–bandwidth product, and be fabricated by using standard electron-beam lithography and ion-etch technology. The various algorithms used to generate the interconnection hologram are discussed, and the algorithms are compared by their performance. The algorithms we have investigated for hologram generation include the cell-based techniques, error diffusion, the Gergchberg–Saxton process, simulated annealing, random-search error minimization, a hybrid of the Gergchberg–Saxton and random-search error minimization, and the genetic algorithm. The hybrid Gergchberg–Saxton/error minimization process has produced the highest interconnect accuracy and highest diffraction efficiency of the algorithms tested to date.
Image reconstruction for computer tomography with missing projections by using the bimodal optical computer
Authors: Habli M. A.
Published: February 2023

The bimodal optical computer (BOC) is a hybrid optoelectronic system that can solve a system of linear equations in a fast and accurate way. In this paper the BOC is used for image reconstruction. A computer tomography problem that uses the algebraic reconstruction technique can be written as a system of linear equations, Ax = p, where A is an m × n matrix that represents the intersection area of the object that needs to be scanned and the projection beam, m is the number of projections, x is an n × 1 vector that represents the unknown density of the object, and p is an m × 1 vector that represents the nonoverlapping projections. Some of the components of the vector p are assumed to be missing, and they are approximated by using interpolation. The BOC is used to solve for x in the equation Ax = p.
The effect of charge accumulation on resonant tunneling
Authors: Kovanis Vassilios , Cardimona D. A. , Purvis R. K. , Richardson D. Z.
Published: February 2023

We introduce charge accumulation in quantum wells through the use of the nonlinear Schrodinger equation: where the symbols here have their usual meanings and ξ is a measure of the strength of the charge-accumulation effect. Letting V(x) be an infinite square well allows us to calulate the new energy spectrum, including the effects of charge accumulation (ξ|Φ(x)|2). This gives us insight into the new resonant tunneling energies that arise because of the quasibound states being shifted by the reaction field built up through the accumulation of charge. Using a normal quantum well potential between two finite square barriers, we calculate the transmission coefficient and contrast it with the transmission coefficient without charge accumulation. To simplify the results we also go to the limit of two delta-function barriers. Finally, we compare these results to the same cases when there is an external biasing field present by using the exact Airy function solutions of the linear Schrodinger equation with an applied field.
Third-order nonlinear optical interactions of some photodynamic proteins
Authors: Wiley B. J. , Akkara J. A. , Kaplan D. L. , Roach J. F. , Aranda F. J. , Rao D. V. G. L. N.
Published: February 2023

Third-order nonlinear optical susceptibilities χ(3) were measured for the photodynamic protein complexes bacteriorhodopsin (BR), phycocyanin (PC), and B-phycoerythrin (PE) in water and deuterium oxide by using the technique of degenerate four wave mixing with picosecond pulses at 532 nm. From the measured values of χ(3) we obtained the second hyperpolarizability <γ>. These values are for <γ> (BR) = 6.7 × 10−30, <γ> (PC) = 9.8 × 10−30, and <γ> (PE) = 7.0 × 10−29 esu, and the corresponding χ(3) values calculated for pure samples are 6.5 × 10−10, 1.2 × 10−9, and 9.0 × 10−9 esu. Thin film measurements for BR in polyvinyl alcohol matrix also yielded about the same values. After exposure to the green laser light for 1-2 min, the samples of phycocyanin and B-phycoerythrin are bleached and the phase conjugate signal disappears; the signal returns to the original state after 24 h. In the case of bacteriorhodopsin the response is too fast to be observed with our system.
Improvements and injection control of a discharge excited XeF(C–A) laser
Authors: Yongkang Cheng , Minxiao Wang , Deming Ren , Xiaoyan Zhao , Zuguang Ma
Published: February 2023

The performance of the discharge excited XeF(C–A) laser at a pumping rate of 2.76 MW/cm3 and a pressure of 2.2 atm has been improved through the reduction of the ratio of cavity length to discharge length and the use of the five-component gas mixture of He-Xe-NF3-F2-Kr. In order to increase the utility of the XeF (C–A) gain, the optical resonator was shortened from 1.0 m to 0.76 m with 0.5 m gain length. It was found that an optimized very small amount of F2 may effectively increase the laser output by a factor of ~1/4. Output energy of 1.35 mJ for an internal high-Q cavity with a coupler transmission of 7% at 477 nm was measured by an ED-200 energy meter. Lasing occurredwhen the same mirrors were mounted externally with Brewster windows or conventional flat mirrors sealing the discharge chamber. Using an excimer laser-pumped dye laser, we also realized injection control of the discharge XeF(C–A) laser with a positive branch confocal unstable cavity of M = 1.375.
Effect of two photon absorption on soliton switching
Authors: Potasek M. J. , Fang J. M.
Published: February 2023

We investigated quatitatively the effect of two photon absorption (TPA) on soliton switching in a nonlinear directional coupler. We found that TPA decreased the switching efficiency and increased the input peak power required to achieve the all-optical switching. In addition, the output pulse width is broadened. A set of two linearly coupled nonlinear Schrodinger equations, describing soliton switching, were numerically solved by using the beam propagation method. We considered a linear coupling constant of 0.25 for a half-beat length coupler that had unity cw switching power. At low input power, the output occurred at the cross mode. As the input pulse power increased, the output switched to the bar mode. A maximum of 96% of the output energy appeared in the bar mode when the input peak power was about 1.55 (normalized to the cw switching power) and TPA = 0. When TPA was nonzero, the maximum fraction of the output energy in the bar mode decreased. For example, for TPA = 0.1, the maximum fraction was about 83%, while for TPA = 0.2 it was about 66%. Also, the input peak power required to achieve the maximum fraction output in the bar mode increased. For example, for TPA = 0.1 it was about 1.95, while for TPA = 0.2 it was about 2.4.
Fields in dielectric waveguide structures: beam propagation method calculations and microwave measurements
Authors: Sinn Gert , Hensel Norbert , Sawade Guido
Published: February 2023

In model experiments with microwaves (λ = 6 mm) field distributions in the evanescent field near the waveguide surface are measured and compared with beam-propagation method calculations. Rectangular waveguides consist of foamed materials (Styrofoam n = 1.02 in air) and solid plastic materials (Polystyrol n = 1.6 in Styrofoam). Good agreement of calculated and measured field distributions was observed, even for waveguides with higher refractive indices. More complex structures may be formed as combinations of waveguide sections. Directional couplers with two parallel waveguides were investigated. The coupling length L can be evaluated directly from measured and calculated field distributions. At any waveguide discontinuity radiation modes are excited, changing the efficiency of waveguide components. We investigated fields behind step-like variations in cross-section and combinations of such steps with couplers and branches. The superposition of guided and radiation modes behind the step leads to interference beats with period λ
B
. The transmission of complex devices shows periodic variations with the same period, independent of the following structure elements even in distances up to 10λ. Systematic investigations of low cost enlarged microwave model structures yield predictions for properties of the corresponding integrated optic components. The range and validity of numerical methods such as bpm are analyzed by comparison with measured field distributions.
Dynamic range compression in linear GaAs sensory neural-network photodetector arrays
Authors: Darling Robert B. , Dietze William T.
Published: February 2023

Dynamic range compression is an essential feature of sensory neural networks, particularly in vision systems where many decades of mean input luminance must be accepted. Electronic realizations of neural network detector arrays, e.g., electronic retinas or other "smart" pixel arrays, normally employ individual, non-interacting (and therefore non-adaptive) logarithmic equalization elements for each pixel. In the present design, this equalization is provided directly by multiplicative, laterally inhibiting interconnections between the pixels themselves. This construction allows the equalization to adapt itself to mean luminance levels within local sections of the array. A 30-element linear sensory neural-network photodetector array has been constructed as a fully monolithic optoelectronic integrated circuit in GaAs to demonstrate this property. This prototype is based upon only one GaAs FET per unilateral interconnection and an additional three FET's and Schottky diodes for each pixel; thus, the implementation is extremely compact. Modulation of a self-conductance FET for each pixel also allows the threshold at which the inhibition engages to be externally adjustable.
A laser-plasma VUV source for projection x-ray lithography at 13.9 nm
Authors: Rockett P. , Hunter J. , Olson R. , Kubiak G. , Berger K. , Shields H. , Powers M. , Windt D. L.
Published: February 2023

An excimer laser-driven source of 13.9 nm radiation has been developed for use in an integrated soft x-ray projection lithography facility. The source consists of a 0.65J, 20 ns, 200 Hz KrF laser focussed down upon a high-Z target at intensities in the low 1011 W/cm2 range. The laser target consists of either a plating on a semi-infinite substrate or a metal film coated onto a thin plastic base. Extensive measurements have been made of x-ray yield by using absolutely calibrated x-ray diodes. These indicate a 1–1.5% conversion of incident laser light into a 4.5% band about 13.9 nm. Simulations of these experiments by using lasnex/xsn-u (a Lagrangian hydrodynamics code with average-atom radiation production and transport) accurately reproduce all measured parameters. We have been able to predict techniques for optimizing conversion efficiency based upon laser intensity, pulse width, and target design. Projection lithography mandates the minimization of debris to protect multilayer-coated collection optics. This concern has been addressed by the fabrication of a continuous-feed high-vacuum compatible, low-mass tape drive.
Interactions of carbon and oxygen on glass surfaces
Authors: Wang Paul W. , Lu Ling
Published: February 2023

Interactions between carbon and oxygen on glass surfaces under heat treatments have been observed in x-ray photoelectron spectroscopy (XPS) measurements. The reactions of carbon and oxygen on surfaces were monitored by the binding energies of photoelectrons emitted from 1s states of carbon and oxygen. A single XPS C1
s
peak was broadened and two peaks were clearly resolved after the sample was silica heated above 250°C. These two-component carbon peak positions were analyzed through the curve fitting technique. Not only the ratio of high-binding and low-binding peaks of C1
s
but also the relative peak positions were changed with the sample temperature and the period of heat treatment. Comparison studies on the oxygen 1s peak also showed the development of two component peak. The relative concentrations of two peaks changed with sample temperature and the duration of heat treatment. The two-component peaks appeared in C1
s
as well as in Ol
s
′ which strongly indicates that bonds between carbon and oxygen are formed during sample heating.
Optical components in access networks
Authors: Payne D. B.
Published: February 2023

The architectural options for optical access networks revolve around either point to point (star) systems or shared access systems (passive optical networks, or PONs). The PON approach has gained acceptance as the most promising for early economic penetration of fiber in the access network. These systems are, however, a radical departure for telephone companies whose experience lies with a metallic star network. New optical splitting components need to be housed as part of the external plant, and network operational practices must allow activity while the system is live. Once fiber systems penetrate the access network the addition of further optical components, particularly wavelength multiplexing components, can enable the graceful evolution to new broadband services. Optical amplifiers permit consideration of alternative network architectures. We will discuss the network options for optical access networks, including their advantages and potential problems. We will highlight the key components both for early networks and those required for future evolution to networks with full two-way broadband capability.
Parametric study for low loss dispersion-flattened fibers
Authors: Gao Yangsheng
Published: February 2023

The analytical formulas of dispersion and mode field radii variation due to the preformfiber drawing ratio (s) and the core-clad index difference (Δn) is derived to approach low loss dispersion-flattened fibers with multiple-cladding. If s2Δn is constant, bend and splice loss will be approximately invariant; both lowering s and raising Δn will lower the dispersion curve. This approach can result in great waveguide dispersion without increasing loss; if s Δn is enlarged, the dispersion curve can be designed to be basically invariant by appropriately lowering s and raising Δn, while bend and splice loss is reduced. Hence the combination of higher core-clad index difference and smaller drawing ratio will be more reasonable for actual low loss dispersion-flattened fibers. On the other hand, adjusting s can compensate dispersion deviation due to disturbed Δn, especially for λ < 1.55 μm. Beyond 1.55 μm, lowering s and raising Δn might make the dispersion-flattening property poor. By selecting suitable s and Δn and adjusting other parameters of arbitrary quadruple-clad profile, low loss dispersion-flattened fibers may be optimized and trial-fabricated.
Self-modelocking of solid-state lasers
Authors: Sibbett W.
Published: February 2023

The salient underlying physical principles of the self-mode-locking technique will be reviewed. In particular, the various methods by which this self-mode-locking process can be initiated and the primary roles of self-phase modulation and self-focussing will be described within the context of frequency-tunable femtosecond pulses from solid-state laser systems. Although the sub-100-fs performance characteristics of the broadly tunable Ti-sapphire and Cr:LiSAF lasers will be especially highlighted, the more general applicability and potential of this mode-locking method will be discussed. Some related considerations will also be included for laser configurations where the exploitable optical nonlinearities are produced in a passive intracavity medium as distinct from the gain medium itself. Because of the relatively high peak pulse powers directly available from the present generation of self-mode-locked laser oscillators their compatibility with efficient nonlinear up / down frequency- conversion arrangements will be outlined.
Two-wavelength synchronous generation of femtosecond optical pulses with < 100 fs jitter
Authors: Knox W. H. , Beisser F. A.
Published: February 2023

We discuss a new approach for the generation of two independently tunable femtosecond optical pulses at high repetition rate (77 MHz). A self-mode-locked Ti:sapphire laser is used to synchronously pump a HITCI dye laser with 100 fs pulses. The Ti:sapphire laser can be tuned throughout the dye absorption region (740-800 nm), and the dye laser produces 140 fs pulses tunable from 840 to 900 nm. Cross-correlation measurements indicate that the dye laser pulses are synchronized to the Ti:sapphire laser pulses with <100 fs jitter, which is a new regime for synchronous pumping. This source adds greatly to the versatility of Ti:sapphire laser systems, and several experimental applications will be discussed.
Dual Ti:sapphire laser system for ultrafast pump-probe studies
Authors: Luo N. , Ratsavong F. , Robinson G. W.
Published: February 2023

Two self-mode-locked sub-100-fs Ti:sapphire lasers operating at 700-1000 nm generate the pump and probe pulses for an ultrafast pump-probe apparatus. The asynchronous optical sampling approach is employed to perform these studies. To provide an optical delay line the difference in the two cavity lengths is precisely adjusted to give a constantly increasing walk-off between the two laser pulses. The step size of the walk-off provides the time resolution, variable from source-limited 100 fs to a few nanoseconds. The laser beams are sent to a BBO crystal that generates sum frequency pulses when the pulses from the two lasers temporarily overlap. This pulse is then used to define the time-zero position and to initiate a micrometer-millisecond data acquisition process. Data are digitized at the probe laser repetition rate and are then transferred to a micro-computer for storage and analysis. Several laser dyes with excited state lifetimes of picoseconds to nanoseconds have been studied to verify instrument performance. With a uniquely designed cavity length stabilization system, the relative time jitter of the two laser pulses is maintained near 100 fs. By adding frequency doubling crystals, 350-500 nm wavelength coverage can be accessed.
Pattern masking: retinal and cortical processes
Authors: Bowen Richard W. , Wilson Hugh R.
Published: February 2023

We model pattern masking with a retinal luminance adaptation process followed by orientation-selective cortical filtering. We analyzed threshold elevations of a bandpass test stimulus (a 33 ms D6, sixth derivative of a Gaussian) masked by a 433 ms cosine grating, varying test polarity and spatial phase of the mask. The retinal process was defined by threshold elevation on uniform fields of the same luminance as the peak and the trough of the mask. The cortical process was defined by dividing cosine threshold elevation by uniform field elevation. The retinal process can be modeled with a Naka-Rushton nonlinearity. The cortical process is phase dependent, with threshold elevation greatest for negative tests on light bars and positive tests on dark bars of the mask grating. For the cortical process, dark bars produce more masking than light bars. We conclude that the cortical process must involve competitive interaction between on and off systems.
Multilevel electro-optic polymer waveguides
Authors: Girton D. G. , Lytel R. , Lipscomb G. F.
Published: February 2023

Electro-optic (EO) polymers have been used recently to integrate active devices, such as optical modulators, couplers, and switches, as well as passive waveguides, into a single planar level on top of a Si (or other) substrate. A further increase in integration can be realized by stacking one level of integrated devices on top of another, resulting in multilevel structures for optical devices. For this purpose, EO polymers have significant advantages over inorganic materials, such as LiNbO3 and GaAs, because one polymer layer can easily be placed on top of another by using relatively low processing temperatures (≈300°C), and the underlying substrate, such as a semiconductor wafer, will not be affected.
Type II phase matching in KNbO3
Authors: Bosenberg Walter R.
Published: February 2023

The nonlinear optical material potassium niobate (KNbO3, KNB) has established itself as an excellent mid-infrared frequency converter. To date, all work using this biaxial material has been carried out with beams propagating in the principal planes of the crystal. This necessarily dictates the use of Type I phase matching since the effective nonlinear coefficient deff is zero in the principal planes for Type II phase-matched processes. Here, the possibility of using Type II phase matching by propagating beams outside the principal planes is reported. Type II phasematching has the advantages of broader angular acceptance [for second harmonic generation (SHG) and frequency up-conversion] and narrower emitted linewidth [for optical parametic oscillators (OPOs) and frequency down-conversion]. Calculated and experimental SHG and OPO tuning curves will be presented, in addition to data that determines the relative sign of d31 and d32 in KNB. This relative sign has a critical impact on the magnitude of deff for the Type II conversion process.
Quasi-optical techniques for utilizing resonant-tunneling-diode oscillators at frequencies approaching 1 THz
Authors: Brown Elliot R.
Published: February 2023

At frequencies above 100 GHz, the generation and control of coherent radiation is greatly hindered by ohmic loss in semiconductors and metals and by higher-order mode generation in metallic waveguides and coplanar transmission lines. This paper deals with quasi-optical techniques, which are well suited for resonant-tunneling diodes (RTDs) in applications between 100 GHz and 1 THz. For example, semiconfocal open cavities have been used to suppress the phase noise and stabilize the frequency of RTD oscillators up to 200 GHz. Open cavities have also been proposed as a means of synchronizing N-element focal-plane arrays of RTDs, which would produce approximately N times the power of a single device. Finally, open cavities and dielectric waveguides are being analyzed as means of supporting a new type of source—the RTD relaxation oscillator. This source, like the focal-plane array, should have operating characteristics superior to those of the conventional RTD oscillator.
Optical generation of millimeter waves using HBTs driven by semiconductor lasers
Authors: Plant D. V. , Scott D. C. , Prakash D. P. , Fetterman H. R.
Published: February 2023

Millimeter waves have been generated by driving HBTs with both mode locked and cw semiconductor lasers. The mode locked diode lasers incorporated a saturable absorber section and produced <2.5 ps pulses at 65.12 GHz. Millimeter waves generated in the high frequency HBTs were radiated into free space by using integrated printed circuit device/antenna circuits. In subsequent experiments, cw optical mixing techniques were also used to generate millimeter waves. Here, single frequency, stabilized semiconductor lasers operating at both 850 nm and 1.3 μm were mixed in the active regions of the HBTs. These long wavelength lasers were chosen because they are optimally absorbed in the active regions of the devices and therefore provided the highest optical-to-millimeter-wave conversion efficiencies. In order to optimize the performance and configuration of these new millimeter wave sources, we also incorporated them on wafer optical feeds by using polyimide guides deposited with a direct laser writing technique. This approach permits a high degree of fan-out and the use of multiple radiating elements. These experiments demonstrate a new architecture to form compact, all-solid-state sources of millimeter waves that use wafer scale optical interconnections to form novel coherent arrays.
Perceived brightness, but not lightness, is influenced by retinally non-adjacent coplanar surfaces
Authors: Schirillo James A. , Shevell Steven K.
Published: February 2023

We previously reported (OSA, 1991; ARVO, 1992) that perceived brightness of an achromatic surface is influenced by information about the illuminant derived from perceptually coplanar but retinally noncontiguous surfaces. A 6:1 luminance range on a CRT screen simulated the surface reflectances of a single Mondrian. Corresponding spatial locations in a second Mondrian were assigned luminances that were one-fifth that of the first Mondrian. This created the appearance of two Mondrians with identical reflectances, but different illuminations. When viewed through a haploscope each Mondrian was perceived in a separate stereoscopic depth plane. The test appeared in either the depth plane of the far, dimly illuminated Mondrian or the depth plane of the near, brightly illuminated Mondrian. The previous results confound changes of reflectance and illumination. We obtained lightness judgments by using the same stimuli to isolate perceived reflectance. The results show that brightness of the test changed with depth, but not lightness. This supports the claim that brightness measures are due to perceived illumination differences across depth planes.
Disorders of color vision following cortical damage
Authors: Plant Gordon T.
Published: February 2023

Cases of cerebral achromatopsia have increased our understanding of the anatomy of extrastriate cortex. Some features of the reported cases have not so far been explained: for example, 1) Why can some but not all patients read pseudoisochromatic plates? 2) Why do some patients have a relatively greater impairment of short wavelength mechanisms? Results obtained in four cases of cerebral achromatopsia will be presented in an attempt to address these and other issues. One patient showed a marked deterioration in both chromatic processing and achromatic contrast sensitivity at low light levels, suggesting that the testing conditions may be important. In some cases dynamic random luminance masking (which disables achromatic mechanisms) results in a total failure of chromatic discrimination, while in others this has no effect on residual color discrimination. Thus the extent to which discrimination depends upon residual chromatic or achromatic mechanisms may vary. In one case it has been shown by using incremental threshold techniques that S-cone sensitivity may be reduced by 1.5 log units in the presence of near normal L-cone sensitivity, suggesting that the relatively greater impairment of short wavelength mechansisms is reflected in detection thresholds as well as chromatic discrimination. These differences in residual vision are discussed in the context of the underlying anatomy.
Color perception in central dyschromatopsia
Authors: Rizzo Matthew
Published: February 2023

Central dyschromatopsia is an acquired disorder of color vision caused by damage in the visual association cortex of the occipital lobe. Its existence, once questioned by Gordon Holmes, is no longer in doubt. Patients with the disorder may report that colors look "dirty," "dull," "faded," or "wrong" in the affected visual fields. In the worst cases they may report a visual experience of the world in shades of gray, as if viewed on a black-and-white television set. The pattern of psychophysical defects associated with such descriptions may provide insights on how signals from the short, long, and middle wavelength sensitive cones are processed at cortical levels. The problem, however, is that central dyschromatopsia usually affects a quadrant or hemifield and spares fixation, the region where most standard color tests are presented. Consequently, its psychophysical underpinnings remain poorly defined.
Optical transpose interconnection system
Authors: Marsden Gary C. , Marchand Philippe J. , Harvey Phil , Esener Sadik C.
Published: February 2023

The optical transpose interconnection system (OTIS) is an optical interconnection scheme that provides transpose transformations on 2-D indexed 2-D arrays of transmitters and detectors. These transformations are required in shuffle-tree graph1 (STG) architectures. The STG supports various matrix computations, such as matrix transpose, vector outer-product, and matrix-vector multiplications. These computations are useful for signal processing, artificial intelligence, relational databases, artificial neural systems, and crossbar interconnections. The OTIS optical system can also be used to implement

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-shuffle2 multistage interconnection networks (MINs) which have the advantage that only a constant number of optical stages is required for routing or sorting applications. The OTIS optical system is bi-directional. This can prove useful for backpropagation neural networks and MINs. In this case, it allows blocking information inside the MIN to be accessed by a data packet sender. We will present the design and experimental demonstration of the OTIS optical system. We will also present the necessary electronics that connect the transmitter and detector subarrays allowing efficient optoelectronic implementations of shuffle-tree graphs and

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-shuffle architectures.
Probability-law estimation by a principle of minimum physical information
Authors: Frieden B. Roy
Published: February 2023

A principle I–J = min. of minimum Fisher information I = ∫dxp'2(x)/p(x) is often used to estimate an unknown probability density function p(x) in the presence of insufficient information J. The latter is conventionally a Lagrange constraint term. The resulting estimate p(x) may or may not be correct (where there is a "correct" answer), although it is smooth. But suppose the correct answer is required and the user has the resources to choose the particular information J to input. What form J should be chosen, and what form should I – J ≡K take, where K is the "physical" information? The choice of J (and K) follows from three reasonable axioms: (i) K is linear in I, i.e., K measures disorder, (ii) K is a universal value, irrespective of physical phenomenon, i.e., all phenomena p(x) are equivalent in their information content; (iii) there is no preferred space, direct or Fourier, for representing K. The solution is that K = 0 or, numerically, J = 1. However, functionally J depends upon p(x) differently than does I; this dependence, which often arises out of Parseval's theorem, is the required input of information. We show that many of the known laws p(x) of physics may be "estimated" in this way.
Temporal filtering with time lenses
Authors: Lohmann Adolph W. , Mendlovic David
Published: February 2023

We propose to use optics for ultrafast serial processing by employing the well known analogy between optical spatial diffraction and temporal dispersion. The essence of this analogy can be stated briefly like this: The temporal frequency corresponds to the spatial frequency in the lateral direction, and the time t corresponds to the lateral coordinate x. In this project, passing through a dispersive delay line is the analog of free space propagation and the action of a spatial lens is mimicked by a time lens, which multiplies the incoming signal by a chirp. The suggested "temporal filtering" system contains two 2-f configurations in cascade. Both of them perform a temporal Fourier transform. Thus the total configuration is equivalent to the well known 4-f spatial processor, and most of its uses, such as spatial correlation and convolution, can be also implemented in the time domain with the temporal filtering system. Each 2-f system consists of three subsystems in cascade: free space propagation, transfer through the lens, and again free space propagation. Accordingly, we let our temporal signal travel over a distance f, then let it interact with the time lens, and finally propogate it over another length f. By using typical parameters for the dispersive medium and the time lenses several systems were designed and computer simulated, such as 4-f correlator, joint transform correlator, and derivator.
A decision-theoretic approach to accuracy enhancement in optical processors
Authors: Timucin Dogan A. , Walkup John F. , Krile Thomas
Published: February 2023

We presented a complete statistical analysis of a generic optical linear algebra processor previously, determining the signal and noise statistics with no reference to the system component characteristics. In this paper we introduce device statistics into the analysis and evaluate output signal probability densities and power spectra for certain practical device combinations. Based on these statistics, we then apply M-ary hypotheses testing and Wiener filtering techniques to improve the processor accuracy. Both approaches are aided by proper normalizing transforms. Analytical and computer simulation results are presented to quantify the improvements, and optimum approaches are suggested for particular architectures and devices.