bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of chemical changes in photochromic media
Authors: Caron Serge , Roberge Pierre C. , Lessard Roger A.
Published: February 2023

In holographic experiments performed for both chemical and physical investigations, chemical species modulation created in photochromic media is linked to the diffraction efficiency of the hologram, whereas the sensitivity of the media depends on the kinetic constant of the photochemical reaction. Numerical calculation have already been used to evaluate such quantities.1 Moreover, kinetic constant have been evaluated by using the Kogelnik equations approximated for low time of exposure.2 In this paper, exact equations describing the light intensity and molecular concentration of the reactive at any position in the layer and any time of exposure will be given for bleaching and blackening recording media, such as thionine polyvinylalcohol or dichromated gelatin. Theoretical curves will be given for the sinusoidal lightening pattern that is encountered in simple holographic experiments. The equations describing those curves should be used to calculate the modulation of the optical density and the refractive index in the medium. All evaluated values are related to molar absorption and molar refraction coefficients of the chemical reactive and product and to the quantum yield of the photochemical reaction.
Energy storage in quantum-well lasers
Authors: Chen Y. C. , Waters R. G. , Lee K. K. , Wang P.
Published: February 2023

Q-switching in semiconductor lasers is not as efficient as in solid-state lasers, such as Nd:YAG lasers, because of the rapid depletion of the population inversion by the strong spontaneous emission and other higher-order nonradiative recombination processes. Recent studies of the carrier lifetime in GaAs1 and InGaAs quantum-well lasers reveal that the carrier lifetime can be prolonged by the storage of a portion of the carriers in the continuum states of the confinement layers, in which the carrier volume density is diluted and the overall carrier lifetime is prolonged. Thus, the confinement layers behave like a carrier reservoir. This allows the population inversion to build up to a much higher level in a tailored structure for Q switching or pulse amplification. We will present a theoretical analysis that shows that the carrier storage can be achieved with minimal reduction in the gain coefficient of the quantum well. The maximum energy that can be stored and the speed limit imposed by the carrier capture rate will also be discussed.
Further investigations of the technique and applications of rainbow holography using spatial filters
Authors: Grover C. P.
Published: February 2023

We have previously reported on the generation of color blur-free images from holograms in white light by using specially designed external spatial filters. The hologram is made in such a manner that it produces the image of the object in a plane located upstream with respect to the real image plane of its Fourier transform. In effect the hologram is recorded by using the regular off-axis geometry, and the chromatic correction is obtained by observation through an external spatial filter.
Dichromated polyvinyl alcohol for the fabrication of holographic optical elements
Authors: Changkakoti R. , Lessard Roger A. , Couture Jean J. A.
Published: February 2023

For the last decade dichromated gelatin (DCG) has been widely used as a recording material for the fabrication of high efficiency holographic optical elements (HOEs). Although DCG exhibits high diffraction efficiency () and a high signal-to-noise ratio (SNR) it is plagued with some severe drawbacks, such as (a) low environmental stability, (b) irreproducibility of results, and (c) cumbersome wet-processing procedures. Photopolymers and photo-cross-linking polymers seem to be good candidates to overcome some of these limitations.
Electro-optic sensing using total internal reflection at the critical angle
Authors: Butler Douglas L. , Lee Chi H. , Burdge Geoffrey L.
Published: February 2023

We demonstrate electro-optic sensing of a microwave signal by total internal reflection of light at the critical angle. A mode-locked laser beam and a microwave frequency electro-optically mix in a nonlinear crystal near the interface. This process, described by using generalized nonlinear optical formalism at the boundary, provides a sensitive mechanism for studying the electro-optic effect in reflection. To experimentally verify this phenomenon, we use a KDP crystal with a coplanar waveguide on its surface that carries a 109 MHz microwave signal. A100 MHz mode-locked laser is focused through a prism onto the opening in the coplanar waveguide and is internally reflected off the KDP surface. In the region of overlap inside the KDP crystal, the laser beam's evanescent electric field and the microwave signal's electric field interact electro-optically to produce a difference frequency sideband (9 MHz) on the reflected light beam. The strength of the difference frequency signal peaks at the critical angle; when we change the incoming beam's angle by one degree, the signal level drops 25 dB. We have experimentally investigated the signal dependence on polarization, light intensity, and microwave signal power, agree qualitatively with theory.
Picosecond time-resolved imaging of point and plane objects inside highly scattered turbid media
Authors: Wang L. M. , Ho P. P. , Liu C. , Zhang C. , Alfano R. R.
Published: February 2023

It has been recently demonstrated1 that the ballistic component (photons that arrive first) through random media can be separated in time from the diffused scattering component. This report addresses time-resolved two-dimensional imaging of the ballistic signal emanating from point and plane objects located in turbid media. We used an ultrafast Kerr gating system, consisting of a mode-locked ps glass laser, a CS2 Kerr shutter, and a two-dimensional change-coupled device camera with 600400 spatial resolution to record the images. A pair of 200 m point sources separated by 400 m in water solution with scattering beads, was resolved using a fluorescence time gating. A U.S. Air Force bar-test chart was placed inside the water solution filled with beads at OD = 4. The diffused and ballistic signals from the chart were imaged at different times. At T = 0, we obtained a clear bar image with the spatial resolution 500 m. These key observations are the result of ballistic photons arriving first at the Kerr gate. When the gating time was delayed, the images broadened and blurred. The time difference between the ballistic and the diffusive scattering components was measured to be 15 ps.
Laser computed tomography for biology and medicine using coherent detection imaging method
Authors: Toida Masahiro , Kondo Mokoto , Ichimura Tsutomu , Inaba Humio
Published: February 2023

We report the first known experimental demonstration of computer-assisted laser tomography of actual biological objects that uses coherent detection imaging (CDI) based on the optical heterodyne technique for two-dimensional resolution.1 In order to use optical absorption tomography for biomedical applications on the basis of the projection-slice theorem, the following three conditions should be satisfied in principle: (1) Detection sensitivity must be excellent to distinguish the directly transmitted beam component from the widely spread, multiple scattering of light, (2) Lambert-Beer's law must be established for the directly transmitted beam, and (3) The directly transmitted component must be detectable, even in the presence of complex distributions and refractive-index boundaries in the media. We have experimentally verified the fulfillment of these basic conditions by means of the optical heterodyne technique and have used the CDI method in highly scattering, absorptive media in which an object is completely hidden from normal visual observation and from the conventional direct-detection technique. The first successful imaging of laser-computed tomography was achieved with actual biological objects in vitro and in vivo by means of our new CDI method. This method will provide valuable spectroscopic images over the significant thickness of biomedical objects and should be able to exploit their biochemical and physiological information by the use of tunable lasers in the near future.
Eigenstates of the driven Jaynes-Cummings system
Authors: Alsing P. , Guo D.-S. , Lindberg M. , Savage C. M. , Carmichael H. J.
Published: February 2023

The eigenstates of the Jaynes-Cummings Hamiltonian (the dressed atomic states) are widely used to describe the interaction between a single two-level atom and a single mode of the electromagnetic field. They provide a particularly useful basis when the secular approximation is justified. For an atom interacting fog with n photons in a cavity, the secular approximation requires that the n-photon Rabi frequency

2

n

g be much larger than the atomic and cavity linewidths. Normally this condition is met when n is large and the coupling constant g is much smaller than the atomic and cavity linewidths. In this paper we allow g to be larger than the linewidths, and we allow the photon number to be small. We show that when the cavity is driven by a coherent field, the usual secular approximation cannot be used. The natural basis states become are now the eigenstates of the Jaynes-Cummings Hamiltonian plus the external field interaction. We solve this eigenvalue problem by separating the field and atomic parts of the Hamiltonian using a displacement and squeeze in the Hilbert-space of the field. We find that the Rabi frequencies are renormalized downwards as the strength of the driving field is increased. They eventually vanish at a critical field strength. At this critical field strength we observe a spontaneous symmetry breaking in the steady-state solution of the master equation for a single atom interacting with a driven cavity mode.
Spatiotemporal mask affects detection and Vernier acuity
Authors: Waugh Sarah J. , Levi Dennis M.
Published: February 2023

Vernier acuity for abutting stimuli is almost independent of exposure duration providing the target remains equally visible i.e. if the effect of time on detection is accounted for (Hadani et al., 1984; Waugh and Levi, ARVO 1990). Recently Watt1 reported that for a variety of spatial discrimination tasks using line stimuli, thresholds continue to improve with time at least until 1000 msec. However, in Watt's experimental paradigm, a random noise mask immediately followed presentation of the discrimination target. We measured foveal line detection and abutting line vernier thresholds with and without a random noise mask immediately following the stimulus. Stimuli were presented on a uniform background of 132 cd/m2. A self-paced rating-scale method of constant stimuli with feedback was used. The mask produced a significant increase in vernier thresholds for durations less than about 200 msec. However, it also increased detection thresholds over this range of durations. For masked vernier stimuli equated for visibility, no systematic effect of time on vernier acuity was found. These results suggest that for equally visible stimuli, no additional time is required to scan through a range of spatial filters in order to obtain the finest vernier thresholds.
Temporal impulse response from flicker sensitivity: fine-tuning the Stork-Falk procedure
Authors: Dagnelie Gislin
Published: February 2023

Several years ago, Stork and Falk1 introduced a technique to convert flicker sensitivity data into temporal impulse-response functions (IRF). A slightly modified procedure was later suggested by Swanson.2 When this technique is applied to data collected foveally and at photopic brightness levels from normal observers, a plausible, biphasic waveform for the IRF is obtained. Lower flicker sensitivities, however, such as those existing in ophthalmology patients at extrafoveal retinal locations or at low luminance levels, may yield IRF waveforms with a very steep initial flank and late oscillations. The steep initial flank is caused by the first-order extrapolation beyond the measured critical flicker frequency. Late oscillations can be attributed to the assumed flat sensitivity characteristic below the lowest frequency tested. Using the data and models of Kelly, Watson, Roufs, and others, as well as data collected from 20 normal observers and 100 retinitis pigmentosa (RP) patients, I have modified the Stork-Falk procedure to eliminate the influence of sensitivity scaling in normal observers and to yield results that are more plausible in view of our understanding of changes in RP photoreceptors. The choices of high- and low-frequency extrapolations and the applicability of the minimum-phase assumption implicit in the procedure will be discussed.
Using scintillation to obtain turbulent heat fluxes in free convection
Authors: Andreas Edgar L.
Published: February 2023

Local free-convection scaling is one of the obvious triumphs of boundary-layer similarity theory. In free convection there is no dynamic velocity scale; the sensible and latent heat fluxes, therefore, scale directly with the temperature and humidity structure parameters. By using scintillation to measure the refractive index structure parameter at two electromagnetic (EM) wavelengths, we can obtain the temperature and humidity structure parameters and, thus, in effect, measure path-averaged values of the sensible and latent heat fluxes. I describe this so-called two-wavelength method for free convection, derive quantitative guidelines for optimizing the method, and evaluate its potential accuracy. I show that the two-wavelength method works best when one EM wavelength is in the visible or infrared region and the other is in the millimeter or radio region. When the Bowen ratio the ratio of sensible to latent heat fluxesis between 5 and 0.1 or between 0.1 and 5, the expected accuracy of the measured heat fluxes is 1020% typical of what is possible with eddy-correlation measurements. However, with the two-wavelength method, the fluxes represent spatial averages.
Review of theory of propagation through turbulence
Authors: Zavorotny V. U.
Published: February 2023

The fundamental concepts of light propagation in the turbulent medium, which based on the simplest geometric optics and diffraction considerations, are stated. The review of the main results and their practical applications is given.
Enhanced second-harmonic generation in with gamma rays irradiated fibers
Authors: Kamal A. , Weinberger D. A. , Chu J. H.
Published: February 2023

The achievement of high conversion efficiencies for second-harmonic generation (SHG) in germania-doped optical fibers requires an understanding of the material properties of the fiber as well as the saturation mechanisms limiting the growth of the (2) grating. In this paper we report material modification of germania doped fibers by gamma rays irradiation that allows previously un-conditionable fibers to be conditioned for SHG. We also observed significant enhancement in the efficiency and preparation rate of previously conditionable fibers. In the context of our previously developed rate equation model for the evolution of (2) gratings,1 these results suggest an enhancement of the number density of defects participating in the self-organization process. We investigated the nature of these defects and the role of oxygen vacancies in the germanosilicate matrix in the self-organization process by use of high-energy radiation, which can produce oxygen vacancies,2 as well as low energy radiation that is incapable of producing any vacancies. We also present results of a Raman study of gamma-irradiated fibers. New insights into the preform preparation environment and fiber drawing conditions, suitable for writing of self-organized (2), gratings, are gained from these studies.
New technique of excimer laser marking and micromachining
Authors: Ho W. , Sercel J. , Sercel P. , O'Keeffe T.
Published: February 2023

High-peak power short-wavelength excimer laser radiation has been used for a range of applications. Excimer laser direct write marking and micromachining has become a powerful technique for many important applications. In general, excimer laser processing is divided into three categories: (1) Image marking/micromachining, (2) Surface mask scanning, and (3) Direct write marking/ micromachining. Image marking is a simple method. A pre-designed mask is used to image the laser beam onto the work surface. Image processing is straightforward and a relatively large area can be marked simultaneously. However, the mask and tooling time can be costly. Direct write processing overcomes these difficulties. It uses an imaged laser spot as a pencil tip which is moved across the sample with circular interpolation using a CAD/CAM postprocessor. Advantages of direct write processing are that it reduces localized heating by fast scanning and it is more flexible. It also allows the pulse energy, high repetition rate lasers to be used very effectively. When properly implemented, it also permits high Beam Utilization Factor for small beam energy lasers. Results from this direct write processing of various materials and beam delivery techniques will be reported.
Nonlinear-optical interactions involving the real Gaussian field
Authors: Xie Cheng , Klimeck G. , Chen Ce , Elliott D. S.
Published: February 2023

We have developed a method of generating a field whose amplitude is a randomly fluctuating variable, known as a real Gaussian field, as a means of testing the effect of laser bandwidth on nonlinear optical interactions. The frequency of this field is constant, and its amplitude, restricted to real values, varies about a mean value of zero. We have measured the intensity autocorrelation function of the light, and it shows good agreement with expected results. We are now measuring the effect of this field on nonlinear systems. The first is the 3S-5S two-photon resonance in atomic sodium. Enhancement of the two- photon absorption rate by a factor of three over the absorption rate from a monochromatic field of the same average intensity is expected. The real Gaussian field is also being applied to studies of transmission through a Fabry-Perot interferometer. The intensity spectrum is expected to consist of peaks centered at zero frequency and at the difference between the laser frequency and that of the peak of the interferometer transmission.
Space-variant interconnects using diffractive-lenslet arrays
Authors: Jahns J. , Däschner W.
Published: February 2023

Free-space optical interconnects offer a large spatial and temporal bandwidth, which is of interest for applications in VLSI systems and in all-optical computers. Space-variant interconnects, such as the perfect shuffle or cyclic shifting operations, are more useful than space-invariant interconnects but are harder to implement optically. One approach to implementing space-variant interconnects is to use optical systems consisting of lenslet arrays with one lenslet for each input pixel or group of pixels.1,2 In this paper, we investigate the use of diffractive lenslet arrays for this purpose. The lenslets are implemented as phase components with discrete, multiple phase steps by means of photolithographic fabrication techniques.
Optical digital pipeline processor using symmetric self-electro-optic-effect devices
Authors: Craft Nicholas , Prise Michael , LaMarche R. E. , Downs M. M.
Published: February 2023

We constructed an optical digital processor in which large arrays of symmetric self-electro-optic-effect (S-SEED) devices are available for use as optical logic gates. Four arrays were used, and 32 devices on each array were connected to the next array via a free-space optical split and shift network. Patterned masks, which blocked some of the light beams, were used to configure the ma chine. The optical power supply consisted of a pair of 850 nm, 10 mW laser diodes for each gate array. A Dammann grating was used to split each pair of laser beams into an array of 32 beams. When these beams reflected off one of the S-SEED arrays, they became the input signals to the next array. We used polarizing beam splitters and placed patterned mirrors in focal planes to combine the two inputs and the power supply beams at the device and to retrieve the reflected output. The system was clocked by current modulating the lasers. Two circuits were demonstrated: a shift register that used 1-input gates and a selector/decoder that used 2 inputs. The former circuit ran at 1 MHz, the latter at 70 kHz.
Optical hypercube interconnections using a corner-cube array
Authors: Sheng Yunlong , Arsenault Henri H. , Bedard Benoit
Published: February 2023

The retroreflective properties of a corner cube can substantially reduce the need for alignment accuracy in optical chip-to-chip interconnections. We specially designed corner cubes with dihedral angles slightly different from right angles, so that the reflected beams are split into two-, four-, five-, or six-spot image patterns for a point source, depending on the dihedral angles. Arbitrary spot pat terns may be obtained with a corner-cube design by mean sofa ray-tracing and iteration procedure. We have shown that under the paraxial condition, these corner cubes are not sensitive to variations of the incident angles. When the source is laterally shifted by some misalignment, the spot pattern will follow the source and will suffer a second-order infinitesimal deformation. Corner-cube reflectors can be made in the form of micro-tetrahedral prisms with dimensions of several microns that will allow a high fanout number. We propose a geometric arrangement for positioning the sources and detectors on the chip and have demonstrated a 4-cube network in a space-invariant interconnection system using two corner cubes, each having a six-spot image pattern.
Optical disk based acousto-optic spectrum analysis
Authors: Riza Nabeel A. , Psaltis Demetri
Published: February 2023

This paper introduces optical disks in acousto-optic spectrum analyzers. In 2-D time and space integrating acousto-optic folded spectrum analyzers, electronic reference signals are used in the temporal spectral processing. In order to obtain complete folded spectrums, these reference signals have to be of extremely high timebandwidth product, and require extremely fast serial readout rates. It is difficult to generate these signals using electronics, and so far, only incomplete folded spectrums have been obtained. We address the signal generation problem by combining the angular motion, high storage capacity, and parallel access capability of optical disks. The disk is introduced as an optical distributed local oscillator generator and a light sampling 1-D spatial light modulator. The distributed local oscillator architecture forms the basis of a continuous wave 1-D time integrating spectrum analyzer. The reference signals are stored as concentric channels on the disk surface. When the disk spins with a constant angular velocity, each circular channel acts as a modulating light source with a specific on/off frequency. This angular motion creates an array of temporal oscillators along the radial direction of the disk. When the input test signal frequency matches one of the disk channel temporal frequencies, a positive build-up of charge occurs on the time integrating detector, indicating a frequency match. A simple disk system is demonstrated in the laboratory. The disk can also be used in a 2-D time and space integrating architecture, where radial sections of the disk are used for storing the columns of a DFT matrix used for temporal spectrum analysis.
Operation of grating surface-emitting lasers with a buried grating structure
Authors: Liew S. K. , Carlson N. W. , Bour D. P. , Evans G. A. , Vangieson E.
Published: February 2023

The design, fabrication, and operating characteristics are presented for grating surface-emitting lasers containing a buried grating structure.
Measurement of single-beam gain in bistable diode laser amplifiers
Authors: Pan Zeqi , Lin Hongchin , Dagenais Mario
Published: February 2023

Applications of bistable diode laser amplifiers include photonic switching, optical interconnects, and signal processing. Typically, these applications require being able to regenerate the input signal. We present a detailed study of gain in bistable diode laser amplifiers as a function of cavity detuning and for different biasing currents below threshold.
Soft-x-ray optics and their application to lithography
Authors: Hawryluk A. M.
Published: February 2023

In the past decade, there has been tremendous advances in our ability to generate, control, manipulate, focus and detect x-rays. The past few years have witnessed the developments of normal incidence x-ray mirrors, beamsplitters, diffraction limited lenses, etc. Using these capabilities, workers are taking the first steps towards the development of sophisticated soft x-ray optical systems for microlithography. Details of these developments and the requirements for submicron lithography are discussed.
Long-lived states of the quantized field in a laser
Authors: Gea-Banacloche Julio
Published: February 2023

The lifetimes of different pure states of the quantized field in a single-mode laser (Scully-Lamb model) are considered. For operation high above threshold, I have shown number states to have extremely short lifetimes: Long lifetimes require coherent superpositions of neighboring number states with a width of the order of the square root of the average photon number. Thus, the long-lived states approach classical states. I propose a definition of the lifetime, which is found to be maximized by states that resemble the conventional Glauber coherent states, although they are slightly narrower in photon-number distribution. This is in contrast to the steadystate photon-number distribution for an ensemble of identical lasers (as given by the diagonal steady-state density matrix), which is wider than a coherent state. Possible interpretations and implications of these results are discussed.
Contrast sensitivity to a sum of gratings: the effects of orientation range and number of components
Authors: Rovamo Jyhki , Thompson Caroline , Näsänen Kristo
Published: February 2023

Using a two-alternative forced-choice method and computer graphics, we measured contrast sensitivity to a sum of 216 gratings with the same spatial frequency, phase, and contrast but with different orientations. The orientation difference () was the same between all components of the sum. The range of (0180/N) decreased with increasing number (N) of components. Contrast of each component was C/N. Contrast sensitivity was found to decline with increasing β, and the steepness of decline increased with N. However, irrespective of N, the decrease of contrast sensitivity levelled off at the largest values of . In addition, for 23, 4, and 516 components, contrast sensitivity at the largest values of β was respectively less than, equal to, and better than contrast sensitivity to a single component. These results cannot be explained by probability summation and two-dimensional spatial frequency channels with fixed bandwidths. When the Michelson contrast sensitivities were transformed to contrast sensitivities and plotted as a function of the orientation range or components, i.e., (N-1) , it was found that, irrespective of N, contrast sensitivity was at first constant, then decreased, reaching a shallow minimum, and then increased thereafter. This suggests that the effectiveness of the detecting mechanism in collecting signal energy varies little with orientation range and is only slightly affected by N.
Femtosecond-to-picosecond time-resolved detection in amplitude and phase
Authors: Yan Chi , Diels J.-C.
Published: February 2023

An instrument providing a complete signal diagnostic in the femtosecond-to-picosecond is important as a diagnostic tool for ultrashort sources and opens up new possibilities for studying nonlinear interactions. We apply this tool to various real and simulated femtosecond signals. The basic principle is to apply a known, reversible transformation to the pulse to be measured, in order to create a stretched signal that can be completely determined by means of interferometric cross-correlation with the original short signal. The latter is recovered by applying (numerically) the inverse transformation to its stretched-out version. Blocks of glass are used to provide dispersion in the femtosecond scale; a telescope between a grating pair serves the same purpose in the picosecond scale. The key function in determining the phase is the difference between the sum of the lower and upper envelopes, with (calculated function) and without (measurement) chirp. Fast Fourier transforms and appropriate filtering are used to determine these envelopes with maximum accuracy. The original pulse can easily be reconstructed from the complete characterization of the broadened pulse, if the transfer function of the broadening dispersion line is known.
Physics and applications of photosensitive grating formation in germanosilicate optical fibers
Authors: Mizrahi Victor
Published: February 2023

It has been some time since the observation1,2 that permanent phase gratings can be written in the core of certain, nominally ordinary germanosilicate optical fibers by simply exposing them to light from a single longitudinal-mode argon laser. Such gratings, which are automatically Bragg-matched for efficient reflection of the laser beam, typically have spectrally narrow stop bands. In the better fibers the grating grows in seconds, resulting in nearly 100% reflection of the laser beam. Besides the obvious interest in trying to understand the fundamental nature of this phenomenon, there are also clear device implications. In this talk, which will focus on recent work, I will discuss the possible underlying physics of the effect, and will review several applications.
Efficient mode conversion in telecommunication fiber using externally written gratings
Authors: Hill K. O. , Malo B. , Vineberg K. , Bilodeau F. , Johnson D. C. , Skinner I.
Published: February 2023

Optical fibers have been observed to change refractive index with UV exposure. We describe a novel approach to grating writing in optical fiber. This method involves writing the grating point-by-point through the side of the fiber by means of a UV laser source. The point-by-point writing is particularly flexible because the choices of pitch, length, and blaze of the grating are determined independently and thus offer a means of controlling the spectral response of the grating rather precisely. We demonstrate efficient mode conversion between forward-propagating modes, which gives as much as 96% conversion for near-optimal conditions over a FWHM bandwidth / = 1/300. The wavelength at which mode conversion occurs, from the fundamental LP01 to the higher order LP11 modes, is determined by the periodicity of the grating, which can be chosen to couple light at any wavelength of interest within the spectral range 6001700 nm and perhaps beyond. The technique is potentially useful for making devices such as optical fiber wavelength filters and mode converters for optical communications, as well as in interferometric and sensor applications.
Photosensitive fiber reflection gratings at 1.5 µm
Authors: Armitage J. R. , Kashyap R. , Wyatt R. , Davey S. T. , Williams D. L.
Published: February 2023

This paper reports the first demonstration of reflection gratings, operating at the important telecommunications wavelength of 1.5 m, that have been written directly into germanosilicate fibers with an ultraviolet source. Although Meltz et al.1 have recently reported similar gratings, their results were limited to the visible region of the spectrum. In our experiments we used an intracavity frequency-doubled Ar+ ion laser, producing several 10's of milliwatts of power at 257.2 nm, and a single fused silica prism to generate the two overlapping writing beams. Gratings roughly 3 mm long and having reflectivities of nearly 10% have been produced, although simple scaling of our results suggests that reflectivities approaching 100% ought to be achievable. These gratings appear to be polarization-insensitive and show no detectable out-of-band loss. By using one of our gratings as an output coupler for a high-power Er3+ doped fiber laser, we have been unable to detect any degradation in the reflectivity when it is subjected to over 300 mW of infrared power for several hours. The gratings remain stable at room temperature, although our studies have shown that at 600 C the grating reflectivity decays significantly over an hour.
Diagnosis of other vision-related diseases in cataract patients
Authors: Davis Elizabeth T. , Bass Sherry J. , Sherman Jerome , Schnider C. M.
Published: February 2023

Removal of cataracts may not improve visual acuity if the patient also has a macular, optic-nerve, or optic-pathway disease. However standard clinical tests often fail to detect these other diseases in cataract patients, especially in patients with dense cataracts. We assessed the diagnostic value of the patient's age and of a test battery that included use of the laser interferometer, potential-acuity meter, blue-field entoptoscope, and bright-flash visual evoked potentials (VEPs). Discriminant analysis allowed us to determine (1) how well these measures can discriminate cataract patients who have other vision-related diseases from those who do not and (2) which of these measures is most effective in making this discrimination. Our heterogeneous sample consisted of 112 cataract patients who underwent cataract surgery and suffered no surgical or postsurgical complications. Thirty-eight of these cataract patients (34%) had, or were shown later to have had, macular, optic-nerve or optic-pathway disease. Using Bayes' rule to maximize the overall probability of correct categorization, 72-76% of the cataract patients were accurately categorized. The discriminant analysis, however, was more accurate in categorizing cataract patients who did not have other vision-related diseases than it was in categorizing those who did. Moreover, only bright-flash VEPs were effective in making this discrimination.
Second-harmonic generation in optical fibers
Authors: Stolen R. H.
Published: February 2023

Intensive investigation has followed the surprising observation of self-organized second-harmonic generation (SHG) in optical fibers. It is now known that an alternating χ(2) grating has formed in the fiber. The grating grows by mixing of the fundamental and harmonic waves so SHG gratings can be formed quickly by seeding with a coherent second-harmonic wave. The length of the grating is determined by the bandwidth of the input waves and the intensity-dependence of the refractive index. There are now attempts to incorporate saturation and bleaching into the macroscopic mixing model and to understand the growth of the grating and the effect of phase fluctuations on seeding. The microscopic models all require some sort of defect and involve multiphoton absorption. The defects themselves could directly be the source of the dipole-allowed susceptibility, or they could provide charges which are trapped elsewhere. Most models require a large internal field to orient defects or to induce SHG through the macroscopic χ(3). There have been investigations using externally applied dc fields, and there are recent attempts to observe the internal field. While most effort is directed towards efficient doublers, SHG in fibers can provide new insights into structure and defects in glasses as well as self-organized systems in general.
Modified signed-digit higher radix arithmetic for optical symbolic substitution
Authors: Awwal Abdul Ahad S. , Karim Mohammad A. , Islam Muhammad N.
Published: February 2023

Modified signed-digit binary numbers have demonstrated the promise of carry-free addition. In this method, the to-be-added pair of numbers are mapped into an intermediate pair of numbers in such a way that when the latter numbers are added, they do not result in carry generation. The corresponding recognition and substitution operations, referred to as symbolic substitution, can be performed in parallel at all digit positions; thus, the method fits elegantly with optical computing architecture. Three-step, two- step, and single step1,2 carry-free addition based on optical symbolic substitution schemes have already been worked out for the binary system. In this paper, we extend the carry-free addition and borrow-free subtraction scheme to accommodate signed-digit trinary numbers by deriving the necessary substitution rules to perform addition/sub- traction in two steps. A number of possible sets of rules exist for addition and subtraction. The reduced minterms are derived for a possible two-or three-step holographic content addressable memory implementation.1,2
An optical-carry, look-ahead adder based on a content-addressable memory
Authors: Kostrzewski Andrew , Kim Dai Kyun , Li Yao , Eichmann George
Published: February 2023

We will discuss a new optical parallel- arithmetic processing scheme that uses a nonholographic optoelectronic content-addressable memory (CAM). To increase the processing speed, a carry look-ahead addition (CLA) scheme can be used. We will also present the design of a 4-bit CAM-based optical-carry look-ahead adder, as well as our experimental results.
A novel optical technique for realizing real-time logarithmic transforms
Authors: Zhuang Songlin , Zhang Yue , Liu Wenshan , Zhao Feng
Published: February 2023

Optical configurations are capable of performing essentially any linear operation, such as correlation, convolution, and Fourier transformation, on a function of two variables. Many signal processing techniques for radar and sonar applications require nonlinear transforms. Although a few nonlinear processing techniques have been developed, several drawbacks are associated with them. The main disadvantage of these techniques is that they do not operate in real-time. In many cases the processing period needs to be less than 10−5 s. However, no successful techniques for doing this have been reported. In the present paper we propose an optical feedback system that can be used to implement the real-time logarithmic transform. We will use two pictures as input objects to demonstrate the capability of this nonlinear processing system.
Optical higher-order symbolic recognition
Authors: Eichmann George , Koslrzewski Andrew , Kim Dai Hyun , Li Yao
Published: February 2023

We will discuss a new optical parallel-arithmetic processing scheme that uses a nonholographic optoelectronic content-addressable memory (CAM). To increase the processing speed, a carry look-ahead addition (CLA) scheme can be used. We will also present the design of a 4-bit CAM-based optical-carry look-ahead adder, as well as our experimental results.
The effect of an aperture on the spectrum of partially coherent light
Authors: Foley John T.
Published: February 2023

It is shown, for a particular class of partially coherent fields, that when such a field is incident upon a circular aperture, the spectrum of the light at an observation point in the far zone of the aperture is different from the spectrum of the light in the aperture. An expression for the spectrum at such observation points is obtained, and it is shown that the difference between the two spectra depends on the ratio of the radius of the aperture to the effective correlation length of the light in the aperture. Numerical examples are presented. My results support a recent suggestion by Kandpal el al.1 that the discrepancies found in the comparison of spectroradiometric scales maintained by standards laboratories may be due to such changes in the spectrum.
Polarization properties of planar dielectric waveguide grating couplers
Authors: Li Lifeng , Gong Qian , Lawrence George , Burke James J.
Published: February 2023

Experimental and theoretical investigations into the polarization properties of planar dielectric waveguide grating couplers are presented. The ellipticity and azimuth of the polarization ellipse of radiation modes coupled out by several different grating couplers were measured as functions of the angle between the incident guided-wave and the grating rulings. The polarization states were, in general, elliptical, and this finding agrees with the theoretical predictions in the literature. However, a major difference between TE and TM excitations was observed. The ellipticity of the radiation modes was vanishingly small when the guided wave was TE-polarized, but it was very large when the guided wave was TM polarized. This implies that a TE mode is much easier to work with than is a TM mode. The polarization state of the evanescent tail of the guided wave in the grating region is responsible for the polarization state of the radiation modes. We present simple induced dipole model that can qualitatively explain the observed polarization phenomena. Numerical results based on an exact theory and a perturbation theory are also given. The results of this research have significant implications for the design of focusing waveguide grating couplers in optical data storage heads, which will be described in a companion paper by Hwang et al.
Gradient-index materials in manufacturing
Authors: Moore Duncan T.
Published: February 2023

As axial gradient lenses have evolved, many interesting problems associated with the manufacturing of axial gradient materials have been discovered. The problems of reproducibility, of axis direction, and the difficulties of producing finished lenses are discussed.
Design of substrate-mode holographic interconnects with different recording and readout wavelengths
Authors: Amitai Yaakov , Goodman Joseph W.
Published: February 2023

A method for recording a substrate-mode holographic interconnect system has been developed. The system is composed of two identical holographic optical elements (HOEs) that were recorded on the same plate. The first one collimates a coherent point source into a plane wave that is trapped inside the plate by total internal reflection. The second HOE focuses the collimated wave into a detector. Because the possible recording wavelengths for efficient holograms are usually different from the readout wavelengths, the holographic elements must be recorded with complex wavefronts in order to assure high diffraction efficiencies and low aberrations. The complex wavefronts are derived from simple spherical holograms whose readout geometries differ from those used during recording. The method is illustrated with HOEs recorded at 488 nm and read out at 633 nm. Nearly diffraction-limited imaging and high efficiencies were achieved.
Complex homodyne laser-diode velocimeter
Authors: Wyntles Geert , Hercher Michael
Published: February 2023

We describe a laser Doppler velocimeter based on a single illuminating beam from a laser diode and employing a complex homodyne detection system. Conventional laser Doppler velocimeters are based on the detection of light scattered by particles that traverse a region illuminated by intersecting laser beams. Performance is generally improved, particularly in low-velocity applications, by means of heterodyne detection (the intersecting beams differ in optical frequency by the heterodyne frequency). The system we describe is compact and achieves precise and unambiguous measurements through the use of a complex homodyne technique. In this technique we make simultaneous measurements, updated at 5 MHz, of three interferometric signals whose phases differ by 120. These data are processed in real time to provide a linear output of unwrapped phase, whose derivative is proportional to velocity. The sample volume is illuminated by a single beam, and a complex spatial filter is used to generate the three, differently phased interferometric signals. We describe the theoretical basis for the measurement, the sensor design, and a variety of data obtained from both fluids and diffusely scattering surfaces.
Grating beam-splitting polarizer using form birefringence by electron-beam lithography
Authors: Aoyama Shigeru , Ogaki Tatsunori , Yamashita Tsukasa
Published: February 2023

We describe a novel grating polarizer, in which the ultrahigh spatial frequency gratings (USFG) with double duty ratio are alternately replaced on the land and groove of the diffraction grating. The USFG of the land, which is formed perpendicular to that of the groove, is fabricated by electron-beam lithography.1 The periods of the diffraction grating and the USFG are 20 m and 0.3 m, respectively. The depth of the grating is 1.4 m. The USFG duty ratio (L&S) of the land is 3:2, and that of the groove is 2:3. The incident light normal to the device is diffracted by Raman-Nath diffraction. The refractive indices for light polarized parallel and perpendicular to the diffraction grating are different. The duty ratio and depth of the USFG are chosen such that the phase shift is 180 for one polarization direction and 0 for the other. The zero and 1st order diffraction efficiencies were 58% and 12%, respectively, for light polarized parallel to the diffraction grating, and the efficiencies were 10% and 38% for light polarized perpendicular to the grating. The resultant extinction ratios were calculated to be −7 dB for the zero order and −6 dB for the 1st order. By optimizing the fabrication condition, an extinction ratio as high as −40 dB could be obtained.
Effect of pupil apodization on apparent visual direction
Authors: Ye Ming , Bradley Arthur , Thibos Larry , Zhang Xiaoxiao
Published: February 2023

According to standard geometrical optics, monocular visual direction for a defocused image is determined by the chief ray, which locates the center of the resulting blur circle. Recent studies of chromostereopsis have indicated that photoreceptor optics, i.e., the Stiles–Crawford effect (SCE), also affects apparent visual direction of defocused images.1,2 Because photoreceptor directional sensitivity peaks near the normal pupil center, marginal rays are less effective stimuli. If the pupil is displaced with respect to the SCE peak, the effective image may be shifted with respect to the chief ray by the SCE. Using wave optical analysis of a simple water eye model with an apodized pupil to account for the SCE, we calculated that visual direction of defocused images is significantly shifted when the model views through a displaced aperture. We have experimentally measured the effect of the SCE on apparent visual directions by comparing perceived visual directions of defocused images when subjects view through a displaced aperture under photopic and scotopic conditions. As our model predicted, the visual direction under scotopic conditions (no SCE) was determined by the chief ray, but visual direction at photopic levels was significantly different by an amount predicted by the midpoint of zero-crossings in the defocused retinal image in the apodized model eye.
Triangulation principles in confocal scanning laser systems
Authors: Reznichenko Yakov , Milbocker Michael T.
Published: February 2023

Three-dimensional imaging of the vitreous and fundus provides important information for the diagnosis and treatment of eye disease. Topographic representation of the fundus is currently accomplished by means of stereophotogrammetry and confocal laser scanning microscopy. These two methods are compared with the new method of laser scanning triangulation, which combines the concepts of confocal laser scanning and triangulation. Variations in axial distance amount to xy image displacement in the confocal plane, thus eliminating the need for a pair of images. By measuring the centroid position of the spot image in the confocal plane with a two-dimensional charge coupled device, one effectively measures the position of light passing through a confocal diaphragm the size of the smallest spatial resolution element of the detector. The result is enhanced axial spatial resolution. Axial scanning, as used in confocal microscopy, is eliminated, simplifying scanning schemes and alignment. This has the additional advantage of reducing the time required to scan the fundus and consequently reduces the deleterious effect of eye movement.