bluuebunny/crossref_metadata_2025 huggingface dataset:
FSK distribution systems with optical preamplifiers
Authors: Willner Alan E.
Published: February 2023

Frequency-division-multiple-access systems arranged in central passive-star configurations have emerged as a promising means of building communications networks. The necessary devices and systems issues have recently undergone rapid development. Distributed feedback lasers, either fixed-frequency or frequency-tunable, generally serve as transmitters. Although amplitude shift keying is simple, it appears that the modulation format of choice may be frequency-shift keying (FSK), implemented by direct modulation of the laser injection current. FSK systems not only require smaller bias currents but also yield low-chirp compact spectra that are conveniently demodulated and demultiplexed using tunable fiber Fabry-Perot interferometers. If each channel is modulated at 1 Gbit/s, such networks can attain throughputs of several hundred Gbit/s.
Precise optical frequency comb generation based on optical parametric oscillators
Authors: Wong N. C.
Published: February 2023

A novel scheme for generating a comb of precisely known optical frequency markers based on the use of optical parametric oscillators (OPOs) is proposed. The method provides identification and distribution of thousands of channel frequencies in densely packed wavelength or frequency division multiplexed systems, with sub-MHz accuracy over a large bandwidth of 10 THz or more. An OPO converts an input pump of frequency fp into two intense, coherent subharmonic outputs whose frequencies f1 and f2 are tunable and sum to fp. By measuring the beat frequency f1–f2 relative to a microwave frequency reference, the output frequencies are precisely determined, and the OPO functions as an optical frequency divider.1 A single laser can be used to pump several OPOs whose outputs can then be phase locked to provide a comb of precisely known optical frequency markers. Assuming beat detection of 500 GHz, a set of ten OPOs would cover a ten-THz band. Absolute frequency reference can be obtained if one of the outputs or the pump is locked to an atomic line. This system’s precision is limited by the pump linewidth and the OPO mechanical stability. Recent experimental work on KTP OPO-dividers is discussed.
Different effects of retinal blur on chromatic and achromatic contrast sensitivity
Authors: Valberg Arne , Seim Thorstein , Lee Barry B.
Published: February 2023

Cataract and poor refraction cause reduction of visual acuity and of sensitivity to luminance contrast. However, a blurred retinal image effects the visibility of a suprathreshold chromatic contrast much less than the same suprathreshold luminance contrast.1 The advantage of color is even more marked at threshold. A retinal blur, which reduced visual acuity from normal to between 0.1–0.05, increased luminance thresholds for large stationary targets (greater than 2–3°) and coarse gratings by a factor of 5–10, while causing only minor changes in the thresholds for detecting isoluminant gratings consisting of chromatic and white bars. The dependency of a blur-to-normal sensitivity ratio on spatial frequency is presented for luminance gratings and equiluminous chromatic/achromatic gratings. These results, and accompanying temporal dependencies, demonstrate clear differences in the physiological processing of chrominance and luminance. This was confirmed in an electrophysiological experiment where +5 diopter blur reduced the response of primate retinal Mα-cells to luminance contrast significantly, whereas the response of Pβ-cells to chrominance contrast was virtually unaffected.
Communicating with quantum interference
Authors: Rarity J. G. , Tapster P. R.
Published: February 2023

In recent experiments1 the phenomenon of two-photon interference has been studied, and apparent nonlocal interference effects have been convincingly demonstrated.2 In all these experiments interference effects are not manifest in the singles count rates but appear in the coincidence rate or rate of detection of pair events and are a result of entanglement of the pair photon wavefunction. Modulation of the coincidence rate provides the basis of various covert communications schemes. We have previously demonstrated a free-space propagation communication system using a classical time shift coding out to ranges of 200 m using light levels 1/1000th of ambient daylight levels. This has been extended to a fiber (200-m) based system that exploits nonlocal interference using a scheme first proposed by Franson? With high visibility interference effects single photons can be used to code individual bits of information leading to extremely secure communication.
Phase-conjugate quantum communication at zero error probability with finite average photon number
Authors: Shapiro Jeffrey H.
Published: February 2023

The Susskind-Glogower (SG) phase operator underlies quantum phase for a single-mode field—its phase eigenkets generate the probability operator measure (POM) for maximum-likelihood quantum phase estimation.1 For an arbitrary state, the associated phase representation is the Fourier transform of the more familiar number representation. Thus, because the number representation is a one-sided sequence, the Paley-Wiener theorem constrains the possible phase measurement probability densities for finite-energy single-mode fields,2 precluding error-free phase-modulated communication.3 The SG-POM is not an observable on the signal state space. However, by adjoining an unexcited apparatus mode, the SG-POM can be made as a pair of commuting observables on the extended, signal × apparatus, state space.2 We show that a correlated signal × apparatus state—called a number-product vacuum state—leads to a two-sided Fourier relationship that thwarts the Paley-Wiener theorem. Using this arrangement, with a phase-conjugate modulator, we obtain error-free transmission of K phase shifts at a root-mean-squares photon number of K/2. Use of this construct in interferometric precision measurements is discussed.
Quantum multiwave mixing with a local field correction
Authors: Sargent Murray , An Sunghyuck , Sipe John E.
Published: February 2023

We calculate the four coefficients for the quantum theory of multiwave mixing1 including a local field correction resulting from dipole–dipole interactions.2 We make contact with the semiclassical calculations of probe absorption and four-wave mixing coupling coefficients, and illustrate the effects of local field corrections on resonance fluorescence and coupled-mode flouorescence spectra. The method uses the hybrid quantum-Langevin-equation master-equation approach of An and Sargent.3,4 We find shifts and changes in the spectral shapes, which can be used to measure local-field corrections.
Optimization of source distributions under various constraints
Authors: Cairns Brian
Published: February 2023

The merits of various types of directed radiation beam have recently been the subject of consider able discussion. One specific area of controversy concerns the comparison of a truncated Bessel beam with a Gaussian beam, with different authors reaching different conclusions about the relative efficacy of the two beams.1 The fact that the discussion centers around the distinction between two types of beam appears to us to be inappropriate. What one really wishes to deter mine is the optimum beam field, given that there are constraints imposed by the finite aperture and by the finite amount of available energy. For this reason we reformulate the problem as one of finding the field distribution in an aperture plane that gives the best match to a desired intensity distribution in a given plane, located some chosen distance behind the aperture, given the aperture size and the available energy. We solve the problem by variational techniques. We obtain the solution in the form of an integral equation with an Hermitian kernel which, in a number of cases of interest, can be solved analytically. The extension of this method to optimizing the energy distribution in a given volume, or optimizing both the intensity distribution and the depth of focus is also presented. It results in integral equations with Hermitian kernels that depend on the quantities to be optimized. This technique makes it possible to design an optimum physically realizable beam.
How reliable are photonic band calculations?
Authors: Sozuer H. S. , Haus J. W. , Inguva R.
Published: February 2023

We have examined several methods of performing photonic band structure calculations, compared those methods with one another, and studied their rate of convergence. When the medium has a host/guest topology we found that the convergence rate is vastly different for the different methods we studied. The wrong method choice for a given medium can lead to inaccuracies of as much as 50%. This is a direct consequence of the discontinuous nature of the dielectric function and the electromagnetic fields. In the diamond lattice,1 which was reported to have a 15% band gap between the second and third bands, we find at most a 3% band gap at the maximum volume filling fraction and none for the lower filling fractions. We attribute these discrepancies to inadequate numerical convergence of the previous calculations.2 Our approach is novel in that it looks for consistency between the various methods while gradually employing up to 1100 plane waves. The trend thus observed shows that the gap is closing. Results are also reported for spheroidal particles on an FCC lattice. We found that when the medium has a host/guest topology, the effective dielectric constant is well modeled by the Maxwell-Garnett theory. The enhancement of the nonlinear optical response of the particles is also examined.
Photon emission, transverse quantum correlations and thresholdless laser action in the optical microscopic cavity
Authors: Cairo F. , De Martini F. , Mataloni P. , Santasuosso M. , Tommasini R. , Verzegnassi F.
Published: February 2023

Anomalous quantum processes in the context of spontaneous emission (SpE)1,2 and stimulated emission (StE)3,4, which are closely related to the fundamental dynamics of photon emission and to the related plane-wave quantum photon delocalization process4,5 were studied by our laboratory by use of the optical microcavity. The most efficient method we adopt in our present studies consists of a detailed investigation of the Bose-Einstein (BE) transverse quantum correlation process established within the microcavity active plane between two identical cylindrical microlasers (with diameter δ≈30 μm) excited by two identical focused pump beams (at wavelength λ
p
= 0.53 μm when working within nanosecond exciting pulse-duration (Δτ) conditions, SHG by an unstable-cavity Nd-YAG laser) and coupled to the same and common microcavity plane-wave, forward k-mode. Our investigation of the quantum coupling process consists of the determination of the thresholdless laser-gain (g) of the overall active device as a function of the radial distance s between the microlasers and determined by the position of the pump focused beams. The solution of the detailed QED intermicrolaser coupling equations leads to the determination of the s-dependence of the relevant dynamical quantity α(s), the degree of BE transverse quantum correlation by assuming the microcavity spacing

d
=

d
¯

N
,

d
¯

≡
λ
/
2

as a relevant parameter. The overall laser output radiation is detected by a high quantum efficiency, cooled photomultiplier by previous focusing onto a 20-μm pinhole, making a spatial filter that dis criminates efficiently against detection of radiation emitted on FP-cavity modes other than the forward-mode.4
Observation of picosecond dark soliton trains in optical fibers
Authors: Rothenberg Joshua E. , Heinrich Harley K.
Published: February 2023

The generation of temporal dark solitons has proved to require considerable experimental effort,1,2 where a longer pulse was modulated either in the time1 or frequency domain.2 Recently it was predicted3 that, by nonlinearly copropagating a delayed pulse pair in an optical fiber, one naturally forms a train of dark pulses that adiabatically follow the dark soliton solution. Previous attempts to observe these soliton trains using averaged cross-correlation techniques were hampered by the great sensitivity of the time position of the dark pulses to the shape, intensity, and relative phase of the input pulse pair. These parameters vary somewhat over many input pulses and thus the sharp dark pulses wash out in the background. However, by using a high-resolution single shot streak camera, this difficulty is eliminated, thus enabling the direct observation of the generated dark soliton trains. Experimentally, the dark soliton trains were generated by passing a pair of 2-psec pulses within 5-10 psec delay between them through a 100-m polarization preserving fiber. It is observed that periodic dark pulse trains are formed, and the pulse isolation and sharpness demonstrates that the intensity modulation has nonlinearly evolved from the sinusoidal interference one expects from linear propagation into dark solitons. A comparison performed between measurement and theory yields good qualitative agreement.
Ultralong haul multi-channel soliton transmission experiments
Authors: Olsson N. A. , Andrekson P. A.
Published: February 2023

Using an erbium-doped fiber amplifier loss compensated fiber loop, we have investigated the effects of soliton collisions on multiwavelength soliton data transmission. Asymmetric collisions centered at the input of the fiber or taking place over distances short compared to the amplifier spacing,1 produces permanent soliton frequency shifts that severely degrade soliton based communication systems. In extreme cases, the soliton fuses together and never separates. Symmetric collisions, that take place over distances significantly longer than the amplification period are found to produce only temporary frequency shifts of the solitons. The measured frequency shifts are inversely proportional to the wavelength separation, which agrees well with previous theoretical calculations.2 For a channel separation of more than 7 Å, soliton collisions had no measurable effect on the bit error rate and two 2-GBit/s (01010…) soliton pulse trains were propagated >9.000 km <10-9 bit error rate.
Photoinduced second-harmonic generation in rare earth-doped fibers
Authors: Krol D. M. , Simpson J. R. , DiGiovanni D. J.
Published: February 2023

The presence of defects in glass optical fibers is considered a key factor for the observation of photoinduced SHG.1 Most studies have ben concerned with Ge-doped silica fibers in which Ge-defects are the active species. Recently we have reported photoinduced SHG in rare earth-doped optical fibers that do not contain Ge.2 Conversion efficiencies in such fibers exceed those observed in most Ge-doped fibers. In an aluminosilicate fiber doped with 0.008 wt.% Ce we have observed SHG conversion efficiencies of 1.5% at input infrared peak powers of 200 W. We have investigated the dependence of the SHG efficiency on Ce concentration. Permanent χ(2) gratings were written with infrared (1.06 μm) and green (0.532 μm) light (seeded SHG) in 40-cm lengths of fiber. We discuss the SHG results as well as the luminescence spectra excitation at 1.06 μm for fibers with varying Ce concentration. Finally we have studied fibers doped with other rare earth ions and we compare their behavior with that of the Ce-doped fibers.
χ(2) tensor properties and multiwavelength erasure rates for optically encoded second-harmonic generation in semiconductor microcrystallite-doped glasses
Authors: MacDonald R. L. , Lawandy N. M.
Published: February 2023

Recently, optically encoded second-harmonic generation (SHG) in semiconductor microcrystal lite-doped glasses (SDG) has been observed.1 The most likely mechanism is the encoding of an effective χ(2) due to χ(3) of the crystallites and a periodic frozen-in de field. To clarify if this is indeed the case we have studied the properties of the effective χ(2) tensor induced during the encoding process. The SDG studied were prepared with linearly polarized fundamental (1064-nm) and second harmonic (532-nm) radiation from a Q-switched Nd:YAG laser producing 8-ns pulses. The glasses were then illuminated with fundamental light polarized linearly with an angle of polarization varied from 0° to 360° relative to the encoding polarization direction. The SHG was analyzed both parallel and perpendicular to the encoding polarization. The measured behavior matches that predicted from internal filled dc field mixing with the χ(3) of the crystallites to produce an effective χ(2). The influence of the band-gap resonance on χ(2) is determined by using glasses with band gaps above and below 532 nm. Since the de field is believed to be caused by electrons swept into surface traps during the encoding process and the ultimate use of these materials will be determined by their stability in optically illuminated conditions, we have measured the intensity and wavelength dependence of optical erasure and in prepared SDG. The results are used to distinguish between erasure by bandgap excitation and trap to conduction band processes.
Influence of H2O treatment on the photoluminescence of CdSe-doped glass
Authors: Hata C. , Hiraga H. , Omi S. , Uchida K. , Asahara Y. , Ikushima A. J. , Tokizaki T. , Nakamura A.
Published: February 2023

Semiconductor-doped glass (SDG) is an attractive nonlinear material because of its relatively large optical nonlinearity and fast response. The photoluminescence spectrum of SDG usually consists of two bands: one is a less intense and higher energy band, which is assigned to the direct carrier recombination and the other is a lower energy broader band, which seems to be caused by a trapped carrier recombination. The latter has a relatively slow decay and is required to be illuminated for fast nonlinear response.
Observation of large gain in a nonlinear acoustooptic device
Authors: Vachss Frederick , McMichael Ian
Published: February 2023

When light diffracts from sound waves in an acoustooptic (AO) device the diffraction process results in a nonlinear amplification or reduction of the acoustic signal strength in the device which, in turn, alters the intensity of the diffracting optical beams.1 We describe recent experiments using prototype AO devices designed to optimize this nonlinear response. In particular we show that the overall diffraction efficiency of these devices may be increased more than one hundred times under illumination by pulsed optical beams with intensities in the 1 MW/cm2 range. This large increase in diffraction implies that we have provided again mechanism that more than compensates for the usual attenuation experienced by high frequency acoustic waves in AO media, thus providing the potential for optically pumped acoustic oscillation. After describing our experiments and the theoretical underpinnings of these phenomena, we discuss some potential device applications of the novel AO nonlinearity.
Photorefractive wave mixing with finite beams
Authors: Krolikowski W. , Cronin-Golomb Mark
Published: February 2023

While the interaction of optical beams in photorefractive crystals can often be accurately described in terms of 1-D plane-wave approximation, 2-D models are sometimes more suitable, as suggested by recent work.1 Here we discuss some aspects of photorefractive interaction of finite size optical beams. We have solved the system of partial differential equations governing two- and four-wave mixing numerically by using iterative procedures. Simulations of beam amplification in two-beam coupling show strong beam deformation even without any spatial information imposed on them. Spatially nonuniform energy transfer is responsible for this effect. The pump beam loses energy during propagation and at the end of its passage through the beam intersection region (which was completely inside the crystal) it is strongly depleted and cannot contribute significantly to beam amplification. As the pump beam crosses through the probe, it amplifies most strongly that side of the probe that it meets first. By the time the pump has reached the far side of the probe, it is strongly depleted and less effective at probe amplification. In the case of phase conjugation through four-wave mixing, we found that the conjugate beam is strongly deformed only when the coupling constant is negative (corresponding to deamplification of the probe input beam). For positive coupling constants the output conjugate beam is a good replica of the input probe beam.
Measurements of photorefractive response times with low-irradiance picosecond and cw light sources
Authors: Yarrison-Rice Jan M. , Salamo Gregory J. , Clark William W. , Sharp Edward J. , Wood Gary L. , Neurgaonkar Ratnakar R.
Published: February 2023

Following Valley’s work,1 the theoretical expression for the space-charge field’s (Esc) buildup is derived for both cw and picosecond-pulsed low-irradiance excitation, I ≫ Isat, where Isat is the intensity at which the number of excited charges saturates. The cw and picosecond-pulsed expressions for the time-dependent Esc both reduce to where m is the modulation index of the grating and τdi is the dielectric relaxation time. An explanation of how saturation affects the growth of the space-charge field for cw vs picosecond- pulsed excitation is presented. The differential equation for the space-charge field’s time dependence is solved numerically and compared to the quasi-cw result. Theoretically, saturation effects become noticeable for an input intensity of 10−3Isat. For 10 kW/cm2 peak intensity, 22.6-ps pulses, no evidence of saturation is observed experimentally for cerium-doped Sr0 6Ba04Nb2O6 (SBN). The rise times are com parable for pulsed and cw inputs of the same average intensity, over a range of average intensities. This provides a lower limit on the saturation intensity of 10 MW/cm2. An SPPC signal is observed in rhodium-doped SBN in the first 150 pulses (3.69-ps pulsewidth) of illumination yielding an early grating formation time of no longer than 554 ps.
Optoelectronic system for 2-D nested crossbar architectures
Authors: Feldman Michael R. , Marsden Gary C.
Published: February 2023

The nested crossbar class of optoelectronic matrix vector architectures allows a varying degree of detectors, transmitters, optical fanout, area and execution time.1 The 2-D dedicated link nested crossbar is especially attractive since it performs an N×N matrix vector multiplication in O(log N) time while requiring only O(N3/2) transmitters (with O(1) fanout) and O(N3/2) detectors, thereby reducing demands on transmitter technology. The 2-D nested crossbar decomposes the matrix vector multiplication into the preliminary calculation on N3/2 partial sums, with these partial sums then being added to yield the output vector. The optoelectronic system consists of three planes of processing elements (PEs) with N PEs per plane. The first plane consists of vector input PEs each having N1/2 transmitters. The second plane consists of N PEs, each having N1/2 detectors, N1/2 transmitters, and an N1/2 × N1/2 electronic crossbar. Each second plane PE calculates N1/2 partial sums to calculate one output vector element.
Quantum well asymmetric Fabry-Perot array for second-order neural nets
Authors: Jennings Andrew , Horan Paul , Hegarty John
Published: February 2023

Multiple quantum well electrooptic (EO) devices based on the quantum confined Stark effect have been studied widely. Asymmetric Fabry-Perot (AFP)1 devices in these materials have shown promise as normal incidence devices allowing freedom for generating device arrays. We report on an array of EO AFP reflection devices that has been designed and fabricated specifically for use in a second-order neural network system. The device structure consists of 70 gallium arsenide wells 90 Å in width and 60-Å aluminum/gallium arsenide barriers within a PIN structure and an AFP resonator with back and front reflectivities of 98% and 30%, respectively. A linear array of twenty-five devices each 100 mm wide and 2.5 mm long form a 2.5-mm square of active device area, representing a binary vector with twenty-five elements. By having a double pass on the device array and rotating the device image by 90° between passes, all the terms of the autocorrelation matrix (vector cross product with itself) are generated.2 This is a basic requirement for any second-order neural network.
Wave diffraction by superposed gratings in the strongly scattering regime
Authors: Tu K.-Y. , Tamir T.
Published: February 2023

Volume holographic applications, such as high- capacity optical interconnects, involve media whose dielectric properties are modulated by multiple periodic variations which are viewed as many gratings superposed inside a single volume. To treat the corresponding electromagnetic problems, we have recently developed1 a multiple-scattering approach that uses a flow-graph representation of the scattered fields. This approach leads to very fast calculations of the relevant diffracted orders, but its application was restricted to obtaining transmitted fields in the presence of small-amplitude modulations only. Because those situations correspond to weakly scattering regimes in which backward scattering could be neglected, we have extended the multiple-scattering approach to strongly scattering regimes that require the inclusion of backward scattering effects. The improved formulation thus permits the evaluation of both transmitted and reflected fields. Numerical results will be discussed and compared with results obtained by coupled-wave methods.
10 Gb/s, 2000 km Transmission Experiment Using 28 Erbium Doped Fiber Amplifiers
Authors: Bergano Neal S. , Davidson C. R. , Maybach R. L. , Homsey G. M. , Mills M. A.
Published: February 2023

We report error-free transmission for a 10 Gb/s 215-1 NRZ signal over 2000 km of dispersion-shifted fiber using 28 optical amplifiers. The bit rate distance product of 20 Tb-km/sec is the highest yet reported for a straight-line experiment.[1][2]
Study of Pulsed CO2 Laser Beam Welding
Authors: Shimokusu Y. , Kanabushi T. , Kuri S. , Mega M. , Ishide T.
Published: February 2023

In this paper, the authors have investigated the influences of laser plasma, and thermal lens of optical components on CO2 laser welding properties. And pulsed CO2 laser beam welding have been studied in order to reduce these influences on laser welding.

On the basis of these results, we applied CO2 laser welding to the parts in the nuclear power plants.
Observation of quantum frequency conversion
Authors: Huang Jianming , Kumar Prem
Published: February 2023

Quantum frequency conversion,1 a process with which one beam of light can be converted into another of a different frequency while preserving the quantum state, is experimentally demonstrated. An implementation of quantum frequency conversion requires that an input beam to a sum-frequency generator be completely up-converted. One needs to generate a quantum state (e.g., a squeezed state or a twin- beam state) at one frequency and then show that the properties of the same state appear at the up-converted frequency. We have chosen to use nonclassical intensity correlation of the twin beams as the input quantum property because large correlations can be easily obtained by pumping an optical parametric amplifier with a mode-locked and Q-switched laser.2 After one of the twin beams is up-converted, nonclassical intensity correlations appear between the up-converted beam and the remaining twin beam. In our experiment the 1064nm output signal beam of the parametric amplifier, possessing >3 dB nonclassical intensity correlation with the 1064nm output idler beam, is up-converted into a 532nm beam. The 532nm beam shows >2 dB nonclassical correlation with the 1064nm idler beam, demonstrating the quantum frequency conversion process.
Ultrafast optical gain nonlinearities in GaAs/AlAs type-II quantum wells
Authors: Fu Winston S. , Klem J.F. , Olbright G. R. , Harris J. S.
Published: February 2023

We describe the femtosecond optical gain nonlinearities for the unusual case of electrons which are distributed between the direct-GaAs and indirect-AlAs layers in a type-II GaAs/AlAs multiple quantum-well (MQW) structure. We are able to vary the magnitude of the optical gain using a longitudinal static electric field to control the distribution of electrons bewteen the GaAs and AlAs layers. In type-II MQWs electrons initially optically excited in the GaAs layers transfer on a subpicosecond timescale to the lower lying energy level in the AlAs layers,1 resulting in electrons and holes separated in both real and reciprocal spaces. By applying an electric field in the growth direction of the MQWs we decrease the difference between the indirect- and direct-electron energy levels. The presence of the electric field redistributes the electrons toward the GaAs layer, and consequently, increases the magnitude of the optical gain. Near the indirect-to-direct crossover region, we observe ultrafast optical gain and absorption nonlinearities that replicate those observed for type-I GaAs/Al0.45Ga0.55As QWs,2 whereas in flat band (no applied field; strictly type-II) we observe the recently reported femtosecond optical nonlinearities for type-II MQWs.3
Optoelectronic Interferometry and Spectroscopy beyond 6THz
Authors: Ralph S. E. , Grischkowsky D.
Published: February 2023

We report a new interferometric technique1, to measure freely propagating THz radiation. Via this new technique which uses unamplified, 100MHz, 60fs laser pulse excitation of a two source interferometer, we demonstrate useful THz power beyond 6THz. Additionally, we were able to demonstrate the applicability of the technique to spectroscopy by measuring the absorption of GaAs beyond 5.0 THz. We used the newly developed THz radiation source2, based trap enhanced electric fields, to produce THz radiation with a total average power of 30 nW for 4 mW of incident laser power. The optoelectronic interferometer consists of two identical THz radiation sources, a high resistivity Silicon beam splitter and a cooled bolometer. The interferometer is mechanically fixed; the interferogram is obtained by scanning the relative time-delay between the two laser excitation beams. The signal to noise ratio of a single 2Hz scan was often greater than 50:1, thereby permitting iterative adjustments in real time. The interference is characterized by excellent overall symmetry and near total extinction and a temporal width of 200fs. The spectroscopic demonstration establishes the usefulness of the interferometric technique with the advantage of increased bandwidth as compared to direct measurements with fast photoconductors.
Measuring the Intensity and Phase of a Femtosecond Pulse Using Spectrally Resolved Self-Diffraction*
Authors: Kane Daniel J. , Trebino Rick
Published: February 2023

The technology of ultrashort-pulse measurement has been under development since the advent of short-pulse lasers over two decades ago. Early methods yielded only the intensity autocorrelation of the pulse.1,2 Later developments have allowed the determination of various phase distortions common to ultrashort pulses by either interferometric autocorrelations or degenerate-four-wave-mixing techniques.3,4 These methods do not yield the pulse shape or the phase (or, equivalently, the instantaneous frequency) evolution of the pulse, but instead yield traces that only roughly indicate each and require an assumed model of the pulse. Some work has been done to extract these quantities,5-7 but general methods have not yet emerged; in most of these techniques, there remains a fundamental inherent ambiguity in the direction of time, and hence also in the sign of a chirp.6 In addition, nearly all techniques that provide more than a simple intensity autocorrelation are very difficult to implement. Interferometric autocorrelations, for example, require position stability to < .1 μm.
Seeing overall structures in preattentive vision
Authors: Zhou Wei , Ouyang Xitong
Published: February 2023

According to the recent psychological researches by Julesz[1-3], Beck[4-6], and Treisman[7], human visual system operates in two distinct modes: preattentive mode and attentive mode. Preattentive vision detects local conspicuous features, called textons and directs attentive vision to the location where texton-gradients occur. The preattentive texture discrimination is the result of difference in first-order statistics of textons. Based on this theory, several computational models have been built to compute texture boundaries by computing local features and their local distributions [8-11]. Evidences presented in this paper show that preattentive texture discriminability is not merely determined by the first-order statistics of textons, but it is also under the influence of the overall structures of the textures. The overall structures of the textures which can be preattentively perceived are built on the local lightness or colors rather than the local spatial features or textons. Therefore preattentive vision is not merely engaged in detecting local features, it can also grasps the overall structures based on the variations of local lightness or colors.
Reliability of backscattering from remotely sensed reflectance
Authors: Weidemann Alan , Stavn Robert
Published: February 2023

Monte Carlo simulation is used to evaluate the reliability of backscattering calculated from remotely sensed reflectance following the equations of Zaneveld (1989). The required optical properties include upwelling nadir radiance, downwelling scalar irradiance, and the hydrosol absorption. By assuming that "shape factors" were close to unity, Zaneveld concluded that the backscattering coefficient could be calculated to within ±30%. The shape factors for Zaneveld's model relate the volume scattering function and the radiance distribution to more routinely measured quantities. This hypothesis is examined over a variety of oceanic environments with chlorophyll concentrations ranging from 0.1 mg m-3 to 1.0 m m-3 and with quartz concentrations derived from Mullenberg for Sargasso Sea. For comparison, a "blue water model" simulation containing molecular water absorption and scattering from quartz and molecular water is included. The simulations are carried out for a flat ocean surface with homogeneous inherent optical properties. Preliminary results support Zaneveld's original conclusion that the backscattering estimates error by about 30%. There is a trend for the backscattering coefficient calculated with Zaneveld's equations to overestimate the actual backscattering coefficient. Backscattering coefficients calculated employing the Preisendorfer/Mobley model, and the backscattering calculated from Morel and Gordon are also presented for comparison.
Bisection acuity as a function of stimulus energy
Authors: Traynor Charles , Palmer John
Published: February 2023

Is hyperacuity performance a complex function of stimulus luminance and duration or can it be described solely as a function of stimulus energy? This energy hypothesis is supported by the reanalysis of data from a study by Westheimer and McKee.1 Their data shows a regular relationship between subject performance and stimulus energy for a Vernier acuity task. We attempt to extend these results using bisection acuity. Subjects were shown a display consisting of three vertical parallel lines. The two outside, or reference, lines remained at a fixed separation while the middle, or test, line was free to move to the right or left. In a two-alternative forced choice paradigm, subjects were asked to determine whether the test line was positioned to the right or left of center. Thresholds were measured as a function of stimulus luminance and duration. In particular, we focused on conditions where luminance and duration vary while total stimulus energy was held constant.
Modal theory of lamellar gratings in a conical diffraction mount
Authors: Li Lifeng
Published: February 2023

Botten et al.1,2 developed a rigorous modal theory of lamellar gratings of arbitrary refractive indices and groove depth at the classical mount (grating groove perpendicular to the plane of incidence). Later, certain numerical aspects of their work was improved by Suratteau et al.3 In this paper, the results of these two groups of authors are extended to the conical diffraction mount (arbitrary angle of incidence). First, the fields in the grating region are decomposed into the H⊥ and E⊥ components. Then the coupled differential equations and the associated boundary conditions are separated into two sets identical to those for the TE and TM fields in the classical mount, provided that the wavelength is replaced by a reduced wavelength. Hence the completeness and orthogonality of the basis functions are proved, and all the theoretical results and numerical techniques of Refs. 1-3 can be used. The relative merits of different projection schemes in the final step of solving the grating problem using the method of moments are discussed. Computational results of diffraction efficiencies and polarization characteristics of lamellar gratings in conical diffraction mount are included.
Equivalence of passive and active lockin rates in a ring laser gyro
Authors: Tehrani M. M.
Published: February 2023

Passive optical gyros were believed to be devoid of the lockin effect observed in (active) ring laser gyros. The passive cavity gyro proposed by Ezekiel and Balsamo is one such concept in which electronic servo loops perform the resonance frequency tracking function. It was pointed out in Ref. 1 that the notion of resonance frequency tracking leads to the lockin effect. In Ref. 2 observation of such lockin effect was reported and various means to circumvent it were suggested. We have measured the lockin rates of twenty ring laser gyros in both passive and active modes. A computer-controlled station was developed for these experiments that measures the passive lockin rate of the test gyro. By measuring the random walk of the same gyro in the active mode its active lockin rate was obtained.
Broadband beam steering with optical arrays
Authors: Myers L. E. , Barnes L. J. , Karim M. A.
Published: February 2023

A beam steerer is necessary in laser radar systems to position the narrow transmitter beam in a larger field of regard.1 A nonmechanical technique, such as that using an optical array with a cell of electronically addressed liquid crystal phase shifters,2 is expected to replace mechanical output steering mirrors in large aperture systems with high agility requirement. Many laser radars also require a passive acquisition sensor, which should share large optical components with the active channel.1 However, the grating structure of array beam steerers causes dispersion in the broadband passive channel. This work describes results of an analysis of the far-field performance of optical array beam steerers and laboratory verification measurements. The angular dispersion is many times the far-field beam diameter for typical sensor apertures, steering angles, and bandwidths, which has a detrimental effect on resolution and sensitivity. Two correction schemes are currently being investigated: deconvolution filtering and cascaded holographic gratings. The status of their analysis and implementation is also reported.
Transient response of a two-level atom to bichromatic laser field excitations
Authors: Wu Qilin , Gauthier Daniel J. , Mossberg T. W.
Published: February 2023

Theoretical studies have shown that the transient dynamics of an undamped two-level atom, driven by a bichromatic laser field consisting of a strong resonant pump and a moderate strength tunable perturber, are complex. Among the interesting results, it has been found that the strong field tends to stabilize the atom against the influence of the perturber field.1 Exceptions occur when the perturber is detuned from the strong field by the Rabi frequency of the pump or its subharmonics. In addition, it has been found that the atomic response depends strongly on the initial relative phase of the two excitation-field components.1,2 We have constructed an experimental apparatus to study the transient response of two-level like Yb atoms to bichromatic field excitations. The transient bichromatic laser field is generated by sending a dye laser beam double pass through an AOM driven by a bichromatic rf field. All the optical field parameters, amplitudes, frequencies, and phases, are controlled by corresponding rf field parameters.
Computations of solar-induced in vivo fluorescence of phytoplankton in the ocean
Authors: Gordon Howard R. , Gong Weiyan
Published: February 2023

A quasisingle scattering (QSS) model is developed for the radiative transfer of light generated at 683 nm through the solar-induced fluorescence of chlorophyll a contained in marine phytoplankton. The model utilizes the product of the spectral scalar irradiance (as a function of depth) at the exciting wavelength and the phytoplankton spectral absorption coefficient for the fluorescence source function. The radiative transfer equation is then solved using the QSS approximation. The results of the computational model are compared to, and validated by, a dual wavelength (excitation–emission) Monte Carlo simulation of the entire process including all orders of multiple scattering at both wavelengths. The QSS solution for the fluoresced irradiance, which utilizes the Monte Carlo results for the exciting wavelength, agrees with the results of the full Monte Carlo simulation to within ~2%. In contrast, while the simpler solution used by Gordon1 works well very near the surface, it fails to predict the correct fluorescence as a function of depth. The QSS model is combined with a biooptical model of the spectral inherent optical properties of phytoplankton to study the influence of the chlorophyll concentration and its vertical profile on the apparent optical properties of the ocean within the fluorescence band. The practice of modeling the fluorescence with the aid of a spectrally averaged plankton absorption is examined and shown to be valid only near the surface.
The evolution from SEEDs to smart pixels
Authors: Miller David A. B.
Published: February 2023

The physics behind interconnection in digital systems argues strongly for the use of arrays of optical devices. System experiments in switching and computing suggest that the devices interconnected should, however, be relatively smart. Otherwise the optics, which excels at global connections, is used inefficiently to make local connection. The smart pixel might have several optical inputs and outputs, performing a relatively complex logical function such as a switching node. Symmetric self-electrooptic-effect devices (S-SEEDs)1-4. allow parallel arrays of simple logic gates as large as 128 × 256 (Ref. 4). This same technology, without any changes in the processing steps, can produce many other devices and smart pixels, all based on local electrical connection of quantum well diodes. Devices demonstrated include differential modulator arrays, differential logic gates and set-reset latches, multistate devices, switching nodes, an extended logic family consisting of a complete set of analogs of NMOS and CMOS transistor circuits2(recently demonstrated in large arrays3, and spatial light modulators.4Integrations with field effect transistor logic and with silicon integrated circuits are possible extensions of this technology.
Image speckle reduction using a synthetic aperture transmitter sparse receiver architecture
Authors: Sica Louis
Published: February 2023

An architecture and signal processing for an imaging laser radar has previously been described1 which uses a transmitter array and a spatially integrating receiver. The light reflected by an irradiated object is sensed and the time dependent signal processed so that each pair of aperture locations of the transmitter yields the Fourier transform of the object at a corresponding spatial frequency. In the case of a redundant transmitter array, the image computed from the observed Fourier transform formally corresponds to that of an object under partially coherent irradiation from a source having the same size, shape, and location as the receiver. This implies a reduction in coherent artifacts independently of object surface statistics. Image behavior in the case of nonredundance of the transmitter array has no conventional optics analog, and lower signal-to-noise ratios for speckle noise suppression.
Adaptive reconfigurable interconnects using a LCLV
Authors: Awwal Abdul Ahad S. , McAulay Alastair D. , Wang Junqing , Liu H. K.
Published: February 2023

In signal processing, optical computing, communication, holographic memory lookup, pattern recognition, capability of reconfigurable interconnection is an extremely desirable feature. Optics can offer very high bandwidth, high propagation speed, noninterfering, high density, parallelism, and also dynamic reconfigurability. Multiple correlation can be achieved using an interconnections1,2 network. Recording interferometer patterns generated by a multiple source of light, an interconnection grating may be designed. A collimating beam can be split and then reflected by plane mirrors. The reflected beams are allowed to interfere with one another and then the interference pattern is recorded on a recording device such as a liquid crystal light valve. The interference pattern, if illuminated by a plane wave, will result in providing interconnection between the read beam and different locations of the output. For reconfigurability, the angular orientation of the mirrors can be controlled by changing the actuation input to the piezoelectric mirrors or certain beams may be prohibited from interfering using electronic shutters.
Nonlinear joint transform correlator with gain using a LCLV
Authors: Awwal Abdul Ahad S. , McAulay Alastair D. , Wang Junquing
Published: February 2023

Conventional or phase-only correlators suffer from the requirement of fabrication and accurate alignment of the complex filter in the Fourier plane. A joint transform correlator, on the other hand, does not require fabrication of any complex filter and therefore is more attractive for real-time uses. In a JFT setup, the joint transform power spectrum of the input objects (i.e., the reference object and the input object) is generated and then, by performing subsequent an inverse Fourier transform on these interference fringes, the cross-correlations between these objects are produced.1 In our setup, the LCLV is used to generate the intensity fringes, and then used to provide gain. Unlike other methods no optic-to-electronic conversion is performed, since the function of the square law detector is preformed by the LCLV as required by the JFT. Therefore this system is an all-optical setup. Nonlinear operation is then achieved by changing the power of the write beam. The correlation output is fed back to observe its effect on the correlation peak.2
Polarization-encoded optical shadow-casting: efficient multiplier design
Authors: Ahmed Jamal U. , Awwal Abdul Ahad S.
Published: February 2023

A polarization-encoded optical shadow-casting (POSC) system1 exploits the parallelism of optics to process 2-D coded input data in parallel. Previously, a multiplier2 was designed capable of generating four output bits in parallel; however, each input required 9-pixel subcells for encoding. In the current work, the previous design is optimized using minterm pairing and associative sharing of minterm pairs1 among different output bits. The resulting size of the pixel then becomes 6. The design process exemplifies how in a systematic way one can design a highly optimized POSC computing module. All multiplier outputs are generated and detected in parallel. The resulting coding of the inputs and the space variant output decoding mask to detect the outputs in parallel are provided.