bluuebunny/crossref_metadata_2025 huggingface dataset:
Average dwell times in a semiconductor laser
Authors: Fabiny Larry , Roy Rajarshi
Published: February 2023

Experiments have shown that the output of semiconductor lasers can exhibit mode hopping between two longitudinal modes. Although the total output power remains constant, the power in one mode will switch cleanly between two values, with the time between switches varying randomly. The average dwell times in each state have been observed to be functions of the ratio of the time-averaged powers of the two modes. A theory based on a first passage time formalism is applied to calculate this dependence in two-mode semiconductor lasers. Beginning with the coupled Lamb equations for a two-mode laser, the solution of a Fokker-Planck equation yields analytic results for the mode intensity averages. Average vs dwell times are calculated from the average first passage time between states for one mode. Analytic results for the average relative mode intensities vs dwell times are compared with experimental data for a semiconductor laser.
Observation of tangent bifurcation in an active interferometer
Authors: Liu Yun , Ohtsubo Junji
Published: February 2023

Recently, we presented an optical bistable system that consists of a laser diode interferometer with an optoelectronic feedback circuit. We analyzed the nonlinear property of the system and predicted that the unstable light output of the laser diode exhibits chaotic behavior provided an appropriate time lag is introduced in the feedback loop. In the present paper, we report the experimental observation of tangent bifurcation in the light output. We show that the laser output turns out to be a stable period three-cycle in a certain range of the bias injection current. This stable period three-cycle, however, will become unstable and evolves into its higher-even-order harmonic solutions with the increase of the delay time. Up to eighth-order harmonic solutions are experimentally observed. A reasonable interpretation of the phenomenon is given by considering the continuity model for the actual system. At the nearby parameter value of the tangent bifurcation, we also observed an unstable light output. Such instability may be considered as a type of intermittent chaos.
Cavity quantum electrodynamics
Authors: Hinds E. A.
Published: February 2023

A description was not available at time of publication.
Mathematical techniques for guide star experimental analysis and design
Authors: Tyler Glenn A. , Roberts Phillip H. , Steinhoff Karl E. , Moretti William
Published: February 2023

The utility of various mathematical techniques in assessing and predicting the performance of guide star wavefront compensation experiments is addressed. The techniques discussed include optimal estimation theory, matrix reconstruction, rapid evaluation of guide star performance using Gegenbauer polynomials and Mellin transforms, noise theory, and techniques for wave optics simulation of guide star experimental performance. After a brief introduction to the theory a comparison of the analytical predictions are made with the results of experiments. The H-matrix wavefront reconstruction technique used in the first guide star experiment is discussed. This technique is of note because it was the first time that an optimal estimator was used that took the statistics of turbulence and noise into consideration. In addition, the design of the reconstructor was such that an assessment of r0 and the subaperture tilt measurement noise was also reported. Because of these factors an accurate comparison between the experimental results and theory could be made; the degree of agreement was excellent.
Smart pixels for a two-butterfly interconnection network
Authors: Lu Dau-Tsuong , Paturi Ramamohan , Fainman Yeshaiahu , Lee Sing H.
Published: February 2023

Packet routing on multistage interconnection networks such as butterfly and shuffle-exchange experiences a delay of

O

(

N

)

, where N is the number of processing elements, when several packets have to travel the same path. Furthermore, these interconnection networks do not provide good fault tolerance because a small number of physical paths correspond to each logical path even when additional stages are used. Expander graphs have been shown to support asymptotically optimal parallel algorithms and routing. Leighton and Maggs1 demonstrated that random permutations applied to the conventional butterfly network tend to distribute the messages equally on the average over all links, thus significantly reducing contention. Simulations show that these two-butterfly networks have significantly lower delay and better fault tolerance (up to N3/4 random faults). Arora et al.2 recently gave an on-line algorithm for nonblocking routing using two back-to-back 2-butterflies. We examine the implementation requirements of the two-butterfly network and conclude that optoelectronic technology is favorable for large scale implementation.
Polarization modulation in shaped microparticle suspensions
Authors: Rogovin D. , Scholl J. , Pizzoferrato R. , de Spirito M. , Marinelli M. , Zammit U.
Published: February 2023

This paper presents a combined theoretical and experimental study of polarization modulation of laser light in an aqueous suspension of shaped PTFE microparticles that are maintained in an ac electric field. Both steady-state and transient behavior are examined, with theory and experiment being in excellent agreement. This work complements previous studies of the influence of an electric field on the optical characteristics of shaped microparticle suspensions that focused on electric field-induced birefringence. Furthermore, these studies examine the transient and steady-state properties of PTFE in both the weak (electric) field, i.e., the diffusive regime, as well as the strong field, drift regime yielding a complete picture of the suspension’s dynamics and optical characteristics. As a result of the large microparticle anisotropic susceptibilities of PTFE, the different polarization states can be readily achieved with relatively modest electric field strengths of the order of several hundred volts/cm for volume fractions on the order of 1%.
Chaotic energy exchange via multiple four-wave mixing in single-mode optical fiber
Authors: Thompson John R. , Roy Rajarshi
Published: February 2023

Understanding the nonlinear interactions of multiple frequencies in optical fiber is of interest because of its relevance to wavelength division multiplexing. We consider the copropagation of two pump pulses at frequencies ω1 and ω2 down a single-mode polarization maintaining a fiber. At sufficiently high intensities the two lasers will interact by four-wave mixing (FWM) to produce symmetric pairs of sidebands at ω1 - ω2 and 2ω2 - ω1. This process can continue to produce cascading pairs of sidebands. We develop a theoretical framework describing the interaction of six frequencies (the two pump lasers and two pairs of FWM sidebands) by seven different FWM processes. Numerical studies demonstrate the possibility for periodic and chaotic energy exchange between the six waves as they propagate in the fiber. This chaotic energy exchange is probed both numerically and experimentally by studying the statistical properties of the first pair of sidebands in conditions where the model predicts periodic behavior and where the model predicts chaos.
Field–atom dynamics of the Jaynes-Cummings model for large initial fields
Authors: Gea-Banacloche Julio
Published: February 2023

For large initial fields, the evolution of the Jaynes-Cummings model is shown to simplify considerably. For two special initial atomic states (the eigenstates of the semiclassical problem) one finds a disentangled, quasipure-state evolution for both the field and atom. For an arbitrary initial atomic state the evolution is a linear super-imposition of these two privileged alternative paths. New results include the fact that the state of the atom at half-revival time is pure and independent of the initial state (nonunitary evolution), and that the state of the field at that time is a coherent super-imposition of macroscopically distinct states (Schrodinger cat).
Electromagnetic simulation of image formation
Authors: Yuan Chi-Min
Published: February 2023

Optical methods are predominantly used in the photolithography process for linewidth measurement, mask and wafer alignment, and photoresist image formation. As the feature size required for modern semiconductor devices shrinks, it is becoming more difficult to accurately print and measure these fine features on the wafer surface. Simulation of the image formation can aid us in understanding the usefulness and limitation of these optical methods, so that improvement can be made to achieve better accuracy. Approximate theories such as scalar diffraction theory do not explain many of the phenomena, and sometimes rigorous E&M theories beyond Born and Wolf’s level have to be used. Several rigorous scattering models applied in the photolithography areas are introduced first. Most of these models fall into two categories: time-domain solvers and frequency-domain solvers. Maxwell equations are solved by these models to different degrees of rigor to compromise between accuracy and speed. Hardware constraints may exist because of the different algorithms used for the models. The pros and cons of these models are discussed. Finally, the discrepancies existing in today’s models as well as the future needs for more rigorous electromagnetic simulations are explained. Hopefully the photolithography simulation community can benefit from the people who specialize in the E&M field but do not specifically work in the integrated circuit area.
Electrooptic polymer films with organic photoconductors
Authors: Schildkraut Jay S.
Published: February 2023

We describe electrooptic (EO) polymer films that also exhibit photoconductivity. An acrylic polymer containing a stilbene chromophore with a high second-order nonlinear susceptibility was doped with a perylene sensitizer for photocharge generation and a triarylamine hole transporting molecule. A polymer film was fabricated that had an EO coefficient of 2.5 pm/V. Absorption of light by the sensitizer results in a photocurrent and charge trapping. The efficiency of photocharge generation at 515 nm with 120 V applied across a 1.27-µm film was 1.4 × 10-3 mobile charges per absorbed photon. The photorefractive sensitivity was 3.7 × 10-6 cm3/J. We also describe a multi-layer structure with the following layers: an indium tin oxide electrode, an electrooptic polymer film, a mixed perylene-triarylamine film, a pure triarylamine film, and a gold electrode. The two films that contain the triarylamine hole transporting molecule act as a photodiode.
Plasma activated chemical vapor deposition of polythiophene thin films
Authors: Targove J. D. , Haaland P. D.
Published: February 2023

Polythiophene thin films with useful nonlinear optical properties have been deposited by a novel plasma-based technique. In the work, an excited argon metastable flow is created by a 13.56-MHz plasma discharge. A gas flow of 2,5-dichlorothiophene in an argon carrier gas is then injected downstream of the discharge so that the monomer is not subjected to the harsh plasma environment. We believe that electronically excited argon atoms excite the monomer by Penning ionization, with the ions depositing onto the growing film. 2,5-dichlorothiophene is required to drive 2,5-polymerization and to achieve piconjugation in the films: thiophene starting material results in films with random 2,5- and 2,4-polymerization, limiting the conjugation. The resulting films are microscopically dense and smooth, and a third-order susceptibility of 10-11 esu has been measured at 602 nm by degenerate four-wave mixing.
Imaging with off-axis guide stars
Authors: Tyler Glenn A. , Steinhoff Karl E. , Moretti William
Published: February 2023

The theory associated with using a guide star beacon in a different direction than the direction associated with an object is discussed in detail. It is shown that conventional anisoplanatism does not significantly degrade the performance of a synthetic guide star. The theoretical predictions are shown to be in agreement with the results of a guide star imaging experiment used to view binary stars. This work concludes with a discussion of an advanced concept that utilizes an optimal estimator to combined wavefront sensor data from a nearby guide star several isoplanatic patch sizes away from the object and wavefront sensor data from an artificial guide star to compensate the image. The results of this work illustrate that the typical D5/3 (where D is the telescope diameter) scaling law for mean-squares wavefront error is no longer obeyed when this approach is used. As a consequence, this technique allows one to compensate telescopes with diameters larger than what would normally be the case with conventional guide star imaging techniques.
Effect of dead space on gain and noise double-carrier-multiplication avalanche photodiodes
Authors: Hayat Majeed M. , Saleh Bahaa E. A. , Teich Malvin C.
Published: February 2023

The effect of dead space on the mean gain and the excess noise factor of double-carrier multiplication avalanche photodiodes has been studied using recurrence relations in the form of coupled integral equations. The dead space is the minimum distance that a newly generated carrier must travel to acquire sufficient energy to become capable of causing an impact ionization. These equations are solved numerically to produce the mean gain and the excess noise factor. We have found that dead space reduces the mean gain since it results in fewer ionizations. The reduction is relatively greater as the hole-to-electron ionization ratio k approaches unity since the growth rate of the branching process is reduced by the inhibiting effect of dead space. We also show that dead space causes a lower excess noise factor since it introduces some orderliness in the random ionization process. In certain conditions the dead space has a beneficial effect on the performance of the optical detector when used in optical receivers with circuit noise. It may therefore be advantageous to select materials for which the dead space is enhanced, without jeopardizing other parameters such as large electron ionization coefficient and small k.
Backscatter from a tilted rough disk
Authors: Schertler Donald J. , George Nicholas
Published: February 2023

We present theoretical and experimental results for the backscattered intensity from a roughened metallic disk tilted at an arbitrary angle to the incident illumination. As the rms roughness is increased from 1 to 10 µm the zero-tilt intensity decreases by >1000 but at a 75° tilt it is shown to increase by >100. We also investigate the decor-relation of speckle with wavelength at various tilt angles. Tilting the surface to the illumination and then observing the intensity pattern in the specular direction gives a means of characterizing the roughness parameters. In performing the calculation the effect of shadowing must be included. We analyze this effect by comparing the calculated results with shadowing to those without shadowing. The effect becomes significant for moderate tilt angles (>60°) and large roughness. In addition we review recent developments in enhanced backscatter as applied to rough surfaces. Several techniques for producing the roughened surfaces are also described including beadblasting, photolithography/ion-etching, and exposing the photoresist to controlled speckle patterns. These techniques give us the ability to produce surfaces with rms roughnesses ranging from 1 to 10 µm and correlation lengths from 1 to 50 µm.
Substrate inclination measurement monitor using a linear grating coupler
Authors: Shiba Masataka , Fukuda Kenichiro , Hira Yasuo
Published: February 2023

To obtain higher optical performance in semiconductor lithography or metrology systems, inclination control of the wafer substrate surface is becoming more important. An inclination measurement monitor attached to these systems requires high measurement accuracy, ability to deal with patterned and resist coated wafer, and compact size. The linear grating coupler of the optical waveguide element is sensitive to the incident beam angle. This characteristic was considered a weakness when used in a conventional optical measurement system. However, for the inclination measurement, this becomes a valuable characteristic. To verify inclination measurement ability of the linear grating coupler (TiO2) formed on the optical waveguide device (Ti-diffused LiNbO3), an experimental system was produced. A collimated s-polarized He-Ne laser illuminated the wafer surfaces (incident angle = 60°) and coupled light intensity of the reflected or scattered light from the tested surface was detected. Inclination of the substrate was obtained from the maximum intensity position. Standard deviation of the measurement accuracy of the order of < 10-6 radian(σ) was confirmed even when a patterned and resist coated wafer was measured. The experimental results fit the numerically simulated results.
Use of rigorous diffraction analysis for characterization of latent image gratings
Authors: Bishop Ken , Gaspar Susan , Hickman Kirt , Sohail S. , Naqvi H. , McNeil John R.
Published: February 2023

Rigorous coupled-wave analysis developed by Moharram and Gaylord is used to model the diffraction from arbitrarily shaped latent image gratings. Latent image gratings are of wide interest because of their use in photolithography and, therefore, the microelectronics industry. A photomask with a grating pattern is used to expose periodic lines in the photoresist, producing a periodic index variation in the photoresist (latent image). The resultant lines after development of the photoresist are directly related to the shape of the latent image. The capability to characterize submicron gratings is of great importance as a result of the decreasing dimensions of feature sizes. Modeling of the latent image considers the effects of linewidth, sidewall angle, groove depth, and other arbitrary index profiles. The intensities diffracted into the various orders is greatly dependent upon the geometry of the grating. Utilizing the information provided by the zeroth-, first- and second-order diffracted powers, we are able to predict many characteristics of line geometries.
Moving optical-index gratings in shaped microparticle suspensions
Authors: Pizzoferrato R. , De Spirito M. , Marinelli M. , Zammit U. , Rogovin D. , Scholl J.
Published: February 2023

Experimental and theoretical studies of moving optical-index gratings created by circularly polarized laser radiation in liquid suspensions of polytetrafluoroethylene (PTFE) are reported. The transient and steady-state optical characteristics of these gratings were studied at visible wavelengths using coherent beam combination via nondegenerate two-wave mixing (NDTWM) as a probe. In NDTWM, coherent energy transfer is achieved by creating optical-index gratings that are out of phase with respect to the coherent electromagnetic interference pattern that establishes them. This can be achieved by using two beams operating at different laser frequencies, ω1, and ω2, to construct an index grating oscillating at the laser difference frequency. The coherently scattered, high frequency photons acquire the phase, frequency, and wave vector of the low frequency wave. The dependence of the two-wave mixing gain coefficient on beam polarization, laser frequency-difference, pump intensity, and volume fraction was measured and found to be in accord with theory. In addition, transient studies were conducted that examined the formation and decay of moving optical-index gratings in these media which confirmed the theory. Finally, beam combination was also achieved using degenerate laser beams and moving the suspension relative to the laser interference pattern.
How to pick a winning product, market it, and build a successful business around it: a panel discussion
Authors: Kressel Henry , Schlater James , Berger Joseph
Published: February 2023

Summary not available.
Squeezing in an optical parametric oscillator with arbitrary mirror out-coupling
Authors: Prasad Sudhakar , Abbott Bartram S.
Published: February 2023

We consider here the problem of quantum noise in light produced by an optical parametric oscillator operating below threshold inside a singlesided cavity. By employing the correct boundary conditions on quantum fields at the output mirror, a procedure that is valid for arbitrary mirror transmission, we derive exact expressions for quantum noise reduction for arbitrary pump phase and mirror out-coupling. We find that for a given out-coupling, squeezing of quantum noise in the intracavity field increases to a final value of 50%, as the pump intensity is increased and the oscillation threshold is approached. The output field on the other hand exhibits perfect squeezing of noise in one quadrature of its central Fourier component at threshold regardless of the mirror out-coupling. The present approach, which is based on boundary conditions, is quite general and applicable to any matter-field interaction problem inside a cavity. In fact, we have previously employed this approach in the calculation of the intrinsic linewidth of a laser with arbitrary out-coupling.1
Design and optimization of multilayer waveguide devices
Authors: Houde-Walter S. N.
Published: February 2023

Truly monolithic integration of optoelectronics requires compromises between the individual component and system performances. Design of integrated systems can benefit from the full power of an optimization algorithm, especially in the presence of competing design requirements. Evaluation of the merit function during optimization requires repeated calculation of waveguide modes. Combing the complex plane for solutions to the dispersion relation is too computation-intensive to be practical, particularly for multi-moded and lossy structures, and there is no guarantee that all solutions will be found. Instead, we have demonstrated a numerical technique, based on Cauchy’s integral equation that allows unambiguous identification of all modes in structures with arbitrarily high losses using very short computation times.1 Further, by plotting the solutions in the complex plane as a function of the square of the complex propagation constant, we observe that the solutions tend to be highly patterned in such a way as to lend insight into the behavior of a wide variety of waveguides.
Femtosecond generation of x-rays below 0.4 Å
Authors: Kmetec J. D. , Gordon C. L. , Lemoff B. E. , Harris S. E.
Published: February 2023

We have observed substantial hard x-ray emission from a high-power femtosecond laser-produced plasma. The laser is based upon chirped pulse amplification in Ti:sapphire, and produces 60-mJ 125-fsec pulses at 10 Hz at 807 nm. This output is focused onto a heavy metal in vacuum. The focused intensity is approximately 5 × 1017 W/cm2, with a repetition rate of 10 Hz. We estimate an incident laser energy to x-ray energy conversion efficiency of ~10-5 when gold is the target material. The conversion efficiency includes only those x-rays that pass through 4.7 mm of aluminum (photon energy greater than ~35 keV). We have demonstrated that this is a sufficient number of x-ray photons (~1 μJ) to record an x-ray shadowgraph with one laser shot. We anticipate that the x-ray pulse duration is similar in time duration to the driving laser pulse.
Cavity QED enhanced emission in microdroplets
Authors: Campillo A. J. , Eversole J. D. , Lin H.-B.
Published: February 2023

We observe spontaneous emission lifetime shortening and enhanced lasing gain in 10 μm diameter liquid droplets. Nearly transparent microdroplets act as high Q resonators; the feedback provided by totally internally reflected light waves at the droplet–air interface that fold back on themselves. Purcell’s formula predicts significant enhancement (>106) of molecular emission in droplets of this size. Such large values are not easily achieved in direct lifetime measurements because typical broad fluorophor emission bands generally encompass spectral regions of inhibition as well as enhancement. We observe lifetime shortening of 2.5× in the emission lifetime of [Eu(BTF)4P] in DMF/alcohol solution droplets. Lasing gain measurements, however, have a spectral advantage (inherently narrow linewidth) and yield enhancements that approach the Purcell value. We observe1 enhancements in excess of 100 for Rhodamine 6G in ethanol solution droplets when mode Q values are only 3 × 103. First, we identify the various modes observed lasing since specific mode order determines Q which can vary from 103 to 108. Next, the concentration N, of the dye is reduced until a point is reached where the specific mode of interest fails to lase. The cavity loss per unit length, estimated from Lorenz-Mie theory, may then be equated to gain per unit length to yield an enhancement, η [i.e., Nησcm ≈ 2πzmx/Q]. Here x is k times the droplet radius, σcm the noncavity emission cross section, and m the index refraction.
Solitons for long-distance transmission
Authors: Mollenauer L. F.
Published: February 2023

This tutorial describes ultralong distance transmission of solitons through a chain of erbium amplifiers and dispersion shifted fiber segments. In particular, it is shown how solitons are robust against reasonable fiber and other system defects, and how the transmission capacity is limited only by the effects of amplified spontaneous emission noise. Experimental verification, including measurement or error rates to less than 10-9 at multi-Gbit/s rates over distances of 9000 km or greater, is described. It is also shown how single channel rates of 2.5 or 5 Gbit/s can be multiplied at least several times by wavelength division multiplexing (WDM), or by a combination of WDM and polarization division multiplexing.
Experimental quantum nondemolitional measurements using soliton collisions
Authors: Friberg S. R. , Machida S. , Yamamoto Y.
Published: February 2023

The collision of two optical solitons, one a probe and the other a signal, writes out the energy of the signal soliton as a phase shift of the probe soliton. Consequently, a readout of the probe phase shift gives the photon number of the signal soliton. If the collision takes place in a low-loss optical fiber with the usual Kerr nonlinearity, the photon number of the signal soliton is preserved, and the measurement can be a quantum nondemolitional (QND) measurement. We describe experimental progress towards soliton collision QND measurements. We have collided two solitons at 1.460 nm (probe) and 1.463 nm (signal) and with the help of a delayed reference soliton (identical to the probe) in a homodyne detector system, we have measured the resulting probe soliton phase shifts. Toward a QND measurement, we correlate the shot noise fluctuations of the signal soliton with the corresponding phase noise fluctuations written on the probe. We present our current results.
Forward Brillouin scattering in dual-mode optical fiber
Authors: Russell P. St. J. , Pannell C. N.
Published: February 2023

Forward stimulated Brillouin scattering (FSBS) is similar in physical origin to conventional backward SBS (BSBS), except that it occurs in a forward direction between two nondegenerate copropagating optical modes of a dual-mode optical fiber.1 FSBS may, however, be the only example of a nonlinear effect where the threshold falls as the mode spot size is increased. This curious behavior is a consequence of the fact that the acoustic gain depends on an electrostrictive moment and not (as in conventional SBS) a pressure. Intermodal beating between an LP01 and a frequency shifted LP11 mode gives rise to a moving interference pattern with regions of constructive interference that alternate across the core. In the correct matching conditions, electrostriction will feed optical energy into a flexural mode of the fiber. The results of a theoretical study of FSBS are presented, including calculations of the threshold power (only weakly dependent on the laser linewidth, owing to the copropagating nature of the process) with a discussion of the novel phenomenology caused by long phonon lifetimes. We also show how the theory may be used to design special fibers in which the FSBS threshold power is many times smaller than in BSBS.
Dynamic theories of nonlinear interface switchings
Authors: Khoo I. C. , Zhou P. , Lindquist R. G. , LoPresti P.
Published: February 2023

Using highly nonlinear and transparent liquid crystals in their mesophases and liquids, it is possible to construct practical optical switches that operate in the visible as well as the infrared spectral regimes, using the nonlinear interface electrodynamic effects (total internal reflection to or from transmission states). We show by theories and experiments that the dynamics of these processes are all highly dependent on the thickness of the nonlinear film, as well as other spatio-optical-geometrical factors. Furthermore, in the case of total reflection to transmission switching, the increasing penetration of the incident laser into the nonlinear film, in conjunction with its spatial intensity profile, could lead to highly intensity dependent spatial phase modulation effects. With appropriate coatings and optical system designs, these effects could be used to enhance the performance of nonlinear optical switches.
Tunable fiber filter technology for dense WDM systems
Authors: Miller Calvin M.
Published: February 2023

Until recently, optical receivers using coherent detection were considered the only alternative for achieving the high sensitivity and selectivity needed for dense WDM systems. Within the last two years high-gain erbium-doped fiber amplifiers (EDFAs) and tunable narrowband fiber Fabry-Perot (FFP) filters have been used at the input of high performance, direct detection receivers and proposed as practical alternatives to coherent detection. Aside from 2- or 3-dB less sensitivity, these direct detection receivers offer significant reductions in complexity and polarization sensitivity and are easily achievable from commercially available all-fiber system oriented components. The FFP filters used in these direct detection receiver experiments combine the extremely high optical resolution of Fabry-Perot interferometry, the subangstrom positioning capability of piezoelectric transducers, and the superior stability characteristics of the rotary mechanical splice. This FFP configuration is mechanically stable and with 97% reflecting multilayer mirrors spaced from 10 to 1,000 pm generates filters with bandwidths from 1 to 100 GHz. Filters with less than 1-dB insertion loss have been reported, and commercially available devices can have less than 2-dB loss. With improved tolerances, a finesse of 200 or greater appears feasible with little or no additional loss penalty. These filters will allow 100 dense WDM channels in the 30-nm gain spectrum of an EDFA.
Development of an intelligent optical associative memory system
Authors: Lu X. , Ohyama N. , Yamaguchi M. , Honda T. , Oita M. , Ohta J. , Kyuma K.
Published: February 2023

The hardware, which can be associatively recall information as does a brain, is one of the attractive applications of neural networks. Here a new type of optical neural network system, which can simulate the brain’s intelligent associative ability, is proposed. The combination of both the associative ability of neural networks and the logical decision-making of electrical computer is achieved through a modification of the system cost function. In our experiment, a work-reader system is built by introducing human knowledge—a dictionary—which makes the system recall a meaningful combination of patterns. A fully interconnected optical neural network with 7×7 input neurons and 7×7 output neurons is implemented by LCTV to memorize the alphabetical patterns. Dictionary information is introduced into the network by changing the threshold levels of the output neurons dynamically. The experiment shows that the system possesses almost the same recognition ability as a brain even when a low dynamic range of LCTV is used as the key hardware for interconnection. Most of the local minima caused by the hardware inhomogeneity, inaccuracy or maybe the imperfectness of the memory model, can be effectively avoided. The whole system is now being integrated on a VLSI chip in Mitsubishi Electric Corporation for practical uses.
Effect of target size on the fast and slow rod pathways
Authors: Sharpe Lindsay T. , Fach Clemens , Hofmeister Jörg , Stockman Andrew
Published: February 2023

Psychophysical and electroretinographic observations in normal observers and achromats (who lack cone vision) suggest that rod signals have access to two retinal pathways: one, slow and sensitive; the other, fast and insensitive. The two are revealed by double-branched rod-detected flicker threshold vs intensity (ftvi) curves, and by a suprathreshold intensity region (below cone detection)—the perceptual null—within which the sensation of 15-Hz flicker is canceled. The cause of the null is believed to be destructive interference between signals conveyed by the two pathways. Here we report that the break in the 15-Hz ftvi curve and the perceptual null is not found, in either the normal or achromat observer when the flickering target is ≤2° in diameter. Phase measurements (relative to a cone standard) indicate that the faster rod pathway mediates flicker detection for targets of ≤2°, not because the signals from the slow pathway are severely diminished but because destructive interference between the slow and fast rod flicker signals keeps the slow signals from ever exceeding threshold. There is therefore no need to invoke differences in spatial integration between the two pathways to explain the large difference in the ftvi curves.
Transform image enhancement
Authors: Aghagolzadeh Sabzali , Ersoy Okan K.
Published: February 2023

Blockwise transform image enhancement techniques are discussed. Previously, transform image enhancement has usually been based on the discrete Fourier transform (DFT) applied to the whole image. Two major drawbacks with the DFT are high complexity of implementation involving complex multiplications and additions, with intermediate results being complex numbers, and the creation of severe block effects if image enhancement is done blockwise. In addition, the quality of enhancement is not very satisfactory. In this paper, it is shown that the best transforms for transform image coding, namely, the scrambled real discrete Fourier transform, the discrete cosine transform, and the discrete cosine-III transform, are also the best for image enhancement. Three enhancement techniques discussed in detail are alpha-rooting, modified unsharp masking, and filtering based on the human visual system response (HVS). With proper modifications, it is observed that unsharp making and HVS filtering are basically equivalent. Block effects are completely removed by using an overlap-save technique in addition to the best transform. In conclusion, transform image enhancement yields highly satisfactory performance, it is biologically sound, provides parallel models for implementation, and can be performed simultaneously with transform image coding.
Error diffusion on a serpentine raster
Authors: Knox Keith T.
Published: February 2023

A recently developed mathematical analysis of error diffusion by Weissbach et al.1 describes the output spectrum of the error diffusion algorithm in terms of a linear filter equation. Their analysis showed that the output spectrum is given by the sum of the input spectrum and a high-pass filtered error spectrum. This analysis has been extended to error diffusion implemented on a serpentine raster. A serpentine raster is one in which the direction of processing is reversed for every scanline. The rationale behind this method is that the repeated reversal of the processing direction eliminates the directional artifacts in the output image that are caused by the asymmetrical distribution of errors in the algorithm. The new analysis of error diffusion on the serpentine raster shows that the nonsymmetric parts of the error spectrum are not eliminated but instead are reduced in magnitude and shifted to half the scanning frequency.
High frequency response in a ferroelectric liquid crystal via the Pockets electrooptic effect in a thin film waveguide
Authors: Liu J. Y. , Robinson M. G. , Johnson K. M. , Doroski D.
Published: February 2023

Second-order nonlinear effects have been observed in chiral smectic C* ferrorelectric liquid crystal (FLC) materials through second harmonic generation (SHG). Recently, we reported new FLC materials with reasonably high nonlinear d coefficients {d22(W3l4) = LiNbO3}.1,2 With these new nonlinear materials, modulation schemes through the expected large linear electrooptic effect (nanosecond response) should be possible. We present results on novel measurements of the EO coefficient using a prism coupled thin film waveguide technique. Optical TE eigenmodes are excited inside the FLC waveguide, which is sandwiched between two polyvinyl alcohol (PVA) cladding layers supported by a pair of indium-tin-oxide (ITO) coated prisms. By applying a dc biased voltage pulse train, the refractive index of the FLC is modulated by the electric field through the EO effect. This small change of the refractive index then modulates the propagation constant β of the waveguide modes. Preliminary results indicate that the EO coefficient r32 ≈ 0.3 pm/V for the commercially available British Drug House mixture SCE9. Analysis indicates this method is very sensitive compared with alternatives such as the direct interferometric measurement of phase modulation or Fabry-Perot multiple reflection interferometry.
Organic polymer phase modulator
Authors: Yuen S. F. , Chrostowski J. , Syrett B. A.
Published: February 2023

There has been an increasing interest in using organic polymers to implement optical waveguide devices. Organic polymers have low intrinsic losses, and devices built with these materials can easily be fabricated using standard VLSI technology. However, most organic polymers have a glass transition temperature (T
g
) of less than 100°C. This affects the long term stability of polymer devices in practical use. This paper reports the characteristics of phase modulators built with polymers having T
g
> 300°C. The prototype devices are fabricated on silicon substrates. A 4-μm layer of SiO2 bottom cladding is deposited on top of an aluminum ground electrode. The core consists of 5 μm of photosensitive polyimide doped with 2-methyl-4-nitroanaline. The top electrode is separated from the core by a second layer of photosensitive polymer. Channel waveguides are then subsequently defined by poling the core with a static field of the order of 100 V/μm. Both Dupont PI2700 and Probimide 400 series polyimide were used as the polymer host in the core. The polymer NA61 was used in the top cladding layer.
Optical behavior of tissue during intense laser irradiation
Authors: Jacques Steven L.
Published: February 2023

Laser radiation of tissues presents new and challenging problems of radiative transport. The most intense laser-tissue interactions occur when laser radiation first enters a tissue where classical light diffusion theory is inadequate. Monte Carlo simulations provide solutions in this region. Moreover, tissue optical properties can change during laser irradiation. Absorption centers can be saturated (e.g., during short intense laser pulses) or irreversibly degraded (e.g., during photodynamic therapy with photosensitive dyes). Browning and charring of tissue during high power continuous or long-pulses laser irradiation can increase absorption. Thermal coagulation of some tissue structures (e.g., globular proteins) will cause increased scattering, and coagulation of other tissue structures (e.g., collagen) will cause decreased scattering. Examples of altered light scattering in tissues due to coagulation are the heart myocardium, prostate, liver, and skin. Laser dosimetry becomes a nonlinear dynamic problem when optical properties change during the irradiation.
Effects of thermal insult on optical behavior of tissue
Authors: Motamedi Massoud , Rastegar Sohi
Published: February 2023

The effects of tissue coagulation on light and temperature distribution in laser irradiated tissue were quantified based on measurements of optical properties of thermally damaged tissue. The changes in optical properties can significantly influence the expected response.
Photon tissue interaction
Authors: Prahl S. A. , van Wieringen N. , van Gemert M. J. C. , Welch A. J.
Published: February 2023

A method is described for finding the optical properties (scattering, absorption, and scattering anisotropy) of a slab of turbid material using reflection and transmission measurements. Previously, it has been difficult or impossible to quantify a method’s intrinsic error due to restrictions on the boundary conditions, the scattering anisotropy, the ratio of scattering to absorption, or the thickness of the slab. By eliminating these constraints, the inverse adding-doubling method is applicable to turbid media with any optical thickness, albedo, or phase function and its intrinsic error may be quantified.
New perfect optical instrument
Authors: Shafer David
Published: February 2023

The gradient-index Maxwell fish-eye lens is an example of an absolute instrument, meaning that it stigmatically images a 3-D domain. An additional characteristic of such a system is that the image is an accurate geometrical projection of the object, i.e., there is no distortion. The ray paths inside this gradient-index lens are always sections of circles. A much more common situation is that of an aplanatic surface, which only perfectly images one spherical surface onto another one. This case is much more limited than a Maxwell’s lens, as it cannot perfectly image an extended volume of space; it is therefore not a perfect system. The number of known perfect systems can be counter on two thumbs: variations of the Maxwell lens and a plane mirror. This paper describes a new perfect instrument, which forms a perfect real image, at unit magnification, of a 3-D object volume. It is a single-element catadioptric design, involving one reflection. All orders of all aberrations are zero. In its most useful embodiment, it images one plane surface onto another, perfectly. The Dyson design and the Wynne-Dyson design can be regarded as crude approximations to this new system.
Laser radiation transfer through the optical rotary joint
Authors: Jamieson Thomas H.
Published: February 2023

The transfer of radiation is often required between a fixed high power laser transmitter and a rotating or gimballed optical projection head. This can be achieved using a set of optical fibers, coupled to each other by small optical systems, at which continuous rotation can occur. We term this system an optical rotary joint. The ideal rotary joint should be efficient, compact, simple, and able to operate with large angles between source and receiver fibers. In this use the radiation transfer is between fibers of a diameter that is large compared to the wavelength, and is a problem in geometrical nonimaging energy concentration. The fiber to fiber radiation transfer process has a closer affinity to geometric imaging theory than, say, solar energy concentration, since the ray angles as well as positions are significant to en sure continued fiber transmission. The basic geometrical requirements for efficient transfer are developed, together with some theoretical limitations. The transfer efficiency of some single surface reflective and simple refractive optical systems is explored. A general method of computing the transfer efficiency using ray tracing is described, and a practical design of optical rotary joint is described in detail.
Classical and quantum noise transformations generated by a Kerr nonlinearity
Authors: Joneckis Lance G. , Shapiro Jeffrey H.
Published: February 2023

The Ken nonlinearity is the source of important phenomena in both classical and quantum optics. Previously we had shown that a material dependent time constant plays a pivotal role in the quantum noise transformations produced by the Kerr nonlinearity.1 In that work, we presented the classical and quantum noise correlations for propagation of an initially phase-insensitive beam through a lossless, dispersionless, Kerr medium. In the present paper, we extend the earlier work to an arbitrary Gaussian input state. Central to both developments is the inclusion of a coarse grained time constant, τ
q
, which models the non-instantaneous nature of the Kerr nonlinearity. Output spectra based on Gaussian as well as other types of input spectra are presented. Also predicted is a quantum recurrence length, equal to an interaction length which yields a 2π nonlinear phase shift for an energy density of the 1 photon/cτ
q
m. The possibility of experimental verification of this theory is also discussed.
Exception to the cloning limit—amplification of amplitude-squared squeezed states
Authors: Hillery M. , Yu D.
Published: February 2023

An amplifier consists of a collection of inverted two-level atoms. It can be used to amplify a light signal but in the process the fluctuation behavior of the lights will be modified. In particular, for sufficiently large gains, nonclassical input states will become classical at the output. Hong, Friberg, and Mandel examined the effect of amplification on sub-Poissonian photon statistics and normal squeezing. They found that both of these effects disappear at the output if the intensity gain |G|2 > 2. The gain |G|2 = 2 is known as the photon cloning limit because one gets two photons out for every one that goes in. This gain has stood as an upper limit for the amplification of nonclassical behavior.
Computational method using finite element theory for analyzing 2-D lateral shearing interferograms
Authors: Zhu Yucong
Published: February 2023

A lateral shearing interferogram can be expressed by the following differential equation Using finite element theory, we can construct a triangle-wave function at the sample points of the wavefront: where h
i
= x = x
i
− x
i
−1.
Photonic band structures in 2-D periodic media
Authors: Villeneuve Pierre R. , Reid Andre , Piche Michel
Published: February 2023

The existence of photonic band gaps in periodic dielectric structures has been the subject of many recent investigations.1,2 The band structure in any periodic media can be computed from an exact solution of Maxwell’s equations. In this paper, we investigate the band structure in 2-D periodic media. Several periodic structures are considered in order to find one for which propagation would be forbidden in the plane of the modulation. We consider arrays of rods with square cross-sections and 2-D grids. We predict band gaps for TE and TM modes. The width of the bands is a function of the index contrast and the occupation fraction of each material in the structure. In arrays of rods (grids), the minimum index contrast required to produce a TE band gap is larger (smaller) than the one required to produce a TM band gap. In all the structures that we investigated, the minimum index contrast required to produce a TM gap was not very sensitive to the filling fraction. Furthermore, there was no overlap of TE and TM bands in any of the structures, hence there were no complete band gaps. Other periodic structures with a more circle like Brillouin zone will be considered, taking into consideration that the symmetry of the atom in the lattice may induce band degeneracy.
Interaction of (2+1)-D spatial dark solitons
Authors: Swartlander G. A. , Law C. T. , Andersen D. R. , Kaplan A. E.
Published: February 2023

We have previously observed that dark soliton stripes can exist in the transverse cross-section of a laser beam1,2 that propagates through a self-defocusing type nonlinear material. This phenomenon allows opportunities to explore fundamentally new types of soliton formations and interactions that are not possible in fibers or waveguides. Owing to the fact that these spatial dark solitons exist in the plane, interactions between non-parallel solitons can be observed. What is more, we have observed soliton branching, where a single soliton splits into two solitons. In addition, soliton termination was also observed in cases when the soliton did not span across the entire beam. These and other fascinating results will be presented.