bluuebunny/crossref_metadata_2025 huggingface dataset:
Deterministic chaos in double external cavity semiconductor lasers
Authors: McInerney John G. , Park Jong-Dae
Published: February 2023

Semiconductor injection lasers are frequently operated in external cavities for spectral narrowing and mode stabilization, although the result can also be self-pulsations and chaos. Single external mirror cavities can select a single longitudinal mode (cavity length Lext ~ laser diode length Ld) or narrow the modal linewidth (Lext ≫ Ld). For greatest coherence, grating external cavities are used for low-power (~1 mW) semiconductor lasers, and double external cavities or intracavity etalons are best for medium-to-high power devices.1 Here we describe experimental and theoretical studies of the properties of double external cavity semiconductor lasers. Our experiments have used a GaAs/GaAlAs index-guided laser (Hitachi HLP-1400) coupled to two long (10–60 cm) linear external cavities, without frequency-selective elements such as gratings or etalons. Our theory rests on rate equations for the carrier density, electric field amplitude and phase, including two coherent optical feedback terms. These are solved for the steady-state modes, then a linear stability analysis is performed to study the self-pulsations observed experimentally. Finally, the rate equations are integrated numerically with optional Langevin noise terms, showing self-pulsations leading to period-doubling or quasiperiodic routes to chaos. The observed behavior is similar to that of the single external cavity laser with off-axis tilt asymmetry.2 Stability conditions and spectral narrowing in the double external cavity laser are also discussed.
Influence of noise on deterministic chaos in a coherence-collapsed semiconductor laser
Authors: Li Hua , Ye Jun , McInerney John G.
Published: February 2023

Semiconductor injection lasers are frequently operated in external cavities for spectral narrowing and mode stabilization. However, the external cavity laser can exhibit coherence collapse, a catastrophic broadening of the spectral linewidth to tens of gigahertz under moderate external feedback.1 For fundamental and practical reasons, one needs to know whether this behavior is stochastic (noise-driven) or deterministic. Here we describe experimental and theoretical studies of the coherence-collapsed semiconductor laser. Our experiments have used GaAs/GaAlAs index-guided lasers (Hitachi HLP-1400), operated from 1.1–1.5 times threshold and coupled to long (10–60 cm), weakly coupled (~10-3–10-4 in intensity) linear external cavities. The theoretical analyses of these experiments are based on rate equations for the carrier density and complex optical field; phase-amplitude coupling, gain saturation and coherent feedback terms are included. These equations are integrated for the free-running laser and the coherence-collapsed laser with and without noise terms: the time series, return map, autocorrelation function, power spectrum and correlation dimension are calculated in each case. The results show that the coherence-collapsed state is chaotic, with a correlation dimension of ~2.5, and the most likely explanation is mixing between external cavity mode partition fluctuations and feedback induced relaxation oscillations. The addition of noise tends to obscure the finer features of the chaotic attractor and makes the correlation dimension more difficult to determine.
Ultrafast electrooptic effect in poled polymer films
Authors: Ferm P. M. , Knapp C. , Wu C.-J. , Yardley James T. , Hu B.-B. , Zhang X.-C. , Auston D. H.
Published: February 2023

We investigate the sensitivity and ultrafast electrooptic response of poled polymer films. Using a copolymer consisting of methyl methacrylate and red dye substituted methacrylate, we have poled films and integrated them into GaAs-based photoconductive switches. Our laser is a hybrid mode-locked dye laser providing 100-fs pulses at 830 nm. An excitation beam creates electrical transients and a probe beam is used for detection in the polymer via electrooptic sampling. We have sandwiched a 4-µm poled film on top of a monolithic GaAs switch and coplanar transmission line. Performing this experiment in the reflection mode, we measure risetimes in the polymer of 1.7 ps, indicating a measurement bandwidth of at least 200 GHz.
Excited-state nonlinearity in polythiophene
Authors: Yang Lina , Wang Q. Z. , Dorsinville R. , Alfano R. R. , Zamboni R. , Taliani C.
Published: February 2023

The sign and the magnitude of both the real and the imaginary part of the third-order optical nonlinear susceptibility χ3 at 532 nm in polythiophene (PT) thin films has been determined by the Z-scan method. Both the real part of χ3532 nm (-6.1 × 10-9 esu) and the imaginary part of χ3532 nm (-1.9 × 10-9 esu) are shown to be negative. Strong saturation absorption effects in PT at 532 nm have been observed from open aperture measurements. The results show that the nonlinear response in the single photon π–π* transition band in polythiophene thin films is dominated by absorption saturation.
Architectural and technological design tradeoffs for optoelectronic multistage interconnection networks
Authors: Kiamilev F. , Krishnamoorthy A. V. , Marchand P. , Esener S. , Lee S. H.
Published: February 2023

An optoelectronic multistage interconnection network (OE MIN) is a system of optoelectronic switching elements and free-space optical links that interconnect processing elements in a parallel processing system. Previously, we have designed an OE MIN based on the 2-D shuffle-exchange network and compared its performance and cost with VLSI implementations.1 We have also optimized the performance and cost of this system with variable grain-size (e.g., using 4 × 4, 16 × 16, or 64 × 64 electronic switching elements).2 In this paper, we analyze possible modifications of the system architecture, such as contention-free switches or Batcher-Banyan networks, in terms of system performance vs cost.
Degenerate four-wave mixing in solutions of diphenyl polyenes
Authors: Fleitz P. A. , Fernelius N. C. , Pottenger T. , Epling B. L. , Natarajan L. V. , Sutherland R. L. , Tondiglia V. P.
Published: February 2023

Recently, optical limiting has been demonstrated in solutions of diphenyl polyenes, and χ(3) values an order of magnitude larger than CS2 have been measured.1 In this report, degenerate four-wave mixing (DFWM) has been used to investigate the origin of the nonlinear response in solutions of diphenyl polyenes. The DFWM measurements were made using a frequency doubled Q-switched Nd: YAG laser producing 7 nsec pulses at 532 nm. The temporal profile of the phase-conjugate signal observed contains two features separated by ~5 ns. These results indicate that the nonlinear response of these materials contains both a fast and a slow component. The fast component is attributed to intrinsic nonlinearities. The slow component is attributed to slowly responding processes such as thermal effects and has been studied using polarization and time delay experiments. The results of these experiments indicate that the slow component is not simply explained and may consist of more than one nonlinear response. The molecules are known to have two-photon absorption near the laser wavelength that may be contributing to the slow component that is observed.
Degenerate four-wave mixing studies of CS2 with femtosecond optical pulses
Authors: Rosker M. J. , Chang T. Y. , Marcy H. O.
Published: February 2023

The third-order nonlinear optical susceptibility χ(3) of CS2 on short time scales has been studied extensively, primarily via optical Kerr effect (OKE) measurements.1,2 We extend these results using degenerate four-wave mixing (DFWM) experiments in a forward geometry. Our experimental setup using 100-fs pulses resembles the OKE geometry but contains an added degree of freedom. The temporal overlap of the two orthogonally polarized collinear (pump) beams and a third noncollinear (probe) beam inside the CS2 cell are controlled independently. The OKE results (induced birefringence) are reproduced in our experiments for the special case where the two pump beams temporally overlap and the probe arrives subsequently. We also observe a DFWM signal when the probe and either of the pumps overlap in time and the other pump arrives later; this behavior is attributed to phase gratings formed in the Kerr media and is related to different χ(3)ijkl components.
Unusual nonlinear optics near the nematic-isotropic phase transition point of liquid crystals
Authors: Khoo I. C. , Lindquist R. G. , Li Hong , Liang Yu , LoPresti P. , Normandin R.
Published: February 2023

In the vicinity of the phase transition temperature, approached from either the nematic of the isotropic phase, pulsed laser-induced individual and collective molecular recorientations, thermal and density fluctuations show interesting critical and dynamic effects. Using a transient dynamic grating technique, the magnitude of the nonlinearities and their rise- and decay-time dependences for both phases have been measured and analyzed by a quantitative nematogen theory. Unusually large and fairly fast nonlinear responses are observed and compared.
Propagation of arbitrary-profile beams through moving and stationary gratings
Authors: Min Sung-Oh , Chatterjee M. R.
Published: February 2023

Bragg-domain scattering of arbitrary-profile optical beams by gratings (moving or stationary) has been studied for weak and strong interactions in two dimensions, and weak volume interactions. In many cases, exact analytical solutions are unavailable, even though representative coupled-wave and integral equations may be derived. Recent work based on paraxial optics and small Bragg angles indicated that the center of a Gaussian-profile beam shifts away from the axis in the asymptotic limits of large grating phase delays and Qs.1 In this paper, this work is extended and modified to include arbitrary Bragg angles and optical profiles, as well as the noncurved nature of stationary and uniformly periodic plane holographic gratings. Three different types of optical profile are then numerically tested in small and large Bragg angle limits, for varying grating phase delays and Q-parameters. Of special interest is the study of a Bessel function-type profile, for which earlier studies have shown a minimum spatial spreading from a self-diffraction effect. Such a characteristic, if achieved, would be of particular interest in the design of diffraction-free beam propagation from optical holograms in efficient interconnection systems.2
Stereopsis and the interocular sign of brightness contrast
Authors: Cogan A. I. , Sutter E. E. , Rossi A. F. , White B. W.
Published: February 2023

We studied depth perception and the effects of interocular (i/o) delay in correlated (C) and anticorrelated (a/C) stereograms (same or opposite sign of brightness contrast on corresponding retinal loci, respectively). (i) Depth was readily obtained with all (briefly presented) contoured objects, but stereothresholds were higher with a/C than C objects. Above threshold, depth persisted up to some 120 msec of i/o delay whose only effect upon perception of a/C objects was a reduction of rivalry. (ii) In dynamic random dot stereograms (DRDS), i/o delay evoked perception of rotational 3-D motion that persisted up to 50 msec i/o delay1; with anticorrelated DRDS, motion went in the opposite direction.2 Disparity-based depth in correlated DRDS persisted to ~40 msec of i/o delay.1 With or without an i/o delay, depth was never seen with anticorrelated DRDS. This negative result held for a range of stimulus durations and interstimulus internals with the background either dark or at the mean grey level.
Motion parallax and size cue integration in low vision observers
Authors: Stefurak David , Legge Gordon , Candee Ryan
Published: February 2023

Normal and low-vision observers judged the relative depths of three nonoccluding vertical cylinders (low vision: the inability to read newsprint at a normal reading distance). The featureless cylinders, appearing as white stripes, varied unpredictably in width between trials. Monocular discriminations of depth were made in two tasks: (1) a target cylinder was located relative to the common plane of the remaining two, and (2) the cylinders were uniquely ordered in depth. Observers made judgments without head motion and then following free horizontal head translations. Normal observers performed indistinguishably from low-vision observers for judgments made without head motion for both tasks. Normal observers improved to near perfect depth discrimination for judgments made following head translation in both tasks while the performance of low-vision observers was unchanged within each task. The error judgments of normal observers making head translations showed reduced reliance on the uninformative size cue in both tasks. The depth errors of low-vision observers making head translations showed a maintained reliance on spurious size cues.
Coloring the vacuum with a superconfocal cavity
Authors: Morin S. E. , Gauthier Daniel J. , Mossberg T. W.
Published: February 2023

The boundary conditions imposed on the vacuum field by the superconfocal cavity (SCC) create a region of space, the active volume, at the cavity center in which the spectral structure of the vacuum field is perturbed. These perturbations transform the normally white spectrum of the free-space vacuum field into a colored vacuum whose spectrum is a comb of peaks coincident with the cavity resonance frequencies. Operating as designed, atoms resonant with the cavity and in the active region will experience a vacuum field mode density 1.5 times that in free-space. Perturbations in the vacuum field mode density of this magnitude and operative over so large an active volume (1.4 × 107µm3) have not, to our knowledge, been previously achieved in an open optical cavity. We expect to observe a plethora of new and novel phenomena associated with laser–atom interactions in the presence of a colored vacuum. The first experiment will focus on the dynamic suppression of spontaneous emission1 which predicts a dramatic narrowing of the central Mollow peak as the Rabi frequency becomes larger than the FWHM of the SCC-induced peaks in the vacuum field mode density.
Characterization of a new thermosetting nonlinear optical polymer
Authors: Shi Y. Q. , Steier W. H. , Chen M. , Yu L. P. , Dalton L. R.
Published: February 2023

We have studied a new class of thermosetting nonlinear optical polymers for electrooptic (EO) devices. The new material is a two-component system that is mixed just before thin film spin-coating. After thermal polymerization at elevated temperature, a fully cross-linked polymer network is obtained with disperse red nonlinear active groups covalently connected to the polymer backbone. Thin films from 0.1 to 5 µm thick with good optical qualities can be obtained from spin-coating. The polymer films are rigid and chemical resistant. From our second-harmonic generation (SHG) measurement, the resonance enhanced d33 coefficient was ~ 140 pm/V at 1.06-µm fundamental wavelength. With a Mach-Zehnder interferometer, the EO coefficient r13 = 14 pm/V was measured at 633-nm wavelength with 3-kHz modulation frequency, in good agreement with that derived from SHG d31(d31 = d33/3) coefficient with two-level model. Compared with other fully crosslinked polymer systems, this relatively large value results from the incorporation of non-linear groups of higher hyperpolarizabity.
In situ electric field measurements during corona poling of second-order nonlinear polymers
Authors: Molau N. E. , Knoesen A.
Published: February 2023

The large magnitude of second-order nonlinearities routinely obtained by the corona poling technique can contribute to a large electric poling field. However, because of the nature of the corona poling process, measurement of the electric field during corona poling is difficult. The electric field is a fundamental property that influences the poling of nonlinear polymers. An understanding of how the electric field in a nonlinear polymeric film is affected when parameters such as temperature and poling current are varied can be used to optimize the poling processing conditions. An optimum poling procedure is required that maximizes the orientational order and nonlinear stability, while minimizing optical losses. Results are reported of a study of an experimental technique that can be used to perform an in situ measurement of the electric field in a nonlinear polymeric film during corona poling.
Crystal growth and characterization of N-(2,4-dinitrophenyl)-1-chloro-3-phenyl-2-propanamine: a new organic material for nonlinear optics
Authors: Sugiyama T. , Shigemoto T. , Komatsu H. , Ukachi T.
Published: February 2023

We have succeeded in developing a new organic molecule, N-(2,4-dinitrophenyl)-1-chloro-3-phenyl-2-propanamine (DNCPA).
Phase grating design for interconnecting processor arrays
Authors: Kuznia C. B. , Sawchuk A. A.
Published: February 2023

Computer-generated phase gratings (CGPG) have been proposed for optical interconnection schemes to provide source fan-out to output locations.1Fan-out is achieved using the CGPG in the Fourier plane of an imaging system to produce a point-spread function having many output spots in some interconnection pattern. A computer is used to design a phase grating function whose power spectrum is the desired connection pattern. The Dammann grating is one example of a binary CGPG commonly used for generating 2-DN×Narrays of uniform intensity beams for optical powering.2Other papers have shown that arbitrary 2-D patterns can be created.3The Dammann grating is a periodic function so that the optical Fourier transform can be approximated by its Fourier series coefficients. The grating function is found by setting each Fourier series coefficient to a nonzero value for a connection or zero for no connection, and then numerically solving for the periodic binary function that satisfies these Fourier coefficients. However, for large array sizes the computing complexity becomes extreme. A computationally easy way to create CGPG for some specific interconnection pattern is based on the Gerchberg-Saxton algorithm. The interconnection pattern is represented as a function having values of one or zero, corresponding to the desired connection pattern, with arbitrary phase. The task is to find a phase-only grating function whose power spectrum resembles this interconnection function. The desired phase grating function is found by iteratively Fourier transforming the grating function and modifying the phase of the interconnection function until the desired values of on/off ratio, connection uniformity, and/or diffraction efficiency are achieved. The cellular hypercube interconnection4is the main pattern discussed with some generalization to other types of interconnection pattern. Implementation of these CGPG for interconnecting processor arrays is also discussed.
High-speed optical response of InGaAs heterojunction bipolar transistors
Authors: Carruthers T. F. , Aina O. , Mattingly M. , Serio M.
Published: February 2023

The emitter photocurrent transient of a double­heterojunction
InP/Ga0.47In0.53As/InP bipolar transistor has
been found to be much faster than its ~15-GHz microwave bandwidth
would suggest, since optical injection bypasses the base resistance.
Slower components, due to holes residing in the base, can be
eliminated with appropriate base biasing; this feature may be useful
in optical receiver circuits. At a base bias of +0.5 V, the
photocurrent transient has a 12-ps duration in response to both 620-
and 1530-nm ultrafast optical pulses. At higher biases a slower
transient component appears, as does a transient of opposite sign but
with the same ~100-ps time constant at lower base biases. One slow
component, a charge-neutrality-preserving collector current, has a
base-bias-controlled gain; the other components can therefore be made
to cancel. The device does not possess gain when operated in this
manner, but the data suggest a design for an ultrafast photodetector
with gain. The device studied is as fast a photodetector at visible
wavelengths as at infrared, and the additional absorption provided by
the InP emitter layer increases its short-wavelength sensitivity.
Dual-wavelength method for high-density optical data storage
Authors: Wang Beijing , Zhao Yang , Auner Gregory W.
Published: February 2023

Optical date storage systems use diffraction-limited optics. The recording density will be greatly increased by using a short wavelength. Currently, a second-harmonic generation semi-conductor laser with stable high power output is not available. Moreover, a system requiring less power is usually much more reliable and stable. Therefore, it is critical to reduce the power requirement of a short wavelength source in optical data storage systems. One possible way is to apply the antireflection coating technique to the magnetooptic (MO) medium. The key point is to achieve low reflectivity when writing and a large figure of merit when reading. We consider two different but close wavelengths for reading and writing. In the multilayer antireflection coating design, the loss in the MO medium was taken into account. After carefully selecting the number of thin film layers and their indices as well as thicknesses, a good result for a Co/Pt MO medium was obtained. The reflectivity at the writing wavelength is almost zero, showing that the incident light at this wavelength can be efficiently absorbed by the MO medium. At the reading wavelength, we obtained the enhanced Kerr rotation and relatively large reflectivity. The figure of merit Rθk2 can be as large as 0.25.
Volume holography using the orthogonal data storage approach
Authors: Rakuyljic George A. , Leyva Victor , Yariv Amnon
Published: February 2023

Holographic volume data storage has long been an intriguing subject of research interest. The main reason for this interest is the promise of enormous data storage capacities. In a 1-cm3 volume, storage of 1012 bits or more is possible using visible light.1 However, past attempts at attaining and demonstrating a volume holographic data storage system of this density have fallen far short of this theoretical limit.2 Although material limitations contributed to this shortcoming, of more fundamental importance however were the problems associated with the angular multiplexing schemes used to holographically access the volume of the storage medium.3 In addition, photorefractive materials were often used as the holographic storage media4; however, such materials have lacked an effective and efficient fixing mechanism.
Phase stability measurements of ferroelectric liquid crystal switches
Authors: Hartman N. F. , Gaylord T. K. , Drabik T. J. , Hanschy M. A.
Published: February 2023

The increasing importance of ferroelectric liquid crystal (FLC) devices in a variety of applications makes an understanding of the optical properties of FLC materials essential. In particular, thermal effects associated with switching and environmental conditions need to be understood to assess the potential of FLC devices in optical computing and optical processing and provide design information. Toward these goals, a transmission device consisting of a surface-stabilized cell filled with a smectic C
*
FLC was optically characterized. The cell was designed with a λ/(2Δn) thickness where Δn is the birefringence of the uniaxial FLC. Using a specialized SLM interferometric characterization system, the relative phase birefringence as a function of temperature was determined. Phase shift data as a function of temperature are presented; these results are then compared with optical axis tilt angle data as a function of temperature. The latter data were generated by monitoring optical transmission between crossed polarizers.
Photovoltaic optically addressed spatial light modulator
Authors: Mao C. C. , Landreth B. , Johnson K. M. , Moddel G.
Published: February 2023

We present the physical structure of and experimental results on a photovoltaic optically addressed spatial light modulator (OASLM), which does not need the externally applied electric field. This device consists of an amorphous silicon (a-Si:H) photosensor and a ferroelectric liquid crystal (FLC) light modulator. The photosensor is composed of a stack of four p-i-n photodiodes. The thickness of each photodiode is optimized so that each one absorbs the same fraction of incident He-Ne laser light. The liquid crystal in this device is a 1-µm thick layer of SCE-13 FLC (British Drug Houses).
Novel acoustooptic SHG modulator
Authors: Soos J. I. , Wang X. L. , Liu Y. G. , Han J.R. , Xu B. , Jiang M. H.
Published: February 2023

We have demonstrated, the first to our knowledge, acoustooptic second-harmonic generation (AOSHG) modulator. A LiNbO3 longitudinal piezoelectric transducer was bounded in a 1.06–0.53-µm KTP* SHG crystal. The modulator is operated at 100 MHz and with 50 MHz bandwidth. The modulation of green light has been achieved.
Field of view required for optimal optic-low discrimination
Authors: Turano Kathleen
Published: February 2023

Optic-flow discrimination requires the integration of image motion signals across the retina. In the limit, the size of the retinal area (field of view) that is stimulated with image motion will affect discrimination performance. Furthermore, the field of view required for optimal optic-flow discrimination may change as a function of eccentricity. I have systematically varied the field of view (2-32° of visual angle) and eccentricity (0-20°) of computer simulated optic-flow patterns and measured observers’ ability to discriminate the direction of 3-D curvilinear motion in a 2AFC experiment. The results show that performance is optimal at 0° eccentricity across all fields of view. Furthermore, at 0° eccentricity, performance remains fairly constant across fields of view down to ~2°. At eccentricities >0 performance decreases monotonically with decreasing fields of view, and the rate of decline increases with eccentricity.
Stimulated Raman scattering: fluctuations and diffraction
Authors: Scalora M. , Haus J. W.
Published: February 2023

Using a dynamic model that includes both pump depletion and diffraction effects, we investigate the statistics of Stokes emission in stimulated Raman scattering. The amplified fluctuations display specific features that can be quantified through statistical analysis. The phase wave fluctuations1 are responsible for soliton formation, which is manifest through pump repletion; diffraction effects change the qualitative behavior of the soliton and we found that gain-focusing during propagation2 is important. The probability of pump repletion as well as its height is affected by the interplay between phase wave initiation and diffractive coupling. The stokes pulse energy statistics have also been determined. The Stokes energy distribution is a sensitive function of the diffractive coupling. The nonlinear regime is characterized by small energy fluctuations; in general, the energy distribution is narrowed by the loss of spatial coherence when the diffractive coupling is weakened. The beam profiles are also affected by the interplay of fluctuations and diffraction and the Stokes emission maximum occurs off-axis, i.e., beam pointing fluctuations.
In situ x-ray mask distortion measurement by a shear interferometer
Authors: Chen Gong , Wells Greg Marshal , Cerrina Franco
Published: February 2023

We describe the in situ x-ray mask distortion measurement by a shear interferometer. The principle and a detailed layout of the shear interferometer are presented and the relationship between mask distortion and interference patterns is also explored. The in-plane and out-of-plane distortion of an x-ray mask during a synchrotron radiation x-ray exposure are observed on the shear interferometer. We believe this is the first reported experiment on the observation of the in situ x-ray mask distortions during synchrotron radiation exposure. We also have recorded the interferogram and measured the amount of distortions from interference fringes. The measurement of the in situ mask distortion helps us to understand the physical causes of the mask distortion.
Nonlinear optical properties of anisotropic Kerr materials
Authors: Kralik John C. , Malcuit Michelle S.
Published: February 2023

We have measured the optically induced birefringence of several anisotropic Kerr materials. An artificial Kerr material is a suspension of dielectric particles whose size is smaller than the wavelength of light. It has been predicted that artificial Kerr materials that are anisotropic should have large optical nonlinear susceptibilities resulting from the reorientation of the particles when a strong optical field is applied.1 The materials we have studied include TiO2, polytetrafluoroethylene (PTFE), and poly-γ-ben zyl-L-glutamate (PBLG). The optical anisotropy of these materials can result from form birefringence due to the anisotropic shape of the particle or from intrinsic birefringence of the material because of its crystalline structure. We have studied several different particle shapes including nearly spherical and needlelike geometries. The induced birefringence is measured using an argon-ion laser for the various materials at several different concentrations. The nonlinear susceptibility χ(3) is calculated from the measured induced birefringence. We find that is as large as 10-5 esu. The measured response time for TiO2 suspended in water is ~1 ms which is ~100 times faster than the response time of isotropic Kerr materials where the nonlinearity results from the translational motion of the particles.
Stark-enchanced nonlinear optics in shaped microparticle suspensions: beam combination
Authors: Rogovin D. , Scholl J. , Pizzoferrato R. , DeSpirito M. , Marinelli M. , Zammit U.
Published: February 2023

Electromagnetic alignment of the microparticles, by either a uniform electric field or polarized radiation, changes the gain spectrum for energy transfer via nondegenerate two-wave mixing in three distinct ways: (1) the low frequency peak of the gain spectrum, arising from the translational grating, is enhanced, (2) the high frequency portion of the gain, arising from the orientational grating, is enhanced, and (3) the high frequency portion of the gain spectrum is upshifted so that the orientational peak will occur at higher frequencies. The blue shift in the orientational peak arises because microparticle alignment reduces the rotational response time. The enhancement of the low frequency portion of the gain spectrum arises from the formation of an additional density grating that possesses some orientational characteristics. Enhancement of the high frequency orientational portion of the gain spectrum arises from two causes: the orientational grating is made deeper when the microparticles are aligned, and the formation of an additional orientational grating that has some translational characteristics. This feature of the suspension’s nonlinear electrodynamics reflects the appearance of new coherent scattering mechanisms resulting from the loss of symmetry in the presence of either a uniform electric field or polarized radiation.
Frequency-tunable squeezed light for spectroscopy
Authors: Polzik E. S. , Carri J. , Kimble H. J.
Published: February 2023

A frequency-tunable source of squeezed light would allow investigations of the atom-field interaction in a regime where fundamental new phenomena have been predicted.1 There are also opportunities for spectroscopy with sensitivity beyond the shot-noise limit. Toward these objectives, in our experiment we employ a single-frequency Ti-sapphire laser with tuning optimized around 852 nm (cesium resonance transition). The infrared output of the laser is frequency doubled in an external buildup cavity with a KNbO3 crystal as the nonlinear element. Efficient doubling provides 0.65 W of tunable blue output for 1.35 W of infrared input. This blue output is then used to pump an optical parametric oscillator (OPO) containing a second KNbO3 crystal for downconversion back to the infrared. The high power of the blue pump that we have achieved and the large nonlinearity of KNbO3 allows us to employ an OPO that is resonant only for the subharmonic infrared light. This design facilitates tuning of the OPO compared with the case in which the blue pump and the infrared are both resonant. The doubling cavity, OPO, and laser itself are locked relative to a stable reference cavity by an rf sideband technique, thus providing the possibility for tunability of the system with a single knob.
Squeezed amplification in a gain-saturated parametric amplifier
Authors: Wong N. C. , Sun K. X. , Shapiro J. H.
Published: February 2023

Recently optical parametric amplifiers (OPAs) with vacuum inputs have been extensively studied and shown to generate a significant amount of squeezing, but little is known about the quantum noise behavior of an OPA with an injected signal field. We have performed a linearized quantum analysis of a nondegenerate OPA operated in the saturated gain regime showing that the amplified output intensity of a coherent-state input signal becomes squeezed when the classical small-signal gain falls below unity. In uses such as master-oscillator power amplifiers, for which the signal of interest is the mean output intensity, the output signal-to-noise ratio (SNR) can be higher than the input SNR over a broad operating range. For an OPA pumped at 90% of threshold, the SNR improvement is about a factor of 3, and with a 10-Db amplitude squeezed pump, the improvement increases to about a factor of 7. Such a tunable gain-saturated OPA with large-signal gain and improved SNR can be potentially useful in digital communication.
Ion exchanged waveguides in Corning Polarcor glass
Authors: Bloemer Mark J. , Haus Joseph W.
Published: February 2023

Corning Polarcor glasses contain submicron-size silver particles embedded in a soda-lime glass host. The elongated silver particles have their major axes oriented in a common direction. The glasses polarize light by selective absorption. The absorption is from surface plasmon excitation in the silver particles. Planar waveguides were fabricated by a K-Na ion exchange process. Singlemode guides at 836 nm were obtained from a potassium nitrate melt at 340 C with an exchange time of 31 h. TE and TM pass polarizers had measured extinction ratios >39 dB/mm at 836 nm with <1.5 dB/mm propagation loss for the pass axis. Using the bulk values for the dielectric response of silver, the effective dielectric tensor for the composite is calculated and the extinction ratio is determined.
Effect of structure and composition of the thermal lensing and permanent laser-induced refractive-index changes in glasses
Authors: Taheri B. , F. A. Munoz , Powell R. C. , Blackburn D. H. , Cranmer D. C.
Published: February 2023

We have previously reported the ability to produce permanent refractive-index gratings in rare earth-doped glasses through the creation of laser-induced local structural changes and have shown how thermal lensing affects the grating properties. We present here the extension of this research to the investigation of the effects of glass structure and composition on thermal lensing and on the ability to produce permanent gratings. New types of lithium borate, lead and magnesium silicates and germanates, and a lead phosphate glass were investigated. The results of four-wave mixing experiments show that the grating scattering efficiency is strongly dependent on the strength of the chemical bonds and the charge to radius ratio of the glass components. The thermal lensing properties of these materials under 7-ns pulsed excitation at 457nm can be attributed to the molecular polarizibility of their components. They are also dependent on lead concentration and are stronger in the silicates and germanates, having continuous random network structures, compared to the phosphates and borates with more constrained chain- and ring-type structures, respectively. A model is presented to interpret the results of thermal lensing experiments.
CAD tools for optoelectronic simulation and design
Authors: Young Terry
Published: February 2023

As the thrust to demonstrate novel optoelectronic components subsides, pressure is mounting to deliver devices routinely, to specification and on time. Along with advances in packaging and processing, high quality design tools are needed to achieve these targets. Moreover, one must combine optical analysis with electronic, thermal and mechanical design methods to model components as a whole.
InP/InGaAs optical microstructures
Authors: McCall S. L. , Levi A. F. J. , Logan R. A. , Pearton S. , Slusher R. E.
Published: February 2023

Optical microstructures with high dielectric contrast are of interest to control spontaneous emission, reduce laser thresholds, and increase the binding energies and dipole moments of quantum well excitons. We have fabricated barstool structures where the seat is 2–10 μm in diameter with thicknesses in the 100–500-Å range. These thin films are free standing in air, supported only by an InP pedestal. The pedestals are parallelograms in cross section with dimensions as small as 0.5 μm on a side. Pedestal heights above the InP substrate are in the 2–3-μm range. Composition of the thin films is layered with InGaAs quantum wells between InGaAsP barriers or layers of InGaAs or InGaAsP above. The etch selectivity determines the range of P concentration that can be obtained. Initial results show good photoluminescent efficiencies for the quantum well films with thicknesses in the 500-Å range. Limits on the diameter, thickness, surface quality, and luminescent efficiency are being studied.
Polarization-selective inhibited spontaneous emission of a quantum wire
Authors: Ho Seng-Tiong
Published: February 2023

Inhibited spontaneous emission from excitons in semiconductors is an attractive phenomenon from the optical device point of view. We show that the spontaneous-emission rate for a quantum wire can be reduced by embedding a quantum wire of high refractive index in a bulk material of low refractive index. Furthermore, the reduction of the emission rate is strongly dependent on the polarization of emission. We show that the emission rate for the two polarizations perpendicular to the wire is proportional to the fifth power of the refractive-index ratio. However, the emission rate for the polarization parallel to the wire is only proportional to the first power of the refractive index ratio. For example, if we embed a quantum wire of n = 3.5 material in n = 1.5 bulk material, the emission rate for the two polarizations perpendicular to the wire is reduced by more than 50× over that an n = 3.5 bulk material. This makes the emission predominantly in the polarization parallel to the wire. Such a single-polarization emission would be useful in achieving low-threshold microcavity lasers.
Time-dependent characteristics of semiconductor resonant structures
Authors: Walker D. B. , Glytsis E. N. , Gaylord T. K.
Published: February 2023

Double-barrier tunneling structures operate based on quantum mechanical tunneling through two barriers.1 Quantum electron wave structures operate based on traveling-wave propagation above all conduction band edges.2 These are the fundamental structures proposed to achieve ballistic electron transport devices in semiconductors. The time-dependent behavior of resonant tunneling structures has been discussed extensively in the literature, but no such analysis has been performed on quantum wave structures. A numerical solution of the time-dependent effective mass equation is used to calculate the traversal time of a Gaussian packet and the percentage of the packet transmitted for resonant tunneling and quantum wave structures.
Sources and sinks of waves in annular lasers
Authors: D'Angelo E. , Izaguirre E. , Green C. , Tredicce J. R.
Published: February 2023

It is advantageous to reduce the transverse degrees of freedom of the laser system to simplify the spatial intensity profile and its dynamic behavior. We do this by inserting a dot on the Brewster window and a diaphragm inside a laser with large Fresnel number, which reduces the intensity profile to an annulus. The annulus radius depends on the size of the dot and the radii of curvature of the mirrors.
Benefits of intrawaveguide saturable absorbers in external cavity mode-locked semiconductor lasers
Authors: Derickson D. J. , Helkey R. J. , Mar A. , Thornton R. L. , Bowers J. E.
Published: February 2023

Actively mode-locked semiconductor lasers need high quality antireflection coatings to avoid multiple pulse formation and mode-locking in clusters. The addition of an intrawaveguide saturable absorber eliminates these problems by absorbing the reflected pulses from the antireflection coating. Saturable absorption also causes pulse shortening and introduces self-phase modulation opposite in sign to that of saturable gain. Two section lasers with four GaAs quantum well active regions were compared using active and hybrid mode-locking techniques. The saturable absorber is formed by reverse biasing an 80-μm end segment and high reflection coating the facet. The opposite facet has a 10-3 antireflection coating for a 200-ps roundtrip time external cavity. Active mode-locking produced 9.5-ps pulses with a 400-GHz spectral width at 1-mW average power. Mode-locking was in clusters as evidenced by 8-dB nulls in the spectrum due to laser diode Fabry-Perot modes. The addition of the saturable absorber reduced the pulse width to 2.5 ps with an 800-GHz spectral width. The spectral ripple was reduced to 0.5 dB and the time–bandwidth product improved from 3.8 to 2.0. The impulse response of the saturable absorber photocurrent was measured as 45 ps showing that a p-i-n reversed biased absorber can recover quickly without the need for proton bombardment or other means to shorten electronic lifetime.
New kind of classifier neural network using RBFs
Authors: Servin M. , Cuevas F. J.
Published: February 2023

Neural networks based on RBFs have recently gained a wider acceptance over the backpropagation topology because of its faster learning rates due to the decoupling between the hidden and output layers.1 We have derived still another network topology based on normalized RBFs, which do not require learning time. This normalization process makes the classifying network behave radically different from the conventional RBFs classifier, because it creates sharp classifying boundaries among the classes. This new topology has been applied to the classical problem of character recognition degraded by a noisy binary channel. The classifying properties obtained by this system are equivalent to a system formed by a classical RBF approximation followed by a winner-takes-all network (WTA), without the disadvantages of the convergence time required by a WTA network. Also, as mentioned above, a powerful advantage of this network is that is does not require learning time. Only a representative number of templates are needed; they can be fed into the network without any prior processing.
Space and Fourier domain holographic associative memory for robust pattern recognition
Authors: Lu Taiwei , Kostrzewski Andrew , Chou Hung , Lin Freddie
Published: February 2023

A 2-D associative memory of N×N input/output elements require a 4-D memory matrix of N4 elements. It is difficult to implement a fully parallel large size electronic associative memory in view of the 1-D interconnection limitations. Optical holographic media provides high resolution, large dynamic range, and 3-D reconstruction capabilities. These properties lead to the design of a large scale holographic associative memory (HAM) for parallel auto- and heteroassociations. A new N4 recording scheme has been employed in an automatic recording system that is capable of recording a 4-D memory matrix to a 2-D array of up to 256 × 256 holograms. An interpattem association training model is used to extract special features of the stored patterns and to construct excitatory and inhibitory interconnections in the associative memory. An LCTV based prototype system has been constructed and a 32 × 32 element HAM installed for real-time pattern recognition. Since most spatial domain HAMs cannot perform distortion invariant pattern recognition, a Fourier domain HAM is proposed to store multiple synthetic filters for prompt shift-scale-rotation invariant pattern recognition.
Pyro-electro-optic transient phase gratings
Authors: Ducharme Stephen
Published: February 2023

There are many mechanisms for generating transient optical phase gratings. Though particular advantage can be taken of semipermanent mechanisms such as photorefractive and photochromic effects, there are also uses for purely transient mechanisms such as those based on the third-order nonlinear susceptibility (c(3) or n2), population changes, or thermal (dn/dT) mechanisms. Transient grating mechanisms have the virtue of allowing real-time interaction of interfering waves as in phase conjugation, image amplification and manipulation, optical switching and modulation, nonlinear resonators, or neural networks. A new mechanism of transient optical phase grating formation, called the pyro-electro-optic effect, is proposed which combines the pyroelectric and electro-optic effects to convert spatial intensity variations into transient phase gratings. The pyro-electro-optic mechanism has a figure-of-merit that is proportional to the pyroelectric, electro-optic and absorption coefficients and inversely proportional to the specific heat. The grating response time is proportional to the specific heat and inversely proportional to the thermal conductivity. Diffraction efficiencies approaching unity are predicted in several readily available inorganic and organic electro-optic materials with modest pulse energies from Q-switched Nd:YAG lasers. Pyro-electro-optic gratings are also compared with third-order thermal (dn/dT), and photorefractive mechanisms.
Is the hole mobility proportional to the dc dielectric constant in photorefractive BaTiO3?
Authors: Mahgerefteh Daniel , Kirillov Dimitry , Feinberg Jack
Published: February 2023

According to the band-conduction model the erasure rate Γ of a photorefractive grating is given by where e is the electric charge, μm is the carrier mobility, and ε the dielectric constant along the direction of charge migration, n0 is the density of free carriers, and f(k
g
, ε) is a function that is nearly unity for small grating wavevector k
g
. Because both the dielectric constant and the free-carrier mobility vary with direction in a BaTiO3 crystal, the erasure rate Γ∝μ/ε of a photorefractive grating is also expected to depend strongly on the grating’s orientation. In fact, we find that it does not. Previous work1 showed that pm/e is approximately independent of direction at T = 25 °C. To study μm/ε with ε changing, we heated a type A crystal2 of BaTiO3 from T = 16°C to 45°C. Over this range ε⊥ decreases by 40%, while ε|| increases by 20%. We find that the rates are the same for both grating orientations in spite of the different temperature dependencies of ε⊥ and ε||.
Temporal modulation sensitivity in silent cone substitution
Authors: Smith Vivianne C. , Pokorny Joel , Davis Monica K. , Yeh Tsaiyao
Published: February 2023

Silent cone substitution was exploited by Estévez & Spekreijse1 to measure presumed photoreceptor temporal modulation sensitivity. Kelly and van Norren2 emphasized the role of higher-order neural elements sensitive to achromatic and chromatic modulation. We tested the Kelly and van Norren hypothesis using 556- and 642-nm stimuli. We first collected temporal MTF data for chromatic and achromatic sine—waves of time-average luminance 1256 td and chromaticity 595 nm. We defined silent M and silent L substitution in two ways: (1) We reduced peak modulation depth (642-nm LED for silent L and 556-nm LED for silent M) to maintain time-average luminance and chromaticity. (2) We reduced the luminance of the 642-nm LED for silent L (1047 td, 589.5 nm) and increased it for silent M (4358 td. 622 nm). We defined achromatic modulation as (L + M) and chromatic modulation as (L - kM), where L and M are the Smith-Pokomy fundamentals and k normalized the chromatic channel to the time average chromaticity. We calculated the residual modulation depth for the four silent conditions and used these values to weight the sine wave temporal MTFs. Silent L revealed chromatic processing; silent M revealed chromatic processing at low frequencies and achromatic processing at high frequencies.