bluuebunny/crossref_metadata_2025 huggingface dataset:
Dark spatial solitons formed by complex gratings
Authors: Swartzlander C. A. , Andersen D. R. , Kaplan A. E.
Published: February 2023

We have previously observed bands, and even a grid, of dark solitons in the cross-section of a laser beam propagating through a self-defocusing material when a diffracting screen was placed at the entrance face of the nonlinear medium. The creation of spatial solitons is attributed to the coupling of diffracted radiation into a self-guiding nonlinear channel. Information encoded as spatial solitons may therefore be transferred in parallel over long distances without the need for large (or any) collection optics. A diffracting screen is a building block of spatial soliton devices. We have found the soliton eigenvalues (each corresponding to the normalized angle and depth of a soliton) for a generalized screen composed of units with two closely spaced opaque regions of width xA separated by a region of width xB and arbitrary phase ΦB. If the value of xB is large, fundamental dark solitons can form when ΦB = π. On the other hand, when xB is small, diffractive coupling of radiation from the opaque regions splits the degeneracy of the eigenvalues, much like level-splitting in coupled quantum wells. When a pure phase grating exists (xA = 0), a single pair of solitons is formed. Numerous applications of spatial dark solitons can be envisioned, including optical interconnecting, limiting, and computing operations.
Soliton decay and gain focusing in stimulated Raman scattering
Authors: Haus J. W. , Scalora M.
Published: February 2023

We have studied diffraction effects on soliton formation using the semiclassical model of stimulated Raman scattering. We generate the soliton by placing a phase shift on the weak input Stokes field, and we study three-dimensional propagation effects in this system. Diffraction plays an unexpected role in enhancing the on-axis intensity of the Stokes field. The laser soliton is found to revert to its original on-axis intensity for Fresnel numbers around 10, and, at the same time, the on-axis Stokes field increases. This unusual phenomenon is accompanied by a narrowing of the Stokes and laser fields by a factor of five. These results will be explained, and further analysis will be presented.
Image reconstruction digital shearing laser interferometry
Authors: Fienup J. R. , Cederquist J. N. , Marron J. C. , Seldin J. N.
Published: February 2023

We propose a new kind of shearing interferometry employing laser illumination, heterodyne detection, and digital shearing. An array of heterodyne measurements are made of an optical field reflected from a distant coherently illuminated object but are perturbed by phase errors. As the object rotates slightly or translates, additional realizations of the optical field, but with the same phase errors, are measured. The product of the optical field with the complex conjugate of a sheared version of the optical field is digitally computed and averaged over the realizations. This is performed for two orthogonal shears, and the phases of the resulting averages approximate phase differences of the phase-error function. The phase-error function is then reconstructed from the phase differences by means of the same reconstruction algorithms as are used in conventional shearing (or Hartmann) wavefront sensors. The phase-error function, thus computed, can be digitally subtracted from the phase of each of the realizations of the measured optical fields and yields corrected measurements from which diffraction-limited, coherent, speckled images of the object can be computed by Fourier (or Fresnel) transformation. The squared magnitudes of these speckled images can be averaged to yield a speckle-free, incoherent image of the object.
Shot-noise-limited optical measurements at baseband with noisy lasers
Authors: Hobbs Philip C. D.
Published: February 2023

The theoretical performance of many types of optical measurements is extremely good. With a 5 mW He–Ne laser, the shot noise limit (1 Hz bandwidth) corresponds to an extinction uncertainty of 2 parts in 108 or, in a Michelson interferometer, to a position uncertainty of 2 fm. Practical measurements do not approach this accuracy, except by great effort, because of excess laser noise and environmental perturbations. This paper describes several types of optical extinction and homodyne measurements performed at baseband (without choppers or modulators), that achieve shot-noise limited performance, even though the lasers used are up to 55 dB noisier than the laser described above. The measurements include diode-laser optical-absorption spectroscopy, measurement of aerosol particles by optical extinction, coherent lidar, and phase-sensitive microscopy. The measurement techniques all rely on a novel, all-electronic noise cancellation scheme. Although related to earlier differential and ratiometric techniques, it has much better noise cancellation performance, is effective at modulation frequencies up to 100 MHz, and requires no critical adjustments. With this system, it is often possible to achieve the performance of a complex heterodyne system by means of a much simpler homodyne approach.
Two-body relative attitude control system: experimental results
Authors: Kendrick Richard L. , Sommer Tom , Duncan A. L.
Published: February 2023

We have performed an experiment to characterize the performance of a device designed to accurately maintain the relative alignment of large-aperture optical telescopes separated by large distances. Two-body relative attitude control system (TRACS) measures and controls relative angular motions between two V-shaped Zerozur mirrors separated by 2 m. The design eliminates first-order errors due to laser instability and small amplitude motions in the optical components. This makes it possible to measure all three relative tilts to within 0.2 µrad. This is accomplished by directly comparing the beam that samples the orientation of the Zerodur mirrors to a reference beam that carries common path errors. The experiment, which was performed in a vacuum, measured the resolution of TRACS by means of two identical systems that took independent sets of data simultaneously from the same pair of platforms. By applying thermal loading to the most sensitive components, the thermal stability of TRACS was also determined.
Correlator with a complex reference generated iteratively
Authors: Mahlab Uri , Rosen Joseph , Shamir Joseph
Published: February 2023

A complete learning, and pattern-recognition system based on the joint-transform correlator is presented. By employing an iterative process, a complex synthetic-discriminant function (SDF) for pattern classification is generated, which takes into account all the constraints and distortions of the actual system. To effectively implement a complex reference function with a binary mask, the following steps are taken. The input pattern, multiplied by a grating, is introduced into the correlator at some distance from a binary reference function. After an optical Fourier-transform is performed on the input plane, a region around the first diffraction order is recorded by a television camera and is displayed on a spatial light modulator (SLM). The correlation is achieved by a second optical Fourier-transformation. The classification criterion is a high peak for one class of a training set and a uniform distribution for a second class. The elements of the SDF are the variables of a cost function, which is minimized by an iterative method to achieve this recognition criterion. All Fourier transforms are performed optically, but the cost function is calculated on a digital computer. Experimental results demonstrate high quality performance even with a poor SLM.
Imaging science subsystem for NASA’s comet rendezvous/asteroid flyby mission and Cassini mission to Saturn
Authors: Kahn Cynthia L.
Published: February 2023

The Comet Rendezvous/Asteroid Flyby (CRAF) mission to Comet Kopff and the Cassini mission to Saturn will be briefly outlined, with emphasis on the environmental considerations that constrain the design of the imaging science subsystem (ISS). The ISS employs both wide- and narrow-angle cameras, which share a common electronics module. The narrow-angle camera contains a 2000 mm focal-length, Ritchey–Chretien telescope operating at f/10.5 over a spectral range of 200–1100 nm. The wide-angle camera contains a 300 mm focal length refractor operating at f/2.5 over a spectral range of 380–1100 nm. Dust covers will protect the optics during the missions. A two wheel filter mechanism will be employed, which is similar to that flown on the wide-field planetary camera of the Hubble space telescope. The shutters will be of the two-blade focal plane design used on the Voyager and Galileo cameras. The detectors will be Ford 1024 × 1024 charge coupled devices (CCDs) with 12µm pixels, a full well of greater than 50,000 electrons/pixel, and read noise of less than 10 electrons/pixel rms. Dark current will be suppressed by cooling the devices to -110°C. Radiation damage will be controlled by using tantalum and quartz shielding around the CCD.
Real-time acousto-optic photorefractive optical correlator
Authors: Sherman C. J. , Lawler W. B. , Moharam M. G. , Montgomery R.
Published: February 2023

We report the implementation and demonstration of a real-time, acousto-optic, photorefractive optical correlator. A dynamic range of up to 50 dB and phase stability of less than 1° is achieved by a heterodyne detection scheme. The basic operation of the system is as follows. A laser beam is modulated with the first signal. It then diffracted by an acoustooptic Bragg cell that is driven by the second signal. The diffracted beams are imaged on a photorefractive crystal. If the two signals have identical frequencies, a stationary, spatially periodic intensity distribution that is proportional to the product of the first signal and the time-delayed second signal is produced. Time integration of the product is accomplished by means of the buildup in the photorefractive space-charge field. A detector tuned to the frequency of the signal monitors the correlation between the two signals, which is weighted by the second signal. The acousto-optic Bragg cell operates at 75 MHz. A frequency mismatch of a few hertz results in a moving grating in the photorefractive material so that no field will build up, which leads to zero correlation. The operation and the limitations of the system, as well as potential applications in adaptive filtering, will be discussed.
Determination of fracture parameters by means of interferometric-type optical fiber sensors
Authors: Narendran Nadarajah , Shukla Arun , Letcher Stephen
Published: February 2023

This study illustrates the applicability of attached and embedded fiber-optic sensors in fracture-mechanics problems. Fracture studies of metals and nonmetals in the laboratory are important in predicting and preventing failures of machines and structures. Within the elastic domain, crack propagation in a material is governed by the stress-intensity factor, which completely defines the stress field near the crack tip. The experimental results for the mode I stress-intensity factor, obtained with single-edge notched specimens fabricated from aluminum, compare well with theoretical predictions. This indicates that the mode I stress-intensity factor can be accurately determined by choosing the proper orientation and size of the single-mode fiber-optic sensor. The advantage of this technique is that it can be effectively used to measure subsurface strains in thick cracked bodies, because the fiber can be easily embedded during the fabrication process.
Upconversion in laser materials and the upconversion laser
Authors: Jenssen Hans P.
Published: February 2023

Upconversion, a process in which two low-energy excitations combine to yield one excitation at the sum energy, occurs in most solid-state laser materials. The effect is particularly strong when the doping concentrations are high and when the excited-state level populations are high. In the search for more efficient lasers and for new wavelengths we usually encounter these conditions. Examples incluse the Cr-sensitized Nd laser and the Tm-sensitized Ho laser. In both of these, upconversion results in the potential loss of efficiency. Another example is the Er 2.8μm laser, where upconversion is necessary and should ideally yield a quantum efficiency of 2 when pumped by 800 nm diode lasers. Even though the upconversion phenomenon has been known for a long time, there is little reliable information on the parameters governing the process. This talk will summarize what is known about upconversion, how it affects various laser schemes, and what we need to know to profitably live with upconversion.
Multiple soliton beams
Authors: Reynaud F. , Maneuf S. , Barthelemy A.
Published: February 2023

Fundamental soliton beams have been observed in nonlinear Kerr media. Several soliton beams propagating simultaneously are coupled by the nonlinear effect. These couplings lead to high order soliton beams for superimposed input fundamental solitons or to soliton beam interactions (attraction, repulsion or energy transfer) for separate input fundamental solitons. In this paper, we report experimental observations of second and third order solitons and attraction or repulsion of two separate fundamental soliton beams. High-order solitons have been studied in a CS2 planar waveguide having a half soliton period length. The source was a doubled frequency Nd:YAG laser followed by a pulse shaping device. A quasi-steady excitation by a plateau shaped pulse has enabled us to observe the beam narrowing of the second order soliton and the beam splitting of the third one, after half soliton period propagation. Using a bell shaped pulse excitation and a temporal analysis of the output beam by a streak camera, the half soliton period pattern evolution has been recorded for slow power scanning up to the third order soliton power. Even with such continuous power variation only pure 1st, 2nd, and 3rd soliton patterns have been observed with very fast transitions. Soliton beam interactions have been observed in an equivalent two dimensional nonlinear propagation (CS2 cell). The source was still a doubled Nd:YAG laser but without a pulse shaping device. The laser beam passing through a Micheleon interferometer and imaging devices gives rise to two soliton beams of adjustable spacing and relative phase. Attraction and repulsion among the two beams have been observed for inphase and out of phase by π input solitons respectively. Influence of beam spacing on the interaction intensity has also been demonstrated.
Loss mechanisms in zinc sulfide thin-film waveguides
Authors: Himel Marc D.
Published: February 2023

Until recently, the losses in ZnS waveguides have been attributed primarily to scattering at the coating interfaces. Our results, however, show that the total waveguide attenuation is caused by a combination of volume and surface losses. By relating the losses of multiple guided modes to their individual field properties, namely, the field amplitudes at the interfaces and the power-confinement factor, we are able to separate volume and surface contributions to the total waveguide attenuation. If the losses are caused mostly by surface scattering, the higher losses may be attributed to an increase in the rms surface roughness, which can result from larger crystallites. However, initial investigations show that the surface losses, which are approximately 1.5 dB/cm, are independent of the total attenuation, which varies over 3-10 dB/cm. This suggests that the losses in ZnS waveguides may not be dominated by surface roughness. We employ a two-dimensional charge-coupled device camera interfaced with a computer to measure the losses of ZnS waveguides. By using these data, in conjunction with x-ray diffraction measurements of crystallite size and one-dimensional surface profiling, we hope to gain further understanding of the mechanisms that contribute to the losses in ZnS waveguides.
Electrochemically generated bubbles for bistable optical switching
Authors: Jackel Janet L. , Johnson John J. , Tomlinson W. J.
Published: February 2023

Bistable, polarization- and wavelength-independent optical switching has been accomplished by using the electrochemical generation and destruction of bubbles in an aqueous solution. Formation or destruction of bubbles in slots cut or etched into the 90° intersection of waveguides routes light into one or the other of the two guides. If the fluid is index-matched to the guide and no bubble is present, light passes straight through the intersection. When a bubble displaces the fluid, total internal reflection routes the light into the intersecting guide. Bubbles are formed by the electrolytic dissociation of water into oxygen and hydrogen and are destroyed by catalyst-assisted recombination. They can be formed or destroyed in less than a second and remain indefinitely; such time scales are suitable for protection switching. We have previously reported a demonstration of this concept that uses macroscopic slots cut in planar waveguides. Here we describe the behavior of bubbles in slots of the size needed for a waveguide matrix switch; typical slots are 6 µm deep and 3-15µm wide. Bubble formation, the achievement of longterm stability, and conditions for complete destruction of bubbles will be discussed, and a means of integrating large numbers of these switches into a matrix will be presented.
Red-green and yellow-blue hue cancellation on binocularly fused adapting fields
Authors: Gille Jennifer , Larimer James , Piantanida Thomas , Lanham Jennifer
Published: February 2023

Larimer and Piantanida investigated hue cancellation for red-green increments flashed on chromatic adapting fields consisting of a center disk with annular surround. The disk/annulus boundary was either stabilized or not, and thus the disk could have the color appearance of the annulus or not. They found that, in some conditions, the appearance of the disk, rather than its actual wavelength composition, determined the red-green ratio at which the increment appeared uniquely yellow. The appearance of an adapting field can also be altered by means of binocular fusion. Our study, part of which replicates the work of Humanski and Shevell, examined hue cancellation with red-green or blue-yellow increments on either monocular adapting fields or fused binocular adapting fields. Stimuli were presented on a color monitor driven by a microcomputer. Results show that the hue-cancellation functions cannot be simply related to the composition of the monocular adapting field, the color appearance of the fused adapting field, or the additive effect of the dichoptic adapting fields.
A vectorial beam-propagation method for guided optical fields
Authors: Gomelsky L. , Liu J. M.
Published: February 2023

The existing beam-propagation method is based on the scalar Helmholtz wave equation. Its use is limited to waves of uniform linear polarizations, in which the vector nature of the fields does not have to be considered in the calculation. This scalar beam-propagation method (SBPM) cannot adequately describe the polarization properties of fields in waveguiding structures. To take into account the effect on the field polarization imposed by the structural geometry and material properties of a waveguide, a vectorial beam-propagation method (VBPM) based on the vector wave equation has been developed. The VBPM takes full account of the polarization properties of the field and is capable of dealing with fields in waveguides of any structural geometry and material anisotropy and nonuniformity. Numerical results on polarized fields in waveguides of rectangular and circular geometries, as well as results of polarized fields in anisotropic media, will be presented. Comparison between the newly developed VBPM and the existing techniques, such as SBPM and mode calculations, will be given.
Use of holographic optical elements in optical storage
Authors: Ono Yuzo
Published: February 2023

Reflection holographic optical elements for CD/CD-ROM optical pickups and polarizing holographic optical elements for WO and MO disk read/write heads have been developed. This talk discusses how holographic optical elements fit for optical heads, including their advantages and disadvantages from the view point of application approach.
Chemical-beam epitaxy for advanced optoelectronic devices
Authors: Kolodziejski Leslie A.
Published: February 2023

As a hybrid technology of MBE and MOCVD, chemical beam epitaxy exploits the major advantages of the two epitaxial growth techniques. The fabrication of sophistacated heterostructures and quantum-well device structures based on advanced II-VI and III-V sermiconductors will be highlighted.
Synthesis of resonator for active control of laser radiation
Authors: Apollonov V. V. , Chetkin S. A. , Kislov V. I. , Vdovin G. V.
Published: February 2023

Intracavity adaptive optics for output radiation control is an advanced trend of laser engineering. In this work on the base of the Freshnel integral, we derive an algorithmic relation, which permits us to synthesize the profile of resonator mirrors for given distribution of the output radiation complexamplitude. With this relation we formulate a deterministic algorithm to be used for controlling the unstable confocal resonator loss without beam quality degradation via an appropriate profiling of active mirrors. The efficiency of single-channel correction of a heat lens in a laser with Fabry–Perot resonator is estimated theoretically and experimentally. A new type of metal membrane active mirror for intracavity power control and heat lens correction is proposed. In experiments with 20-Watt YAG:Nd3+ laser, equipped with this mirror, the heat lens correction resulted in a decrease of output radiation divergency in far field by a factor of 1.5–3.
Beryllium mirror fabrication technology into the 21st century
Authors: Fink Robert L. , Gardopee George
Published: February 2023

The high-performance, lightweight Be mirrors for use on space systems that will be operational in the 21st century are being conceived, designed, and prototyped now. This paper explains the integrated set of processes, techniques, and technologies in use today at Hughes Danbury Optical Systems (HDOS) to produce lightweight, closed-back, aspheric mirrors from near-net-shaped hot isostatic pressed substrates. The process starts from scratch with two givens: mirror performance specification and Be powder. The specifications drive the design of the mirror substrate and determine the internal geometries and tooling required to incorporate the optimal radius into the as-HIP'ed, near-net-shaped blank. The patented technique for configuring the internal tooling to accomplish this is presented, as are the stringent controls implemented during the powder loading, sealing, outgassing, hipping, decanning, and machining operations. The optical-finishing technologies from controlled grind/etch through superpolish are described, along with the metrology systems for validating that the requirements are met. The processes, techniques, and technologies are illustrated through actual aspheric mirrors built by HDOS. These mirrors are directly applicable to space applications in the 21st century.
Scale invariance of the Mellin transform filters
Authors: Sheng Yunlong , Arsenault Henri H.
Published: February 2023

The Mellin radial harmonic filters recently reported are based on the radial Mellin transform of objects in a polar coordinate system. The filters provide scale-invariant pattern recognition by matching the angular information of the object. Phase-only Mellin filters coded similarly in the Fourier plane were also reported. But both filters have only approximative scale invariance. In their definition, a small radius r=0. The r0 remains constant for objects with different sizes, that leads to scale dependence. We show that strict scale invariance can be achieved only when the object function is constant for 0 0. We also consider the behavior of the Mellin filters as a function of the position of the polar coordinate origin. We found that the proper centers for the Mellin filters are usually located outside the object.
A novel, thermally-stable InGaAs/GaAs structure for 1.3 μm IMSM photodetectors
Authors: Masum Choudhury A. N. M. , Jagannath C. , Elman B. , Armiento C. A.
Published: February 2023

A novel super-lattice enhanced InGaAs/GaAs interdigitated-metal-semiconductor-metal (IMSM) photodetector structure operating at 1.3 μm has been realized. The structure is stable after high temperature rapid thermal annealing, thus offering the potential monolithic integration with ion implanted GaAs MESFETs. The photodetectors have low dark current, an internal quantum efficiency of 86%, and a bandwidth of 14 GHz.
High uniformity, low cost packaging of multi-channel InGaAs photodetector arrays for parallel-bus optical interconnects
Authors: Chan E. Y. , Tanielian M. , Popoff A. , Self D. , Fu R. , Burnett A. , Hong C. S.
Published: February 2023

A novel packaging technique, which facilitates the alignment and coupling of a backside-illuminated InGaAs photodetector array with an array of v-groove embedded fibers, has been demonstrated. The packaged 6-element array shows a dark current of < 29 nA, a responsivity of >0.7 A/W, a rise/fall time of <1 ns, and an overall uniformity better than 5%.
Giga-bit rate receiver OElCs grown by OMVPE for long-wavelength optical communications
Authors: Yano H. , Aga K. , Kamei H. , Sasaki G. , Hayashi H.
Published: February 2023

Receiver OEICs, in which AlInAs/GaInAs HEMTs and GaInAs pin PDs are monolithically integrated, are described. The receiver OEIC was grown by OMVPE on a recessed InP substrate and processed by a simple full-wafer fabrication technique. The receiver exhibited high sensitivity to giga-bit rate signals.
Real-time pattern recognition using a computer-generated hologram displayed on a liquid-crystal television
Authors: LeClerc Luc , Drolet Jean-Jacques , Sheng Yunlong , Arsenault Henri H.
Published: February 2023

We report on experiments using a slightly modified low-cost 128 × 128 pixel liquid-crystal television (LCTV) as a spatial light modulator (SLM) in the Fourier plane of an optical correlator. The LCTV usually displays a binary phase-only filter. A recently proposed holographic coding method enables the efficient coding of a complex 64 × 64 pixel filter on a 128 × 128 pixel SLM or LCTV. Translation- and rotation-invariant pattern recognition can be obtained by coding a circular harmonic filter by this method. Theoretical and experimental results will be shown.
Diffraction tomography in the distorted-wave Born approximation
Authors: Lin F. C. , Alavi A. , McGahan R. , Fiddy M. A.
Published: February 2023

In many imaging applications, the wavelength of the illuminating wave is comparable in scale to the structural features of interest. Hence, the scattering and diffraction effects have to be incorporated in the inversion algorithms for the conventional diffraction tomography, in which the distribution of scattering centers can be recovered only if the scatters are weak or are slowly fluctuating. An inversion algorithm, which extends the limitations of conventional diffraction tomographic techniques based on the firstorder Born or the Rytov approximations is presented. This algorithm preserves a Fourier relationship between scattered-field data and the scatterer. When prior knowledge about the scatterer is available, the distorted-wave Born approximation can be used. This technique improves both the weak-scattering approximation and the required Fourier data interpolation and extrapolation. The procedure is illustrated with both simulated and microwave-scattered data taken at 10 GHz.
Tilt sensor based on the dispersion of two media interface
Authors: Apollonov V. V. , Chetkin S. A. , Vdovin G. V.
Published: February 2023

A new physical principle and configuration for a sensitive miniature optical-tilt sensor is proposed. The experimentally measured threshold sensitivity of the sensor is 2 × 10–7 radians with a range of linear response up to 10-3 radians. The possibility of a Hartmann wave-front sensor creation, based on the proposed device, is discussed.
Novelty filtering using hybrid amorphous silicon/ferroelectric liquid-crystal devices
Authors: Johnson Kristina M. , Mao Chongchang
Published: February 2023

We report here novelty filters using three kinds of optically addressed spatial light modulators (OASLMS) composed of amorphous silicon photosensers and ferroelectric liquid-crystal (FLC) light modulators. These novelty filters are based on polarization modulation of the OASLMs.1 The first novelty filter is constructed by placing a photovoltaic-transmission-mode OASLM between two polarizers. The optic axis of the liquid crystal in the OFF state and the transmission axes of the two polarizers are aligned in parallel. When an intensity-modulated lightbeam is incident upon the OASLM, the beam passes through the second polarizer before the device can respond to the signal. After the OASLM responds to the optical signal, the optic axis of the FLC rotates by 45°, thus rotating the polarization of the input light by 90°, causing it to be blocked by the second polarizer. Therefore, a novelty filtering of the input is obtained at the output. The second novelty filter uses two OASLMs with an externally applied voltage. The two OASLMs are connected by an ac power supply such that they are alternatively turned ON when they are illuminated by a light beam. The third novelty filter uses an OASLM with a special alignment of the FLC. This system performs novelty filtering by using the charge spreading property of the OASLM.
Effect of coupling hole position in coupled unstable resonators
Authors: Shakir Sami A. , Erkkila John H.
Published: February 2023

A common method of coupling unstable resonators is adjoint coupling through a hole. In this configuration, a portion of the magnified beam in one resonator is injected, as a demagnified beam, through a hole into the neighboring resonator. If the hole is small, diffraction effects are important. We show that the mutual coupling-strength of the two unstable resonators is roughly proportional to the hole size. The amplitude of the mutual coupling parameter oscillates as the position of the coupling hole is varied with respect to the optical axis. The absolute maximum value of mutual coupling takes place when the hole is on the optical axis. We show results for a strip unstable resonator and a three-dimensional resonator, and we discuss an interpretation of the mutual coupling strength in terms of Fresnel zones.
Enhanced stable-locking range in side-mode injection-locked semiconductor lasers
Authors: Luo Jhy-Ming , Osinski Marek
Published: February 2023

Injection locking has been used to improve static and dynamic lasing characteristics of semiconductor lasers for various applications, including both long-haul, highspeed digital fiber transmission and coherent communication systems. However, a strong phase-amplitude coupling in semiconductor lasers imposes stringent operational requirements for stable locking and limits the practical benefits of the injection locking technique. It is therefore important to examine whether these limitations can be somewhat ameliorated by choosing a target mode different from the free-running dominant mode. In our investigation of side-mode injection locking characteristics, we have developed a model based on multimode rate equations, including a phase equation for the injected mode. Consideration of multimode effects is especially important when the target mode is different from the free-running dominant mode. The locking range for side-mode injection differs from the conventional result by an extra frequency offset term that is caused by an increased threshold gain deficit. We investigate the dynamic stability of injection-locked states by considering small fluctuations around the stationary solutions. As in peak-mode injection, only a part of the possible locking range is dynamically stable. However, the stable locking bandwidth can be increased significantly by injection into a side mode. This implies that better locking and eased operating tolerances can be expected with side-mode injection. Analysis of the variation of carrier concentration as a function of the injection level reveals a well-defined threshold effect for side-mode injection. This new effect can be used for fast, all-optical channel switching, and we are now exploring it experimentally. In addition, selecting a target mode at the shorter-wave-length side of the gain peak results in an increased relaxation-oscillation frequency, thus enhancing the direct modulation bandwidth.
Algebraic analyses of high-order propagation techniques
Authors: Glasner Moses , Yevick David
Published: February 2023

We present several algebraic techniques that considerably simplify the determination of the component operators in the fourth-order electric field propagation methods suggested by Hermansson and Yevick. We also discuss possible realizations of sixth-order algorithms using these methods.
Three-dimensional lensless imaging using laser frequency diversity
Authors: Marron Joseph C. , Schroeder Kirk S.
Published: February 2023

A laser radar system for three-dimensional lensless imaging is analyzed in theory and by experiment. Three-dimensional imaging is accomplished by making use of the relationship between the wavelength dependence of an object's scattered light and its three-dimensional Fourier transform. The concept is demonstrated by obtaining a three-dimensional image with a charge-coupled device detector array and an argon-ion laser with a tunable intracavity etalon.
An optical-ring interconnect for single-instruction-multiple-data array processors
Authors: Li Y. , Ha B. , Wang T. , Eichmann G.
Published: February 2023

The single-instruction-multiple-data (SIMD) processing environment requires that in each time cycle an identical processing or interconnect be performed. Various optical free-space interconnect schemes for a SIMD processor array have been proposed. A common feature of these schemes is that the processors are distributed on a rectangular grid. A major problem with rectangular array topologies is that their optical implementations require the use of both space-invariant and space-variant optical elements. For example, the nearest-neighbor and the barrel-shifter networks require linearspace-invariantoperations for their center elements and spacevariant (wrap-around) operations for their edge and corner elements. In addition, because of the different geometrical distances between the rectangularly distributed processing elements, the latency problem, in which signals transmitted on the network over different paths undergo different delays, may seriously limit the processing rate of the system.
X-ray imaging near the diffraction limit
Authors: Raab E. L. , Tennant D. M. , Waskiewicz W. K. , MacDowell A. A. , Freeman R. R.
Published: February 2023

A principle motivation for producing soft x-ray imaging systems is to surpass the resolution of visible-light systems. Such systems have been demonstrated for ~13 nm radiation using multilayer-coated mirrors with normal-incidence reflectivities of approximately 40%. Unique impediments to achieving diffraction-limited resolution arise due to the phased nature of multilayer reflection, as well as the stringency at 13 nm of the λ/8 surface figure requirement. To examine the consequences of the multilayer coating, we performed a Foucault knife-edge test on a spherical optic both before and after a molybdenum/silicon coating was deposited. A 22-period undulator source was sufficiently powerful at 13 nm to provide a measurable reflection even without the multilayer coating. The results of the knife-edge scans were fit by a diffraction model, with the mirror’s effective surface characterized by Zemike polynomials. We noted a slight difference in the image after the multilayer was deposited. This was attributed to a slight decrease in some of the higher-order aberration terms. The difference in effective surface figure was less than λ/8 for the two measurements, indicating that a multilayer coating does not alter the effective surface figure of an optic in a way that is detrimental to the resolutions.
Laser printer design
Authors: Starkweather Gary
Published: February 2023

Laser printers have become a common-place technology for many people and represent one of the most eclectic combinations of technology available. Printers range from large high-speed systems costing upwards of $400,000 to new small personal units costing less than $1500. While the cost and performance range is large, the design elements are not radically different. What we shall explore in this discussion are the design elements and fundamental system taxonomyi of laser printers. The architectural alternatives will be reviewed as well as the potential extensibility of the scanner technology. Laser printer systems are available with or without controllers, and we shall review the importance of the controller and its future potential. Printer spatial resolutions from about 300 pixels/in. to over 3000 pixels/in. are commercially available and can print to a variety of media. Laser scanners also operate in either binary or greyscale mode and have been adapted to color laser printers as well. The remarkable reduction in cost of laser scanners is a combination of both good design and manufacturing volume. In summary, we shall review the past, present, and future of this pervasive and very profitable technology.
Kidney stone identification from x-ray images using neural networks
Authors: Lo Edmond Y. , Rosen David I. , Bailey Albert W.
Published: February 2023

A priori knowledge of kidney stone composition is an important factor in determining the optimal method of therapy. In this study, we have shown that stone composition can be determined from x-ray images. This was accomplished by using 25 mathematical constructs to describe the stone image and by using these as inputs to a neural network for pattern recognition. A data base of stone images spanning the compositions of commonly occurring kidney stones of calcium oxalate, uric acid, struvite, and brushite and cystine stones was created by digitizing of the x-ray images. For each image, a region-of-interest inscribed by the image area was defined, from which descriptors of the image were calculated. A subset of the images was used to train the neural network, and the remaining cases were used to test the trained network. Based on the small data base available, the overall accuracy was found to be greater than 70%. For this study, specimen radiographs, i.e., radiographs of stones taken outside the body, were used. We are extending the identification scheme to use radio graphs of stones in vivo.
Phase-sensitive multiphoton ionization
Authors: Chen Ce , Yin Yi-Yian , Elliott D. S.
Published: February 2023

We have demonstrated an interference between multiphoton ionization processes that results in a phase-sensitive enhancement or inhibition of the net ionization rate. We focus two laser beams, either of which can induce an atomic transition between the same two states, into a cell containing atomic mercury. One of the fields is at a wavelength of 185 nm and can linearly induce the 6s 1S0 → 6p 1P1 transition in mercury. The other field is at a wavelength precisely three times as long, and it can excite the 6p resonance by a three-photon process. The absorption of two additional visible photons ionizes the mercury. In the presence of both fields, the transition amplitudes interfere, and their relative phases become very important. Their phases can be controlled by controlling the phases of the optical fields inducing the transitions. Coherence between the two fields, vital for the interference, is ensured by generating one field from the other using a nonlinear third-harmonic process. We have also demonstrated the effect of spatial phase variations between the two fields on the local photo-ionization rate.
Complex inverse estimation of the psychophysical impulse response without minimum phase assumptions
Authors: Tyler Christopher W.
Published: February 2023

Measurement of the temporal modulation threshold function (TMTF) in retinal diseases shows that diverse patterns of temporal loss are found in different diagnostic groups. Complete specification of the temporal losses requires specification of the visual impulse response (VIR) in each type of loss, which can be achieved by a new "temporal deblurring" technique for measurement of the relative phase shifts of all the frequency components of the response. The amplitude attenuation is measured psychophysically by a standard TMTF paradigm, and then compensated by increasing harmonic strength in proportion to the visual attenuation. The phase of each frequency component is then adjusted so as to maximize the internal response amplitude. The amplitude and phase values may be converted by inverse Fourier transformation into the estimated VIT for the particular stimulus conditions.
Differences in detection of stationary and moving targets in optic neuritis
Authors: Johnson Chris A. , Casson E. J. , Osako Masahiro
Published: February 2023

In some optic neuritis (ON) patients, the relative sensitivity loss for stationary versus moving targets (statokinetic dissociation, or SKD) has been attributed to selective losses of mechanisms sensitive to low temporal frequency modulation. Our work suggests that ON patients exhibiting SKD show relatively good sensitivity to moving targets over a range of angular velocities (1-8°/s) despite substantial losses in flicker sensitivity at all frequencies (2-20 Hz). This finding is based on a comparison of the results of automated static, kinetic, and flicker perimetry in ON patients with SKD. In many cases, severely reduced sensitivity to flicker occurred within the region where moving targets were readily detected. Because the apparent superiority of motion sensitivity can occur in spite of large losses in flicker sensitivity, the former maybe based on spatial, rather than temporal, abnormalities. This abnormal spatial summation was confirmed by comparing static perimetry results for size III (0.43°) and size V (1.72°) targets. Thus, both temporal and spatial abnormalities are present in ON patients with SKD. Contrary to previous hypotheses, SKD does not appear to be based on a selective loss of mechanisms sensitive to low temporal frequency modulation. Spatial summation abnormalities may form the primary component underlying SKD.
Simultaneous measurement of laser scintillation and atmospheric turbulence structure parameter and inner scale
Authors: Consortini Anna , Cochetti Fausto , Churnside James H. , Hill Reginald J.
Published: February 2023

Intensity scintillation of a diverged laser beam was measured at NOAA's Table Mountain Field Site near Boulder, Colorado, where turbulence homogeneity is excellent. The horizontal propagation path was 1200 m. Scintillation strength ranged from weak to very strong. Refractive-index structure parameter and inner scale were measured simultaneously. Measured values of intensity variance will be shown and compared with those from computer simulations or approximate and numerical solutions of the fourth moment equation.
Functional integral solution for wave propagation in random media
Authors: Gozani Joseph
Published: February 2023

Path integral formulation originated in quantum mechanics and probability theory and was widely used from the 1970s on to provide a formal solution to wave propagation in random media. The use of path integration arose because of the similarity of the parabolic approximation of the Helmholtz equation and the Schrodinger equation used in quantum mechanics. However, the inability to compute the path integral results lead only to asymptotic approximations. In the meantime, other methods—the multiple-phase screens and the multiple-scale expansion—were developed. These methods provided an approximation, valid though in-accurate, for arbitrary fluctuation strength. Later, researchers realized that the same results can be obained by using the configuration and phase space path integral procedures. Recently the interaction picture formulation, originated in quantum mechanics, provided an important link in the unification of all these procedures. It was shown that the approximations reached by the multiple-phase screens and the multiple-scale expansion methods are just crude approximations, valid for a thick phase screen. A surveyi of the functional solutions will be followed by a functional multiple-scale expansion formulation equivalent to the other functional solutions. If time will allow, computational aspects and open questions will be discussed.
Second-harmonic generation in periodic electric-fields-poled optical
Authors: Kashyap Raman , Williams D. L. , Davey S. T.
Published: February 2023

Fermann et al.1 induced a (2) in an optical fiber by simultaneous blue-light excitation and dc-electric-field poling and subsequently demonstrated second-harmonic generation into a phase-matched higher-order mode from a 1208 nm pump wavelength. Unfortunately, it is not possible to design a fiber for the most desirable phase-matched interaction into the lowest order HE211 frequency-doubled mode, so only a less efficient interaction can be achieved by the poling scheme used by Fermann et al. However, by applying a spatially periodic electric field across a fiber, the fundamental wavelength mode can be phase-matched to any of the propagating second-harmonic modes.2,3 In this paper we report the first results on periodic poling and seeding of an optical fiber using spatially periodic static fields. We show that applying a spatially periodic electric field can quasi-phase match the 1064 nm wavelength mode to the lowest order 532 nm wavelength mode. The presence of the 532 nm mode and the periodic electric field permanently poles the fiber periodically and can also seed the fiber. There appears to be competition between seeded and poling-induced SHG. The significant and important uses of periodic poling are in extending the frequency-doubling capability of optical fibers into the infrared wavelengths and removing the need for designing a fiber for phase-matched interaction.
Mono-intense writing and readout and re-exposure measurements in frequency-doubling optical fibers
Authors: Selker M. D. , Lawandy N. M.
Published: February 2023

The saturation of the second-harmonic generation process in optical fibers has been a subject of interest since it was first observed by Osterberg and Margulis. The phenomenon was subsequently modeled by Oullette who thought it was due to the change in the phase-matching condition brought about by the intensity dependence of the index of re fraction. We have tested this dependence at a fundamental level, using monointense pulses.
Performance of diffractive lenses with nonunity diffraction efficiency
Authors: Buralli Dale A. , Morris G. Michael
Published: February 2023

The unique optical properties of diffractive optical elements make them attractive candidates for a wide variety of applications. Unlike conventional optical elements, however, diffractive optics can simultaneously produce more than one image, resulting from the various diffracted orders. Rigorous electromagnetic grating diffraction theory shows that, in general, the diffraction efficiency can be a function of pupil position and field angle. If the diffractive lens is not 100% efficient in diffracting the incident light into the desired diffracted order, the resulting image can be degraded by the increased background illumination. We consider the effects of the unwanted diffracted orders on the point-spread function and modulation transfer function (MTF) of systems that contain diffractive lenses. With a nonunity diffraction efficiency, the diffraction-limit MTF at low spatial frequencies is reduced by an amount equal to the fraction of energy in the diffraction order of interest. Fourier theory shows that this amount of degradation is given by the pupil-averaged efficiency. This average efficiency thus makes a convenient merit function for estimating image quality. For scanned imaging systems, the average efficiency acts as the equivalent of system transmittance in reducing the flux incident on the detector.