bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical cavity surface-emitting laser diodes
Authors: Tai K. , Fischer R. J. , Huang K. F. , Deppe D. G. , Ren F. , Chu S. N. G. , Cho A. Y.
Published: February 2023

We reported all-MBE grown vertical resonator diodes with an active layer made of GaAs bulk and of GaAs/AlGaAs quantum wells. Vertical current injection through two semiconductor mirrors was made possible by a novel reflector structure on the p-side of the diode. This so-called hybrid-Bragg reflector makes use of constructive interference between a distributed Bragg reflector and a metal layer for enhanced reflectivity. Because of enhanced reflectivity of this combination, fewer pairs and lower index difference are required for the Bragg reflector which allows sufficiently high electrical conductance. Low current threshold laser emission from the etched hole in the substrate was observed in these devices. For example, threshold currents as low as 12 and 22 mA were achieved, respectively, for 10- and 15-µm diam devices with a 0.25-µm active bulk GaAs layer. Pulsed emission power exceeding 10 mW and an external slope efficiency of ~20-25% were observed. The short active layer thickness indicates the high degree of mirror reflectivity (R1R2 > 96%).
Numerical simulation of mode locking in a semiconductor laser
Authors: Hsu Kevin , Verber Carl M. , Roy Rajarshi
Published: February 2023

Multimode complex electric field equations are employed to numerically simulate the transient process of active mode locking in a semiconductor laser coupled to an external cavity formed by an AlGaAs or InGaAsP waveguide. Langevin noise sources for the complex fields and the carrier population which contribute to the partially incoherent interference among the modes are included. The simulation starts with a free-running multimode laser. The physical mechanism governing the mode coupling is cross saturation of the gain. Use of sinusoidal gain modulation is seen to cause the evolution of a mode-locked pulse. Fluctuations of the mode-locked pulse height and width due to spontaneous emission noise are observed in our simulations. These represent a fundamental limit of the pulse-to-pulse stability that can be attained in a mode-locked laser.
Quantum well optical tristate devices
Authors: Lentine A. L. , Hinterlong S. J. , Cloonan T. J. , Mccormick F. B. , Miller David A. B. , Chirovsky L. M. F. , D'asaro L. A. , Kopf R. F. , Kuo J. M.
Published: February 2023

We demonstrate integrated quantum well tristate logic devices for possible use in bus architectures. The devices have two optical output beams which represent the logic state of the output data depending on their relative power. When the power in one output beam exceeds the other, the logic state is a logic one or zero depending on which beam has the largest optical power. When the power in both output beams is equal, the device is in a disabled state. These optical devices are analogous to the tristate devices often used in electronic buses, where each device can be actively on, actively off, or disabled, with, at most, one device on the bus active at a time. We show two methods of generating tristate data, one using tristate quantum well modulators and one using tristate self-electrooptic effect devices (SEEDs),1 and we demonstrate a simple optical bus consisting of three such devices. Finally, we comment on the limitations on the number of devices that can be connected to a bus of this type.
Shape from highlights
Authors: Bulthoff Heinrich H. , Blake Andrew
Published: February 2023

In two psychophysical experiments we tested how stereoscopically viewed highlights or specularities can serve as cues for material properties and 3-D local surface geometry. In the first experimental subjects can change interactively both horizontal and vertical disparities of a highlight relative to a textured surface. When the relative disparities of the highlight are veridical the whole surface appears glossy. However, when horizontal relative disparity is non veridical, the surface ceases to look glossy. In a second experiment we asked if the visual system can accommodate to variations in specular disparities by changing its hypothesis about surface curvature, rather than its hypothesis of glossiness. Naive observers, asked where a specularity appears to be in relation to the surface that generated it, usually reply that it appears to lie on the surface. We have shown that their early visual system knows better, choosing for convex/concave ambiguous surfaces (e.g., crater illusion) a configuration which is consistent with the physics of specular reflection. Human visual analysis appears to employ a physical model of the interaction of light with curved surfaces—a model firmly based on ray optics and differential geometry.
Properties of polarization in double-clad elliptical fibers
Authors: Zhang Feng , Lit John W. Y.
Published: February 2023

By using Gaussian approximation, the modal spot size equation of a weakly guiding double-clad elliptical (DCE) fiber has been numerically solved. The variations of both the spot size and the field intensity with core ellipticity are examined. The results show that, compared with single-clad elliptical fibers, a smaller spot size and a more confined field distribution can be obtained. The polarization properties are also examined and presented as curves in terms of the three parameters: major/minor core axis ratio, inner cladding and core index difference, and inner cladding/core radius ratio. The curves of birefringence as a function of normalized frequency for the different parameters show that high bire-fringence can be obtained within the single-mode region by using DCE fibers.
Nonlinear interactions between modulated waves in a single-mode fiber
Authors: Lichtman E. , Friesem A. A. , Tang S. , Waarts R. G.
Published: February 2023

The nonlinear interaction, induced by the Kerr effect, between a modulated wave and a carrier wave propagating in a single-mode optical fiber, has been investigated both theoretically and experimentally for three common modulation schemes: amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). Such interactions may lead to cross-phase modulation and to the generation of new frequencies which may have deleterious effects on coherent communication systems. Our results reveal that the Kerr effect leads to the generation of two new waves via four-wave mixing. The spectrum of one of the generated waves is a copy of the spectrum of the modulated input wave, while the spectrum of the second is an autoconvolution of the modulated input wave spectrum. The spectrum of the carrier is not changed for pure PSK or FSK. For ASK, however, the carrier becomes phase modulated. Furthermore, the depletion caused by the generation of the two new waves leads to amplitude modulation of the carrier. This depletion and thus the crosstalk are minimized for an intensity ratio of 2:1 between the modulated and the carrier waves.
Guidelines for the design of fiber optic transversal filters
Authors: Ghosh Anjan K. , Lisle Sam , Allen Susan D.
Published: February 2023

A transversal filter is the most basic optical signal processing device that can be built from a fiber optic tapped delay line. If x(t) represents the lightwave signal in the fiber, the output of the transversal filter is given by where {hn} = tap weights determined by a spatial light modulator and dn = time delay for the (n + 1)th tap. Selecting values of the impulse response terms {hn} and the tap delays we can design low-pass, high-pass, bandpass, and bandstop filters, arithmetic Fourier transform calculators, equalizers, etc. The characteristics of analog fiber optic processors are affected by the optical error sources: spatial errors in tap weights, attenuation and position errors in taps, detector noise, and dispersion in fiber. The total effect of these error sources produces a new transfer function, H′(ω) = H(ω) + D(ω) − jωT[H(ω) ∗ S(ω)] + E(ω), where D(ω), S(ω), and E(ω) are Fourier transforms of the spatial errors, the time delay errors, and the detector noise, T = sampling time and ∗ represents a convolution. From this theory upper bounds on the deviations in the performance measures of a transversal filter have been determined. We found that low-pass transversal filters are robust with respect to optical roundoff errors. We observed that the use of Hamming and Hann windows can make fiber optic transversal filters more robust.
Three-dimensional optical memory
Authors: Rentzepis Peter M. , Parthenopoulos Dimitri A.
Published: February 2023

A novel 3-D optical memory device is presented which has the potential of storing extremely high (~1013-bits/cm3) bit densities. The information may be accessed randomly and in parallel by utilization of two beams which overlap inside the medium allowing volume optical information storage. The 3-D memory device is based on two-photon writing, reading, and erasing of information in a photochromic material embedded in a polymer matrix. An infrared beam and a visible beam combined induce a structural change on the photochromic material which corresponds to the write cycle. Subsequent to that, the initially transparent molecule absorbs in the visible and can be read by a combination of two near-infrared beams. The observed fluorescence, which is induced by the two-photon absorption of the infrared beams, constitutes the read signal. Erasing of the imprinted information can be achieved by warming the molecule with two infrared beams on which the molecule reverts to the original unwritten structural form. The written information persists for many days at dry ice temperatures (−78°C).
Third-order optical nonlinearities of Metallophthalocyanines at 1.064 μm
Authors: Shirk James S. , Lindle J. R. , Bartoli F. J. , Hoffman C. A. , Kafafi Zakya H. , Snow Arthur W.
Published: February 2023

We explore the influence of metal substitution in phthalocyanines on their nonlinear optical susceptibility. Specifically, the χ(3) at 1.064 μm of metal free tetrakis- (cumylphenoxy)phthalocyanine and that of several metal complexes including Co, Ni, Cu, Zn, Pt, and Pb are reported and compared. The third-order susceptibility of these phthalocyanines in CHCl3 solution was measured by degenerate four-wave mixing at 1.064 μm, far from the nearest strong absorption. The laser pulse width was nominally 35 ps and intensities of up to several GW/cm2 in each of the pump beams were used. The solution χ(3) was measured relative to CS2.
Stationary and transient multiwave mixings — detailed theory and experimental observations
Authors: Khoo I. C. , Zhou P. , Michael R. R. , Lindquist R. G. , LoPresti P.
Published: February 2023

We present a detailed general theory of multiwave mixing effects in a nonlinear medium produced by two incident coherent laser beams. Calculations are performed for localized as well as diffusive types of nonlinearities. The theory accounts for all the relevant parameters such as laser pulse widths, medium response times, nonlinearities, interaction length, intensities, beam ratio, phase modulation effects, losses, and side diffractions. The interrelationship between two- and multiwave mixing effects and the evolution of transient to stationary behavior is explicitly worked out. In particular, the gain experienced by a weak incident probe beam via these mixing effects is quantitatively analyzed as a function of the aforementioned parameters.
Effect of input modulation on the output of an acoustooptic correlator
Authors: Reeve C. D. , Wombwell J. F.
Published: February 2023

A novel twin Bragg cell, space-integrating correlator is described, in which the spatial integration is achieved by summing the light intensity on a photodiode. It is found that the nature of the output depends on the type of amplitude modulation used to apply the signals to the Bragg cell carrier frequency. With suppressed carrier modulation the correlation of the squares of the input signals is obtained but when large carrier modulation is used the true correlation of the signals may be obtained by high pass filtering the detector output. It is shown that the phase of the correlation function is preserved.
Mechanical properties of optical thin films
Authors: Pulker Hans K. , Edlinger Johannes
Published: February 2023

The mechanical properties of thin films are strongly dependent on structure, micro structure, physicochemical activity, and composition. They can be influenced by the production technology and the parameters chosen. Relatively low intrinsic tensile stresses in the 108-dyn·cm-2 range occur in ~50-nm thick Ag and Al films made by fast evaporation and condensation in nonreactive high vacuum. Cr films show much higher values of ~1010 dyn·cm-2. In oxygen doped Cr and Al films the stress decreases and in Al films even changes sign, becoming compressive. Further oxygen supply decreases the compressive stress and, by reactive deposition, favors the formation of tensile stressed Al2O3 films. Quarterwave thick dielectrics are often tensile stressed when low refractive and compressive when high refractive. Intrinsic stresses may be masked by thermal effects due to a high temperature of preparation and be influenced by H2O sorption and grain boundary segregation effects. Dielectric films prepared by sputtering, ion assisted deposition, and ion plating show compressive stresses in the 109-dyn·cm-2 range for metal oxides and 1010 dyn·cm-2 for nitrides. Stress can be reduced by use of lower bombarding ion and coating material energy during film growth.
Stress and structure in mixed thin TiO2-SiO2 Films
Authors: Sankur H. , Gunning W.
Published: February 2023

In this paper we discuss the stress and sorbed moisture in mixed SiO2-TiO2 thin films and the dependence of these on deposition temperature and pressure, chemical composition of the film, and annealing conditions. SiO2 and TiO2 commonly used visible range optical thin film materials in gradient-index coatings. Films deposited by evaporative techniques have a porous microstructure. This microstructure and the sorption of moisture in the pores give rise to mechanical stress, which can cause catastrophic failure of the coating. Therefore, techniques to eliminate moisture sorption and to minimize stress are highly desired. It was observed that sorption of water causes compressive stress in SiO2 rich films, indicating different bonding arrangements of sorbed water at the grain surfaces in these two materials. Deposition conditions that promote a denser film microstructure, such as high substrate temperature, low background pressure, or energetic ion bombardment tend to reduce sorbed water and the tensile stress of TiO2 rich films. For a given set of deposition conditions the stress becomes more tensile as the TiO2 content increases. However, this composition dependence is sensitive to the method of mixing, being linear with composition in alternating layered mixtures and nonlinear in codeposited mixtures. Annealing reduces water in the films and increases tensile stress as the film undergoes densification. High temperature annealing also causes segregation and crystallization of TiO2. The grain size dependence on composition and annealing time have been determined for the entire range of compositions.
Thermal stress in zirconium dioxide thin films
Authors: Mao Yalan , Bovard B. G. , Lehan J. P. , Zhao T. , Olinger D. , Macleod H. Angus
Published: February 2023

The total stress is composed of the intrinsic stress due to growth mechanisms, the thermal stress due to the thermal expansion mismatch between film and substrate, and the external stress due to external loading. If thermal stress is increased, brittle materials (ceramics) crack while plastic materials (metals) deform until they melt. Zirconium dioxide is a refractory ceramic with valuable optical properties. Its stress behavior under temperature cycling is investigated.
Optical systems using arrays of symmetric self-electrooptic effect device
Authors: Prise M. E. , Lamarche R. E. , Craft N. C. , Downs M. M. , Walker S. J. , Chirovsky L. M. F. , D'asoro L. A.
Published: February 2023

Designs for digital optical processors such as optical computers and packet switches using arrays of optical logic gates with optical interconnects have been proposed. Large arrays of S-SEEDs have been fabricated and can be used as optical logic gates. Some optical systems have been proposed. The optical system described here illustrates the design issues which must be addressed for any optical systems intended to utilize large arrays of optoelectronic devices incorporating GaAs multiple quantum well modulators. We have demonstrated the operation of a single cascadable optical logic module with a 7 × 3 array of S-SEEDs 40 μm apart with 5- × 10-μm windows. By using two diode lasers this module solves the problem of presetting the S-SEEDs. The combination of all the required signal and power supply beams was carried out without significant power loss and without reduction of the optical system resolution by using patterned reflectors and polarization beam splitters. The cascading of two arrays of S-SEEDs using two such modules is described and the system alignment difficulties and solutions discussed. The extension of this optical system to much larger arrays requires more advanced optical design to overcome the problems of aberration and field curvature.
Optical mesh and hypercube perfect shuffle by space invariant multiple imaging
Authors: Sheng Yunlong , Arsenault Henri H.
Published: February 2023

Incoherent space invariant multiple imaging is used in a class of systems for free-space interconnections. They are classical imaging systems using mirror array, off-axis lens array, beam splitter, or holograms for multiple imaging. Their point spread function is a number of points shifted by tilting the mirrors. These systems can implement many types of regular interconnection. In mesh networks, the input nodes in a 2-D array have the same interconnection pattern. They are implemented by multiple imaging with the number of images equal to the fan out number. In the hypercube and perfect shuffle networks, the input nodes in different locations in a 2-D array require different interconnection patterns. They can also be implemented in space invariant systems. Only the number of multiple images has to be larger than the fan out number. This introduces a loss of power. We used eight mirrors for four-cube network and four mirrors for 2-D perfect shuffle. The space invariant systems can have a very large number of input nodes, high spatial density of interconnects, and potentially a very large fan out number for massive parallel interconnections.
Guided wave and ellipsometric characterization of spin coated polymer films
Authors: Naylor David L. , Amleshi Peerouz
Published: February 2023

The development of integrated optical devices using electrooptic polymers requires an understanding of the effects of fabrication conditions on the optical properties of polymer films. We report on the use of guided mode studies of spin coated planar polymethyl methacrylate waveguides as a technique for characterizing the effects of processing conditions (e.g., polymer solution concentration, viscosity, spin speed, and surface preparation) on the thickness, refractive index, and optical quality of the resultant films. These in situ measurements are supplemented by ellipsometric measurements which are able to confirm the optical constants by out-of-plane measurements. The polymer films are spin coated onto thermally oxidized silicon wafers. Guided wave studies are reported at both 633 and 1064 nm for which a thick (2-μm) oxide lower cladding layer is necessary to prevent absorption in the silicon substrate. The effects of an upper cladding layer on reducing losses due to surface roughness are presented. Semiconductor substrates for optical waveguides are of technological significance not only because of optical interconnection applications but also for the development of micromachining techniques to facilitate coupling of optical signals between fibers and waveguide films. We report on our progress in this area.
Wide field diffractive singlets for imaging, scanning, and Fourier transformation
Authors: Buralli Dale A. , Morris G. Michael
Published: February 2023

Conventional holographic optical elements are limited in their utility by uncorrected field aberrations: coma for planar HOEs and astigmatism for curved elements. However, manufactured diffractive elements, produced by precision machining or photolithographic techniques, can have a designer-specified diffractive structure. This freedom, along with the choice of aperture stop location and bending of the diffractive lens substrate allows for the control of geometric aberrations. We have developed a set of design equations for a diffractive singlet which is free from third-order coma, astigmatism, and field curvature, for a specified conjugate ratio. The aberrations are controlled by the location of the diffracting zones and the placement of the aperture stop. The bending of the substrate can be used to provide a desired (non-zero) amount of spherical aberration or distortion. The aperture size is limited by the remaining spherical aberration, and a suitable tolerance can be found by applying Marechai's criterion. One application which requires a prescribed amount of distortion is a laser scanning lens. In this case, it is desired to have the lens corrected for the f-theta condition. We present an example of a flat field diffractive singlet which satisfies the f-theta condition and is suitable for scanning an 8.5-in. paper width at a resolution of 1000 dots/in.
Oblique imaging in the paraxial approximation
Authors: Chastang Jean-Claude
Published: February 2023

Oblique imaging does not receive much attention in textbooks yet it is an interesting topic which can have practical applications as in many instances the objects that one wishes to image are not necessarily limited to planes perpendicular to the optical axis. The lack of popularity of oblique imaging is, of course, due to the severe alteration that it induces in the appearance of the object which is being imaged since it is accompanied in most instances by keystone distortion and anamorphosis in large amounts. Another reason might be that the paraxial relationships between object and image are not as simple as in the conventional perpendicular case, in particular the rendition of a 3-D structure is not without surprises. Yet one advantage of oblique imaging is that the height information is not lost as a result of the imaging process as long as the structure in question is contained within the depth-of-focus range.
Conic sections revisited
Authors: Foreman J. W.
Published: February 2023

In most treatments of the reflecting properties of the conic sections, the properties are stated without proof. In this paper the conic sections are derived from first principles as surfaces which produce specific effects on light rays. For example, the ellipse is taken to be a surface which reflects all rays emanating from one fixed point in a plane through a second fixed point in the plane. Each of the conic sections defined in this way is described by a first-order differential equation of second degree. The differential equations are solved and are shown to produce the expected results. These derivations should prove useful in introductory optics courses to give students a better feel for the reflecting properties of the conic sections.
Dispersion of the electronic n2 originating from two-photon absorption in semiconductors
Authors: Sheik-Bahae M. , Hagan D. J. , Van Stryland E. W.
Published: February 2023

Recently we reported large third-order nonlinear susceptibilities in semiconductors in the presence of two-photon absorption as measured on a picosecond time scale DFWM.1,2 These nonlinearities have fast response (resolution limited by the laser pulse width ≃25-ps FWHM) and are distinguished from the slowly decaying carrier effects which appear as fifth-order effects. Using the newly developed Z-scan technique (a simple single beam method for n2 measurements3), we have determined the sign and magnitude of these nonlinearities. These measurements show the changing sign of n2 from positive to negative ZnSe and CdS when going from 1- to 0.5-μm radiation. Using a Kramers-Kronig transformation on the two-photon absorption spectrum of the direct gap semiconductors as calculated from second-order perturbation theory, we have been able to account not only for the dispersion but the magnitude of these nonlinearities. This simple formalism yields a general scaling formula for n2 as where A is a nearly material independent constant and G2 is the calculated dispersion function. The above expression also gives an estimate of the low frequency electronic n2 (positive) for a large number of transparent materials (e.g., glasses) which possess nonlinearities that are 2-3 orders of magnitude smaller than the semiconductors.
Orientation and doping dependence of two-photon absorption in semiconductors
Authors: Schroeder W. Andreas , Stark Thomas S. , Dawson Martin D. , Smirl Arthur L.
Published: February 2023

Considerable interest has been shown in measurements of nonlinear optical effects in semiconductors using picosecond pulses. Carrier diffusion, photorefractive effects, nonlinear pulse propagation, and transient energy transfer, for example, have all been investigated on these time scales. Such studies often involve semiconductor samples having deep (subbandgap) defect states, whether introduced intentionally, e.g., by doping, or otherwise, which are resonant or near-resonant with the photon energy of the exciting pulses. Such studies may also require the use of a specific crystal orientation. An accurate knowledge of two-photon absorption coefficient β is needed to describe and model these interactions. However, several other nonlinear absorptive processes are possible in these circumstances, in particular saturation of the deep level absorption via single photon excitation and stepwise two-photon absorption via the defect levels. We describe single-beam nonlinear transmission measurements in a variety of semiconductor samples; GaAs:EL2, GaAs:Cr, GaAs:Si, CdTe:V, InP:Fe, and undoped GaAs and CdTe in several orientations. By using 5-ps pulses at 960 nm of fluence up to 2 mJ cm−2, provided by a styryl 13 synchronous dye amplifier system, we work in a regime where the virtual two-photon absorption process dominates. Values of β are thus extracted unambiguously. Several of these samples have demonstrated photorefractive beam coupling at this wavelength and pulse duration. The β-values are thus of both fundamental interest and important in analyzing those experiments.
Electric field sensors using nonlinear optical polymers
Authors: Hayden L. M. , Sauter G. F. , Chun C. S. L. , Pasillas P.
Published: February 2023

This work is part of a continuing project that is investigating the use of integrated optical (IO) waveguides and optical fibers coated with nonlinear optical (NLO) polymers as electric field sensing devices. The IO waveguides were fabricated using three different techniques: (1) in the NLO polymer itself (on glass and silicon substrates), (2) in glass microscope slides using thin film silver diffusion and silver ion exchange methods, and (3) in thin film optical epoxies. The Ag+ glass and UV cured optical epoxy waveguides were subsequently coated with NLO polymers; the 3-D patterned waveguides provided lateral confinement of the optical wave that propagated in the polymer. A low index buffer layer of polysiloxane glass resin (Owens Illinois GR650E) was needed on the silicon substrates to decrease the propagation loss. The NLO polymers were dip coated or spun on these substrates and were poled with a corona poling technique with fields of the order of 3 MV/cm. Interferometric and polarization rotation methods were used to measure the effects of applied electric fields on the NLO devices at wavelengths of 633, 780, and 830 nm. Electrooptic coefficients were determined and compared with similar coefficients obtained using second harmonic generation methods on the same NLO polymers.
Investigation of spectroscopic properties of nonlinear optical crystals and their relationship to structural radicals
Authors: Xu D. , Lin J. T. , Chai B. H. T.
Published: February 2023

Since many of the organic conjugated compound crystals have nonlinear optical coefficients of at least 1-2 orders of magnitude higher than those of the inorganic oxide compounds, these crystals have drawn the attention of many researchers. However, the major drawback of these organic compounds is their poor UV transparency which greatly limits their potential applications.
Detection of linear, low-contrast tracks in noisy images via optical Hough Transform
Authors: Lin Shih-Chun , Boughton R. Scott
Published: February 2023

The Hough transform is a pattern recognition technique for identifying straight lines in a 2-D picture. With this technique, any straight line or collinear line segments in the object domain are transformed to a point in the feature domain, thus allowing a higher degree of detectability. For uses requiring real time processing such as industrial product inspection and track detection, several optical implementations have been proposed. In this paper we report detection of low-contrast linear tracks in noisy images by a simple optical Hough transform setup. Films containing noisy 512×512 digital images, each with a 2-pixel wide track, were used as inputs. The output spot was detected by a linear CCD array. Both coherent light and incoherent light were tried. It was found that with coherent light the outputs were completely swarmed by speckle noise. With incoherent light, the signal-to-noise ratio of the output depends on the contrast of the track to the background.
Experimental study of a binary phase-only joint transform correlator based on liquid crystal television
Authors: Tam Eddy C. , Tanone Aris , Yu Francis T. S. , Gregory Don A.
Published: February 2023

Liquid crystal TV has attracted much attention in the optical image processing community mainly because of its high versatility at very low cost. Here we report the optical property of an active matrix LCTV (Seiko LVD 202 LCTV) and demonstrate one of its uses as a binary phase-only SLM. A series of measurements have been carried out to investigate the device's contrast ratio, modulation transfer function, polarization effect, phase uniformity, etc. As foreseen, the performance of this device is superior to the older generation LCTVs reported before.1 Since it has a large polarization angle between the ON and OFF state, this LCTV is suitable to operate as a binary phase-only SLM. To achieve binary phase-only modulation, the second analyzer is oriented perpendicular to the bisector of the two transmitted polarization states.1 In reference to the binary phase-only joint transform correlator proposed,2 we implement this correlator with a LCTV operated in the phase modulation mode. The merits of the phase-only correlator must be the increase of diffraction efficiency, decrease in dc light energy, and others as mentioned in Refs. 2 and 3.
Exploring the design space: a systematic approach to lens design
Authors: Sturlesi Doron , O'shea D. C.
Published: February 2023

This paper deals with the search for optimum solutions in optical designs. The design space of optical systems is typically a complicated multidimensional parameter space, which often has a large number of local minima. The limited successes of the conventional design method in finding the global minimum is due to the fact that the search in most optimization routines is crucially dependent on the initial configuration. This proposed search algorithm provides a set of promising initial configurations that can serve as an input to the second stage which is based on conventional optimization. First, the complete space is searched using a coarse interval for a collection of promising regions. This sampling procedure is enhanced by using parallel processing mechanisms. Specific heuristic optics rules are then applied to screen out some unfavorable configurations. Finally, after further optimization, a set of different configurations is constructed. This sampling algorithm was tested on some cases and was found to be an attractive new approach to optical design. It gives complete information on the performance limits, sensitivities, and trade-offs from a given design space. Furthermore, there is no need here to come up with any expert guesses for an initial configuration because of the systematic nature of this algorithm.
Long and thick: use of the glass path in optical design
Authors: Shafer David
Published: February 2023

The early history of the double-Gauss design is that of dramatic performance improvement due to increased thickness of the inner glass shells. Generally speaking, many designs benefit from some very thick elements, which help correct astigmatism and reduce higher-order aperture aberrations. Such thick elements may not be practical to build unless the system focal length is quite short. Scan lenses and video disk read-out heads are examples where increased length and element thickness can have big performance payoffs. Chromatic variation in aberrations can also be reduced by this approach. Somewhat surprisingly, the long glass path is not easily eliminated by simply splitting elements or adding additional new ones. This trick, in some thick elements, becomes especially powerful when combined with a long total length for the design.
Microwave L-Band pumped XeCl Laser without Preionization Techniques
Authors: Klingenberg H. H. , Gekat F.
Published: February 2023

Microwave techniques have been applied as alternative means to excite laser plasmas. However, there needs still the problem to be solved how the microwave power couples into the discharge region. An approximate calculation of the electrical field distribution in a waveguide by using the field code URMEL T will be presented. Utilizing the same code, a rectangular waveguide coupling geometry is optimized for the microwave L-band. The so determined coupling scheme has been tested using a CO2 gas mixture for laser action. Furthermore, inserting a double ridge as part of the coupling structure yields, a high enough electrical field strength over density (E/N-) value to excite high pressure gas discharges such as rare-gas halide gas mixtures. A power of 2.5 megawatt of a pulsed microwave L-band generator is used to pump such a double ridge coupling geometry with a quartz capillary as a discharge tube. A XeCl excimer gas mixture was pumped up to the laser threshold without any preionization techniques. We believe this to be the first realization of a L-band pumped excimer laser in a rectangular waveguide. The evaluation of the used coupling structure features future design considerations.
Vertical Cavity Laser Arrays with Planar Lateral Confinement
Authors: Orenstein M. , Von Lehmen A.C. , Chang-Hasnain C. , Stoffel N. , Florez L.T. , Harbison J. , Clausen E.M.
Published: February 2023

Surface emitting laser (SEL) arrays(1,2) are important for a variety of applications such as parallel optical signal processing. In this paper we report on the fabrication of vertical cavity strained layer (InGaAs/GaAs) SEL structures in which lateral laser definition is achieved using proton inplantation. Low threshold currents and good differential quantum efficiencies are obtained in both pulsed and cw operation at room temperature. For example, for 10 micron lasers, we measure ~4 ma threshold currents at approximately 4 volts, with 20% single facet differential efficiency in pulsed operation. Cw operation has been achieved with nearly the same operating characteristics. The proton implantation process which defines the laser structure is attractive for several reasons. It produces no exposed surfaces which lead to current loss. It allows for relatively efficient heat conduction compared to etched structures. The sample remains planar, facilitating integration with other devices and resulting in mechanically robust structures. Further, this process essentially allows for decoupling of optical and current confinement, providing greater control over spatial mode characteristics. Measurements on 10,20 and 40 micron diameter devices will be presented. A 1024-elenent electronically addressable array will briefly be described.
Binary-Phase Wavefronts Reconstructed from Internal-Reflection Metal on Glass Holograms
Authors: Taghizadeh M.R. , Turunen J. , Vasara A.
Published: February 2023

The problem of generating binary phase relief structures with a phase delay of π radians appears in the context of enhancing the diffraction efficiency of (conventionally binary-amplitude) image display holograms, matched filters, computer-generated holographic memories and interferograms, but it is especially severe in fabricating Fourier-domain optical interconnects. Two major types of phase error are of concern here. Incorrect absolute value of the phase delay (phase mismatch) results in excessive brightness of the undiffracted field component, which is always disturbing and implies a reduction of light efficiency into the desired wavefront. The variation of the phase delay over the hologram surface (phase non-uniformity) causes distortions in the diffracted wavefield and consequently reconstruction errors in the image. Other problems in accurate phase profile generation with conventional techniques such as ion-beam and plasma etching include the tilt of the edges of etched features and scattering from small-scale surface roughness. These factors effectively prevent the full utilization of the accuracy of the advanced lithographic patterning techniques. In this paper we investigate a novel method of generating binary-phase wavefields. Our method only requires a metal on glass binary-amplitude computer hologram with the structure corresponding to that of the desired wavefield (and, in practise, a right angle prism). Use is made of a combination of phase delays that occur in total internal reflection and in reflection from a glass-metal interface. Our initial experiments show that a significant increase in the diffraction efficiency of binary-phase grating beam splitters (by about a factor of four) is achievable.
Aperture Filling Using Phase Plates At Self-Imaging Planes
Authors: Cassarly Bill , Finlan J. Michael
Published: February 2023

Coherent arrays of lasers, especially diode lasers, are receiving increasing attention because of their ability to provide high power. However, arrays frequently require large spacings between elements, and this results in an unacceptable number of lobes in the far-field pattern. We demonstrate the use of binary phase plates at self-imaging (sub-Talbot) planes of the array to reduce the number of lobes and to increase the on-axis irradiance in the far field. The phase plates are etched in fused silica.
Theoretical and Experimental Results for Strongly Guiding Semiconductor Rib Waveguide S-Bends
Authors: Rolland C. , Mak G. , Fox K.E. , Adams D.M. , Springthorpe A.J. , Yevick D. , Hermansson B.
Published: February 2023

We have fabricated a series of S-bends in MBE-grown epilayers on (100) n+ GaAs substrates. The epilayer structure is a 1.1µm thick GaAs guiding layer above a 3.0µm Al.16Ga.84As cladding layer. The 2.3µm wide rib waveguides are reactive ion etched to a depth of 0.85µm into the guiding layer. The centers of our rib waveguide S-bends follow the equation x(z) = h{z/L − sin(27πz/L)/2π} with h = 10µm and 25µm ≤ L ≤ 400µm. The optical loss was determined experimentally to within ±0.1dB by measuring the Fabry-Perot fringe contrast of the cleaved waveguide sample with TE polarized light from a temperature tuned λ ≈ 1.3µm semiconductor diode laser.
Observation of Spatial Dark Waves and Solitons
Authors: Swartzlander G. A. , Andersen D. R. , Regan J. J. , Kaplan A. E.
Published: February 2023

In our recent research we observed a strange phenomenon whereby a beam of light passing through a rectangular grid of wires in a nonlinear defocusing medium exhibits the formation of almost identical images of the grid cell in the far-held area, instead of a linear diffraction pattern. Our ongoing research strongly suggests that this phenomenon is due to the formation of dark waves in the nonlinear medium, and even dark solitons. It appears that, unlike temporal dark solitons, spatial dark solitons can, in principle, be easily formed in a self-defocusing nonlinear medium. In particular, we observed these waves when a single wire was placed in the beam path, as well as when a grid of wires was used. These results are also consistent with our computer simulation for both the 2-D and 3-D cases. The new phenomenon may be useful in optical computing and communication systems.
Radiative Momentum Transfer to Atoms by a Phase-Conjugate Mirror
Authors: Bochove E.J. , Milonni P.W.
Published: February 2023

We demonstrate, by solution of the Heisenberg equations of motion of the pseudo-spin and momentum operators of a two-level atom interacting with a phase- conjugate mirror (PCM) and a quantized radiation field, that a force is exerted by the PCM on the ground state atom. The expression found for the force is F=gRA(P1-P2)pvn̂, where P1 and P2 are the ground and excited state occupation probabilities, A=Einstein A-coefficient, pv=photon momentum at resonance, R=PCM reflectivity, n̂=unit outward normal to the PCM, and g=an aperture factor (g=9/64 for a dipole parallel to the plane of the PCM and solid angle=Ω= 2╔) . This result has a simple physical interpretation in terms of vacuum fields that are conjugated or amplified by the PCM (1,2).
Chromatic axis effects in motion, size, and orientation processing
Authors: Cavanagh Patrick
Published: February 2023

Krauskopf and his colleagues have proposed a color space with three cardinal axes—the differences in activation in long-and medium-wavelength selective photopigments (an R-G cone axis), the activation in short-wavelength selective photopigments (a B-cone axis), and the combined activation of all three photopigments (an achromatic or R + G + B axis)—each of which is based on a linear combination of cone excitation. We have studied performance in several different visual tasks as a function of chromatic axis. Results from tilt aftereffects, size aftereffects, an opposing motion task, and a color shift task support the hypothesis of independent coding of visual information in at least three mechanisms that correspond fairly closely to the suggested cardinal axes. There is, however, a basic problem in the geometry of this color space. Specifically, although the two axes of the equiluminant plane (R-G and B) are mutually orthogonal, the achromatic axis is not, in fact, orthogonal to either of the two color axes. It is the luminance direction (the R + G direction) that is orthogonal to the equiluminant plane and the luminance direction is not an achromatic direction: R + G varies along the luminance direction but B does not and therefore hue must change. Even though these axes are not orthogonal in the color space suggested by Krauskopf, the performance in the tasks we have examined does show functional orthogonality. Tests of response linearity for each axis may point to possible color spaces that do have orthogonal axes.
Dynamics of chemical reactions and photochemical processes using high resolution VUV lasers
Authors: Lee Yuan T. , Liu D. J. , Cromwell E. , Vrakking M. J. J. , Kung A. H.
Published: February 2023

Detection of product hydrogen molecules by multiphoton ionization using a high resolution VUV laser source gives the vibration, rotation, and kinetic energy distribution of hydrogen molecules following UV photolysis of 1,4-cyclohexadiene. The results show that the process is consistent with a concerted molecule elimination mechanism and provide a qualitative understanding of the transition state involved. Details of the Doppler profile of product hydrogen indicate that the kinetic energy of hydrogen gained from the dissociation process is dominated by the potential energy barrier.
Collimation of a rubidium beam below the Doppler limit
Authors: Sheehy B. , Shang S.-Q. , Metcalf Harold J. , Hatamian S.
Published: February 2023

We have discovered a new cooling process that uses an applied magnetic field to mix differentially light shifted atomic ground state sublevels. In related experiments cooling is achieved by mixing caused by polarization gradients. Because the energy loss mechanism stems from the light shift and not the momentum transfer of a scattering event, the accessible temperature is much lower than the limit of Doppler cooling. We used this method for optical collimation of an 85Rb atomic beam to a transverse rms speed of 3 cm/s, well below the

v
=

(
7
ℏ
γ
/
20
M
)

≅
10
 
cm
/
s

of the Doppler limit for two-level atoms in this 1-D optical molasses. This low velocity, limited only by experimental geometry, is achieved only when a magnetic field of ~20 µT is applied perpendicular to the axis of the circularly polarized diode laser beam. We use a thermal beam of natural Rb produced by an oven at T ~ 150°C with an ~0.33-mm diam aperture and a defining aperture of ~0.33-mm diam about 24 cm away. The atoms are optically collimated by laser beams transverse to their motion that excite the transition at λ = 780 nm. The atomic beam profile is measured with a vertically oriented scanning hot tungsten wire, 25 µm in diameter, 1.3 m away.
Atomic beam deflection in a quantum field
Authors: Meystre Pierre , Schumacher E. , Stenholm S. , Wright E. M.
Published: February 2023

We investigate to which extent the quantum nature of light modifies laser-induced atomic beam deflection in a plane standing wave. Our model considers a single two-level atom interacting with a single quantized standing wave mode of the electromagnetic field. We neglect spontaneous emission into other field modes, an approximation valid for short enough times. We find that there is an essential qualitative difference between the cases of a coherent field and a thermal field. For a coherent field, the atomic momentum distribution after interaction has two symmetric peaks on the wings and resembles the semiclassical result of Arimondo et al. [Phys. Rev. A 24, 898 (1981)]. For a thermal field, this distribution has its maximum at p = 0. It is characterized by a constant contribution at p = 0, some sharp interference features, and near-Gaussian wings. The only feature common to both cases is that in the Raman-Nath regime of scattering, the range on transverse momenta grows linearly with time at a rate proportional to

〈
n
〉

, where

〈
n
〉

is the mean number of photons in the field.
Optical implementation of the Kittler-Young Transform for image classification
Authors: Li Xiaoyang , Yu Francis T. S. , Gregory Don A.
Published: February 2023

The Kittler-Young (K-Y) transform is a nonparametric method for feature selection, which does not require detailed assumptions about the probability structure of the problem and has obvious practical potential. The feature selection criterion for K-Y transform is the averaged mutual distance between class means. Thus, the K-Y transform maps random input images into a feature space in which the differences between class means are maximized. And the information on the class means and variances is utilized optimally. Using a joint transform correlator (JTC), the K-Y transform has been implemented optically to solve a two-class problem of image classification. Having calculated the K-Y basis images, which are real in general, the two most significant K-Y basis images are directly written onto a LCTV at the input plane of a JTC as reference images with a bias added. The outputs from the JTC, which take the form of bright spots, are the correlations between the input image to be classified and the reference images. Finally, these bright spots are detected electronically and the feature vector is taken into a microcomputer to perform a classification.