bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of noise due to passive and active spatial light modulators in optical matrix–vector multipliers
Authors: Batsell Stephen G. , Jong T. L. , Walkup John F. , Krile Thomas F.
Published: February 2023

A major source of noise in optical matrix-vector multipliers is the fluctuation of the emitted light.1 For LED and laser diode light sources, the counting distributions are Poisson. With the introduction of a spatial light modulator (SLM), however, the distribution changes. To determine the role of the SLM on the overall system noise, we measure the effect of the SLM on the noise distribution of the light, first using film (passive) and then using a magnetooptic SLM (active). We then compare the results with other noise sources in an optical matrix–vector multiplier. This comparison can be used to establish the accuracy limits of the processor.
Broadband fiber lasers
Authors: Liu K. , Digonnet M. , Fesler K. , Kim B. Y. , Shaw H. J.
Published: February 2023

Miniature broadband optical sources are of interest for fiber-optic gyroscopes to reduce coherent errors due to backscattering and polarization coupling. As an alternative to superluminescent diodes (SLDs), which suffer from a 300–400-ppm/°C wavelength sensitivity to temperature and spectrum sensitivity to feedback, two new types of 1060-nm broadband source involving an optically pumped Nd-doped fiber have been developed. The first relies on superfluorescence emission in a fiber provided with a high reflector on the pump input end. The onset of superfluorescence threshold was observed at Pabs ~ 70 mW, a pump power level which can be provided by a high power laser diode array. The second source is a resonant fiber laser which utilizes the inhomogeneous nature of the Nd3+ electronic transitions to produce a broad emission bandwidth. This fiber laser involves one high reflector bonded at each end and exhibits a much lower threshold (Pabs = 1–2 mW). With a 30-mW diode laser as a pump, a 2.5-mW output signal with a 19-nm bandwidth was observed. As expected from the thermal stability of the host, both sources exhibit a tenfold increase in spectrum stability with temperature over SLDs.
Degradation of mode discrimination in distributed feedback lasers due to spatial hole burning
Authors: Rabinovich William S. , Feldman B. J.
Published: February 2023

Distributed feedback (DFB) lasers have become of increasing interest in fields which require single longitudinal mode (SLM) sources. This SLM behavior occurs because the threshold gain for a longitudinal mode in a DFB laser increases as that mode’s frequency moves away from the Bragg frequency. We have derived coupled-mode equations for the above threshold behavior of homogeneously broadened DFB lasers, including the spatial hole burning grating induced by the laser modes. These equations were numerically integrated for boundary conditions appropriate to a variety of DFB structures. To study the mode discrimination of the DFB laser, we allow one longitudinal mode to exceed threshold and induce a spatial hole burning grating. We simultaneously solve for the threshold of a second longitudinal mode in the presence of both this field-induced grating and the externally induced grating. The ratio of the threshold of this second longitudinal mode to the average saturated line center gain available in the laser is defined as the mode discrimination. The higher the discrimination the more likely the laser is to be SLM. Our analysis shows that the mode discrimination of DFB lasers with nonsaturable index coupling, such as semi-conductor DFB lasers, is seriously degraded as the laser exceeds output powers a few times above threshold. The same does not hold true for gain coupled DFB lasers, indicating that these types of laser may be more suitable for high output power SLM applications.
Detection of phase-modulated optical signals through two-wave mixing in photorefractive materials
Authors: Boutsikaris L. , Davidson Fred
Published: February 2023

Two-wave mixing in photorefractive crystals has been shown to combine coherently a modulated optical signal beam with a strong pump optical field.’ For a phase-modulated signal beam, the induced index of refraction phase grating inside the crystal yields a coupling of the optical fields of the pump and signal so that subsequent intensity detection results in apparent intensity modulation of the transmitted signal or pump beams. This provides an easy way to detect phase differences between two optical beams. Some of the advantages the above scheme offers over commonly used coherent optical phase detection schemes are: no loss of 3 dB in the signal beam intensity at the 50/50 beam splitter (used to combine signal and local oscillator fields); automatic alignment of the index of refraction grating with the two incident optical wavefronts; insensitivity to slow random changes in the phases of both beams. Experimental results are given, and a new definition for the resulting mixing gain for the phase-modulated beam is introduced, through which optimal conditions for input beam intensity ratios can be found. Applications to coherent homodyne detection are discussed.
Highly parallel WDM network using DCG holoplanar waveguide technology
Authors: Zaleta David , Lin Freddie , Jannson Tomasz
Published: February 2023

Current multiplexer designs employ one of three different technologies: (1) dichroic interference filters (primarily for two to five channel systems); (2) diffraction gratings; or (3) interferometric techniques. While interferometric techniques provide an extremely narrow passband bandwidth (gigahertz), they are extremely sensitive to extraneous environmental conditions. Most grating-type multiplexer designs also suffer performance degradation due to shock or vibration. Therefore, they are unacceptable in a rugged industrial/military operating environment.
Einstein-Podolsky-Rosen and Bell’s inequality experiments using energy and time
Authors: Davis Lloyd M.
Published: February 2023

By considering a multimode treatment of the parametric downconversion of light,1 in which the incident pump also consists of a bandwidth-limited pulse, it is possible to devise experiments in which the energy (frequency) and time occurrence of the parametric photons serve as the conjugate dynamical variables of an Einstein-Podolsky-Rosen (E-P-R) or Bell's inequality experiment. The physical connection between E-P-R and Bell’s inequality and the design of Bell’s inequality experiments with dynamical variables which have continuous spectra are reviewed along with several experiments performed to date. The realizability of experiments using frequency and time is discussed with reference to fundamental measurement resolution limitations,2 as well as presently achievable experimental capabilities. This lends deeper understanding to the nature of the paradoxes and the status of these variables within quantum theory.
Violations of Bell’s Inequality in an eight-port receiver
Authors: Oliver Brian J. , Stroud C. R.
Published: February 2023

It is shown that a system of correlated electromagnetic field modes in an eight-port balanced homodyne detector is useful for testing Bell's inequality. This system is different from all previously considered tests of Einstein locality that use photons1-3 in that the correlated field modes present in the eight-port are all of the same polarization, and no polarizing filters are used. The variables that replace the angular orientation of the polarizing filters in the other systems are the optical path lengths between the beam splitters in the eight-port. A variety of different states of the free electromagnetic field may be tested for violations of locality using this system. It is shown that combinations of a number state and any other free- field state as inputs to the eight-port can demonstrate violations of the inequality, thus indicating the failure of locality for a specific set of input states.
High energy subpicosecond pulse generation at 1 kHz
Authors: Weston J. , Heritier J. M. , Ettelbrick R. N. , Aubuchon D. , Aubert R.
Published: February 2023

We report development of a high repetition rate flashlamp-pumped Nd:YAG regenerative amplifier used to pump an ultrashort pulse dye amplifier. The novel feature of the regenerative amplifier is that the flashlamps are pulsed at repetition rates of up to 1080 Hz. When seeded by a few nanojoules 60-ps pulse from a cw mode-locked laser, output energies of over 2 mJ are obtained from the regenerative amplifier. Further amplification in two single-pass flashlamp-pumped amplifiers increases the pulse energy to over 25 mJ. This is to be compared to cw-pumped schemes where output energies are restricted to 1 mJ or less1 resulting in amplified ultrashort pulse energies of only several microjoules.
Increased quantum linewidth of lasers with nonorthogonal eigenmodes
Authors: Mussche Paul L. , Doumont J.-L. , Siegman A. E.
Published: February 2023

It is well known that open-sided laser resonators have nonorthogonal transverse eigenmodes, where these eigenmodes are defined as the Fox-Li modes of the resonator, i.e., the modes that reproduce themselves after one round trip in the resonator. We outline a class of resonator having nonorthogonal eigenmodes and then study in more detail the cases of unstable resonator lasers with variable reflectivity output mirrors or hard-edged output mirrors. We show analytically and numerically that lasers built with such resonators should exhibit very large excess noise factors for large magnification or large Fresnel number.
Direct overwrite in magnetooptic data recording
Authors: Watson M. , Savage C. M. , Meystre P.
Published: February 2023

There exists considerable interest in the development of erasable optical data storage devices. Potential candidates include dye/polymer and phase-change, as well as magnetooptic, media. Direct overwrite schemes are crucial to the attainment of high data rates. This paper compares the physios of several direct overwrite schemes in magnetooptic (MO) media. We have developed a numerical model that evaluates the time dependence of the temperature profile in a moving MO subjected to heating by a laser diode. This profile indicates the net pressure acting on a domain wall attributable to the wall energy and the demagnetizing field in a way similar to magnetic bubble modeling. Noncylindrical symmetry of the domains as well as multiple MO layers can be considered. Our model is sufficiently general to investigate different overwrite proposals, such as the bilayer scheme,1 domain nucleation and annihilation,2 domain destabilization,3 magnetic-field modulation,4 and resonant bias coil.5
Component pattern recognition or unknown multispread fluorescent images
Authors: Kawata S. , Minami S. , Sasaki M.
Published: February 2023

In conventional pattern recognition studies, individual components are classified by their spatial features, such as shape, size, spatial statistics, and spatial frequencies. For the cases in which the components could not be classified by the spatial features because of their mutual dependence, we have developed a distinct method based on the optimization theory, using the image data of a scene sensed at a number of different wavelengths (colors).1,2 In this paper, we present a novel idea of unknown-component reconstruction from unknown mixture scenes. The sample is excited (illuminated) at two different wavelengths separately, and the fluorescent images are sensed at different wavelengths. If the absorption spectra of components (which are equivalent to excitation spectra) are independent of each other, the component patterns can be uniquely found, because we have doubled the equations for fluorescent-emission spectra and spatial patterns of components, by two-wavelength excitation.
Injection locking of diode-pumped monolithic lasers
Authors: Cheng Emily A. P.
Published: February 2023

A method of coherently summing the outputs of two diode-pumped ring lasers has been tested. The output of one such Nd:YAG laser (the master laser) at 1064 nm was mode-matched into a similar laser (the slave laser). The frequency of the slave laser was tuned toward that of the master laser by adjusting the crystal temperature (and thus the optical path length). The difference frequency was detected until the locking range was reached, when the free-running oscillation of the slave laser was completely injection-locked by the injected signal. With the master laser power of 15 mW and the slave laser power of 5 mW, the locking frequency occurred at ~23 MHz. The combined output power during locking ranged from ~20 to 21 mW with the maximum representing a 5% increase over the summation of the unlocked free-running lasers. Locking was held for periods >15 min. These results indicate the possibility of chaining together this type of laser to obtain coherent single-mode outputs with higher powers than currently possible.
Lorentz-group Berry phases in squeezed light
Authors: Chiao Raymond Y. , Kwiat Paul G. , Vareka William A. , Jordan Thomas F.
Published: February 2023

The Berry phases most often observed in experiments are produced by rotations. Berry phases produced by Lorentz transformations are almost as simple mathematically. They have been discussed at length, but there has been no suggestion of observing them in an experiment. Indeed, it has been shown that in one context they can be removed by a canonical transformation; thus they appear to be a property of the mathematical description that could not be observed physically. Here we show that the essential element of these Berry phases could be observed as a change of phase of the electromagnetic field in squeezed states of light or microwaves, as could be produced by degenerate parametric amplifiers. It could be seen as a fringe shift in interference experiments. In this way, a physical effect of the squeezing could be measured without measuring anything like photon statistics or noise.
Photorefractive properties of doped KTa1−xNbO3 crystals in the cubic phase
Authors: Leyva Victor , Agranat A. , Yariv Amnon
Published: February 2023

We describe results of measurements of the diffraction efficiency of KTa1−
x
Nb
x
O3:Cu,V in the cubic phase using the quadratic electrooptic effect. Diffraction efficiencies of over 50% in a 3mm thick sample were measured. In addition, by making use of the quadratic electrooptic effect, it is possible to couple the amplitude of the index grating directly to an applied electric field, thus enabling amplitude modulation and switching of the diffracted beam. Control of the photorefractive gain by an external electric field was demonstrated at modulation rates up to 30 kHz.
Approximate solution to nonlinear pulse propagation in optical fibers
Authors: Bélanger Pierre-Andre , Morin F. , Mathieu P.
Published: February 2023

Soliton pulse propagation in optical fibers is now currently exploited. Since the original proposal by Hasegawa and Tappert1 of using solitons in optical communication, many other applications have been proposed including the control of a laser by a soliton formed in an optical fiber.2 Generally, in applications, the initial pulse parameters are not exactly equal to those required to generate pure soliton solutions. In such a case, the nonlinear Schrodinger equation must be solved numerically. However, to extract the salient features of the solution, it is of interest to search for a simple approximate solution. Such a solution is presented here. It consists in a hyperbolic secant with a variable width and linearly chirped phase. In a first-order approximation, the nonlinear Schrodinger equation is reduced to a nonlinear differential equation for the width, which can be integrated easily. This also yields simple relations for the linear chirp coefficient and peak amplitude. These results are then compared with the numerical solutions obtained by the beam propagation method. A good agreement is observed for the amplitude and phase factor up to energy of the order of the energy of an N = 2 soliton solution. The results obtained here by the approximate solution are also similar to those obtained by Anderson3 using a variational approach based on Gaussian trial functions. Our simple model could be useful for some application (for example, modeling the soliton laser), and it provides a better understanding of the interplay between dispersion and nonlinear effects.
Accommodation in chicks: off-axis refraction and mechanical model
Authors: Schaeffel Frank , Romano Virginia , Yau Tom , Howland Howard C.
Published: February 2023

We measured the mechanical properties of excised chicken eyes to test the possibility of a role of the intraocular pressure for corneal accommodation. It was found that the full range of corneal accommodation (~8 diopters) can be produced by small changes (~4 Torr) in intraocular pressure. We measured the speed of natural accommodation in the intact chick and found it to be ~10 times faster than human accommodation (50-80 diopters/s vs 4-6 diopters/s). A calculation of the aqueous outflow necessary to produce such a fast response in corneal accommodation showed that a model based solely on pressure changes is insufficient. Furthermore, we examined the off-axis refractive state in normal chicks both at rest and during accommodation. It was found that the refractive state is constant across the horizontal meridian but is more myopic in the lower visual field in most but not all individuals. During accommodation, the relative difference in refractive state is preserved in the different sectors of the visual field: accommodation is radially symmetrical.
Resolution of blue cones as a function of eccentricity In man
Authors: Uusvaara Juho , Rovamo Jyrki
Published: February 2023

In the central retina grating resolution is proportional to cone density, whereas in the peripheral retina resolution is proportional to the sampling density of ganglion cells.1 For red and green cones, density is maximal at 0 deg of eccentricity but for blue cones at 1 deg of eccentricity.2 When the red and green cones are strongly light-adapted by bright long-wavelength light, the perception of dim short-wavelength stimuli remains mediated by blue cones only. Sine wave gratings with 90% contrast were generated on a white (P4) CRT screen. The screen was covered with a blue filter (Lee 141, transmitting wavelengths shorter than 575 nm) and metal cloth (open surface 25%) woven of thin (0.0025-mm) steel wires. The light from two slide projectors was projected through yellow filters (Wratten 16, transmitting wavelengths longer than 555 nm) onto the metal cloth. The average luminance of the blue grating field was 2.3 phot. cd/m2, and the average luminance of the yellow adapting field was 750 phot, cd/m2 corresponding to 610 scot. cd/m2. Blue-cone resolution was found to have its maximum of 5 cycles/deg at 1 deg of eccentricity. At eccentricities of 1-20 deg, blue-cone acuity was directly proportional (1:5) to the acuity measured without the yellow adapting field.
Considerations of Gabor functional descriptions of visual receptive fields
Authors: Stork David G. , Wilson Hugh R.
Published: February 2023

We consider key assumptions and data underlying the Gabor function (GF): Gaussian-modulated cosine descriptions of cortical simple cell receptive fields (RFs). We show that the implied metric of spatial and spatial-frequency localization has not been justified by others. In fact, alternate metrics yield plausible receptive fields. We review the interdependence of such metric considerations with information theoretical explanations of the RF function. We review comparisons of fits to neurophysiological and psychophysical data which show that other RF functions are superior to GFs.
Interaction between longitudinal and lateral chromatic aberrations
Authors: Zhang Xiao Xiao , Bradley Arthur , Thibos Larry
Published: February 2023

Human eyes exhibit both longitudinal and lateral chromatic aberration. Achromatizing lenses have been designed to correct longitudinal chromatic aberration. However, these lenses are not designed to correct for the lateral chromatic aberration of the eye. Based on optical models of human eyes and two different achromatizing lenses,1,2 we have evaluated the relative effects on retinal image quality of longitudinal and lateral chromatic aberrations separately and in combination. The eye’s 2 diopters of longitudinal chromatic aberration may seem large, but with a 5-mm pupil its effect in the retinal image quality for a white p4 phosphor is comparable with that for a monochromatic source with only 0.1-0.2 diopters of blur. Although correction of longitudinal chromatic aberration improves paraxial image quality, it can degrade off-axis image quality. This is because longitudinal chromatic aberration can protect the eye from the contrast degradation effect of lateral chromatic aberration. Also, special care is required when using achromatizing lenses to prevent the introduction of more lateral chromatic aberration in the retinal image than is normally present in the unaided eye.
Variations of horizontal phoria at near during recovery from general anesthesia
Authors: Letourneau J. E. , Denis R.
Published: February 2023

The purpose of the study was to evaluate recovery from general anesthesia in a day-care surgery unit. A group of forty-three patients underwent surgery under general anesthesia with enflurane (N = 14), isoflurane (N = 10), or halothane (N = 19). Anesthesia lasted 20-95 min (average, 45.3 min). Heterophoria was measured with the Maddox Wing; results are expressed in prism diopters. Patients were measured before anesthesia (condition 1) 1.5, 2.5, and 3.5 h after the end of anesthesia (conditions 2, 3, and 4).
Influence of tissue elasticity on the damage zone in laser surgery
Authors: Frenz M. , Zweig A. D. , Romano V. , Weber H. P.
Published: February 2023

IR lasers (2.94 and 10.6 μm) are excellent sources for precise cutting with minimal thermal damage in microlaser surgery due to their strong absorption in water. We explain laser cutting of tissue and its substitute gelatin and agar by a combined action of evaporation, ejection of liquid, and elastic deformation of the region of laser impact. Using high-speed photography we studied this deformation caused by the pressure induced by the recoil of evaporated target material. We found a correlation between temporally well-separated spikes of a 250-μs long ER laser pulse and the diameter of the crater which varies along the crater axis so that zones of big and small diameters alternate. When drilling with the smoothly shaped CO2 pulse no diameter variation was detected. A more dramatic dynamic deformation was measured by drilling holes in a target containing several layers of different elasticity. The diameter of the hole within the most elastic layer is up to four times larger than the focal spot diameter of 260 μm. This result is in good agreement with the more extended damage zone of the highly elastic muscle cells compared with the surrounding rigid connective tissue that we obtain by cutting mouse skin with a laser.
Fiber-optic sensor based on surface plasmon wave resonant coupling
Authors: Moslehi Behzad , Ng Joel
Published: February 2023

Surface plasmon waves (SPWs) have recently been employed in applications such as thickness and refractive-index measurement of dielectric and metallic coatings1 and prism-based sensing.2 We introduce all-fiber sensing devices based on resonant coupling interaction between fiber guided modes and SPWs generated in a metal-dielectric interface. The configuration involves a short fiber section (sensing region) where part of the cladding is removed and replaced with thin layers of proper phase-matching dielectric buffer and surface-active metallic materials covered with a suitable superstrate sensing layer. The phase matching buffer layer is used to bias properly the sensor. The TM-polarized guided wave in the fiber can excite the SPW by resonant coupling, which is extremely sensitive to refractive-index change of the sensing layer, while the TE polarization propagates unchanged. Using the TE polarization as the reference, the sensed information impressed on the TM polarization can be recovered accurately at the fiber output. In addition to being stable and simple, this sensor configuration has the potential to sense index change as small as 10−5. Detailed results are presented.
Ringing revivals In the Interaction of a two-level atom with squeezed light
Authors: satyanarayana M. Venkata , Vyas Reeta , Carmichael Howard J. , Rice Perry R.
Published: February 2023

When the displacement and squeeze parameters for a squeezed coherent state are chosen appropriately, the squeezed state has an oscillatory photon number distribution P(n). Schleich and Wheeler1 have shown that the oscillations arise from the interference between contributions to P(n) from two regions in phase space where an elongated error ellipse, characterizing the squeezed coherent state, overlaps the annuli characterizing the number states. We study the Jaynes-Cummings model for the interaction of a two-level atom with a single mode of the radiation field when the radiation field is initially in such a squeezed coherent state. Revivals of the atomic inversion occur which have a quite different appearance from those produced when the radiation field is initially In a coherent state.2 Each revival is followed by a series of echoes—a phenomenon we call ringing revivals. We discuss the relationship between these echoes and the oscillations in P(n). There is a one-to-one correspondence between echoes and the peaks in P(n); however, interference between the contributions to the inversion from different peaks in P(n) plays an important role in forming the ringing structure of the revivals.
Compact free-space optical programmable logic array
Authors: Li Yao , Kostrzewski Andrew , Kim Dai Hyun , Eichmann George
Published: February 2023

To implement a parallel optical digital computer, in addition to the two variables, multiple variable optical logic gates are needed. One way to implement a generalized multiple variable optical logic device is to use an optical programmable logic array. We propose a new method to realize a medium scale, compact, and free-space optical programmable logic array. Using either a 2-D or an array of 1-D optical spatial light modulators inside a lens-based multiple-beam path cavity, an array of optical multiple variable logic product (AND gate) term is generated. This device, together with a programmable multiple variable logic OR matrix, can be used to implement any Boolean combinatorial logic operations. For an optical binary combinatorial logic computation, the proposed methods efficiently use 3-D space and optical elements. Preliminary experimental results obtained using an inexpensive liquid-crystal TV are included.
Phase distortion compensation in a joint Fourier transform correlator by phase conjugation
Authors: Yu Francis T. S. , Wu Shudong , Mayers Andrew
Published: February 2023

In a coherent image processing system, the input object must be free from phase distortion. Unfortunately, most real-time spatial light modulators (SLMs) suffer from phase distortions. Liquid gates can be used to compensate for external distortion but do not remove internal nonuniformities in the devices. Holographic elements can correct phase distortion but require critical alignment. We investigate the use of a phase conjugate wave compensating technique to correct for phase distortions in a joint Fourier transform correlator. Because the object beam passes through the objects twice, the contrast of the objects is increased. In the experimental setup, a BSO crystal was utilized as the phase conjugating mirror. The experimental result verified that the phase conjugating technique can compensate for the phase distortion in a joint transform correlator.
Optical correlation with a deformable mirror device in the matched filter plane
Authors: Hudson Tracy D. , Trivett David W.
Published: February 2023

The VanderLugt optical correlator has been widely used for pattern recognition purposes in research laboratories since the early 1960s. However, this correlator has not been extensively used in real-world applications because the photographic process required to produce a holographic matched filter limits real-time applications. Furthermore, multiple exposures are necessary for the recognition of an image which has a different orientation or scale from the original input image used to produce the matched filter. Sequentially stepping through a bank of matched filters for the identification of an image at various orientations and scales has been proposed but is difficult to implement optically.
Demonstration of soliton transmission over more than 4000 km in fiber with loss compensated by Raman gain
Authors: Mollenauer L. F. , Smith K.
Published: February 2023

By recirculating soliton pulses many times around a closed 42-km fiber loop with loss exactly compensated by Raman gain, we have successfully demonstrated transmission without electronic regeneration over distances in excess of 4000 km.1 The loop is closed on itself with an all-fiber version of a Mach-Zehnder interferometer so that pump light at 1500 nm (~300 mW from a cw color center laser, power precisely controlled by feedback) is efficiently coupled into the loop, while at the same time ~95% of the signal light (a train of 55-ps pulses from a mode-locked color center laser operating at 1600 nm) continues to recirculate around the loop. The trip is terminated when the pump is turned off. A sample of the signal train leaving the loop is detected by an ultrafast diode (response time, 9 ps), whose output is sent to a microwave spectrum analyzer. We then infer the pulse shape in time from the measured pulse envelope spectrum. Up to ~4000 km, we see almost no change in effective pulse width. At ~4800 km,

τ

eff

=
\

2

τ
0

¯

, but this apparent broadening is due to jitter in pulse arrival times. We have also been able to study interaction between closely spaced soliton pairs over thousands of kilometers. Our experiments have strong and positive implications for the development of an all-optical long-distance transmission system.
Three-dimensional diffraction tomography using circular-grating interferometry
Authors: Shentu Lian , Leith Emmett N.
Published: February 2023

We previously described a 2-D diffraction tomography process using a grating interferometer with incoherent illumination.1 We extend this to the third dimension by using an incoherently illuminated grating interferometer formed by a pair of circular gratings.
FOCI: a generalization of intensity interferometry
Authors: Ebstein Steven M. , Korff David
Published: February 2023

A generalization of intensity interferometry and imaging laser correlography (Hanbury Brown-Twiss effect) is described. The technique measures 〈l(x)A*(x + Δ + ϵ)A(x + Δ)〉, the correlation of the intensity at x with the field cross product at x + Δ over a distance ϵ. The result yields a term, μ*(Δ + ϵ)μ(Δ), analogous to the cross spectrum measured with the Knox-Thompson method for astronomical speckle imaging. The modulus and phase of the spatial coherence function can be recovered from this phase-difference-type term. The measurements involved do not require co-phasing over the large distance Δ. A light bucket measures l(x), and an interferometer with aperture ϵ (a lens is sufficient) measures A*(x + Δ + ϵ)A(x +Δ). The two measurements are numerically correlated. The results of a demonstration experiment that shows that the technique recovers modulus and phase information are presented.
Genetics of Rayleigh matches and photometric matches in normals
Authors: Lutze Margaret , Cox Nancy J. , Smith Vivianne C. , Pokorny Joel
Published: February 2023

At the 1988 ARVO meeting we presented Rayleigh match midpoint and photometric match data collected from a population of nonrelated males and from family members. Photometric matches between a 667- and 551-nm stimulus were obtained using heterochromatic modulation photometry (HMP). We employed statistical methods to determine whether the source of variation for each of these traits was due to allelic variation at a single gene locus, variation at multiple loci (polygenic), or environmental factors. Results indicated that variations in Rayleigh match midpoints and HMP photometric matches in observers with normal color vision were each consistent with allelic variation at a single gene locus.
Phasic ganglion cells show additivity and transitivity in flicker photometry
Authors: Lee B. B. , Martin P. R. , Valberg A.
Published: February 2023

The retina of the primate contains two main classes of ganglion cells: tonic wavelength-opponent cells and the phasic nonopponent cells. When tested with flicker photometry, phasic cell activity goes through minima at intensities close to those set by human observers. Spectral sensitivity so determined approximates the V function. The activity of tonic cells shows a complex pattern and does not go through a minimum at any flicker frequency. Further properties of flicker photometry are applicability of laws of linearity and independence of flicker frequency. We tested ganglion cells of the macaque with such paradigms. Response minima of phasic cells showed both transitivity and additivity. For transitivity, if intensities of wavelengths A and B were adjusted to give minimum response, and also of A and C, then B and C when alternated also provided a minimum. For additivity, alternation of A with 1/2B + 1/2C provided a minimal response. Response minima of phasic cells were also temporal frequency independent. Responses of tonic cells with such paradigms were complex and not to be related to flicker photometric performance. We conclude that phasic ganglion cells are responsible for human performance on this task.
A Stochastic Optoelectronic Learning Machine
Authors: Farhat Nabil H. , Shae Zon Yin
Published: February 2023

We report on what we believe to be the first demonstration of a fully operational optical learning machine. Learning in this machine is stochastic taking place in a self-organizing tri-layered opto-electronic neural net with plastic connectivity weights that are formed in a programmable nonvolatile spatial light modulator. The net, which can also be called a Boltzmann Learning Machine, learns by adapting its connectivity weights in accordance to environmental inputs. Learning is driven by error signals derived from statevector correlation matrices accumulated at the end of fast annealing bursts that are induced by controlled optical injection of noise into the network. Operation of the machine is made possible by two important developments in our work: Fast annealing by optically induced noisy thresholding, and stochastic learning with binary weights. Preliminary results obtained with a 24 neuron prototype show that the machine can learn, with a learning score of about 60%, to associate three 8-bit vector pairs in 10-60 minutes with relatively slow (60 msec response time) neurons and that, shifting to neurons with 1 μsec response time for example, could reduce the learning time by roughly 104 times. Methods for improving the learning score are presently under investigation and initial results are encouraging. They indicate that reducing the number of vectors to be learned by the prototype from three to two and use of on-on correlations alone in computing the coincidence probabilities and corresponding error signals controlling synaptic weight modification and adjusting the number of hidden neurons can increase the learning score to 95%. A short video of the machine in operation as it learns will be shown. We close by describing methods for constructing large-scale photonic learning machines of 103-105 neurons that utilize the concepts developed and speculate on potential applications.
Optoelectronic Generation of 350 Femtosecond Electrical Pulses
Authors: Krökel D. , Grischkowsky D. , Ketchen M. B.
Published: February 2023

We report observations of a new optoelectronic mechanism to generate 180 mV, 350 fsec electrical pulses. For this mechanism to operate the laser excitation beam should be focused to a spot smaller than the separation between the two lines of a charged coplanar transmission line fabricated on an unimplanted silicon-on-sapphire (SOS) substrate, and should be positioned between the two lines partially illuminating the back side of the positive line. When these conditions were satisfied, we always observed a strong short pulse followed by a much weaker step function. For positive bias the signal strength was proportional to the bias voltage across the line. However, when the voltage polarity was changed the initial short pulse changed sign and was reduced in amplitude by 10 times. Increasing the focal spot size to completely fill the space between the two lines caused the short pulse to disappear and the expected step function for unimplanted material was obtained.
Efficient Second-Harmonic Generation at 432 nm by Passive Optical Locking of a GaAlAs Laser Diode to a Nonlinear Power Buildup Cavity
Authors: Dixon G.J. , Tanner Carol E. , Wieman Carl E.
Published: February 2023

A substantial improvement in the harmonic conversion efficiency of low power sources is made possible by resonating the fundamental in an external high-finesse cavity containing the nonlinear medium1,2. External resonant harmonic generation with laser diodes is somewhat simpler than with conventional sources since optical feedback from an external cavity can be used to lock the laser diode on resonance and spectrally narrow its emission3. Significant intracavity power buildup has previously been demonstrated in the Self-locking power Buildup Cavity (SBC)4.
Picosecond Shock-wave Generation on a Hyperabrupt-diode GaAs Nonlinear Transmission Line
Authors: Madden C.J. , Marsland R.A. , Rodwell M.J.W. , Bloom D.M. , Pao Y. C.
Published: February 2023

Circuits for generating picosecond transition time electrical signals have many applications in wide bandwidth instrumentation and communication systems. The fastest signals have often been generated optically, but nonlinear wave propagation has made an all electronic system just as fast. We have measured a 6 Volt, 1.6 ps falltime shock-wave signal generated on a GaAs Nonlinear Transmission Line (NLTL) having Schottky diodes with a hyperabrupt doping profile.
Generation of 100 fs, 20 Gw Pulses in Alexandrite using Chirped Pulse Amplification
Authors: Pessot Maurice , Mourou Gerard
Published: February 2023

Chirped pulse amplification has led to the development of high brightness sources with peak powers in the terawatt range [1]. Recently, we reported on the generation of 300 fs pulses at the millijoule level in an alexandrite regenerative amplifier [2]. In this paper we present new results extending the CPA technique to the generation of 100 fs pulses with peak powers of 20 Gw.
Low-voltage high-speed 4×4 optical switch
Authors: Pedersen Paul R. , Nightingale J. L. , Kincaid B. E. , Vrhel J. S. , Becker R. A.
Published: February 2023

We report on a fully electrically packaged and fiber pigtailed 4×4 crossbar optical switch operating at 1530 nm. The switching matrix uses balanced bridge-type optical switching elements.1 The balanced bridge optical switch is similar in design to the commonly used Mach-Zehnder intensity modulator with the Y splitters replaced by 3-dB directional couplers. The switch is fabricated on x-cut y-propagating lithium niobate using Ti-indiffused waveguides fabricated by conventional liftoff lithography. The total switch length is 70 mm with 7-mm unit switching elements and input/output waveguide separations of 250 μm. The switching voltage of 13 V and the average extinction ratio of 20 dB are comparable to values recently reported for other 4×4 switches,2,3 while a bandwidth exceeding 1 GHz makes this the fastest switching matrix yet reported. Details of the measured channel-to-channel crosstalk and electrical layout are discussed.
Electrooptic cutoff modulator using diffused channel waveguide bends
Authors: Koai Kwang T. , Su Shing-Fong
Published: February 2023

Electrooptic intensity modulators are important components for fiber-optic communication and high-speed signal processing. The on/off extinction ratio, drive voltage, and insertion loss are important parameters that determine the performance of the modulators. Recently, an electrooptic cutoff modulator using a Ti-indiffused LiNbO3 channel waveguide with asymmetric strip electrodes was demonstrated with an extinction ratio of >56 dB.1 When a voltage is applied, the asymmetric configuration prevents most of the radiated light from being transferred back to the guide, thus greatly improving the on/off extinction ratio. The drive voltage of such a device, however, is quite high since the gap between the electrodes is considerably wider than the channel width. We propose an electrooptic cutoff modulator using low-loss-diffused channel waveguide bends. The proposed device shows an asymmetric effective index profile by which electrooptic modulation can be enhanced. Analysis based on the beam propagation method has shown that this device has a high extinction ratio with a low drive voltage. Design considerations are presented.
Optical novelty filtering using photorefractive fanout
Authors: Ford Joseph E. , Fainman Y. , Lee Sing H.
Published: February 2023

We demonstrate a single-beam interferometer which effectively subtracts an exponentially weighted history of the input from the current value, thus functioning as a novelty filter. The filter uses signal depletion by photorefractive amplification of noise (fanout). Input which is stationary for longer than the photorefractive response time is strongly depleted, but any portions of the Input which change their phase, amplitude, wavelength, or polarization are immediately transmitted.
Bistable resonator utilizing saturable photorefractive gain and loss
Authors: Lininger Diana M. , Martin Peter J. , Anderson Dana Z.
Published: February 2023

We report the observation of bistability in a unidirectional ring resonator that employs photorefractive barium titanate for gain and also for saturated loss. One photorefractive crystal provides gain via two-beam coupling in a conventional unidirectional ring configuration.1 A second crystal is arranged to couple light out of the resonator using two-beam coupling, thereby producing loss. The orientations of the two crystals are chosen so that the magnitude of the small signal loss is greater than the magnitude of the small signal gain. Thus the oscillation in the ring cannot build up from noise since there is no net gain. However, the pump intensity for the gain medium is made larger than that for the loss medium. This means that the loss saturates at a lower signal level. Hence, at large intensities, gain can exceed net loss so oscillation can occur.
Microwatt picosecond pulse autocorrelator using photorefractive GaAs:Cr
Authors: Johnson A. M. , Glass A. M. , Simpson W. M. , Bylsma R. B. , Olson D. H.
Published: February 2023

Recently, the 1.06-μm photorefractive response of semi-insulating GaAs and InP has been measured.1,2 Preliminary experiments have now been performed using the photorefractive effect in GaAs:Cr as a sensitive nonlinearity for simple low-power picosecond pulse diagnostics at IR wavelengths. In these beam coupling or two-wave mixing2 experiments, a photorefractive index grating is formed by the interference of two 4-ps duration 1.06-μm beams in a 1,5-mm thick GaAs:Cr crystal. The optical pulses were obtained from a fiber-grating compressed cw mode-locked Nd:YAG laser. The temporal profile of these pulses was obtained by detecting the fraction of chopped pump beam scattered by the index grating into the probe beam as a function of delay between the two beams, using an InGaAs PIN photodiode and lock-in amplifier. The measured temporal profile was identical to that obtained by standard noncollinear background-free correlation using second harmonic generation in a 1-mm LilO3 crystal and photomultiplier tube (PMT). With only 2 μW of average power per beam, photorefractive autocorrelation measurements were made with SNRs greater than 5:1 in this nonoptimized experiment. The beam coupling efficiency can be improved by several orders of magnitude by using a longer crystal, antireflection coatings, and an applied electric field. Beam coupling in GaAstCr is linear in intensity and photosensitive beyond 1.6-μm,1 while the harmonic process is quadratic in intensity and the quantum efficiency of typical PMTs is poor at 0.8-μm and beyond. Therefore, photorefractive auto-correlation may prove to be very attractive for real-time measurement of the temporal diagnostics of low-power long-wavelength mode-locked semiconductor lasers.
Ion beam interference coatings: principles, status, and outlook
Authors: Wei David T. , Kaufman Harold R.
Published: February 2023

The ion beam interference coatings1 (IBICs) made with a Kaufman gun2 have produced ultralow optical loss (R > 99.995%) mirrors due to its unique ability to reduce scattering and absorption to very low ppm levels. A main obstacle in the development is the trade-off in the coating speed with the stoichiometry of the coating deposition. Improvement can be sought in two directions: (a) The ion beam current and the accelerator voltage play central roles for the coating speed and the throughput, but the development time is longer and depends on the demand of the coating market, (b) Fine control of the gradient of oxygen partial pressure from the deposition to the target can substantially improve the coating speed without sacrificing stoichiometry. This development is relatively short. It is believed that the speed and throughput of IBICs are comparable with that of the e-beam in the 1990s, while the superior coating quality prevails.
Superconducting Y1Ba2Cu3O7–x thin films on Si and GaAs without postannealing
Authors: Witanachchi S. , Kwok H. S. , Shaw D. T.
Published: February 2023

There is a tremendous interest in high T
c
superconducting thin films of Y1Ba2Cu3O7–
x
for device applications. However, most of the superconducting film fabrication techniques reported so far consist of a postannealing step in oxygen at temperatures around 850°C.1 Degradation of the film surface and enhanced interfacial diffusion are major drawbacks in these techniques. We have developed a plasma-assisted laser evaporation technique that enables us to produce as-deposited superconducting Y1Ba2Cu3O7–
x
thin films at processing temperatures lower than 450°C. A composit target of Y1Ba2Cu3O7–
x
is evaporated by an excimer laser in the presence of an oxygen plasma. Plasma at 1-m Torr oxygen backpressure is triggered and sustained by the laser. Superconducting films of 0.5-μm thickness deposited on SrTiO3 (110) showed a zero resistance at 85 K. Critical currents by transport method at 80 K was ~105 A/cm2.2 On Si and GaAs, ultrathin MgO layers were deposited, using the same technique, prior to the deposition of Y1Ba2Cu3O7–
x
. This layer helps to reduce the diffusion as well as to form the superconducting orthorhombic structure. Auger sputter depth profiles of these films reveal the sharp interfaces with very low diffusion.
Characterization studies of the Los Alamos Fourier transform spectrometer
Authors: Palmer Byron A. , Hof Douglas E.
Published: February 2023

We have conducted characterization studies of the Los Alamos Fourier transform spectrometer to determine its resolution, spectral range, and noise characteristics. These studies show that we have achieved the theoretical resolution limit of 0.0026 cm−1 with a spectral coverage of >14 μm to <210 nm. The precision of the servo system for mirror movement is <1/1000 of a fringe (632.8 nm). Wavelength and intensity accuracy are discussed as well as the SNR for the various experiments.