bluuebunny/crossref_metadata_2025 huggingface dataset:
Focus anisoplanatism for a multiple spot guide star pattern
Authors: Fried David L. , Vaughn Jeffrey L.
Published: February 2023

A seemingly obvious way to circumvent the focus anisoplanatism d0-limitation on a useful aperture diameter that goes with use of a (single) guide star spot is to use a multiplicity of relatively closely spaced spots, using the wavefront distortion data from each only for the portion of the aperture directly below that spot, and to stitch these patches of data together to form a wavefront distortion estimate that covers the full aperture. We present results for the mean-squares wavefront error, E2, that go with guide star spot patterns of (1) a dense array of spots at a single altitude, (2) dense arrays of spots at two altitudes, and (3) an equilateral triangle pattern of three spots at a single altitude. In all cases we find that we can write E2 = (D/d0)5/3. Expressions have been developed for d0 for all cases. A key feature in the development of these results is the incorporation of the effect of our not being able to determine exactly where each of the guide star spots really is.
Optical interconnection using cascaded vertical to surface transmission electrophotonic devices
Authors: Yamanaka Y. , Yoshihara K. , Ogura I. , Numai T. , Kasahara K. , Ono Y.
Published: February 2023

The vertical to surface transmission electrophotonic (VSTEP) device, which consists, for example, of pnpn structure,1 has multiple functions such as light emission, light absorption, thresholding, and latching. This multifunctional feature makes it easy to construct a cascaded interconnection, compared with the use of a spatial light modulator, because sources and optics for readout are not necessary. To achieve a stable operation, differential VSTEP devices, which consist of two VSTEPs connected in parallel through a common load resistance, are used. Cascaded interconnection characteristics were measured by using a surface-emitting laser mode VSTEP with vertical cavity.2 A 150-fJ and a 1.7-pJ switching energy have been achieved at 1- and 10-MHz clock frequency, respectively.3 The drive clock signal frequency is >10 MHz, which includes reset, precharge (light absorption), and set times. This frequency may be improved by optimizing the device structure.
Quantum-limited image detection
Authors: Sequeira Raul E. , Gubner John A. , Saleh Bahaa E. A.
Published: February 2023

Image detection in low-light-level conditions is treated as a hypothesis-testing problem based on a finite set of samples, Z1,...,Z
K
, from a filtered 2-D Poisson process. Since it is not feasible to compute the joint probability distribution of Z1,...,Z
K
, a straightforward likelihood-ratio test is not a possibility.
Neural network image classifier using photon-limited input
Authors: Saaf Lennart A. , Morris G. Michael
Published: February 2023

We have developed an image classifier that uses data from a photon-counting camera as input to a feedforward neural network. The photon-counting camera consists of a photocathode, a stack of microchannel plates, a resistive anode, and position-computing electronics. Incoherently illuminated images are used, and the x- and y-coordinates of the photoevents are passed to a microcomputer. A fixed number of photoevents are collected and are input to a three-level feed­forward neural network, implemented in the microcomputer. The three-level network is trained beforehand using a modification of the backpropagation method, which takes into account the photon-limited nature of the input images. Experimental results are presented for the classification of printed alphabetic characters of different typefaces. Theoretical calculations are presented that describe the statistical nature of the photon-limited images and predict the classification performance of the neural network. Good classification results are obtained with <1000 detected photoevents. Some advantages of using photon-limited images for feedforward neural networks are discussed. One advantage is the network’s invariance to changes in object illumination level, which arises from the practice of collecting a fixed number of photoevents.
Reconstruction of scanned optical holograms using an electron beam addressed spatial light modulator
Authors: Duncan Bradley D. , Poon Ting-Chung
Published: February 2023

Real-time holographic recording has been demonstrated using the optical heterodyne scanning technique proposed by Poon.1,2 In this paper we discuss the recording and reconstruction of holograms generated by the heterodyne scanning technique. The primary concentration is on real­time reconstruction using an electron beam addressed spatial light modulator (EBSLM). For comparison, coherent reconstruction methods are also presented. Additional topics to be addressed are the operation and the spatial frequency limitations of the EBSLM, and the incoherent point-spread function (PSF) of the holographic imaging system. Based upon the derived PSF, the reconstructed real image of a simple slit object is formulated and compared to experimental observations. Our findings indicate that indeed the EBSLM affords the advantage of real-time display of holographic images. However, because of low spatial resolution (~7.4 lp/mm), only holograms of simple objects are suitable for reconstruction using the EBSLM.
Motion capture of chromatic and achromatic borders
Authors: Ramachandran V. S. , Kleffner D. , Plummer D. J.
Published: February 2023

A yellow square was displayed on an equiluminous grey background. When a set of black spots was superimposed on the square and moved horizontally, the yellow square appeared to move in the same direction as the spots, an effect we call motion capture.1 We now report several new experiments: (a) An achromatic low contrast square was also captured although less vividly than chromatic borders. (b) TV snow was superimposed on the yellow square. If a small oscillating spot was tracked in the vicinity of the square, the square appeared to move along with the eyes, perhaps due to misapplied reafferance signals. Even if the tracking was stopped the square sometimes continued to oscillate for a few cycles. (c) Stereoscopic movement of spots in the Z-axis caused the square to be captured in the Z-axis as well. (d) If the spots moved continuously as in a conveyor belt, the square appeared to move but not change location. If a whole row of appropriately spaced squares was used, the row appeared to move continuously.
Sensitivity to spatial variations in image motion
Authors: Watson Andrew B.
Published: February 2023

Extending a method of van Doorn and Koenderink,1 I have examined visibility of spatial modulations of image motion. The stimulus was the sum to two moving bandpass noise images with different velocities. Over the vertical extend of the stimulus, the two noise images were contrast modulated in antiphase by the square root of a stationary sinusoid. For large modulation amplitude, the typical appearance is alternating horizontal stripes of differing velocity. At smaller amplitudes, the stripes disappear. The experimental task was forced-choice discrimination between zero and some nonzero modulation amplitude. A staircase measured the threshold amplitude for various modulation frequencies to determine a velocity-modulation sensitivity function. Data were collected for several noise spatial frequencies and velocities. For each noise frequency tested, modulation sensitivity falls off steeply about one octave below the noise frequency. In certain conditions, sensitivity also declines at low modulation frequencies, consistent with differentiation of motion estimates, as might be employed in a motion-edge sensor.
Inversion problems with quasihomogeneous scatterers
Authors: Fischer David G. , Wolf Emil
Published: February 2023

Inversion formulas are presented for determining the second-order correlation properties of spatially random media of a certain class, namely, quasihomogeneous media,1 from the knowledge of the spectra of the scattered field. In general, the far zone spectra of the scattered field must be known for all directions of incidence and all directions of scattering. The solution yields a low-pass filtered version of the cross-correlation function of the scattering potential.
Trends in optical metrology in the nineties
Authors: Davidson Mark
Published: February 2023

A number of new types of optical or optical/electronic instrument are being utilized in an attempt to meet the metrology requirements for semiconductor manufacturing. These technologies include: Linnik interference microscopes in the coherence probe mode of operation; white light confocal microscopes; laser scanning confocal microscopes; Mireau interference microscopes in the correlation mode of operation; sophisticated direct and inverse scattering simulations of microscope images complementing and enhancing optical instruments; deep ultraviolet classical and confocal microscopes; darkfield laser scanning microscopes; "laser scatterometry” instruments, etc. All this optical innovation has failed so far to prevent the market penetration of the scanning electron microscope for the linewidth measurement task, but optical methods are the dominant technology for overlay measurement. The combination of more sophisticated modeling techniques with advanced optical instrumentation promises to deep optics in the running for some time to come, but the technical challenges are considerable.
Optical power limiting with nonlinear periodic structures
Authors: Herbert Christopher J. , Capinski William S. , Malcuit Michelle S.
Published: February 2023

We have observed optical power limiting using a colloidal crystal doped with an organic dye. The colloidal crystal is composed of charged 0.086-μm polystyrene spheres suspended in water. For volume filling fractions of ~5%, these microspheres spontaneously form a FCC crystal structure with lattice spacing of ~250 nm. Bragg reflection from the (111) plane of the crystal is utilized to provide a highly reflective distributed feedback structure. The lattice spacing of the crystal is controlled by the filling fraction. The crystal used in the experiment is 100 μm thick and has a lattice spacing of slightly longer than 257 nm. The transmission of the crystal is studied as a function of the incident intensity for various dye concentrations and lattice spacings. The transmission of the dye-doped crystals is found to decrease dramatically with increasing intensity. The response time of the optical limiting is measured to be ~200 μs.
Advances in solid-state laser technology
Authors: Mooradian A.
Published: February 2023

Recent progress is discussed in solid-state lasers including diode-pumped microchip laser arrays with uses for laser radar and atmospheric spectroscopy. The unique characteristics of very short cavity microchip lasers include tunable single frequency output, short pulse operation, and multigigahertz linear frequency modulation. These capabilities, which can exceed those of ordinary solid-state lasers, may be incorporated in 2-D arrays of microchip lasers pumped by diode lasers with the array performing with the characteristics of a single microchip. The 1-D heat flow in microchip laser arrays implies an arbitrary scaling of arrays to high power. Coherent locking of these 2-D arrays is discussed as well as the individual pixel addressability. Comparison of this technology is made with diode laser array pumping of slab geometry solid-state lasers. The relative requirements on the diode pump laser arrays for each of these solid-state laser systems are discussed. Technology of nonlinear frequency conversion is also discussed with emphasis on sum frequency mixing the output from Nd: YAG lasers to produce a high energy source at 589 nm to study the mesospheric sodium layer.
Analysis of PbSe claddings on BaF2 waveguides
Authors: Khodr M. F. , Sluss J. J. , Batchman T. E.
Published: February 2023

Mode coupling between a dielectric waveguide and a semiconductor cladding has been investigated for a number of possible applications.1,2 In this paper, we present an analysis of the modes that propagate in a waveguide structure consisting of a IV-VI semiconductor cladding on a II-A fluoride insulator. The IV-VI semiconductors, commonly known as lead salts, are of interest for infrared detector use and because they can be grown as lattice-matched layers on II-A fluoride insulators. The structure analyzed consisted of an air cover layer, a lead selenide (PbSe) cladding, a barium fluoride (BaF2) guiding layer, and a calcium fluoride (CaF2) substrate. For a free-space wavelength of 3.4 μm and a BaF2 thickness of 5 μm, the mode index and attenuation constant were determined as functions of the PbSe thickness. From these data, we determined the mode set for the waveguide structure and examined the mode coupling that occurs between the BaF2 and the PbSe. Our results indicate that a significant amount of energy can be coupled into the PbSe cladding, suggesting that efficient integrated waveguide photodetectors and polarizers are feasible. Such devices would be suitable for use with optical fiber systems and optical integrated circuits operating in the 3-5-μm range. References
Nonlinear grating coupling in a silicon-on-insulator waveguide
Authors: Prelewitz David F. , Brown Thomas G.
Published: February 2023

Silicon-on-insulator (SOI) structures are of interest for VLSI compatible integrated optoelectronics. We observe optical limiting and switching processes in SOI waveguides due to Kerr type nonlinearities in the region of the input coupler. Spatial and temporal interactions between the incident field, guided field, and the grating coupler influence the intensity dependent coupling efficiency of the structure.1 To study these effects experiments were performed, utilizing a pulsed Nd:YAG laser (1.06 μm) to couple into a lightly doped silicon on SiO2 waveguide via a grating coupler. Measurements were taken at various detuning angles, input energies, and input beam locations with respect to the input coupler. Simultaneous monitoring of the input signal, output signal, and transient photoconductivity allowed us to observe the carrier dynamics during the nonlinear interaction process.
How can we tell if S-cones are more vulnerable to disease?
Authors: Swanson William H.
Published: February 2023

S-cone increment thresholds are strongly affected by the state of adaptation of all three cone types. Models of opponent and nonopponent mechanisms suggest that decreased lateral inhibition affecting all pathways equally could selectively elevate S-cone increment thresholds. Therefore, S-cone increment thresholds do not provide unambiguous evidence of selective S-cone-pathway damage. To evaluate S-cone function in patients in conditions in which lateral inhibition is insignificant, S-cone grating orientation acuity functions were gathered with a 500-nm 0.9-log td test field and a 590-nm 4.6-log td adapting field. S-cone acuities for twenty-five normal subjects were comparable with anatomical data on individual variations in the SWS-cone mosaic. For thirty-four normals and patients, test fields were reduced as much as 1.5-log unit; conversion to S-cone contrast indicated that S-cone resolution did not vary with S-cone adaptation state. Varying L/M-cone adaptation state (using lower adapting field luminances) also did not affect S-cone resolution. These data suggest that the high frequency limb of the S-cone-mediated contrast sensitivity function is relatively unaffected by adaptation state and provides an important complement to clinical S-cone increment thresholds.
Optimization of thermal properties of etched-well surface-emitting GaAs/AIGaAs diode lasers
Authors: Nakwaski Wlodzimierz , Osinski Marek
Published: February 2023

Vertical cavity surface-emitting lasers (VCSELs) are known to suffer from excessive heating that seriously limits their cw performance. Recently, we have developed a self-consistent thermal electrical model of etched-well VCSELs, which features realistic distribution of heat sources and 2-D current and heat spreading.1 In this paper, we apply this model to optimize the device design with the goal of reducing the relative power loss from heating and maximizing the optical output power. The etched-well structure considered is similar to that described in Ref. 2, with a double-heterostructure active region defined by a blocking p-n-p junction. The primary parameter of interest is the active region diameter, since for small diameters the output power is expected to scale with the device size. Our calculations indicate that the optimal active region diameter, at which the heating effects are still relatively moderate, is ~16 μm. This value corresponds to a maximum excess of supplied power over the cw lasing threshold power at the corresponding active region temperature. Note that the maximum occurs in the middle of the operating current range, with the lower bound due to threshold for cw operation and the upper bound caused by thermal runaway.
Highly directional spontaneous emission from periodic quantum wells
Authors: Raja M. Yasin Akhtar , Aktas Yildirim
Published: February 2023

Various schemes of periodic quantum wells with integrated epitaxial high reflectors have recently created great excitement and hope for realizing very low threshold surface-emitting laser arrays1 and efficient high-power optically pumped surface-emitting laser structures with resonant periodic gain (RPG).2 Here we report investigations of photoluminescence (PL) properties of In0.2Ga0.8As/Al0.2Ga0.8As periodic quantum wells on GaAs substrate, i.e., RPG without integrated mirrors. The angular distribution of the PL shows strong directionality of the spontaneous emission along with normal to the surface. The investigated samples include 20-, 40-, 60-period RPG and single quantum well on GaAs substrates with and without back-surface polished and/or antireflection coating. The enhancement in the directionality of PL with the number of quantum well periods is pronounced compared with the single quantum well case. There is also a marked reduction in the amplified spontaneous emission in the transverse direction. A proper phase relationship between a previously emitted photon and that being emitted may enhance or inhibit the emission process in a given direction.
Optical perceptron-based quadratic neural network
Authors: Huynh Alex V. , Walkup John F. , Krile Thomas F.
Published: February 2023

Optical quadratic neural networks are currently being investigated because of their advantages over linear neural networks.1 Based on a quadratic neuron already constructed,2 an optical quadratic neural network utilizing four-wave mixing in photorefractive barium titanate (BaTiO3) has been developed. This network implements a feedback loop using a charge-coupled device camera, two monochrome liquid crystal televisions, a computer, and various optical elements. For training, the network employs the supervised quadratic Perceptron algorithm to associate binary-valued input vectors with specified target vectors. The training session is composed of epochs, each of which comprises an entire set of iterations for all input vectors. The network converges when the interconnection matrix remains unchanged for every successive epoch. Using a spatial multiplexing scheme for two bipolar neurons, the network can classify up to eight different input patterns. To the best of our knowledge, this proof-of-principle experiment represents one of the first working trainable optical quadratic networks utilizing a photorefractive medium.
Red- and green-cone pathways have different temporal properties: implications for photometry
Authors: Hamer Russell D. , Tyler Christopher W.
Published: February 2023

Detection of temporally modulated light is linear at high temporal frequencies; near critical flicker frequency (CFF), threshold is determined by the absolute amplitude of the modulation, independent of the luminance or the Weber ratio associated with the stimulus. We measured CFF at 555 nm and 660 nm over a 5-log unit range of intensities. The resulting CFF/logintensity functions were linear, obeying the Ferry-Porter law over the entire range. However, the slope for 555-nm light was significantly steeper, by as much as 17% in the foveola and 25% at 35° eccentricity. If the R- and G-cone pathways had identical temporal properties, and if detection were based on the most sensitive mechanism, the 555-nm and 660-nm CFF/log/ functions would necessarily have identical slopes; however, the signals from the two cone types were combined. This implies that the G-cone pathway has a faster linear temporal response that the R-cone pathway, invalidating the assumptions of heterochromatic flicker photometry. At high intensities, the differing temporal properties of the two cone pathways can lead to more than a log unit mismatch in luminance for a pair of stimuli that appeared matched at low a intensity. A new, threshold based definition of luminance is proposed.
Number states, twin beams, and photon duplication
Authors: Yuen Horace P.
Published: February 2023

It has been known for a while that coherent high-intensity photon number eigenstate fields can be generated through nonlinear optical parametric processes,1 the same ones that give rise to quadrature squeezing.2,3 In contrast to quadrature squeezing which is essentially a single-mode phenomenon, although it is widely misunderstood that it is a two-mode phenomenon, the generation of single-mode number states through three- or four-wave mixing depends on two separate signal and idler modes that are perfectly correlated in photon numbers, in other words a twin beam. The nature of such twin beams is elucidated in both the Schrodinger and the Heisenberg pictures. In particular, it is shown that strong photon number correlation in a twin beam can still be obtained in an amplifier rather than an oscillator configuration, another widely missed point.
Effects of randomly varying birefringence on soliton interactions in optical fibers
Authors: Wai P. K. A. , Menyuk C. R. , Chen H. H.
Published: February 2023

The effect of a randomly oriented birefringence on soliton interaction is studied numerically. The random variation in birefringence in linearly birefringent fibers is modeled by random shift in orientation of the birefringence axes and a random phase difference between the pulse amplitudes in the two polarizations which occurs periodically. Analytical calculations show that the averaged behavior is governed by the Manakov equation.1 The evolution of a pair of solitons with an initial pulse separation T0 ranging from 2τ to 70τ is studied, where T is the soliton pulse width. It is observed that for T0 < 10τ, the interaction is dominated by the phase-dependent short range interaction. The randomly varying birefringence leads to breakup of a two-soliton pair that is originally in phase. For T0 > 10τ, the solitons interact through the dispersive radiation that is generated by the random birefringence, but the interaction is too weak to explain the phase independent long-range interaction observed experimentally.3
Generation of femtosecond high-power optical pulses from a hybrid mode-locked semiconductor laser
Authors: Delfyett Peter J. , Florez L. , Stoffel N. , Gmitter T. , Andreadakis N. , Alphonse G.
Published: February 2023

Compact and efficient sources of high repetition rate, high peak power optical pulses are needed to replace the standard ultrashort optical pulse generation schemes because of their relatively large size and poor wall plug efficiency. In this paper, we present a hybrid mode-locked semiconductor laser system that is capable of producing optical pulses of 207 fsec in duration with peak powers in excess of 150 W. To the best of our knowledge, these optical pulses are both the shortest and most intense ever produced from an all-semiconductor laser diode system. The optical pulses were generated by forming a hybrid mode-locked external cavity semiconductor laser, which incorporates a GaAs/AlGaAs semiconductor traveling wave amplifier as the gain medium, a multiple quantum well (MQW) saturable absorber, and a four-prism sequence to compensate for group velocity dispersion.
Soliton fiber ring laser using an erbium-doped fiber amplifier
Authors: Chen C.-J. , Wai P. K. A. , Menyuk C. R.
Published: February 2023

Fiber ring lasers using erbium-doped fibers as gain media have attracted much attention recently because of their simple structures and rapid progress in erbium-doped fiber technology. We theoretically study a fiber ring laser that consists of a few kilometers of fiber, a delay stage, a polarization controller, an isolator, a Fabry-Perot interferometer, an Er-doped fiber amplifier, and an output coupler.1 When loss is compensated by gain, solitons propagate. The repetition rate is set by the fiber Fabry-Perot interferometer. The fiber is modeled by the nonlinear Schrodinger equation and the fiber Fabry-Perot interferometer by a comb filter in the frequency domain. Our numerical simulations show that a pulse train will not self-start unless a saturable absorber is introduced and a frequency limiter is present. A possible source of the saturable absorption is the combined effect of cross-phase modulation in the fiber and polarization sensitive components in the ring structure.
Photorefractive phase-conjugate resonator
Authors: He Q. Byron , Gu Claire , Yeh Pochi
Published: February 2023

A phase-conjugate resonator is formed when the transmitted pump and diffracted beams from a photorefractive crystal are fedback from an active phase-conjugate mirror. Such a resonator may be used as an approach to sustain a dynamic hologram in the photorefractive materials.1 We have investigated the oscillation conditions, the dynamic processes, and the competition phenomena in the high coupling and pump depletion regime. We assumed that the active phase conjugate mirror has instantaneous response and amplitude reflectivity of ρ. One of the beam is amplified by a factor of g via a two-wave mixer. In the steady state, analytical solutions are obtained for the intensities inside and outside the cavity. Threshold conditions are presented as functions of photorefractive coupling constant γl, phase conjugate reflectivity ρ, and amplification factor g. The transient process is studied by numerical techniques. Competition phenomena are investigated when more than one beam are oscillating in the resonator with different coupling constants. The potential impact on the hologram dynamic fixing is discussed.
Optical neural network using mirror array interconnection
Authors: Yu Francis T. S. , Yang Xiang Y. , Yin Shizhuo , Gregory Don A.
Published: February 2023

Optical neural networks using a lenslet array interconnection have been reported recently,1,2 in which two inexpensive liquid crystal televisions are used to generate the input pattern and the interconnection weight matrix (IWM). Each of the lenses images the entire IWM, but only one of the IWM-submatrices is used for interconnection. Thus the overall interconnection light efficiency of the systems is bounded by a factor of 1/N2, which would limit the performance of a large-scale neural net operation. To improve the light efficiency of the optical neural network, we have replaced the lenslet array by a mirror array. N × N mirrors are affixed on a parabolic substrate. The position and orientation of the mirrors are finely tuned so that each mirror would reflect a corresponding IWM-submatrix onto the output detector. Compared with the lenslet array technique, the light efficiency of the system would be increased N2 times.
Optical neural network using novel electron trapping materials
Authors: Yu Francis T. S. , Yang Xiang Y. , Wu Shudong , Jutamulia Suganda , Storti George M. , Lindmayer Joseph
Published: February 2023

Massive interconnection is one of the key features of artificial neural networks, which can be implemented optically by encoding the interconnection weight matrix (IWM) on a spatial light modulator (SLM) and superimposing all the IWM-submatrix with a lenslet array. The low dynamic range and very limited resolution of the currently available SLMs are the main concern for the development of optical neural network (ONN). So far the largest ONNs with lenslet array contain only 64 neurons and 4096 interconnections,1,2 which can have little practical use. However, the weakness can be effectively strengthened by a novel electron trapping (ET) material that has a resolution of ~100 lines/mm, dynamic range of 4 orders of magnitude, and is suitable for a 3-D interconnection implementation. An ONN architecture with 128 × 128 neurons is proposed in this paper. The massive interconnections are stored in 100 layers of ET thin film. The page-addressable 3-D ET memory offers a huge information capacity and may have vast uses in real-time target tracking and pattern recognition. The proposed system can store a total of 2.7 × 1010 interconnections and have a processing speed as high as 5.4 × 1011 interconnections per second. System design considerations as well as performance evaluations are provided.
Laser-induced index gratings in thin-film superconductors
Authors: Glass N. , Rogovin D.
Published: February 2023

Optical index gratings are radiation-induced periodic spatial variations in an active medium’s dielectric constant. These structures are responsible for numerous active optical processes and are of central interest to nonlinear optics. In this paper these concepts are extended to superconducting thin films. Notably, theory asserts that optical index gratings can be created in thin film superconducting structures from coherently interfering laser beams. The presence of the optical interference pattern gives rise to pair-splitting processes that generate quasiparticle (qp) population gratings. In turn, these qp gratings establish conductivity gratings within the thin-film super-conductor, that are active for frequencies below the pair-splitting frequency. Since the conductivity has both real and imaginary parts, both phase and amplitude gratings are established in the superconducting thin film. We examine the steady-state and transient dynamics of these index gratings and show that they form quite rapidly, on the order of 0.5 ns for Nb superconducting thin films. Furthermore, it is shown that the existence of these optical index gratings can be verified by measuring the angle resolved transmittance and reflectance of millimeter waves. In particular, our theoretical analysis shows that well-defined off-specular peaks, corresponding to the grating diffraction orders, appear.
Optical air data sensor techniques for atmospheric parameter measurements
Authors: Poultney Sherman K.
Published: February 2023

One of the challenges of an all-optical air data system is to measure the local atmospheric parameters of interest (e.g., pressure altitude, true air temperature, humidity, etc.), all with a sensor that meets size, weight, and power requirements. A variety of sensor techniques have been investigated at HDOS for the altitude range 0–100 km and are reviewed here. The ideal technique would allow one to reach out to the nearby undisturbed air and would measure a physical or spectroscopic parameter related to the desired atmospheric parameter without requiring knowledge of the absolute power in transmitted or received power in the optical probe beam. This ideal technique is not usually possible because of a variety of fundamental and practical limitations. The more practical techniques reviewed here include cooperative spectral absorption near 200 nm, cooperative laser absorption near 760 nm, cooperative laser absorption near 860 nm, and laser-induced fluorescence near 200 nm.
High-precision target dynamics using a speckle-tracking laser radar
Authors: Shirley Lyle G. , Payson Harold , Hallerman Greg
Published: February 2023

When an object is illuminated by a laser radar, the scattered light interferes with itself and forms a speckle pattern. If the object rotates by a small angle, the entire speckle pattern that surrounds it will also rotate about the same axis and in the same direction. To a monostatic radar, this rotation appears as a translation of the speckle pattern in a direction ϕ that is perpendicular to the projected axis of rotation. Thus, small changes in an object’s viewing angle can be sensed, and its angular motion can be characterized by observing the time dependent ϕ(t). For a circularly symmetric, spinning, and precessing object, this method allows the coning half angle, angular momentum aspect angle, instantaneous radar aspect angle, and precession period to be determined. With sufficient resolution, the wobble arising from a mass imbalance can also be obtained. In cases where internal or external forces disturb the free-body motion, the resulting perturbation can be measured, so that with appropriate models, either the disturbing forces or properties of the object, such as its mass, can be estimated. We demonstrate the speckle tracking technique by placing target models in a positioning system that simulates spin and precession. The resulting speckle motion is observed with a CCD array, and ϕ(t) is extracted using either a streaking or a cross-correlation algorithm. The measured ϕ(t) is then fitted to the theoretical model, and the coning half angle and momentum aspect angles are extracted to within a fraction of a degree.
Bistable phase-conjugate resonator using an intracavity saturable absorber
Authors: Klein M. B. , Dunning G. J. , McCahon S. W. , Pepper D. M.
Published: February 2023

Phase-conjugate resonators have several attractive properties for image processing and storage. In the work described here, we demonstrate improved thresholding and storage properties of a phase-conjugate resonator (PCR) by the addition of an intracavity saturable absorber. It can be shown that the resonator will be bistable if (1) the small-signal absorption of the saturable absorber exceeds the small-signal gain of the phase-conjugate mirror, and (2) the absorption saturates more readily than the gain (i.e., reflectivity) of the PCM. Recently, a saturable absorber was used inside a PCR to control the transverse modes,1 but no evidence of bistability was obtained. In our experiment, we used a PCR bounded at one end by a conventional mirror and at the other end by an externally pumped BaTiO3 PCM. The saturable absorber was a solid film of fluorescein- doped boric acid glass.2 By adjustment of the total intensity and beam ratio at the PCM, we were able to demonstrate bistability. The input in our experiment was an incoherent control beam incident noncollinearly onto the intracavity saturable absorber. In the absence of a control beam, no oscillation was observed. When the control beam was turned on, the resonator switched to the on state in ~5 sec. The control beam could then be removed, and the cavity oscillation continued. To return to the off state, the resonator path was blocked.
Brillouin-induced wave mixing using cw signals
Authors: Lebow Paul S. , Ackerman John R.
Published: February 2023

High performance forms of Brillouin mediated two-wave mixing [stimulated Brillouin scattering (SBS) amplification] and four-wave mixing [Brillouin enhanced four-wave mixing (BEFWM)] are documented to be sensitive to quite low energy, i.e., picojoule level, pulsed signals. These thresholds are small enough to be exceeded by the energy delivered by a laser diode pumped cw Nd:YAG laser during the several nanoseconds in which the pulsed pump radiation is present in the nonlinear medium. We have observed, we believe for the first time, SBS amplification and BEFWM phase conjugation of cw signals using pulsed pumping with enhancements that agree well with those obtained using low energy pulsed signals. The cw input eliminates the precise pump-signal synchronization required when all inputs are pulsed. Heterodyne mixing of the cw input with the cw injection seeding beam of the pulsed pump laser yields precise knowledge and control of the nearly degenerate input frequency relationships without using SBS frequency shifting. Resonance spectra of BEFWM and SBS amplification as a function of geometry recorded in these improved experimental conditions reveal detunings that do not appear to be entirely accounted for by standard Brillouin scattering theory.
Quantum mechanical Fresnel relations
Authors: Rai Jagdish
Published: February 2023

Several authors1,2 have studied the lossless beam splitter on a quantum mechanical basis. In this approach the action of the beam splitter is described by unitary transformations that act on the operators for the radiation fields present. In this paper we study quantum mechanically the general case of reflection and transmission from a boundary. We obtain the quantum analog of the classical Fresnel relations. We find that the general operators that describe reflection and transmission at a boundary are a series of unitary operators involving appropriate radiation fields. The generalization for the nonlinear media presents many interesting situations where the classical laws of reflection and refraction are modified. This provides an interesting description of phase conjugation.
Effect of Raman scattering on Fraunhofer lines in the ocean
Authors: Ge Yuntao , Gordon Howard R. , Voss Kenneth J.
Published: February 2023

By measuring the change of Fraunhofer lines in the solar spectrum in the water column, information on inelastic scattering process can be extracted. In this paper we model the effect of Raman scattering on Fraunhofer lines in ocean water. The change of Fraunhofer lines in ocean was calculated via Monte Carlo simulations. Six lines, 396.8, 422.7, 486.1, 518.4, 589.0, 656.3 nm, were investigated. Here η, defined as the ratio of the irradiance at the center of the Fraunhofer line to the background, was used to characterize the change of the Fraunhofer lines. It was found that η for 589.0 and 656.3 nm goes to 1 quickly as the depth increases, both for upwelling and downwelling irradiance. The 396.8- and 422.7-nm lines show a different behavior: η for the downwelling irradiance is almost constant while for the upwelling irradiance it is largest at the surface and decreases with depth. The 486.1- and 518.4-nm lines appear to be a dividing point between the shortwave and longwave range. At these wavelengths, η does not change with depth and is always larger in the upwelling irradiance than in the downwelling irradiance.
Optically powered smart pixels
Authors: Forrest S. R.
Published: February 2023

Recently, there is an increasing interest in smart pixel arrays for use in high density, high bandwidth interconnection networks.1,2 Optoelectronic integrated circuits (OEICs) are attractive components for such arrays. There are, however, critical limitations associated with 2-D chip architectures that prevent the OEIC-based design from achieving the expected high performance. One issue is the electrical voltage supply and pixel logic control lines which must be routed to each pixel. The nonzero impedance of these interconnects introduces crosstalk which ultimately limits the bandwidth of the system. In addition, the dc bias lines and their associated ac decoupling circuitry consume valuable chip area. We propose a novel interconnection architecture to confront the issues of crosstalk and layout, which utilizes the principle of optically powered smart pixels.3 Here, optical powering is locally provided to each pixel using an integrated photovoltaic cell. In this paper, we demonstrate an optically powered, integrated smart pixel. The InP based circuit can be dynamically tuned with an optical control beam to operate as an amplifier, bistable switch or as a latch/reset. The circuit has an optoelectronic gain of 2.5–11, and operates at 80 Mbit/s with an optical switching energy of only 3.8 pJ.
Eight-channel space-multiplexed optical CAM-based MSD adder
Authors: Li Yao , Gao Xing Qiou , Ha Berlin
Published: February 2023

Modified signed-digit (MSD) number representation with its inherent weak interdigit dependence is capable of performing parallel addition and subtraction operations. A MSD-based multiplication scheme that contains an array of parallel additions has proved to be a competitive multiplication method. Optical implementation of an MSD arithmetic processor has recently been studied. A single-step optical content-addressable memory-based MSD adder has been proposed. Since to generate a single-step 1-bit MSD addition result, as many as fifty-six reduced logic product terms have to be stored in a CAM, direct parallel stacking of N + 1 such 1-bit MSD adders for an TV-bit MSD addition operation will occupy a huge volume. In this paper, a novel scheme is proposed to make a space-multiplexed optical CAM for an N-bit MSD addition. The N-bit input data are first permuted to form a data matrix. By modifying an existing triple-matrix multiplier, a space-multiplexed CAM is formed in a compact and efficient way.
Real-time defect enhancement diagnostic system using a spatial light modulator and a phase-conjugate mirror
Authors: Gaeta C. J. , Mitchell P. V. , Pepper D. M.
Published: February 2023

For real-time nondestructive evaluation of periodic structures (e.g., masks), it is preferable to suppress the intended periodic features to enhance defect visualization (e.g., scratches and digs). Previous demonstrations1 employed a phase-conjugate mirror (PCM) placed at the spatial Fourier transform plane of an optical processor. The spatially transformed defect features, which are broadband and typically of low intensity, can be enhanced in the presence of the transformed intense periodic structure(s) by exploiting pump depletion of the PCM reflectivity for the latter features. The dynamic range and response time of the PCM are typically constrained by the intensity ratios of the defect and periodic features. Our approach relaxes these constraints by using a spatial light modulator (SLM) at the transform plane, followed by a PCM.1 The SLM performs the function of intensity discrimination by suppressing the intense periodic features of the mask, while allowing the low-intensity defect features to be passed onto the PCM. The PCM ensures system auto-alignment and compensation for propagation errors, resulting in reverse transit of the desired information back through the transform lens for subsequent mask inspection. Our system is capable of large dynamic range and can operate at video frame rates.
Crystal growth and spectroscopic characterization of Nd-doped SrGdGa3O7
Authors: Quarles Gregory J. , Rosenblatt Gregg H. , Randles Mark H. , Esterowitz Leon
Published: February 2023

We have spectroscopically evaluated crystals of Nd3+:SrGdGa3O7(Nd3+:SGGM) to assess their potential for use as diode pumped solid-state laser materials. The single crystals were grown by the Czochralski method, and the samples were oriented using x-ray diffraction. The host, SrGdGa3O7 is a uniaxial crystal with tetragonal symmetry and is a subset of the melilite series of minerals. The samples studied here were doped with 2 at. % Nd3+ in the melt with respect to the Gd ion. Polarized absorption spectra reveal that the absorption coefficient for light having its E vector perpendicular to the c-axis, Eσ is larger than that for E parallel, Eπ. The absorption coefficient for Eσ at 809 nm is 6.6 cm-1, more than two times larger than that for Eπ at the same wavelength. Similar differences in transition strengths have been measured in the emission spectra. Significant inhomogeneous broadening occurs in Nd:SGGM; the absorption linewidth at 809 nm is 10 nm FWHM. For a diode pumped solid-state laser this represents a significant improvement over the 1-nm FWHM linewidth in Nd: YAG at 810 nm. The fluorescence lifetime for the 4F3/2 → 4I11/2 transition at 1.06 µm is 245 µm in our Nd:SGGM crystals, which is 40% longer than lifetimes measured previously for Nd:SGGM crystals grown by the laser heated pedestal growth method,1 and is comparable to the 230-µm lifetime for Nd:YAG.
Analysis of phase modulation in a joint transform correlator
Authors: Gregory Don A , Kirsch James C. , Yu Francis T. S. , Tanone Aris , Yin Shi-zuo , Tam Eddy C.
Published: February 2023

The joint transform architecture is well known in optical processing. Normally object and reference are presented to the system as purely real scenes. If the reference and object are identical, the joint transform power spectrum (JTPS) is the Fourier transform modulated by a cosinusoidal fringe pattern. This pattern is then itself transformed to produce the two correlation signals. Our analysis assumes that reference and object are real but that they are displayed on a device that can only modulate phase. A calculation is done for the resulting power spectrum, and the effect of displaying this power spectrum itself on a device that can only modulate phase is also modeled. Results indicate that good correlation peaks should be experimentally obtained. The effect of using an on-axis stop in the Fourier transform plane is also modeled. The correlation width can be improved greatly with a judicious choice of stops. This can be thought of as an extreme nonlinearity that imitates the behavior of photographic film in a joint transform correlator.1
Recent studies with nonlinear matched filtering
Authors: Ersoy O. K. , Yoon T. , Zimmerman D.
Published: February 2023

Nonlinear matched filters involve the transformation of the filter transfer function and/or the signal spectrum through pointwise nonlinearities before they are multiplied in the transform domain.1,2 By using special transform techniques, very high power of discrimination and resolution are achieved, in a way similar to inverse filtering but without the associated ill-conditioned behavior of inverse filters. In certain cases, optical implementation is also sufficiently simple. In this paper, most recent studies with these papers are reported.
Optical logic gates using spatial light modulators
Authors: Li Yulin , Zhao Mingjun
Published: February 2023

In the last few years, spatial light modulators (SLMs) have been used to implement binary optical logic operations, because binary logic optical operations are the basic procedures in a digital optical computing system. This paper presents the optoelectronic hybrid approaches of the new linear optics and nonlinear encoding by using optically and electrically addressed spatial light modulators. The main advantages of these SLMs are in terms of the 2-D parallel processing capacity and the possible global interconnections for optical computing.
Complex susceptibility of rare earth-doped fiber amplifiers in the saturation regime
Authors: Shore K. A. , Halus R.
Published: February 2023

A basic understanding of the susceptibility of fiber amplifiers (SOFA) is required to undertake device optimization, e.g., for uses in optical communications systems. In recent work Desurvire1 has developed a semiclassical treatment of the SOFA for erbium-doped fiber amplifiers (EDFAs) taking account of the Stark splitting of the energy levels in the Er-doped glass. That work, which utilized the standard Kramers-Kronig relationships, was applicable to the unsaturated regime of operation. In this contribution, generalized Kramers-Kronig relations2 are utilized to obtain analytical expressions for the SOFA valid even in the saturation regime. It is then shown how, given experimentally measurable absorption cross-sections, the SOFA may be calculated in any operating conditions. In this way gain and refractive-index changes occurring in EDFAs may be deduced, again having universal validity.