bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrable GaAs correlator using surface emitting second harmonic generation
Authors: Vakhshoori Daryoosh , Wang Shyh
Published: February 2023

We report the first realization of an AlGaAs/GaAs broadband integrable optical correlator with the potential of subpicosecond pulse measurement. The correlation action is based on the surface emitting second harmonic generation technique developed earlier.1,2 Following the technique described in Ref. 2, as the fundamental pulsed beam propagates in a waveguide cavity, the forward and backward propagating TE0 and TM0 beams interact via the nonlinearity of the waveguide material (in our case GaAs) to generate a standing wave of second harmonic polarization along the length of the waveguide cavity. The period of the standing wave polarization is proportional to the difference in the propagation constant of TE0 and TM0, and the envelope of the second harmonic signal is proportional to the pulse width of the fundamental beam; 7-ps compressed pulses at 1.06 μm were coupled to an AlGaAs/GaAs waveguide cavity. The average (peak) power in the cavity is estimated in be 100 μm (140 mW). A 1600 Fuji film was used to record the envelope of the green light (0.532 μm) across the waveguide. Using a sinclike function for the pulse shape, a pulse width of 7 ps is determined.
Scanning interferometer using active liquid crystal cells
Authors: Lakkaraju H. S. , Williams G. T. , Yatskar A. , Chan K. C. , Lam L.
Published: February 2023

We have developed a two-beam scanning interferometer utilizing different liquid crystal cells as active elements controlled by externally applied low-frequency fields. The response time of these scanning elements is typically in milliseconds or longer. The role of the applied fields as well as the schlieren response of the medium in the operation of the interferometer is discussed in the light of the observed performance.
Time-reversal symmetry of Berry’s phase
Authors: Malcuit Michelle S. , Tompkin Wayne R. , Boyd Robert W. , Chiao Raymond Y.
Published: February 2023

We have studied experimentally the time-reversal symmetry of Pancharatnam’s phase, an optical manifestation of Berry’s topological phase, through the use of optical phase conjugation. Pancharatnam’s phase is the phase acquired by a beam of light when its polarization state is changed successively so that a closed path is traced out on the surface of the Poincare sphere. Numerically, this phase is equal to minus one half the solid angle subtended by the closed path. Pancharatnam’s phase, due to its topological origin, is independent of the system’s Hamiltonian, including its symmetry properties, and, therefore, remains odd even when the time-reversal symmetry of the total system is broken.
Phase shift of a self-pumped phase conjugate mirror
Authors: Tomita Y. , Yahalom R. , Yariv A.
Published: February 2023

Self-pumped phase conjugate mirrors (SPPCMs) have become a key component in an ever increasing array of image processing and interferometric applications. The key issue in all these applications is the relationship between the phase (more precisely the change of phase) of the input beam and that of the output (i.e., the reflected) beam. We report experimental results showing the dependence of phase shifts of conjugate beams from a SPPCM on a spatially uniform phase change of one of the input beams. We find that (a) for a single-beam input to the SPPCM, despite the distortion-correction capability, the SPPCM reflects a conjugate beam with the same uniform phase change as that of the input; (b) for a two-beam input, the relative phase between the two conjugate beams is reversed, as required for wavefront reversal, and the phase shift of each conjugate beam is almost a linear function of the uniform phase change of one of the inputs, while the rate of the change depends on the relative power of the two input beams. Most of these results are consistent with the past observations.1,2
Dynamics of switching and spatial first-order phase transition in intrinsic optical bistability
Authors: Inguva Ramarao , Bowden Charles M.
Published: February 2023

A system of coherently driven spatially distributed two-level atoms, coupled with each other via dipole–dipole interaction, exhibits intrinsic optical bistability (IOB) at solid-state densities,1 i.e., optical bistability without optical feedback. The origin of the IOB was shown to be due to inversion-dependent renormalization of the single-atom resonance frequency caused by dipole–dipole interaction among the atoms located mainly within an atomic resonance wavelength.2 For normally incident plane waves of intensity beyond threshold, a spatially dependent discontinuity in the nonlinear refractive index was shown to exist inside the medium,1 corresponding to spatial separation of the high and low absorption phases of the IOB. We present numerical results for the time-dependent solutions of the equations of motion and dynamics of the field propagation.
Instabilities in a hybrid bistable system without delayed feedback
Authors: Narducci F. A. , Bromley D. W. , Tredicce Jorge R.
Published: February 2023

The dynamic behavior of hybrid bistable systems has been studied widely. Self-pulsing in the transmitted intensity has been predicted and observed whenever the feedback loop is affected by a sufficiently long delay.1 Here we show that instabilities can also arise from the inclusion of an amplifier in the feedback loop. An amplifier is necessary, in general, to close the loop between the detector whose typical signal amplitude is hundreds of millivolts and the nonlinear device (electrooptic or acoustooptic modulator), which requires higher voltages to operate. We use a typical hybrid system2 with an acoustooptic modulator (AOM). The output intensity is detected by a photodiode whose output is amplified and sent back into the driver of the AOM with no further delays except those introduced by the wires (30 cm). We study the dynamic behavior of the system for different amplifier gain and bandwidth. We present evidence of Hopf bifurcations, period doubling, deterministic chaos, and collisions of stable and unstable orbits.
Laminar flow mirrors
Authors: Shen Gon-Yen
Published: February 2023

In describing the laminar flow mirrors, a general comparison between laminar flow cooling and turbulent flow cooling shows that the two cooling techniques can achieve comparable mirror thermal performance. However, the cooling flow rates required for the laminar flow mirrors can be significantly reduced. The emphasis of reducing the hydraulic diameter as the primary scheme to increase the film transfer coefficient in the laminar flow cooling technique is significantly different from that employed in conventional turbulent cooling, which relies on high fluid velocity to achieve the same objective. The fabrication technology of such laminar flow mirrors is being developed.
Parametric sensitivity of an object class in an optical target recognition system
Authors: Leib Kenneth G. , Soel Michael A.
Published: February 2023

We present a comprehensive study of parametric sensitivity problems associated with a 2-D optical target recognition system. To this end a class of related targets—was examined to determine a set of parameters yielding optimum target recognition in a matched filter (MF) correlation system. Image variances such as rotations, scalings, and distortions within the object class were investigated to determine the intraclass discrimination tolerances.
Optical holographic planar interconnections: an integrated optics approach
Authors: Jannson Tomasz , Lin Freddie
Published: February 2023

The large bandwidth, immunity to interference, large fanout, and electrical isolation provided by optical communication techniques have led to recent interest in optical VLSI interconnection. Due to the advantages of highly parallel and global communications in optical holographic interconnects, optical holography has become an appealing alternative to wired interconnections (such as channel waveguides and fibers) on several levels of communication hierarchy within VLSI interconnect systems.
Distortion-invariant filters and their use in hybrid ATRs
Authors: Fatterly Donald , Casasent David , Visaya Kumar B. V. K.
Published: February 2023

A review of synthetic discriminant function filters (SDFs) for 3-D distortion-invariant object recognition and the hybrid ATRs to implement them are presented. Projection, correlation, peak to sidelobe (PSR), and minimum autocorrelation plane energy (MACE) filters and their differing applications are addressed. General formulations of distortion-invariant filters from which all SDF filters (and their relatives) can be derived are also provided.
Use of polarization modulation Fourier transform infrared spectroscopy
Authors: Nafie Laurence A.
Published: February 2023

Within the past decade, polarization modulation has been successfully combined with Fourier transform infrared interferometry. The majority of measurements have employed the double modulation technique to measure vibrational circular dichroism.1 With this approach, polarization modulation is effected by a photoelastic modulator operating at a frequency well above the interferometric Fourier frequencies. Demodulation is first carried out for the polarization modulation followed by Fourier transformation of the band of Fourier frequencies. Sensitivity to polarization difference spectra as small as 6 orders relative to the parent absorption spectra has been achieved by this approach. More recently, a second approach to polarization modulation interferometry has been proposed2 termed interferometric modulation. In this method, the conventional beam splitter is replaced by a polarizing grid beam splitter after the design of Martin and Puplett.3 The output of such an interferometer is pure polarization for each wavelength at its own Fourier frequency without, in principle, any intensity modulation. Conversion to intensity modulation is achieved by insertion of a polarizer from whence phase correction can be obtained. Relative to this phase correction, without the polarizer in place, linear dichroism is obtained by the real part of the complex Fourier transform, and circular dichroism is obtained from the corresponding sine transform.
Development of a flight polarimeter for solar magnetic field measurements
Authors: West Edward A. , Reichmann Edwin J.
Published: February 2023

A breadboard design to prove the operational feasibility of a solar activity monitor experiment (SAMEX) vector magnetograph is being developed at the Marshall Space Flight Center (MSFC). Since the transverse magnetic field (which is related to linear polarization measurements) is much weaker than the longitudinal magnetic field (circular polarizations) and represents the greatest uncertainty in the description of the vector magnetic field on the sun, the polarimeter design has been optimized for those measurements assuming that they obtained in space. Although the SAMEX polarimeter is not optimum for a ground-based patrol instrument, the design concept can be confirmed from ground-based measurements and direct comparisons with the existing MSFC vector magnetograph, and the calibration techniques can be developed to correct for systematic errors in the polarimeter.
Some new ideas for improving the rate of convergence of the Gerchberg superresolution algorithm
Authors: Kani L. M. , Dainty J. C.
Published: February 2023

Obtaining resolution beyond the diffraction limit is desired in many image processing applications. The Gerchberg algorithm,1 being an iterative technique, has the advantage over noniterative techniques of being less noise sensitive as well as being more robust since physical constraints may be imposed throughout the iteration process and which can be updated as more information about the object is recovered. Such constraints include positivity and space-limitedness properties of real objects. The well-known shortcoming of the algorithm—its slow convergence—is shown to be a direct result of overestimation of the boundary of the object. A technique is developed to detect the occurrence of stagnation in the algorithm where-upon a reduction of the boundary is carried out. A safeguard against overreduction is employed. Use of further a priori information, namely, the definite integral property of Fourier transform pairs is also investigated.
Slip cast silica, a low-cost approach to large terrestrial mirrors
Authors: Krim Michael
Published: February 2023

Slip cast silica is an ideal mirror material having all the desirable attributes of quartz, with the exception that the surface needs to be densified to achieve the necessary degree of specularity after polishing. The slurry is cast at room temperature in a plaster mold which can incorporate plaster or Stryofoam core blocks to enable it to be inherently lightweight. Subsequent to drying, the casting is fired at ~1000°C in a firebrick kiln. After firing the surface is generated to within several waves of its final shape. Then the surface is densified and the final figuring accomplished. We have successfully polished small-scale samples subsequent to densifying the surface with electroless nickel and demonstrated that very useful optics can indeed be produced with this material. We have also characterized this material mechanically and thermally and using these data developed a 6m mirror design. In principle, we believe that the mirror may be brought to the site in the form of barrels of slurry, a truck full of bricks and propane tanks, and a modified computer controlled polisher. The latter is a Perkin-Elmer proprietary machine/process used for figuring large optical elements. A plan for actually casting the mirror blank and figuring it at an observatory site is presented to provide a basis for estimating the cost of producing and delivering a large mirror by this method.
Automated feature extraction from fluid flow data
Authors: Helman James L. , Hesselink Lambertus
Published: February 2023

Much research has been devoted to image understanding and the automated analysis of images of 2-D scalar data, but comparatively little work has been devoted to understanding higher dimensional data. Experiments and numerical calculations of fluid flows yield large data sets consisting of vector data on 2-, 3-, and 4-D domains. These are often too complicated for manual inspection, manipulation, and display. As with scene analysis, an abstract representation of the data set would greatly facilitate these tasks. Such a representation based on the flow topology can be constructed by locating and characterizing the critical points of the velocity vector field. These points serve as a basis for building a representation of the global topology as determined by the tangent curves of the vector field. This paper describes methods for the implementing this analysis on a computer and results from their application to 2- and 3-D fluid flow data sets.
Image recognition techniques with the discrete rectangular wave transform
Authors: Ersoy O. K. , Kim D. Y.
Published: February 2023

This paper deals with further studies with real-time image recognition based on the discrete rectangular wave transform (DRWT).1 The methods proposed drastically decrease the time of computation and cost of implementation while they also increase the quality of recognition in the presence of noise.
New method for measuring phase factor
Authors: Zhuang Songlin , Zhang Yue , Huang Yanping
Published: February 2023

We propose a new optical method for determining the optical phase term from the intensity distribution. The basic idea of the new method is as follows: Consider a simple Fourier optical setup or 4f system. An object f(x) = |f(x)| exp [jθ(x)] is put in the object plane, and the detector is inserted in the image plane. Obviously the intensity distribution I(x′) determined here does not include any phase information. However, if we use a spatial filter to modulate the spectrum distribution of the object function, the new intensity I(x′) will be related not only to the amplitude term |f (x)| but also to the phase term θ(x). The relationship between I(x′) and θ(x) is also changed by using differential filters. Therefore, the phase factor θ (x) can be obtained from a series of intensity measurements. It can be shown that the phase term of the object function can be uniquely determined by using two different modulated plates.
Shift-invariant binary signal transformation for optical processors
Authors: Jahns Jurgen
Published: February 2023

Signal processing is an interesting field for all-optical digital computing. One reason for this is the fact that signal processing operations can be pipelined very efficiently. This eliminates the need for a complex memory system as it is required for general purpose systems. For example, we consider the M-transformation. The M-transformation is a binary signal transformation which requires only the implementation of AND and OR operations. It belongs to a class of shift-invariant transformations which are described in Ref. 1. The property of shift-invariance makes it interesting for pattern recognition applications. We propose an optical implementation for 2-D signals, which is based on the use of crossover interconnections.
Dynamic symmetries of the vacuum field Jaynes-Cummings model
Authors: Aravind P. K. , Hu Guanghui
Published: February 2023

We use the standard Jaynes-Cummings model with the field initially in the vacuum state and the atom in an arbitrary superposition state to illustrate the concept of dynamic symmetry in quantum optics. By dynamic symmetry we mean a situation in which a Hamiltonian is expressible as a linear combination of operators obeying a Lie algebra. This circumstance permits a psuedospin (or coherence vector) treatment to be given of the dynamics of the system. We give two such interpretations of the Jaynes-Cummings model. In the first we regard the atom and the field as a pair of interacting two-level systems and formulate a SU(2)-SU(2) dynamic symmetry. In the second we interpret the composite atom-field system is a three-level system and formulate a SU(3) dynamic symmetry. The former model illustrates the ideas of Fano1 and the latter those of Hioe and Eberly.2 We give a complete pseudospin description from both points of view and also obtain all the constants of motion.
Enhancement of second harmonic conversion in optical fibers by hydrogen and heat treatment
Authors: Ouellette Francois , Hill Kenneth O. , Johnson Derwyn C.
Published: February 2023

Efficient second harmonic generation in optical fibers is still a largely unexplained phenomenon.1 In particular, neither the microscopic mechanism nor the defects or impurities that might be involved have been identified yet. We present new results that may contribute toward a solution of this problem. We modified the defect content of a Ge-doped-core fiber by subjecting it to a hydrogen and heat treatment that led directly to enhancement of the achievable second harmonic conversion efficiency. The fiber was placed in a pressure chamber with 3-atm H2 at room temperature for 3 days and was then removed and heated at 250°C for 6 h. Strands of this fiber, 15 cm long, were prepared for second harmonic generation: each was seeded with light at 1.06 μm and 532 nm at fixed power levels for a fixed time, long enough to reach saturation of the conversion efficiency.2 The conversion efficiency of the treated fiber was compared with that of untreated strands of the same fiber seeded in identical conditions. To date, an enhancement by more than a factor of 2 has been observed in such treated fibers.
New four-channel polarimeter for time-resolved ellipsometry
Authors: Jellison Gerald E.
Published: February 2023

A new four-channel partial polarimeter has been designed and fabricated for use in time-resolved ellipsometry measurements. The device outputs four parallel equispaced beams from a single input beam. By detecting and digitizing the intensities of these four beams, the intensity as well and two of the three elements of the reduced Stokes vector can be determined. The time resolution of the device is limited only by the photodetectors and digitizers used; nanosecond time resolution is possible with either photodiodes or phototubes as photodetectors, and picosecond time resolution is possible with a streak camera as both photodetector and digitizer.
Experimental demonstration of the rotating-detector ellipsometer (RODE) and the two-detector ellipsometer
Authors: Nick David C. , Azzam Rasheed M. A.
Published: February 2023

RODE is a simple handedness-blind ellipsometer1 that measures the ellipse of polarization of a totally polarized light beam or the first three Stokes parameters of partially polarized light. We constructed and operated a RODE using a single Si planar-diffused photodiode at the He-Ne laser wavelength of 632.8 nm. The detector surface, which has an oxide-layer coating of halfwave thickness, intercepts the incoming light beam at an ~70° angle of incidence (AOI). The output signal of the detector is recorded at equispaced, 5° apart, angular positions as it is rotated around the incident light beam as an axis. Fourier analysis (or least-squares fit) of this sampled signal determines the polarization parameters of incident light. The instrument is calibrated first to determine the modulation depth m
L
for linearly polarized incident light and is tested subsequently with elliptically polarized light. RODE is found to determine with reasonable accuracy the azimuth and ellipticity of such light. An important source of error is the small fluctuation of the AOI as the detector is rotated. We found that this AOI sensitivity can be greatly reduced by proper choice of the oxide-layer thickness and incidence angle. For example, with a 514.2-nm film, mL varies by ±0.1% when the AOI is changed from 73.4 to 79.0°.
Photonic band structure: observation of an energy gap for light in 3-D periodic dielectric structures
Authors: Yablonovitch E.
Published: February 2023

By analogy to electron waves in a crystal, light waves in a 3-D periodic dielectric structure should be described by band theory. Recently, the idea of photonic band structure1 has been introduced. This means that the concepts of reciprocal space, Brillouin zones, dispersion relations, Bloch wave functions, Van Hove singularities, etc. must now be applied to optical waves. If the depth of index of refraction modulation is sufficient, a photonic band gap can exist. This is an energy band in which optical modes, spontaneous emission, and zero point fluctuations are all absent. Therefore, inhibited spontaneous emission can now begin to play a role in a semiconductors and solid-state electronics. It makes sense then to speak of photonic band structure and of a photonic reciprocal space, which has a Brillouin zone ~1000 times smaller than the Brillouin zone of the electrons. If the dielectric constant is periodically modulated in all three dimensions, it is possible to have a photonic band gap which overlaps the electronic band edge and for spontaneous electron-hole recombination to be rigorously forbidden. Indeed the photonic band gap is essentially ideal since the dielectric response can be real and dissipationless. It is interesting that the most natural real space structure for the optical medium is face centered cubic (fee), which is also the most famous atomic arrangement in crystals. The comparison between electronic and photonic band structure is revealing: (a) The underlying dispersion relation for electrons is parabolic, while that for photons is linear. (b) The angular momentum of electrons is 1/2, but the scalar wave approximation is frequently made; in contrast, photons have spin 1 and the vector wave character will likely play a major role in the band structure. (c) The band theory of electrons is only an approximation due to electron-electron repulsion, while photonic band theory is essentially exact since photon interactions are negligible.
Image formation in a scanning phase-conjugate microscope
Authors: Mao Chongchang , Johnson Kristina M. , Cathey W. Thomas
Published: February 2023

Previously1 we showed that replacing the ordinary mirror in a double-pass scanning microscope with a phase-conjugate mirror had the advantages of not inverting the reflected light distribution, aberration correction, and ease of system alignment. We present a detailed analysis which shows that the phase-conjugate scanning microscope also resolves two-point and straight edge objects better than the conventional, single-pass, and double-pass microscope.
Passive one-way aberration correction using four-wave mixing
Authors: Tompkin Wayne R. , MacDonald Kenneth R. , Boyd Robert W.
Published: February 2023

We have demonstrated a passive device that removes in one pass the aberrations incurred by a light wave in propagating through a distorting medium.1 Light from the extended object of interest and a nearby reference point source pass through a thin phase aberrator located near the entrance pupil of the optical system. By imaging the aberrator into the nonlinear medium, the image-bearing and reference wavefronts at the nonlinear medium contain information about the aberrator only in identical exponential phase factors, which cancel out in the nonlinear polarization induced in the nonlinear medium. Consequently, the wave generated by this nonlinear polarization is free of the effects of the aberration and can be split off to recover the unaberrated image. This aberration-correction device is an implementation using real-time degenerate four-wave mixing of an idea advanced by Goodman et al.2 One example of an application of this method is the improvement in the quality of astronomical observations by removing some of the effects of atmospheric turbulence. A significant component of the distortion incurred by astronomical images occurs at the interface between the telescope structure itself and the surrounding atmosphere. The principal hindrance to implementing this scheme is the difficulty of nonlinear mixing of light which is weak and temporally or spatially incoherent, or both, as in the case of starlight.
Instrument matrix of the four-detector photopolarimeter: physical meaning of its rows and columns and constraints on its elements
Authors: Azzam Rasheed M. A.
Published: February 2023

The four-detector photopolarimeter (FDP) is an arrangement of four photodetectors for measuring the state of polarization of light. The output current vector I of the FDP is related to the input Stokes vector S by I = AS, where A is called the instrument matrix. The rows of A can be viewed as projection operators that determine the output currents of the detectors. This leads to the recognition of four special totally polarized input states, each of which maximizes the output of one detector. The associated four orthogonal states produce minimum signals. Because each detector is absorptive and its output is non-negative, eight inequalities must be satisfied by the elements of A. For optically isotropic detectors, one element is identically zero, and another can be made zero by an appropriate coordinate rotation.
Fourier transform spectropolarimeter
Authors: Chipman Russell A. , Chenault David B.
Published: February 2023

Experimental techniques for determining Mueller matrices as a function of wavelength are described. The properties of Mueller matrices are briefly described. Techniques of measuring Mueller matrices described by Azzam1 and Bickel and Bailey2 are used to determine completely the polarizing properties of a sample as a function of wavelength in a modified Fourier transform infrared spectrometer (FTIR). Implications of the instrumental polarization of the FTIR and the dependence on wavelength of the properties of the optical elements are discussed, in particular, the variation of retardance of the quarter waveplates and the variation of the diattenuation of the polarizers.
Squeezed states of light
Authors: Kimble H. J.
Published: February 2023

Squeezed states of the electromagnetic field are characterized by a reduction of fluctuations for one of two quadrature phase amplitudes below the level of fluctuations for the vacuum state. This reduction is a manifestly quantum or nonclassical feature which is of great interest in its own right but also potentially important for precision measurement with sensitivity beyond the shot-noise or vacuum-state limit. We describe three different experiments in which squeezed light has been generated in our laboratory involving parametric downconversion, intracavity frequency doubling, and optical bistability with two-state atoms. By employing the squeezed light produced by a subthreshold optical parametric oscillator, we have achieved improvements in sensitivity beyond the vacuum-state limit for the detection of both phase and amplitude changes of the electromagnetic field. An alternate route to sensitivity beyond the vacuum-state limit is through quantum nondemolition measurement, where we have suggested and are implementing a scheme involving parametric conversion and polarization mixing.
Amplitude squeezing of light
Authors: Giacobino E. , Fabre C. , Heidmann A. , Reynaud S. , Debuisschert T.
Published: February 2023

In the past few years several schemes have been demonstrated to generate squeezed states of light. We describe two new methods to achieve amplitude squeezing.
Design of a 16- × 16-bit digital optical multiplier using the residue number system
Authors: Heinrich Mark L. , Athale Ravindra A. , Haney Michael W. , Stirk Charles W.
Published: February 2023

The residue number system (RNS) provides two main advantages to arithmetic computation: high dynamic range problems are subdivided into several independent modules of reduced dynamic range; and the arithmetic operations of addition, subtraction, and multiplication are performed in parallel with no carries between residue digits. Thus a high-accuracy multiplication can be divided into several medium-accuracy multiplications which can all be performed in parallel. Traditionally, m × m position-coded RNS look-up tables (LUTs) exhibit a spatial complexity (defined as the number of active elements) of m2 for each modulus m, yielding a quadratic system complexity of

Σ

m
i
2

, where the summation is over all the residue digits and m, is the particular modulus.
Experimental studies of dark soliton propagation in fibers
Authors: Weiner A. M. , Heritage J. P. , Thurston R. N. , Leaird D. E. , Kirschner E. M. , Tomlinson W. J. , Hawkins Raymond J.
Published: February 2023

Solitons are intense ultrashort pulses which propagate without distortion in optical fibers. Bright solitons, which exist for negative group velocity dispersion (GVD), have been investigated extensively over the past decade. Dark solitons, which consist of a short hole superimposed on a broad background pulse and which occur for positive GVD, have been studied much less, in part due to the lack of a convenient technique for producing the required specially shaped input dark pulses. We have developed a technique for precise synthesis of femtosecond optical waveforms, and we apply this technique to investigate nonlinear propagation of femtosecond dark pulses in single-mode fibers. Our experiments utilize carefully tailored antisymmetric input pulses, which closely correspond to the form of the fundamental dark soliton. At a power level consistent with theory, the dark pulse propagates without broadening. Our measurements are in quantitative agreement with numerical solutions to the nonlinear Schrodinger equation and constitute the first clear observation of the fundamental dark soliton. At significantly higher powers, we discover a dark soliton self-frequency shift, characterized by a spectral blue shift of the output dark pulse. We show that numerical solutions to a modified NLSE which includes Raman gain are consistent with our experimental findings.
Numerical studies of high power dark optical solitons and the dark soliton self-frequency shift
Authors: Hawkins Raymond J. , Tomlinson W. J. , Weiner A. M. , Heritage J. P. , Thurston R. N. , Stolen Roger H.
Published: February 2023

We have explored the power dependence of dark optical solitons in both infinite and finite-width background pulses through numerical solutions of the nonlinear Schrodinger equation. The dark optical soliton is found to have a critical power for the formation of the high (unity) contrast fundamental soliton; at higher powers additional soliton pairs of lower contrast are generated. At all powers examined, the fundamental soliton retains its unity contrast and maintains a velocity identical to that of the background pulse. Subsequent experiments showed good agreement with these results at low and moderate powers but deviated at powers significantly higher than the soliton power. At the highest powers the fundamental soliton lost contrast and developed a velocity different from that of the background pulse. This suggested a Raman-induced self-frequency shift. The effect of stimulated Raman scattering was modeled by incorporating an experimentally determined time-dependent Raman response function into our description of the nonlinear susceptibility. Using this model we found essentially no change in dark soliton propagation at moderate power and reproduced the experimentally observed self-frequency shift and loss of contrast at high power. Further studies of dark soliton propagation influenced by Raman scattering and other higher-order nonlinear effects are discussed.
Experimental study of high-order soliton propagation in optical fibers
Authors: Cazzola L. , Cisternino F. , Roccato D.
Published: February 2023

In the context of nonlinear fiber-optic propagation, It is important to investigate the validity range of the nonlinear Schrodinger (NLS) equation for high input powers; possible applications to optical transmissions have also been foreseen In this regime.1 To this end, we experimentally studied high-order soliton propagation, which shows in a spectacular way the effect of Kerr nonlinearity; existing data2 are not completely clear above N = 3, especially regarding the optical spectrum. The pulses, 14-ps FWHM, were produced by a color center laser tuned around 1.5 µm, and launched into a 1360-m optical fiber, corresponding to about one-sixth of the soliton period. The output autocorrelation trace shows an increasing number of well-resolved peaks with the increase of the input power. Detailed features of the spectral shape, like a central dip and several lateral maxima, over a few nanometers span, are clearly resolved in the experimental data. Both autocorrelation and spectrum are in surprisingly good agreement with theory compared with previous results. Solitons until N = 8 are well identified, while for greater input powers the NLS equation seems to break; the output pulse is always a sharp peak (500 fs) with a polarization-dependent pedestal; the spectrum shifts toward lower frequencies, presumably because of the Raman effect.
Nonlinear propagation of femtosecond optical pulses in fibers: contribution from frequency-dependent mode size
Authors: Knox W. H. , Stolen Roger H. , Gordon J. P. , Tomlinson W. J. , Hawkins Raymond J.
Published: February 2023

We study nonlinear propagation of intense femtosecond pulses in a short single-mode optical fiber considering the fact that the mode size is frequency dependent. The importance of this effect has not been recognized to date. We include this effect in the nonlinear Schrodinger equation formalism by scaling the nonlinear interaction in a frequency-dependent manner. We evaluate this effect for parameters which are appropriate for compression of 40-fs input pulses to 8 fs or less1,2 and find that significant asymmetries result from this effect alone. We compare the magnitude of this correction with that of other corrections that have been investigated and find that it is one of the largest.
Observation of modulation instability induced by cross-phase modulation in optical fibers
Authors: Baldeck P. L. , Alfano R. R. , Agrawal Govind P.
Published: February 2023

Modulation instability (Ml) refers to a process in which a weak time modulation (from the noise) grows exponentially as a result of an interplay between nonlinearity and group velocity dispersion. This amplitude modulation corresponds to the generation of picosecond and femtosecond subpulses in the time domain and frequency sidelobes in the spectral domain. We report the first observation of Ml in the normal-dispersion regime. This new kind of Ml, induced by cross-phase modulation, was recently predicted.1 In this work, Ml is observed at 532 nm by propagating intense picosecond or nanosecond pulses in short lengths of a single-mode optical fiber. It has been found that sidelobes appear about the pump frequency as a result of the cross-phase modulation induced by the simultaneously generated stimulated Raman scattering pulses. Sidelobe shifts ranged from 1.5 to 8.5 nm, which corresponded to the generation of 670–120-fs time-duration subpulses. The Ml results are in good agreement with theory.
Sensitivity changes in color mechanisms
Authors: Zaidi Qasim , Hood Donald C.
Published: February 2023

Instantaneous nonlinearities of the visual system have been assessed with a flashed increment threshold technique. Brief adapting lights (flashes) elevate the threshold for simultaneously presented test lights (probes). The shape of the probe threshold vs flash intensity function changes with adaptation state, and these changes can be related to the mechanisms of adaptation.1 Here we assess adaptation processes of specific color mechanisms. We have previously (ARVO ’88) reported on nonlinearities in opponent and nonopponent color mechanisms at a constant state of adaptation. On a steady white adapting field, 50-ms probes and 500-ms flashes were varied along either an isochromatic radiance axis (light-dark), an isoluminant constant S cone axis (red-green), or an isoluminant constant L and Mcone axis (yellow-blue).
Real matrix evaluation of leaky and absorbing planar waveguides
Authors: Pillai Ramadas , Garmire Elsa
Published: February 2023

A simple method for obtaining propagation characteristics of optical waveguides of arbitrary refractive-index profile is presented. The method involves dividing the inhomogeneous profile into a suitable number of homogeneous layers of equal/unequal thicknesses and choosing real field equations appropriately to construct a real matrix eigenvalue equation, which may be readily solved. When the waveguide becomes leaky or absorbing, the propagation constant β and the eigenvalue equation become complex. However, the matrices still can be made real except for layers of complex indices. If one now writes the eigenvalue equation as F(β) = 0, a plot of 1/|F|2 gives Lorentzians peaked at a real part of β and having an HWHM equal to the imaginary part of β. The procedure is extremely simple for simple structures. One can use a computer which does not have the facility to handle complex numbers. Also, this method requires much shorter computer time compared with other methods. Owing to the general approach and simplicity, the method should find application in a variety of waveguiding problems.
Coupling of modes in on-fiber devices
Authors: Shankar P. Mohana
Published: February 2023

On-fiber devices are fabricated by removing the cladding over a short length of the multimode fiber and replacing it with an active medium like electrooptic or magnetooptic material. When a field is applied, the index of the modified cladding in this active region goes up, leading to a redistribution of modal amplitudes, which may or may not be accompanied by optical power loss due to radiation modes. Significant optical power loss occurs when the induced index charge is large, while modal redistribution of amplitudes takes place with negligible power loss when the index change is very small.
Airborne lidar system for measurements of ozone and aerosols in the Antarctic ozone hole
Authors: Browell Edward V.
Published: February 2023

The NASA Langley Research Center’s airborne differential absorption lidar (DIAL) system was operated from the NASA Ames DC-8 aircraft to obtain profiles of ozone and polar stratospheric clouds (PSCs) in the lower stratosphere during the 1987 airborne Antarctic ozone experiment (AAOE). The DIAL system simultaneously transmitted four laser wavelengths (301, 311, 622, and 1064 nm) above the DC-8 for DIAL measurements of ozone profiles and multiple wavelength aerosol backscatter measurements between 11 and 22 km ASL.
Temperature dependence of the picosecond photoconductive response of conducting polymer films
Authors: Walser Ardie D. , Seas A. , Dorsinville R. , Alfano R. R. , Tubino R.
Published: February 2023

We have investigated the temperature dependence of the fast component of the picosecond transient photoconductivity in highly oriented trans-polyacetylene films using a 30-ps pulse at 530 nm from a mode-locked YAG laser. The fast photoresponse was measured for two configurations parallel and perpendicular to the stretched direction. Only when the dc field is parallel to the stretched direction does the fast response become temperature independent. For current flow perpendicular to the stretched direction, the fast response decreased with temperature from 300 to 200 K and was constant below 200 K. The present experimental results are discussed on the basis of the existing model for the photogeneration of the charged carriers and their motion in polymeric semiconductors.
Broadband cubic phase correction with Gires-Tournois Interferometers
Authors: Li Kathryn D. , Pearson Nathaniel M. , Knox Wayne H.
Published: February 2023

Ultrashort optical pulses in the regime of 10 fs or less are very susceptible to frequency-dependent phase errors as a result of their large bandwidth. We have designed, constructed, and tested devices which provide negative quadratic group delay correction (cubic phase) in a broadband centered about 620 nm. These devices are Gires-Tournois interferometers1 which we operate exactly on the first resonance, consisting of a single high index layer of TiO2, 70.1 nm thick, on specifically selected low dispersion broadband high efficiency substrates in S polarization. We have selected two kinds of substrate for their broadband high reflectance and low frequency-dependent group delay errors: single-stack dielectrics, and thin dielectric stacks on metal films. The substrates are critical to the device operation. We measure the frequency dependence of the group delay with 1-fs accuracy using a white-light interferometric technique.2 These devices will be useful for ultrashort pulse generation, compression, and measurement applications.
Output criteria for a synchronously pumped dye laser
Authors: Bao Xiaoyi , Wu Cunkai
Published: February 2023

Because mode locking of a synchronously pumped dye laser is operated by modulating the gain, if we want to understand clearly the characteristics of the laser system, we must start from the gain medium and study the relationship of the gain medium and the operating characteristics of the laser system in optimum output conditions. As far as we know, a satisfactory discussion about this important problem for the synchronously pumped dye laser has not been given. Nor has the operating range for the gain at optimum output been obtained. This is because the circumstances of the laser system at threshold have not been studied in detail; thus the output criteria for the synchronously pumped dye laser cannot be given. The importance of this work has been realized,1–3 and some special values for determined parameters have been calculated by computer, but the expression for the gain range cannot be given. Only some special values can be evaluated.
Three-point joint density functions for intensity and phase of a monochromatic laser speckle pattern
Authors: Rao Gudimetla V. S. , Holmes J. Fred
Published: February 2023

Recently there has been a growing interest in understanding the triple correlations of fluctuating phenomena and the related bispectra in optics. In the past the triple correlations have been used in spectroscopy, 3-D laser Doppler velocimeter, and the study of intensity fluctuations of laser beams. Recently they have been found useful in the new computer architectures and in speckle interferograms in optical astronomy. Given the growing importance of the triple correlations, it would be useful if an expression could be obtained for the three-point density functions for the intensity and phase of a monochromatic laser speckle pattern. For the Gaussian speckle one can use the Reed theorem to obtain all the higher-order triple moments of the intensity (intensity only but not of phase) if the fields are complex-Gaussian, which does not require knowledge of the three-point density functions. In problems connected with optical radar and information processing, where there is a need to estimate the probability of error in SNR calculations and to evaluate the conditional density functions, the three-point density functions are needed. Keeping this in mind, the three-point density functions for the intensity and phase of a laser speckle pattern are developed.
Quantum-limited speckle correlography
Authors: Schils George F.
Published: February 2023

Focal imaging using speckle correlography can reconstruct distant objects even with very few returned photons. If the distant object is optically rough, the intensity detected in the far field will be a laser speckle pattern. As shown by idell and Fienup,1 this speckle intensity pattern can be processed to extract information about the unknown object autocorrelation function. Then the original object can be reconstructed from its autocorrelation by performing a phase retrieval.
Point diffraction interferometer with visibility adjustment
Authors: Sargent R. B. , Horowitz F. , Macleod H. A.
Published: February 2023

A point diffraction interferometer (PDI) consists of a partially transmitting film having a pinhole smaller than the central ring of the Airy disk under test. The wavefront under test is focused onto the film in the vicinity of the pinhole, and the interference between the spherical wavefront produced by the pinhole and the test wavefront is observed. The fringe contrast depends on the test beam f/No., the size of the pinhole, the transmittance of the thin film, and the location of the pinhole in the Airy ring pattern. Consequently, high-contrast fringes are only observed in particular configurations. A thin film of aluminum deposited at oblique incidence displays a polarization effect due to its columnar microstructure. Using such a film as the partially transmitting layer in a PDI, it is possible to adjust the ratio of the test and reference beam intensities using an analyzer located after the interferometer. This allows compensation for the reduction in fringe contrast resulting from a change in f/No., etc. Problems associated with the fabrication and durability of this interferometer are discussed.
Radio telescope surface measurement with a sharing Fourier transform spectrometer
Authors: Serabyn E. , Masson C. R. , Phillips T. G.
Published: February 2023

A broadband technique for measuring the surface accuracy of near millimeter wavelength radio telescopes has been developed. The near millimeter wavelength radiation from a distant astronomical point source is first focused by the telescope’s primary and secondary mirrors and then recollimated by an off-axis tertiary paraboloid for passage through a Twyman-Green interferometer. The end mirrors of the interferometer are situated so that the combination of tertiary paraboloid and beam splitter creates two identical images of the primary on their surfaces. By rotating one of the end mirrors out of its plane, the wavefronts are sheared with respect to each other, with the result that the focal plane pattern is scanned across the detector, where it interferes with the reference arm pattern. A 2-D Fourier transform of the focal plane data then yields the telescope’s aperture plane electric field. To separate the effects of different frequencies, the second end mirror is scanned. The resultant sheared interferograms, after being inverted, give the frequency dependence of the electric fields. Thus a 3-D Fourier transform of a grid of sheared interferograms simultaneously provides a measurement of the telescope surface at a number of frequencies.