bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarization multiplexing with solutions
Authors: Evangel ides S. G. , Mollenauer L. F. , Gordon J. P.
Published: February 2023

We have examined, through numerical simulations, experiment, and analytic theory, the behavior of the polarization state of a stream of solitons in a long distance, all-optical transmission system consisting of spans of dispersion shifted fiber having a small (~0.2 ps/km1/2 randomly varying birefringence and periodically spaced erbium-doped fiber amplifiers. From the theory and simulations we find that a stream of solitons, all launched into such a system in the same polarization state, will emerge with all the solitons approximately in a common, well defined, polarization state. The pulse-to-pulse deviations from this average polarization state are small, as they are determined only by the component of the amplifier ASE noise in the polarization mode orthogonal to the soliton itself. An extinction ratio of 23 dB is predicated at 10,000 km, and we have confirmed this experimentally by using a 2.5-GHz stream of 50-ps solitons in a 75-km recirculating loop. From these results it follows that solitons launched in orthogonal polarization states maintain their orthogonality as they traverse the system, as we confirm through numerical simulations.
Generation of 21-200-fs pulses by an external-cavity surface-emitting semiconductor laser
Authors: Friberg S. R. , Xiang W. H. , Watanabe K. , Machida S. , Iwamura H. , Yamamoto Y.
Published: February 2023

Mode-locking of an In0.53Ga0.47As/InP multiple quantum well laser in a surface-emitting external-cavity configuration produced ~30 ps optical pulses at 1.5 μm with average powers of 260 mW (100-MHz repetition rates) and with a broad spectral bandwidth of 20 nm. Three different compression techniques were used to reduce the width of these pulses, which initially were strongly up-chirped. The techniques were grating-pair pulse compression, negative group-velocity-dispersion (GVD) fiber pulse compression, and grating-pair compression followed by fiber compression. Grating-pair compression alone eliminated most of the chirp, reducing the pulse widths to as low as 153 fs. Then, average powers were 55mW, peak powers were >3.6 kW, and the time–bandwidth product ΔνΔt was reduced from 86 to a Fourier-transform limited valued of 0.38. Fiber compression alone, using a 400-m negative GVD fiber, reduced pulse widths to 79 fs. At the beginning of the fiber, propagation removed the chirp. Further down the fiber, pulse intensities increased and soliton-effect compression further shortened the pulse. Grating-pair compression followed by fiber compression (using the 400-m fiber) produced the shortest pulses, as small as 21 fs.
Noise of mode-locked lasers
Authors: Mecozzi A. , Haus H. A. , Lai Y.
Published: February 2023

In recent years, many solid-state lasers have been mode-locked successfully, using the additive pulse mode-locking (APM) principle. It has been shown that, under appropriate approximations, the theory of APM is congruent with that of saturable absorber mode-locking, supplemented by self-phase modulation and group velocity dispersion. When the shortest pulses are achieved, the pulses behave like transform-limited solitons, perturbed by the gain-bandwidth limiting and the APM action. In this limit, a perturbation theory is feasible that is closely related to that of soliton perturbation theory. Noise is handled by perturbation theory; an adiabatic perturbation of the pulse changes its amplitude, phase, carrier frequency and timing. Contrary to soliton perturbations, amplitude and frequency perturbations of mode-locked solitary pulses do not persist but shed some of their energy into the continuum. This is a consequence of the gain saturation and gain-bandwidth limitation not encountered with solitons (nonlinear Schrodinger equation). The timing experiences a random walk, and so does the phase. The latter leads to a Lorentzian line-shape of the resonant cavity modes, similar to that of a free-running oscillator. The spectrum of the amplitude and frequency are Lorentzian because both have nonzero relaxation times. The frequency relaxes to the center frequency of the gain, the amplitude to the value required to equate gain to loss.
Efficient second-harmonic generation in Eu2+-doped aluminosilicate optical fibers
Authors: Driscoll T. J. , Lawandy N. M. , Morse T. F. , Kilian A. , Reinhart L.
Published: February 2023

Since the discovery of second-harmonic generation (SHG) in germanosilicate optical fibers only two other glass materials have exhibited efficient SHG and only one other fiber system. Semiconductor microcrystallite-doped glasses produced optically encoded SHG in bulk and in ion exchanged waveguides while Ce3+-doped aluminosilicate glass produced SHG in optical fibers. The discovery of new glasses is of paramount importance to understanding this problem and to the possibility of a unified understanding of the effect in the various materials. We have recently discovered that silica fibers with Eu2+-doped (200 ppm) aluminosilicate (3 wt.%) core can be prepared for SHG using a cw model-locked (76-MHz) laser operating at 1.06 μm. Fibers with 11.5-μm core diameter were prepared by simultaneous exposure to average intrafiber powers of 8 W and 30 W at 1.06 μm and 532 nm, respectively. The fiber was prepared by launching into the LP01 mode for both fields. The prepared fiber exhibited an ultrastable (<5%) output at 532 nm with a conversion efficiency of 1.5 × 10-4 with 8 W of IR average readout power. Of particular interest is that a sharp IR preparation intensity behavior is observed at around the same value found in germanosilicate glasses (~1 GW/cm2). Finally, the fiber could be erased over periods of minutes using 488-nm light from an argon-ion laser.
Rare earth-doped glassed for fiber amplifiers
Authors: Miniscalco William J.
Published: February 2023

Work on rare earth-doped fiber lasers and amplifiers has focused on silica and fluorozirconate glasses primarily because fiber synthesis techniques are better developed for these compositions. Because pure silica is a poor host for rare earth ions the use of codopants is critical to controlling device properties. The addition of A12O3 significantly increases the solubility of rare earths, preventing clustering and its associated inefficiency. Al2O3-codoping also substantially increases the gain bandwith of silica Er3+-doped fiber amplifiers (EDFAs) by providing a broad emission spectrum more typical of a fluoride of fluorophosphate glass. For Er3+-doped silica, cross sections at 1500 nm are sensitive to codopants primarily through changes in the shape of the absorption and emission bands. While codopants can enhance the efficiency of EDFAs pumped at 800 nm, significant improvement can only be obtained by going to other glasses such as fluorophosphates. Composition has less influence on performance when exciting at 980 or 1480 nm, the latter pump band suffering from an inherent noise penalty of 1-2 dB. The strong 1060-nm transition of Nd3+ has a lower small-signal gain efficiency than ER3+, regardless of host. The weaker 1300-nm transition suffers additionally from excited state absorption, a process that is sensitive to composition.
Optoelectronic connectionist machines
Authors: Zhang L. , Johnson K. M.
Published: February 2023

The optoelectronic connectionist machine (OCM) presented in this paper consists of three primary components: a 1 × 256 electrically addressed, SmA ferroelectric liquid crystal (FLC) modulator, which represents the input neurons, a 2-D, optically addressed spatial light modulator (OASLM), which is used to encode and modify the connections between input and output units, and a CCD camera that differentially detects the bipolar connections and inputs the resultant output vector to the controlling IBM PC via a data translation board. The input patterns are amplitude encoded on 100 μm × 25.4-mm FLC pixels in the input array. The synaptic weights are displayed on a computer driven cathode ray tube (CRT) and written onto the reflection-mode OASLM. The Litton CRT contains (640 × 480) 30-μm pixels in a 1-in. screen. Each pixel has a maximum of sixty-four gray levels. The OASLM has a resolution of 70 lp/mm at 50% MTF. The OCM was designed to interconnect 256 input units to 256 output units at megahertz rates using the high speed, electroclinic FLC input SLM.
How much does illuminant color affect unasserted colors?
Authors: Arend Lawrence E.
Published: February 2023

After adapting to a new illumination, does the light coming from a surface (as opposed to the surface color) appear the same as before the illumination changed? Many answers have been proposed over the past century but all have been unsatisfactory. The hardest measurement problem is to provide a comparison stimulus that is unaffected by the adaptation being tested. My subjects used a mental standard. Under 4000K, 6500K, and 10000K adaptation (the extremes and average of daylight) they produced on a CRT unique hues with a constant saturation (memorized during training). The hardest evaluation problem is how to determine theoretical invariant chromaticity shifts for comparison with the data. Like most previous investigators, I used light sources rather than actual surfaces and illuminants. Using a new technique I determined the chromaticities that surfaces would have under the test illuminants. Using Cohen’s basis vectors, I derived theoretical reflectances that under 6500K would produce the chromaticities that the subject chose as unique hues. The chromaticities of those same reflectances under 4000K and 10000K are theoretical points representing invariant appearance of the light coming from the surfaces. Even for this small range of illuminants there were systematic departures from invariance.
Quantum diffusion in soliton position measurements
Authors: Drummond P.D. , Yamamoto Y.
Published: February 2023

The usual view of a soliton in an optical fiber is that it obeys the classical Maxwell equations, and propagates unchanged down a lossless fiber. Of course, it is well known that an optical amplifier introduces noise in position. It is less well known that even a perfectly lossless fiber, without an amplifier, is unable to support the classical invariant solution. Instead, all solitons experience quantum noise in position and phase, and this noise increases with propagation distance. Experimenters at IBM laboratories have recently observed the first quantum effects in solitons. These experiments focussed on quadrature squeezing, and were able to detect the large increase in phase-quadrature noise that is predicted quantum-mechanically. In this paper we treat the effects of pulse-position noise, and indicate how this noise source can limit information transmission using solitons. While these effects are small in currently proposed communication systems, they place a fundamental limit on future enhancements of soliton communications using pulse-position modulation. Of most scientific interest is the macroscopic nature of the quantum fluctuations, which can alter the location of a huge number of cooperatively positioned photons, and possible implications for QND momentum measurements.
Backscattering from perturbed gratings of gaussian grooves
Authors: Knotts M.E. , O'Donnell K.A.
Published: February 2023

We present new experimental studies of the far-field scattering patterns produced by perturbed diffraction gratings consisting of equally spaced, gaussian-shaped grooves with randomly fluctuating depths. These surfaces, which have been fabricated in photoresist using a computer-controlled scanning apparatus, exhibit backscattering enhancement similar to that seen in light scattering from random surfaces with gaussian statistics. Through a series of measurements conducted on similar gratings with differing perturbation strengths, we probe the transition from the perturbed case (fluctuating groove depths) to the fully deterministic case (uniform groove depths). Since the polarization dependence of rough surfaces exhibiting backscattering enhancement is non-trivial and apparently related to multiple scattering, we also carefully investigate the polarization properties of these surfaces. Finally, we show how the power in various diffraction orders, for light scattered from a perfectly uniform grating of gaussian-shaped grooves, oscillates as the angle of incidence is changed — an interesting behavior that we believe is related to multiple scattering within the grooves.
Large Second-Order Nonlinearity in Poled Fused Silica*
Authors: Myers R. A. , Muhkerjee N. , Brueck S. R. J.
Published: February 2023

We report the first observation of a permanent second-order nonlinearity in the near surface region of commercially available bulk fused SiO2 induced by a combined temperature / static electric field poling process. The observed χ(2) is three to four orders of magnitude larger than found in fiber experiments and approaches that of LiNbO3. The preparation process for generating the χ(2) nonlinearity involves heating to 250-325°C, in laboratory ambient, while applying a DC bias of 3-5 kV across the nominally 1.6-mm thick samples. After approximately 15 minutes the sample is allowed to cool with the bias still applied. Once cooled, a permanent nonlinearity is observed without any bias by second- harmonic generation (SHG) experiments. The nonlinearity can be erased by heating alone and reestablished by repeating the poling procedure. Poled samples kept at room temperature for almost a year without any special precautions show no noticeable degradation of the nonlinearity. The depth profile of the nonlinearity, probed with a chemical etching process, was found to be exponential with a characteristic decay length of a few μm's. The χ(2) coefficient, measured by comparing the SHG power generated in LiNbO3, was χ(2)33 ≈ 1x10-12 m/V. Additional measurements suggest that the nonlinearity is associated with a strong electric field frozen into the near surface region of the SiO2 by electrons in deep traps associated with impurities and by charge transport of mobile ions such as Na+ under the applied field. Because of the ready manufacturability of silica and its established integration with semiconductor electronics and optoelectronics, this nonlinearity will have important applications.
Generation of 150 femtosecond tunable pulses in Cr:LiSrAlF6 and Cr:LiSrCaAlF6
Authors: Chai Bruce H T , LiKamWa Patrick , Wang Hai-Sheng , Miller Alan
Published: February 2023

In this talk, we present the first demonstration of cw mode-locked operation of wavelength tunable Cr3+ doped LiSrAlF6 (Cr:LiSAF) and LiSr0.8Ca0.2AlF6 (Cr:LiSCAF). The Czochralski grown crystals, with a nominal chromium concentration of 2% in the melt, were Brewster cut and polished to 15mm lengths and mounted in a four mirror X-fold cavity. Cr:LiSAF1 and Cr:LiSCAF2 crystals showed similar cw and mode-locked performance. Pumping with a cw krypton laser (Laser Ionics) gave a threshold power of 210mW using the red doublet. The output power peaked at around 300mW with 1.5W input. The tuning range was 800 to 900nm using a birefringent filter, limited by the mirror bandwidths. To achieve mode-locked operation, a NEOS high-Q, acousto-optic modulator with broadband anti-reflection coatings centered at 800nm was used. An intracavity two prism sequence was inserted to compensate for group velocity dispersion. A stable, 82MHz mode- locked train was achieved with 1W of krypton pump. When fully optimized, intensity and interferometric autocorrelation and pulse bandwidth measurements confirmed chirp-free pulses of 150fsec duration. Tuning across the 800 to 900nm range was achieved using an intracavity slit. It is likely that self-phase modulation assists the spectral broadening and pulse shortening. The pump wavelength, lack of concentration quenching for the chromium doping and the low threshold makes these crystals good candidates for diode and flashlamp pumped ultrashort pulse sources.
Femtosecond Pulse Shaping Using Large Bandwidth, 20 fs Optical Pulses
Authors: Reitze D.H. , Weiner A.M. , Leaird D.E.
Published: February 2023

The synthesis of arbitrarily shaped femtosecond pulses with 100 fs features is traditionally accomplished by linear spectral filtering in a nondispersive grating/lens system in which a spatial mask modifies the amplitudes and/or phases of spatially dispersed frequency components.1 However, the shaping of shorter pulses with significantly greater bandwidth is compromised by the presence of the lenses, which distort the pulses transmitted through the shaper by adding substantial cubic phase dispersion. Here we report on the extension of the pulse shaping technique to pulses 20 fs in duration and demonstrate shaped femtosecond pulses with 20 fs features using a modified shaping apparatus. For input pulses, we use 0.5 μJ, 20 fs pulses compressed using a novel pulse compression technique which utilizes the self-trapping of bright, two-dimensional spatial solitons in bulk nonlinear media.2 The shaping apparatus consists of a pair of gratings placed at the outside focal planes a unit magnification, confocal pair of concave mirrors, which replace the achromatic lenses traditionally used in pulse shapers.1 As an example, we demonstrate 10THz repetition rate pulse trains produced using phase-only filtering.
Implementation of a Smart Pixel With an Integrated DOES Technology
Authors: Kiely P. , Taylor G. , Doctor D. , Claisse P. , Vang T. , Evaldsson P. , Sargond S. , Daryanani S. , Cool P. , Tel B.
Published: February 2023

A new smart pixel technology is demonstrated using the DOES device technology. The pixel performs the optical or electrical inversion function and is configured to be extendible to any complexity of electronic logic. The circuit uses the DOES for the optical output emission and the electronic output in its three terminal configuration. The third termina is controlled by the output current of an HFET/BICFET photodetector providing excellent optical and electrical I/O isolation. The pixel incorporates two HFETs as load devices for the DOES and the detector.
A Novel Ultra-Fast Polarimeter for use in Optical Fibre Systems
Authors: Siddiqui A. S.
Published: February 2023

We have developed a new type of , fully automated and personal computer (PC) controlled, polarimeter for use in optical fibre systems. The instrument is small, robust and easy to use and will play an important role in future polarisation-related work in the areas of active and passive optical and optoelectronic components, optical fibre communication systems and optical fibre sensors. The optical signal under investigation is coupled into the polarimeter through a standard optical fibre connector and the instrument can then be operated, as desired, in one of the following three measurement modes.
Why is there a set-size effect in visual search set?
Authors: Palmer John , Ames Cynthia T.
Published: February 2023

In visual search, a set-size effect may be due to an attentional effect on perception or to several alternative effects. One alternative is a sensory effect such as masking and another is that attention may affect decision instead of perception. In simple search tasks such as detecting a long line among short lines, we have previously found the modest set-size effect predicted by an attentional effect on only decision. There was no evidence for any additional effect of attention on perception. To pursue this result, we investigated more complex search tasks that have been claimed to have larger attentional effects. They included tasks that required memory, tasks that used discrimination rather than detection, and tasks that used complex rather than simple shapes. Several of these tasks did yield larger set-size effects. The critical question is whether these larger set-size effects were due to an attentional effect on perception or due to one of the other possible causes.
Ultrafast measurement of the thermal expansion of a GaAs surface
Authors: Pennington D. M. , Harris C. B.
Published: February 2023

We report the use of the transient grating method to time resolve the ultrafast thermal expansion of a surface. Measurements are performed on p-type GaAs (100) in the reflection grating geometry. By utilizing a 100-fs ultraviolet probe with visible excitation beams, the effects of interband saturation and carrier dynamics become negligible; thus lattice expansion from heating and subsequent contraction caused by cooling provide the dominant influence on the probe. The signal observed has a 22-ps rising edge due to thermal expansion and a 280-ps decay from heat propagation away from the heated region. The diffracted signal is composed of two components, heat conduction into the bulk perpendicular to the surface and heat flow parallel to the surface that fills in the nulls of the transient grating. By varying the fringe spacing of the grating it should be possible to separate the signal contributions to the expansion and contraction of the lattice. In this case, the dominant contribution to the rising edge appears to be the expansion perpendicular to the surface, while the conduction of heat away from the region has contributions from both components.
Time-resolved studies of chemical reactions in clusters
Authors: Syage Jack A.
Published: February 2023

Excited-state proton transfer (ESPT) rates in molecular clusters were measured as a function of cluster size using picosecond spectroscopy in a molecular beam mass spectrometer. ESPT from the S1 state of phenol to basic solvent clusters (NH3)n occurs for a critical solvent cluster size n ≥5 with a rate constant of k= (60 ± 10 ps)-1 for n = 5−7. ESPT showing critical cluster-size dependencies was also observed in the basic solvent N(CH3)3 (n ≃ 3). Proton transfer was not observed in the less basic solvent clusters (CH3OH)
n
and (H2O)
n
. Mixed solvent studies indicate that the addition of a dissimilar molecule to an otherwise neat solvent cluster impedes ESPT presumably due to a disruption of the hydrogen bonding network.
Semiconductor laser with a phase-conjugate external cavity
Authors: Liby B. , Statman D. , McIver J. K.
Published: February 2023

Although laser diode-pumped ring passive phase-conjugate mirrors (PPCM) have been studied before, not much interest has been paid to the system formed by a semiconductor laser with a phase-conjugate external activity. To this end we have been investigating the properties of just such a coupled cavity. Here we present the results of our beam quality measurements. In our experiment we use a ring PPCM that includes an optical isolator to make it unidirectional. This gives it the characteristics of a double phase-conjugate mirror (DPCM). It is coupled by a variable attenuator to a Hitachi HLP-1400 laser diode. Because of the slow response time of the nonlinear medium (barium titanate) the PPCM can act as either a phase conjugator or a dynamic hologram depending on the time scale chosen for the experiment. We investigate both cases and compare the results to a conventional external cavity. We find the beam quality of the ring PPCM to be rather poor. The rise time of the fidelity is slower than that of the phase-conjugate reflectivity. External cavity modes of the system are measured as well. We observe nonphase-conjugate spots directed back to the laser.
Quasiphase-matching waveguides in lithium niobate and lithium tantalate: a comparison
Authors: Arvidsson Gunnar , Ahlfeldt Henrik , Webjorn Jonas
Published: February 2023

Recently there has been a great interest in quasiphase-matching (QPM) waveguides for frequency conversion. Such waveguides have been fabricated in lithium niobate, lithium tantalate, KTP, and organic materials. In LiNbO3 and LiTaO3 a number of different fabrication techniques have been employed to obtain the required periodic reversal of the ferroelectric domain orientation. We have demonstrated generation of blue light by frequency doubling in QPM waveguides, fabricated in LiNbO3 as well as in LiTaO3. In the latter case, domain inversion was obtained by proton exchange in combination with a heat treatment. We now report on a comparison, based on simulations and experiments, between these two types of QPM waveguide. For the LiTaO3 the domain inverted regions show an approximately semicircular cross-section, compared with a more triangularly shaped cross-section in LiNbO3 more promising for a high conversion efficiency. In particular it should be more easy in LiTaO3 to come close to the theoretical limit when using third-order quasiphase matching. To utilize the possibility of a more efficient interaction by going to first-order QPM, it is, however, critically important to obtain a very tight mode confinement. It is also concluded that the duty cycle is an essential parameter to optimize.
Use of deformable mirror devices in optical logic functions
Authors: Hoq Mohammed E. , Krile Thomas F. , Walkup John F.
Published: February 2023

Weighted-outer-product processing, a generalization of the bilinear transform, plays an important role in many computing, signal processing, and image processing applications. A technique for the implementation of optical logic functions, the use of such a processor, is presented in this paper. Texas Instruments’ deformable mirror device (DMD), a 1-D spatial light modulator, allows real-time operation of such a logic function implementation by providing controllable optical encoding of the two input vectors that are required for the outer product. Using liquid crystal television and magnetooptic spatial light modulators as weighing matrices is also presented.
Bloch vector model of Raman coupled system
Authors: Gerry Christopher C.
Published: February 2023

I study the coherent interaction of a three-level atom in the lambda configuration with pump, Stoke, and anti-Stokes laser fields. The pump laser field drives transitions from the two non-degenerate lower levels to the excited state which is highly detuned for either transition. This excited state is also coupled to each of the lower states by Stokes or anti-Stokes transitions so that this system may represent a model of four-wave mixing. Assuming large detunings, the excited state is adiabatically eliminated from obtaining an effective two-level system with Raman coupling between the levels. Optical Bloch equations are obtained for this effective two-level system, and phenomenological damping terms are added for collisional dephasing of the Raman transitions. The equations are solved for the steady-state as well as by the method of adiabatic following. From these solutions we obtain the polarization.
Optical bistability in semiconductor CdHgTe etalon
Authors: Shi Qiuhu , Yang Ya-wen
Published: February 2023

We have observed bistability of the n-type Cd
x
Hg1−
x
Te in Auger-dominated in the following conditions: the input probe beam, obtained by splitting the CO2 laser with a ZnSe splitter, was incident upon the CdHgTe detector 1. The output probe beam, passing through the Fabry-Perot etalon, was detected by the CdHgTe detector 2. All beams were chopped using a mechanical chopper with a tunable mark/space ratio between 20:1 at a high speed synchronous motor. The signals of the incident and transmission intensity synchronously detected by using the CdHgTe detectors at 77 K were displayed on an oscilloscope. Our specimen was n-type Cd
x
Hg1−
x
Te (x = 0.225) at 77 K, the intrinsic carrier concentration n = 9.8 × 1014 cm-3, the mobility μ = 3.15 × 104 (cm2/V sec). The absorption coefficient α = 72 cm was polished plane parallel to form an etalon 215 μm thick, the reflectivities of which are R
F =
R
B
= R = 32%. In our experiment, the incident intensity I is 750 W/cm2 and both the laser mode and power stability met the standards.
Dual crossed Fourier transform spectrometer
Authors: Berlinghieri Joel C. , Hilleke R. O. , Rembiesa P. J.
Published: February 2023

A Fourier transform spectrometer has been built using dual, common path, orthogonal, ring interferometers and 2-D CCD array as detector. A channelled Fourier-Fraunhofer hologram is produced from the sheared images of the source. The advantages of the use of a single Sagnac interferometer have been previously published1 and results reported.2 The problem of aliasing associated with obtaining higher resolution spectra over a large spectral range has been addressed without the need for narrow band filters. The use of an orthagonally oriented, second ring interferometer sorts the normally overlapping orders formed when the interference pattern is undersampled. Results of the measurement of optical spectra will be shown.
Inter-LAN WDM single-fiber bridge for multimedia communication
Authors: Sun Zongjian , Jannson Tomasz , Ingold Joe , Oleksa Joe
Published: February 2023

We propose a novel inter-Lan communication architecture based on multi-mode fiber optics and wavelength division multiplexers (WDMs), in the form of an inter-Lan WDM single-fiber bridge for multi-media communication. The new passive fiber optic system consists of a pair of multi-mode WDMs connected through (1–10 km) multi-mode (62.5/125 µm) single fiber with multiwavelength (3–6) multi-longitudinal mode (MLM) and single-longitudinal mode (SLM) laser diodes (LDs), and avalanche photodiode (APD) receivers. It has been demonstrated that the speed of the MLM-LD 780 nm channel is limited only by the fiber’s multi-mode dispersion (~500 MHz • 1 km). Thus, it can be used for RGB-video transmission. For example, while the SLM-LD channels (750 nm, 810 nm, 840 nm) are used for voice, computer data, and sensor-reporting systems, respectively, because of the APD receivers, the power margin is extended by at least 10 dB. This provides a higher bandwidth and longer distance communication than currently available fiber optic multi-mode links. In this communication, we present experimental results demonstrating transmission capabilities of the WDM system. An inter-Lan medium distance (1–10 km) WDM (wavelength division multiplexing) multimode (62.5/125 µm) (RGB-video, voice, computer-data. sensor-data) single-fiber bridge multimedia communication system is presented.
Internal management of video tape projects
Authors: Zavislan Jeanette D.
Published: February 2023

If you’re convinced that a video tape is the right medium for your project, here’s help to get you started and keep you on track. Video tape production requires a project manager and a few technical specialists. Their tasks will be described and explained so you can accomplish the project’s objectives, stay on schedule, stay within your budget, and maintain your sanity. You can have fun too if you understand the critical tasks and consider contingencies during the planning phase. Topics we’ll discuss include: contracting a vendor; determining the tape’s goals, objectives, and the target audience; supervising the script development; keeping within the budget; tracking the schedule; getting approvals; shooting the scenes; overseeing the off-line and on-line edits; taping the voice over; planning distribution; and lastly, determining the effectiveness of the tape and performing a post-mortem to determine how to improve your next video tape.
Surface corrected for spherical aberration for all conjugates
Authors: Shafer David
Published: February 2023

The Herschel condition is the axial counterpart to the sine condition; its satisfaction guarantees that spherical aberration not change for small axial displacements of the object. The more general case would be a system that is corrected for spherical aberration for all conjugate distances. Wynne has shown that four separate conditions must be met for this to be possible. For an optical system of thin elements in contact, one of the conditions requires a certain amount of Petzval curvature—a surprising result with no obvious relationship to the imaging of axial points. This turns out to be difficult to achieve in a thin system except in a catadioptric design. Then the Petzval curvature and the net power can be controlled completely independently. The simplest conventional-type example of a system with correction for third-order spherical aberration for all conjugates is a particular single element aspheric Mangin mirror. More exotic, but simpler still, is a single reflective surface with a binary optics diffractive overlay. This is discussed, as well as one application—its use in a zoom laser beam expander.
Spectral absorption of water
Authors: Sogandares Frank M. , Qi ZhangFen , Fry Edward S.
Published: February 2023

We have measured the spectral absorption of water from 340-640 nm using a laser photothermal technique. Transmissive techniques have generally been used to measure the spectral absorption of water but such measurements require corrections for scattering. Because of the inherent freedom from these effects, photothermal spectroscopy is ideally suited to this problem. In the past, many absorption meters have been calibrated at only one wavelength; our photothermal absorption meter has been calibrated at every measurement wavelength (every 10 nm). The measurements made in this study indicate that the absorption of water in the blue and violet spectral regions is lower than previously thought.
New method for improving output power stability of a laser: the laser cavity using an optical bistable element
Authors: Li Shenping
Published: February 2023

We put forward a new scheme for improving the output power stability of a laser. The basic idea is to replace one of the laser mirrors with an optical bistable element. The cases of operation with absorptive, dispersive, and hybrid elements are investigated. The conditions for operating the lasers working at the steady state are drawn up. Computer simulations on the stabilization effect of the laser cavity for the output power of lasers are shown, and static stabilities of the lasers for three cases are calculated. As an output power stabilized laser, the lasers using absorptive and dispersive bistable elements have potential uses in optics communications and integrated optics. Because the nonlinear medium is not used in the hybrid bistable element, this method is useful for stabilizing the high output power lasers, such as Nd:YAG, CO2, and Ar+ lasers.
Facial recognition using image and transform representations
Authors: Wang Shen-ge , George Nicholas
Published: February 2023

Automatic recognition of faces is now a reality. In our experiments we seek to establish bounds on the information content required as a function of the configuration of the machine. In general with the direct image, excellent recognition is obtained for information capacity below Harmon’s (1973) benchmark value of 500. Our main data base is gathered from twenty-five people consisting of three views (front, 30° turn, 60° turn) and ten separate exposures for each view. Typically, these are grouped into a learning set of five and a testing set of five. In the first series of experiments, an optical Fourier transform configuration is used which includes a ring-wedge photodetector interface together with neural network software. Good recognition is obtained, and we report on the training using front and side views. In the second series of experiments, frame-grabbed images are used, again with the neural network software. Tests are made of the information capacity required as a function of the image coding. Comparative error rates are presented for recognition in the following cases: with 256 grey levels or using global binarization or using an error-diffusion halftoning algorithm. Particularly good results are obtained from the error-diffusion form of the imagery.
Rotation invariant pattern recognition in the presence of signal-dependent noise
Authors: Terrillon Jean-Christophe , Arsenault Henri H.
Published: February 2023

We show that image restoration used as a preprocessing tool improves rotation invariant pattern recognition. The effects of signal-dependent random noise on rotation invariant pattern recognition were investigated. Computer simulations were performed on 10,000 noisy realizations of each member of a set of binary and grey level images using circular harmonic, phase-only circular harmonic, and binary phase-only circular harmonic filters. A significant number of false detections have been observed in the correlation plane, thus establishing the filters as less robust with respect to noise than the corresponding non rotation invariant matched filters.1 The noisy images giving rise to false detections were restored by locally adaptive filters. We show that, as a result, false detections were eliminated.
Adaptive pattern recognition for binary images
Authors: Lu Jianyi , Lin T. William
Published: February 2023

It is understood that the correlation process between similar patterns generally introduces ambiguity in decision making. This problem is much more profound in the binary pattern recognition process. For example, the cross-correlation between letters E and F exhibits the same main peak intensity as that in the autocorrelation of letter F. Many attempts have been made to overcome this difficulty, including the recognition technique based on a comparison of pattern’s perimeters, and the recognition of patterns in moment spaces or feature spaces. However, the phenomenon that causes the ambiguity can be converted and utilized as a feedback parameter when an adaptive process scheme is chosen in pattern recognition. In this paper, the relationship between pattern shapes and correlation results is analyzed first, followed by a proposed hybrid optical-electronic adaptive joint transform correlator. The adaptive capability of the system is achieved through interfacing between an optical correlator and a computer. The intensity distribution of correlation peaks detected in the optical correlator serves as a feedback to update reference images in the input plane of the correlator, so that an optimal decision can be made for the recognition process through adaptive iterations. In the iteration process, the saturating phenomenon in the intensity of correlation peaks is used as a guideline in designing a proper feedback scheme. Several uses in binary pattern recognition are demonstrated with results obtained from computer simulations as well as experimentally.
Advances in laser diode arrays
Authors: Endriz J.
Published: February 2023

In recent years, pulsed and cw laser diode arrays in the form of 1-cm (nominal) bars or 2-D arrays of such bars have been successfully used in numerous diode pumped solid-state laser applications or related nonpumping applications. As a result, such bars are now viewed as readily available, reliable, and affordable.
Integrating a machine vision system for cosmetic inspection of optical parts
Authors: Fantone Stephen D.
Published: February 2023

A multistation inspection center has been built that performs cosmetic inspection of small lenses. The system design considerations and tradeoffs involved in constructing the system are discussed. Included are such issues as central vs distributed image processing, speed, and cost. Of particular importance are issues of defining and characterizing cosmetic defects on a machine vision system that correlates with visual grading. A distributed processing system with a central controller was developed. It provides characterization of nine different defects including scratches, pits, haze, dimples, and several other defects relating to the method of manufacture.
Nonlinear dynamics of optical waveguide arrays
Authors: Finlayson N. , DeLong K. W.
Published: February 2023

We have studied the nonlinear dynamical properties of 2,3, and 5 element optical waveguide arrays in both short and long propagation range limits. At least in principle, these arrays have the potential for demonstrating chaotic behavior in an environment that can be well controlled, i.e., the number of interacting modes can be selected. As such the arrays represent possible testing grounds for the evolution of nonlinear dynamics from few oscillator motions to the continuum limit. The dynamics are characterized by spectra-power diagrams, Lyapunov curves, and Poincare maps. Nearest neighbor couplings between elements are assumed. In the short range limit these waveguide arrays yield sharp all-optical switching features and large differential gain. In the long propagation range limit, the arrays exhibit a rich variety of nonlinear dynamic features ranging from spatio–temporal solitons to chaos. In some conditions chaos can manifest itself at arbitrarily low power. Regular stochastic transitions are ubiquitous in the system.
Reflective optical baffle concept
Authors: Foo Leslie D. , Stavroudis Orestes N.
Published: February 2023

In the past the optical baffle usually consisted of a cylindrical tube assembly with a black interior vane structure to create a highly absorptive labyrinth to trap and absorb light before it propagated further into the optical system. This type of baffle is well developed and is suitable for a myriad of optical system uses. However, in certain stressing environments or conditions, the black baffle degrades and may fail to absorb a sufficient amount of stray light. To address these conditions, an approach to optical baffle design based on reflection rather than absorption has been developed. Although similar reflective baffle structures have been studied and developed, this new approach utilizes all reflective confocal conic surfaces to reject incident specular energy. Total specular rejection of incident energy is achieved by using a combination of vane surfaces described as oblate spheroids and hyperboloids of one sheet which have common foci at the entrance aperture of the baffle assembly. When surfaces are arrayed in this manner to create a series of baffle vanes, light incident on the vanes is reflected by these surfaces back out of the assembly through the entrance aperture with no specular propagation further into the baffle assembly.
Design of a nonpolarizing beam splitter inside a glass cube
Authors: Gilo Mordechai
Published: February 2023

The reflectance and transmittance of dielectric thin films at oblique angles of incidence have strong polarization effects. For some uses these effects are undesirable. In this paper a nonpolarizing beamsplitter design concept is shown, based on the fact that in a quarterwave stack at λo, two effective indices that obey the Brewster condition for the p-state affect only the spectral performance of the s-state at λo. When added to a quarterwave stack with a certain p-state transmittance, these layers can change the s-state transmittance to almost any desired value without affecting the p-state. This concept can be applied to a wide range of angles and transmittance values, using effective quarterwave layers of at lease three different materials.
Using the power spectrum of a rough thin film surface to determine whether its statistics are Gaussian or exponential
Authors: Varnier Francoise , RaSigni Georges , Llebaria Antoine
Published: February 2023

The method we have been developing for many years to reconstruct the profiles of statistically rough surfaces (based on a microdensitometer analysis of electron micrographs of shadowed surface replicas) makes it possible both to know the profile along many lines and to judge the quality of the reconstruction. This method proved to be particularly appropriate for microroughness studies. It is then possible to compute the autocovariance function and the power spectrum, which quantitatively characterize the surface. An analytical fit of the power spectrum is easy to obtain, especially in the high spatial frequencies range. This fit in turn allows us to determine accurately the Gaussian or exponential shape of the autocovariance function. Such a study was carried out on an extensive set of real microrough surfaces (ranging from rolling to ragged structures and from metallic to dielectric films). Parameters such as noise characteristics and level or sampling distance compared with autocovariance length and surface features’ sizes were carefully investigated. Hence, it is possible to answer the question: Gaussian or exponential autocovariance function? and to explain the discrepancies between results obtained with various methods (replica method, optical methods, profilometry…).
Scattering of light by a coated component depends on the direction of illumination
Authors: Apfel Joseph H.
Published: February 2023

Scattering of light by optical components is usually deleterious to the overall performance of an optical system. The scattered light, besides being absent from the geometric image, appears where it is not expected in the form of ghosts, flare, veiling glare, etc. The scattering by surfaces, including coated surfaces, is a function of direction of illumination. The performance of an optical system may be optimized by the proper orientation of filters and by placing an optical coating on the preferred surface of a component. The overall scattering by two parallel surfaces may be predicted with equations that account for the multiple reflections at the surfaces.
Self-calibration technique for determination of the spectral responsivity of semiconductor photodiodes in the soft x-ray range
Authors: Krumrey M. , Tegeler E.
Published: February 2023

In the VUV and soft x-ray region photoelectron yield data are frequently used to estimate absolute photon fluxes. Calibrated photoemissive diodes are not available for the photon energy range above 250 eV. In the visible uncertainties as low as 0.1% have been achieved with semiconductor photodiodes, for which the responsivity can be calculated from a few basic parameters of the diode, using the so-called self-calibration technique. Since stable photodiodes for the soft x-ray range are now available, a similar technique can be used also in this spectral range. The thicknesses of surface dead-layers and depletion layer as well as the diffusion length are determined by fitting the measured angular dependence of the photocurrent according to a model using absorption coefficients from the literature. For the absolute responsivity the mean energy for electron-hole pair creation is determined with the known photon flux of the electron storage ring BESSY. Total uncertainties of 4% for the spectral responsivity in the photon energy region 90 eV–4 keV are achieved. The result of our calibration is compared to conventional calibration techniques as well as to measurements with an electrically calibrated cryogenic bolometer.
Possible use of undulator radiation in VUV and soft x-ray radiometry
Authors: Kincaid Brian M.
Published: February 2023

A new generation of synchrotron radiation light sources covering the VUV, soft x-ray and hard x-ray spectral regions is under construction in several countries. They are designed specifically to use periodic magnetic undulators and low emittance electron or positron beams to produce high brightness near-diffraction-limited synchrotron radiation beams. Although they have been designed to maximize source brightness and flux, it may be possible to use specially designed undulators and wigglers in the new light sources for radiometry in the VUV and soft x-ray regions. Some of the novel features of the new sources are discussed, with emphasis on the Advanced Light Source, a third generation 1.5-GeV storage ring optimized for undulator use. A brief introduction to the physics of undulator radiation is presented. This is followed by a discussion of some of the challenges faced by users of these new sources, including high beam power, partial coherence, harmonics, optics contamination, and the unusual spectral and angular properties of undulator radiation. The limitations of the presently planned undulators as radiometric sources and the design criteria for a possible radiometry undulator are discussed.