bluuebunny/crossref_metadata_2025 huggingface dataset:
1 × 500 Optic fiber distributive coupler
Authors: Pan J. J.
Published: February 2023

Fiber optic local area networks, microwave and optical phased arrays, multiplexers/demultiplexers, and signal processing systems demand distributive couplers with low excess loss as well as low loss deviation. Various techniques, including biconical fusion and channel waveguide, have been experimentally tried out to construct 1 × N couplers, with N less than 100. However, these conventional techniques have disadvantages of poor reproducibility, high insertion loss, and large loss deviation among output ports. A new 1 × 516 multimode fiber optic coupler was fabricated using semiautomated apparatuses, a submicron accuracy alignment technique, and a GRIN lens. The multimode glass fibers have a core diameter of 50 µm and cladding diameter of 125 µm. To minimize the fractional loss at the interface facet of a GRIN lens, the multimode fibers are precisely etched to 40-µm diameter. The well-arranged fiber bundle is then accurately aligned with the GRIN lens and the input fiber. The outputs of the 1 × 516 fiber coupler are individually identified employing an image processing system. Calibration, test, and data recording of the couplers were performed by a multichannel computer-aided measurement system. The 1 × 516 coupler has an excess loss of 5.25 dB and a loss deviation of ±2.5 dB. The excess loss varies less than ±0.2 dB over the temperature range from −20 to ±60°C.
Perturbed wave in a single-mode fiber
Authors: Li Chuan , Li Zhengzhi , Liang Hong
Published: February 2023

When a light passes through a single-mode fiber, a perturbed wave will be excited by geometric and index deformations. With the help of the electromagnetic field theory, the formula for the spatial period of the perturbed wave is derived for both step index and distributive parabolic index distribution single-mode fibers, which show that the period is related to the geometric and optical parameters of the fibers, and the wavelength of the transmitting light.
Dark optical solitons: generation, propagation, and amplification
Authors: Zhao W. , Bourkoff E.
Published: February 2023

As indicated by our recent publications,1,2 dark solitons are found to have better stability against loss and noise. However, due to the difficulty in obtaining dark pulses, only dark solitons under decaying background have been produced, where complex laser systems and pulse shaping apparatus have to be used. In this talk we propose a novel method for generating dark solitons with cw background, including simulated outputs showing effects of system parameter variations. The input to our proposed device is a cw optical beam, the output is a train of odd dark solitons on a cw background. We also show that for a nonsoliton input in the normal dispersion regime of an optical fiber, the central pulse will evolve into a primary soliton having the same amplitude and speed as the input, but with different pulse width. The generated secondary solitons, having smaller amplitudes and larger pulse widths, will move away from the primary pulse at varying speeds. The dark solitons preserve their shape after collision and have unique coupling properties, to be described in detail. Finally, we show how a dark soliton pulse train propagating in a lossy fiber can retain its shape by periodic amplification using the stimulated Raman scattering process.
Integrated optic low pass filter
Authors: Anemogiannis E. , Kenan R. P.
Published: February 2023

Modern communication systems ask for fast signal processing devices, and IO delay line architectures promise to fulfill these needs. These architectures are implemented on LiNbO3 plate and are comprised of electrooptic (EO) tapping gratings to tap light from the optical delay line, and holographic gratings to direct tapped light to the output integrating lens. The distance between each tapping grating corresponds to the period of the input pulse amplitude modulated (PAM) signal. For the delay line to realize N positive coefficients ci with the constraint the EO tapping gratings must have efficiency ηi: where 0 ≤ ηi ≤ 1. The above relation is derived with the condition that ηn−1 = 1. Therefore any non-negative coefficient set can be represented within a normalization constant.
Spectroscopic analysis and diode array side-pump lasing properties
Authors: Allik T. H. , Ferry M. J. , Reeves R. J. , Powell R. C. , Hovis W. W. , Caffey D. P. , Utano R.
Published: February 2023

Nd3+:Ba2ZnGe2O7 (BZAG) is an attractive diode array pump material due to its long fluorescence lifetime of 340 µs and broad absorption band centered at 804 nm. In addition, the crystal has a broad fluorescence spectra and offers turnability both at 1.05 and 1.34 µm. BZAG possesses the Akerminite crystal structure and the Nd ions substitute into the Ba2+ site with charge compensation. Time-resolved site-selection spectroscopy measurements revealed ten different crystal field sites for Nd3+ in BZAG and showed the presence of strong energy transfer between ions in nonequivalent sites. The laser performance of Nd3+:BZAG rods was studied using a 2-D diode array. The rods were 5 mm in diameter, 11 mm in length, and AR and HR coated at 1054 nm on opposite ends. The pump was close coupled to the polished AR coated rod barrel. An optical slope efficiency of 23% was observed and the round trip (Findlay-Clay) resonator loss was 4.2%.
Free space generation of femtosecond electrical pulses by electrooptic Cherenkov radiation
Authors: Hu B. B. , Zhang X.-C. , Auston D. H.
Published: February 2023

The rectification of femtosecond optical pulses in electrooptic crystals by the electrooptic Cherenkov effect has proved to be an effective technique for generating femtosecond electrical pulses having base bandwidths of many terahertz.1 A major disadvantage, however, of this approach has been the difficulty of extracting these electrical pulses from the crystals due to total internal reflection. In lithium tantalate, the crystal used for these experiments, the index of refraction in the submillimeter wave band is 6.53. This results in an escape cone of only 8°. In the normal geometry used, the signal is thus totally internally reflected, which severely limits the applications of this technique for measuring the properties of materials.
Frequency locking of a laser by injected atomic coherence
Authors: Carty Tim , Sargent Murray
Published: February 2023

We consider a single-mode unidirectional ring laser containing a homogeneously broadened two-level medium whose atoms are injected in a coherent superposition of states. Provided appropriate phase matching conditions are met, the injected coherence contributes directly to the polarization of the medium and hence to the laser gain. We suppose the field is classical and perfectly phase matched with the injected coherence. We find that laser oscillation can occur below the usual laser threshold and even in the absence of an inversion. In these cases the steady state laser frequency is locked to the atomic line center. As the excitation increases, the ability of the injected atomic coherence to lock the laser frequency decreases. Slightly above the usual laser threshold, the system unlocks and produces an output weakly modulated in time.
Single-stage optical binary full-adder
Authors: Li Y. , Turner M. , Neos P. , Dorsinville R. , Alfano R. R.
Published: February 2023

A straightforward optical binary full-adder implementation can be achieved through a cascade of several two-variable optical logic elements. However, the use of cascaded optical elements introduces additional problems such as signal energy loss and speed reduction. A bistable etalon based single-stage binary full adder was proposed. This scheme, however, is an analog scheme that could suffer from an inherent large error rate.
Comparison of number systems in truth-table look-up processing
Authors: Mirsalehi Mir M. , Gaylord Thomas K. , Fielder Daniel C. , Guest Clark C.
Published: February 2023

An important issue in truth-table look-up processing is the number representation used for data. In this paper, the effects of number representation are investigated for the important case of 8-bit addition as a specific example. The inputs are two 8-bit binary numbers together with an input carry. The output is a full-precision 9-bit binary sum. For the intermediate processing, three number representations are treated: binary, residue, and modified signed digit. The numbers in all three representations are in binary-coded form throughout the processing. The critically important steps of encoding the numbers into the residue and modified signed digit systems and then decoding the results back into the direct binary are also performed by applying truth-table look-up methods. For each case, the complexity has been found by listing all the required reference patterns (minterms) and reducing this list using logical minimization techniques. Also, for the binary number case, analytic expressions have been derived for the number of reduced reference patterns. It is shown that the residue processor is superior in required hardware while the binary processor is the fastest.
Thermal modeling of optical coating performance
Authors: Gregory G. Groot , Fantone Stephen D.
Published: February 2023

The performance of optical thin film filters often deviates from design. These deviations are typically caused by the manufacturing process and are attributed to errors and nonuniformities in layer thickness and refractive index. The design performance is also affected by variations in the filter's environment. A computer program for thin film coating design has been enhanced to model the effect of temperature variations on the filter's characteristics as well as to provide optimized designs with a desired temperature performance.
Uniform asymptotic description of ultrashort Gaussian pulse dispersion
Authors: Oughstun Kurt E. , Laurens Judith
Published: February 2023

The uniform asymptotic description of the propagation of an input Gaussian modulated harmonic signal of fixed angular frequency ω
c
and initial pulse width T into the half-space z > 0 that is occupied by a single resonance Lorentz medium is described. The asymptotic theory shows that the propagated field can be expressed solely in terms of a generalized Sommerfeld and Brillouin precursor field structure. If the applied signal frequency ω
c
is either below or near the medium resonance frequency, the propagated field is found to be dominated by the generalized Brillouin precursor field, while if ω
c
is well above the medium resonance frequency it is dominated by the generalized Sommerfeld precursor field. The resultant pulse distortion in the dispersive medium is shown to be due solely to the manner in which the initial Gaussian pulse envelope spectrum modifies the precursor field amplitude. Finally, the frequency dependence of the pulse velocity in the single resonance Lorentz medium is described.
Laser diode bar collimation using binary optics
Authors: Jackson John E. , Foresi James S. , Burkhardt Gordon H.
Published: February 2023

Design, fabrication, and testing results are given for a laser diode collimator which uses a binary optics corrector (BOC). Previous collimator designs used an acylindrical lens which was difficult and expensive to fabricate. The BOC was designed for use on a flat fused silica substrate which was cemented to a biconvex cylindrical F/1 microlens to form a single-axis collimator for a linear array of laser diode outputs at 860 nm. Test results show that the microcollimator system is diffraction-limited (100% localized Strehl ratio). The tolerance analysis indicates a highly producible lens with high yield. The capital equipment requirements to process and fabricate the BOC are modest and very cost-effective when compared to alternate approaches. Both a two-level and an eight-level BOC were produced as part of the development process, with both performing as predicted by the design analysis. Standard antireflection coatings were applied to achieve high transmission. Assembly of the lens and corrector required only that the pieces be placed on a suitably flat surface and bonded together.
Spectroscopy and structure of carbo-ions
Authors: Oka Takeshi
Published: February 2023

Recent development of high sensitivity high resolution infrared laser spectroscopy has led us to spectroscopic observations of ionic species that had not previously been studied in any spectral region. Using this method to study highly reactive carbo-ions such as

CH

3
+

, HCCH+,

C
2

H
3
+

, and

C
2
−

is discussed.
Plasma plated laser end mirrors
Authors: Lefebvre Paul M. , Klinger R. E. , Allen T. H.
Published: February 2023

All-dielectric high reflector coatings produced by plasma plating were evaluated for their applicability as low loss, UV stable intracavity end mirrors. Although ultimately intended for ion laser applications, the design wavelength was set at 633 nm, taking advantage of existing scatter and total loss instrumentation. The total loss using an optoacoustic loss instrument was tracked during exposure to a low pressure mercury lamp simulating the UV environment of an optical cavity. This source has its strongest emission at 248 nm. The reflectors consisted of quarterwave stacks of alternating high and low index materials with halfwave overcoats of low (silica). Four high index materials were examined: titania, zirconia, tantala, and hafnia. Titania/silica stack scatter losses exceeded 2000 ppm. No further testing was attempted with this combination. The zirconia stack scatter averaged 550 ppm, while the tantala and hafnia could be produced with loss averaging ~200 ppm. In selected areas the scatter was under 100 ppm. After annealing at 400°C for 1 h, the total losses closely matched the combined losses from scatter and transmission, with the bake having no measurable effect on scatter. In standard plasma plating deposition conditions, the zirconia, tantala, and hafnia all had similar UV exposure characteristics suggesting a common loss mechanism. Each reached a saturation loss level ~500 ppm higher than its starting value after ~30 min of UV exposure. Unlike conventionally deposited films which degrade rapidly under UV exposure, samples produced omitting the halfwave overcoat had UV-induced losses of only ~100 ppm with a time constant of <2 min.
Bandpass AR coating for the photorefractive materials LiNbO3, BaTiO3, CdTe, and PLZT
Authors: Karim Z. , Tanguay A. R.
Published: February 2023

Uncoated electrooptic and photorefractive materials such as LiNbO3, BaTiO3, CdTe, and PLZT all exhibit large first surface reflectivities (~20%) due to their high refractive indices (n ~ 2.2-2.6). Therefore, photorefractive recording in volume holographic applications suffers from reduced optical throughput (~64%) as well as problematic multiple reflections that tend to reduce the grating modulation while recording extraneous gratings. This situation is further aggravated by the necessity to operate photorefractive devices over a broad range of wavelengths, polarizations and input angles, often simultaneously. An effective bandpass antireflection (AR) coating previously developed for bismuth silicon oxide (Bi12SiO20) consisting of an electron-beam deposited double layer quarterwave stack of magnesium fluoride and zirconium dioxide has been modified to apply to the specific substrate indices and operating wavelengths of the photorefractive materials listed above. The as-deposited AR coatings exhibit desirable broadband characteristics with reflectivities well below 1%. In addition, measured reflectivities were shown to be relatively insensitive to both polarization (TE, TM) and angles of incidence over the 0-45° range.
Integrating cavity optical absorption meter
Authors: Fry Edward S. , Kattawar George W. , Pope Robin M.
Published: February 2023

The absorption coefficient is one of the most important fundamental parameters of ocean optics. It is essential for studies of light propagation and of pigment distributions. Unfortunately, its accurate measurement is severely restricted by systematic effects due to scattering. Many attempts have been made to minimize and/or correct for these effects. A new integrating cavity absorption meter that should, in fact, be rigorously independent of scattering effects is described. It involves illuminating the sample isotropically and measuring the radiation density in the cavity. The theoretical basis for this device is developed and experimental results for the absorption coefficient of water in the presence of various concentrations of scatterers are presented. These results show that, for example, at a wavelength of 633 nm, the absorption of water (0.00303 cm-1) can be measured to an accuracy of ~1% even in the presence of suspended MgO particles at a concentration that makes the suspension look opaque.
Interaction of coherent beams in electrically poled BaTiO3 crystal
Authors: Moghbel M. , Venkateswarlu Putcha , Sekhar P. Chandra , George M. C.
Published: February 2023

Beam coupling and pulsations in BaTiO3 were discussed earlier.1 We report here interaction of two mutually coherent beams A1 and A
2
from a He-Ne laser. The beam crossing angle in BaTiO3 is 5°, with A1 making 78° with the C-axis. With individual pumpings, detectors D1 and D2 record self-pumped phase conjugates A1 and A2. With both beams on, they record [A1(t) + Â2(t) – Δ2] and [A2(t) + Â1(t) — Δ2], respectively, where Â2 and Â1 represent cross coupling beams of A2 and A1 along A1 and A2, respectively, and Δ1 and Δ2 represent the erasure effects on A1 and A2 by A2 and A1 By recording first the intensities at D1 and D2, keeping both A1 (3.25 mw) and A2 (3.00 mw) on, and then turning off A2, D1 falls down suddenly in intensity to (A1 — Δ1) which rises and saturates at A1(t), giving the relative values (a1:Â2: Δ1) = (165:77:112). Similar observations by putting off A1 give (a2: Â1: Δ2) = (88:62:64). Intensity with simultaneous pumping will be smaller or larger than with individual pumping depending on whether Â < Δ or Â > Δ.
Light-induced transport and delocalization in transparent materials
Authors: Lawandy Nabil M.
Published: February 2023

When an intense nonresonant field interacts with a two-level system, the wavefunctions are modified. Several approaches may be used to study this problem including the techniques of dressed state theory. When the two-level system is comprised of two midgap sites separated by a distance Rab and an energy in the absence of light shifts Wba, the light shifted energy separation becomes This effect acts on level pairs and therefore shifts all the energy levels closer to each other. With these results and the rough criteria for Anderson localization W > B (B is the energy bandwidth), we may arrive at a condition for which a transition from localized to extended states could occur. The resulting critical intensity is given by Using typical values of R = 15 Å, v = 3 ×1014 Hz, α = 0.2 AX−1, and W = 0.4 eV, we arrive at critical intensity for delocalization of I
c
= 10GW/cm2.
Nonclassical states of light
Authors: Caves Carlton M.
Published: February 2023

Nonclassical light has the potential to provide improvements in signal-to-noise ratio in a variety of applications. This tutorial provides a characterization of nonclassical light, describes its two present manifestations—quadrature-squeezed and number-squeezed (antibunched) light — discusses methods for generating and detecting these two kinds of nonclassical light, and considers potential applications with a critical view as to when nonclassical light might be useful.
Photon statistics of a nondegenerate optical parametric oscillator
Authors: Vyas Reeta , Singh Surendra
Published: February 2023

Photon statistics of light produced by a nondegenerate optical parametric oscillator operating below threshold are calculated. Positive-P representation is used to map quantum dynamics onto a set of classical Langevin equations for the complex field amplitudes associated with the annihilation and creation operators for the field produced by the oscillator. Using a Karhunen Loeve expansion of the resulting stochastic processes the moment generating function for photon counting statistics is obtained.
Spectral characteristics of computer-generated phase-quantized diffractive lenses
Authors: Cowan James J.
Published: February 2023

A diffractive lens is a surface-relief structure made lithographically by exposing computer-generated zone plate patterns of clear and opaque rings in chromium masks into layers of photoresist and subsequently ion etching the substrate. A two-level or binary zone plate results from a single mask, while the use of two or more masks results in multilevel asymmetric profile zone plate ring structures. The equally spaced steps constitute a phase-quantized profile, and the magnitude of the step heights determines the spectral response. If the phase shifts due to the steps in a single zone sum to 2π, the diffracted spectrum is typically broadband and blazed, with most light being diffracted into a single order. The diffraction efficiency increases with the number of steps. If, on the other hand, the phase shift is 2π for each single step in the zone, the spectral response is typically narrowband, with an increase in the number of steps resulting in higher efficiency, but also causing the bandwidth to become narrower. Incident broadband radiation for this case can be divided into several high efficiency, narrowband, and nearly nonspectrally overlapping orders. These shallow surface-relief lenses can be readily replicated by nickel mastering and embossing into plastic.
Optical testing of an unusual aspheric surface with a binary optic as a null corrector
Authors: Shu Ker-Li , Tausanovitch J.
Published: February 2023

Binary optics, which are capable of accurately generating arbitrary wavefront profiles in monochromatic light, can be very suitable for use as diffractive null correctors in the interferometric null test of an unusual aspheric surface. Unlike a computer-generated hologram, binary optics can be made with multiple levels causing them to resemble a blazed grating which concentrates energy into a single diffraction order such that order separation is not necessary. We present a null test design which uses a binary optic as a null corrector for the test of an unusual nonsymmetric aspheric surface. The selection of the test configuration, the design strategy, and the modeling/designing of the binary diffractive null corrector are discussed. As a demonstration, we show some interferograms from an experiment that uses a binary phase corrector to nullify the residual wavefront aberrations of a sphere tested at a conjugate other than its center of curvature.
Self-pumped multiwave mediated ring oscillator and phase conjugator with Kerrlike nonlinear media
Authors: Khoo I. C. , Wang W. , Michael R. R. , Lindquist R. G. , Zhou P.
Published: February 2023

Recent experimental observation of large probe beam gain at moderate laser power in a Kerrlike nonlinear medium demonstrated the possibility of constructing a self-pump ring oscillator and phase conjugator. We present a detailed theory, based on experimental parameters, of the working principles of such multiwave mixing mediated devices. The theory accounts for the side diffractions, which are responsible for probe beam gain in a Kerrlike medium, and other relevant parameters such as noise, loss, phase modulation, intensity dependences, etc.
Fabry-Perot type photorefractive feedback system using BaTiO3 phase conjugate mirrors
Authors: Itoh Masahide , Kuroda Kazuo , Ogura Iwao
Published: February 2023

We propose an optical circuit unit consisting of two beam splitters and two Ba- TiO3 phase conjugate mirrors (PCMs). The reflective gain of a PCM is up to 260% using r42 electrooptic coefficient. Circuits of this type can be connected in cascade because of the high gain. An input beam goes to the first PCM (PCM1) through the beam splitter, and its amplified reflected beam is led to the second PCM (PCM2). As the two PCMs are connected by the two beam splitters, a feedback loop is constructed between them. PCM1 forms a phase conjugate (PC) image of the input in the mask plane, and PCM2 forms a PC image of this PC image, that is, it reconstructs the original in the output plane. Because of the beam splitters a beam passes back and forth between the two PCMs. In the mask plane, the PC image by PCM1 and the original image by PCM2 coincide although they propagate in opposite directions. Controlling transmittance of the mask, we can perform a nonlinear operation to the input image with this feedback system.
Compensation of aberrations due to wavelength shift in waveguide grating couplers by gradient-index methods
Authors: Lawrence George N.
Published: February 2023

Waveguide gratings, like most holographic devices, exhibit aberrations when used at other than the design wavelength. For high numerical aperture devices the usable spectral range may be very small, perhaps less than the expected shift in a laser diode light source. Unlike the conventional hologram, the waveguide devices may, in principle, be made self-compensating by matching the spectral change of optical path lengths in the guide layer and the freespace propagation path. This requires a variable propagation constant for the waveguide which may be achieved by controlling the thickness and/or the index of refraction of the guide layer. In this paper we describe the theory of this method and calculate the necessary range of refractive index. For large numerical aperture devices, variations of index of 50% or better are needed.
Fundamental noise limitations in optical linear algebra processors
Authors: Batsell S. G. , Walkup J. F. , Krile T. F.
Published: February 2023

Regardless of the particular architecture chosen, certain operations such as multiplication, addition, and the generation, propagation, and detection of light must be performed in an optical linear algebra processor. We show that each of these operations introduces fundamental noise limitations which affect the overall accuracy of the processor. These limitations are examined for various types of light including polarized thermal light, unpolarized thermal light, and laser light, as well as for low light levels. The effects of various spatial light modulators on the accuracy of the multiplication process are considered. Likewise, the effect of the type of addition used (i.e., space integrating or time integrating) on the resulting accuracy is considered.
Submicron metal grid mirror liquid crystal light valve for optical processing applications
Authors: Efron U. , Bak C. S. , Au A. , Goodwin N. W. , Reif P. G. , Garvin H. L. , Welkowsky M. S.
Published: February 2023

A submicron metal grid mirror was incorporated into the structure of a silicon liquid light valve. This polarization-sensitive mirror allows the use of the LCLV as a bistable device. In our experiment, a 0.5-µm period, aluminum wire grid mirror was used in conjunction with a 90° twisted nematic configuration. Theoretical analysis predicts a 5:1 peak-to-threshold level ratio of the output levels using a He-Ne beam. A sharp threshold with a peak-to-threshold ratio of 3:1 was experimentally observed. The threshold intensity level was tunable from 2.5 to 50 µW/cm2 by changing the bias voltage from ~5 to 25 V. This tunability allows the device to be used as an adaptive image thresholder. The polarization-sensitive mirror allows the device to be used also as an interfacing device for an optical coprocessor as well as for optical implementation of Hopfield-Anderson association and for phase conjugation.
Computer simulation of pixelated optical correlators
Authors: Gianino P. D. , Horner J. L. , Woods C. L.
Published: February 2023

Electronically addressed spatial light modulators (SLMs) are generally pixelated structures. Each pixel consists of a phase-or amplitude-modulating active area within an inactive (or dead) zone. Computer simulations of correlation have been made for optical correlators having an input SLM with gray level input and a filter SLM with either a classical matched filter, a phase-only filter, or a binary phase-only filter written on it. The correlation peak, energy throughput, and signal-to-noise ratio (SNR) have been studied as a function of dead zone area in both the input and filter SLMs. Input plane sampling is carefully chosen to give accurate discrete Fourier transform results. Calculations using multiple point/pixel sampling are compared with those for single point/pixel sampling. In general, it is found that as dead zone area increases, SNR changes at most by 10%, whereas peak intensity and energy throughput decrease substantially.
Frequency stabilization of a single-mode titanium sapphire laser
Authors: Boyd Timothy L. , Shevy Y. , Kimble H. J.
Published: February 2023

We report the active frequency stabilization of a cw titanium sapphire (Ti:Al2O3) laser. Our preliminary efforts employ the simplest possible arrangement consisting of a piezoelectrically translated cavity mirror for servo control of the laser frequency and result in a fast laser linewidth of 20-kHz rms (detection bandwidth > 10 Hz). The Ti:Al2O3 laser used in our experiments is a commercial ring laser1 and is locked to a stable optical cavity (FWHM = 2.4 MHz) with an FM reflection technique. The frequency noise characteristics of the locked system are measured with an independent diagnostic cavity (FWHM = 17 MHz) with broadband subtraction of amplitude noise. Although the piezoelectric mirror assembly in the laser cavity is not optimized for low mass or speed and the maximum servo unity gain bandwidth does not exceed a few kilohertz, we nonetheless observe that broadband components of the FM noise spectrum make negligible contributions to the laser linewidth above ~300 Hz for closed loop operation. At present, the residual linewidth of 20-kHz rms is dominated by a number of sharp features associated with mechanical resonances in the laser cavity and with line related harmonic noise.
Multigigahertz bandwidth FM response of two-electrode DFB lasers
Authors: Willner A. E. , Kuznetsov M. , Kaminow I. P. , Koren U. , Koch T. L. , Burrus C. A. , Raybon G.
Published: February 2023

We report the experimental and theoretical characterization of the FM response of a two-section DFB laser emitting at 1.3 µm. Such tunable lasers have emerged as important components for various FDM and FSK optical communication systems. Experimentally determined FM responses for similar structures have been reported previously only for modulation frequencies below ~1 GHz. We extend these measurements of two-section DFB lasers into the multigigahertz frequency range. The FM response magnitude is large and flat for frequencies from 10 kHz up to several hundred megahertz. This is followed by a dip in the response at ~1 GHz and a relaxation resonance peak at a few gigahertz. However, this dip does not limit the speed of the device, as is evident from the flat AM response of this laser at 1 GHz. In proper bias conditions, an FM response magnitude >1 GHz/mA and a 3-dB FM bandwidth of ~5 GHz is demonstrated, including the shallow dip and increased response of the resonance; we believe this to be the widest FM bandwidth reported to date for such lasers. As the bias is increased in the modulated section, the resonance peak becomes damped and moves out to higher frequencies. Both the characteristic response dip found at ~1 GHz and the resonance at a few gigahertz depend strongly on the bias conditions. The laser can be biased in a regime where there is either a red or blue frequency shift with static current tuning. In comparison with the static red-shifted FM response, the blue-shifted response has a more severe dip at ~1 GHz and a strongly damped resonance. Consequently, a blue-shift-bias produces a much lower 3-dB bandwidth than a red-shift bias. The observed behavior is well represented by theoretical curves derived from a small-signal analysis of the coupled rate equations. This model characterizes the laser behavior by only a few parameters; namely, the relaxation frequency, the photon and carrier lifetimes, a damping factor, and the asymmetry between the two sections.
Low threshold electrically pumped vertical cavity surface emitting microlasers
Authors: Jewell Janet L. , Lee Y. H. , Walker S. , Scherer A. , Harbison J. P. , Florez L. T. , Mccall S. L.
Published: February 2023

We report electrically pumped lasing at room temperature in microresonators 2-5 µm in diameter. The active media were three quantum wells of 80-Å In0.2Ga0.8As with 100-Å barriers. The mirrors were GaAs/AlAs quarterwave stacks with 20.5 pairs on the bottom n-doped and 12 pairs, p-doped, on top. Additionally, the top mirror had a fraction of a quarterwave AlAs, 30-Å δ-doped GaAs, and was capped by 1500-Å Au. The semiconductor heterostructure was grown by molecular beam epitaxy, and chemical beam ion-beam assisted etching etched through the Au cap and the >5-µm heterostructure. The substrate backside was polished and grounded while an electrical probe contacted the Au cap. The <2-Å wide 958-nm output was linearly polarized. With 50-ns pulses a 3-µm device had a 1.3-mA threshold with ~15% internal slope efficiency on a linear slope. We attained duty cycles >25%. Resistance was very high, ~10 kΩ due to its small diameter, probe contact, and well/ barrier nature of the mirrors. Use of a single quantum well and surface passivation should reduce thresholds to ~10 µA, making such resistances tolerable and allow cw operation.
Laser-induced combustion and spectroscopic studies of coal
Authors: Venkateswarlu Putcha , Subbarao V. , Sekhar P. Chandra , George M. C. , Miahnahri A. , Curly M. , Osei A.
Published: February 2023

The second harmonic (532 nm) of a pulsed Nd:YAG laser with a pulse width of 10 ns and an energy maximum of 300 mJ/ pulse was used to induce combustion on a rotating coal target prepared by compressing powdered coal to 15,000 psi in a die. The spectrum was recorded with a double monochromator coupled with a Hamamatsu P636 photomultiplier and a boxcar integrator. The B2Σ+ – X2Σ+ system of CN at 3883 Å involving transitions (0,0), (1,1), (2,2), (3,3), and (4,4) was observed. The Swan system of C2 corresponding to d
3
II
g
–a3II
u
involving (1,0), (2,1), (3,2), (4,3), (6,5), (0,0), and (1,1) transitions were prominent. The bands of the B1Σ+–AlII angstrom system of CO involving (0,1) and (0,2) transitions were also recorded. The resonance doublets of sodium and potassium atoms have also been observed in the laser-induced combustion. It is found that the relative intensities of the band systems among themselves as well as in relation to those of the alkali doublets changed with experimental conditions indicating their dependence on laser power and therefore on temperature.
Nonlinear spectra of a homogeneously and inhomogeneously broadened two-level system
Authors: Marcano A. , Salazar O. M. C. , Paz J. L. , Reif I. , Franco H. J.
Published: February 2023

Polarization and Rayleigh type optical mixing spectra of a homogeneously and inhomogeneously broadened two-level system are calculated. We show that the nonlinear signal has contributions from the population pulsation and saturation effect. In the homogeneous system these effects can induce an asymmetric spectrum when the probe frequency is different from the resonant value. In the inhomogeneous system the spectral response is always symmetric independent of the probe frequency value. Line saturation and dynamic stark splitting are substantially reduced in the inhomogeneous case. The mentioned differences can be used to identify the type of broadening of a given spectral line.
Multipurpose 1.5-m telescope system
Authors: Aruga T. , Itabe T. , Hiromoto N. , Smith W. S. , Kimbrell J. E.
Published: February 2023

A new optical system with a 1.5-m diam telescope was designed and constructed in the CRL. The distinctive feature of the new telescope system is its flexibility as well as its capability for fast and accurate tracking. The system is flexible, that is, applicable to multiple studies. These are (1) satellite tracking (including geostationary satellites), (2) space optical communication, (3) laser ranging, (4) astronomy (IR/ visible), (5) laser radar, and (6) radiometry (remote sensing of planetary atmospheres). There are many foci, i.e., Nasmith (two), bent-Cassegrain (two), Cassegrain (usually not used due to tertiary mirror installation), and coude (instrument selection is avail able in four directions). Azimuth/elevation encoder resolution is 0.0001° and fast tracking (up to Az 15°/sec, El 5°/sec) is possible. The subsystems which have been integrated include a high sensitivity CCD camera and an image intensification tube camera for spacecraft tracking, point- ahead/fine-tracking assembly for space optical communication, 110-mJ/70-ps Nd:YAG laser for satellite ranging, 124 × 124 element IR camera and FT spectrometer for astronomy, and several CO2 and isotope lasers as well as heterodyne receiver for lidar and radiometer.
Sample translation interferometer measurement system
Authors: Gardner Leo R. , Moore Duncan T.
Published: February 2023

A harmonic ac interferometer was built by interfacing a Macintosh computer to modulation and data collection electronics as well as a translation stage assembly. The phase sample to be measured was mounted on the stage and translated through the test arm of the interferometer. This configuration resulted in accurate measurements that were independent of the quality of the optics, as well the alignment of the interferometer cavity. The lateral dimension of the phase sample under test was limited only by the range of motion of the translation stage and not by the aperture of the interferometer. An electronic fringe counting scheme was used to keep track of fringes during movement of the sample, and the stage was stopped at predetermined step sizes in order for accurate phase measurements to be made.
Local spectral analysis of texture gradients
Authors: Turner Mark R.
Published: February 2023

The perspective image of an obliquely inclined textured surface exhibits shape and density distortions of texture elements. These distortions also systematically shift the projection of the spatial frequencies of which the texture is comprised. Using a set of filters with suitable spatial frequency and orientation resolution, the inclination angle of many textured surfaces may be estimated from these frequency shifts. An algorithm has been developed which uses the amplitude distributions of 2-D Gabor filters to perform this calculation on planar surfaces. The algorithm may be viewed as operating in parallel on a number of patches of the image and consolidating a global inclination value of lateral propagation of local inclination estimates between regions.
Orthophorization of heterophorias among children
Authors: Letourneau J. E.
Published: February 2023

The purpose of the study was to measure the distribution of phorias among children. Vertical and horizontal phorias were measured at far and at near among (N = 2048) 6-13-yr old children. Kolmogorov-Smirnov goodness of fit tests showed that horizontal phoria at near (D = 6.76) and at far (D = 9.84) and vertical phoria at near (D = 20.59) and at far (D = 17.81) were not distributed normally. Results also showed that the data were not skewed. Sign tests gave identical results. The sample was divided into nine groups according to age. Krus- kall-Wallis one-way ANOVAs showed that horizontal phoria at near (X2 = 8.52) and at far (X2 = 14.78) and vertical phoria at near (X2 = 3.78) and at far (X2 = 17.52) did not vary with age. Scheffe's S ANOVAs also showed that horizontal phoria at near (F = 1.24) and at far (F = 1.28) and vertical phoria at near (F = 1.39) and at far (F = 2.17) did not vary with age. Orthophorization of vertical phoria appears at least at age 6 and no variation of phoria with age seems to appear before puberty. Comparisons of any individual findings with the general distribution curve should take the nonGaussian distribution of phorias into account. Moreover, nonparametric methods would be more appropriate since the distribution of phorias is non-Gaussian at least among children.
Infrared laser absorption spectrometers: can fixed-frequency IR rare gas lasers compete with IR diode lasers?
Authors: Schwab James J.
Published: February 2023

Techniques to increase the sensitivity and capabilities of IR laser based sensors for atmospheric measurement are rapidly expanding. This paper addresses research into the development of fixed-frequency rare gas lasers and their role in the development of state-of-the-art measurement techniques. In particular, work in progress developing a laser absorption spectrometer using a neon laser transition near 8 μm is described. The instrument is designed to use the neon laser, a CdTe electrooptic modulator (EOM), a specially designed offaxis resonator multipass absorption cell, and a very high bandwidth IR detector. The EOM and high bandwidth detector are necessary to exploit the very sensitive detection methods of frequency modulation spectroscopy. Potential and realized advantages of fixed-frequency IR lasers are addressed, as well as some drawbacks and limitations.
Influence of pinhole size on the image formation in a phase conjugate scanning
Authors: Mao C. C. , Johnson Kristina M. , Cathey W. T.
Published: February 2023

We have shown previously1 that the phase conjugate scanning microscope can image intensity objects much better than previous optical microscopes. We present here the theoretical analysis and experimental results concerning the effect of pinhole size on lateral resolution, depth of field, and image of phase objects. The results show that when the diameter of the pinholes is less than the halfwidth of the impulse response of the lenses, the imaging system has higher lateral resolution and better sectioning discrimination than other optical microscopes. It also can image phase objects. When the pinhole positioned in front of the phase conjugator is larger than the width of the intensity impulse response, the system has no improvement of lateral resolution and depth discrimination compared to the single-pass scanning microscope, and cannot image phase objects.
Superresolution in scanning microscopy
Authors: Bouwhuisn G.
Published: February 2023

The minimum spot size of a focused homogeneous beam is determined by wavelength and numerical aperture, scanning an object with a spot yield transfer of spatial frequencies up to a definite cutoff frequency which is determined by the same parameters. The frequency range may be enlarged, however, by simply placing a screen with a small hole in the center of the focused spot. In general any local optical disturbance in the spot gives rise to resolution above the conventional cutoff frequency. A disturbance of the spot can be realized with thin layers of materials which behave nonlinearly with respect to transmission or reflection; i.e., the transmissivity depends on the incident power density. For example, in the case of a saturable absorber the top of the spot makes a hole in the layer and the long, tailing slopes disappear; the diffraction-limited spot is sharpened. The nonlinearity is often due to a highly temperature dependent (complex) index of refraction. Experiments with optical disks coated with proper layers, yielded signals at more than twice the conventional cutoff frequency, albeit at a low level.
Crystal growth and optical properties of large size single crystals of bismuth silicon oxide
Authors: Zhang S. A. , Lin J. T. , Chai B. H. T.
Published: February 2023

Single crystal bismuth silicon oxide (Bi12SiO20, or BSO) is a photorefractory material. Since it also has photoconductive and linear photoelectric effects, it has the potential for many varied applications, such as holographic storage, interferometry, photorefractory imaging, phase conjugation, and real time image processing.
Fresnel lens-encoded binary phase-only filters for optical pattern recognition
Authors: Davis Jeffrey A. , Cottrell Don M. , Drayton Stuart H. , Davis Jeffrey E. , Lilly Roger A.
Published: February 2023

We report a technique for improved performance with optical correlators using binary phase-only filters (BPOFs). Since the impulse response function of the BPOF normally contains both the target object and inverted version of it, the output consists of the correlation of the input object with both of these objects. This has two consequences. First, inverted images can result in a positive correlation, which may be undesirable in many situations. Second, there is an added noise term due to the correlation with the inverted version of the target. In our work, a Fresnel phase plate lens is encoded onto the BPOF. As a result, the correlation with the desired target is on a converging beam. The correlation with the undesired inverted image of the target is on a diverging beam and is out of focus at the detector. This BPOF can be easily implemented using the short optical correlator design. Experimental results confirm that these filters reject inverted input objects.
Mirror surface quality requirements for XUV FEL resonators
Authors: Mcvey Brian D. , Goldstein John C. , Newnam Brian E.
Published: February 2023

Mirror surface quality requirements are theoretically investigated for XUV FEL oscillators. The resonator configuration considered is a grazing incidence ring using metal coatings. Starting at the end of the wiggler, the optical train consists of (1) a grazing incidence hyperboloid to magnify the optical beam expansion, (2) a multifaceted mirror to retroreflect the beam (the multifaceted mirror is composed of several flats and an off-axis paraboloid to collimate the expanding beam), (3) a scraper to output couple the optical energy, and (4) a second multifaceted mirror and hyperboloid pair to focus the optical beam to the wiggler entrance. For this resonator configuration, we evaluate FEL performance degradation due to mirror surface imperfections which can result from polishing errors and thermal distortion. The concept of mode matching is applied to the resonator design. Mode matching in an FEL oscillator is defined as despacing (translating) the paraboloidal mirrors to match the optical properties of the resonator to the FEL gain region (wiggler).
Digital phase holograms by error diffusion
Authors: Weissbach Severin , Wyrowski Frank , Bryngdahl Olof
Published: February 2023

An interesting and powerful method of binarizing gray tone distributions is the error correction and diffusion method. Its basic idea is to distribute the local quantization error in a sequential procedure among pixels not yet processed. We have generalized this concept to phase structures. The complex amplitude is then corrected by diffusing complex valued errors.
Zone plate fabrication for x-ray microscopy
Authors: Anderson Erik H.
Published: February 2023

Although zone plates have been used as focusing elements since the 1870s, recent advances in fabrication technology have made possible high resolution zone plates for x-ray microscopy use. The zone plate pattern can be either produced holographically by the interference of two coherent wavefronts or by a high resolution tool such as an electron beam lithography system where a small diameter electron beam, under computer control, writes the pattern. This paper concentrates on the latter. The diffraction-limited resolution of x-ray zone plates is approximately equal to the smallest zone width so small linewidth structures are required for high resolution. Producing small linewidth features is not sufficient, since each zone must be placed in the proper position to a tolerance which is a fraction of the outermost zone width. Also, practical working distances require long focal lengths. For a given resolution, the longer the focal length the larger the zone plate diameter. Therefore, the challenge for the lithographer is to produce a pattern over a relatively large area with small linewidth features that are precisely placed. To rest the result various moire techniques can be used as well as the actual x-ray optical performance. Experimental results are presented.