bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase-mismatched degenerate four-wave-mixing: measurement of the complex third-order nonlinear optical susceptibility in thin films
Authors: Strohkendl F. P. , Dalton L. R. , Hellwarth R. W.
Published: February 2023

In degenerate four-wave mixing (DFWM), three beams of the same frequency ω overlap in a medium to generate a fourth , or more,1 new beams, also of frequency ω. At low beam intensities, the power in each newly generated beam is proportional to the product of the powers of the three incident intensities, and the constant of proportionality has as a factor the absolute square of an element of a third-order susceptibility tensor , χ(3)(−ω, ω, ω, −ω). As the beam frequency ω is increased to where it approaches or exceeds either (1) the lowest "one-photon" resonance frequency of the medium, or (2) half of the lowest "two-photon" resonance frequency of the medium, χ(3) passes from being a positive real number to a complex number that varies in a complicated way with frequency ω. Knowledge of the phase of χ(3), as well as of its magnitude, is relevant for the understanding of the electronic structure of materials as well as for the estimation of their device potential. We obtain this knowledge for a C60 film by interference of its generated beam with that from the CaF2 substrate.
The optical polarizability of excited C60 molecules
Authors: Guan Huapeng , Hellwarth Robert W. , Partanen Jouni P. , Tang Nansheng
Published: February 2023

Over a dozen reports of optically-induced changes of up to a factor of 5 in the absorption cross-section of the C60 molecule at 532 nm1 have prompted us to investigate whether there might be a correspondingly large change in the (in-phase) polarizability of C60 at the same wavelength. Unfortunately for nonlinear optical applications, we have found a negative answer: the change is less than 3% for the polarizability of C60 upon excitation to either the lowest singlet or triplet state. In the course of this investigation, we have made, we believe, a more accurate determination of the absorption cross-sections σS and σT of the lowest excited singlet and triplet states of C60 molecules. This is achieved with a picosecond pump-probe technique not previously applied to C60. Our measurements of the polarizability changes were done with time-delayed degenerate four-wave mixing experiments. Our experiments were performed in a solution of 0.68 g/L of C60 in benzene.
Pump-Probe Experiments in Organic Solutions for Optical Limiting
Authors: Dogariu Arthur , Buck Paul M. , Hagan David J. , Van Stryland Eric W.
Published: February 2023

We report a series of picosecond excite-probe and femtosecond continuum excite-probe experiments performed on solutions of organic dyes. These experiments show the dynamics and spectral range of utility for these materials which have shown promise for applications in optical limiting devices. The metallo-organic dye solutions used were: Silicon Naphthalocyanine (SiNc) in methanol, tetrakis(β-cumylphenoxy) Lead Phthalocyanine (PbPc(β-CP)4) in chloroform and Zinc meso-Tetra(p-methoxyphenyl)Tetrabenzporphyrin (ZnTMOTBP) in tetrahydrofuran (THF). Initial studies involved Z-Scan and picosecond pump-probe measurements on these solutions at 532 nm.[1-3] All of these materials exhibited large reverse saturable absorption (RSA), i.e. the excited-state cross-section is larger than that of the ground-state.
Semiconductor Amplifier as Element of Optical Communication Systems
Authors: Settembre Marina , Matera Francesco , Hägele Volker , Gabitov Ildar , Mattheus Arnold , Turitsyn Sergei K.
Published: February 2023

Recent progress in the fabrication of polarization-insensitive Semiconductor Optical Amplifiers (SOAs) has stimulated interest in investigating transmission systems with in-line SOAs [1-3]. The SOAs cover broad wavelength range from 0.7 to 1.6 μm, they are pumped electrically and are substantially cheaper than fiber amplifiers, therefore, SOA is the natural candidate to be an element of all-optical transparent transmission systems.
Intersubband Quantum Box Laser Based on Image Charges
Authors: Khurgin J. B. , Lee S. J.
Published: February 2023

Ever since the inception of lasers there has been a consistent effort towards reducing their threshold which in general can be achieved by two means: reduction of the active region size and eliminating the residual absorption. Rapid progress in the reduction of size has culminated in quantum well and microcavity lasers [1]. However, elimination of absorption, long used in NH3 masers by the “spatial sorting-out” of excited atoms, is clearly not applicable in solid state lasers. It is only recently that “lasing without inversion”, in which quantum interference causes reduced absorption, has been suggested for semiconductor quantum wells [2]. This method, however, is inherently complicated for reasons such as requiring separate probe and coupling laser beams, etc.
Enhancement of χ3 in nanoparticle composite media exhibiting electrostriction and quantum confinement
Authors: Flynn G. , Schwarze C. , Pommet D.A. , Fiddy M. A.
Published: February 2023

A new model is described that combines the interaction between quantum confinement in nanoparticles and electrostriction on the bulk optical nonlinearity of a medium. While modeling the two nonlinear mechanisms independently has been widely reported, there have been few attempts to consider the interplay between two such nonlinearities when both are present and of similar magnitude. We show that local field effects can greatly enhance the bulk nonlinear optical properties of the medium.
Excitonic Enhancement of Third-order Optical Nonlinearity in Regioregular Head-to-Tail Coupled Poly(3-Hexylthiophene)
Authors: Kawahara H. , Ueno Y. , Morito N. , Ema K. , Rikukawa M. , Ogata N.
Published: February 2023

Conducting polymers are of interest for its application to novel electro-optical devices and ultrafast all-optical devices. Over the past few years it has become apparent that the electrical and optical properties are strongly influenced by their morphology and molecular organization. Although several groups have reported that the control of regularity and orientation in the polymetric structure leads to remarkable enhancements in the electrical properties [1], the enhancement in optical nonlinearity has not been reported. We measure the third-order nonlinearity of regioregular head-to-tail coupled poly(3-hexylthiophene) (HT-PHT) and regiorandom poly(3-hexylthiophene) (R-PHT) using degenerate four-wave mixing (DFWM). we observe the enhancement of third-order optical nonlinearity around exciton resonance in HT-PHT.
Femtosecond non-degenerate four wave mixing in C60/polymer blends
Authors: Maniloff Eric , McBranch Duncan , Wang Hsing Lin , Mattes Ben
Published: February 2023

Transient holographic gratings using third-order nonlinear optical processes have been suggested as possible elements for a variety of optical applications, particularly in the areas of interconnection networks and optical computing. Many of the materials suggested for applications relating to holographic optical processing rely on effects such as photorefractivity or photo-isomerization, both of which occur on time scales of milliseconds to minutes [1]. While these materials are well suited to applications such as optical storage, faster materials have a higher probability of proving useful for real-time processing. Recently it has been discovered that in certain polymers doped with C60, charge transfer occurs after excitation across the π – π
*
energy gap of the polymer to the dopant C60 molecules [2]. Using transient absorption measurements, it has been shown that this charge- transfer process occcurs at times shorter than 300 fs, and can persist up to millisecond time-scales. Since the third order nonlinear optical susceptibility, χ(3), includes a component which is related to the excited charge distribution, charge transfer to C60 can be used to increase the lifetime of this incoherent contribution to χ(3) in polymers.
Dye-doped liquid crystal films for potential wave-mixing, limiting, and photorefractive applications at 1320nm.
Authors: LoPresti Peter G. , Hemphill Daniel
Published: February 2023

It has been demonstrated that the nonlinear response of liquid crystalline materials can be beneficially modified through the introduction of a variety of dopant materials1,2,3. Novel wave-mixing phenomena, reduced energy density thresholds for limiting applications, and recently permanent holographic gratings2,3 have been observed for visible wavelength inputs. In this paper, we report the results of a series of experiments conducted on liquid crystal samples appropriately doped to respond to infrared wavelengths (specifically 1320nm), where initial measurements show promise for a variety of applications in infrared processing and communications systems.
Measurement of Photorefractive Dynamics Using Time Autocorrelaton Function
Authors: Statman David , Rendulic Traci L.
Published: February 2023

Photorefractive dynamics are typically described by the material equations referred to as the Kukhtarev Equations. In dimensionless form these equations are given by where time is scaled to τ = ε/eμNA, length to λ/(4πn sin θ/2), and density to NA. N is the carrier density, N is the ionized donor density, ND is the donor density, E is the electric field, 1D is the Debye screening length, f is the excitation rate, and γ is the recombination coefficient. The space charge field responsible for the photorefractive grating is given by These equations are inherently nonlinear, and cannot, in general, be integrated analytically. In order to do so, the equations are linearized with the anticipation that higher order terms are not significant. Recent work, however, has demonstrated that under certain conditions, typical of many experiments, the linearization of these equations is not appropriate. For those cases, any connection between model and experiment becomes quite difficult.
Current Induced Second Harmonic Generation in Semiconductors
Authors: Khurgin Jacob B.
Published: February 2023

Second order nonlinear optical effects have been thoroughly studied and used ever since the very first experiment in the early 1960’s It is also well known that only materials lacking the center of inversion symmetry possess the second order susceptibility χ(2)[1]. At the same time, externally applied fields can break the symmetry and cause the so-called field induced second order susceptibility. For example, this effect is believed to be behind the “seeded” second harmonic generation (SHG) in glass fibers where external field is produced by space charge [2]. In insulating materials it is not difficult to apply external fields high enough to produce appreciable χ(2), One can then envision that this DC-induced SHG can be used to probe and map the distribution of the electric field. But what about the metals and semiconductors, where the electric fields are small while the currents can be quite strong? Here, using simple two-band model, we show that in the presence of a direct current a second order nonlinear susceptibility, proportional to the current exists.
Application of nonlinear optics for probing of silicon-based circuits
Authors: Kurz H. , Ohlhoff C. , Meyer G. , Lüpke G. , Löffler T. , Pfeifer T. , Roskos H.G.
Published: February 2023

Rapid progress in the development of silicon monolithic millimeter-wave integrated circuits (MMIC) operating at frequencies up to 100 GHz demands for new test techniques with high temporal and spatial resolution.[1] Nonlinear optical methods based on the internal Pockels effect have been used effectively to noninvasively probe both analog and digital signals in GaAs MMIC’s. While this approach is adequate for measuring voltage waveforms in III/V-based circuits it is not applicable to silicon integrated circuits. Silicon exhibits no bulk second-order nonlinearities, because of its centrosymmetric crystal structure. To overcome this limitation and simultaneously retain the noninvasiveness of direct electro-optical probing, we apply electric field-induced second-harmonic generation (EFISHG) to monitor the internal electric field distribution in silicon MMIG’s. We present the first results of a picosecond EFISIIG study showing a free-running microwave signal on a. photoconductive dipole antenna, fabricated on a radiation-damaged silicon-on-sapphire substrate.[2]
Theory of the Third-Order Nonlinear Optical Response of Organic Materials
Authors: Abe Shuji , Shakin V. A.
Published: February 2023

Optical nonlinearity of organic materials has been studied for a long time. In mid 1970’s it was recognized that delocalization of electrons in long conjugated polymers is an important enhancement factor for the third-order nonlinear susceptibility. Since then many experimental and theoretical studies have been conducted on the nonlinear optical properties of conjugated polymers.
Optical Nonlinearities Due to Carrier Transport in Semiconductors
Authors: Garmire Elsa
Published: February 2023

This paper describes a new class of optical nonlinearities which can be important in semiconductors. This nonlinearity relies on the motion of optically-excited carriers due to internal fields within the semiconductor. Such fields can exist. for example. in semiconductor depletion regions. The charge motion sets up a resultant space charge which acts opposite to the internal fields, reducing their value. The resultant decrease in electric field changes the absorption and/or refractive index through electro-absorption, electro-refraction, electro-optic effect or quantum confined Stark effect, depending on the geometry. To understand these new nonlinearities, we draw from concepts of photorefractivity, n-i-p-i structures, the quantum confined Stark effect (QCSE) in multiple quantum wells (MQW), and relations to the self-electro-optic effect device (SEED).
Optimal Phase Matching of Three Wave Mixing in BBO and KTP Crystals
Authors: Lin J. T. , Yao J. Q. , Liu K. C.
Published: February 2023

The newly developed crystals of Beta-Barium-Borate(BBO) and KTP have been identified as the excellent candidates for the generation of coherent sources in UV (using BBO) and visible (using KTP), and mid-IR(2-4 um) (using KTP and BBO). BBO crystal with an effective nonlinear coefficient(deff) about 4-7 times that of KDP promises various applications through its features of high damage threshold(5-10 GW/cm), wide transparency(0.19-3 um) wide temperature acceptance(55 degrees) and chemically and mechanically stable. KTP crystal on the other hand has a cut-off doubling phase-matching at about 1 micron. This crystal, however, is still attractive due to its high deff(12-17 times that of KDP) and the extremely wide temperature, angular and spectral acceptance widths. Comparison with second harmonic generation(SHG), much less work has been done in frequency-mixing using BBO and KTP crystals. The three-wave-mixing(TWM) processes to be discussed in this paper shall include sum-frequency-mixing (SFM), difference-frequency-mixing(DFM) and optical parametric oscillation(OPO). The optical deff for various polarization configurations will be calculated for both type I and type II BBO and KTP. The key issues for the performance of TWM in these crystals will be analyzed. Finally, applications for the generation of tunable coherent sources will be presented.
Raman Scattering from Ultrathin Multilayer Structures
Authors: Lockwood D.J. , Dharma-wardana M.W.C. , Aers G.C. , Baribeau J.-M.
Published: February 2023

In spite of the large lattice mismatch between Ge and Si, high quality layers of Ge1-xSix covering the entire range of alloy compositions have been grown utilizing strained-layer epitaxy methods. Such work has led to the study of artificial crystals containing GemSin structures with m and n less than seven,1 of quasiperiodic Fibonacci superlattices,2 and of multiple layers of Ge grown on Si substrates.3 The study of such materials is of much interest both from a basic physics point of view and for designing devices with unusual electro-optic properties.
Optical Waveguide Fabrication in Neodymium Doped Lithium Niobate
Authors: Li M.J. , De Micheli M.P. , Ostrowsky D.B. , Lallier E. , Breteau J.M. , Papuchon M. , Pocholle J.P.
Published: February 2023

We report the realization of high-quality proton exchanged optical waveguide structures in neodymium doped lithium niobate which will permit the realization of highly efficient semiconductor laser pumped amplifiers, lasers, and non-linear elements.
Degenerate Four-Wave Mixing and Optical Bistability in Manganese-Oxide-Doped Glasses
Authors: Yumoto Junji , Uesugi Naoshi
Published: February 2023

Glasses doped with CdS
x
Se1−
x
microcrystallites have recently attracted interest because of their large third-order nonlinearities and fast response times.[1] Optical bistability with a fast switching time has already been observed.[2] Optical nonlinear properties of CdS
x
Se1−
x
-doped glasses are explained by the band-filling mode[3], which is applied to the nonlinear property of other materials at frequencies around the bandgap. Thus, new glass materials doped with various microcrystallites having different bandgaps are expected to have similar nonlinear properties. However, there are few reports on nonlinear glass materials other than CdS
x
Se1−
x
-doped glasses.
Applications of low-saturation-intensity nonlinear-optical materials
Authors: MacDonald Kenneth R. , Tompkin Wayne R. , Boyd Robert W.
Published: February 2023

Low-saturation-intensity, highly nonlinear materials, such as boric-acid glass doped with fluorescein1 and lead-tin fluorophosphate glasses doped with acridine dyes,2 are promising candidates for applications involving the nonlinear mixing of light from conventional and natural sources. One such application which we recently demonstrated is a passive method for recovering an image that has been distorted by passing through a thin phase-aberrating medium.3 This technique could, in principle, be used to compensate for the effects of atmospheric turbulence in astronomical observation. In this paper, we will discuss the feasibility of realizing these device applications.
On New NLO Crystals of the Borate series — LBO VS BBO
Authors: Chuangtian (C.T. Chen) Chen
Published: February 2023

β-BaB2O4(BBO) is an excellent UV NLO crystal(1). Its salient features may be summarized as follows: 1) it possesses a rather wide phase-matchable range from infrared region to ca. 190 nm; 2) it has a very high damage threshold up to 13 GW/CM2 at 1,064 nm and 1 ns pulsewidth as well as a very wide temperature acceptance width (55°C for SHG at 1,064 nm); 3) it exhibits a NLO coefficient ca. 4 times that of d-36(KDP). As a result, this crystal has been identified as a prime NLO crystal for frequency of dye lasers to generate deep UV radiation. However, BBO crystal has the following shortcomings: 1) since d31≈0, deff of this crystal will decrease with increasing phase-matching angle θpm, and thus BBO crystal cannot be used for 90° noncritical phase-matching; 2) the absorption edge of the crystal appears at 189 nm in the UV range, ca. 30 nm longer than that of the KB5 crystal, thus BBO cannot be used to generate deep UV radiation of wavelength shorter than 200 nm at room temperature; 3) its small angle acceptance width (≈0.80 mrad-cm) also limits its applications in harmonic generation of lasers with larger divergences.
Dynamic Gain Equalization in Two-Stage Fiber Amplifiers
Authors: Giles C. R. , Digiovanni D.
Published: February 2023

Relative gain differences among channels in WDM amplified lightwave systems can be corrected in two-stage fiber amplifiers having complementary gain spectra in each stage. With two channels spaced by 2.5 nm, relative gain corrections of 1 dB were demonstrated. Simulations show that this method can be used to dynamically equalize the channel gain in long-distance transmission systems.
An Ultra-Efficient Erbium-Doped Fiber Amplifier of 10.2 dB/mW at 0.98 μm Pumping and 5.1 dB/mW at 1.48 μm Pumping
Authors: Nakazawa Masataka , Kimura Yasuo , Suzuki Kazunori
Published: February 2023

Recent progress on erbium-doped fiber amplifiers (EDFAs) has been very rapid since they show a great potential for opening many new fields in optical communication [1]~[4]. The main advantages of EDFA are polarization-insensitive high gain, low insertion loss, low-noise, and a wide bandwidth in the loss-minimum region of silica fibers. In order to evaluate the performance of the EDFAs, high output power, high gain coefficient, and low noise characteristics are important. From these, a high gain coefficient EDFA is attractive since it offers the possibility of a low-noise high gain EDFA with a very low pump power as a preamplifier. With a view to realizing a high gain coefficient EDFA, the gain characteristics of a high NA (Numerical Aperture) EDFA have been investigated [5]~[7]. The high NA EDFA has a small spotsize so that efficient pumping is realized, resulting in a high gain coefficient.
Passive modelocking of an erbium-doped fiber laser
Authors: Avramopoulos Hercules , Houh Henry , Whitaker Norman A. , Gabriel M. Christina , Morse Ted
Published: February 2023

Passive modelocking of an all-fiber erbium laser using a nonlinear optical loop mirror has been demonstrated. A terahertz modelocked bandwidth was observed.
Attenuation Free, Dispersion Shifted Fiber Doped With Distributed Erbium
Authors: Tanaka D. , Wada A. , Sakai T. , Yamauchi R.
Published: February 2023

An attenuation free transmission line can be obtained by using a distributed erbium-doped fiber amplifier which compensates the fiber loss.1) In this attenuation free line, suppression of spontaneous emission is expected. Therefore, the distributed EDFA transmission line has an advantage from the view point of noise characteristics. If we control not only gain but also chromatic dispersion of the fiber, it is possible to realize a perfect transmission line which is free from attenuation and chromatic dispersion with excellent noise characteristics. This type of fiber can be applied to various fields.
Limits of Performance of a Nd3+-Doped Fiber Amplifier at 1.3 μm
Authors: Dakss M. L. , Miniscalco W. J.
Published: February 2023

There has been a continuing interest in developing fiber amplifiers for the 1.3 μm window which is used for most optical communications traffic. Neodymium-doped fibers remain potential candidates for this function despite the problem of excited state absorption (ESA) near 1.3 μm which can lead to loss rather than gain, particularly at shorter wavelengths [1]. The effects of ESA are known to be a function of glass composition: Aluminum/phosphorus-doped silica [2-4] and phosphate glass [5] exhibit gain at shorter wavelengths than Ge-doped silica, and fluorozirconate glass has provided gain at wavelengths as short as 1.32 μm [6-9]. Despite these results, the practicality of Nd3+-doped fiber amplifiers is still in question. We have addressed this issue by constructing a fiber amplifier model which exploits the availability of measured cross sections for a wide variety of Nd3+-doped glasses.
Pump Sources for Erbium-Doped Fiber Amplifiers
Authors: Uehara Shingo
Published: February 2023

Erbium-doped fiber amplifiers (EDFAs) have attracted much interest in the field of optical transmission research, due to their superior amplification at the third telecommunication window (around 1550 nm) [1-3]. Pump sources, which supply energy to the amplifying media, are major component of the EDFA. Semiconductor pump sources are indispensable for practical EDFAs which require compact and efficient pumping. Experimental application of EDFAs to transmission systems has been progressing with the help of high-power laser diode pump sources. This paper describes the state-of-the-art EDFA semiconductor pump sources: 980-nm InGaAs/GaAs and 1480-nm InGaAsP/InP lasers.
Laser Amplifier Detector for Broadband Network Control
Authors: Koai K. T. , Olshansky R. , Hill P. M.
Published: February 2023

In subcarrier multiplexed (SCM) or other broadband networks, a simple and low-cost network surveillance and control channel is desirable. It has been demonstrated that inline laser amplifiers (LA) can significantly improve the power budget of broadband networks including the point-to-multipoint SCM distribution system [1]. It is also well understood that LA's can be used to amplify and detect signals at the same time [2]. A number of applications have been reported, including laser characterization, frequency control, amplifier gain control, etc. [3-5]. In this paper we report for the first time the feasibility study of using a travelling-wave laser amplifier (TWLA) as an inline optical amplifier for multiple broadband FSK channels and simultaneously as a control channel detector/amplifier in an SCM system. Bit-error-rate and carrier-to-noise performances for both the control channel and the FSK channels are presented.
An Optically Preamplified 1 Gbit/s/channel Multichannel Grating Demultiplexer Receiver
Authors: King J.P. , Kanabar Y. , Baker N. , Brannan J.
Published: February 2023

The Multichannel Grating Demultiplexer (MGD)1 receiver is an attractive component for High Density Wavelength Division Multiplexing (HDWDM) systems. It combines a diffraction grating with an array receiver to provide multiple channel access. However, demultiplexer losses and the need for array operation may lead to insufficient receiver sensitivity for some applications. To improve sensitivity a semiconductor laser amplifier (SCLA) has been included before the MGD. The wide gain spectrum allows a single SCLA to preamplify many parallel HDWDM channels2, while peak optical input, and consequently intensity modulation (IM) crosstalk, is minimised3. The MGD also provides a ~2.6 nm optical filter for the spontaneous emission, reducing its noise contribution at the receiver.
High-Efficiency Erbium-Doped Fiber Amplifier using Mode Field Diameter Adjusting Technique
Authors: Wada A. , Sakai T. , Tanaka D. , Nozawa T. , Yamauchi R.
Published: February 2023

For efficient operation of an Er-doped fiber amplifier (EDFA) at 1.55 µm band it is essential to maximize the pump intensity in the Er-doped region because of the three level system [1], A high NA structure of EDF is effective to reduce the mode field diameter (MFD) of the pump and to achieve strong pump intensity [2], and has resulted in excellent gain performance [3],[4], In practical use, however, such small MFD fibers have a connection/splicing problem due to the mode field diameter mismatching. For example, approximately 1 dB splice loss is expected between an EDF with a 5 µm MFD and a conventional dispersion shifted fiber (DSF) with a 8 µm MFD. The smaller MFD of EDF, the higher splice loss. The increase of splicing loss causes noise figure degradation in pre-amplifiers and decreasing of conversion efficiency in booster amplifiers.
Bit-Error-Rate Measurements of a Multi-Thousand-Kilometer Fiber-Amplifier Transmission System Using a Circulating Loop
Authors: Bergano Neal S. , Aspell Jennifer , Davidson C. R. , Trischitta P. R. , Nyman B. M. , Kerfoot F. W.
Published: February 2023

Recently, we reported the results of a 2.4 Gb/s and 5 Gb/s feasibility demonstration of long distance erbium-doped fiber amplifier (EDFA) transmission systems using a circulating loop[1] The significance of this experiment was threefold. First, it demonstrated that high bit rate all-optical EDFA transmission systems are capable of achieving transoceanic distances. Second, it demonstrated a new measurement technique in which bit-error-rate (BER) is measured in a circulating loop. And, third, it achieved a new record in bit rate distance products.
Diode-Pumped, Electrically Tunable Erbium-Doped Fiber Ring Laser with Fiber Fabry-Perot Etalon
Authors: Zyskind J. L. , Sulhoff J. W. , Stone J. , DiGiovanni D. J. , Stulz L. W. , Presby H. M. , Piccirilli A. , Pramayon P. E.
Published: February 2023

An all fiber, diode-pumped, electrically tunable ring laser is reported. Gain is provided by an erbium-doped fiber and tuning by a Fiber Fabry-Perot etalon. The threshold at 1.566 µm is 2.9 mW, the slope efficiency is 0.15 and the output power is 4.2 mW with 32 mW of pump power. The output wavelength can be tuned from 1.525 to 1.586 µm with a variation in power of less than 3.5 dB.
Nonlinear Effects in Semiconductor Optical Amplifiers
Authors: Mukai Takaaki , Saitoh Tadashi
Published: February 2023

A traveling-wave semiconductor laser amplifier (TWA) [1]-[4] can greatly simplify optical repeaters used in wavelength-division-multiplexed (WDM) systems, since its wide gain band width allows a single TWA to simultaneously amplify signals of different wavelengths. Even though such system performance in the linear gain regime is determined only by amplifier noise properties [5],[6], the onset of nonlinear effects in optical amplifiers result in crosstalk [7].
High Power 980 nm Ridge Waveguide Laser in Single Mode Fiber Coupled Package
Authors: Murison Richard F. , Lee Shuyen R. , Holehouse Nigel , Moore Alan H. , Dzurko Kenneth M. , Righetti Aldo , Grasso Giorgio , Fontano Flavio , Schaus Christian F. , Sun Shangzhu , Dinkel Nancy A. , Connolly John C.
Published: February 2023

Rapid progress in strained quantum well InGaAs/AlGaAs laser diodes has led to the wide acceptance of 980 nm diodes as potential pump sources for Er3+-doped fiber amplifiers (EDFA). In particular, ridge waveguides have proven to be ideal structures for such devices[1,2], promising ease of manufacture, and potentially high reliability[3]. In this paper, we report high coupled power from ridge waveguide lasers into large NA single-mode fiber designed for use in EDFA systems, using an industry-standard 14-pin DIL package outline. We also report systems performance obtained using these lasers as the pump source in a broad-band EDFA power amplifier.
Barium titanate self-pumped conjugation for GaAIAs and 1.09-µm Ar+ lasers
Authors: Cronin-Golomb Mark , Lau Kam Y. , Yariv Amnon
Published: February 2023

We report photorefractive passive phase conjugation1 of GaAIAs laser radiation at 815-865 nm and Ar+ laser radiation at 1090 nm. A ring passive phase conjugate mirror was used with BaTiO3 as the real-time holographic gain medium. At least 1.5 mW (50 mW/cm2) was required for the PPCM to begin operation. At 3.6 mW (126 mW/cm2) the reflectivity reached 16%, corresponding to 25% after correction for Fresnel reflections. The rise time, defined here as time taken to 90 % of steady state, was approximately 5/1 s W/cm2 at 514.5 and 815 nm, where /is the incident intensity. When the GaAIAs laser was replaced by an Ar+ laser emitting 35 mW (1.4 W/cm2) at 1090 nm the rise time measured 500// s W/cm2. In spite of the length of this time, the steady-state reflectivity reached 18% uncorrected for Fresnel reflections. We describe effects of the phase conjugate feedback into GaAIAs lasers and attempts at active mode locking. The fact that the PPCM operates at 1090 nm indicates that it can be used to correct distortions in Nd:YAG laser systems where aberrations in the solid-state gain medium might possibly be severe.
General vector theory of beam coupling in photorefractive media
Authors: Foote P. D. , Hall T. J. , Connor L. M. , Jaura R.
Published: February 2023

The constraints of crystal symmetries in photorefractive media necessitate a general vector treatment of light scattering to explain fully the qualities of observed photorefractive effects. Commonly used photorefractive crystals1 are generally anisotropic (as is evident from their natural birefringence and electrooptic properties). Previous treatments of wave coupling phenomena in these materials have included the imposition of vector properties (by consideration of special cases of input beam polarization states and crystal orientations) on results from essentially scalar coupled wave theories. We report an approach to the beam coupling problem in which no such scalar field approximations are made. This work has revealed new results, supported by experiment, which do not arise from previous less general analyses.
Detection of high frequency gratings in the periphery
Authors: Thibos Larry N. , Walsh David J.
Published: February 2023

It has been known since the classic work of Wertheim (1891) that visual resolution in the periphery falls off so rapidly that at 20° of eccentricity acuity is reduced by the factor 10 relative to the fovea. Although optical quality deteriorates somewhat in the periphery, evidently a broad range of spatial frequencies may be present but not resolvable in the peripheral retinal image. One wonders what role, if any, these image components play in peripheral vision. During experiments designed to measure resolution in the periphery it became evident that this band of frequencies was more a range of confusion than a range of invisibility. When confronted with a grating well above the resolution limit, subjects were confident that a spatial pattern was present because they could perceive contrast. With practice it became possible for some individuals to perceive, for a fixed stimulus, a cavalcade of gratings of rapidly changing orientation and relatively low spatial frequency. This perceptual ambiguity vanished when the stimulus frequency was reduced to a value near the accepted limit for grating resolution. The most likely explanation for these observations is aliasing caused by the relatively low sampling density of neurons in peripheral retina.
Phase-conjugate fiber-optic gyro
Authors: Yeh Pochi , McMichael Ian , Khoshnevisan M.
Published: February 2023

We describe a new type of fiber-optic gyro which utilizes the phase reversal of the conjugation process, and we report some preliminary experimental results. Polarization scrambling is a well-known source of signal fading and noise in fiberoptic gyros. Polarization-preserving fibers and couplers must be used to decouple the two states of polarization and hence improve the sensitivity.1 In the phase conjugate fiber-optic gyro, a scalar phase conjugator is employed to restore the severely scrambled waves to their original state of polarization. This eliminates the signal fading and noise due to polarization scrambling. Consider a fiber loop which contains a phase conjugate reflector at the end. The net phase shift of light completing a round trip is proportional to the rotation rate and can be used for rotation sensing. In addition, if the phase conjugate reflector is scalar2, the polarization state will not change on reflection. Such a scalar phase conjugator will produce a true time-reversed version of the incident wave and will undo all the reciprocal changes (e.g., polarization scrambling, modal aberration, temperature fluctuation) when the light propagates backward from the phase conjugator to the input coupling. Since the polarization scrambling and modal aberration of the multimode fibers can be corrected by scalar phase conjugation, even multimode fibers can be used in this new type of gyro. We have demonstrated the correction, by scalar phase conjugation, of polarization scrambling and modal aberration, in single and multimode fibers. We have also measured the conjugate phase shift introduced by rotation.
Restoration of blurred images by convolution of arbitrary point spread function
Authors: Jiang Yaguang , Zhang Chenghua , Zheng Ling-Cheng
Published: February 2023

The holographic inverse filter produced in 19831 has proved successful in the deblurring of linear blurred and defocused images. The purpose of this paper is to further demonstrate its new use, i.e., the restoration of blurred images resulting from convolution of arbitrary point spread function. The characteristic features of the holographic inverse filter are (1) it is generated by using a weak reference beam instead of a sandwich filter; (2) to compensate the narrow dynamic range of the recording material, a mask is inserted in front of the holographic plate to attenuate the object and reference beams at the same rate; (3) a noise suppression technique is used with the holographic inverse filter to eliminate noise and achieve high image clarity.
Coherent mode representation of a Bessel-correlated source and of the field it generates
Authors: Kim K. , Foley John T.
Published: February 2023

The coherent mode expansion1 of the cross-spectral density of a Bessel-correlated primary spherical source is presented. Explicit expressions for the coherent mode eigenvalues and eigenfunctions are obtained. The dependence of the eigenvalues on the correlation length of the source is analyzed. The corresponding coherent mode expansion of the cross-spectral density of the field generated by this source is also investigated.
Photorefractive resonators
Authors: Ewbank M. E. , Yeh Pochi
Published: February 2023

The strong nonlinear optical coupling in photorefractive crystals, such as BaTiO3, readily permits the construction of efficient phase-conjugate reflectors and self-pumped optical resonators. These latter devices1 exhibit two peculiar properties. First, the oscillating beam differs in frequency2 from the pumping beam by a small amount (Δω/ω ~ 10−15) and, second, the self-oscillation apparently occurs at any optical cavity length. Careful experiments reveal that, when the self-oscillation is confined to a single spatial mode, the frequency difference between the oscillation and pumping beams is directly proportional to the amount of cavity length detuning away from an integer number of optical wavelengths (mλ). That is, when the resonator cavity length is slightly less than mλ, the self-oscillation frequency is upshifted with respect to the pump frequency; when the length is slightly greater than mλ, the oscillation frequency is downshifted; and when the length exactly equals mλ, there is no frequency difference. This observation is explained by an appreciable optical phase shift that accompanies nondegenerate two-wave mixing. In a photorefractive unidirectional ring resonator, the theoretical threshold conditions for oscillation are uniquely determined by the two-wave mixing gain (γL), the response time of the photorefractive crystal, and the ring cavity losses. Theoretical predictions agree with the experimentally observed oscillation threshold behavior.
Photorefractive deflection technique using parallel and overlapping probe pump beams
Authors: Gagne M. C. , Galarneau P. , Chin S. L.
Published: February 2023

Most of the experimental work on photoacoustic (PA) and photothermal (PT) effects in gases, performed with the optical beam deflection technique, concerns either the propagation of a sound wave1 (thus probing the area far from the irradiated region), or the thermal properties of these gases2 (thus probing the boundary of the irradiated region with a probe beam crossing the pump beam). In this paper we report on an experimental study of a photorefractive deflection technique in which the probe beam used is principally inside the irradiated region. Our results are therefore a complement to the aforementioned works. To probe the interior of the irradiated region, no crossing of the probe and pump beams is allowed. Thus, in the present work, the two beams are parallel. This method can be used to align collinearly several cw laser beams to an error better than 3 µm.
Numerical simulation of Injection-locking of diode laser arrays
Authors: Hadley G. Ronald
Published: February 2023

Diode laser arrays which possess lateral asymmetry in the gain have been shown to radiate into a single off-axis lobe in the far field. This effect has been ascribed to tilted phase fronts induced by the gain variation.1 Recent experiments indicate that a similar effect may be produced by injection of an external beam into one of the outside stripes. In this case, the single-lobed pattern is assumed to be due to the gain imbalance resulting from the injection. In this paper we report the numerical simulation of the injection locking of a five-stripe gain-guided diode laser array which predicts the above observations as well as changes in the far-field emission pattern which result from scanning the injection frequency. Our numerical calculations provide a useful tool for the understanding of mode control in injection-locked diode laser arrays.
One-step encoding technique for the archival storage of color films utilizing white-light processing
Authors: Chao T. H.
Published: February 2023

A one-step encoding technique for the archival storage of color films utilizing a white-light grating interferometer is described. The white-light grating interferometer comprised of three pairs of diffracting gratings each with a different azimuthal orientation and an imaging system is employed to simultaneously produce different spatial carriers to each of the tricolor components of the input color image such that the color encoding process can be implemented in one step. This real-time encoding technique greatly simplifies the traditional color encoding process.1,2 Since a spatially extended white-light source is utilized, low-noise high-fidelity recording of a color image on monochrome film can be obtained. Experimental demonstrations are also provided.
Spatiotemporal patterns of bleaching in rod photoreceptors
Authors: Makino Clint L. , Howard Louis N. , Williams Theodore P.
Published: February 2023

In vertebrates, the cylindrically shaped rod photoreceptors are oriented with their long axes facing the incoming light. Therefore, the rhodopsin molecules housed in the photoreceptors will not bleach uniformly when the eye is exposed to light. Rhodopsins located at the base, closest to the inner segment, will receive the incoming light first and momentarily screen the rhodopsins located at the more sclerad distal tip. As the basal rhodopsins bleach, photons become available farther along the outer segment to bleach more distal rhodopsins. An effort was made to describe this bleaching gradient. A mathematical model was proposed for a case in which the following assumption was made: if photoexcitation caused a rhodopsin to bleach, the bleaching occurred immediately and permanently. The validity of the model was tested with the aid of a microspectrophotometer. Absorbance was measured as a function of location along the outer segment in individual photoreceptors. Finding good agreement, the model is currently being extended to the case of steady state bleaching, by taking into account the recent finding that bleached pigments regenerate nonrandomly in situ.1 These spatiotemporal patterns of bleach are likely to have a functional significance with respect to light and dark adaptational processes.
Design of aspherical laser cavities
Authors: Shealy David L. , Chao Shao-Hua
Published: February 2023

Most previous attempts reported in the literature to reshape the Gaussian energy density profile of the fundamental mode of a laser into a more uniform irradiance beam have been accomplished by using lenses, mirrors, or gratings external to the laser cavities.1,2 The idea of deforming one mirror of a laser resonator by introducing a second discontinuity of the mirror surface to reduce diffraction effects has been investigated.3 The geometrical optics properties of aspherical optical resonators with nonuniform magnification have also been investigated.4 In the present work, a new method to reshape the energy profile of laser beams is explored. Kirchhoff diffraction theory has been applied to the design of confocal aspherical laser cavities, which represents an extension of the Fox-Li laser cavity theory. The added degrees of freedom of aspherical cavity mirrors offer attractive options for obtaining more uniform irradiance laser beams, taking into account diffraction effects.
Competition between coherent and incoherent nonlinear optical processes
Authors: Gauthier Daniel J. , Malcuit Michelle S. , Boyd Robert W.
Published: February 2023

Competition has been observed between amplified spontaneous emission (ASE) and four-wave mixing (FWM). Previously, competition between an incoherent and coherent process was observed in the form of suppression of multiphoton ionization by third harmonic generation.1,2 In our experiment, an input laser was tuned precisely to the 3s → 3d two-photon allowed transition in atomic sodium vapor and the emission was observed in both the forward and backward directions. In these conditions, either FWM or ASE can occur. Ignoring the possibility of competition between these two processes, the calculated gain for ASE is much larger than that for FWM. However, we have observed experimentally that FWM and not ASE occur. To determine that it is the presence of efficient FWM that suppresses ASE, we have excited the atomic vapor instead with counterpropagating pump waves of different frequency. In this case, FWM, being a phase-matched process, cannot occur and strong ASE is observed. The nature of this competition is explained by solving the coupled Maxwell and density matrix equations for a three-level system. It is found that the suppression is due to the destructive interference between two different pathways of excitation of the 3d level which results in trapping of the population in the ground state.
Why rod cone interactions?
Authors: Buck Steven L. , Knight Roger , Hogden John
Published: February 2023

Scotopic backgrounds can raise increment thresholds for photopic test stimuli (CXR) and vice versa (RXC). CXR is ubiquitous with variation of test stimulus duration (20-1000 ms) and size (6-120 min of arc) but varies tremendously with retinal eccentricity. At 4°, only 0.2-0.4 log unit of CXR is found, and only on small backgrounds. At 10°, up to 1.4 log unit of CXR is found, with at least 0.2 log unit on any size background. These results parallel previous findings for RXC1 except that the direction of eccentricity dependence is reversed. The results are consistent with the center-surround model of interaction and parallel with spatial sensitization.
Theory of two-photon multiwave mixing
Authors: Ovadia Shlomo , Sargent Murray , Lu Mao Hong
Published: February 2023

Two-photon transitions have provided the basis for numerous useful nonlinear interactions with radiation. In this paper we calculate the absorption and coupling coefficients for one-, two-, and three-wave mixing in two-photon homogeneously broadened media. The resulting field equations form the basis for understanding saturation spectroscopy, phase conjugation,1 and single-mode instabilities2 in lasers and optical bistability in two-photon media. We assume that the wave frequencies are not resonant with any intermediate state j and that the probe and conjugate waves cannot saturate the two-photon transition. This allows us to use the two-photon two-level model and to transfer much of our knowledge of the one-photon two-level systems to the two-photon case. Two major differences occur between the two models. First, dynamic Stark shifts of the active levels play an important role in generating asymmetric spectra and nonzero dispersion (≃ω
s
T1) at line center. Second, high pump intensities do not bleach the absorption coefficient at the Rabi sidebands.
Reflectivity of a spatially dispersive nonlinear Fabry-Perot etalon
Authors: McGinnis B. P. , Sarid Dror , Peygham-Barian N.
Published: February 2023

The effect of spatial dispersion in a Fabry-Perot etalon containing an excitonic system, for a normally incident light field, is to generate two coupled exciton polariton modes. The interference of these modes provides extra reflectivity features. We have calculated1 polariton density-dependent reflectivities and by employing the upper- and lower-branch polariton energy velocities,2 found the absolute internal cavity intensity. We now report on the spectral reflectivity response using an iterative method where the internal polariton density is adjusted to maintain a constant incident intensity. The resultant figures can be directly compared to experimental results. We will discuss the role of the mechanical contribution to the Poynting vector and the oscillator energy density as well as the effects of boundary conditions and energy conservation on the model.2 Comparison with reflectivities from a nonspatiaily dispersive model shows a convergence toward similar spectral reflectivities for high incident intensities.