bluuebunny/crossref_metadata_2025 huggingface dataset:
Near Infrared Absorption Properties of PTS and Poly(4-BCMU) Crystals and Thin Films
Authors: Krug William P. , Miao Edward
Published: February 2023

Conjugated organic polymers are promising nonlinear optical materials for high-speed photonic switching1,5 and signal processing applications. For their potential use in light-control-by-light serial guided-wave wideband devices, large optical refractive nonlinearities6,7, n2, and ultrafast response times, τ, are widely recognized as important material parameters. However, low linear optical absorption, α, has received considerably less attention. In an optical device based upon a nonlinear refractive optical material, a large n2/α is required to minimize the optical energy dissipated.
Ultrafast Dynamical Nonlinearities in GaAs Microstructures
Authors: Oudar J.L.
Published: February 2023

Direct-gap semiconductors, such as GaAs, present strong dynamic optical nonlinearities. The saturation of their absorption caused by the photoexcitation of electron-hole pairs, and its associated nonlinear refractive index, have attracted particular interest since both effects allow the operation of optical gates and bistable devices. Since the response time of these nonlinear optical effects is governed by the relaxation dynamics of the excited states, it is important to improve our understanding of the relaxation mechanisms which influence the behaviour of electron-hole pairs.
Superradiative Decay and Enhanced Optical Nonlinearity of Excitons in Qunatum Wells
Authors: Hanamura E.
Published: February 2023

We evaluate the exciton coherence length and discuss theoretically how it determines its superradiative decay time and its third-order optical nonlinearity in the qunatum wells and microcrystallites.
Applications Requirements for Nonlinear Optical Devices and the Status of Organic Materials
Authors: Boyd G. T.
Published: February 2023

Much of the history of organic nonlinear optical (NLO) materials has involved measurements and calculations of intrinsic NLO properties, motivated by the promise of device applications1. The requirements of NLO devices are used here to assess the status of organic materials and suggest research directions.
Erbium-Doped Fiber Amplifiers for Optical Fiber Communications
Authors: Desurvire E.
Published: February 2023

The field of erbium-doped fiber amplifiers (EDFA) [1-4] has expanded rapidly, from the developments in rare-earth-doped fiber fabrication [5-8], to the more recent demonstration of practical laser-diode pumped devices [9-11]. Because of their many advantages, it is likely that EDFA’s will contribute to significant progress in future 1.5μm optical fiber communication systems [12]. The interest of using optical amplifiers, as an alternative to electronic repeaters, is that they make it possible to upgrade the information-carrying capacity of a system by simply increasing the data rate and/or the number of optical channels.
Erbium-Doped Fibers Improvement For Optical Amplifier Modules
Authors: Marcerou J.F. , Fevrier H. , Auge J. , Clergeaud C. , Landais S. , Briancon A.M. , Jacquier B.
Published: February 2023

Erbium-doped fiber amplifiers (EDFA) are very attractive for all optical long span transimissions in the third telecommunication spectral window. Recently, over 2000km repeaterless transmission experiments have been performed with EDFA [1]. Two pump wavelengths appear truly excellent because of their very high performances and laser diode pumping feasibility : 1.48μm and 0.98μm, each of them having its own specificity [2]. Today’s best reported pump efficiency are 2.6dB/mW for color center laser pumping near 1.48μm [3] and 4.9dB/mW for a 0.98μm laser diode pumped amplifier [4]. The increase of the last year published EDFA performances clearly demonstrate that we may be far from optimized fibers.
18-dB Fiber to Fiber Gain in Packaged Semiconductor Laser Amplifiers
Authors: Tsuji S. , Haneda M. , Toyonaka T. , Nakano H.
Published: February 2023

Packaged semiconductor laser amplifier with 18-dB fiber to fiber gain is firstly demonstrated. Internal gain is estimated to be 28-dB, by the precise measurement of coupling efficiency using TE and TM mode gain difference for various pumping currents.
Multi-Section Semiconductor Laser Structures for Optical Traveling Wave Amplifiers
Authors: Ludwig R. , Schnabel R. , Schunk N. , Weber H.G.
Published: February 2023

Multi-section lasers are proposed as traveling wave amplifiers. First experiments reveal that they are better adjustable to various applications than conventional single-section devices.
A 2.5 Gb/s, 364 km CPFSK Repeaterless Transmission Experiment Employing an Er-DOPED Fiber Amplifier and SBS Suppression Optical Link
Authors: Sugie Toshihiko , Ohkawa Norio , Imai Takamasa , Ito Takeshi
Published: February 2023

In conjunction with an erbium-doped fiber(EDF) booster amplifier of about +20 dBm output and Raman amplification, a repeaterless transmission over 364.3 km optical fiber suppressing Stimulated Brillouin Scattering(SBS) is demonstrated by 2.5 Gb/s CPFSK heterodyne detection system.
Spectral Dependence of Gain Saturation and Effect of Inhomogeneous Broadening in Erbium-Doped Aluminosilicate Fiber Amplifiers
Authors: Desurvire E. , Sulhoff J. W. , Zyskind J. L. , Simpson J. R.
Published: February 2023

As erbium-doped fiber amplifiers (EDFA) [1-3] promise to play a major role in optical fiber communications [4], the optimization of the amplifier pumping efficiency and saturation power is becoming an important issue. In the large-signal regime, the effect of inhomogeneous gain broadening [5] results in gain hole-burning, which reduces both efficiency and power extraction. It was shown that aluminosilicate Er:glass has an advantageously large (26nm) homogeneous gain bandwidth [6] with comparatively small (11.5nm) inhomogeneous component [7]. On the other hand, for germanosilicate Er:glass inhomogeneous saturation is observed at relatively low signal powers [8]. Theoretical models evolved so far [6,9] assumed homogeneous broadening and therefore cannot be used for an in-depth study of saturation effects in these two types of fiber amplifiers. In this paper, the spectral dependence of gain saturation in an aluminosilicate EDFA is studied experimentally and theoretically. A theoretical model representing, to our knowledge, the first attempt to model both homogeneous and inhomogeneous gain saturation in EDFA’s, is presented. A second model using the same parameters but assuming completely homogeneous broadening is used for comparison. The calculated signal and amplified spontaneous emission (ASE) spectra are then compared to experimental data. It is observed that the strong spectral dependence of gain saturation is quite well described by the homogeneous model. However, the inhomogeneous model is seen to provide a more detailed description of the changes in the ASE spectrum.
Noise Figure of a Gain-Saturated Erbium-Doped Fiber Amplifier Pumped at 980 nm
Authors: Way W. I. , Von Lehman A. C. , Andrejco M. J. , Saifi M. A. , Lin C.
Published: February 2023

Erbium-doped fiber amplifiers (EDFAs) have recently been extensively studied for applications in long-distance transmission[1] [2] and subscriber loop distribution systems[3][4][5]. The noise figure of the fiber amplifier is a parameter that must be considered in these systems to optimize overall system performance. Noise figures of an EDFA pumped at 1480 nm and 980 nm were reported to be near 5 dB[6], and 3 dB[7], respectively. However, these numbers were measured when the amplifiers were operated in the linear region. An EDFA may be operated in the gain saturation region when it is used as a power amplifier in the subscriber loop[3] [5], or when it is one of the latter stages of many cascaded amplifiers in a transmission system. In the latter case, the amplifier gain saturates because of the accumulated amplified spontaneous emission (ASE) noise, which may be due to the finite passband of interstage optical filters, or because there is not enough inter-stage loss to compensate the amplifier gain. Under the above conditions, questions arise as to whether the amplifier noise figure increases while the gain is saturated, and what are the parameters that control this noise figure degradation. The subject of this paper is to examine these questions.
1.3/1.55 μm Band Simultaneous Amplifier Comprising Nd3+-Doped and Er3+-Doped Fluoride Fibers
Authors: Miyajima Yoshiaki , Sugawa Tomoki , Komukai Tetsurou
Published: February 2023

The rare-earth ion doped silica fiber amplifier is being studied as a very attractive device for use in telecommunication systems, because it has high gain, polarization-insensitive, low-noise and low-insertion loss characteristics. However, the disadvantage of a narrow bandwidth has been pointed out for Er3+-doped silica fibers. There is also a disadvantage with Nd3+-doped silica fibers in that it is very difficult to use them to obtain a gain around 1.3 μm.
Four-Wave Mixing Levels in a Semiconductor Optical Amplifier with FSK Modulation at 155 Mb/s
Authors: Inoue H. , Sessa W. B. , Elrefaie A F. , Wagner R. E. , Tsuji S.
Published: February 2023

Semiconductor optical amplifiers (SOAs) are expected to increase the network application capabilities of future lightwave systems. Traveling-wave (TW) SOAs are particularly suitable for multi-channel coherent systems, where several tens of lightwave signals with different frequencies may be amplified by the TW-SOA after multiplexing [1]. Recently, a photonic integrated circuit with 4 DBR lasers, a combiner and a TW-SOA has been reported as an excellent example of the use of TW-SOAs in frequency division multiplexing (FDM) transmitters [2]. It has been pointed out, however, that for close channel spacing and at high amplifier input power level, there can be significant crosstalk among the channels arising from nondegenerate four-wave mixing (FWM) in the TW-SOA [3]. In this paper, we evaluated the FWM signal powers, including first and higher orders, under CW condition and with FSK modulation at 155 Mb/s. We find that a channel spacing larger than 10 GHz is necessary to avoid crosstalk due to FWM in a conventional TW-SOA with a high total input power level of about -7 dBm at the amplifier facet.
Intermodulation Distortion and Crosstalk in Cascaded Laser Amplifiers
Authors: Durhuus T. , Mikkelsen B. , Stubkjaer K.E.
Published: February 2023

It is anticipated that more than one optical amplifier will be inserted between transmitters and receivers in distribution networks as well as in long haul links for which the transmission is limited by loss and not by dispersion. Further, if densely spaced multichannel systems are implemented for effective utilization of the transmission medium, optical amplifiers may introduce intermodulation distortion (IMD) and crosstalk between the channels [1]-[3], [5], and [7]. In this paper we present an experimental and theoretical analysis of carrier induced nonlinearities in cascaded laser amplifiers. Previously, an analysis of noise accumulation in cascaded amplifiers was presented [4].
Wavelength Division Multiplexers for 980 nm Pumping of Erbium-Doped Fiber Optical Amplifiers
Authors: Hall D. W. , Truesdale C. M. , Weidman D. L. , Vance M. E. , Button L. J.
Published: February 2023

The choice of wavelength division multiplexer (WDM) couplers for use in fiber-based optical amplifiers is extremely important to obtain optimum device performance. At a minimum, these devices need to have low insertion loss at the doped-fiber pump and signal wavelengths, λp and λs. Small splice losses between the coupler input pigtail and the incoming telecommunication fiber at λs and between the coupler output pigtail and the Er-doped gain fiber at λs and λp are important to maximize amplifier signal-to-noise and to efficiently use available pump power. In addition, in high-gain amplifier applications, coupler backscatter and crosstalk may also impact noise. Finally, as practical amplifiers tend towards smaller physical size, bend induced loss in the coupler pigtails also becomes an important factor.
A Multi-Gb/s Self-Synchronized Optical Regenerator Using a 1.55 μm Traveling-Wave Semiconductor Optical Amplifier
Authors: Izadpanah H. , Elrefaie A. , Sessa W. , Lin Chinlon , Tsuji S. , Inoue H.
Published: February 2023

We demonstrate experimentally and by computer simulation that the semiconductor optical amplifiers (SOAs) are capable of performing a variety of optoelectronic (OE) functions useful in fiber-optic networks and optical signal processors at multi-Gb/s rates[1,2]. An example of OE functions obtained is a complete optical regeneration of data pulses which are amplified, retimed, and reshaped in optical domain. In this paper, we present results on a 1.55 μm traveling-wave (TW) SOA optical regenerator with a novel clock recovery circuit for retiming and synchronization. The regenerator operates at a 2.5 Gb/s rate, with a 10 dB fiber-to-fiber gain. In contrast to the 1.31 μm SOA reflective regenerator reported recently[1] at 560 Mb/s, the present amplifier is a packaged 1.55 μm traveling-wave amplifier[3], which operates at much higher bit rate, higher gain, and includes the self-synchronized clock recovery circuit.
Radiation Sensitivity of Erbium-Doped Fiber Amplifiers
Authors: Wada A. , Sakai T. , Tanaka D. , Yamauchi R.
Published: February 2023

Erbium-doped fiber amplifiers are promising as a booster, a repeater and a preamplifier in the long haul transmission systems like submarine transmission lines because of their desirable features1). Radiation resistance characteristics are one of the important reliability issues for such long haul lines. Several radiation-induced loss measurements have been reported2,3), however a dierct measurement of gain reduction by irradiation has not been seen so far. We report in this paper on the radiation sensitivity including the gain reduction for Er-doped fiber amplifiers.
Preamplified Direct Detection Versus Heterodyne Detection: Can they be Equivalent?
Authors: Tonguz Ozan K. , Wagner Richard E.
Published: February 2023

In this paper the interrelationship of heterodyne receivers and preamplified direct-detection receivers is explained. We show that under certain conditions these two lightwave receiver types have equivalent performance. Furthermore, it is shown that this is a general result which is independent of the modulation format used.
A High Power and Low Noise Transmitter for AM-VSB Transmission Using Erbium-doped Fiber Post Amplifier
Authors: Shigematsu Masayuki , Nishimura Masayuki , Okita Toshio , Iizuka Kazuo
Published: February 2023

Erbium doped fiber amplifiers(EDFAs) with high output power and no distortion degradation are very useful for the amplitude-modulated vestigial-sideband(AM-VSB) transmission systems which require a relatively high received power for a preferred carrier to noise ratio(CNR) and a low distortion[1][2], A field trial was conducted and feasibility of multidistribution for trunk lines was confirmed[3].
Dynamics of DFB Semiconductor Laser Amplifiers
Authors: Wang Z. , Durhuus T. , Mikkelsen B. , Stubkjaer K. E.
Published: February 2023

DFB laser amplifiers are very attractive for optical filtering because they can serve both as channel and noise filters and at the same time provide amplification. They may be used as filters in switching network or as receiver preamplifiers in multichannel direct detection systems [1]. Amplifiers incorporating DFB structures have also been suggested for wavelength converters [2]. For such applications it is important to understand the dynamic behaviour of DFB amplifiers when they are used in high speed systems. Especially, it is interesting to know the influence of the very narrow gain spectrum on short optical pulses.
Measurement of Polarization Dispersion in the Components of In-Line Erbium Doped Fiber Amplified Links
Authors: Bernard J.J. , Bruyere F. , Guillon J.
Published: February 2023

An experimental investigation of polarization dispersion of an in-line erbium doped fiber amplified link has been carried out. Results show a non negligible contribution of the isolators.
Automatic Gain Control of Erbium-Doped Fiber Amplifier by Detecting Spontaneous Emission Power along the Fiber
Authors: Aida Kazuo , Masuda Hiroji
Published: February 2023

EDFA gain control is achieved by detecting the spontaneous emission power radiated along the EDF and modulating the pump LDs with optoelectronic feedback.
Optimized Nonregenerative Repeater Using Cascaded Erbium-Doped and Raman Fiber Amplifier
Authors: Zhang S. L. , O’Reilly J. J.
Published: February 2023

Fiber-based optical amplifiers such as the erbium-doped fiber amplifier (EDFA) and Raman fiber amplifier (RFA) offer the attraction of high gain, low coupling loss and polarization insensitivity. Hence their use in combination to form a nonregenerative repeater (NRR) deserves consideration. This paper provides a theoretical analysis and gain optimization for this form of NRR. This arrangement is found to provide higher gain than either an EDFA or a RFA repeater alone and offer the potential of extending the NRR span to over 300 km.
System Limitations for Fiber Amplifier Cascades
Authors: Ito Takeshi
Published: February 2023

The performance of an amplifier cascade system is taken to be the product of transmission bit rate, B, and transmission distance, L. In amplifier cascade systems using the IM/DD scheme, signal spontaneous beat noise, spontaneous-spontaneous beat noise and shot noise are present in addition to receiver thermal noise, while local oscillator shot noise and local oscillator-spontaneous beat noise are additional factors in coherent systems. Signal-spontaneous and spontaneous-spontaneous beat noises generally predominate in IM/DD systems if many cascaded amplifiers are used.
Widely Tunable Actively Modelocked Erbium Fibre Ring Laser
Authors: Pfeiffer Th. , Schmuck H.
Published: February 2023

Erbium fibre lasers offer a large variety of features such as large tuning range /1/, high output power /1/, modelocking at repetition rates beyond 10 GHz /2/, Q-switching /3/ and single longitudinal mode opera tion /4/. In this paper we present a 980 nm laser diode pumped erbium-doped fibre ring laser that combines a large tuning range of 33 nm with picosecond pulse generation by active modelocking at repetition rates up to 6 GHz.
Coupling Between Barrier and Quantum Well Energy States in A Multiple Quantum Well Optical Amplifier
Authors: Tessier N. , Nagar R. , Eisenstein G. , Koren U. , Raybon G.
Published: February 2023

Multiple quantum well (MQW) optical amplifiers have recently been demonstrated. It has been shown that these MQW amplifiers have excellent characteristics such as high gain, large saturation power and low noise [1–3]. In addition to being excellent devices, they can serve as convenient tools to study the gain dynamics in an inverted MQW media.
Phase Modulation and Optical Switching by Semiconductor Laser Amplifier
Authors: Labrujere A.C. , Steenbergen C.A.M. , van der Laar C.J.
Published: February 2023

Operation of a semiconductor laser amplifier simultaneously as phase modulator and optical switch is proposed. Theoretical and experimental results on performance in saturation are reported.
Accurate modeling of distributed Erbium-doped Fiber Amplifiers with bidirectional pump
Authors: Desurvire E. , Chen D.
Published: February 2023

In this paper, we present an analysis of unsaturated erbium-doped fiber amplifiers (EDFA) with fiber back-ground loss and bidirectional pumping. This analysis provides an exact closed-form expression for the amplifier gain as a function of input pump power. This model is useful to study distributed EDFA's [1,2] and to determine the optimal Er3+ concentration and pumping configuration that minimizes the required pump power, as shown in this paper. In the case of forward pumping, it is also shown that a simple relation exists between the input pump power required for EDFA transparency and pump threshold, which can be usefully applied to EDFA characterization.
Non-linear excited state absorption in Er3+-doped fibre with high-power 980nm pumping
Authors: Sceats M.G. , Krug P.A. , Atkins G.R. , Guy S.C. , Poole S.B.
Published: February 2023

We report the measurement of non-linear excited state absorption (ESA) in Er3+-doped fibres pumped at 980nm. The implications for high-power high-gain amplifiers are discussed.
Amplification Reduction in Fiber Amplifiers Due to Up-Conversion at Er3+-Concentrations Below 1000 ppm.
Authors: Blixt P. , Nilsson J. , Carlnäs T. , Jaskorzynska B.
Published: February 2023

One of the key parameters for optimizing erbium-doped fiber amplifiers (EDFAs) is the Er3+-concentration profile. Below the concentration for onset of component clustering, up-conversion may play a significant role [1]. Recent experiments have shown that up-conversion is a considerable deteriorating mechanism even below an erbium concentration of 1000 ppm by weight
Erbium-Doped Fiber Amplifiers Pumped in the 800-nm Band
Authors: Pedersen B. , Zemon S. , Miniscalco W. J. , Singh M. P.
Published: February 2023

The performance of fiber amplifiers is extremely sensitive to the material-dependent properties of the pump band. High-power, reliable, low-cost diode lasers are currently only available at 800 nm, a poor pump band for Er3+ due to the low strength of the ground state absorption (GSA) transition and an intense, overlapping excited state absorption (ESA) band. High gains have been achieved with silica fibers by pumping the long-wavelength wing of the GSA band at ≈820 nm [1,2], thereby avoiding the ESA at shorter wavelengths but introducing another problem by reducing the already low GSA cross section at the pump wavelength. Alternatively, the use of other glass host compositions with reduced ESA has been proposed [3]. We have examined both approaches using experimentally determined parameters in a highly quantitative numerical model to compare the performance of Al/P-silica, Ge/P-silica, and fluorophosphate fiber amplifiers. The analysis was performed for co- and bi-directional pumping and included treatments of waveguide design, Er3+ confinement, pump-wavelength dependence of gain and noise figure, and quantum conversion efficiency for power amplifiers.
Natural and Induced Space Radiation Effects on Coated Laser Optics
Authors: Donovan T. M.
Published: February 2023

The reflectance of metal-enhanced, high-reflectance mirrors containing amorphous Si and SiO multilayers has been found to be stable in a simulated natural space environment containing the combined effects of solar ultraviolet light, energetic protons, and electrons.1 By eliminating the metal-enhancing layer from the stack and depositing the coating design on a silicon or fused silica substrate, the resulting low atomic number (Z) structure presents a low-absorption cross section for x-rays. Thus, it becomes an interesting design for studying the thermal and thermomechanical response of multilayer coatings to pulsed x-ray deposition.
Optics for the Free Electron Laser
Authors: Karr Thomas J.
Published: February 2023

Summary not available.
Variation of the Index of Refraction in Glasses Exposed to Ionizing Radiation
Authors: Englert Thad J. , Flohr Mark
Published: February 2023

The attenuation of lightwaves propagating through optical fibers that have been exposed to ionizing radiation has been the subject of considerable experimental and theoretical investigation during the past few years.1

This attenuation has been attributed to the creation of color centers within the glass comprising the core and cladding of the fiber, these color centers generally being located at impurity sites.2 Very little effort has been reported dealing with any study of the effects on the index of refraction of the materials of the fiber as a result of radiation exposure however.
Intracavity laser spectroscopy is more than a curiosity
Authors: Stoekel Fredéric
Published: February 2023

Use of lasers in spectroscopy has been demonstrated for several years by techniques as different as photoacoustic, optogalvanic, laser-induced fluorescence photoionization, and more recently frequency modulation. Each of these methods depends on some parameters which need calibration before quantitative measurements are made. Here we discuss a new type of high sensitivity intracavity laser absorption spectroscopy (ICLAS). Discovered fifteen years ago, this technique has now become more than just a curiosity. We show that if the laser is controlled in time (generation time) and the spectrum also resolved in time, ICLAS is similar to classical absorption with the advantage of an adjustable optical path length created by variation of the generation time.1 Path length of more than 100 km can in principle be obtained. We discuss the discrepancy in sensitivity obtained by different authors and show that the sensitivity can be completely explained by a time-dependent theory published by Mironenko and Yudson.2 Description of an intracavity laser spectrometer with a sensitivity of α = 10−9 cm−1 and a resolution of λ/Δλ = 800.000 is presented. The limitation in sensitivity is discussed.
Compact holographic sight
Authors: Upatnieks Juris
Published: February 2023

An optical sight was designed incorporating an edge-illuminated hologram and a remotely located He–Ne laser. The hologram projects a virtual image of a reticle at infinity and is illuminated by a laser through a fiber-optics lightguide. Edge illuminated holograms have several advantages over front illumination: laser light not diffracted by the hologram remains inside the glass plate and is not scattered by surface contamination, and sunlight is not diffracted into the viewers’ eyes. Edge illumination allows the sight to be compact with large exit aperture. Edge-illuminated hologram recording presents a number of unique problems. Recording in ordinary holographic plates results in low diffraction efficiency and low-contrast images. Preprocessing of the plates to reduce silver-halide content improves the results. Exact refractive-index matching between the photographic plate, emulsion, and cover plate is needed to avoid excessive surface reflections. Photographs of the sight module and projected reticle are shown.
Exposure optimization for incoherent computer holography
Authors: Gaynor Edwin S. , Rhodes William T.
Published: February 2023

Computer holograms can be formed of 3-D objects by exposing the hologram sequentially to lightwaves from different points on the computer-specified object (combined with an appropriate reference). For objects containing many resolvable points, the resultant exposures have low signal-to-bias ratios; if displays with adequate signal-to-noise ratio are to be obtained, optimization of the many recording parameters is essential. Because of the low signal-to-bias ratio, optimization methods differ from those applicable to conventional holography. However, they are generally more tractable theoretically. Of particular interest to us is optimization for bleached holograms. An analysis of the problem and its solutions, along with the results of experimental studies, are presented.
Mass and energy analysis of thin-film evaporant streams generated by pulsed laser heating
Authors: Nelson Jeffrey G.
Published: February 2023

Little is known about the physics of film growth with laser evaporation, compared with more conventional techniques such as thermal or sputtering. For example, there is evidence that the atomic nature of the laser evaporated materials may be responsible for the observed epitaxial growth at comparatively low temperatures. It is of fundamental interest to study the physical processes which lead to such results. Oxides (ZnO, Al2O3, SiO2) and fluorides (PbF2), which have been used to form high quality optical thin films, were evaporaed using a CO2 TEA laser with power densities exceeding 109W/cm2. The chemical state (atoms, molecules, or clusters) of the evaporants was determined using a residual gas analyzer (RGA). The relative concentrations of the different chemical species were measured as a function of laser conditions. Using the RGA in conjunction with a time-of-flight apparatus, the kinetic energy of the evaporants was also studied as a function of laser conditions. Finally, the effect of reactive (O2) and inert (N2, He) gases on the evaporation process was also studied.
Ion-beam-assisted deposition of metal oxide optical thin films
Authors: McNally J. J. , Al-Jumaily G. A. , McNeil J. R.
Published: February 2023

The properties of dielectric (Al2O3,
Ta2O5, HfO2, and TiO2)
films deposited using ion beam assisted deposition (IAD) have been
examined. Previously1 we have described the importance of
oxygen-ion energy and flux in applying IAD to dielectric materials and
examined some of the properties of TiO2 and SiO2
films. In this work we present results illustrating ion bombardment
effects on the thin film properties of Al2O3,
Ta2O5, and HfO2; in particular, film
stoichiometry is strongly dependent on the ion beam flux and energy, a
reduction in optical scatter is observed, and higher values of
refractive index are obtained for films deposited with simultaneous

O
2
+

bombardment. Also, in certain cases, Raman spectroscopy indicates a
crystalline phase change is induced by the O2 bombardment
of samples during film deposition.
Squeezing of classical and quantum noise in an optical fiber
Authors: Levenson Marc D. , Shelby R. M.
Published: February 2023

Near-degenerate four-wave parametric mixing in an optical fiber couples fluctuations in signal and idler frequency bands in such a way that the noise at a particular optical phase is reduced while that in an orthogonal phase quadrature is amplified. We have performed experiments on this effect and explained our results in terms of a theory which incorporates a nonlinear dispersion effect. The nonlinear dispersion alters the mathematical character of the solutions and limits the effective interaction length. For relatively low frequency shifts (<100 GHz) and 100 m of fiber, the heterodyne detected optical noise can be reduced by 5 dB in the squeezed quadrature. Theory predicts that this parametric interaction should reduce the noise level below the standard quantum limit. In a realistic fiber, phase noise due to guided acoustic wave Brillouin scattering (GAWBS) dominates the quanturn noise and cannot be reduced by four-wave mixing. Narrow gaps in the GAWBS noise can be engineered into special fibers. At the frequencies of these gaps, the noise level indeed can be squeezed below the quantum limit.
Monitoring quantum transitions in a three-level atom
Authors: Kimble H. J. , Cook R. J.
Published: February 2023

In a recent publication1 the question of the possibility of observing directly the quantum jumps associated with the excitation and deexcitation of an atomic electron in a three-level transition was considered. While the analysis of Ref. 1 reveals the manner in which the fluorescence from a strong transition of a lifetime T1 is modulated by the absorption and emission processes of a weak transition of lifetime T2 (T1 ≪ T2), it was restricted to the case of incoherent excitation of the two transitions. The purpose of the present work is to reconsider this problem for monochromatic excitation in which a variety of coherent effects come into play. The analysis proceeds in a straightforward fashion in the Heisenberg representation to yield expressions for field and atomic correlation functions representing probabilities for the detection of successive photons from the same transition as well as for cross correlations of emission probabilities. In the limit of T1 ≪ T2, a coarse graining of time with respect to the strong transition produces expressions analogous to those presented in Ref. 1. The roles of Autler-Townes splitting, frequency detuning, and saturation of the weak transition are discussed.
High precision measurements of atomic number densities
Authors: Hill Wendell T. , Ueda Kiyoshi
Published: February 2023

A quick and simple technique for determining line of sight number densities in atomic vapor ovens will be presented. The technique is based on measuring the frequency-dependent distortion of interference fringe profiles which is produced when an absorbing vapor is placed in one arm of a Mach-Zehnder interferometer. In contrast to previous interferometric methods, in which only the peak intensity positions of the fringes are measured, this method relies on measuring the entire intensity profiles of the fringes. This is made possible by placing a 1024-channel diode array detector at the exit plane of a spectrograph. The density is then determined with a precision of 1 % or better by fitting the experimental data to a simple analytic expression.
Schottky-type photovoltaic junctions with transparent conductor films
Authors: Croitoru N. , Zafrir M. , Amirhaghi S. , Harzion Z.
Published: February 2023

Junctions between transparent conductor (ITO) and single-crystal silicon or polycrystalline silicon (poly-Si) were prepared. Electrical I–V and C-V, as well as photovoltage decay (PVD) measurements, were performed. Data of open circuit voltage (Voc), short circuit current (Isc), fill factor (FF), efficiency (η), built-in potential (ϕ-
bl
), and lifetime were obtained. It was found that the lifetime of photogenerated carriers in the poly-Si/ITO junction is much shorter than in single crystal. There are two types of recombination center that have an essential influence on the efficiency of the solar cells; those at the contact between ITO and the silicon; and those due to the grain boundaries (GB) between the crystallites in poly-Si. The solar cells were annealed, either by heating them in vacuum or by irradiation with the light of a Cd–Ne laser (441.6 nm). The annealing reduced the influence of the recombination centers at the contact, whereas those at the GB were not affected. Passivation of GB with iodine improved the characteristics of the solar cells. This improvement is attributed to the reduction of the recombination centers at GB. The influence of the annealing and passivation on the lifetime of this type of cell was studied by measuring PVD.
High frequency modulation spectroscopy with tunable GaAs and lead salt diode lasers
Authors: Lenth W. , Gehrtz M. , Young A. T.
Published: February 2023

Tunable diode lasers covering the 0.8-30-μm spectral region are attractive light sources for the detection of gaseous species in applications like stack gas monitoring, pollution control, and industrial process monitoring. High frequency modulation spectroscopy with semiconductor lasers combines the simple and convenient tuning and modulation methods available for diode lasers with the high sensitivity and fast time response of optical heterodyne spectroscopy. We have tested the sensitivity limits of this technique, using NO2 and N2O absorption lines, and for the first time have implemented it with a lead salt diode laser. Semiconductor lasers can readily be frequency modulated at rf frequencies by directly modulating the injection current. However, the desired frequency modulation is accompanied by additional amplitude modulation. The zero background property of pure frequency modulation spectroscopy can be restored by careful adjustment of the local oscillator phase in the phase sensitive detection circuitry. The sample-induced signal arises from zero background and is detected at rf frequencies where diode lasers have little noise. The minimum detectable NO2 absorption (signal-to-noise ratio ≅ 1) was 1 × 10−7 for 1-Hz bandwidth and 5 × 10−4 for 20-MHz bandwidth. The sensitivity limit was essentially given by shot noise. The inherently fast response time of high frequency modulation spectroscopy is of particular interest for the investigation of gas kinetics and combustion processes.
Frequency modulation spectroscopy with microwave sidebands
Authors: Janik G. , Carlisle C. , Gallagher Thomas F.
Published: February 2023

Using a high efficiency resonant cavity phase modulator at 8.4 GHz and a new low frequency demodulation technique, we have performed frequency modulation spectroscopy with a multimode laser. This system enables the sensitive detection of small absorptions by broad spectral lines as are found in atmospheric pressure broadened molecules. The technique should be especially useful for the monitoring of small concentrations of pollutants in the atmosphere. The wide continuous tunability of a multimode cw dye laser opens up applications in basic molecular spectroscopy which we are currently exploring.
Photodissociation cross section of Pb2
Authors: Lombardi Gabriel G.
Published: February 2023

A novel technique was used to measure the photodissociation cross section of Pb2. This technique has the important advantage that the Pb2 density need not be known. An excimer laser (XeCI) operating at 308 nm photodissociated the Pb2, while a single-mode argon-ion laser probed the ground state dimer absorption at 496.5 nm. The Pb2 was produced in a heat pipe at ~1300°C. A similar technique was described by Kwong et al.1 and applied to atomic transition probability measurements; however, their approach requires a measurement of the ground state atomic density. The technique reported in this paper makes use of the fact that the laser-induced change in the ground state Pb2 density depends only on the fluence of the dissociating laser and the photodissociation cross section. Consequently, from a measurement of the relative change in the density as a function of fluence, the cross section may be deduced. The above analysis is valid in the approximation that the molecular vapor is optically thin at the frequency of the dissociating laser. The widespread availability of excimer lasers with emission into the vacuum ultraviolet should make this technique readily applicable to the measurement of absolute photoionization and photodissociation cross sections.
200-ps recovery of an optical gate in a GaAs etalon array
Authors: Lee Y. H. , Warren M. , Olbright G. , Gibbs Hyatt M. , Peyghambarian N. , Venkatesan T. , Smith J. S. , Yariv Amnon
Published: February 2023

The fastest recovery time (certainly <200 ps) of an optical NOR/AND gate at room temperature in a GaAs etalon is reported. This recovery time is at least an order of magnitude shorter than that for previous etalons consisting of GaAIAs/GaAs/GaA- IAs heterostructure. Our sample consists of 1.5-μm bulk GaAs and 0.25-μm GaAIAs, without a top GaAIAs window. A 2-D array of 10 × 10-μm GaAs pixels with 20-μm center-to-center spacing was defined by reactive ion etching. The array was sandwiched between high reflectivity (>90%) dielectric mirrors. Additionally, a somewhat longer recovery time was observed in a windowless GaAs etalon prepared from the same bulk crystal but without defining an array. The NOR gate contrast was 3-1 in both cases. The fast recovery is attributed to faster surface recombination of carriers at the GaAs-dielectric mirror interface compared with that at a GaAs-GaAIAs interface. The definition of windowless pixels, which limits diffusion and enhances recombination even further, should lead to arrays of small-volume ultrafast optical gates operating at several gigahertz rates.
New technique for optical butting of linear arrays
Authors: Jain S. C. , McDuff O. P.
Published: February 2023

Linear image sensors like charge-coupled devices (CCD) operating the push-broom mode can be optically butted together to improve the resolution. In the normal butting methods the field of view of the optics is increased, which is given by the field of view of one array times the number of arrays butted. The scheme proposed in this paper can be used for butting two CCD arrays without doubling the field of view. The different photosites in a CCD array are separated by the channel stoppers. The areas corresponding to these stoppers remain uncovered in the image. The two arrays in the proposed scheme are butted in such a way that the centers of the photosite of one array optically coincide with the centers of the channel stoppers of the other array. This can be accomplished by butting the two arrays on the two faces of a rectangular prism (having semisilvered diagonal surface) and offsetting them to align the centers of photosites and channel stoppers of the two arrays. The composite array developed by this method is having double the number of resolution elements without doubling the field of view.
Adaptive optics by image sharpening
Authors: Boucher Richard H. , Mahajan Virendra N.
Published: February 2023

A typical wave front sensor in an adaptive optical imaging system requires a point source or a glint on the object to operate, as do the various image-based phase retrieval methods. However, with the image sharpening method,1,2 one can sense the aberrations from the aberrated image of a point or extended object. This is done by introducing aberrations in various modes with an adaptive mirror to maximize the image sharpness. We describe simulations of image sharpening in single and multiaperture systems imaging extended objects. In simulating a multiaperture system the algorithm has been successfully applied to phase the elements of an array by correcting their piston and tilt errors. We define a noise equivalent aberration as the amount required to discern changes in the sharpness function over the system noise and describe a relationship between it and the image signal-to-noise ratio. We determine the efficiency of various optimization schemes to maximize the sharpness such as successive linear searches and multidimensional gradient searches. The algorithm performance with different amounts of photon and additive noise is also evaluated.
Ultraviolet absorption spectroscopy with frequency-doubled mode-locked lasers
Authors: Whittaker Edward A.
Published: February 2023

Recent advances in frequency-modulation (FM) spectroscopy1 allow quantum-limited absorption measurements on unmodulated species with visible absorption lines. This method opens up the possibility of absorption detection for applications such as atmospheric remote sensing and combustion studies. There are two impediments to extending FM to ultraviolet transitions: Most phase modulators are ineffective in the ultraviolet, and even with adequate modulators, direct generation of cw ultraviolet light is problematic. Here I point out that both of these problems may be overcome by using an actively mode-locked visible dye laser as a source of quasi-cw light, which may then be phase modulated and subsequently doubled with high efficiency. Tran et al.2 have demonstrated that a frequency-modulated laser remains frequency modulated after doubling. In addition, a mode-locked pulse train may be used for FM spectroscopy as long as the modulation frequency and spectroscopic feature width are much greater than the bandwidth of the pulse train. In that case each locked mode will contribute coherently to the FM signal. This state of affairs holds for suitably adapted sync-pumped dye lasers and many molecules of interest.
Testing aspheric surfaces using two-wavelength phase-shifting interferometry
Authors: Creath Katherine , Wyant James C.
Published: February 2023

Two-wavelength holography and phase-shifting interferometry are combined to measure the phase contours of deep wave fronts and surfaces, like those produced by aspheres, with a variable sensitivity. When interference fringes are very closely spaced, the phase data contain high frequencies where 2π ambiguities cannot be resolved, and many fringes are likely to fall on a single detector element. To reduce the problem of averaging fringes in a single pixel, an array of pinholes is used to mask the detector array enabling point sampling of the single-wavelength fringes. In this technique, the phase of the wave front is calculated modulo 27π using phase-shifting techniques at each of two visible wavelengths. The difference between these two phase sets is the phase of the wave front as it would be measured at a synthesized equivalent wavelength λeq = λ1λ2/|λ1 − λ2|, assuming that 2π ambiguities can be removed. The integrated two-wavelength data are used to correct the 27π ambiguities in the single-wavelength data, which increases the measurement range and keeps single wavelength precision. This technique enables aspheric surfaces with hundreds of waves of optical path difference to be measured to λ/100 in the visible.
Progress report on optical fiber FDM communications
Authors: Izzo M. , Meng H. L. , Asif G. , Shapiro A. M. , Ih Charles
Published: February 2023

Optical fiber systems promise an enormous information bandwidth for data communications. These high bandwidth systems are ideal for LANs on which multichannel video, audio, and digital information can be exchanged freely between work stations. If a complete digital system is used, the bit rate for a single video channel (similar to a TV channel) would approach 100 mbit/s. This may not be the most economical and/or reliable system for such an application in such an environment. We have suggested and investigated an optical fiber FDM system for this use. The most severe obstacle among others to using the optical fiber FDM is the well-known problem of serious intermodulation between channels. The intermodulation has been traditionally believed due to the device's nonlinearities. Our investigations show that the optical intensity modulation and the characteristics of the fiber may contribue more to the intermodulation. Computer simulations and some experimental evidence related to these and schemes for implementing the FDM system are discussed.
Propagation and identification of modes in a Iaow V-value optical fiber waveguide
Authors: Sunak Harish R. D.
Published: February 2023

We have carried out experiments of mode propagation and identification in a nominally single-mode fiber having 1.2 µm cutoff wavelength. We operated at a low V-value of 6.2 by launching mode-locked pulses from a dye laser operating at λ = 615 nm. These pulses were measured to have FWHM of 97 ps being detector-oscilloscope limited. Other measurements furnished FWHM of 165 fs. The pulses had a repetition rate of 130 MHz. The modes we identified at the output of 1-km long fiber were LP01, LP11, LP12, LP02, LP21 and LP31. These modes were identified by looking at the output intensity distributions and moving the focused spot size laterally at the input end of the fiber. This enabled each mode to be launched preferentially and hence be identified. We calculated the temporal modal dispersion, between the fundamental LP01 and each higher-order mode, using Gloge’s weakly guiding theory, and observed good correlation with the measured values. The broadened output pulses are explained in terms of material dispersion, which is 280 ps/nm/km at the launching wavelength. By introducing a V-groove mode mixer at the input end, we could eliminate all the higher-order modes and be left with only the LP01 mode.
Frequency noise cancellation in semiconductor lasers by nonlinear heterodyne detection
Authors: Bondurant R. S. , Welford D. , Alexander S. B. , Chan Vincent W. S.
Published: February 2023

Frequency noise degrades the performance of optical heterodyne communications systems: the error rate performance of an FSK system is limited to a floor caused by cross talk due to nonzero laser linewidth. Recently it was pointed out that the use of nonlinear heterodyne detection coupled with differential FSK modulation can alleviate this limitation.1 We present preliminary experimental results confirming this prediction. Two semiconductor lasers were used in a heterodyne communications experiment. Commercial acoustooptic modulators were used to modulate one laser in a binary differential FSK format at 1 Mbps. At the receiver, the intermediate frequency signal was squared and the difference-frequency component extracted. This component is free from the effects of frequency noise. Error rate measurements showed that the performance of this system was not limited by a floor as in a conventional case. The effective signaling linewidth was <100 kHz, even for laser linewidths of 100 MHz.