Showing papers in "Optical and Quantum Electronics in 1993"
TL;DR: H holographic optical data storage systems implemented with photorefractive media are considered, including angular, phase-encoded, and wavelength-multiplexing techniques, and several approaches to increasing the signal-to-noise ratio of the recordings.
Abstract: We consider holographic optical data storage systems implemented with photorefractive media. Our viewpoint emphasizes the close interaction between materials and device issues. First we discuss our current understanding of photorefractive physics as it pertains to the holographic data storage problem. Then we consider architecture issues, including angular, phase-encoded, and wavelength-multiplexing techniques, and several approaches to increasing the signal-to-noise ratio of the recordings. Finally, we discuss materials issues related to crystal growth and how crystal quality impacts the performance of data storage systems. Both bulk and fibre crystal growth techniques are reviewed.
141 citations
TL;DR: In this article, a review of the gain and saturation behavior of semiconductor lasers is presented, with special attention given to rate equation models and to the possibility of so-called gain nonlinearities that might affect the CW and modulation performance.
Abstract: Several approaches have been developed for modelling the gain and saturation behaviour of semiconductor lasers, and this study includes a historical review of these various approaches. Special attention is given to rate equation models and to the possibility of so-called gain nonlinearities that might affect the CW and modulation performance of semiconductor lasers. Discussions are mainly limited to the GaAs/GaAIAs and InGaAsP/InP systems, for which the gain and gain nonlinearities have been most extensively studied.
91 citations
TL;DR: In this article, the influence of ion-pair concentration on the dynamical behaviour of erbium-doped fiber lasers was demonstrated. But the authors focused on the effect of ion pair density on the output of the laser and showed that the output intensity evolves continuously from an infinite train of pulses to a CW steady state as the pumping ratio increases.
Abstract: We demonstrate experimentally the influence of ion-pair concentration on the dynamical behaviour of erbium-doped fibre lasers. At low pair densities, the laser has a CW output, while at higher densities it exhibits a self-pulsing behaviour. For intermediate pair concentrations, the output intensity evolves continuously from an infinite train of pulses to a CW steady state as the pumping ratio is increased.
66 citations
TL;DR: In this paper, it was shown that thermal focusing and birefringence set an intrinsic limitation to the fundamental mode volume, such that the maximum usable TEM00 spot size in the rod is about 1 mm.
Abstract: The output characteristics of a continuous-wave lamp-pumped Nd:YAG laser using a rod of 6.4 mm diameter and stable resonators with large fundamental mode volume have been systematically investigated by testing various resonators. It is shown that, independently of the resonator, thermal focusing and birefringence set an intrinsic limitation to the fundamental mode volume, such that the maximum usable TEM00 spot size in the rod is about 1 mm, even if in principle the rod cross-section could sustain a much larger mode. A qualitative theoretical model explains the experimental data. A maximum output power of about 40 W was observed in a nearly diffractionlimited beam.
50 citations
TL;DR: In this article, the output intensity of an erbium-doped fiber laser was studied with three pumping wavelengths: 514.5 nm, 810 nm and 980 nm.
Abstract: The output intensity of an erbium-doped fibre laser was studied. Experiments were performed with three pumping wavelengths: 514.5 nm, 810 nm and 980 nm. The laser output intensity exhibits three different dynamical behaviours: steady-state, sinusoidal variation or self-pulsing. In particular, in a bad (high-loss) cavity configuration, when the pumping ratio is increased above the lasing threshold the output intensity changes continuously from a steady-state to an infinite train of pulses. We also show that, depending on the cavity configuration, the transient oscillations display different forms.
49 citations
TL;DR: In this paper, the effects of self-phase modulation, stimulated Raman scattering, and parametric four-photon interaction in an 8-μm core fibre of 4 m length with the effect of selective spectral attenuation in a ruby rod resulted in a rather smooth spectra extending from 685 nm to 830 nm (spectral width ≈ 2300 cm-1).
Abstract: Picosecond light pulses of a passively mode-locked ruby laser (pulse duration Δt
L≈35 ps) are spectrally broadened in optical fibres of core diameters from 4 μm to 600 μm. Combining the effects of self-phase modulation, stimulated Raman scattering, and parametric four-photon interaction in an 8-μm core fibre of 4 m length with the effect of selective spectral attenuation in a ruby rod resulted in rather smooth spectra extending from 685 nm to 830 nm (spectral width ≈2300 cm-1).
41 citations
TL;DR: Capacities for angular and wavelength multiplexed holographic data storage systems are considered andLimitations due to the spatial resolution of the recording and reconstructing fields and to the holographic recording process are derived.
Abstract: Capacities for angular and wavelength multiplexed holographic data storage systems are considered. Limitations due to the spatial resolution of the recording and reconstructing fields and to the holographic recording process are derived. © 1993 Chapman & Hall.
31 citations
TL;DR: In this article, the analytical relationship between the different reported definitions of beam moments, extended to the general partially coherent case, is established and explicit equivalence formulae between both families of beam moment are given.
Abstract: The analytical relationship between the different reported definitions of beam moments, extended to the general partially coherent case, is established. Explicit equivalence formulae between both families of beam moments are given. The validity of the corresponding propagation laws through ABCD optical systems is thus confirmed.
30 citations
TL;DR: In this paper, the optical properties of the interference wedge are analyzed for the case of restricted laser beam illumination and some useful dependencies concerning the wedge reflection and transmission for laser applications are obtained and experimentally demonstrated.
Abstract: The optical properties of the interference wedge are analysed for the case of restricted laser beam illumination. By further development of Brossel's method, equations describing this case are derived and used to calculate the reflected and transmitted beam profiles for typical intracavity laser beam diameters (0.2–0.6 mm) for Gaussian and uniform intensity distributions. In particular, the experimentally observed formation of bright fringes outside the beam impact area at resonant wavelengths is explained. some useful dependencies concerning the wedge reflection and transmission for laser applications are obtained and experimentally demonstrated.
30 citations
TL;DR: In this paper, the design, fabrication and characterization of electrooptical modulators and switches based on pseudomorphic InGaAs/GaAs multiple-quantum-well (MQW) structures is presented.
Abstract: The design, fabrication and characterization of electrooptical modulators and switches based on pseudomorphic InGaAs/GaAs multiple-quantum-well (MQW) structures is presented. The absorption and refractive index changes (Δα, Δn) of In0.2Ga0.8As/GaAs MQW structures due to the quantum-confined Stark effect are examined in detail. The figures of merit Δα/α0 and Δn/α0 give information on the design of modulation and switching devices. Based on these results, we develop two types of efficient and high-speed modulators, vertical and waveguide modulators, and for the first time an InGaAs/GaAs intersectional X-type switch. Recent experimental results for each device are presented.
28 citations
TL;DR: In this article, a tapered electrode structure was proposed to make the ratio of the coupling coefficient to the difference of propagation constants between two coupled waveguides in a directional coupler switch a constant throughout it.
Abstract: We propose a tapered electrode structure to make the ratio of the coupling coefficient to the difference of propagation constants between two coupled waveguides in a directional coupler switch a constant throughout it. In this way, the crosstalk caused by the existence of tapered sections is entirely eliminated.
TL;DR: In this paper, the amplification of light signals (angular frequency ωS in some isotropic media (D2O, fused silica, and Schott type SF10 glasses) by noncollinear phase-matched parametric four-photon interaction ω1+ω2→ωS+ω1 is studied theoretically.
Abstract: The amplification of light signals (angular frequency ωS in some isotropic media (D2O, fused silica, and Schott type SF10 glasses) by noncollinear phase-matched parametric four-photon interaction ω1+ω2→ωS+ω1 is studied theoretically. Computer simulations are carried out for fundamental and second-harmonic pump pulses of a mode-locked Nd: glass laser. Degenerate interaction (wavelength λ1=λ2=1054nm or 527 nm) and nondegenerate interaction (λ1=1054nm, λ2=527 nm are considered. Characteristic phase-matching parameters and gain parameters versus wavelength are determined. Limitations by spectral bandwidth, optical absorption, optical damage, self-phase modulation, self-focusing and stimulated Raman scattering are analysed.
TL;DR: In this article, the optical elements required for focusing laser light into a narrow ring, a wide ring and a set of rings were computed using numerical and analytical approaches, and a numerical comparison of the various computational techniques was reported.
Abstract: Using numerical and analytical approaches, we have computed the optical elements (focusators) required for focusing laser light into a narrow ring, a wide ring and a set of rings A numerical comparison of the various computational techniques is reported Finally the operation of a fabricated rotor axicon to focus light into a ring is reported
TL;DR: In this paper, a copper HyBrID laser (λ=510.6, 578.2 nm) was reported which produced 121 W at 2.2% efficiency, with a pulse recurrence frequency of 18 kHz.
Abstract: A copper HyBrID laser (λ=510.6, 578.2 nm) is reported which produced 121 W at 2.2% efficiency (based on stored energy), with a pulse recurrence frequency of 18 kHz. For an output power of 100 W, the efficiency was 2.6%. A 21% enhancement in output power was achieved by eliminating parasitic stimulated emission due to back-reflection from the silica discharge-tube windows.
TL;DR: The asymmetric Fabry-Perot modulator (AFPM) as discussed by the authors offers high on-off contrast, low insertion loss, and low operating voltage swing, among other advantages.
Abstract: Free-space ‘smart-pixel’ optical interconnect architectures promise to relieve the interconnect ‘bottleneck’ in high-speed parallel computers and switching systems. One of the most promising output devices that has been advanced for use in these systems is the asymmetric Fabry-Perot modulator, or AFPM, which offers high on-off contrast, low insertion loss, and low operating voltage swing, among other advantages. In this paper we summarize our work on optimizing the AFPM for high-speed operation, including analysis of the material structure design considerations, fabrication of small (16×20 μm) devices, and high-speed electrical and optical characterization of the finished modulators. We conclude that at relatively high incident optical intensities the modulators' speed appears to be limited by transit effects to about 18 GHz, but that at lower optical intensities their frequency response outstrips that of our 20 GHz measurement apparatus — that is, these AFPMs are still capable of large signal modulation (20 dB contrast, 1.5 dB insertion loss) at low AC voltage swings (±3 V) for operating frequencies up to 20 GHz. We presume that further investigation will prove them to be RC-limited in this low-intensity regime to speeds of about 35 GHz.
TL;DR: In this article, the variational analysis of Ti:LiNbO3 strip waveguides is resolved into two related one-dimensional problems, which provides a new iterative approach for the calculation of the mode parameters and the propagation constant.
Abstract: The variational analysis of Ti:LiNbO3 strip waveguides is resolved into two related one-dimension problems, which provides a new iterative approach for the calculation of the mode parameters and the propagation constant. The analytical expressions of the local effective index profiles can be obtained from the variational analysis. The parameters of four trial solutions for the fundamental mode in a diffused-channel waveguide have been determined by using the present method. Comparison with results using the effective method shows that these four approximate expressions are accurate enough. It is also shown that this method converges very quickly and is suitable for both diffused channel waveguides and optical waveguides with rectangular cross-section.
TL;DR: In this paper, a theoretical model of the single and multiple emission line spectra of tunable microcrystal lasers is derived by means of a set of criteria, based on the shift of the resonator frequencies due to the thermally induced shift of optical resonator length.
Abstract: A theoretical model is derived by which the occurrence of the single and multiple emission line spectra of tunable microcrystal lasers is described. These spectra in general exhibit several emission lines, arising from the Stark-split atomic levels of the lasing ions in the crystal field. The model is based on the shift of the resonator frequencies due to the thermally induced shift of the optical resonator length and demonstrates that the coincidence of the resonator frequencies with the laser gain lines leads to the emission of single or multiple line spectra of microcrystal lasers. These spectra can be described by the model. The model is given as a set of criteria. In this way not only can predictions of the single emission-line tuning range be made but also resonator lengths can be optimized in order to obtain a maximum tuning range. Furthermore, Q-switched operation can be achieved for specific parameters by periodically shifting the resonator frequencies. The linewidth of the gain used in this model depends on the laser threshold and is folded with the thermal shift of the atomic transitions. Therefore the centre wavelength of the gain is assumed to be constant. The advantage is that this experimentally relevant linewidth can be measured easily with microcrystal lasers themselves, whereas spectroscopic data do not take laser threshold behaviour into account. It is shown that the results of the model are in good agreement with experimental data measured for two different Nd: YAG crystals. Simply by inserting other material and laser parameters, the model can easily be applied to other laser crystals and other wavelengths.
TL;DR: The photorefractive effect as a device technology for the problem of pattern recognition is reviewed and aPhotorefraction realization of an adaptive pattern classifier is described.
Abstract: Photorefraction is a nonlinear optical effect in which large nonlinearities can be observed at relatively low optical power levels. This phenomenon has evolved from a laboratory curiosity to a useful device technology for optical information processing applications. In particular, the abilities to form holograms in real time and also to store thern for extended periods of time have aided the implementation of several pattern-reccgnition machines that are adaptive and possess a high degree of parallelism. This paper reviews the photorefractive effect as a device technology for the problem of pattern recognition and describes a photorefractive realization of an adaptive pattern classifier.
TL;DR: In this paper, the propagation of two light beams with orthogonal polarization in a nonlinear medium is considered and it is shown that because of the interaction of the beams there are two different self-focusing regimes: monotonous and oscillatory.
Abstract: The propagation of two light beams with orthogonal polarization in a nonlinear medium is considered. It is shown that because of the interaction of the beams there are two different self-focusing regimes: monotonous and oscillatory. Analytical results are confirmed by computer simulation.
TL;DR: In this article, the spectral index method for solving general planar waveguiding problems is analyzed. But the solution is so fast that the method can be used as a subroutine, making it possible to solve many two-dimensional problems fully, even for coupled rib waveguides, without using effective index approximations.
Abstract: The scope of the spectral index method for solving general planar waveguiding problems is analysed by first showing how simple it is to set up a closed-form transcendental equation whose solution is very accurate; the solution is so fast that the method can be used as a subroutine, making it possible to solve many two-dimensional problems fully, even for coupled rib waveguides, without using effective index approximations. The method is then extended to the uniformly buried waveguide of rectangular cross-section, and the corresponding coupler, thereby unifying the effective index, transverse resonance and spectral index methods for the first time, and giving an asymptotic expression for the coupling length without using overlap integrals. Finally, sample numerical results and optical field profiles are given for the rib waveguide and rib waveguide coupler.
TL;DR: In this paper, a new approach is presented to determine the profile characteristics of planar optical waveguides, where the mode index value is developed into the Lagrange series in terms of mode number, which allows one to find analytical expressions for the coefficients of that series.
Abstract: A new approach is presented to determining the profile characteristics of planar optical waveguides. The mode index value is developed into the Lagrange series in terms of mode number, which allows one to find analytical expressions for the coefficients of that series. This method is applied to evaluating the coefficients of mode index distribution for the step-index and four-layer step-index profiles.
TL;DR: In this article, an attenuated total reflection (ATR) geometry is used in which a quartz electrooptic crystal onto which a thin Ag film has been evaporated is contacted to the hypotenuse face of a high-index prism.
Abstract: Electrooptic reflection with surface plasmons is studied both experimentally and theoretically. An attenuated total reflection (ATR) geometry is used in which a quartz electrooptic crystal onto which a thin Ag film has been evaporated is contacted to the hypotenuse face of a high-index prism. Modulation in the ATR of an He−Ne beam near the angle for surface plasmon excitation is observed when a low-frequency electric field is applied to the quartz crystal. Experiments have been done with both single and multiple boundary surface waves. The angular spectra show phase reversal structure due to the interference of the modulated reflected wave with the ATR wave. The modulated reflectance is calculated directly from a well-known solution to the boundary value problem in nonlinear optics. Good quantitative agreement with the observations is obtained.
TL;DR: In this paper, the authors show that materials with the ability to form persistent spectral holes under illumination have frequency as an additional optically parallel accessible degree of freedom that may be incorporated into associative memory.
Abstract: We show that materials with the ability to form persistent spectral holes under illumination have frequency as an additional optically parallel accessible degree of freedom that may be incorporated into associative memory. This opens new possibilities for increasing the number of interconnections in optical models of neural networks. In our first example, a 144-element autoassociative memory matrix is constructed on two 12-bit vectors and has two dimensions (x and frequency ω). The probe vector at the memory input carries two erroneous bits (out of 12 bits) and is onedimensional (spatial coordinate x); the memory output-with the error bits correctedis one-dimensional in frequency ω. The second example uses memory input that is twodimensional (image in coordinates x, y); the memory matrix is four-dimensional (x, y ω, t), where t (time coordinate) is given by the temporal delay of photochemically accumulated stimulated photon echo signal; memory output is two-dimensional (ω and t) and corrects two bits out of the 12-bit vector. In the third example, quadratic autoassociative memory is coded in three dimensions (coordinates x, y, ω) and materializes 32×32×32=32768 optical interconnections; the probe vector is given as a 32×32 spatial matrix (coordinates x, y); the output is one-dimensional, consists of 32 bits along the frequency axis, and corrects four erroneous bits.
TL;DR: In this article, the dynamical behavior of Fabry-Perot type semiconductor lasers is modelled, including the relevant many-body Coulomb effects of the excited carriers, and conditions are given under which a parametrization of the full model is possible, allowing simple analytic relations for local gain, refractive index and linewidth enhancement factor.
Abstract: The dynamical behaviour of Fabry-Perot type semiconductor lasers is modelled, including the relevant many-body Coulomb effects of the excited carriers. Conditions are given under which a parametrization of the full model is possible, allowing simple analytic relations for local gain, refractive index and linewidth enhancement factor. The parameters of the simplified model are uniquely determined by the microscopic theory and have to be optimized for the respective operating conditions. The theory is evaluated for bulk and quantum-well GaAs active material and a variety of laser structures, including strongly and weakly index-guided structures, as well as purely guided single-and twin-stripe lasers.
TL;DR: In this article, the authors describe the growth and device performance of electroabsorption modulators on GaAs substrates operating near 1.3 μm, the dispersion minimum for silica fibres.
Abstract: This paper describes the growth and device performance of electroabsorption modulators on GaAs substrates operating near 1.3 μm, the dispersion minimum for silica fibres. The key to the successful molecular beam epitaxial (MBE) growth of these devices was the incorporation of a linearly-graded buffer layer beneath the InGaAs/AlGaAs multi-quantum-well active layer. Both transmission and reflection modulators are produced. For transmission devices, larger modulation is achieved when the buffer is graded more slowly: The maximum modulation reported was 22% for ΔT/TOcorresponding to a 0.86 dB contrast ratio with an insertion loss of roughly 5 dB at 1.34 μm. Antireflection coating a transmission modulator yields a reasonable reflection modulator. However, improved performance is reported for a reflection modulator using a novel technique of integrating the bottom quarter-wave mirror into a buffer with linearly-graded In composition. At 1.33 μm, a normally-off reflection modulator with an integrated mirror exhibited a ΔR/ROof 73%, a constrast ratio of 2.38 dB, and an insertion loss of 4 dB.
TL;DR: In this paper, a single quantum well waveguide modulator was used to measure the escape of photogenerated carriers from a quantum well, and the effects of exciton saturation and external field screening were observed in the transient transmission change.
Abstract: Picosecond excite-probe studies are performed on a single quantum well waveguide modulator giving a direct measure of the escape of photogenerated carriers from a quantum well. Both the effects of exciton saturation and external field screening are observed in the transient transmission change. The results are consistent with the escape of carriers by thermionic emission.
TL;DR: In this article, a brief review of excimer lithography for ULSI is presented with an emphasis on the recent progress made in KrF excimer stepper technology, in particular, the types of projection optics, excimer laser and the related performance of steppers are explained in detail.
Abstract: A brief review of excimer lithography for ULSI is presented with an emphasis on the recent progress made in KrF excimer stepper technology. In particular, the types of projection optics, excimer laser and the related performance of steppers are explained in detail. The resist patterns obtained with a recent excimer stepper are shown. Although there are many problems to be overcome for future lithography, it is anticipated that not only 0.35 μm design rules but also 0.20 to 0.25 μm design rules will be achieved using excimer lasers.
TL;DR: In this article, a quantum well resonant cavity structure is modelled using energy balance considerations by computing the Poynting vectors across the absorbing region and the dependence of the quantum efficiency and the bandwidth on the position of the wells, the cavity Q, and the number of wells.
Abstract: A quantum well resonant cavity structure is modelled using energy balance considerations by computing the Poynting vectors across the absorbing region. We have examined the dependence of the quantum efficiency (η) and the bandwidth (BW) on the position of the wells, the cavity Q, and the number of wells. The model includes standing wave effects. Experimental results corroborate the model.
TL;DR: In this article, the contribution of factors such as the backbone, conformation of the chain, sidegroups and polymerization catalyst on the optical nonlinearities of polyphenylacetylene chains was investigated.
Abstract: Conjugated polymers with sidegroups such as methyl, trimethylsilyl, p-methoxy phenyl, o-methoxy phenyl, and hexyl groups on a polyphenylacetylene chain are studied in an attempt to understand the contribution of factors such as the backbone, conformation of the chain, sidegroups and polymerization catalyst on the optical nonlinearities. The results of degenerate four-wave mixing experiments at 532 nm with nanosecond pulses indicate that the substitution of an electron-donating group away from the backbone can enhance the third-order susceptibility. Some of the polymers show optical limiting action at this wavelength. The thermal contribution to the measured susceptibility is also determined.
TL;DR: Passive pulse stretching in a Q-switched Nd: glass laser using a dye as a two-photon absorber is described in this article, where the length of pulses is evaluated by means of computer calculations.
Abstract: Passive pulse stretching in a Q-switched Nd: glass laser using a dye as a two-photon absorber is described. The lengthening of pulses was evaluated by means of computer calculations. Pulses 350-ns long have been observed experimentally.