bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical simulation of bistable semiconductor lasers
Authors: Paradisi A. , Montrosset I.
Published: February 2023

In this paper an extensive analysis of the methods (See Refs. 1-3 for a review) used for the simulation of bistable lasers with a saturable absorber has been carried out. In particular a comparison between mean field1 and traveling-wave2 monomode1 and multimode2 models has been made with respect to the static behavior (switch on-off current, width of the hysteresis loop, spectrum of emission) of typical structures.
Simple variational approach to optical rib waveguides
Authors: Huang W. P. , Haus H. A.
Published: February 2023

Rib waveguides have received much attention recently because of advances in III-V semiconductor technology. The simplicity of fabrication and the ease of control of lateral and vertical index profiles make rib waveguide structures attractive for integrated optical applications. Despite the progress in fabrication, the modeling and analysis of rib waveguides are difficult. The approximate analytical approach, such as in the effective-index method, is simple and efficient but may not be accurate enough for all practical cases. The rigorous numerical approach, such as in the finite-difference2 (FD) and the finite-element3 (FE) methods are accurate and versatile but often are complicated and computer intensive. Therefore a simple approach that gives accurate results would be useful as a practical tool for modeling and analysis for the purpose of device design and fabrication. Such an approach has been developed by the authors' and is applied to optical rib waveguides in this paper.
Optical fiber resonators
Authors: Isaev S. K. , Kornienko L. S. , Yatsenko Yu. P.
Published: February 2023

Optical fibers are widely used in modern nonlinear optics and quantum electronics for the transformation and generation of coherent radiation. They operate either as nonlinear or linear waveguide elements. The following two types of optical schemes are used: (i) those without a resonator, with useful effect, i.e., the transformation of radiation achieved at a single pass along the fiber; (ii) those with a resonator that ensures recirculation of radiation and accumulation of the useful effect. Case ii is actually a laser of a special type —a fiber laser.
Extremely high degree of N-soliton pulse compression in an optical fiber
Authors: Akhmediev N. N. , Mitzkevich N. V.
Published: February 2023

A number of papers1-3 deal with the problem of multisoliton pulse self-compression in an optical fiber. Mathematically speaking theproblem reduces to seeking for the evolution of N-soliton solution of the nonlinear Schrodinger equation (NLS) for a given initial condition. In the fiber the pulse envelope ψ obeys: where ξ is a dimensionless longitudinal coordinate and τ is a dimensionless retarded time variable. Because of the early work of Satsuma and Yajima4 the solution of the problem with initial condition has been studied extensively. This is the most simple and convenient form of initial conditions but not the best one if we wish to have the maximum degree of compression.
Quasi-phase-matched second-harmonic generation in LiNbO3 waveguides
Authors: Fejer M. M. , Lim E. J.
Published: February 2023

Nonlinear frequency conversion is an attractive technique for extending the spectral range of solid-state coherent sources. Waveguide interactions are useful to increase the efficiency of devices based on low-power pump lasers, e.g. second harmonic generation (SHG) of the output of AlGaAs laser diodes to produce blue light. While the large nonlinear susceptibility and well-developed waveguide technologies available in LiNbO3 are attractive for device design, LiNbO3 does not have adequate birefringence for phasematching SHG of blue light. Compensating for phase-velocity mismatch by reversing the sign of the nonlinear susceptibility with a period equal to the coherence length, quasi-phase-matching (QPM), allows phase-matching of any interaction within the transparency range of the crystal using the large d33 nonlinear coefficient. QPM has been investigated in LiNbO3 waveguides, where the sign changes were due to periodic reversal of the orientation of the ferroelectric domains accomplished by a patterned doping process.1-3 We have succeeded in generating green and blue light by QPM SHG of the output of infrared lasers in such waveguides.
Performance of fiber-optic devices in AM applications
Authors: McGrath Carl J.
Published: February 2023

Lightwave systems for CATV super trunk and trunk applications have been deployed in several architectures. In this review we look at the fundamentals of AM transmission links using real, manufacturable optoelectronic components, and then we focus on achieved results in several applications. We conclude with an analysis of our performance to date with respect to the fundamental limits imposed by devices and the transmission media itself.
Observation of modulational gain and analysis of polarization instabilities in optical fiber with twist
Authors: Feldman Sandra F. , Weinberger Doreen A. , Winful Herbert G.
Published: February 2023

When birefringence induced through the optical Kerr effect in an unperturbed, weakly birefringent fiber is comparable with the natural fiber birefringence, polarization instability and asymmetry between the fast and slow fiber axes arise. A signature of the instability is that small changes in input intensity may result in large changes in intensity transmitted through a crossed polarizer at the fiber exit, leading to the possibility of substantial amplitude modulation (AM) gain.
Vertical-cavity surface-emitting microlasers
Authors: Jewell J. L. , Scherer A. , Lee Y. H. , McCall S. L , Harbison J. P. , Florez L. T. , Sandroff C. J. , Tucker R. S. , Burrus C. A.
Published: February 2023

Vertical-cavity surface-emitting lasers1-5 are generating much interest because of their geometric suitability for forming two-dimensional arrays and their potential for achieving ultra-low thresholds. Here, we report on electrically driven vertical-cavity microlasers (µlasers) which have transverse dimensions of a few micrometers and active material lengths of a few hundred angstroms. The small volumes are a key factor in achieving low thresholds.
Experimental determination of refractive-index dependence on hydrogen concentration in proton-exchanged LiNbO3
Authors: Howerton M. M. , Skeath P. R. , Greenblatt A. S. , Burns W. K.
Published: February 2023

Interest in proton-exchanged LiNbO3 and LiTaO3 waveguides has recently increased because of reports of stable index profiles, fully restored electro-optic coefficients, low propagation losses, and high optical damage thresholds, which occur either with the use of Li-buffered melts or after post-exchange annealing. Although we know qualitatively that samples should be annealed until they reach a single (α) phase condition, the systems (particularly PE LiTaO3) are not fully defined in terms of exchange and anneal diffusion coefficients, phase versus composition (LiTaO3), and index change versus composition. This presentation addresses the dependence of index change versus H concentration for PE LiNbO3, which has not been published. We also discuss the mechanisms that contribute to the index change.
Simulation studies of silicon electro-optic waveguide devices
Authors: Giguere Stephen R. , Friedman Lionel , Soref Richard , Lorenzo Joseph
Published: February 2023

Novel three-terminal field effect transistor (FET) optical waveguides are simulated to demonstrate that crystalline silicon is a credible material for guided-wave optics. Unlike LiBNO3, silicon does not exhibit a linear electro-optic (Pocket's) effect, and second-order effects, such as the Kerr effect, are too small for practical optical switch applications. Therefore, refractive-index changes based on charge refraction are used. To create a silicon electro-optic phase modulator, the device must be able to move electrons and holes within a confined waveguiding region to induce a charge refraction effect. If a sufficient concentration of charge carriers can be injected or depleted, the refractive index of the waveguide will be altered and an electro-optic phase modulator can be designed by using the index of refraction changes induced in the waveguide.
CLADISS – a new diode-laser simulator
Authors: Vankwikelberge Patrick , Morthier Geert , David Klaus , Baets Roel
Published: February 2023

The behavior of DBR, DFB, and other diode lasers with a complex cavity structure is not always fully understood and cannot always be modeled accurately by simple analytic or numeric models.1,2 Therefore we developed a new diode-laser computer model, compound cavity laser diode simulation software -CLADISS- within the framework of the European RACE-1010 (CMC) project.
Microwave characteristics of a traveling-wave electrode in electro-optic modulators
Authors: Chung Haeyang , Chang William S. C. , Betts Gary E.
Published: February 2023

It is well known that the frequency response and the drive power requirement of a traveling-wave modulator (or switch) are determined by the velocity difference between optical and microwave radiations, the impedance, the microwave propagation loss, and the electrode length as well as the optical parameters of the device.1 The impedance and the loss of the asymmetric coplanar strip (ACPS) and the coplanar waveguide (CPW) transmission lines on LiNbO3 without the dielectric buffer layer have previously been reported.2 However, an analysis of the effects of the buffer layer on microwave characteristics has not yet been available in the literature.
Critical rate of optical feedback for coherence collapse in semiconductor lasers
Authors: Lenstra Daan , Cohen Julius S.
Published: February 2023

We have used our self-sustained noise model of coherence collapse in a semiconductor laser with optical feedback for investigating the extent to which the linewidth parameter (α) is responsible for causing this instability.1 In this model the laser is driven by the same noise that it had emitted one feedback delay time τ earlier.2 The linearized coupled rate equations for the phase, power, and carrier density lead to a self-consistent solution for the power spectrum and related noise properties, e.g., coherence time. This solution depends on the feedback rate γ, linewidth parameter α, and relaxation oscillation parameters λ
R
(damping) and ω
R
(frequency).
Semiconductor nonlinear directional coupler operating close to 1.55-μm wavelength
Authors: Fisher M. A. , Stewart N. M.
Published: February 2023

The nonlinear directional coupler (NLDC) can be used to achieve a number of all-optical signal processing functions that will be required in future switching and routing systems. Particularly attractive would be such a device operating at diode laser wavelengths with the possibility of integration with other optoelectronic components. Previous work on GaAs-based material has demonstrated nonlinear switching in NLDCs at wavelengths near 1 μm.1,2 In this paper we present results of measurements made on a NLDC fabricated in InP-based material operating close to 1.55 μm, which is to our knowledge the first demonstration of a NLDC suitable for integration at this important wavelength for optical fiber transmission.
Picosecond and subpicosecond switching and modulation in GaAs/AlGaAs nonlinear directional couplers
Authors: Gibbs H. M. , Jin R. , Harten P. A. , Sokoloff J. P. , Chuang C. L , Lee S. G. , Warren M. , Peyghambarian N. , Polky J. N. , Pubanz G. A.
Published: February 2023

Previously, we demonstrated all-optical switching in GaAs/AlGaAs multiple quantum-well (MQW) nonlinear directional couplers (NLDCs) using 10-ps pulses1 for which the origin of the nonlinearities was due to photoexcited real carriers. Recently, we have improved the fabrication of the NLDC, resulting in better reproducibility and switching contrast when picosecond pulses are used (see Fig. 1). We have also observed subpicosecond all-optical modulation in a GaAs/AlGaAs NLDC using femtosecond pulses. The origin of such ultrafast modulation is attributed to the optical Stark effect.2
Fully integrated two-stage acousto-optic filter with no net Doppler shift
Authors: Smith D. A. , Johnson J. J. , Cheung K. W. , Jackel J. L. , Baran J. E.
Published: February 2023

For the first time, to our knowledge, orthogonal proton-exchange polarizers have been fabricated on a single LiNbO3 substrate, allowing for the total integration of two acoustically tunable optical filters (ATOFs). This is a major step toward the development of a low-loss, non-frequency-shifting laser intracavity tuning element.1,2This wavelength-selective component will be suitable for a variety of wavelength ranges, including the Ti:sapphire gain range (650-1000 μm) and the optical communication band between 1.2 and 1.6μm and beyond. The tuning range is limited only by the laser gain profile because of the tremendous spectral tuning range achievable with the ATOF (up to 50% tuning range may be possible with chirped interdigital transducers).
New guided-wave lens structure in GaAs substrates
Authors: Minot Mark M. , Lee Chin C.
Published: February 2023

Numerous different integrated optic lens structures have been developed.1-4 Many of them have poor off-axis performance or fabrication difficulties. We have developed a new structure that has exceptional off-axis performance and is capable of realizing near-diffraction-limited performance at large numerical aperture. Some preliminary results of this new structure have been reported.5 In this paper we present the most recent results.
Subpicosecond ring fiber laser modelocked with a nonlinear loop reflector
Authors: Duling Irl N.
Published: February 2023

With the increasing importance of erbium doped fibers for amplifiers in 1.5 μm optical communication systems, there is a need to develop efficient sources capable of producing ultrashort pulses at high powers and high repetition rates. Modelocked laser diodes, in addition to having low output powers require high-frequency current modulation to achieve high repetition rates. Passive modelocking allows any number of pulses to exist in the cavity simultaneously.
Fiber Bragg grating devices and applications
Authors: Meltz Gerald
Published: February 2023

Experiments in our laboratory1-3 and elsewhere4,5 show that the refractive index of germanosilicate fiber can be modified by a few parts in 105 to upwards of 5 × 10-4 by photobleaching the oxygen vacancy band of germania. Typically, the fiber core is exposed through the side of the cladding to UV radiation at a wavelength from 230 to 266 nm. Permanent phase gratings are "written," with a specified period, by using a pair of intersecting coherent beams. The periodic index modulation forms a Bragg grating that can be used for very narrow stop and pass-band filters, or as a means to stabilize laser diodes, and as reflectors in rare earth-doped fiber lasers. Other applications include taps and launchers, which are made by blazing the grating and selecting a suitable period to couple a bound mode into a radiating mode,6. and mode coupler and filters. This paper will review the design and performance of both active and passive Fiber Bragg Grating (FBG) components, and discuss the thermal stability and aging characteristics of the photo-induced index changes.
New design for wavelength-flattened 2×2 tapered fused couplers for single- and few-mode fibers
Authors: Gonthier F. , Ricard D. , Lacroix S. , Bures J.
Published: February 2023

A well-known way of realizing wavelength-flattened couplers is to fuse and taper two different optical fibers.1,2 These couplers, however, are difficult to realize because of the control required in the asymmetry as well as with the usual coupler parameters. We propose an alternate method using identical fibers.
In-line fiber polarization detector
Authors: Scholl Bernhard
Published: February 2023

In the following paper a new polarization detector is presented, which couples out a small part of the light in the fiber in order to measure the polarization state and to represent the polarization with the help of a simulation program in a Poincaré-sphere.
All-fiber birefringent WDM devices
Authors: Cousins Sarah , Carlsen W. John
Published: February 2023

Birefringent wavelength-division multiplexers (BWDMs) have been described previously.1,2 In general, any optical transmittance function which can be constructed from a discrete Fourier series of sine waves (of optical frequency) whose highest harmonic component is N times the lowest can be synthesized from a stack of N equal-thickness birefringent plates. The device is made polarization-insensitive by separating the two polarization components, processing them separately, and recombining them at the outputs.
Spliced W-tunneling fiber polarizer
Authors: Stolen R. H. , Pleibel W. , Reed W. A.
Published: February 2023

W-tunneling polarizers1,2 are fibers only a few cm long which can be spliced to ordinary or polarization-preserving single-mode fibers. We demonstrate here such an inline fiber polarizer at 1.55 μm which is spliced to ordinary single-mode transmission fiber. The insertion loss is 1.5 dB and the extinction ratio is about 26 dB at 1.55 μm for a polarizer 4.3 cm. long.
A linear array of twelve graded-index lenses butted coaxially against single-mode fibers using silicon V-groove technology
Authors: Watson Hugh A.
Published: February 2023

The AT&T MAC-II optical fiber connector uses silicon V-groove technology to align an array of twelve fibers. The fibers on each side of the connector are epoxied to a pair of silicon V-groove blocks, as illustrated in Fig. 1. Steel alignment rods which rest under spring pressure in larger V-grooves at the ends of the blocks serve to align the two sides of the connector. The center-to-center spacing between the fibers is 0.25 mm.
Characteristics and applications of high performance, tunable, fiber Fabry-Perot filters
Authors: Miller Calvin M.
Published: February 2023

In 1987, Stone and Stulz described three configurations of fiber Fabry-Perot (FFP) interferometric filters that could span a wide spectrum of bandwidths and tuning ranges.1 In 1990, the author commercialized a filter based on the above work providing researchers with a stable, field-worthy, manufacturable optical filter with optimum performance.2
In-line acousto-optic frequency shifter in two-mode fiber
Authors: Lisboa O. , Carrara S. L. A.
Published: February 2023

An optical fiber frequency shifter is a key component for the implementation of optical fiber signal processing, communications and sensor systems. Several works reported in the literature address the various problems encountered when trying to fabricate a practical device.1,2,3 The main driving force behind these efforts is the stringent specification requirements to be met for closed-loop operation of high-performance optical fiber gyroscopes. Desired features in a fiber frequency shifter for such systems include: (a) high sideband and carrier suppression, (b) road acoustic and optical bandwidth, (c) low driving power, (d) easy splicing into single-mode fiber systems, with low insertion loss, and (e) ruggedness and compacticity. The basic configuration of a two-mode fiber frequency shifter,4 employs mode conversion between the two lowest-order modes (LP01 and LP11) through scouto-optic interaction with a flexural wave traveling in the fiber, the freqeuncy-shifted output light is guided in the LP11 mode, which requires an evanescent-field modal coupler and special fiber design to achieve connectivity into single-mode fiber systems. While our work was in progress some devices where reported addressing this issues as well as image sideband and carrier suppression.2,3,5 The first two employ double conversion in two interaction regions where the acoustic flexural waves are excited by the same transducer, imposing a critical compromise between acoustic bandwidth and carrier suppression. Only up-shift by twice the acoustic wave frequency is obtained with this configuraiton. The latter utilizes a specially designed double-core fiber and so far represents a trade-off between carrier suppression and insertion loss.
Spot-size transformer by ARROW-B waveguide
Authors: Kokubun Yasuo , Tamura Shuichi , Kondo Tatsumasa
Published: February 2023

We proposed a dual-tapered waveguide type spot-size transformer (SST),1 and demonstrated a low-loss and wide range transformation ration (5 and 1/5). However, this structure requires precise control of refractive index because the index difference between the core and the cladding must be small to satisfy the single-mode condition in the spot-enlarged waveguide. It is difficult to control the refractive index precisely by a sputtering technique and other thin-film deposition techniques.
Directional couplers in a high index silica waveguide
Authors: Welbourn D. , Beaumont C. , Nield M.
Published: February 2023

Silica-on-silicon waveguides are of growing interest for passive optical components and hybrid optical motherboards. Maximum functionality on a motherboard requires the optical interconnect to have high packing density and low coupling loss to lasers without compromising waveguide components or the fiber interface.
Recent algorithm development for solving Schrödinger type and Helmholtz equations
Authors: Fleck J. A.
Published: February 2023

In recent years substantial progress has been made by many workers in accurately modeling integrated optics devices using beam propagation techniques. The BPM is based on the symmetric factorization of a unitary evolution operator for the paraxial or Schrödinger wave equation into unitary parts representing free space propagation and phase changes induced by a space-dependent refractive index. the accuracy of the BPM is due in part to the stability guaranteed by the unitary form of the factored evolution operator as well as the accuracy with which the free space propagation operator can be represented using FFT techniques. The BPM, however, has important shortcomings including the following: it is restricted to second order in the propagation step due to commutation error, it cannot be applied to coordinate systems other than Cartesian, and it is restricted to slowly varying refractive index inhomogeneities. The latter restriction limits the accuracy of the BPM for some applications to semi-conductor ridge waveguide structures, for example.
A novel finite-difference beam-propagation method for large Δn and Δz
Authors: Majd M. , Splett A. , Petermann K.
Published: February 2023

The BPM is the technique used mostly for the simulation of integrated-optical waveguides and components. It is based on a propagation term, relating the field at (z + Δz) to the field at z as: with the differential operator The various BPM techniques, as proposed so far,1-3 mainly differ in the evaluation of the exponential operator in Eq. (1).
Second-harmonic generation in waveguide structures
Authors: Bierlein John D.
Published: February 2023

Optical waveguides offer potentially significant advantages to bulk crystals for efficient second harmonic generation from relatively low power sources because the fundamental optical beam can be tightly confined over long interaction lengths. However, since channel waveguides must be used to achieve this confinement, phase matching becomes a severe problem. Because the channel orientation is predefined, birefringence angle tuning, which is commonly used with bulk crystals, cannot be used and temperature tuning, when it can be used, usually requires precise temperature control. Also, since the effective propagation constants depend on guide geometry, the waveguide dimensions must be tightly controlled over the entire optical path length. Although guided second harmonic generation has been observed in uniform channel waveguides using both LiNbO3 and KTiOPO4 normalized conversion efficiencies have not exceeded about 5%/W-cm2 and considerable sample-to-sample variation in efficiency and/or phase matching temperature is common.
Efficient blue second-harmonic generation from a Ta2O5/KTiOPO4 waveguide
Authors: Tamada Hitoshi , Isobe Chiharu , Saitoh Masaki
Published: February 2023

A compact coherent blue light source is strongly desired for higher density optical disc systems. Several types of blue second-harmonic generation (SHG) have been reported thus far.1-3. Among them, only Cerenkov radiation SHG is free from the severe phase-matching constraint and is rather stably obtained regardless of the small changes in a temperature and of a fundamental wavelength. However, the wave front has alarge abberation fora proton-exchanged LiNbO3 waveguide1 because of a large (16°) radiation angle. The aberration becomes much smaller if the radiation angle is reduced to less than 1°. Realizing a small (<1°)radiation angle and a high SHG efficiency at the same time is the objective of this research.
Second-harmonic generation of blue light in a periodically poled LiTaO3 waveguide
Authors: Matsumoto S. , Lim E. J. , Fejer M. M. , Hertz H. M.
Published: February 2023

The demand for sources of coherent blue light with milliwatt output powers has stimulated much research activity in guided-wave devices for second-harmonic generation (SHG). To address the inability of otherwise-suitable materials to phase-match birefringently, quasi-phase-matching (QPM) has been used for SHG of visible radiation in LiNbO3,1,2 polymer,3 and KTP4 waveguides. This paper reports blue light generated by quasi-phase-matched SHG in a periodically poled LiTaO3 waveguide.
Quantum-well interdiffusion for integrated photonics
Authors: Ralston J. D. , Dischler B. , Eastman L. F.
Published: February 2023

Selective interdiffusion of semiconductor quantum-well (QW) structures is a versatile process for the fabrication and integration of both new and existing photonic devices. The impurity-free defect diffusion process has previously been demonstrated to facilitate continuous tuning of the effective bandgap of GaAs/AlGaAs QWs over an energy range of at least 40 meV while still preserving the room-temperature exciton-related absorptive and refractive properties of the QWs.1 In the present work the above interdiffusion process is further demonstrated to facilitate fabrication of efficient waveguide modulators operating over a wide range of wavelengths in a single epitaxial wafer. In addition, interdiffusion is demonstrated for the first time to facilitate tuning of the intersubband transitions in QWs.
Wavelength tunable lasers using selective partial intermixing
Authors: O’Brien S. , Shealy J. R.
Published: February 2023

Semiconductor quantum wells can be selectively interdiffused by using a variety of methods and exhibit blue-shifted (n = 1) optical transitions relative to the as-grown square wells. This makes bandgap engineering possible in the lateral dimension across an epitaxial wafer. Common interdiffusion techniques involve the introduction of impurities into the crystal. However, an impurity-free interdiffusion technique is advantageous for bandgap tuning applications for active devices since the presence of impurities could be detrimental to the operation of the device. Here we use an impurity-free interdiffusion technique to fabricate lasers that operate at significantly different wavelengths (Δλ ≈ 120 Å) on the same substrate.
Integrated-optic displacement sensor in glass with 1 nm resolution
Authors: Jestel D. , Baus A. , Voges E.
Published: February 2023

An integrated-optic displacement sensor is described. A double Michelson interferometer,1 built up by ion-exchanged, monomode (633-nm) waveguides in glass, combines a fast forward/backward movement detection by orthogonal signals with a high-resolution (1-nm) displacement sensing by optical heterodyning. The complex optical structure in combination with a collimating gradient-index lens provides two reference arms, offering a fast displacement detection over a wide measuring range (10 cm) with a limited resolution of 1/8 wavelength (79 nm). An integrated thermo-optical modulator increases the resolution of the sensor up to 1 nm by an optical phase modulation single sideband detection2 technique with 1-kHz frequency offset.
Hole transport at the heterointerfaces of InGaAs/InP avalanche photodiodes
Authors: Tsuchiya H. , Ogawa M. , Miyoshi T.
Published: February 2023

The high speed response of avalanche photodiodes (APDs) is degraded by hole trapping at the heterointerface between the separated absorption and multiplication region. The photo-excited holes are trapped in a triangular quantum well formed at the heterojunction and escape from the quantum subbands only by thermionic emission. Practically, the insertion of a thin quaternary layer at the heterojunction (QI structure) has been successful in eliminating hole trapping. However, to design the proper transition region at the heterojunction, a quantum mechanical simulation model describing hole transport is required.
Analysis of a rib waveguide filter response with variable separation
Authors: Burke S. V. , Kendall P. C.
Published: February 2023

An asymmetric coupler consisting of two dissimilar waveguides can be designed to operate as a narrowband filter if the propagation constants of the individual guides coincide at one wavelength, λo. The filter response is approximately a (sinc)2 function with high sidelobes of -9 dB, undesirable for WDM applications. The sidelobes can be reduced by controlling the coupling coefficient k(z) along the coupler by varying the interguide separation t according to certain window functions. This was demonstrated theoretically by solving the coupled-wave equations1 and experimentally with one-dimensional waveguides.2
Velocity matched traveling wave directional coupler optical modulator in AlGaAs/GaAs
Authors: Khan M. Nisa , Gopinath Anand , Bristow Julian P.G.
Published: February 2023

The design for a new velocity matched traveling wave directional coupler modulator (DCM) in AlGaAs/GaAs material is proposed. The DCM characteristics are compared with those of the n-i-n modulator proposed by Kim et al.1 and the GaAs superstate modulator proposed by Nees et al2 In this paper, velocity matching in the DCM is achieved by covering the modulator and its electrode structure with a dielectric material of high dielectric constant which reduces the micro wave phase velocity to match the lightweight velocity. The dielectric materials used for the velocity matching analysis are alumina (Al2O3) and tantalum pentoxide (Ta2O5), whose relative dielectric constants at microwave frequencies are 10.0 and 27.0, respectively. The optical and microwave characteristics of the modulator are analyzed using the effective index method (EIM) and the finite difference method (FDM) repectively.
Nonorthogonal longitudinal eigenmodes and the Peterman K-factor
Authors: Hamel W. A. , Lenstra D. , Woerdman J. P.
Published: February 2023

In conventional laser theories it is standard practice to deal with orthogonal eigenmodes. Indeed, orthogonality is a good approximation when dealing with high-Q resonators but exact orthogonality only occurs in hypothetical resonators which are fully isolated from the outside world. Even if those systems could be realized they would not be interesting for applications because no signal could get in or out. So, from the fundamental point of view there is an obvious need to include nonorthogonality in a modal description of a laser with output coupling. From the practical point of view this inclusion becomes even essential when dealing with high-gain laser systems with bad cavities. The large output coupling of these systems has a substantial influence on the electromagnetic mode structure, which in turn modifies the spontaneous and stimulated emission processes. A convincing experimental demonstration of these principles was reported in Ref. 1. Here the measured linewidths of identical semiconductor lasers with different mirror reflectivities were compared with theoretical predictions based on Petermann's excess-noise factor.2 Reasonably good agreement was obtained.
BPM simulation of transverse mode characteristics in surface emitting laser
Authors: Shimizu M. , Koyama F. , Iga K.
Published: February 2023

A vertical cavity surface emitting (SE) laser is becoming one of important devices for parallel optical processing and optical disk memories, because of its narrow circular beam, longitudinal single mode operation and two-dimensional parallelism. For these applications, the transverse mode must be well stabilized and some discussion has been made by approximation analysis.1 This approach, however, can not be applicable to the analysis for obtaining characteristics such as side mode suppression ratio and the maximum output power under single transverse mode operation. There may be influenced by the spatial change of refractive index and gain in an active medium by carrier variation. The advantage of using a beam propagation method (BPM)2 is to propagate the beam in the medium which has both refractive index and gain distributions. We, therefore, have employed a three-dimensional BPM and simulated the metal organic chemical vapor deposition (MOCVD) grown circular buried heterostructure (CBH) SE laser.3 In order to perform this simulation, we use the supercomputer ETA10 and automatic vectorization of this system.
Dispersion-related amplification in a lossy nonlinear fiber pumped by counterpropagating waves
Authors: Law C. T. , Kaplan A. E.
Published: February 2023

We have demonstrated previously that counterpropagating waves (with the same frequency) in a Kerr nonlinear medium with linear dispersion may become unstable when their intensities exceed certain threshold.1 It has been shown recently2 that the system exhibits large amplification when the pumping is below the threshold of instability. Here we explore the opportunity of using this system in optical amplification and show that its gain is appreciable even when linear absorption is taken into consideration. The mechanism of amplification in our system can be explained in terms of positive distributed feedback from the Kerr nonlinear index grating formed by two strong pumping laser waves.
Unconditionally stable formulation of the collocation method
Authors: Sharma Anurag , Taneja Anju
Published: February 2023

We have earlier developed a method-the Collocation method for propagating beams or total fields through optical waveguiding structures1,2 which is numerically more efficient and capable of giving better accuracy in comparison to commonly used propagating beam method (PBM). The collocation method, which converts the Helmholtz equation into a matrix total differential equation to facilitate direct numerical solution, suffers, however, from one drawback. For moderately large extrapolation intervals (typically 10 μm) the method becomes unstable and error increases exponentially. This kind of behavior is typical of simultaneous equations. Special methods have to be used to circumvent this problem which may not be very convenient and the advantage of computational efficiency may be lost. We have, therefore, developed an alternative method to solve the matrix differential equation. The new formulation involves only unitary operators, like in PBM, and is unconditionally stable with respect to the values of the extrapolation intervals. The method still has its computational advantage over PBM.
A scalar finite-difference time-domain method for guided-wave optics
Authors: Huang W. P. , Chu S. T. , Goss A. , Chaudhuri S. K.
Published: February 2023

Modeling and simulation are important to the optimum design and precise prediction of the possible performance of optical guided-wave devices. One of the commonly used numerical methods for the simulation of wave propagation in optical waveguides is the beam propagation method (BPM)1,2 and its variations.3,4 Since all these methods assume Fresnel approximation, the reflection of the waves due to the inhomogeneous perturbations along the waveguiding axis has been neglected. The reflection, however, may not be negligible at abrupt junctions and certainly become dominant in structures such as distributed feedback reflectors. A finite-difference time-domain technique (FDTD) that solves the Maxwell′s equations directly has been recently introduced and in principle can be applied to the structures that both the reflection and the polarization effects become important.5 Since most practical optical waveguides are weakly-guiding, the scalar analysis is often sufficient. Therefore, as an alternative approach, we propose to apply FDTD technique to the scalar analysis.
Comparative performance of phase modulators in GaAs/AlGaAs on silicon and GaAs substrates
Authors: Kim Young S. , Lee Sang S. , Ramaswamy Ramu V.
Published: February 2023

GaAs-on-Si devices have attractive applications for opto-electronic integrated circuits because of their combined optical and electronicmerits. With the recent breakthroughs in the heteroepitaxial growth of high-quality GaAs films on Si substrates, a number of devices such as diode lasers, photodetectors and FET's have been demonstrated. In this paper, we report the growth and characterization of Schottky-barrier GaAs/AlGaAs phase modulators on Si as well as GaAs substrates. Experimental and theoretical studies were performed to access the feasibility of GaAs-on-Si waveguide devices as well as the probable effect of thermal stress on the electro-optic coefficient. We demonstrate for the first time that the interfacial stress does not affect the electro-optic coefficient and hence the phase shift efficiency.
A new technique to measure the effective refractive indices of semiconductor slab waveguides
Authors: Chiang Kenny H. , Summers Christopher J. , Kenan Richard P.
Published: February 2023

Currently, prism couplers are often used to measure the mode indices of glass and LiNbO3 waveguides.1 Recently, silicon prisms were also used to measure InP and InGaAsP waveguides.2,3 However, buried waveguides cannot be measured by prism couplers. The high refractive index of semiconductor waveguides also makes the measurement difficult over a wide wavelength range. In this paper, a new non-destructive and non-contact measuring technique that can accurately measure the mode indices (N) of single mode GaAs/AlGaAs slab waveguides is presented. This measurement technique could be a useful tool for wafer selection in the fabrication of distributed feedback laser.
Nonlinear propagation and coupling effects in silicon-on-insulator waveguides
Authors: Prelewitz D. F. , Sankey N. D. , Brown T. G.
Published: February 2023

Silicon on insulator structures have been proposed as possible low-loss waveguides for eventual monolithic integration of both optical and electronic components. In this paper we present an experimental investigation of optical nonlinearities in waveguides fabricated by the bond and etch-back technique. This procedure consists of ion implantation, annealing, bonding, and dopant-selective chemical etching. Measurements at a wavelength λ=1.06 μm show the waveguide losses to be close to the material absorption for silicon (11 cm−1). This allows the use of both pulsed and CW Nd:YAG lasers for the investigation of nonlinear coupling and propagation over distances up to several millimeters.
A 1.5-μm vertically coupled semiconductor laser amplifier for optically pre-amplified receiver
Authors: Lee H. P. , Scherer A. , Zah C. E. , Orenstein M. , Bhat R. , Beebe E. D. , Andreadakis N. , Koza M. A. , Hong W. P.
Published: February 2023

Optically pre-amplified detection employing semiconductor laser amplifier at the input stage has attracted considerable interests for high speed, high sensitivity lightwave receiver systems.1 However, the current hybrid method using discrete laser amplifier followed by a narrow band filter and detector incurs a high coupling loss (varies from 3.5 to 9 dB) and lacks integration capability. In the monolithic integration scheme,2 on the other hand, suppression of residual optical reflection is difficult to achieve and the incorporation of an optical filter is difficult to implement. We have demonstrated in this work, a vertically coupled InGaAsP/InP laser amplifier at 1.5 μm which can circumvent these problems. The device schematic is shown in Fig. 1. A 4 μm wide ridge laser with a tapered rear end which extends to 10 μm is first fabricated by conventional method.3 A 45° mirror is then formed by focused ion beam etching on the tapered end of the device which deflects the amplified signal (incident from the front facet) onto the backside of the substrate for detection. The substrate is thinned down to 120-150 μm, polished on the backside and contacted electrically. The cavity of the gain medium, formed by cleaving the front facet of the laser amplifier, has a typical length (between the front facet and the 45° mirror) of 400 μm. Figure 1 also shows the beam size on the 45° mirror and on the backside of the substrate respectively. For a near field pattern of 8.1 μm by 3.4 μm, on the 45° mirror, a nearly diffraction-limited far field pattern of 15 μm by 32 μm is obtained on the substrate side. Figures 2 and 3 show the light versus current and the emission spectra of the device before and after anti-reflection (AR) coating at the front facet. The device functions as a multimode laser prior to AR coating and displays periodic intensity modulation in its longitudinal modes due to residual reflection between the 45° mirror and the polished backside of the substrate. These gain ripples are suppressed after AR coating at the front facet and an external gain (fiber to detector) of 15.4 dB at 1.490 μm (from a DFB laser) is obtained at an injection level of 170 mA with a gain ripple < 2 dB. Owing to the vertical propagation of the output beam and enlarged output spot size (15 μm by 30μm), the device has advantages for low insertion loss and compact integration with narrow band dielectric DBR filters4 (externally coated or epitaxially grown) and photodetectors (via hybrid flip-chip bonding5 or monolithic integration on the backside of the substrate) in high sensitivity, high bit-rate lightwave communication systems.
Femtosecond time domain diagnostics of nonlinear and linear waveguide properties
Authors: Fujimoto J. G. , Haus H. A.
Published: February 2023

Short pulse time domain measurements can provide the basis for a comprehensive diagnostic technology to characterize both nonlinear and linear optical properties of waveguide devices. This paper outlines methods for characterizing waveguide devices using femtosecond time- resolved measurement. These investigation provide fundamental information on linear and nonlinear device behavior. In addition, by developing interferometric measurement techniques we can obtain insights into the mechanisms of all-optical switching in waveguide devices. Based on these studies, we formulate criteria on material properties that must be satisfied to achieve high-speed all-optical switching and discuss performance issues for simple all-optical switching device designs.
Improved optical switch recovery time by carrier sweep-out in a GaAs/GaAlAs multi-quantum well waveguide directional coupler
Authors: LiKamWa P. , Miller A. , Roberts J. S. , Robson P. N.
Published: February 2023

We have previously reported all-optical switching of picosecond pulses in a zero-gap directional coupler containing GaAs quantum wells.1 The intensity dependent refractive index causing the switch originates from the effect of photo-generated carriers on the position of the absorption edge and the screening of the excitons. The dynamics of the free carriers generated by the laser pulses that induce the switching therefore determine the speed of response. Since the generation of carriers is instantaneous, the rise time of the switch is of the order of the laser pulse width. However, the recovery time is dependent on the speed at which the carriers are relaxed usually by recombination between electrons and holes. In an earlier experiment,1 we measured the recovery time of a zero-gap directional coupler containing a single quantum well to be 1ns which indicated that lateral diffusion of the carriers was also contributing to the switch response. In this work we shall demonstrate the reduction in recovery time that is achieved by the application of an external reverse bias to sweep out the photo-generated carriers.
Self-organizing guided wave demultiplexers and switches
Authors: Anderson Dana Z. , Saffman Mark , Benkert Claus
Published: February 2023

We have borrowed a few concepts from neural-network modeling to implement a class of guided wave frequency demultiplexers and switches that adapt themselves to their input signals. The adaptation feature is useful in demultiplexing cases where the signal carrier frequencies are a priori unknown, or where the frequencies are subject to drifts. Given two carrier frequencies ω1 and ω2 copropagating along a fiber, for example, the demultiplexer's task is to separate the two channels. In the present case, the demultiplexing is done through a nonlinear competitive process that takes place in a multimode photorefractive ring resonator. Each of (in this case) two modes associates itself with one of the carrier frequencies while rejecting the other. In a slightly different configuration, the demultiplexer becomes a switch for which the destination is determined by a spatial pattern imposed by a transmitter using a multimode waveguide. Although our experimental work uses bulk optical components, the schemes are particularly well suited to integrated approaches.
Photonic band structure: the path to three-dimensional microcavities
Authors: Yablonovitch E.
Published: February 2023

Analogous to electron waves in a crystal, light waves in a three-dimensionally periodic dielectric structure should be described by band theory. The concept of photonic band structure1 is gaining rapid2−5 acceptance. The concepts of reciprocal space, Brillouin zones, dispersion relations, Block wave functions, van Hove singularities, etc. are now being applied to optical waves.
Picosecond studies of cross-well carrier sweep-out rates in multiple quantum wells
Authors: Miller A. , Park C. B. , Hutchings D. C. , LiKamWa P.
Published: February 2023

We have recently demonstrated that the recovery time of a MQW waveguide directional coupler switch can be significantly improved by carrier sweep out through the application of an electric field perpendicular to the quantum wells.1 The high frequency operation of a number of other MQW devices based on the SEED principle also depend on cross-well carrier transport in transverse fields. In this work, we have carried out a detailed study of the dynamics of charge transfer perpendicular to the quantum wells as a function of both applied electric field and optical power using the quantum confined Stark effect to monitor the sweep-out rate on picosecond timescales.
Polarization-insensitive optical amplifiers: modelling and measurement
Authors: Young Terry , Janson Mats , Gustavsson Mats
Published: February 2023

The need for simulation tools in designing and tolerancing integrated-optical components has long been recognized. Here we present a modeling study of an optical amplifier, using structural data obtained from SEMs, and compare the predictions with measurements.
Computational methods in microwaves applicable to optoelectronics
Authors: Davies J. Brian
Published: February 2023

Microwaves are distinctive—physically by their concern with waves whose wavelengths are comparable with dimension of the components—and by their applications, mainly to radar and to communications. Component design and analysis at microwaves often follows from the above first property, that it operates around the resonance region, which sits between the optical region and the low-frequency region (to use the language of scattering). But it is equally true in optoelectronics that relevant physical dimensions are comparable with the operating wavelength. So, as much of communications has shifted from the microwave to the optical region, it is natural than many, although not all, microwave techniques will follow this upward shift of frequency.