Showing papers in "IEEE Journal of Quantum Electronics in 2004"
TL;DR: In this paper, a general temporal coupled-mode theory for multimode optical resonators is proposed, which incorporates a formal description of a direct transmission pathway, and is therefore capable of describing Fano interference phenomena in multimode cavities.
Abstract: We develop a general temporal coupled-mode theory for multimode optical resonators. This theory incorporates a formal description of a direct transmission pathway, and is therefore capable of describing Fano interference phenomena in multimode cavities. Using this theory, we prove a general criterion that governs the existence of nonorthogonal modes. The presence of nonorthogonal modes creates interesting transport properties which can not be obtained in normal resonator systems. We validate our theory by comparing its predictions with first-principles finite-difference time-domain simulations and obtaining excellent agreement between the two.
604 citations
TL;DR: In this paper, a novel chaotic radar (CRADAR) system utilizing laser chaos is investigated both numerically and experimentally, which has the advantages of very high-range resolution, unambiguous correlation profile, possibility of secure detection, low probability of intercept, and high electromagnetic compatibility.
Abstract: A novel chaotic radar (CRADAR) system utilizing laser chaos is investigated both numerically and experimentally. Compared with conventional radars, the proposed CRADAR has the advantages of very-high-range resolution, unambiguous correlation profile, possibility of secure detection, low probability of intercept, and high electromagnetic compatibility. Generated by an optically injected semiconductor laser, chaotic waveforms with bandwidths larger than 10 GHz can be readily obtained. In this paper, the time series, the phase portraits, and the power spectra of the chaotic states are presented. The correlation traces between the signal and the reference waveforms are plotted. The peak sidelobe level with different correlation lengths is investigated. The capability of anti-jamming and the performance under additive white Gaussian noise are studied. To show the feasibility of CRADAR, proof-of-concept experiments using a pair of planar antennas with a 1.5-GHz bandwidth covering the range from 1.5 to 3 GHz are demonstrated. A range resolution of 9 cm is achieved, which is currently limited not by the bandwidth of the chaotic states but by the detection bandwidths of the real-time oscilloscope and the antennas used.
238 citations
TL;DR: In this paper, an experimental investigation of the transfer characteristics of a fiber ring resonator for various values of the resonator finesse was carried out to measure the spectral dependence of the intensity transmission and the induced phase shift in the undercoupled, critically coupled, and overcoupled regimes.
Abstract: We present the results of an experimental investigation of the transfer characteristics of a fiber ring resonator for various values of the resonator finesse. In particular, we measure the spectral dependence of the intensity transmission and the induced phase shift in the undercoupled, critically coupled, and overcoupled regimes. We also demonstrate tunable optical (true time) group delay via a fiber ring resonator and show that a high finesse is unnecessary. Our laboratory results are in excellent agreement with theoretical predictions.
238 citations
TL;DR: In this paper, an integrated SOA-based Mach-Zehnder interferometer (SOA-MZI) at 20 and 40 Gb/s was used for all-optical XOR functionality.
Abstract: All-optical XOR functionality has been demonstrated experimentally using an integrated SOA-based Mach-Zehnder interferometer (SOA-MZI) at 20 and 40 Gb/s. The performance of the XOR results has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to >100 Gb/s.
201 citations
TL;DR: In this paper, a quantum key distribution (QKD) system was developed using a standard telecommunications optical fiber, which is capable of operating at clock rates of greater than 1 GHz.
Abstract: A quantum key distribution (QKD) system has been developed, using a standard telecommunications optical fiber, which is capable of operating at clock rates of greater than 1 GHz. The QKD system implements a polarization encoded version of the B92 protocol. The system employs vertical-cavity surface-emitting lasers with emission wavelengths of 850 nm as weak coherent light sources, and silicon single photon avalanche diodes as the single photon detectors. A distributed feedback laser of emission wavelength 1.3 /spl mu/m, and a linear gain germanium avalanche photodiode was used to optically synchronize individual photons over the standard telecommunications fiber. The QKD system exhibited a quantum bit error rate (QBER) of 1.4%, and an estimated net bit rate (NBR) greater than 100 000 bits/sup -1/ for a 4.2-km transmission range. For a 10-km fiber range, a QBER of 2.1%, and an estimated NBR of greater than 7000 bits/sup -1/ was achieved.
170 citations
TL;DR: In this paper, a theory for pulse amplification and saturation in quantum dot (QD) semiconductor optical amplifiers (SOAs) is developed, and the maximum bit rate at which a data stream of pulses can be amplified without significant patterning effects is investigated.
Abstract: A theory for pulse amplification and saturation in quantum dot (QD) semiconductor optical amplifiers (SOAs) is developed. In particular, the maximum bit rate at which a data stream of pulses can be amplified without significant patterning effects is investigated. Simple expressions are derived that clearly show the dependence of the maximum bit rate on material and device parameters. A comparative analysis of QD, quantum well (QW), and bulk SOAs shows that QD SOAs may have superior properties; calculations predict patterning-free amplification up to bit rates of /spl sim/150-200 Gb/s with pulse output energies of /spl sim/0.2-0.4 pJ. The superiority of QD SOAs is based on: 1) the faster achievement of the regime of maximum gain in QD SOAs compared to QW and bulk SOAs and 2) the lower effective cross section of photon-carrier interaction in QDs.
146 citations
TL;DR: In this paper, it is shown that amplified spontaneous emission acts to decrease the inversion of the wetting layer states, thus helping to quench the gain of these states, which might otherwise dominate.
Abstract: Based on extensive numerical calculations, quantum-dot (QD) amplifiers are predicted to offer higher output power and lower noise figure compared to bulk as well as quantum well amplifiers. The underlying physical mechanisms are analyzed in detail, leading to the identification of a few key requirements that QD amplifiers should meet in order to achieve such superior linear characteristics. The existence of a highly inverted wetting layer or barrier region, acting as a carrier reservoir, is central to this performance enhancement. It is shown that amplified spontaneous emission acts to decrease the inversion of the wetting layer states, thus helping to quench the gain of these states, which might otherwise dominate.
144 citations
TL;DR: In this article, a prepulse-free short-pulse Nd:glass laser system of 0.9-PW peak power was developed to heat a pre-imploded high-density plasma.
Abstract: We have developed a prepulse-free short-pulse Nd:glass laser system of 0.9-PW peak power to heat a pre-imploded high-density plasma. An optical parametric chirped amplification system is introduced to reduce the prepulses to an amplitude (1.5/spl times/10/sup -8/) of that of the main pulse. The compressor is a double-path grating pair system 94 cm in diameter compressing the 50-cm-diameter laser beam to 470 fs. An off-axis parabolic mirror has focused the 420-J energy to an intensity of 2.5/spl times/10/sup 19/ W/spl middot/cm/sup -2/. Part of the front end of the chirped pulse is seeded into the preamplifier of the GEKKO XII laser, used to implode a pellet target, to enable the petawatt laser to irradiate the pre-imploded pellet during stagnation of a few tens of picoseconds.
144 citations
TL;DR: In this paper, a monolithically integrated near-infrared fluorescence detection system is presented, which integrates vertical-cavity surface-emitting laser (VCSEL), optical filters, and photodetectors through a modification to a typical VCSEL structure.
Abstract: Vertical-cavity surface-emitting lasers (VCSELs), optical emission filters, and PIN photodetectors were fabricated as part of a monolithically integrated near-infrared fluorescence detection system. The integration of these micro-fabricated components with micro-arrays, flow channel arrays, and biochips can drastically reduce cost and enable parallel sensing architectures. An optoelectronic design is presented that integrates VCSELs, optical filters, and photodetectors through a modification to a typical VCSEL structure. System designs were simulated and compared, leading to several innovative approaches for integrated sensors. The laser and detector modules were characterized independently and subsequently integrated to form a complete sensor. VCSELs with oxidation apertures measuring 4, 7, 14, and 20 /spl mu/m showed a lasing wavelength of /spl lambda/=773 nm, threshold current densities from 6400 to 1300 A/spl middot/cm/sup -2/, and maximum output powers of 0.6-4 mW, with transverse single-mode and multimode operation. PIN photodetectors were fabricated with integrated emission filters. Quantum efficiencies above 85% were observed with a dark current of 500 fA/(mm detector diameter). Complete sensor units were tested and near-infrared fluorescent molecules (IR-800) were detected. A theoretical detection limit of 10/sup 5/ fluorophores//spl mu/m/sup 2/ was determined. The compact parallel architecture, high-power laser, and low-noise photodetector make this sensor a good candidate for biomedical fluorescence-based sensing applications.
126 citations
TL;DR: In this article, a theoretical and experimental study of thermal lensing in Yb-doped crystals is presented, where the authors derive an expression of the temperature distribution with account of absorption saturation and pump beam divergence inside the crystal, and address a general discussion on the particularities of quasi-three-level lasers, as far as thermal effects and fracture issues are concerned.
Abstract: A theoretical and experimental study of thermal lensing in Yb-doped crystals is presented. In this first part, we focus on theoretical considerations and we describe an original technique suitable for thermal lensing measurements in end-pumped materials. We first derive an expression of the temperature distribution with account of absorption saturation and pump beam divergence inside the crystal, and we address a more general discussion on the particularities of quasi-three-level lasers, as far as thermal effects and fracture issues are concerned. The thermal lens was then measured using a simple technique based on a Shack-Hartmann wavefront analyzer, under lasing and nonlasing conditions. We demonstrate that the technique allows precise wavefront measurements even on small spots. Thermal lensing measurements are finally presented in Yb-doped YAG, GGG, YCOB, GdCOB, KGW, and YSO crystals.
124 citations
TL;DR: In this article, the authors investigated the optical gain for the modes guided by semiconductor nanowires and showed that the confinement factors for nanowire lasers are very large in comparison to those for heterostructure lasers, and can even exceed unity.
Abstract: We investigate optical gain for the modes guided by semiconductor nanowires. We focus on optically anisotropic wurtzite-type semiconductors (such as GaN) and the situation when the optical axis of the crystal coincides with the geometrical axis of the nanowire. For GaN nanowire lasers, the calculation of the modal gain requires the knowledge of two confinement factors for a given mode and two gain coefficients for the bulk crystal. We show that the confinement factors for nanowire lasers are very large in comparison to those for heterostructure lasers, and can even exceed unity. To estimate the bulk gain in GaN we use the free-carrier model and emphasize the importance of accounting for anisotropy of gain. Using the calculated confinement factors and bulk gain, we predict that free-standing nanowires with small radius (R /spl lsim/ 70 nm) lase into the HE/sub 11/ mode, thicker nanowires (70 nm /spl lsim/ R /spl lsim/ 90 nm) lase into the TE/sub 01/ mode.
TL;DR: In this paper, high-power laser experiments yield an optical-to-optical conversion efficiency of 30% for Nd (0.6 at%):YAG ceramic as compared to 34% for an Nd single crystal.
Abstract: Nd: YAG ceramic materials have been synthesized using vacuum sintering technique with the raw materials prepared by the nano-crystalline methods. The spectroscopic studies suggest overall improvement in absorption and emission and reduction in scattering loss. Judd-Ofelt analysis has been employed to compute the relevant spectroscopic and radiative parameters of the material. The SEM and TEM measurements reveal the excellent optical quality of the ceramic with low pore volume and narrow grain boundary. Fluorescence and Raman measurements reveal that the Nd/sup 3+/-doped YAG ceramic is almost equivalent to its single-crystal counterpart in its radiative and nonradiative properties. Individual Stark levels for /sup 2s+1/L/sub J/ manifolds are obtained from the absorption and fluorescence spectra and are analyzed to identify the stimulated emission channels possible in the Nd: YAG ceramic. Laser performance studies favor the use of high-concentration Nd: YAG ceramics in the design of an efficient microchip laser. With 4 at% Nd: YAG ceramic acting as a microchip laser, we obtained a slope efficiency of 40%. High-power laser experiments yield an optical-to-optical conversion efficiency of 30% for Nd (0.6 at%):YAG ceramic as compared to 34% for an Nd (0.6 at%):YAG single crystal. The oscillation experiments at 1.3 mm gives a slope efficiency of 35%. Optical gain measurements conducted in these materials also show values comparable to single crystal, supporting that these materials could be suitable substitutes to single crystals in solid-state laser applications.
TL;DR: In this paper, the I-V characteristics and photoresponse spectra have been measured and analyzed for a 5 mm/spl times/5 mm area device leakage current lower than 10/sup -15/ A at zero bias and 1.2/spltimes/10/sup 15/ cmHz/sup 1/2//W at 300 nm.
Abstract: Pt/4H-SiC Schottky photodiodes have been fabricated with the device areas up to 1 cm/sup 2/. The I-V characteristics and photoresponse spectra have been measured and analyzed. For a 5 mm/spl times/5 mm area device leakage current lower than 10/sup -15/ A at zero bias and 1.2/spl times/10/sup -14/ A at -1 V have been established. The quantum efficiency is over 30% from 240 to 320 nm. The specific detectivity, D/sup */, has been calculated from the directly measured leakage current and quantum efficiency are shown to be higher than 10/sup 15/ cmHz/sup 1/2//W from 210 to 350 nm with a peak D/sup */ of 3.6/spl times/10/sup 15/ cmHz/sup 1/2//W at 300 nm.
TL;DR: In this article, the authors derived the spectral dispersion law for the virtually imaged phased array (VIPA) based on paraxial wave theory using the Fresnel diffraction analysis.
Abstract: We derive the spectral dispersion law for the virtually imaged phased array (VIPA) based on paraxial wave theory using the Fresnel diffraction analysis. The validity of the dispersion law is verified by comparison with experiments. This spectral dispersion law is compared to a previous law based on plane wave theory. At small incident angles where the VIPA provides its largest spectral dispersion, the paraxial wave law provides a much better fit to the data than the plane wave law does.
TL;DR: In this article, the erbium and ytterbium ion concentrations in the host yttrium calcium oxaborate have been optimized for diode pumped continuous-wave (CW) operation using spectroscopic measurements, modeling of energy transfer and population rate equation analysis, resulting in 270 mW of CW output from a diode-pumped Er,Yb:YCOB laser.
Abstract: The erbium and ytterbium ion concentrations in the host yttrium calcium oxaborate have been optimized for diode pumped continuous-wave (CW) laser operation using spectroscopic measurements, modeling of energy transfer and population rate equation analysis, resulting in 270 mW of CW output from a diode-pumped Er,Yb:YCOB laser.
TL;DR: In this article, the contribution of the photoelastic effect to the total thermal lens cannot be neglected for either terbium gallium garnet (TGG) or FK51 glass.
Abstract: Two methods of compensation of thermal lensing in high-power terbium gallium garnet (TGG) Faraday isolators have been investigated in detail: compensation by means of an ordinary negative lens and compensation using FK51 Schott glass possessing a negative dn/dT. Key thermooptic constants for TGG crystals and FK51 glass were measured. We find that the contribution of the photoelastic effect to the total thermal lens cannot be neglected for either TGG or FK51. We define a figure of merit for compensating glass and show that for FK51, an ordinary negative lens with an optimal focus is more efficient, but requires physical repositioning of the lens for different laser powers. In contrast, the use of FK51 as a compensating element is passive and works at any laser power, but is less effective than simple telescopic compensation. The efficiency of adaptive compensation can be considerably enhanced by using a compensating glass with figure of merit more than 50, a crystal with natural birefringence or gel.
TL;DR: In this article, the authors reformulate the existing auxiliary differential equation (ADE) technique in the context of the finite-difference time-domain analysis of Maxwell's equations for the modeling of optical pulse propagation in linear Lorentz and nonlinear Kerr and Raman media.
Abstract: We reformulate the existing auxiliary differential equation (ADE) technique in the context of the finite-difference time-domain analysis of Maxwell's equations for the modeling of optical pulse propagation in linear Lorentz and nonlinear Kerr and Raman media. Our formulation is based on the polarization terms and allows simple and consistent implementation of such media together with the anisotropic perfectly matched layer (APML) absorbing boundary condition. The disadvantages of the ADE technique, i.e., requiring additional storage for auxiliary variables, has been overcome by adopting the high-order finite-difference schemes derived from the previously reported wavelet-based formulation. With those techniques, we demonstrate in two-dimensional setting an effective and accurate numerical analysis of the spatio-temporal soliton propagation as a consequence of the physically originated balanced phenomena between the self-focusing effect of nonlinearity and the pulse broadening effects of the temporal dispersion and of the spatial diffraction.
TL;DR: In this article, the first continuous-wave edge-emitting GaAs-based laser operation beyond 1.5 µm was reported, with a threshold current density of 1.06 kA/cm/sup 2, external quantum efficiency of 31%, and characteristic temperature T/sub 0/ of 139 K.
Abstract: We present the first continuous-wave (CW) edge-emitting lasers at 1.5 /spl mu/m grown on GaAs by molecular beam epitaxy (MBE). These single quantum well (QW) devices show dramatic improvement in all areas of device performance as compared to previous reports. CW output powers as high as 140 mW (both facets) were obtained from 20 /spl mu/m /spl times/ 2450 /spl mu/m ridge-waveguide lasers possessing a threshold current density of 1.06 kA/cm/sup 2/, external quantum efficiency of 31%, and characteristic temperature T/sub 0/ of 139 K from 10/spl deg/C-60/spl deg/C. The lasing wavelength shifted 0.58 nm/K, resulting in CW laser action at 1.52 /spl mu/m at 70/spl deg/C. This is the first report of CW GaAs-based laser operation beyond 1.5 /spl mu/m. Evidence of Auger recombination and intervalence band absorption was found over the range of operation and prevented CW operation above 70/spl deg/C. Maximum CW output power was limited by insufficient thermal heatsinking; however, devices with a highly reflective (HR) coating applied to one facet produced 707 mW of pulsed output power limited by the laser driver. Similar CW output powers are expected with more sophisticated packaging and further optimization of the gain region. It is expected that such lasers will find application in next-generation optical networks as pump lasers for Raman amplifiers or doped fiber amplifiers, and could displace InP-based lasers for applications from 1.2 to 1.6 /spl mu/m.
TL;DR: In this paper, a diode-pumped fiber laser with a high-contrast semiconductor saturable absorber mirror (SESAM) is presented, and the cavity is simple since no dispersion compensators are used and the SESAM-based mode locking mechanism is robust and self-starting.
Abstract: We report here a compact diode-pumped fiber laser that represents a promising route to designing a portable and rugged picosecond light source. The laser presented in this paper is based on a high-contrast semiconductor saturable absorber mirror (SESAM) and targets reliable picosecond-range sources. The cavity is simple since no dispersion compensators are used, and the SESAM-based mode locking mechanism is robust and self-starting, resulting in low-maintenance turn-key operation. We investigated pulse formation in a short-length fiber cavity and found that nonlinear effects in a near-resonant SESAM in combination with large-cavity dispersion provide the predominant mechanism that causes pulse shaping. The role of a resonant high-contrast SESAM in preventing low-frequency Q-switching instability has been elucidated. The effect of the recovery time of the SESAM on the stretched pulse width and spectrum for resonant-type absorber mirrors was also studied.
TL;DR: In this paper, a distributed feedback (DFB) laser optimization method based on the effective cavity length was proposed to increase the pump-to-signal conversion ratio by 40% for the same total device length and pumping conditions.
Abstract: The standard distributed feedback (DFB) laser optimization method is critically investigated and a new design approach based on the effective cavity length is presented. By applying this method in an erbium-ytterbium co-doped fiber, the pump-to-signal conversion ratio is increased by 40% for the same total device length and pumping conditions. The laser with the proposed design is produced and the theoretical results are verified by the experimental work.
TL;DR: In this article, a theoretical and experimental study of thermal lensing in Yb-doped crystals is presented, and two parameters valuable for laser design and power scaling are derived.
Abstract: A theoretical and experimental study of thermal lensing in Yb-doped crystals is presented. This papers follows the presentation of theoretical considerations and experimental wavefront measurements, which have been the subject of Part I. In this paper, we study the evolution of thermal lensing versus absorbed pump power, and we derive two parameters valuable for laser design and power scaling. The quantum efficiency and the thermo-optic coefficient, in Yb-doped YAG, GGG, GdCOB, YCOB, KGW and YSO. The clear difference between thermal lensing under lasing and nonlasing conditions is the proof that nonradiative effects occur in all the crystals under investigation. An analytical model which takes into account the laser extraction efficiency enables to explain all the experimental features and allows to infer the fluorescence quantum efficiency of the samples (in the range 0.7-0.96). Under nonlasing conditions, the thermal lens dioptric power experiences a roll-off, for which we propose an explanation based on the theory presented in Part I. These results are then used to yield the thermo-optic coefficient of the crystals. At last, we propose a simple analytical formulation useful for a rough estimation of the focal length.
TL;DR: In this article, a three-level Tm:KGd(WO/sub 4/)/sub 2/ was studied as a three level laser on the /sup 3/F/sub4/sub/4/ /spl rarr/ /sup 2/H/sub 6/ transition and a tunable source in the 2/spl mu/m spectral range, operating at room temperature.
Abstract: Tm:KGd(WO/sub 4/)/sub 2/ is studied as a three-level laser on the /sup 3/F/sub 4/ /spl rarr/ /sup 3/H/sub 6/ transition and a tunable source in the 2-/spl mu/m spectral range, operating at room temperature. An overall tunability extending from 1790 to 2042 nm is achieved with maximum output powers of 400 mW for an absorbed pump power of 1 W. Various doping levels, pump wavelengths and polarization configurations are compared and the advantages of the monoclinic double tungstates over other Tm-hosts are outlined.
TL;DR: In this article, the dispersion and loss characteristics of surface-plasmon-polaritons supported by a metal stripe are calculated for a silver stripe embedded in silicon.
Abstract: The surface-plasmon-polaritons supported by a metal stripe are of theoretical and experimental interest. The well-known symmetric and antisymmetric modes of the slab model become the respective fundamental modes of the stripe. Their dispersion and loss characteristics are calculated for a silver stripe embedded in silicon. In contrast to the slab case, higher order modes also occur for the stripe. Corner modes that have no analogous modes in the slab model are obtained. The method of calculation used is a full-vectorial finite difference scheme for the coupled transverse components of the magnetic field.
TL;DR: In the 30 years since tunable ultraviolet (UV) lasers based on 5d /spl rarr/4f transition of trivalent lanthanides doped into solid-state hosts were first demonstrated, tremendous progress has been made in these unique laser systems as discussed by the authors.
Abstract: In the 30 years since tunable ultraviolet (UV) lasers based on 5d /spl rarr/ 4f transition of trivalent lanthanides doped into solid-state hosts were first demonstrated, tremendous progress has been made in these unique laser systems. Today, cerium-doped fluoride lasers offer wide tunability (280-333 nm), high efficiency (up to 62%) and narrow-band output. These lasers can also be used for femtosecond pulse amplification in the UV. Cerium lasers represent a logical route to generation of tunable UV in all-solid-state systems. In this paper, we review the current state-of-the-art cerium laser crystal development and cerium laser systems.
TL;DR: In this paper, the authors considered a high-temperature loss-increase mechanism, which includes two factors that bring about an increase in the absorption coefficients: 1) electronic conductivity due to thermal ionization of a Ge-doped silica core and 2) thermochemical SiO production in silica glass.
Abstract: The unsteady-state thermal conduction process in step-index single-mode (SM) optical fiber was studied theoretically with the explicit finite-difference method. We considered a high-temperature loss-increase mechanism, which includes two factors that bring about an increase in the absorption coefficients: 1) electronic conductivity due to the thermal ionization of a Ge-doped silica core and 2) thermochemical SiO production in silica glass. The core-center temperature changed suddenly and reached over 4/spl times/10/sup 5/ K when a 1.064-/spl mu/m laser power of 2 W was input into the core layer heated at 2723 K. This rapid heating of the core initiated the "fiber fuse" phenomenon. The high-temperature core areas were enlarged and propagated toward the light source. The propagation rates of the fiber fuse, estimated at 1.064 and 1.48 /spl mu/m, were in fair agreement with the experimentally determined values. We found that the threshold power for initiating the fiber fuse increases from 0.98 to 1.26 W when the input laser wavelength is increased from 1.06 to 1.55 /spl mu/m.
TL;DR: In this article, a detailed analytical model describing the noise properties of quantum-dot (QD) optical amplifiers operating in the linear and saturated regimes is presented, where the optical noise at the amplifier output shows a broad-band spectrum with an incoherent spectral hole due to the gain inhomogeneity.
Abstract: We present a detailed analytical model describing the noise properties of quantum-dot (QD) optical amplifiers operating in the linear and saturated regimes. We describe the dependence of the optical noise on the main physical parameters characterizing the QD gain medium as well as on operating conditions. The optical noise at the amplifier output shows a broad-band spectrum with an incoherent spectral hole due to the gain inhomogeneity. A coherent spectral dip stemming from noise-signal nonlinear interactions is superimposed on that broad-band spectrum. The broad-band incoherent component is also calculated using an approximate model which makes use of an equivalent inhomogeneous population inversion factor. The validity of the approximation is examined in detail. We also calculate the electrical relative intensity noise and observe a spectral hole corresponding to the spectral shape of the optical noise. The most important characteristics of the optical and electrical noise spectra are determined by the degree of inhomogeneous broadening and by the fast carrier dynamics of QD amplifiers. The fast dynamics causes a very wide noise spectral hole which has important potential consequences for detection of fast data and for all optical signal processing.
TL;DR: In this article, the authors analyzed the relationship between the air core geometry and the presence or absence of the surface modes in air-core PBFs with a triangular hole pattern, and identified ranges of core radii for which the fiber supports no surface modes over the entire wavelength range of the bandgap.
Abstract: It is known that the coupling of core modes to surface modes in air-core photonic-bandgap fiber (PBF) can give rise to large propagation losses. Using computer simulations, we analyze the relationship between the air-core geometry and the presence or absence of the surface modes in air-core PBFs with a triangular hole pattern. We identify ranges of core radii for which the fiber supports no surface modes over the entire wavelength range of the bandgap, i.e., only core modes are present. In particular, for a hole radius /spl rho/=0.47/spl Lambda/, where /spl Lambda/ is the hole spacing, the core supports a single mode and no surface modes for core radii between 0.8/spl Lambda/ and 1.1/spl Lambda/. The absence of surface modes suggests that fibers within this range of configurations should exhibit a very low propagation loss. We also show that the existence of surface modes can be predicted quite simply from a study of the bulk modes alone, which is much simpler and faster than carrying out a full analysis of the defect modes.
TL;DR: In this paper, the effects of electronic current overflow and inhomogeneous carrier distribution on the laser performance of InGaN QW lasers operating at different wavelengths are investigated with a LASTIP simulation program.
Abstract: Laser performance of several InGaN quantum-well (QW) lasers with an emission wavelength of 392-461 nm are numerically studied with a LASTIP simulation program. Specifically, the effects of electronic current overflow and inhomogeneous carrier distribution on the laser performance of InGaN QW lasers operating at different wavelengths are investigated. Simulation results indicate that the use of an AlGaN blocking layer can help reduce the electronic current overflow and, in addition to the dissociation of the InGaN well layer at a high growth temperature during crystal growth, the inhomogeneous carrier distribution in the QWs also plays an important role in the laser performance. From the simulation results, we conclude that the lowest threshold current density is obtained when the number of InGaN well layers is two if the emission wavelength is shorter than 427 nm and one if the emission wavelength is longer than 427 nm, which are in good agreement with the results observed by Nakamura et al. in their experiments.
TL;DR: The possibility of using semiconductor lasers to conveniently generate diverse microwave waveforms for radar and microwave applications is studied both numerically and experimentally in this article, where a broad-band chaotic waveform with a clean single-spike /spl delta/-function-like correlation profile is demonstrated experimentally.
Abstract: The possibility of using semiconductor lasers to conveniently generate diverse microwave waveforms for radar and microwave applications is studied both numerically and experimentally. Such waveforms are generated from the dynamical states of semiconductor lasers in different perturbation schemes and varying operating conditions. Using an optical injection scheme, broad-band chaotic microwave waveforms and tunable narrow-band harmonic microwaves over a broad frequency range can be generated. Using an optoelectronic feedback scheme, chaotic pulsing, regular pulsing, frequency-locked pulsing, and quasi-periodic pulsing waveforms are generated. These optically generated microwave waveforms can be easily amplified and radiated out using microwave amplifiers and antennas. The power spectra, time series, and autocorrelation traces of such waveforms are studied. The peak-sidelobe level is calculated to quantitatively compare the correlation characteristics of these waveforms. A broad-band chaotic waveform with a clean single-spike /spl delta/-function-like correlation profile useful for radar and other applications that demand unambiguous correlation profile is demonstrated experimentally.
TL;DR: In this article, the authors proposed a conceptual model that relates the gain-cavity detuning at RT to the temperature sensitivity of the active region performance, which qualitatively describes the threshold current-temperature characteristic typical of VCSELs.
Abstract: Record-long emission wavelengths up to 1.3 /spl mu/m have recently been demonstrated from highly strained InGaAs-GaAs double-quantum-well (DQW) vertical-cavity surface-emitting lasers (VCSELs). The operation of InGaAs VCSELs at such long wavelengths has relied on a large detuning between the spectral positions of QW gain maximum and cavity resonance. This detuning also affects the high-temperature performance and temperature sensitivity of such devices. In this paper, we present and evaluate the threshold current-temperature characteristic of such lasers in relation to the gain-cavity detuning at room temperature (RT). For a near-zero gain peak offset from the emission wavelength at RT, the minimum threshold current is found at the temperature where the gain peak wavelength and the cavity resonance are approximately aligned. This is well in line with a common design rule for GaAs-based VCSELs. However, we show that this design rule fails in the case of larger gain-cavity misalignment at RT. Instead, a minimum threshold current is obtained considerably below the temperature of zero gain offset. We propose a conceptual model that relates the gain-cavity detuning at RT to the temperature sensitivity of the active region performance, which qualitatively describes the threshold current-temperature characteristic typical of VCSELs. The results demonstrate the importance of improving the temperature characteristic of the active region in order to reduce the high temperature sensitivity of devices with large detuning.