Showing papers in "IEEE Journal of Quantum Electronics in 2007"
TL;DR: In this article, an improved curvature loss formula for optical waveguides is presented, which is shown to accurately predict the bend loss of both single-mode and multimode fibers.
Abstract: This paper presents an improved curvature loss formula for optical waveguides, which is shown to accurately predict the bend loss of both single-mode and multimode fibers. The formula expands upon a previous formula derived by Marcuse, greatly improving its accuracy for the case of multimode fiber. Also presented are the results of bent fiber simulations using the beam propagation method (BPM), and experimental measurements of bend loss. Agreement among simulation, formula and measurement support the validity of both theoretical methods. BPM simulations showed that the lowest order modes of the bent fiber were reduced to their linearly polarized constituents prior to the onset of significant bend loss. This implies that certain LP mode orientations should propagate with much lower loss than previously expected, and should impact the mode stripping ability of bent large mode area fibers, as employed in fiber lasers and amplifiers.
327 citations
TL;DR: In this article, the authors investigated the intrinsic tradeoffs and suggested solutions to substantially increase the propagation length of surface plasmon polaritons combining high-index dielectrics and metal structures.
Abstract: We present a deep-subwavelength-size metal slot-waveguide structure which can efficiently propagate surface plasmon polaritons (SPPs) at 1.55 mum within a high-index material. Through a systematic design analysis, we investigate the intrinsic tradeoffs and suggest solutions to substantially increase the propagation length of SPPs combining high-index dielectrics and metal structures. By studying several metal/dielectric geometries, we have found that the slot-waveguide size can be significantly decreased by the use of high-index materials without compromising the overall propagation losses. Our analysis also indicates that the device size-scaling is ultimately limited by a cutoff thickness for the metal film in which the slot is defined. For film thicknesses below cutoff, radiation modes exist which leak out of the guiding region. For certain operating frequencies, the radiant energy leaks out into both free space modes as well as surface plasmons guided along the top/bottom metal surfaces of the device. We have shown that, by using a silicon filling, the cutoff thickness of a 100-nm-wide slot waveguide can be as small as 90 nm, compared with 750 nm for the unfilled reference structures. In addition, we have demonstrated that by the use of SiO2 gap regions surrounding the Si dielectric core in a 200times400-nm silver slot region (partially filled metal slot), we can considerably reduce the overall propagation losses to less than 0.14 dB/mum, corresponding to a propagation length of approximately 50 mum
120 citations
TL;DR: In this article, the optical properties of a-, m-, and c-plane InGaN-GaN quantum-well (QW) structures with an arbitrary crystal orientation were investigated using the multiband effective-mass theory.
Abstract: Electronic and optical properties of a-(Phi = 0) and m-plane (Phi = pi/6) InGaN-GaN quantum-well (QW) structures are investigated using the multiband effective-mass theory with an arbitrary crystal orientation. These results are compared with those of c-plane or (0001)-oriented wurtzite InGaN-GaN QWs. We derive explicitly the Hamiltonians with their elements and the interband optical matrix elements with polarization dependence for the a-, m-, and c-planes. The bandgap transition wavelength of the QW structure with the m-plane is found to be longer than that of the QW structures with the a-plane. The average hole effective masses of the topmost valence band along k'y for the a-and m-planes are significantly lower than that of the c-plane. Here, the prime indicates physical quantities in a general crystal orientation. In addition, their optical gain and optical matrix element show strong in-plane anisotropy. The optical gain of the y'-polarization is much larger than that of the x'-polarization because the optical matrix element for the y'-polarization is larger than that of the x'-polarization.
118 citations
TL;DR: In this article, the Yb-laser was continuously tunable from 1003.7 to 1073.0 nm with a birefringent filter, achieving slope efficiencies as high as 74.6% without special cooling for the pi-polarization.
Abstract: Tetragonal (space group f4 macr) single crystals of NaY(WO4)2 doped with Yb to a density of 4.52 times 1020 cm-3 have been employed as laser active materials for the 1-mum spectral range, operating at room temperature. Using Ti:sapphire laser pumping, slope efficiencies as high as 74.6% were achieved without special cooling for the pi-polarization. The Yb-laser was continuously tunable from 1003.7 to 1073.0 nm with a birefringent filter. Pulses as short as 53 fs were obtained at 1035 nm by SESAM passive mode-locking with intracavity dispersion compensation and additional extracavity pulse compression using analogous prism pairs. Experimental data on the spectroscopic properties of Yb3+ in the 5-300 K temperature range and the room temperature optical properties of this novel Yb-host is also presented.
105 citations
TL;DR: In this article, a detailed analysis of fundamental thermal frequency noise in distributed feedback fiber lasers (DFB FL) is presented, and an expression relating the laser frequency noise spectrum to the spectrum of thermal (temperature) fluctuations in the fiber, accounting for the nontrivial DFB FL mode shape, is derived.
Abstract: A detailed analysis of fundamental thermal frequency noise in distributed feedback fiber lasers (DFB FL) is presented. An expression relating the laser frequency noise spectrum to the spectrum of thermal (temperature) fluctuations in the fiber, accounting for the nontrivial DFB FL mode shape, is derived. A new expression for the thermal fluctuation spectrum of single-mode optical fiber is derived which predicts high-frequency thermal noise 3 dB higher than previously published results. Theoretical predictions are compared against experimental measurements for a well characterized DFB FL. Anomalous 1/f noise at low frequency is discussed
99 citations
TL;DR: In this paper, the influence of the degree of quantum confinement on the carrier recovery times in semiconductor optical amplifiers (SOAs) was assessed through an experimental comparative study of three amplifiers, one InAs-InGaAsP-In-GaA-InP quantum dot (0-D) and two quantum well (1-D), all of which operate near 1.55mum wavelengths.
Abstract: We assess the influence of the degree of quantum confinement on the carrier recovery times in semiconductor optical amplifiers (SOAs) through an experimental comparative study of three amplifiers, one InAs-InGaAsP-InP quantum dot (0-D), one InAs-InAlGaAs-InP quantum dash (1-D), and one InGaAsP-In-GaAsP-InP quantum well (2-D), all of which operate near 1.55-mum wavelengths. The short-lived (around 1 ps) and long-lived (up to 2 ns) amplitude and phase dynamics of the three devices are characterized via heterodyne pump-probe measurements. The quantum-dot device is found to have the shortest long-lived gain recovery (~80 ps) as well as gain and phase changes indicative of a smaller linewidth enhancement factor, making it the most promising for high-bit-rate applications. The quantum-dot amplifier is also found to have reduced ultrafast transients, due to a lower carrier density in the dots. The quantum-dot gain saturation characteristics and temporal dynamics also provide insight into the nature of the dot energy-level occupancy and the interactions of the dot states with the wetting layer.
98 citations
TL;DR: In this article, the dynamics of optical gain in semiconductor quantum dots (QDs) are investigated and simple analytical expressions are derived, which directly connect the laser dynamical response to capture and intradot relaxation rates.
Abstract: The dynamics of optical gain in semiconductor quantum dots (QDs) is investigated. Simple analytical expressions are derived, which directly connect the laser dynamical response to capture and intradot relaxation rates. The effect of hole spreading in the valence band and spectral hole burning in the QD ensemble is also quantitatively assessed. The analysis shows that intradot relaxation constitutes the main limitation in the dynamics and points to possible routes towards the improvement of QD lasers
95 citations
TL;DR: In this article, a numerical model for the analysis of the chirp dynamics of quantum-dot (QD) semiconductor laser under large signal current modulation is presented, and the model is based on the multipopulation rate equation formalism, and it includes all the peculiar characteristics of the active QD material such as the inhomogeneous broadening of the gain spectrum, the presence of an excited state confined in the QDs and the nonconfined states due to the wetting layer and the barrier.
Abstract: We present a numerical model for the analysis of the chirp dynamics of quantum-dot (QD) semiconductor laser under large signal current modulation. The model is based on the multipopulation rate equation formalism, and it includes all the peculiar characteristics of the active QD material such as the inhomogeneous broadening of the gain spectrum, the presence of an excited state confined in the QDs and the presence of nonconfined states due to the wetting layer and the barrier. In this paper the model is applied to the analysis of the chirp of two QD single-mode lasers emitting from the ground state and from the excited state, respectively. In order to make comparisons of the chirp in various operating conditions, we define some equivalent parameters for quantifying the adiabatic and transient contributions to the chirp. These parameters are then used to analyze the chirp as function of the bias current, of the modulation depth and of the modulation frequency. All the various simulation results show that the carrier accumulation in the QD states, poorly involved in the stimulated emission process and the carrier dynamics in these states, can cause a nonzero chirp under current modulation even for the ideal condition of zero linewidth enhancement factor (or -parameter) at the laser threshold.
94 citations
TL;DR: In this article, self-assembled InAs-InGaAs-GaAs quantum dots are exploited for the development of large-format long-wavelength infrared focal plane arrays (FPAs).
Abstract: Epitaxially grown self-assembled InAs-InGaAs-GaAs quantum dots (QDs) are exploited for the development of large-format long-wavelength infrared focal plane arrays (FPAs). The dot-in-a-well (DWELL) structures were experimentally shown to absorb both 45deg and normal incident light, therefore, a reflection grating structure was used to enhance the quantum efficiency. The devices exhibit peak responsivity out to 8.1 mum, with peak detectivity reaching ~1times1010 Jones at 77 K. The devices were fabricated into the first long-wavelength 640times512 pixel QD infrared photodetector imaging FPA, which has produced excellent infrared imagery with noise equivalent temperature difference of 40 mK at 60-K operating temperature
89 citations
TL;DR: In this paper, a spectral line-by-line pulse shaping of a frequency comb generated by an optical frequency comb generator (OFCG) was demonstrated for optical fiber communication applications.
Abstract: We demonstrate optical processing based on spectral line-by-line pulse shaping of a frequency comb generated by an optical frequency comb generator (OFCG) The OFCG is able to generate a smooth, broad, stable, known-phase frequency comb, which is ideal for recently developed spectral line-by-line pulse shaping technology applications We demonstrate line-by-line pulse shaping on 64 lines at 10-GHz line spacing, generate transform-limited 16-ps short pulses at 10 GHz by combining two pulses in each period directly from the OFCG, and show various examples for optical arbitrary waveform generation Further, we demonstrate that these pulse sources are of sufficient quality to support optical fiber communication applications as confirmed by bit error rate measurements
87 citations
TL;DR: In this article, a review of the recent developments in GaAs-based 1.55mum lasers grown by molecular beam epitaxy (MBE) is presented, including the nitrogen plasma conditions, ion removal from the nitrogen flux, surfactant- mediated growth, the roles of various V-II ratios, the growth temperature, the active region thermal budget, proper annealing, and composition.
Abstract: We review the recent developments in GaAs-based 1.55-mum lasers grown by molecular beam epitaxy (MBE). While materials growth is challenging, the growth window appears to be relatively broad and is described in detail. The key considerations for producing high-quality GalnNAsSb material emitting at 1.55-mum regime are examined, including the nitrogen plasma conditions, ion removal from the nitrogen flux, surfactant- mediated growth, the roles of various V-II ratios, the growth temperature, the active region thermal budget, proper annealing, and composition. We find that emission may be tuned throughout the 1.55-mum communications band without penalty to the optical quality varying only one parameter - the total growth rate. This powerful result is validated by the demonstration of low-threshold edge-emitting lasers throughout the 1.55-mum regime, including threshold current densities as low as 318 A/cm2 at 1.54 mum. Additional characterization by Z-parameter techniques, cavity length studies, and band offset measurements were performed to better understand the temperature stability of device performance. Lasing was extended as far as 1.63 mum under nonoptimized growth conditions. The GaAs-based dilute-nitrides are emerging as a very promising alternative to InP-based materials at 1.55-mum due to their high gain, greater range of achievable band offsets, as well as the availability of lattice-matched AlAs-GaAs materials and native oxide layers for vertical-cavity surface-emitting lasers (VCSELs). Indeed, this effort has enabled the first electrically injected C-band VCSEL on GaAs.
TL;DR: In this article, a tensile strained germanium QW with a direct band gap for the electron and hole confinements can be realized by using a ternary SixGeySn1-x-y material system as the barriers.
Abstract: We develop a theoretical model for optical gain of a strained Ge--SixGeySn1-x-y quantum-well (QW) structure. By using a ternary SixGeySn1-x-y material system as the barriers, a tensile strained germanium QW with a direct band gap for the electron and hole confinements can be realized. We show our theoretical model for the strained band structure and the polarization dependent optical gain spectrum of the tensile strained germanium QW laser taking into account the carrier occupations in both the Gamma- and L-valleys of the conduction band. Reasonable material parameters are used to estimate the transition energy, optical gain spectrum, and effects of the carrier leakage in presence of the quantized subbands
TL;DR: In this paper, the 4H-SiC p-i-n avalanche photodiodes (APDs) with very low dark current were reported, and the peak responsivity at unity gain is 93 mA/W (external quantum efficiency = 41%) at lambda = 280 nm.
Abstract: We report 4H-SiC p-i-n avalanche photodiodes (APDs) with very low dark current. When biased for a photocurrent gain M of 1000, a 100-mum-diameter device exhibits dark current of 5 pA (63 nA/cm2), corresponding to primary multiplied dark current of 5 fA (63 pA/cm2). The peak responsivity at unity gain is 93 mA/W (external quantum efficiency = 41%) at lambda = 280 nm. The excess noise factor corresponds to k = 0.1. Detection of several tens of femtowatts of ultraviolet light is reported.
TL;DR: Avalanche multiplication and excess noise arising from both electron and hole injection have been measured on a series of In0.52Al0.48 diodes with nominal avalanche region widths between 0.1 and 2.5 mum as mentioned in this paper.
Abstract: Avalanche multiplication and excess noise arising from both electron and hole injection have been measured on a series of In0.52Al0.48As p+-i-n+ and n +-i-p+ diodes with nominal avalanche region widths between 0.1 and 2.5 mum. With pure electron injection, low excess noise was measured at values corresponding to effective k=beta/alpha between 0.15 and 0.25 for all widths. Enabled ionization coefficients were deduced using a non-local ionization model utilizing recurrence equation techniques covering an electric field range from approximately 200 kV/cm to 1 MV/cm
TL;DR: In this paper, an optimized design for a plasmonic metal-semiconductor-metal photodetector with interdigitated electrodes with subwavelength dimensions and a single GaInNAs quantum well (QW) as an absorbing layer is presented.
Abstract: We present an optimized design for a plasmonic metal-semiconductor-metal photodetector with interdigitated electrodes with subwavelength dimensions and a single GaInNAs quantum well (QW) as an absorbing layer. The excitation of surface plasmons at the metal-semiconductor interface leads to a strong field enhancement near the metallic electrodes. This results in an increased absorption in the QW, allowing both fast electrical response of the photodetector and high quantum efficiencies. With a grating periodicity of 820 nm and electrode finger width of 460 nm a 16-fold increase in the absorption of p-polarized light in the QW is achieved in comparison to the case without electrodes.
TL;DR: In this article, the phase correlation between the longitudinal modes selected by the DBR mirror has been experimentally demonstrated and a theoretical model based on coupled rate equations for three modes has been developed to study the time evolution of phases and amplitudes of the modes.
Abstract: In this paper, self-pulsation (SP) in a distributed Bragg reflector (DBR) semiconductor laser without a saturable absorber is experimentally and theoretically investigated. Detailed experimental characterizations of the SP DBR laser are reported in the optical and radio-frequency domains. Phase correlation between the longitudinal modes selected by the DBR mirror has been experimentally demonstrated. A theoretical model based on coupled rate equations for three modes has been developed to study the time evolution of phases and amplitudes of the modes. The carrier density modulation, resulting from the beating between adjacent longitudinal modes generates four-wave mixing (FWM) and is responsible for mutual injection locking, leading to passive mode-locking. The calculated power spectral density of the frequency noise derived from the model is in agreement with experimental results and proves that the phases of the longitudinal modes are identically correlated through the FWM process in this type of SP lasers
TL;DR: The developed QKD networks are capable of transmitting over distances consistent with the span of access links for metropolitan networks, at clock frequencies ranging up to 3 GHz.
Abstract: We present the application of quantum key distribution (QKD) technologies to fiber-based broad-band passive optical access networks. This application is based on our 850-nm wavelength gigahertz clock-rate single-receiver system, is compatible with existing telecommunications fiber and exploits a wavelength band not currently utilized in access networks. The developed QKD networks are capable of transmitting over distances consistent with the span of access links for metropolitan networks (10 km), at clock frequencies ranging up to 3 GHz
TL;DR: In this article, the effects of modulation p-doping on 1.3mum InGaAs-InAs quantum-dot (QD) lasers are systematically investigated using a series of wafers with doping levels from 0 to 18 acceptors per QD.
Abstract: The effects of modulation p-doping on 1.3-mum InGaAs-InAs quantum-dot (QD) lasers are systematically investigated using a series of wafers with doping levels from 0 to 18 acceptors per QD. Various characterization techniques for both laser diodes and surface-emitting light-emitting diode structures are employed. We report: 1) how the level of modulation p-doping alters the length dependant laser characteristics (in turn providing insight on various key parameters); 2) the effect of modulation p-doping on the temperature dependence of a number of factors and its role in obtaining an infinite T0; 3) how increasing concentrations of modulation p-doping affects the saturated gain, differential gain, and gain profile of the lasers; and finally, 4) the effect modulation p-doping has on the small signal modulation properties of 1.3-mum QD lasers. In each of these areas, the role of modulation p-doping is established and critically discussed.
TL;DR: In this paper, a theoretical model based on rate equations is used to investigate static and dynamic behaviors of InAs-InP (113)B quantum-dot (QD) lasers emitting at 1.55 mum.
Abstract: In this paper, a theoretical model based on rate equations is used to investigate static and dynamic behaviors of InAs-InP (113)B quantum-dot (QD) lasers emitting at 1.55 mum. More particularly, it is shown that two modelling approaches are required to explain the origin of the double laser emission occurring in QD lasers grown on both, GaAs and InP substrates. Numerical results are compared to experimental ones by using either a cascade or a direct relaxation channel model. The comparison demonstrates that when a direct relaxation channel is taken into account, the numerical results match very well the experimental ones and lead to a qualitative understanding of InAs-InP (113)B QD lasers. Numerical calculations for the turn-on delay are also presented. A relaxation oscillation frequency as high as 10 GHz is predicted which is very promising for the realization of directly modulated QD lasers for high-speed transmissions.
TL;DR: In this paper, a wide-band steady-state model of a tensile-strained bulk InGaAsP optical amplifier is described, and a parameter extraction algorithm based on the Levenberg-Marquardt method is described.
Abstract: A wide-band steady-state model of a tensile-strained bulk InGaAsP semiconductor optical amplifier is described. An efficient numerical algorithm of the steady-state model and a parameter extraction algorithm based on the Levenberg-Marquardt method are described. The parameter extraction technique is used to determine the material Auger recombination coefficient, effective intraband lifetime, the average strain and molar fraction of Arsenic in the active region. Simulations and comparisons with experiment are given which demonstrate the accuracy and versatility of the model
TL;DR: In this article, the authors investigated the polarization and transverse mode behavior of vertical-cavity surface-emitting laser (VCSEL) under orthogonal optical injection as a function of the injection strength and of the detuning between the injection frequency and the free-running frequency of the solitary laser.
Abstract: In this paper, we report on theoretical and experimental investigation on polarization and transverse mode behavior of vertical-cavity surface-emitting lasers (VCSELs) under orthogonal optical injection as a function of the injection strength and of the detuning between the injection frequency and the free-running frequency of the solitary laser. As the injection strength increases the VCSEL switches to the master laser polarization. We find that the injection power necessary to obtain such polarization switching is minimum at two different values of the frequency detuning: the first one corresponds to the frequency splitting between the two linearly polarized fundamental transverse modes, and the second one appears at a larger positive frequency detuning, close to the frequency difference between the first-order and the fundamental transverse modes of the solitary VCSEL. We show theoretically that both the depth and the frequency corresponding to the second minimum increase when the relative losses between the two transverse modes decrease. Bistability of the polarization switching is obtained for the whole frequency detuning range. Such a bistability is found for the fundamental mode only or for both transverse modes, depending on the value of the detuning. The theoretical and experimental optical spectra are in good agreement showing that the first-order transverse mode appears locked to the external injection
TL;DR: In this paper, the authors present measurements and analysis of the currently known relative frequency uncertainty of femtosecond laser frequency combs (FLFCs) based on Kerr-lens mode-locked Ti:sapphire lasers.
Abstract: We present measurements and analysis of the currently known relative frequency uncertainty of femtosecond laser frequency combs (FLFCs) based on Kerr-lens mode-locked Ti:sapphire lasers. Broadband frequency combs generated directly from the laser oscillator, as well as octave-spanning combs generated with nonlinear optical fiber are compared. The relative frequency uncertainty introduced by an optically referenced FLFC is measured for both its optical and microwave outputs. We find that the relative frequency uncertainty of the optical and microwave outputs of the FLFC can be as low as 8times10-20 and 1.7times10-18, with a confidence level of 95%, respectively. Photo-detection of the optical pulse train introduces a small amount of excess noise, which degrades the stability and subsequent relative frequency uncertainty limit of the microwave output to 2.6times10-17
TL;DR: In this paper, the magneto-optical elements are made three to four times shorter either by cooling them to nitrogen temperatures or by increasing the magnetic field, which is shown to increase maximum average laser power passing through the Faraday isolators up to 50 kW.
Abstract: Faraday rotators with short magneto-optical elements are created and experimentally studied. The magneto-optical elements are made three to four times shorter either by cooling them to nitrogen temperatures or by increasing the magnetic field. These ways are shown to increase maximum average laser power passing through the Faraday isolators up to 50 kW
TL;DR: In this paper, an approach for automatically measuring the linewidthenhancement factor (LEF) of semiconductor lasers using optical feedback self-mixing interferometry (OFSMI) is proposed.
Abstract: This paper proposes an approach for automatically measuring the linewidth-enhancement factor (LEF) of semiconductor lasers using optical feedback self-mixing interferometry (OFSMI), which works in weak optical feedback regime and where the external target is subject to simple harmonic vibration with unknown vibration frequency and magnitude. According to well-known Lang-Kobayashi theory the waveform of the modulated optical output power from the OFSMI system is influenced by multiple parameters, including the LEF, the optical feedback level factor, and the parameters related to the movement of external target. In order to estimate LEF, other parameters must also be considered and, hence, a multiple parameter estimation strategy is required. We propose a solution for this multiple parameter estimation problem based on the principle of data-to-theoretical model match. In particular, a strategy for minimizing a cost function in order to achieve the best fitting is proposed with which all the unknown parameters can be estimated. The performance of the proposed approach is tested using experimental data in comparison with other two approaches. It is seen that, over different experimental signals, the standard deviation for estimated LEF is less than 4.58% on average, which shows that results have excellent consistency. Moreover, the proposed approach also provides a solution for vibration measurement (that is, vibration frequency and magnitude).
TL;DR: In this paper, the authors derived several basic properties of the substrate modes by simple estimates and employed a 2-D finite element electromagnetic simulation tool to simulate periodic variations in the cavity gain spectrum that explain the measurements in terms of absolute value and oscillation amplitude.
Abstract: In semiconductor laser diodes layers with high refractive index can act as parasitic waveguides and cause severe losses to the optical mode propagating in the longitudinal direction. For (Al,In)GaN laser diodes, the parasitic modes are typically caused by the SiC or GaN substrate or buffer layers, hence the name substrate modes. A set of four different experiments shows the effect of substrate modes in the near-field (the most direct evidence of substrate modes), as side lobes in far-field, oscillations of the optical gain spectra, and as dependency of threshold current on n-cladding thickness. We derive several basic properties of the substrate modes by simple estimates. For a quantitative analysis we employ a 2-D finite element electromagnetic simulation tool. We simulate periodic variations in the cavity gain spectrum that explain the measurements in terms of absolute value and oscillation amplitude. We show that it is necessary to include the refractive index dispersion in order to get the correct period of the gain oscillations. Furthermore, we use the simulations to optimize the laser diode design with respect to substrate mode losses within the constraints given, e.g., by growth conditions
TL;DR: In this paper, nine different experimental techniques for measuring the linewidthenhancement factor alpha are discussed and tested on a single 760-nm vertical-cavity surface-emitting laser.
Abstract: Nine different experimental techniques for measuring the linewidth-enhancement factor alpha are discussed and tested on a single 760-nm vertical-cavity surface-emitting laser. Techniques included in the comparison are based on linewidth measurements, current modulation, optical injection, and optical feedback
TL;DR: In this article, the peculiarities of cross-gain modulation in quantum-dot semiconductor optical amplifier (QD SOAs) related to the inhomogeneous broadening are theoretically studied.
Abstract: The peculiarities of a cross-gain modulation (XGM) in quantum-dot semiconductor optical amplifier (QD SOAs) related to the inhomogeneous broadening are theoretically studied. We have solved numerically the electron rate equations for the QD SOA model including an excited state, a ground state and a continuum wetting layer (WL), and the propagation equations for the pump and the signal lightwaves. It is shown that XGM in QD SOA is possible for a comparatively large detuning close to the inhomogeneous broadening because in such a case QDs with substantially different resonant frequencies interact directly through WL.
TL;DR: In this article, the authors explored the use of the two-photon photovoltaic effect as a means to counter free carrier scattering and serendipitously scavenges the optical energy lost to twophoton absorption.
Abstract: Optical amplification, wavelength conversion, and a myriad of other functions that were once considered to be beyond silicon's reach have been made possible by the material's nonlinear optical properties. The common feature of such devices is the high optical intensity that is required to induce the nonlinear optical interactions. Concurrent with the useful nonlinearities (Raman and Kerr) are two-photon absorption and free carrier scattering, which are two related and harmful phenomena that render silicon lossy at high intensities. This paper explores the use of the two-photon photovoltaic effect as a means to counter these phenomena in an energy-efficient manner. The effect reduces losses due to free carrier scattering and serendipitously scavenges the optical energy lost to two-photon absorption. Analytical and numerical modeling of the two-photon photovoltaic effect in silicon devices is presented. The model is validated through comparison with experimental results and is used to establish the limits of this approach for creating energy-efficient silicon photonic devices.
TL;DR: In this article, a transfer matrix method is used to analyze the modal gain of transverse Bragg resonance (TBR) structures and three different feedback mechanisms are proposed to select the desired TBR modes.
Abstract: We use a transfer matrix method to analyze the modal gain of transverse Bragg resonance (TBR) structures. We show that these TBR structures can support two types of modes characterized by different modal angles: small mode angle (SMA) modes and TBR modes. We discuss the origin, modal properties and field distributions of both the TBR modes and SMA modes. Three different feedback mechanisms are proposed to select the desired TBR modes.
TL;DR: In this article, the continuous-wave laser operation of Nd-doped tetragonal NaLa(WO 4)2 crystal is studied at room temperature by optical pumping in the spectral region overlapping AlGaAs diode laser emission.
Abstract: The continuous-wave laser operation of Nd-doped tetragonal NaLa(WO 4)2 crystal is studied at room temperature by optical pumping in the spectral region overlapping AlGaAs diode laser emission. This crystal has inhomogeneously broadened optical bands. From the room-temperature spectroscopic parameters determined it is found that the optimum Nd concentration for the 4F3/2rarr4IJ laser channels must be in the 3-5 at.% range. For J=11/2 and 13/2 channels (lambdaap1.06 and 1.3 mum) the most favourable polarization configuration is parallel to the crystallographic c axis, while for J=9/2 little polarization dependence of the laser efficiency is predicted. Laser operation was achieved with a 3.35 at.% Nd-doped sample grown by the Czochralski method. The laser operation was tested in an hemispherical optical cavity pumped by a Ti:sapphire laser. Stimulated emission at lambda=1056 nm was achieved for a wide spectral pumping range, lambda=790-820 nm. Stimulated Raman scattering was achieved in the picosecond regime with an efficiency similar to that of monoclinic KY(WO4)2 reference compound