Showing papers in "IEEE Journal of Quantum Electronics in 2011"

Time Scales of a Chaotic Semiconductor Laser With Optical Feedback Under the Lens of a Permutation Information Analysis

Abstract: We analyze the intrinsic time scales of the chaotic dynamics of a semiconductor laser subject to optical feedback by estimating quantifiers derived from a permutation information approach. Based on numerically and experimentally obtained times series, we find that permutation entropy and permutation statistical complexity allow the extraction of important characteristics of the dynamics of the system. We provide evidence that permutation statistical complexity is complementary to permutation entropy, giving valuable insights into the role of the different time scales involved in the chaotic regime of the semiconductor laser dynamics subject to delay optical feedback. The results obtained confirm that this novel approach is a conceptually simple and computationally efficient method to identify the characteristic time scales of this relevant physical system.

Performance Optimization of Antenna-Coupled ${\rm Al}/{\rm AlO}_{x}/{\rm Pt}$ Tunnel Diode Infrared Detectors

Abstract: Signal-to-noise ratio (SNR) is a valuable figure of merit in determining the operating scope of infrared detectors. Antenna-couple metal-oxide-metal diodes have been shown to detect infrared radiation without cooling or applied bias, but so far have been hampered by their SNR. This paper details a comprehensive study of the fabrication parameters that control the formation of the tunneling oxide barrier to optimize the performance of these detectors. Since the tunneling barrier affects both current-voltage and infrared detection characteristics, fabrication parameters can be optimized to improve device performance. The current-voltage characteristics of the devices are detailed in this paper; resistance, nonlinearity, and curvature coefficient are parameterized on fabrication procedures. Infrared detection characteristics are detailed and SNR is studied as a function of device nonlinearity and biasing conditions.

Dense-Coding Attack on Three-Party Quantum Key Distribution Protocols

Abstract: Cryptanalysis is an important branch in the study of cryptography, including both the classical cryptography and the quantum one. In this paper we analyze the security of two three-party quantum key distribution protocols (QKDPs) proposed recently, and point out that they are susceptible to a simple and effective attack, i.e., the dense-coding attack. It is shown that the eavesdropper Eve can totally obtain the session key by sending entangled qubits as the fake signal to Alice and performing collective measurements after Alice's encoding. The attack process is just like a dense-coding communication between Eve and Alice, where a special measurement basis is employed. Furthermore, this attack does not introduce any errors to the transmitted information and consequently will not be discovered by Alice and Bob. The attack strategy is described in detail and a proof for its correctness is given. Finally, the root cause of this insecurity and a possible way to improve these protocols are discussed.

Optical Theorem Helps Understand Thresholds of Lasing in Microcavities With Active Regions

Abstract: Within the framework of the recently proposed approach to view the lasing in open microcavities as a linear eigenproblem for the Maxwell equations with exact boundary and radiation conditions, we study the correspondence between the modal thresholds and field overlap coefficients. Macroscopic gain is introduced into the cavity material within the active region via the “active” imaginary part of the refractive index. Each eigenvalue is constituted of two positive numbers, namely, the lasing wavenumber and the threshold value of material gain. This approach yields clear insight into the lasing thresholds of individual modes. The Optical Theorem, if applied to the lasing-mode field, puts the familiar “” condition on firm footing. It rigorously quantifies the role of the spatial overlap of the mode E-field with the active region, whose shape and location are efficient tools of the threshold manipulation. Here, the effective mode volume in open resonator is introduced from first principles. Examples are given for the 1-D cavities equipped with active layers and distributed Bragg reflectors and 2-D cavities with active disks and annular Bragg reflectors.

Time-Domain Travelling-Wave Model for Quantum Dot Passively Mode-Locked Lasers

Abstract: We present a time-domain travelling-wave model for the simulation of passive mode-locking in quantum dot (QD) lasers; accurate expressions for the time varying QD optical susceptibility and the QD spontaneous emission noise source are introduced in the 1-D wave equations and numerically described using a set of infinite-impulse response filters. The inhomogeneous broadening of the density of states of the whole QD ensemble as well as the homogeneous linewidth of each QD interband transition are properly taken into account in the model. Population dynamics in the QD, quantum well, and barrier states under both forward and reverse bias conditions are modeled via proper sets of multi-population rate equations coupled with the field propagation equations. The model is first applied to the study of gain and absorption recovery in a QD semiconductor optical amplifier under both forward and reverse bias conditions. Simulations of passive mode-locking in a two-section QD laser are then performed as a function of the bias parameters. Gain and absorption dynamics leading to the generation of mode-locking pulses is described. The onset of a trailing-edge instability at low currents is observed and fully explained in the framework of the described model.

High-Performance Near-IR Photodiodes: A Novel Chemistry-Based Approach to Ge and Ge–Sn Devices Integrated on Silicon

Abstract: Ge/Si heterostructure diodes based on n++Si(100)/i-Ge/p-Ge and p++Si(100)/i-Ge/n-Ge stacks and intrinsic region thickness of ~350 and ~900 nm, respectively, were fabricated using a specially developed synthesis protocol that allows unprecedented control of film microstructure, morphology, and purity at complementary metal-oxide-semiconductor compatible conditions. From a growth and doping perspective, a main advantage of our inherently low-temperature (390°C) soft-chemistry approach is that all high-energy processing steps are circumvented. Current-voltage measurements of circular mesas (60-250 μm in diameter) show dark current densities as low as 6 ×10-3 A/cm2 at -1 V bias, which is clearly improved over devices fabricated under low thermal budgets using traditional Ge deposition techniques. Spectral photocurrent measurements indicate external quantum efficiencies between 30 and 60% of the maximum theoretical value at zero bias, and approaching full collection efficiency at high reverse biases. The above Ge devices are compared to analogous low-temperature-grown (350°C) Ge0.98Sn0.02 diodes. The latter display much higher dark currents but also higher collection efficiencies close to 70% at zero bias. Moreover, the quantum efficiency of these Ge0.98Sn0.02 diodes remains strong at wavelengths longer than 1550 nm out to 1750 nm due to the reduced band gap of the alloy relative to Ge.

SWIR/MWIR InP-Based p-i-n Photodiodes With InGaAs/GaAsSb Type-II Quantum Wells

Abstract: This paper presents the performance characteristics of InP-based p-i-n photodiodes with strain-compensated and lattice-matched InGaAs/GaAsSb type-II multiple quantum well (MQW) absorption regions. The results show that photodiodes with strain-compensated and lattice-matched absorption regions have optical response out to 3.4 and 2.8 μm with dark current densities of 9.7 and 1.66 mA cm-2,respectively, at 290 K under -0.5 V reverse bias. The carrier transport mechanism responsible for the difference in responsivity and detectivity between strain-compensated and lattice-matched InGaAs/GaAsSb MQWs is discussed.

Growth and Characterization of Long-Wavelength Infrared Type-II Superlattice Photodiodes on a 3-in GaSb Wafer

Abstract: We report the molecular beam epitaxial growth and characterization of high-performance Type-II superlattice photodiodes on a 3-in GaSb substrate for long-wavelength infrared detection. A 7.3-μm-thick device structure shows excellent structural homogeneity as demonstrated by atomic force microscopy and X-ray diffraction characterization. Optical and electrical measurements of the photodiodes reveal not only the uniformity of the Type-II superlattice material but also of the fabrication process. Across the wafer, at 77 K, photodiodes with a 50% cut-off wavelength of 11 μm exhibit more than 45% quantum efficiency and a dark current density of 1.0 × 10-4 A/cm2 at 50 mV, giving a specific detectivity of 6 × 1011 cm Hz1/2/W.

Diode Pumped Erbium Cascade Fiber Lasers

Abstract: Cascading the 4I11/2→4I13/2 transition at 2.8 μm and 4I13/2→4I15/2 transition at 1.6 μm offers a solution to the thermal management of high power Er3+-doped fluoride fiber lasers. We demonstrate an output power of 8.2 W at 2.8 μm from an Er3+-doped fluorozirconate fiber laser with 56 W of launched pump power at 975 nm by cascade laser operation with the 1.6-μm ground-state transition. By careful selection of the Er3+ concentration that prevents significant interaction between Er3+ ions, it is shown that cascade lasing can occur from simple resonator arrangements including Fresnel reflection from the ends of the fiber only. The unsaturated output power suggests that no competing transitions are oscillating which advocates that radiative quenching of the metastable 4I13/2 level provides an elegant way of reducing undesired heat generation. We show that core temperature increases at the tip of the pumped end of the fiber can be an order of magnitude lower than fiber lasers employing single transition oscillation. The potential of further power scaling is demonstrated and the experimental results are verified with the use of a numerical model.

Modeling Passive Mode-Locking in Quantum Dot Lasers: A Comparison Between a Finite-Difference Traveling-Wave Model and a Delayed Differential Equation Approach

Abstract: We present a detailed quantitative comparison between a finite-difference traveling wave (FDTW) model and a delayed differential equation (DDE) approach for the simulation of passive mode-locking in quantum dot lasers with both ring and Fabry-Perot (FP) cavities. Modifications with respect to the standard DDE models available in the literature are proposed. The new DDE approach improves the quantitative agreement with the FDTW model when applied to the simulation of passive mode-locking in FP lasers, preserving a very high computational efficiency. The modifications proposed in the DDE model also apply to the simulation of quantum-well and bulk devices.

Responsivity and Noise of Self-Mixing Photodetection Schemes

Abstract: Responsivity and noise properties of the self-mixing (SM) detection process are analyzed. Starting with the photodiode and SM laser scheme as a detector of weak optical echoes from remote targets, we find equivalence to a coherent homodyne detection of the returning signal. In particular, in the VIS-NIR wavelength range, echoes can be detected down to about -90 dB of relative amplitude, typically. Then we consider the laser-diode voltage self-mixing (LV-SM) detection and find it is also a coherent homodyne scheme, though noise performance is limited by shot-noise of the bias current and by the relatively small signal supplied as an output. Theoretical results are finally compared to recent experimental data, finding a substantial agreement and confirming that the LV-SM is an attractive alternative to conventional photo-detection, especially for THz waves and other spectral ranges where good low-noise detectors may be difficult to employ.

Implant Defined Anti-Guided Vertical-Cavity Surface-Emitting Laser Arrays

Abstract: Anti-guided vertical-cavity surface-emitting laser (VCSEL) arrays can be designed to consistently operate in-phase, i.e., with a narrow, on-axis peak in the far field. However, the fabrication of such arrays typically requires anisotropic etching and epitaxial regrowth steps. We have found that anti-guiding behavior can be realized in implant-defined VCSEL arrays. The primary advantage is that the laser arrays can be designed to operate in-phase without requiring any fabrication steps more complicated than those used for conventional implant VCSELs. We present our array structure, a theoretical treatment of the anti-guiding confinement, and experimental results showing the behavior characteristic of anti-guided arrays.

SOA-MZI-Based Nonlinear Optical Signal Processing: A Frequency Domain Transfer Function for Wavelength Conversion, Clock Recovery, and Packet Envelope Detection

Abstract: We present analytic expressions for the frequency-domain transfer function of semiconductor optical amplifier Mach-Zehnder interferometric (SOA-MZI) switches that employ a single optical control signal and a continuous wave input optical beam. Our analysis relies on first-order perturbation theory approximations applied both to the SOA response as well as to the SOA-MZI characteristics, yielding a frequency response that enables a qualitative insight into the different SOA-MZI operational regimes. The final transfer function expression is utilized for the analysis and evaluation of the multifunctional potential of SOA-MZI switches, concluding with the necessary conditions for supporting a number of completely different SOA-MZI-based nonlinear signal processing applications that have been demonstrated experimentally: wavelength conversion, packet envelope detection (PED), and clock recovery (CR). The theoretically obtained operational conditions are in close agreement with experimental observations, showing that SOA-MZIs can serve as functional circuit elements in applications with different requirements depending on its operational parameters: as low-pass filtering devices with cut-off frequencies in the megahertz regime or in the multi-gigahertz regime, and as resonant modules resembling band-pass filtering structures. The validity of our theoretical SOA-MZI frequency-domain system model is further confirmed by its successful incorporation in a Fabry-Perot assisted SOA-MZI subsystem, demonstrating PED and CR operations through the exploitation of typical systems theory tools.

Modeling of Mid-Infrared Quantum Cascade Laser by Means of Nonequilibrium Green's Functions

Abstract: Nonequilibrium Green's function (NEGF) calculations of mid-infrared quantum cascade laser (QCL) that preserve real-space basis have been performed. The approach developed in this paper relies on two improvements introduced to nonequilibrium Green's functions/Poisson computational scheme. First, the boundaries of single laser stage were carefully designed as to maintain its periodicity with the whole quantum cascade structure. Second, the NEGF/Poisson solver was equipped with several controlling features that enable the restoration of convergence of the method for quite complex structures with many resonances and boundary conditions for Poisson equation set inside the structure. With this simulation tool, calculations for an anticrossed diagonal design of mid-infrared QCL have been performed. Results agree with experimental data (threshold current of ~4.2 kA/cm2 at material gain of ~70/cm) and the current understanding of carrier transport in such devices.

Geiger-Mode Operation of Ge-on-Si Avalanche Photodiodes

Abstract: Single-photon detection is reported for Ge-on-Si separate-absorption-charge-multiplication avalanche photodiodes. Single-photon detection efficiency of 14%, dark count rate of 108 s-1, and timing resolution of 117 ps were achieved.

Temperature Dependence of Leakage Current in InAs Avalanche Photodiodes

Abstract: Measurement and analysis of the temperature dependence of bulk and surface leakage currents in InAs avalanche photodiodes have been performed between 77 K and 290 K. At unity gain, SU-8 passivated InAs photodiodes have low dark current densities of 100 mA/cm2 at 290 K and 150 nA/cm2 at 77 K. An avalanche multiplication factor of 25 was measured at 13 V and 19.5 V at 290 K and 77 K, respectively. The photodiodes exhibit dynamic resistance-area products, calculated at 0.1 V of 34 Ω-cm2 at 290 K and 910 MΩ-cm2 at 77 K. Our analysis showed that between the temperatures of 200 K and 290 K, the bulk leakage current is proportional to ni2 whereas the surface leakage current is proportional to ni from 77 K to 290 K, where ni is the intrinsic carrier concentration. The activation energies deduced were 0.36 eV and 0.18 eV suggesting diffusion dominated bulk current and generation and recombination dominated surface current.

Generalized Master Equation for High-Energy Passive Mode-Locking: The Sinusoidal Ginzburg–Landau Equation

Abstract: A generalized master mode-locking model is presented to characterize the pulse evolution in a ring cavity laser passively mode-locked by a series of waveplates and a polarizer, and the equation is referred to as the sinusoidal Ginzburg-Landau equation (SGLE). The SGLE gives a better description of the cavity dynamics by accounting explicitly for the full periodic transmission generated by the waveplates and polarizer. Numerical comparisons with the full dynamics show that the SGLE is able to capture the essential mode-locking behaviors including the multi-pulsing instability observed in the laser cavity and does not have the drawbacks of the conventional master mode-locking theory, and the results are applicable to both anomalous and normal dispersions. The SGLE model supports high energy pulses that are not predicted by the master mode-locking theory, thus providing a platform for optimizing the laser performance.

Frequency-Noise Dynamics of Mid-Infrared Quantum Cascade Lasers

Abstract: By measuring the frequency-noise power spectral density of a cryogenically-cooled mid-infrared quantum cascade laser, we investigate the different contributions to the noise spectrum and identify the main differences with respect to standard bipolar semiconductor devices. In particular, the existence of a thermal cut-off on the 1/f noise allows to identify the current fluctuations through the heterostructure as the physical mechanism, intrinsic to the device, at the basis of the measured flicker noise. This result, marking the difference with bipolar semiconductor devices, is confirmed analyzing the laser frequency response to a modulation of the driving current.

Large-Signal Analysis of a Transistor Laser

Abstract: Small- and large-signal analyses of transistor lasers (TLs) are demonstrated for 0.98-μm wavelength GaInAs/GaAs and 1.3-μm AlGaInAs/InP systems. The modulation bandwidth of the TL was larger than that of a laser diode due to the lower damping effect in the former. Comparisons between TLs with different numbers of quantum wells indicated that a large signal response and high modulation bandwidth could be realized simultaneously. However, in the case of large-signal analysis, the calculated eye diagrams were degraded by a resonance oscillation peak. By changing structural parameters such as the facet reflectivity and by controlling the damping effect, the resonance frequency peak was suppressed and clear eye diagrams of >;40 Gb/s were obtained.

A Narrow-Linewidth On-Chip Toroid Raman Laser

Abstract: In this paper, we report a narrow-linewidth on-chip toroid Raman laser. Under free-running condition, we have obtained the minimum fundamental linewidth of 3 Hz and the maximum unidirectional output power of 223 μW. Lasing under the same condition in continuous-wave mode over 90 min is achieved at an average power level of 21 μW and a standard deviation of 0.17 μW. We further derived the frequency noise spectrum and identified an enhancement of frequency noise due to Kerr non linearity. In addition, we have observed the shifting of relaxation oscillation frequency as a consequence of weak mode splitting.

Single-Photon Multiparty Quantum Cryptographic Protocols With Collective Detection

Abstract: In order to reduce the requirements on quantum devices, Shih proposed two three-party quantum key distribution (QKD) protocols . However, Gao presented a simple and effective attack strategy (i.e., dense-coding attack) upon the two protocols . In this paper, we make a deep analysis on the reason why Shih three-party QKD protocols are not secure. Meanwhile, we improve the three-party QKD protocols so that they can resist the Gao attack. On this basis, we present a formalism of single-photon multiparty quantum cryptographic protocol with collective detection. In this formalism, single photons are employed and all participants, except one whom we call as the center, only need to have the ability to perform single qubit unitary operations. Considering the expensive quantum devices, this formalism is low-priced which means it is easy to realize. Further more, this formalism can be widely used in various quantum cryptographic protocols, such as quantum secret sharing, quantum coin flipping, and quantum secure direct communication.

Photon-Timing Jitter Dependence on Injection Position in Single-Photon Avalanche Diodes

Abstract: In recent years, a growing number of applications demand better timing resolution from single-photon avalanche diodes (SPADs). The challenge is pursuing improved timing resolution without impairing other device characteristics such as quantum efficiency and dark count rate. This task requires a clear understanding of the statistical phenomena involved in the avalanche current growth in order to drive the device engineering process. Past studies state that in Si SPADs the avalanche injection position statistics is the main contribution to the photon-timing jitter. However, in recent re-engineered devices, this assumption has been questioned. To address this issue, we developed an experimental setup capable of characterizing the photon-timing jitter as a function of the injection position by means of a laser focused on the device active area. The results not only confirmed that the injection position statistics is not the main contribution to photon-timing jitter, but also evidenced interesting dependences of the timing performances on the injection position. Furthermore, we found a relationship between the photon-timing jitter and the specific resistance of the devices, which has been investigated by means of photoluminescence measurements.

Scaling Fiber Lasers to Large Mode Area: An Investigation of Passive Mode-Locking Using a Multi-Mode Fiber

Abstract: The mode-locking of dissipative soliton fiber lasers using large mode area fiber supporting multiple transverse modes is studied experimentally and theoretically. The averaged mode-locking dynamics in a multi-mode fiber are studied using a distributed model. The co-propagation of multiple transverse modes is governed by a system of coupled Ginzburg-Landau equations. Simulations show that stable and robust mode-locked pulses can be produced. However, the mode-locking can be destabilized by excessive higher-order mode content. Experiments using large core step-index fiber, photonic crystal fiber, and chirally-coupled core fiber show that mode-locking can be significantly disturbed in the presence of higher-order modes, resulting in lower maximum single-pulse energies. In practice, spatial mode content must be carefully controlled to achieve full pulse energy scaling. This paper demonstrates that mode-locking performance is very sensitive to the presence of multiple waveguide modes when compared to systems such as amplifiers and continuous-wave lasers.

Lasing Action on Whispering Gallery Mode of Self-Organized GaN Hexagonal Microdisk Crystal Fabricated by RF-Plasma-Assisted Molecular Beam Epitaxy

Abstract: GaN hexagonal microdisks were fabricated on Ti-mask (4 nm in thickness) nanohole-patterned m-plane (10-10) GaN substrates by radio frequency-plasma-assisted molecular beam epitaxy. The GaN hexagonal microdisks, which were supported by ~300 nm-diameter GaN nanocolumns, consisted of thin hexagonal c-plane plates with a hexagon side length of 1-2 m and a typical thickness of 200 nm. The GaN hexagonal microdisks were optically pumped under a high optical excitation density with a 355-nm-wavelength Nd:YAG laser, and ultraviolet lasing actions on the quasi-whispering gallery mode (WGM) were observed at room temperature. The lasing wavelength was 372 nm and the threshold excitation density was approximately 250 kW/cm2. The quasi-WGM resonance was numerically analyzed using a simple plane wave model and a 2-D-flnite difference time domain method, the behaviors of the WGM and quasi WGM were analyzed, revealing that the quasi-WGM has a higher Q-factor, thus, it was clarified that the laser actions of the GaN hexagonal microdisks occurred on the quasi-WGM resonance.

Dynamics Scenarios of Dual-Beam Optically Injected Semiconductor Lasers

Abstract: The nonlinear dynamics of a dual-beam optically injected semiconductor laser are studied. Most of the observed dual-beam injection dynamics can be understood from competitions of single-beam injection dynamics that are associated separately with each injection beam. Three general scenarios are identified and mapped for various combinations of detuning frequencies and injection strengths of the two injection beams. In Scenario A, simultaneous injection of two beams completely suppresses the dynamics due to separate single-beam injection and replaces them with the dynamics resulting from strong nonlinear interactions of the two injection beams. In Scenario B, simultaneous injection of two beams does not suppress the dynamics due to single-beam injection of one of the two beams but modifies such dynamics through nearly degenerate four-wave mixing with the other injection beam associated with the suppressed dynamics. In Scenario C, simultaneous injection of two beams does not suppress the dynamics due to single-beam injection of either of the two beams but allows the two dynamics to coexist and mix nonlinearly.

Long Wavelength Infrared InAs/GaSb Superlattice Photodetectors With InSb-Like and Mixed Interfaces

Abstract: We report on long wavelength infrared photodetectors using InAs/GaSb superlattices (SLs) with InSb-like and mixed interfaces (IFs). X-ray diffraction (XRD) measurements indicate that the SLs with mixed IFs have a narrower linewidth. The full-width at half-maximum of the XRD satellite peak is 24 arcsec for the sample with InSb-like IFs and is only 17 arcsec for the sample with mixed IFs. However, in terms of infrared photodetection, InSb-like IFs are superior to the mixed ones. Stronger photoluminescence and photoresponse signals are observed for the sample with InSb-like IFs.

Route for Bulk Millimeter Wave and Terahertz Metamaterial Design

Abstract: A possible route for the design of 3-D metamaterials in the millimeter and terahertz (THz) frequency range is proposed in this paper. It consists of stacks of spatial filtering screens made of resonant subwavelength metallic elements deposited on polypropylene (PP) film substrates by a contact photolithography technique. A thorough characterization of PP films as a substrate in THz and its extension to millimeter waves is carried out. Then, a description of the fabrication process, followed by a thorough analysis of the yield of this process as well as the material properties, is reported. As a direct application, several filtering screens are studied, including the performance of multilayer configurations. It is shown that the losses do not increase significantly in the multilayer case, enabling both the fabrication and use of PP at these frequency ranges. Additionally, slow wave has been measured in a multilayer prototype. Full-wave electromagnetic simulations have been compared with measurement from several configurations, showing reasonably good agreement. These results open the possibility of implementing low-loss metamaterials in the millimeter and THz spectrum.

Polarization Switching in Long-Wavelength VCSELs Subject to Orthogonal Optical Injection

Abstract: Polarization switching (PS) appearing in long-wavelength vertical-cavity surface-emitting lasers (VCSELs) subject to orthogonal optical injection is investigated theoretically and experimentally. We have studied the injected optical power required for PS as a function of the frequency detuning between the injected light and the orthogonal linear polarization of the VCSEL. For a wide range of bias currents applied to the device, the injected power required for the occurrence of PS exhibited a minimum and a plateau with respect to the frequency detuning. The minimum (plateau) was found at negative (positive) frequency detuning. The bistable behavior of the polarization is described. Our experimental results confirm the theoretical predictions of Sciamanna and Panajotov. The levels of the minimum and the plateau were observed to increase as higher bias currents were applied to the VCSEL. A first theoretical and experimental observation of the disappearance and further appearance of PS when increasing the injected power in long-wavelength VCSELs is described. This situation is obtained for small levels of negative frequency detuning and for large enough values of applied bias current. A good overall qualitative agreement is found between our theoretical and experimental results.

Role of Interionic Processes in the Efficiency and Operation of Erbium-Doped Fluoride Fiber Lasers

Abstract: Great increase in the output power of erbium-doped fluoride fiber lasers has recently been achieved, but the predicted high slope efficiency was not observed. We conduct an investigation into the possible underlying reasons, based on the newly available spectroscopic data, and our measurements on the running fiber laser are compared against computer simulation. The results indicate that interionic processes in the present fibers are much weaker than previously expected and only allow for an operation with 15-30% efficiency where the excited-state absorption is shown to have an important contribution.

Avalanche Multiplication and Excess Noise in InAs Electron Avalanche Photodiodes at 77 K

Abstract: The findings of a study of impact ionization, avalanche multiplication and excess noise in InAs avalanche photodiodes at 77 K are reported. It is shown that hole impact ionization is negligible in practical devices which continue to operate as electron avalanche photodiodes, as they do at room temperature. A new electron ionization coefficient capable of modeling multiplication at 77 K is presented and it is shown that significant multiplication can be achieved in practical devices without excessive tunneling currents. The characteristic changes observed between room temperature and 77 K are discussed. This paper helps to demonstrate the potential for practical InAs electron avalanche photodiodes, operating cooled.