Low Internal Loss Research Articles

Quantum yield in induced-junction silicon photodiodes at wavelengths around 400 nm

The quantum yield in silicon has previously been assumed to be of significance only in the ultraviolet spectral range. Due to the low internal losses of induced-junction silicon photodiodes and their predictability it is possible for the first time to make more accurate estimation of the quantum yield. We report on measurement of quantum yield in induced-junction silicon photodiodes. The results show that the quantum yield can be larger than unity even at wavelengths around 450 nm. A model of the quantum yield has been fitted to the experimental data and can be implemented in the spectral responsivity models to maintain high accuracy predictability to around 160 ppm down to 360 nm.

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

Calculating the equivalent elastic moduli and their influence on modelling the sound insulation of softwood cross laminated timber (CLT)

There are characteristics unique to natural materials such as timber that must be dealt with carefully to develop successful sound insulation prediction models. Timber has low internal losses typical of low-density building materials but with material properties that vary according to growth conditions. To study these factors in cross laminated timber (CLT) products, orthotropic thin plate and isotropic thick plate models are investigated. Equivalent elastic moduli are obtained using two methods from values and limits provided in the timber standards and literature, or by the manufacturer. The equivalent moduli are used to calculate the sound insulation of three- and five-layer CLT plates. Appropriate upper and lower limits are calculated from the combined material parameters and compared with sound insulation results measured in accredited laboratories for the first time. EN ISO 10140 test standards require that surface density of the sample be documented in the laboratory; additional precision information such as the fifth percentile of the material density is not required. However, considering the limits on the internal loss factors and elastic moduli only in the thin plate sound insulation model, gives a poor overall prediction performance (23.6% within the upper and lower limits). In this paper we combine the limits on elastic moduli, internal loss factors, and density. With these combined parameters the prediction is improved; less than half of the measured sound insulation values fall within the upper and lower limits of a typical thin plate model (44.0%). The single figure sound reduction index values are underestimated in seven out of nine cases. The prediction is further improved when a thick plate model is considered. There are several layers of complexity in the measurement and modelling conditions that must be carefully considered. The contributions from these compounding factors are discussed, and additional moduli and density parameters are proposed for inclusion in the literature and standards.

Improving Charge Carrier Transport Properties in AlGaN Deep Ultraviolet Light Emitters Using Al-Content Engineered Superlattice Electron Blocking Layer

In this study, we investigate a unique Al-content engineered superlattice electron blocking layer (AESL-EBL) for improving the charge carrier transport properties of AlGaN quantum well (QW) deep ultraviolet (DUV) light-emitting diode (LED) structures. LED structures without EBL, with conventional bulk EBL (BEBL), and superlattice EBL (SL-EBL) are used for comparison. It is found that the LED structure with the AESL-EBL can exhibit superior electron blocking and hole injection, leading to reduced efficiency droop and improved light output power, compared to LED structures without EBL and with BEBL. Notably, the LED structure with AESL-EBL also outperforms the LED structure with SL-EBL, benefitting from the Al-content engineered SL. In the end, such an ASEL-EBL is applied to a DUV laser diode structure, and by optimizing the device structure low Mg-induced internal loss of around 1 cm−1 can be obtained.

48 W Continuous-Wave Output From a High- Efficiency Single Emitter Laser Diode at 915 nm

Improving the power and efficiency of 9xx-nm broad-area laser diodes has a great help in reducing the cost of laser systems and expanding applications. This letter presents an optimized epitaxial structure with high power and conversion efficiency. Laser diodes with 230 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> emitter width and 5 mm cavity length deliver continuous-wave output power up to 48.5 W at 48 A, 30 °C, the highest power reported for 9xx-nm single emitter lasers so far. The slope efficiency is as high as 1.23 W/A due to a low internal optical loss of 0.31 cm−1 and a high internal efficiency of 96%. The maximum power conversion efficiency reaches 72.6% at 15.3 W and 67.3% at the operating power of 30 W under a heatsink temperature of 25 °C. Life test results show no failure in 1000 hours for 55 laser diodes.

Importance of optical homogeneity for high-quality transparent ceramics

Two types of transparent Y2O3 ceramics without including large scattering sources such as residual pores, one with very high optical homogeneity (type A) and another one with slightly insufficient optical homogeneity (type B), are purposely prepared, and their optical properties are investigated and compared qualitatively and quantitatively. Type A ceramic exhibits transmittance characteristics with very low internal loss in the visible to infrared wavelength region, while type B ceramic is inferior in various optical performances especially in the short (visible) wavelength region. In type B ceramic, birefringence occurs due to optical inhomogeneity in the visible region, resulting in a decrease in the extinction ratio. Non-uniform refractive index distribution is also observed in the Schlieren image of type B ceramic, hence the laser beam quality through that material is degraded. This study proved the importance of optical homogeneity of transparent ceramics and clarified the problems in actual applications.

A Review on Coupled Bulk Acoustic Wave MEMS Resonators.

With the introduction of the working principle of coupled resonators, the coupled bulk acoustic wave (BAW) Micro-Electro-Mechanical System (MEMS) resonators have been attracting much attention. In this paper, coupled BAW MEMS resonators are discussed, including the coupling theory, the actuation and sensing theory, the transduction mechanism, and the applications. BAW MEMS resonators normally exhibit two types of vibration modes: lateral (in-plane) modes and flexural (out-of-plane) modes. Compared to flexural modes, lateral modes exhibit a higher stiffness with a higher operating frequency, resulting in a lower internal loss. Also, the lateral mode has a higher Q factor, as the fluid damping imposes less influence on the in-plane motion. The coupled BAW MEMS resonators in these two vibration modes are investigated in this work and their applications for sensing, timing, and frequency reference are also presented.

High Power Single Mode 1300-nm Superlattice Based VCSEL: Impact of the Buried Tunnel Junction Diameter on Performance

High power single mode wafer-fused 1300-nm VCSELs with a gain region based on InGaAs/InAlGaAs short period superlattice are fabricated. An InP-based optical cavity and two AlGaAs/GaAs distributed Bragg reflector heterostructures were grown by molecular beam epita&#x00F5;y. The current and optical confinement is provided by a lateral-structured buried tunnel junction with etching depth of <inline-formula> <tex-math notation="LaTeX">$\sim 25$ </tex-math></inline-formula> nm. It is shown that optimal diameter of the buried tunnel junction for high-power single mode emission is <inline-formula> <tex-math notation="LaTeX">$\sim 5$ </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">$6~\mu \text{m}$ </tex-math></inline-formula>. The VCSEL demonstrates more than 6 mW single mode continuous-wave power and a threshold current less than 1.5 mA at 20 &#x00B0;C. The output optical power exceeds 1 mW at 85 &#x00B0;C. A -3dB modulation bandwidth up to 8 GHz and 6 GHz is obtained at 20 &#x00B0;C and 85 &#x00B0;C, respectively. The gain coefficient of <inline-formula> <tex-math notation="LaTeX">$\sim 650$ </tex-math></inline-formula> cm^&#x2212;1 and the transparency current density of <inline-formula> <tex-math notation="LaTeX">$\sim 630$ </tex-math></inline-formula> A/cm² are estimated at zero gain-to-cavity detuning (\sim 60 &#x00B0;C). The ultimate low internal optical losses about 0.08 &#x0025; per round-trip (distributed losses &#x007E;3.2 cm^&#x2212;1) at 20 &#x00B0;C and 0.13 &#x0025; per round-trip (distributed losses &#x007E;5.5 cm^&#x2212;1) at 100 &#x00B0;C were obtained.

Designs for III-nitride edge-emitting laser diodes with tunnel junction contacts for low internal optical absorption loss

The lasing mode and internal optical absorption loss profiles of III-nitride edge-emitting laser diode (LD) designs operating at 440 nm were modeled using the transfer matrix method. These models indicate absorption losses are minimized in LDs utilizing tunnel junction (TJ) contacts that (1) optimize the TJ to be as close to fully depleted as possible; (2) spatially separate the metal contact from the lasing mode using lightly doped n-GaN located above the TJ; (3) in designs with optimized TJs, minimize the total thickness of p-type material. These features reduce absorption losses in the model, relative to comparable LD models with an unoptimized TJ contact or with a transparent conducting oxide p-contact, by up to 15.3% and 12.5%, respectively, while at the same time eliminating most or nearly all p-type material.

Analysis of internal optical loss of 1.3 μm vertical-cavity surface-emitting laser based on n-=SUP=-++-=/SUP=--InGaAs/p-=SUP=-++-=/SUP=--InGaAs/p-=SUP=-++-=/SUP=--InAlGaAs tunnel junction

The analysis of internal optical loss and internal quantum efficiency in 1.3 μm-range InAlGaAsP/AlGaAs a composite n+-InGaAs/p+-InGaAs/p+-InAlGaAs tunnel junction obtained in the frame of molecular-beam epitaxy and wafer fusion technology. The level of internal optical losses in the lasers under study was varied by depositing a dielectric layer on the surface of the output mirror. It is shown that it is possible in principle to achieve low internal optical loss of less than 0.08% and 0.14% per one pass (round-trip) at temperatures of 20oC and 90oC, respectively. Keywords: vertical-cavity surface-emitting laser, wafer fusion, tunnel junction, superlattice, internal optical loss.

Interband cascade lasers with short electron injector

We demonstrate GaSb-based interband cascade lasers (ICLs) emitting around 3.65 µm, which exhibit a room-temperature continuous-wave (CW) output power above 100 mW. Cavity-length analysis showed that the laser structure has a low internal loss of 3 cm-1 while maintaining a total internal quantum efficiency greater than one. After 6400 h CW operation at 25°C, the threshold current of the laser increased by 3%, and the output power decreased by 7%, indicating good reliability of the device.

Electromagnetic wave beam manipulator based on an all-dielectric THz coding metasurface.

In this paper, we proposed an all-dielectric THz coding metasurface that can effectively manipulate electromagnetic waves. This structure was composed of sub-wavelength coding units with different reflection phases. The encoding unit is composed of a rectangular base with a cross dielectric column. Different encodings were designed by changing the thickness of the X arm of the dielectric column. We designed a variety of coding modes and implemented the modulation of the number of far-field reflection beams and the angle of reflection direction at 0.85 THz by 1- and 2-bit coding. Our theoretical calculations and numerical simulations of the structure suggested that the far-field scattering obtained by full-wave simulation matched the theoretical calculation when the incident direction of electromagnetic wave was perpendicular to the metasurface. We chose all-dielectric materials to design the coding unit due to the low cost, strong corrosion resistance, and low internal electromagnetic loss. As a result, the all-dielectric materials avoided the serious internal loss of metal materials and demonstrated the flexibility to regulate the reflected beam in the THz band to realize abnormal refraction and beam splitting.

InAs/GaAsSb in-plane ultrahigh-density quantum dot lasers

InAs in-plane ultrahigh-density quantum dots (IP-UHD QDs) were grown on GaAsSb/GaAs(001) by molecular beam epitaxy and introduced into the active layer of a ridge-waveguide AlGaAs/GaAs laser. The IP-UHD QD density was 5 × 1011 cm−2. Despite having a short cavity length, no high-reflective coating on the cavity edge and a small number of stacked QD layers, stable laser operation up to 80 ℃ has been achieved. IP-UHD QD lasers without p-type doping exhibited a characteristic temperature of 77 K. IP-UHD QD lasers have the same low internal loss as conventional QD lasers. Improved uniformity in IP-UHD QDs promises the achievement of ultralow threshold current.

Prevalence of fatigue in adults with congenital heart disease.

The aim of this cross-sectional study was to examine the prevalence of the multidimensional phenomenon of fatigue in adults with congenital heart disease. Adults with congenital heart disease are a growing population, and patient-reported outcomes can provide valuable information about the patient's experience of living with CHD. Fatigue is a multidimensional phenomenon that can be described as an overwhelming feeling of exhaustion with a reduced capacity of mental and physical work. Fatigue can be observed clinically in adults with congenital heart disease, but the actual prevalence is unknown. Fatigue was assessed by the Multidimensional Fatigue Inventory which enables the respondent to report the presence of fatigue according to five dimensions: "general fatigue," "physical fatigue," "mental fatigue," "reduced motivation," and "reduced activity." The questionnaire was sent to 463 patients in Lund and Umeå. Four groups with complex CHD and two groups with moderately complex CHD were included. The reliability (internal consistency) of the Multidimensional Fatigue Inventory was tested for all dimensions and groups of diagnosis. The response rate was 56.6% (n= 262). In patients with complex CHD, 40.0-59.4% reported severe to very severe general fatigue, and patients with a single ventricle reported the highest prevalence (59.4%). Among patients with complex CHD, 29.2-40.0% reported severe to very severe mental fatigue. The Multidimensional Fatigue Inventory had a high reliability measured with Cronbach's alpha. The study findings show a relatively high prevalence of fatigue in adults with congenital heart disease, and general fatigue was the most prevalent. Further studies are needed regarding fatigue and its causes and consequences in adults with congenital heart disease. The Multidimensional Fatigue Inventory proved to be an instrument with high reliability and low internal loss, which suggests that the instrument may be suitable to use as a patient-reported outcome in the care of adults with congenital heart disease, preferably at repeated occasions.

High‐Efficiency Monolithic Photosupercapacitors: Smart Integration of a Perovskite Solar Cell with a Mesoporous Carbon Double‐Layer Capacitor

The integration of solar cells with supercapacitors into hybrid monolithic power packs can provide energy autonomy to smart electronic devices of the Internet of Things (IoT) by mediating between intermittent load and supply. Herein, such a photorechargeable supercapacitor (also called a photosupercapacitor) is developed via a three‐electrode integration of a p–i–n halide perovskite solar cell with a gel electrolyte‐type supercapacitor that uses mesoporous N‐doped carbon nanospheres (MPNC) as the active electrode material. Benefiting from the large surface area, well‐defined mesoporous structure, and homogeneous particle size of the MPNC material, the supercapacitor demonstrates high capacitance, resulting in large energy and power densities with a high charge/discharge efficiency. Its integration with a large‐area (1 cm2) FA0.75Cs0.25Pb(I0.8Br0.2)3 perovskite solar cell, with an optimized layer sequence to minimize degradation, results in a photosupercapacitor exhibiting fast (&lt; 5 s) photocharging up to 1 V. The outstanding peak overall photoelectrochemical energy conversion efficiency of 11.5% is a result of a high solar cell power conversion efficiency of 12.5%, a high supercapacitor storage efficiency of 92%, and low internal energy losses due to monolithic integration. These results underline the high potential of this type of device toward application in the IoT.

High-power operation and lateral divergence angle reduction of broad-area laser diodes at 976 nm

Broad-area diode lasers with high output power and low lateral divergence angle are highly desired for extensive scientific and industrial applications. Here, we report on the epitaxial design for higher output power and a flared waveguide design for reduced divergence, which leads to high power operation with a low lateral divergence angle. A vertically asymmetric epitaxial structure was employed and optimized for low internal optical loss and high efficiency to realize high output power operation. Using a flared waveguide design, the lateral divergence angle was efficiently reduced by decreasing the number of high-order lateral optical modes significantly. The flared waveguide design introduces a smooth modification of the ridge width along the cavity without deteriorating laser performance. Based on the optimized epitaxial and waveguide design, we scaled the waveguide width to realize high continuous-wave power of 34.5 W at 25 °C. A low lateral divergence angle of 8° and high power conversion efficiency of 60% were achieved at the operating power level of 25 W. The life test data (30 A at 45 °C for 39 units, 0 failures in 1000 h) demonstrated reliable operation illustrating the efficient design for reduced lateral divergence angle and high operating power.

Novel 900 nm diode lasers with epitaxially stacked multiple active regions and tunnel junctions

A multi-active-region bipolar-cascade edge-emitting laser emitting at nearly 900 nm is presented. The three active regions and two tunnel junctions located in a single waveguide core share the same third-order vertical mode. A slope efficiency of 3.6 W/A was measured with a threshold current density of 230 A/cm2. The epitaxial layer stack developed features with very low internal optical losses of 0.7 cm−1. The voltage extrapolated to vanishing current is only 0.3 V larger than 3 times the voltage of 1.4 V originating from the photon energy.

Анализ внутренних оптических потерь вертикально-излучающего лазера спектрального диапазона 1.3 &amp;mu;m с туннельным переходом на основе слоев n-=SUP=-+-=/SUP=--InGaAs/p-=SUP=-+-=/SUP=--InGaAs/p-=SUP=-+-=/SUP=--InAlGaAs

The analysis of internal optical loss and internal quantum efficiency in 1.3 μm-range InAlGaAsP/AlGaAs a composite n++-InGaAs/р++-InGaAs/р++-InAlGaAs tunnel junction obtained in the frame of molecular-beam epitaxy and wafer fusion technology. The level of internal optical losses in the lasers under study was varied by depositing a dielectric layer on the surface of the output mirror. It is shown that it is possible in principle to achieve low internal optical loss of less than 0.08% and 0.14% per one pass (round-trip) at temperatures of 20°С and 90°С, respectively.

Internal loss of AlGaN-based ultraviolet-B band laser diodes with p-type AlGaN cladding layer using polarization doping

Aluminum gallium nitride (AlGaN)-based ultraviolet-B band laser diodes (LDs) with a p-type AlGaN cladding layer using polarization doping were fabricated on lattice-relaxed Al0.6Ga0.4N/AlN/sapphire. The threshold current density Jth and lasing wavelength of this LD were 25 kA cm−2 and 298 nm, respectively. The internal loss (αi) was estimated by means of a variable stripe length method using optical excitation. The αi value of this LD was relatively low (i.e. <10 cm−1), thus suggesting that the device is characterized by both, proper light confinement and low internal loss.

Light Emitting Devices Based on Quantum Well-Dots

We review epitaxial formation, basic properties, and device applications of a novel type of nanostructures of mixed (0D/2D) dimensionality that we refer to as quantum well-dots (QWDs). QWDs are formed by metalorganic vapor phase epitaxial deposition of 4–16 monolayers of InxGa1−xAs of moderate indium composition (0.3 &lt; x &lt; 0.5) on GaAs substrates and represent dense arrays of carrier localizing indium-rich regions inside In-depleted residual quantum wells. QWDs are intermediate in properties between 2D quantum wells and 0D quantum dots and show some advantages of both of those. In particular, they offer high optical gain/absorption coefficients as well as reduced carrier diffusion in the plane of the active region. Edge-emitting QWD lasers demonstrate low internal loss of 0.7 cm−1 and high internal quantum efficiency of 87%. as well as a reasonably high level of continuous wave (CW) power at room temperature. Due to the high optical gain and suppressed non-radiative recombination at processed sidewalls, QWDs are especially advantageous for microlasers. Thirty-one μm in diameter microdisk lasers show a high record for this type of devices output power of 18 mW. The CW lasing is observed up to 110 °C. A maximum 3-dB modulation bandwidth of 6.7 GHz is measured in the 23 μm in diameter microdisks operating uncooled without a heatsink. The open eye diagram is observed up to 12.5 Gbit/s, and error-free 10 Gbit/s data transmission at 30 °C without using an external optical amplifier, and temperature stabilization is demonstrated.