High-temperature operation of 1.3-μm tapered-active-stripe laserfor direct coupling to single-mode fiber

High-temperature operation of 1.3-μm wavelength multiquantum-well (MQW) lasers with an active stripe horizontally tapered over whole cavity, for direct coupling to single-mode fibers (SMFs), are reported. The lasers have reduced the output-beam divergence in a simple structure which does not contain an additional spot-size transformer. To improve high-temperature characteristics, we have investigated the influence of the thickness of separate-confinement-heterostructure layers and the number of quantum wells (QWs) on the threshold current and the output-beam divergence at high temperature. As a result, the fabricated lasers show low-threshold current (~18 mA) and high-slope efficiency (~0.4 mW/mA) with narrow output-beam divergence (~12°) at 85°C. Moreover, we have obtained maximum coupling efficiency of -4.7 dB in a direct coupling to a SMF, and the reliability of longer than 10⁵ h (MTTF) by a lifetime test of over 2000 h at 85°C     

Monolithic integration of spot-size converters with 1.3-μmlasers and 1.55-μm polarization insensitive semiconductor opticalamplifiers

To reduce packaging costs, it is necessary to use passive alignment between the laser diodes and optical fiber. Such an alignment requires low-coupling loss and large positional alignment tolerances. This is achievable with integrated spot-size converters, which permit to match the near field of a laser to that of a flat-end single-mode fiber (SMF). In this paper, we first review briefly the different technological approaches to realize spot-size converters. Then, we focus on the double-core structure developed both for 1.3-μm Fabry-Perot lasers and 1.55-μm semiconductor optical amplifiers (SOAs). The spot-size expansion is simulated using a two-dimensional (2-D) beam propagation method analysis. Short spot-size converters (100 μm) integrated with 1.3-μm lasers and 1.55-μm SOAs exhibit beam divergences as low as 12°×12° and 12°×15°, respectively. The performances of devices with integrated spot-size converters are reported and discussed. A 2-in wafer process is used thanks to the versatility of the double-core structure and its compatibility with buried ridge stripe technology     

An alternative evaluation of distribution transformers to achievethe lowest TOC

The 65°C rise rating of a distribution transformer is a thermal life rating of its insulation system, not the best efficiency condition. Total owning cost (TOC) is reference at 85°C which is based on a 20°C ambient plus a 65°C rise. For better efficiency, a transformer should be operated at a lower temperature. Transformer design programs calculate a design for the lowest TOC at the 85°C reference temperature. These programs do not calculate a design for the lowest possible temperature rise or lowest TOC regardless of reference temperature. As a consequence, the lowest TOC is not realized. An evaluation method is proposed that will provide the user with a distribution transformer design which has a lower operating temperature rise, thus improving both the transformer's efficiency and the customer's TOC     

Strongly gain-coupled (SGC) coolerless (-40°C~+85°C) MQWDFB lasers

Single mode operation in a wide temperature range (-40°C~+85°C) has been obtained, from an etched-QW strongly gain-coupled (SGC) distributed-feedback laser at 1.3 μm. The SGC lasers exhibit an excellent sidemode-suppression-ratio (SMSR) of around 45-55 dB in continuous-wave operation, and a very good transient SMSR (TSMSR) of more than 35 dB during a gain-switched operation, both are over the entire temperature range. When mounted P-side up, the threshold current is about 12 mA at room temperature and 28 mA at +85°C. The output power is more than 20 mW with only 120-mA injection current at +85°C     

Ultralow threshold 1.3-μm InGaAsP-InP compressive-strainedmultiquantum-well monolithic laser array for parallel high-densityoptical interconnects

An ultralow-threshold 1.3-μm InGaAsP-InP 10-element monolithic laser array is achieved through careful optimization of a strained multiquantum-well active layer, especially the amount of strain, the well thickness, the barrier thickness, the number of wells, and the active laser width. This array has a record-low threshold current, highly uniform threshold current characteristics (1.3±0.09 mA and slope efficiency of 0.37±0.01 W/A), extremely low operating current of 14 mA under 5-mW output power, and long-term reliability. This array is suitable as light sources for a parallel high-density optical interconnection system. In addition, a record low CW threshold current of 0.58 mA at 20°C and 1.62 mA at 90°C, as a long-wavelength laser, is obtained by employing a short cavity (100 μm) uith high-reflection coatings     

Laser diodes with integrated spot-size transformer as low-costoptical transmitter elements for telecommunications

We have realized laser diodes with integrated spot-size transformer to achieve a high-coupling efficiency to a standard single-mode fiber (SMF) without microoptical elements. A coupling loss of about 1 dB has been achieved with tolerances of 12 μm in both vertical and horizontal direction. We have fabricated both distributed-feedback (DFB) and Fabry-Perot (FP)-type lasers. In the case of the FP lasers the longitudinal single-mode emission was stabilized by means of an external fiber Bragg-grating which was directly butt-coupled to the laser. We have experimentally and theoretically investigated the optical and electrical properties of the devices using a transmission line model     

1.3-μm spot-size-converter integrated laser diodes fabricated bynarrow-stripe selective MOVPE

High-performance 1.3-μm spot-size-converter integrated laser diodes (SSC-LDs) have been developed by using narrow-stripe (<2.0 μm) selective MOVPE. In order to decrease leak current at high temperature, a p-n-p-n current blocking structure was added using a self-alignment process. These LD's no longer require a semiconductor etching process. Superior lasing characteristics, such as a low driving current of 56 mA for output power of 10 mW, and high-slope efficiency at 85°C, were achieved by using a high-quality multiple-quantum well (MQW) active layer of narrow-stripe selective MOVPE and a p-n-p-n current blocking structure. A narrow radiation angle of 12° was obtained by optimizing the tapered-waveguide profile. A high-coupling efficiency of -2.8 dB was achieved between a LD chip and a single-mode fiber (SMF). This SSC-LD is very appropriate as a light source for access network systems, which require a low-cost LD module. It has excellent coupling efficiency, using a SMF, and a simple fabrication process, using selective MOVPE     

Charge storage in double layers of thermally grown silicon dioxideand APCVD silicon nitride

Experimental results on charge storage and discharge in double layers of silicon dioxide and silicon nitride will be reported and discussed. SiO₂ with a thickness of 300 nm was thermally grown on silicon wafers, while cover layers of Si₃N₄ with thicknesses of 50, 100, and 150 nm were deposited chemically at atmospheric pressure. The samples were charged by the point-to-grid corona method. At room temperature, the measured surface potential V was stable during a period of almost three years. Isothermal measurements under different environmental conditions showed an improved charge retention compared to a single layer grown silicon dioxide. After ~3 h at 300°C, the observed voltage drop was <10% for the double layers and ~60% for bare SiO₂. Similar results were obtained under a humid condition of 95%RH and 60°C. Besides, thermally stimulated current (TSC) was measured in setup with a temperature ramp of 200°C/h. For the double layers, a current peak with a maximum temperature at ~500°C was observed. The measured current in the range of 300 to 400°C, the location of current maxima observed in thermally grown silicon dioxide or APCVD silicon nitride, was negligible. In addition to improved electret properties the internal stress in the investigated double layers can be adjusted by a proper thickness ratio of oxide layer to nitride layer. Therefore double layers of silicon dioxide and nitride seem to be promising materials for integrated sensors and actuators based on the electret effect     

Very high characteristic temperature and constant differentialquantum efficiency 1.3-μm GaInAsP-InP strained-layer quantum-welllasers by use of temperature dependent reflectivity (TDR) mirror

A very high characteristic temperature T₀ of 150 K (25-70°C) or 450 K (25-50°C) and an almost constant differential quantum efficiency operation in the temperature range of 25-70°C were achieved in 1.3-μm GaInAsP-InP strained-layer quantum-well (SL-QW) lasers by use of a novel temperature dependent reflectivity (TDR) mirror composed of multiple quarter-lambda thickness α-Si-SiOx dielectric films with quarter-lambda shift in the vicinity of center portion, The mechanism of high T₀ and constant differential quantum efficiency were explained using the structural parameters, transparent current density and gain coefficient of a SL-QW laser that are derived experimentally. The effect of TDR mirror was confirmed by measuring the temperature dependence of net gain of a SL-QW laser with TDR mirror. It was found that less temperature dependent net gain due to the decrease of mirror loss with temperature played an important role for improving the temperature characteristics of threshold current. Almost constant differential quantum efficiency over a wide temperature range is attributed to the increase of the facet reflectivity with temperature     

An active‐clamping zero‐voltage‐switching flyback converter with integrated transformer

This paper proposes an active‐clamping flyback converter using an integrated transformer. The proposed converter is composed of two active‐clamp flyback converters. The presented converter can balance the total load current between secondary sides of two transformers so that the rectifier diode conduction loss is reduced. Also, the main switch of one converter is the auxiliary switch for the other converter, so that only two switches are required and both can achieve zero‐voltage‐switching operation. The two transformers are integrated into one magnetic core; therefore, the volume and copper loss of transformer can be reduced. Detailed analysis and design of this integrated magnetic active‐clamping flyback converter are described. Experimental results are recorded for a prototype converter with an AC input voltage ranging from 85 to 135 V, an output voltage of 24 V and an output current of 5 A, operating at a switching frequency of 100 kHz. Copyright © 2014 John Wiley & Sons, Ltd.     

Reliable wide-temperature-range operation of 1.3-μmbeam-expander integrated laser diode for passively aligned opticalmodules

A novel structure for a 1.3-μm beam-expander integrated (BEX) laser diode is demonstrated. It combines a thickness-tapered InGaAsP-InP multiple quantum-well (QW) crystal grown by a novel silicon shadow masked metalorganic vapor phase epitaxy and a simple reverse-trapezoid-ridge waveguide laser structure that offers smooth mode field expansion and improved high-temperature lasing performance. We found this new BEX laser quite suitable for operation over a wide range of temperatures above 85°C and highly efficient lens-free coupling to a single-mode fiber (SMF) of less than 3 dB. These excellent lasing properties along with reliability under severe environmental conditions make this BEX-LD a promising candidate for practical use for low-cost long-wavelength light-source modules using optical passive alignment techniques     

200°C operation of a 500-W DC-DC converter utilizing powerMOSFETs

This paper presents results from the operation of the power stage of a 500-W DC-DC converter at an ambient temperature of 200°C. This converter is designed to provide an output voltage of 12-Vdc from a 28-Vdc input. It utilizes an H-bridge configuration composed of eight International Rectifier power MOSFETs (parallel connections of two MOSFETs) and four Motorola diodes to convert the DC input voltage to a high-frequency square wave which can then be stepped up with a transformer. The transformer output voltage is then rectified and filtered to produce the DC output voltage. A phase-shifted pulse-width modulation (PWM) switching scheme is utilized to control the MOSFETs in the H bridge. This scheme allows zero-voltage turn-on of the MOSFETs to improve the efficiency. The efficiency of this converter when operated on the laboratory bench was measured to be 89%. The H bridge and transformer were then placed in an oven and operated over an ambient temperature range of 20°C-200°C. The efficiency varied from 86.1% to 85.4% over this temperature range. The long feedthroughs for oven operation caused the efficiency to decrease from 89% to 86.1%     

Optical current transformer for gas insulated switchgear usingsilica optical fiber

The high accuracy optical current transformer (optical CT) for gas insulated switchgear (GIS) using a silica optical fiber has been developed. The linear birefringence was reduced by twisting the newly developed double coated optical fiber. The current of up to 8000 A was measured within electric noise error of 3.8 Arms and a sensitivity change of ±0.4% was observed over the temperature range from -20 to 90°C. This change corresponds to the temperature dependence of the Verdet constant of silica. When the vibrating acceleration of 8G was applied by the gas circuit breaker motion, no signals were distinguished from the background noise level of 3.8 Arms. The long term test was carried out and the accuracy of the measurements was kept to within ±0.15% during 8 hours. This is the first practical optical CT to satisfy all requirements for GIS     

Modulation and free-space link characteristics of monolithicallyintegrated vertical-cavity lasers and photodetectors with microlenses

We present temperature, modulation, and free-space link characteristics of monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The devices have been integrated using a novel structure that makes it possible to fabricate devices with through-the-substrate emission and detection. Taking advantage of the substrate emitting/detecting architecture, we monolithically integrate microlenses on the substrate side of the devices and flip-chip bond arrays without via processes or substrate removal. Low-threshold high-efficiency VCLs exhibit maximum small-signal modulation bandwidths, which are limited by parasitics, of ~9.5 GHz at 20°C and ~8.4 GHz at 70°C. The VCLs have the lowest reported bias currents required to reach bandwidths of up to ~8 GHz. A free-space optical link is demonstrated with flip-chip-bonded arrays of microlensed, monolithically integrated VCLs and detectors. The link is found to be tolerant to temperature differences of ±75°C between the VCL and detector, with error free (BER<10^-12) data transmission demonstrated in each case     

Coupling and conversion characteristics of spot-size-converterintegrated laser diodes

The coupling and conversion characteristics of four types of spot-size converter integrated laser diodes (SS-LDs) to a single-mode fiber (SMF) in the 1.3-μm-wavelength region are numerically clarified. The SS-LDs are categorized into types with vertical tapers and types with a combination of a lateral taper and a thin-film core. The eigenmodes are obtained by the finite-element method (FEM). The semivectorial 3-D finite-difference (FD) beam propagation method (BPM) is used to calculate the propagating beams     

低温环境下电子式电流互感器激光供电情况的分析与研究

激光供电是有源型电子式电流互感器的关键器件之一,它的性能直接影响电子式互感器的性能。激光供电系统受环境条件影响较大,特别是低温下有可能使电子式互感器不能正常工作,该文介绍了激光供电系统在不同温度下的试验结果,根据实验结果采取的改善激光供电系统性能的温度补偿方法,并在实际工程中得到了应用。该文对有源式电子式互感器的设计人员和工程使用人员都有一定的参考价值。     

Integrated GaInAsP laser diodes with monitoring photodiodes throughsemiconductor/air Bragg reflector (SABAR)

A 1.3-μm GaInAsP laser diode (LD) is integrated with a monitoring photodiode (M-PD) through a semiconductor/air Bragg reflector (SABAR). Instead of conventional cleavage, the SABAR can provide not only Fabry-Perot resonance with high reflectivity, but also possibility of integration of laser with other functional devices. The design, fabrication, and some characteristics including threshold current, monitoring photocurrent, SABAR reflectivity as a function of the number of semiconductor/air pairs N are reported. The threshold current of ridge waveguide laser with SABAR (cavity length L=160 μm, ridge width W=7 μm, SABAR pairs N=3) is 20 mA. The threshold current is reduced by improving butt-coupled interface between active and passive waveguides employed in this laser and is expected 2 mA/μm. The monitoring photocurrent responds linearly with output power from the laser and 0.024 mA at laser output power of 5 mW. From the threshold characteristics, SABAR reflectivity is determined to >80%. The increase of photocurrent can be achieved by optimizing the number of SABAR pairs to N=1. We have obtained threshold current of 22 mA in the followed laser structure (L=270 μm, W=7 μm, N=1), and detector photocurrent of 1.13 mA (@5 mW). The experimental SABAR reflectivity is ~50%, which is estimated by threshold characteristics and efficiency of light output power. The laser has a mode field converter section, resulting in narrow beam divergence 11° along vertical axis. This integrated laser is very promising candidate for coming optical module in low-power consumption and low-cost access network systems     

Static electrification and partial discharges induced by oil flowin power transformers

This paper presents the study of the major parameters on static electrification, using full-scale shell type transformers (570 MVA, 405 kV and 100 MVA, 500 kV). The consequences of static electrification on the dielectric strength and the conditions of partial discharge occurrence also are studied with oil flow rate up to 5 times the nominal value. It shows that the leakage currents are strongly influenced by temperature, applied voltage and oil flow rate Q. The latter is the most influential parameter. The winding leakage current I varies as Qⁿ , where 1⩽n⩽3. The maximum value of I is observed at room temperature (20°C) when the transformer is energized     

Room-temperature lasing operation of GaInNAs-GaAssingle-quantum-well laser diodes

We have succeeded in demonstrating continuous-wave (CW) operation of GaInNAs-GaAs single-quantum-well (SQW) laser diodes at room temperature (RT). The threshold current density was about 1.4 kA/cm², and the operating wavelength was approximately 1.18 μm for a broad-stripe geometry. Evenly spaced multiple longitudinal modes were clearly observed in the lasing spectrum. The full-angle-half-power far-field beam divergence measured parallel and perpendicular to the junction plane was 4.5° and 45°, respectively. A high characteristic temperature (T₀) of 126 K under CW operation and a small wavelength shift per ambient temperature change of 0.48 nm/°C under pulsed operation were obtained. These experimental results indicate the applicability of GaInNAs to long-wavelength laser diodes with excellent high-temperature performance     

Tapered rib adiabatic following fiber couplers in etched GaAsmaterials for monolithic spot-size transformation

Design details and demonstration data are presented for an (Al,Ga)As monolithic tapered rib waveguide achieving modal spot-size transformation. The tapered rib adiabatic following fiber coupler structure (TRAFFIC) achieves two-dimensional (2-D) expansion of the output optical mode of single-transverse-mode semiconductor waveguide modulators and lasers using a one-dimensional (1-D) taper between noncritical initial and final taper widths which are compatible with optical lithographic techniques. Measurements are presented of total mode expansion losses between ~1.5-2.0 dB and semiconductor to single-mode-fiber waveguide coupling losses of ~0.5-1.0 dB for doped pin optical-modulator-type waveguides using the TRAFFIC waveguide. A semiconductor laser with a TRAFFIC tapered-rib mode-expansion section and measured coupling loss between the laser output and single-mode fiber of only 0.9 dB is described. Finally, a TRAFFIC Spot-size transformer for undoped waveguide modulators with total mode expansion losses of 1.84 dB and excellent modal behavior at 1.32-μm wavelength is presented. The TRAFFiC structure is particularly well suited for integration with both active and passive etched rib waveguide devices. Fabrication is relatively simple, requiring only patterning and etching of the tapered waveguide and uniform-width outer mesa waveguide without any epitaxial regrowth