High power, low-jitter encoded picosecond pulse generation using an rf-locked self-q-switched multicontact GaAs/GaAlAs diode laser

The RF locking of a self-Q-switching diode laser is shown to reduce the jitter of a 2.48 GHz train of 1 W peak power picosecond pulses to less than 300 fs. By using direct modulation of the loss in the Q-switched laser, direct encoding of data has been achieved at rates in excess of 2 Gbit/s.

Narrow line high power picosecond pulse generation in a multicontact distributed feedback laser using modified Q switching

High power bandwidth-limited picosecond pulses with peak powers in excess of 200 mW have been generated using multi-contact distributed feedback laser diodes for the first time. The pulses have widths typically less than 10 ps, time-bandwidth products of as little as 0·24, and can be generated on demand at generator limited repetition rates of up to 140 MHz.

Predictive optimisation of high-power IGBT switching under Active Voltage Control

Active Voltage Control (AVC) is an implementation of classic Proportional-Derivative (PD) control and multi-loop feedback control to force IGBT to follow a pre-set switching trajectory. The initial objective of AVC was mainly to synchronise the switching of IGBTs connected in series so as to realise voltage balancing between devices. For a single IGBT switching, the AVC reference needs further optimisation. Thus, a predictive manner of AVC reference generation is required to cope with the nonlinear IGBT switching parameters while performing low loss switching. In this paper, an improved AVC structure is adopted along with a revised reference which accommodates the IGBT nonlinearity during switching and is predictive based on current being switched. Experimental and simulation results show that close control of a single IGBT switching is realised. It is concluded that good performance can be obtained, but the proposed method needs careful stability analysis for parameter choice. © 2013 IEEE.

High-performance 2 mm gate width GaNHEMTs on 6H-SiC with output power of 22.4 W @ 8 GHz

Optimized AlGaN/AlN/GaN high electron mobility transistors (HEMTs) structures were grown on 2-in semi-insulating (SI) 6H-SiC substrate by metal-organic chemical vapor deposition (MOCVD). The 2-in. HEMT wafer exhibited a low average sheet resistance of 305.3 Omega/sq with a uniformity of 3.85%. The fabricated large periphery device with a dimension of 0.35 pm x 2 nun demonstrated high performance, with a maximum DC current density of 1360 mA/mm, a transconductance of 460 mS/mm, a breakdown voltage larger than 80 V, a current gain cut-off frequency of 24 GHz and a maximum oscillation frequency of 34 GHz. Under the condition of continuous-wave (CW) at 9 GHz, the device achieved 18.1 W output power with a power density of 9.05 W/mm and power-added-efficiency (PAE) of 36.4%. While the corresponding results of pulse condition at 8 GHz are 22.4 W output power with 11.2 W/mm power density and 45.3% PAE. These are the state-of-the-art power performance ever reported for this physical dimension of GaN HEMTs based on SiC substrate at 8 GHz. (c) 2008 Elsevier Ltd. All rights reserved.

An ultra-low power CMOS random number generator

This paper proposes an ultra-low power CMOS random number generator (RING), which is based on an oscillator-sampling architecture. The noisy oscillator consists of a dual-drain MOS transistor, a noise generator and a voltage control oscillator. The dual-drain MOS transistor can bring extra-noise to the drain current or the output voltage so that the jitter of the oscillator is much larger than the normal oscillator. The frequency division ratio of the high-frequency sampling oscillator and the noisy oscillator is small. The RNG has been fabricated in a 0.35 mu m CMOS process. It can produce good quality bit streams without any post-processing. The bit rate of this RNG could be as high as 100 kbps. It has a typical ultra-low power dissipation of 0.91 mu W. This novel circuit is a promising unit for low power system and communication applications. (c) 2007 Elsevier Ltd. All rights reserved.

Analog-digital and digital-analog converters using single-electron and MOS transistors

This paper proposes two kinds of novel single-electron analog-digital conversion (ADC) and digital-analog conversion (DAC) circuits that consist of single-electron transistors (SETs) and metal-oxide-semiconductor (MOS) transistors. The SET/MOS hybrid ADC and DAC circuits possess the merits of the SET circuit and the MOS circuit. We obtain the SPICE macro-modeling code of the SET transistor by studying and fitting the characteristics of the SET with SPICE simulation and Monte Carlo simulation methods. The SPICE macro-modeling code is used for the simulation of the SET/MOS hybrid ADC and DAC circuits. We simulate the performances of the SET/MOS hybrid 3-b ADC and 2-b DAC circuits by using the H-SPICE simulator. The simulation results demonstrate that the hybrid circuits can perform analog-digital and digital-analog data conversion well at room temperature. The hybrid ADC and DAC circuits have advantages as-follows: 1) compared with conventional circuits, the architectures of the circuits are simpler; 2) compared with single electron transistor circuits, the circuits have much larger load capability; 3) the power dissipation of the circuits are lower than uW; 4) the data conversion rate of the circuits can exceed 100 MHz; and 5) the resolution of the ADC and DAC circuits can be increased by the pipeline architectures.

Technique for enhancing generation power density of silicon photovoltaic devices

A new type of photovoltaic system with higher generation power density has been studied in detail. The feature of the proposed system is a V-shaped structure with two polycrystalline solar cells. Compared to solar cells in a conventional approach, the V-shaped structure enhances external quantum efficiency and leads to an increase of 24% in power conversion efficiency.

1-mm gate periphery AlGaN/AIN/GaN HEMTs on SiC with output power of 9.39 W at 8 GHz

AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with high mobility GaN channel layer were grown on 50 min diameter semi-insulating (SI) 6H-SiC substrates by metalorganic chemical vapor deposition and large periphery HEMT devices were fabricated and characterized. High two-dimensional electron gas mobility of 2215 cm(2)/V s at room temperature with sheet electron concentration of 1.044 x 10(13)/cm(2) was achieved. The 50 mm diameter HEMT wafer exhibited a low average sheet resistance of 251.0 Omega/square, with the resistance uniformity of 2.02%. Atomic force microscopy measurements revealed a smooth AlGaN surface with a root-mean-square roughness of 0.27 nm for a scan area of 5 mu mi x 5 pm. The 1-mm gate width devices fabricated using the materials demonstrated a very high continuous wave output power of 9.39 W at 8 GHz, with a power added efficiency of 46.2% and power gain of 7.54 dB. A maximum drain current density of 1300 mA/mm, an extrinsic transconductance of 382 mS/mm, a current gain cutoff frequency of 31 GHz and a maximum frequency of oscillation 60 GHz were also achieved in the same devices. (C) 2007 Elsevier Ltd. All rights reserved.

A differential recursive scheme for suppression of Peak to average power ratio for OFDM

A differential recursive scheme for suppression of Peak to average power ratio (PAPR) for Orthogonal frequency division multiplexing (OFDM) signal is proposed in this thesis. The pseudo-randomized modulating vector for the subcarrier series is differentially phase-encoded between successive components in frequency domain first, and recursion manipulates several samples of Inverse fast Fourier transformation (IFFT) output in time domain. Theoretical analysis and experimental result exhibit advantage of differential recursive scheme over direct output scheme in PAPR suppression. And the overall block diagram of the scheme is also given.

Realization of GaAs/AlGaAs quantum-cascade lasers with high average optical power

Quasi-continuous-wave operation of GaAs/AlGaAs quantum-cascade lasers with high average optical power is demonstrated. Double X-ray diffraction has been used to investigate the quality of the epitaxial material. The compositional gradients and the interface quality are controlled effectively. The corrected average power of per facet about 17 mW and temperature tuning coefficient of the gain peak about 0.91 nm/K from 83 K to 140 K is achieved in pulse operation. Best value of threshold current density is less than 3.0 kA/cm(2) at 83 K. (C) 2005 Elsevier Ltd. All rights reserved.

Design consideration and performance of high-power and high-brightness InGaAs-InGaAsP-AlGaAs quantum-well diode lasers (lambda=0.98 mu m)

In this paper, we conduct a theoretical analysis of the design, fabrication, and performance measurement of high-power and high-brightness strained quantum-well lasers emitting at 0.98 mum, The material system of interest consists of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. Some key parameters of the laser structure are theoretically analyzed, and their effects on the laser performance are discussed. The laser material is grown by metal-organic chemical vapor deposition and demonstrates high quality with low-threshold current density, high internal quantum efficiency, and extremely low internal loss. High-performance broad-area multimode and ridge-waveguide single-mode laser devices are fabricated. For 100-mum-wide stripe lasers having a cavity length of 800 mum, a high slope efficiency of 1.08 W-A, a low vertical beam divergence of 34 degrees, a high output power of over 4.45 W, and a very high characteristic temperature coefficient of 250 K were achieved. Lifetime tests performed at 1.2-1.3 W (12-13 mW/mum) demonstrates reliable performance. For 4-mum-wide ridge waveguide single-mode laser devices, a maximum output power of 394 mW and fundamental mode power up to 200 mW with slope efficiency of 0.91 mW/mum are obtained.

High-power operation of quantum cascade lasers endured prolonged air-oxidation

High-power strain-compensated In1-xGaxAs/ln(1-y)Al(y)As quantum cascade lasers (lambda similar to 5.5 mu m) are demonstrated. Peak power at least 1.2W per facet for a 32 mu mx2mm uncoated laser stored in ambient condition for 240 days, is obtained at 80 K. Considering the collection efficiency of 60%, the actual output power is 4W at this temperature.

SOI-based thermo-optic waveguide switch matrix with spot size converters

A SOI-based thermo-optic waveguide switch matrix worked at 1.55 mu m, integrated with spot size converters is designed and fabricated for the first time. The insertion loss and polarization dependent loss are less than 13dB and 2dB, respectively. The extinction ratio is larger than 19dB. The response time is less than 5 mu s and the power consumption of the switch cell is about 200mW.

Thermoelectric Cooling and Power Generation

In a typical thermoelectric device, a junction is formed from two different conducting materials, one containing positive charge carriers (holes) and the other negative charge carriers (electrons). When an electric current is passed in the appropriate direction through the junction, both types of charge carriers move away from the junction and convey heat away, thus cooling the junction. Similarly, a heat source at the junction causes carriers to flow away from the junction, making an electrical generator. Such devices have the advantage of containing no moving parts, but low efficiencies have limited their use to specialty applications, such as cooling laser diodes. The principles of thermoelectric devices are reviewed and strategies for increasing the efficiency of novel materials are explored. Improved materials would not only help to cool advanced electronics but could also provide energy benefits in refrigeration and when using waste heat to generate electrical power.

HIGH-POWER 2-DIMENSIONAL QUANTUM-WIRE LASER ARRAYS

GaAs/AIGaAs two-dimensional quantum-well wire laser arrays fabricated by metal-organic chemical vapour deposition on nonplanar substrates have realised a linear light pulse output Fewer of over 100mW. This is the highest figure reported to date for all kinds of quantum-well wire lasers.