Compact ultra-high gain multi-pass Nd:YAG amplifier with a low passive reflection phase conjugate mirror

Coherence collapse is a dramatic spectral broadening that occurs in single-mode semiconductor lasers subject to weak (10-3–10-4) optical feedback well above threshold.1 It is a particularly vexing and elusive phenomenon because it mimics the properties of deterministic chaos and noise-driven instabilities. Here we describe what we believe to be the first experimental observation of coherence collapse using phase-conjugate external feedback. A GaAs/AlGaAs index guided laser diode (Hitachi HLP-1400) is coupled by a variable attenuator—consisting of two polarizers and a half-wave plate—to a passive phase conjugate mirror (PPCM) that uses a barium titanate crystal.2 An optical isolator is placed in the ring to make the PPCM undirectional. This avoids deleterious effects caused by counterpropagating beams. The line broadening was observed with a 16.5-GHz Fabry-Perot interferometer. External cavity modes were seen in the rf intensity noise spectra. This PPCM could produce reflectivites up to 15% at the laser facet. For these experiments, the reflectivity was varied from zero up to 2 × 10-3. At the lower reflectivites (10-4) the initially well-behaved laser experiences undamped relaxation oscillations which beat with the external cavity modes in the nonlinear laser medium to produce the broadband (~10 GHz) single-mode spectra characteristic of coherence collapse.

Synchronously launching lots of projectiles to form barrage against missile is necessary in some occasions . This paper presents four new concept of electromagnetic rail launchers volleying projectiles powered by single high-power pulsed power supply, named respectively as multi-barrel parallel, common armature, multi-barrel serial, armature serial. This paper gives their work principles, equivalent circuits for analysis in theory, basic equations, and compares them with each other. At last it is indicated that these inventions are significant and valuable for the development of electromagnetic launch technology and science, and they have a lot of potential applications.

We generate linearly polarized, 287 W average-power, 5.5 ps pulses using a cryogenically cooled Yb:YAG amplifier at a repetition rate of 78 MHz. An optical-to-optical efficiency of 41% is obtained at 700 W pump power. A 6 W, 0.4 nm bandwidth picosecond seed source at 1029 nm wavelength is constructed using a chirped-pulse fiber amplification chain based on chirped volume Bragg gratings. The combination of a fiber amplifier system and a cryogenically cooled Yb:YAG amplifier results in good spatial beam quality at large average power. Low nonlinear phase accumulation as small as 5.1 x 10(-3) rad in the bulk Yb:YAG amplifier supports power scalability to a > 10 kW level without being affected by self-phase modulation. This amplification system is well suited for pumping high-power high-repetition-rate optical parametric chirped-pulse amplifiers.

Because the ring and semilinear passive phase conjugate mirrors use dynamic transmission holograms, they are insensitive to vibration and may be pumped with light of short coherence length or with picosecond mode-locked laser light. Experimental demonstrations of these modes of operation are described.

A PIN/JFET using an InP‐based material for receiving an optical signal at a wavelength of 1 μm has been developed. From a practical viewpoint, operation using a single power supply is desirable. In this study, an opto‐electric integrated circuit (OEIC) composed of a PIN/PD, JFET, feedback resistor, etc., was fabricated on a semi‐insulating substrate and then the characteristics of each component were evaluated. The pinchoff voltage and cutoff frequency of the JFET were 1.2 V and 900 MHz, respectively. The transimpedance in operation was 965 ft, which was almost the same as the feedback resistance. When the power supply voltage was 5 V, the 3‐dB cutoff frequency was 220 MHz, indicating that operation using a single power supply is feasible. The 1/f noise of JFET was 20 nV √Hz and the receiver sensitivity was −24.1 dBm. High reliability could be ensured by employing a 50‐hr THB screening test.

A new AC-coupled amplifier for portable ECG without reference electrode

A low-voltage single supply CMOS electrically erasable read-only memory (CMOS-EEROM) is described. It combines long-term charge retention and the possibility of being read, written, and erased from a single power supply. Negative write and erase voltages are generated on-chip by voltage multipliers. It is shown that writing by avalanche injection and erasing by Fowler-Nordheim emission, are compatible with the low power output associated with these multipliers. In order to reduce the programming voltages below 40 V, injection oxide thickness is locally reduced by one additional photolithographic step compared to conventional silicon-gate CMOS technology. The influence of this oxide thickness and of polysilicon doping on write and erase characteristics, endurance, and charge retention are analyzed.

We report photorefractive passive phase conjugation1 of GaAIAs laser radiation at 815-865 nm and Ar+ laser radiation at 1090 nm. A ring passive phase conjugate mirror was used with BaTiO3 as the real-time holographic gain medium. At least 1.5 mW (50 mW/cm2) was required for the PPCM to begin operation. At 3.6 mW (126 mW/cm2) the reflectivity reached 16%, corresponding to 25% after correction for Fresnel reflections. The rise time, defined here as time taken to 90 % of steady state, was approximately 5/1 s W/cm2 at 514.5 and 815 nm, where /is the incident intensity. When the GaAIAs laser was replaced by an Ar+ laser emitting 35 mW (1.4 W/cm2) at 1090 nm the rise time measured 500// s W/cm2. In spite of the length of this time, the steady-state reflectivity reached 18% uncorrected for Fresnel reflections. We describe effects of the phase conjugate feedback into GaAIAs lasers and attempts at active mode locking. The fact that the PPCM operates at 1090 nm indicates that it can be used to correct distortions in Nd:YAG laser systems where aberrations in the solid-state gain medium might possibly be severe.

Ultrafast lasers are of interest for applications in medicine, material processing and as drivers for mid-IR optical parametric frequency converters. Recently a sub-picosecond operation of Ho:YAG chirped pulse amplification (CPA) system was realized by extending the amplified pulse spectrum over two emission peaks centered at 2090 nm and 2096 nm [3], which required strong adaptive spectral shaping of the seed pulse to equalize spectral amplitude gain. In addition, dispersion management of the CPA was complicated due to the resonant spectral phase distortion and could only be accomplished by using an acousto-optic programmable dispersive filter (DAZZLER). The most intense emission line of Ho:YAG is centered at 2090 nm, and, without compensation of gain narrowing, supports amplified bandwidth of >1.5 nm corresponding to <; 4 ps pulses, an attractive pulse duration for the above-mentioned applications.

The concept of the thin-tapered-rod Yb:YAG amplifier with waveguide pumping is proposed and implemented. It is shown that such an amplifier demonstrates considerably higher small signal gain and is less affected by thermal effects than the thin-rod ("single-crystal fiber") amplifier. In the developed amplifier, a small signal gain as high as 23 per pass is achieved.

We describe a novel decision-directed structure that extends the passive phase conjugation (PPC) array demodulation method of Rouseff et al.. The PPC transmission scheme is a single source and multiple receive sensors. Our algorithm uses an initial training period with known data, followed by block-update LS channel estimation via LSQR (Paige and Saunders1982) iterations, and subsequent memoryless decisions. Decisions are circulated back into the LS model for the next estimation block. Performance on a shallow-water acoustic channel is shown at ranges up to 4.6 km under windy surface conditions and shipping noise. The algorithm demonstrates good bit error rates, and robustly tracks time-varying channels. Its unquantized output can be further processed by conventional equalizers.

As large arrays of actuators become increasingly common in smart structures, many systems do not have enough power supplies to control each actuator individually due to design, weight, or cost constraints. This issue can be addressed by grouping multiple actuators together and powering each group with a single power supply. As this is done, it is important to determine which actuators to group together. For best performance, the grouping of actuators must be optimized. Currently, genetic algorithms and other heuristic algorithms are used to determine this grouping, but a global optimum is not guaranteed. In order to accurately group the actuators and guarantee that the global optimum is found, we have developed a new method to achieve such purpose — the En Masse Elimination (EME) technique. This is an optimization algorithm used to determine the grouping of actuators when there is a constraint on the number of power supplies, specifically when there are more actuators than power supplies present. The first step in this method is for a solution that satisfies the power supply limitation to be found. The required control authority is determined for this solution. Next, some actuators are grouped while the power supply constraint is temporarily relaxed for all the other actuators. If the control authority of this solution is no better than the control authority of the acceptable solution, than large areas of the design space can be eliminated. This process is continued until the entire design space has been searched, and the global optimum is found. Unlike other methods, the global optimum is found without having to examine every possible combination. In this paper, a detailed explanation of the EME algorithm is given and the efficacy of this method is demonstrated. An example consisting of a beam with static deformation, multiple actuators, and varying constraints on the number of power supplies is used to illustrate the concept.

The advent of greater concern with the safety and environmental effects of automobiles has resulted in the generation of many new electronic systems (similar to those used in industrial control), which are directed at making improvements in these areas. The implementation of these systems requires a new generation of low-cost linear integrated circuits specifically designed for operation from the single power supply that is available. The operational amplifiers and comparators that are described in this paper are among the first of this generation. These circuits offer both cost and applications advantages in the emerging automotive electronic systems and also in existing industrial control applications.

With growing of applications of the embedded system technology to mobile systems, energy efficiency is becoming an important issue for designing real time embedded systems. One of the possible techniques to reduce the energy consumption is the Dynamic Voltage Scaling (DVS). DVS utilizes the slack time and adjusts the supply voltage so as to reduce the energy expense. However, how to optimally adjust the supply voltage is a NP hard problem. This paper focuses the combinational optimization problem, namely, the problem of minimizing schedule length with energy consumption constraint and the problem of minimizing energy consumption with schedule length constraint. These problems emphasize the tradeoff between power and performance and are defined such that the power-performance product is optimized by fixing one factor and minimizing the other. We propose the analytical result which gives the variation factor of each power supply which depends on the workload and provides the same power supply while meeting the constraints. We address to the use of genetic algorithm to schedule the tasks and then find the optimal power supplies and determine the schedule length on the multiprocessor system.

A novel low-voltage triode-mode CMOS transconductor is presented. Enhanced linearity and tuning range are achieved by implementing body-driven technique and gain-enhancement scheme. Simulation results using 0.18 /spl mu/m N-well CMOS technology confirm the superior performance of this transconductor. With 1.5 V single power supply, the transconductor is linearly tunable over one decade. For differential input signal with peak amplitude up to 0.4 V, the THD is less than -50 dB for the entire transconductance tuning range. The proposed highly linear transconductor is suitable for realizing continuous-time filters with reduced power supply.