Input Power Range Research Articles

Self-guided propagation of femtosecond light pulses in water.

We report experimental evidence of self-guided propagation of femtosecond laser pulses in water. A light filament induced by 170-fs, 527-nm pulses has a diameter of 60 microm (at the 1/e2 level) and persists over a distance of 20 mm. The filamentary mode is sustained over a wide range of input power, and the energy excess is converted into conical emission. In the time domain, the pulse trapped in a filamentary mode experiences a number of splittings occurring in the early stage of filament formation.

Small-Signal Analysis Method of Noise Transfer of All-Optical Wavelength Converters

Noise transfer characteristics of wavelength converters based on cross gain modulation (XGM) in semiconductor optical amplifiers (SOAs) is analyzed with a small signal model. The numerical simulation results show that the input pump power and probe power and the gain of SOA have direct influence on the noise transfer. In an appropriate range of input power, the noise can be effectively suppressed, and quality of converted signal is improved.

All-optical gain control for bidirectional optical add-drop multiplexer using ASE noise path through multi-port circulators

An all-optical gain control method for a bidirectional optical add-drop multiplexer using an amplified spontaneous emission noise path through multi-port circulators is reported. The device provides constant gain and low noise figure over a large input power range, has low crosstalk and removes Rayleigh backscattered and back-reflected light.

Effects of Sc2O3 and MgO passivation layers on the output power of AlGaN/GaN HEMTs

The low temperature (100/spl deg/C) deposition of Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> or MgO layers is found to significantly increase the output power of AlGaN/GaN HEMTs. At 4 GHz, there was a better than 3 dB increase in output power of 0.5×100 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> HEMTs for both types of oxide passivation layers. Both Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and MgO produced larger output power increases at 4 GHz than conventional plasma-enhanced chemical vapor deposited (PECVD) SiN/sub x/ passivation which typically showed /spl les/2 dB increase on the same types of devices. The HEMT gain also in general remained linear over a wider input power range with the Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> or MgO passivation. These films appear promising for reducing the effects of surface states on the DC and RF performance of AlGaN/GaN HEMTs.

All-optical clock recovery for both RZ and NRZ data

An all-optical clock recovery scheme for both the nonreturn-to-zero and the return-to-zero formats has been proposed and successfully demonstrated. Clock extraction, enhancement, and clock-to-data suppression were realized by a semiconductor optical amplifier and a fiber Bragg grating. Clock recovery was achieved using a two-section gain-coupled distributed-feedback laser. The scheme has large dynamic range of input power for both formats.

Beam quality considerations of high power Nd:YAG lasers

High power Nd:YAG lasers with fiber optic beam delivery have introduced new capabilities for material processing applications. Here, we present the stable resonator design for high power Nd:YAG lasers to optimize beam quality for fiber optic transmission. Dependence of beam parameters on position and dioptric power of thermal lens has been investigated and optimized to achieve efficient fiber optic beam delivery. With the optimum resonator configuration, an efficient fiber optic beam delivery over the entire operating range of input power has been achieved. The results of stable resonator design with good beam quality and output power have been presented.

低電力ホールスラスタの基本作動特性と推進性能

Laboratory-model low-power Hall thrusters, named the THT-III-series, were operated in order to examine influences of ceramics species of the acceleration channel walls, and shape and strength of radial magnetic field in the acceleration channels on the operational characteristics. For the THT-IIIA-BN thruster both with acceleration channel walls made of boron nitride and with more intensive concentration of magnetic field lines near the acceleration channel exit, a higher thrust efficiency was achieved with a lower discharge current and a higher thrust for an optimum magnetic field strength regardless of discharge voltage at a constant xenon mass flow rate. Accordingly, both the thrust and the specific impulse ranged from 10 to 70mN and from 1,200 to 2,300s, respectively, at discharge voltages of 200–500V with mass flow rates of 1–3mg/s in a wide input power range of 250–1,800W. The thrust efficiency ranged from 30 to 45%.

Study on the dynamic range of input power for wavelength converter based on cross-phase modulation in SOAs

In this paper, the dynamic range of input power for wavelength converter based on cross-phase modulation (XPM) in semiconductor optical amplifier (SOA) is studied. The dynamic range of input power is associated with the linewidth enhancement factor α, which is influenced by optical wavelength and power. Shorter wavelength and larger power can induce smaller α and lead to a larger dynamic range, while the gain modulation is more severe. Through dynamically controlling the current of the phase arm of the XPM wavelength converter by the detection of the input signal power level, the dynamic range of input power can be increased from 2 to 17 dB.

All-optical gain-clamped erbium-doped fiber-ring lasing amplifier with laser filtering technique

A unique laser filtering technique of a gain-clamped erbium-doped fiber amplifier based on ring-laser cavity is demonstrated. The filtering mechanism is achieved using a single fiber Bragg-grating, which also functions as a laser feedback reflector at the output end of the amplifier. This new design has low noise and most important, shows up to 98% reduction in output laser intensity as compared with a previous design studied earlier. An optimum result with gain and noise around 25 and 3.5 dB, respectively, obtained for a dynamic range of input signal power up to -8 dBm.

New nonlinear design tools for self-oscillating mixers

New nonlinear design tools for self-oscillating mixers are presented here, with the aim to increase the designer's control over their behavior. The new tools enable fixing the self-oscillation frequency and selecting the optimum self-oscillation amplitude for maximum conversion gain. They can also be applied for the optimized design of harmonic self-oscillating mixers. Using bifurcation-theory concepts, it has been possible to increase the input-power range with self-oscillating-mixer operation. A self-oscillating mixer with 5.5 GHz input frequency has been designed and simulated obtaining very good agreement with the experimental results.

Enhanced performance with optimized input power and increased dynamic range for wavelength conversion using four-wave mixing in SOAs

We investigate the converted optical signal-to-noise ratio, intersymbol interference, and bit-error-rate performance of all-optical wavelength converter based on four-wave mixing in semiconductor optical amplifiers as functions of the input pump and signal powers. The minimum power penalty less than 1 dB is achieved by optimizing the input signal and pump power. In addition, two approaches to expand the dynamic range of input signal power have been presented with the resulting dynamic ranges of more than 25 and 12 dB respectively and both show good tolerance to variations in input signal power.

Spectroscopic Temperature Measurements in Direct Current Arc Plasma Jets Used in Thermal Spray Processing of Materials

An experimental study was conducted to determine the plasma temperature field and its parametric variation with respect to plasma operating conditions using emission spectroscopy. The focus of our study was the direct current (DC) arc plasma systems used in thermal spray processing of ceramic materials. A commercial plasma system (Metco 9M series) was operated with mixtures of argon and hydrogen in the power input range from 12 to 36 kW. Temperature measurements were based on the detection of emission line intensities from Ar-I neutral species. Spatially resolved measurements were obtained of the plasma temperatures in axisymmetric plasma jets using Abel deconvolution. The variation of plasma axial and radial temperature distributions was measured as a function of the plasma input power, the total gas flow rate, and the binary gas composition of argon and hydrogen. Time-averaged plasma gas temperatures were found to increase with increasing plasma input power, increasing hydrogen content of the plasma gas, and decreasing total gas flow rate. Plasma temperatures decrease progressively with increasing distance from the nozzle exit. The peak temperatures near the nozzle exit are in the range of 12,500 to 14,000 K. The radial temperature profiles show an approximately self-similar decay in the near field of these plasma jets. It was also determined from time resolved intensity measurements that there are significant fluctuations in the argon emission intensity with increasing hydrogen fraction in the mixture. These fluctuations with a typical frequency of 5.2 kHz are attributed to the arc root instabilities observed before. Finally, the measured plasma temperature field is empirically correlated in terms of radial and axial coordinates, plasma electrical input power, plasma efficiency, and gas composition. These temperature data can be used to validate numerical simulations as well as in choosing locations where different materials can be introduced into the plasma jets. This is particularly important for “nanostructured” materials, which loose their structure upon melting as a result of being exposed to high plasma temperatures.

Overdense Plasma Production in a Low-power Microwave Discharge Electron Source

Plasma characterization of a low-power microwave discharge electron source was conducted. The electron source, which was developed for the neutralization of the 150 mA-class ion beam exhausted from an ion thruster, consists of a small discharge chamber of 18 mm diameter, into which an L-shape antenna is directly inserted into the magnetic circuit comprised of permanent magnets and iron yokes. An overdense plasma production for the 4.2 GHz microwave was observed for an input power range from 3 to 26 W and for the mass flow rate of 0.5–2.0 sccm. In such a wide range, the plasma density inside the discharge chamber can be proportionally increased as the microwave input power. This is because the direct insertion of the microwave antenna into the ECR magnetic field removes the accessibility difficulty of the microwave, and enables energy transmission from the antenna to the plasma even in the overdense mode. In addition, high-energy electrons above the ionization energy were observed for the large microwave input power above 10 W, and these electrons from the antenna also contribute to plasma production.

Forced convection boiling in a microchannel heat sink

Micromachining technology was utilized to fabricate a transparent microchannel heat-sink system by bonding glass to a silicon wafer. The micro heat sink consisted of a microchannel array, a heater, and a temperature sensor array. This integrated microsystem allowed simultaneous qualitative visualizations of the flow pattern within the microchannels and quantitative measurements of temperature distributions, flow rates, and input power levels. Boiling curves of temperature as a function of the input power were established. No boiling plateau was observed in the boiling curves, consistent with our previously reported data but different from results reported for macrochannel heat sinks. Three stable boiling modes, depending on the input power level, have been distinguished from the flow patterns. Local nucleation boiling was observed in microchannels with a hydraulic diameter as small as 26 /spl mu/m at the lower input power range. At the higher input power range, a stable annular flow was the dominant boiling mode. Bubbly flow, commonly observed in macrochannels, could not be developed in the present microchannels. Consequently, no boiling plateau was detected in the boiling curves.

A channel-number insensitive erbium-doped fiber amplifier with automatic gain and power regulation function

The design scheme for an erbium-doped fiber amplifier (EDFA) with automatic channel-by-channel gain and power regulation function is discussed with much emphasis on the pump power control scheme and the requirement for feedback circuitry. Based on both wavelength and time-resolved simulation technique, an amplifier repeater employing novel high-speed automatic gain control (AGC) and automatic level control (ALC) functions is designed and implemented. The AGC and ALC scheme can suppress the transient power fluctuation of a surviving channel caused by adding or dropping all other channels less than 0.45 dB and keep output power constant over 9-dB input power range.

Gain-clamped fibre amplifier using an ASE end reflector

All-optical gain clamping in an erbium-doped fibre amplifier is demonstrated using a broadband fibre Bragg grating that reflects the amplified spontaneous emission centred at 1530 nm with a 14 nm bandwidth. Experiments on an eight-channel wavelength division multiplexing system show promise when the gain is clamped at 21 dB. Gain flatness is less than 0.6 dB across all channels and gain variation is about 0.2 dB over the input signal power range.

Improvement of the input power dynamic range for wavelength converters based on cross-gain modulation employing a probe power control loop

A technique for improving the input power dynamic range of wavelength converters based on cross-gain modulation in a semiconductor optical amplifier is presented. By experimentally investigating the effect of pump and probe powers on the operating performance in terms of power penalty for a conventional wavelength converter, we show that the optimal performance depends on the ratio of pump and probe powers coupled into the semiconductor optical amplifier in a certain input power range. Based upon the experimental result, a wavelength converter with a wide dynamic range has been proposed, in which the probe power is automatically adjusted to have the power proportional to the pump power. We show that a dynamic range of >20 dB is achievable for a 2.5 Gbit/s signal at a 2-dB penalty.

B-Spline Based, Large-Signal DC and Microwave-Model for SOI MOSFETs

We present a large/small-signal, non-quasi-static, charge conserving, SOI MOSFET modeling technique suitable for DC and high frequency circuit design. The device model is extracted from small signal microwave iso-thermal Y-parameter data and DC I–V characteristics. Low frequency dispersions associated with self-heating and floating body effects are verified to not limit the performance of this technique since it relies on both DC and transient I–V characteristics. The technique is applied to the modeling of a short-channel, partially depleted, SOI nMOSFET simulated on PISCES. The model generated is incorporated into a circuit simulator, which is used to perform large-signal transient and harmonic balance simulations. The transient I–V and gate charge extracted from the iso-thermal small-signal microwave Y-parameters, are in excellent agreement with the iso-thermal transient I–V and gate charge obtained from PISCES, respectively. The model topology is extended with a parasitic bipolar sub-circuit which automatically calculates the DC operating point for self-biasing circuits. Transient and non-linear power characterization results predicted with this model agree well with those obtained from PISCES for a wide range of input power drives. A complete electro-thermal model is proposed and verified to be able to predict temperature and transient I–V response.

A 1.9-GHz Direct Conversion Transmitter IC with Low Power On-Chip Frequency Doubler

A direct conversion transmitter IC including a proposed frequency doubler, a quadrature modulator, and a 3-bit variable attenuator was fabricated using BiCMOS technology with f_T of 12 GHz. This architecture employing frequency doubler is intended for realizing wireless terminals that are low in cost and small in size. The architecture is effective for reducing serious interference between PA and VCO by making the VCO frequency different from that of PA. The proposed frequency doubler comprises a current-driven 90° phase-shifter and an ECL-EXOR circuit for both low power operation and wide input power range of local oscillator (LO). The proposed frequency doubler keeps high output power even when rectangular wave from LO is applied owing to use of the current-driven 90° phase-shifter instead of a voltage-driven 90° phase-shifter. An LO leakage of less than −25 dBc, an image rejection ratio in excess of 45 dBc, and a maximum attenuation of 21 dB were measured. The transmitter IC successfully operates at LO power above −15 dBm and consumes 68 mA from 2.7 V power supply voltage. An active die size is 1.5 mm×3 mm.

All optical gain-locking in erbium-doped fiber amplifiers using double-pass superfluorescence

All optical gain-locking in an erbium-doped fiber amplifier (EDFA) is demonstrated. A double-pass superfluorescence is created by using a broad-band fiber reflector centered at 1530 nm at the output of the EDFA, to lock the gain at 21 dB. Experiments on an eight-channel wavelength-division-multiplexing system shows promise with gain variation between channels of less than 0.6 dB over the input signal power range. While, gain variation with input signal power is about 0.2 dB for all channels.