Mean Output Power Research Articles

50-Gb/s Direct Modulation of a 1.3-μm InGaAlAs-Based DFB Laser With a Ridge Waveguide Structure

We demonstrate 50-Gb/s direct modulation by using 1.3-μm distributed-feedback lasers with a ridge waveguide structure. We employed InGaAlAs material for a multiple-quantum well to obtain a low damping factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> , and fabricated a ridge waveguide structure buried in benzocyclobutene to realize a structure with a low parasitic capacitance. In addition, to obtain high maximum frequency relaxation oscillations fr, we designed the cavity length <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> ), and achieved a 3-dB-down frequency bandwidth of 34 GHz. We realized 50-Gb/s clear eye openings with a back-to-back configuration, and achieved a mean output power of over 5.0 dBm, and a dynamic extinction ratio of 4.5 dB. We measured the 50-Gb/s transmission characteristics, and obtained clear eye openings for transmissions over 20-, 40-, and 60-km single-mode fibers (SMF). We also measured the bit-error-rate performance, and obtained an error-free operation and a power penalty of less than 0.5 dB after a 10-km SMF transmission.

What is the best treatment to decrease pro-inflammatory cytokine release in acute skeletal muscle injury induced by trauma in rats: low-level laser therapy, diclofenac, or cryotherapy?

Currently, treatment of muscle injuries represents a challenge in clinical practice. In acute phase, the most employed therapies are cryotherapy and nonsteroidal anti-inflammatory drugs. In the last years, low-level laser therapy (LLLT) has becoming a promising therapeutic agent; however, its effects are not fully known. The aim of this study was to analyze the effects of sodium diclofenac (topical application), cryotherapy, and LLLT on pro-inflammatory cytokine levels after a controlled model of muscle injury. For such, we performed a single trauma in tibialis anterior muscle of rats. After 1h, animals were treated with sodium diclofenac (11.6mg/g of solution), cryotherapy (20min), or LLLT (904 nm; superpulsed; 700 Hz; 60 mW mean output power; 1.67 W/cm(2); 1, 3, 6 or 9 J; 17, 50, 100 or 150 s). Assessment of interleukin-1β and interleukin-6 (IL-1β and IL-6) and tumor necrosis factor-alpha (TNF-α) levels was performed at 6h after trauma employing enzyme-linked immunosorbent assay method. LLLT with 1J dose significantly decreased (p < 0.05) IL-1β, IL-6, and TNF-α levels compared to non-treated injured group as well as diclofenac and cryotherapy groups. On the other hand, treatment with diclofenac and cryotherapy does not decrease pro-inflammatory cytokine levels compared to the non-treated injured group. Therefore, we can conclude that 904 nm LLLT with 1J dose has better effects than topical application of diclofenac or cryotherapy in acute inflammatory phase after muscle trauma.

76 Less common indications for LLLT

Burn wounds exhibit impaired healing as the progression through the normal sequential stages of tissue repair gets hampered by epidermal barrier disruption, compromised blood circulation, abrogated defence mechanism, pathologic inflammation, and septicemia. Our earlier results reported that superpulsed 904 nm LLLT enhanced healing and attenuated inflammatory response in burn wounds. The present study investigated the effect of superpulsed 904 nm LLLT (200 ns pulse width; 100 Hz; 0.7 mW mean output power; 0.4 mW/cm2 average irradiance) on biochemical and molecular markers pertaining to bioenergetics and redox homeostasis on full-thickness burn wounds in experimental rats. Results indicated that superpulsed laser irradiation for 7 days post-wounding propelled the cellular milieu towards aerobic energy metabolism as evidenced by significantly enhanced activities of key energy regulatory enzymes viz. HK, PFK, CS and G6PD, whereas LDH showed reduced activity as compared to the non-irradiated controls. LLLT showed a significant increased CCO activity and ATP level. Moreover, LLLT also regulated redox homeostasis as evidenced by enhanced NADPH levels and decreased NADP/NADPH ratio. Western blot analysis demonstrated that LLLT produced an up-regulation of GLUT1, pAMPKα and down-regulation of glycogen synthase1 (GS1). Our findings suggest that superpulsed 904 nm LLLT augments burn wound healing by enhancing intracellular energy contents through modulation of aerobic metabolism for maximum energy output. Bioenergetic activation and maintenance of redox homeostasis could be one of the noteworthy mechanisms responsible for the beneficial NIR photobiomodulatory effect mediated through superpulsed 904 nm LLLT in burn wound healing.

78 Photodynamic therapy in treating peritonitis (experimental study)

Burn wounds exhibit impaired healing as the progression through the normal sequential stages of tissue repair gets hampered by epidermal barrier disruption, compromised blood circulation, abrogated defence mechanism, pathologic inflammation, and septicemia. Our earlier results reported that superpulsed 904 nm LLLT enhanced healing and attenuated inflammatory response in burn wounds. The present study investigated the effect of superpulsed 904 nm LLLT (200 ns pulse width; 100 Hz; 0.7 mW mean output power; 0.4 mW/cm2 average irradiance) on biochemical and molecular markers pertaining to bioenergetics and redox homeostasis on full-thickness burn wounds in experimental rats. Results indicated that superpulsed laser irradiation for 7 days post-wounding propelled the cellular milieu towards aerobic energy metabolism as evidenced by significantly enhanced activities of key energy regulatory enzymes viz. HK, PFK, CS and G6PD, whereas LDH showed reduced activity as compared to the non-irradiated controls. LLLT showed a significant increased CCO activity and ATP level. Moreover, LLLT also regulated redox homeostasis as evidenced by enhanced NADPH levels and decreased NADP/NADPH ratio. Western blot analysis demonstrated that LLLT produced an up-regulation of GLUT1, pAMPKα and down-regulation of glycogen synthase1 (GS1). Our findings suggest that superpulsed 904 nm LLLT augments burn wound healing by enhancing intracellular energy contents through modulation of aerobic metabolism for maximum energy output. Bioenergetic activation and maintenance of redox homeostasis could be one of the noteworthy mechanisms responsible for the beneficial NIR photobiomodulatory effect mediated through superpulsed 904 nm LLLT in burn wound healing.

Field Evaluation of the Human Exposure From Multiband, Multisystem Mobile Phones

Mobile phones present the strongest source of radiofrequency electromagnetic held exposure to the human head. Mobile phones are routinely assessed with respect to safety by specihc absorption rate measurements at maximum output power. The difference of the exposure due to power control during normal usage was evaluated. A mobile measurement system to assess the effect of the power control in real networks was developed. It presents a realistic load to the phone and is able to measure the output power and band synchronously for the GSM900, DCS1800, and UMTS1950 bands. The system has a dynamic range of 60 dB and a measurement uncertainty of <;1 dB for GSM and <;1.5 dB for UMTS. Using the system, three mobile phones were evaluated in the three Swiss networks in urban and rural areas. The phones were tested in dual system (GSM and UMTS) and GSM only modes. The results show a small change of the mean output power in GSM mode (from -2 to -10 dB) compared to 30-dB power control dynamic range. The mean output power in UMTS was a factor >100 lower than GSM. In urban areas, UMTS was generally available and preferably used by the phones with rare fall backs to GSM. In the suburban/rural area, UMTS was hardly available or used by the phones.

High-bandwidth generation of duobinary and alternate-mark-inversion modulation formats using SOA-based signal processing

We report on the novel all-optical generation of duobinary (DB) and alternate-mark-inversion (AMI) modulation formats at 42.6 Gb/s from an input on-off keyed signal. The modulation converter consists of two semiconductor optical amplifier (SOA)-based Mach-Zehnder interferometer gates. A detailed SOA model numerically confirms the operational principles and experimental data shows successful AMI and DB conversion at 42.6 Gb/s. We also predict that the operational bandwidth can be extended beyond 40 Gb/s by utilizing a new pattern-effect suppression scheme, and demonstrate dramatic reductions in patterning up to 160 Gb/s. We show an increasing trade-off between pattern-effect reduction and mean output power with increasing bitrate.

Simulation of a Duffing oscillator for broadband piezoelectric energy harvesting

Vibration energy harvesters are usually resonant mechanical systems working at resonance.The subsequent mechanical amplification results in output powers multiplied by themechanical quality factor when compared to non-resonant systems. The maindrawback is the difficulty of matching a given vibration frequency range to theenergy harvester’s resonance frequency. Among several techniques, the use ofnonlinear mechanical resonators was proposed in several studies for enlarging energyharvester power bandwidth. In addition, microelectromechanical systems becomenonlinear when driven even at moderate levels due to their small size. This paperis devoted to a theoretical study of a Duffing oscillator exhibiting piezoelectricelectromechanical coupling. After presenting the dimensionless model, it is solved both inthe frequency domain and in the time domain. The frequency-domain simulationsshow that a huge gain in bandwidth is possible when the resonator is highlynonlinear. Special attention has been paid to the influence of electromechanicalcoupling. However, this encouraging result is counterbalanced by the difficultyto make the resonator reach high level vibration. Indeed, the Duffing oscillatorexhibits a frequency range where two harmonic solutions are possible. When excitedwith sine bursts or colored noise, the oscillator remains most of the time on thelowest solution. From simulations in the time domain, it is shown that fast burstperturbation (FBP) applied to the piezoelectric voltage may induce the jump from lowestsolution to highest solution. Consequently a huge gain may be expected in outputpower. Finally, the resonator is excited with colored noise and the previouslydeveloped strategy is applied. Once again, the mean output power may be greatlyenhanced.

An experimental study of low-level laser therapy in rat Achilles tendon injury

The aim of this controlled animal study was to investigate the effect of low-level laser therapy (LLLT) administered 30 min after injury to the Achilles tendon. The study animals comprised 16 Sprague Dawley male rats divided in two groups. The right Achilles tendons were injured by blunt trauma using a mini guillotine, and were treated with LLLT or placebo LLLT 30 min later. The injury and LLLT procedures were then repeated 15 hours later on the same tendon. One group received active LLLT (λ = 904 nm, 60 mW mean output power, 0.158 W/cm2 for 50 s, energy 3 J) and the other group received placebo LLLT 23 hours after LLLT. Ultrasonographic images were taken to measure the thickness of the right and left Achilles tendons. Animals were then killed, and all Achilles tendons were tested for ultimate tensile strength (UTS). All analyses were performed by blinded observers. There was a significant increase in tendon thickness in the active LLLT group when compared with the placebo group (p < 0.05) and there were no significant differences between the placebo and uninjured left tendons. There were no significant differences in UTS between laser-treated, placebo-treated and uninjured tendons. Laser irradiation of the Achilles tendon at 0.158 W/cm2 for 50 s (3 J) administered within the first 30 min after blunt trauma, and repeated after 15 h, appears to lead to edema of the tendon measured 23 hours after LLLT. The guillotine blunt trauma model seems suitable for inflicting tendon injury and measuring the effects of treatment on edema by ultrasonography and UTS. More studies are needed to further refine this model.

New Adaptive All-pass Based Notch Filter for Narrowband/FM Anti-jamming GPS Receivers

The global positioning system (GPS), which provides accurate positioning and timing information, has become a commonly used navigation instrument for many applications. The application of a new adaptive all-pass based notch filter (ANFA) for narrowband/FM interference suppression and frequency estimation in GPS receivers is proposed. An ANFA structure that achieves better unbiased characteristics with its coefficients is employed to accurately estimate the narrowband interfering signals in online fashion. A variable convergence factor that optimizes the maximal mean square error (MSE) reduction in each iteration is applied in a modified adaptive Gaussian–Newton (MAGN) algorithm. The proposed MAGN algorithm can lead to both faster convergence speed and higher estimation accuracy. Simulation results show that the ANFA offers a better performance than conventional linear predictors in terms of the SNR improvement and the mean output power (MOP) under the interference environments of interest.

Dysprosium-doped PbGa_2S_4 laser excited by diode-pumped Nd:YAG laser

We realized a compact mid-IR room temperature operating Dy(3+):PbGa(2)S(4) laser, excited by a diode-pumped Nd:YAG laser at a wavelength of 1318 nm. The pumping laser was operating in pulsed mode with a pulse length of 4 ms and repetition rate of 20 Hz. Maximum pumping energy at a wavelength of 1318 nm was 15 mJ. Energy up to 90 μJ and mean output power of 1.8 mW was obtained at a wavelength of 4290 nm with a slope efficiency with respect to absorbed pumping energy better than 3%.

Highly-stable monolithic femtosecond Yb-fiber laser system based on photonic crystal fibers

A self-starting, passively stabilized, monolithic all-polarization- maintaining femtosecond Yb-fiber master oscillator / power amplifier with very high operational and environmental stability is demonstrated. The system is based on the use of two different photonic crystal fibers. One is used in the oscillator cavity for dispersion balancing and nonlinear optical limiting, and another one is used for low-nonlinearity final pulse recompression. The chirped-pulse amplification and recompression of the 232-fs, 45-pJ/pulse oscillator output yields a final direct fiber-end delivery of 7.3-nJ energy pulses of around 297 fs duration. Our laser shows exceptional stability. No Q-switched modelocking events were detected during 4-days long observation. An average fluctuation of only 7.85 x 10(-4) over the mean output power was determined as a result of more than 6-hours long measurement. The laser is stable towards mechanical disturbances, and maintains stable modelocking in the temperature range of at least 10 - 40 (0)C.

Emission characteristics and parameters of gas-discharge plasma in mixtures of heavy inert gases with chlorine

The ultraviolet (UV) radiation from longitudinal glow-discharge plasma in three- and four-component mixtures of argon, krypton, and xenon with chlorine has been investigated. The total radiation of Ar, Kr, and Xe monochlorides and chlorine molecules in the spectral range 170–310 nm has been optimized with respect to the composition and the pressure of gas mixtures, as well as the discharge current. The mean output power, the electric power of discharge, and the efficiency of a broadband low-pressure exciplex halogen lamp have been determined. Parameters of the glow discharge in Ar-Kr-Cl2 and Kr-Xe-Cl2 mixtures have been simulated numerically. The electron energy distribution functions have been determined through the solution of the Boltzmann kinetic equation. These functions have been used to calculate the plasma parameters, namely, electron transfer characteristics, specific losses of discharge power for electronic processes, and ionization and attachment coefficients.

Converting solar energy into laser radiation using a fullerene-oxygen-iodine laser with solar pumping

The concept of a system for directly converting solar energy into laser radiation on the basis of a fullerene-oxygen-iodine laser has been developed. It is shown that this system has advantages and is competitive with other similar solar-energy-conversion systems. Various versions of singlet-oxygen generators based on solid-phase fullerene-containing structures are analyzed. Based on this analysis, it is concluded that such a generator needs to be operated with molecular oxygen passing through a porous fullerene-containing coating deposited on a substrate with a porous structure to compensate the loss of oxygen in the coating as it undergoes photodesorption. Experimental research into the processes of solar-energy conversion into laser radiation has been carried out, using a prototype that has been developed of a fullerene-oxygen-iodine laser with pumping by a solar-radiation simulator. Lasing in the pulsed-periodic regime of laser operation has been obtained, with repetition rate 10Hz and mean output power 30W. Lasing energy per unit volume of the active medium of 9J∕L has been achieved.

双前向同步抽运的稳定L波段超荧光光纤光源特性

We investigate the characteristics of the dual-forward synchronously pumped L-band erbium-doped superfluorescent fiber source (SFS). The effects of pump ratio and fiber length arrangements on the output characteristics of the L-band SFS in terms of mean wavelength, spectral linewidth, and output power are analyzed. It is shown that the optimized pump ratio and fiber length arrangements provide broadening spectral linewidth and enhanced pumping efficiency, while the synchronous pump ensures stable mean wavelength operation. A new single-forward pumping scheme with a section of unpumped fiber is proposed to achieve a mean wavelength stable L-band SFS with a broadening linewidth of 50.4 nm and a pumping efficiency of 33.5%.

High stability mono-wavelength output optical fiber laser based on polarization-maintaining erbium-doped fiber

A photosensitive polarization-maintaining erbium-doped fiber was fabricated experimentally and a high efficiency resonance cavity was set up by writing three fiber Bragg gratings on this fiber using UV laser. The mono-wavelength laser with mean output power of 9.20dBm and mean wavelength of 1554.554nm was produced by pumping at a power of 23.617dBm and wavelength of 976nm. The fluctuations of output power and wavelength were less then ±0.05dB and ±0.0015nm for a test time of 800min, respectively, at room temperature.

Broadband Interference Suppression Performance of Minimum Redundancy Arrays

The broadband interference suppression performance of the minimum redundancy array (MRA) used in the linearly constrained minimum variance (LCMV) beamformer is studied in this paper. The ideal continuous-time, infinite-length filter instead of the realistic finite-order digital filter is assumed in the array processor. The expressions of the power spectrum of the beamformer output in different scenarios are derived to compute the mean output power. Several original properties of the performance of the MRA compared with that of the uniform linear array (ULA) are obtained by mathematical proofs and numerical studies.

Investigation of the conditions of efficient I*2 (342 nm) luminescence in a barrier discharge in a Kr-I2 mixture

The energy and spectral characteristics of a barrier discharge in a mixture of iodine vapor with krypton have been investigated theoretically and experimentally. The emission spectrum consists of the single I*2 molecular band D′ → A′ peaking at 342 nm, the iodine resonance line at 206.2 nm, and the group of bands corresponding to iodine emission. The highest intensity of the I*2 (342 nm) band was obtained at a mixture pressure near 450 Torr. A mean output power and an efficiency of 550 mW and 1.6%, respectively, have been achieved. It is shown that, for the I2 barrier-discharge excilamp, the homogeneous, rather than filamentary form of discharge glow is optimal from the viewpoint of the highest mean output power. The maximal calculated value of the emission efficiency for the 342-nm band was 5%. The main processes determining energy losses in plasma have been found, and ways to increase the efficiency of emission in the D′ → A′ band of the I*2 molecule have been proposed.

Comparison of evaporative inlet air cooling systems to enhance the gas turbine generated power

The gas turbine performance is highly sensitive to the compressor inlet temperature. The output of gas turbine falls to a value that is less than the rated output under high temperature conditions. In fact increase in inlet air temperature by 1°C will decrease the output power by 0.7% approximately. The solution of this problem is very important because the peak demand season also happens in the summer. One of the convenient methods of inlet air cooling is evaporating cooling which is appropriate for warm and dry weather. As most of the gas turbines in Iran are installed in such ambient conditions regions, therefore this method can be used to enhance the performance of the gas turbines. In this paper, an overview of technical and economic comparison of media system and fog system is given. The performance test results show that the mean output power of Frame-9 gas turbines is increased by 11 MW (14.5%) by the application of media cooling system in Fars power plant and 8.1 MW (8.9%) and 9.5 MW (11%) by the application of fog cooling system in Ghom and Shahid Rajaie power plants, respectively. The total enhanced power generation in the summer of 2004 was 2970, 1701 and 1340 MWh for the Fars, Ghom and Shahid Rajaie power plants, respectively. The economical studies show that the payback periods are estimated to be around 2 and 3 years for fog and media systems, respectively. This study has shown that both methods are suitable for the dry and hot areas for gas turbine power augmentation. Copyright © 2007 John Wiley & Sons, Ltd.

Q-switched chemical cw HF laser

The characteristics of a cw chemical HF laser mechanically Q-switched at a frequency of up to 1000 Hz are studied. It is shown that the peak power of laser pulses increases by a factor of at least five for modulation frequencies from 17 to 250 Hz. The mean output power in the repetitively pulsed mode is appreciably lower than that in the cw lasing mode, but, as the modulation frequency increases (within the same frequency range), the mean power rises more rapidly than the peak power does. The possible factors causing the revealed discrepancies between the experimental and calculated laser characteristics are considered.

Porosity reduction in Nd–YAG laser welding of stainless steel and inconel alloy by using a pulsed wave

This study investigates the influence of the Nd–YAG laser power wave mode on the porosity and mechanical properties of SUS 304L and inconel 690 weldments. Initially, a rectangular laser power waveform is specified. The output is then progressively changed from a pulsed wave mode to a continuous wave mode by reducing the value of ΔP (ΔP = Pp−Pb, where Pp is the peak power and Pb is the base power) to zero. Bead-on-plate (BOP) and butt welding are performed at a constant mean output power (1.7 kW). The BOP results demonstrate that the depth/width (D/W) ratio of both materials increases with ΔP and attains a maximum value when full penetration just occurs. The D/W ratio and the travel speed for full penetration are higher for SUS 304L than for inconel 690. In butt-welds of inconel 690 and SUS 304L, the porosity ratio decreases from 7.1% to 0.5% and from 2.1% to 0.5%, respectively, as ΔP increases from 0 to 2780 W. Therefore, the tensile strength and percentage elongation are enhanced significantly in inconel 690. The degree of porosity reduction in inconel 690 exceeds that of SUS 304L. This suggests that the viscosity of the molten inconel 690 metal is higher than that of SUS 304L. Consequently, the effect of porosity reduction due to the increase in molten metal fluidity caused by increasing ΔP is greater for inconel 690 than for SUS 304L.