Input Peak Power Research Articles

High-efficiency Raman conversion in SF6- and CF4-filled hollow-core photonic bandgap fibers.

We present a comparative experimental investigation of vibrational stimulated Raman scattering in hollow-core photonic bandgap fibers pressurized with sulfur hexafluoride (${{\rm SF}_6}$SF6) and tetrafluoromethane (${{\rm CF}_4}$CF4) gases. Nanosecond-duration pulses at a wavelength of 1030 nm are coupled into the gas-filled fiber, and the first and second Stokes orders are measured at the fiber output. We characterize the conversion process as a function of gas, fiber length, and input power. With a 15 m fiber filled with ${{\rm SF}_6}$SF6, we obtain conversion efficiency to the first Stokes of 55.7% at an input peak power of 0.63 kW. In comparison, with ${{\rm CF}_4}$CF4, we obtained a higher conversion threshold and maximum conversion efficiency of 45.4%. To the best of our knowledge, this is the first reported conversion experiment with hollow-core fibers filled with ${{\rm SF}_6}$SF6 gas.

Narrowband ultraviolet generation in dispersion-shifted few-mode fiber via combined effect of intermodal four-wave mixing and nonlinear mode coupling

We report here the first experimental demonstration of the generation of narrowband ultraviolet wavelength in a few-mode dispersion shifted fiber utilizing the intermodal phase matching between the first two guided modes (LP01 & LP11) of the fiber. An intense anti-Stokes wave in mixed mode states (LP01 & LP11) is observed at 416.8 nm for a Q-switched nanosecond pump pulse in the LP01 mode at 532 nm. A nonlinear modal conversion of these anti-Stokes waves with non-zero angular momentum (LP11 modes) to zero-angular momentum (LP01 mode) has also been witnessed for the first time. The anti-Stokes line with LP01 modal component then acts as the secondary pump to produce discrete UV peaks at 341.6 nm with linewidth of 1.3 nm via cascaded intermodal four-wave mixing at an input peak power of 4.88 kW. A four-fold enhancement of conversion efficiency in cascaded intermodal four-wave mixing is achieved when compared to standard single mode fiber.

Characterization of power input and its impact on mass transfer in a rocking disposable bioreactor

The impact of specific power input on gas-liquid mass transfer and mixing has not been extensively reported for rocking disposable bioreactors. An electrical method was applied for measuring the specific power input into a disposable rocking (Wave) bioreactor at benchtop scales. The peak power input was shown to be suitable for characterizing the impact of operational parameters including rocking frequency, rocking angle and liquid volume. The average power inputs ranged from 66.5 W/m3 to 680.1 W/m3 which were comparable to those for stirred tank and orbitally-shaken disposable bioreactors. The gas-liquid oxygen mass transfer coefficient was shown to correlate with the peak power input in a power law model, confirming that the mass transfer capacity rapidly increased with power input, especially at 600 W/m3 and greater. The correlation between mixing time and power input indicated that power input at higher than 400 W/m3 was sufficient to induce relatively rapid mixing.

Numerical study on nonlinear and chaotic effects in standard fibre using RK4IP method

In this paper, we carry out a numerical study on nonlinear and chaotic effects produced by the propagation of hyperbolic secant optical pulse in standard fibre. We use the fourth-order Runge–Kutta in the interaction picture (RK4IP) method to analyse the pulse interaction in the fibre medium, this method was employed due to its potential to reduce the numerical error while simultaneously allow increasing the step size. During the study, the input peak power was varied up hundreds of kW trough 1 km of standard single-mode fibre (SMF-28); as a consequence, it was possible to observe the generation of nonlinear and chaotic effects on the final spectrum. These numerical results show the spectral and temporal evolution of energy in a 3D rendering, here, it was possible to demonstrated break frequencies and fragmentation of packets of energy by changing the pump power. Finally, we show that this analysis can be used in subsequent studies employing complex dynamic pulses (noise-like pulses, NLPs).

Influence of the spatial confinement on the self-focusing of ultrashort pulses in hollow-core fibers

The collapse of a laser beam propagating inside a hollow-core fiber is investigated by numerically solving different nonlinear propagation models. We have identified that the fiber confinement favors the spatial collapse, especially in case of pulses with the input peak power close to the critical value. We have also observed that when using pulses in the femtosecond range, the temporal dynamics plays an important role, activating the spatial collapse even for pulses with input peak powers below the critical value. The complex self-focusing dynamics observed in the region below the critical power depends on the temporal evolution of the pulse and, also, on the interaction between the different spatial modes of the hollow-core fiber.

Greater than 50 times compression of 1030 nm Yb:KGW laser pulses to single-cycle duration

Generation of octave-spanning spectrum that spans from 570 nm to 1300 nm utilizing 1030 nm 170 fs pulses from a Yb:KGW laser and a two-stage multiple-plate arrangement is demonstrated. 3.21 fs sub-single-cycle pulses are obtained after dispersion compensation. The high compression ratio of more than 50 times is achieved for two scenarios with widely different parameters including high input peak power at 1 kHz repetition rate and modest peak power at a high repetition rate of 100 kHz. The output pulses have good spatial mode quality and exhibit long-term stability. The achieved compression ratio and flexibility are unprecedented in ultrafast pulse compression to single-cycle regime. The experiments demonstrate that the technique of multiple-plate pulse compression is versatile and applicable for a wide range of laser pulse parameters.

Mid-infrared supercontinuum generation and its application on all-optical quantization with different input pulses**Project supported by the National Natural Science Foundation of China (Grant Nos. 61307109 and 61475023).

Supercontinuum generation (SCG) and its application on all-optical quantization of all-optical analog-to-digital conversions (AOADCs) at the mid-infrared region in an AlGaAs strip waveguide are investigated numerically. The simulation results show that when the parabolic pulse is input, not only broader and higher-coherence SCG is obtained and a higher effective number of bits (ENOB) can be achieved, compared with the input pulse with hyperbolic-secant and Gaussian shaping. A four-bit quantization resolution is achieved along with a signal-to-noise ratio of 24.02 dB and an ENOB of 3.99 bit, and the required input peak power is 760 mW.

Efficient Spectral Compression of Wavelength-Shifting Soliton and Its Application in Integratable All-Optical Quantization

In this paper, we numerically demonstrate efficient spectral compression (SPC) of wavelength-shifting soliton in a chalcogenide strip waveguide. It is found that the profiles of group-velocity dispersion (GVD) and Kerr nonlinearity play key roles in determining SPC. After calculating the dispersion of Kerr nonlinearity and Raman spectrum for three kinds of chalcogenide materials, Ge11.5As24Se64.5 is chosen as the material for designing the chalcogenide strip waveguide (CSW). The geometric parameters of CSW are optimized to obtain the desired GVD and Kerr nonlinearity. Simulation results show that in the designed CSW, an input spectrum width of 52.04 nm can be compressed to 7.23 nm along with wavelength shift of 17 nm when the input peak power is 25 W. With the input peak power increasing to 75 W, the SPC is slightly weakened, but wavelength shift can be up to 190 nm. The proposed CSW is applied to integrated all-optical quantization and an effective quantization number of 3.66-bit is achieved. It is expected that our research results can find important applications in on-chip integrated spectroscopy, all-optical signal processing, etc.

Compression of femtosecond pulses in a wide wavelength range using a large-mode-area tapered fiber

We report the design of a tapered fiber that can be used for the compression of pulses at different central wavelengths. The proposed fiber is a three-layer W-type large-mode-area fiber, which has been tapered to transform the mode area from 1700 µm2 to 900 µm2. We determine the exact length of the maximum pulse compression and numerically demonstrate the compression of a 250 fs, 100 kW peak power input pulse to 15 fs, 850 kW at 1.55 µm wavelength and compression of 250 fs, 120 kW peak power input pulses to 28 fs, 700 kW and to 46 fs, 500 kW at 1.8 µm and 2 µm wavelengths, respectively. Such a fiber can find wide ranging applications, including in communication, spectroscopy and medicine.

MULTI® - rope-less elevator demonstrator at test tower Rottweil

Background: The world’s first linear motor driven passenger elevator system MULTI® started test operation at test tower Rottweil, Germany. A full scale showcase has been installed, the commissioning is finished and extensive testing activities are performed. The new test tower in Rottweil provides the perfect test and certification environment to get this ground-breaking product onto the market.
 The propulsion of the cars is based on an ironless long-stator linear motor with distributed active drive, motor and sensor elements. This technology allows cars to move individually in the same elevator shaft without any ropes. The same type of linear motor will also be used to exchange cars horizontally from one shaft to another. Herewith a movement of the cars in a loop or any vertical and horizontal travel path can be realized. The testing procedures to characterize the operation of the MULTI® include measurements of electrical, mechanical and thermal quantities.
 Smart energy management feeds power of descending cars for rising cars. To overcome the high power demand for acceleration cars, an energy buffering system is installed.
 Aim: This paper focuses on the power and energy management of the MULTI® demonstrator. The benefit of intelligent buffering strategy is depicted.
 Methods: Full scale prototype, numerical simulation, testing and measurement. 
 Results: This paper presents first measurement results of the MULTI® demonstrator mainly focusing on the power and energy characteristics of the propulsion system.
 Conclusion: Using an energy buffering system, the peak input power of the MULTI® can be reduced to 50% of the peak power level without energy buffer. The power from downward moving cars is recuperated and used for upward driving cars, balanced by the energy buffer without stressing the grid.

A Compact MW-Class Short Pulse Generator

A megawatt-range short pulse generator based on the diode step recovery phenomenon and the Marx generator idea is presented. This generator utilizes both opening and closing switches in one circuit. The proposed circuit is compact, light, and low cost and is driven by a low-power source. By using a three-stage Marx generator, the output peak power of 0.6 MW was obtained. The dimensions of the generator are 8 cm $\times8$ cm. Experimental measurements of the output pulse characteristics showed a rise time of 100 ns for a 16- $\Omega $ load. The input peak power was 4 W which showed more than 105 times increase in the pulse peak power.

Design of dispersion-engineered As2Se3 channel waveguide for mid-infrared region supercontinuum generation

In recent years, low cost and scalable integrated optics compatible planar waveguides have emerged for an ultrabroadband supercontinuum generation between ultraviolet and mid-infrared region applications. A 20-mm-long integrated photonics compatible highly nonlinear As2Se3 channel waveguide, which exhibited wider as well as lower magnitude and nearly flat anomalous dispersion region, designed and modeled by employing GeAsSe glass for its upper and lower claddings. Using pump source at 6 μm with a pulse duration of 170-fs, an ultrabroadband long wavelength region supercontinuum broadening covering the wavelength from 3.5 μm to 15 μm could be predicted with the largest input peak power of 10 kW. Increasing the power further to 20 kW does not enhance the supercontinuum expansion noticeably beyond 15 μm. This numerical demonstration could be the longest supercontinuum generation by an on-chip integrated photonics compatible planar waveguide which can be used for a variety of mid-infrared region applications.

Modeling of dispersion engineered chalcogenide rib waveguide for ultraflat mid-infrared supercontinuum generation in all-normal dispersion regime

A rigorous numerical investigation has been carried out through dispersion engineering of chalcogenide rib waveguide for near-infrared to mid-infrared ultraflat broadband supercontinuum generation in all-normal group-velocity dispersion regime. We propose a novel design of a 1-cm-long air-clad rib waveguide which is made from $$\text {Ge}_{11.5}\text {As}_{24}\text {Se}_{64.5}$$ chalcogenide glass as the core with either silica or $$\text {Ge}_{11.5}\text {As}_{24}\text {S}_{64.5}$$ chalcogenide glass as a lower cladding separately. A broadband ultraflat supercontinuum spanning from 1300 to 1900 nm could be generated when pumped at 1.55 $$\upmu \text {m}$$ with a low input peak power of 100 W. Shifting the pump to 2 $$\upmu \text {m}$$ , the supercontinuum spectra extended in the mid-infrared region up to 3400 nm with a moderate-input peak power of 500 W. To achieve further extension in mid-infrared, we excite our optimized rib waveguide in both the anomalous and all-normal dispersion pumping regions at 3.1 $$\upmu \text {m}$$ with a largest input peak power of 3 kW. In the case of anomalous dispersion region pumping, numerical analysis shows that supercontinuum spectrum can be extended in the mid-infrared up to 10 $$\upmu \text {m}$$ , although this contains high spectral amplitude fluctuations over the entire bandwidth which limits the supercontinuum sources in the field of high precision measurement applications. On the other hand, by optimizing a rib waveguide geometry for pumping in all-normal dispersion region, we are able to generate a smooth and flat-top coherent supercontinuum spectrum with a moderate bandwidth spanning the wavelength range 2–5.5 $$\upmu \text {m}$$ with less than 5 dB spectral fluctuation over the entire output bandwidth. Our proposed design is highly suitable for making on-chip SC light sources for a variety of applications such as biomedical imaging, and environmental and industrial sensing in the mid-infrared region.

Enhanced optical nonlinearities in CMOS-compatible ultra-silicon-rich nitride photonic crystal waveguides

We present the design, fabrication, and characterization of photonic crystal waveguides (PhCWs) on an ultra-silicon-rich nitride (USRN) platform, with the goal of augmenting the optical nonlinearities. The design goals are to achieve an optimized group index curve on the PhCW band edge with a non-membrane PhCW with symmetric SiO2 undercladding and overcladding, so as to maintain back-end CMOS compatibility and better structural robustness. Linear optical characterization, as well as nonlinear optical characterization of PhCWs on ultra-silicon-rich nitride is performed at the telecommunication wavelengths. USRN's negligible two-photon absorption and free carrier losses at the telecommunication wavelengths ensure that there is no scaling of two-photon related losses with the group index, thus maintaining a high nonlinear efficiency. Self-phase modulation experiments are performed using a 96.6 μm PhCW. A 1.5π phase shift is achieved with an input peak power of 2.5 W implying an effective nonlinear parameter of 1.97 × 104 (W m)−1. This nonlinear parameter represents a 49× enhancement in the nonlinear parameter from the slow light effect, in good agreement with expected scaling from the measured group index.

Ultra-broad Mid-IR Supercontinuum Generation in Single, Bi and Tri Layer Graphene Nano-Plasmonic waveguides pumping at Low Input Peak Powers

This article presents four different plasmonic structures using Graphene which yielded an efficient plasmonic mode with low loss for Supercontinuum(SC) generation. At an operating wavelength of 1550 nm in these structures, we generated a multi-octave broadband SC spectrum ranging from 1.5 um–25 um at a low input peak power of 1 W. Due to pumping in the anomalous dispersion region with two Zero Dispersion Wavelengths (ZDWs) and the process of cross phase modulation with soliton fission, red-shifted dispersive waves were generated which led to large broadening from 1.5 um–25 um. Two other Supercontinua ranging from 1–10 um and 0.85–2.2 um also at low input peak powers of 2 W and 0.1 W respectively were generated. These three supercontinua are useful for applications in the fields of biomedical sensors, spectroscopy, fluorescence lifetime imaging and in the design of many other new optical devices. Furthermore, we have also discussed our results on behaviour of Graphene as a metal, even without the negative real value of dielectric constant.

DSRD-Based High-Power Repetitive Short-Pulse Generator Containing GDT: Theory and Experiment

A high-power short-pulse generator based on the diode step recovery phenomenon and high repetition rate discharges in a two-electrode gas discharge tube is presented. The proposed circuit is simple and low cost and driven by a low-power source. A full analysis of this generator is presented which, considering the nonlinear behavior of the gas tube, predicts the waveform of the output pulse. The proposed method has been shown to work properly by implementation of a kW-range prototype. Experimental measurements of the output pulse characteristics showed a rise time of 3.5 ns, with pulse repetition rate of 2.3 kHz for a 47- $\Omega $ load. The input peak power was 2.4 W, which translated to about 0.65-kW output, showing more than 270 times increase in the pulse peak power. The efficiency of the prototype was 57%. The overall price of the employed components in the prototype was less than U.S. $2.0. An excellent agreement between the analytical and experimental test results was established. The analysis predicts that the proposed circuit can generate nanosecond pulses with more than 100-kW peak powers by using a subkW power supply.

Secrecy sum-rate of multi-user MISO visible light communication systems with confidential messages

This paper studies the information theoretic secrecy sum-rate for multi-user multiple-input single-output (MU-MISO) visible light communication (VLC) systems with confidential messages. The well-known zero-forcing (ZF) precoding technique is employed to ensure confidentiality among legitimate users and, at the same time, to prevent eavesdropper(s) from obtaining any information. Different from radio frequency (RF) counterpart where the average input power constraint is usually imposed on the derivation of channel capacity, the input data signal of VLC systems is amplitude constrained, leading to a peak input power constraint. The amplitude constraint gives rise to the complexity in obtaining an analytical expression for the capacity. In this paper, we analytically investigate a novel bound on the secrecy sum-rate of all legitimate users in MU-MISO VLC systems, which is valid in high signal-to-noise ratio (SNR) regime. The secrecy sum-rate performance is then derived for two scenarios: known and unknown eavesdropper's channel state information (CSI) at the transmitter.

Development of new S-band RF window for stable high-power operation in linear accelerator RF system

For stable high-power operation, a new RF window is developed in the S-band linear accelerator (Linac) RF systems of the Pohang Light Source-II (PLS-II) and the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL). The new RF window is designed to mitigate the strength of the electric field at the ceramic disk and also at the waveguide-cavity coupling structure of the conventional RF window. By replacing the pill-box type cavity in the conventional RF window with an overmoded cavity, the electric field component perpendicular to the ceramic disk that caused most of the multipacting breakdowns in the ceramic disk was reduced by an order of magnitude. The reduced electric field at the ceramic disk eliminated the Ti–N coating process on the ceramic surface in the fabrication procedure of the new RF window, preventing the incomplete coating from spoiling the RF transmission and lowering the fabrication cost. The overmoded cavity was coupled with input and output waveguides through dual side-wall coupling irises to reduce the electric field strength at the waveguide-cavity coupling structure and the possibility of mode competitions in the overmoded cavity. A prototype of the new RF window was fabricated and fully tested with the Klystron peak input power, pulse duration and pulse repetition rate of 75 MW, 4.5 μs and 10 Hz, respectively, at the high-power test stand. The first mass-produced new RF window installed in the PLS-II Linac is running in normal operation mode. No fault is reported to date. Plans are being made to install the new RF window to all S-band accelerator RF modules of the PLS-II and PAL-XFEL Linacs. This new RF window may be applied to the output windows of S-band power sources like Klystron as wells as the waveguide windows of accelerator facilities which operate in S-band.

2 μm Raman fiber laser based on a multimaterial chalcogenide microwire

We report a Raman fiber laser based on a multimaterial chalcogenide microwire. The microwire structure comprises a core of As38Se62, a cladding of As38S62, and a coating of poly-methyl methacrylate. The microwire is a robust, high confinement waveguide compatible with the mid-infrared. With the microwire inserted in a ring cavity, Raman laser oscillation at a wavelength of 2.025 μm occurs from synchronous pumping at a wavelength of 1.938 μm. The input peak power required to reach threshold is 4.6 W and the power slope efficiency is 4.5%. Numerical simulations are in good agreement with experimental results and predict chirp-free femtosecond pulses.

Wideband TEM-TE11 mode convertor for HPM applications.

The mode convertor design of fundamental coaxial TEM to the lowest asymmetric TE11-mode of a circular waveguide was proposed and optimized with ANSYS HFSS software. It includes axially aligned parts: the input coaxial line with the high voltage insulator, conical coaxial matching line, wave-coax transition section and output circular waveguide. The most losses in this type of convertor caused by the wave of coaxial TE11-mode running back to the microwave source. To minimize these losses, there is the matching conical coaxial line with the cut-off insertion for coaxial TE11-mode. Characteristics of the convertor are as follows: the maximum input peak power – 3GW, the input impedance – 28Ohm, the central operating frequency – 1.14GHz. The power conversion efficiency to the output mode is from 90% upto 100% in the frequency band of 20%.