Pumping Scheme Research Articles

Gain‐clamping in L‐band zirconium–erbium co‐doped fiber amplifier with FBG based lasing control

AbstractIn this study, gain clamping performance in an L‐band zirconium‐erbium co‐doped fiber amplifier (Zr‐EDFA) with a very short length of heavily doped fiber and FBG based lasing control structure was presented. A simple gain clamping design based on a symmetrical narrow band C‐band fiber Bragg grating (FBG) pair addition was used in the L‐band Zr‐EDFA with bidirectionally pumping scheme. An L‐band gain of higher than 25 dB was obtained with a maximum noise figure (NF) of 5 dB in the conventional Zr‐EDFA design which was higher than the previous results obtained with forward pumping scheme. When a couple of narrow band FBGs at Bragg reflection wavelength of 1542 nm are used as the lasing mechanism for gain clamping in L‐band operation, small signal gain of Zr‐EDFA decreases, but on the other hand, the gain is clamped at almost 15.5 dB with a flattened gain spectrum along a dynamic range of 25 dB for the signal input powers between −30 and −5 dBm with the expense of 1.5 dB NF penalty.

Comprehensive investigations on the tandem pumping scheme employing the pump fiber laser operating at an extremely short wavelength.

In this work, with the aim of improving the nonlinearity threshold in tandem-pumped fiber amplifiers for higher output power, theoretical and experimental work was carried out to enhance the pump absorption and thereby decrease the required length of ytterbium-doped fiber by employing shorter-wavelength fiber lasers as the pump sources. Systematical simulations were first carried out to optimize the cavity parameters of a short-wavelength fiber oscillator at 1007 nm, and subsequently, the performance of the 1007 nm fiber laser in tandem pumping was simulated and compared with that of the 1018 nm fiber laser pumped results. Considerable absorption increment and efficiency improvement could be realized in the 1007 nm fiber laser pumped fiber amplifier relative to the 1018 nm fiber laser pumped one. Furthermore, according to the simulation results, a fiber laser operating at 1007.7 nm with the output power of ∼170 W and a slope efficiency of ∼72.90% was experimentally demonstrated. By applying this fiber laser in tandem pumping a 1080 nm fiber amplifier with different gain fiber lengths, improved performance was acquired in comparison with the 1018.6 nm tandem pumping scheme, the experimental results of which were coherent with the simulation results. This work could provide an effective approach for improving the nonlinearity threshold of tandem-pumped fiber amplifiers and paving the way for higher output power.

Time‐Resolved Second‐Order Coherence Characterization of Broadband Metallic Nanolasers

AbstractHigh‐bandwidth metallic coaxial nanolasers are of high interest to investigate laser physics such as thresholdless coherence transitions, and have a large variety of promising applications enabled by their ultrasmall size and large spectral bandwidth. Optical coherence properties are commonly characterized in Hanbury‐Brown and Twiss experiments. However, those are difficult to perform in broadband lasers when the coherence time is an order of magnitude shorter than the temporal resolution of the single‐photon detectors, thus requiring significant spectral filtering. This paper demonstrates a new approach in investigating the temporal dynamics of the photon statistics associated with the nanolaser emission, obtained without the requirement of spectral filtering. While optically pumping the nanolasers with nanosecond pulses, time‐resolved second‐order coherence properties are evaluated over the time duration of the pump pulse. Coherence transitions from thermal emission to lasing are observed in the gathered time‐resolved photon statistics, linked to the temporal change in optical power of the nanosecond pump pulses. As nanolasers show better performance for the pulsed pumping scheme, the temporal envelope modulation of these pulses results in varying degrees of coherence within the nanolaser pulse envelope. This approach can also be readily applied to characterize a large variety of broadband lasers.

Evaluating the impact of doping concentration on the performance of in-band pumped thulium-doped fiber amplifiers

Abstract This study is to investigate the impact of thulium concentration on the performance of in-band pumped thulium-doped silica fiber amplifiers with considering ion–ion interactions. Due to the fluorescence quenching in silica glass, the fluorescence lifetimes are required to compute at every Tm concentration. The theoretical model of fluorescence decay curves at in-band pumped thulium-doped silica fiber is used to determine the fluorescence lifetimes of the 3F4 and 3H4 levels. The calculated lifetimes of the commercially available thulium-doped silica fiber are 650 µs for 3F4 level and 14 µs for 3H4 level and these results are consentient well with the experimental reported results. The theoretical evaluating of the amplifier performance shows that the gain amplifier reduces with concentration increase because of the impact of both fluorescence quenching and the reverse cross-relaxation process. Thus, in contrast to pumping wavelength at 790 nm, there are negative effects of the high doping concentration of Tm ions on the amplifier performance at the in-band pumping scheme.

Laser Performance of Active Segment Cladding Fiber Under Heat Load

An amplifier model based on the Yb-doped segment cladding fiber (SCF) is proposed in this paper. Three contributions to heat source are taken into account in the proposed model, including the quantum defect (QD), photodarkening (PD), and propagation loss (PL). Thermal-induced mode characteristics, amplification performance, modal gain competition, and high order modes (HOMs) filtering effect are theoretically investigated. Results show that the heat load generated from the Yb-doped SCF core makes the pre-design refractive index distribution into parabolic profile, and results in mode loss and effective mode area decline. Therefore, HOMs with low mode loss are amplified easily. Modal gain competition increases power content of HOMs that leads to laser performance degradation. Leaky cladding and bending operation introduce HOMs discrimination that can suppress HOMs amplification effectively. In high power pump, the counter-pumping amplifier presents higher temperature increase than the co-pumping one, while the high temperature location in Yb-doped SCF depends on pumping schemes. The results in this paper will provide guidance to optimize the structure of Yb-doped large mode area SCF and improve the thermal management of the high-power fiber lasers.

Single-shot imaging of ultrafast all-optical magnetization dynamics with a spatiotemporal resolution.

We present a laboratory system for single-shot magneto-optical (MO) imaging of ultrafast magnetization dynamics with less than 8fs temporal, micrometer spatial resolutions and a MO Faraday's rotation sensitivity of 4 mdeg/μm. We create a stack of MO images repeatedly employing a single pair of pump and defocused probe pulses to induce and visualize MO changes in the sample. Both laser beams are independently wavelength-tunable, allowing for a flexible, resonant adjustable two-color pump and probe scheme. To increase the MO contrast, the probe beam is spatially filtered through a 50 μm aperture. We performed the all-optical switching experiment in Co-doped yttrium iron garnet films (YIG:Co) to demonstrate the capability of the presented method. We determine the spatiotemporal distribution of the effective field of photo-induced anisotropy, driving the all-optical switching of the magnetization in the YIG:Co film without an external magnetic field. Moreover, using this imaging method, we tracked the process of the laser-induced magnetization precession.

Automated method of calculation of parameters for non-traditional heating technologies and conditioning of buildings

Purpose. Develop an automated method for calculating parameters for heat pump systems for heating, air conditioning and hot water supply, designed for use in domestic conditions with non-standard heat transfer flows. Methodology. Mathematical modeling of thermodynamic processes occurring in heating, air conditioning and hot water supply systems. Findings. The automated method of calculating the parameters of non-traditional technology, which uses standard heat pump equipment of the water heating system for the cooling mode of the air in the warm period of the year, and the discharge of heat dissipated into the ground, was substantiated and developed; and for the needs of hot water supply heat pump air-liquid, acting as a high-speed water heater. The estimation of technologies of the thermal energy utilization in buildings developed earlier by authors is executed. The first technology involved the use of a heat pump and heat accumulator scheme in the cold season, and halved the consumption of conventional fuel compared to a gas column for hot water at the same facility. The second technology involved heat recovery with the help of a heat accumulator in a complex system of air conditioning and hot water supply in the warm period, which saves from 74 to 82% of conventional fuel compared to the scheme with boiler and air conditioner without heat accumulator. Critical conclusions were drawn about the need to use additional dimensional equipment for these technologies and the excess amount of hot water received. Possibilities of realization of such scheme were analyzed. Analytically substantiated recommendations on the design (ribbing of heat exchange surfaces) of heating devices and parameters of their operating modes in the cold and warm periods of the year were given. The condition of invariance of heat exchange areas of heating devices and basic water consumption in the heating system was fulfilled. The need to regulate the air conditioning regime by changing the water flow in the system to maintain a constant indoor air temperature with fluctuations in outdoor air temperature was substantiated. Originality. For the first time, attention is paid to the study of non-traditional methods of using heat pump heating for heating, air conditioning and hot water supply of residential premises. The automated method for determining rational parameters for these technologies was developed. Practical value. The automated method of forming the control dependence of the mass flow of water in the system on the outside air temperature on the condition of constancy of the set comfortable indoor air temperature was developed. The use of air-liquid heat pump for hot water supply in the warm period was analyzed, a high energy conversion factor was noted (14 ... 22). The savings of conventional fuel from the application of the considered technology from 13% to 18% in comparison with the technology using a heat accumulator were substantiated.

Raman Amplification Optimization in Short-Reach High Data Rate Coherent Transmission Systems.

We compared the transmission performances of 600 Gbit/s PM-64QAM WDM signals over 75.6 km of single-mode fibre (SMF) using EDFA, discrete Raman, hybrid Raman/EDFA, and first-order or second-order (dual-order) distributed Raman amplifiers. Our numerical simulations and experimental results showed that the simple first-order distributed Raman scheme with backward pumping delivered the best transmission performance among all the schemes, notably better than the expected second-order Raman scheme, which gave a flatter signal power variation along the fibre. Using the first-order backward Raman pumping scheme demonstrated a better balance between the ASE noise and fibre nonlinearity and gave an optimal transmission performance over a relatively short distance of 75 km SMF.

Analysis of flow field characteristics of cycloidal pump based on fluid solid interaction

At present, in the aspect of numerical simulation of a cycloid pump, most researchers are based on CFD (computational fluid dynamics) to analyze the pump under different operating conditions (such as speed, temperature), and the performance of a pump under FSI (fluid solid interactions) is rare. Firstly, a model of cycloidal pump is established in COMSOL. The simulation results obtained by applying CFD and FSI are verified by experiments. Then, the flow in the rotating region and the inlet and outlet cavities are analyzed. Finally, through further analysis of the internal flow, improved design scheme of the cycloid pump is put forward, the inlet flow of the cycloid pump increased by 5.8% compared with the unoptimized, the inlet flow pulsation decreased by 32.7%. The discharge flow of the cycloid pump increased by 16.3%, the pulsation rate of discharge flow decreased by 47%. It provides a reference for other pump research, analysis and improvement design.

Implementation of Optimal Thermal Radiation Pumps Using Adiabatically Modulated Photonic Cavities

We numerically implement the concept of thermal radiation pumps in realistic photonic circuits and demonstrate their efficiency to control the radiation current, emitted between two reservoirs with equal temperature. The proposed pumping scheme involves a cyclic adiabatic modulation of two parameters that control the spectral characteristics of the photonic circuit. We show that the resulting pumping cycle exhibits maximum radiation current when a cyclic modulation of the system is properly engineered to be in the proximity of a resonance degeneracy in the parameter space of the photonic circuit. A developed Floquet scattering framework, which in the adiabatic limit boils down to the analysis of an instantaneous scattering matrix, is offering an engineering tool for designing and predicting the performance of such thermal pumps. Our predictions are confirmed by time-domain simulations invoking an adiabatically driven photonic cavity.

Ultrafast bipolar conductivity driven by intense single-cycle terahertz pulses in a topological insulator Bi2Se3

We present the measurement of ultrafast terahertz (THz) conductivity of a 50 nm thick topological insulator Bi2Se3 at low temperature 5 K by using a THz pump and THz probe spectroscopy scheme. The THz conductivity driven by a single-cycle intense THz pump exhibits a bipolar lineshape and frequency-dependent relaxation dynamics due to the separated surface and bulk charge carriers with distinctly different scattering rates and relaxation times. We also demonstrate THz pump field-dependent excitation of the surface and bulk spectral weights, which suggests one of the optimal THz excitation conditions for generating the most charge carriers from the topology-protected surface state relative to the bulk. This also allows THz control of surface and bulk transport channels in a selective way.

Strong phonon-cavity coupling and parametric interaction in a single microcantilever under ambient conditions

Parametrically tuning the oscillation dynamics of coupled micro/nano-mechanical resonators through a mechanical pump scheme has recently attracted great attention in areas ranging from fundamental physics to various applications. However, the special design of the coupled resonators and the requirement for low-dissipation operating conditions significantly restrict the wide application of this tuning technique. In this study, we show that under ambient conditions, a mechanical pump can parametrically control the oscillation dynamics in a single commercial microcantilever resonator. Strong phonon-cavity coupling with a cooperativity of up to ∼398 and normal-mode splitting is observed in the microcantilever. The parametric interaction with the phonon-cavity coupling enables a mechanical pump to achieve 43 dB for parametric amplification and 3 dB for parametric cooling, respectively. Utilizing a mechanical pump, the potential sensitivity and signal-to-noise ratio of frequency-modulated Kelvin probe force microscopy operated in the ambient environment can be significantly improved by ∼16 times and 31 dB, respectively. Furthermore, both single-mode and two-mode thermomechanical noise-squeezing states can be created in the microcantilever by the application of a mechanical pump.

Comparison of 1480 nm and 980 nm-pumped Gallium-Erbium fiber amplifier.

Background: One way to reduce the length of the gain medium in Erbium-Doped Fiber Amplifier (EDFA) is by doping the fiber core with a high concentration of Erbium. However, this method caused ion clustering effects, which limits the EDFA's efficiency. In this research, the use of Gallium as a new co-dopant in erbium-doped silica fiber is explored. Methods: The new fiber, namely Gallium co-doped Erbium fiber (Ga-EDF), is used as a gain medium in an optical fiber amplifier setup. A 2-meter length of the Ga-EDF fiber was used in a single pass configuration with a forward pumping scheme at 150 mW pump power. The Ga-EDF amplifier's gain and noise figure while pumping at 980 nm and 1480 nm were compared. The amplifier's performance was evaluated as the input signal power varied between -30 dBm to 3 dBm, over the wavelength range of 1520 nm to 1580 nm. Results: The 980 nm-pumped Ga-EDF amplifier achieved the maximum small-signal gain of 22.45 dB and the corresponding noise figure of 5.71 dB at the input signal wavelength of 1535 nm. Meanwhile, the 1480 nm-pumped Ga-EDF amplifier attained the maximum small-signal gain of 20.83 dB and the corresponding noise figure of 5.09 dB at the input signal wavelength of 1550 nm. At the input signal power below -20 dBm and the wavelength range 1520 nm to 1547 nm, the Ga-EDF performs better when pumped at 980 nm. Their performance is comparable at the input signal wavelength range between 1547 nm to 1580 nm. At the input signal power above -20 dBm, the 1480 nm-pumped Ga-EDF outperformed the 980 nm-pumped amplifier. Conclusions: The overall performance indicates that the gain saturation point of the 1480 nm-pumped amplifier is higher than the 980 nm-pumped.

High gain boost converter fed asynchronous motor drive for water pumping system

ABSTRACT High gain dc–dc boost chopper are rapidly expanding substituting power converters for Photo Voltaic (PV) appliances. Investigators are creating different schemes to accomplish greater voltage gain, low ripple, switch stress, decreases the cost of converters and reduces the fluctuations at the photovoltaic operation point. This paper proposes a two-stage converter for standalone solar photovoltaic (PV) water pumping drive system. High Gain (HG) cell combined with DC-to-DC boost converter. This compound converter provides dc voltage fed asynchronous motor drive system. The utilisation of three-phase asynchronous motor introduces a superior solution to the industrial DC motor-based water pumping scheme. A three-phase asynchronous motor connected to voltage source inverter (VSI), which in turning throws the centrifugal pump. The scheme comprises of a PV array, high-gain DC–DC chopper, 3-Phase Voltage Source Inverter (VSI), motor and a pump. Incremental conductance method used to obtain maximum power from a solar PV structure. Indirect Field Oriented Control of an asynchronous motor is employed to achieve soft starting of the motor. The scheme setup is simulated using MATLAB/Simulink. The proposed system is tested experimentally. The results accomplished demonstrate the scheme fitness for PV water pumping.

Resonantly Pumped Bright-Triplet Exciton Lasing in Cesium Lead Bromide Perovskites.

The surprising recent observation of highly emissive triplet-states in lead halide perovskites accounts for their orders-of-magnitude brighter optical signals and high quantum efficiencies compared to other semiconductors. This makes them attractive for future optoelectronic applications, especially in bright low-threshold nanolasers. While nonresonantly pumped lasing from all-inorganic lead-halide perovskites is now well-established as an attractive pathway to scalable low-power laser sources for nano-optoelectronics, here we showcase a resonant optical pumping scheme on a fast triplet-state in CsPbBr3 nanocrystals. The scheme allows us to realize a polarized triplet-laser source that dramatically enhances the coherent signal by 1 order of magnitude while suppressing noncoherent contributions. The result is a source with highly attractive technological characteristics, including a bright and polarized signal and a high stimulated-to-spontaneous emission signal contrast that can be filtered to enhance spectral purity. The emission is generated by pumping selectively on a weakly confined excitonic state with a Bohr radius ∼10 nm in the nanocrystals. The exciton fine-structure is revealed by the energy-splitting resulting from confinement in nanocrystals with tetragonal symmetry. We use a linear polarizer to resolve 2-fold nondegenerate sublevels in the triplet exciton and use photoluminescence excitation spectroscopy to determine the energy of the state before pumping it resonantly.

Experimental study of the efficiency of a multi-pass pumping scheme for solar lasers

Here we present the results of our study on the feasibility of a multi-pass pumping scheme in solar lasers. A secondary concentrator has been developed to ensure the multiple passage of solar photons through the active medium. When using a multi-pass pumping scheme, an increase of 12.5% in the luminescence spectra of Nd:YAG is observed in the vicinity of the lasing line at a wavelength of 1064 nm

S1-State Decay Dynamics of Benzenediols (Catechol, Resorcinol, and Hydroquinone) and Their 1:1 Water Clusters.

The S1-state decaying rates of the three different benzenediols, catechol, resorcinol, and hydroquinone, and their 1:1 water clusters have been state-specifically measured using the picosecond time-resolved parent ion transients obtained by the pump (excitation) and probe (ionization) scheme. The S1 lifetime of catechol is found to be short, giving τ ∼ 5.9 ps at the zero-point level. This is ascribed to the H-atom detachment from the free OH moiety of the molecule. Consistent with a previous report (J. Phys. Chem. Lett. 2013, 4, 3819-3823), the S1 lifetime gets lengthened with low-frequency vibrational mode excitations, giving τ ∼ 9.0 ps for the 116 cm-1 band. The S1 lifetimes at the additional vibronic modes of catechol are newly measured, showing the nonnegligible mode-dependent fluctuations of the tunneling rate. When catechol is complexed with water, the S1 lifetime is enormously increased to τ ∼ 1.80 ns at the zero-point level while it shows an unusual dip at the intermolecular stretching mode excitation (τ ∼ 1.03 ns at 146 cm-1). Otherwise, it is shortened monotonically with increasing the internal energy, giving τ ∼ 0.67 ns for the 856 cm-1 band. Two different asymmetric or symmetric conformers of resorcinol give the respective S1 lifetimes of 4.5 or 6.3 ns at their zero-point levels according to the estimation from our transients taken within the temporal window of 0-2.7 ns. When resorcinol is 1:1 complexed with H2O, the S1 decaying rate is slightly accelerated for both conformers. The S1 lifetimes of trans and cis forms of hydroquinone are measured to be more or less same, giving τ ∼ 2.8 ns at the zero-point level. When H2O is complexed with hydroquinone, the S1 decaying process is facilitated for both conformers, slightly more efficiently for the cis conformer.

Excitons and carriers in transient absorption and time-resolved ARPES spectroscopy: An ab initio approach

I present a fully abinitio scheme to model transient spectroscopy signals in presence of strongly bound excitons. Using LiF as a prototype material, I show that the scheme is able to capture the exciton signature both in time-resolved ARPES and transient absorption experiments. The approach is completely general and can become the reference scheme for modelling pump and probe experiment in a wide range of materials.

Development of a double-barreled Tracer Encapsulated Solid Pellet (TESPEL) injection system for LHD

For performing a study of impurity transport efficiently by using a Tracer-Encapsulated Solid Pellet (TESPEL) in Large Helical Device (LHD), a new double-barreled TESPEL injection system was recently developed and installed on the LHD. The TESPEL in each injection line can be injected with different timing and acceleration pressure which can be set individually. To prevent the high-pressured gas for the TESPEL acceleration from getting into the vacuum vessel of the LHD, a 3-stage differential pumping scheme was applied. Since the available space is very limited, the 3-stage differential pumping system is shared with each TESPEL injection line. And for the same reason, one of the guide tubes in one injection line of the new TESPEL injection system was purposely bent (bending radius of about 40 m). The guide tubes in the other injection line of the new TESPEL injection system are straight. We performed a laboratory test to check the TESPEL transferring capability with the guide tubes in the new injection system. The points of TESPEL impact on the target foil are found to be within the circles defined by a possible pellet divergence full angle, 2 degrees. Therefore, we confirmed that the TESPEL can pass through both the slightly bent and the straight injection lines of the new injection system without any problem. The blank shot test shows that the increment of the total pressure even by using both the injection lines simultaneously is much below the base pressure of the LHD vacuum vessel during the discharge. This result successfully demonstrated the capability of the applied 3-stage differential pumping scheme in the new injection system.

Design of EDFA based 16 channel WDM system using counter directional high pump power

Abstract In this paper, design of erbium-doped fiber amplifiers (EDFA) based 16 channel wavelength-division multiplexing (WDM) system for different pump powers and input signal levels using counter propagating pumping scheme is reported. Wavelength range between 1548 and 1560 nm in C-band with channel spacing of 0.75 nm at a bit rate of 10 Gbps are used. Input power given to all the channels is taken between −20 and −35 dBm with 3 dBm variation. Pump power levels between 100 and 500 mW at 980 nm wavelength are used. Low gain flatness with high gains and low noise figures are achieved with the proposed scheme.