Output Coupling Coefficient Research Articles

Improvement and analysis of a recirculating delayed self-heterodyne interferometer for laser linewidth measurement

This paper presents an improved scheme of a passive recirculating delayed self-heterodyne interferometer (RDSHI) for laser linewidth measurement. The proposed scheme includes two additional fiber couplers in a regular RDSHI to independently control the reference beam and the loop signal for best system performance. The analysis and experimental results have confirmed that an initial equal power split for the reference beam is best suited to enhance the maximal number of detectable beat notes. The output coupling coefficient of the fiber loop has also been experimentally studied for system optimization. The experimental results have confirmed that the proposed modification to a basic RDSHI can achieve more detectable beat notes (14 vs. 12) and finer linewidth resolution (∼14% improvement) than a basic RDSHI in our test setup of 2-km-long delay line.

A quantitative calculation method of RF parameters for traveling wave accelerating structures

Equivalent circuit model of the coupled cavity chain has been widely used to analyze the properties of RF parameters of periodic accelerating structures. In this paper, the equivalent circuit model of disk-loaded waveguide traveling wave accelerating structure and its circuit equations are discussed and analyzed further. Based on analysis of relationship between the RF parameters of each cavity and the field distribution in the coupled cavity chain, a new method to calculate the frequency deviation of each cavity and the output coupling coefficient of the accelerating structure quantitatively is presented. This method is applied in a 10 MeV traveling wave accelerating structure tuning and results verify its correctness and effectiveness.

Maximum efficiency tracking control of underwater wireless power transfer system using artificial neural networks

In the underwater wireless power transfer system for the marine vehicle, the system transfer efficiency is influenced by factors including coupling state and load condition. To solve the problem of transfer efficiency decrease caused by the dynamic changes of coupling coefficient and load conditions, a maximum efficiency tracking method based on the dynamic identification of optimal output voltage and coupling coefficient is proposed. Moreover, the approximation characteristic to the nonlinear function of artificial neural networks is used to dynamically adjust the output voltage of DC/DC converter, and the deviation between the output voltage and optimal voltage can be kept within the allowable error range leading to maximum efficiency tracking. The experimental results show that the control method can calculate the optimal output voltage correctly, adjust the output voltage quickly and accurately, and achieve the maximum efficiency of the wireless power transfer system when the coupling coefficient and load conditions change dynamically.

A Design Method to Implement ZVS for Electric Vehicle Wireless Charging System With Double-Side LCC Compensation

In this article, the zero voltage switching (ZVS) of the inverter in the electric vehicle wireless charging system is realized through the parameter optimization design of compensation components, which is conducive to the high efficient operation of the system. The effects of the parameter adjustment of each compensation component on the input impedance angle and output current of the double-side LCC compensation topology were analyzed under the conditions of different output voltages and coupling coefficients, which provides a basis for the component optimization design of the inverter ZVS realization. The quantitative relationship between the optimized component parameter and the soft switching implementation conditions was analyzed. Then, a specific parameter design method was proposed, according to the results analyzed earlier. At last, the effectiveness of the proposed method was verified by a 3.3-kW wireless charging system prototype. Experimental results show that the optimized system is always able to achieve soft switching, the system efficiency is up to 95.2% at the rated power, and it is higher than 93% even under the condition where the coupling coefficient and output voltage are both reduced by half.

Design and Control of Inductive Power Transfer System for Electric Vehicles Considering Wide Variation of Output Voltage and Coupling Coefficient

In this paper, a design and control scheme of the inductive power transfer (IPT) system for electric vehicles are proposed, considering a wide variation in output voltage and coupling coefficient. The characteristics of the proposed IPT system and a design method for the resonant network are suggested. By utilizing the battery management converter at the secondary side, the design and control can be simplified while managing the output voltage and power of the battery. In order to achieve high efficiency by reducing the voltage–ampere rating, zero phase angle tracking control is proposed. In addition, a phase-shift control is applied to the primary side to ensure the stable system operation by limiting output voltage. A 3.3-kW laboratory prototype with magnetic power pads is manufactured, and the validity of the proposed design and control is verified through experimental results using the laboratory prototype.

A method for designing a variable-channel high-power cavity combiner**Supported by National Natural Science Foundation of China (11079034)

Cavity combiners have been put forward for high power combining due to their advantages of larger combining ability, variable input channels and less power loss. For a high power cavity combiner, it is better to keep the power loss ratio in a reasonable range, because large power loss would lead to strict requirements on the cooling system. A combiner with variable input channels is convenient for outputting different power levels according to practical demands. In this paper, a method for designing a variable-channel high-power cavity combiner is proposed, based on the relation between input and output coupling coefficients obtained by analyzing the equivalent circuit of the cavity combiner. This method can put the designed cavity combiner in a matching state and keep its power loss rate in a reasonable range as the number of input channels changes. As an example, a cavity combiner with 500 MHz and variable input channels from 16 to 64 is designed, and the simulation results show that our proposed method is feasible.

DOA estimation and mutual coupling calibration with the SAGE algorithm

In this paper, a novel algorithm is presented for direction of arrival (DOA) estimation and array self-calibration in the presence of unknown mutual coupling. In order to highlight the relationship between the array output and mutual coupling coefficients, we present a novel model of the array output with the unknown mutual coupling coefficients. Based on this model, we use the space alternating generalized expectation-maximization (SAGE) algorithm to jointly estimate the DOA parameters and the mutual coupling coefficients. Unlike many existing counterparts, our method requires neither calibration sources nor initial calibration information. At the same time, our proposed method inherits the characteristics of good convergence and high estimation precision of the SAGE algorithm. By numerical experiments we demonstrate that our proposed method outperforms the existing method for DOA estimation and mutual coupling calibration.

Amplification process in a high-Q cryogenic whispering gallery mode sapphire Fe3 + maser

This paper reports on the analysis of a high-Q (109) cryogenic whispering gallery mode (WGM) sapphire resonator maser oscillator based on residual impurities of the Fe3 + ion (1 ppm). A theoretical model is developed to determine the evolution of the maser output power versus the pump power and the resonator output coupling coefficient. Comparison of the theoretical model and experimental data shows a good agreement.

Active quasioptical Ka-band rf pulse compressor switched by a diffraction grating

Results of numerical calculations and experimental investigations of an active Ka-band microwave pulse compressor are presented. The compressor is based on a running-wave, three-mirror, quasioptical resonator utilizing a diffraction grating whose channels embody plasma discharge tubes that constitute the active switch. The principle of compression is based on rapidly changing the resonator's output coupling coefficient ($Q$ switching) by initiating plasma discharges in the grating channels. Excitation of the resonator was achieved with up to 250 kW of 34.29 GHz microwaves in 700 nS pulses from the magnicon at the Yale Ka-band Test Facility. A power gain of at least $7\ensuremath{\mathbin:}1$ in the compressed pulse with a pulse duration of 10--15 ns was achieved.

Photopolymer-Based Diffractive and MMI Waveguide Couplers

Diffractive and multimode-interference waveguide couplers constructed from photopolymer materials are presented. Two-material grating-in-the-waveguide optical interconnects are fabricated and tested with respect to waveguide propagation loss and grating out-coupling. Waveguide/grating interconnects have been constructed with both index-defined and air-clad waveguide channel regions, where air-clad channels exhibit measured propagation losses of /spl alpha//sub wg/=0.47-3 dB/cm. Measurements of output coupling coefficients of volume grating couplers terminating various waveguide channels range from /spl alpha//sub g/=1.4-5.3 mm/sup -1/. A 1 /spl times/ 4 photopolymer-based multimode-interference power-splitting coupler fabricated and tested for the provision of in-plane optical coupling is found to demonstrate 0.3-0.6-dB output power uniformity.

All-optical time-division demultiplexing and spatial pulse routing with a GaAs/AlGaAs microring resonator

We report what is to our knowledge the first demonstration of all-optical time-division demultiplexing and spatial pulse routing in a compact nonlinear GaAs/AlGaAs microring resonator operating at 1.55 microm . Switching is through the refractive-index change induced by two-photon absorption. The switching time of the device, limited by the ring-charging time and the recombination time of the induced carriers, is measured to be 30 ps. The switching on-off contrast, limited by the slight mismatch between the input and output coupling coefficients, exceeds 8 dB. The device can be used for time-division multiplexing as well.

Uncertainty analysis of the transmission-type measurement of Q-factor

The transmission-type measurement of the Q-factor of a microwave resonator is analyzed with a goal of establishing uncertainty limits on the unloaded Q-factor. The three major sources of systematic errors which are discussed are: the instrumentation inaccuracy, the inequality of the input and output coupling coefficient, and the effect of coupling losses. It is shown that, for tightly coupled resonators, the uncertainty of the transmission-type method is significantly increased.

Operating parameter optimization of optically pumped CH3OH far-infrared laser

By solving the density matrix equations of a quantum system, the output power intensity of an optically pumped CH3OH FIR laser (CH3OH-OPFIRL) was calculated by means of iteration method, and the spectral characteristics were got. Base on the calculation, optimization of operating parameters including operating gas pressure, pumped power and output coupling coefficient of the CH3OH cavity laser were systematically studied. Experimental, a series of FIR emissions of the CH3OH cavity laser pumped by TEA-CO2 laser with 9P(16) line were measured. The experimental results were in good agreement with theoretical calculations.

Optimum output coupling for an optically pumped CF 4 laser

The optimum output coupling coefficient for an optically pumped gas laser has been evaluated using a rate equation approach. The theoretical study takes into account the spatial variation of the gain distribution, the self-absorption of the laser emission, the depletion of the pump beam, and the effects of superfluorescent emission on the performance of the laser. Our calculations indicate that a considerable increase in the output laser energy density can be achieved under conditions of reduced superfluorescent emission, by a proper choice of the output coupling coefficient.

Mode competition and control in free-electron-laser oscillators

The problem of longitudinal mode competition in free-electron lasers is addressed. It is shown that for small enough ratios of the current to output coupling coefficient many single-mode states are possible. However, the time required to reach these states becomes extremely long for typical devices. Before reaching a single-mode state the radiation field becomes relatively constant in amplitude with modulations of its phase. Finally, a simple method for reaching the stable single-mode state with maximum efficiency is suggested.

The measurement of far-infrared laser gain and loss using a Michelson coupler

It is demonstrated that small values of small-signal gain and total internal losses in far-infrared lasers can, in principle, be determined by measuring the optimum and threshold output coupling coefficients with a Michelson coupler. Experimental results show that although accurate determination of the small-signal gain can be made, only a good approximation of the internal losses is obtained by this method. The gain of the 220-μm transition of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O is shown to increase from 0.24 percent m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> to 0.43 percent m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with the addition of helium to 0.25 tort H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O at a discharge current of 1.8 A.

Time-resolved spectroscopy of a pulsed H2–F2 laser with well-defined initial conditions

The time-resolved spectral output of a pulsed H2–F2 laser has been investigated as a function of initiating atomic fluorine concentration. Fast initiation, as well as variation of initial F-atom concentration, was accomplished by photodissociation of F2 in a flowing H2–F2–N2 mixture utilizing a variable-amplitude 30-nsec second harmonic pulse from a Q-switched ruby laser. Initial HF concentration due to prereaction was reduced to ∼0.01% of the final HF content by cryogenic cooling of the reagent premixer. The 30-cm-long reactor cell was contained within a 113-cm stable resonator cavity having a 70% output coupling coefficient. Lasing was observed on a number of P-branch transitions in the four lowest vibrational bands of HF for a gas mixture H2 : F2 : N2 = 7.5 : 7.5 : 75 Torr. For each of the nine dominant lines, variation of initiation time, pulse duration, peak intensity, and total energy was observed as a function of initiating F-atom concentration. Strong initial intensity transients observed for highest gain transitions are indicative of relaxation oscillation effects not included in conventional HF laser simulation codes based on the threshold gain constraint. Trends in temporal J progression predicted by such codes were observed, but simultaneous lasing on multiple lines within a given vibrational band indicates that usual assumptions of Boltzmann rotational distribution and gain saturation to threshold are overrestrictive. The observations show strong correlation between peak intensity and relative gain of the individual transition. Energy content of individual lines does not exhibit such correlation.