RF characters study of a pick-up parallel-setting HOM coupler

A pick-up parallel-setting high order mode coupler(pps-HOM coupler)has been fabricated at Peking University.It has been tested on a coaxial transmission line and a 2-cell TESLA-shape copper cavity.The test result of the 2-cell TESLA cavity shows that the coupler can cut off the fundamental mode TM010 and absorb HOMs electively.As its RF properties are insensitive to the probe dip length,there is no need to adjust the probe repeatedly during practical operation.     

A coaxial HOM coupler for a superconducting RF cavity and its low-power measurement results

A resonant buildup of beam-induced fields in a superconducting radio frequency(RF)cavity may make a beam unstable or a superconducting RF cavity quench. Higher-order mode(HOM)couplers are used for damping higher-order modes to avoid such a resonant buildup. A coaxial HOM coupler based on the TTF (TESLA Test Facility)HOM coupler has been designed for the superconducting RF cavities at the Proton Engineering Frontier Project(PEFP)in order to overcome notch frequency shift and feed-through tip melting issues. In order to confirm the HOM coupler design and finalize its structural dimensions, two prototype HOM couplers have been fabricated and tested. Low-power testing and measurement of the HOM couplers has shown that the HOM coupler has good filter properties and can fully meet the damping requirements of the PEFP low-beta superconducting RF linac.     

Stop band characteristics of a TESLA cavity coaxial-type HOM coupler

A TTF-type coaxial higher order modes (HOM) coupler has been used in a TESLA 9 cell cavity. It is impossible to measure the stop band characteristics of the HOM coupler with the cavity. A measurement device for the coaxial transmission line type for the HOM coupler has been designed at Peking University. Experimentally it was shown that the average voltage standing wave ratio of the coaxial transmission line is smaller than 1.08. The experimental results of the stop band characteristics of the TTF-type HOM coupler have been fitted for the simulation. This paper describes the design of the measurement device and discusses the experimental and simulation results of stop band characteristics of the HOM coupler.     

Study and design of RF coupler for Chinese ADS HWR superconducting cavity

An RF power coupler is a key component of the superconducting accelerating system in Chinese ADS proton linac injector I, which is used to transmit 15 kW RF power from the power source to the superconducting HWR cavity. According to the requirement of working frequency, power level, transmission capability and cooling condition, the physics design of coupler has been finished, which includes RF structure optimization, thermal simulation, thermal stress analysis and so on. Based on this design, the prototype of HWR coupler has been fabricated, and it has successfully passed the high power test.     

Innovative coupler design based on a tapered light pipe with lens

Natural light illumination system （NLIS） generates increasing research interest because of the recent trend toward green energy. Various crucial optical components used in a NLIS are analyzed, designed, and fabricated to obtain high efficiency. A large amount of light is loss because of the large viewing angle during light transmission. A tapered light pipe （TLP） is used to collimate light viewing angles. In this letter, we combine a TLP and a traditional lens as a new coupler based on Etendue theory. The original efficiency is only 17.54%, but the efficiency reaches more than 70% when the new coupler is applied.     

Directional coupler design based on coupled cavity waveguides in photonic crystals

We propose a directional coupler design based on coupled cavity waveguide in photonic crystals. The plane wave expansion is used to give the dispersion of the coupled cavity waveguides and two parallel such waveguides. The couple length is got from the dispersion curves. Based on the research of the dispersion, we present a directional coupler and the transmission property is given. This structure is potentially important for highly efficient directional coupler in integrate optical circuit.     

Computer aided design of inverted strip dielectric waveguide millimeter wave ring-resonator and coupler

A computer aided design technique has been developed for the design of millimeter-wave ring resonator and hybrid-ring coupler using inverted strip dielectric waveguides. The scattering matrix analysis for hybrid-ring coupler has also been developed. Numerical results for these components at f₀=80 GHZ with 3-dB coupling have been presented along with the variation of width, spacing, and radii with frequency.This work was supported by the faculty research committee of the University of North Dakota under research grant no. 1813/0909/2027 and partially funded by E.F. Johnson Co., Waseca, Minnesota, under grant no. 9009/8183.     

用于CEPC探测器超导磁体的液氮虹吸实验研究

概括了环形正负电子对撞机(CEPC)探测器超导磁体拟采用的虹吸冷却低温系统的研制背景,重点介绍了液氮虹吸实验平台的设计、组装及检漏。分别以氮气液化后的液氮填充相分离器的1/5和1/3体积的要求进行了两次实验,其常温常压下的体积分别为0.32m~3和0.47m~3。实验发现当充装量为0.32m~3时,蒸发侧加热功率达到10W后发生了烧干现象;充装量为0.47m~3时,蒸发侧加热功率达到20W后液氮回路仍循环良好,管路最大温差不到1K,管路温度分布均匀,未发生烧干现象。实验结果表明,氮气的充装量以及蒸发侧的加热功率是影响虹吸冷却效果的两个重要因素。     

Study of CEPC performance with different collision energies and geometric layouts

The Circular Electron-Positron Collider(CEPC) is one of the largest projects planned for high energy physics in China.It would serve first as a Higgs factory and then upgrade to a hadron collider.In this paper we give the 50 km and 100 km design for both single ring and double ring schemes,including Z boson,W boson and Higgs boson,by using an optimized method.Also,we give the potential of CEPC running at the Z and W poles.We analyse the relationship of luminosity with circumference and filling factor,which gives a way to evaluate the choice of geometry,and compare the nominal performances of CEPC-SPPC,LHC and FCC.     

Cross section and Higgs mass measurement with Higgsstrahlung at the CEPC

The Circular Electron Positron Collider(CEPC) is a future Higgs factory proposed by the Chinese high energy physics community. It will operate at a center-of-mass energy of 240–250 Ge V. The CEPC will accumulate an integrated luminosity of 5 ab-1over ten years of operation, producing one million Higgs bosons via the Higgsstrahlung and vector boson fusion processes. This sample allows a percent or even sub-percent level determination of the Higgs boson couplings. With GEANT4-based full simulation and a dedicated fast simulation tool, we have evaluated the statistical precisions of the Higgstrahlung cross section σZH and the Higgs mass m H measurement at the CEPC in the Z →μ~+μ~-channel. The statistical precision of σZH(m_H) measurement could reach 0.97%(6.9 MeV) in the model-independent analysis which uses only the information from Z boson decays. For the standard model Higgs boson, the m H precision could be improved to 5.4 Me V by including the information from Higgs decays. The impact of the TPC size on these measurements is investigated. In addition, we studied the prospect of measuring the Higgs boson decaying into invisible final states at the CEPC. With the Standard Model ZH production rate, the upper limit of B(H → inv.) could reach 1.2% at 95% confidence level.     

Perpendicular coupler for whispering-gallery resonators

In this Letter, we report on a perpendicular coupler (PC) for whispering-gallery resonators; it is a near field waveguide optimized for high coupling efficiency. The PC provides highly efficient tunneling coupling between the waveguide and microresonator without the need of a phase matching condition, and saves space for integration components. Compared to the Lorentz-shape in the transmission spectrum of the parallel coupler, the reflection spectrum of the PC shows an asymmetric Fano-shape near resonance. Furthermore, we demonstrate that the collection efficiency can be enhanced by near field scatterers, with a maximal efficiency of about 75%. Our simulations show that the PC is not sensitive to most parameters (including the refractive index of the waveguide), which makes the PC optimal for the application of whispering-gallery modes.     

Simple design of optical fiber displacement sensor using a multimode fiber coupler

A simple design sensor is demonstrated using a fabricated multimode plastic fiber coupler in conjunction with reflective intensity modulation technique. The performances of this sensor are investigated for different light sources. This sensor uses only one fiber for sending and receiving the light and therefore only the back slope exists. The sensor shows the highest performance with the use of yellow light source, which has the highest intensity and the smallest beam divergence. The sensitivity, linear range, resolution and dynamic range of the sensor are obtained at 0.0001 mV/μm, 1500 μm, 70 μm, and 5.0 mm, respectively. The simplicity of the design, high degree of sensitivity, dynamic range and the low cost of the fabrication make it suitable for real field applications.     

Nonlinear directional coupler for polychromatic light

We demonstrate that a nonlinear directional coupler with special bending of waveguide axes can be used for all-optical switching of polychromatic light with a very broad spectrum covering all of the visible region. The bandwidth of the suggested device is enhanced five times compared with conventional couplers. Our results suggest novel opportunities for the creation of all-optical logical gates and switches for polychromatic light with white-light and supercontinuum spectra.     

用于光纤Sagnac干涉仪的全息耦合器

我们利用重铬酸明胶作为全息记录介质,制得了分光比接近1:1,总衍射效率超过60%的双重全息透镜.本文讨论了这种全息透镜作为Sagnac光纤干涉仪的耦合器的优点,并给出了初步的实验结果.本文还推导了倾斜光栅的Q因子,提出了全息光栅的等效Bragg定律,并通过它们设计出所需的全息透镜.     

All-fiber wavelength- and mode-selective coupler for optical interconnections

We experimentally demonstrate a new wavelength- and mode-selective coupler utilizing intermodal coupling between a standard single-mode fiber (SMF) and a hollow optical fiber (HOF). The fabricated device routes optical signals such that a 1.3-microm signal is directed to the HOF port, adiabatically converting the LP(01) mode into a ring-shaped mode, which can be further connected to a gigabit ethernet link, reducing the differential mode-dispersion penalty. Optical signals near 1.5microm , meanwhile, stay in the LP(01) mode of the SMF arm for further connection to conventional wavelength-division multiplexing links based on erbium-doped fiber amplifiers. The performance of the device is characterized in terms of insertion loss, channel isolation, and mode-conversion efficiency.     

Fast tunable coupler for superconducting qubits

A major challenge in the field of quantum computing is the construction of scalable qubit coupling architectures. Here, we demonstrate a novel tunable coupling circuit that allows superconducting qubits to be coupled over long distances. We show that the interqubit coupling strength can be arbitrarily tuned over nanosecond time scales within a sequence that mimics actual use in an algorithm. The coupler has a measured on/off ratio of 1000. The design is self-contained and physically separate from the qubits, allowing the coupler to be used as a module to connect a variety of elements such as qubits, resonators, amplifiers, and readout circuitry over distances much larger than nearest-neighbor. Such design flexibility is likely to be useful for a scalable quantum computer.     

Non-Hermitian topological coupler for elastic waves

Non-Hermitian topological systems,by combining the advantages of topological robustness and sensitivity induced by nonHermiticity,have recently emerged and attracted much research interest.Here,we propose a device based on the topological coupler in elastic waves with non-Hermiticity,which contains two topological domain walls and four ports.In this device,topological robustness routes the transmission of waves,while non-Hermiticity controls the gain or loss of waves as they propagate.These mechanisms result in continuous and quantitative control of the energy distribution ratio of each port.A nonHermitian Hamiltonian is introduced to reveal the coupling mechanism of the topological coupler,and a scattering matrix is proposed to predict the energy distribution ratio of each port.The proposed topological coupler,which provides a new paradigm for the non-Hermitian topological systems,can be employed as a sensitive beam splitter or a coupler switch.Moreover,the topological coupler has potential applications in information processing and logic operation in elastic circuits or networks,and the paradigm also applies to other classical systems.     

LOM and HOM damping study in a superconducting deflecting cavity for ALS at LBNL

Superconducting deflecting cavities can be used in synchrotron light source to generate subpicosecond X-ray pulses while the impedance of the lower order modes (LOM) and higher order modes (HOM) in the cavity should be kept below an accepted level to avoid beam instability. These modes can be damped by adding waveguide on beam pipe. Detailed simulation of Q in CST Microwave Studio is introduced and experiment results on an aluminum model cavity with damping waveguide are reported to make a comparison.     

Optical irradiation method for fiber coupler fabrications

An optical irradiation method for high-speed fiber coupler fabrications without contamination is proposed. In optical fiber taper fabrications we found an interesting effect that fiber elongation is self-arrested although laser irradiation is continued. This is a typical effect in the optical irradiation method, but is not seen in the flame method or the thermal heating method. The “self-controlled fiber taper shape effect” is theoretically explained by considering thermal energy flows, and optical fiber couplers are fabricated using this effect. From our experiments, we show that optical fiber coupler fabrications at high-speed without contamination are possible using the optical irradiation method.