Nonreciprocal two-photon transmission and statistics in the chiral waveguide QED system

We study the nonreciprocal properties of transmitted photons in the chiral waveguide QED system, including single- and two-photon transmissions and second-order correlations. For the single-photon transmission, the nonreciprocity is induced by the effects of chiral coupling and atomic dissipation in the weak coupling region. It vanishes in the strong coupling regime when the effect of atomic dissipation becomes ignorable. In the case of two-photon transmission, there exist two ways of going through the emitter: independently as plane waves and formation of bound state. Besides the nonreciprocal behavior of plane waves, the bound state that differs in two directions also alters transmission probabilities. In addition, the second-order correlation of transmitted photons depends on the interference between plane wave and bound state. The destructive interference leads to the strong antibunching in the weak coupling region, while the effective formation of bound state leads to the strong bunching in the intermediate coupling region. However, the negligible interactions for left-propagating photons hardly change the statistics of the input coherent state.

Numerical Investigation and Design of Electrically-Pumped Self-Pulsing Fano Laser Based on III-V/Silicon Integration

A self-pulsing III-V/silicon laser is designed based on the Fano resonance between a bus-waveguide and a micro-ring resonator, partially covered by the graphene as a nonlinear saturable absorption component. The Fano reflector etched on the straight waveguide is used as one of the cavity mirrors in the coupling region to work with the graphene induced loss and nonlinearity to achieve pulsed lasing in GHz repetition frequency. The detailed lasing characteristics are studied numerically by using the rate equation and finite-difference time-domain (FDTD) simulations. The results show that the CMOS compatible hybrid laser can generate picosecond pulses with repetition rate at 1~3.12 GHz, which increases linearly with the injection current.

Center-Slotted Wideband Hybrid 10 dB Coupler

In this paper, a wideband microstrip hybrid coupler designed, simulated, built and tested. These couplers have advantage of easy fabrication, lightweight and incorporation with other microwave devices and validated using 3D planar electromagnetic softwares like Sonnet Suites. The final design is composition of two parallel lines with symmetric slits and a center slot. Directional coupler is designed and simulated to operate in the frequency range from 1 GHz to 5 GHz with 2.4 Ghz coupling -10 dB return loss bandwidth between 1.6 - 4 GHz. The fabricated coupler shows good agreement between measured and simulated results with very low isolation characteristics. Four symmetric orthogonal U-Shaped structures at the center of the coupling region distinguishes the proposed design with other works. It makes significant improvement in calculation duration thereby achieving lower response latency and lowers the possible manufacturing errors compared with previously published similar works.

Tilted Nano-Grating Based Ultra-Compact Broadband Polarizing Beam Splitter for Silicon Photonics

An ultra-compact broadband silicon polarizing beam splitter is proposed based on a tilted nano-grating structure. A light cross coupling can be realized for transverse-magnetic mode, while the transverse-electric light can almost completely output from the through port. The length of the coupling region is only 6.8 μm, while an extinction ratio of 23.76 dB can be realized at a wavelength of 1550 nm. As a proof of concept, the device was fabricated by a commercial silicon photonic foundry. It can realize a 19.84 dB extinction ratio and an 80 nm working bandwidth with an extinction ratio of larger than 10 dB. The presented device also shows a good fabrication tolerance to the structure deviations, which is favorable for its practical applications in silicon photonics.

Color confinement and Bose-Einstein condensation

We propose a unified description of two important phenomena: color confinement in large-N gauge theory, and Bose-Einstein condensation (BEC). We focus on the confinement/deconfinement transition characterized by the increase of the entropy from N0 to N2, which persists in the weak coupling region. Indistinguishability associated with the symmetry group — SU(N) or O(N) in gauge theory, and SN permutations in the system of identical bosons — is crucial for the formation of the condensed (confined) phase. We relate standard criteria, based on off-diagonal long range order (ODLRO) for BEC and the Polyakov loop for gauge theory. The constant offset of the distribution of the phases of the Polyakov loop corresponds to ODLRO, and gives the order parameter for the partially-(de)confined phase at finite coupling. We demonstrate this explicitly for several quantum mechanical systems (i.e., theories at small or zero spatial volume) at weak coupling, and argue that this mechanism extends to large volume and/or strong coupling. This viewpoint may have implications for confinement at finite N, and for quantum gravity via gauge/gravity duality.

A compact, broadband three-way substrate integrated waveguide power divider with improved isolation

Purpose This paper aims to present a compact, broadband substrate integrated waveguide (SIW) three-way power divider with improved isolation based on six-port SIW coupler. Design/methodology/approach The power coupling among the three output ports occurs due to short openings in the narrow walls of the central SIW channel. Performance improvement in the isolation and return loss among ports is achieved using matching posts placed at the input and output ends of the coupling region. This enhances the coupling between TE10 and TE30 modes. The input matching ports enhance the return loss, whereas the isolation is alleviated by both the input and output matching posts. The bandwidth enhancement is achieved by optimizing the outer SIW channel widths. Findings The measured fractional bandwidth of 27.3% with over 15 dB of isolation and return loss is achieved. The coupling length is 1.55 λg at the centre frequency. The power divider achieves better than 15 dB isolation between non-adjacent output ports. The measured reflection and isolation coefficients are in close agreement with simulated results over 8.2 to 10.8 GHz. Practical implications Isolation between the adjacent and non-adjacent ports is an important parameter as the reflections from these ports will interfere with signals from other ports reducing the fractional bandwidth of the power divider and affecting the overall performance of the transmitters and receivers. Originality/value The authors present the enhancement of isolation between the output non-adjacent ports by optimizing the SIW channel width and matching post in the coupling region to reduce the reflected signals from non-adjacent ports entering into other ports. To the author’s knowledge, this is the only SIW three-way power divider paper showing non-adjacent port isolation among six-port couplers based three-way power dividers.

Compact Full Ka-Band Waveguide Directional Coupler Based on Rectangular Aperture Array with Stairs

This article presents a compact 3 dB waveguide directional coupler with full waveguide bandwidth. It consists of a pair of rectangular waveguides with stairs structures in the coupling region. The waveguides are placed parallel to each other along their broad wall, which has a rectangular aperture array. The compact size, broad bandwidth, good in-band coupling flatness, and good return loss are achieved by using the proposed structure. For verification purposes, a prototype of the proposed coupler was designed, manufactured, and measured. The experimental results show that over the full waveguide bandwidth a return loss of input port better than 17.46 dB, coupling strength varying between −2.74 dB and −3.80 dB, power-split unbalance within 0.76 dB, and an isolation better than 20.82 dB were obtained. The length of the coupling region was only 15.82 mm.

A quasi-nonlocal coupling method for bond-based peridynamics with classical continuum mechanics

PurposeThe purpose of this paper is to propose a novel quasi-nonlocal coupling of the bond-based peridynamic model with the classical continuum mechanics model to fully take advantage of their merits and be free of ghost forces.Design/methodology/approachThis study reconstructs a total energy functional by introducing a coupling parameter that alters only the nonlocal interactions in the coupling region rather than the whole region and a modified elasticity tensor that affects the local interactions. Then, the consistency of force patch test is enforced in the coupling region to completely eliminate the ghost force in a general energy-based coupling scheme. For a one-dimensional problem, these coupling parameters are further determined through an energy patch test to preserve the energy equivalence or through an l1-regularization. And, for a two- or three-dimensional problem, depending on the existence of a solution to the discretized force patch test, they are determined through an l1-minimization or l1-regularization.FindingsOne- and two-dimensional numerical examples under affine deformation have been conducted to verify the accuracy of the quasi-nonlocal coupling method, which exhibits no ghost force. Moreover, the coupling model can reproduce almost the same deformation behaviors of points near the crack for a cracked plate under tension as that from a pure peridynamic model, the former with a rather low computational cost and an easier application of boundary conditions.Originality/valueThis work is aiming at getting over long-standing ghost force issues in the energy-based coupling scheme. The numerical results from the cracked plate problem are exhibited promising extension to dynamic problems.

Probing loop effects in wrong-sign Yukawa coupling region of Type-II 2HDM

In the framework of 2HDM, we explore the wrong-sign Yukawa region with direct and indirect searches up to one-loop level. The direct searches include the latest $$H/A \rightarrow f{\bar{f}}, VV, Vh, hh$$ H / A → f f ¯ , V V , V h , h h reports at current LHC, and the study of indirect Higgs precision measurements works with current LHC, future HL-LHC and CEPC. At tree level of Type-II 2HDM, for degenerate heavy Higgs mass $$m_A=m_H=m_{H^\pm }<800$$ m A = m H = m H ± < 800 GeV, the wrong-sign Yukawa regions are excluded largely except for the tiny allowed region around $$\cos (\beta -\alpha )\in (0.2,0.3)$$ cos ( β - α ) ∈ ( 0.2 , 0.3 ) under the combined Higgs constraints. The excluded region is also nearly independent of parameter $$m_{12}$$ m 12 or $$\lambda v^2=m_A^2-m_{12}^2/(\sin \beta \cos \beta )$$ λ v 2 = m A 2 - m 12 2 / ( sin β cos β ) . The situation changes a lot after including loop corrections to the indirect searches, for example $$m_A=1500 \text {~GeV}$$ m A = 1500 GeV , the region with $$\lambda v^2<0$$ λ v 2 < 0 will be stronger constrained to be totally excluded. Whilst parameter space with $$\lambda v^2>0$$ λ v 2 > 0 would get larger survived wrong-sign region for $$m_A=800 ~\text {~GeV}$$ m A = 800 GeV compared to it at tree level. We also conclude Higgs direct searches works better on constraining $$\lambda v^2 \approx 0$$ λ v 2 ≈ 0 GeV range than theoretical constraints. We also find that the loop-level wrong-sign Yukawa limit only occurs at mass decoupling scale.