arXiv subjects

M. Pang

Publications and source records attributed to M. Pang.

7 recordsLinked to original sources

arXiv2022

Higher-order-modes enhanced phase-matched dispersive-wave generation in the deep-blue and UV spectral region

During the last few decades, solid-core photonic crystal fibers (PCFs) have been extensively explored to generate broadband, high-coherence supercontinua (SC). Limited by the material absorption and relatively low nonlinearity of fused silica, spectral broadening in silica PCF-based SCs is usually restricted to the blue to near-infrared spectral regions, even in developed commercial sources. The output spectra of these sources are missing short wavelengths of the full range. Many efforts have been spent to break the limitation. Among them, dispersive-wave (DW) generation has been investigated for triggering new frequencies in short wavelengths. With satisfied phase-matching conditions, excessive energy can be directly transferred from solitons of the anomalous dispersion region to DWs of the short wavelengths. However, a systematical study of factors, including phase-matched DWs, strongly related to the dispersion tailoring of higher-order modes (HOMs), has rarely been shown. This study reports the experimental observations of HOM-enhanced phase-matchings for the DW generation in the deep-blue and ultraviolet regions. A solid-core PCF-based, UV-extended SC source spanning a 2.8-octave-wide (350 nm to 2500 nm) is demonstrated. Meanwhile, we carefully verify our findings via numerical calculations.

physics.optics↗

arXiv2018

Non-covalent bonds between optical solitons in an optoacoustically mode-locked fiber laser: Analysis & modelling

Binding of particles through weak (non-covalent) interactions plays a central role in multiple modern disciplines, from Cooper pairing of electrons in superconductivity to formation of supramolecules in biochemistry. Optical solitons, which are analogous in many ways to particles, arise from a balance between nonlinearity and dispersion and have only been known to be able to form molecule-like, localized structures through covalent interactions due to direct overlapping. Non-covalent binding of optical solitons that based on long-rang interactions have, however, so far escaped experimental observations. Long-range interactions between optical solitons have proven almost impossible to control, generally leading to disorder. In this paper, however we show that by tailoring weak, long-range soliton interactions, a large population of optical solitons in an optoacoustic mode-locking fiber laser can assemble into stable, highly-ordered structures that resemble biochemical supramolecules. We demonstrate here a theoretical model of the non-covalent binding mechanism, and provide some experimental results supporting this model.

physics.optics↗

arXiv2017

Supramolecular transmission of soliton-encoded bit streams over astronomical distances

A stream of optical pulses, transmitted over long distances in optical fiber, will be affected by a variety of noise sources, leading to degradation in the signal-to-noise ratio. This noise accumulation sets generic capacity limits of all fiber-based optical signal transmission systems and has long been regarded as unavoidable. We report that by tailoring long-range, non-covalent inter-pulse interactions, optical solitons in a fiber laser loop can robustly couple to each other and self-assemble into supramolecular structures that exhibit long-term stability, elementary diversity and the possibility of information encoding. We demonstrate error-free transmission of such self-assembled solitonic structures over many astronomical units without any active retiming, opening up the possibility of using bit-bit interactions to overcome noise accumulation in optical fiber telecommunications and bit-storage systems.

physics.optics↗

arXiv2015

Landau level transitions in InAs/AlSb/GaSb quantum wells

The electronic structure of InAs/AlSb/GaSb quantum wells embedded in AlSb barriers and in the presence of a perpendicular magnetic field is studied theoretically within the $14$-band ${\bf k}\cdot{\bf p}$ approach without making the axial approximation. At zero magnetic field, for a quantum well with a wide InAs layer and a wide GaSb layer, the energy of an electron-like subband can be lower than the energy of hole-like subbands. As the strength of the magnetic field increases, the Landau levels of this electron-like subband grow in energy and intersect the Landau levels of the hole-like subbands. The electron-hole hybridization leads to a series of anti-crossing splittings of the Landau levels. The energies of some Landau level transitions and their corresponding transition strengthes are calculated. The magnetic field dependence of some dominant transitions is shown with their corresponding initial-states and final-states indicated. This information should be useful in analyzing an experimentally measured magneto-optical spectrum. At high magnetic fields, multiple transitions due to the initial-state splitting can be observed. The dominant transitions at high fields can be roughly viewed as two spin-split Landau level transitions with many electron-hole hybridization induced splittings. The energy separations between the dominant transitions may decrease or increase versus the magnetic field locally, or may be almost field independent. The separations can be tuned by changing the width of InAs layer or the width of middle AlSb layer. When the magnetic field is tilted, the electron-like Landau level transitions show additional anti-crossing splittings due to the subband-Landau level coupling.

cond-mat.mtrl-sci↗

arXiv2013

Exact wave functions for the edge state of a disk-shaped two dimensional topological insulator

We report the exact wave functions for the eigen state of a disk-shaped two dimensional topological insulator. The property of the edge state whose energy lies inside the bulk gap is studied. It is found that the edge state energy is affected by the radius of the disk. For a fixed angular momentum index, there is a critical disk radius below which there exists no edge state. The value of this critical radius increases as the angular momentum index increases. In the limit of large disk radius, the energy of the edge state approaches a limiting value determined by the system parameters and independent of the angular momentum index. The derivation from this limiting value is inversely proportional to the radius with a coefficient proportional to the angular momentum index. In the general case, the energy differences between two edge states with adjacent angular momentum indexes are not equal. The exact and analytical wave functions also facilitates the investigation of electronic state in other structures of the two dimensional topological insulator.

cond-mat.mes-hall↗

arXiv2013

Influence of bulk inversion asymmetry on the magneto-optical spectrum of a HgTe topological insulator

The influence of bulk inversion asymmetry in [001] and [013] grown HgTe quantum wells is investigated theoretically. The bulk inversion asymmetry leads to an anti-crossing gap between two zero-mode Landau levels in a HgTe topological insulator, i.e., the quantum well with inverted band structure. It is found that this is the main contribution to the anti-crossing splitting observed in recent experimental magneto spectroscopic measurements. The relevant optical transitions involve different subbands, but the electron-electron interaction induced depolarization shift is found to be negligibly small. It is also found that the splitting of this anti-crossing only depends weakly on the tilting angle when the magnetic field is tilted away from the perpendicular direction to the quantum well. Thus, the strength of bulk inversion asymmetry can be determined via a direct comparison between the theoretical calculated one-electron energy levels and experimentally observed anti-crossing energy gap.

cond-mat.mes-hall↗

arXiv2013

Efficiency of electrical manipulation on two-dimensional topological insulators

We investigate the efficiency of electrical manipulation on two-dimensional topological insulators by considering a lateral potential superlattice on the system. The electronic states under various conditions are examined carefully. It is found that the dispersion of the mini-band and the electron distribution in the potential well region display an oscillatory behavior as the potential strength of the lateral superlattice increases. The probability of finding an electron in the potential well region can be larger or smaller than the average as the potential strength varies. This indicates that the electric manipulation efficiency on two-dimensional topological insulators is not as high as expected, which should be carefully considered in designing a device application that bases on two-dimensional topological insulators. These features can be attributed to the coupled multiple-band nature of the topological insulator model. In addition, it is also found that these behaviors are not sensitive to the gap parameter of the two-dimensional topological insulator model.

cond-mat.mes-hall↗