Polar Quasi-Confined Optical Phonon Modes in Wurtzite Quasi-One-Dimensional GaN/Al_xGa_(1-x)N Quantum Well Wires

Based on the dielectric continuum model and Loudon＇s uniaxial crystal model,quasi-confined （QC） optical phonon modes and electron-QC phonon coupling functions in quasi-one-dimensional （QID） wurtzite quantum well wires （QWWs） are deduced and analyzed. Numerical calculations on an AIN/GaN/AIN wurtzite QWW are performed. The results reveal that the dispersions of the QC modes are quite obvious only when the free wavenumber kz in the z-direction and the azimuthal quantum number m are small. The reduced behavior of the QC modes in wurtzite quantum systems is clearly observed. Through the discussion of the electron-QC mode coupling functions,it is found that the lower-frequency QC modes in the high-frequency region play a more important role in the electron-QC phonon interactions. Moreover,our computations also prove that kz and m have a similar influence on the electron-QC phonon coupling properties.

Effects of transverse mode coupling and optical confinement factor on gallium-nitride based laser diode

We have investigated the transverse mode pattern and the optical field confinement factor of gallium nitride （GaN） laser diodes （LDs） theoretically. For the particular LD structure, composed of approximate 4 μm thick n-GaN substrate layer, the maximum optical confinement factor was found to be corresponding to the 5^th order transverse mode, the so-called lasing mode. Moreover, the value of the maximum confinement factor varies periodically when increasing the n-side GaN layer thickness, which simultaneously changes and increases the oscillation mode order of the GaN LD caused by the effects of mode coupling. The effects of the thickness and the average composition of Al in the AlGaN/GaN superlat.tice on the optical confinement factor are also presented. Finally, the mode coupling and optimization of the layers in the GaN-based LD are discussed.

RESEARCH ON TRANSVERSE STRESS CHARACTER OF SINGLE MODE OPTICAL FIBER

This paperdetails experimental work done to quantify stress measurements made optically utilizing ordinary single mode optical fibers. Strain-induced changes of birefringence for ordinary single mode optical fiber responses are characterized against standard stress measurements in a well understand configuration. The experimental scheme for this work and the results are presented in detaial. In this paper, POssible applications for this transverse stress character of single mode fibers are also proposed.

Phonon States and Dispersive Spectra of Polar Optical Phonons in Quasi-One-Dimensional Nanowires of Wurtzite ZnO and Zinc-Blend MgO Semiconductors

Within the framework of the macroscopic dielectric continuum model and Loudon＇s uniaxial crystal model, the phonon modes of a wurtzite/zinc-blende one-dimensional （1D） cylindrical nanowire （NW） are derived and studied. The analytical phonon states of phonon modes are given. It is found that there exist two types of polar phonon modes, i.e. interface optical （IO） phonon modes and the quasi-confined （QC） phonon modes existing in 1D wurtzite/zinc-blende NWs. Via the standard procedure of field quantization, the Fr6hlich electron-phonon interaction Hamiltonians are obtained. Numerical calculations of dispersive behavior of these phonon modes on a wurtzite/zinc-blende ZnO/MgO NW are performed. The frequency ranges of the IO and QC phonon modes of the ZnO/MgO NWs are analyzed and discussed. It is found that the IO modes only exist in one frequency range, while QC modes may appear in three frequency ranges. The dispersive properties of the IO and QC modes on the free wave-number kz and the azimuthal quantum number m are discussed. The analytical Hamiltonians of electron-phonon interaction obtained here are quite useful for further investigating phonon influence on optoelectronics properties of wurtzite/zinc-blende 1D NW structures.

High-speed polarization mode dispersion compensation in a 43-Gb/s RZ-DQPSK transmission system over 1200 km of standard single-mode fibre

This paper reports that the designed optical polarization mode dispersion compensator shows a good performance under the real-time variation of differential group delay, state of polarization and principal state of polarization in a （40×43）-Gb/s dense-wavelength-multiplexing, 1200-km enhanced return-to-zero differential-quadrature-phase-shift- keying （RZ-DQPSK） system. The polarization mode dispersion tolerance of the system is improved by 26 ps using the optical polarization mode dispersion compensator. The short and long time stabilities are tested with the bit error ratio recorded.

Characteristics of High-power GaAs Laser Beams and Their Coupling with Fibers

The beams of 980nm high-power LDs are analyzed, and the reasons that aspect ratio of LD beams is high are explained. It is certified by the test that cylindrical lens can efficiently compress the perpendicular divergence angle of the beam. Some typical and popular lensed fibers were compared and analyzed according to coupling characteristics. The factors which affect the coupling efficiency and tolerance of the wedged-shaped GRIN tipped lensed fiber are pointed out, and some methods to reduce the coupling loss of the lensed fibers are proposed finally.

Ru thickness-dependent interlayer coupling and ultrahigh FMR frequency in FeCoB/Ru/FeCoB sandwich trilayers

The antiferromagnetic(AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic(FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance(FMR) frequency. Changing the non-magnetic spacer thickness is an effective way to control the interlayer coupling type and intensity, as well as the FMR frequency. In this study, Fe Co B/Ru/Fe Co B sandwich trilayers with Ru thickness(tRu) ranging from 1 A to 16 A are prepared by a compositional gradient sputtering(CGS) method. It is revealed that a stress-induced anisotropy is present in the Fe Co B films due to the B composition gradient in the samples. A tRu-dependent oscillation of interlayer coupling from FM to AFM with two periods is observed. An AFM coupling occurs in a range of 2 A ≤ tRu≤ 8 A and over 16 A, while an FM coupling is present in a range of tRu< 2 A and 9 A ≤ tRu≤ 14.5 A. It is interesting that an ultrahigh optical mode(OM) FMR frequency in excess of 20 GHz is obtained in the sample with tRu= 2.5 A under an AFM coupling. The dynamic coupling mechanism in trilayers is simulated, and the corresponding coupling types at different values of tRuare verified by Layadi’s rigid model. This study provides a controllable way to prepare and investigate the ultrahigh FMR films.

Controlling multiple optomechanically induced transparency in the distant cavity-optomechanical system

We theoretically investigate a two-cavity optomechanical system in which each optical cavity couples to a mechanical resonator via radiation pressure force,and the two optical cavities couple to each other via a distant waveguide.Our study shows that the multiple optomechanically induced transparency can be observed from the output field at the probe frequency.The number and width of the transparent windows can be tuned by the classical driving power Pl.We also analyze the distance of the two outermost transparency windows,which shows a linear relation with the parameters Pl andλ.Our approach is feasible for controlling multipartite induced transparency,which represents a valuable step towards quantum networks with photonic and phononic circuits.

First principles study and comparison of vibrational and thermodynamic properties of XBi(X=In,Ga,B,Al)

In the present work, vibrational and thermodynamic properties of XBi（X = B, Al, Ga, In） compounds are compared and investigated. The calculation is carried out using density functional theory（DFT） within the generalized gradient approximation（GGA） in a plane wave basis, with ultrasoft pseudopotentials. The lattice dynamical properties are calculated using density functional perturbation theory（DFPT） as implemented in Quantum ESPRESSO（QE） code. Thermodynamic properties involving phonon density of states（DOS） and specific heat at constant volume are investigated using quasiharmonic approximation（QHA） package within QE. The phonon dispersion diagrams for InBi, GaBi, BBi, and AlBi indicate that there is no imaginary phonon frequency in the entire Brillouin zone, which proves the dynamical stability of these materials. BBi has the highest thermal conductivity and InBi has the lowest thermal conductivity. AlBi has the largest and GaBi has the smallest reststrahlen band which somehow suggests the polar property of XBi materials. The phonon gaps for InBi, GaBi, BBi and AlBi are about 160 cm^-1, 150 cm^-1, 300 cm^-1, and 150 cm^-1, respectively. For all compounds,the three acoustic modes near the gamma point have a linear behavior. C_V is a function of T-3 at low temperatures while for higher temperatures it asymptotically tends to a constant as expected.

Generation of entangled TEM_(01) modes with periodically poled KTiOPO_4 crystal

Spatial quantum optics based on the high-order transverse mode is important for the super-resolution measurement and quantum image beyond the shot noise level. Quantum entanglement of the transverse plane Hermite–Gauss TEM（01） mode has been demonstrated experimentally in this paper. Two squeezed TEM（01） modes, which are generated by a pair of degenerate optical parametric amplifiers（DOPA） with the nonlinear crystals of periodically poled KTi OPO4, have been combined to produce TEM（01） mode entanglement using a beam splitter. The 1.5 dB for the sum of amplitude and 1.2 dB for the difference of phase below shot-noise level is achieved with the measurement system of a Bell state detection.

Guided Modes of Hollow Optical Fiber Based Components: Analytical Solutions

Guided modes in a hollow optical fiber are investigated using both scalar approximation and exact vectorial analysis. Effective indices of modes are seen to exhibit "nearly degenerate" groups. Besides providing an insight of modal characteristics, the analysis would prove to be useful to define design parameters for realizing components based on these fibers, and to explore new possibilities.

Optical Wavelength Filter Using Mode Conversion in Multimode Waveguide

A wavelength filter with simple structure using multimode waveguide is proposed. The device uses mode conversion by a grating structure fabricated simultaneously with the multimode waveguide.

Effects of the slot width and angular position on the mode splitting in slotted optical microdisk resonator

A novel slotted optical microdisk resonator, which significantly enhances light–matter interaction and provides a promising approach for increasing the sensitivity of sensors, is theoretically and numerically investigated. In this slotted resonator, the mode splitting is generated due to reflection of the slot. Remarkably, effects of the slot width and angular position on the mode splitting are mainly studied. The results reveal that the mode splitting is a second function of the slot width, and the maximum mode splitting induced by the slot deformation is achieved with 2.7853 × 10~9Hz∕nm. Therefore, the slotted resonator is an excellent candidate for pressure and force sensing. Besides, the influence of the slot angular position on the mode splitting is a cosine curve with the highest sensitivity of 1.23 × 10^(11)Hz∕deg; thus, the optical characteristic demonstrates that the slotted resonator can be used for inertial measurements.

Optical fiber sensor based on the short-range surface plasmon polariton mode

An optical fiber sensor for ultrathin layer sensing based o51 short-range surface plasmon polariton （SRSPP） is proposed, and the sensing characteristics are theoretically analyzed. Simulation results indicate that even for a detecting layer much thinner than the vacuum wavelength, a resolution as high as 3.7×10-6 RIU can be obtained. Moreover, an average ttfickness-detection sensitivity of 6.2 dB/nm is obtained, which enables the sensor to detect the thickness variation of the ultrathin layer up to tens of nanometers. The sensitive region of thickness could be adjusted by tuning the structure parameters.

Fiber guiding at the Dirac frequency beyond photonic bandgaps

Light trapping within waveguides is a key practice of modern optics,both scientifically and technologically.Photonic crystal fibers traditionally rely on total internal reflection(index-guiding fibers)or a photonic bandgap(photonic-bandgap fibers)to achieve field confinement.Here,we report the discovery of a new light trapping within fibers by the so-called Dirac point of photonic band structures.Our analysis reveals that the Dirac point can establish suppression of radiation losses and consequently a novel guided mode for propagation in photonic crystal fibers.What is known as the Dirac point is a conical singularity of a photonic band structure where wave motion obeys the famous Dirac equation.We find the unexpected phenomenon of wave localization at this point beyond photonic bandgaps.This guiding relies on the Dirac point rather than total internal reflection or photonic bandgaps,thus providing a sort of advancement in conceptual understanding over the traditional fiber guiding.The result presented here demonstrates the discovery of a new type of photonic crystal fibers,with unique characteristics that could lead to new applications in fiber sensors and lasers.The Dirac equation is a special symbol of relativistic quantum mechanics.Because of the similarity between band structures of a solid and a photonic crystal,the discovery of the Dirac-point-induced wave trapping in photonic crystals could provide novel insights into many relativistic quantum effects of the transport phenomena of photons,phonons,and electrons.

A tutorial introduction to graphene-microfiber waveguide and its applications

Graphene-microfiber with the advantage of graphene material and the microfiber has been hailed as a wonderful waveguide in optics. A tutorial introduction to the graphene-microfiber （GMF） waveguides including the effect of graphene on waveguide, fabrication and applica- tions has been presented. Here, we reviewed recent progress in the graphene waveguides from mode-locking and Q-switching in fiber laser to gas sensing and optical modulation. A brief outlook for opportunities and challenges of GMF in the future has been presented. With the novel nanotechnology emerging, GMF could offer new possibilities for future-optic circuits, systems and networks.

One-phonon resonant electron Raman scattering in multilayer coaxial cylindrical Alx Gal_xAs/GaAs quantum cables＊

We have presented a theoretical calculation of the differential cross section （DCS） for the electron Ra- man scattering （ERS） process associated with the interface optical （IO） and surface optical （SO） phonons in mul- tilayer coaxial cylindrical AlxGal-xAs/GaAs quantum cables （QC）. We consider the Frohlich electron-phonon interaction in the framework of the dielectric continuum approach. The selection rules for the processes are stud- ied. Singularities are found to be sensitively size-dependent and by varying the size of the QC, it is possible to control the frequency shift in the Raman spectra. A discussion of the phonon behavior for the QC with different size is presented. The numerical results are also compared with those of experiments.

Review on developments of novel specialty fibers： performance, application and process

This paper reviews the development progress of optical fiber, the producing and application of the specialty optical fiber in the world. Finally it states the leading technology of optical fiber of the world. Specialty optical fibers are series of optical fiber which could satisfy special requirements. Recently, the rapidly growing need from fiber to the home （FTTH）, sensors, active optical link, energy conversion and delivery and fiber laser attracts researchers and optical companies to explore more possibilities of optical fiber and some novel specialty optical fibers were invented for the efforts. Bending insensitive optical fiber with the ability of extreme 3 mm bending diameter makes it possible to use the optical fiber as the electric wire in some extremely compact devices. Higher power was achieved in the fiber laser field with the development of rare earth doped fiber. Nanomaterials such as Au particles and ZnO nanostructures were utilized to extend the application in sensors and energy conversion. Pure silica design was commercialized to improve the radiation resistance of sensors based on fiber optics.