High transmission through waveguide bends by use of polycrystalline photonic-crystal structures

A hybrid photonic-crystal structure is presented as a candidate for enhancing transmission through sharp photonic-crystal waveguide bends built on a perforated dielectric slab. This structure, which we refer to as a polycrystalline structure, combines two photonic-crystal lattices. Polycrystalline photonic-crystal structures offer the ability to minimize reflections as well as mismatches that a propagating wave might encounter while undergoing a sharp corner or a discontinuity between different waveguide sections. The availability of polycrystalline structures in photonic crystals opens a broad range of possibilities for the development of optical devices. Numerical experiments are performed with two- and three-dimensional finite-difference time domain methods.     

Quantitative measurement of low propagation losses at 1.55 mum on planar photonic crystal waveguides

The Fabry-Perot resonance technique has been used to determine the propagation losses of planar photonic crystal (PC) waveguides. The structures are patterned into a GaInAsP confining layer on an InP substrate. Losses as low as 11 dB/mm have been measured on a guiding structure with three missing rows. The influence of the PC guide width and air-filling factor is demonstrated.     

Femtosecond quadrature-squeezed light generation in CdSe at 1.55 mum

We generated pulsed quadrature-squeezed light by cross-phase modulation in single-crystal hexagonal CdSe at wavelengths of 1.4 to 1.55mum . We measured 0.4-dB squeezing (0.7 dB is inferred at the crystal) with 100-fs laser pulses. The wavelength and the intensity dependence, as well as variations in the local oscillator configuration, are examined. At higher intensities squeezing is shown to deteriorate owing to competing nonlinear processes.     

Second-harmonic generation frequency-resolved optical gating analysis of low-intensity shaped femtosecond pulses at 1.55 mum

We illustrate observation and characterization of medium- and low-intensity shaped ultrashort pulses at lambda=1.55mum through single-shot geometry (multishot-average) second-harmonic generation-frequency-resolved optical gating. The pulses are shaped by amplitude filters in the Fourier plane of a compact folded shaper. Sensitivity to pulses with energies of less than 20 pJ and high dynamic range is reported for this configuration. Application of this method to the propagation of ~170-fs pulses through a 50-m fiber link is also illustrated.     

BaTiO3 thin-film waveguide modulator with a low voltage-length product at near-infrared wavelengths of 0.98 and 1.55 microm

A BaTiO3 thin-film electro-optic waveguide modulator with a low half-wave voltage-length product has been demonstrated at near-infrared wavelengths of 1-1.6 microm. Half-wave voltage-length products as small as 0.25 and 0.5 V cm were measured for a 5-mm-long device at wavelengths of 973 and 1561 nm, respectively. The effective electro-optic coefficients were calculated as 420 pm/V at 973 nm and 360 pm/V at 1561 nm. Further improvements in device performance by optimizing the ferroelectric domain structure are anticipated.     

Ultracompact waveguide bends with simple topology in two-dimensional photonic crystal slabs for optical communication wavelengths

Ultracompact waveguide bends with simple topology in two-dimensional photonic crystal slabs are proposed by using an annular air groove at the bend corner to improve transmissions of the bends. Analysis indicates that the guided light wave experiences a very slight difference of propagation properties between straight waveguides and bends (with 60 degrees and 120 degrees bending angles). Transmissions of more than 90% can be achieved in the 60 degrees and 120 degrees bends for light waves at 1.55 microm with bandwidths of 101 and 74 nm, respectively.     

Observation of chirped soliton dynamics at lambda = 1.55 microm in a single-mode optical fiber with frequency-resolved optical gating

We present an experimental observation of the dynamics of an initially chirped optical soliton at 1.55microm that is propagating through a single-mode optical fiber, using frequency-resolved optical gating (FROG). FROG permits observation of both the amplitude and the phase profiles of ultrashort pulses, providing complete information on the pulse evolution. The features that are detected, which include what is believed to be the first experimental observation of phase slips, are in quantitative agreement with numerical simulations that employ the nonlinear Schr?dinger equation.     

Trapping of surface plasmon polaritons in a multiple-teeth-shaped waveguide at visible wavelengths

We numerically and theoretically demonstrate that a metal–insulator–metal (MIM) waveguide with multiple-teeth-shaped graded depths can strongly slow light as the propagation velocities of surface plasmon polaritons (SPPs) are reduced over a large frequency bandwidth at visible wavelengths domain. Since the wavelength of the trough of transmission is dependent on the depth of the tooth-shaped dielectric in the MIM waveguide, the guided SPPs at different frequencies can be localized at different spatial positions of the multiple-teeth-shaped graded depths MIM waveguide, which can be proved by the scattering matrix method. The separation between trapped waves can be tuned by changing the grade of the tooth-shaped depths and the lifetime of SPPs in the waveguide may be long enough for some meaningful nano-photonic applications.     

Calculation of effective index for different dielectric waveguides structures made of PVCi/PMATRIFE polymers at telecom-wavelength \lambda =1.55\,\upmu m

In this paper, a number of polymeric waveguide structures have been analyzed by using two distinct techniques which are: effective index method (EIM) and numerical simulation based on finite difference method (FDM). The main aim of this investigation is the calculation of effective indexes (EI) of the following structures: rib, ridge and buried channel waveguides at telecom wavelength $\lambda =1.55\,\upmu \hbox {m}$ for different dimensions of waveguide cores varying from 1.5–4  $\upmu \hbox {m}$ . Moreover, other optical propagation characteristics such as: confinement factor, normalized and propagation constant have been studied in TE polarisation. Otherwise the effect of the structure parameters and dimensions on the dispersion characteristics has been investigated. On the other hand, the optical field distribution has been computed using commercial software named OlympIOs. The polymers applied in the design of waveguide structures are the PVCi (n = 1,562 $\lambda = {1.55}\,\upmu $ m) used as core layer and the PMATRIFE (n = 1,409 $\lambda = 1.55\,\upmu $ m) used as substrate or cladding layer. The results obtained using EIM and simulation based on FDM show that effective index and field confinement factor of TE fundamental mode increase monotonously with the increasing dimension of core. The obtained results are in good agreement with published data based on other numerical methods.     

Enhancing transmission efficiency of bending waveguide based on graded sonic crystals using antireflection structures

The conventional antireflection coating (ARC) structure for sonic crystal devices is to place the cylinders at the interface between a sonic crystal device and a background medium. The radius of ARC cylinders and the distance between the ARC and the sonic crystal device are adjusted to obtain an optimal antireflection effect. We propose that ARC structures are directly designed by using the conventional ARC theory instead of scanning the geometric and spatial parameters of the conventional ARC structures. According to the concept of the effective refractive index of sonic crystals, the exact ARC structures can be implemented by sonic crystals. The transmission efficiency of a bending waveguide designed by graded sonic crystals can be enhanced by introducing the ARC structures based on sonic crystals. The performances of different ARC structure designs are compared and discussed.     

慢光在光子晶体弯折波导中的高透射传播

研究了慢光模式在SOI(silicon-on-insulator)材料光子晶体线缺陷弯折波导中的传输特性. 通过优化波导弯折处的结构参数,慢光模式在光子晶体60°与120°弯折波导中的透射率提高10倍以上,归一化透射率分别达到80%和60%以上. 为了进一步减慢光速,设计了新颖的高Q值耦合腔弯折波导结构,在归一化透射率达到75%的基础上,光波群速度低至c/170(c为真空光速). 研究结果对于增强光子晶体的慢光效应,提高光子晶体慢光器件的微型化和集成化都有一定的积 关键词： 光子晶体 慢光 弯折波导 透射率     

Phase-matched four-wave mixing of isolated waveguide modes of high-intensity femtosecond pulses in a hollow photonic-crystal fiber

Hollow-core photonic-crystal fibers with a special dispersion profile are shown to allow phase-matched nonlinear optical interactions of isolated air-guided modes of high-intensity femtosecond laser pulses confined in the hollow fiber core. We present theoretical and experimental studies of the four-wave mixing of fundamental and second-harmonic pulses of a Cr:forsterite laser with an initial pulse duration of about 50 fs and an intensity on the order of 10¹⁴ W/cm² in waveguide modes of a hollow photonic-crystal fiber with a core diameter of about 13μm.     

Fine structural adjustment of lasing wavelengths in photonic crystal waveguide laser arrays

We propose new and simple designs that allow one to adjust the relative frequency of photonic crystal waveguide lasers included in a laser array. Using numerical simulations, we demonstrate that wavelength shifts smaller than 2 nm can be achieved while remaining compatible with common lithographic precision. Specific details of the implemented methods allow to deal with relative shifts as small as ≈2×10⁻⁴.     

Experimental demonstration of two methods for controlling the group delay in a system with photonic-crystal resonators coupled to a waveguide

We measure the group delay in an on-chip photonic-crystal device with two resonators side coupled to a waveguide. We demonstrate that such a group delay can be controlled by tuning either the propagation phase of the waveguide or the frequency of the resonators.     

Frequency dependence of acoustooptic interaction efficiency in anisotropic graded-index waveguide

An analysis of the dependence of the Bragg acoustooptical interaction efficiency of TE modes in a graded-index optical waveguide on the acoustic surface wave (ASW) frequency has been made. It is shown that two waveguides having different optical parameters but the same number of modes are described practically by the same frequency dependence. This conclusion is confirmed by the calculation for two four-mode waveguides on the Y-cut lithium niobate. The frequency dependence for various processes in the range 50÷550 MHz has been experimentally measured.     

Performance of a low-loss pulsed-laser-deposited Nd:Gd(3) Ga(5)O(12) waveguide laser at 1.06 and 0.94 mum

We report the laser performance of a low-propagation-loss neodymium-doped Gd(3)Ga(5)O(12) (Nd:GGG) waveguide fabricated by pulsed-laser deposition. An 8- mum -thick crystalline Nd:GGG film grown upon an undoped Y(3)Al(5)O(12) substrate lases at 1.060 and 1.062 microm when pumped by a Ti:sapphire laser operating at 740 or 808nm.Using a 2.2% output coupler, we observed a 1060-nm laser threshold of 4mW and a slope efficiency of 20%. Laser action was also achieved, for what we believe is the first time in Nd:GGG, on the quasi-three-level 937-nm transition. With a 2% output coupler at this wavelength a laser threshold of 17mW and a 20% slope efficiency were obtained. This demonstration of low propagation loss combined with the fact that these waveguides have a very high numerical aperture (0.75) makes pulsed-laser-deposited thin films attractive for high-power diode-pumped devices.     

Mode analysis of surface plasmon metal-dielectric-metal nanowire array waveguide at sub-wavelength scale

The investigation of quantum and classical correlations has mostly concentrated on two-qubit states because the minimization in the classical correlation is quite complicated for high-dimensional states. Thermal quantum and classical correlations are studied for a two-qutrit system with various coupling constants, external magnetic fields, and temperatures as well, where the quantum correlation is described in terms of the quantum discord that has been extensively used in recent literature. The entanglement negativity is calculated for comparison. It is shown that the discord is nonzero whereas the negativity is zero in some ranges of system parameters and temperature. Moreover, the discord is more robust than the entanglement against temperature and magnetic field. However, at lower temperatures all three correlations behave similarly. Those are useful for understanding quantum correlations in high-dimensional mixed states and quantum information processing.