Novel optical packet with non-return-to-zero label and duobinary carrier-suppressed return-to-zero payload

A novel packet format with non-return-to-zero (NRZ) label and duobinary carrier-suppressed return-to-zero (DCS-RZ) payload is proposed for optical packet switching networks.NRZ label is followed by DCS-RZ payload with a certain guard time.The spectra of the low-rate NRZ label locate around the optical carrier frequency where some parts of the corresponding spectra of the high-rate DCS-RZ payload have been suppressed due to DCS-RZ modulation.At the switching node,the label or payload extraction can be realized simply through an optical bandpass or notch filter respectively.The feasibility of the scheme is verified by the simulation on the famous photonic design platform designed by Virtual Photonics Inc.(VPI).The effects of optical filter bandwidth on the received signal quality are discussed by analyzing bit error rate(BER)and contrast ratio performances.     

高下路空气孔型光子晶体环形谐振腔的设计

提出一种基于二维正方晶格光子晶体空气孔型高下路效率的环形谐振腔,通过压缩线缺陷波导的宽度实现单模有效控制,同时讨论内围光子晶体列数对传输场的影响,然后运用二维时域有限差分方法数值分析了耦合强度及环区局部折射率调制对下路效率、品质因子以及下路波长等参量的影响.结果表明:当波导宽度为0.7个晶格常量,耦合强度为0个晶格常量,在信道波长为1 528.1 nm时,下路效率为99%,品质因子Q为379;当耦合强度提高到1个晶格常量,下路波长稍微漂移为1 524.3 nm,品质因子显著提高到1 397,而下路效率下降为89%.同时,下路波长会随着环区折射率的增加呈线性红移.     

Photonic crystal LEDs – designing light extraction

Photonic crystals (PhCs) have attracted much attention during the last decade as a solution to overcome the low extraction efficiency of as‐grown light‐emitting diodes (LEDs). In this review we describe the underlying physics and summarize recent results obtained with PhC LEDs. Here, the main focus is on diffracting PhC. In order to quantify the benefit from the incorporation of PhCs for diffracting light a comparison by simulations between a PhC LED and a standard state‐of‐the‐art LED is carried out. Finally, the impact of the PhC on the LEDs emission characteristics will be discussed with respect to étendue‐limited applications.     

光子学及其讨论

本文简述了光子学提出后,国内外的反响。并就处理高速摄影与光子学的关系问题,提出了“高速光子学”,把它作为光子学的一个分支。这个分支的主要研究对象是高速过程或超快现象,并以时间—空间分辨方式提供信息。末了,探讨了光子学本身的发展前景:随着光计算机研究工作的进展和实现,将确立光子学的牢固地位。     

Epitaxial Growth of Aligned Semiconductor Nanowire Metamaterials for Photonic Applications

A novel class of optical metamaterials is presented consisting of high densities of aligned gallium phosphide (GaP) nanowires fabricated using metal‐organic vapor phase‐epitaxy. Starting from a gold island film as a catalyst for nanowire growth, a sequential combination of vapor–liquid–solid and lateral growth modes is employed to obtain a continuous tunability of the nanowire volume fraction from 7% to over 35%. By choosing different crystallographic orientations of the GaP substrate, metamaterials are designed with different nanowire orientations. The anisotropy of the nanowire building blocks results in strong optical birefringence. Polarization interferometry demonstrates a very large polarization extinction contrast of 4 × 10³ combined with a sharp angular resonance which holds promise for optical sensing. Nanowire metamaterials may find applications in photonics, optoelectronics, non‐linear and quantum optics, microfluidics, bio‐, and gas sensing.     

Investigation on chalcogenide and silica based photonic crystal fibers with circular and octagonal core

In this paper, a novel chalcogenide and silica photonic crystal fiber (PCF) structure is designed with circular air-holes located in the cladding and the various optical properties, namely, dispersion, nonlinearity and group velocity dispersion parameters are compared for two different core structures, namely, circular and octagonal. The objective is to obtain high nonlinearity with dispersion flattened PCF. The prime focus is to obtain high non-linear effects as it plays great role in speed and capacity of optical communications. The proposed chalcogenide octagonal and circular PCF exhibits a dispersion of +77.55 ps/(nm km) and +77.34 ps/(nm km), respectively, whereas, the nonlinearity is in the order of 4506 W⁻¹ km⁻¹ and 4498 W⁻¹ km⁻¹, respectively. Also, the silica octagonal and circular PCF exhibits a dispersion of +19.03 ps/(nm km) and +0.97 ps/(nm km) respectively, whereas the nonlinearity is in the order of 169.41 W⁻¹ km⁻¹ and 182.41 W⁻¹ km⁻¹ respectively.     

Formation and control of Turing patterns and phase fronts in photonics and chemistry

We review the main mechanisms for the formation of regular spatial structures (Turing patterns) and phase fronts in photonics and chemistry driven by either diffraction or diffusion. We first demonstrate that the so-called ‘off-resonance’ mechanism leading to regular patterns in photonics is a Turing instability. We then show that negative feedback techniques for the control of photonic patterns based on Fourier transforms can be extended and applied to chemical experiments. The dynamics of phase fronts leading to locked lines and spots are also presented to outline analogies and differences in the study of complex systems in these two scientific disciplines.     

AlGaN-based high-performance metal–semiconductor–metal photodetectors

Design, structure growth, fabrication, and characterization of high performance AlGaN-based metal–semiconductor–metal (MSM) photodetectors (PD) are reported. By incorporating AlN nucleation and buffer layers, the leakage current density of GaN MSM PD was reduced to 1.96 × 10⁻¹⁰ A/cm² at a 50 V bias, which is four orders of magnitude lower compared to control devices. A 229 nm cut-off wavelength, a peak responsivity of 0.53 A/W at 222 nm, and seven orders of magnitude visible rejection was obtained from Al_0.75Ga_0.25N MSM PD. Two-color monolithic AlGaN MSM PD with excellent dark current characteristics were demonstrated, where both detectors reject the other detector spectral band with more than three orders of magnitude. High-speed measurements of Al_0.38Ga_0.62N MSM PD resulted in fast responses with greater than gigahertz bandwidths, where the fastest devices had a 3-dB bandwidth of 5.4 GHz.     

Structural symmetry of two-dimensional metallic arrays: Implications for surface plasmon excitations

We report our recent investigation of the (0, ±1)-type SPP excitation of a gold two-dimensional nano-cavity array using finite-difference time-domain methodology. Our particular focus is on the symmetry properties of (0, ±1)-SPPs excited by different polarizations of light. Based on a group theory approach, we have shown that these (0, ±1) modes are originated from different symmetry modes at the Γ-point, and the B-(0, ±1) dispersion curve converges to the A-(−1, 0) dispersion curve at the Γ-point. This indicates these (0, ±1) modes are very different in their symmetry properties. As a result, the control of polarization may provide important insights into the manipulation of SPPs.     

Dinuclear Metal–Organic Material for Binary Optical Recording

A diimine ligand tethered to anthracene in the 9‐position, 4′‐(9‐anthrylethyl)‐4‐methyl‐2,2′‐bipyridine (bpy‐An), was dimerized through cycloaddition photochemistry. The resultant head‐to‐tail photodimer (bpy‐PD) was used as a bridging ligand in the preparation of a new dinuclear Ru^II complex, [Ru(dmb)₂(bpy‐PD)Ru(dmb)₂]⁴⁺ (dmb = 4,4′dimethyl‐2,2′‐bipyridine). The corresponding mononuclear species containing anthracene ([Ru(dmb)₂(bpy‐An)]²⁺ was also synthesized and serves as a model compound in this study. UV photolysis (λ < 300 nm) of the strongly luminescent Ru^II dinuclear complex results in cycloreversion, generating two anthracene‐containing mononuclear species, [Ru(dmb)₂(bpy‐An)]²⁺, whose emission is largely quenched as a result of nonradiative triplet–triplet energy transfer. The photophysical and photochemical properties of the dinuclear system have been studied in CH₃CN solutions and in solid polyvinyl alcohol (PVA) thin films. The “on”–“off” luminescence switching characteristics and concomitant non‐destructive readout properties suggested that these molecules could be useful in read‐only memory (ROM) applications. In the solid state, micrometer‐sized objects were imaged using visible light, taking advantage of the luminescence contrast generated from the UV photochemical reaction. These written images were stable for at least 6 months, indicating that long‐term binary data storage is indeed feasible in these ROM metal–organic materials.