Ruggedized multimode star coupler for military applications

The development of a high-performance, ruggedized multimode star coupler intended for use in fiber optic data transmission networks aboard naval surface ships is reported. The coupler was designed to exhibit superior optical performance in terms of both low loss and highly uniform coupling. It was also designed to survive a range of severe environmental and mechanical tests, including impact from a 400-lb hammer dropped from a 5 foot height, and a temperature range of - 62°C to 125°C. The coupler sizes produced ranged from 8 × 8 to 64 × 64 port devices. Essential features of the design along with sample performance data are presented.     

Coupling characteristics of 4 × 4 elliptical core optical waveguide couplers

Coupling characteristics of 4 × 4 elliptical core optical waveguide couplers that consist of four highly elliptical core fibers, whose centers form a rectangle, are obtained. The effect of the aspect ratio of the individual elliptical core fibers as well as that of their rectangular arrangement on the coupling characteristics have been obtained. It is shown that the state of polarization of the input signal through such a coupler is maintained.     

Ring resonators with N × M couplers

Multiple-zero multiple-pole optical filter transfer functions may be implemented more efficiently in an integrated optics architecture if higher order N × M optical couplers are utilized. For example, a coherent ring resonator made from two 3×3 couplers offers some advantages over the three mirror Fabry-Perot etalon, which is its analog. To this end we develop the formalism for obtaining the transfer functions and scattering matrices of ring resonators made from two N × M couplers. We then present a methodology for analyzing serial and parallel systems of N × M optical coupler ring resonators.     

Fabrication and Characterization of Monolithically Fused Wavelength-Independent 1 × 4 Couplers

A new method for the fabrication of a monolithic 1 × 4 single-mode fused coupler is described together with details of its performance in terms of coupling ratio, spectral response and polarization sensitivity. The fabricated device exhibits ultra-broadband performance with low polarization dependent loss. The coupling pattern exhibits identical coupling to all interacting fibers, enabling an easy control on fabrication parameters of the device.     

Multiple-Output Fiber-Ring Lasers and Amplifiers in a Hybrid CATV and ADSL Broadcasting Optical Fiber Communication System

In this article we propose two kinds of new fiber ring structure with a semiconductor optical amplifier. The first structure is a one-fiber-ring amplifier with an 8 × 8 fiber coupler and a semiconductor optical amplifier (SOA). The second fiber ring structure is a two-fiber-ring laser including an 8 × 8 fiber coupler, a 2 × 2 E/O modulator, and an SOA. The 14-output spectra of the fiber laser are measured. The gain coefficients of each port of the multiple-output-fiber-ring amplifiers are also measured. We apply these two kinds of fiber ring structures in a hybrid CATV and ADSL broadcasting optical fiber communication system. This application can develop a broadcasting system with large coverage area without using many laser diodes and optical amplifiers. The performance of such a system is also analyzed in this article.     

Polymer-waveguide-based vertical coupler

A 2 × 2 polymer-waveguide-based vertical coupler was designed and fabricated. The relationships between the coupling efficiency and the key optical design parameters of vertical coupler (such as the crossing angle, gap thickness between two waveguide layers and the waveguide dimensions) were investigated by using beam propagation method. Based on these simulations, a fully polymer vertical coupler was demonstrated.     

Branes, geometry and N = 1 duality with product gauge groups of SO and Sp

We study N = 1 dualities in four-dimensional supersymmetric gauge theories as the world volume theory of D4 branes with one compact direction in type IIA string theory. We generalize the previous work for SO(N_c1) × Sp(N_c2) with the superpotential W = TrX⁴ to the case of W = TrX^4(k+1) in terms of brane configuration. We conjecture that the new dualities for the product gauge groups of SO(N_c1) × Sp(N_c2) × SO(N_c3), SO(N_c1) × Sp(N_c2) × SO(N_c3) × Sp(N_c4) and higher multiple product gauge groups can be obtained by reversing the ordering of NS5 branes and D6 branes while preserving the linking numbers. We also describe the above dualities in terms of wrapping D6 branes around 3-cycles of Calabi-Yau threefolds in type IIA string theory. The theory with adjoint matter can be regarded as taking multiple copies of NS5 brane in the configuration of brane or geometric approaches.     

3-D Electromagnetic Modeling of Polarization-Dependent Coupling Characteristics of 1×3 Linear Array Weakly Fused Fiber Couplers

Based on the full-wave surface integral equations method and the steplike approximation technique, a three-dimensional (3-D) electromagnetic model for simulating polarization-dependent power-coupling behavior of 1×3 linear array weakly fused fiber couplers is proposed. The accuracy of the proposed numerical model is confirmed to be good by comparing with the measured power transfer behavior at the fusing and elongating process of the couplers. In the 3-D modeling view, the polarization-dependent coupling behavior of two practical couplers, 1/3 power splitter and wavelength-flattened coupler, are numerically studied. It is seen that as the coupler is designed in a very weakly fused condition the polarization-dependent loss (PDL) is significantly increased. For designing the 1×3 coupler with low PDL, it is suggested that the aspect ratio has to be controlled in stronger fused range between 0.8 and 0.9.     

Fused biconical tapered fiber-optic devices: Application to data buses

Abstract

The technology of fiber-optic couplers based on fused biconical tapered structures is reviewed, and the linear and star data-bus configurations that can be constructed using these couplers are discussed. A useful network topology for interconnecting star couplers using the hybrid transmission-reflection star coupler is also proposed. This network configuration has the advantage of requiring significantly less optical fiber than networks employing a single transmission or reflection star.     

Fused biconical tapered fiber-optic devices: Application to data buses

The technology of fiber-optic couplers based on fused biconical tapered structures is reviewed, and the linear and star data-bus configurations that can be constructed using these couplers are discussed. A useful network topology for interconnecting star couplers using the hybrid transmission-reflection star coupler is also proposed. This network configuration has the advantage of requiring significantly less optical fiber than networks employing a single transmission or reflection star.     

In-Field n × 40 Gb/s Transmission Experiments with In-Line All-Optical Wavelength Conversion

In this work, WDM transmission with 40-Gbit/s per channel bit rate has been experimentally demonstrated over a 500-km link. Different chromatic dispersion conditions have been managed and in-line all-optical wavelength conversion has been carried out with a periodical poled lithium niobate (PPLN) device in a polarization-independent scheme. The link was obtained by connecting the fibers contained in an installed cable between Roma and Pomezia (25 km), encompassing single-mode (G.652) and high-end (G.655, non-zero dispersion with a particular value and flat curve for chromatic dispersion) fibers. Some 40 Gb/s channels were propagated in the link 500 km long and one channel was dropped from the link after 300-km propagation, wavelength converted, and added to the other channels for the next 200 km. The electrical data interfaces exploited a 4 × 10 Gbit/s to 1 × 40 Gbit/s MUX at the transmitter, along with a 1 × 40 Gbit/s to 4 × 10 Gbit/s DMUX at the receiver. Successful transmission of 4 channels, 200-GHz spaced, has been achieved over 500 km along both G.652 and G.655 links. No evidence of penalty comparing converted and unconverted channels has been reported. Transmission experiments of 8 × 40 Gbit/s, with 100 GHz frequency spacing, are also reported. No significant degradation has been observed in the case of the G.652 link.     

Enhanced performances of ZnO-TFT by improving surface properties of channel layer

Top-contact thin film transistors with ZnO as the channel layer and thermally grown SiO₂ as the gate dielectric were fabricated by using rf sputtering. The performances of ZnO-TFTs with different thicknesses of the active layer were investigated and the optimized condition was obtained. With the active layer thickness from 25 to 70 nm, the leakage current of devices increased from 10⁻¹⁰ to 10⁻⁸ A, and the on/off ratio decreased from 1.2×10⁷ to 2×10⁴. Atomic force microscope research indicated that with the thickness increased, the surface morphology of the active layer improved noticeably at first and then deteriorated. The 25-nm-thick ZnO TFT had the best surface morphology, and showed the best performance with a field effect mobility of 5.1 cm²/V S, on/off ratio of 1.2×10⁷ and threshold voltage of 20 V. This indicates that the surface properties of the channel layer have crucial affects on the performances of ZnO-TFTs.     

Adsorption mode change from adlayer- to restructuring-type with increasing coverage, evidenced by structural determination of c(2 × 2)→(4 × 4)→(5 × 5) sequence formed on Ni(001) by Li deposition

We determined surface structures in a structural sequence c(2 × 2)→(4 × 4)→(5 × 5) formed on Ni(001) at 370 K with increasing Li coverage by a dynamical low-energy electron diffraction analysis. The (4 × 4) and (5 × 5) are complex surface-structures involving restructuring of substrate surface atoms, and are analogous to the previously determined (3 × 3) and (4 × 4) structures formed for Li/Cu(001). The c(2 × 2) at low coverages is a Li adlayer, so a change of the adsorption mode from adlayer- to restructuring-type is evidenced in the course of increasing coverage within a monolayer range.     

Surface reconstructions of the Si(100)–Ge system

The surface reconstruction of epitaxial Ge layer on Si(100) was studied with ultrahigh vacuum scanning tunneling microscopy. The surface with 0.8 ML Ge grown in the presence of a hydrogen surfactant reveals the same structures as found in chemical-vapor-deposited Ge on Si(100): (i) defective (2×1) structure at 290°C, (ii) irregular (2×N) in Ge layer and defective (2×1) in bare Si regions at 420°C, and (iii) (2×N) in Ge-covered regions and c(4×4) in bare Si regions at 570°C. The morphology of step edges does not change with temperature, implying that the c(4×4) reconstruction is anisotropic in nature.     

The effect of nitrogen ion implantation on tungsten surfaces

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to study the phase, composition and chemical states of elements at the tungsten surface. The measurement results indicate that nitrogen-containing phase of tungsten were formed by nitrogen ion implantation (energy 40 keV, implantation doses of 4×10¹⁷, 8×10¹⁷ and 1.6×10¹⁸ ions/cm²). The formation of the W_x(O,N) and WN in the surface layer occurred as a result of nitrogen ion irradiation. A decrease in concentration of W_x(O,N) is observed with increasing N⁺ while that WN increases. Due to residual oxygen in the chamber WO₃ still exists at the surface of the specimen.     

Design and fabrication of compact 3-dB coupler in silicon-on-insulator

A novel compact 3-dB coupler is proposed and fabricated in silicon-on-insulator. The new coupler provides large output waveguide spacing of 125.0 μm with short device length of 867.0 μm and large cross-section of 6.0 × 4.0 μm. The device length can be remained essentially unchanged even when the output spacing is further enlarged to realize the complex applications in photonic integrated circuits. The fabricated device exhibits excess loss of 6.3 dB and low imbalance of 0.26 dB.     

A novel (8 × 4) superstructure as precursor to the c(4 × 4) phase during Sb/Si(0 0 1) desorption

The role of kinetics in the superstructure formation of the Sb/Si(0 0 1) system is studied using in situ surface sensitive techniques such as low energy electron diffraction, Auger electron spectroscopy and electron energy loss spectroscopy. Sb adsorbs epitaxially at room-temperature on a double-domain (DD) 2 × 1 reconstructed Si(0 0 1) surface at a flux rate of 0.06 ML/min. During desorption, multilayer Sb agglomerates on a stable Sb monolayer (ML) in a DD (2 × 1) phase before desorbing. The stable monolayer desorbs in the 600–850 °C temperature range, yielding DD (2 × 1), (8 × 4), c(4 × 4), DD (2 × 1) phases before retrieving the clean Si(0 0 1)-DD (2 × 1) surface. The stable 0.6-ML (8 × 4) phase here is a precursor phase to the recently reported 0.25-ML c(4 × 4) surface phase, and is reported for the first time.     

Multiplexed fiber optic sensors matrix demodulated by a white light interferometric Mach–Zehnder interrogator

A multiplexed white light interferometric fiber optic sensors matrix system was designed and demonstrated. In this system, a Mach–Zehnder optical path interrogating technique is used to demodulate each sensor of the sensors matrix. The sensors matrix consists of M×N sensing elements linked by a 1×M star coupler. The multiplexing capacity of the sensing scheme has been analyzed and an experimental result with a 2×2 sensors matrix was presented.     

新型大规模全光星形耦合器

提出了一种新型大规模全光星形耦合器。这种星形耦合器不但能提供巨大的端口数,而且由其构成的波分复用（WDM）星形网具有极大的组网灵活性,能方便地实现网络在线扩容,升级,满足未来超大规模双向波分复用网络系统的需求,同时也适用于目前广泛应用的单向波分复用网络系统。     

Comparison between MeV Ni and He ion-implanted planar optical waveguides in quartz

Optically polished crystalline quartz samples were implanted at room temperature by 2.6 MeV Ni⁺ ions with a dose of 9×10¹⁴ ions/cm² and 2.0 MeV He⁺ ions with a dose of 1.5×10¹⁶ ions/cm², respectively. A comparison of the MeV Ni⁺ ion-implanted planar waveguide formation was made with the MeV He⁺ ion-implanted one. The prism-coupling method was carried out to measure the dark modes in the quartz waveguides by using model 2010 prism coupler. Five modes were observed in the Ni⁺ implanted waveguide while 15 modes were found in the He⁺ ion-implanted one. Reflectivity calculation method was applied to fitting the refractive index profile. TRIM’98 (transport of ions in matter) code was used to simulate the damage profile in quartz by MeV Ni⁺ and He⁺ ions implantation, respectively. It is found that the refractive index profile in MeV Ni⁺ ions implanted waveguide is somewhat different in shape from that in MeV He⁺ ions implanted waveguide.