Radiation integral areas are localized and reduced based upon the locality of scattering phenomena. In the high frequency, the scattering field is given by the currents, not the entire region, but on the local areas near the scattering centers, such as the stationary phase points and edge diffraction points, due to the cancelling effect of integrand in the radiation integral. The numerical calculation which this locality is implemented into has been proposed for 2-dimensional problems. The scattering field can be approximated by integrating the currents weighted by the adequate function in the local areas whose size and position are determined appropriately. Fresnel zone was previously introduced as the good criterion to determine the local areas, but the determination method was slightly different, depending on the type of scattering centers. The objective of this paper is to advance the Fresnel zone criteria in a 2-dimensional case to the next stage with enhanced generality and applicability. The Fresnel zone number is applied not directly to the actual surface but to the virtual one associated with the modified surface-normal vector satisfying the reflection law. At the same time, the argument in the weighting function is newly defined by the Fresnel zone number instead of the actual distance from the scattering centers. These two revisions bring about the following three advantages; the uniform treatment of various types scattering centers, the smallest area in the localization and applicability to 3-dimensional problems.

We propose a built-in planar lens for coupling light to a waveguide on a 2-D photonic crystal (PhC) membrane. A 2-D PhC waveguide with the built-in lens has been fabricated with AlGaAs. Improvement in coupling performance is discussed in comparison to waveguides with straight ends as cleaved.

Radio frequency on free-space optical (RoFSO) technology is regarded as a new universal platform for enabling seamless convergence of fiber and FSO communication networks, thus extending broadband connectivity to underserved areas. In this paper, we investigate the performance to characterize the transmission of code division multiple access (CDMA) based wireless signals over RoFSO system using aperture averaging (AA) technique under strong turbulence conditions. An analytical model including a modified carrier-to-noise-plus- interference ratio (CNIR) form and a novel closed-form expression for the bit-error rate (BER) is derived. Unlike earlier work, our model takes into consideration the effect of using the AA technique modeled by the gamma-gamma distribution, the optical noises, the intermodulation distortion term due to the laser diode non-linearity and the multiple interference access. By investigating the impact of AA on our model in the strong turbulence regime, we show that there is a design trade-off between the receiver lens aperture and the number of users to achieve a required CNIR ensuring a substantial scintillation fade reduction. The presented work can be used as baseline for the design and performance evaluation of the RoFSO system's ability to transmit different broadband wireless services signals over turbulent FSO links in real scenarios.

We investigate electronic mitigation of linear and nonlinear fibre impairments and compare various digital signal processing techniques, including electronic dispersion compensation (EDC), single-channel back-propagation (SC-BP) and back-propagation with multiple channel processing (MC-BP) in a nine-channel 112 Gb/s PM-mQAM (m=4,16) WDM system, for reaches up to 6,320 km. We show that, for a sufficiently high local dispersion, SC-BP is sufficient to provide a significant performance enhancement when compared to EDC, and is adequate to achieve BER below FEC threshold. For these conditions we report that a sampling rate of two samples per symbol is sufficient for practical SC-BP, without significant penalties.

We describe a concept and realization of distance-adaptive (DA) resource allocation in spectrum-sliced elastic optical path network (SLICE). We modify the modulation format and cross-connection bandwidth of individual fixed-bit rate optical paths to optimize performance with respect to transmission distance. The shorter paths are allocated a smaller amount of resources which allows reducing the spectrum occupied by the channel. We show in calculation a reduction in required spectral resources of more than 60% when compared to the traditional traffic allocation schemes based on ITU-T grid. The concept is verified experimentally.

We demonstrate an all-optical picosecond pulse duration-tunable nonreturn-to-zero (NRZ)-to-return-to-zero (RZ) data format conversion using a Raman amplifier-based compressor and a fiber-based four-wave mixing (FWM) switch. A NRZ data signal is injected into the fiber-based FWM switch (AND gate) with a compressed RZ clock by the Raman amplifier-based compressor, and convert to RZ data signal by the fiber-based FWM switch. The compressed RZ clock train acts as a pump signal in the fiber-based FWM switch to perform the NRZ-to-RZ data format conversion. By changing the Raman pump power of the Raman amplifier-based compressor, it is possible to tune the pulse duration of the converted RZ data signal from 15 ps to 2 ps. In all the tuning range, the receiver sensitivity at bit error rate (BER) of 10-9 for the converted RZ data signal was about 1.31.7 dB better than the receiver sensitivity of the input NRZ data signal. Moreover, the pulse pedestal of the converted RZ data signals is well suppressed owing to the FWM process in the fiber-based FWM switch.

The diffraction by a composite wedge composed of a perfect conductor and a lossy dielectric is investigated using the hidden rays of diffraction (HRD) method. The usual principle of geometrical optics is employed to trace not only ordinary rays incident on the lit boundary but also hidden rays incident on the shadow boundary. The modified propagation constants are adopted to represent the non-uniform plane wave transmission through the lossy dielectric. The HRD diffraction coefficients are constructed routinely by the sum of the cotangent functions, which have one-to-one correspondence with both ordinary and hidden rays. The angular period of the cotangent functions is adjusted to satisfy the edge condition at the tip of the composite wedge. The accuracy of the HRD diffraction coefficients in the physical region is checked by showing how closely the diffraction coefficients in the complementary region satisfy the null-field condition.

Locality of high frequency electromagnetic scattering phenomena is embodied and imported to the Method of Moments (MoM) to reduce computational load. The proposed method solves currents on small areas only around inner and edge stationary phase points (SPPs) on the scatterer surfaces. The range of MoM area is explicitly specified in terms of Fresnel zone number as a function of frequency, source and observer positions. Based upon this criterion, scatterer of arbitrary size and shape can be solved with almost frequency independent number of unknowns. In some special cases like focusing systems, locality disappears and the method reduces to the standard MoM. The hybrid method called PO-MoM is complementarily introduced to cope with these cases, where Fresnel zone number with analogous but different definition is used. The selective use of Local-MoM and PO-MoM provides frequency insensitive number of unknowns for general combination of source and observation points. Numerical examples of RCS calculation for two dimensional flat and curved surfaces are presented to demonstrate the accuracy and reduction of unknowns of this method. The Fresnel zone, introduced in the scattering analysis for the first time, is a useful indicator of the locality or the boundary for MoM areas.

The effect of wavefront compensation in beam transmission is estimated for ground to satellite laser communications. A numerical analysis is performed using the combination of the isoplanatic angle, the atmospheric coherence length and the point-ahead angle to find the aperture size of the beam transmission with which the wavefront compensation effect appears most strongly.

We present a BPSK coherent optical wireless link in a multiple-beam, multiple-aperture configuration. The data are recovered using the signal obtained by the coherent addition of a set of maximum likelihood optical phase estimates and a select-largest stage. The proposal offers higher performance than the combining methods commonly used in optical wireless systems with diversity transmission and coherent detection.

With the increase of communication demand and the emergence of new services, various innovative wireless technologies have been deployed recently. Free Space Optics (FSO) links combined with Radio over Fiber (RoF) technology can realize a cost-effective heterogeneous wireless access system for both urban and rural areas. In this paper, we introduce a newly developed advanced DWDM Radio-on-FSO (RoFSO) system capable of simultaneously transmitting multiple Radio Frequency (RF) signals carrying various wireless services including W-CDMA, WLAN IEEE802.11g and ISDB-T signals over FSO link. We present an experimental performance evaluation of transmitting RF signals using the RoFSO system over a 1 km link under different deployment environment conditions. This work represents a pioneering attempt, based on a realistic operational scenario, aiming at demonstrating the RoFSO system can be conveniently used as a reliable alternative broadband wireless technology for complementing optical fiber networks in areas where the deployment of optical fiber is not feasible.

We fabricated a high-speed wavelength tunable arrayed-waveguide grating (AWG) and an AWG integrated with optical switches using (Pb,La)(Zr,Ti)O3-(PLZT). PLZT has a high electro-optic (EO) coefficient, which means these devices have considerable potential for use in reconfigurable optical add drop multiplexers (ROADMs). The PLZT waveguides in this work have a rib waveguide structure with an effective relative index difference (Δ) of 0.65%. Both AWGs have 8 channels with a frequency spacing of 500 GHz. The fabricated wavelength tunable AWGs allows us to freely shift the output at a particular wavelength to an arbitrary port by applying voltages to 3 mm long electrodes formed on each of the waveguides. We confirmed that the maximum tuning range with driving voltage of 22 V was approximately 32 nm at 1.55 µm. With the integrated 8-ch PLZT waveguide switch array, we could also select the output port by setting the drive voltage applied to the switch array. 2 2 directional coupler switches were used for the switch array. The two devices exhibited insertion losses of 17 dB and 19 dB, adjacent crosstalk of -18.5 dB and -19.7 dB, and a maximum extinction ratio of 19.6 dB and 12.6 dB, respectively. The tuning speed of both devices was 15 ns and their physical sizes were 9.0 23.0 mm and 8.0 29.5 mm, respectively.

This paper reviews our recent progress on arrayed waveguide gratings (AWGs) using super-high-Δ silica-based planar lightwave circuit (PLC) technology and their application to integrated optical devices. Factors affecting the chip size of AWGs and the impact of increasing relative index difference Δ on the chip size are investigated, and the fabrication result of a compact athermal AWG using 2.5%-Δ silica-based waveguides is presented. As an application of super-high-Δ AWGs to integrated devices, a flat-passband multi/demultiplexer consisting of an AWG and cascaded MZIs is presented.

We have proposed a unique and simple modification to the definition of surface-normal vectors in Physical optics (PO). The modified surface-normal vectors are so defined as that the reflection law is satisfied at every point on the surface. The PO with currents defined by this new surface-normal vector has the enhanced accuracy for the edged scatterers to the level of Geometrical Theory of Diffraction (GTD), though it dispenses with the knowledge of high frequency asymptotic techniques. In this paper, firstly, the remarkable simplicity and the high accuracy of the modified PO as applied to the analysis of Radar Cross Section (RCS) is demonstrated for 2 dimensional problems. Noteworthy is that the scattering not only from edge but also from wedge is accurately predicted. This fringe advantage is confirmed asymptotically by comparing the edge and wedge diffraction coefficients of GTD. Finally, the applicability for three dimensional cube is also demonstrated by comparison with experimental data.

We propose and experimentally demonstrate an all-optical broadband wavelength conversion scheme with simultaneous power amplification based on a pump-modulated fiber optic parametric amplifier (FOPA). All-optical tunable wavelength conversion from one to two wavelengths was achieved with ≥13 dB extinction ratio and <2.7-dB power penalty, accompanied by a high (≥37 dB) and flat ( 3 dB variation) FOPA gain spectrum over 47 nm.

We propose and demonstrate a simple one-bus two-ring configuration where the two rings are mutually coupled that has advantages over the one-ring structure. Unlike a one cavity system, it can exhibit near critically-coupled transmission with a broader range of loss. It can also significantly enhance the cavity finesse by simply making the second ring twice the size of the bus-coupled one, with the enhancement proportional to the intensity buildup in the second ring.

A compact arrayed-waveguide grating with small-bend waveguides incorporating air trenches and high mesa structures has been proposed. An 8-channel, 100-GHz-spacing silica arrayed-waveguide grating was fabricated, and its size was reduced dramatically to 1/4 of that of a conventional device.

We propose a new label recognition system for photonic label routing network. Binary-coded labels in binary phase-shift-keying format are considered. The system consists of an optical waveguide circuit with tree-structure passive asymmetric X-junctions and time gates. The system uses self-routing propagation of an identifying bit by performing interference with address bits. The identifying bit is placed in advance of the address bits in the label. The identifying bit pulse is routed to the destination output port corresponding to the code of the address. The operation principle is described. It is shown that all the binary number codes can be recognized with this system. We discuss the feasibility of the system by evaluating its crosstalk. To reduce the crosstalk, an improved scheme is also presented. The label recognition operation with the optical waveguide device is verified by numerical simulation using the finite-difference beam propagation method.

This paper presents a model for the variation in height of the subscriber station (SS) antenna with respect to the path loss for microwave-band wireless access systems. The propagation mechanism that causes the dependency of the height variation characteristics of the received level at an SS on the SS location and operating frequency is clarified in terms of geometrical optics (GO) using the uniform geometrical theory of diffraction (UTD). The height variation characteristics strongly depend on whether or not regular reflected waves that have a higher level than that of the diffracted wave arrive at the SS. A representation of the model is shown. The model is validated using measured data at 2.2, 5.2, and 25.15 GHz and the validity of the model is shown. This model is useful in the radio zone design of microwave-band broadband wireless access (BWA) systems operating in a non-line-of-sight environment, and in estimating the height gain at a mobile station antenna for mobile communications.

We have numerically evaluated the filtering characteristics of two vertically coupled microring resonator filters. In this evaluation we used the finite-difference time-domain method as the numerical analysis method. The structure we designed allows only a specific wavelength to pass. The filtering characteristics of this structure can be altered by changing the layout of the microring resonator. By using this structure the interval between peak wavelengths at a specific wavelength in the output spectrum can be increased. Specifically, the interval between peak wavelengths can be increased from 20 nm to 40 nm at wavelengths near 1.46 µm.