A wideband NRD guide and rectangular waveguide H-plane transition is proposed to transfer millimeter waves from a dielectric strip to the outer conductor surface of NRD guide through a short length of waveguide made through the conductor plate. As a result, it has a bandwidth about 6.7 GHz of |S11| -15 dB and a low transition loss about 0.35 dB at 60 GHz band.

This letter describes a millimeter wave slot array antenna using a rectangular waveguide and a ferrite. The radiation direction of the leaky wave from the slot array can be scanned by applying a dc bias magnetic field parallel to the ferrite. The radiation pattern of a prototype antenna has been measured at 40 GHz. The main beam direction changes from 10 to 3 degree by the bias magnetic field of 0.73 T.

This paper presents a free access mat consisting of tightly coupled double layered microstrip resonator array to provide an easy access for devices in short range wireless communications. While in a conventional wireless access system the electromagnetic wave is radiated from a device to another through the free space using built-in antennas, the proposed wireless access system uses the free access mat to propagate the wave and the proximate coupling between the waveguide and the devices. The propagation loss in the mat is small, which is demonstrated by numerical simulation for basic elements of the free access mat. We also demonstrate small transmission loss including the coupling loss between dipole antennas and the free access mat. Finally experimental confirmation for all demonstrated characteristics is provided so that the free access mat is effective as a novel waveguide for a short range wireless access systems.

This paper presents some structures of artificial coplanar waveguide with very slow phase velocity and their applications to a design of compact 3-dB branch-line couplers. The slow-wave structure is constructed by periodically loading both of series inductance and shunt capacitance. First, a basic miniature branch-line coupler is designed and consequently considerable size-reduction of about 1/4 is obtained. Next, a broadband design technique is described using open-circuited quarter-wavelength series-stubs added at each port as a matching network. By size-reducing the series-stubs and branchline sections, a very compact broadband coupler with a good hybrid performance over a wide bandwidth of 31 percent or more is realized. The design concepts and procedures are verified both numerically and experimentally.

Leaky wave radiation from evanescent-mode left-handed (LH) transmission lines is investigated that are composed of a cut-off parallel plate waveguide loaded with a one-dimensional (1-D) array of the disc type dielectric resonators. The apertures are placed on side walls of the parallel plate waveguide. First of all, the dispersion diagram is numerically obtained with the complex eigenmode solutions. The simulated and measured backward wave radiation characteristics validate the backward wave propagation along the 1-D waveguides. Based on the concept, the backfire leaky wave antenna was designed and demonstrated with the 15-cell structure. The beam scanning with the operational frequency was achieved by more than 30 degrees.

This paper proposes a new type of compact waveguide directional coupler, which is constructed from two crossed E-plane rectangular waveguide with two metallic posts in the square junction and one metallic post at each port. The metallic posts in the square junction are set symmetrically along a diagonal line to obtain the directivity properties. The metallic post inserted at each input/output waveguide port can realize a matched state. Tight-coupling properties 0.79-6 dB are realized by optimizing the dimension of the junction and the positions/radii of the posts. The design results are verified by an em-simulator (Ansoft HFSS) and experiments.

In this letter, the fabrication of a compact and high performance semi-lumped coplanar waveguide low-pass filter (CPW-LPF) on high resistivity silicon (HRS) substrate at millimeter wave is proposed. The design procedure and the equivalent circuit of the proposed semi-lumped CPW-LPF is discussed. The filter structure of is very simple but its performances is fairly good. This designed filter at cutoff frequency fc of 31 GHz has very good measured characteristics including the low insertion loss, sharp rejection and low group delay, due to the reduced substrate loss of HRS. Experimental results of the fabricated filter show a good agreement with the predicted results.

The reflection method is an accurate and simple method for measuring the radiation efficiency of a small antenna. However, it takes too long and has the disadvantage of underestimating the efficiency due to resonance in the cavity formed by the straight waveguide and two sliding shorts. To reduce the measurement time, one sliding short can be fixed while the other one is moved. To improve the accuracy of this technique, we can set the antenna to be measured at the center of the two sliding shorts or at a local anti-node of the standing wave in the waveguide. When one of the sliding shorts is fixed, the measured efficiency becomes negative at certain frequencies. We examine these reductions in efficiency using an equivalent transmission line model for the reflection method. We also derive analytical expressions for the overall efficiency in the above cases and verify new procedures that enable measurements to be performed without any drops in the measured efficiency.

This paper presents design of an alternating-phase fed single-layer slotted waveguide array for a sector shaped beam in the E-plane radiation pattern. A sector beam pattern is very effective for radar applications for detecting obstacles in a certain angular range without mechanical or electronic scanning. The sector shaped beam with 13 degree beam width is synthesized by a cascade of T-junctions in the feed waveguide which excite the radiating waveguides with a longitudinal shunt slot array. In order to realize the required excitation distribution of the radiating waveguides for the sector shaped beam, 30 T-junctions with symmetrical arrangement are designed by tuning a width of the coupling window, an offset of the window, and a width of the feed waveguide cascaded to the subsequent T-junction, respectively. Design and measurement are performed in 60 GHz band. The prototype antenna assembles easily; the slotted plate is just tacked on the groove feed structure and is fixed by screws at the periphery, which is the key advantage of the alternating-phase fed arrays. The measured sector pattern with low sidelobe level agrees well with the predicted one. Validity of the sector beam design as well as the performance of the alternating-phase fed array is confirmed by the measurement.

The proton-exchanged waveguide formed on MgO-doped lithium niobate crystals is resistant to the optical damage or the photorefractive effect. Therefore, this waveguide is believed to be a promising device for optical information and processing. However, the optical damage can also be an important problem for this waveguide in the communication wavelength since the high-power optical source is used. In this report, a brief general review on the optical properties and its practical application of the lithium niobate crystal as the optical waveguide are given. Then the experimental research work aimed to clarify the properties and its mechanism of the electrooptic effect and the optical damage or photorefractivity of the lithium niobate optical waveguide is described. In this work, the optical damage in this proton-exchanged waveguide is measured quantitatively at various optical wavelengths including blue and red light by using the holographic grating method and the infrared communication wavelength (1550 nm) by using the prism coupler method. The optical damage is significant not only in blue wavelength but also in the red, and even at 1550 nm with high power (100 mW) laser diode for communication. So the optical damage cannot be negligible also in the communication wavelengths. The effect of annealing temperature is also discussed. At the relatively high temperatures, the optical damages are founde to be annealed out. The effect of the applied electric field to the optical damage is experimentally discussed and its enhancement is observed to the applied d.c. and a.c. fields. In conclusion, the optical properties as the electrooptic constant and the optical damage are experimentally measured and the many fundamental data are obtained to realize the useful and practical optical devices.

We studied a silicon (Si) waveguide using ferro-electric liquid crystal (FLC) cladding for various applications in optical networks. The FLCs in the cladding layer change their effective refractive index corresponding to the applied voltage polarity, and give a phase shift to the traveling lightwave in the waveguides. The phase change coefficients of three-layer slab waveguides with FLC/Si/SiO2 structure were calculated. We observed an amplitude change in the output light of an experimental modulator consisting of a Mach-Zehnder interferometer with FLC-cladding Si-rib waveguides on a silicon-on-insulator wafer, and evaluated the phase shift at a wavelength of 1550 nm. We propose optical switching devices using Si-rib waveguide Mach-Zehnder interferometers having FLC cladding. Switching of experimental devices operating at 1550 nm wavelength was demonstrated.

The potential of optical circuit packaging technology is discussed. Special attention is paid to introduction of "optical wiring" at the printed wiring board level (i.e., in the "last 1 meter area") to overcome the bandwidth limitations of electrical copper-based wiring. The suitability of optical surface mount technology (O-SMT) as a possible solution is reviewed. It is shown that the key to the utility of O-SMT is high efficiency and alignment-free coupling between optical wiring and optical devices. O-SMT requires a method to change the beam direction from the horizontal to the vertical and vice versa in order to couple optical wiring in an OE-board and OE-devices mounted on the board. A novel method using an "optical pin" is proposed and investigated. Furthermore, an optical coupling method using a self-written waveguide called "optical solder" is reviewed. Several applications of self-written waveguides using a green laser and a photo-mask are demonstrated.

Light-induced self-written (LISW) technology is a unique and simple method of forming low-loss 3-dimensional (3-D) optical circuits in photopolymers using radiation from an optical fiber. Since this technology is applicable to almost all kinds of optical fiber and optical wiring, many studies have been carried in a number of different organizations on the applications of this technology. The technology helps simplify optical interconnections, and it is expected that it will reduce the cost of mounting optical devices. In this paper, we introduce LISW technology and report on related studies developed in our research group.

Transitions between a post-wall waveguide and a microstrip line are proposed as the key components for cost-effective millimeter-wave modules. A transition with a coaxial structure is investigated for LTCC laminated layers and 11.3% bandwidth for the reflection smaller than -15 dB is realized in 60 GHz band. The overall connector loss with 1 cm post-wall would be about 0.8 dB. The degradation due to fabrication error is also assessed. The transition in LTCC substrate fulfills electrical and manufacturing demands in millimeter-wave bands.

The propagation characteristics of the leaky TE mode in a two-dimensional photonic crystal waveguide is analyzed using the Fourier series expansion method combined with the Chew's perfectly matched layer (PML). The complex propagation constant and mode field profiles are numerically tested in detail. It is shown that the leakage phenomena can be well modeled by choosing the PML parameters in proper range.

A ridge-type Zn-indiffused Mach-Zehnder modulator operating at 1.55 µm wavelength is demonstrated on a z-cut LiNbO3 substrate for the first time. The measured results show that the values of voltage-length product can be reduced from 9.6 V-cm to 8.1 V-cm with the etched depth of 1.7 µm.

We investigate the usefulness of the topology optimization with the finite element method in the optimization of an H-plane waveguide component. Design sensitivity is computed efficiently using the adjoint variable method. Employing the optimization procedure, optimized structures of an H-plane waveguide filter and T-junction are obtained from an initial homogeneous structure.

A waveguide-based surface plasmon resonance (SPR) sensor with an adsorbed layer is analyzed using the beam-propagation method. For two-dimensional (2-D) models, numerical results show that the change in thickness of the adsorbed layer placed on the metal leads to a significant shift of the maximum absorption wavelength. Through eigenmode analysis, the maximum absorption wavelength is found to be consistent with the cutoff wavelength of the second-order surface plasmon mode. The designed 2-D sensor shows an absorption wavelength shift from 0.595 to 0.603 µm, when the analyte refractive index is increased from 1.330 to 1.334. After a basic investigation using the 2-D models, we next study 3-D models. When the metal with the absorbed layer is wide enough to cover the core region, the 3-D results are similar to the 2-D results. However, as the metal width is reduced, the absorption wavelength shifts toward a shorter wavelength and the sensitivity to the refractive index change degrades gradually. The degradation of the sensitivity is considerable when the metal width is narrower than the core width. As a result, the metal width of the practical SPR sensor should be slightly wider than the core width so as to maintain the sensitivity corresponding to that obtained for the 2-D model.

This paper presents moment method analysis of a plane wave generator in an oversized rectangular waveguide; its finite size is taken into account. Power divisions of the series of coupling windows and eigenmode excitation coefficients in the oversized waveguide are quantitatively evaluated by the analysis. In order to have a better understanding of array design, the relation between these mode coefficients and the radiation patterns is discussed. Control of the mode coefficients in the oversized waveguide is directly related to the far-field radiation pattern synthesis. These calculated results are verified by measurements in the 61.25 GHz band.

We report on a channel drop filter with a mode gap in the propagating mode of a photonic crystal slab that was fabricated on silicon on an insulator wafer. The results, simulated with the 3-dimensional finite-difference time-domain and plane-wave methods, demonstrated that an index-guiding mode for the line defect waveguide of a photonic crystal slab has a band gap at wave vector k = 0.5 for a mainly TM-like light-wave. The mode gap works as a distributed Bragg grating reflector that propagates the light-wave through the line defect waveguide, and can be used as an optical filter. The filter bandwidth was varied from 1-8 nm with an r/a (r: hole radius, a: lattice constant) variation around the wavelength range of 1550-1600 nm. We fabricated a Bragg reflector with a photonic crystal line-defect waveguide and Si-channel waveguides and by measuring the transmittance spectrum found that the Bragg reflector caused abrupt dips in transmittance. These experimental results are consistent with the results of the theoretical analysis described above. Utilizing the Bragg reflector, we fabricated channel dropping filters with photonic crystal slabs connected between channel waveguides and demonstrated their transmittance characteristics. They were highly drop efficient, with a flat-top drop-out spectrum at a wavelength of 1.56 µm and a drop bandwidth of 5.8 nm. Results showed that an optical add-drop multiplexer with a 2-D photonic crystal will be available for application in WDM devices for photonic networks and for LSIs in the near future.