榎原 晃

Doubled frequency optical two-tone generation and optical single sideband (SSB) modulation by the dual-electrode-type electro-optic (EO) modulator with a single Mach-Zehnder (MZ) interferometer were considered. We theoretically showed that redundant spectrum components in the modulated optical signals, which are caused by the imbalance of light splitting ratio between the two arms of the interferometer, are significantly suppressed by controlling the input power ratio of RF modulation signals applied to each electrode. This effect was confirmed by the experiment, where an optical two-tone with the redundant components 49.8 dB lower than the primary two-tone components in intensity level was obtained. This method is also valid for suppression of undesired frequency components of RF signals that are generated at a photo detector from the optical two-tone waves propagated through a dispersive optical fiber.

This paper treats a band-broadening design technique of a dual-band branch-line coupler with matching networks composed of an impedance step and a short-circuited stub based on the equivalent admittance approach. By replacing each right-handed transmission line (RH-TL) with a composite right/left-handed transmission line (CRLH-TL), very flat couplings over a relative bandwidth of about 10% can be obtained at two arbitrary operating frequencies in comparison with previous CRLH-TLs branch-line couplers. Furthermore, by adding periodical open-circuited stubs into RH-TLs of the designed CRLH-TLs branch-line coupler with matching networks, the entire size of the coupler can be reduced to about 50%. Verification of these band-broadening and size-reduction design techniques can be also shown by an electromagnetic simulation and experiment.

This paper treats broadband branch-line couplers with arbitrary power split ratios utilizing microstrip series stubs as matching networks. Proposed series stubs are structurally integrated in input/output microstrip transmission lines. Based on the equivalent admittance approach, dual-band/wide-band characteristics with relative bandwidths of over 30 % can be obtained in the case of a coupler with a power split ratio of 1 to 5. Validity of this design procedure can be demonstrated by electromagnetic simulations and experiment. © 2010 EuMA.

A new measurement method of chirp-para meters is proposed for electro-optic (EO) intensity modulators with the Mach-Zehnder (MZ) waveguide interferometer. This method is suitably applied for the measurement of the small chirp with operation at a specific RF-frequency. To determine the chirp-parameter, optical spectrum components of the modulated light are observed with varying the relative optical phase difference between the two arms of the MZ waveguide interferometer. The chirp-parameter of 0.17, which is a value small enough for EO intensity modulation, was successfully measured by the experiment. (C) 2009 Elsevier B.V. All rights reserved.

We demonstrated ultra low-chirp and high extinction-ratio modulation, by using an integrated lithium niobate modulator. The odd order optical sideband components were highly suppressed to achieve a chirp-free intensity modulated frequency doubled signal. © 2009 IEEE.

This paper treats a novel lumped-element quadrature Wilkinson power divider. The proposed divider consists of a parallel LC-ladder circuit, a series RL circuit connected though two output ports, and phase shifters consisting of Π/T networks. Under this construction broadband characteristics with a relative bandwidth of 33.4%can be obtained in comparison with lumped-element Wilkinson power dividers using Π/T networks. Verification of this design method is also shown by EM simulation and experiment. ©2009 IEEE.

The fabrication of LiNbO3 (LN) Bragg gratings, which have the grooves of 400 nm depth, in LN ridge optical waveguide is shown in this paper. The 400 nm depth grooves in LN Bragg gratings with high uniformity, precision and no damage were achieved for the first time. In order to fabricate the fine structure of LN Bragg gratings, we optimized the condition for LN dry etching and introduced the Cr metal as a mask material to our fabrication process. We also have investigated the favorable structure to realize the large optical group delay and discussed the importance to fabricate the Bragg gratings with deep grooves. We successfully fabricated Bragg gratings in LN ridge optical waveguide and demonstrated the measurement of transmission property. The etching process developed in this paper brought good performance to the fabrication of the deep grooves in LN Bragg gratings. From these results, the possibility of large group delay and slow-wave electro-optic modulators in LN optical waveguides was revealed. (c) 2008 Elsevier B.V. All rights reserved.

2-dimentional photonic crystal structure was using a c-axis oriented LiNbO3 thin film on a substrate. The dispersion characteristics in the photonic crystal structure were measured in detail by the attenuated total reflection (ATR) method. The results imply that the photonic band-gap was obtained for TE modes in the fabricated structure.

マッハツェンダ導波路型進行波型電極電気光学変調器に分極反転構造を適用すると,光波と変調波の擬似速度整合のみならず,マッハツェンダ導波路の二つの光路における光変調の相対位相を制御することが可能である.この特性を利用することにより,単一RF信号で動作する高速光SSB変調器を実現することができる.本論文では,無線信号の光ファイバ伝送(Radio-On-Fiber : ROF)システムにおけるキーデバイスである高速光SSB変調器について,分極反転構造を適用した新しい構成を提案して,その設計,試作,動作実験と,これを用いた準ミリ波帯信号のROF伝送実験の結果について述べる.試作した変測器は,良好な光SSB変調特性を示すことを確認した.光SSB変調動作詩のサイドバンド間消光比は23dBを得た.更に,試作した変調器を用いて準ミリ波(〜26 GHz)無線信号を光信号に変換して,長さ〜20kmの単一モードシリカファイバ中を伝送させた.伝送された光信号をフォトダイオードで検波して得られた準ミリ波信号を観測したところ,試作光SSB変調器を用いた場合には光DSB変調器を用いた場合に比べて光ファイバの分散による信号劣化が大きく改善されることを確認した.

A novel structure of a resonator type guided-wave electrooptic intensity modulator is introduced that uses a higher-order harmonic resonant electrode of coupled microstrip lines combined with polarization-reversed structure. The light modulation cancellation caused by the light transit-time effect in the resonant electrode, which is longer than the wavelength of the standing wave, is compensated for to enhance modulation efficiency. The modulator for 26 GHz operation was designed and fabricated with a LiTaO3 substrate. The modulation electrode is 9.03 mm long for seventh order harmonic resonance by RF signal. The workability of the modulator was confirmed by experiments with 1.3 mu m wavelength light.

A new periodic waveguide structure with grooves etched on the surface of a proton-exchanged LiNbO3 ridge is demonstrated. The grooves were fabricated by ICP dry etching. A steep stop band of 3.2 nm width at 1.545 mu m was obtained by the 355 mu m-long periodic waveguide. Induced optical group delay was estimated at 4.6 ps per 1 mm waveguide length.

Guided-wave electro-optic phase modulators with long resonant electrodes and polarisation reversals are proposed and experimentally demonstrated. Adopting polarisation-reversal structures to electro-optic modulators with standing-wave resonant electrodes operated in a higher-order harmonic resonance mode, high-efficiency optical modulation is obtained by compensation of the transit-time effect.

A novel structure of guided-wave electro-optic modulators is proposed and their operation of the optical intensity modulation is successfully confirmed. The modulators use a newly developed modulation electrode consisting of coupled microstrip lines. A high voltage can be induced by the resonance of the odd propagation mode to realize efficient electro-optic modulation in spite of the microstrip-line configuration. The properties of the coupled microstrip lines were analytically evaluated by using the method of conformal transformations and the effectiveness as a modulation electrode was presented. The modulation electrodes of the half-wavelength coupled microstrip line resonator were designed at 10 GHz and 26 GHz, where the electrode lengths were 3 mm and 1.2 mm, respectively. The modulators using these electrodes with the Mach-Zehnder interferometer of LiTaO3 waveguides were fabricated. The measured modulation coefficient of the 26 GHz modulator normalized at 100 mW signal input was 0.13 rad.

38GHz optical single-sideband (SSB) modulation by using new guided-wave electrooptic SSB modulators with polarization reversals was experimentally demonstrated and their applications to the radio-on-fiber (ROF) systems are reported. The power penalty of the transmitted 38GHz signal caused by fiber chromatic dispersion was drastically reduced by using the fabricated SSB modulator. The proposed device should lead to useful millimeter-wave signal converters in the ROF systems.

A novel structure of the electro-optic intensity modulator designed with a higher-order resonant electrode and the polarization-reversed structure is proposed. The light-modulation degradation caused by the optical transit-time effect in the electro-optic (EO) modulation area is eliminated by this scheme so that the modulation-efficiency is significantly enhanced. The modulator for 26 GHz operation was fabricated with a LiTaO3 substrate. The modulation electrode consisted of resonant coupled-microstrip-lines and the length was set at 9.03 mm, around seven times as long as a half-wavelength, to excite the seventh order harmonic resonance by the 26 GHz RF signal. The workability of the modulator was confirmed by the experiment using 1.3 μm wavelength light.

A novel guided-wave electro-optic modulator Is proposed and its operation of optical intensity modulation by 60 GHz millimeter-wave signals is successfully confirmed. The modulator uses a newly developed electrode structure consisting of coupled micostrip lines. A high voltage can be Induced by the resonance of the odd propagation mode to realize efficient electro-optic modulation even at millimeter-wave frequencies. The properties of the coupled microstrip lines were evaluated to show the effectiveness as a modulation electrode. The modulator designed at 60 GHz was fabricated with LiNbO 3 waveguides. The measured modulation coefficient normalized at 1 cm electrode length and 100 mW signal input was 2.4 rad.

26GHz optical single-sideband (SSB) modulation by use of novel guided-wave electrooptic SSB modulators with periodically polarization-reversed structures was experimentally demonstrated and their applications to the radio-on-fiber systems are reported for the first time. The power penalty of the transmitted 26GHz microwave signal caused by the chromatic dispersion of a silica optical fiber was drastically reduced by use of the fabricated optical SSB modulators compared to a double-sideband modulator. The proposed SSB modulators should lead to useful microwave-lightwave converters in the radio-on-fiber systems for mobile communication networks.

A newly proposed electrode structure consisting of coupled microstrip-lines can achieve an efficient modulation by using the resonance of the odd propagation-mode. The modulator with the 1.2 mm-long electrode for 26 GHz operation was fabricated and its workability was experimentally confirmed.

The single sideband (SSB) modulation of a lightwave of ∼1.3μm by the SSB modulator of a modified structure was presented. By utilizing the controllability of the phase of the electrooptic modulation by a spatial shift of the periodic domain-inversion in the quasi velocity matching (QVM) travelling wave modulators, a pair of balanced modulations with a π/2 phase shift was obtained. The frequency dependence of the device was found to be less sensitive to the optical wavelength of ∼1.3μm. The operational power for the SSB modulator was relatively large as ∼30dBm, which was due to the microwave propagation loss in the CPW and the degradation of the electrooptic effect by the proton exchange process.

The newly proposed electrode structure can realize efficient electrooptic modulation by using the odd propagation-mode resonance in spite of the microstrip configuration. The modulator designed at 10GHz was fabricated and its workability was experimentally confirmed. © 2003 Optical Society of America.

26 GHz bandpass filter and duplexer using TM11δ rectangular-mode dielectric cavity resonators are proposed. These have a configuration compact and suitable for mounting on circuit boards. The resonators consisting of the Ba(Mg,Ta)O3 ceramic material showed a high quality factor value of 2600, which is roughly comparable to that of conventional E-plane waveguide filters. The dielectric losses of the ceramic material were experimentally evaluated from the viewpoint of the high frequency operation and the dielectric loss tangent of 7.4 × 10-5 was observed at 20 GHz. A three-stage Tchebyscheff bandpass filter with 0.4% relative bandwidth was fabricated and the passband insertion loss was 1.7 dB. A duplexer designed with two TM11δ mode filters and a microstrip T-junction is also presented.

A novel structure of 26GHz bandpass filters using TM11δ rectangular-mode dielectric cavity resonators is introduced. The resonator of high-permittivity ceramics shows a high quality factor (Q) value of 2600, which is roughly comparable to that of waveguide type ones, in spite of its small structure. A three-stage Tchebyscheff bandpass filter with 0.4% relative bandwidth was fabricated and the passband insertion loss was measured to be 1.7 dB. The filter has input/output ports of microstrip lines for the surface mounting. A duplexer, consisting only of two TM11δ mode filters and a microstrip T-junction, is also presented. These filter and duplexer have a configuration compact and easy to manufacture as well as the high-Q performance.

On the future digital communication system, distortion of transmitted signals should be eliminated as much as possible for high communication quality. However, the need to both minimize distortion of signal amplifiers and continue to provide good filtering protection can become difficult to achieve with conventional devices. In this paper, the RF coplanar circuit filter using elliptic-disc resonators is proposed and investigated, This proposition makes it possible to miniaturize power filter circuits and to realize high performance of power ability of high-temperature superconducting (HTS) filters. An end spread signal coupling electrodes is investigated in order to adjust the coupling degree between disc and feedline circuits and provide proper characteristic impedance of circuit. Two-mode coupling operation in the elliptic disc are then explained. Electromagnetic-field distribution change caused by this mode coupling can protect current and heat concentration, and realize power-handling capability over 100 W. Finally, the design principle of a multiple-disc filter is introduced for high performance of out-of-band rejection and passband flatness. It has been confirmed that an elliptic-disc resonator filter can bring out the excellent performance of HTS materials. © 2000 IEEE.

A new or future system of mobile telecommunication is built by new digital technologies to provide an improved and more consistent quality of service for the customers. These digital systems can provide greater number of transmission channel allocation for their subscribers and security. On the digital communication system, distortion of transmitted signal should be eliminated as much as possible for high communication quality. However, the need to both minimize distortion of signal amplifiers and continue to provide good filtering protection can become difficult to achieve with conventional high power amplifiers and filters. In this paper, the application of high-Tc superconducting (HTS) power filters on such digital communication systems and recent progress of filter device developments for those are discussed.

高温超伝導体の早期応用分野として期待され,研究が進められたマイクロ波受動素子は,携帯電話などの移動体通信システムの高性能基地局フィルタ-としての実用化が期待されている.超伝導マイクロ波受動素子の実現のため,超伝導表面抵抗による高周波損失,超伝導非線形性による電力特性や周波数分散性の問題について考察し,これらを前提とした超伝導フィルターについて,その設計法,冷却に有利な小型化のためになされた試み,周辺技術などの現状を展望する.

A 1.5-GHz four-stage microstrip bandpass filter was designed with the miniaturized hairpin resonator structure to reduce the configuration in size. The filter was fabricated using high-Tc superconducting films on a 12 × 12 mm2 LaAlO3 substrate. The passband insertion loss of the filter was measured to be -0.4 dB at 77 K, while it was estimated by a planar electromagnetic simulator to around -19 dB when gold films are used instead of the superconducting films. © 1997 Plenum Publishing Corporation.

A high-Tc superconducting filter of the planar structure is proposed for handling higher power signals and for miniaturizing the filter configuration. The filter is designed with a single disk-resonator shared by two degenerate modes to operate as a two-stage bandpass filter. Thereby the proposed filter is expected to possess high power handling capability as a conventional filter with two resonator disks does while the filter configuration is about a half in area compared to the conventional one. The Tchebyscheff type filter with 5.1 GHz center frequency and 1% relative bandwidth was fabricated using a high-7"c superconducting thin film. The passband insertion loss, Lo, was approximately 0.8 dB at 77 K. The low loss performance due to the superconductivity was observed at incident signal levels up to +41.2 dBm (around 15 W) at 20 K, which is limited by the power devices in the measurement setup. In addition, good linearity in the filter responses was confirmed by observing the intermodulation distortion with the two-tone method, which indirectly shows a stable operation with higher power incident signals.

We have observed many-body effects in both the Cu 2p photoelectron and 2p 3/2- valence-valence (L 3 V V) Auger electron spectra for thin films of Bi2Sr2CaxCu1+ xO6+2 x (x=0, 1, 2), La2- xSrxCuO4 (x=0, 0.13), and ErBa2Cu3O7- x, y (x&lt y). We reviewed the relationship between the many-body effects and high-T c superconductivity of cuprate superconductors. Enlargements of both intensity ratio and energy separation of the |cd 10L&gt to |cd 9&gt lines in the 2p spectra corresponded with an increase of the mixing of |d 8L&gt and |d 7&gt states in the L 3 VV spectra. Enlargement of the parameters of many-body effects resulted from an increase in covalency of the Cu–O bond. An enlargement of the transfer integral is required for realization of high-T c superconductivity of Bi–Sr–Ca–Cu–O and La–Sr–Cu–O systems. The 90 K superconductivity in Er–Ba–Cu–O and Y–Ba–Cu–O systems was realized by increasing the charge transfer energy. © 1994 IOP Publishing Ltd.

Many-body effects in Cu 2p x-ray photoemission of Bi2Sr2CaxCu1-xO6+2x (x=0,1,2), La2-xSrxCuO4 (x=0,0.13), and ErBa2Cu3O7-x,y (x<y) were observed and correlations between the many-body effects and high-T(c) superconductivity of cuprate superconductors were reviewed. For the Bi2Sr2CaxCu1+xO6+2x (x=0,1,2) and La2-xSrxCuO4 (x=0,0.13) systems, proper high-T(c) superconductivity was realized by increasing the transfer integral and the interaction strength of the Cu-O bond of the crystal determined the superconducting properties. However, for the ErBa2Cu3O7-x and YBa2Cu3O7-x systems, 90 K superconductivity was realized by increasing the charge transfer energy. The extended valence state including the Cu, Ba, and O valence states in the crystal determined the superconducting properties of the ErBa2Cu3O7-x and YBa2Cu3O7-x systems.

Superconducting bandpass filters of 4.9 GHz with 0.5% relative bandwidth were designed using miniaturised microstrip hairpin resonators and fabricated with GdBa2Cu3Ox thin films prepared on MgO. The passband insertion loss was 0.5 dB at 20 K and the filter configuration was defined in an area less than 5 x 5 mm2. © 1992, The Institution of Electrical Engineers. All rights reserved.

スパッタによる薄膜化プロセスにおいて,原子層オーダーでの精密制御の限界についての最近の研究について述べる。本解説では,Bi層状ペロブスカイト構造の高温超電導体を多元マグネトロンスパッタでlayer-by-layer蒸着すると,1/2格子ユニット程度(10～20A)までは化学組成・結晶構造の制御が可能であり,また,このIayer-by-1ayerスパッタで,1/2格子ユニット単位で構成した人工超格子物質が創成されることを示した。この種のスパッタリング法は,人工歪超格子強誘電体や触媒・人工酵素などバイオミメテック材料のような新材料の創成にも有望なプロセスである。

Bi2Sr2CaCu2Ox thin films prepared on (100) MgO substrates by rf magnetron sputtering were irradiated with ultra-violet (UV) light in He gas of about 500 Pa using a low pressure mercury lamp. The zero-resistance temperature and the critical current density were gradually decreased with irradiation time. X-ray photoemission spectra showed that the mean Cu valence of the film was decreased approximately from +2 to +1 by the irradiation while the valence of Bi ions was not changed. These imply that the UV light irradiation selectively reduces Cu ions and the superconductivity strongly depends on the Cu valence. © 1991 IEEE

An enhancement of the critical current density (to more than 106 A/cm2 below 65 K) of Gd1Ba2Cu3O7-x superconducting thin films was achieved by X-ray irradiation with oxygen annealing. This process of X-ray irradiation with oxygen annealing introduced stable pinning centers into the crystal and also increased the activation energy from 0.1 eV to 0.25 eV. © 1990 Springer-Verlag.

ErBa2Cu3O7-x superconducting thin films prepared on MgO single-crystal substrates by RF magnetron sputtering were irradiated with X-rays emitted from an Rh X-ray tube for 100 h. The superconducting properties were damaged to disappear the zero-resistance state and then were recovered by oxygen annealing at 450°C. No change in the crystallinity causing the radiation damage was observed in the X-ray diffraction patterns. The X-ray photoemission spectra showed that the mean Cu valence was close to +1 after the irradiation and was increased to about +2 by the annealing. The X-ray irradiation must induce oxygen vacancies, which can be filled by the oxygen annealing. © 1989.

The effects of Ar ion-beam etching were investigated for Gd-Ba-Cu-O superconducting thin films prepared on (100) MgO substrates at 650°C by rf magnetron sputtering. Etching at acceleration voltages below 2 kV did not change the zero-resistivity temperature and the critical current at 50 K in spite of a reduction of film thickness. A nonsuperconducting layer was formed near the surface. Surface analyses by X-ray photoelectron spectroscopy suggest that the crystal structure was deformed and the mean value of a Cu valence reduced to +1 by the Ar ion bombardment. © 1989 The Japan Society of Applied Physics.

An integrated-optic fluid sensor utilizing the heat-transfer phenomenon is proposed. An optical waveguide interferometer is used to convert the temperature of the waveguide surface exposed to the surrounding fluid into an intensity modulated light signal. The temperature changes with the variation of a certain physical property of the fluid when the substrate is steadily heated. The expected characteristics are discussed for measurement of the rarefied gas pressure and the air humidity. Also a humidity sensing experiment was carried out by constructing and testing a device using a LiNbO 3 waveguide to confirm its basic performance. © 1988, Optical Society of America.

The Gd-Ba-Cu-O film of 500 nm thickness was prepared on a (100) MgO single-crystal substrate at 650°C by an rf magnetron sputtering. This thin film having a smooth surface was patterned to a 2- µm wide and 100-µm long strip line by a conventional Ar ion beam etching (IBE) technique using the negative-type photoresist mask. Without any heat treatments, the patterned strip indicated a zero-resistivity temperature, Tc, of 69 K and critical current density, Tc, of 1.0×106 A/cm2 at 4.2 K. © 1988 The Japan Society of Applied Physics.

The method of polarization-rotated reflection is applied to sensors with polarization-maintaining optical fibers. By the use of this scheme, stable measurement can be realized because the fluctuation of the light propagation characteristics in the fiber is canceled automatically without any additional active phase compensation techniques. Several kinds of sensors were designed for the measurement of different physical values. A magnetic field sensor and a temperature sensor were built and the performances were tested to confirm their basic features experimentally. Copyright © 1987 by The Institute of Electrical and Electronics Engineers, Inc.

Temperature sensor of the integrated optic structure was constructed using a Michelson interferometer configuration with an asymmetric X junction and a grooved reflector on a LiNbO&lt inf&gt 3&lt /inf&gt substrate. With this structure, larger difference in the optical paths lengths for two beams is provided to realize higher sensitivity. Also a humidity sensor of the optical guided-wave structure is proposed and its first known demonstration is reported. © 1986 IEEE

As a novel application of integrated optics, a detection method of microdisplacement is proposed and its first demonstration is reported. The sensor has the Michelson interferometer configuration composed of an optical waveguide hybrid coupler. The operation was confirmed by building and testing the sensor using a Ti-diffused LiNbO3 waveguide. © 1982, The Institution of Electrical Engineers. All rights reserved.

As a novel guided-wave passive device, the optical-waveguide hybrid coupler is proposed and its first known demonstration is reported. The proposed device consists of symmetric and nonsymmetric branching forks connected at a junction. An explanation of the working mechanism is presented. The feasibility of the device is confirmed by constructing and testing the hybrid coupler with an integrated Mach-Zehnder interferometer composed of a Y junction and phase shifters using a Ti-diffused LiNbO3waveguide. © 1982 Optical Society of America.