Akira Enokihara

Elliptic-disc filters of high-T/sub c/ superconducting films for power-handling capability over 100 W

On future digital communication systems, 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. End spread signal coupling electrodes are 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 is 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.

Lumped-element quadrature wilkinson power divider

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 II/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 II/T networks. Verification of this design method is also shown by EM simulation and experiment.

Guided-Wave Electro-Optic Modulators Using Novel Electrode Structure of Coupled Microstrip Line Resonator

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 LiTaO 3 waveguides were fabricated. The measured modulation coefficient of the 26 GHz modulator normalized at 100 mW signal input was 0.13 rad.

60 GHz guided-wave electro-optic modulator using novel electrode structure of coupled microstrip line resonator

A 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 microstrip 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/sub 3/ waveguides. The measured modulation coefficient normalized at 1 cm electrode length and 100 mW signal input was 2.4 rad.

Design method of unequal Wilkinson power divider using LC-ladder circuits for multi-way power dividers

This paper describes unequal Wilkinson power dividers using LC-ladder circuits for size reduction of multi-way Wilkinson power dividers. The proposed unequal Wilkinson power dividers consist of a couple of LC-ladder circuits and a series RL circuit between two output ports. For the verification of this design method, the circuit layout of a 5-way power divider utilizing unequal Wilkinson power dividers is decided by using an electromagnetic simulator, and the 5-way divider is fabricated at a center frequency of 300MHz. The experimental results of fabricated 5-way power divider indicate low reflection and high isolation and very flat power division with in-phase signals.

Pure intensity modulated frequency doubled optical clock signal generation by using ultra low-chirp and high extinction-ratio optical modulation

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.

Demonstration of 26GHz signal optical fiber transmission by use of guided-wave electrooptic single-sideband modulators with periodically polarization-reversed schemes

26GHz optical single-sideband (SSB) modulation by use of 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.

Compensation of third-order intermodulation distortion of electro-optic modulator by using frequency chirp modulation

A new electro-optic modulator for compensating the nonlinear distortion is proposed. The third-order intermodulation distortion (IMD3) in receiver output is optically suppressed by the frequency-chirp modulation in the dual-parallel Mach-Zehnder modulator (DPMZM) structure. All of optical branches of the DPMZM are symmetric. The performance was analyzed by numerical calculations. First, we made an experiment to confirm the performance using a DPMZM with a microwave hybrid coupler for applying 10GHz two-tone signals to each electrode of the DPMZM. The chirp parameters of two Mach-Zehnder modulators (MZMs) of the DPMZM were set to opposite signs to each other, +1 and −1. It is seen from the experiment that the intensity ratio of IMD3 to signal in the receiver output was less than −58dB at modulation indices below 0.55 (0.175π) rad and that the minimum of the ratio was less than −80dB at around 0.5 (0.16π) rad. In contrast, for a conventional single-MZM the ratio was less than −27dB below 0.55rad modulation indices. These experimental results agreed well with the calculation ones. Next, we designed and fabricated the modulator of the single-chip structure and the single-input operation for smallsizing and simple operation. The microwave rat-race circuit (RR), which operates as a 180° hybrid coupler, was designed on a Lithium Niobate (LN) substrate at 10GHz and was integrated with modulation electrodes of the DPMZM. The RR and modulation electrodes were formed with a gold thin film pattern at a time. The IMD3 suppression operation was confirmed for the fabricated modulator as well.

Frequency chirp modulation by electro-optic modulator integrated with microwave rat-race circuit and measurement of chirp parameter by using optical fiber dispersion

The rat-race (RR) circuit, which operates as a 180-degree hybrid, with an asymmetric power split ratio was integrated with the dual electrode type electro-optic modulator on the same substrate. Thereby, frequency chirp modulation with a compact configuration was realized. The RR circuit was designed with 4.5:1 power split ratio on a z-cut LiNbO3 substrate. The operation of the modulator was confirmed by observing the output light spectra. Moreover, the chirp parameter was directly measured by using the chromic dispersion of the optical fiber, where the power penalty of detected modulation signals transmitted through optical fiber was observed as a function of the fiber distance. The chirp parameter of the modulated light at 10 GHz was confirmed to be 0.47 by the measurement.

Parallel ring-line rat-race circuit with very loose coupling utilizing short-circuited coupled transmission lines

This paper describes a novel rat-race circuit with very loose coupling less than −10dB utilizing parallel ring-lines composed of a quarter wavelength transmission line and a short-circuited quarter wavelength coupled one. For a conventional rat-race circuit, the minimum coupling factor is limited by the highest impedance of the ring-line which can be manufactured by a general PCB technology. The proposed rat-race circuit with parallel ring-lines can be realized the circuit with a very loose coupling factor of less than −10dB. By using the proposed structure, we can successfully design the compact rat-race circuit with a coupling factor of −20dB. The validity of this design procedure is confirmed by carrying out electromagnetic simulation and experiment. The fabricated −20dB rat-race circuit is actually realized −33dB reflection, −40dB isolation, and −21dB coupling at a center frequency of 4GHz, respectively.