Edited by Sadakuni Shimada

A1. Time and Frequency Standards and Time Transfer Technique

Northwest Pacific Loran-C Chain (GRI-9970), in which the master station was located at Iwojima, was operated by US Coast Guard until September 30th, 1993 and its operation was taken over by Japan Maritime Safety Agency. On 1st October, 1994 the master station was moved to Niijima and concurrently the new Northwest Pacific Loran-C Chain was set up with GRI-8930. The chain synchronization to Universal Time Coordinated (UTC(CRL))is controlled within the tolerance of 0.2 s.

CRL (Communications Research Laboratory), NAO (National Astronomical Observatory) and NRLM (National Research Laboratory of Metrology) continue routine base GPS time transfers each other. They send weekly data to BIPM via e-mail to contribute to the Coordinated Universal Time (UTC).

CRL cesium beam primary frequency standard Cs1, whose purpose is to contribute to UTC (CRL) and TAI. The design, experimental production and measurement of special characteristics are discussed, as well as the sources of uncertainties in accuracy evaluation [Nakagiri et al., 1992].

Aiming at realization of an operational primary standard, an optically pumped Cs frequency standard is performed at NRLM. [Ohshima et al., 1994]. Optically pumped cesium frequency standards are under development at the CRL and NTT (Nippon Telegraph and Telephone Corporation) [Umezu et al., 1992; Hisadome et al., 1994].

In order to develop a high resolution Ramsey resonance spectrometer has been developed by employing the technique of launching of laser cooled Cs atoms (atomic fountain) is being performed [Ohshima et al., 1995a].

A new vertical type cesium beam frequency standard is under construction at Kinki University. Its main features are vertical low velocity beam selection by recycling beam collimator and 4-pole electromagnets, solenoid

coil C-field and a H-bend Ramsey cavity [Nakagiri, to be published].

The effects of relative intensity noise and residual FM-noise of a diode-laser and the light shift effect on the frequency stability of a laser-pumped Rb gas cell standard were investigated. The measurement showed the best stability is characterized as 1x10-12t-1/2 for t < 200 s, 7x10-14 for 200 s < t < 1500 s and 2x10-15t1/2 for 1500 s < t [Saburi et al., 1994].

At the NRLM, a single Yb+ ion, trapped in a rf trap, was laser-cooled to a temperature of 150 mK. Quantum jumps were observed with laser-cooled trapped Yb+ ions. The Yb+ ions excited in the metastable states reacted with H2 or O2 molecules into YbH+ or YbO+. This effect is one of the causes of the disappearance of fluorescence from the trapped Yb+ ions [Sugiyama et al., 1995].

Ca+ ions were trapped and laser-cooled to below 1 K. To observe the electric-quadrupole-allowed transitions (clock transitions), the laser diode operated at low temperature was developed. The clock transitions were observed using the shelved electron double resonance method [Urabe et al., 1994]. CRL's new ring ion-trapping system for frequency standard which can store a large number of ions with low susceptibility to the second-order Doppler effect was proposed [Kajita et al., 1993].

Accuracy and stability of the 657 nm Ca optical frequency standard were investigated, in which a dye laser was frequency stabilized to the optical Ramsey fringe center observed in a thermal Ca atomic beam. High resolution diode laser spectrometer has been also developed and applied to the high sensitive detection of high resolution Ca Ramsey fringes [Ito et al., 1994].

The two-way time transfer experiments using an INTELSAT Ku-band satellite in eastern Asia in cooperation between the (CRL, Japan), Korea Research Institute of Standard and Science (KRISS, Korea), and the Telecommunication Laboratory (TL, Taiwan) were carried out during 1992. The CRL-KRISS experiment attained a short term precision of better than 1 ns [Engelkemier et al., 1995].

CRL has started a project which applies millisecond pulsars to time and frequency standards, and developed a basic observation system. Using this system, the authors can observe a millisecond pulsar, PSR 1937+21, and obtain an observation precision of 10 ms/t which is primarily influenced by system noise [Hanado et al., 1994].

(Yasuhiro Nakadan)

A2. Laser Stabilization and Frequency Multiplication

The stabilized lasers reported in these three years are mainly Laser Diodes at 1.55 mm (for optical communications) and 788 nm (which is close to SHG of 1.55 mm), LD excited cw-YAG lasers (which are important for detecting the Gravitational Waves). Following is the summary of the papers.

1) Stabilization of Laser Diodes

A 1.56 mm DFB laser diode was, at first time, stabilized to the saturated absorption spectrum of the HCN. The low pressure absorption gas cell was set in a 20-cm-long Fabry-Perot cavity and 8 mW of LD power used for the experiment [de Labachelerie et al., 1994]. An GaAlAs LD was stabilized to the saturation absorption line of Rb D2 by using the Faraday effect. The reference spectrum were Doppler-free and so the direct laser frequency modulation was not necessary. The improvement of the stability was obtained by changing the biased magnetic field strength [Ueno et al., 1993]. An GaAlAs laser diode(780 nm) was stabilized by using the zerocrossing signal of the Zeeman line from the 85Rb cell which was placed in the solenoid coil. As the zerocrossing signal was obtained by modulating the magnetic field of the coil, so the method did not need the modulation of the laser frequency. The obtained stability was between 2x10-12 and 2x10-14 at the averaging time of 100 ms < t < 100 s [Tanaka et al., 1994].

2) LD Pumped Nd:YAG Stabilization

LD pumped Nd:YAG laser was stabilized to the high-finesse(25600) Fabry-Perot cavity as a reference. By using the high-power acceptance photodetector, the shot-noise limit of 4.2x10-5 Hz/Hz1/2 below the Fourier frequency of 500 Hz. By beating two such stabilized lasers, 16 Hz linewidth of the beat signal was obtained [Uehara et al., 1994]. The LD pumped Nd:YAG was also stabilized by using an extra-cavity electro-optic modulator as a fast phase transducer and shot-noise limit of 7x10-5 Hz/Hz1/2 with cavity input power of 30 mW was obtained. By improving the short-term frequency stability by vibrational isolation of the reference cavities and by reducing the noise lower than 1 Hz/Hz1/2 at Fourier frequency higher than 5 Hz, minimum noise obtained was 7x10-3 Hz/Hz1/2. And Allan variance about 10-14 for t = 0.01 s was obtained [Nakagawa et al., 1994a].

3) Stabilization of the Other Lasers

Optically-pumped far infrared(CH3OH, HCOOH, CH3I) lasers were stabilized by adopting concave dichroic output couplers and adding the buffer gas. By comparing with a harmonics of PLL'ed Gunn oscillator, they measured the FWHM of 10 kHz after stabilization. They also tried stabilization of the laser by using the personal computer [Hori et al., 1993].

(Eiichi Sakuma)

A3. Laser Application and Measurement

In a two beam, white-light or polychromatic-light interferometer, any path-length difference in the beam splitter introduces wavelength-dependent path delay because of the glass dispersion [Doboz et al., 1995]. A technique to align balanced path is described. The method is based on two- or three-wavelength simultaneous interferometry. Difference in intensity of fringes placed symmetrically around the zero interference order is used to measure and equalize the beam splitter path. As a polycromatic source of light, 660-, 840-, and 780-nm wavelength mixed beams of multimode laser diodes are applied. The technique allows us to balance the path difference with an accuracy better than +-0.2 mm. Theoretical background and experimental verification of the method is presented.

Picometer interferometry of moving objects is demonstrated experimentally over the frequency range 0 to 160 Hz [Fujimoto et al., 1995]. Active feedback is adopted to reduce the lowest frequency noise component due to coupling between geometrical fluctuations of the laser beam incident on the interferometer optics and imperfections in its optical elements. Passive measures to reduce the noise due to thermally induced change of optical elements both in the geometrical arrangement and in the optical properties are introduced by decreasing the sensitivity to temperature change. With these methods the resultant noise is reduced to 3 pm.

A simpler method is presented for measuring the refractive index of air, which uses two frequency-doubling crystals as optical components of an interferometer [Matsumoto et al., 1994]. It is based on a two-color method utilizing a fundamental wave of a laser-diode-pumped YAG laser and its second-harmonic wave. Their waves are input into another frequency-doubling crystal for generating interference fringes. The refractive index of air is measured with a resolution better than 1x10-7 at a traveling distance near 50 cm.

Novel method for simultaneous 3-D imaging using chirped ultrashort light pulses is reported[Minoshima et al., 1994]. Simultaneous imaging without scanning is possible by means of the conversion between the time and the color axes mediated by the chirped pulse. The efficacy of this method is proved by measuring an area composing three flat steps made of three gauge blocks of different lengths with an accuracy of better than 0.3 mm. This technique is applicable for imaging of the shape of moving objects, or surface testing of inspection.

(Hiroyoshi Yajima)

A4. Realization of Electrical Units

An automated 1-V Josephson-junction-array-voltage-standard (JJAVS) system which is almost similar with the JJAVS system of the ETL (Electrotechnical Laboratory) has been continuously operated for daily calibration of conventional voltage reference standards at an industry as well as at the national standard laboratory (i.e. ETL) [Yoshida et al., 1993a]. In the 1-V JJAVS system, the frequency stability of the millimeter-wave source has been improved to about 1x10-11 using a particular phase-locking circuit [Yoshida et al., 1993b].

A comparison among three sets of similar 1-V automated JJAVS systems was carried out to confirm that each system can be operated with assigned uncertainty of about 1x10-8 for daily calibration work of the Zener diode-based reference standards (ZDRSs) [Iwasa et al., 1994].

A 10-V calibrating system in which an automated voltage divider and a 1-V JJAVS system are combined has been used for daily calibration of 10-V ZDRSs at ETL since January 1991 [Sakamoto et al., 1993].

A 10-V Josephson junction array has been developed at ETL. It has been confirmed that the 10-V array generates voltage steps up to 14 V and the 10-V array should be used to set up a voltage standard system of 10-V [Murayama et al., 1995] [Endo et al., 1995].

A dc-SQUID (Superconducting QUantum Interference Device) magnetometer has been developed as a sensitive current detector [Nakanishi et al., 1994]. A resistance ratio bridge has been developed using a CCC (Cryogenic Current Comparator) in addition to the dc-SQUID magnetometer [Nakanishi et al., 1995].

Stable operation of a SET (Single Electron Tunneling) device with three gates has been theoretically analyzed under a condition that the device is operated by sinusoidal gate voltages [Fukushima et al., 1995].

Co-tunneling rate has been theoretically calculated for a SET device operated by sinusoidal gate voltage [Iwasa et al., 1995].

In order to re-evaluate the present ac-dc transfer standard of ETL, a new system has been developed combining a comparator system of thermal converters and a fast-reversed dc source [Sasaki et al., 1993].

(Tadashi Endo)

A5. EM Field, Power Density and Antenna Measurement

The sensitivity of an electromagnetic field sensor which uses a LiNbO3 electrooptical crystal and an optical-fiber link was improved by employing a Mach-Zehnder interferometer and a diode-laser pumped YAG laser. The improved sensor can measure an electromagnetic impulse whose peak value is larger than 10 V/m and whose width is wider than 5 ns [Kuwabara et al., 1992].

The optical transmission technology was applied to a spherical dipole antenna for electromagnetic field measurements. An optical-electric (for a transmitting antenna) or an electric-optical (for receiving one) converter was built in the spherical antenna and an optical fiber was used as a signal line. Using the transmitting and receiving antennas, the site attenuation of a Electromagnetic Interference (EMI) test site can be evaluated without cable disturbances [Murakawa et al., 1994].

Characteristics of commonly used dipole antennas in EMI measurements were experimentally investigated. It was found that the antenna balun may not seriously affect the height patterns, but the antenna type (tuned/half-wave or shortened) causes great effects on measurement results, especially for the case of vertical polarization [Morikawa et al., 1994].

The near-field 3-antenna method for measuring antenna factors was proposed. The attenuation levels of three transmission systems were measured in the near-field region. The antenna factors were calculated from the attenuation values and theoretically obtained near-field correction factors [Iida et al., 1995].

The complex antenna factor (CAF) with phase information was introduced to measure fast transient fields. CAF of a monopole antenna was measured in the frequency range up to 6 GHz by the modified near-field 3-antenna method [Ishigami et al., 1995].

To improve the standard site method (SSM) for EMI antenna calibration, it was proposed that transmitting and receiving antennas were fixed at a same height during the site attenuation measurements. It was concluded that the proposed method was more accurate than the conventional SSM [Sugiura et al., 1995].

(Takashi Iwasaki)

A6. Power, Attenuation and Impedance Measurement

A broadband power standard using a coaxial calorimeter was developed in the frequency region from 10 MHz to 40 GHz. It uses the waveguide of 2.9 mm diameter type and K-type connectors, The uncertainty of typical power meter calibration was evaluated to be 0.19 % to 1.23 % in one standard deviation expression [Inoue, 1993]. A calorimeter for optical fiber power measurement was developed. It has a compensative absorber to stabilize environmental disturbance, and two types of adapter for optical fibers and light beam. The uncertainty in measurement of 1 mW and 10 mW optical fiber power was evaluated as 0.18 and 0.45 % respectively, expressed as two standard deviations [Suzuki, et al., 1993]. A cryogenic calorimeter operating near liquid Helium temperature has been studied for weak laser power measurement. Experiments on 0.1-1 mW measurement have shown scatter of 2.5-0.1 % depending the power level. The source of the noise equivalent power was evaluated [Inoue et al., 1993]. A new microwave radiometer has been developed to make it possible to compare a noise source independently of its reflection coefficient whose measurement error becomes one of sources of error. It is a modification of a correlation radiometer with a quadrature hybrid coupler as the hybrid junction followed by a noise injection circuit for realizing temperature balance. The usefulness has been confirmed with a 10 GHz system [Kato, 1993].

A homodyne system for measuring attenuation at 10 GHz and 30 MHz is constructed and evaluated. The radio frequency attenuation is converted to 1 kHz attenuation with homodyne detection and balanced modulation. The converted attenuation is measured by the 1 kHz receiver. A 1 kHz voltage ratio standard is also proposed to check the accuracy of the receiver for maintain the long term accuracy [Kawakami et al., 1993]. A complex attenuator consisting of a variable attenuator and two fixed attenuator (or two isolators) was presented for use as a transfer standard of attenuation in the radio frequency. The mismatch error in calibrations were analyzed [Kawakami, 1992]. An attenuator with polarization free was developed for an intercomparison of attenuation value in 1.3 mm single-mode system. The maximum attenuation change due to the center wavelength change 0.01 mm was within 0.05 dB/10 dB.

A novel method is presented for calibrating a six-port reflectometer using only one sliding load of unknown reflection coefficient and one short as a calibration standard, The validity and utility of the method were confirmed in the frequency range of 8.5-12 GHz [Yakabe et al., 1994].

(Hiroyoshi Yajima)

A7. Optical Communication System Measurement

Optical time-domain reflectometer (OTDR) can be widely applied to the optical fiber and device measurements. An enhanced coherent OTDR was constructed for use in testing optical cable spans in transmission lines containing erbium-doped fiber amplifiers(EDFA's), which is based on heterodyne detection using acousto-optic (AO) switches [Furukawa et al., 1995]. A dynamic range of 42 dB with 5 dBm less probe power was achieved. Performance limit of coherent OTDR enhanced with EDFA's due to optical nonlinear phenomena was theoretically and experimentally clarified [Izumita et al., 1994]. In the research, single-way dynamic range of 48 dB was experimentally obtained. A coherent self-heterodyne Brillouin OTDR for the measurement of Brillouin frequency shift distribution in optical fibers was demonstrated [Shimizu et al., 1994]. This system, whose single-way dynamic range is 16 dB, can be applied to measuring fiber-distributed tensile strain. The design and performance of a 1.65-mm-band single-mode OTDR with a laser diode source was reported [Takasugi et al., 1993a]. This system makes it possible to test a in-service optical fiber without interrupting services using a test light wavelength different from that used for communication.

Optical frequency-domain reflectometer (OFDR) has a potential for high spatial resolution. In coherent OFDR, lightwave frequency is swept linearly with respect to time so that an optical path difference between a backscattered lightwave and and a reference lightwave is identified by their frequency difference. A coherent OFDR using a 1.55-mm linewidth-narrowed laser diode was demonstrated [Tsuji et al., 1995]. The Rayleigh backscattering profile for a 16.4-km-long fiber was measured. An in-service fiber line identification scheme based on OFDR was proposed and demonstrated for single star, survivable, and passive double star architectures [Katsuyama, 1995]. The system can measure a wide range of length differences from 4 cm to 3 km.

A new reflectometry, optical coherence domain reflectometry by synthesis of optical coherence function (OCDR), for high resolution measurements of unwanted back-reflections using a laser diode as a light source [Hotate, 1993]. This method has no mechanical moving parts, and the oscillation frequency of the laser diode is directly controlled. A millimeter-resolution optical low coherence reflectometer (OLCR) that exhibits reduced jaggedness in the Rayleigh backscatter signal was reported [Takada et al., 1994]. The spatial resolution was 1.2 mm, and the hidden spaces defined by the full-widths at -20 dB and -60 dB maximum of a Fresnel response of the OLCR were 6 mm and 1.2 cm, respectively.

Gain monitoring by detecting the spontaneous emission emitted by 0.98-mm laser diode pumped erbium-doped fiber amplifiers was investigated [Masuda, 1993]. The minimum gain accuracy was less than +-0.21 dB for an EDFA with launched pump power from 10 to 30 mW. The noise figure of a cascaded in-line EDFA is monitored with an accuracy of 0.05 dB and a reproducibility of +-0.03 dB [Masuda, 1993].

Optical fiber communication systems have advantages in its high-speed and wide-bandwidth characteristics. The timing jitter due to both the carrier phase noise of laser diode pulse sources and the Gordon-Haus effect in soliton transmission was analyzed [Iwatsuki et al., 1995]. A technique to measure the difference in the carrier linewidth of two pulse sources was proposed. Frequency control techniques for cold start and channel recognition functions in coherent multichannel local area networks were reported [Ohshima et al., 1995b]. The frequency deviation of the optical transmitter was estimated to be less than +-1 GHz.

(Takao Matsumoto)

A8. Telecommunication System Measurement

Terrestrial mobile communications have been a hot field of activity for these period. In particular, CDMA was extensively studied as a candidate system for FPLMTS (Future Public Land Mobile Telecommunication Systems). As the wideband transmission is a basic element for DS-CDMA, the propagation measurements in 2 GHz band were carried out [Moriyama et al., 1992; Iwai et al., 1993; Kozono, 1994]. One of the key technologies to increase the capacity is the interference canceller, and the various techniques were proposed [Fukawa et al., 1994; Yoshida et al., 1994; Kawahara et al., 1995]. Meanwhile, PHS (Personal Handyphone System) which is the advanced personal communications system based on digital cordless telephone technologies [Ishikawa, 1995; Hattori, 1995] started its commercial service in 1995. PHS employs micro cellular structure and the propagation characteristic is different from macro cellular counterparts. Many papers which dealt with the channel model and propagation measurements based on street microcells were published [Kozono et al., 1993; Nakazawa et al., 1994; Taga et al., 1995; Yamaguchi et al., 1995].

In fixed radio communications, the development on high capacity digital radio-relay systems has already matured. The general trend of research is the semi-fixed wireless access systems which support multimedia services provided by B-ISDN [Kohiyama, 1995]. The frequency band will be above 20 GHz and the transmission characteristic was also studied [Manabe et al., 1993]. In relation to the wireless access systems, the study on WLL (Wireless Local Loop) has been started [Minami, 1995].

N-STAR, the communication satellite for domestic use, was launched in 1995. N-STAR adopts multibeam system and covers S-band, C-band, Ku-band and Ka-band [Nakagawa et al., 1994b]. The domestic mobile satellite communications system operating in S-band was developed and was accommodated in N-STAR satellite. This system is used for maritime telephone service and complements the terrestrial cellular mobile systems [Hagiwara et al., 1994].

(Yoichi Saito)


de Labachelerie, M., K. Nakagawa, M. Ohtsu, and M. Sasada, Compact narrow linewidth 1.5 mm frequency references for laser diode frequency stabilization, IQEC'94 Summaries of papers presented at the International Quantum Electronic Conference, 9, 59-60 (1994)

Doboz, M., H. Matsumoto, and S. Iwasaki, Beam splitter path equalization for white light interferometry, Optical Eng., 34, 2, 493-498 (1995)

Endo T., Y. Sakamoto, Y. Murayama, A. Iwasa, and H. Yoshida, 1-V Josephson-junction-array voltage standard and development of 10-V Josephson junction array at ETL, IEICE (The Institute of Electronics, Information and Communication Engineers) Trans. Electron., E78-C, 503-510 (1995)

Engelkemier, B. S., K. Imamura, F. Takahashi, T. Yoshino, Nak Sam Chung, and Chia-Shu Liao, Two-way time transfer experiments among Japan, Korea, and Taiwan, IEEE Trans. Instrum. Meas. 44, 2, 98-102 (1995)

Fujimoto, H., M. Tanaka, and K. Nakayama, Noise reduction in an optical interferometer for picometer measurements, IEEE Trans. IM 44, 2, 471-474 (1995)

Fukawa, K., and H. Suzuki, Orthogonalizing matched filter (OMF) detection for DS-CDMA mobile radio systems, IEEE Globecom '94, 385-389 (1994)

Fukushima A., A. Iwasa, J. Kinoshita, K. Yoshihiro, and T. Endo, Sinusoidal gate voltages for a three-gate single electron pump, IEEE Trans. Instrum. & Meas., 44, 561-563 (1995)

Furukawa, S., K. Tanaka, Y. Koyamada, and M. Sumida, Enhanced coherent OTDR for long span optical transmission lines containing optical fiber amplifiers, IEEE Photon. Tech. Lett., 7, 5, 540-542 (1995)

Hagiwara, E., K. Satoh, Y. Nishi, H. Komagata, and Y. Yasuda, S-band mobile satellite communication system using N-STAR satellite, AIAA 15th ICSSC, 673-675 (1994)

Hanado, Y., M. Imae, M. Sekido, H. Kiuchi, and S. Hama, New millisecond pulsar observation system at CRL, Jpn. J. Appl. Phys. 1, Regul. Pap. Short Notes (Japan), 33,, 3B, 1681-1686 (1994)

Hattori, T., Personal communication system and wireless technology, NTT Review, 7, 56-65 (1995)

Hisadome, K., and M. Kihara, Short-term frequency stability estimation of an optically pumped cesium beam frequency standard, Jpn. J. Appl. Phys. 1, Regul. Pap. Short Notes (Japan), 33, 3B, 1669-1673 (1994)

Hori, T., and N. Hiromoto, The power increase and absolute frequency-stabilization of an optically-pumped far infrared laser, Jpn. J. Appl. Phys., 32, 5552-5557 (1993)

Hotate, K., and O. Kamatani, Optical coherence domain reflectometry by synthesis of coherence function, IEEE J. of Light. Tech., 11, 10, 1701-1710 (1993)

Iida, H., S. Ishigami, I. Yokoshima, and T. Iwasaki, Measurement of antenna factor of dipole antennas on a ground plane by 3-antenna method, IEICE Trans. Commun., E78-B, 2, 260-267 (1995)

Inoue, T., Broadband microwave power standard using coaxial calorimeter, Abstract of the 25th General Assem. of the URSI, A-2-2, 4 (1993)

Inoue, T., and K. Yamamura, A cryogenic calorimeter for precise measurement of weak laser power, Sensors and Material 4, 217-228 (1993)

Ishigami, S., H. Iida, and T. Iwasaki, Complex antenna factors of transient field sensors, 1995 Asia-Pacific Microwave Conference Proceedings, S12-1, 252-255 (1995)

Ishikawa, H., Personal communication system--System overview and outlook for future development--, NTT Review, 7, 37-47 (1995)

Ito, N., J. Ishikawa, and A. Morinaga, Evaluation of the optical phase shift in a Ca Ramsey fringe stabilized optical frequency standard by means of laser-beam reversal, Opt. Comm., 109, 414-421 (1994)

Iwai, H., and Y. Karasawa, Wideband propagation model for the analysis of effect of the multipath fading on the near-far problem in CDMA mobile radio channel, IEICE Trans. Commun., E76-B, 103-112 (1993)

Iwasa A., Y. Sakamoto, H. Yoshida, and T. Endo, Mutual comparisons of fully automated Josephson junction array voltage standard systems, IEEE Trans. Instrum. & Meas., 42, 368-391 (1994)

Iwasa A., A. Fukushima, and A. A. Odinsov, Practical analysis of single electron pump with harmonic drive, Jap. J. Appl. Phys., 34, 860-865 (1995)

Iwasaki, T., A single-mode optical fiber attenuator for intercomparison of attenuation, IEEE, IM-43, 837-842 (1994)

Iwatsuki, K., S. Kawai, S. Nishi, and M. Saruwatari, Timing jitter due to carrier linewidth of laser-diode pulse sources in ultra-high speed soliton transmission, IEEE J. of Light. Tech., 13, 4, 639-649 (1995)

Izumita, H., Y. Koyamada, S. Furukawa, and I. Sankawa, The performance limit of coherent OTDR enhanced with optical fiber amplifiers due to optical nonlinear phenomena, IEEE J. of Light. Tech., 12, 7, 1230-1238 (1994)

Kajita, M., and A. V. Zvyagin, A new ring trap for frequency-standard application, Applied Physics B, 58, 295-301 (1993)

Kato, Y., Reflection-free microwave radiometer, IEEE Trans. IM-42, 1014-1019 (1993)

Katsuyama, Y., In-Service fiber line identification based on high-resolution fiber length measurement, IEEE J. of Light. Tech. 13, 1, 6-13 (1995)

Kawahara, T., and T. Matsumoto, Joint decorrelating multiuser detection and channel estimation in asynchronous CDMA mobile communications channels, IEEE Trans. Veh. Tech., 44, 506-515 (1995)

Kawakami, T., An analysis of mismatch error in RF variable attenuator, Bulletin of the Electrotechnical Laboratory, 56, 1294-1303 (1992)

Kawakami, T., M. Nagatsuka, M. Maeda, and M. Igarashi, RF attenuation measurement system with 1 kHz voltage ratio standard, IEEE, IN-42, 1014-1019 (1993)

Kohiyama, K., Advanced wireless access system, Proc. of Telecom '95, Technical Summit, 2, 341-345 (1995)

Kozono, S., Received signal level characteristics in a wideband mobile radio channel, IEEE Trans. on Veh. Tech., 43, 480-486 (1994)

Kozono, S., and A. Taguchi, Mobile propagation loss and delay spread characteristics with a low base station antenna on an urban road, IEEE Trans. Veh. Tech., 42, 103-109 (1993)

Kuwabara, N., K. Tajima, R. Kobayashi, and F. Amemiya, Development and analysis of electric field sensor using LiNbO3 optical modulator, IEEE Trans. on Electromagnetic Compatibility, 34, 4, 391-396 (1992)

Manabe, T., and T. Yoshida, Digital transmission characteristic on millimeter waves, IEEE ICC'93, 1602-1605 (1993)

Masuda, H., and K. Aida, Gain monitoring of erbium-doped fiber amplifiers by detecting spontaneous emission, IEEE Photon. Tech. Lett., 5, 9, 1017-1019 (1993)

Masuda, H., K. Aida, and K. Nakagawa, Noise figure monitoring of a cascaded in-line erbium-doped fiber amplifier, IEEE Photon. Tech. Lett., 5, 12, 1436-1438 (1993)

Matsumoto, H., and L. Zeng, High-accuracy measurement of air refractive index using two frequency-doubling crystals, Optics Communications, 104, 241-244 (1994)

Minami, S., Wireless access system is the optimum solution, Proc. of Telecom '95, Technical Summit, 2, 417-421 (1995)

Minoshima, K., H. Matsumoto, Z. Zhang, and T. Yagi, Simultaneous 3-D imaging using chirped ultrafast optical pulses, J. J. A. P, 33, L1348-1351 (1994)

Morikawa, T., and M. Tokuda, Spherical dipole antenna, Proceedings of 1994 International Symposium on Electromagnetic Compatibility, 18A6PS08, 811 (1994)

Moriyama, E., M. Mizuno, and T. Iwama, Development of multipath measurement and simulation equipment for wideband mobile radio, IEEE VTC'92, 536-539 (1992)

Murakawa, K., A. Sugiura, K. Koike, and K. Harima, Characteristics of dipole antenna for EMI measurements, Proceedings of 1994 International Symposium on Electromagnetic Compatibility, 19P603, 763-766 (1994)

Murayama Y., Y. Sakamoto, A. Iwasa, M. Nakanishi, H. Yoshida, U. Klein, and T. Endo, Ten-volt Josephson junction array, IEEE Trans. Instrum. & Meas., 44, 218-222 (1995)

Nakagawa, N., A. S. Shelkovnikov, T. Katsyda, and M. Ohtsu, Fast frequency stabilization of a diode-laser-pumped monolithic Nd:YAG laser with an extra-cavity electro-optic modulator, Opt. Commun., 109, 446-450 (1994a)

Nakagawa, K., M. Minomo, M. Tanaka, and T. Itanami, N-STAR--Communication satellite for Japanese domestic use, AIAA 15th ICSSC, 1129-1134 (1994b)

Nakagiri, K., M. Shibuki, M. Kajita, N. Kotake, and K. Sebata, Atomic frequency standards. Cesium beam primary frequency standard, J. Commun. Res. Lab. (Japan), 39, 1, 23-41 (1992)

Nakagiri, K., Design, and preliminary results of a vertical cesium beam frequency standard, Proc. 5th Symp. Freq. Std. and Metrology (to be published)

Nakanishi M., DC superconducting quantum interference device magnetometer for cryogenic current comparator, Jap. J. Appl. Phys., 33, 5713-5717 (1994)

Nakanishi M., J. Kinoshita, and T. Endo, Resistance ration bridge using cryogenic current comparator with dc-superconducting quantum interference device magnetometer, Jap. J. Appl. Phys., 34, 3284-3289 (1995)

Nakazawa, I., and T. Takeuchi, Frequency domain analysis and measurement on multi-path propagation for wideband microcellular environment, IEEE VTC'94, 155-159 (1994)

Ohshima, S.-I., A. D. DeMarchi, C. H. Oh, and Y. Nakadan, Velocity distribution by time-of-flight measurement in an optically pumped Cs beam frequency standard, Jpn. J. Appl. Phys. 1, Regul. Pap. Short Notes (Japan) 33, 10, 6058-6059 (1994)

Ohshima, S., T. Kurosu, T. Ikegami, and Y. Nakadan, Cesium atomic fountain with-dimensional moving molasses, Jpn. J. Appl. Phys., 34 Part2.9A 1170 (1995a)

Ohshima, S., M. S. Nakamura, S. Baba, T. Tomioka, M. Miyachi, and Y. Shimomura, Frequency control technique in coherent multichannel LAN's, IEEE J. of Light, Tech., 13, 9, 1838-1846 (1995b)

Saburi, Y., Y. Koga, S. Kinugawa, T. Imamura, H. Suga, and Y. Ohuchi, Short-term stability of laser-pumped rubidium gas cell frequency standard, Elect. Lett., 30, 8, 633-634 (1994)

Sakamoto, Y., T. Endo, and T. Sakuraba, A 10-V calibrating system using an automated voltage divider and a 1-V Josephson array, IEEE Trans. Instrum. & Meas., 42, 583-587 (1994)

Sasaki, H., K. Takahashi, M. Klonz, and T. Endo, High-precision ac-dc transfer standards at ETL, IEEE Trans. Instrum. & Meas., 42, 603-607 (1993)

Shimizu, K., T. Horiguchi, Y. Koyamada, and T. Kurashima, Coherent self-heterodyne Brillouin OTDR for measurement of Brillouin frequency shift distribution in optical fibers, IEEE J. of Light. Tech., 12, 5, 730-736 (1994)

Sugiura, A., T. Morikawa, K. Koike, and K. Harima, An improvement in the standard site method for accurate EMI antenna calibration, IEICE Trans. Commun., E78-B, 8, 1229-1237 (1995)

Sugiyama, K., and J. Yoda, Disappearance of Yb+ in excited states from a rf trap by background gases, Jpn. J. A. P., 34, L584-L586 (1995)

Suzuki, Y., A. Chida, Murata, and T. Inoue, A calorimeter for optical power standard and advantages in calibration of optical fiber power meters, IEEE Trans, IM-42, 430-433 (1993)

Taga, T., T. Furuno, and K. Suwa, Channel modeling for 2 GHz band urban line-of-sight street microcells, IEEE VTC'95, 246-251 (1995)

Takada, K., and M. Horiguchi, Jaggedness-free millimeter-resolution low coherence reflectometry, IEEE J. of Light. Tech., 12, 4, 658-663 (1994)

Takasugi, H., N. Tomita, J. Nakano, and N. Atobe, Design of a 1.65-mm-band optical time-domain reflectometer, IEEE J. of Light, Tech., 11, 11, 1743-1748 (1993a)

Takasugi, H., N. Tomita, H. Suzuki, and T. Akai, A new fault-identification method using a dichroic reflective optical filter in optical subscriber loops, IEEE J. of Light. Tech., 11, 2, 351-357 (1993b)

Tanaka, U., and T. Yabuzaki, Frequency stabilization of diode laser using external cavity and Doppler-free atomic spectra, Jpn. J. Appl. Phys., 33, 1614-1622 (1994)

Tsuji, K., K. Shimizu, T. Horiguchi, and Y. Koyamada, Coherent optical frequency domain reflectometry for a long signal-mode optical fiber using a coherent lightwave source and an external phase modulator, IEEE Photon. Tech. Lett., 7, 7, 804-809 (1995)

Uehara, N., and K. Ueda, Ultrahigh-frequency stabilization of a diode-pumped Nd:YAG laser with a high-power-acceptance photodetector, Opt. Lett., 19, 728-30 (1994)

Ueno, T., T. Nakazawa, H. Bakano, T. Sato, and M. Shimba, Frequency stabilization of a semiconductor laser using the Faraday effect of the saturated absorption spectroscopy signal of the Rb atoms, Trans. IEICE, J76C-1, 10-17 (in Japanese) (1993)

Umezu, J., T. Maeno, H. Saito, and Y. Ohta, Atomic frequency standards. An optically pumped cesium beam frequency standard, J. Commun. Res. Lab. (Japan), 39, 1, 53-62 (1992)

Urabe, S., K. Hayasaka, M. Watanabe, H. Imajo, and R. Ohmukai, Trapping and laser cooling of Ca+ ions toward future optical frequency standards: observation of clock transitions, 1994 Conference on Precision Electromagnetic Measurements Digest, 440-441 (1994)

Yakabe, T., M. Kinoshita, and H. Yabe, Complete calibration of six port reflectometer with one sliding load and one short, IEEE Trans. IM-42, 2035-3029 (1994)

Yamaguchi, A., K. Suwa, and R. Kawasaki, Received signal level characteristics for wideband radio channel in microcells, IEEE PIMRC'95, 1367-1371 (1995)

Yoshida, H., F. Katada, Y. Sakamoto, A. Iwasa, and T. Endo, Use of the Josephson junction array voltage standard in industry, Jap. J. Appl. Phys., 32, 3643-3648 (1993a)

Yoshida, H., Y. Sakamoto, U. Klein, and T. Endo, Improvements in the millimeter-wave subsystem for Josephson junction array voltage standard systems, IEEE Trans. Microwave Theory & Techniques, 41, 2353-2358 (1993b)

Yoshida, S., A. Ushirokawa, S. Yanagi, and Y. Furuya, DS/CDMA adaptive interference canceller on differential detection in fast fading channel, IEEE VTC'94, 780-784 (1994)