Yuko Hanado

Development of multichannel dual-mixer time difference system to generate UTC (NICT)

A multichannel dual-mixer time difference (DMTD) system has been developed by the National Institute of Information and Communications Technology (NICT) for a measurement system to generate the UTC(NICT) time scale based on Coordinated Universal Time (UTC). This system measures time differences between a reference signal and 24 device under test (DUT) signals, simultaneously. We have confirmed that this system has enough accuracy to measure hydrogen maser and cesium clocks at an averaging time of 1 s.

The New Generation System of Japan Standard Time at NICT

NICT has completed a new generation system for the realization of Japan standard time. There are various renewals in this system. One of the big changes is the introduction of hydrogen masers as signal sources for UTC(NICT) instead of Cs atomic clocks. This greatly improves the short-term stability of UTC (NICT). Another big change is the introduction of a newly developed 24ch dual-mixer-time-difference system (DMTD) as the main tool for measurements. The reliability of the system is also improved by enhanced redundancy and monitoring systems. The new JST system is in regular operation since February 2006.

Precise Evaluation of a Phase-Locked THz Quantum Cascade Laser

We have demonstrated the phase-locking of a THz quantum cascade laser (THz-QCL) toward the realization of an accurate and stable local oscillator for a high-resolution receiver. The beat note between the THz-QCL and a THz reference was obtained by heterodyne mixing in a superconducting hot electron bolometer mixer (HEBM) and used for stabilizing the phase of 3.1 THz radiation from the THz-QCL. The phase-locked 3.1 THz radiation was fully evaluated with a superlattice harmonic mixer operating in the THz band, and this revealed that the THz-QCL synchronized with the microwave reference with a fractional frequency instability of 3×10-15 at an averaging time of 100 s, corresponding to a center frequency deviation within 1 mHz, and the imposed phase noises during the heterodyne mixing were negligibly small.

Millisecond pulsar observation system using acousto-optic spectrometer

We have developed a unique system using an acoustooptic spectrometer for precise timing of millisecond pulsars. This system can handle a signal of 50 MHz bandwidth with a frequency resolution of 200 kHz and a time resolution of 13 /spl mu/s, and it can average 2/sup 24/ (7 h) pulses without any dead time. >

Microwave synthesis from a continuous-wave terahertz oscillator using a photocarrier terahertz frequency comb.

A low-phase-noise microwave signal was synthesized from 0.3THz radiation using a photocarrier frequency comb in a photoconductive antenna. This technique potentially transfers the phase information of THz radiation into accessible microwave region.

SI-traceable measurement of an optical frequency at the low 10^−16 level without a local primary standard

SI-traceable measurements of optical frequencies using International Atomic Time (TAI) do not require a local primary frequency reference, but suffer from an uncertainty in tracing to the SI second. For the measurement of the 87Sr lattice clock transition, we have reduced this uncertainty to the low 10-16 level by averaging three sets of ten-day intermittent measurements, in which we operated the lattice clock for 104 s on each day. Moreover, a combined oscillator of two hydrogen masers was employed as a local flywheel oscillator (LFO) in order to mitigate the impact of sporadic excursion of LFO frequency. The resultant absolute frequency with fractional uncertainty of 4.3 × 10-16 agrees with other measurements based on local state-of-the-art cesium fountains.

Upgrading of UTC(CRL)

The problems in the current UTC(CRL) were solved. One problem was a large variation of frequency when a clock was withdrawn from the ensemble, which was caused by an inadequately predicted frequency of each cesium clock in the ensemble. We succeeded in solving this problem by changing the definition of the predicted frequency. Another problem was a variation in the daily-steering frequency of the UTC(CRL). We found that this problem was caused by a large variation in the measured time offset between the clocks. Improving the measured value was not easy, so we adopted a moderate adjustment and thereby succeeded in solving it. These solutions improved the frequency stability of the UTC(CRL).

Pulsar VLBI experiment with the Kashima (Japan)–Kalyazin (Russia) baseline

Abstract The position of PSR0329+54 on the International Celestial Reference Frame was measured at epochs March 1995, May 1996, and May 1998. Our observations detected the proper motion of PSR0329+54. The position and proper motion agreed well with the position determined by Bartel et al. (1985) . From combined analysis with our data and that of Bartel, the proper motion of PSR0329+54 was determined: μ α =+17.4±0.3 mas yr −1 , μ δ =−11.0±0.3 mas yr −1 . These results are consistent with the value by Harrison et al. (1993) measured with the MERLIN interferometer. We also determined the coordinates of PSR0329+54 very accurately within the ICRF: α =03 h 32 m 59 s .3761±0 s .0002, δ =54°34′43′′.5119±0′′.0015 at 1995.

Phase-coherent transfer and retrieval of terahertz frequency standard over 20 km optical fiber with 4 × 10−18 accuracy

We demonstrate a terahertz (THz) frequency reference transfer with high accuracy and stability. Phase information of the THz frequency standard is coherently duplicated onto an optical carrier as an intermediary for exploiting low-loss optical-fiber technology. The transferred information on the optical carrier is retrieved into the THz domain without phase decoherence. The THz reference transfer system, which comprises frequency-comb-based THz-to-optical and optical-to-THz synthesizers connected by a 20 km phase-noise-compensated fiber, is operated with 4 × 10−18 fractional frequency accuracy at 0.3 THz. This THz reference transfer is available for the remote frequency calibration of diverse instruments working in the THz region.

Improvement of Rate Shift in Average Atomic Time Scale Algorithm

In an average atomic time scale algorithm, we developed a new method of suppressing the influence of a large sudden rate shift in some clocks. The method entails two points. One is to add a clock rate check process. The weight of a bad clock is forced to be zero if its latest rate largely changes from the past rate. The other is to change the weighting itself of clocks. Inversely proportional weighting to the square of Allan deviation, which is thought to be one of the standard methods, turned out to occasionally make the time scale instable, by emphasizing inadequate clocks. We adopted two other loose weightings, namely, even weighting and inverse proportional weighting to Allan deviation. We tested the above two steps by simulation with 16 Cs atomic clocks at the National Institute of Information and Communication Technology (NICT), and showed a successful improvement in the stability of the standard algorithm of the average atomic time scale.