Performance of Optical Fibers for Reference Frequency and IF Signal Transmissions in VLBI Observation

摘要

We have constructed a 6 mm antenna system in the Nobcyarna Radio Observatory (NRO) complex of the National Astronomical Observatory, Japan. This system is used for the International Radio Interferometric Surveying trans- Pacific (IRIS-P VLBI) network observation of the International Earth Rotation Service with the Mark-111 VLBI Back-end and the hydrogen maser frequency standard operating at the control room of the 45 m antenna III the NRO. This 6 m antenna is located about 880 m apart from the control room, Therefore, the 10 MHz reference frequency signal and the IF signals should be transmitted over 880 m distance without signal phase fluctuations in the Mark-111 VLBI observations. The phase stabilized signal transmission should be attained by using phase stabilized optical fiber (PSOF), Prior to introduction of this system, we have made a phase stability estimator by experiments, The PSOF is currently developed at Sumitomo Electric Industries, Ltd. of Japan. We have tested the prototype of this PSOF signal transmission system of which the length is 1000 m. The phase stability of the 1000 m PSOF system is 3.95 x 10(sup-l5) (t=1000 sec.) in Allan standard deviation (ASD) at the stabilized temperature of 21.4C +/- 0.5C and at the frequency of 20.9 MHz. The stability is about 55 times better than the ordinary coaxial cable transmission system. In the environment of temperature variation of +30 C, the stability of this PSOF is 1.97 x 10(sup -14) (t=1000 sec.) in ASD.