PROGRESS IN LABORATORY RESEARCH-AND-DEVELOPMENT FOR FUNDAMENTAL PHYSICS SPACE MISSIONS - WEAK LIGHT PHASE-LOCKING, FIBER-LINKED HETERODYNE INTERFEROMETRY, FIBER DELAY-LINE AND PICOMETRE REAL-TIME MOTION CONTROL

Since 1992, we have engaged in laboratory studies for astrodynamical m issions to test relativistic gravity in the solar system. The techniqu es developed are also relevant to other fundamental space missions suc h as LISA and the space interferometer for astrometry. Here we report our progress in weak light phase-locking, long fibre-linked heterodyne interferometry, fibre delay line and picometre real-time motion contr ol during the last year. We demonstrated that for two lasers with offs et locking up to 2.5 GHz, the heterodyne linewidth after travelling th rough a 26.27 km fibre-linked interferometer is less than 1 mHz. For w eak light phase-locking, we achieved 4.3 nW locking with a 3.4 mW loca l oscillator. We improved our side-polishing technique to polish more than eight fibres simultaneously and reached a tunable sensitivity as high as 85-90 dB in liquid-drop tests. Using these side-polished fibre s, we are currently in the process of making tunable directional coupl ers and fibre delay lines. For laser metrology, we use mid-point cycli c averaging to reduce the nonlinearity error, and use a fitting method to cancel the drift, and have reached 1.5 pm linearity. Currently, wi th modulation and real-time cyclic averaging, we reach a real-time mea suring precision of 560 pm and real-time motion-control precision of 7 00 pm.