Local oscillator laser phase stabilization

A phase-lock of the LO-signal between the fast receiver-photodiodes at the telescopes has been demonstrated in the laboratory with λ/10 precision using two 5m-fiber arms whose ends have been bent close together:  
Measurement of the phase stabilization: Instead of the broadband signal from the telescopes, a part of the laser is shifted by 50 MHz (fiber frequency shifter, FFS) and injected to the receivers, so that an intermedium-frequency (IF) signal of 50 MHz is detected. The phase difference of the two IF- outputs is analyzed on a two-channel digital oscilloscope. The ends of  the two 5m-fiber arms are bent close together, and the fibers of the 50MHz-shifted laser injection are rolled up together and kept between foam-plates for identical and stable temperature.

Over-night result under quite lab conditions (air conditioning switched off).