An alternative scheme of round-trip phase correction

In photonic LO (Local) system, a two-wavelength optical beatnote is transmitted by optical fiber from the AOS technical building to antennas. At an antenna, a photo mixer converts the optical beatnote into a microwave-signal which works as a reference signal for the Worm Multiplier Assembly (WMA). The compensation of instability of transmission line is essential for interferometer to obtain fringes, and is an indispensable process for keeping signal coherence. However, it is delicate to measure an optical cable length delay, because the measured delay includes polarization mode dispersion (PMD). In order to accomplish the phase compensation on the optical fiber, we consider a double-difference method with a polarization alignment servo system. 1. BASIC CONCEPT OF DOUBLE-DIFFERENCE METHOD In order to accomplish the phase compensation on the transmission radio signal, we consider a double-difference method. The basic configuration of a system is shown in Figure 1. Firstly, for analysis of the instrumental delay, we will discuss the phase relationship of the signals in one of two optical signals. The suffixes (Opt1 and Opt2) denote the optical wavelength. The input optical signal phase, the source of the signal is the Laser Synthesizer, is defined as &(t)