Continuous phase stabilization and active interferometer control using   two modes
  We present a computer-based active interferometer stabilization method that can be set to an arbitrary phase difference and does not rely on modulation of the interfering beams. The scheme utilizes two orthogonal modes propagating through the interferometer with a constant phase difference between them to extract a common phase and generate a linear feedback signal. Switching times of 50ms over a range of 0 to 6 pi radians at 632.8nm are experimentally demonstrated. The phase can be stabilized up to several days to within 3 degrees. 
Gregor Jotzu, Tim J. Bartley, H. B. Coldenstrodt-Ronge, Brian J. Smith   and Ian A. Walmsley
physics.optics quant-ph