Balanced-path homodyne I/Q-interferometer scheme with very simple optical arrangement using a polarizing beam displacer.

A new balanced-path homodyne I/Q-interferometer scheme using a specially designed polarizing beam displacer (PBD) is described. The PBD is designed for splitting the s- and p-polarization components of the input beam into two parallel output beams which can be used as two beams of a balanced-path interferometer. The interferometer has a very simple optical arrangement because all of seven optical components used for interfacing two arms of the interferometer into the I/Q-demodulator in the previous schemes are replaced by the single PBD. A simple optical arrangement makes the interferometer less susceptible to environmental perturbations. It will be shown that the RMS fluctuations during a long-term phase noise measurement for 24 hours is ~7 × 10^-5 rad. in an open lab environment. In addition, the separation between two arms of the interferometer is adjustable which makes the interferometer very flexible for many sensor applications. Potential use of our new interferometer as an interferometric sensor will be demonstrated by employing a displacement sensor arrangement.