Optical feedback characteristics of two orthogonally polarized light beams in a HeNe laser during cavity tuning

Abstract

We can get optical feedback signals of the two orthogonally polarized light beams in a HeNe laser during the cavity tuning process when the period of the driving signal of the feedback mirror is set much shorter than that of the cavity mirror. The experiments are done under three different optical feedback conditions: only perpendicular light is fed back, only parallel light is fed back and both lights are fed back. When both lights are fed back, there is a phase delay less then 180 degrees between the two lights' intensity curves. When only one polarized light is fed back into the laser cavity, the two lights' intensity curves are inverted with respect to each other. We can subtract one light's intensity curve from the other one to improve the sensitivity of the optical feedback system. Especially when only perpendicular light is fed back, both lights' modulation amplitudes are large in a wide range of gain curve with the DC component stable. This property can be used to reduce the miscount of the system.