  Very low intensity and phase fluctuations are present in a bright light field
such as a laser beam. These subtle quantum fluctuations may be used to encode
quantum information. Although intensity is easily measured with common
photodetectors, accessing the phase information requires interference
experiments. We introduce one such technique, the rotation of the noise ellipse
of light, which employs an optical cavity to achieve the conversion of phase to
intensity fluctuations. We describe the quantum noise of light and how it can
be manipulated by employing an optical resonance technique and compare it to
similar techniques, such as Pound-Drever-Hall laser stabilization and homodyne
detection.
