Coupling of two waves with different polarization states in a photorefractive crystal of cubic symmetry is discussed. We show that a proper choice of the polarization states allows linear transformation of small transient phase shift between the coupled waves into intensity modulation of the transmitted light even in the case when the space-charge field is formed using the diffusion-type mechanism. Comparison of the proposed phase-demodulation technique with known adaptive interferometers is given considering the sensitivity and the response time. The proposed technique is very promising for laser-ultrasound receivers since it allows design adaptive interferometers possessing the best combination of the sensitivity and adaptability.