Noise-free, high-gain signal beam amplification using beam fanning in a photorefractive KNbO3:Fe crystal

A low-noise, high-gain optical image amplifier is the ultimate goal of two-wave coupling in the photorefractive crystal with large values of two-wave coupling coefficients. However, the beam fanning is also very strong in the photorefractive crystal with high two-wave coupling coefficient, which corrupts greatly the optical quality of the amplified image. Recently many techniques were demonstrated to get a high-gain, low-noise amplifier, in all of which people were making an effort to get rid of the beam fanning. On contrary, here we reported a new scheme utilizing the beam fanning effect to get a noise-free, high-gain amplified image by two-wave coupling.