We propose an approach of a reference modulation in a collinear holographic storage system to increase the signal-to-noise ratio (SNR). We derive a solution that shows that the point-spread function is related to the autocorrelation function of the reference pattern times a defocusing phase term. Accordingly, the lens-array phase modulation is proposed and demonstrated theoretically. The SNR of the system can be dramatically enhanced to 63.2, rather than 2.3 in the traditional approach.