Limits on the bitwise information density of spectral storage

We compute the mutual information between stored and retrieved signals in a spectral hole-burning optical memory. Under the assumption of bitwise data detection we evaluate the maximum achievable storage capacity and density that can be obtained for both time-domain and frequency-domain architectures. Noise arising from crosstalk in both the time- and frequency-domains is combined with the material shot noise to arrive at optimal system designs in terms of material volume and number of bits per spatial location. Time-domain results demonstrate the existence of an optimum data signal strength and the analogous frequency-domain results indicate an optimal hole depth. We find that realistic information storage densities of 40 bits/μm³ are possible using typical material parameters.