Communication apparatus and techniques, such as for optical communication, can include providing a reference frequency derived from an atomic energy level transition or a molecular energy level transition, generating at least two specified optical carrier signals at least in part using the reference frequency, coherently modulating the specified optical carrier signals using respective baseband information signals to provide respective coherently-modulated optical subcarriers. A combined optical information signal comprising the optical subcarriers can be transmitted to a receiver, such as via a fiber optic cable. In an example, a received optical information signal can be optically Fourier transformed to provide respective coherent outputs, which can be coherently downconverted.