1. A photonic digital-to-analog converter comprising: a) at least one substrate; b) a plurality of resonant cavities formed on said at least one substrate; c) a plurality of heterojunction thyristor devices formed in said resonant cavities; d) a plurality of voltage divider networks operably coupled to said heterojunction thyristor devices; and e) summing circuitry operably coupled to said voltage divider networks, wherein a plurality input optical signals are injected into corresponding resonant cavities, said input optical signals including input digital optical signals that synchronously encode a plurality of bits of information that are logically arranged from a most-significant-bit (MSB) to a least-significant-bit (LSB), wherein said heterojunction thyristor devices and voltage divider networks are arranged as first pairs each corresponding to a different one of said input digital optical signals, and each first pair cooperating to produce an output electrical signal whose magnitude corresponds to a given bit encoded by the corresponding input digital optical signal, and wherein said summing circuitry sums said output electrical signal produced by each first pair to generate an output analog electrical signal whose magnitude corresponds to said plurality of bits synchronously encoded by said input digital optical signals.