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A unified framework is developed for optimizing the bit error rate incurred in the simultaneous differential modulation of the optical resources of polarization (pol.), phase, and amplitude over channels wherein the optical phase slowly wanders relative to the symbol rate, as applicable to high-bit-rate optical transmission. The modulation formats of pol. shift keying (POLSK), differential phase shift keying (DPSK), and amplitude shift keying (ASK), as well as recent and novel combinations thereof, are interpreted as instances of a new conceptual format called multichip differential state of POLSK, whereby it is the states of pol. in a block of D time slots that are differentially modulated and detected block-by-block. The classical description of pol. in terms of the four Stokes parameters (SPs), recently extended to D2 generalized SPs, underlies the conception of optimal receivers for these schemes. The theory is applied to rigorously establish the optimality of known POLSK receivers, to identify new optimal receiver structures for multipower POLSK, and to assess the optimality of recently introduced differential phase ASK and multichip DPSK modulation formats.