Figure 1: Components of an AO isolator are shown schematically at four different length scales. Sizes are approximate. Forward propagating light enters from the left with slow polarization. Polarizers (possibly tilted fiber Bragg gratings) are oriented to pass the slow polarization. Copropagating torsional acoustic waves generated by transducers act as 50% polarization couplers. Transducer 2 returns forward light to the slow polarization, while transducer 1 shifts backward light entirely to the fast polarization.