Nonreciprocal magneto-optics for millimeter waves

The magnetooptical principles that form the basis for isolators and circulators at infrared wavelengths, i.e. 0.8 and 1.3 μm, have been successfully applied at 1 cm (35 GHz). Unlike the infrared case, which functions on the wings of a crystal-field absorption line, millimeter-wave rotation originates from ferrimagnetic resonance, and its magnitude is directly proportional to the ferrite magnetization. The basic theory is adapted to interpret experiments over a band from 26 to 40 GHz, with unmatched iron-garnet rotation elements used in a Gaussian-beam spectrometer and with the addition of antireflection quarter-wave plates. An experimental demonstration of a 45° rotator yielded an effective isolation greater than 40 dB, with a total insertion loss substantially less than 0.1 dB over a 20% bandwidth