Abstract: An electromagnetic wave ring resonator is disclosed wherein means in included for spatially rotating the electromagnetic field distribution of waves resonant therein, such rotation being about the direction of propagation of such waves. With such arrangement the electromagnetic field distribution rotating means provides a phase difference between waves of opposite polarization sense, thereby enabling the waves to resonate with different frequencies. In a four frequency laser gyroscope the electromagnetic field distribution rotating means includes a catoptric arrangement which reduces the loss, scatter and linear birefringence associated with a ring resonator included in such gyroscope.