of an integrated optical circuit the second phase modulation signal 135 is applied to the second phase modulator 130 the second phase modulation signal 135 may be a periodic signal for example a sinusoidal signal described by a sin u03c9t where u03c9 2 u03c0f accordingly the phase of the optical signal passing through the first phase modulator will vary according to the function a sin u03c9t alternatively the first and second phase modulation signals 120 135 may be sinusoidal functions or any other periodic function having the same amplitude and frequency with a phase difference of u03c0 2 the second optical filter 140 may be an optical bandpass filter the second optical filter 140 may be implemented in any manner as would be known to one of skill in the art for example a bragg grating or ring resonator the second optical filter 140 may have a bandwidth centered on the carrier frequency of the cw laser and may have a bandwidth sufficient to reject any wideband artifacts that result from the first and second phase modulators 115 130 the operation of the optical isolator 100 will now be described in the forward direction the phase modulation applied by the first and second phase modulators 115 130 on an optical signal output from the cw laser 105 is as follows a cos u03c9 t a sin u03c9 t u2212 u03b4t a cos u03c9 t a cos u03c9 t u2212 u03b4t u2212 u03c0 2 a cos u03c9 t a cos u03c9 t u2212 u03c0 0 thus there is no net modulation in the reverse direction the net phase modulation applied by the first and second phase modulators 115 130 is as follows a sin u03c9 t.