two paths will be obtained by placing a half wave plate in each of the two interferometric paths with an angle of 45 u00b0 between their slow axes an additional u00b1 90 u00b0 polarization difference is obtained between the two optical paths with the sign depending on the propagation direction the total polarization axis rotation due to the faraday rotators and half wave retarders results in 0 u00b0 polarization axis difference between the two arms in the forward direction and 180 u00b0 polarization axis difference in the backward direction or vice versa it should be noted that a rotation of the polarization by 180 u00b0 is equivalent to a phase shift of 180 u00b0 this configuration is general so that a 4 port circulator a 3 port circulator and an isolator can be designed by changing the input and output port numbers accordingly the shifter is designed to have the same sequence of film devices in both arms in this way only the minimal number of grooves the number of faraday rotator films and one groove for the half wave plate needs to be fabricated while previous designs require the fabrication of at least one extra groove fig1 a is a schematic block diagram of an isolator circulator 1100 consisting of two mach zehnder based polarization splitters and a nonreciprocal polarization converter 1100 in accordance with the invention it should be.