Endless phase shifting

An optical apparatus comprising:

• a first Mach-Zehnder interferometer (MZI) switch including a phase shifter;
• a second MZI switch including a phase shifter;
• and
• a line phase shifter structure optically connecting the first MZI to the second MZI, said line phase shifter structure including two waveguides, at least one of the waveguides having a phase shifter;
• wherein the phase shifter included in the first MZI switch and the phase shifter included in the second MZI switch are configured to substantially simultaneously switch from π/2 to 3π/2 and 3π/2 to π/2 respectively, in response to a value of substantially 0 or 4π exhibited by the line phase shifter.