On-chip interferometry system for high secret key rate quantum key distribution based on entangled photonic qudits

A device comprising:

• a linear series of N optical switches;
• N−1 pairs of waveguides wherein each pair of waveguides of the N−1 pairs of waveguides is disposed between a predetermined optical switch of the N optical switches and a sequential optical switch of the N optical switches to the predetermined optical switch of the N optical switches;
• and
• an optical waveguide coupled to the output of the final optical switch of the N optical switches;
• wherein
• each pair of waveguides comprises:
• a waveguide coupled from an output port of the associated predetermined optical switch of the N optical switches and an input port of the associated sequential optical switch of the N optical switches;
• and
• another waveguide from another output of the predetermined optical switch of the N optical switches and another input of the associated sequential optical switch of the N optical switches introducing a predetermined delay to optical signals propagating within the another waveguide relative to those optical signals propagating within the waveguide;
• the predetermined delays for the N−1 pair of waveguides are 2M·T where M=0, 1 . . . N−1 and T is a defined delay;
• and
• N is a positive integer greater than or equal to 3.