Managing evanescent optical coupling in photonic integrated circuits

An article of manufacture comprising:

• a first waveguide core structure configured to
• confine an optical wave at a first wavelength to a first mode over a coupling region, and
• confine an optical wave at a second wavelength to a second mode over the coupling region;
• and
• a second waveguide core structure configured to
• confine an optical wave at the first wavelength to a third mode over the coupling region, and
• confine an optical wave at the second wavelength to a fourth mode over the coupling region;
• wherein the coupling region comprises a structure in which a portion of the first waveguide core structure is in proximity to a portion of the second waveguide core structure over a coupling distance and is configured to
• provide a first coupling between the first mode and the third mode, at a first location along the coupling distance, that is greater than a second coupling between the second mode and the fourth mode at the first location, and
• provide a third coupling between the second mode and the fourth mode, at a second location along the coupling distance different from the first location, that is greater than a fourth coupling between the first mode and the third mode at the second location.