Broadband optical switches based on a ring-assisted Mach-Zhender interferometer

A method of forming a structure for an optical switch, the method comprising:

• forming a Mach-Zehnder interferometer that includes a first arm and a second arm, wherein the first arm comprises a first waveguide core, and the second arm comprises a second waveguide core;
• forming a ring resonator that comprises a third waveguide core, wherein the third waveguide core has a first thickness, and the third waveguide core includes a portion that is adjacent to a portion of the first waveguide core over a light coupling region;
• forming a slab layer that connects the portion of the first waveguide core to the portion of the third waveguide core, wherein the slab layer has a second thickness that is less than the first thickness, and the first waveguide core and the third waveguide core including upper regions that project above the slab layer by a height equal to a difference between the first thickness and the second thickness;
• and
• forming a thermo-optic phase shifter associated with a portion of the second waveguide core of the second arm,
• wherein the first waveguide core and the second waveguide core of the Mach-Zehnder interferometer, the third waveguide core of the ring resonator, and the slab layer comprise silicon.