Fabrication-tolerant waveguides and resonators

A device comprising:

• a strongly confining optical waveguide including:
• a first core region disposed over a substrate, the first core region having a first substantially rectangular cross-section and comprising a first core material, the first core material comprising a semiconductor and being substantially transparent within an operating wavelength range having a first free-space center wavelength selected from the range of 500 nm to 3000 nm;
• and
• a first cladding region surrounding the first core region, the first cladding region (i) comprising at least one cladding material having a refractive index, and (ii) having a first maximum cladding refractive index equal to the largest refractive index of the at least one cladding material,
• wherein a core refractive index of the first core material is at least 1.5 times the first maximum cladding refractive index,
• wherein the first rectangular cross-section has a first aspect ratio AR defined by a ratio of a width of the first rectangular cross-section to a height of the first rectangular cross-section, the first aspect ratio is at least 5:1 and at most 20:1, and a height of the first core region is between 1/150 and 1/10 of the first free-space center wavelength, and
• wherein the waveguide comprises a section having a bending radius between twice and ten times the first free-space center wavelength.