Arrangements using air trench cladding enables minimization of the evanescent tail to suppress light coupling to radiation modes, resulting in low-loss bends and splitters. Structures including sharp bends and T-splitters without transmission loss, crossings without crosstalk, and couplers from/to fibers and with out-of-plane waveguides without substantial loss are provided with such air trench claddings. Air trench sidewall cladding of waveguides pushes evanescent tails toward top and bottom claddings to enhance coupling between vertically positioned waveguides. Fabrication processes using wafer bonding technology are also provided.