An optical coupler apparatus, comprising: a waveguide region (102, 451, 551, 702, 728, 751, 752) configured to guide light propagating along a first direction; wherein the waveguide region comprises a first reflector region (106, 453,478, 484, 553, 706, 761, 791) configured to i) reflect, by a particular reflectivity, a portion of the light propagating in the waveguide region and ii) transmit another portion of the light propagating in the waveguide region to the interference region; a second reflector region (114, 424, 452, 476, 552, 714, 762, 792) configured to reflect light incident on second reflector region, wherein the light incident on the second reflector region is of the light propagating along the first direction; an interference region (110, 454, 554, 710, 770) formed between the waveguide region and the second reflector region, the interference region configured to create a standing wave pattern through interference between the incident light and the reflected light and to confine at least a portion of interference light formed by the incident light and the reflected light, wherein the first reflector region (106, 453,478,484,553,706,761,791) and the second reflector region (114, 452, 476, 552, 714, 762, 792) provide reflective surfaces that form a cavity in the interference region where the standing wave pattern is formed, wherein the cavity has a fixed cavity length that defines the standing wave pattern; and a grating region (120, 455, 555, 720, 721, 920, 921, 922, 923, 932) comprising a grating formed on the interference region confining at least a portion of the interference light, the grating configured to couple at least a portion of the interference light along a second direction that is different from the first direction, wherein a grating periodicity of the grating region matches an interference periodicity of the standing wave pattern of the light inside the interference region such that optical loss due to mismatch is within an order of magnitude. a waveguide region (102, 451, 551, 702, 728, 751, 752) configured to guide light propagating along a first direction; wherein the waveguide region comprises a first reflector region (106, 453,478, 484, 553, 706, 761, 791) configured to i) reflect, by a particular reflectivity, a portion of the light propagating in the waveguide region and ii) transmit another portion of the light propagating in the waveguide region to the interference region; a second reflector region (114, 424, 452, 476, 552, 714, 762, 792) configured to reflect light incident on second reflector region, wherein the light incident on the second reflector region is of the light propagating along the first direction; an interference region (110, 454, 554, 710, 770) formed between the waveguide region and the second reflector region, the interference region configured to create a standing wave pattern through interference between the incident light and the reflected light and to confine at least a portion of interference light formed by the incident light and the reflected light, wherein the first reflector region (106, 453,478,484,553,706,761,791) and the second reflector region (114, 452, 476, 552, 714, 762, 792) provide reflective surfaces that form a cavity in the interference region where the standing wave pattern is formed, wherein the cavity has a fixed cavity length that defines the standing wave pattern; and a grating region (120, 455, 555, 720, 721, 920, 921, 922, 923, 932) comprising a grating formed on the interference region confining at least a portion of the interference light, the grating configured to couple at least a portion of the interference light along a second direction that is different from the first direction, wherein a grating periodicity of the grating region matches an interference periodicity of the standing wave pattern of the light inside the interference region such that optical loss due to mismatch is within an order of magnitude.