An image sensor, comprising: a first sensor portion; and a second sensor portion coupled to the first sensor portion, wherein: the first sensor portion comprises a frontside-illumination image sensor for NIR/IR light detection comprising: a first photodetector; a first metal-interconnect layer; and a hollow first light pipe through the first metal-interconnect layer, the second sensor portion comprises a backside-illumination image sensor for visible-light detection comprising: a second photodetector; a second metal-interconnect layer; and a hollow second light pipe through the second metal-interconnect layer, and the first metal-interconnect layer is bonded to the second metal-interconnect layer to form a combined metal-interconnect layer, such that the first photodetector aligns with the second photodetector about a common axis, wherein the first light pipe is aligned with the second light pipe about the common axis to form a cavity within and through the combined metal-interconnect layer between the first photodetector and the second photodetector to allow light to pass from the second photodetector, through the combined metal-interconnect layer, and to the first photodetector and wherein the second sensor portion is thinner than the first sensor portion. a first sensor portion; and a second sensor portion coupled to the first sensor portion, wherein: the first sensor portion comprises a frontside-illumination image sensor for NIR/IR light detection comprising: a first photodetector; a first metal-interconnect layer; and a hollow first light pipe through the first metal-interconnect layer, the second sensor portion comprises a backside-illumination image sensor for visible-light detection comprising: a second photodetector; a second metal-interconnect layer; and a hollow second light pipe through the second metal-interconnect layer, and the first metal-interconnect layer is bonded to the second metal-interconnect layer to form a combined metal-interconnect layer, such that the first photodetector aligns with the second photodetector about a common axis, wherein the first light pipe is aligned with the second light pipe about the common axis to form a cavity within and through the combined metal-interconnect layer between the first photodetector and the second photodetector to allow light to pass from the second photodetector, through the combined metal-interconnect layer, and to the first photodetector and wherein the second sensor portion is thinner than the first sensor portion. the first sensor portion comprises a frontside-illumination image sensor for NIR/IR light detection comprising: a first photodetector; a first metal-interconnect layer; and a hollow first light pipe through the first metal-interconnect layer, a first photodetector; a first metal-interconnect layer; and a hollow first light pipe through the first metal-interconnect layer, the second sensor portion comprises a backside-illumination image sensor for visible-light detection comprising: a second photodetector; a second metal-interconnect layer; and a hollow second light pipe through the second metal-interconnect layer, and the first metal-interconnect layer is bonded to the second metal-interconnect layer to form a combined metal-interconnect layer, such that the first photodetector aligns with the second photodetector about a common axis, wherein the first light pipe is aligned with the second light pipe about the common axis to form a cavity within and through the combined metal-interconnect layer between the first photodetector and the second photodetector to allow light to pass from the second photodetector, through the combined metal-interconnect layer, and to the first photodetector and wherein the second sensor portion is thinner than the first sensor portion. a second photodetector; a second metal-interconnect layer; and a hollow second light pipe through the second metal-interconnect layer, and the first metal-interconnect layer is bonded to the second metal-interconnect layer to form a combined metal-interconnect layer, such that the first photodetector aligns with the second photodetector about a common axis, wherein the first light pipe is aligned with the second light pipe about the common axis to form a cavity within and through the combined metal-interconnect layer between the first photodetector and the second photodetector to allow light to pass from the second photodetector, through the combined metal-interconnect layer, and to the first photodetector and wherein the second sensor portion is thinner than the first sensor portion.