Compact, energy-efficient, and low-power optoelectronic devices can be realized through advancements in nanophotonics. (1) Flatband photodetectors achieve a compact form factor by integrating three optical elements—polarizer, color filter, and sensor—into a single thin layer of silicon p-i-n diode. (2) Chiral flatbands enable precise control of photodetectors sensitive to circularly polarized light. (3) Silicon nanobeam cavities support low-threshold lasing and significantly reduce power consumption in most optical systems.