Miniaturized polarization sensors integrated with wire-grid polarizers

Miniaturized polarization sensors integrated with aluminum (Al) nanowire-grid polarizers have been developed for compact optical rotary encoders. The sensor consists of Al wire grid polarizers sandwiched between two glass substrates, an InGaAs photodiode (PD) chip and a Si substrate with a cavity and through silicon vias (TSVs). Two polarizers that can detect two orthogonally polarized components were integrated in a single device. The glass substrates with wire-grid polarizers were vertically stacked on the Si substrate for chip size packaging. Integration of PD chips and sealing were performed using Au-Au surface activated bonding using atmospheric-pressure plasma with mixed gas of Ar and H₂ at a relatively low bonding temperature of 150 °C. The feasibility of rotational angle measurement of linear polarizer was demonstrated by differential detection of two orthogonally polarized components.