Development of a fiber-bundle-type polarization-based rotary encoder utilizing four-directional wire-grid polarizers

We propose and demonstrate a novel fiber-bundle-type polarization-based rotary encoder that integrates a reflective optical configuration with four-directional wire-grid polarizers (WGPs). A four-directional WGP chip was fabricated using electron beam lithography and a lift-off process, and subsequently bonded to the end face of an optical fiber bundle. By combining this chip with a reflective polarizing element, photodiodes, and signal processing circuits, we constructed a compact rotary encoder with optical fiber transmission. Transmission measurements confirmed that the fabricated WGP chip functions as a polarizer with extinction ratios of up to 17.5 dB at 850 nm. Performance evaluation of the prototype showed an angle detection error ranging from −0.67° to 0.61° and a resolution of 12,585 pulses per revolution, ensuring stable angle detection over a 180° range. These results verify the potential of the proposed configuration as a miniaturized, high-resolution, and noise-robust rotary encoder for precision positioning applications.