Optical Polarization Encoding Using Chip-Scale GaN Optoelectronic Devices

In this work, a compact polarization sensing device for optical encoding is introduced by integrating a GaNbased optoelectronic chip with linear polarizing films. The GaN chip with a size of $2.1 \mathrm{~mm}^{2}$ comprises a light-emitting diode (LED) and four photodetectors (PDs) on a transparent sapphire substrate. Each PD region is affixed with a linear polarizing film oriented at distinct angles of $0^{\circ}, 45^{\circ}, 90^{\circ}$, and 135°. The light emitted from the LED passes through these on-chip polarizing films, behaving as unpolarized light. The amount of light reflected to the PDs depends on the polarization properties of the measured plane. Moreover, changes in the angle between the device and external polarizers result in variations in photocurrents of the PDs, enabling the precise measurement of rotational angles and validating the feasibility of the device as an optical encoder. Experimental outcomes indicate an angular resolution of 0.8° and a strong linear correlation between the rotation angle and photocurrent. The compact design, operational simplicity, and cost-effectiveness of the developed device make it suitable for practical uses in optical encoders.