IME encoder schematic and/or electric design

I’m curious about how the IME encoders work. On the IME printed circuit board it looks like there’s two LEDs or light sensors, with some kind of light shielding using stacked printed circuit boards. The top circuit board has two cutouts, which may indicate a quadrature encoder. With the simple optical target, I’m assuming an analog encoder.

Does anyone have the schematic for the IME printed circuit board?