How can I reuse this rotary encoder inside my mouse with an arduino?

I disassembled a very old optical computer mouse (so old that it has a PS/2 connector and not USB). I was mainly interested in the optical sensor chip, which I found and it has a lot of literature online that set me straight on how I can salvage it.

My question is regarding the rotary encoder for the scroll wheel
Here's the picture

The pointed thing is the IR blaster of course and the black thing on the other side should be the encoder. The scroll wheel sits in the middle of these two things.

There's my problem, I don't know what kind of rotary encoder that is. It doesn't have a parts number of anything. It just has 3 terminals, how do I figure out what terminal does what? I want to salvage it and use it with my arduino. Any clues?

Thanks in advance

Can you say "LED" instead of blaster?
The black thing is a transistor that is turned on and off when the encoder wheel is moved to allow the light to shine through the encoder wheel or when it is stopped.

Yes, probably should've said LED.

I can't figure out how to get the terminals connected to my Arduino.

I can't either. The transistor is actually two transistors so the direction of the encoder wheel movement can be determined. So, that device will have 4 pins, two for each transistor.

I'm going to desolder it and then see if I can see any identification anywhere

The 3 pins may be one ground connected to both phototransistor emitters and one each for the phototransistor collectors. If so the way to wire them to an Arduino is: Collectors go to digital inputs (may want interrupt inputs for one or both). There will need to be pullup resistors on each collector to Vcc. Those can be external or they can be the internal pullups on the digital inputs. Then, of course, ground to ground.

The 4.7K resistors are not needed if the internal pullups are used and strong enough.

Thank you my man. I'd have to look into your suggestion