@magduf has the correct answer. The Sun optical mouse used dual photodiodes and had two grids in the mousepad. One blue, one red. The filters on the photo diodes allowed one to see both x & y grid lines and the other to see only the red stripes. Then based on their signalling you could extract a motion vector. The upside was no ball to pick up dirt and clog sensors, the downside was you needed the mousepad with the lines etched on it. You would also get less reliable results if the mouse pad was not in the expected orientation with the mouse.
Still I really enjoyed that mouse. It had excellent tactile feedback on the buttons as well.
The old optical mice used IR to detect the grid lines on the old mouse pads. Today's mice take an image of the surface, and compare it to another image taken quickly after. Faster chips/better optics enabled this.
No, that's not it. Sun Microsystems had optical mice too, back in the early 90s, on their SPARCstations.
The difference was that the early optical mice required a special mousepad for them to work. I think they just used some photodiodes and looked at the reflections from the mousepad, which had a pattern built in. The optical mouse starting with MS's worked in a different way, using an actual camera to track movement, so you could use them on almost any surface.
I had the same recollection - I'm pretty sure I used a Sun Workstation with an optical mouse back in the late 80s. Clearly Microsoft did not invent the optical mouse, but the early ones required a special gridded pad.
I had always assumed that they worked like optical mice (i.e. shine a light at a slightly-textured surface and watch the surface move underneath), but it's much simpler than that.
But even Wikipedia got it wrong. Sun had optical mice in the 1980's and you could get a version for the PC from Hewlett Packard in 1997 that used an IR sensor.
TIL: the optical mouse works by taking a picture of the desk surface and does Optical Flow with the previous capture to get relative position.
The result reminded me of the old Logitech Scanman handheld scanner. except that had a 1d light sensor (like a flatbed scanner) and a radial encoder attached a to a roller to advance the scan lines down and the user pulled it down. (kind of like a 1d mechanical mouse.) I had a ton of fun with that growing up.
That answer is talking about the sensors used in mechanical mice, not optical mice. (Most mechanical mice did use optoelectronic sensors, but nobody would call the mice "optical" just for that.)
This might explain why early optical mice used a grid patterned mouse pad. I had one from Mouse Systems and the mouse pad it came with was a metal plate printed with a fine grid pattern.
I remember working on a Sun Sparc 4 (I think, about 1996) with an optical mouse that would only work on a special mat, and wondering what was the point? Glad to see they solved that particular problem.
And it's a curious feeling to stumble upon memories I haven't touched in years -- I used to love idly disassembling computer mice, cleaning out fuzz and gunk from the little rollers and the ball, and putting them back together. It was one of things I had to consciously stop myself from doing if I was sitting at someone else's desk.
Optical mice have been around so long now, I had completely forgotten how they used to work, and that odd little pleasure of maintaining a simple mechanical device.
Edit: this confuses me, though: The basic approach — pairing a freely-rolling ball with a optoelectronic system — was used by generations of mice that followed, changing only incrementally until optical mice did away with trackballs altogether.
Is that right? The mice I was always taking apart normally detected the motion of the trackball with two little white rollers, for Y and X motion. That's neither of these systems.
There are CMOS sensors with in-array edge detection. More flexibly, all optical mice have integrated sensors that do motion processing in the same package if not the same die.
I think my first experience with an optical mouse was on a Data General unix workstation around 1990 or so. It needed a special pad; the pad was metal and had a grid pattern on it. The mouse was somewhat less responsive than ball mice at the time.
Still I really enjoyed that mouse. It had excellent tactile feedback on the buttons as well.
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