Sharp Infrared sensor-Filtering supply ripple
This sensor draws like 300mA in bursts, likely you can see that on the power.
I have had a similar problem with driving servos, which made huge spikes on the power line when powering from a lab psu.

I suggest to:


power this all with a battery with small internal resistance, i.e. alkaline AA cells, or LiPo
increase c3 to at least 470uF or 1000uF
(might try LC filter on the power lines)


The output signal is not bad with 30mV of noise. Your idea of the RC filters look correct. I'd give also a try with bigger C and smaller R, like R of not more than 1k, and C of some microfarads.