Thank You zachtheterrible, Ron H and Sebi for the immediate reply.
Ron H: I know which part of the circuit is the opto pair. I have worked with IR emitters and detectors. I have also googled for "opto pair" (and other combinations) in vain. Iam getting more "opto couplers" in the results, which I am quite sure is not an opto pair, judging by context.
But I am not sure if an opto pair is as simple as an IR Emitter-detector pair. In the actual physical form of the circuit, the emitter is supposed to be stationary and detector is supposed to be on the rotor of a motor. (The detector is supposed to pick up the IR every time it crosses over the emitter while rotating.) This requires a separate supply for the emitter as it is not possible to take out a wire from the rotating part of the design (where the source is). But this is not specifically mentioned in the circuit. That is why I thought that maybe an opto pair is not a simple IR emitter-detector pair, but it may be something that has both the IR emitter and detector facing each other in the same housing, where the emitter sends out pulses at specified intervals. (Something like the OPB706 which is actually an Opto-reflector.) In this way, the emitter and detector can be mounted on the motor, so one supply would be enuf.
I hope I am not boring you all with my long post. But I would be really grateful if someone could give me some ideas....
Thank You