IR trasmitter

i had a doubt,what is the output of an ir transmitter and receiver pair and that of ir transmitter and photo diode.i mean wheather it is a positive one or negative i.e when lightr is transmitted high voltage is generated or low voltage at receiver?

Welcome, kamalraj!

Interestingly, there can be a voltage generated by the photo transistor, but ordinarily the IR xmitter/rcvr pair act as a switch (or to a degree, the rcvr can act as a variable resistor with a variable signal from the IR xmitter).

As such, there's no "high" or "Low" voltage generation, rather it is a voltage across the rcvr component (whether a diode or a transistor) that is being controlled.

The diode (or transistor) will, of course, have a polarity that will dictate the polarity of your connection.