Optical isolator (VO0600T) circuit not working
Not the cause of your problem, but something that may confuse some users: Vee generally implies a negative supply, but I assume you have a positive supply there - we'd normally call that Vcc.

The output is "open collector" (really, open drain) - the drain of the output FET is only connected to the output pin, not to any internal circuitry, so you need an external pull-up resistor to Vcc to pull the output High.  The datasheet recommends a 330 Ohm to 4K Ohm pull-up.