Tom,
The part you reference does not have an external light path. In the types of devices being discussed here, the opto isolator prevents the introduction of errors due in a large part to circulating currents. When the controller is far away from the controlled part, they are often on different power supplies and sometimes different phases or transformers of the main distribution system. When connection is made between systems that are powered this way, any voltage differences cause this circulating current that may compromise or injure the equipment or user. By having the input circuit be an LED that is on one power supply and the detector on another power supply, the current is not able to flow between these devices but the signal is coupled by the light path internally. Opto isolators are usually specified for their isolation measured in volts, kilovolts as in the case of my DTV transmitter 32 kilovolts. The LED can be supplied by a 5 volt power supply while the detector is powered by a similar power supply that has it's ground reference terminal at -32,000 volts.
If you can tell me what your criteria would be, I will try an look through the catalog and pick a few that may work. I really like the Banner Sensors that were supplied in the KOP in past seasons. They were able to be set for distances up to a few feet and could be extended with the use of reflective tape. They were easy to interface to digital inputs and were able to run from a breaker on the PD for the supply.
http://www.bannerengineering.com/en-...M-QS18-Series/