The video above shows how the IR light from the transmitter becomes weaker with distance, and also how to overcome this problem using a lens. As shown in the diagram below, a lens focuses light at a particular point, making it more intense.
The video above and diagrams below show another way to extend the range of the transmitter. A straw reflects IR light from its internal surfaces, so nearly all the light gets trapped inside.

To make the range even longer, you can use more than one straw. The diagram below shows how to connect straws to each other to make a chain of straws.
