Try it sometime. So to see a picture in 3-D, you need your two eyes to see two different images, and those images need to be offset from each other by the amount that they would be offset in real life. A stereoviewer is a device that separates the views seen by your two different eyes. Another way to see a picture in 3-D would be to use red and blue filters. But light waves aren't always traveling in the same plane.
Waves can travel in any plane they want.
Align the filters perpendicular and observe that they block the light. Show also that they transmit maximally when they are aligned parallel to each other. One good way to think about how waves can be in any plane is to draw them on pieces of board. Taken literally, this picture might make you think that if you have two filters, light will get through both only if the filters are in exactly the same orientation. Two fences at a slight angle should stop all boards.