On the left is an image of IR light from an LED in a DVD-player’s remote control. On the right, you can see feint IR Laser light coming out the TX side of an “LC” fiber-optic connector. The LC patch cord was plugged into a single-mode fiber (LX or LH) Gigabit Ethernet transceiver. Both photos were taken with my Sony Ericsson W880i’s humble 2 mega-pixel phone camera:

I learned this trick from a Datacentrix SAN engineer, and I’ve found it useful as a simple test when debugging fiber-optic Ethernet links. Sure, you could use a “fiber torch” (glorified Laser pointer) or fancier test equipment, but the former won’t tell you if the optic at the end is dead, and the latter is less likely to be in your pocket than your mobile phone.

One final and important note: NEVER look directly into any fiber-optic connectors or interfaces, regardless of the Laser class.