The sender is for outside plant and single-mode fiber. The connector output can be adapted to any cable plant with hybrid adapters or hybrid cables. This unit is easy to operate with a wavelength/power switch, which selects optical wavelengths or disables the unit. There is also a switch which select between either the CW or 2 kHz output for the transmitting wavelength. The CW or 2Khz tone is for sending a tone down the fiber it is useful if the end user has a tone identifier that ca be clipped onto to the fiber to identify and individual fiber. The light source is designed for performing insertion loss measurements on fiber optic links when used with an optical power meter. Whether testing outside plant or premise an optical source is the perfect tool when combined with an optical power meter. The output is stabilized to ensure accurate test results per current TIA/EIA requirements. The wavelengths are individually adjustable with a mechanical screw to have a variable attenuator or to reduce the output power. This make it able to save battery power when high optical output power is not necessary, or to turn up the power to test long runs. The sender is delivered in a protective rubber boot.