EXFO OTDR 2 - Manual (Page 166)

Using the OTDR as a Light Source
158 OTDR
6. Tap Turn On. You can stop light emission at any time by tapping Turn
Off.
Using an EXFO power meter with tone-detection features, such as the
FOT-930 or FPM-300, an operator at the other end will be able to
quickly locate the correct fiber or perform loss measurements. Refer to
the power meter user guide for details.