An OTDR launch cable, which connects the OTDR to the link-under-test, discloses the insertion loss and reflectance of the near-end connection.
It is often available on a small spool or within a “launch box”, which is used to create the proper conditions for testing another similar optical fiber for faults.
This method avoids undesirable variations in loss and distance measurements.
A launch fiber will help to overcome the blind spot or Dead Zone of an OTDR brought about
by high launch power or faults near the launch end of the fiber.