Patent ID: 6930768

Claim:
A system for determining discontinuities or events over a span of a multimode optical fiber, comprising: an optical time domain reflectometer (OTDR) having an operating port and a display stage; a singlemode optical fiber (SMF) having a first end face coupled to the operating port of the OTDR, and a second end face opposite the first end face, wherein (i) light pulses produced by the OTDR propagate from said operating port into the first end face of the SMF and emerge from the second end face of the SMF, and (ii) backscatter light incident on the second end face of the SMF propagates toward the first end face of the SMF to enter the operating port; and an alignment stage constructed and arranged operatively to couple and align the second end face of the SMF with a first end face of a span of multimode optical fiber (MMF) having a fiber core with a known radius, wherein a second end face of the MMF at a remote end of said fiber has an index matching termination, and the alignment stage (i) launches the light pulses emerging from the second end face of the SMF into the first end face of the MMF at a number of selected radial positions on said fiber core for exciting corresponding mode groups in the MMF, and (ii) couples backscatter light produced in the MMF in response to each excited mode group to the operating port of the OTDR through the SMF; the alignment stage is constructed and arranged to displace the SMF in a radial direction with respect to the axis of the MMF so that the light pulses emerging from the second end face of the SMF are launched into the first end face of the MMF at selected radial positions on the core of the MMF; and the display stage of the OTDR is operative to indicate locations and values of events detected along the MMF by the OTDR for each of the selected radial positions.