Fiber span characterization utilizing paired optical time domain reflectometers
A system for providing advanced characterization of an optical fiber span is based upon the use of a pair of optical time domain reflectometers (OTDRs), located at opposing end terminations of the span being characterized. Each OTDR performs standard reflectometry measurements and transmits the resulting OTDR trace to monitoring equipment in a typical manner. The pair of OTDR traces is thereafter combined in a particular manner (“stitched together”) to create an OTDR trace of the entire fiber span (essentially doubling the operational range of prior art OTDR measurement capabilities). The transmit portion of one OTDR may be paired with the receive portion of the other OTDR, with time-of-light measurements (or signal loss measurements) used to determine optical path length and/or optical signal loss of the span. Using a multi-wavelength light source in the paired transmit/receive arrangement allows for a characterization of chromatic dispersion of the span.
1. A system for characterizing an optical fiber span, comprising
a near-end optical time domain reflectometer (OTDR) coupled to a near-end termination of the optical fiber span, the near-end OTDR including a near-end light source for injecting an optical probe into the optical fiber span, a near-end receive component for measuring a near-end back-reflected light exiting the optical fiber span, and a near-end processing module for generating a near-end OTDR trace of optical power loss along a y-axis as a function of the optical fiber span path length along an x-axis;
a far-end OTDR coupled to a far-end termination of the optical fiber span, the far-end OTDR including a far-end light source for injecting an optical probe into the optical fiber span, a far-end receive component for measuring a far-end back-reflected light exiting the optical fiber span, and a far-end processing module for generating a far-end OTDR trace of optical power loss along a y-axis as a function of the optical fiber span path length along an x-axis, wherein the near-end and far-end processing modules are configured to control the activation of the near-end and far-end OTDRs such that only one OTDR is operational at any point in time, where both the near-end light source and the far-end light source operate at a same, single wavelength; and
a characterization element in communication with both the near-end OTDR and the far-end OTDR, the characterization element configured to estimate a span-based parameter from a combination of the near-end back-reflected light measurements and the far-end back-reflected light measurements for then combining the near-end OTDR trace with the far-end OTDR trace in a trace-stitching procedure using a mid-point of the span-based parameter as a stitching point to create as an output an end-to-end OTDR trace that characterizes the optical fiber span.
2. A system as defined in claim 1 , where both the near-end light source and the far-end light source generate a train of individual optical pulses as the optical probe, where the individual optical pulses are separated by a defined time interval used in generating an OTDR trace.
3. A system as defined in claim 1 , where both the near-end light source and the far-end light source generate a continuous wave optical beam as the optical probe.
4. A system as defined in claim 1 , where the characterization element is included within one or both of the near-end processing module and the far-end processing module.
5. A system as defined in claim 1 , where the characterization element is a remote component that communicates with both the near-end processing module and the far-end processing module.
6. A system as defined in claim 1 , where the near-end light source comprises a multi-wavelength optical light source, and the characterization element is further configured to provide a measurement of optical path length as a function of wavelength, based upon a transit time of the optical probe from the near-end multi-wavelength light source to the far-end receive component, the characterization element recording each estimated path length with an associated optical probe wavelength.
7. A system as defined in claim 6 , where the characterization element is further configured to provide a measurement of optical power loss as a function of wavelength, based upon a difference between an input power of the optical probe at the near-end multi-wavelength light source and a received power at the far-end receive component, the characterization element recording each estimated power loss with an associated optical probe wavelength.
8. A system as defined in claim 6 , where the near-end multi-wavelength light source comprises a plurality of separate lasers, each operating at a different, fixed wavelength, and a selector controlled by the characterization element utilized to energize each individual laser of the plurality of separate lasers in a defined sequence.
9. A system as defined in claim 6 , where the near-end multi-wavelength light source comprises a tunable laser pulse source, providing an output pulse at a defined wavelength based on a control signal applied thereto.
10. A system as defined in claim 9 , where the far-end OTDR further comprises a wavelength tunable filter disposed at an input to the far-end receive component to adjust a center wavelength of receive light measured by the far-end OTDR receive component.
11. A system as defined in claim 10 , where the characterization element provides wavelength adjustment control signals to both the tunable laser source in the near-end OTDR and the wavelength tunable filter in the far-end OTDR.