Micro-OTDR™ Technology (µOTDR™)

Micro-OTDR™ Technology – Fast Fiber Fault Finder™

Our iSFC® and iDFC™ Micro-OTDR SFP Transceivers support all eighteen (18) CWDM Wavelengths, plus the 1625 nm monitor channel for operation above the CWDM data channels.  

The identical part number model is used on both sides of the optical fiber link, that is, there is no requirement for matched pairs, or complementary pairs.  This means fewer SKUs to inventory, track and manage, as well as, less splicing in the field, simplified fiber optics inventory and higher Network Reliability. 

Complete end-to-end optical link ZonuColor Coding simplifies operation, reduces installation time and reduces installation errors.


Reflection Immune Operation - RIO®Micro-OTDR™ - μOTDR™Design, Statistical Analysis & Detection ProbabilityContact Engineering

Reflection Immune Operation - RIO®

RIO® (Reflection Immune Operation) Incorporates Two (2) Elements:

1) Checks the optical power source to ensure that there is no “self -lock” (i.e. will never allow the SFP to link with its own reflected signal).

2) Uses the DPS feature to overcome the operational issue of opening an active link (a more difficult problem to handle).


Reflection Immune Operation – RIO™ Eliminates Reflection Problems which Plague Legacy SFSW SFPs.  Single Fiber Single Wavelength (SFSW) Transceivers transmit and receive at the same wavelength, on single fiber, doubling the optical fiber plant capacity.  SFSW transceivers offer many potential benefits to the Network Operator – e.g. seamless CWDM integration, half the fiber, half the CWDM passives and easier fiber management.


Open connectors, fiber faults and intermittent connections, which commonly occur in field deployments, create optical reflections of varying intensities.  SFSW transceivers can be susceptible to signals generated by these reflections in the optical fiber cable plant. For example, the reflection from an open non-angle polished (PC or UPC - Blue) optical connector is about 15 dB.  The reflected signal may return to the receiver section of the originating transceiver at power levels well within the operating sensitivity range of the receiver. This may cause the originating transceiver to detect this false signal, appearing to the network switch (or any host equipment) as though it was receiving a proper signal.  But, in fact, an optical loopback condition is created in the network, wreaking havoc with network operations.


Since SFSW transceivers suffer such drawbacks in the presence of optical reflections, their application under real-world conditions has been limited compared to that of their two-wavelength single fiber, or, two-fiber cousins.  Because SFSW transceivers offer many potential benefits to the Network Operator, a comprehensive solution to the reflection sensitivity problems would provide significant benefits.


RIO technology solves the SFSW reflection problems.  Optical Zonu’s SFC™ and iSFC° Transceivers incorporate Reflection Immune Operation, or RIO°, for short.  This feature means that our transceivers can recognize reflected signals and will never report a link based upon a false reflected signal…ever.


Integrated into the SFC™ and iSFC° Transceiver hardware and firmware, RIO° is totally automatic in operation and transparent to the host network gear and optical fiber network (PC and UPC Blue or APC Green optical connector types). 

Now, for the first time, SFC and iSFC SFSW transceivers may be substituted anywhere a standard two-fiber SFP Optical Link exists.


In Summary -  The network operator and network users may now enjoy the benefits of SFSW operation, without any of the drawbacks associated with legacy systems.  Reflection Immune Operation - RIO°  resolves self-reflection from an open connector and/or other reflectors in the optical fiber network.  Only the legitimate remote data is ever transferred to the host equipment.

Delta Power Sense (DPS)

Delta Power Sense (DPS)  detects instantaneous pptical spikes (i.e. fast changes in optical power, up or down.

Monitors for:

  • Intrusion Attempts
  • Accidental Connector Openings
  • Cracked Fiber
  • Failing Splices, etc.
  • Link Breaks for a few hundred milliseconds then Re-Links.

Sense Priority – Factory Default (Recommended)

Measures and Stores the New Reflection Values before returning to data transport mode.

Link Priority – Optional

Returns to data transport as soon as possible (no Micro-OTDR measurement taken).

Micro-OTDR™ - μOTDR™

New Approach to Optical Fiber Fault Monitoring – SFP and SFP+ Transceivers with built-in automatic OTDR feature.



Detecting a reflection from an unpowered remote transceiver will:

  • Confirm power outage or other equipment problem at remote end of Link.
  • On installation, allow capture of baseline Link distance for network database.
  • Provide security insight, if the measured Link distance varies from baseline.

At installation Micro-OTDR™ is used to record baseline Link distance. What are the Benefits for the Network Operator?

  • With Micro-OTDR™ at both ends of the Link, there is virtually no “blind spot”.
  • All faults are detectable with high probability over the entire Link span.
  • Data generated supports “network map” to depict fault location in real time.
  • Support for better SLAs which offer competitive advantage.

Operation Modes and Location - The Micro-OTDR™ may be operated in different ways:

  • Fully Automatic with Data Transport – Recommended.
  • Manually Controlled – Network Operator chooses when to run the Micro-OTDR.
  • Monitoring-Only Full Time – Micro-OTDR runs repeatedly on CWDM or 1625 nm Channel.

Design, Statistical Analysis & Detection Probability

Optical Fiber Fault Detection must be Fast, Distributed and Pervasive


To materially improve the reliability of the Access Network, fault detection must be fast, distributed and

pervasive.  The detection of a fault needs to be fast so that the operation of the network, particularly an Ethernet based

one, is minimally impacted.   A fault should be detected, located and reported to the Host Switch within a fraction of a second.  If the fault is momentary, then the link should instantly recover. If not, then there ought to be the capability to initiate a series of diagnostic and/or repair options.

Such responsiveness to a service disruption may translate directly into improved Service Level Agreements (SLAs) and the competitive advantages they may offer the Communications Service Provider (CSP).

Having a sophisticated piece of equipment monitoring a small number of optical fibers (thereby “consuming” these fibers, making them unavailable for revenue generation), is not very efficient in the extremely high link density  environment found at the “edge” of the Access Network. We know that the link distances are relatively short (under 40 Km) and that the performance requirements of an OTDR to operate in this segment are modest.

A large number of moderate performance monitors, and their associated OTDRs, distributed throughout the Access Network, makes more sense than fewer, higher performance (and much more costly) systems.

In order to have the highest level of effectiveness, these distributed moderate performance monitors and OTDRs need to be virtually everywhere.  Near 100% fault detection may be achieved when large numbers of (or preferably all) optical links incorporate this performance monitoring.  

Optical fiber fault detection is based upon the reflected signal from the point of fault.  Fiber faults and intermittent connections present optical reflections of varying intensities.  The reflection intensity of a fiber break has a known statistical distribution. The distribution of the return signal from a fiber break/cut has been empirically determined. 

To achieve a detection probability of greater than 95%, the sensitivity of the detection circuit must be better than 51 dB.

Since the Fiber Fault Histogram indicates that the detection probability of an optical fiber fault follows a Normal Distribution, modeling to predict outcomes is straightforward.  A series of curves for the likely optical fiber cable deployments encountered in the Access portion of the Communications Network may be developed.

For any combination of Micro-OTDR Dynamic Range (DR) values, Optical Fiber Spans to be monitored, Location of Micro-

OTDR SFPs and number of Optical Fibers to be monitored, a Chart of Detection Probability for Random Faults (random location and random reflectance or ORL) may be developed. These Charts offer guidelines to the network architect for the deployment of Micro-OTDR SFPs into a network.  Examples of these charts shown here.

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