Macrobend Buster™ is VeEX's trademark name for a fiber optics macro-bend detection technique applied to OTDR analysis, events table and its simplified Link Map representation, for dark and live fiber optics networks, including PON. It helps experienced and inexperienced OTDR users identify macro-bends easily.
Macro-bends are non-reflective events caused by bending fiber optics strands beyond their critical curvature value. Exceeding their critical angle for total internal reflection, forces light to escape. The effects of macro-bends are wavelength dependent, affecting longer wavelengths the most. The maximum bend radius and total loss also depend on the type of fiber being used.
The OTDR traces in the explanation above are a clear example of a macro-bend affecting the 1550 nm signal, but barely noticeable in the 1310 nm trace. That is the clear signature of a fiber bend.
To effectively detect macro-bends, the OTDR analyzes the fiber link using two wavelengths to pinpoint event inconsistencies between two traces, which manifest as characteristic macro-bend signatures. The Macrobend Buster test uses a specialized 1650 nm out-of-band signal, frequently employed in live monitoring of optical distribution networks (ODN), as well as a carefully chosen 1350 nm wavelength to avoid disruptions to active PON services.
Using conventional OTDRs, with 1310/1550 nm pulses, only works for dark fibers, but it would interfere with active PON services and generate rogue signals, which could adversely affect live network performance and disrupt service.
A "rogue ONT" refers to an unauthorized or malfunctioning Optical Network Terminal (ONT) that transmits data outside of its assigned time slot, disrupting network performance and potentially causing issues to other subscribers.
The following video provides an overview of the Macrobend Buster functionality featured in VeEX's FX150+ OTDR.
Additional Applications
Another application for Macrobend Buster OTDRs is in troubleshooting single-strand BiDi Ethernet links. This functionality extends beyond mere macro-bend detection; it also safeguards the OTDR sensor from saturation due to signals originating from the Central Office (CO). The Macrobend Buster OTDR's sensor employs FWDM filters to ensure its sensitivity is restricted to the supported wavelengths. The 1350 and 1650 nm wavelengths were carefully selected to avoid conflicts with common services.
Given that common BiDi wavelengths include 1270/1330, 1310/1490, 1310/1550, and 1490/1550 nm, any incoming signal within these ranges will be effectively blocked if present in the fiber link under test. The use of 1350 and 1650 nm test pulses, and their respective filters, guarantee reliable measurements even if the CO or CPE sides are still "hot".
On the other hand, if a common 1310/1550 nm OTDR is used in the presence of a live BiDi signal, it will display a "Signal Present!" warning message and needs to be disconnected from the link. In that case, depending on the direction being troubleshot, field technicians must either call the NOC or go to the customer's premises to turn the signal off, before continuing with the link diagnostic procedures. Either way, it takes time before the technician can resume troubleshooting the link, hindering the mean time to repair (MTTR), efficiency, productivity and increasing operational cost.
Bi-Directional (BiDi) Transceivers enable full-duplex transmission over a single optical fiber using a simplex LC connector, with combined transmit (TX) and receive (RX) functions, unlike conventional transceivers with duplex LC for separate TX and RX ports.
Related Test Solutions
- FX150+ - PON-optimized Mini OTDR for FTTx and Metro Fiber Networks
- Get a copy of the OTDR Basics poster