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Why Filtered 1625 nm Wavelength Is Used For Live Fiber Testing?

Why Filtered 1625 nm Wavelength Is Used For Live Fiber Testing?


With the incredible advancements in new-age fiber optic technology and modern fiber network deployments, the testing methods have improved a lot. The OTDR testing methods have become an indispensable choice for developing, validating, maintaining, and troubleshooting fiber optic systems. OTDR, or an Optical Time Domain Reflectometer, is a modern instrument essential for measuring and developing a visual overview of a fiber optic cable route. The critical data obtained through the instrument can deliver vital information on the condition and performance of fibers. It also exhibits if there are any passive optical components in the cable path. It may be connectors, splices, splitters, and multiplexers. 


The essentiality of 1625 nm wavelength for testing


For more than a decade the transmission wavelengths were only limited to 850nm, 1310nm, and 1550nm. In the current scenario, it is evident that the fiber networks may not get tested at the wavelength of 1625 nm. Why? Because the temperature can create multiple problems at 1625nm compared to lower wavelengths. If you are associated with the field of optical fiber networks, it is essential to recognize the wavelength aspects. The temperature creates multiple problems at a wavelength of 1625 nm. It is less for lower wavelength values. Temperature-induced cable loss or TICL could be detected at a wavelength of 1625 nm. It is more than that of other wavelengths. It will generate more losses in the optical cable. The current connectors, splices, and components are not optimized for the 1625 nm wavelength signals. In the long run, the signal reflections and losses could appear at this wavelength of 1625 nm.


Fiber testing and its impacts


The bending impact in fiber testing is not something new. With the introduction of the 1550 nm wavelength, one could find something other than the 1310 nm transmission wavelength. Since then, the bending effect played a significant part. Research and testing programs have compared the 1550 nm splice losses with the 1310 nm splice loss. Reviewing the bending effects is critical to obtain accurate reports. Here are some critical bending impacts you must review and note. 


Micro bend And Macro bend Issues

Micro bend and macro-bends are prominent problems in an installation. Why? Because these cables can induce loss of signal. Micro bend is created for the deviation of the core measured from the axis of the optical fiber. Many elements of stress can develop micro bends, such as -

  1. Loopholes during fiber manufacturing.
  2. Management of the fiber during cable manufacturing.
  3. Cable installation operations and equipment pieces, including tie wraps and clamps.
  4. Environmental stresses like pressure, hits, etc.


Micro-bending is a vital aspect. It has a robust impact on the signal loss versus wavelength. In contrast, the macro bend is developed as a result of a large bend in the optical fiber. In such cases, the possible L and U bands may be –


  • 1565 – 1625 nm – It is defined as the long L band 
  • 1625 – 1675 nm – It is defined as the ultralong U band 


If the long L band and the ultralong U band get used, the process of loss testing becomes indispensable. It is necessary to test at transmission wavelengths with an upper limit of the band. Thus, modern test equipment pieces have introduced the 1625 nm testing facilities. The vital fiber parameters for network installation include - splice loss, link loss, ORL or optical return loss, etc. 


The role of OTDR


Currently, the fastest-growing segment of the fiber testing market is OTDR equipment. The OTDR equipment manufacturers have leveraged the benefits of the equipment piece. With the rapid and worldwide expansion of OTDR across all product categories, the essentiality is growing at a fast rate. For instance, 5G adoption is ushering opportunities and challenges. The impacts are related to fiber regulation, installation, manufacturing, etc. The top-notch industry-leading OTDR manufacturers can vouch for the requirements of OTDR safety, efficiency, and product quality. 


The OTDR transmits a light pulse based on the wavelength while the fiber link is operational. The typical wavelength is 1625 nm for single-mode fiber. The filtered 1625 nm or 1650 nm wavelengths could be vital for in-service maintenance and evaluation, eliminating the interference of live traffic wavelengths.


Testing and OTDR – Know the future.


With time, OTDR has succeeded in providing better functionality, accuracy, etc. It has also fetched resolution at a lower price. The impeccable impact and improvement in OTDR auto-test algorithms have reduced the hassles of technicians and increased operational acceptance.  


Without modern technology like OTDR testing, the advanced application of fiber optics may not yield feasible outcomes. The ability to inspect and review what is inside thousands of miles of optical fiber with a thickness less than a human hair has become straightforward. It has become a practical necessity with the 5G network data loads and smart city projects.  



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