![\"OTDR](\"https:\/\/firstfibertech.com\/wp-content\/uploads\/2026\/10\/OTDR-trace-showing-a-non-reflective-Gainer-step-of-0.15-dB-at-15.24-km-1024x765.webp\")
<\/figure>\n\n\n\nHow to Handle the Upward Curve: A 3-Step Field Protocol<\/h2>\n\n\n\n1. Do Not Pass Directly or Re-splice Blindly<\/h3>\n\n\n\n\n- Why do it:<\/strong> The negative loss measured in a single direction is merely an artifact. Passing it directly might allow a genuinely poor splice to slip through; cutting and re-splicing blindly wastes installation time, as you could re-splice ten times and still get a negative reading.<\/li>\n\n\n\n
- What to check:<\/strong> Keep the splice intact. Understand that this unidirectional data serves only as a warning and cannot be used as the final acceptance standard.<\/li>\n<\/ul>\n\n\n\n
2. Perform Bidirectional Testing<\/h3>\n\n\n\n\n- Why do it:<\/strong> Since the forward direction shows a false gain due to backscatter changing from “low to high,” shooting light from the opposite end will experience a change from “high to low,” resulting in an exaggerated high loss. By calculating the algebraic average of the forward “negative loss” and the reverse “high loss” (adding them and dividing by two), you obtain the true physical attenuation of that splice point.<\/li>\n\n\n\n
- What to check:<\/strong> Look strictly at the averaged value of the two bidirectional tests. As long as this average meets the project standard (e.g., <0.03dB), the splice is qualified.<\/li>\n<\/ul>\n\n\n\n
3. Record the Fiber Types on Both Sides (e.g., G.652 \/ G.657)<\/h3>\n\n\n\n\n- Why do it:<\/strong> Documenting the mixed use of dissimilar fibers provides data support for the link acceptance report, preventing clients or auditors from questioning the data integrity during project handover.<\/li>\n\n\n\n
- What to check:<\/strong> Check the optical cable markings, verify the exact fiber models on both sides, and add a clear note in the test report confirming the dissimilar fiber splicing.<\/li>\n<\/ul>\n\n\n\n
Boundary Judgments: When to Relax and When to Worry <\/h2>\n\n\n\n
Once the mechanism is clear, field engineers must establish a strong boundary of trust. When you explicitly know that the fibers on either side of the splice are dissimilar (for example, splicing a backbone cable to a drop cable, or mixing fibers from different manufacturers), a negative loss gain is a completely normal accompanying phenomenon. It simply proves the OTDR’s detection sensitivity is functioning properly; you only need to proceed with bidirectional averaging. However, if both sides are definitively identical fibers of the same type, manufacturer, and batch, yet a distinct negative loss repeatedly occurs after splicing, you must be highly vigilant. This typically indicates deformed fiber end-faces due to aging splicer electrodes or severe geometric defects in the fiber itself. In this case, immediately troubleshoot the equipment or replace the fiber.<\/p>\n\n\n\n
By following these three steps, splice loss can be accurately qualified. Admittedly, manually calculating bidirectional averages is tedious. If your field equipment natively supports bidirectional test analysis, automatic averaging, and fiber type presets, this verification process becomes significantly more efficient. To learn how smart equipment can simplify your testing workflow, visit our [OTDR Series Product Page].<\/p>\n\n\n\n
To help installation teams standardize data acceptance for dissimilar fiber splicing and avoid audit disputes caused by negative loss phenomena, we have compiled a standard field recording format. Download the “Dissimilar Fiber Splicing: OTDR Bidirectional Test Record Template”<\/strong> below to standardize your daily acceptance procedures.<\/p>\n\n\n\nOTDR-Bidirectional-Test-Record-Template<\/a>Download<\/a><\/div>\n\n\n\nFAQ<\/h2>\n\n\n\nIs negative loss normal? <\/h3>\n\n\n\n
Yes, negative loss is a normal physical artifact during dissimilar fiber splicing. It is caused by differences in fiber backscatter coefficients, not a real fault.<\/p>\n\n\n\n
When should I worry about false gain? <\/h3>\n\n\n\n
You should be concerned when you repeatedly measure negative loss on fibers from the same batch and model. This usually indicates aging splicer electrodes or severe optical fiber defects.<\/p>\n\n\n\n
Is bidirectional testing always necessary? <\/h3>\n\n\n\n
Bidirectional testing is mandatory when encountering a false gain. The true attenuation of the splice can only be determined by calculating the algebraic average of the forward and reverse test data.<\/p>\n","protected":false},"excerpt":{"rendered":"
Gdy odczyt strat w miejscu po\u0142\u0105czenia na ekranie reflektometru OTDR wskazuje warto\u015b\u0107 ujemn\u0105, a krzywa przebiegu wykazuje tendencj\u0119 wzrostow\u0105 zamiast spadkow\u0105, nale\u017cy natychmiast podj\u0105\u0107 decyzj\u0119 techniczn\u0105: jest to fa\u0142szywy artefakt spowodowany niedopasowaniem wsp\u00f3\u0142czynnik\u00f3w rozpraszania wstecznego lub \u015brednic p\u00f3l modowych (MFD) mi\u0119dzy dwoma po\u0142\u0105czonymi w\u0142\u00f3knami. Zdecydowanie nie jest to prawdziwe \u201coptyczne \u2026 Dowiedz si\u0119 wi\u0119cej<\/a><\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[98],"tags":[],"class_list":["post-4137","post","type-post","status-publish","format-standard","hentry","category-otdr-wiki"],"_links":{"self":[{"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/posts\/4137","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/comments?post=4137"}],"version-history":[{"count":1,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/posts\/4137\/revisions"}],"predecessor-version":[{"id":4140,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/posts\/4137\/revisions\/4140"}],"wp:attachment":[{"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/media?parent=4137"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/categories?post=4137"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/tags?post=4137"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- \n
- Why do it:<\/strong> The negative loss measured in a single direction is merely an artifact. Passing it directly might allow a genuinely poor splice to slip through; cutting and re-splicing blindly wastes installation time, as you could re-splice ten times and still get a negative reading.<\/li>\n\n\n\n
- What to check:<\/strong> Keep the splice intact. Understand that this unidirectional data serves only as a warning and cannot be used as the final acceptance standard.<\/li>\n<\/ul>\n\n\n\n
2. Perform Bidirectional Testing<\/h3>\n\n\n\n
- \n
- Why do it:<\/strong> Since the forward direction shows a false gain due to backscatter changing from “low to high,” shooting light from the opposite end will experience a change from “high to low,” resulting in an exaggerated high loss. By calculating the algebraic average of the forward “negative loss” and the reverse “high loss” (adding them and dividing by two), you obtain the true physical attenuation of that splice point.<\/li>\n\n\n\n
- What to check:<\/strong> Look strictly at the averaged value of the two bidirectional tests. As long as this average meets the project standard (e.g., <0.03dB), the splice is qualified.<\/li>\n<\/ul>\n\n\n\n
3. Record the Fiber Types on Both Sides (e.g., G.652 \/ G.657)<\/h3>\n\n\n\n
- \n
- Why do it:<\/strong> Documenting the mixed use of dissimilar fibers provides data support for the link acceptance report, preventing clients or auditors from questioning the data integrity during project handover.<\/li>\n\n\n\n
- What to check:<\/strong> Check the optical cable markings, verify the exact fiber models on both sides, and add a clear note in the test report confirming the dissimilar fiber splicing.<\/li>\n<\/ul>\n\n\n\n
Boundary Judgments: When to Relax and When to Worry <\/h2>\n\n\n\n
Once the mechanism is clear, field engineers must establish a strong boundary of trust. When you explicitly know that the fibers on either side of the splice are dissimilar (for example, splicing a backbone cable to a drop cable, or mixing fibers from different manufacturers), a negative loss gain is a completely normal accompanying phenomenon. It simply proves the OTDR’s detection sensitivity is functioning properly; you only need to proceed with bidirectional averaging. However, if both sides are definitively identical fibers of the same type, manufacturer, and batch, yet a distinct negative loss repeatedly occurs after splicing, you must be highly vigilant. This typically indicates deformed fiber end-faces due to aging splicer electrodes or severe geometric defects in the fiber itself. In this case, immediately troubleshoot the equipment or replace the fiber.<\/p>\n\n\n\n
By following these three steps, splice loss can be accurately qualified. Admittedly, manually calculating bidirectional averages is tedious. If your field equipment natively supports bidirectional test analysis, automatic averaging, and fiber type presets, this verification process becomes significantly more efficient. To learn how smart equipment can simplify your testing workflow, visit our [OTDR Series Product Page].<\/p>\n\n\n\n
To help installation teams standardize data acceptance for dissimilar fiber splicing and avoid audit disputes caused by negative loss phenomena, we have compiled a standard field recording format. Download the “Dissimilar Fiber Splicing: OTDR Bidirectional Test Record Template”<\/strong> below to standardize your daily acceptance procedures.<\/p>\n\n\n\n
OTDR-Bidirectional-Test-Record-Template<\/a>Download<\/a><\/div>\n\n\n\nFAQ<\/h2>\n\n\n\n
Is negative loss normal? <\/h3>\n\n\n\n
Yes, negative loss is a normal physical artifact during dissimilar fiber splicing. It is caused by differences in fiber backscatter coefficients, not a real fault.<\/p>\n\n\n\n
When should I worry about false gain? <\/h3>\n\n\n\n
You should be concerned when you repeatedly measure negative loss on fibers from the same batch and model. This usually indicates aging splicer electrodes or severe optical fiber defects.<\/p>\n\n\n\n
Is bidirectional testing always necessary? <\/h3>\n\n\n\n
Bidirectional testing is mandatory when encountering a false gain. The true attenuation of the splice can only be determined by calculating the algebraic average of the forward and reverse test data.<\/p>\n","protected":false},"excerpt":{"rendered":"
Gdy odczyt strat w miejscu po\u0142\u0105czenia na ekranie reflektometru OTDR wskazuje warto\u015b\u0107 ujemn\u0105, a krzywa przebiegu wykazuje tendencj\u0119 wzrostow\u0105 zamiast spadkow\u0105, nale\u017cy natychmiast podj\u0105\u0107 decyzj\u0119 techniczn\u0105: jest to fa\u0142szywy artefakt spowodowany niedopasowaniem wsp\u00f3\u0142czynnik\u00f3w rozpraszania wstecznego lub \u015brednic p\u00f3l modowych (MFD) mi\u0119dzy dwoma po\u0142\u0105czonymi w\u0142\u00f3knami. Zdecydowanie nie jest to prawdziwe \u201coptyczne \u2026 Dowiedz si\u0119 wi\u0119cej<\/a><\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[98],"tags":[],"class_list":["post-4137","post","type-post","status-publish","format-standard","hentry","category-otdr-wiki"],"_links":{"self":[{"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/posts\/4137","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/comments?post=4137"}],"version-history":[{"count":1,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/posts\/4137\/revisions"}],"predecessor-version":[{"id":4140,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/posts\/4137\/revisions\/4140"}],"wp:attachment":[{"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/media?parent=4137"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/categories?post=4137"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/firstfibertech.com\/pl\/wp-json\/wp\/v2\/tags?post=4137"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- What to check:<\/strong> Check the optical cable markings, verify the exact fiber models on both sides, and add a clear note in the test report confirming the dissimilar fiber splicing.<\/li>\n<\/ul>\n\n\n\n
- What to check:<\/strong> Look strictly at the averaged value of the two bidirectional tests. As long as this average meets the project standard (e.g., <0.03dB), the splice is qualified.<\/li>\n<\/ul>\n\n\n\n
- What to check:<\/strong> Keep the splice intact. Understand that this unidirectional data serves only as a warning and cannot be used as the final acceptance standard.<\/li>\n<\/ul>\n\n\n\n