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<p>A simple and cost-effective centralized monitoring scheme, for simultaneously (in one step) identifying all branch fiber failures in passive optical networks (PONs) is proposed, to overcome the drawbacks of optical time domain reflectometer (OTDR), in finding branch specific faults in PONs due to identical reflected pulses from faulty-fiber branches. In our scheme, a narrow optical pulse launched from the optical line terminal (OLT), to all the branches of the PON, is uniquely encoded and mapped at each optical network unit (ONU). A pair of Fiber Bragg Gratings (FBGs) interconnected by a unique delay line, encoder, imprints a unique spread sequence code, which is reflected back to OLT and detected by a bank of <i>N</i> matched filters. As encoded sequences are mapped to branches, the absence of a sequence indicates fiber fault in the corresponding branch. Proof-of-concept experiment for 2 users is carried out. Our scheme has several advantages: fiber and ONU faults are distinguishable, encoders are passive, not lossy, and identical two FBGs used across all the branches keeps the design simple when compared to other reported techniques. To the best of our knowledge, the encoding method adopted in this paper supports a given number of ONUs at the lowest spread sequence length (SSL). For example, to support 64/128 ONUs, SSL required is 65/129.</p>

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Design and demonstration of a FBG based passive encoding technique at ONUs for branch monitoring in PONs

  • 期刊论文

  • 发表日期：

    2026年3月1日

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  • Naveenkumar Mahadevachar,
  • Shivaleela Esamudra Sharanappa

摘要

A simple and cost-effective centralized monitoring scheme, for simultaneously (in one step) identifying all branch fiber failures in passive optical networks (PONs) is proposed, to overcome the drawbacks of optical time domain reflectometer (OTDR), in finding branch specific faults in PONs due to identical reflected pulses from faulty-fiber branches. In our scheme, a narrow optical pulse launched from the optical line terminal (OLT), to all the branches of the PON, is uniquely encoded and mapped at each optical network unit (ONU). A pair of Fiber Bragg Gratings (FBGs) interconnected by a unique delay line, encoder, imprints a unique spread sequence code, which is reflected back to OLT and detected by a bank of N matched filters. As encoded sequences are mapped to branches, the absence of a sequence indicates fiber fault in the corresponding branch. Proof-of-concept experiment for 2 users is carried out. Our scheme has several advantages: fiber and ONU faults are distinguishable, encoders are passive, not lossy, and identical two FBGs used across all the branches keeps the design simple when compared to other reported techniques. To the best of our knowledge, the encoding method adopted in this paper supports a given number of ONUs at the lowest spread sequence length (SSL). For example, to support 64/128 ONUs, SSL required is 65/129.