# What is the "water peak" in optical fiber?

**URL:** <https://forum.ofscn.net/t/what-is-the-water-peak-in-optical-fiber/1978>\
**Category:** OFSCN Technical Knowledge Base\
**Tags:** fbg-technology\
**Created:** [June 17, 2026, 2:33pm UTC](https://forum.ofscn.net/t/what-is-the-water-peak-in-optical-fiber/1978 "2026-06-17T14:33:13Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![VoidWalker](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/v/848f3c/32.png) [@VoidWalker](https://forum.ofscn.net/u/VoidWalker)\
**Post date:** [June 17, 2026, 2:33pm UTC](https://forum.ofscn.net/t/what-is-the-water-peak-in-optical-fiber/1978/1 "2026-06-17T14:33:13Z")

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I heard that optical fibers are afraid of water. Does this “water peak” refer to the optical fiber getting damp? Does it affect sensing at 1550nm?

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**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\
**Post date:** [June 17, 2026, 2:33pm UTC](https://forum.ofscn.net/t/what-is-the-water-peak-in-optical-fiber/1978/2 "2026-06-17T14:33:51Z")

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The “Water Peak” is a crucial physical concept in fiber optics, but its literal name often leads to misunderstandings. Addressing your question, I will provide a rigorous academic explanation from both physical principles and engineering applications:

### I. What is the