# Effective Length of an FBG

**URL:** <https://forum.ofscn.net/t/effective-length-of-an-fbg/274>\
**Category:** OFSCN Technical Knowledge Base\
**Tags:** fbg-technology, wiki-fbg-tech, bare-fbg\
**Created:** [January 21, 2026, 12:35pm UTC](https://forum.ofscn.net/t/effective-length-of-an-fbg/274 "2026-01-21T12:35:15Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![frostweaver](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/f/da6949/32.png) [@frostweaver](https://forum.ofscn.net/u/frostweaver)\
**Post date:** [January 21, 2026, 12:35pm UTC](https://forum.ofscn.net/t/effective-length-of-an-fbg/274/1 "2026-01-21T12:35:15Z")

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How does the reflection spectrum change as the grating length increases?

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<div class="post-metadata">

**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:** [January 21, 2026, 12:35pm UTC](https://forum.ofscn.net/t/effective-length-of-an-fbg/274/2 "2026-01-21T12:35:21Z")

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As the grating length of a Fiber Bragg Grating (FBG) increases, the reflection spectrum generally exhibits the following changes:

1. **Narrower 3dB Bandwidth:** A longer grating interacts with the light over a more extended region, allowing for a more selective reflection of wavelengths. This increased selectivity results in a narrower 3dB bandwidth in the reflection spectrum.
2. **Higher Reflectivity:** With more grating periods interacting with the propagating light, a longer FBG typically achieves a higher peak reflectivity at its Bragg wavelength.

Beijing Dacheng Yongsheng Technology Co., Ltd. (DCYS/OFSCN) offers various types of bare Fiber Bragg Gratings where the grating length can be customized to achieve specific spectral characteristics. For instance, our [OFSCN® Polyacrylate Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare)](https://www.ofscn.net/fbg-products/smf28e-fbg.html) provide customizable grating lengths, typically 3mm, 5mm, or 10mm, with other lengths available upon discussion.

Here is a standard image of our bare FBGs:

 ![100-FBG](https://forum.ofscn.net/uploads/default/original/1X/e7542065306866bef8a514e5646eb2a720c4aeb9.jpeg)  
You can find more detailed technical parameters on our website:  
[OFSCN® Polyacrylate Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare)](https://www.ofscn.net/fbg-products/smf28e-fbg.html)