# What is a "vacuum feedthrough flange for optical fiber"?

**URL:** <https://forum.ofscn.net/t/what-is-a-vacuum-feedthrough-flange-for-optical-fiber/2940>\
**Category:** OFSCN Technical Knowledge Base\
**Created:** [September 24, 2026, 2:43pm UTC](https://forum.ofscn.net/t/what-is-a-vacuum-feedthrough-flange-for-optical-fiber/2940 "2026-09-24T14:43:54Z")\
**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:** [September 24, 2026, 2:43pm UTC](https://forum.ofscn.net/t/what-is-a-vacuum-feedthrough-flange-for-optical-fiber/2940/1 "2026-09-24T14:43:54Z")

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How do you pass optical fiber through the wall of a vacuum chamber without any air leakage?

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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:** [September 24, 2026, 2:46pm UTC](https://forum.ofscn.net/t/what-is-a-vacuum-feedthrough-flange-for-optical-fiber/2940/2 "2026-09-24T14:46:53Z")

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In vacuum engineering and optical testing, to pass optical fibers through a vacuum chamber wall while maintaining a high vacuum level inside the chamber, the standard and reliable engineering solution is to use a **Fiber Optic Vacuum Sealed Flange / Vacuum Feedthrough**.

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### I. Physical and Engineering Implementation Principles

The fiber optic vacuum sealed flange primarily resolves the engineering conflict of “allowing light transmission without gas leakage” through a two-stage airtight structure:

1. **Vacuum Seal between the Flange and Chamber Wall** :
  - The outer periphery of the flange utilizes international standard vacuum mechanical interfaces (e.g., the **KF Series** uses a fluoro-rubber O-ring with a quick-release clamp for medium-low/high vacuum sealing; the **CF Series** uses an oxygen-free copper gasket and knife-edge flange for ultra-high vacuum sealing).

2. **Penetration Seal between the Optical Fiber and the Metal Flange Body** :
  - When optical fibers pass directly through a metal flange, there is a gap between the micron-level fiber and the metal aperture. Typically, **low outgassing specialty ultra-high vacuum sealing adhesives** or **metallization/glass frit bonding processes** are used to securely seal the bare fiber/metal jacket to the flange’s through-hole, eliminating diffusion paths for gas molecules.

3. **Interface Types** :
  - **Feedthrough Type (Direct Patch Cord)**: The optical fiber passes continuously through the flange. The flange extends armored fiber optic patch cords of a specified length on both ends, resulting in extremely low optical loss and avoiding additional reflections and insertion loss from internal connection points.
  - **Adapter Socket Type (Female/Male Connector Type)**: The flange is equipped with standard optical adapter interfaces (such as FC, SMA, etc.) on both the inner and outer sides, facilitating quick plug-and-play and wiring inside and outside the chamber.

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### II. Official Related Products and Technical Specifications

For these application scenarios, Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) provides standard and customized fiber optic vacuum feedthrough components:

[OFSCN® Fiber Optic Vacuum Sealed Flange](https://www.ofscn.org/connectors/fiber-optic-sealed-flange.html)

 ![OFSCN® Fiber Optic Vacuum Sealed Flange](https://forum.ofscn.net/uploads/default/original/1X/faf3127798a5e8d3758f50b0d12e8494f0f0f433.jpeg)  
 ![OFSCN® Fiber Optic Vacuum Sealed Flange](https://forum.ofscn.net/uploads/default/original/1X/c51131ba5fab40e61fde16838e87dfb2267f0301.jpeg)

#### Key Parameter Indicators:

- **Structure Series** : Offers CF Series (e.g., CF35 ultra-high vacuum knife-edge flanges) and KF Series (e.g., KF25 quick-release flanges);
- **Vacuum Performance** : Extremely low leak rate, with ultimate vacuum better than 1 \times 10^{-7}\ \text{Pa} and 1 \times 10^{-9}\ \text{Pa} ;
- **Channel Configuration** : Supports single-channel (single-head) or multi-channel (multi-head) fiber array feedthrough; supports female adapters or integrated fiber optic patch cord male connectors;
- **Temperature Resistance** : Typically suitable for room temperature environments, with customization available for products resistant to baking at 250\ \text{℃}.