Single Mode Fluoride Glass Optical Fiber

  • Single Mode ZBLAN or InF3 Fluoride Fiber Manufactured In-House
  • Transmissive from the UV to Mid-IR
  • Single Mode Operation Over 2.3 - 4.1 µm or 3.2 - 5.5 µm
  • Stable in Typical Lab Environments and Easy to Handle
IRZS23 End Face


Fluoride Fiber Cross Section

(Not to Scale)

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Fluoride Optical Fiber Manufacturing Overview


  • Spectroscopy
  • Fiber Lasers
  • Supercontinuum Light Sources
  • Environmental Monitoring
  • Surgical Lasers
  • Chemical Sensing
  • IR Imaging
Indium Fluoride and Zirconium Fluoride Fiber Comparison
Click to Enlarge

Click for Raw Data
Compared to standard silica glass fibers, Thorlabs' single mode
fluoride fibers are transmissive at much longer wavelengths.


  • Fluoride Glass Fibers Manufactured at Thorlabs' Fiber
    Draw Facility
    • Fluorozirconate (ZBLAN) for 285 nm - 4.1 µm
    • Fluoroindate (InF3) for 310 nm - 5.5 µm
  • Single Mode Wavelength Range:
    • 2.3 µm - 4.1 µm for ZLBAN
    • 3.2 µm - 5.5 µm for InF3
  • World-Class Attenuation, Strength, and Geometry Control
  • Custom Core Sizes and Cutoff Wavelengths Available by Contacting

Thorlabs' single mode fluoride glass fibers are manufactured in-house and have world-class purity, precision, and strength. For more information about fluoride glass and our manufacturing process, see the Manufacturing tab and our main fluoride fiber web presentation.

Fluoride fibers offer low attenuation in the mid-IR wavelength range, aided by an extremely low hydroxyl ion (OH) content. Our IRZS23 fiber is made from ZBLAN (fluorozirconate) glass and is highly transmissive over the 285 nm - 4.1 µm range, with single mode operation from 2.3 µm to 4.1 µm. Our IRFS32 fiber is made from InF3 (fluoroindate) glass, is highly transmissive over the 310 nm - 5.5 µm range, and exhibits single mode operation from 3.2 µm to 5.5 µm. The graph to the right shows how the wavelength-dependent attenuation compares to that of a standard silica glass fiber.

The refractive index of fluoride glass is near that of silica. As a result, optical fibers manufactured using fluoride glass exhibit low return losses and Fresnel reflections at both fiber-air and fiber-silica interfaces. Graphs of refractive index, numerical aperture (NA), and attenuation can be seen in the Graphs tab.

Since fluoride glass is softer than standard silica glass, extra care should be taken while cleaning and handling. See the Handling tab for suggested procedures.

Thorlabs also manufactures multimode fluoride fiber. See the selection guide below for links to the main web presentation for each type of component we offer.

† ZBLAN and ZrF4 are used interchangeably to refer to fluorozirconate glass.

Custom Fluoride Fiber

If our standard offerings do not meet your needs, please contact us to discuss customization and potential fiber draws. Some of the many customization options we provide for fluoride fibers include:

  • Hand-Selected Extra-Low-Loss Fibers to Meet Strict Attenuation Requirements
  • Custom Core and Cladding Geometries
  • Dual-Polymer Claddings Available
  • Increased Power Handling Capabilities


Fluoride Fibers and Components

Fluoride Fiber Overview Multimode Fluoride Bare Fiber Single Mode Fluoride Patch Cables Multimode Fluoride Patch Cables
AR-Coated Multimode Fluoride Patch Cable Vacuum-Compatible Multimode Fluoride Patch Cable Multimode Fluoride Bundles MIR Reflection/Backscatter Bundles
Item # IRZS23 IRFS32
Fiber Type Fluorozirconate (ZBLAN)a Fluoroindate (InF3)
Transmission Rangeb 285 nm - 4.1 µm 310 nm - 5.5 µm
SM Operating Wavelength 2.3 - 4.1 µm 3.2 - 5.5 µm
Cutoff Wavelength ≤2.3 µm ≤3.2 µm
Typical Attenuationc,d 30 dB/km @ 2.5 µm 150 dB/km @ 3.6 µm
Maximum Attenuationd <200 dB/km
(from 2.3 - 3.6 µm)
<450 dB/km
(from 3.2 - 4.6 µm)
NAe 0.19 ± 0.02 @ 2 µm 0.26 ± 0.02 @ 2 µm
MFDf 10.5 ± 0.5 µm @ 2.5 µm 11.0 ± 0.5 µm @ 3.6 µm
Core Diameter 9 ± 0.5 µm
Cladding Diameter 125 +1/-2 µm
Coating Diameter 260 ± 15 µm 245 ± 15 µm
Core/Cladding Concentricity ≤2 µm
Core Circularity ≥94%
Long-Term Bend Radiusg,h ≥30 mm
Short-Term Bend Radiush ≥10 mm
Operating Temperature -55 to 90 °C
End Face Imagei
(Click for Scale)
  • ZBLAN and ZrF4 are used interchangeably to refer to fluorozirconate glass.
  • Defined as the Wavelength Range with ≤3000 dB/km Attenuation
  • Hand-selected extra-low-loss fiber is available by contacting
  • At or Above the Minimum Long-Term Bend Radius
  • The NA is defined by the index difference between the core and cladding. This specification is given at 2 µm, but the NA changes minimally with wavelength over the single mode operating range of each fiber (see the Graphs tab).
  • Mode Field Diameter is a nominal value, calculated using the fiber’s typical NA and core diameter.
  • Calculated Values for <0.2% Failure Rate, for a 10 m Length of Fiber Over >20 Years
  • Proof testing is available upon request. Contact for more information.
  • Visible damage in the coating and at the coating-cladding interface is due to the cleaving procedure and is not present in the continuous fiber.

This tab contains plots of the typical attenuation, bend-induced attenuation, mode field diameter, dispersion, numerical aperture, and core and cladding refractive indices of our single mode fluoride fibers as a function of wavelength. Variations in these properties can occur between fiber draws. Please contact Tech Sales to discuss whether these fibers are appropriate for your application.


These graphs show the typical measured attenuation of our single mode fluoride fibers. The red shaded regions denote the range of single mode operation with guaranteed attenuation for each fiber, while the blue shaded regions denote the range of single mode operation without guaranteed attenuation. The peak just below the single mode cutoff wavelength is caused by attenuation of the second-order mode.


Bend-Induced Attenuation

This data was obtained by measuring the attenuation of a bend-free 1 m length of fiber, and comparing with the attenuation of the same length when a single loop with the given radius was added. These graphs show the additional attenuation introduced by the loop. The red shaded regions denote the range of single mode operation with guaranteed attenuation for each fiber, while the blue shaded regions denote the range of single mode operation without guaranteed attenuation.

Click to Enlarge
Click for Raw Data
Data for additional bend radii is available in the raw data file.


Mode Field Diameter

These graphs show the typical mode field diameter of our single mode fluoride fibers, calculated from the measured core diameter and calculated numerical aperture of each fiber. The blue shaded regions denote the range of single mode operation for each fiber.



These graphs show the typical chromatic dispersion of our single mode fluoride fibers, calculated from the refractive indices. The blue shaded regions denote the range of single mode operation for each fiber.


Numerical Aperture

These graphs show the typical numerical aperture (NA) of our single mode fluoride fibers, calculated from the core and cladding refractive indices. The blue shaded regions denote the range of single mode operation for each fiber.


Refractive Indices

These graphs show the typical refractive indices of the core and cladding of our single mode fluoride fibers. The graphed data was obtained by fitting the Sellmeier equation to measured data. The Sellmeier equation and best-fit parameters for each fiber's core and cladding can be seen below each graph. The blue shaded regions in the graphs denote the range of single mode operation for each fiber.

Modified Sellmeier Equation for MIR Fiber
Sellmeier Equation
ZBLAN Sellmeier Coefficients
Coefficient Core Cladding
u0 0.5463 0.705674
u1 0.7566 0.515736
u2 1.782 2.204519
u3 0.000 0.087503
u4 0.116 0.087505
u5 21.263 23.80739
A 0.9562 1
InF3 Sellmeier Coefficients
Coefficient Core Cladding
u0 0.47627338 0.68462594
u1 0.76936893 0.4952746
u2 5.01835497 1.4841315
u3 0.0179549 0.0680833
u4 0.11865093 0.11054856
u5 43.64545759 24.4391868
A 1 1

Click to Enlarge

This diagram compares on-axis tension, which can be safely applied, to off-axis tension, which can induce unsafe curvature and damage the fiber.

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The recommended procedure for removing tape from the bare fiber spools is shown in this image. The tape should be pulled parallel to the fiber when removing, while the other hand applies gentle force to stabilize the fiber.

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These images depict the recommended stripping procedure. A: Immerse the target fiber secion in stripping liquid.
B-C: Gently pinch the base of the soaked section with FSGT tweezers and pull toward the end of the fiber.
D: The coating should slide off, leaving a stripped section.

The material properties of fluoride glass differ from those of silica glass. This tab details recommended handling procedures for our fluoride fibers and patch cables.

Safety and Disposal
ZBLAN and InF3 glasses may present health risks. Information about the composition of our fluoride fibers is available from Tech Support upon request. When handling bare, stripped fluoride fiber, chemically resistant gloves such as our nitrile gloves should always be worn. Fiber shards generated from cleaving should be disposed of in a sharps container such as our FTDU fiber optic disposal unit.

Thorlabs will accept and dispose of any fluoride fiber or filled disposal units that you wish to discard. Please contact Tech Support before returning fiber or filled disposal units. If you wish to dispose of fiber locally, please follow all applicable local laws and regulations.

Because fluoride glass is softer than silica glass, exposed end faces are easily scratched during storage, and care should be taken to ensure that they are not exposed to mechanical abrasion. Storage under normal lab temperatures and humidities will not affect the integrity of the fiber. Prolonged, direct contact with liquid water or water vapor should be avoided.

Bending and Tension
Fluoride fiber is strong in tension, but can break easily if forces are applied off-axis or if it is bent to a small radius. These fibers should never be bent to smaller than their short-term bend radii. Moderate on-axis forces can be safely applied to the fiber, such as tension applied during spooling. The diagram to the right demonstrates safe on-axis tension and unsafe off-asix tension.

Our bare fluoride fibers ship on a spool, with their ends taped to the spool body. When removing the fiber, the tape should be pulled parallel to the fiber, as shown in the image to the top right.

For protection, our fluoride patch cables are jacketed with PVDF furcation tubing or stainless steel tubing that is stiffer than the jackets used in typical patch cables. As long as the jacket is not forced to bend below its specified minimum radius, the fiber will remain intact. For out patch cables with PVDF jackets, the tubing will become discolored if the bending limit is exceeded. Our patch cables with stainless steel tubing are designed so that the tubing mechanically limits the fiber to be unable to bend below its minimum radius.

Fluoride fibers are susceptible to damage when conventional mechanical stripping techniques are used, owing to the softness of the glass. Our FSGT Coating Stripping Tweezers can be used along with a chemical stripping agent to effectively strip these fibers without scratching or nicking the cladding.

To strip a fiber, the coating should first be exposed to a stripping liquid such as a paint stripper for three to five minutes. Placing the stripping liquid in a long vessel such as a syringe with a long tip is recommended to increase ease of application. If using a gel-type stripper, it can be applied manually to the exterior of the fiber. Note that the required soaking time will depend on the particuar stripping agent being used as well as the chemical composition of the coating. For example, if a dicholomethane (DCM) based stripping liquid is used, the required time may be shorter.

The coating on the section of the fiber soaked in stripping liquid will visibly swell, as seen in section B of the image to the right. A pair of FSGT tweezers can then be used to gently pinch the fiber in the soaked section, and pull toward the end of the fiber. Care should be taken to ensure that only moderate pressure is applied, or else the fiber may break. The soaked coating should slide off the end of the fiber, leaving the cladding exposed. If residue remains on the stripped section, it can be cleaned as detailed below.

Refer to any safety documentation for the chemical stripping agent before use.

Click to Enlarge

These images depict the recommended procedure for cleaning end faces with a solvent.
A: Wet a stack of five or mote TCW604 wipes with an appropriate solvent (see the text for examples).
B: Gently pass the fiber end face across the wet wipe.

Because fluoride glass is soft, end faces and stripped sections of our fluoride fibers and patch cables can be easily scratched during cleaning. If particulates are present on the glass surface, first try to remove them using compressed air. If compressed air is insufficient, then an appropriate solvent can be used with our TCW604 TechniCloth®† Lint-Free Wipes to clean the tip, as shown in the image to the left. Methanol and isopropanol are examples of appropriate solvents, while acetone is unsuitable. Wiping with a dry cloth is not recommended as it may scratch the surface.

Please note that Kimwipes®†† are extremely likely to scratch the fiber tip and should not be used.

Our fluoride fibers can be cleaved using a tension-and-scribe cleaver such as our Vytran® LDC401 large-diameter fiber cleaver. Note that cleaving these fibers may generate shards. Safety glasses and chemically resistant gloves should always be worn when cleaving.

TechniCloth® is a registered trademark of the Illinois Tool Works, Inc. Corporation.
Kimwipes® is a registered trademark of the Kimberly-Clark Corporation.

View our recorded webinar, in which we highlight our manufacturing techniques, the history of fluoride fiber R&D, and the state of fluoride fiber technology today and in the future.

Thorlabs manufactures ZBLAN zirconium fluoride (ZrF4) and indium fluoride (InF3) fibers at our vertically integrated fiber draw facility. The facility handles raw materials, glass preforms, fiber draw, and patch cable production, all in the same location. By controlling the process from start to finish, Thorlabs can ensure fibers consistently meet world-class specifications, including low attenuation, high mechanical strength, and precise geometry control. 

The facility, located in Newton, NJ, USA, is well-equipped for high-volume manufacturing and is capable of producing many kilometers of fiber with consistent performance. In addition, because the fiber stays within Thorlabs' facilities from start to finish, the manufacturing process can be adjusted to accommodate unique custom orders or R&D needs.

Fluoride Characteristics
Fluoride fibers are ideal for transmission in the mid-IR wavelength range, and Thorlabs' fibers feature low attenuation over this range as a result of stringent manufacturing processes yielding an extremely low hydroxyl ion (OH) content. Fluoride fibers also have lower refractive indices and lower chromatic dispersion when compared to other fibers that offer transmission in the mid-IR range, such as chalcogenide glass fibers. Thorlabs' tightly controlled processes mitigate scattering and point defects in the fiber, as well as eliminate micro-crystallization in the glass matrix.

Fluoride Fiber Characterization and Testing
In addition to manufacturing fiber, Thorlabs offers testing and characterization services for our fiber products. We precisely measure the properties of each drawn fiber to ensure that it meets our high standards of quality. Extensive testing also provides feedback for our fiber draw team, enabling tight control of each step in the manufacturing process. Customers can request custom testing of any Thorlabs-manufactured fiber, which is then provided with the shipped fiber. Testing of third-party fiber samples provided by customers is also available upon request.
Available tests and services include:

Click to Enlarge

A Thorlabs engineer mixes raw materials in our fluoride glass fabrication facility.

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A Glass Drop During the Fiber Draw Process
  • Spectral Attenuation Measurement
    • UV / Visible / NIR / MIR Wavelength Range
    • SM or MM Fiber and Bulk Glass
  • SM Fiber Cutoff Wavelength Measurement
  • Fiber NA Measurement
  • Fiber Glass / Coating Geometry Measurement
    with Sub-µm Accuracy
  • MIR High-Power Screening for MM Fibers
  • Fiber Tensile Strength Testing
  • Defect / Break Analysis
  • Degree of Cure Testing for Fiber Coatings

Request testing for Thorlabs or third-party fibers by
contacting Tech Sales.

Click to Enlarge

These graphs show Thorlabs' steady improvement in the average attenuation of all fiber draws during the given year.

Technical Team
Thorlabs' team of MIR fiber researchers and engineers has many years of experience in fluoride glass research and development, production, and fiber draw. Their knowledge and expertise have resulted in consistent improvement in the quality of our fluoride fiber. See the graphs to the left for the progression of our fluoride fiber performance.

Custom Fluoride Fiber and Patch Cables
If our standard offerings do not meet your needs, please contact Tech Support to discuss customization and potential fiber draws. Some of the many customization options we provide for fluoride fibers and patch cables include:

Bare Fiber
  • Hand-Selected Extra-Low-Loss Fluoride Fibers to Meet Strict Attenuation Requirements
  • Custom Core and Cladding Geometries
  • Dual-Polymer Claddings Available
  • Increased Power Handling Capabilities
Patch Cables
  • Custom Options: Fiber Type, Length, Termination, and Tubing
  • OEM Patch Cables: Designed for Application Requirements
  • AR-Coated Patch Cables
  • Ruggedized Cabling for Harsh Environments

Click to Enlarge

Thorlabs' Fiber Draw Tower
MFD Definition
Click to Enlarge

The left image shows the intensity profile of the beam propagated through the fiber overlaid on the fiber itself. The right image shows the standard intensity profile of the beam propagated through the fiber with the MFD and core diameter called out.

Definition of the Mode Field Diameter

The mode field diameter (MFD) is one measure of the beam width of light propagating in a single mode fiber. It is a function of wavelength, core radius, and the refractive indices of the core and cladding. While much of the light in an optical fiber is trapped within the fiber core, a small fraction propagates in the cladding. The light can be approximated as a Gaussian power distribution as shown to the right, where the MFD is the diameter at which the optical power is reduced to 1/e2 from its peak level.

Measurement of MFD
The measurement of MFD is accomplished by the Variable Aperture Method in the Far Field (VAMFF). An aperture is placed in the far field of the fiber output, and the intensity is measured. As successively smaller apertures are placed in the beam, the intensity levels are measured for each aperture; the data can then be plotted as power vs. the sine of the aperture half-angle (or the numerical aperture for an SM fiber).

The MFD is then determined using Petermann's second definition, which is a mathematical model that does not assume a specific shape of power distribution. The MFD in the near field can be determined from this far-field measurement using the Hankel Transform.

Posted Comments:
Guangtao Zhu  (posted 2023-09-25 13:32:51.413)
This comment is from Mizuno Lab., Yokohama National University, Japan. We are conducting research on ZBLAN fiber with your product. Could you offer the detailed information of the proportion of each dopant in this product? (XXZrF4-XXBaF2-XXLaF3-XXAlF3-XXNaF) Thank you!
Nouman Zia  (posted 2023-09-11 07:11:30.49)
Hi, We have IRZS23 fiber and we are facing stripping issues. Can you please suggest which stripping chemical should we use and does thorlabs prove that chemical?
cdolbashian  (posted 2023-09-25 09:32:44.0)
Thank you for reaching out to us with this inquiry! We provide some guidelines in this "handling" tab above regarding stripping this particular fiber. While we do not sell the thinner required for stripping, I have reached out to you directly to discuss your application.
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Single Mode Fluoride Fiber

Due to the fluoride fiber manufacturing process, Thorlabs is not able to guarantee the availability of long continuous fibers. If your order is for 20 m of fiber or more, you may be
shipped multiple shorter fibers, with a minimum length of 10 m each. If you require a longer continuous fiber, please contact Please note that orders for
a continuous length longer than 35 m will be subject to a surcharge.

Fibers with specific attenuation requirements, as well as bend radius proof testing, can also be requested. Please note that our fluoride fibers will typically ship within two days,
but special orders may be subject to longer lead times.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
IRZS23 Support Documentation
IRZS23Customer Inspired! Single Mode ZBLAN Fiber, 2.3 - 4.1 µm, 0.19 NA, 10.5 µm MFD
Per Meter
Volume Pricing
IRFS32 Support Documentation
IRFS32Customer Inspired! Single Mode InF3 Fiber, 3.2 - 5.5 µm, 0.26 NA, 11.0 µm MFD
Per Meter
Volume Pricing