What is the difference between step-index and graded-index multimode fibers?

Step index optical fibers are characterized by a uniform distribution of the core refractive index. This means that the refractive index is the same everywhere inside the core. On the other hand, graded index optical fibers are characterized by a core whose refractive index varies with radial position. For a graded index fiber, the refractive index of the core tends to be higher near the center and smaller radially outward.

What is an optical mode in optical fibers?

There are many ways to think about optical modes. One way is to think of a mode as one possible solution of the wave equation in a waveguide, fiber, or free space. It is the spatiotemporal distribution/propagation of the optical (electromagnetic) wave inside the fiber. A single mode corresponds to one such solution with a defined periodicity (wavelength) and phase velocity. Multimode optical fibers are designed in such a way that multiple optical modes can simultaneously be propagated inside the fiber without deterioration.

What are the key advantages of using multimode fibers?

Multimode fibers are characterized by a wide core and an overall bigger cross-section than single-mode fibers. This makes them easier to align with other devices like lasers and less likely to suffer from breakage. Additionally, connectors and attachments to multimode fiber are cheaper as they are easier to fabricate. Multimode fibers are also ideal for short-distance communication networks.

Is propagation in multimode fibers affected by temperature fluctuations?

Yes, a change in temperature can induce small variations in the index of refraction of multimode temperature which could cause undesired effects such as power loss or birefringence. However, many multimode fibers are designed to operate at temperatures as high as 700 degrees Celsius.

How big is the core of a multimode fiber?

The core diameters of multimode fibers can range from 50 µm to 500 µm or more. In general, multimode fibers with larger core diameters can sustain higher number of modes.

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Fiber Optics
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Multi-Mode Fibers

Multi-Mode Fibers

Q: What is the difference between single-mode fibers and multimode fibers?

While single-mode fibers can only support one mode, multimode fibers can propagate thousands of modes due to the larger size of the core. The number of modes supported by an optical fiber is dependent on the radius of the core, the wavelength, and the index of refraction of the core and the cladding materials.

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FiberTech Ultrasol Fibers - 84808016F

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Sold by: Weinert Fiber Optics Ships from: United States

Specifications
Core Diameter:	500 um
Wavelength Range:	190 – 250 nm
Fiber Core Material:	Silica
Fiber Length:	Custom
Fiber Type:	Solar Stable

MIL-Spec Radiation Hard Multimode Fiber 50/125/245µm

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Core Diameter:	50 um
Wavelength Range:	850 – 1300 nm
Cable Length:	1100 m
Fiber Core Material:	Silica
Core Diameter:	50 ± 3 µm

Optran® WF – Low-OH Standard NIR Fiber (700–2400 nm)

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Sold by: Ceramoptec Ships from: Germany

Specifications
Numerical Aperture (NA):	0.12 ± 0.02 \| 0.22 ± 0.02 \| 0.28 ± 0.02 or customized
Operating Temperature:	-190 to +350°C
Core Diameter:	30 to 3000 μm
Standard Core / Cladding Ratios:	1 : 1.04 \| 1 : 1.06 \| 1 : 1.1 \| 1 : 1.15 \| 1 : 1.2 \| 1 : 1.25 \| 1 : 1.4 or customized
OH Content:	low (< 1 ppm)

Optran® WFNS – Low-OH Standard NIR Fiber (300–2400 nm)

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Sold by: Ceramoptec Ships from: Germany

Specifications
Numerical Aperture (NA):	0.12 ± 0.02 \| 0.22 ± 0.02 \| 0.28 ± 0.02 or customized
Operating Temperature:	-190 to +350°C
Core Diameter:	30 to 3000 μm
Standard Core / Cladding Ratios:	1 : 1.04 \| 1 : 1.06 \| 1 : 1.1 \| 1 : 1.15 \| 1 : 1.2 \| 1 : 1.25 \| 1 : 1.4 or customized
OH Content:	low (< 1 ppm)

Optran® PUV – High-NA Fiber with Silicone Cladding (350-2200 nm)

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Sold by: Ceramoptec Ships from: Germany

Specifications
OH Content (Optran PUV):	high (> 700 ppm)

Optran® PWF – Low-OH Fiber with Silicone Cladding (350-2200 nm)

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Sold by: Ceramoptec Ships from: Germany

Specifications
OH Content (Optran PWF):	low (< 1 ppm)

Optran® UVNSS – Solarization-Resistant High-OH Fiber (190–1200 nm)

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Sold by: Ceramoptec Ships from: Germany

Specifications
Numerical Aperture (NA):	0.12 ± 0.02 \| 0.22 ± 0.02 \| 0.28 ± 0.02 or customized
Operating Temperature:	-190 to +150°C
Standard Core / Cladding Ratios:	1 : 1.06 \| 1 : 1.1 \| 1 : 1.2 \| 1 : 1.4 or customized

Optran® UVNS – Non-Solarizing UV Fiber (190–1200 nm)

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Sold by: Ceramoptec Ships from: Germany

Optran® UV – High-OH UV Fiber (220–1200 nm)

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Sold by: Ceramoptec Ships from: Germany

Specifications
Numerical Aperture (NA):	0.12 ± 0.02 \| 0.22 ± 0.02 \| 0.28 ± 0.02 or customized
Operating Temperature:	-190 to +350°C
Core Diameter:	50 to 3000 μm

Optran® HWF – High Numerical Aperture VIS-NIR Optical Fiber

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Sold by: Ceramoptec Ships from: Germany

Specifications
OH Content Optran HWF:	low (< 1 ppm)

Optran® HUV – High-NA UV Fiber (350-2200 nm)

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Sold by: Ceramoptec Ships from: Germany

Specifications
OH Content:	high (> 700 ppm)

Optran® WFGe – Germanium-Doped Fiber (400–2400 nm)

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Sold by: Ceramoptec Ships from: Germany

Specifications
Wavelength / Spectral Range:	400 – 2400 nm
Core Diameter:	50 to 1000 μm
Standard Core / Cladding Ratios:	1 : 1.04 \| 1 : 1.06 \| 1 : 1.1 \| 1 : 1.15 \| 1 : 1.2 \| 1 : 1.25 \| 1 : 1.4 or customized

Optran® UVWFS – Broadband Low-OH Fiber (200-2000nm)

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Sold by: Ceramoptec Ships from: Germany

Specifications
Numerical Aperture (NA):	0.12 ± 0.02 \| 0.22 ± 0.02 \| 0.28 ± 0.02 or customized
Operating Temperature:	-190 to +350°C
Core Diameter:	100 to 800 µm \| standard 200 µm
OH Content:	~ 5 ppm

Optical Fiber Series

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Sold by: Evolve Sensing Ships from: United States

Specifications
UV-VIS Waveband Optical Fibers:	200 - 1100 nm
UV-VIS Short Optical Fibers:	200 - 1100 nm
VIS-IR Waveband Optical Fibers:	400 - 2200 nm
VIS-IR Short Optical Fibers:	400 - 2200 nm
Customized Y-type, Multicore, And Dip Probe Fibers:	Various ranges

j-fiber 100/140µm & 100/125µm Graded Index Multimode Fiber

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Core Diameter:	100 ± 4.0 µm
Cladding Diameter:	140 ± 3 µm
Cladding Diameter:	125 ± 2 µm
Coating Diameter:	242 ± 7 µm
Numerical Aperture:	0.290 ± 0.020

MIL-Spec Radiation Hard Multimode Fiber 50/125/500µm

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Type:	Multimode
Class:	graded index
Size:	50/125
Composition:	Glass & Glass Silica
Wavelength:	850 & 1300 nm

j-fiber Multimode Fiber 50/125µm for Sensor Applications

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Core Diameter:	50 ± 2.5 µm
Core Non-Circularity:	≤ 5.0 %
Core/Clad Concentricity Error:	≤ 1.5 µm
Cladding Diameter:	125 ± 1 µm
Cladding Non-Circularity:	≤ 1.0 %

62.5/125 Radiation Hard Multimode Fiber for Military and Aerospace

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Attenuation Coefficient At 850nm:	≤ 2.8 dB/km
Attenuation Coefficient At 1300nm:	≤ 0.8 dB/km
Attenuation Coefficient At 1383nm:	≤ 0.7 dB/km
Att. Discontinuities (OTDR 1300nm):	< 0.05 dB
Radiation Induced Attenuation (RIA) At 1300nm:	≤ 50 dB

High-Temperature Polyimide Coated Optical Fibers for Extreme Environments

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Operating Temperature Range:	-65 to +300 °C
Coating Material:	Polyimide
Cladding Diameter:	125 ± 2 µm
Coating Diameter:	155 ±10 µm
Attenuation (50/125 @ 850/1300nm):	≤ 3.0 / 1.0 dB/km

BIMMF 50/125 Multimode Fiber for Sensing Applications

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Bandwidth (Overfilled Launch) 850nm OM2+:	≥ 750 MHz.km
Bandwidth (Overfilled Launch) 1300nm OM2+:	≥ 500 MHz.km
Bandwidth (Overfilled Launch) 850nm OM3:	≥ 1500 MHz.km
Bandwidth (Overfilled Launch) 1300nm OM3:	≥ 500 MHz.km
Bandwidth (Overfilled Launch) 850nm OM4:	≥ 3500 MHz.km

j-BendAble OM3 HTC High-Temperature Bend-Insensitive Fiber

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Coating Material:	High-temperature Acrylate
Operating Temperature Range:	-60 to +150 °C
Max. Temperature Short Term:	200 °C
Max. Temperature Intermediate:	180 °C
Max. Temperature Long Term:	150 °C

j-fiber Pure Silica Large Core Fibers for UV/IR Applications

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Core Diameter:	50 um
Wavelength Range:	200 – 800 nm
Cable Length:	Not Specified
Fiber Core Material:	Silica
Core Composition:	SiO2

MIL-Spec Radiation Hard Multimode Fiber 62.5/125/245µm

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Core Diameter:	62.5 ± 3 µm
Core Non-Circularity:	≤ 6.0 %
Core/Clad Concentricity Error:	≤ 4 µm
Clad Diameter:	125 ± 1 µm
Cladding Non-Circularity:	≤ 2.0 %

Step-index Fiber 190/200/245 High NA Ge-doped Low-OH

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Sold by: j-fiber GmbH Ships from: Germany

Specifications
Core Diameter:	190 ± 9 µm
Cladding Diameter:	200 ± 5 µm
Cladding Non-circularity:	≤ 1.5%
CCDR (nominal):	1.05
Coating Diameter:	245 ± 10 µm

Did You Know?

Multimode fiber is an optical fiber that is designed to carry multiple light modes, each at a slightly different reflection angle within the optical fiber core. Multimode fiber gives you high bandwidth at high speeds over short to medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable's core typically at 850 or 1300nm. Typical multimode fiber core diameters are 50, 62.5, 100um. As the number of light reflections passing through the core increases, this leads to high dispersion and attenuation rate and eventually the quality of the signal is reduced over long distances. Multimode fibers are typically used for short distances, e.g. for audio/video applications in LANs. RF broadband signals, which cable companies commonly use, cannot be transmitted over multimode fibers.

Related Resources

Medical applications of fibers

Frequently Asked Questions

While single-mode fibers can only support one mode, multimode fibers can propagate thousands of modes due to the larger size of the core. The number of modes supported by an optical fiber is dependent on the radius of the core, the wavelength, and the index of refraction of the core and the cladding materials.

Multi-Mode Fibers: Versatile Solutions for Short to Medium Distance Data Transmission

Multi-mode fibers are designed to carry multiple light modes simultaneously, making them highly suitable for short to medium distance applications such as local area networks (LANs), data centers, and industrial automation. These fibers typically have larger core diameters, commonly 50 or 62.5 microns, allowing multiple modes to propagate, which simplifies coupling with light sources like LEDs and VCSELs.

FindLight offers a variety of multi-mode fiber products, including radiation-hard multimode fibers that maintain performance even in high-radiation environments such as nuclear facilities, aerospace, or medical equipment. These fibers ensure signal stability and integrity despite harsh conditions.

Another notable product is the power delivery silica core fiber, designed for applications involving high-power laser transmission. These fibers offer excellent optical properties like low attenuation and high damage thresholds, enabling efficient laser energy delivery in industrial cutting, welding, or medical laser systems.

Multi-mode fibers are valued for their cost-effectiveness and ease of installation, especially in environments where ultra-long distances and ultra-high bandwidths are not necessary. They support high data rates over distances up to a few kilometers, making them ideal for intra-building communication.

Choosing the right multi-mode fiber involves considering core size, numerical aperture, attenuation, and environmental factors such as temperature range and mechanical stress tolerance. FindLight’s broad catalog provides fibers optimized for different wavelengths, bandwidths, and operational conditions.