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Round-to-Linear Fiber Optic Bundles


  • Fiber Bundles with Low-OH or High-OH Multimode Fiber
  • One Linear and One Round Bundle End
  • Optimized for Use with Spectrometers with an Entrance Slit

Application Idea

Round-to-Linear Bundle Connected
to a CCS200 Spectrometer

SMA Connector with
Linear Bundle 

SMA Connector with
Round Bundle 

BFL200HS02

Black Rubber and Metal Threaded
Dust Caps Included

Related Items


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Item # BFL105HS02 BFL105LS02 BFL200HS02 BFL200LS02
Number of Fibers 7
Fiber Core Size Ø105 µm Ø200 µm
Linear End Fiber
Dimensions
0.90 mm x 0.13 mm 1.55 mm x 0.23 mm
Round End Effective
Core Diameter
355 µm 640 µm
Fiber NA 0.22a
Hydroxyl Ion Content High OH Low OH High OH Low OH
Wavelength Range 250 - 1200 nm 400 - 2400 nm 250 - 1200 nm 400 - 2400 nm
Fiber Attenuation Plot
Length 2 +0.075/-0 m
Connectors SMA905
Center Root-Mean-Square-Deviation 
(Click for Details)b
1.67 µm 1.09 µm
Center-to-Center Distance (Click for Details)c 125.38 µm ± 0.14 µm 220.00 µm ± 0.06 µm
  • The NA of the bundle is the same as that of the individual fibers.
  • The Root-Mean-Square-Deviation represents the sample standard deviation of the fiber's center compared to the center line of the bundle. This data is from a small sample group; slight variations will occur from fiber to fiber. Click here for more details.
  • The Center-to-Center Distances represents the distance between one fiber and its nearest neighbor. This data is from a small sample group; slight variations will occur from fiber to fiber. Click here for more details.
Round Bundle End
Click to Enlarge

Round Bundle End
Linear Bundle End
Click to Enlarge

Linear Bundle End

Features

  • One Linear and One Round End
  • Low- or High-OH, Ø105 µm or Ø200 µm Core Multimode Fiber
  • 2 m Long Cables with SMA905 Connectors
  • No Dark (Broken) Fibers
  • Linear End Matches the Entrance Slit of a Spectrometer for Higher Signal Levels
  • Linear End can Generate a Line Illumination Pattern

These fiber bundles contain 7 fibers arranged in a line configuration (linear) at one end and a circular configuration (round) at the other end. Round-to-linear fiber bundle cables are commonly used to increase the coupling efficiency into spectrometers and other optical devices that have an entrance slit. The linear end matches the shape of the entrance slit better than a single fiber or round bundle configuration and therefore increases the amount of light entering the device (see the Bundles vs Cables tab for more information). The linear end can also be used as a line source of light.

Linear Fiber Array Alignment Mark
Click to Enlarge

End Face of a BFL105HS02 Fiber Bundle Behind the 20 µm x 2 mm Entrance Slit of a CCS100 Spectrometer
Linear Fiber Array Alignment Mark
Click for Details

An Engraved Mark on the Connector's Strain Relief Sleeve Indicates the Axis of the Linear Fiber Array

These round-to-linear fiber bundles use SMA905 connectors for compatibility with most spectrometers, including Thorlabs' CCD Spectrometers. They are built using our Ø105 µm or Ø200 µm core multimode fiber with either a high or a low hydroxyl ion (OH) content for use in the 250 - 1200 nm or 400 - 2400 nm range, respectively. For increased durability, these cables incorporate stainless steel protective tubing (FT05SS).

When plugging the linear end of the bundle cable into the spectrometer or another device, the fiber array must be aligned with the entrance slit. For ease of alignment, the fiber array's axis is indicated by a line on the connector sleeve, as shown in the photo to the right. Precise alignment of the bundle and slit is not critical, but misalignment of more than ±5° can cause a reduction in signal strength. In order to maximize signal intensity, we recommend rotating the bundle while monitoring light levels in the spectrometer; once optimized, tighten down the threaded portion of the SMA connector to lock the bundle in place. When using these bundles with our CCD Spectrometers, the fiber array should be oriented vertically.

Each patch cable includes two rubber and two metal protective caps that shield the connector ends from dust and other hazards. Additional CAPM Rubber Fiber Caps and CAPMM Metal-Threaded Fiber Caps for SMA-terminated ends are also offered separately.

Please note that the fibers are not mapped between the two connector ends.

Linear Fiber Bundles vs. Single-Fiber Patch Cables

Entrance Slit Throughput Comparison
Linear fiber bundles provide significantly more light throughput for a slit compared to a standard fiber patch cable containing a single optical fiber. The images below show how light exiting a linear fiber bundle more closely matches the geometry of a spectrometer's entrance slit than that from a standard patch cable. The accompanying graphs show comparison spectra of a SLS201L broadband light source measured with a CCS100 spectrometer when using a linear bundle versus a standard patch cable. As shown in the graphs below, the Ø105 µm core linear bundles provide a maximum power increase of ~500% versus a comparable single-fiber cable, while the Ø200 µm core linear bundles provide a maximum power increase of ~300%.

 

Ø105 µm Core Cable Comparison

7 Fiber Bundle
Linear Fiber Array Alignment Mark
Click to Enlarge
Single-Fiber Cable
Linear Fiber Array Alignment Mark
Click to Enlarge

Left: Light exiting the end face of a BFL105HS02 linear bundle placed behind the 20 µm x 2 mm entrance slit of the CCS100 spectrometer.
Right: Light exiting the end face of an M15L01 fiber patch cable placed behind the 20 µm x 2 mm entrance slit of the CCS100 spectrometer.

Linear Fiber Array Alignment Mark
Click to Enlarge

Comparison of the spectra of an SLS201L broadband light source obtained with a CCS100 spectrometer when using the BFL105HS02 linear fiber bundle versus an M15L01 single-fiber patch cable. The linear bundle provides a ~500% maximum increase in signal strength.

 

Ø200 µm Core Cable Comparison

7 Fiber Bundle
Linear Fiber Array Alignment Mark
Click to Enlarge
Single-Fiber Cable
Linear Fiber Array Alignment Mark
Click to Enlarge

Left: Light exiting the end face of a BFL200HS02 linear bundle placed behind the 20 µm x 2 mm entrance slit of the CCS100 spectrometer. Note: The outer ~2 fibers of the bundle are truncated by an internal Ø1.2 mm aperture adjacent to the slit in the spectrometer.
Right: Light exiting the end face of an M25L01 fiber patch cable placed behind the 20 µm x 2 mm entrance slit of the CCS100 spectrometer.

Linear Fiber Array Alignment Mark
Click to Enlarge

Comparison of the spectra of an SLS201L broadband light source obtained with a CCS100 spectrometer when using the BFL200HS02 linear fiber bundle versus an M25L01 single-fiber patch cable. The linear bundle provides a ~300% maximum increase in signal strength.
Fan Out Cable
Click to Enlarge

Custom 1-to-4 Fan-Out Cable

Sample Fiber Bundle Connector Configurations

Custom Fiber Bundles

Thorlabs is pleased to offer custom straight and fan-out fiber bundles with random or mapped fiber configurations. The table below outlines some of our current bundle production capabilities. We are in the process of expanding these production capabilities, so do not hesitate to inquire if you do not see the bundle that you require described here.

Some custom bundles will require techniques outside of our usual production processes. As a result, we cannot guarantee that we will be able to make a bundle configuration to fit the requirements of your specific application. However, our engineers will be happy to work with you to determine if Thorlabs can produce a fiber bundle that fulfills your needs. To receive a quote, please provide a drawing or draft of your bundle configuration.

Fluoride Fiber Bundle
Click to Enlarge

Custom Silica Fiber Bundle with SMA905 Connectors
Custom Bundle Capabilities
Bundle Configuration Straighta Fan Out (2 or More Legs)a,b
Fiber Types Single Mode Standard (320 to 2100 nm), Ultra-High NA (960 to 1600 nm),
Dispersion Compensating (1500 to 1625 nm), Photosensitive (980 to 1600 nm)
Multimode 0.10 NA Step Index (280 to 750 nm), 0.22 NA Step Index (190 to 2500 nm),
0.39 NA Step Index (300 to 2200 nm), Multimode Graded Index (750 to 1450 nm),
Multimode ZrF4 (285 nm to 4.5 µm)
Tubing Optionsc Thorlabs' Stock Furcation Tubing, Stainless Steel Tubing or Black Heat Shrink Tubing
Connectors SMA905 (Ø2 mm Max Core), FC/PC (Ø1 mm Max Core), Ø1/4" Probe, or
Flat-Cleaved Unterminated Fiber
Length Toleranced ±0.07 m
Active Area Geometrye Round or Linear
Angle Polishing On Special Request. Please Inquire for More Information.
  • In a bundle of 20 fibers, up to one dark fiber is typical (i.e., 95% of the fibers in a bundle will be unbroken). For bundles with more than a single fiber per leg, 5-10% of the fibers are typically dark.
  • These bundles are not intended for applications that require an even power distribution.
  • Tubing selection will be further constrained by fiber type, number of fibers in the bundle, and length. Typically, more than one type of tubing will be used in the custom bundle, particularly for fan-out bundles.
  • The length tolerance applies to bundles ≤2 m. To discuss tolerances on longer bundles, please contact techsupport@thorlabs.com.
  • We cannot guarantee the distance between the fibers or the geometrical structure at the common end of a fan-out bundle.

Our cable engineers are available to help manufacture a bundle for your application.
Please contact techsupport@thorlabs.com with your custom bundle requests.
Please provide a drawing or draft of your custom bundle to expedite quote processing.

Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Undamaged Fiber End
Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Damaged Fiber End

Laser Induced Damage in Silica Optical Fibers

The following tutorial details damage mechanisms in unterminated (bare) and terminated optical fibers, including damage mechanisms at both the air-to-glass interface and within the glass of the optical fiber. Please note that while general rules and scaling relations can be defined, absolute damage thresholds in optical fibers are extremely application dependent and user specific. This tutorial should only be used as a guide to estimate the damage threshold of an optical fiber in a given application. Additionally, all calculations below only apply if all cleaning and use recommendations listed in the last section of this tutorial have been followed. For further discussion about an optical fiber’s power handling abilities within a specific application, contact Thorlabs’ Tech Support.

Damage at the Free Space-to-Fiber Interface

There are several potential damage mechanisms that can occur at the free space-to-fiber interface when coupling light into a fiber. These come into play whether the fiber is used bare or terminated in a connector.

Unterminated Silica Fiber Maximum Power Densities
Type Theoretical Damage Threshold Practical Safe Value
CW
(Average Power)
1 MW/cm2 250 kW/cm2
10 ns Pulsed
(Peak Power)
5 GW/cm2 1 GW/cm2

Unterminated (Bare) Fiber

Damage mechanisms in bare optical fiber can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber (refer to the table to the right). The surface areas and beam diameters involved at the air-to-glass interface are extremely small compared to bulk optics, especially with single mode (SM) fiber, resulting in very small damage thresholds.

The effective area for SM fiber is defined by the mode field diameter (MFD), which is the effective cross-sectional area through which light propagates in the fiber. To achieve good efficiency when coupling into a single mode fiber, a free-space beam of light must match the diameter given by the MDF. Thus, a portion of the light travels through the cladding when matching the MFD. The MFD increases roughly linearly with wavelength, which yields a roughly quadratic increase in damage threshold with wavelength. Additionally, a beam coupled into SM fiber typically has a Gaussian-like profile, resulting in a higher power density at the center of the beam compared with the edges, so a safety margin must be built into the calculated damage threshold value if the calculations assume a uniform density.

Multimode (MM) fiber’s effective area is defined by the core diameter, which is typically far larger than the MFD in SM fiber. Kilowatts of power can be typically coupled into multimode fiber without damage, due to the larger core size and the resulting reduced power density. For MM fibers, a free-space beam of light must be focused down to a spot of roughly 70 - 80% of the MFD to be coupled into the fiber with good efficiency.

It is typically uncommon to use single mode fibers for pulsed applications with high per-pulse powers because the beam needs to be focused down to a very small area for coupling, resulting in a very high power density. It is also uncommon to use SM fiber with ultraviolet light because the MFD becomes extremely small; thus, power handling becomes very low, and coupling becomes very difficult.

Example Calculation
For SM400 single mode fiber operating at 400 nm with CW light, the mode field diameter (MFD) is approximately Ø3 µm. For good coupling efficiency, the light must fill the MFD of the fiber. Thus, the effective diameter is Ø3 µm with an effective area of 7.07 µm2:

Area = πr2 = π(MFD/2)2 = π • 1.52 µm2 = 7.07 µm2

This can be extrapolated to a damage threshold of 17.7 mW. We recommend using the "practical value" maximum power density from the table above to account for a Gaussian power distribution, possible coupling misalignment, and contaminants or imperfections on the fiber end face:

250 kW/cm2 = 2.5 mW/µm2

7.07 µm2 • 2.5 mW/µm2 = 17.7 mW

Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
The limiting factor with optical fiber terminated in a connector is free-space light entering the fiber.

Terminated Fiber

Optical fiber that is terminated in a connector has additional power handling considerations. Fiber is typically terminated by being epoxied into a ceramic or steel ferrule, which forms the interfacing surface of the connector. When light is coupled into the fiber, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, inside the ferrule.

The scattered light propagates into the epoxy that holds the fiber in the ferrule. If the light is intense enough, it can melt the epoxy, causing it to run onto the face of the connector and into the beam path. The epoxy can be burned off, leaving residue on the end of the fiber, which reduces coupling efficiency and increases scattering, causing further damage. The lack of epoxy between the fiber and ferrule can also cause the fiber to be decentered, which reduces the coupling efficiency and further increases scattering and damage.

The power handling of terminated optical fiber scales with wavelength for two reasons. First, the higher per photon energy of short-wavelength light leads to a greater likelihood of scattering, which increases the optical power incident on the epoxy near the end of the connector. Second, shorter-wavelength light is inherently more difficult to couple into SM fiber due to the smaller MFD, as discussed above. The greater likelihood of light not entering the fiber’s core again increases the chance of damaging scattering effects. This second effect is not as common with MM fibers because their larger core sizes allow easier coupling in general, including with short-wavelength light.

Fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. This design feature, commonly used with multimode fiber, allows some of the connector-related damage mechanisms to be avoided. Our high-power multimode fiber patch cables use connectors with this design feature.

Combined Damage Thresholds
As a general guideline, for short-wavelength light at around 400 nm, scattering within connectors typically limits the power handling of optical fiber to about 300 mW. Note that this limit is higher than the limit set by the optical power density at the fiber tip. However, power handing limitations due to connector effects do not diminish as rapidly with wavelength when compared to power density effects. Thus, a terminated fiber’s power handling is "connector-limited" at wavelengths above approximately 600 nm and is "fiber-limited" at lower wavelengths.

The graph to the right shows the power handling limitations imposed by the fiber itself and a surrounding connector. The total power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at that wavelength. The fiber-limited (blue) line is for SM fibers. An equivalent line for multimode fiber would be far above the SM line on the Y-axis. For terminated multimode fibers, the connector-limited (red) line always determines the damage threshold.

Please note that the values in this graph are rough guidelines detailing estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, damage is likely in these applications. The optical fiber should be considered a consumable lab supply if used at power levels above those recommended by Thorlabs.

Damage Within Optical Fibers

In addition to damage mechanisms at the air-to-glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening.

Bend Losses
Bend losses occur when a fiber is bent to a point where light traveling in the core is incident on the core/cladding interface at an angle higher than the critical angle, making total internal reflection impossible.Under these circumstances, light escapes the fiber, often in one localized area. The light escaping the fiber typically has a high power density, which can cause burns to the fiber as well as any surrounding furcation tubing.

A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

Photodarkening
A second damage mechanism within optical fiber, called photodarkening or solarization, typically occurs over time in fibers used with ultraviolet or short-wavelength visible light. The pure silica core of standard multimode optical fiber can transmit ultraviolet light, but the attenuation at these short wavelengths increases with the time exposed to the light. The mechanism that causes photodarkening is largely unknown, but several strategies have been developed to combat it. Fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening. Other dopants, including fluorine, can also reduce photodarkening.

Germanium-doped silica, which is commonly used for the core of single mode fiber for red or IR wavelengths, can experience photodarkening with blue visible light. Thus, pure silica core single mode fibers are typically used with short wavelength visible light. Single mode fibers are typically not used with UV light due to the small MFD at these wavelengths, which makes coupling extremely difficult.

Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV light, and thus, fibers used with these wavelengths should be considered consumables.

Tips for Maximizing an Optical Fiber's Power Handling Capability

With a clear understanding of the power-limiting mechanisms of an optical fiber, strategies can be implemented to increase a fiber’s power handling capability and reduce the risk of damage in a given application. All of the calculations above only apply if the following strategies are implemented.

One of the most important aspects of a fiber’s power-handling capability is the quality of the end face. The end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Additionally, if working with bare fiber, the end of the fiber should have a good quality cleave, and any splices should be of good quality to prevent scattering at interfaces.

The alignment process for coupling light into optical fiber is also important to avoid damage to the fiber. During alignment, before optimum coupling is achieved, light may be easily focused onto parts of the fiber other than the core. If a high power beam is focused on the cladding or other parts of the fiber, scattering can occur, causing damage.

Additionally, terminated fibers should not be plugged in or unplugged while the light source is on, again so that focused beams of light are not incident on fragile parts of the connector, possibly causing damage.

Bend losses, discussed above, can cause localized burning in an optical fiber when a large amount of light escapes the fiber in a small area. Fibers carrying large amounts of light should be secured to a steady surface along their entire length to avoid being disturbed or bent.

Additionally, choosing an appropriate optical fiber for a given application can help to avoid damage. Large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications. They provide good beam quality with a larger MFD, thereby decreasing power densities. Standard single mode fibers are also not generally used for ultraviolet applications or high-peak-power pulsed applications due to the high spatial power densities these applications present.


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Posted Comments:
Poster:mikael.malmstrom
Posted Date:2016-09-02 06:49:27.017
Could the Ø200 µm or preferably the Ø105 µm version fiber-bundle be used to transmit high power YAG pulses? 100-500 mJ 8ns at 20 Hz and 1064 nm?
Poster:tfrisch
Posted Date:2016-09-06 07:25:31.0
Hello, thank you for contacting Thorlabs. I have a few questions about your application. Typically, the coupling efficiency for a coherent source would be best with a single core fiber rather than a bundle. I will reach out to you directly about the details of your application.
Poster:ehenning
Posted Date:2015-11-19 19:08:54.883
Can this fiber bundle be fabricated with the solarization-resistant fiber (e.g. FG200AEA)? We want to resurrect an old device with deuterium-tungsten light source. Thank you in advance.
Poster:besembeson
Posted Date:2015-11-20 01:44:10.0
Response from Bweh at Thorlabs USA: Yes this can. We do such custom bundles. I will follow-up with you regarding a quotation.

Round-to-Linear Fiber Bundles with Ø105 µm Core Multimode Fiber

Item # Hydroxyl
Content
Wavelength
Range
Fiber
Item #
# of
Fibers
Linear End
Fiber Dimensions
Round End
Effective Core
Fiber Core
Diameter
Fiber Cladding
Diameter
NA Minimum Bend Radius
Short Termb Long Termc
BFL105HS02 High OH 250 - 1200 nma FG105UCA 7 0.90 mm x 0.13 mm Ø355 µm 105 µm ± 2% 125 ± 1 µm 0.22d 19 mm 30 mm
BFL105LS02 Low OH 400 - 2400 nm FG105LCA
  • Solarization may occur over time when used below 300 nm.
  • Limited by the stainless steel tubing.
  • Limited by the optical fiber.
  • The NA of the bundle is the same as that of the individual fibers.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available / Ships
BFL105HS02 Support Documentation
BFL105HS02Customer Inspired!Round-to-Linear Bundle, 7 x Ø105 µm Core Fibers, High-OH, SMA, 2 m Long
$240.00
Today
BFL105LS02 Support Documentation
BFL105LS02Customer Inspired!Round-to-Linear Bundle, 7 x Ø105 µm Core Fibers, Low-OH, SMA, 2 m Long
$240.00
Today

Round-to-Linear Fiber Bundles with Ø200 µm Core Multimode Fiber

Item # Hydroxyl
Content
Wavelength
Range
Fiber
Item #
# of
Fibers
Linear End
Fiber Dimensions
Round End
Effective Core
Fiber Core
Diameter
Fiber Cladding
Diameter
NA Minimum Bend Radius
Short Termb Long Termc
BFL200HS02 High OH 250 - 1200 nma FG200UEA 7 1.55 mm x 0.23 mm Ø640 µm 200 µm ± 2% 220 ± 2 µm 0.22d 19 mm 53 mm
BFL200LS02 Low OH 400 - 2400 nm FG200LEA
  • Solarization may occur over time when used below 300 nm.
  • Limited by the stainless steel tubing.
  • Limited by the optical fiber.
  • The NA of the bundle is the same as that of the individual fibers.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available / Ships
BFL200HS02 Support Documentation
BFL200HS02Customer Inspired!Round-to-Linear Bundle, 7 x Ø200 µm Core Fibers, High-OH, SMA, 2 m Long
$270.00
Today
BFL200LS02 Support Documentation
BFL200LS02Customer Inspired!Round-to-Linear Bundle, 7 x Ø200 µm Core Fibers, Low-OH, SMA, 2 m Long
$262.00
3-5 Days
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Last Edited: Mar 21, 2014 Author: Dave Gardner