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Multimode Fiber Optic Filter/Attenuator Mounts


  • Reflective, Achromatic Design for 250 nm - 450 nm or 450 nm - 20 µm
  • Mount Filters, Cuvettes, or Variable Attenuator in the Optical Path
  • Ideal for Ø200 µm to Ø1000 µm Core Multimode Fibers with ≤0.39 NA
  • Models with FC/PC or SMA Connectors

CFH2-B

Blank Insert

FOFMS

SMA Connectors,
Shown with One Filter
Holder Removed

Two SM1-Threaded (1.035"-40) Filter Holders are Included with Each Mount

Application Idea

Each filter holder can be replaced with a macro or micro cuvette, making the in-line fiber filter mounts ideal for absorption spectroscopy. See the Application tab for details.

CFH2-V

Variable Attenuator Insert

Related Items


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In-Line Filter Mount
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Diagram of the Beam Path Through the In-Line Fiber Filter Mount
In-Line Filter Mount
Click to Enlarge

Ø1" Filters can Easily be
Removed and Replaced

In-Line Filter Mount
Click to Enlarge

FOFMF Mounted to an Optical Table Using a BA2R Magnetic Base

Features

  • Free-Space, Fiber-to-Fiber Coupling System Utilizing Off-Axis Parabolic (OAP) Mirrors
    • UV-Enhanced Aluminum Coating (250 nm - 450 nm) for UV Sources
    • Protected Silver Coating (450 nm - 20 µm) for Broadband Sources
  • FC/PC or SMA Connectors
    • Mounts with Item # Prefix FOFMF Accept Both 2.2 mm Wide Key and 2.0 mm Narrow Key Connectors
    • Mounts with Item # Prefix FOFMS Accept SMA905 Connectors
  • Two CFH2-F Ø1" Filter Holders Included With Each Mount
  • Compatible with Macro and Micro Cuvettes (Not Included, See Specs Tab for Details)
  • Bottom-Located 1/4"-20 (M6) Tap for Mounting to a Post or any Mounting Base
  • Accessories Available Separately Below
    • Replacement Filter Holder Insert
    • Blank Insert
    • Variable Attenuator Insert
    • Light-Tight Cover

Thorlabs' In-Line Fiber Optic Filter Mounts are ideal for fiber-based applications that require light to be spectrally filtered or reduced in intensity. As shown in the diagram to the right, each mount is composed of two removable CFH2-F filter holders within a fixed, free-space fiber-to-fiber coupling system. The system utilizes two off-axis parabolic (OAP) mirrors to collimate the light out of the input fiber and couple it into the output fiber. The use of these mirrors provides high reflectance, high NA, and achromatic performance over the reflection band. For more information about the OAP mirrors, please see the Specs tab. The all-reflective design eliminates phase delays and absorption losses introduced by transmissive optics.

Either filter holder can be replaced with a 12.5 mm x 12.5 mm UV fused quartz cuvette (not included), making these mounts ideal for use in absorption or transmission spectroscopy measurements (see the Application tab for details). The system is light tight when two filter holders are used or with the use of the FOFM-CV light-tight cover.

For custom fiber bulkheads, mirror coatings, or filter holders, please contact Tech Support.

Fiber Compatibility
Thorlabs' In-Line Fiber Optic Filter Mounts are designed to work with multimode patch cables. In general, the mounts cannot be used with single-mode fibers because significant losses are incurred when light is coupled to the narrow core of these fibers in the absence of precision alignment. However, a single mode fiber can be used as the input of the mount provided that the output is connected to a multimode fiber.

Filter Holders, Blank Plates, and Variable Attenuation Insert
Each SM1-threaded (1.035"-40) filter holder can be used to mount various Ø1" filters up to 0.31" (8.0 mm) thick. The precision, spring-loaded, dovetail design of the removable holders ensures reproducible positioning. Two laser-engraved boxes on top of each holder are used for labeling and identification of the mounted optic. Additionally, Ø1/2" filters can be mounted using the SM1A6T Thread Adapter. Extra filter holders are sold separately below. 

If the included filter holder does not suit your application, the CFH2-B Blank Plate is also available separately below. This plate uses the same mounting method as the included CFH2-F and can be machined to suit your specific requirements. Alternatively, it can also be used as a manual shutter. The CFH2-V Variable Attenuation Insert can be inserted in place of one of the filter holders to partially or completely block light from passing. It features an adjuster capable of ±0.01 dB attenuation resolution (when used with Ø200 - Ø1000 µm Core, 0.22 - 0.50 NA fiber) along with the ability to quickly block the aperture via a quick-release mechanism.

Light-Tight Cover
A light-tight cover for the fiber optic filter mounts is available for applications that are particularly sensitive to light. This cover is compatible with cuvettes up to 50 mm (1.96") tall, including the stopper. Please note that the FOFM-CV cover is not compatible with the CFH2-V attenuator insert.

Mounting Options
A bottom-located 1/4"-20 (M6) tap is used to mount the in-line fiber filter mounts onto a Ø1/2" post or post holder base, such as the BA2R Magnetic Base (shown in the image above) or UBP2 Universal Base.

We also offer cuvette holders for applications such as free-space fluorescence measurements. 

Item # FOFMF(/M)-UV FOFMS(/M)-UV FOFMF(/M) FOFMS(/M)
Compatible Connectors FC/PCa SMA905 FC/PCa SMA905
Recommended Input NAb ≤0.39 NA
Insertion Lossc
(No Filters or Cuvettes)
<3.5 dB @ 250 - 350 nmd
<2.0 dB @ 350 - 450 nmd
≤2 dB @ 450 nm - 20 µme
Filter Holders Two Included (CFH2-F)
Compatible Filter Dimensions Ø1" (25.4 mm),
0.31" (8.0 mm) Thick
Compatible Cuvette Dimensionsf 12.5 mm x 12.5 mm
(0.49" x 0.49")
Mount Dimensions (Excluding Filter Holder) 2.00" x 3.31" x 1.60"
(50.8 mm x 84.0 mm x 40.6 mm)
Mount Dimensions (Including Filter Holder) 2.00" x 3.31" x 2.28"
(50.8 mm x 84.0 mm x 57.9 mm)
Tap 1/4"-20 (M6)
Off-Axis Parabolic Mirror Specificationsg
Item # MPD00M9-F01 MPD00M9-P01
Coating UV-Enhanced Aluminum Protected Silver
Reflectance (Average)
Click for Plot
>90%, 250 - 450 nm >97%, 450 nm - 2 µm
>96%, 2 - 20 µm
Off-Axis Angle 90°
Reflected Focal Length 15.0 mm (0.59")
Surface Roughness <100 Å (RMS)
Reflected Wavefront Error  λ/4 at 633 nm
Surface Quality 40-20 Scratch-Dig
  • Compatible with both wide key and narrow key FC/PC connectors.
  • Fiber with NA up to 0.5 can be used but will have increased insertion loss.
  • When a single cuvette is inserted, Fresnel reflections will cause the insertion loss to increase by approximately 0.64 dB. See the Insertion Loss tab for more information. These values for valid for multimode fibers.
  • For Ø200 µm - Ø600 µm core solarization-resistant fiber with ≤0.39 NA in the 250 nm - 450 nm wavelength range.
  • For Ø200 µm - Ø1000 µm core fiber with ≤0.39 NA in the 450 nm - 20 µm wavelength range.
  • Cuvettes are not included, but can be purchased here.
  • Please see our complete presentations for protected silver and UV-enhanced aluminum OAPs for more information.

Beam Diameter After Collimation

In-Line Filter Mount
Click to Enlarge

Diagram of the Beam Path Through the In-Line Fiber Filter Mount

Beam diameter can be calculated very easily using the numerical aperture of the fiber (NA) and the reflected focal length of the OAP. To calculate the beam diameter in the small angle approximation, use the following equation:

Beam Diameter = 2 x NA (Fiber) x Reflected Focal Length

The table below lists the output beam diameter as a function of the reflected focal length of the mirror and the numerical aperture of the fiber. The clear aperture of the OAP should be larger than the desired beam output diameter.

Fiber NA Beam Diameter OAP Clear Aperture
0.10 3 mm >Ø11.43 mm
0.20 6 mm
0.39 11.7 mma
0.50 12.7 mma
  • Limited by the Clear Aperture of the OAP Mirror

Insertion Loss vs Wavelength

The graphs below compare the insertion loss vs wavelength for different fiber types. The shaded region denotes the specified wavelength range and insertion loss of the in-line fiber filter mount. Insertion loss at any given wavelength is also dependent upon the properties of the fiber used and is measured without filters or cuvettes.

Protected Silver at 45 Degree Incident Angle
Click to Enlarge

Excel Spreadsheet with Raw Data
The above plot shows the typical insertion loss versus wavelength for the 450 nm - 250 µm wavelength range in-line fiber filter mounts when MIR multimode fiber patch cables are used with a mode-stripped fiber launch. This can then be compared to the performance of a low-OH silica fiber cable and a theoretical lossless fiber. This data was taken using Thorlabs' SLS202L Broadband Light Source and OSA201C and OSA207C Spectrometer.
Protected Silver at 45 Degree Incident Angle
Click to Enlarge

Excel Spreadsheet with Raw Data
The above plot shows the typical insertion loss versus wavelength for the 250 nm - 450 nm wavelength range in-line fiber filter mount when used with 0.22 NA solarization-resistant patch cables. This data was taken using a broadband light source and CCS200 Spectrometer. Because the data is measured using a spectrometer, the measured insertion loss is similar to that for a mode-stripped fiber launch.
Protected Silver at 45 Degree Incident Angle
Click to Enlarge

Excel Spreadsheet with Raw Data
The above plot compares the typical insertion loss versus wavelength for the 450 nm - 250 µm wavelength range FOFMS and the 250 nm - 450 nm wavelength range FOFMS-UV. Note that the insertion loss increases rapidly when approaching UV wavelengths for the FOFMS with low OH silica fiber. In comparison, the FOFMS-UV, with solarization-resistant fiber, maintains <3.5 dB down to 250 nm.
Protected Silver at 45 Degree Incident Angle
Click to Enlarge

Excel Spreadsheet with Raw Data
The above plot shows the typical insertion loss versus wavelength for the in-line fiber filter mount when used with various 0.22 NA silica fiber patch cables. Note that even for the 50 µm core fiber and fiber bundle, the insertion loss is still around 3 dB. This data was taken using Thorlabs' SLS201L Broadband Light Source and CCS200 Spectrometer. Because the data is measured using a spectrometer, the measured insertion loss is similar to that for a mode-stripped fiber launch.


Insertion Loss at Mode-Stripped and Overfilled Launch Conditions

The graphs below compare the performance of fibers used with the in-line filter mount under different launch conditions. A mode-stripped (70/70) fiber launch condition removes cladding modes that are lost in the in-line filter while an overfilled (>100%) fiber launch condition contains all propagating modes. Because measuring the input and output power using a power meter does not allow for discrimination of these mode types, a mode-stripped launch condition is a better measurement of the actual insertion loss of the in-line fiber filter.

Protected Silver at 45 Degree Incident Angle
Click to Enlarge

Excel Spreadsheet with Raw Data
The above data was taken to show the negative effects of overfilling the input fiber (defined above). In this plot, the pinhole used in the mode-stripped example to the left was removed and the LED output was sent directly into the fiber. The output from the fiber filter holder was then coupled into an S120C Power Meter.
Protected Silver at 45 Degree Incident Angle
Click to Enlarge

Excel Spreadsheet with Raw Data
The above data was taken using a mode-stripped fiber launch (defined above). To achieve these conditions a pinhole with a diameter 70% of the fiber core was placed after the output of an M470F3 Fiber-Coupled LED. The output from the fiber filter holder was then coupled into an S120C Power Meter. This plot shows similar results compared to using a single mode laser source or mandrel wrapping method.
Protected Silver at 45 Degree Incident Angle
Click to Enlarge

Excel Spreadsheet with Raw Data
The above data was taken to show the negative effects of overfilling the input fiber (defined above). In this plot, the pinhole used in the mode-stripped example to the left was removed and the LED output was sent directly into the fiber. The output from the fiber filter holder was then coupled into an S120VC Power Meter.
Protected Silver at 45 Degree Incident Angle
Click to Enlarge

Excel Spreadsheet with Raw Data
The above data was taken using a mode-stripped fiber launch (defined above). To achieve these conditions a pinhole with a diameter 70% of the fiber core was placed after the output of an M385F1 Fiber-Coupled LED. The output from the fiber filter holder was then coupled into an S120VC Power Meter. This plot shows similar results compared to using a single mode laser source or mandrel wrapping method.
Methanol Absorption Spectrum
Click to Enlarge

Absorption Spectrum of Methanol

Absorption Spectroscopy

Absorption spectroscopy is a technique used to characterize the optical properties of a material by measuring the amount of light absorbed by a sample at a given frequency or wavelength. As a broadband light source is sent through a sample, the sample absorbs a fraction of the incident radiation at certain frequencies or wavelengths. These regional decreases in the overall transmission curve describe the material’s unique absorption spectrum. This technique is commonly used in material analysis to gather details about the chemical composition of an unknown substance or the concentration of a molecule in a solution.

Shown to the right is the absorption spectrum of methanol obtained by using Thorlabs' FOFMS In-Line Fiber Optic Filter Mount along with an SLS202L Broadband Light Source, two 0.20 NA, Ø200 µm Core ZrFMIR multimode fiber patch cables, and a CV10Q3500 3500 µL Capacity Quartz Cuvette. Quartz cuvettes are ideal due to their high transmission from the UV to the MIR spectrum. A similar example of this setup can be seen in the image at the top of the page.

As light enters the FOFMF filter system, it is collimated at the first protected silver OAP with a beam diameter of approximately 6 mm (see the Specs tab for details). It then passes through two slots that house a Ø1" optical filter or cuvette. In this case, we loaded a single cuvette with a sample of methanol. Once through the cuvette, the light is couple into the output fiber using the second protected silver OAP mirror and measured using a Fourier Transform Infrared Spectrometer (FTIR).


Posted Comments:
user  (posted 2017-06-06 01:15:07.27)
A motorized version of this would also be very useful.
tfrisch  (posted 2017-06-22 09:50:42.0)
Hello, thank you for your feedback. I have posted it in our internal engineering forum.
cbrideau  (posted 2017-05-03 12:55:52.423)
A version of this that acts as a simple latchable shutter would also be useful for hands-free blocking of the beam.
nbayconich  (posted 2017-05-17 02:37:06.0)
Thank you for contacting Thorlabs. A techsupport representative will reach out to you directly.

In-Line Multimode Fiber Optic Filter Mounts

Key Specificationsa
Item Number FOFMF(/M)-UV FOFMS(/M)-UV FOFMF(/M) FOFMS(/M)
Coating UV-Enhanced Aluminum Protected Silver
Coating Reflectance >90%, 250 - 450 nm >97%, 450 nm - 2 µm
>96%, 2 - 20 µm
Insertion Lossb ≤3.5 dB (250 nm - 350 nm)c
≤2 dB (350 nm - 450 nm)c
≤2 dB (450 - 20 µm)d
Compatible Connectors FC/PCe SMA905 FC/PCe SMA905
Tap 1/4"-20 (M6)
  • See the Specs tab for additional specifications.
  • See the Insertion Loss tab for more information.
  • Specified for Ø200 µm - Ø600 µm core solarization-resistant fiber with ≤0.39 NA.
  • Specified for Ø200 µm - Ø1000 µm core fiber with ≤0.39 NA.
  • Compatible with narrow key and wide key connectors.
  • Mounts for Use from 250 nm - 450 nm or 450 nm - 20 µm
  • Ideal for Ø200 µm to Ø1000 µm Core Multimode Fibers with ≤0.39 NA
  • Compatible with FC/PC or SMA905 Connectors
  • OAP Mirrors with UV-Enhanced Aluminum or Protected Silver Coating

These In-Line Multimode Fiber Optic Filter Mounts contain OAP mirrors for collimating and coupling the beam as it travels through the mount. Mounts with UV-enhanced aluminum coated mirrors are designed for 250 nm to 450 nm, ideal for use with our solarization-resistant fiber patch cables. Those with protected-silver coated mirrors provide broadband performance from 450 nm to 20 µm. These mounts are compatible with our multimode fiber patch cables.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Imperial Price Available
FOFMF-UV Support Documentation
FOFMF-UVNEW!In-Line Multimode Fiber Optic Filter Mount, 250 nm - 450 nm, 1/4"-20 Tap, FC/PC
$515.00
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FOFMS-UV Support Documentation
FOFMS-UVIn-Line Multimode Fiber Optic Filter Mount, 250 nm - 450 nm, 1/4"-20 Tap, SMA
$554.14
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FOFMF Support Documentation
FOFMFCustomer Inspired! In-Line Multimode Fiber Optic Filter Mount, 450 nm - 20 µm, 1/4"-20 Tap, FC/PC
$504.29
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FOFMS Support Documentation
FOFMSCustomer Inspired! In-Line Multimode Fiber Optic Filter Mount, 450 nm - 20 µm, 1/4"-20 Tap, SMA
$544.21
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+1 Qty Docs Part Number - Metric Price Available
FOFMF/M-UV Support Documentation
FOFMF/M-UVNEW!In-Line Multimode Fiber Optic Filter Mount, 250 nm - 450 nm, M6 Tap, FC/PC
$515.00
Today
FOFMS/M-UV Support Documentation
FOFMS/M-UVIn-Line Multimode Fiber Optic Filter Mount, 250 nm - 450 nm, M6 Tap, SMA
$554.14
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FOFMF/M Support Documentation
FOFMF/MCustomer Inspired! In-Line Multimode Fiber Optic Filter Mount, 450 nm - 20 µm, M6 Tap, FC/PC
$504.29
Today
FOFMS/M Support Documentation
FOFMS/MCustomer Inspired! In-Line Multimode Fiber Optic Filter Mount, 450 nm - 20 µm, M6 Tap, SMA
$544.21
Today

Removable Filter Holder and Blank Inserts

  • Extra Removable Filter Holders for the In-Line Fiber Optic Filter Mounts
  • CFH2-F Filter Holder Mounts Ø1" Filters up to 0.31" (8.0 mm) Thick
  • CFH2-B Blank Filter Holder for Custom Designs
  • Light Tight When Used with the Mounts Sold Above

These Removable Filter Holders integrate easily into the In-Line Fiber Optic Filter Mounts sold above. Extra filter holders allow users to replace lost components or quickly swap between filters during an experiment. Two top-located, laser-engraved boxes allow the user to label the filter holder with for easy identification of the mounted optic. Up to two filter holders can be slotted in an in-line filter mount.

The CFH2-F can accommodate Ø1" optics up to 0.31" (8.0 mm) thick and is equipped with SM1 threading (1.035"-40), making it compatible with any of Thorlabs’ SM1-threaded components. In addition, the CFH2-B Blank Plate can be used as a manual shutter or machined to suit your specific requirements.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
CFH2-F Support Documentation
CFH2-FCustomer Inspired! Extra Filter Holder for Ø1" Optics for use with CFH2(/M)
$61.99
Today
CFH2-B Support Documentation
CFH2-BCustomer Inspired! Blank Plate for use with CFH2(/M)
$56.47
Today

Variable Attenuator Insert

app shot
Click to Enlarge
Pushing the adjuster down on the CFH2-V quickly closes the shutter.
  • Attenuates Light with a Vertical Shutter
  • Black Oxide Coating Minimizes Back Reflections
  • 3/16"-120 Adjuster Provides ±0.01 dB Attenuation Resolution (Ø200 - Ø1000 µm Core, 0.22 - 0.50 NA Fiber)
  • Quickly Close Aperture by Pressing Down on Adjuster (See Photo the the Right)
  • Light Tight When Used with the Mounts Sold Above

The CFH2-V is a variable attenuator insert compatible with the In-Line Fiber Optic Filter Mounts sold above. This insert is equipped with a black-oxide-coated variable shutter to partially or fully block light. The shutter moves vertically from the top across the Ø0.54" aperture and is controlled with an 3/16"-120 adjuster. When used with Ø200 - Ø1000 µm, 0.22 - 0.50 NA multimode fiber and a maximum 0.50" beam diameter, the CFH2-V can provide at least 0.01 dB attenuation resolution. Fine adjustments on the adjuster can be performed using the included 5/64" hex key. To quickly close the shutter, press the adjuster down (see photo above); letting go of the adjuster will return the shutter to the set position (within 0.0005").

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
CFH2-V Support Documentation
CFH2-VVariable Attenuator Insert for use with CFH2(/M) and Fiber Optic Filter Mounts
$183.34
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Cover for Fiber Optic Filter Mounts

FOFMF In-Line Fiber Mount Shown With and Without the FOFM-CV Light-Tight Cover Installed.
  • Black Anodized Aluminum Cover for Our In-Line Fiber Filter Mounts
  • Interior Geometry Allows for a Snug, Light-Tight Fit
  • Accomodates Cuvettes up to 50 mm (1.96") Tall, Including the Stopper

The FOFM-CV is a light-tight cover that is compatible with the In-Line Fiber Optic Filter Mounts sold above. The cover protects the cuvettes that are being held from stray and ambient light that would enter from the top of the holder, as shown in the image to the right. Once placed on a filter mount, there will be 1.15" (29.2 mm) between the mount and the lid.

The cuvetter holder is designed to accomate cuvettes up to 50 mm (1.96") tall, including the stopper. Please note that the FOFM-CV is not compatible with the CFH2-V attenuator insert.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
FOFM-CV Support Documentation
FOFM-CVLight-Tight Cover for In-Line Fiber Optic Filter Mounts
$22.00
Today
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