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Mid-Infrared Optical Fiber
Multimode MIR Bare Fiber
Multimode MIR fibers are ideal for gas phase spectroscopy. Above, light from a ZrF4 patch cable is coupled into a sample chamber. Our Optical Spectrum Analyzers operate from 350 nm to 12.0 µm (i.e., down to 833 cm-1).
Custom Ruggedized MIR Patch Cable
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ZrF4 fiber has flatter attenuation than InF3 fiber in the MIR, while the InF3 fiber is transparent to longer wavelengths. Silica fiber, typically used in patch cables, is not MIR-transparent. For information on run-to-run variations, please see the Graphs tab.
Custom MIR 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 MIR fibers and patch cables include:
Thorlabs manufactures an extensive family of mid-infrared fiber and fiber patch cable products; fibers with many other core sizes and configurations are currently under development. Products available from stock with same-day shipping include single mode and multimode patch cables, as well as bifurcated fiber bundles for transmission applications and reflection/backscatter probes designed for spectroscopy. Specifications for the fibers used in these products are included in the table below. Bare MIR fiber can be requested by contacting Tech Support.
Our IRphotonics® MIR fibers and patch cables, based upon ZBLAN zirconium fluoride (ZrF4) and indium fluoride (InF3) glasses, feature excellent mechanical flexibility, good environmental stability, and high transmission over the 285 nm - 4.5 µm spectral range or 310 nm - 5.5 µm spectral range, respectively. Like the rest of our fiber selection, fluoride fibers can be provided in a range of core diameters, cutoff wavelengths, and numerical apertures, suiting a variety of applications (see the tables below for fiber specifications).
Thorlabs' fluoride fibers are manufactured using a proprietary technique that provides world-class purity, dimensional control, and strength. This technique gives us excellent control over the fibers' optical and mechanical properties, allowing a wide range of configurations to be drawn (see the MIR Manufacturing Tab for more information). Fluoride fibers offer a flat attenuation curve in the MIR wavelength range (see the Graphs tab), aided by an extremely low hydroxyl ion (OH) content. The refractive index of fluoride glass is near that of silica; therefore, optical fibers manufactured using fluoride glass exhibit lower return loss and low Fresnel reflections compared to chalcogenide glass fibers.
Multimode Fluoride Patch Cables
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This plot contains the measured attenuation from five independent draws of the Ø200 µm core ZrF4 fiber. This data is representative of our Ø100 µm, Ø200 µm, and Ø450 µm core fibers.
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This plot contains the measured attenuation from five independent draws of the Ø600 µm core ZrF4 fiber.
MIR Optical Fiber Manufacturing Overview
Testing and Characterization Capabilities
Request testing for Thorlabs or third-party fibers by contacting Tech Support.
Thorlabs' optical fiber draw facility produces ZBLAN zirconium fluoride (ZrF4) and indium fluoride (InF3) fibers in addition to silica fiber. ZrF4 and InF3 fibers feature high transmission over the 300 nm - 4.5 µm and 300 nm - 5.5 µm spectral ranges, respectively. Key fiber properties include no material absorption peaks, excellent mechanical strength, and good environmental stability.
Fluoride fibers are ideal for transmission in the MIR 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 a lower refractive index and lower chromatic dispersion when compared to other fibers that offer transmission in the MIR range, such as chalcogenide glass fibers. Thorlabs' fluoride fibers are ideal for use in applications including MIR spectroscopy, fiber optic sensors, imaging, and fiber lasers.
Fluoride Preform Manufacturing and Fiber Draw Process
After preparation, the preform is loaded into the down-feed unit at the top of the tower and drawn into fiber. Fluoride glass fiber is drawn using preform techniques similar to that used for silica fibers. This technique is well developed and has proven to be very effective in controlling fiber parameters, such as fiber diameter, concentricity, and the refractive index profile. The drawing temperature range of fluoride glasses is lower than that of silica, significantly reducing the cooling time. Thus, our fluoride fiber draw tower is much shorter than our silica fiber towers. The diagram below to the right details the components on our fluoride fiber draw tower.
Thorlabs' team of MIR fiber researchers and engineers has many years of experience in fluoride glass research and development, production, and fiber draw. Our team is divided into two groups: one dedicated to production of catalog items and the second devoted to research and development and custom fiber manufacturing. Their knowledge and expertise, as well as flexible tower configurations and draw schedules, allow us to produce both catalog items as well as custom orders. For details on our custom fluoride fiber capabilities, please contact Tech Support.
Fluoride Fiber Characterization and Testing
Schematic of Our MIR Fiber Draw Tower
Thorlabs Lab Facts: Modifying Beam Profiles with Multimode Fibers
We present laboratory measurements demonstrating how the output beam profile from multimode fiber can be affected by the beam entry angle. In some applications, an alternative beam distribution such as a top hat or donut is desired instead of the inherent Gaussian distribution provided by typical optics. Here we investigated the effect of changing the input angle of a focused laser beam into a multimode fiber patch cable. Focusing the light normal to the fiber face produced a near-Gaussian output beam profile (Figure 1) and increasing the angle resulted in top hat- (Figure 2) and donut-shaped (Figure 3) beam profiles. These results demonstrate how multimode fibers can be used to change the shape of a beam profile.
For our experiment, we used an M38L01 Ø200 µm, 0.39 NA, Step-Index Fiber Patch Cable (Bare Fiber Item # FT200EMT) as the test fiber into which we launched the focused laser beam. The input light was set incident at 0°, 11°, and 15° to the input face of the multimode fiber to create the initial, top hat, and donut profiles, respectively. Each time the angle was changed, the alignment of the input fiber was optimized while the output power was monitored with a power meter to ensure maximum coupling was achieved. Images were then acquired with a 9 second exposure and the shape of the beam profile was evaluated. Note that during the exposure, a 1500 grit diffuser was manually rotated between the coupling optics (before the fiber under test) to reduce the spatial coherence and create a clean output beam profile.
Assuming a ray tracing model, there are two general types of rays that propagate along a multimode fiber: (a) meridional rays, which pass through the central axis of the fiber after each reflection, and (b) skew rays, which never pass through the central axis of the fiber. The figures below illustrate the three basic ray propagation scenarios observed during the experiment. Figures 4 and 6 depict meridional and skew ray propagation through multimode fiber, respectively, and the associated theoretical beam distribution at the fiber output. As illustrated in Figure 6, skew rays propagate in a helical path along the fiber that is tangent to the inner caustic of the path with radius r. Figure 5 depicts the beam propagation and beam distribution from a combination of meridional and skew rays. By changing the input angle of the light launched into a multimode fiber, we were able to modify the proportion of light rays propagating as meridional rays vs. skew rays, and consequently, modify the output from a near-Gaussian distribution (primarily meridional rays, see Figure 1) to a top hat (mixture of meridional and skew rays, see Figure 2) to a donut (primarily skew rays, see Figure 3). The beam profiles shown in Figures 4 through 6 were obtained at a distance of 5 mm from the fiber end face. These results demonstrate the ability to use a standard multimode fiber patch cable as a relatively inexpensive method to modify an input Gaussian profile into a top hat and donut profile with minimal loss. For details on the experimental setup employed and these summarized results, please click here.
Figure 1. Near-Gaussian Beam Profile
Obtained at 0° Input Angle (Normal to Fiber Face)
Figure 3. Donut Beam Profile
Obtained at 15° Input Angle
Figure 2. Top Hat Beam Profile
Obtained at 11° Input Angle