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Fixed Focus Collimation Packages: SMA905 Connectors
543 nm, Focal Length: 10.92 mm
Fixed Focus Collimators Contain
F240SMA-A Collimator Mounted in an
These fiber collimation packages are pre-aligned to collimate light from an SMA905-terminated fiber with diffraction-limited performance. Because these fiber collimators have no movable parts, they are compact and easy to integrate into an existing setup. Due to chromatic aberration, the effective focal length (EFL) of the aspheric lens is wavelength dependent. The design wavelength indicates the wavelength of ideal beam divergence (see the Divergence Plots and Calculations tabs for more information). Collimation packages at select design wavelengths are available with different collimated beam diameters. Select a wavelength from the quick links table to the right for details.
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The aspheric lens is factory aligned for collimation at the design wavelength when connected to its specified single mode fiber patch cable. In addition, the aspheric lens has an AR coating on both sides that minimizes surface reflections. For some applications they may also be used at other wavelengths within the AR coating range; please refer to the theoretical divergence plot for each collimator to determine if it is appropriate for your application. The operating temperature range for these collimators is -40 °C to 93 °C. Please note that these collimation packages are not vacuum compatible. Collimation packages with custom alignment wavelengths, operating temperature ranges, or vacuum compatibility are available by contacting Tech Support.
These fiber collimators are intended for use with single mode patch cables but can also be used with small-core, low-NA, multimode fiber optic patch cables. For improved performance, we recommend using these collimators with our AR-coated multimode patch cables. These cables feature an antireflective coating on one fiber end for increased transmission and improved return loss at the fiber-to-free-space interface. Please note performance specifications are guaranteed only when used with single mode fiber.
To mount these fiber collimation packages, we recommend using our collimator mounting adapters, including our kinematic collimator mounting adapters that provide pitch and yaw adjustment. In addition to Ø1/2" and Ø1" unthreaded versions, options are available with external SM05 (0.535"-40), RMS (0.800"-36), or SM1 (1.035"-40) threading. The collimation packages with external M12 x 0.5 threading can be mounted directly into our cage plate CP1M12(/M) to be integrated into our 30 mm cage systems.
The divergence angle (in Degrees)
where D and f must be in the same units.
Divergence Angle Comparison
The divergence angle can be estimated using the formula shown to the right, given that the light emerging from the fiber has a Gaussian intensity profile. This formula works well for single mode fibers but will underestimate the divergence angle for multimode fibers where the light emerging from the fiber has a non-Gaussian intensity profile.
Simulations of the theoretical divergence when using one of our standard collimators at wavelengths other than the design wavelength are shown in the graphs below. For example, if you need to collimate 700 nm light from a fiber into a ~1.5 mm diameter beam, the F240SMA-780 collimator (represented by the '-780' line in the F240 graph below) can be used but will provide a higher divergence than at its design wavelength of 780 nm. Individual theoretical divergence plots and raw data are also available below for each collimator. Please contact Tech Support to request a collimator aligned at a custom wavelength.
Theoretical Approximation of the Divergence Angle
The beam diameter as a function of propagation distance was simulated for each of our collimators at the design wavelength, assuming input from the design fiber and a Gaussian intensity profile. The design wavelength and fiber are specified in the caption for each graph.
Theoretical Approximation of the Divergence Angle
The full-angle beam divergence listed in the specifications tables is the theoretically-calculated value associated with the fiber collimator. This divergence angle is easy to approximate theoretically using the formula below as long as the light emerging from the fiber has a Gaussian intensity profile. Consequently, the formula works well for single mode fibers, but it will underestimate the divergence angle for multimode (MM) fibers since the light emerging from a multimode fiber has a non-Gaussian intensity profile.
The Full Divergence Angle (in degrees) is given by
where MFD is the mode field diameter and f is the focal length of the collimator. (Note: MFD and f must have the same units in this equation).
When the F220FC-A collimator (f ≈ 11.0 mm; not exact since the design wavelength is 543 nm) is used to collimate 515 nm light emerging from a 460HP fiber (MFD = 3.5 µm), the divergence angle is approximately given by
θ ≈ (0.0035 mm / 11.0 mm) x (180 / pi) = 0.018°.
When the beam divergence angle was measured for the F220FC-A collimator, a 460HP fiber was used with 543 nm light. The result was a divergence angle of 0.018°.
Theoretical Approximation of the Output Beam Diameter
The output beam diameter can be approximated from
where λ is the wavelength of light being used, MFD is the mode field diameter, and f is the focal length of the collimator. (Note: MFD and f must have the same units in this equation).
When the F240FC-1550 collimator (f = 8.18 mm) is used with the P1-SMF28E-FC-1 patch cable (MFD = 10.4 µm) and 1550 nm light, the output beam diameter is
d ≈ (4)(0.00155 mm)[8.18 mm / (pi · 0.0104 mm)] = 1.55 mm.
Theoretical Approximation of the Maximum Waist Distance
The maximum waist distance, which is the furthest distance from the lens the waist can be located in order to maintain collimation, may be approximated by
where f is the focal length of the collimator, λ is the wavelength of light used, and MFD is the mode field diameter. (Note: MFD and f must have the same units in this equation).
When the F220FC-532 collimator (f = 10.9 mm) is used with the P1-460B-FC-1 patch cable (MFD ≈ 4.0 µm; calculated approximate value) and 532 nm light, then the maximum waist distance is approximately
zmax ≈ 10.9 mm + [2 · (10.9 mm)2 · 0.000532 mm] / [pi · (0.004 mm)2] = 2526 mm.
Insights into Best Lab Practices
Scroll down to read about a practice we follow when setting up lab equipment.
Click here for more insights into lab practices and equipment.
Fiber Collimators: Tip for Mounting with Adapters
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Figure 1: The components shown above are joined using threaded interfaces. Since unscrewing the fiber connector could unintentionally loosen connections between the other components, Thorlabs suggests applying epoxy to the other two interfaces to immobilize them.
Fiber collimators are often used to introduce light into an optical setup from a fiber coupled source. Thorlabs offers a variety of fiber collimator packages, some only provide a smooth barrel (like the triplet collimators) and others have a metric thread at the end of the barrel (like the asphere collimators).
For both packages, Thorlabs typically suggests the use of an adapter with a nylon tipped set screw that holds the barrel against a two line contact.
Adapters for the external thread are available (AD1109F) that allow the user to thread the fiber collimator into a mount.
However, the use of these adapters results in a stack up of threaded interfaces (threaded fiber connector, threaded collimator, and threaded adapter). As a result, it is possible that unscrewing the fiber connector could inadvertently loosen another thread interface and create an unknown source of instability in the setup.
For this reason, Thorlabs suggests epoxying the threaded fiber collimators into the threaded mounts if that mounting mechanism is preferred.
Figure 1 indicates the assembly order and places to apply the epoxy.
Date of Last Edit: Dec. 4, 2019
Fiber Collimator Selection Guide
Click on the collimator type or photo to view more information about each type of collimator.
Although this collimator is factory aligned for a specific wavelength, it has low divergence angles over a broad range of wavelengths. Therefore, it may be used at other wavelengths within the AR coating range. Please refer to the theoretical divergence plot for this collimator to determine if it is appropriate for your application.
Although this collimator is factory aligned for a specific wavelength, it has a low divergence angle over a broad range of wavelengths. Therefore, it may be used at other wavelengths within the AR coating range. Please refer to the theoretical divergence plot for this collimator to determine if it is appropriate for your application.