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Fiber Holders and Force Sensors for Multi-Axis Flexure Stages
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Basic Structure of a Typical Optical Fiber
This page contains our selection of accessories for multi-axis flexure fiber stages. These include fiber clamps, fiber holders, and axial force sensors. We also manufacture magnetic clamps that hold fibers in our V-groove fiber holders. We also offer bare fiber chucks and a rotator for Fiber Launch platforms, as well as other Fiber Optomechanics.
The V-groove fiber holders on this page are typically used to clamp fibers with the coating intact. The diagram to the right shows the structure of a typical fiber, which consists of a core, a cladding, and a coating (note that the diagram is not to scale). The coating serves to protect the cladding of glass fibers from particulates that may land on the surface of the fiber, causing it to become brittle. Although this layer may also have optical properties that allow it to double as a second cladding, it is still referred to as the coating layer due to the protective properties. The term “buffer” is often used instead of “coating” when the layer surrounding the cladding is composed of Tefzel, as this material bonds differently to the glass cladding than other common coating materials such as acrylate or TECS. Some fibers may also have an additional jacket, or buffer applied on top of the coating layer. To determine whether one of the clamps available below is compatible with the fiber used in your application, you must know the diameter of the outer layer (coating, additional jacket, or buffer layer). This value needs to be within the range of specified fiber diameters for the clamp.
Insights into Optical Fiber
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What factors affect the amount of light coupled into a single mode fiber?
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Figure 2 Conditions which can reduce coupling efficiency into single mode fibers include anything that reduces the similarity of the incident beam to the optical properties of the fiber's guided mode.
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Figure 1 For maximum coupling efficiency into single mode fibers, the light should be an on-axis Gaussian beam with its waist located at the fiber's end face, and the waist diameter should equal the MFD.
Adjusting the incident beam's angle, position, and intensity profile can improve the coupling efficiency of light into a single mode optical fiber. Assuming the fiber's end face is planar and perpendicular to the fiber's long axis, coupling efficiency is optimized for beams meeting the following criteria (Figure 1):
Deviations from these ideal coupling conditions are illustrated in Figure 2.
These beam properties follow from wave optics analysis of a single mode fiber's guided mode (Kowalevicz).
The Light Source can Limit Coupling Efficiency
The coupling efficiency of light from multimode lasers or broadband light sources into the guided mode of a single mode fiber will be poor, even if the light is focused on the core region of the end face. Most of the light from these sources will leak out of the fiber.
The poor coupling efficiency is due to only a fraction of the light in these multimode sources matching the characteristics of the single mode fiber's guided mode. By spatially filtering the light from the source, the amount of light that may be coupled into the fiber's core can be estimated. At best, a single mode fiber will accept only the light in the Gaussian beam output by the filter.
The coupling efficiency of light from a multimode source into a fiber's core can be improved if a multimode fiber is used instead of a single mode fiber.
Date of Last Edit: Jan. 17, 2020
Is the max acceptance angle constant across the core of a multimode fiber?
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Figure 3: Step-index multimode fibers have an index of refraction ( n ) that is constant across the core. Graded-index multimode fibers have an index that varies across the core. Typically the maximum index occurs at the center.
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Figure 5: Graded-index multimode fibers have acceptance angles that vary with radius ( ρ ), since the refractive index of the core varies with radius. The largest acceptance angles typically occur near the center, and the smallest, which approach 0°, occur near the boundary with the cladding
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Figure 4: Step-index multimode fibers accept light incident in the core at angles ≤|θmax | with good coupling efficiency. The maximum acceptance angle is constant across the core's radius ( ρ ). Air is assumed to surround the fiber.
It depends on the type of fiber. A step-index multimode fiber provides the same maximum acceptance angle at every position across the fiber's core. Graded-index multimode fibers, in contrast, accept rays with the largest range of incident angles only at the core's center. The maximum acceptance angle decreases with distance from the center and approaches 0° near the interface with the cladding.
Step-Index Multimode Fiber
Regardless of whether rays are incident near the center or edge of the core, step-index multimode fibers will accept cones of rays spanning angles ±θmax with respect to the fiber's axis.
Graded-Index Multimode Fibers
Cones of rays with angular ranges limited by the core's refractive index profile are illustrated Figure 5. The cone of rays with the largest angular spread
Step-Index or Graded Index?
However, the graded-index profile causes all of the guided modes to have similar propagation velocities, which reduces the modal dispersion of the light beam as it travels in the fiber.
For applications that rely on coupling as much light as possible into the multimode fiber and are less sensitive to modal dispersion, a step-index multimode fiber may be the better choice. If the reverse is true, a graded-index multimode fiber should be considered.
Date of Last Edit: Jan. 2, 2019
These connectorized fiber holders are compatible with the mounting platforms of our multi-axis flexure stages. Each holder is designed to securely hold the center of the connector 12.5 mm (0.49") above the flexure stage platform. The design virtually eliminates fiber tip motion when the fiber cable is moved and significantly improves the repeatability of the positioning of the fiber tip.
This quick-release, adjustable-force fiber clamp has many features that make it our most versatile fiber clamp. The top knob is used to adjust the force that the clamping arm exerts on the fiber. This feature is useful when working with specialty fibers, such as highly birefringent fibers, photonic crystal fibers, or exotic glass fibers containing fluoride or tellurite.
The fiber holder features a grooved central ferrule with six mounting surfaces, which together accept fibers or other cylindrical objects that have an outer diameter between 125 µm to 2.66 mm. Simply rotate the ferrule to align the correct mounting groove with the clamping arm and secure with the included M4 setscrew. It has been designed to allow rapid mounting and dismounting of a variety of photonic components, including bare optical fibers, optical fibers mounted in ceramic ferrules, and multi-channel waveguides.
To determine whether this clamp is suitable for your application, you must know the diameter of the cylindrical object that you wish to secure in the clamp, such as the outer layer (coating or additional jacket or buffer layer) of your fiber or the size of your ferrule. The table to the right specifies the minimum and maximum diameters a cylindrical object can have in order to be securely held by each groove in the HFF001.
For a simpler clamp for coated fiber, please consider the HFF003 Quick-Release Fiber Clamp listed below.
For ease of mounting and experimental flexibility, the HFV001 Standard V-Groove Fiber Holder is an ideal solution for securing bare (coating intact), single mode fibers. The fiber is held in the precision V-groove by two magnetic clamps. The clamps have a special elastomer pad that locally distorts around the fiber to provide a secure but delicate grip. The base of the holder is made of anodized aluminum, and the top plate is made of magnetic stainless steel.
For a longer holder optimized for fiber coupling to smaller devices, please consider the HFV002 Tapered V-Groove Fiber Holder sold below. The HFM001 Magnetic Clamps are also available separately below.
The HFV002 Tapered V-Groove Fiber Holder, which is longer than our HFV001 Fiber Holder sold above, is designed to allow access to smaller devices. When butt-coupling fibers to small waveguide devices (particularly when the device is mounted on a waveguide manipulator), it is often difficult to support and position the end of the fibers close enough to the input ports of the waveguide with standard V-groove holders. The tapered top plate of this mount improves the user's ability to visually observe the fiber-waveguide interface.
The fiber is secured with the two provided HFM001 Magnetic Clamps. These clamps are also available separately below.
This fiber clamp is intended for applications that do not require the extra features offered by the HFF001 Fast-Release Fiber Clamp listed above. The clamping arm is designed to swing approximately 120° from the clamping surface to allow easy loading of the fiber into the V-groove. A rare earth magnet is used to hold the clamping arm in place once it is lowered onto the fiber. A M4 (1.5 mm hex) magnetic setscrew is also embedded in the arm to provide a simple means of adjusting the clamping force.
This strain relief accessory ensures that disturbances to the fiber cable are not translated into unwanted movement of the fiber end face, saving time while setting up and running experiments. It is especially useful for large-diameter fibers. A M2.5
To determine whether this clamp is suitable for your application, the diameter of the outer layer (coating or additional jacket or buffer layer) of the fiber must be known. The table above specifies the minimum and maximum diameters that can be held securely. For an brief summary of fiber terminology, please see the Overview tab above.
These magnet assemblies are used to securely hold fibers to our V-groove style fiber holders. Please note that two of these fiber clamps are included with each V-groove style fiber holder. We offer these magnetic clamps as replacement parts. They are also useful for customers building customized fiber optic assemblies.
The HFA001 Fiber Array Holder uses a single actuator knob to simultaneously move both sides of the clamping mechanism. This two-sided mechanism ensures the device being mounted is centered on the support surface. Three angled clamping surfaces provide a slight downward pressure and stable, three-point contact. The third clamping point is located at the end of a spring-loaded flexure rod that allows the holder to adapt to differently sized optical elements.
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The FSC103 secured onto the AMA034 has the same deck height as our
The FSC103 Axial Force Sensor is a force-sensing cell that can be used to position an optical fiber with respect to another device in the direction of the optical axis. When the fiber makes contact with the device, a force arises that is detected by a strain gauge. This generates an electrical signal that is available for the actuator controller to indicate that the desired position has been reached. The FSC103 comes with two mounting cleats that are used to secure components to the platform.
These cells mount in the groove of our AMA034 and AMA035 Post Assemblies. The AMA034 delivers a deck height of 62.5 mm (optical height of 75 mm), which is the same as our 3-axis NanoMax, RollerBlock, and MicroBlock platforms. It includes two mounting cleats to hold the FSC103. The AMA035 delivers a 112.5 mm deck height (optical height of 125 mm), which matches our NanoMax 600 6-axis stages.
The FSC103 sensor is compatible with the other flexure stage accessories sold on this page. The KSG101 K-Cube™ Strain Gauge Reader is ideal for monitoring the output of the stage's sensor. A PAA622 cable is included with the force sensor for connection to the strain gauge reader.
This force-sensing cell uses the same principle as the FSC103 Axial Force Sensor sold above, but is used to position a bare optical fiber with respect to another device. When the fiber makes contact with the device, a force arises that is detected by a strain gauge. This generates an electrical signal that is available for the actuator controller to indicate that the desired position has been reached.
The fiber is secured with the two provided HFM001 Magnetic Clamps. These clamps are also available separately above.
To lock an accessory in place, rotate the AMA010 cleat so that the flat is facing the stage's groove. Place the accessory into the groove between the cleats, rotate the cleat so that the rounded edge covers the edge of the mount, and lock down the cap screw.
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Accessories mounted in close proximity using the AMA110 Mounting Block.
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Close proximity mounting using the AMA010 Cleat and AMA111 Clamp.
The AMA010(/M) Cleats have a flat milled along one side. To lock an accessory along the center alignment groove, rotate the cleat so that the flat is facing the groove. Place the accessory into the groove between the cleats, rotate the cleat so that the rounded edge covers the edge of the mount, and lock down the 6-32 (M3) locking screw and washer. The cleats can be rotated without needing to remove the locking screws. See the animation to the right for details. The included screws are 5/16" (8 mm) long and are used with a 3/32" (2.5 mm) hex key.
For mounting multiple components in close proximity, we offer the AMA110 mounting blocks. These mounting blocks feature a line of nylon-tipped setscrews to secure components, and allow for easy repositioning and very close mounting. The blocks are secured via two holes and are supplied with either 6-32 or M3 cap screws.