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Optical Fiber Clamps, PostMountable and SM1Threaded
Ø1" Lens Tube SM1 External SM1F1250 Soft Rubber Pad Securely Clamps Ø250 µm Fiber in Machined VGroove Magnetically Coupled Swing Arm Simplifies Loading/Unloading Fiber 832 (M4) Tap T711250 Please Wait
Features
These general purpose fiber clamps provide easy means for incorporating glass or plastic optical fibers into optomechanical post assemblies or SM1threaded components. The precision Vgroove and rubber pad are designed to clamp onto the buffer of single mode or multimode fibers without damaging them. The combination of a magnet in the main mounting body and magnetic steel setscrew in the clamping arm provide a means to dynamically adjust the clamping force. Move the magnetic setscrew closer to the main body to increase the clamping force. Conversely, adjusting the setscrew away from the magnet decreases the clamping force. This product is often used along with one of our popular Aspheric Lenses to create a fiber output collimator that provides neardiffractionlimited performance. We also offer integrated FiberPort Collimators/Couplers for FiberBench systems. For our Fiber Launch stage systems, we offer bare fiber mounts, chucks, and rotators. Please see our complete collection of Fiber Optomechanics. Insights into Optical FiberScroll down to read about:
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When does NA provide a good estimate of the fiber's acceptance angle?Click to Enlarge Figure 1: Rays incident at angles ≤θ_{max} will be captured by the cores of multimode fiber, since these rays experience total internal reflection at the interface between core and cladding. Click to Enlarge Figure 2: The behavior of the ray at the boundary between the core and cladding, which depends on their refractive indices, determines whether the ray incident on the end face is coupled into the core. The equation for NA can be found using geometry and the two equations noted at the top of this figure. Numerical aperture (NA) provides a good estimate of the maximum acceptance angle for most multimode fibers, as shown in Figure 1. This relationship should not be used for single mode fibers. NA and Acceptance Angle Rays with an angle of incidence ≤θ_{max }are totally internally reflected (TIR) at the boundary between the fiber's core and cladding. As these rays propagate down the fiber, they remain trapped in the core. Rays with angles of incidence larger than θ_{max }refract at the interface between core and cladding, and this light is eventually lost from the fiber. Geometry Defines the Relationship The equations at the top of Figure 2 are expressions of Snell's law and describe the rays' behavior at both interfaces. Note that the simplification sin(90°) = 1 has been used. Only the indices of the core and cladding limit the value of θ_{max }. Angles of Incidence and Fiber Modes Single Mode Fibers are Different Single mode fibers have only one guided mode, the lowest order mode, which is excited by rays with 0° angles of incidence. However, calculating the NA results in a nonzero value. The ray model also does not accurately predict the divergence angles of the light beams successfully coupled into and emitted from single mode fibers. The beam divergence occurs due to diffraction effects, which are not taken into account by the ray model but can be described using the wave optics model. The Gaussian beam propagation model can be used to calculate beam divergence with high accuracy. Date of Last Edit: Jan. 20, 2020
Why is MFD an important coupling parameter for single mode fibers?Click to Enlarge Figure 3 For maximum coupling efficiency into single mode fibers, the light should be an onaxis Gaussian beam with its waist located at the fiber's end face, and the waist diameter should equal the MFD. The beam output by the fiber also resembles a Gaussian with these characteristics. In the case of single mode fibers, the ray optics model and NA are inadequate for determining coupling conditions. The mode intensity (I ) profile across the radius ( ρ ) is illustrated. As light propagates down a single mode fiber, the beam maintains a cross sectional profile that is nearly Gaussian in shape. The mode field diameter (MFD) describes the width of this intensity profile. The better an incident beam matches this intensity profile, the larger the fraction of light coupled into the fiber. An incident Gaussian beam with a beam waist equal to the MFD can achieve particularly high coupling efficiency. Using the MFD as the beam waist in the Gaussian beam propagation model can provide highly accurate incident beam parameters, as well as the output beam's divergence. Determining Coupling Requirements Single mode fibers have one guided mode, and wave optics analysis reveals the mode to be described by a Bessel function. The amplitude profiles of Gaussian and Bessel functions closely resemble one another, which is convenient since using a Gaussian function as a substitute simplifies the modeling the fiber's mode while providing accurate results (Kowalevicz). Figure 3 illustrates the single mode fiber's mode intensity cross section, which the incident light must match in order to couple into the guided mode. The intensity (I ) profile is a nearGaussian function of radial distance ( ρ ). The MFD, which is constant along the fiber's length, is the width measured at an intensity equal to the product of e^{2} and the peak intensity. The MFD encloses ~86% of the beam's power. Since lasers emitting only the lowestorder transverse mode provide Gaussian beams, this laser light can be efficiently coupled into single mode fibers. Coupling Light into the Single Mode Fiber The coupling efficiency will be reduced if the beam waist is a different diameter than the MFD, the crosssectional profile of the beam is distorted or shifted with respect to the modal spot at the end face, and / or if the light is not directed along the fiber's axis. References Date of Last Edit: Feb. 28, 2020
Why is MFD an important coupling parameter for single mode fibers?Significant error can result when the numerical aperture (NA) is used to estimate the cone of light emitted from, or that can be coupled into, a single mode fiber. A better estimate is obtained using the Gaussian beam propagation model to calculate the divergence angle. This model allows the divergence angle to be calculated for whatever beam spot size best suits the application. Since the mode field diameter (MFD) specified for single mode optical fibers encloses ~86% of the beam power, this definition of spot size is often appropriate when collimating light from and focusing light into a single mode fiber. In this case, to a first approximation and when measured in the far field,
is the divergence or acceptance angle (θ_{SM }), in radians. This is half the full angular extent of the beam, it is wavelength
Gaussian Beam Approach Instead, this light resembles and can be modeled as a single Gaussian beam. The emitted light propagates similarly to a Gaussian beam since the guided fiber mode that carried the light has nearGaussian characteristics. The divergence angle of a Gaussian beam can differ substantially from the angle calculated by assuming the light behaves as rays. Using the ray model, the divergence angle would equal sin^{1}(NA). However, the relationship between NA and divergence angle is only valid for highly multimode fibers. Figure 4 illustrates that using the NA to estimate the divergence angle can result in significant error. In this case, the divergence angle was needed for a point on the circle enclosing 86% of the beam's optical power. The intensity of a point on this circle is a factor of 1/e^{2} lower than the peak intensity. The equations to the right of the plot in Figure 4 were used to accurately model the divergence of the beam emitted from the single mode fiber's end face. The values used to complete the calculations, including the fiber's MFD, NA, and operating wavelength are given in the figure's caption. This rate of beam divergence assumes a beam size defined by the 1/e^{2} radius, is nonlinear for distances z < z_{R}, and is approximately linear in the far field (z >> z_{R}). The angles noted on the plot were calculated from each curve's respective slope. When the far field approximation given by Equation (1) is used, the calculated divergence angle is 0.098 radians (5.61°). References Date of Last Edit: Feb. 28, 2020
The T711/M250 postmountable fiber clamp features a precision Vgroove and rubber pad designed to clamp onto the buffer of single mode or multimode fibers without damaging them. With an 832 (M4) tap, this fiber clamp is compatible with Thorlabs' family of Ø1/2" Posts and can be integrated into optomechanical breadboards or optical table assemblies. Click to Enlarge SM1F1250 Mounting a Bare Fiber to a Power Sensor
The SM1F1250 fiber clamp consists of a twopart assembly that allows the centration of the fiber to be changed independently from a lens tube. The Vgroove and rubber pad design provide excellent holding force without damaging the fiber. With external SM1 threads and a locking ring, this fiber clamp is compatible with our SM1threaded products, including threaded kinematic mounts (as shown to right) and Ø1" lens tubes. Alternatively,this mount can be used to secure a bare fiber end so that the output is incident on a power sensor, as seen in the photo to the far right. The outer profile of this clamp will fit through the clear aperture of a Ø1" lens tube, allowing a second lens tube to be screwed on for lighttight applications.  
