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Fiber Coupling and Spatial Filter Systems


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Fiber Coupling and Spatial Filter Systems

Focusing Optics
Item #Description
C220TME-A400 - 600 nm, f = 11.0 mm, NA = 0.25 Aspheric Lens
C220TME-B600 - 1050 nm, f = 11.0 mm, NA = 0.25 Aspheric Lens
C220TME-C1050 - 1620 nm, f = 11.0 mm, NA = 0.25 Aspheric Lens

Features

  • High-Precision Differential Adjusters Provide Submicron Translation
  • Easy-to-Follow Instructions and Alignment Tools
  • KT110 Fiber Coupler Accepts FC or SMA Fiber Cables
  • KT310 Spatial Filter Directly Compatible with Ø9 mm Aspheric Lens Housings

Fiber Launch Systems

Thorlabs' KT110(/M) fiber launch system couples free-space laser beams into fiber optic cables. This system, which can be used with single or multimode fiber, is equipped with high-precision differential adjusters capable of submicron translation.

This fiber launch system only includes optomechanical components (see the Components tab for a complete list of components). The table to the right lists the recommended optics for focusing collimated light into the output fiber (KT110).

Spatial Filter Systems

Many applications, such as holography, require a beam with uniform intensity. The KT310 spatial filter is ideal for producing a clean, spatially uniform, Gaussian beam. The input of this system consists of a Z-axis translator, which can house a diffraction-limted aspheric lens. This aspheric lens focuses the beam through a pinhole, which can be mounted in the XY translator. The output consists of a Ø1" cage mount, which holds and centers a collimating optic.

This filter system only includes optomechanical components (see the Components tab for a complete list of components). The aspheric lens, collimating optics, and pinhole must be purchased separately. Please refer to the Tutorial tab for more information on choosing the appropriate optics and pinhole for your application.

Principles of Spatial Filters

For many applications, such as holography, spatial intensity variations in the laser beam are unacceptable. Our KT310 spatial filter system is ideal for producing a clean Gaussian beam.

The input Gaussian beam has spatially varying intensity noise. When a beam is focused by an aspheric lens, the input beam is transformed into a central Guassian spot (on the optical axis) and side fringes, which represent the unwanted noise. The radial position of the side fringes is proportional to the spatial frequency of the noise. By centering a pinhole on the central Gaussian spot, the clean portion of the beam can pass while the fringes are blocked (see figure below):

Spatial Filter System Ray Diagram

Figure 1 - Spatial Filter System

The diffraction-limited spot size at the 99% contour is given by

Spot Size

Diffraction-Limited Spot Size


where λ = wavelength, f = focal length, and r = input beam 1/e2 radius. A pinhole that is approximately 30% larger is chosen to allow the focused Gaussian spot to pass while blocking the noise fringes that are shifted off axis.

Choosing the Correct Optics and Pinhole for Your Spatial Filter System

The correct optics and pinhole for your application depend on the input wavelength, source beam diameter, and desired exit beam diameter.

For example, suppose that you are using a 650 nm diode laser source that has a diameter (1/e2) of 1.2 mm and want your beam exiting the spatial filter system to be about 4.4 mm in diameter. Based on these parameters, the C560TME-B mounted aspheric lens would be an appropriate choice for the input side of spatial filter system because it is designed for use at 650 nm, and its clear aperture measures 5.1 mm, which is large enough to accommodate the entire diameter of the laser source.

The equation for diffraction limited spot size at the 99% contour is given above, and for this example, λ = (650 x 10-9 m), f = 13.86 mm for the C560TM-B, and r = 0.6 mm. Substitution yields

Spot Size Example

Diffraction-Limited Spot Size (650 nm source, Ø1.2 mm beam)


The pinhole should be chosen so that it is approximately 30% larger than D. If the pinhole is too small, the beam will be clipped, but if it is too large, more than the TEM00 mode will get through the pinhole. Therefore, for this example, the pinhole should ideally be 19.5 microns. Hence, we would recommend the mounted pinhole P20S, which has a pinhole size of 20 μm. Parameters that can be changed to alter the beam waist diameter, and thus the pinhole size required, include changing the input beam diameter and focal length of focusing lens. Decreasing the input beam diameter will increase the beam waist diameter. Using a longer focal length focusing lens will also increase the beam waist diameter.

Finally, we need to choose the optic on the output side of the spatial filter so that the collimated beam's diameter is the desired 4.4 mm. To determine the correct focal length for the lens, consider the following diagram, which is not drawn to scale. From the triangle on the left-hand side, the angle is determined to be approximately 2.48o. Using this same angle for the triangle on the right-hand side, the focal length for the plano-convex lens should be approximately
50 mm.

Spatial Filter Diagram

For this focal length, we recommend the LA1131-B plano-convex lens [with f = 50 mm at the design wavelength (λ = 633 nm), this is still a good approximation for f at the source wavelength (λ = 650 nm)].

Note: The beam expansion equals the focal length of the output side divided by the focal length of the input side.

For optimal performance, a large-diameter aspheric lens can be used in place of a plano-convex lens if the necessary focal length on the output side is 20 mm (see AL2520-A, AL2520-B, AL2520-C). These lenses are 25 mm in diameter and can be held in place using the supplied SM1RR Retaining Ring.

KT100KT110/MDescriptionQty.
CP02CP02/MSM1-Threaded 30 mm Cage Plate1
CPA130 mm Cage System Alignment Plate1
E09RMSExtended RMS to M9 x 0.5 Adapter1
ER2Cage Assembly Rod, 2" Long4
ER3Cage Assembly Rod, 3" Long4
MA2MA2/MØ1.5" Post Mounting Adapter1
P1.5P30/MØ1.5" Mounting Post1
PB1Mounting Post Base1
SM1A3Adapter with External SM1 Threads and Internal RMS Threads1
SM1D12SM1 Lever-Actuated Iris Diaphragm1
SM1FCFC/PC Fiber Adapter Plate1
SM1RRSM1 Retaining Ring3
SM1ZZ-Axis Translation Mount1
SPW301Spanner Wrench for a M9 x 0.5 Optics Housing1
SPW801Adjustable Spanner Wrench1
ST1XY-DST1XY-D/MXY Translator with Differential Drives1
SM1SMASMA Fiber Adapter Plate1

KT310KT310/MDescriptionQty.
CPA130 mm Cage System Alignment Plate1
E09RMSExtended RMS to M9 x 0.5 Adapter1
ER2Cage Assembly Rod, 2" Long8
MA2MA2/MØ1.5" Post Mounting Adapter1
P2P50/MØ1.5" Mounting Post1
PB1Mounting Post Base1
SM1L03SM1 Lens Tube, 0.3" Thread Depth1
SM1A3Adapter with External SM1 Threads and Internal RMS Threads1
SM1RRSM1 Retaining Ring3
SM1ZZ-Axis Translation Mount1
SPT1SPT1/MCoarse ±1 mm XY Slip Plate Positioner1
SPW301Spanner Wrench for a M9 x 0.5 Optics Housing1
SPW801Adjustable Spanner Wrench1
ST1XY-AST1XY-A/MXY Translator with 100 TPI Drives1
Basic Square Cage Plate
An example of the standard cage
plate measurements determining
cage system compatibility.

Cage System Overview

The Cage Assembly System provides a convenient way to construct large optomechanical systems with an established line of precision-machined building blocks designed for high flexibility and accurate alignment.

16 mm, 30 mm, and 60 mm Cage System Standards

Thorlabs offers three standards defined by the center-to-center spacing of the cage assembly rods (see image to right). The 16 mm cage, 30 mm cage, and 60 mm cage standards are designed to accomodate Ø1/2", Ø1", and Ø2" optics, respectively. Specialized cage plates that allow smaller optics to be directly inserted into our larger cage systems are also available. All locking setscrews used in these cage plates are standard 4-40 setscrews, which use a 0.05" hex key.

Standard Threads

The flexibility of our Cage Assembly System stems from well-defined mounting and thread standards designed to directly interface with a wide range of specialized products. The three most prevalent thread standards are our SM05 Series (0.535"-40 thread), SM1 Series (1.035"-40 thread), and SM2 Series (2.035"-40 thread), all of which were defined to house the industry's most common optic sizes. Essential building blocks, such as our popular lens tubes, directly interface to these standards.

Standard Cage System Measurements
Cage System16 mm30 mm60 mm
Thread SeriesSM05SM1SM2
Rod to Rod Spacing16 mm (0.63")30 mm (1.18")60 mm (2.36")
Total Length25 mm (0.98")41 mm (1.60")71.1 mm (2.8")
Cage Components
Cage Rods16 mmThese rods are used to connect cage plates, optic mounts, and other components in the cage system. The SR Series Cage Rods are compatible with our 16 mm cage systems, while the 30 mm and 60 mm cage systems use ER Series Cage Rods.
30 mm
60 mm
Cage Plates16 mmThese serve as the basic building blocks for a cage system. They may have SM-threaded central bores, smooth bores sized for industry standard optics or to accommodate the outer profile of our SM Series Lens Tubes, or specialized bores for other components such as our FiberPorts.
30 mm
60 mm
Optic Mounts16 mmThorlabs offers fixed, kinematic, rotation, and translation mounts specifically designed for our Cage Systems.
30 mm
60 mm
Cage Cubes16 mmThese cubes are useful for housing larger optical components, such as prisms or mirrors, or optics that need to sit at an angle to the beam path, such as beamsplitters. Our cage cubes are available empty or with pre-mounted optics.
30 mm
60 mm
Post and Breadboard Mounts and AdaptersMounting options for cage systems can be found on our Cage System Construction pages. Cage Systems can be mounted either parallel or perpendicular to the table surface.
Size AdaptersCage System Size Adapters can be used to integrate components from different cage system and threading standards.
Specialized ComponentsThorlabs also produces specialized cage components, such as Filter Wheels, a HeNe Laser Mount, and a FiberPort Cage Plate Adapter, allowing a wide range of our products to be integrated into cage-mounted optical systems. Explore our Cage Systems Visual Navigation Guide to see the full range of Thorlabs' cage components.
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Posted Comments:
Poster: dreamangelfly
Posted Date: 2013-02-01 00:53:58.73
Do you have a complete list of the components in KT110/M? I wonder if you have both SMA and FC adapters in the package? The sales told us only one of them is included. However, the picture in the website show both. Thanks.
Poster: clairekthomas
Posted Date: 2012-10-28 16:21:17.34
I have a very large (r~5mm), non-gaussian beam of CW 980nm light that is collimated from a 6 Watt diode. I want to clean up the beam as best I can before sending it through an AO and fiber. I think that the KT310 is what I need, but I'd like to use a long focal length asphere (e.g. 50mm), so that I can put my large beam in and still have a pretty large diffraction limit (~20microns). This way I can use the high power 25micron pinhole (P25C) and stay below the intensity damage threshold (any smaller and I think the intensity would be too high.) Will I be able to put a large asphere into the input mount, or is there another solution I should be pursuing? Best, Claire Thomas UC Berkeley Physics
Poster: tcohen
Posted Date: 2012-09-20 12:12:00.0
Response from Tim at Thorlabs to Stefan: It seems you may be viewing an Airy Disk which could indicate the focal length and pinhole are not appropriately matched to block the fringes. I will contact you to get more information on the components you are using.
Poster: Greg
Posted Date: 2011-01-13 10:58:51.0
A response from Greg at Thorlabs to naveedbinqasim: I apologize for any issues you are having with the KT310. An Applications Engineer has been put in contact with you to help optimize the performance of your spatial filter.
Poster: naveedbinqasim
Posted Date: 2010-12-31 06:49:04.0
we bought spatial filter system KT-310 from you. but beam after passing through the pinhiole doesnt produce clean beam.i ve alligned KT-310 very precisely,but the output is distorted. Naveed Bin Qasim Research Assistant SSE Physics Lahore University of Management Sciences.
Poster: technicalmarketing
Posted Date: 2007-11-26 09:40:51.0
In response to mthiels post, we have updated the web presentation to included recommended optics/pinhole parts for use with the KT310. In addition, there is now a "tutorial tab" that explains how to choose optics given an incident wavelength and beam diameter. Thank you for your feedback. we hope this additional information is helpful when it comes to choosing optics for use with your spatial filter.
Poster: mthiel
Posted Date: 2007-11-13 05:27:02.0
Regarding KT310/M: In the Katalog Vol18 there were some Recommended Parts (optics): 1. Lens Item #c220tme 2. Lens Item #la1131 3. Lens Item #p25s Now, where it is missing in the new catalog V19 and Web - customer (aspecially those who got no clue what optics to use) start discussions with tech support about optics. -So the recommended Parts would save some time for techies.
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Free-Space to Fiber Coupler
  • Accepts FC or SMA Fiber Cables
  • Accepts Microscope Objectives
  • High-Precision Differential Adjusters Provide Submicron Translation
  • Easy-to-Follow Instructions and Alignment Tools

The KT110 fiber launch system is designed to couple free-space laser beams into fiber optic cables terminated with either FC or SMA connectors. This fiber launch system is directly compatible with many of our diffraction-limited aspheres, which offer superior performance when compared to traditional microscope objectives. The C230TME aspheric lens, which has an equivalent microscope maginification of 35X, is an ideal choice for most free-space coupling applications.

Note: The individual optomechanical parts used in the KT110 assembly are imperial or universal, while the parts used in the KT110/M assembly are metric or universal.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal/Imperial Price Available / Ships
KT110 Support Documentation
KT110 Fiber Launch System: Free Space (Coupling Optic Sold Separately)
$1,041.75
Today
+1 Qty Docs Part Number - Metric Price Available / Ships
KT110/M Support Documentation
KT110/M Fiber Launch System: Free Space, Metric (Coupling Optic Sold Separately)
$1,041.75
Today
Spatial Filter System
  • Produces a Clean Gaussian Beam
  • Wide Assortment of Compatible Pinholes, Aspheric Lenses, and Collimating Lenses
  • Pre-Assembled System of Stock Catalog Components

The KT310 spatial filter is ideal for producing a "clean" Gaussian beam. The input side consists of a Z-translator that will hold a diffraction-limited aspheric lens to focus the laser through a pinhole. For easy adjustment, the pinhole should be mounted in the XY translator. Threaded holes on the output side are provided for mounting and centering a Ø1" collimating optic. Please see the Tutorial tab for more information on selecting the appropriate optics and pinhole for your application.

Note: The individual optomechanical parts used in the KT310 assembly are imperial or universal while the parts used in the KT310/M assembly are metric or universal.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal/Imperial Price Available / Ships
KT310 Support Documentation
KT310 Spatial Filter System (Optics & Pinhole Sold Separately)
$853.71
Today
+1 Qty Docs Part Number - Metric Price Available / Ships
KT310/M Support Documentation
KT310/M Spatial Filter System, Metric (Optics & Pinhole Sold Separately)
$853.71
Today
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