Polaris® Kinematic Collimators

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Figure 1.1  There are two methods for adjusting the angle of our Polaris^® kinematic collimators: using a 5/64" (2.0 mm) hex key in the end of the adjuster, or using the same or smaller hex key through the Ø0.07" (Ø1.8 mm) adjuster side holes

Features

• Machined from Heat-Treated Stainless Steel with Low Coefficient of Thermal Expansion (CTE)
• Pre-Aligned Fiber Collimators with FC/PC Connectors (Three 2.2 mm Wide Key Slots) for Single Mode Patch Cables
• Collimators Aligned for 532, 633, 780, or 850 nm Wavelengths
• Hardened Stainless Steel Ball Contacts with Sapphire Seats for Durability and Smooth Movement
• 8-32 (M4 x 0.7) Threaded Mounting Hole for Post Mounting
• Matched Actuator/Body Pairs Provide Smooth Kinematic Adjustment
• Testing Guarantees ≤2 μrad Deviation after 16 °C Temperature Cycle (See the Test Data Tab for Details)
• Passivated Stainless Steel Surface Ideal for Vacuum and High-Power Laser Cavity Applications
• Custom Mount Configurations and Alignment Wavelengths Available by Contacting Tech Sales

Polaris^® Kinematic, Fixed Focus Collimators combine the high-quality beam output of our fixed focus collimation packages with the remarkable mechanical properties of our Polaris^® mounts, making them the ultimate solution for fiber collimation applications requiring stringent long-term alignment stability. These fiber collimation packages are pre-aligned to collimate light from an FC/PC-terminated fiber with diffraction-limited performance. Due to chromatic aberration, the effective focal length (EFL) of the aspheric lens is wavelength dependent. The alignment wavelength indicates the wavelength of ideal beam divergence (see the Graphs and Calculations tabs for more information).

The aspheric lens is factory aligned for collimation at the alignment 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 (see the Graphs tab). 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 -30 °C to 200 °C.

These fiber collimators are optimized for use with single mode fiber patch cables. For improved performance, we recommend using these collimators with our AR-coated single mode fiber optic 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.

Design
Machined from heat-treated stainless steel, Polaris mounts utilize precision-matched adjusters with ball contacts and sapphire seats to provide smooth kinematic adjustment. As shown in the Test Data tab, these mounts have undergone extensive testing to ensure high-quality performance. The Polaris design addresses all of the common causes of beam misalignment; please refer to the Design Features tab for detailed information.

Post Mounting
The design of the kinematic elements on these mounts prevents the user having to put their hand in front of the collimator when doing a kinematic adjustment or having to uninstall the collimator to mount this onto a post. Unlike the traditional counterbore on our Polaris mounts, this design comes with two 8-32 (M4 x 0.7) threaded holes for mounting on a post; one 8-32 (M4 x 0.7) cap screw is included with each collimator. They also feature Ø2 mm alignment pin holes around each mounting hole, allowing for precision alignment when paired with our counterbored Ø1/2" or Ø1" Posts for Polaris Mounts. They can also be mounted on threaded posts, however caution should be used when using anything other than the included cap screw to ensure that the screw being used does not make contact with the collimator itself.

Cleanroom and Vacuum Compatibility
All Polaris collimators sold on this page are designed to be compatible with cleanroom and vacuum applications. See the Design Features tab for more information.

Alternatives
We offer another line of adjustable collimation packages called FiberPorts that are well suited for a wide range of wavelengths. These are ideal solutions for adjustable, compact fiber couplers. For other collimation and coupling options, please see our Collimator Guide tab or contact Tech Sales.

Polaris^® Kinematic Collimators Test Data

All of the Polaris Kinematic Collimators have undergone extensive testing to ensure high-quality performance. After mounting a PF2F63 collimator to a PLS-C15 (collimator 1) or PLS-P150 (collimator 2) Ø1" stainless steel post, the assembly was secured to a stainless steel optical table in a temperature-controlled environment. The beam output by each collimator was then measured by a position sensing detector. While these collimators are designed for use with the PLS-Cxx series of counterbored posts, they can also be mounted on threaded posts; however, caution should be used when using anything other than the included cap screw to ensure that the screw being used does not make contact with the collimator itself.

Positional Repeatability After Thermal Shock

Purpose: This testing was done to determine how reliably the kinematic collimator returns the beam, without hysteresis, to its initial position. These measurements show that the alignment of the optical system is unaffected by the temperature shock.

Procedure: The temperature of two PF2F63 kinematic collimators, collimator 1 mounted on a PLS-C15 counterbored post and collimator 2 mounted on a PLS-P150 threaded post, was elevated and maintained for a given soak time. Then the temperature of each of the collimators was returned to the starting temperature. The results of these tests are shown in Figures 4.1 - 4.3.

Results: As can be seen in the plots in Figures 4.1 - 4.3, when the Polaris collimators were returned to their initial temperature, the angular position (both pitch and yaw) of the collimators returned to within 2.0 µrad of their initial positions. The performance of each collimator was tested further by subjecting them to repeated temperature change cycles. After each cycle, the collimator's position reliably returned to within 2.0 µrad of its initial position.

For Comparison: To get a 2.0 µrad change in the collimator's position, the 130 TPI adjuster on a Polaris collimator needs to be rotated by only 0.0655° (1/5500 of a turn). A highly skilled operator might be able to make an adjustment as small as 0.3° (1/1200 of a turn), which corresponds to a 9 µrad change in position.

Conclusions: The Polaris kinematic collimators are high-quality, ultra-stable mounts that will reliably return the collimated beam after cycling through a temperature change. As a result, Polaris collimators are ideal for use in applications that require long-term alignment stability.

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Figure 4.1  These plots show the pitch and yaw deviation of collimator 1 (a PF2F63 collimator mounted on a PLS-C15 counterbored post) as it undergoes a heating and cooling cycle.

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Figure 4.2  These plots show the pitch and yaw deviation of collimator 2 (a PF2F63 collimator mounted on a PLS-P150 threaded post) as it undergoes a heating and cooling cycle.

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Figure 4.3  This plot shows the final angular position of two PF2F63 collimators for 10 consecutive thermal shock tests. Collimator 1 is mounted on a PLS-C15 counterbored post while collimator 2 is mounted on a PLS-P150 threaded post. The change in temperature is the difference between the starting temperature and the temperature at the end of the test and includes factors such as the variation in room temperature.

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Figure 5.1  Design Features of the Polaris Kinematic Collimators

Several common factors typically lead to beam misalignment in an optical setup. These include temperature-induced hysteresis of the optic's position, crosstalk, drift, and backlash. Polaris mounts are designed specifically to minimize these misalignment factors and thus provide extremely stable performance. Hours of extensive research, multiple design efforts using sophisticated design tools, and months of rigorous testing went into choosing the best components to provide an ideal solution for experiments requiring ultra-stable performance from a kinematic mount.

Thermal Hysteresis
The temperature in most labs is not constant due to factors such as air conditioning, the number of people in the room, and the operating states of equipment. Thus, it is necessary that all mounts used in an alignment-sensitive optical setup be designed to minimize any thermally induced alignment effects. Thermal effects can be minimized by choosing materials with a low coefficient of thermal expansion (CTE), like stainless steel. However, even mounts made from a material with a low CTE do not typically return the optic to its initial position when the initial temperature is restored. All the critical components of the Polaris kinematic collimators are heat treated prior to assembly since this process removes internal stresses that can cause a temperature-dependent hysteresis. As a result, the alignment of the optical system will be restored when the temperature of the mount is returned to the initial temperature.

Crosstalk
Crosstalk is minimized by carefully controlling the dimensional tolerances of the front and back plates of the mount so that the pitch and yaw actuators are orthogonal. In addition, sapphire seats are used at all three contact points. Standard metal-to-metal actuator contact points will wear down over time. The polished sapphire seats of the Polaris mounts, in conjunction with the hardened stainless steel actuator tips, maintain the integrity of the contact surfaces over time.

Drift and Backlash
In order to minimize the positional drift of the collimator and backlash, it is necessary to limit the amount of play in the adjuster as well as the amount of lubricant used. When an adjustment is made to the actuator, the lubricant will be squeezed out of some spaces and built up in others. This non-equilibrium distribution of lubricant will slowly relax back into an equilibrium state. However, in doing so, this may cause the position of the front plate of the mount to move. The Polaris mounts use adjusters matched to the body or bushings that exceed all industry standards so very little adjuster lubricant is needed. As a result, alignment of the Polaris mounts is extremely stable even after being adjusted (see the Test Data tab for more information). In addition, these adjusters have a smooth feel that allows the user to make small, repeatable adjustments.

Vacuum Compatible and Low Outgassing
All Polaris mounts sold on this page are designed to be compatible with cleanroom and vacuum chamber applications. They are chemically cleaned using the Carpenter AAA passivation method to remove sulfur, iron, and contaminants from the surface. After passivation, they are assembled in a clean environment and then double vacuum bagged to eliminate contamination when transported into a cleanroom.

The sapphire contacts and the collimating lens are each bonded into place using a NASA-approved low outgassing procedure. In addition, DuPont LVP High-Vacuum (Krytox) Grease, an ultra-high vacuum compatible, low outgassing PTFE grease, is applied to the adjusters. These features provide high vacuum compatibility and low outgassing performance. When operating at pressures below 10^-5 Torr, we highly recommend using an appropriate bake out procedure prior to installing the mount in order to minimize contamination caused by outgassing. Please note that the 8-32 and M4 x 0.7 cap screws included with the Polaris mounts are not rated for pressures below 10^-5 Torr. The plastic caps included with each part are not vacuum compatible.

Cleanroom-Compatible Packaging
Each vacuum-compatible Polaris mount is packaged within two vacuum bag layers after assembly in a clean environment. The vacuum-tight fit of the bags stabilizes the mount, limiting translation of the front plate due to shocks during transportation. The tight fit also minimizes rubbing against the bag, preventing the introduction of bag material shavings that would contaminate the clean mount.

In the vacuum-sealing process, moisture-containing air is drawn out of the packaging. This eliminates unwanted reactions on the surface of the mount without the need for desiccant materials. The vacuum bags protect the mount from contamination by air or dust during transport and storage, and the double-vacuum bag configuration allows for a straightforward and effective cleanroom entry procedure. The outer bag can be removed outside of the cleanroom, allowing the contaminant-free inner bag to be placed into a clean container and transferred into the cleanroom while retaining the benefits of vacuum-bag packaging. Inside the cleanroom, the mount can be removed from the inner bag when ready for use.

The calculations below can be used to theoretically approximate the divergence angle, maximum waist distance, and output diameter of a beam through a fiber collimator. For a macro-enabled Excel file with these and other useful calculations when working with fiber collimators, please click on the Fiber Collimator Calculator button. It is recommended to download and open the file in the Excel desktop application, as some features are not supported in the web version of Excel. The file includes calculations for the following parameters:

• Full Divergence Angle
• Maximum Waist Distance
• Output Beam Diameter
• Beam Diameter at a Certain Distance Away
• Fiber Coupling Efficiency

Please note that macros must be enabled to use the Excel file. To enable macros, click the "Enable Content" button in the yellow message bar upon opening the file.

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).

Example:

When the PF2F53(/M) collimator (f ≈ 10.9 mm; not exact since the design wavelength is 532 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 / 10.9 mm) * (180 / 3.1416) = 0.018°.

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: λ, MFD, and f must have the same units in this equation).

Example:

When the PF2F53(/M) 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

z_max = 10.9 mm + [(2 * (10.9 mm)² * 0.000532 mm) / (3.1416 * (0.004 mm)²)] = 2526 mm.

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).

Example:

When the PF2F53(/M) collimator (f = 10.9 mm) is used with the P1-405B-FC-1 patch cable (MFD ≈ 3.4 µm; calculated approximate value) and 532 nm light, the output beam diameter is

d ≈ (4 * 0.000532 mm) * [10.9 mm / (3.1416 * 0.0034 mm)] = 2.17 mm.