Schäfter+Kirchhoff 60SMF-LSA Series User manual

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1
Laser Beam Couplers Series 60SMF-LSA
The Schäfter+Kirchhoff laser beam couplers launch a laser beam into, or from a polarization-maintaining
single-mode fiber. This document provides assistance in installing and adjusting the laser beam couplers
series 60SMF-LSA. It describes how a fiber cable is attached, and how a fiber coupling is optimized.
1. Before You Start
The laser beam coupler is shipped with a protection cap for the fiber receptacle and with a front cap.
Please remove all the protection caps first and do not use them as beam
dumps (risk of photo contamination).
Notice:
There is a polymer cap on the receptacle. Please perform the following steps in order to remove this cap:
Figure 1:
First, remove the cap from the fiber
receptacle of the laser beam coupler.
Figure 2:
Then, slightly loosen the small pin
screw. Use the screwdriver 9D-12.
Make sure to not loosen it too far, as it
is small and easily lost.
Now, make sure that the connector of the fiber you want to attach matches the receptacle type of the laser
beam coupler:
• Use fibers with APC (8°-polish) connectors for laser beam couplers with an inclined coupling axis
(60SMF-LSA-4).
• Use fibers with PC (0°-polish) connectors for laser beam couplers with a coaxial axis
(60SMF-LSA-0).
The laser beam couplers are compatible to all fiber connectors of type LSA, DIN, AVIO and AVIM.

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• Do not touch either the optical surface of the lens or the fiber end-face.
• If the coupler is not in use, reattach both rear and front protection caps.
Notice:
Refer to the laser instruction manual for all instructions regarding laser
safety!
• Do not stare directly into the laser beam (which can cause permanent
damage to the eyes).
• Do not stare at the reflected beam from reflective objects.
• Do not point the laser beam to other individuals.
Caution!
2. Attaching a Fiber Cable to the Laser Beam Coupler
For attaching a fiber cable to the laser beam coupler perform the following steps:
Figure 3:
To prevent damage to the sensitive
fiber end-face, always insert the fiber
connector`s ferrule Aat an angle, with
the connector key Bproperly aligned
to the receptacle notch C.
Figure 4:
When the ferrule tip is safely located
in the inner cylinder of the receptacle,
align the connector to the receptac-
le axis and carefully introduce the
connector into the laser beam coupler.
Figure 5:
Then, orient the connector key in a
way that it is pressed gently onto
the right-hand side of the receptacle
notch.
A
B
C

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Figure 6:
Gently screw on the connector cap
nut onto the receptacle until it is
finger-tight.
In case of fiber connectors of type AVIM we recommend to fasten the hex
nut of the connector with a torque of 0.3 Nm.
Notice:
Figure 7:
Finally, gently tighten the fiber grub
screw to reduce the free play of the
ferrule in the receptacle.
The free play in between the connector ferrule and receptacle is only a few microns, but necessary for
inserting the ferrule without force.
The tightened grub screw and the right-hand orientation rule for the connector, ensure a high reproducibility
in mode field position and angle, which is especially important for attaching and reattaching polarization-
maintaining fibers reproducibly.

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3. Adjusting the Focus Setting
Focus adjustment (adjustment of the coupling lens in z-direction) is a demanding task and should be
performed preferably using a collimating telescope.
The laser beam coupler is shipped pre-adjusted for the labeled wavelength
and, often, it is not necessary for the customer to readjust the coupling lens
position. This is why you can skip this step in most cases.
Notice:
A fine-adjustment of the focus setting of a laser beam coupler already installed and adjusted is described in
Chapter 10.
To check the collimation setting of the laser beam coupler, couple a radiation source of appropriate wavelength
into the fiber connected to the laser beam coupler. Direct the beam to a target about half a Rayleigh length zR
away:
zRπ∙∅2
beam
=
2 λ∙8
Here λ is the optical wavelength and Øbeam the collimated beam diameter (1/e2level).
Refer to the laser instruction manual for all instructions regarding laser
safety!
• Do not stare directly into the laser beam (which can cause permanent
damage to the eyes).
• Do not stare at the reflected beam from reflective objects.
• Do not point the laser beam to other individuals.
Caution!
When correctly collimated, the laser spot diameter on a target about zR/2 away must have approximately the
same diameter such as the beam directly behind the laser beam coupler. Additionally, make sure that there is
no focused spot between the laser beam coupler and the target at zR/2.
The lens position is adjusted by means of an eccentric key. The eccentric key type 60EX-4 is used for laser
beam couplers with focal lengths ≤11 mm. For laser beam couplers with focal lengths ≥12 mm please use the
eccentric key type 60EX-5.
For adjusting the lens position perform the following steps:
Figure 8:
Loosen the two grub screws fixing the
lens position by means of a screwdriver
type 9D-12.

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Figure 9:
Insert the eccentric key type 60EX-4 or
type 60EX-5 into the large hole.
Figure 10:
Now, adjust the focus setting by ro-
tating the eccentric key. Adjust the
collimation by minimizing the size of the
laser spot on the target about half the
Rayleigh length zRaway.
Figure 11:
Finally, fix the two grub screws in order
to lock the focus setting.

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4. Adapter for the Lateral Adjustment
The laser beam coupler can be connected to your laser system or optical bench by using an adapter flange or
it can be attached directly to a multicube element from Schäfter+Kirchhoff.
It is very important for an efficient coupling that the laser beam passes the aperture of the laser beam coupler
centrally.
Many lasers, such as HeNe lasers or DPSS lasers, have a 1´´ x 1´´ drilling pattern around the beam exit. For the-
se lasers, Schäfter+Kirchhoff offers an adapter flange which can be moved laterally in oversized holes in order
to center the adapter flange to the laser beam (Figure 12). Always attach the flange with the recommended
washers and spring washers.
Figure 12:
DPSS laser with a 1´´ x 1´´ drilling
pattern and attached adapter type
60A19.5-F.
The proper centering of the beam can be tested by attaching an aperture type 13H or a variable iris diaphragm
type 13BL1-13 instead of the laser beam coupler (Figure 13).
For centering the adapter flange, perform the following steps:
Figure 13:
Instead of a 60SMF laser beam
coupler, an aperture 13H is attached.
Measure the power transmitted by this aperture. Maximize the transmitted power by laterally shifting the
adapter. The adjustment is most sensitive if the aperture diameter is chosen to be about 70% of the collimated
beam diameter (1/e2).

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Figure 14:
Laterally shift the adapter in order to
maximize the radiation that is trans-
mitted by the aperture.
Only a coarse alignment is necessary, which can be done by hand (Figure 14), as the positioning accuracy
must only be a fraction (7 - 10 %) of the collimated beam diameter.
Figure 15:
Finally, fix the adapter and remove the
aperture.

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5. Connecting the Laser Beam Coupler to Your System
Before you install the laser beam coupler we recommend to measure the output power of the laser as a
reference for the next steps.
Now, perform the following steps:
Figure 16:
Locate the three radially arranged
tapered pin screws in the adapter
flange (Figure 17) and loosen them
using the hex screwdriver 50HD-15.
Figure 17:
Gently introduce the laser beam
coupler into the vacant aperture. Make
sure that none of the tapered pin
screws are located in the gap.
The ∅19.5 mm system mount of the 60SMF laser beam coupler has a steel
ring. This steel ring has a gap of approx. 2 mm, see Figure 17. Please make
sure that none of the three pin screw is located in the gap of the steel ring.
Otherwise the connection in between the adapter and the laser beam coupler
and therefore the alignment is not long-term stable.
Attention:
If a polarization-maintaining single-mode fiber is attached to the laser beam coupler, the laser beam coupler
needs to be aligned correctly to the polarization axis of the laser source. In this case, locate the flat part of
the connector receptacle of the laser beam coupler and coarsely rotate the laser beam coupler so that the flat
surface is perpendicular to the polarization axis of the source. (Figure 18).
A fine-adjustment of the polarization axis is performed in a later step, see Chapter 11.

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Figure 18:
The small grub screw has to point into
the direction to the polarization axis of
the laser (dashed line).
Figure 19:
Now fix the three tapered pin screws
at the adapter flange. please use the
same torque of about 0.48 Nm for all
three pin screws, respectively.

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6. Tilt Adjustment: Finding a Signal
When coupling into single-mode fibers, the laser beam couplers should produce a diffraction-limited spot at
the fiber end-face that matches the mode field diameter and - at the same time - the divergence of the fiber.
Fiber-coupling with high coupling efficiency can only be achieved when this condition is met. Thus, coupling a
laser beam into a single-mode fiber requires precise adjustment and needs some patience.
Refer to the laser instruction manual for all instructions regarding laser
safety!
• Do not stare directly into the laser beam (which can cause permanent
damage to the eyes).
• Do not stare at the reflected beam from reflective objects.
• Do not point the laser beam to other individuals.
Caution!
Measure the coupled light at the opposite end of the fiber cable using a light detector or power meter. The
detector may have to be adjusted to maximum sensitivity in order to detect a low transmission level possible in
the first few coupling steps.
Perform the following steps:
Figure 20:
Loosen the locking screws
(grub screws) by 2 - 3 turns.
The adjustment screws (hex with head, Figure 21,D) now are turned in a way that each possible adjustment
point is met once. Use hex screwdriver 50HD-15. For example, turn one of the screws just a little. Then, turn
the next adjustment screw in a large range back and forth. Repeat the procedure by turning the first screw a
litter further and the next adjustment screw again in a large range. Go on, until the detector shows a reaction
and the beam is found.
Figure 21:
Coarse adjustment of the laser beam
coupler with the three adjustment
screws D(hex with head).
D

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If no signal at all is found then the signal area can be increased by slightly loosening the threaded collar of the
FC connector and slightly pulling back the fiber connector. This increases the diameter of the laser spot at the
fiber end-face. Finding the first signal becomes easier. Once a signal is found then gently tighten the collar
and the connector again, remembering to locate the connector key positively against the right-hand side of the
groove in the laser beam coupler, as described in Chapter 2.
7. Tilt Adjustment: Adjustment Procedure, Coarse Adjustment
Once a signal is found, tighten one of the three headed screws (Figure 21), so that the signal is maximized.
Adjust the detector sensitivity as required.
Move on to the next headed screw clockwise (or anti-clockwise) and proceed as described before. After two or
three complete cycles of adjusting all headed screws the last screw is tightened and maximum power at fiber
end is achieved. The adjustment should be now at optimum.
The fine-adjustment to provide the maximum coupling efficiency is done by the locking screws in the next
step.
From now on, the headed adjustment screws are not used anymore.
Notice:
8. Tilt Adjustment: Fine-Adjustment and Locking
Now, the locking screws are used to fine-adjust and lock the setting. First, fasten the three locking screws
(grub screws, Figure 22,E) equally with very gentle force until you feel some resistance. Use the hex key
50HD-15. The detector at the fiber end now shows a signal, but it usually differs from the maximum signal seen
before. The three locking screws are now tightened one after another, e.g. in a clockwise direction. Each screw
is tightened so that the power signal is a little beyond the maximum. The procedures is repeated for each
screw until two are three complete cycles of adjustment are completed. The last screw in the last adjustment
round is tightened in a way, so that the detector shows maximum power at the fiber end. Please note, that the
maximum torque for these screws must not exceed 40 Ncm.
Figure 22:
Fine-adjustment and locking of the
laser beam coupler with the three grub
screws E.
9. Checking the Alignment, ‚Thumb Test‘
As a useful check of the optimal alignment, the fiber connector can gently be pressed by hand in different
directions (Figure 23). The coupling efficiency, i.e. the maximum power seen on the detector will change.
However, the induced slight displacement is reversible. Once you stop pressing onto the fiber connector,
the coupling efficiency will be as high as before. When optimally aligned, this slight displacement of the fiber
E

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should always reduce the coupling efficiency. If the coupling efficiency increases by pressing in one direction,
the locking screw shifting the fiber position into the desired direction has to be tightened further, see Figure 23.
Figure 23:
Thumb test: Pressing of the fiber
connector in the shown direction has
the same effect such as fastening the
marked locking screw F.
10. Focussing the Laser Beam Coupler
Focus adjustment (adjustment of the coupling lens in z-direction) is a demanding task and should preferably be
performed using a collimating telescope.
The laser beam coupler is shipped pre-adjusted for the given wavelength
and, often, it is not necessary for the customer to readjust the coupling lens
position. This is why you can skip this step in most cases.
Notice:
A fine-adjustment of the focus setting of a laser beam coupler - if necessary - is performed in the following
steps:
Figure 24:
Slightly loosen the lens by the loo-
sening the two grub screws. Use the
screwdriver type 9D-12.
Figure 25:
Use the eccentric key type 60EX-4 or
60EX-5 for fine-adjusting the focus
setting.

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Figure 26:
Finally, lock the focus setting by
fixing the two grub screws using the
screwdriver type 9D-12.
11. Alignment of the Fiber Polarization Axis
When coupling a laser beam into a polarization-maintaining single-mode fiber, the polarization axis of the
fiber must be aligned with respect of the polarization axis of the source in order to obtain a high polarization
extinction ratio. The polarization axis of the fiber is adjusted by rotating the laser beam coupler. Since both
laser beam coupler and fiber are connected, this means that the fiber polarization axis is rotated with respect
to the polarization axis, as well.
The following steps have to be performed only if the laser beam coupler is
used with a polarization-maintaining fiber cable.
Notice:
In order to adjust for the polarization axis, perform the following steps:
Figure 27:
Slightly loosen the three radially
arranged pin screws at the adapter.
Figure 28:
Now, gently rotate the laser beam
coupler. You can use the eccentric
key type 60EX-4 or 60EX-5 just as as a
lever.
The polarization extinction of the laser radiation transmitted by the fiber cable is measured using a polarization

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analyzer, such as the SK010PA Polarization Analyzer from Schäfter+Kirchhoff.
Figure 29:
Finally, fix the three radially arranged
pin screws at the adapter. Please
consider a comparable torque for the
three screws and the gap of the steel
ring such as described in Chapter 5.

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13. Accessories
Figure 30:
Adapter type 60A19-5-F.
Other adapter types are available.
14. Adjustment Tools
For assembling and adjusting the laser beam couplers series 60SMF you need the following tools:
Figure 31:
Screw driver type 9D-12, hex key
50HD-15, and eccentric key type 60EX-4
or type 60EX-5.
Figure 32:
Aperture 13H and as an alternative the
adjustable iris diaphragm 13BL1-13.

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Copyright
• © Unless expressly authorized, forwarding and duplicating of the document and the utilization
and communication of its contents are not permitted. Violations will entail an obligation to pay
compensation.
• All rights in the event of granting of patents or registration of a utility model.
• Schäfter+Kirchhoff GmbH and the Schäfter+Kirchhoff logo are registered trademarks.
• The specifications are subject to change; the manual is not covered by an update service.
• The system shown on the photos and drawings of this manual may differ in detail from the
system delivered.
Date of issue: 20.05.2021
Schäfter+Kirchhoff GmbH
Kieler Straße 212, 22525 Hamburg, Germany
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Web: http://www.sukhamburg.com