Schäfter+Kirchhoff 60SMF-LSA Series User manual

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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