Preliminary EOT 1030-1090nm 6.2 and 9mm Aperture
Polarization Independent Faraday Isolators
For Use with High Average Power Yb:Fiber Lasers
USER’S GUIDE
Thank you for purchasing your Faraday Isolator from EOT. This user’s guide will help
answer questions you may have regarding the safe use and optimal operation of your
Faraday Isolator.
TABLE OF CONTENTS
I. Faraday Isolator Overview…………………………………………………..………..1
II. Safe use of your EOT Faraday Isolator……………………………………….….….4
III. Using your Faraday Isolator………………………………………………….….….6
IV. Warranty Statement and Repair………………………………………………….…9
V. Specifications…………………………………………………………….………….10
I. Faraday Isolator Overview
Your EOT Faraday Isolator is essentially a uni-directional light valve. It is used
to protect a laser source from destabilizing feedback or actual damage from backreflected light. The figures below provide outline drawings for the three models
avaible in the 6-9mm aperture regime. The devices are polarization insensitive
and will transmit and isolate any arbitrary polarization state as well as unpolarized
light. This feature distinguishes these isolators from traditional isolators that
require a polarized input of a specific orientation. The Faraday isolator is a
cylindrically shaped magneto-optic device. Strong Neodymium Iron Boron
permanent magnets are used to generate high (>10,000 Gauss) axially oriented
fields within the magnet housing. The strong longitudinal field causes 45 degrees
of non-reciprocal polarization rotation for propagating light via the Faraday Effect
in the magneto-optic contained within. In the forward direction, the beam is
shifted by approx. 1.4mm in the vertical plane, while maintaining beam pointing,
quality, and optical power. Typical transmission ratios are greater than 97%.
However, in the reverse direction, the beam is split between the two linear
polarizations that exit at an angle of approx. 1 deg, independent of the
polarization state incident. This device is particularly useful in the delivery of
high average power from an unpolarized or randomly polarized source to a highly
reflective work piece where a Faraday isolator is essential to protect a fiber laser
from high power backreflections.
Both the 9mm and 6.2mm aperture isolators produce the same optical offsets and
have the same mechanical outline. The 6.2mm aperture isolator is intended for
use at power levels less than 75W of power. There are two versions of the 9mm
isolator, one rated for 100W (Model No. PI-YB-100) and one rated for 300W
(Model No. PI-YB-300). Units are available with or without a BDO (Beam
Delivery Optic) clamp. All models are shipped with a serial number.
Figure 1: EOT 9mm Aperture Polarization Insensitive Isolator
Model PI-9.0-YB-100 (Also Available with BDO clamp)
Figure 2: EOT 9mm Aperture Polarization Insensitive Isolator with BDO Clamp
Model PI-9.0-YB-300 (Also Available without BDO Clamp)
Figure 3: EOT 6.2mm Aperture Polarization Insensitive Isolator
Model PI-6.2-YB (Also Available with BDO Clamp)
II. Safe use of your EOT Faraday Isolator
The operational hazards presented to operating personnel by the use of your EOT
Faraday Isolator are listed below. An explanation of how the Faraday Isolator is
designed together with procedures users can employ to eliminate or minimize
these hazards is presented in italics.
1.
Danger of sharp ferromagnetic objects being attracted to the residual
permanent magnet fields outside of the Faraday rotator. This hazard is of most
concern if such fields cause flying objects when being handled.
Your EOT Faraday Isolator requires strong internal magnetic fields to operate
properly. Efforts have been made to minimize external fields from the device
while still maintaining a relatively small and cost effective package. The external
fields are designed to be well within Federal safety guidelines which limit
external fields from magnetic devices to be less than 2KGauss at a radial distance
of 5cm from the outside of the device. However, such fields can be sufficient to
attract nearby objects such as knives and razor blades. Should attraction of such
objects begin to occur there would be a strong attractive force directing these
objects towards the interior of the magnet housing. This could be particularly
likely to result in injury (e.g. a cut or puncture wound) if such attraction occurred
while the device was being handled –particularly if a body part of the operating
personnel is near a beam Aperture (i.e. end) of the device.
To minimize the above risks remove all loose ferromagnetic objects from the path
over which your EOT Faraday Isolator is to be moved prior to attempting to move
it. Do not pick up the isolator by its ends (i.e. apertures) where the attractive
magnetic fields are strongest. Always pick the isolator up along its sides.
2.
Failure of operating personnel to observe standard laser safety by sighting
down through the Faraday Rotator when laser radiation is present.
The optical elements within the EOT Faraday Isolators can be transmissive
throughout the visible and near infrared. Consequently it is never appropriate to
view through the device in either the transmission or isolation direction when
laser radiation is present –even with laser safety goggles.
Never sight through your EOT Faraday Isolator in either direction when there
is any possibility of laser radiation being present.
3.
Harm caused by external magnetic fields.
Your EOT Faraday Isolator has been designed to meet existing Federal safety
guidelines for external fields as noted previously. Such guidelines could change
in the future as more information becomes known or reviewed regarding the
interaction between magnetic fields and human health. Since there exist various
claims regarding the potential harmful (and beneficial!) effects of magnetic fields
on humans it is prudent to limit interaction with these fields as much as possible.
Personnel with any magnetically sensitive implants such as pacemakers should
present a copy of this report and consult their medical doctor regarding any
potential complications which could arise from the isolator external magnetic
fields.
4. Other non-health related hazards.
The Faraday Isolator external magnetic fields can draw ferromagnetic objects
into the magnet housing which can damage the optical elements within the device.
Keep a suitable area from
the Faraday Isolator in all directions clear of any loose ferromagnetic objects.
Ideally, use non-magnetic tools (such as stainless steel or titanium) and hardware
to secure the Faraday Isolator. If only ferromagnetic tools are available use
extreme care when using them around the Faraday Isolator. It is always helpful
to bring such tools towards an aperture (or end) radially rather than along the
optical beam path. Doing this ensures that the fields will tend to pull such objects
into the magnet housing endplate rather than into the optical aperture. Where
possible use two hands, one to hold the tool and the other to guide it to the
desired destination.
Another concern regarding external magnetic fields is their effect on magnetically
sensitive devices. The external fields are strong enough to induce a pulse of
current in electronic devices (such as digital watches) that can destroy them. The
fields can also disrupt the operation of other mechanical devices with
ferromagnetic parts in them. Finally, the external fields can erase information
from magnetic strips such as are found on credit and ID cards. Remove all
magnetically sensitive materials and devices such as watches, computer hard
drives and magnetic strips from operators prior to working in the proximity of an
isolator.
5. Use with fiber collimators.
The backreflected light leaves the isolator out of the input of the device at an
angle of +/-1 deg. Therefore, if a fiber collimator is used on the input of the
device, it must be able to withstand high average power that is deposited in the
cladding. A mode-stripping collimator suitable for handling high average power
is necessary to avoid damage to the collimator. Section III describes different
system configurations and provides more information on how the device should
be used in each condition. Please contact EOT for further details.
III. Using your Faraday Isolator
A. Basic operation: The device should be aligned such that in the forward direction
the beam is centered on the input and output apertures. The maximum
recommended 1/e2 beam diameter is 3.1mm for the 6.2mm aperture and 5mm for
the 9mm aperture devices. The device will transmit any arbitrary input
polarization condition. When operating at high average power, particularly above
100 W, thermal lensing effects should be considered. For operating temperatures
outside of room temperature, the isolation ratio of the device will be reduced.
Please refer to the EOT website, www.eotech.com or email [email protected]
for further information.
Figure 4: Forward and Reverse Propogation
Forward or Transmission Operation
Wedge
Faraday
Rotator
Wedge
Displacer
Reverse or Isolation Operation
Wedge
Faraday
Rotator
Wedge
Displacer
B. Safe handling of backreflections:
Appropriate use of the isolator depends on the application of the user. Most users
can be grouped within three categories or system configurations:
1. The laser exits a high power fiber collimator that can withstand high power
incident radiation that is not coupled into the fiber, i.e. capable of so-called
high power cladding mode-stripping. Following transmission through the
laser head, the beam is incident on an EOT polarization insensitive isolator.
The beam then passes through an optical system that focuses the beam on to a
work piece (located at the focal plane of the optical system). An example
setup is displayed in figure 5. In this case, there is no distance requirement
for the separation between the isolator and the laser head. Any back-reflected
light will travel back through the optical system and exit the isolator at +/-1
deg. and get deposited in the laser head, which is rated for high power.
Figure 5: Application Configuration #1
Scan Head
Beam
Expanding
Telescope
Fiber Laser Collimator
Polarization
Insensitive
Faraday Isolator
Focusing
Lens
Work Piece
2. The laser exits a fiber collimator that is not rated for high power radiation that
is not coupled through the fiber. However, the remainder of the optical
system described in condition 1 applies. It is important that the workpiece be
located directly at the focal plane. In this instance, power that is reflected
from the work piece will make its way back through the optical system and
exit the isolator at +/-1 deg. The isolator must be located >355mm from the
laser source if the isolator has an aperture of 6.2mm, or >515mm for the 9mm
aperture model. Figure 6 shows the location of the separation distance and an
aperture beam dump. This is a beam dump that has an aperture located in the
center to allow the forward traveling beam to transmit while blocking the
backward traveling rejected beams (in red). The aperture should be twice the
1/e^2 diameter of the exiting beam and no larger than the aperture of the
Faraday isolator used.
Figure 6: Application Configuration #2
Aperture Beam Dump
Separation Distance
3. The third configuration is that the beam is left collimated and is not used in a
focusing condition and the laser head is not rated for high power. In this
scenario, the isolator should be separated from the laser head with the same
distance requirements described in scenario 2 and an aperture beam dump
should be used as well, with the same stipulations of scenario 2. On the
output end of the isolator, it should be separated from reflective elements by
the same distance as the isolator to laser head separation. For a 6.2mm
aperture, this is >355mm or >515mm for the 9mm aperture model. This is
illustrated in Figure 7. These reflective elements are illustrated as the optical
system on the far left.
Figure 7: Application Configuration #3
Optical System
Separation Distance
Aperture Beam Dump
Separation Distance
IV. Warranty Statement and Repair
EOT warrants its Faraday rotators/isolators to be free of defects in
materials and workmanship for a period of one year after date of shipment. Any
unauthorized modifications made by the customer to EOT’s Faraday
rotators/isolators will render the warranty null and void. If the customer believes
there is a problem with the rotator/isolator, they should immediately contact
EOT’s Sales/Customer department at 231-935-4044 or [email protected].
EOT’s customer service department will either issue an RMA for the device, or
provide the customer with a procedure and authorize the customer do modify the
device. All returns reference the RMA No. on the outside of the shipping
container and should be sent to:
Electro-Optics Technology, Inc.
Attn: Sales/Customer Service
5835 Shugart Lane
Traverse City, MI. 46984 USA
EOT reserves the right to inspect rotators/isolators returned under for
warranty to assess if the problem was caused by a manufacturer defect. If EOT
determines the problem is not due to a manufacturer defect (an example would be
damage to an optical element caused by impact from a loose balldriver or
exceeding the damage threshold of the device), repairs will be done at customer
expense. EOT will always provide a written or verbal quote prior to peroforming
repairs at customer expense. Never attempt to disassemble the magnetic
housing of your Faraday rotator/isolator. Injury could result. Any
indications that an attempt to disassemble the magnetic housing was made will
render the warranty null and void.
V. Specifications:
Specification
Clear Aperture
Max 1/e2 beam dia.
Isolator Type
Operating Temp.
Storage Temp.
Isolation at 23°C
Min. Isolation
Across Op. Temp.
Transmission
Return Loss
Operating Humidity
Max. Power
Handling Range
Focal Length
of Thermal Lens at
Maximum Power
And 1/e2 Beam Diameter
Range of Absorbed Power
Minimum Distance
From Laser Head
(Refer to section III)
PI-6.2-YB
6.2mm
3.1mm
Wedge
5-50°C
-20 to 60°C
>30dB
PI-9.0-YB-100
9.0mm
5.0mm
Wedge
5-50°C
-20 to 60°C
>27dB
PI-9.0-YB-300
9.0mm
5.0mm
Wedge
5-50°C
-20 to 6
>25dB
>20dB
>94%
<-50dB
95%
75W
>18dB
>94%
<-50dB
95%
100W
>18dB
>94%
<-50dB
95%
300W
5.7-9.6m
11.2-18.7m
5.5-6.2m
0.23-0.38W
355mm
0.3-0.5W
516mm
0.9-1.0W
516mm