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Sales & Tech Support: 231-935-4044

Pavos Ultra Series 1010 nm - 1080 nm Faraday Rotators & Optical Isolators - Large Aperture (>5 mm) User Guide

Pavos Ultra Series 1010 nm - 1080 nm High Power
Faraday Rotators & Optical Isolators - Large Aperture (>5 mm)

USER GUIDE

Thank you for purchasing your Pavos Ultra Series Faraday Rotator or Optical Isolator from EOT.  This user’s guide will help answer questions you may have regarding the safe use and optimal operation of your Faraday Rotator or Optical Isolator.

TABLE OF CONTENTS

I. Pavos Ultra Series Optical Isolator Overview

II. Safe use of your Pavos Ultra Series Optical Isolator

III. The Pavos Ultra Series 1010 nm - 1080 nm Optical Isolator

IV. Using your Pavos Ultra Series Optical Isolator

V. Tuning your Pavos Ultra Series Optical Isolator

VI. Diagrams: Pavos Ultra Series 1010 nm - 1080 nm Faraday Rotator / Optical Isolator

VII. Warranty Statement and Repair

VIII. Specifications: Pavos Ultra Series 1010 nm - 1080 nm Faraday Rotators and Optical Isolators

I. Pavos Ultra Series Optical Isolator Overview

Your Pavos Ultra Series Optical Isolator is essentially a unidirectional light valve.  It is used to protect a laser source from destabilizing feedback or actual damage from back-reflected light.  Figure 1 below identifies the main elements of your Optical Isolator.

The Optical 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 terbium gallium garnet (“TGG”) crystal located within the magnet housing.  In operation the magnet housing is sandwiched between input and output polarizers that have their transmission axis oriented 45 degrees relative to each other to account for the 45 degrees of Faraday rotation in the TGG crystal in the forward (transmission) direction.  In the reverse (isolation) direction the non-reciprocal Faraday rotation and the 45 degree polarizer transmission axis angle add so that the polarization transmitted by the output polarizer is rejected at the input polarizer.

Your Pavos Ultra Series Optical Isolator is labeled with a serial number on the baseplate of the device.

II. Safe use of your Pavos Ultra Series Optical Isolator

The operational hazards presented to operating personnel by the use of your Pavos Ultra Series Optical Isolator are listed below with an explanation of how the Optical Isolator is designed with procedures users can employ to eliminate or minimize these hazards.

1.  Danger of sharp ferromagnetic objects being attracted to the residual permanent magnet fields outside of the ISP Rotator.  This hazard is of most concern if such fields cause flying objects when being handled.

Your Pavos Ultra Series Optical 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 2 K Gauss 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 Pavos Ultra Series Optical Isolator is to be moved prior to attempting to move it.  Do not pick up the optical isolator by its ends (i.e. apertures) where the attractive magnetic fields are strongest.  Always pick the isolator up along its sides.

2. Never attempt to disassemble the magnetic housing of your Faraday Rotator/Isolator. Serious injury could result.

3. Reflection of rejected beams from the input and output polarizer.

The polarizer covers have been rotated at the factory to block all beams rejected from the polarizers.  In the event that your Optical Isolator will be used with transmitted average powers in excess of 25 W, or will block backward propagating light in excess of 0.5 W average power, these polarizer covers must be rotated to allow rejected beams to exit through the escape ports (see Figure 1) onto user-supplied beam dumps. These rejected beams can represent a hazard to users and/or their colleagues.  Care must be exercised to ensure that all rejected beams (both transmission and isolation directions) are accounted for and terminated into functional beam dumps.  Wherever possible keep the strongest rejected beams in the horizontal plane of the table or otherwise safest direction (typically down into the table).  Always wear laser safety glasses or goggles consistent with all laser frequencies and power levels present.  See Sections III and IV for further details.

4. Failure of operating personnel to observe standard laser safety by sighting down through the ISP Rotator when laser radiation is present.

The optical elements within the Pavos Ultra Series Optical 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 Optical Isolator in either direction when there is any possibility of laser radiation being present.

5. Harm caused by external magnetic fields.

Your Pavos Ultra Series Optical 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 various claims exist 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.

6. Other non-health related hazards.

The Optical 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 Optical 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 Optical Isolator.  If only ferromagnetic tools are available use extreme care when using them around the Optical 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 those 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 optical isolator.

III. The Pavos Ultra Series 1010 nm - 1080 nm Optical Isolator

With the polarizer covers off, a polarizing beamsplitter cube (“PBSC”) can be seen at each end of the device.  The inscribed arrow on the baseplate shows the transmission direction.  The output PBSC is seen to be oriented with its transmission axis rotated 45 degrees relative to the input PBSC.  The input polarization shown is horizontal.  The central magnet housing together with the TGG crystal residing in its center forms a Faraday Rotator.  The Faraday Rotator rotates the input horizontal transmission axis by 45 degrees so that transmitted light has a polarization aligned with the output transmission axis.  The input and output PBSCs work in conjunction with the central Faraday Rotator to form an Optical Isolator as described previously in Section I. Figures 3 and 4 below show input views of a Pavos Ultra Series 1010 nm - 1080 nm Optical Isolator.

Figure 3 shows a device aligned for a horizontal input polarization.  The “dot” superimposed on one of the polarization transmission axis scribe lines on the endplate of the input polarizer mount denotes the side of the input PBSC to which backward propagating (i.e. isolation direction) light will get directed.  In the case shown this direction is to the right.

Figure 4 shows a device aligned for a vertical input polarization.  Since the “dot” is on the bottom side of the polarizer, backward propagating light will get directed downward as shown.

Figures 5 and 6 below show output views of a Pavos Ultra Series 1010 nm - 1080 nm Optical Isolator.  In both cases, the Optical Isolators have been adjusted for horizontal input polarization.

Figure 5 shows an Optical Isolator configured for negative Z rotation.  Coarse wavelength tuning adjustment can be made by aligning the polarization transmission scribe lines to the appropriate scribe line on the polarizer clamp ring.  When the polarization transmission axis scribe line is aligned with the line labeled “1030” the device is nominally adjusted to operate optimally at 1030 nm.  If the polarization transmission axis scribe line is aligned with the line labeled “A” then the device is nominally adjusted to operate optimally at 1010 nm.  If the polarization transmission axis scribe line is aligned with the line labeled “B” then the device is nominally adjusted to operate optimally at 1045 nm.  Again, the “dot” on the output polarizer mount denotes the side of the output PBSC to which backward propagating (i.e. isolation direction) light will get directed.  In the case shown this direction is upward and to the left.

Figure 6 shows an Optical Isolator configured for positive Z rotation.  Again, when the polarization transmission axis scribe line is aligned with the line labeled “1030” the device is nominally adjusted to operate optimally at 1030 nm.  However, if the polarization transmission axis scribe line is aligned with the line labeled “A” then the device is nominally adjusted to operate optimally at 1045 nm.  Conversely, if the polarization transmission axis scribe line is aligned with the line labeled “B” then the device is nominally adjusted to operate optimally at 1010 nm.  Again, the “dot” denotes the side of the output PBSC to which backward propagating (i.e. isolation direction) light will get directed.  In the case shown this direction is upward and to the right.

Pavos Ultra Series Optical Isolators are factory aligned as per the model number specified in a purchase order.  The information below shows the range for each field in the model number together with the definition of the coordinate axis system which defines the Z rotation sense.

Numbering Fields and Coordinate System for Pavos Ultra Series 1010 nm - 1080 nm Optical Isolator

General Format for Numbering Field:  AA-B-CCCC-DDD-EEE

Field Description:

1.         “AA” is the aperture size, e.g. 08=8 mm.

2.         “B” is the device type. I=isolator; R=rotator. 

3.         “CCCC” is the operating wavelength in nm. 

4.         “DDD” is the input polarization axis angle.  A right hand X, Y, Z Cartesian coordinate system is used, in which the direction of beam propagation away from the laser source is along the positive Z axis.  The X axis is in the plane of the baseplate.  The Y axis is vertical, normal to the plane of the baseplate.  The XY plane forms the plane of polarization.  The XZ plane forms the plane of the baseplate. As an example, a horizontal input polarization is 000 or 0 degrees.  A vertical polarization is 090, or 90 degrees.  If no polarization is selected by the customer, 000 will be assigned. For rotators, this field does not apply.

5.         “EEE” is the output polarization, which is 45 degrees from the input polarization if no waveplate is used.  If a waveplate is used and no output polarization is specified, the default setting is the input polarization plus 90 degrees. The angle convention is the same as described for “DDD”.  For rotators, this field does not apply.

IV. Using your Pavos Ultra Series Optical Isolator

Observe the guidelines for safe use of your Optical Isolator found in Section II above when removing your optical isolator from its shipping container.  Do not remove the protective dust-cover end caps from the polarizers until the device is in a clean, relatively dust-free environment.

Save the protective end caps, packaging material and containers in the event that the device should ever need to be returned to EOT.

Verify that the input and output polarization states are consistent with the intended mode of operation as described by the purchase order model number.  If not, either send the device back to EOT (see Section VII) or, if desired, readjust the optical isolator as required (see Section V).

With the source laser off, or running at very low power (less than 250 mW), position the Optical Isolator such that the source laser beam can be directed through the input aperture. Critical alignment of the Optical Isolator should be done at low power (less than 250 mW) in order to prevent optical damage to your optical isolator or laser source.

Use IR cards, IR viewers, or heat-sensitive film to ensure that the source laser beam is centered on the input and output apertures.  It is also preferable to use an IR viewer to ensure that weak reflections from AR coated optical surfaces in the Optical Isolator are not being directed back into the source laser.  The optical surfaces in the Optical Isolator are angled slightly to reduce these reflections.  However, if any such reflections exist the device may typically be tilted by a small amount to ensure that such back-reflections are not coaxially aligned with the source laser beam.  Increasing the distance between the Optical Isolator and the source laser can also help ensure that no reflections couple back into the source laser if necessary.

At this point the Optical Isolator should be secured to the work surface with two (2) ¼ - 20 or M6 screws – one for each slot in the baseplate flanges.  Steel (ferromagnetic) ball drivers or other such wrenches will be attracted to the external magnetic field surrounding the device.  If possible use anti-magnetic stainless steel or titanium tools.  If ferromagnetic tools are used it is desirable to introduce them slowly towards the device from the sides along the direction of the baseplate flange slots.

If the Optical Isolator will be used with average powers in excess of 25 W transmitted or 0.5 W rejected backward propagating radiation the polarizer covers will need to be rotated so that the escape ports allow rejected polarization light to be safely dumped onto a beam dump.  Failure to allow these rejected polarizations to escape can cause the device to heat up.  Such heat can degrade the performance of the Optical Isolator, or in severe cases, cause damage to optical components in the optical isolator.  While working with low alignment level power and wearing safety glasses physically grasp the polarizer cover and rotate it by 90 degrees.  Any rejected polarized beams (in either the forward or backward propagating directions) can now exit the polarizer cover.  Use an IR viewer or IR card to locate these beams.  Ensure that they are terminated on beam dumps consistent with the maximum amount of power that may be in such beams.  In addition to high rejection (>30 dB) of any undesired linear polarization component in transmission, the input and output PBSC may reflect as much as 3% of the desired transmitted polarization.  Again, backward propagating rejected beams will exit from the PBSCs from the side which has a “dot” superimposed on the transmission axis scribe line.  Forward transmission rejected beams will exit from the other side of the PBSCs.  If the Optical Isolator is used in application where strong reflections and/or optical gain elements (amplifiers) exist there may be very high power rejected beams for backward propagating light at the input polarizer.  If the average power levels used do not exceed 25 W transmitted or 0.5 W of backward propagating power then the polarizer covers may be kept in their factory positioned orientation – all rejected beams will then be blocked by the polarizer cover.  However, if the Optical Isolator is to be used with very high peak intensities it is prudent to allow rejected beams to escape on to external beam dumps to prevent any ablation damage to the nickel-plated polarizer covers.  Follow the same procedure above as for high average powers in order to safely terminate all rejected beams.

V. Tuning your Pavos Ultra Series Optical Isolator

            A. Adjusting Input Polarization

The transmission axis of the input polarizer is parallel to the scribe line found on the input polarizer endplate.  If the linear polarization of the laser source is geometrically known aligning the input polarization of the Optical Isolator to that of the laser source is straightforward.  Simply loosen the #4-40 socket head baseplate clamp screw in the baseplate until the magnet housing rotates freely.  Continue to rotate the magnet housing until the input polarizer transmission axis scribe line is aligned to that of your laser source.  If the direction of any rejected polarizations at the input polarizer is important they can be determined by noting that the “dot” superimposed on one of the endplate scribe lines is associated with the direction that a backward propagating beam will be directed.  Retighten the baseplate clamp screw.

If it is desired to critically adjust the input polarization for maximum transmission of the Optical Isolator the power rejected by the input PBSC in transmission can be minimized.  This rejected beam can be accessed as per Section IV above.  As always, use caution when allowing rejected beams to escape from the polarizer covers.  Confirm the direction and safe termination of these beams at low power.  Wear laser safety glasses or goggles.  Protect your colleagues by safely terminating beams and ensuring that they are wearing safety glasses or goggles as appropriate.  At the desired operating power level minimize the power in the rejected input polarization with a power meter or other suitable power indicator.  When the power is minimized retighten the baseplate clamp screw.

B. Coarse Wavelength Adjustment

If it becomes necessary to operate the Optical Isolator at a wavelength other than the factory aligned wavelength it is possible to optimize the isolation of the devices anywhere within the wavelength range of 1010 nm - 1045 nm or 1045 nm - 1080 nm.  This can be achieved quickly by simply aligning the polarization scribe line on the output polarizer with the appropriate wavelength indicator scribe line on the polarizer clamp ring.  The optimal operating wavelength corresponding to scribe lines labeled “A” and “B” is a function of the rotation sense of the device ordered (see Section III for definition).  Use the table below to determine the optimal operating wavelength corresponding to each scribe line.

 
Negative Z Rotation
Positive Z Rotation
Scribe Line
1010 nm - 1045 nm
1045 nm - 1080 nm
1010 nm - 1045 nm
1045 nm - 1080 nm
"A"
1010 nm
1045 nm
1045 nm
1080 nm
"1030 nm"
"1064 nm"
1030 nm
1064 nm
1030 nm
1064 nm
"B"
1045 nm
1080 nm
1010 nm
1045 nm


To realign the output polarizer mount, loosen the three button head polarizer clamp ring screws just enough to allow the output polarizer mount to rotate easily.  Once adjusted, retighten the polarizer clamp ring screws by equal amounts.

          C. Fine Wavelength Adjustment

The above procedure is convenient for a quick realignment of the operating wavelength.  To achieve maximum isolation for a given wavelength the following procedure should be used.

With the source laser operating at an average power of 0.5 W or less (attenuate the beam if necessary to achieve such a low power level) direct the source laser beam through the Optical Isolator in the reverse direction – through the output polarizer first and then through the input polarizer.  Use an IR viewer to view the transmitted radiation to ensure that it is directed onto a power meter.  The power meter should be sensitive enough to detect power levels below 0.5 µW.  If necessary, loosen the baseplate clamp screw to allow the output polarizer transmission axis to be rotated parallel to the source laser polarization axis. Retighten this screw when complete.

Loosen the three button head output polarizer clamp ring screws just enough so that the output polarizer mount can be rotated (the output polarizer is adjacent to the laser source at this point).  Rotate the output polarizer mount until a minimal reading is indicated on the power meter.  Retighten the output polarizer clamp ring screws.  The minimal reading should be below 0.5 µW.  If not, call EOT (see Section VII below).  The Optical Isolator is now optimized to operate at the new laser source operating wavelength.  It may now be installed for operation in transmission with the laser source as per Section IV.

          D. Changing the direction of Output Polarizer PBSC Rejected Beam Steering

Section A above described how to orient the input polarizer to steer rejected beams as desired.  If the output polarizer rejected beam steering direction needs to be changed, loosen the three output polarizer clamp screws and rotate the output polarizer mount by 180° before retightening the screws.  Depending upon the isolation requirements, follow either Procedure B (coarse adjustment) or Procedure C (fine adjustment) in order to fully optimize the isolation of the device with this output polarizer orientation.

E. Waveplate Option and Adjustment

As described in Section III above in the Numbering Fields and Coordinate System section, it is possible to order a Optical Isolator with a half-wave plate on the output.  Should any of the above adjustments become necessary, or if the desired output polarization changes, the waveplate will need to be adjusted.  To realign the waveplate loosen the radially-oriented setscrew in the output polarizer endplate and rotate the waveplate until the desired output polarization is achieved.  Retighten the waveplate set screw.  Do not over-tighten.

VI. Diagrams: 1010 nm - 1080 nm Faraday Rotator / Optical Isolator

A. Pavos Ultra Series 1010 nm - 1080 nm Faraday Rotator

B.  Pavos Ultra Series 1010 nm - 1080 nm Optical Isolator

VII. Warranty Statement and Repair

EOT warrants its products to be free from defects in material and workmanship and complies with all specifications. EOT will at its option, repair or replace any product or component found to be defective during the warranty period. This warranty applies only to the original purchaser and is not transferrable for a period of one year after date of original shipment. The foregoing warranties shall not apply, and EOT reserves the right to refuse warranty service, should malfunction or failure result from:

a. Damage caused by improper installation, handling or use.

b. Unauthorized product modification or repair.

c. Operation outside the environmental or damage specifications of the product.

d. Contamination not reported to EOT within 30 days of the original ship date.

e. EOT’s output isolators contain a “spacer” at the end of the isolator. Under certain   conditions, an off-axis back-reflection from the workpiece could focus down onto the output displacer or polarizer inside the isolator. The purpose of the spacer is to eliminate the conditions under which this could happen. Should EOT’s output isolators be purchased without the spacer, or should the spacer be removed, damage to the output displacer or polarizer will not be covered under warranty and the customer will be responsible for all costs associated with such an occurrence. 

This warranty is exclusive in lieu of all other warranties whether written, oral, or implied. EOT specifically disclaims the implied warranties of merchantability and fitness for a particular purpose. In no event shall EOT be liable for an indirect, incidental, or consequential damages in connection with its products.

If the customer believes there is a problem with the Faraday Rotator / Optical Isolator, they should immediately contact EOT’s Sales/Customer department at 231-935-4044 or customerservice@eotech.com.  EOT’s Customer Service department will either issue an RMA for the device, or provide the customer with a procedure and authorize the customer to modify the device.  All returns should reference the RMA number on the outside of the shipping container and should be sent to:

Electro-Optics Technology, Inc.
Attn: Sales/Customer Service
3340 Parkland Ct.
Traverse City, MI 46986   USA

EOT reserves the right to inspect Faraday Rotators/Optical Isolators returned under 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 ball driver or exceeding the damage threshold of the device), repairs will be done at the customer’s expense.  EOT will always provide a written quote for repair prior to performing repairs at the customer’s expense.  Never attempt to disassemble the magnetic housing of your Faraday Rotator / Optical Isolator.  Injury could result.  Any indications that an attempt to disassemble the magnetic housing was made will render the warranty null and void.

VIII. Specifications: 1010 nm - 1080 nm Faraday Rotators and Optical Isolators

 
1010 nm - 1080 nm Rotator
1010 nm - 1080 nm Isolator
Transmissiona
>95%
>95%
Isolationa
N/A
>33 dB typical
>27 dB minimum
Extinctiona
>36 dB typical
>30 dB minimum
N/A
Rotationa
45° +2°/-5°
45° +2°/-5°
Damage Threshold
7 J/cm2 at 10ns
0.6 J/cm2 at 8ps
7 J/cm2 at 10ns
0.6 J/cm2 at 8ps

aAt customer-specified wavelength and temperature

 

Notes:

1.  Operating Temperature: Performance of EOT’s Faraday Rotators / Optical Isolators is related to operating temperature.  For information on the effect of operating temperature on EOT’s Faraday Rotators / Optical Isolators, please review our application note, Thermal Lensing Analysis of TGG.

2.   For apertures >12 mm: you may either contact EOT’s sales department at sales@eotech.com or view our Custom Products page on our website.