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Alignment Inst.

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Optical Isolator

General Isolator Alignment Instructions

Below are the general isolator alignment instructions. Specific instruction sheets are available for each body type. If something is unclear or does not seem to match your specific isolator please email info@ofr.com and include the isolator model number and we will send you the model specific instructions. Also if you need any technical assistance that you can not find on the website please do not hesitate to call (973)-579-7227.

 

HOW THE ISOLATOR WORKS

OFR isolators are used to reduce or eliminate the effects of optical feedback - reflections of the laser's energy back into itself. These effects include noise, amplitude fluctuation, and even laser damage .

OFR isolators protect the laser, while maintaining beam alignment and providing maximum forward transmission and reverse isolation.

An isolator consists of a Faraday rotator, two polarizers and a housing. The Faraday rotator consists of a magneto-optic material within a magnetic field.

Operation

The forward mode: Laser light enters the isolator via the input polarizer and is linearly polarized. It then enters the rotator, which rotates its plane of polarization 45 ° . It then exits via the output polarizer, whose axis is 45 ° from the input plane of polarization.

The reverse mode: Some random beam reflections will be reflected back towards the laser. This feedback re-enters the isolator via the output polarizer and is polarized at 45 ° . It continues into the rotator and is rotated by another 45 ° . The feedback, now polarized at 90 ° relative to the input polarizer, is extinguished.

The laser is now isolated from its own reflections.

 

USING THE ISOLATOR

Notes: OFR aligns the isolator for horizontal input polarization unless the customer requests otherwise.

If you have an “LP” model, do not place the isolator < 6” from the laser - LP polarizers reject at 7° from the passing beam, and the rejected feedback can strike a close laser.

Initial alignment:

  1. Remove the protective tape from the polarizer cells.
  2. Place the isolator in the laser beam. Place a detector > 8” from the output polarizer. Center the beam.
  3. Loosen the set screws on the polarizer cells.
  4. Rotate the input polarizer until transmission is maximized, thus aligning it to the laser’s plane of polarization . Lock down its set screw.
  5. Rotate the output polarizer until transmission is maximized. This occurs nominally at 45° CW* or CCW* (* model specific inquire) relative to the input plane of polarization .

    Exception:     Occasionally, OFR will not fix the output polarizer cell in place, allowing the user to tune the isolator for different wavelengths. For instructions in this case, discuss with OFR.

    Fine tuning to optimize isolation:
  6. Reverse the isolator, so the output polarizer faces the laser and the detector is a few inches from the input polarizer. Center the beam.
  7. Adjust the output polarizer (now facing the laser) by 1-2° until transmission is minimized. Lock down its set screw.
  8. Return the isolator to the operating position. Center the beam.
  9. The isolator is now aligned and ready for use.

 

 

Optics for Research · Ph 973-579-7227 · Fax 973-300-3600 · Email: info@ofr.com
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