Polarization Extinction Ratio (PER)

In most applications for PM fiber, only one of the two polarization orientations (states) is used - this is sometimes called the ‘wanted’ polarization-state. The extinction ratio simply compares the optical power held on the wanted axis to that which is on the unwanted axis, the orthogonal polarization state, expressed in decibels (dB).

Polarization Extinction Ratio (PER)

So you can see, an Extinction-Ratio of -30dB is 1000:1 and -20dB is 100:1

The value of extinction ratio is dependant upon the length of fiber and the environmental conditions.  If you subject the fiber to high mechanical stress and small-diameter bends, then it is possible to disrupt the internal stress (which generates the birefringence) and this reduces the extinction-ratio significantly.

Typical PER under various deployment conditions are indicated below.



Extinction Ratio


Loose-tube cabled, wound on a 300mm cable reel

-25 to -30dB


Wound at low tension on a 150mm spool

-30 to -35dB


Wound at low tension (<5g) on a 60mm spool

-25 to -30dB


Laid straight


*limit of measurement resolution; ask about our test set-up


For more information, please request our technical note 'PER and Crosstalk'.


Related Products: PM Coupler Fiber, PM Erbium Doped Fiber, PM Gyro Fiber, Polyimide Coated PM Fiber, Standard PM Fiber, Telecoms PM Fiber, Zing™ Polarizing Fiber

Related Terms: Birefringence, Birefringent Fiber, Bow-Tie Fiber, H-Parameter, Highly Birefringent (HiBi), Macro-Bending loss, Micro-Bending Loss, Polarization Extinction Ratio (PER), Polarization Maintaining (PM) Fiber, Polarization Mode