Fixed Couplers

Coupler Arrays

Variable Ratio Couplers

Piezo Fiber Stretchers

Non-contact Displacement Sensor

Evanescent Access Blocks

Patch Cords

954P Fixed Ratio Polarization Maintaining Evanescent Couplers and Taps

954P Mini-Coupler Spec Sheet (see Reliability tests)


General Product Data:

  • Low loss and backreflection 
  • High isolation
  • Small ratio variation with temperature
  • Compact package
  • Standard polarization maintaining (PM) fibers
  • Low ratio taps with PM or SM output
  • Bandwidth is a function of Coupling Ratio

Fibers are side polished in glass substrate blocks to remove cladding material on one side of the core without distorting the core region. In the case of PM fibers, one stress member remains. Two polished fibers are placed into optical contact with their polarization axes aligned, and coupling from core to core occurs by the evanescent wave interaction. Precise loading of the substrate blocks ensures the fibers remain in low stress contact over a broad range of temperatures.

Polarization isolation of -30 dB is attainable using this technique.



Evanescent wave couplers offer inherent performance advantages because there is no deformation or tapering of the waveguiding cores. These devices have low loss and backreflection. Also, short interaction lengths (1-2 mm) allow small device packages to be realized.

The interface essentially vanishes with optical contact between identical silica surfaces. There is no intermediate material which can change its refractive index or thickness with age or environmental effects. The coupler behaves optically as if the fibers were fused and is very stable with temperature variations.


Coupler Bandwidth

Polarization Isolation

High Isolation types:
Standard PER <-24dB

Ratio Tolerances (set at room temperature on slow axis)



Standard Tolerance Also Available
50/50 +/-3% +/-2%
   80/20 +/-2% +/-1%
90/10 +/-1.5% +/-1%
99/1 +/-0.25%  








Above table represents the most common ratios, any ratio from 99/1 to 1/99 is possible.

Available wavelengths:

0.488 to 2.04um

Operating Temperature:

-15  to +55 degC

Excess Loss:

<0.1dB for wavelengths >980nm, <0.15dB for wavelengths 700 to 980, <0.2dB 590nm to 700nm

Return Loss (Backreflection):

-70 dB typical

Power Handling:

These very low loss couplers allow CW power approaching that of the fiber itself.

The only restrictions we have noted is very high peak power, picosecond and femtosecond pulses that cause non-linear changes in the fiber that increases loss due to reduced guidance.

Packaging & Sleeving:

No sleeving over fiber (coupler unpackaged) dim. 0.59" x 0.1" x 0.1"

Pigtails sleeved in 900 micron HYTREL (coupler in aluminum tubing) dim. Length 1.125" x Dia. 0.19"

Pigtails sleeved with 3mm cable (coupler housed in 2.5" x 2.5" aluminum package)


1 m standard length (longer available - up to 20m in 3mm sleeved configurations)