954P Fixed Ratio Polarization Maintaining Evanescent Couplers and Taps
954P Mini-Coupler Spec Sheet (see Reliability tests)
POLARIZATION MAINTAINING COUPLERS
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.
Specifications
Polarization Isolation
Ratio Tolerances (set at room temperature on slow axis)
|
Ratio | 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 shrink tubing) dim. 0.8" x 0.14" x 0.14"
Pigtails sleeved with 3mm cable (coupler housed in 2.5" x 2.5" aluminum package)
Pigtails:
1 m standard length (longer available - up to 20m in 3mm sleeved configurations)
Terminations:
FC/SPC, FC/APC, LC/APC, SC/APC, SC/PC
Product Data 954P-HI
HIGH ISOLATION COUPLERS
Polarization preserving fibers used at wavelengths well above cut off tend to show differential bend loss in the TE and TM modes (fast and slow axes). A fiber coil of a few turns can give as much as 10 dB differential loss with 0.5 dB or less loss in the slow axis. This effect can be used to make an in line polarizer on the input/output ports of a coupler. The penalty is launching into a smaller core fiber with lower guidance and increased bend loss sensitivity. Splicing to larger core fibers also requires more effort.
Fibers with a cut off in the 1 nm range can be used for 1.55 nm operation, 954P-P WDM Pump Couplers are an example. Combined with a long output fiber of about 7 turns in a nominally 50 mm diameter coil, the result is a splice free in line output polarizer with low loss.
Polarization isolations of -28 dB are typical with some less than -30dB with selected fiber.
If polarization isolation is more important than low loss then using a lower cut off fiber is a very effective means of removing cross coupled components.
This is especially important in arrays of PM couplers where modulation due to interference of cross coupled components is a major problem.