Fiber Pump Combiner

Combined pump power, étendue budget, tapered-bundle diameter and pump NA after the taper for an N×1 or (N+1)×1 fiber pump combiner.

Model: Textbook approximation

Pump Ports NCentre Signal FibrePump Power per Port (W)Pump Transmission (%)Pump Fibre Core Ø (µm)Pump Fibre Cladding Ø (µm)Pump Fibre NASignal Insertion Loss (dB)Output Pump-Guide Ø (µm)Output Pump-Guide NA

Results

Total pump input:180.0 W

Combined pump output:176.4 W

Lost in combiner:3.6 W

Étendue used N·(d·NA)²/(D·NA)²:34.3 %

Ideal port limit (étendue):17

Bundle Ø before taper:660 µm

Taper ratio:1.650

Pump NA after taper:0.363 ≤ 0.46

Pump brightness in / out:6.28e+3 / 2.11e+3 W/(mm²·sr)

Signal transmission:97.72 %

Formulas

P_out = N·P_port·η

Étendue: N·(d_p·NA_p)² ≤ (D_out·NA_out)²

Hex bundle Ø = (2n + 1)·d_clad; taper ratio TR = max(1, Ø/D_out)

NA after taper = NA_p·TR ≤ NA_out

The taper test includes the cladding and packing gaps, so it is stricter than the étendue bound. The signal fibre is taken with the pump cladding Ø. The bundle diameter (2n + 1)·d assumes full hexagonal rings around a centre fibre, so for 2–4 fibres without a centre fibre it overstates the bundle (N = 2: 3d vs 2d) and the taper NA, which errs on the safe side.

Model and references

Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers

Lossless adiabatic taper (NA × taper ratio) of a hexagonal bundle of equal fibres; étendue π·A·NA² of the cores. Transmission and signal loss are inputs, not modelled.

Kosterin A., Temyanko V., Fallahi M., Mansuripur M. (2004). Tapered fiber bundles for combining high-power diode lasers. Appl. Opt. 43, 3893. Étendue conservation, taper NA. doi:10.1364/AO.43.003893

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