Tool · Optical alignment

Fiber Coupling Efficiency Calculator

Estimate Gaussian beam to single-mode fiber coupling efficiency from beam waist, fiber MFD, and alignment offsets. Uses paraxial mode overlap.

Beam waist w₀ (μm, 1/e² radius)

Lensed-fiber typical: 2–6 μm. Collimated SMF: ~5.2 μm at 1310 nm.

Fiber MFD (μm, full width)

SMF-28: 9.2 μm @ 1310 nm, 10.4 μm @ 1550 nm. HI-1060: 6.2 μm @ 1060 nm.

Lateral offset (μm)

00.0 μm12

Longitudinal offset (μm from focus)

00 μm200

Wavelength (nm)

Coupling efficiency

100.0%

0.00 dB insertion loss

Excellent. Near-optimal mode match.

Lateral alignment tolerance (3 dB): ±4.5 μm

Efficiency vs. lateral offset

Black dot shows current position. Solid line is efficiency sweep at fixed beam waist and longitudinal offset.

Method

Computed from the paraxial mode overlap integral for two Gaussian modes. Size mismatch term: η_size = (2 w_b w_f / (w_b² + w_f²))². Lateral offset term: η_x = exp(-2x² / (w_b² + w_f²)). Longitudinal offset modeled as Rayleigh-range beam expansion. Estimates do not include angular mismatch or surface reflections.