Specialty Fiber Types

Compare data-sheet properties of specialty optical fibers (PM, erbium-, ytterbium- and thulium-doped, ZBLAN, chalcogenide): V-number, cutoff, mode-field diameter and loss.

Model: Illustrative

FiberLength (m)Wavelength (nm)

Polarization-maintaining fibre: stress rods give a beat length of 5.0 mm at 1550 nm.

Data sheet: Thorlabs PM1550-XP (Ge-doped silica, B-doped stress rods). Typical catalogue values for one product, not limits for the fibre class.

Core / cladding, NA

8.5 / 125 µm

NA 0.125

V-number at λ

2.15

single-mode (λ above the sheet cutoff)

Second-mode cutoff

1380 nm

data sheet; step-index 2πa·NA/2.405 gives 1388 nm

Mode-field diameter

10.1 µm at 1550 nm

Marcuse estimate 10.1 µm at λ, 10.1 µm at the sheet λ

Background attenuation

1 dB/km

at 1550 nm, max (< 1.0 dB/km)

Attenuation over length

0.010 dB

10 m × figure at 1550 nm only

V-Number vs Wavelength

V = 2πa·NA/λ (amber) from the data-sheet core and NA; the fibre is single-mode where it lies below 2.405 (red, dashed), i.e. above the cutoff wavelength.

Numerical Aperture Comparison

Data-sheet core NA of each fibre (selected: Thorlabs PM1550-XP, NA 0.125).

Model

V = 2πa·NA/λ; single-mode for V < 2.405, λ_c = 2πa·NA/2.405

w = a(0.65 + 1.619V^−1.5 + 2.879V^−6); loss (dB) = α (dB/m) × L

The step-index formulas ignore stress rods and graded dopant profiles. Losses are single data-sheet figures at one wavelength, not spectra: doped-fibre absorption changes by orders of magnitude across a band and bleaches under pumping.

Model and references

Illustrative. A simplified model that shows trends and orders of magnitude. Don't use its numbers for design. About the tiers

Typical data-sheet values for one commercial fibre per class (linked). V = 2πa·NA/λ, step-index cutoff and Marcuse MFD from the sheet's core and NA. Losses are single-wavelength figures, not spectra.

Thorlabs PM1550-XP spec sheet TTN019885-S01 (PANDA PM fibre). thorlabs.com
nLIGHT LIEKKI Er16-8/125 and Yb1200-4/125 data sheets (via Thorlabs). thorlabs.com
Coherent SM-TSF-9/125 thulium-doped fibre data. coherent.com
Thorlabs IRZS23 ZBLAN single-mode fibre spec sheet TTN028984-S01. thorlabs.com
IRflex IRF-S series As₂S₃ fibre data sheet (V202408) and product page. irflex.com
Gloge D. (1971). Weakly guiding fibers. Appl. Opt. 10, 2252. V and the LP11 cutoff. doi:10.1364/ao.10.002252
Marcuse D. (1977). Loss analysis of single-mode fiber splices. Bell Syst. Tech. J. 56, 703. doi:10.1002/j.1538-7305.1977.tb00534.x

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