How much continuous laser power can a nanofibre carry?
A silica fibre thinner than a wavelength of light carried 13 watts of steady laser power while losing only a small fraction of it, far more than previously shown.
Source
High-power continuous-wave optical waveguiding in a silica micro/nanofibre
Study at a glance
- Design
- Other — Laboratory optics experiment on taper-drawn silica micro/nanofibres driven by an amplified 1552-nm continuous-wave laser, plus a finite-element thermal model.
- N
- No sample count; results come from individual fabricated fibres (e.g., a 1.2-µm fibre for heating, a 779-nm fibre for harmonic generation).
- Population
- Silica micro/nanofibres drawn from standard single-mode telecom fibre
- Outcome
- Transmittance versus guided power, temperature rise and extrapolated damage threshold, optomechanical particle motion, and harmonic-generation efficiency
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What they did
The team tapered standard telecom fibre down to micro/nanofibres (as thin as 410 nm) in a cleanroom and sealed them in nitrogen. They sent up to 13 W of 1552-nm continuous-wave light through them and measured output power, scattering and long-term stability. They measured heating by tying a fibre into a knot resonator and tracking its resonance shift, then used a thermal model to extrapolate a damage threshold. They also used the strong guided field to push droplets and microspheres in air and to generate second and third harmonics.
What they found
Transmittance stayed above 95% up to 13 W, over 30 times the previous record, with no hysteresis and no degradation over more than 10 hours of operation. The thermal model predicted optical damage at roughly 70 W, when the fibre would reach about 1100 °C. An oil droplet began sliding at about 0.04 W and reached 2.1 mm/s at 2.2 W. Harmonic power scaled as the cube (third harmonic) and square (second harmonic) of pump power, with continuous-wave conversion efficiencies of 4.9 × 10^-6 and 8.2 × 10^-8.
The limits
What it doesn't show
The 70 W damage threshold is an extrapolation from a thermal model, not a measured failure, because the available amplifier topped out below 15 W. The model ignores convective cooling in air and assumes a constant absorption coefficient, so the real threshold is uncertain. The fibres' defect absorption is much higher than bulk silica, and results come from a handful of individual fibres rather than a statistical sample. Harmonic conversion efficiencies, while notable for continuous-wave light, remain very small in absolute terms.
Key terms
- Micro/nanofibre (MNF)
- An optical fibre stretched until its diameter is around or below the wavelength of the light it guides, so much of the light travels just outside the glass.
- Evanescent field
- The part of a guided light wave that extends outside the fibre surface and decays with distance; it can push particles and interact with surroundings.
- Optical damage threshold
- The power at which the fibre would be permanently harmed, here estimated from the temperature it would reach.
- Phase matching
- The condition where the fundamental and harmonic light travel with matched phase velocities so harmonic light adds up coherently along the fibre.
- Knot resonator
- A fibre tied into a small loop that acts as an optical cavity; its resonance wavelength shifts with temperature, making it a thermometer.
Flashcards
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Quiz yourself
What limited the maximum power tested in this study?
Common questions
Why can such a thin fibre carry so much power without melting?
Silica absorbs extremely little light at 1550 nm and the drawn fibre surface is very smooth, so little power turns into heat, and light couples into the taper almost losslessly.
How did they know the damage threshold without destroying a fibre?
They measured temperature rise at powers they could reach, fitted a heat-dissipation model to it, and extrapolated to the power where the fibre would hit silica's annealing temperature.
Why does a larger power give much more third-harmonic light?
Third-harmonic generation scales with the cube of the input power and second-harmonic with the square, which matches the measured log-log slopes.
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