Fig. 1. (a) Refractive index profile of the fiber across the core region; (b) cross-section photograph of the confined-doped fiber.
Fig. 2. Experimental schematic of the confined-doped fiber amplifier (PSC, pump and signal combiner; YDF, ytterbium-doped fiber; CMS, cladding mode stripper).
Fig. 3. (a) The output power and optical-to-optical efficiency as a function of the pump power; (b) the beam quality factor evolution as a function of the output power.
Fig. 4. The TMI threshold and extracted power as a function of seed laser power.
Fig. 5. The experimental schematic of the power controllable seed laser based on the bending loss mechanism.
Fig. 6. The experimental schematic of the S2 measurement (TFL, tunable fiber laser; FUT, fiber under test; MO, microscope objective; CCD, charge-coupled device).
Fig. 7. S2 measurement results when the bending diameter of the FUT is (a) 35 cm, (b) 20 cm, (c) 15 cm and (d) 8 cm.
Fig. 8. Extracted power at different seed laser powers.
Fig. 9. (a) TMI threshold and the power of the fundamental mode upon the onset of TMI and (b) the mode purity of the output laser as a function of the seed laser mode purity (simulation results).
Fig. 10. The pump gain distribution of HOM-A along the fiber when the seed mode purities are 0.6 and 1.
Fig. 11. (a) Output power as a function of the pump power; (b) output spectra at different output powers.
Fig. 12. The beam quality factor evolution as a function of the output power.
Bending state | A | B | C | D | N |
---|
Bending diameter/m | ~0.15 | ~0.09 | ~0.08 | ~0.06 | No bending | Bending length/m | ~1.0 | ~1.0 | ~0.75 | ~0.5 | Seed power/W | 140 | 110 | 90 | 70 | 180 |
|
Table 1. Bending diameter/length and the seed laser power at different bending states.
Parameter | Value | Parameter | Value |
---|
rcore | 20 μm | rclad | 125 μm | λp | 1018 nm | λs | 1080 nm |
${\sigma}_{\mathrm{ap}}$
| 9.44 × 10–26 m2 |
${\sigma}_{\mathrm{ep}}$
| 7.30 × 10–25 m2 |
${\sigma}_{\mathrm{as}}$
| 2.29 × 10–27 m2 |
${\sigma}_{\mathrm{es}}$
| 2.82 × 10–25 m2 | τ | 840 μs | n | 4.94 × 1025 m-3 | L | 36 m |
$\rho {C}_0$
|
$1.55\times {10}^6$
J/(m3·K) |
${k}_\mathrm{T}$
|
$1.2\times {10}^{-5}$
|
$\kappa$
| 1.38 W/K |
|
Table 2. The main parameters of the fiber amplifier.