Flexible chalcogenide glass large-core multimode fibers for hundred-watt-level mid-infrared 2-5 µm laser transmission.

The rapidly-developed high-power mid-infrared 2-5 µm laser technology requires a compact, flexible low-loss glass fiber for power delivery or laser generation. With the broadest bandwidth of low-loss transmission window in mid-infrared region amongst all mid-infrared glass fibers, chalcogenide glass fiber is the best candidate covering the whole 2-5 µm range. Multi-hundred-watt high-power delivery for 5.4-µm CO laser was previously demonstrated in a multimode chalcogenide fiber with a 1-mm-diameter large core, at the cost of giving up one of the most desirable fiber advantages, the flexibility. Indeed, chalcogenide glass fibers with decent flexibility have never exhibited hundred-watt-level power transmitting capability in the 2-5 µm range. In this paper, we have experimentally demonstrated 100-watt-level power transmission in multimode As2S3 chalcogenide fibers, using a customized high-power 2-µm thulium doped silica fiber laser source. With effective forced cooling, the multimode As2S3 fiber with 200 µm core diameter can resist incident laser power of 120 W and deliver transmitted power of 63 W. Nano-sized scattering center related laser damage mechanism and the cylindrical heat transfer model have been proposed to explain the high-power damage process of chalcogenide glass fibers. The calculation is in good agreement with the experiments. It is promising to further enhance the transmitted power above 100 W in flexible chalcogenide glass large-core fibers.

Few-moded ultralarge mode area chalcogenide photonic crystal fiber for mid-infrared high power applications.

We demonstrate a novel few-moded ultralarge mode area chalcogenide glass photonic crystal fiber for mid-infrared high power applications. The numerical simulation indicates that the fiber has ultralarge mode areas of ∼10500 µm2 and ∼12000 µm2 for the fundamental mode LP01 and the lowest higher-order mode LP11, respectively. Dual-moded operation is confirmed experimentally at 2 µm, in good agreement with the numerical simulation. By selectively launching technique, low bending loss of 0.7 dB/m, equivalent to 0.55 dB/turn, has been observed in the fiber with a small bending radius of ∼12 cm, indicating excellent bending resistance of the few-moded fiber with such a large mode area. The fiber has been demonstrated to sustain an incident power density up to 150 kW/cm2 under 2-µm CW laser irradiation, showing the potential of the fiber for high-power applications in mid-infrared.

All-solid mid-infrared chalcogenide photonic crystal fiber with ultralarge mode area.

In this Letter, we report, to the best of our knowledge, the largest effective single-mode mid-infrared chalcogenide (ChG) fiber. Two thermally matched ChG glasses with a large index contrast of ∼0.35 are chosen for constructing all-solid photonic crystal fiber (PCF) with two rings of "holey" microstructured cladding. Single-mode operation is confirmed in the fabricated ChG PCF with a core diameter of 91.2 µm, from both near-field and far-field observation at 4 µm. Ultralow numerical aperture of <0.025 has been observed at wavelengths between 2.5 and 4.0 µm. The fundamental mode area is calculated to be 5200 µm2 at 4 µm, where the propagation loss of the ChG PCF is measured to be 5.2 dB/m. Broadband 3.5 and 7.5 µm supercontinuum has been generated in a 35-cm-long ultralarge-mode-area PCF.

High-resolution chalcogenide fiber bundles for longwave infrared imaging.

A flexible chalcogenide fiber bundle (FB) with a resolution as high as ~31 lp/mm has been fabricated for delivering thermal images of objects at room temperature. The FB is composed of ~200,000 single fibers with a Ge-As-Te-Se glass core 15 µm in diameter and a polyetherimide (PEI) cladding 16.8 µm in diameter. These Ge-As-Te-Se/PEI fibers show good transparency in the 3-12 µm spectral region. The fabricated FB presents a filling factor of ~72% and a crosstalk of ~1%. High-quality thermal images of a human hand were obtained through the FB, demonstrating good potential of the FB for longwave infrared imaging in the areas such as medicine, industry and defense.

Integration of helicity-control and pulse-modulation for vortex laser based on a black phosphorus plate.

Using a home-made black phosphorus plate (BPP) as handedness controller and Q-switch modulator synchronously, a ~1.6 µm pulsed vortex laser with well-determined handedness is demonstrated in this letter. Stable vortex pulses of LG0, + 1, LG0,-1, LG0, + 2 and LG0,-2 modes were respectively achieved from compact resonant cavities in this experiment. Such pulsed vortex laser should have promising applications in various fields based on its simple structure, controllable handedness, and carried orbital angular momentum.

High-resolution chalcogenide fiber bundles for infrared imaging.

An ordered chalcogenide fiber bundle with a high resolution for infrared imaging was fabricated using a stack-and-draw approach. The fiber bundle consisted of about 810,000 single fibers with an As2S3 glass core of 9 µm in diameter and a polyetherimide (PEI) polymer cladding of 10 µm in diameter. The As2S3/PEI fibers showed good transparency in the 1.5-6.5 µm spectral region. It presented a resolution of ∼45 lp/mm and a crosstalk of ∼2.5%. Fine thermal images of a hot soldering iron tip were delivered through the fiber bundle.

1.8-10 µm mid-infrared supercontinuum generated in a step-index chalcogenide fiber using low peak pump power.

By pumping an 11-cm-long step-index chalcogenide fiber with ∼330 fs pulses at 4.0 µm from an optical parametric amplifier, mid-infrared supercontinuum generation spanning from ∼1.8 to ∼10 µm within a dynamic range of ±15 dB has been demonstrated at a relatively low power threshold of ∼3000 W.