Hoang Tuan Tong

Supercontinuum generation in a suspended core birefringent tellurite microstructured optical fiber pumped in telecommunication band by a picosecond laser

Based on a suspended core birefringent tellurite microstructured optical fiber (BTMOF), the supercontinuum (SC) spectra are generated by pumping near the zero dispersion wavelengths (ZDWs) in the telecommunication band with a tunable picosecond fiber laser. The ZDWs of the suspended core BTMOF are calculated to be 1560 nm and 1532 nm for the X-axis and Y-axis, respectively. When the pump is polarized along the X-axis, the SC broadening is governed by the nonlinear effects of four-wave mixing (FWM), cross-phase modulation (XPM) and stimulated Raman scattering (SRS). When the pump is polarized along the Y-axis, the SC generation is governed by the nonlinear effects of SRS.

Widely tunable soliton self-frequency shift and dispersive wave generation in a highly nonlinear fiber

Widely wavelength tunable soliton self-frequency shift (SSFS) from 1.58 μm to 2.07 μm was experimentally demonstrated in a highly nonlinear fiber pumped with a mode-locked sub-100 fs Er-doped fiber laser. The maximum output spectrum (full width at half maximum, FWHM) around 2 μm is 143 nm. Although the pulse width of SSFS was measured to be a few picoseconds, the large FWHM bandwidth of SSFS spectrum shows that soliton with sub-50 fs could be achieved if the giant chirped pulse is efficiently re-compressed to be transforms limited. Dispersive wave with a minimum pulse width of 50 fs was also observed.

Broad and ultra-flat optical parametric gain in tellurite hybrid microstructured optical fibers

We present the broad and ultra-flat optical parametric gain in the highly nonlinear tellurite fibers with tailored chromatic dispersion. The effect of pump wavelengths and powers on dual-pump configuration of four-wave mixing (FWM) are investigated. It is clarified that an ultra-flat gain bandwidth with 658 nm and ±0.01 dB fluctuation can be achieved at the dual-pumping power of 1.25 W. Moreover, a gain bandwidth with 1524 nm and 60 dB signal gain with gain ripples can be obtained at the dual-pumping power of 3.0 W in 25 cm-long hybrid tellurite microstructured optical fiber.

Experimental investigation cascaded stimulated Raman in chalcogenide optical fiber

Mid-infrared cascaded Stimulated Raman scattering (SRS) is experimentally investigated in an AsS optical fiber which fabricated based on As38S62 and As36S64 glasses and whose fiber loss was ∼0.09 dB/m at ∼2000 nm. Using a nanosecond laser operated at ∼1545 nm as the pump source, mid-infrared cascaded SRS up to eight orders is obtained in a 16 m AsS fiber. To the best of our knowledge, this is the first demonstration of eighth-order cascaded SRS in non-silica optical fibers, and it may contribute to developing tunable Raman fiber lasers in the mid-infrared region based on the C-band pump sources. When the pump wavelength switches to ∼2000 nm, only mid-infrared cascaded SRS up to five orders is obtained.

Highly nonlinear chalcogenide hybrid microstructured optical fibers with buffer layer and their potential performance of supercontinuum generation

We report here the design of a new chalcogenide hybrid microstructured optical fiber (HMOF) with a buffer layer around the core and its potential performance of tailoring chromatic dispersion and supercontinuum (SC) generation. The new chalcogenide HMOF has an AsSe2 core. The refractive index difference Δn between the AsSe2 core and cladding material is supposed to be 0.3. The fiber microstructure and the Δn between the core and buffer materials are designed in order to obtain broad anomalous dispersion regimes with near-zero and flattened chromatic dispersion profiles for broadband SC generation. Moreover, the suppression of chromatic dispersion fluctuation caused by fiber transverse geometry variation is investigated. By using the proposed chalcogenide buffer-embed HMOFs, the calculation shows that near-zero and flattened anomalous chromatic dispersion regimes from 4.5 μm can be obtained. When the variation of fiber structure occurs for ±1, ±5 and ±10 %, the chromatic dispersion fluctuation can be greatly suppressed. In addition, the calculation shows that a broad SC spectrum from 2.5 to more than 16.0 μm can be obtained when a 0.9-cmlong section of the new chalcogenide buffer-embed HMOF is pumped at 5.0 μm by a femtosecond laser with 1-kW peak power.

Mid-infrared supercontinuum generation in chalcogenide multi-step index fibers with normal chromatic dispersion

We experimentally demonstrate mid-infrared supercontinuum (SC) generation in chalcogenide multi-step index fibers (MSIF) pumped by a femtosecond laser. The fabricated chalcogenide MSIF is composed of a high refractive index core (C1) in the center, which is enclosed by a lower refractive index core layer (C2) and an outer cladding. This fiber structure is advantageous to tailor the chromatic dispersion with higher freedom and to keep the effective mode area small at long wavelengths. The high refractive index core, low refractive index core, and the outer cladding materials are As2Se3, AsSe2 and As2S5, respectively. When the diameter of C1 and C2 are 7.8 and 30 μm, respectively, the zerodispersion wavelength (ZDW) of the fiber is 12.5 μm. The chromatic dispersion profile is near-zero and flattened within the range of ±20 ps/km/nm in the wavelength range from 4 to 17 μm and a broad normal dispersion region is obtained in the wavelength range shorter than the ZDW. In practice, a 2.8 cm long fiber is pumped at 10 μm by using a femtosecond laser whose pulse width is ~200 fs. The SC generation extending from 2 to 14 μm is obtained. Most of its spectrum is in the normal dispersion region of the fiber. These results are promising for the highly coherent mid-infrared SC generation.

Optical Parametric Amplification Performance in AsSe2-based Hybrid Microstructured Optical Fibers

The performance of fiber-optical parametric amplification is studied by employing the AsSe2-based hybrid microstructured optical fiber (HMOF). By adding a buffer layer around the core with appropriate diameter and refractive index difference, the chromatic dispersion profile of chalcogenide HMOFs can be tailored to have a near-zero and flattened anomalous dispersion regime in the mid-infrared window. A very broad gain bandwidth can be achieved from 3.0 to 9.0 µm by pumping at 4.7 µm. The signal gain can be as high as 32 dB. In addition, the HMOF with buffer layer can suppress the chromatic dispersion variation caused by the fiber structure fluctuation and maintain the signal gain spectrum.

Coherent mid-infrared supercontinuum generation in all-solid chalcogenide microstructured fibers with all-normal dispersion

We report the coherent mid-infrared supercontinuum generation in an all-solid chalcogenide microstructured fiber with all-normal dispersion. The chalcogenide microstructured fiber is four-hole structure with core material of AsSe2 and air holes are replaced by As2S5 glass rods. Coherent mid-infrared supercontinuum light is generated in a 2-cm-long chalcogenide microstructured fiber pumped by a 2.7 μm laser. The simulated and experimental results have a good match and the coherence property of supercontinuum light in the chalcogenide microstructured fiber has been studied by using the complex degree of coherence theory. Coherent mid-infrared supercontinuum generation is extended to 3.3 μm in this work.

Highly nonlinear chalcogenide optical fibers with flattened chromatic dispersion invariant to the core fluctuation and their performances of parametric amplification

We report here the potential of fiber optical parametric amplification (FOPA) by using highly nonlinear chalcogenide double-cladding fibers. The fibers are designed with an AsSe2-based core layer surrounded by two cladding layers. The size and the refractive index differences (dn) between the core and cladding are investigated to obtain flattened chromatic dispersion spectra over a wide wavelength range up to the mid-infrared window. The inner cladding with dn2 is added to suppress the variation of the chromatic dispersion caused by the fluctuation of the core diameter. Our numerical calculations shows that very broad anomalous dispersion ranges from 5.0 μm up to 11.0 μm where the chromatic dispersion is less than 10 ps/km-nm can be obtained when the core diameter varies from 2.0 to 9.0 μm and the inner cladding diameter is kept at 9.0 μm. The dn1 and dn2 are 0.30 and 0.02, respectively. The FOPA calculation is carried out using a 3-cm-long fiber whose core diameter is 3 μm. When the pump power is 3 W at 5320 nm, a very broad gain bandwidth is obtained from 3.3 up to 11 μm. Moreover, the gain spectrum is flattened (about 32 ± 1 dB) in the ranges from 3.3 to 4.1 μm and from 7.5 up to 11.0 μm. When the core diameter fluctuates from 2.0 to 5.0 μm, the FOPA gain spectra can be maintained.

Flattened supercontinuum generation in tellurite-phosphate and chalcogenide-tellurite hybrid microstructured optical fibers with tailored chromatic dispersion spectra

We report here flattened supercontinuum (SC) generated in tellurite-phosphate and chalcogenide-tellurite hybrid microstructured optical fibers (HMOFs) whose chromatic dispersion spectra are tailored with high freedom due to large refractive index difference (∆n) between the core and cladding glasses. It is shown in the simulation that the tellurite-phosphate HMOF whose chromatic dispersion spectrum is near-zero and flattened with three zero-dispersion wavelengths (ZDWs) over a wide wavelength range from 1000 to 4000 nm is beneficial to obtain broad and flattened SC spectra. By using a large ∆n of 0.49, the tellurite-phosphate HMOF which has flattened chromatic dispersion and three ZDWs is successfully fabricated. When a 20-cm-long tellurite-phosphate HMOF is pumped at 1550 nm with a 1560-W peak power, an SC extended from ~800 to 2400 nm where ~5-dB spectral flatness in the wavelength ranges from 890 to 1425 nm and from 1875 to 2400 nm (~1060-nm bandwidth in total) is observed. In addition, a flattened SC spectrum with ~6-dB spectral flatness over a broad wavelength range from 950 to 3350 nm (2400-nm bandwidth in total) is generated by pumping a 1-cm-long chalcogenide-tellurite HMOF at 2300 nm with a 40-MW peak power.