L. R. Wang

Broadly Tunable Dual-Wavelength Erbium-Doped Ring Fiber Laser Based on a High-birefringence Fiber Loop Mirror

A broadly tunable dual-wavelength erbium-doped ring fiber laser based on a high-birefringence fiber loop mirror (HiBi-FLM) and a polarization controller is demonstrated experimentally. The measured transmission spectrum of HiBi-FLM covers a wide range from 1525 to 1575 nm. The wavelength of proposed laser can be flexibly tunable during this range of ∼50 nm by adjusting the polarization controller. In addition, the spacing of two wavelengths is adjustable by changing the length of HiBi fiber. The dual-wavelength lasers with the HiBi fiber length of 1 and 2 m are experimentally demonstrated and compared. The experimental results show that the proposed laser can stably operate on two wavelengths simultaneously at room temperature, and the output peak power variation is about 0.5 dB during 40 min.

Passively harmonic mode-locked erbium-doped fiber soliton laser with a nonlinear polarization rotation

Based on the nonlinear polarization rotation technique, we report on a stable passive 23rd harmonic mode-locked erbium-doped fiber soliton laser for the first time to the best of our knowledge. In this laser, 23 solitons are uniformly distributed in the cavity simultaneously, and all solitons have the same energy and duration. The increase of the coupler output enhances the dispersive radiation, and the longer cavity strengthens the interaction between solitons and dispersive waves. The two above factors play the key function to generate the 23rd harmonic mode-locked operation.

Spacing-tunable multi-wavelength fiber laser based on cascaded four-wave mixing in highly nonlinear photonic-crystal fiber

A multi-wavelength fiber laser based on the cascaded four-wave mixing in highly-nonlinear photonic-crystal fiber is proposed and investigated. The cascade operation is initiated by two strong pump waves boosted by multi-mode pumping erbium/ytterbium co-doped double-cladding fiber amplification technique. A segment of highly-nonlinear near-zero-dispersion-flattened photonic crystal fiber is employed to induce highly efficient cascaded four-wave mixing. The wavelength spacing can be continuously tunable by stretching the fiber Bragg grating. Experimental results show that multiple wavelengths with a high optical side-mode suppression-ratio of >30 dB are achieved. Furthermore, the proposed multi-wavelength fiber laser exhibits an excellent stability at room temperature.

Evolution of dual-wavelength solitons in an erbium-doped fiber laser

We report on experimental observations of dual-wavelength solitons in a passively mode-locked erbium-doped fiber laser. Two kinds of dual-wavelength solitons with different spectrum shapes are achieved. One is exhibited to have spectrum sidebands and the other one is shown to have the smooth profile without any sideband. The mode-locking mechanism at different central wavelengths is analyzed. Experimental results suggest that the pump level together with the cavity filtering effect play key roles in the generation of the dual-wavelength solitons.

Comparison of pulse evolutions in low and ultra-large anomalous dispersion mode-locked fiber lasers

We have investigated and compared the pulse evolutions in low and ultra-large anomalous dispersion erbium-doped fiber lasers mode-locked by the nonlinear polarization rotation technique. Two lasers deliver the pulses that exhibit quite distinct characteristics such as pulse duration, spectral width, and spectral sidebands. Experimental observations show that the spectral width decreases from several nanometers to less than one nanometer whereas pulse duration extends about three times by changing the cavity dispersion from −0.03 to −15.50 ps2. The solitons in ultra-large anomalous fiber laser show dips in the optical spectrum, which is quite distinct from that of conventional solitons observed in low anomalous regime.

Structural properties and Raman measurement of AlN films grown on Si (111) by NH3-GSMBE

Epitaxial growth of AlN has been performed by molecular beam epitaxy (MBE) with ammonia. The structural properties of materials were studied by cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). XRD and TEM diffraction pattern confirm the AlN is single crystalline 2H-polytype with the epitaxial relationship of (0001)AlNparallel to(111)Si, [11 (2) over bar0](AlN)parallel to[110](Si), [10 (1) over bar0](AlN)parallel to[11 (2) over bar](Si). Micro-Raman scattering measurement shows that the E-2 (high) and A(1) (LO) phonon mode shift 9 cm(-1) toward the low frequency, which shows the existence of large tensile strain in the AlN films. Furthermore, the appearance of forbidden A, (TO) mode and its anomalous shift toward high frequency was found and explained

Supercontinuum generation employing the high-energy wave-breaking-free pulse in a compact all-fiber laser system

Supercontinuum (SC) generation is experimentally achieved in a compact all-fiber laser system by using high-energy wave-breaking-free dissipative soliton (DS) pulses. The pulses exhibit Gaussian (rectangular) shape profiles in spectral (temporal) domain, which is even reversed of the typical rectangular-spectrum DSs. With the increase of pump power the pulse duration enlarges dramatically whereas the bandwidth and peak power of the pulse keep almost constant, which enables the pulse to accumulate much higher energy during the pulse-shaping process. When inputting the amplified pulse into the single-mode fiber, SC with excellent flatness is generated with the spectral range from about 1550 to 1700 nm. Broader SC with the bandwidth of even larger than 1000 nm can also be generated by this kind of pulse in the near-zero-dispersion-flattened photonic-crystal fiber through strong nonlinear effects.

Evolution of dissipative-soliton laser from molecule to multipulse

We report on the evolution of dissipative-soliton laser from single pulse to soliton molecule, lastly to multiple pulses. The experimental observations show that the pulse separation of soliton molecules is oscillating stochastically. It is found that the proposed fiber laser delivers pulses from a soliton to a soliton molecule, two solitons, a soliton molecule together with a soliton, and three solitons, respectively, when, the pump strength is enhanced gradually.

Comparison of supercontinuum generation based on high-energy nanosecond pulses via single-mode and photonic-crystal fibers

We have experimentally investigated the supercontinuum (SC) generation based on high-energy Gaussian-spectrum pulses emitted from an erbium-doped fiber laser with large-anomalous dispersion. The pulses exhibit rectangular shape in temporal domain with the pulse duration of about 16 ns. When the amplified pulses propagate through 10-km single-mode fiber, the SC ranged from 1530 to 1750 nm arises from the stimulated-Raman-scattering effect and the pulses break up due to the modulation instability. Comparatively, when the amplified pulses propagate through a segment of highly-nonlinear zero-dispersion-flattened photonic crystal fiber, super-broad SC beyond the range of 1300–1750 nm is generated due to strong four-wave mixing effect, whereas the pulses almost maintain their shapes.

Supercontinuum generation in standard single-mode fiber pumped by a nanosecond-pulse laser

We have experimentally investigated supercontinuum generation in a conventional single-mode fiber pumped with a nanosecond pulse source. The experimental results show that, when pump power increases, the spectral flatness is improved obviously and the spectral broadening only occurs in a red-shifted radiation rather than a blue-shifted radiation. A supercontinuum source is experimentally reported with a flatness of 4.7 dB over 180 nm (ranging from 1555 to >1735 nm) at pump power PR = 5 W and is predicted to have the flatness of less than 1 dB at PR > 8 W. The cascade of stimulated Raman scattering (SRS) together with soliton fission plays the key roles in supercontinuum generation.