Dongdan Chen

400 mW ultrashort cavity low-noise single-frequency Yb 3+ -doped phosphate fiber laser

A compact, low-noise, single-frequency fiber laser by using a newly developed Yb³⁺ heavily doped single-mode phosphate glass fiber has been demonstrated. Over 400 mW stable continuous wave single transverse and longitudinal mode laser at 1.06 μm was achieved from a 0.8 cm long active fiber. The measured slope efficiency and estimated quantum efficiency of laser emission are 72.7% and 93%, respectively. The signal-to-noise ratio is higher than 72 dB, and the linewidth of the fiber laser is less than 7 kHz, while the measured relative intensity noise is less than -130 dB/Hz at frequencies of over 1.5 MHz.

1.95 μm kHz-linewidth single-frequency fiber laser using self-developed heavily Tm 3+ -doped germanate glass fiber

We demonstrated a kHz-linewidth single-frequency laser at 1.95 μm using the self-developed heavily Tm(3+)-doped single-mode germanate glass fiber with the net gain coefficient of 2.3 dB per centimeter. The maximum output power of the stable single longitudinal mode continuous wave laser is over 200 mW. The slope efficiency measured versus the absorbed pump power is 34.8%, the signal-to-noise ratio is higher than 68 dB and laser linewidth is less than 7 kHz. A wavelength-tuning from 1949.55 to 1951.23 nm was also demonstrated based on changing the tension on the fiber Bragg grating outside the cavity.

A 1014 nm linearly polarized low noise narrow-linewidth single-frequency fiber laser

We present the demonstration of a compact linearly polarized low noise narrow-linewidth single-frequency fiber laser at 1014 nm. The compact fiber laser is based on a 5-mm-long homemade Yb(3+)-doped phosphate fiber. Over 164 mW stable continuous-wave single transverse and longitudinal mode lasing at 1014 nm has been achieved. The measured relative intensity noise is less than -135 dB/Hz at frequencies of over 2.5 MHz. The signal-to-noise ratio of the laser is larger than 70 dB, and the linewidth is less than 7 kHz, while the obtained linear polarization extinction ratio is higher than 30 dB.

Synthesis and optical properties of chromium-doped spinel hollow nanofibers by single-nozzle electrospinning

Novel spinel hollow nanofibers were synthesized by a convenient single-nozzle electrospinning technique. Based on the composition and morphology results by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), a ‘gas-push’ model was proposed to elucidate the formation mechanism of hollow nanofibers during calcination. Photoluminescence (PL) properties of calcined ZnAl2O4: xCr3+ and MgAl2O4: xCr3+ nanofibers were investigated systematically. Under an excitation of 400 nm or 530–550 nm (4A2g→4T1g or 4A2g→4T2g transitions of Cr3+ ions), an emission band at 675–725 nm including a sharp emission line (R-line) at ∼687 nm with several vibrational sidebands was obtained. Compared with the spectroscopic properties of ZnAl2O4: xCr3+ nanofibers, the emission band was broadened and the decay lifetime was shortened for MgAl2O4: xCr3+ nanofibers. By calculation of crystal field strength, the value of Dq/B is estimated to be 3.25 and 2.72 for ZnAl2O4: xCr3+ and MgAl2O4: xCr3+ nanofibers, respectively. The difference of crystal field strength gives a good explanation of the spectroscopic and decay evolution between ZnAl2O4: xCr3+ and MgAl2O4: xCr3+ nanofibers.

Comparative investigation on structure and luminescence properties of fluoride phosphors codoped with Er3+/Yb3+

This paper reports on comparative investigation of structure and luminescence properties of tetragonal LiYF(4) and BaYF(5), and hexagonal NaYF(4) phosphors codoped with Er(3+)/Yb(3+) by a facile hydrothermal synthesis. The products were characterized by X-ray diffractometer, scanning electron microscope, and photoluminescence spectroscopy. Intense visible emissions centered at around 525, 550 and 650 nm, originated from the transitions of (2)H(11/2) --> (4)I(15/2), (4)S(3/2) --> (4)I(15/2), and (4)F(9/2) --> (4)I(15/2) of Er(3+), respectively, have been observed in all the samples upon excitation with a 980 nm laser diode, and the involved mechanisms have been explained. Based on the green up-conversion emission performance, the Yb(3+) concentrations of Er(3+)/Yb(3+)-codoped LiYF(4), BaYF(5), and NaYF(4) phosphors have been optimized to be 10, 20, and 20 mol*%, respectively. The quadratic dependence of fluorescence on excitation laser power has confirmed that two-photon contribute to up-conversion of the green-red emissions.

Microwave Signal Generation From a Dual-Wavelength Single-Frequency Highly

Narrow linewidth microwave signals generated from a heterodyne detection configuration of a dual-wavelength (DW) single-frequency highly Er3+/Yb3+ co-doped phosphate fiber laser is presented. The oscillating cavity of the fiber laser consists of a dual-channel narrow-band fiber-Bragg-grating (DC-NB-FBG), a 0.7-cm-long Er3+/ Yb3+ co-doped phosphate fiber and a wideband FBG (WB-FBG). The wavelength selecting gratings are spatially separated to create partially separated resonant cavities. Highly Er3+/Yb3+ co-doped phosphate fiber ensures that the mode competition is relatively weak under low pump power. DW single-frequency lasing with laser linewidths of 3 kHz is achieved. A 12.014-GHz microwave signal with a 3-dB linewidth of 3 kHz is obtained from the heterodyne detection of the DW fiber laser.

\hbox{Er}^{3+}/\hbox{Yb}^{3+}

The influence of fluoride and shielding gas (O2 or Ar) on the physical and spectroscopic properties of Er3+ doped TeO2-ZnO-ZnF2 glass system is investigated. The larger electronegativity of F than O accounts for the gradual decrease of refractive index, density, and J-O parameters with increasing ZnF2. An analysis on Fourier transform infrared transmission spectra reveals that the absorption coefficient of OH− around 3 μm as low as 0.247 cm−1 can be achieved when 30 mol% ZnF2 containing sample is treated with Ar gas during glass melting process. The reduction of OH− groups combined with the low multiphonon relaxation rate (207 s−1) contributes to the enhanced emissions at 1.5 and 2.7 μm, along with prolonged lifetimes of 4I11/2 and 4I13/2 levels. A high branching ratio (17.95%) corresponding to the Er3+: 4I11/2 → 4I13/2 transition, the large absorption and emission cross section (0.44 × 10−20 cm2 and 0.45 × 10−20 cm2), and good gain cross section demonstrate that oxyfluoride tellurite glass could be a promising material for a diode-pump 2.7 μm fiber laser.

Co-Doped Phosphate Fiber Laser

An all-fiber 10.9 W single-frequency one-stage linearly-polarized master-oscillator power amplifier (MOPA) laser at 1560 nm has been demonstrated. The laser linewidth is less than 3.5 kHz and the polarization-extinction ratio (PER) is greater than 24 dB. The measured signal-to-noise ratio (SNR) is higher than 70 dB and the optical-to-optical conversion efficiency is 29.5%. No obvious stimulated Brillouin scattering and the devastating effects of unwanted coupling light were observed.

Enhanced 2.7 μm emission from Er3+ doped oxyfluoride tellurite glasses for a diode-pump mid-infrared laser

The purity of the synthesized orbital-angular-momentum (OAM) light in the fiber is inversely proportional to channel crosstalk level in the OAM optical fiber communication system. Here the relationship between the fiber structure and the purity is firstly demonstrated in theory. The graded-index optical fiber is proposed and designed for the OAM light propagation with the purity higher than 99.9%. 16 fiber modes (10 OAM modes) have been supported by a specific designed graded-index optical fiber with dispersion less than 35 ps/(km∙nm). Such fiber design has suppressed the intrinsic crosstalk to be lower than -30 dB, and can be potentially used for the long distance OAM optical communication system.

10.9 W kHz-linewidth one-stage all-fiber linearly-polarized MOPA laser at 1560 nm

Er3+ doped tellurite fibers have been fabricated using a convenient suction technique. Different scanning calorimetry (DSC), Electro-probe micro-analyzer (EPMA), Raman, steady and dynamic luminescence spectra were performed to investigate their thermal, structure, and luminescent properties. Broadband 2.7 μm amplified spontaneous emission (ASE) emission with concurrent 1.5 μm and visible up-conversion emissions have been achieved in fibers with various lengths upon the excitation of 980 nm laser diode (LD). A quantitative study of the spectroscopic properties has been further analyzed in detail according to the Jude-Ofelt model, rate equation, and Dexter’s theory to evaluate the competitive relationship among them. The desirable spectroscopic characteristics associated with excellent thermal stability and mechanical properties indicate that the Er3+ doped tellurite fibers are excellent host matrices for 2.7 μm lasing and may provide applications in mid-infrared fiber lasers and amplifiers.