Shanhui Xu

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.

Broadly tuning Bi3+ emission via crystal field modulation in solid solution compounds (Y,Lu,Sc)VO4:Bi for ultraviolet converted white LEDs

For phosphor-converted white LEDs (pc-WLEDs) based on UV chips, it is essential to search for highly efficient phosphors that have broadly tunable emissions and minimal excitation in the visible range. This would allow the designer of pc-WLEDs to select the desirable emission wavelength and, thereby, fabricate the device with color perception comfortable for the human eye. Conventional rare earth schemes, for instance Ce3+ or Eu2+ doped phosphors, can be tuned in emission wavelengths, but they cannot overcome the severe intrinsic excitation in the range from blue to green. We report here that Bi3+, the valence of which is confirmed by X-ray photoelectron spectra, exhibits almost no excitation in the visible range and has an extremely broad emission covering the full visible spectral range with internal quantum efficiency up to 75% when substituted into the solid solution compounds (Y,Lu,Sc)VO4:Bi. When the crystal field around Bi3+ is tuned by gradual substitution of smaller lanthanide ions for larger lanthanide ions in solid solution, the emission peak position can be modulated linearly between 566 nm and 635 nm due to the susceptibility of bismuth naked 6s electrons to the local environment. In accordance with Rietveld refining results, static and transient photoluminescence spectra reveal the existence of a single type of Bi3+ emission center in the sample, and energy transfer from VO43− group to Bi3+ upon excitation into the charge transfer state of VO43− groups. The mechanism of concentration quenching of Bi3+ emission occurs possibly due to dipole–quadrupole rather than exchange interactions. This work shows the potential application of bismuth doped samples in UV converted pc-WLEDs.

3 GHz, fundamentally mode-locked, femtosecond Yb-fiber laser.

We demonstrate a fundamentally mode-locked Yb-fiber laser with 3 GHz repetition rate and ∼206  fs pulse duration. The laser incorporates two enabling technologies: a 1 cm heavily Yb-doped phosphate glass fiber as the gain medium and a high-dispersion (-1300  fs2) output coupler to manage cavity dispersion. The oscillator self-starts and generates up to 53 mW average power.

Low noise single-frequency single-polarization ytterbium-doped phosphate fiber laser at 1083 nm

We present a low noise single-frequency and single-polarization distributed Bragg reflector fiber laser at 1083 nm by using a 1.8 cm long newly developed ytterbium-doped phosphate single mode glass fiber. The maximum output power is more than 100 mW with a slope efficiency of >29.6%. The signal to noise ratio is higher than 61 dB and the laser linewidth of less than 2 kHz is estimated. The obtained relative intensity noise for frequencies of over 4.0 MHz is less than -150 dB/Hz, which approaches the shot noise limit. The achieved linear polarization extinction ratio is more than 30 dB.

Broadband NIR luminescence from a new bismuth doped Ba 2 B 5 O 9 Cl crystal: evidence for the Bi 0 model

A new type of bismuth doped Ba(2)B(5)O(9)Cl crystal is reported to exhibit broadband near infrared (NIR) photoluminescence at room temperature, which has been identified here originating from elementary bismuth atom. Rietveld refining, static and dynamic spectroscopic properties reveal two types of Bi(0) centers in the doped compound due to the successful substitution for two different nine-coordinated barium lattice sites. These centers can be created only in a reducing condition, and when treated in air and N(2)/H(2) flow in turn, they can be removed and restored reversely. As the dwelling time is prolonged in N(2)/H(2) at high temperature, conversion from Bi(2+) to Bi(0), as reflected by changes of their relative emission intensities, is witnessed in the crystal of Ba(2)B(5)O(9)Cl:Bi. The lifetime of the NIR luminescence was observed in a magnitude of ~30 μs, rather different from bismuth doped either glasses or crystals reported previously.

3-Dimensional heat analysis in short-length Er 3+ /Yb 3+ co-doped phosphate fiber laser with upconversion

A 3-dimenstional (3D) heat flow model of laser diode (LD) pumped short-length Er(3+)/Yb(3+) heavily co-doped phosphate fiber laser that includes the energy-transfer upconversion (ETU) effects has been developed. The fully 3D analytical solution with the consideration of longitudinal heat flow has been given to describe the temperature distribution in phosphate fiber. The calculated results show that both ETU processes and longitudinal heat conduction have a great influence on the fiber laser performance. Finally, we have validated the analytical expression by measuring the temperature distribution of an end-pumped short-length Er(3+)/Yb(3+) co-doped fiber laser, which was placed into the copper tube.

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.

Wave-breaking-free pulse in an all-fiber normal-dispersion Yb-doped fiber laser under dissipative soliton resonance condition

We reported on the dissipative soliton resonance (DSR) phenomenon in a mode-locked Yb-doped fiber laser by using the nonlinear polarization rotation technique. It was found that the multi-pulse oscillation under high pump power could be circumvented by properly adjusting the polarization controllers, namely, the wave-breaking-free rectangular pulse in DSR region was achieved. As the DSR signature, the pulse duration varied from 8.8 ps to 22.92 ns with the increasing pump power. Correspondingly, the maximum pulse energy was 3.24 nJ. The results demonstrated that the DSR phenomenon could exist in Yb-doped fiber lasers, which could be used to achieve wave-breaking-free, ultrahigh-energy pulse.

Narrow linewidth single frequency microfiber laser

A compact 2 kHz linewidth single frequency microfiber ring laser is demonstrated. Microfiber, with a diameter of 1.88 μm, which is drawn from an Er(3+)/Yb(3+) co-doped phosphate glass fiber, serves as the gain medium. By using this microfiber, a double-knot resonator with a total length of 1.75 mm is constructed. Based on this resonator, a narrow linewidth single frequency laser with output power higher than 0.95 μW is obtained at the wavelength of 1536.1 nm. The linewidth of this microfiber laser is as narrow as 2 kHz, and the side-mode-suppression ratio is higher than 38 dB.

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.