Single-frequency upconverted laser generation by phase summation

The phase summation effect in sum-frequency mixing process is utilized to avoid a nonlinearity obstacle in the power scaling of single-frequency visible or ultraviolet lasers.Two single-frequency fundamental lasers are spectrally broadened by phase modulation to suppress stimulated Brillouin scattering in fiber amplifier and achieve higher power.After sum-frequency mixing in a nonlinear optical crystal,the upconverted laser returns to single frequency due to phase summation,when the phase modulations on two fundamental lasers have a similar amplitude but opposite sign.The method was experimentally proved in a Raman fiber amplifier-based laser system,which generated a power-scalable sideband-free single-frequency 590 nm laser.The proposal manifests the importance of phase operation in wave-mixing processes for precision laser technology.

High-power 1560 nm single-frequency erbium fiber amplifier core-pumped at 1480 nm-ERRATUM

The publisher apologises that due to a publishing error this article was published into volume 10(2022)rather than volume 11.Unfortunately,we are unable to correct this error and so this article has now been updated to confirm the publishing volume as volume 10(2022).Any accepted and publication dates associated with the article are still correct.

High-power 1560 nm single-frequency erbium fiber amplifier core-pumped at 1480 nm

High-power continuous-wave single-frequency Er-doped fiber amplifiers at 1560 nm by in-band and core pumping of a 1480 nm Raman fiber laser are investigated in detail.Both co-and counter-pumping configurations are studied experimentally.Up to 59.1 W output and 90%efficiency were obtained in the fundamental mode and linear polarization in the co-pumped case,while less power and efficiency were achieved in the counter-pumped setup for additional loss.The amplifier performs indistinguishably in terms of laser linewidth and relative intensity noise in the frequency range up to 10 MHz for both configurations.However,the spectral pedestal is raised in co-pumping,caused by cross-phase modulation between the pump and signal laser,which is observed and analyzed for the first time.Nevertheless,the spectral pedestal is 34.9 dB below the peak,which has a negligible effect for most applications.

Nd3+-doped silica glass and fiber prepared by modified sol-gel method

Large-size Al^(3+)/Nd^(3+)co-doped silica glass with 5000 ppm Nd^(3+)and 50,000 ppm Al^(3+)doping concentrations was prepared by the modified sol-gel method combined with high-temperature melting and molding technology.Electron probe microanalyzer tests indicated that high doping homogeneity was achieved with this sample preparation method.The spectral properties of the Nd^(3+)ions were evaluated.Nd^(3+)-doped silica fiber(NDF)with a core-to-clad ratio of 20/125μm was drawn from the preform with the Al^(3+)/Nd^(3+)co-doped silica glass as the core.In the laser oscillation experiment,a maximum output power of 14.6 W at 1.06μm with a slope efficiency of 39.6%was obtained from the NDF pumped by a commercial808 nm laser diode.To the best of our knowledge,this is the highest laser power reported for an NDF operated at 1060 nm and prepared by a non-chemical vapor deposition method.In the master oscillator power amplifier experiment,a maximum power of 16.6 W corresponding to a slope efficiency of 30.5%at 1061 nm was also demonstrated.The laser performance of the NDF exhibited the great advantages and potential of the modified sol-gel method in fabricating Nd^(3+)-doped silica glass for a new type of NDFs like large mode area fibers and fibers with large diameter ratio of core/cladding.

Temperature dependence of spectral and laser properties of Er3+/Al3+ co-doped aluminosilicate fiber

Using a heavily erbium-doped aluminosilicate fiber prepared by the sol-gel method combined with high temperature sintering, the temperature dependence of the spectrum around the 1.55 nm band and single-mode fiber laser properties were investigated, respectively. The absorption cross section increases 29.2% at ~1558 nm with the temperature increasing from 20℃ to 140℃, while the emission cross section slightly increases4.3%. In addition, the laser slope of the heavily erbium-doped aluminosilicate fiber at 1558 nm decreases4.4% from 10.8% to 6.4% with the temperature increasing from 18℃ to 440℃. Meanwhile, an experiment lasting3 h proves that the fiber laser has excellent stability below 440℃.