Sheng-Ping Chen

Branch arm filtered coherent combining of tunable fiber lasers

A branch arm filtering technique is firstly proposed and experimentally demonstrated. A tunable band pass filter is inserted into one branch arm of the Mach-Zehnder type resonator instead of into the common arm as usual, in the coherent combining of two tunable fiber lasers. The arrangement improves the efficiency of the laser without obvious spectral quality penalty. The laser can be tuned from 1530 nm to 1570 nm with little power fluctuation, which is limited by the tuning range of the filter. A novel scaling scheme is also proposed, allowing the technique to be applied to the tuning of an extremely high power laser with a low power filter. The technique is expected to be compatible with other kinds of lasers such as linearly polarized lasers, Michelson type resonator and bulk lasers as well.

Efficient coherent combining of tunable erbium-doped fibre ring lasers

Two ring cavity tunable erbium-doped fibre lasers are coherently combined by employing a Mach–Zehnder interferometer in the laser cavity. The combining efficiency is about 95% over the tuning range from 1530 to 1565 nm, which is further improved to be larger than 97% by moving the optical tunable filter from the common arm to the branch arm of the Mach–Zehnder interferometer. The proposed combining scheme is expected to exhibit the potential ability of efficiently combining lasers with different powers and even different output coupling ratios.

Dual-stage superfluorescent fiber source with 1.16-W output power centered at 1561 nm

A 1.16-W superfluorescent fiber source (SFS) centered at 1561 nm with a 3-dB bandwidth of 8 nm has been achieved, under the pumping of a 3.56-W 976-nm laser diode array. The optical conversion efficiency reaches 32%. The source is constructed in a dual-stage configuration. The first stage is an ASE seed source with output power about 30 mW in the C band. The second stage is a backward-pumped high-power erbium-ytterbium-codoped double-clad fiber amplifier. An interesting phenomenon has been observed: low-power ASE seed source causes laser oscillation in the SFS, yet a relatively high-power ASE seed source prevents the SFS from lasing. The Rayleigh backscattering and the saturation effect of the amplifier are considered to explain the phenomenon.

Bandwidth broadening and efficiency enhancement of a double-pass forward L-band erbium-doped superfluorescent fibre source

A novel double-pass forward L-band erbium-doped superfluorescent fibre source (SFS) with a segment of unpumped fibre between the reflector and the wavelength division multiplexing (WDM) coupler is presented. The effects of the fibre length arrangement on the output characteristics of the L-band SFS are simulated. The spectral bandwidth is broadened and the conversion efficiency is enhanced by optimizing the fibre length ratio of the unpumped section to the total erbium-doped fibre. A broadband L-band SFS is obtained experimentally, with a 3 dB bandwidth of 46 nm, a power ripple less than 1 dB, and an output power of 23.6 mW.

Double-pass bidirectional pump broadband L-band erbium-doped superfluorescent fiber source

In this paper, a novel double-pass bidirectional pump broadband L-band erbium-doped superfluorescent fiber source (SFS) is demonstrated for the first time. In this fiber source, the EDF is divided into two segments, one of which (EDF2) is bidirectional pumped by a 980nm laser diode through two wavelength division multiplexers (WDM), and the other one (EDF1) is arranged between the reflector and the first WDM. EDF1 is unpumped. The fiber length ratio of the EDF1 length to the total length is defined as RL=LEDF1/(LEDF1+ LEDF2). The pump power ratio of forward to total pump power of EDF2 is defined as K=Pforward/Ptotal. The effects of the fiber length and pump power arrangement on the output characteristics of the L-band fiber source are simulated. With an appropriate pump power ratio K and an optimal fiber length ratio RL, broadband L-band erbium-doped SFS with flat output spectrum can be obtained. Additionally, the optimal fiber length ratio RL is also depended on the pump power ratio K. When K>0.4, the optimal RL tends to be changeless. When K=0.1, the optimal RL is 0 and widest flat spectrum is achieved with a 3-dB bandwidth of 63 nm (1540nm-1603nm).

Cavity optimization of erbium-ytterbium co-doped fiber ring lasers

The cavity configurations of erbium-ytterbium co-doped fiber ring lasers (EYDFL) have been experimentally investigated. Additional attention has been paid to the mode competition effect of the laser. It is demonstrated that even in a traveling wave cavity, mode competition occurs when the cavity configuration or the output splitting ratio are incorrectly chosen. By employing the proper cavity configuration and an optimal output splitting ratio, an extremely stable ring cavity EYDFL with fine-shaped laser spectrum is obtained at 1565.8nm. Output power of 1.07 W is achieved under 3.5W 976nm pump power, with an optical conversion efficiency of 30.6%.

A novel temperature sensor and variable optical attenuator based on a high-birefringence fiber loop mirror

A novel variable optical attenuator based on a high-birefringence fiber loop mirror is described. The fiber loop mirror is placed in a controlled-temperature chamber. As the temperature is increased, the transmission spectrum exhibits a shift, while virtually not changing its shape. The degree of attenuation at a wavelength of 1558 nm exceeds 30 dB, while the introduced losses are about 2.5 dB. The temperature-induced shift of the spectrum is strictly linear. The response of the temperature sensor based on this effect is linear with a correlation coefficient of 0.9997. The obtained experimental data are interpreted based on the results of numerical modeling.

Comparison between the performance of the P-doped and Ge-doped Raman fiber lasers based on numerical simulations

With a published model that describes a nested fiber Raman cavity using FBGs as reflectors, we have made numerical simulations for the comparison between the performance of P-doped and Ge-doped fiber. Although the former fibers are the standard choice for fiber Raman lasers due to the large Raman gain, the latter can be also of interest because they present a large Raman shift so that the configuration of the Raman fiber laser can be simplified. We have considered a two-step Raman laser using a P-doped fiber and a six-step Raman laser using a Ge-doped fiber, both pumped by 1060 nm and emitting at 1480 nm. The effects of the Raman fiber length, output coupler reflectivity and splice loss upon the behavior of both lasers are studied. Simulation results show that the P-doped fiber laser requires a longer fiber length while the Ge-doped fiber laser requires a higher output mirror reflectivity, and the RFL using Ge-doped fiber is more sensitive to the splice loss because of its large Stokes wave number. Finally, by comparison in the optimum configuration, we find that the P-doped fiber laser shows better output characteristics than Ge-doped fiber laser.

Large-mode-area Yb3+-doped photonic crystal fiber laser

In this paper a large mode area Yb3+-doped double cladding photonic crystal fiber laser is reported. The lasers output power reaches as high as 4.3W. The slope efficiency and the maximum optical-to-optical efficiency of laser output are 69.4% and 59.7%, respectively, with respect to absorbed pump power. Single transverse mode operation is obtained at central wavelength of 1072.3nm and the measured mode distribution agrees with the simulation by using scalar beam propagation method.

Spectrum presliced multiwavelength fiber source in bidirectional pumping configuration

A bidirectionally pumped spectrum pre-sliced multi-wavelength fiber source is presented in the paper. Two 980nm laser diodes (LDs) are engaged to provide the pump power. An optimized double pass Mach-Zehnder interferometer with extinction ratio larger than 41dB is utilized as the comb filter. The extinction ratio of the fiber source is larger than 24.5dB in the whole C band, and almost reaches 29dB at 1530nm. Integral power of each channel is 0.58mW at 1550nm under 112.3mW total pump power. Channel spacing and bandwidth are 0.81nm and 0.30nm, respectively.