Shupei Mo

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.

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.

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+}

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.

Co-Doped Phosphate Fiber Laser

A novel linearly frequency modulated narrow linewidth single-frequency phosphate fiber laser has been demonstrated. The output power of the laser is more than 40 mW. A maximum frequency excursion of more than 700 MHz at the modulating bandwidth of 1 kHz has been achieved. Single longitudinal mode operation under modulation is confirmed and the linewidth of the laser is measured to be less than 2 kHz. This type of laser source shows real promise for applications in coherent optical frequency domain reflectometry.

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

We proposed a short-linear-cavity fiber laser with a virtual-folded-ring configuration, which combines the advantages of ring lasers and short-linear-cavity lasers. An all-fiber quarter-wave plate was used inside the cavity to introduce polarization retardation. By retarding the polarization of the travelling waves, the spatial-hole-burning effect was weakened and the efficient cavity length was extended to nearly twice its physical length. As a result, a single-frequency laser output with a linewidth of less than 820 Hz was obtained from the free-running fiber laser. The relaxation oscillation frequency was observed to be around 280 kHz and the signal to noise ratio of the laser output was >72 dB.

A linearly frequency modulated narrow linewidth single-frequency fiber laser

High-efficiency single-frequency compact master-oscillator power amplifiers (MOPAs) based on core-pumped highly Yb-doped phosphate fibers (YPFs), several centimeters long, are investigated theoretically and experimentally. By using numerical modeling and testing different YPF lengths to optimize the amplifier configuration, a stable output of more than 1.06 W, at 1014 nm, was measured experimentally from a MOPA laser, with a 4.0 cm long YPF. An optical-to-optical conversion efficiency of 81.4%, a typical net gain of more than 20.5 dB, and an output power per unit length of up to 265 mW/cm were obtained with this laser system. The measured optical signal-to-noise ratio of the MOPA laser is higher than 62 dB and the estimated laser linewidth is less than 20 kHz, without obvious broadening or degradation after amplification. There is excellent agreement between the results of the simulations and the experiments.

820 Hz linewidth short-linear-cavity single-frequency fiber laser at 1.5 μm

A compact 1064 nm linearly polarized low-noise single-frequency fiber laser has been demonstrated. An over 200 mW stable polarization-maintaining (PM) single-longitudinal-mode laser was achieved from an 8-mm-long custom-built non-PM Yb3+-doped phosphate fiber. The linear polarization extinction ratio (LPER) is larger than 30 dB. The measured relative intensity noise (RIN) is less than -125 dB/Hz at frequencies over 700 kHz. The linewidth of the fiber laser is estimated to be less than 2 kHz.

High-efficiency watt-level 1014 nm single-frequency laser based on short Yb-doped phosphate fiber amplifiers

A thorough investigation of the effect of amplified spontaneous emission (ASE) on the noise characteristics of a heavily Yb-doped phosphate fiber single-frequency laser at 1083 nm was made. Both the intensity noise and the frequency noise were measured and analyzed by introducing a band pass filter (BPF) into the fiber laser. For the intensity noise, it was found that the ASE noise is present at frequencies beyond the resonant relaxation oscillation (RRO) and until 6 MHz at low pump intensity, while it is diminished in the high power regime. Under a pump power of 42 mW, a maximum reduction of over 3 dB of the relative intensity noise (RIN) was observed with the help of the BPF. As for the frequency noise, a transition of the dominating noise sources from ASE noise in the low pump intensity condition to pump noise in the high pump intensity condition was observed. In the low power condition, more than 7 dB of the ASE noise was found to add to the frequency noise spectrum. It is believed that the obtained results will be helpful in understanding and optimizing the noise characteristics of this type of fiber laser.