Jinyong Leng

Coherent beam combination of 1.08 kW fiber amplifier array using single frequency dithering technique.

Coherent beam combination of a 1.08u2009kW fiber amplifier array has been demonstrated for the first time, to our knowledge. In the experiment, nine fiber amplifiers are tiled into a 3×3 array, and the output power of each amplifier is approximately 120u2009W. A single frequency dithering algorithm is used to compensate the phase noises between the elements, which runs on a signal processor based on field programmable gate array for phase control on the fiber amplifiers. When the phase control system goes into closed loop, the fringe contrast of the far-field intensity pattern is improved to more than 85%, and the residual phase error is less than λ/15.

Efficient generation of broad Raman sidebands in an index-guided photonic crystal fiber.

The efficient generation of broad Raman sidebands is experimentally demonstrated in a short piece of index-guided photonic crystal fiber, which is pumped by a high-peak-power pulse near the zero-dispersion wavelength and seeded by a continuous-wave Stokes signal centered at 1117 nm. The Raman sidebands generated via stimulated Raman scattering and cascaded four-wave mixing contain five Stokes and six anti-Stokes peaks and span from 827 to 1398 nm, and the 3 dB linewidth for each peak is smaller than 1 nm. However, the pure Raman sidebands are largely dependent on the pulse pump power as well as the fiber length.

29.2 W, 20 kHz linewidth all fiber single-frequency MOPA laser

We demonstrate a high power all fiber single-frequency MOPA laser. The center wavelength of the single-frequency fiber laser seed is 1064 nm with a linewidth narrower than 20 kHz. A two-stage power amplification configuration is employed. A single-frequency fiber laser with an output power of 29.2 W is obtained, and the optical to optical efficiency is 78%.

Cascaded four-wave mixing seeded by two continuous wave signals

We report on the broadband-cascaded four-wave mixing (CFWM) products generated in a photonic crystal fiber pumped by a picosecond pulse and seeded by two continuous wave (CW) signals. The equal and unequal frequency spaced CFWM products could be obtained through continuously tuning one of the CW wavelengths. Among the equally spaced CFWM products, the smallest frequency spacing was 477 GHz. The influences of the Raman scattering and the third-order dispersion on the CFWM were also discussed.

Phase-locking of rapidly changing phase fluctuations in a strongly pumped fibre amplifier using a stochastic parallel gradient descent controller

We demonstrate phase-locking of the rapidly changing phase fluctuations in a strongly pumped fibre amplifier using a stochastic parallel gradient descent (SPGD) controller. The rapidly changing phase fluctuations are measured using a multi-dithering technique. The bandwidth requirement for an active phase controller is estimated by computing the structure function of the phase fluctuations. It is revealed that in our experimental setup, the phase fluctuation rates of λ/10 averaged amplitude are 830 Hz, 3.1 kHz and larger than 10 kHz under total pump powers of 71 W, 181 W and 230 W, respectively. A DSP-based SPGD controller with an iteration rate of 16 500 times per second is developed. Phase-locking is demonstrated under the pump power of 181 W. The amplified fibre laser beam interferes with a reference beam at the far-field plane to diagnose the phase-locking performance. It is shown that the peak intensity is increased by a factor of 1.57 and the visibility of the far-field pattern is higher than 0.56 when the system is in closed loop. The residual error is computed to be 0.07 waves from the far-field fringe pattern. The control error of the SPGD controller is restricted to be less than 1/25 wavelength by analysing the video document.