Influence of Pump Current Waveform on The Mitigation of Transverse Mode Instability in Fiber Laser Oscillator.

We carry out a detailed investigation of TMI mitigation by pump modulation based on multiple current waveforms in a fiber laser oscillator. Compared with continuous wave (CW), the modulation of various waveforms, including sinusoidal wave, triangular wave, and pulse wave with a duty cycle of 50% and 60%, can increase the TMI threshold. The average output power of a stabilized beam is boosted via the adjustment of phase difference between the signal channels. The TMI threshold is increased to 270 W under a modulation of pulse wave (duty cycle: 60%) with a phase difference of 440 µs, where the beam quality is 1.45. This threshold can be further improved by adding groups of pump LDs and drivers, which is a promising approach for beam stabilization of high-power fiber lasers.

Stable single transverse mode excitation in 50 µm core fiber using a photonic-lantern-based adaptive control system.

We report on the generation of single transverse mode output in large-mode-area fiber with a core diameter of 50 µm using a 3×1 photonic-lantern-based adaptive spatial mode control system. We have designed and fabricated the photonic lantern composed of a single mode fibers bundle taper region and a multi-segment multimode fiber splicing region. From simulation and experiments, we demonstrate that the quality of the output beam is significantly influenced by the size of the fibers bundle's waist and the segmented splicing scheme of the multimode fiber. Stable single transverse mode output is achieved at 1064 nm with M2 ∼1.4, which will provide a possible technical solution to increase the mode instability threshold in high power large-mode-area fiber systems.

Review of MEMS Based Fourier Transform Spectrometers.

Fourier transform spectrometers (FTS), mostly working in infrared (IR) or near infrared (NIR) range, provide a variety of chemical or material analysis with high sensitivity and accuracy and are widely used in public safety, environmental monitoring and national border security, such as explosive detection. However, because of being bulky and expensive, they are usually used in test centers and research laboratories. Miniaturized FTS have been developed rapidly in recent years, due to the increasing demands. Using micro-electromechanical system (MEMS) micromirrors to replace the movable mirror in a conventional FTS system becomes a new realm. This paper first introduces the principles and common applications of conventional FTS, and then reviews various MEMS based FTS devices.

Theoretical proposal of a low-loss wide-bandwidth silicon photonic crystal fiber for supporting 30 orbital angular momentum modes.

We propose a novel four-ring hollow-core silicon photonic crystal fiber (PCF), and we systematically and theoretically investigate the properties of their vector modes. Our PCF can stably support 30 OAM states from the wavelength of 1.5 µm to 2.4 µm, with a large effective refractive index separation of above 1×10-4. The confinement loss is less than 1×10-9 dB/m at the wavelength of 1.55 µm, and the average confinement loss is less than 1×10-8 dB/m from the wavelength of 1.2 µm to 2.4 µm. Moreover, the curve of the dispersion tends to flatten as the wavelength increases. In addition, we comparably investigate PCFs with different hole spacing. This kind of fiber structure will be a potential candidate for high-capacity optical fiber communications and OAM sensing applications using fibers.