Spatiotemporal Mode-Locking in Lasers with Large Modal Dispersion.

Dissipative nonlinear wave dynamics have been investigated extensively in mode-locked lasers with single transverse mode, whereas there are few studies related to three-dimensional nonlinear dynamics within lasers. Recently, spatiotemporal mode locking (STML) was proposed in lasers with small modal (i.e., transverse-mode) dispersion, which has been considered to be critical for achieving STML in those cavities because the small dispersion can be easily balanced. Here, we demonstrate that STML can also be achieved in multimode lasers with much larger modal dispersion, where we find that the intracavity saturable absorber plays an important role for counteracting the large modal dispersion. Furthermore, we observe a new STML phenomenon of passive nonlinear autoselection of single-mode mode locking, resulting from the interaction between spatiotemporal saturable absorption and spatial gain competition. Our work significantly broadens the design possibilities for useful STML lasers thus making them much more accessible for applications, and extends the explorable parameter space of the novel dissipative spatiotemporal nonlinear dynamics that can be achieved in these lasers.

Optofluidic variable optical attenuator controlled by electricity.

An optofluidic variable optical attenuator (VOA) is proposed in this paper, where the microfluidic driving technology adopts the electrically controlled way. The proposed driving technology solves some problems of existing microfluidic driving technologies and introduces a simple structure, a small volume, high precision, and a quick response for the VOA. This VOA has some advantages over other VOAs, such as a wide wavelength band (from visible light to the near infrared), a wide adjustable attenuation range, a low wavelength-dependent loss, and a quick response. The experiment results indicate that the attenuation range of this VOA is more than 80 dB and the wavelength-dependent loss is 0.09 dB at an attenuation of 20 dB in the C-band. Most VOAs have millisecond-scale response times, whereas the response time here is about 155-180 µs. Our work shows a new way to design miniaturized VOAs with good performance and can also promote optofluidics.