A simple iterative model is introduced quantifying the interaction of saturable gain and nonlinear loss in a mode-locked laser cavity. The resulting geometrical description of the laser dynamics completely characterizes the generic multi-pulsing instability observed in experiments. The model further shows that the onset of multi-pulsing can be preceded by periodic and chaotic transitions as recently confirmed in theory and experiment. The results suggest ways to engineer the nonlinear losses in the cavity in order to achieve an enhanced performance.

We demonstrated an all fiber actively mode-locked laser that emits a cylindrical vector beam. An intra-cavity few-mode fiber Bragg grating inscribed in a short section of four-mode fiber is employed to provide mode selection and spectrum filtering functions. Mode coupling is achieved by offset splicing between the single-mode fiber and the four-mode fiber in the laser cavity. A ${\mathrm{LiNbO}}_3$ Mach–Zehnder modulator is used to achieve active mode-locking in the laser. The laser operates at 1547 nm with 30 dB spectrum width of 0.2 nm. The mode-locked pulses have a duration of 2 ns and repetition of 12.06 MHz. Through adjusting the polarization state in the laser cavity, both radially and azimuthally polarized beams have been obtained with high mode purity.

We demonstrate a novel all-fiber laser generating cylindrical vector beams with high slope efficiency and low threshold by introducing a long-period fiber grating into the laser cavity. Highly efficient mode conversion is realized by an LPFG at $\sim 1548\mathrm{nm}$. Mode selection and spectrum filtering are achieved in combination with a two-mode fiber Bragg grating (TM-FBG). The fiber laser operates at a single wavelength of 1547.95 nm with a 30 dB linewidth of less than 0.18 nm and a side-mode suppression ratio (SMSR) of more than 56 dB. The lasing threshold and slope efficiency of the laser are 24.5 mW and 35.41%, respectively. The output power is 72 mW with an absorbed pump power of 225 mW. The variation of slope efficiency with respect to the reflectivity of the TM-FBG is investigated. Through adjusting the intra-cavity polarization controller, high-purity radially and azimuthally polarized beams are both obtained.

With the great developments in optical communication technology and large‐scale optical integration technology, it is imperative to realize the traditional functions of polarization processing on an integration platform. Most of the existing polarization devices, such as polarization multiplexers/demultiplexers, polarization controllers, polarization analyzers, etc., perform only a single function. Definitely, integrating all these polarization functions on a chip will increase function flexibility and integration density and also cut the cost. In this article, we demonstrate an all‐in‐one chip‐scale polarization processor based on a linear optical network. The polarization functions can be configured by tuning the array of phase shifters on the chip. We demonstrate multiple polarization processing functions, including those of a multiple‐input‐multiple‐output polarization descrambler, polarization controller, and polarization analyzer, which are the basic building blocks of polarization processing. More functions can be realized by using an additional two‐dimensional output grating. A numerical gradient descent algorithm is employed to self‐configure and self‐optimize these functions. Our demonstration suggests great potential for chip‐scale, reconfigurable, and fully programmable photonic polarization processors with the artificial intelligence algorithm.

Stable octave-spanning supercontinuum (SC) in the mid-infrared (MIR) region finds extensive applications in spectroscopy, metrology, biochemistry, etc. The absorption of conventional silicon- or silicon oxide-dominated nonlinear media makes SC generation in MIR region technically challenging. In this paper, we propose ultrabroadband MIR-SC generation using a suspended germanium-membrane ridge waveguide. We theoretically showed that when pump pulses centered at 4.8 μm with pulse width at 180 fs and peak power at 800 W are injected into a 4-mm-long proposed ridge waveguide, the SC generated ranges from 1.96-12 μm (about 2.6 octaves), extending deep into the “fingerprint” region. The first-order coherence is calculated to confirm the stability of the generated SC. The performance of the SC-based frequency comb is also investigated by assuming a 100-pulses pump source at a repetition rate of 100 kHz.