High-Q-factor phase-shifted helical fiber Bragg grating by one-step femtosecond laser inscription for high-temperature sensing.

The phase-shifted fiber Bragg grating (FBG) plays an important role in optical communication and sensing due to its ultra-narrow 3-dB bandwidth. Here, we demonstrate the fabrication and thermal property of a high-quality (Q)-factor phase-shifted helical fiber Bragg grating (PS-HFBG). A single-mode fiber is twisted and then inscribed point-by-point with a third-order uniform FBG by a single round of laser irradiation. The grating is curved slightly into a helical shape after the torsion is released, generating a phase shift in the grating. With annealing treatment, the PS-HFBG responds very stably to temperature with a linear sensitivity of 15.24 pm/°C within the range from 100 to 1100°C. Moreover, the PS-HFBG peak tends to narrower for higher temperature and the minimum 3-dB bandwidth is as low as 32 pm, indicating the highest Q-factor of 4.91 × 104. In addition, the PS-HFBG shows a low strain sensitivity (0.896 pm/µ ε). The proposed device is very promising to be applied as a high-precision and stable high-temperature sensor.

Experimental observation of shaking soliton molecules in a dispersion-managed fiber laser.

Recent progress in real-time spectral interferometry enables access to the internal dynamics of optical multisoliton complexes. Here, we report on the first, to the best of our knowledge, experimental observation of shaking soliton molecules by means of the dispersive Fourier transform technique. Beyond the simplex vibrating soliton pairs, multiple oscillatory motions can jointly involve in the internal dynamics, reminiscent of the shaking soliton pairs. Both quasi-periodically and chaotically evolving phase oscillations are approached in the sense of different oscillatory frequencies. In addition, the shaking soliton pair combined with sliding phase dynamics is also observed, and is interpreted as the superposition of two different internal motions. All of these results shed new light on the internal dynamics of soliton molecules with higher degrees of freedom, as well as enrich the framework toward multisoliton complexes.

Design of an arbitrary ratio optical power splitter based on a discrete differential multiobjective evolutionary algorithm.

Traditional photonic integrated devices are designed to predict their optical response by transforming the structure and parameters, and it is often difficult to obtain devices with excellent performance in all aspects. The nanophotonic computing design method based on the optimization algorithm has revolutionized the traditional photonic integrated device design technology. Here, we report a discrete differential evolution algorithm that simulates a natural selection process to achieve an ultracompact arbitrary power ratio splitter. The footprint of the designed splitter is only ${2.5}\;\unicode{x00B5} {\rm m} \times {2}.{5}\;\unicode{x00B5} {\rm m}$2.5µm×2.5µm, the simulated total transmission efficiency is above 90%, the power ratio error is less than 3%, and it can work normally over the C-band. Our algorithm can provide new ideas for the application of genetic algorithms to the automatic optimization of photonic integrated devices.