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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.

We realized a tunable Brillouin laser and a tunable Raman laser by using ultrahigh-quality-factor (Q) hybrid microbottle resonators. The whispering-gallery-mode microresonator-based Brillouin and Raman lasers possess unique advantages (e.g. low threshold, narrow line width, and flexible lasing wavelength region) and various potential applications. Efficient tuning of the Brillouin and Raman microresonator lasers is desirable in many cases. However, the corresponding lasing wavelength tunability is rarely reported. In this work, we realized the ultralow-threshold Brillouin and Raman lasers based on the proposed hybrid microbottle resonators with Q factors over 108. Meanwhile, by feeding the control light through the axial direction of the hybrid microbottle resonators, a Brillouin lasing wavelength tuning range of 2.68 nm and a Raman lasing wavelength tuning range of 2.32 nm are realized, which are one order of magnitude and almost once larger than those reported in the previous works, respectively. Such tunable microlasers could find significant applications in light sources, microwave photonics, and optical sensing.

Polarization measurement has been widely used in material characterization, medical diagnosis and remote sensing. However, existing commercial polarization analyzers are either bulky schemes or operate in non-real time. Recently, various polarization analyzers have been reported using metal metasurface structures, which require elaborate fabrication and additional detection devices. In this paper, a compact and fully integrated silicon polarization analyzer with a photonic crystal-like metastructure for polarization manipulation and four subsequent on-chip photodetectors for light-current conversion is proposed and demonstrated. The input polarization state can be retrieved instantly by calculating four output photocurrents. The proposed polarization analyzer is complementary metal oxide semiconductor-compatible, making it possible for mass production and easy integration with other silicon-based devices monolithically. Experimental verification is also performed for comparison with a commercial polarization analyzer, and deviations of the measured polarization angle are

An all-optical control scheme of electromagnetically induced transparency (EIT) based on two coupled silica microbottle cavities coated with iron oxide nanoparticles is proposed and experimentally demonstrated. The specially designed and fabricated silica microbottle cavity with a short and spherical end, which is coated with iron oxide nanoparticles, possesses a quality (Q) factor of 1.39×108 and large all-optical tunability in a range of 282.32 GHz (2.25 nm) arising from the strong photothermal effect of the nanoparticles. Based on two coupled silica microbottle cavities, we achieve the EIT spectrum with a transparency window bandwidth of 2.3 MHz. The transparency window can be flexibly controlled by tuning the resonant frequency of the higher-Q microcavity. Besides, by tuning the resonant frequencies of the two microcavities separately, the whole EIT spectrum can be shifted with a range of 71.52 GHz, to the best of our knowledge, for the first time. Based on this scheme, we have realized all-optical and independent control of the transparency window and the whole EIT spectrum. We believe this work has great potential in applications such as light storage, optical sensing, and quantum optics.

Switching and routing are critical functionalities for a reconfigurable bandwidth-dense optical network, and great efforts had been made to accommodate mode-division multiplexing technology. Although the reconfigurable routing for spatial-mode groups between different optical paths was realized recently, a demultiplexing-switching-multiplexing process is necessary. Here we present a simplified and compact on-chip 2×2 multimode switch that can be easily upgradable to a larger scale. Fully and reconfigurable routing between not only optical paths but also spatial modes is achieved. To obtain a low loss multimode processing, a novel structure free from demultiplexing and re-multiplexing operations is adopted. The switch enables minimum and maximum insertion losses of 0.3 and 1.2 dB, with a compact footprint of 433 μm×433 μm and low crosstalk of