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The accurate calibration of large-scale switch networks is critical for integrated photonics, in which the integrated optical true time delay chip is typical. In this work, a novel self-calibration method without extra testing ports is proposed by introducing lossless thermo-optic phase shifters instead to calibrate the network. As a demonstration, a 5-bit delay line based on silicon nitride is fabricated and calibrated. The extinction ratio of all the switches is greater than 30.9 dB at the cross and bar states. Using this method, the 5-bit optical delay line which can be tuned in a range of 118.53 ps and reach a low delay time deviation less than ±0.4 ps.

In this work, an ultra-low loss silicon nitride (SiN) edge coupler was designed and fabricated to interface with a single-mode fiber (SMF). Unlike other works that focus on the core structure, this work focuses on the cladding structure. First, it is demonstrated that the cladding structure ultimately determines the size and shape of the mode when the taper tip width is small enough. Then, the thickness of the up-cladding is optimized to provide enough space for mode expansion in the vertical direction. Air trenches are added to confine the mode laterally. In addition, the refractive index (RI) of the up-cladding layer is slightly increased to prevent light from leaking into the Si substrate. This edge coupler is then fabricated on the SiN platform at Chongqing United Microelectronics Center. For the TE mode at 1630 nm, a coupling loss of 0.67 dB/facet was obtained. At 1550 nm, 0.85 dB/facet and 1.09 dB/facet were measured for the TE and TM modes, respectively, which means that the polarization-dependent loss is 0.24 dB. Although the design method and the structure are based on a pure SiN platform, they are applicable to a silicon-on-insulator platform as well.

The opal photonic crystals were fabricated with silica colloidal particles. These opal photonic crystal samples were annealed at 150, 300, 450C separately. For the photonic crystals annealed at 450C, the central wavelength of photonic band gap (PBG) was measured at 572.5 nm, which was greatly different from the calculated result at 605 nm. In addition, the samples showed a blue shift for 22.5 nm and a reduction of the photonic band gap width upon increasing the annealing temperature. The shrink and deformation of silica colloidal particles were observed by SEM. The influence mechanism of the deformation was analyzed quantitatively, and the theoretical model was amended. The central wavelength of PBG re-calculated with the amended dodecahedron model was 558 nm, which fit the measured result much better than that calculated with the old sphere model. The new dodecahedron model provides a way to analyze the optical properties of the deformed opal PCs in theory, and shall be of significant value on the fabrication and application of photonic crystals devices.

A new approach to achieve efficient coupling between photonic crystals and a nanometer waveguide via an asymmetric resonator is proposed. The asymmetric resonator was composed of the photonic crystal and the nanometer waveguide was constructed by elongating a rod of the photonic crystal resonator horizontally. By introducing the asymmetric resonator, the nanometer waveguide served as a part of the resonator, and the coupling between the photonic crystal waveguide and the nanometer waveguide was converted to internal coupling between the photonic crystal devices. The 3D theoretical coupling efficiency reached 91.31%. Such compact, efficient coupling shows great promise for applications in molecular imaging, nanoprobes, integrated photonic circuits and on-chip optical interconnects.

Based on the present coupled mode theory of the photonic crystal resonator array in this paper, we propose a novel side-coupled waveguide to achieve highly efficient coupling of photonic crystal devices. It is found that the coupling efficiency is sensitive to the interval, the total number and the quality factor of the resonator. Considering the coupling efficiency and the coupling region, we select five resonators with an interval of six lattice periods. By optimizing the structure parameters of the waveguide and resonator, the quality factors of the resonator can be modulated and the coupling efficiency of the side-coupled waveguide reaches 95.47% in theory. Compared with other coupling methods, the side-coupled waveguide can realize efficient coupling with a compact structure, a high level of integration and a low degree of operational difficulties.