In this paper, a type of compact nanosensor based on a metal-insulator-metal structure is proposed and investigated through cascading double asymmetric cavities, in which their metal cores shift along different axis directions. The cascaded asymmetric structure exhibits high transmission and sharp Fano resonance peaks via strengthening the mutual coupling of the cavities. The research results show that with the increase of the symmetry breaking in the structure, the number of Fano resonances increase accordingly. Furthermore, by modulating the geometrical parameters appropriately, Fano resonances with high sensitivities to the changes in refractive index can be realized. A maximum figure of merit (FoM) value of 74.3 is obtained. Considerable applications for this work can be found in bio/chemical sensors with excellent performance and other nanophotonic integrated circuit devices such as optical filters, switches and modulators.

We propose theoretically a method for designing a narrowband multi-wavelength Šolc-type filter based on the linear electro-optic effect in aperiodically poled lithium niobate. As one of its applications we demonstrate a thermally tuned 100 GHz spaced four-wavelength filter, whose working electric field is only 0.219 kV mm −1 in an 8 cm long crystal. The filter allows four wavelengths to pass simultaneously with a 3 dB bandwidth of 0.26 nm, a passband of 32.5 GHz and a channel isolation of more than 8 dB, which can be tuned by temperature in a wide range at a rate of −0.69 nm • C −1 . It is found that the domain errors of the aperiodically poled lithium niobate crystal within 25% are beneficial to the performance of the filter. The filter will be useful for dense wavelength division multiplexing optical communication systems.

We theoretically investigate the electro-optic coupling in an optical superlattice of linear chirped-periodically poled lithium niobate. It is found that the electro-optic coupling in such optical superlattice can work in a wide wavelength range. Some of examples, with bandwidths of 20, 40, 80, 120 nm, are demonstrated. The way to determine the electric field for perfect conversion between o- and e-ray and the method using apodized crystals of tanh profile to reduce the ripples are shown. As one of its applications, one kind of broadband Solc-type bandpass filter in optical communication range is proposed.