ABSTRACT
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.
ABSTRACT
The band structures of one-dimensional photonic crystals containing a defect layer with a negative refractive index are studied, showing that the defect modes possess three types of dispersion: positive, zero, and negative types. Based on these three types of dispersion, practical designs for large incident angle filters without polarization effect and for narrow frequency and sharp angular filters are suggested. Moreover, the splitting of one degenerate defect mode into multiple defect modes is observed in the band gap when the parameters of the defect layer vary. This mode splitting phenomenon can be used to design multiple channeled filters or filters with a rectangular profile. The dispersion multiplicity of the defect modes can be understood by an approximate formula, and the critical condition for the defect mode splitting is also analyzed. Based on these analyses, practical optimization design of omnidirectional filter is also suggested.
ABSTRACT
We present, experimentally and theoretically, a polymer material system that supports optical spatial solitons of circular polarization. We demonstrate one-dimensional circularly polarized dark solitons supported by photoisomerization nonlinearity in a bulk polymer.
ABSTRACT
We present theoretically another type of optical spatial soliton in steady state, which is supported by photoisomerization nonlinearity in a polymer. For the photoisomerization nonlinearity with saturation, this type of one- or two-dimensional spatial soliton can be formed in a bulk polymer. The spontaneous soliton of this type can only be dark or gray. Not only a linearly polarized beam, but also a circularly polarized beam can be used to form the soliton, which is impossible for the photorefractive soliton. The effects of wavelength, polarization, and intensity of the beam on the formation of the soliton are discussed in detail.
ABSTRACT
We present a theory for a new type of optical spatial soliton that is based on the angle hole burning mechanism of photoisomerization in some polymers. We predict that the photoisomerization nonlinearity can support steady-state dark and bright spatial solitons in the polymer. We also discuss the dependence of the FWHM of the spatial soliton on wavelengths of the background beams and on the ratio of the intensity of the background beam to that of the signal beam.
ABSTRACT
The charge transfer (CT) process in PAN-C60 copolymer films was studied by absorption and picosecond time-resolved photoluminescence (TRPL) spectra. The CT process can be confirmed from the appearing of new absorption bands and fluorescence quenching of pure PAN in the copolymer films. The TRPL result revealed that excitation state relaxation obeyed biexponential decay process, which were 160 ps and 1,500 ps for the fast and slow decay process, respectively. The fast decay process results from the interaction of chains in the polymer, and a slow decay process comes from the singlet excition recombination. In the copolymer, the singlet excition state lifetime of PAN becomes shorter due to CT process between PAN and C60, which lead to PL quenching of PAN. Additionally, C60 molecules also affect the interchain interaction of PAN by its spacial shape, which closely relates with the fast decay process.
