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The unidirectional light transmission characteristics of a two-dimensional square-lattice photonic crystal heterostructure consisting of rectangular metal rods and air holes immersed in silicon are studied by the finite-difference time-domain method. Compared with all-optical photonic crystal diodes based on the directional bandgap mismatch, this kind of diode can be designed to confine the light wave to travel along a certain direction owing to self-collimation behavior. The working frequencies of this diode are within the photonic crystal's passband, so a higher light transmittance can be obtained. This wideband high-contrast diode has the advantages of combination with other functional devices in the complex integrated optical circuits.

The propagation of ultrashort laser pulses in water has been investigated with the extended nonlinear Schrodinger equation and the electron density equation. With the model that incorporates the diffraction, normal group-velocity dispersion, multiphoton absorption, self-focusing and defocus of light by the generated free electrons, we examined numerically the spatio-temporal development of the on-axis light intensity along the propagation and the laser-induced electron plasma. Simulation of the underlying dynamics of the ultrashort laser propagation in water reveals that the self-focusing interplays competitively with the laser-induced optical breakdown. Moreover, the laser energy, its duration and focusing geometry determine in combination the structure of plasma filament and the reshaping of energy fluence. The results may provide a better understanding and application of the ultrashort laser pulses in medicine.

Background Zona pellucida domain-containing proteins (ZP proteins) have been identified as the principle constituents of the egg coat (EC) of diverse metazoan taxa, including jawed vertebrates, urochordates and molluscs that span hundreds of millions of years of evolutionary divergence. Although ZP proteins generally contain the zona pellucida (ZP) structural modules to fulfill sperm recognition and EC polymerization functions during fertilization, the primary sequences of the ZP proteins from the above-mentioned animal classes are drastically different, which makes it difficult to assess the evolutionary relationships of ZP proteins. To understand the origin of vertebrate ZP proteins, we characterized the egg coat components of Branchiostoma belcheri, an invertebrate species that belongs to the chordate subphylum Cephalochordata. Results Five ZP proteins (BbZP1-5) were identified by mass spectrometry analyses using the egg coat extracts from both unfertilized and fertilized eggs. In addition to the C-terminal ZP module in each of the BbZPs, the majority contain a low-density lipoprotein receptor domain and a von Willebrand factor type A (vWFA) domain, but none possess an EGF-like domain that is frequently observed in the ZP proteins of urochordates. Fluorescence in situ hybridization and immuno-histochemical analyses of B. belcheri ovaries showed that the five BbZPs are synthesized predominantly in developing eggs and deposited around the extracellular space of the egg, which indicates that they are bona fide egg coat ZP proteins. BbZP1, BbZP3 and BbZP4 are significantly more abundant than BbZP2 and BbZP5 in terms of gene expression levels and the amount of mature proteins present on the egg coats. The major ZP proteins showed high polymorphism because multiple variants are present with different molecular weights. Sequence comparison and phylogenetic analysis between the ZP proteins from cephalochordates, urochordates and vertebrates showed that BbZP1-5 form a monophyletic group and share no significant sequence similarities with the ZP proteins of urochordates and the ZP3 subtype of jawed vertebrates. By contrast, small regions of homology were identifiable between the BbZP and ZP proteins of the non-jawed vertebrate, the sea lamprey Petromyzon marinus. The lamprey ZP proteins were highly similar to the ZP1 and ZP2 subtypes of the jawed vertebrates, which suggests that the ZP proteins of basal chordates most likely shared a recent common ancestor with vertebrate ZP1/2 subtypes and lamprey ZP proteins. Conclusions The results document the spectra of zona pellucida domain-containing proteins of the egg coat of basal chordates. Particularly, the study provides solid evidence for an invertebrate origin of vertebrate ZP proteins and indicates that there are diverse domain architectures in ZP proteins of various metazoan groups.