Free-Space Applications of Silicon Photonics: A Review.

Silicon photonics has recently expanded its applications to delivering free-space emissions for detecting or manipulating external objects. The most notable example is the silicon optical phased array, which can steer a free-space beam to achieve a chip-scale solid-state LiDAR. Other examples include free-space optical communication, quantum photonics, imaging systems, and optogenetic probes. In contrast to the conventional optical system consisting of bulk optics, silicon photonics miniaturizes an optical system into a photonic chip with many functional waveguiding components. By leveraging the mature and monolithic CMOS process, silicon photonics enables high-volume production, scalability, reconfigurability, and parallelism. In this paper, we review the recent advances in beam steering technologies based on silicon photonics, including optical phased arrays, focal plane arrays, and dispersive grating diffraction. Various beam-shaping technologies for generating collimated, focused, Bessel, and vortex beams are also discussed. We conclude with an outlook of the promises and challenges for the free-space applications of silicon photonics.

Simultaneous detection of two growth factors from human single-embryo culture medium by a bead-based digital microfluidic chip.

The measurement of growth factors released in a culture medium is considered to be an attractive non-invasive approach, apart from the embryo morphology, to identify the condition of an embryo development after fertilization in vitro (IVF), but the available embryo culture medium in the current method is only a few microlitres. This small sample volume, also of small concentration, makes difficult the application of a conventional detection method, such as an enzyme-linked immunosorbent assay (ELISA). A reliable detection of the growth factor from each embryo culture medium of such a small concentration hence remains a challenge. Here for the first time we report the results of measurement of not just one, but two, growth factors, human IL-1ß and human TNF-α, from an individual droplet of embryo culture medium with a bead-based digital microfluidic chip. The required sample volume for a single measurement is only 520 nL; the total duration of the on-chip process is less than 40 min. Using the culture media of human embryos with normal morphologic features, we found that the concentrations of TNF-α change little from day 3 to day 5-6, but the concentrations of IL-1ß for some embryos might double from day 3 to day 5-6. For other embryos even with similar normal morphologic features, some growth factors, such as IL-1ß, might exhibit different expressions during the culture period. Those growth factors could serve to distinguish the development conditions of each embryo, not merely from an observation of embryo morphology.

Effects of various ions on the dechlorination kinetics of hexachlorobenzene by nanoscale zero-valent iron.

The effect of several anions and cations normally co-present in soil and groundwater contamination sites on the degradation kinetics and removal efficiency of hexachlorobenzene (HCB) by nanoscale zero-valent iron (NZVI) particles was examined. The degradation kinetics was not influenced by the HCO(3)(-), Mg(2+), and Na(+) ions. It was enhanced in the presence of the Cl(-) and SO(4)(2-) ions due to their corrosion promotion. The NO(3)(-) competes with HCB so it inhibits the degradation reaction. The Fe(2+) ions would inhibit the degradation reaction due to passivation layer formed, while it was enhanced in the presence of Cu(2+) ions resulted from the reduced form of copper on NZVI surfaces. These observations lead to a better understanding of HCB dechlorination with NZVI particles and can facilitate the remediation design and prediction of treatment efficiency of HCB at remediation sites.