Survey of enteral feeding of preterm infants and the human milk bank in Japan.

BACKGROUND: In Japan, the first human milk bank (HMB) was established in 2017, which changed the practice of enteral feeding in neonatal care. This study investigated the practice of enteral feeding of preterm infants after the establishment of the HMB in Japan and examined related future issues. METHODS: A survey on enteral feeding and the use of the HMB was conducted in 251 neonatal intensive care units (NICUs) from December 2020 to February 2021. RESULTS: The response rate was 61%. The ideal times to start enteral feeding for extremely-low-birthweight infants (ELBWI) and very-low-birthweight infants (VLBWI) were within 24 h after birth in approximately 59% and 62% of NICUs, however, only 30% and 46% could do so, respectively. Artificial nutrition was used to initiate enteral feeding for ELBWIs and VLBWIs in in 24% and 56% of NICUs, respectively. Of the NICUs, 92% considered the HMB "necessary" or "rather necessary". Fifty-five percent wanted to use the HMB but could not. The major reasons for this were (1) difficulty in paying the annual membership fee, (2) difficulty obtaining approval from the NICU, and (3) complexity in using the facility. The indications for using and discontinuation of use of donor milk varied among the NICUs. Only in 17%, milk expression was within 1h after delivery. CONCLUSIONS: Compared with before the establishment of the HMB, NICUs are currently more willing to start enteral feeding for preterm infants earlier. However, the implementation of enteral feeding appears to be challenging. Issues related to the HMB highlighted by the responses need to be addressed. Additionally, guidelines for using donor milk should be established.

Compound-eye metasurface optics enabling a high-sensitivity, ultra-thin polarization camera.

Polarization imaging is key for various applications ranging from biology to machine vision because it can capture valuable optical information about imaged environments, which is usually absent in intensity and spectral content. Conventional polarization cameras rely on a traditional single-eye imaging system with rotating polarizers, cascaded optics, or micropolarizer-patterned image sensors. These cameras, however, have two common issues. The first is low sensitivity resulting from the limited light utilization efficiency of absorptive polarizers or cascaded optics. The other is the difficulty in device miniaturization due to the fact that these devices require at least an optical-path length equivalent to the lens's focal length. Here, we propose a polarization imaging system based on compound-eye metasurface optics and show how it enables the creation of a high-sensitivity, ultra-thin polarization camera. Our imaging system is composed of a typical image sensor and single metasurface layer for forming a vast number of images while sorting the polarization bases. Since this system is based on a filter-free, computational imaging scheme while dramatically reducing the optical-path length required for imaging, it overcomes both efficiency and size limitations of conventional polarization cameras. As a proof of concept, we demonstrated that our system improves the amount of detected light by a factor of ∼2, while reducing device thickness to ∼1/10 that of the most prevalent polarization cameras. Such a sensitive, compact, and passive device could pave the way toward the widespread adoption of polarization imaging in applications in which available light is limited and strict size constraints exist.

Full-Color Subwavelength Printing with Gap-Plasmonic Optical Antennas.

Metallic nanostructures can be designed to effectively reflect different colors at deep-subwavelength scales. Such color manipulation is attractive for applications such as subwavelength color printing; however, challenges remain in creating saturated colors with a general and intuitive design rule. Here, we propose a simple design approach based on all-aluminum gap-plasmonic nanoantennas, which is capable of designing colors using knowledge of the optical properties of the individual antennas. We demonstrate that the individual-antenna properties that feature strong light absorption at two distinct frequencies can be encoded into a single subwavelength-pixel, enabling the creation of saturated colors, as well as a dark color in reflection, at the optical diffraction limit. The suitability of the designed color pixels for subwavelength printing applications is demonstrated by showing microscopic letters in color, the incident polarization and angle insensitivity, and color durability. Coupled with the low cost and long-term stability of aluminum, the proposed design strategy could be useful in creating microscale images for security purposes, high-density optical data storage, and nanoscale optical elements.

Gap Plasmon Resonance in a Suspended Plasmonic Nanowire Coupled to a Metallic Substrate.

We present an experimental demonstration of nanoscale gap plasmon resonators that consist of an individual suspended plasmonic nanowire (NW) over a metallic substrate. Our study demonstrates that the NW supports strong gap plasmon resonances of various gap sizes including single-nanometer-scale gaps. The obtained resonance features agree well with intuitive resonance models for near- and far-field regimes. We also illustrate that our suspended NW geometry is capable of constructing plasmonic coupled systems dominated by quasi-electrostatics.

Multi-spectral plasmon induced transparency via in-plane dipole and dual-quadrupole coupling.

We experimentally demonstrated an approach based on dipole and dual-quadrupole coupling to construct a planar metamaterial supporting multi-spectral plasmon induced transparency. The structure consists of two short silver wires (dipole) and two long silver wires (dual-quadrupole). The in-plane coupling between the dipole and the dual-quadrupole leads to two transmission windows even in the absorbance linewidth of the dipole. This phenomenon is well described and understood by numerical analyses and a classical oscillator model.

Mutual mode control of short- and long-range surface plasmons.

A symmetric metal slab waveguide simultaneously supports two opposite types of propagation mode similar to a metal film: short-range surface plasmon (SRSP) like mode and long-range surface plasmon (LRSP) like mode. The strong field confinement of SRSP-like mode plays a crucial role for nano-optical integrated circuits in spite of short propagation length. In order to avoid the trade-off between field confinement and propagation length, we demonstrate selective mode excitation and mutual mode conversion for nanofocusing mediated by LRSP-like mode.

Colloidal quantum dot-based plasmon emitters with planar integration and long-range guiding.

We present an experimental demonstration of a quantum dot (QD)-based plasmon emitter controllably integrated in designed patterns on a thin metal film. The generation of surface plasmons polaritons (SPPs) from optically excited QDs on a thin metal film is experimentally demonstrated. Long-range, low-dispersion, two-dimensional isotropic guiding, as well as efficient coupling of the SPPs are also shown. The realization of planar, low loss and efficient plasmon emitter-waveguide integration will offer further development of plasmon circuits.

Excitation control of long-range surface plasmons by two incident beams.

We demonstrate the excitation control of long-range surface plasmon polaritons (LRSPs) by experiments and simulations. We find that LRSPs and short-range surface plasmon polaritons can be selectively excited by two incident beams. This mechanism enables us to realize the excitation control of LRSPs using the phase difference or the intensity ratio between the two input signals. The excitation method analyzed here can be applied to active plasmonic devices based on LRSPs.