Journal Club 2017 | Tanabe Photonic Structure Group

Journal Club

By fiscal year (April-December)

Fiscal Year 2017

Presentation Details:

Silicon is an excellent material for microelectronics and integrated photonics, but the technology to lithograph three-dimensional structures directly onto silicon chips has not yet been available.
We have demonstrated the use of lasers to fabricate complex three-dimensional structures consisting of 1-μm dots and rods of arbitrary length as basic units. Laser-altered silicon can form various optical elements on a chip, and can also be chemically etched to form arbitrary three-dimensional structures.

Presentation Details:

For the purpose of nanoscale color reproduction for a wide range of vivid color palettes, this study compares the properties of silicon nanodiscs with those of aluminum and silver plasmon elements. The various properties of these metal and dielectric resonators will be highlighted under various geometric and illumination conditions to guide the optimization of silicon nanodisc arrays for the production of high-resolution color features and millimetric painting replicas.

Presentation Details:

In this study, broadband optical momentum conversion is demonstrated using asymmetric certain micro optical resonators. The chaotic trajectory of light input to the resonator causes efficient coupling between different whispering gallery modes within a few picoseconds. We also report on the successful generation of third harmonic generation with an efficiency three orders of magnitude higher than that of conventional systems by using such momentum conversion.

Presentation Details:

The perfect absorption structure of subwavelength light based on monolayer graphene has been experimentally analyzed and shown. The mechanism of perfect absorption is due to critical coupling with two-dimensional waveguide modes. An absorption peak with a width of 18 nm at half maximum at a wavelength of 1526.5 nm and an absorption rate exceeding 991 TP2T are shown, in good agreement with the results from the fabricated structure (periodic spacing of 1230 nm) and the simulation. In addition, the geometrical parameters of the structure and the effect of the angle of incidence of light were analyzed by simulation. The absorption structure presented here has great potential in current research with regard to the design of photodetectors and optical modulators.

Presentation Details:

Structural colors have the potential to replace toxic metal oxides and synthetic organic pigments, allowing the creation of non-fading spectra without the use of dyes. However, the key challenge remains to achieve the contrast needed for the full range of colors and to make the process compatible with industrial applications. In this study, we present a simple solution for creating structural colors inspired by bird feathers. We designed core-shell nanoparticles with a highly refractive melanin core and a low-refractive silica shell. The design of these nanoparticles was carried out using a finite difference time domain method. These nanoparticles were self-assembled using a one-pot reverse emulsion process, resulting in aggregates of bright, non-blurred particles. The combination of just two materials, synthetic melanin and silica, can generate a full spectrum of colors. These aggregates can be added directly to paints, plastics, and coatings, and could also be used in UV-resistant inks and cosmetics.

Presentation Details:

In this study, the optical Kerr comb and soliton generation are realized by excitation with a pulse train instead of CW light. The soliton is generated by excitation at a repetition frequency close to the FSR of the pump center of the resonator. Since the soliton is locked to the excitation pulse, the soliton repetition rate and carrier envelope offset frequency can be optically controlled by tuning the excitation pulse. Another advantage is that soliton generation can be achieved at a lower power (average power) than in the case of CW excitation, and whether single or multiple solitons are generated can be controlled deterministically by tuning the excitation pulses.

Presentation Details:

III-V compound semiconductor nanowires such as GaAs have potential applications in photodetectors, lasers, and sensors, etc. Because the band gap can be controlled by changing the crystal structure such as WZ or ZB type, observation techniques are needed to determine the crystal structure of the fabricated devices. In this study, the crystal structure was determined by mapping the intensity distribution from the polarization dependence of second harmonic generation. Unlike conventional methods, this observation method is non-destructive and can be operated at room temperature and in an air environment.

Presentation Details:

Optical solitons generated using micro optical resonators are highly beneficial for large-scale optical coherent communications. By modulating the signal on each carrier of a low-noise, smooth, broadband spectral soliton comb generated by a continuous light source, communication capacities in excess of 50 terabits per second have been achieved. We also demonstrated that the soliton comb can be used for coherent reception. This research demonstrates the possibility of replacing CW laser arrays used in WDM with on-chip micro optical resonators.

Presentation Details:

Vibrating materials that conform to shape in response to external stimuli are of interest for new applications in medicine and robotics. For example, liquid crystal networks can be programmed to deform into various shapes induced by stimuli, such as in response to light. Incorporation of azobenzene molecules into liquid crystalline polymer films often makes the films photoresponsive, but in most cases only the bending response of the films has been studied, and the relaxation after photoisomerization is much slower. In this study, we report the fabrication of photoactive polymer films that exhibit continuous, macroscopic, directional mechanical waves under constant light irradiation and drive a feedback loop by self-shielding, by incorporating azobenzene derivatives into liquid crystal networks, which exhibit fast thermal relaxation from cis to trans The self-shielding of the polymer film drives the feedback loop.

Presentation Details:

Ultrafast control of the polarization state of light could lead to a variety of applications in optics, chemistry, and biology. However, conventional polarization devices such as polarizers and retarders are either static or have slow switching speeds of only gigahertz. In this work, we have used high-mobility indium-doped cadmium oxide (CdO) as a gateway plasmonic material to realize a high-Q Beleman-type perfect absorber at a wavelength of 2.08 µm. Sub-bandgap optical pumping causes a strong redshift of the perfect absorption resonance due to a temporary increase in the ensemble-averaged effective electron mass of the CdO. This causes an absolute reflectance change in p-polarization from 1.0% to 86.3%. We combine this extremely high modulation with the polarization selectivity of the perfect absorber to experimentally demonstrate a reflective polarizer with a polarization extinction ratio of 91 that can be switched on and off within 800 fs.

Presentation Details:

Speech and image recognition technology using machine learning with artificial neural networks has recently become a hot topic due to its high performance, but existing computational hardware is not optimized for neural networks and has not been able to perform the calculations efficiently. In this study, we propose an all-optical neural network based on a new architecture and show that it can actually perform vowel recognition using a program-controllable optical processor.

Presentation Details:

Solar energy is one of the most promising renewable energy sources as an alternative to fossil energy, and its storage is expected to be applied to wearable devices. Recently, energy storage using graphene electrodes fabricated by laser processing has been studied, but its performance is not sufficient compared to that of conventional batteries. In this study, we have applied the leaf structure of ferns, which store energy efficiently, to graphene electrodes, and succeeded in storing energy density about 30 times higher than that of previous studies.

Presentation Details:

Carbon nanotubes have a myriad of structures in terms of diameter and carbon arrangement, and their properties, such as semiconductor properties and photoresponsiveness, differ greatly depending on the structure. However, current methods only produce mixtures of carbon nanotubes because carbon nanotubes with various structures are synthesized simultaneously, and no method has been established to separate carbon nanotubes with a single structure from the mixture. A method to separate single-structured carbon nanotubes from the mixture has not been established. In order to solve this problem, a method to elongate carbon nanotubes from a template molecule to a single-structure carbon nanotube is expected.

Presentation Details:

Polarization is one of the most important properties of light, and a "static" (all polarization states occur with equal probability) and "dynamic" (no correlation at all between the polarizations of neighboring photons in time) unpolarized state of light Single-photon sources that are "dynamic" (i.e., no correlation between the polarizations of neighboring photons in time) and "unpolarized" (i.e., no correlation between the polarizations of neighboring photons in time) are expected to be useful for testing light-based intrinsic random number generators, quantum cryptography, and fundamental problems in quantum mechanics. Although static unpolarized states have been evaluated, dynamic unpolarized states have not been evaluated. In this study, we propose a method to evaluate the dynamic unpolarized state and demonstrate that a single photon generated by a nitrogen-vacancy center (NV center) in diamond is both statically and dynamically unpolarized.

Presentation Details:

Dispersive optical fiber sensors using the Brillouin effect can detect changes in strain and temperature with a spatial resolution of several centimeters over long distances of several tens of kilometers, and are expected to be used to monitor the aging of large-scale structures such as dams and bridges. In this study, a different sweep method for Brillouin optical time-domain analysis (BOTDA) was used to suppress degradation of the pump light, and 1 million plots were successfully sensed with 1 cm spatial resolution over a 10 km distance in less than 20 minutes.

Presentation Details:

Glass is one of the most important high-performance materials used in scientific research, industry and society, but it is well known for its difficulty in forming, requiring high-temperature melting and casting processes and the use of toxic chemicals. Therefore, modern manufacturing techniques such as three-dimensional (3D) printing have not been applied to glass. In this study, transparent fused silica glass parts with a resolution of tens of micrometers were produced by a stereolithographic 3D printer using nanocomposites for casting. The process uses light-curable silica nanocomposites, which are 3D printed and transformed into high-quality fused silica glass by heat treatment. The printed fused silica glass is non-porous, exhibits light transmission similar to commercially available fused silica glass, and has a smooth surface with a roughness of a few nanometers. Colored glasses can also be produced by adding metal salts.

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What is Journal Club?
This is an open lecture series held in Tanabe Photonic Structures Laboratory. Students who are graduate students or above will survey papers related to optics and related technologies such as photonics, materials, bioscience, etc., and explain them in an easy-to-understand manner.

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Attendance is free, regardless of whether you are inside or outside of the university. The seminar will be held periodically, so if you are interested in any of the topics, please feel free to attend. No notice is required to attend, but we will prepare materials if you contact us in advance.

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