Ken Takazawa

Micrometer-Scale Photonic Circuit Components Based on Propagation of Exciton Polaritons in Organic Dye Nanofibers

Since photonic circuits possess advantages over electronic circuits in bandwidth and resistance to electromagnetic wave interference, miniaturized photonic circuits offer promising applications in various fi elds. [ 1 ] However, the diffraction limit of light restricts the degree to which conventional optical waveguide circuits can be miniaturized. Hence, plasmon waveguides, [ 2 , 3 ] photonic crystal waveguides, [ 4 , 5 ] and semiconductor nanofi bers [ 6 , 7 ] have been extensively developed to guide optical signals and to manipulate them below the diffraction limit. In this communication, we report a novel approach to create micrometer-scale photonic circuits by using the propagation of exciton polaritons (EPs) in organic dye nanofi bers. EPs are quasi-particles formed by strong coupling between photons and excitons. This coupling leads to a signifi cantly large refractive index of the crystal, which may allow quasi-one-dimensional structures (nanofi bers) to guide EPs and to manipulate them below the diffraction limit of light. This in turn enables one to create EP-based photonic circuits that can be highly miniaturized as compared to conventional optical waveguide circuits. Organic dye thiacyanine (TC, Figure 1 a) self-assembles into nanofi bers with lengths of up to ∼ 250 μ m in solution. [ 8–10 ]

Optical Microring Resonators Constructed from Organic Dye Nanofibers and Their Application to Miniaturized Channel Drop/Add Filters

We fabricated micrometer-scale optical ring resonators by micromanipulation of thiacyanine (TC) dye nanofibers that propagate exciton polaritons (EPs) along the fiber axis. High mechanical flexibility of the nanofibers and a low bending loss property of EP propagation enabled the fabrication of microring resonators with an average radius (r(ave)) as small as 1.6 μm. The performances of the fabricated resonators (r(ave) = 1.6-8.9 μm) were investigated by spatially resolved microscopy techniques. The Q-factors and finesses were evaluated as Q ≈ 300-3500 and F ≈ 2-12. On the basis of the r(ave)-dependence of resonator performances, we revealed the origin of losses in the resonators. To demonstrate the applicability of the microring resonators to photonic devices, we fabricated a channel drop filter that comprises a ring resonator (r(ave) = 3.9 μm) and an I/O bus channel nanofiber. The device exhibited high extinction ratios (4-6 dB) for its micrometer-scale dimensions. Moreover, we successfully fabricated a channel add filter comprising a ring resonator (r(ave) = 4.3 μm) and two I/O bus channel nanofibers. Our results demonstrated a remarkable potential for the application of TC nanofibers to miniaturized photonic circuit devices.

Zeeman electronic spectra of gaseous NO in very high magnetic fields up to 25 T

Abstract An apparatus for measuring the fluorescence excitation spectra of gaseous molecules in very high magnetic fields generated by a water-cooled resistive magnet has been developed. Spectra due to the A 2 Σ + (v ′ =0)– X 2 Π (v″=0) transition of NO were measured in magnetic fields up to 25 T. The spectra show complicated line structures due to large Zeeman splitting in both the A2Σ+ and X2Π states. The transition energies and line intensities were calculated using Hunds case (a) basis set to assign the observed lines.

Direct electron beam writing of Bragg gratings in exciton polariton waveguides of organic dye nanofibers

We develop a direct electron beam (EB) writing technique to fabricate Bragg gratings in organic dye nanofibers of thiacyanine that propagate exciton polaritons (EPs) along the fibers. The scanning electron beam with elaborately optimized parameters “bleaches” the nanofibers with a 100-nm-scale spatial resolution, leading to variation in the refractive index on that scale. We demonstrate that the fabricated Bragg gratings, with a period number N = 40 and a period length Λ ranging from 150 to 200 nm, reflect propagating exciton polaritons with a reflectance of up to ∼0.7.

Self-oriented pseudoisocyanine J-aggregates in solution

Highly oriented fiber-shaped J-aggregates of pseudoisocyanine (PIC) molecules were prepared by simply growing the aggregates in a narrow glass cell, which allows evaporation of the solution in one direction.

Magnetic field effect on highly excited states near ionization potential of nitric oxide

Abstract Fluorescence excitation spectra due to the A 2∑–X 2Π transition of gaseous nitric oxide (NO) were measured in magnetic fields, H; ranging from 0 ≤ H ≤ 10 T. Lines in the observed spectra were assigned by using quantum mechanical calculations. Based on the assignment, two-color resonance-enhanced multiphoton ionization spectra via a single Zeeman sublevel in the A state were measured to observe the effect of magnetic fields on electronic states near the ionization potential (IP). Complicated structures due to strong n- and l-mixing in highly excited Rydberg states were observed below the IP. It was found that new resonance appears above the IP for H ≤ 4T. By using a semi-classical calculation, this resonance was assigned to the quasi-Landau resonance, which was observed for the first time in molecules.

Miniaturized Photonic Circuit Components Constructed from Organic Dye Nanofiber Waveguides

Self-assembled nanofibers of organic dye thiacyanine (TC) with lengths of up to \( {\sim} 250\,\upmu {\text{m}} \) function as efficient active waveguides that propagate fluorescence (FL) over their entire lengths along the fiber axis. A spectroscopic investigation of the active waveguiding properties revealed that the FL strongly couples with molecular excitons and propagates in the form of exciton-polaritons. Such long-range propagation of exciton-polaritons at room temperature is rarely observed in inorganic materials. The high stability of the exciton-polaritons in the organic dye nanofibers is attributed to the large longitudinal transverse exciton splitting energy and exciton binding energy with respect to thermal energy. Unlike light propagating in conventional waveguides, exciton-polaritons can pass through bends in nanofibers with micron-scale radii of curvature. Utilizing this property, we fabricated miniaturized photonic circuit components using nanofiber building blocks. The fabricated components, including Mach–Zehnder interferometers and microring resonators, exhibit considerably high performance for their micron-scale dimensions. In addition to such photonic device applications, the organic dye nanofibers are ideal systems for studying the physics underlying strong light–matter interactions. In particular, the highly stable nature of the exciton-polaritons at relatively high temperature offers the possibility of a representative novel quantum phenomenon in their Bose–Einstein condensation (BEC). A theoretical analysis of this exciton-polariton BEC in the nanofiber system is presented in this chapter.