Ten-port graded-index waveguide star coupler fabricated by dry ion diffusion process

A ten-port planar star coupler has been developed, utilising multimode waveguides easily formed in a glass substrate by evaporated silver ion diffusion. The waveguides have circular cross-sections with graded-index profile, which matches well to graded-index multimode fibres. Insertion loss of 6 dB and the loss variation of 0.8 dB were attaied.     

Development of Millimeter Wave Fabry-Pérot Resonator for Simultaneous Electron-Spin and Nuclear Magnetic Resonance Measurement

We report a Fabry-Pérot resonator with spherical and flat mirrors to allow simultaneous electron-spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements that could be used for double magnetic resonance (DoMR). In order to perform simultaneous ESR and NMR measurements, the flat mirror must reflect millimeter wavelength electromagnetic waves and the resonator must have a high Q value (Q?>?3000) for ESR frequencies, while the mirror must simultaneously let NMR frequencies pass through. This requirement can be achieved by exploiting the difference of skin depth for the two frequencies, since skin depth is inversely proportional to the square root of the frequency. In consideration of the skin depth, the optimum conditions for conducting ESR and NMR using a gold thin film are explored by examining the relation between the Q value and the film thickness. A flat mirror with a gold thin film was fabricated by sputtering gold on an epoxy plate. We also installed a Helmholtz radio frequency coil for NMR and tested the system both at room and low temperatures with an optimally thick gold film. As a result, signals were obtained at 0.18 K for ESR and at 1.3 K for NMR. A flat-mirrored resonator with a thin gold film surface is an effective way to locate NMR coils closer to the sample being examined with DoMR.     

Programmed High‐Hole‐Mobility Supramolecular Polymers from Disk‐Shaped Molecules

In this paper a simple, casting solution technique for the preparation of two‐dimensional (2D) arrays of very‐high molecular weight (MW) 1D‐Pc supramolecular inorganic polymers is described. The soluble fluoroaluminium tetra‐tert‐butylphthalocyanine (ttbPcAlF) is synthesized and characterized, which can be self‐assembled to form 2D arrays of very‐high‐MW 1D‐Pc supramolecular inorganic polymers. High‐resolution transmission electron microscopy (HRTEM) demonstrates that the 1D‐ttbPcAlF, having a cofacial ring spacing of ～0.36 nm and an interchain distance of ～1.7 nm, self‐assembles into 2D‐nanosheets (～140 nm in length, ～20 nm in width, and equivalent to MW of 3.2 × 10⁵ g mol^?1). The film cast from a 1,2‐dichloroethane (DCE) solution shows a minimum hole‐mobility of ～0.3 cm² V^?1 s^?1 at room temperature by flash‐photolysis time‐resolved microwave conductivity (TRMC) measurements and a fairly high dark dc‐conductivity of ～1 × 10^?3 S cm^?1.     

Development of a Millimeter-Wave Electron-Spin-Resonance Measurement System for Ultralow Temperatures and Its Application to Measurements of Copper Pyrazine Dinitrate

We have developed a millimeter-wave electron-spin-resonance (ESR) measurement system using a ³He-⁴He dilution refrigerator for the ultralow-temperature range below 1 K. The currently available frequency range is 125–130 GHz. This system is based on a Fabry-Pérot-type resonator (FPR) that is composed of two mirrors. The frequency can be changed by adjusting the distance between the mirrors using a piezoelectric actuator installed at the bottom of the resonator. A homodyne detection system with an InSb detector is built into the low-temperature section of the ³He-⁴He dilution refrigerator; this system provides high sensitivity. Using this system, we performed ESR measurements on a Heisenberg quantum-spin chain—copper pyrazine dinitrate, Cu(C₄H₄N₂)(NO₃)₂—over the temperature range from 6.6 down to 0.25 K. The ESR lines change continuously with decreasing temperature. Our results suggest that the ESR spectrum of copper pyrazine dinitrate may be useful as a temperature sensor for the very low-temperature range.     

Electrotunable Non‐reciprocal Laser Emission from a Liquid‐Crystal Photonic Device

A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase‐retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right‐handed helices of different pitches. Electrotunable non‐reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non‐reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage.     

300 ps switching of spontaneous emission by quantum confined fieldeffect in a light emitting triode

A high-speed switching, as fast as 300 ps, of spontaneous emission is achieved in the recently developed quantum-confined field-effect light emitting triode. As a result of the combination of the field control of radiative life time with modulation of carrier-generation rate, the light intensity modulation does not rely on changes in carrier population at all but on the field control of the radiative life time in the quantum well structure of the device. Elaborated is the allowance for the deviation of the modulation depth of injection current from an optimum value in the modulation scheme     

Effects of zinc doping in DFB lasers emitting at 1.3 and 1.55 mu m

Reports on the performance of GaInAsP/InP DFB lasers with Zn-doped active region. At both 1.3 and 1.55 mu m the authors achieved a large bandwidth owing to the increased differential gain. The carrier lifetime of the lasers decreased with doping level. The decreased carrier lifetime had the effect of reducing the pattern effect, and they could obtain a clear eye opening with 4 Gbit/s NRZ modulation.<>     

Enhancement of third-order nonlinear optical susceptibilities incompressively strained quantum wells under the population inversioncondition

Third-order optical nonlinear susceptibilities χ⁽³⁾ in compressively strained and nonstrained InGaAs-InGaAsP quantum wells (QW's) under the population inversion condition are discussed. The small effective mass of compressively strained QW's increases the contribution of the carrier density pulsation effect and the carrier heating effect of χ⁽³⁾. The hole burning effect is also increased due to the decrease of the carrier-carrier scattering rate. The calculation including these effects shows an enhancement of factor 3 due to 0.8% compressive strain. The values of χ⁽³⁾ are experimentally estimated from the data of nondegenerate four-wave mixing in λ/4-shifted distributed feedback lasers. χ⁽³⁾ in 0.8% compressively strained QW's is three times larger than that in nonstrained QW's with the same linear gain     

Relationship between thermal treatment conditions and minority carrier lifetimes in p-type, FZ Si wafers

Minority-carrier lifetimes in FZ-p Si wafers were evaluated at various thermal treatments to investigate the effect of the recombination centers. Bulk lifetimes became longer in the case of annealing in O₂ ambient at around 1000°C, while it decreased drastically in N₂ and Ar ambients. Both N₂ annealing sample and oxidation sample after N₂ annealing were measured using deep level transient spectroscopy. Deep levels related to nitrogen defect were observed for the N₂ annealing sample. However, no deep level was observed for the oxidation samples. These results suggest that recombination of minority carriers in the bulk occurred at deep levels related to the nitrogen-vacancy complex.     

CW operation at - 10°C for InGaAlP visible light laser diodes grown by MOCVD

CW operation at - 10°C for InGaP/InGaAlP double heterostructure (DH) laser diodes has been achieved for the first time. The DH wafers were grown by low-pressure metalorganic chemical vapour deposition using methyl metalorganics as the source of group III elements. Under room-temperature pulsed operation, the lasing wavelength was 663 nm and the lowest threshold current density was 7.8 kA/cm2. The CW characteristic temperature T0 was 63 K at around -30°C.