We present measurements of nu_mu disappearance in K2K, the KEK to Kamioka long-baseline neutrino oscillation experiment. One hundred and twelve beam-originated neutrino events are observed in the fiducial volume of Super-Kamiokande with an expectation of 158.1^{+9.2}_{-8.6} events without oscillation. A distortion of the energy spectrum is also seen in 58 single-ring muon-like events with reconstructed energies. The probability that the observations are explained by the expectation for no neutrino oscillation is 0.0015% (4.3sigma). In a two flavor oscillation scenario, the allowed Delta m^2 region at sin^2(2theta) is between 1.9 and 3.5 x 10^{-3} eV^2 at the 90% C.L. with a best-fit value of 2.8 x 10^{-3} eV^2.
1.5μ band travelling-wave semiconductor optical amplifiers (TWAs), characterised by their window facet structure and symmetrised active waveguide, have been developed. 1.5 dB spectral gain ripple and 1.3 dB TE-TM mode gain difference at 22 dB signal gain were achieved simultaneously. An average facet reflectivity as low as 0.06% was estimated.
Optical heterodyne communication systems1 have been proposed as a possible transmission method to obtain ultralong repeater spacings. Such systems require signal and local oscillator highly coherent light sources. A He-Ne gas laser or external cavity laser diode has been used in prototype heterodyne experiments. However, a practical system will need single-longitudinal-mode (SLM) semiconductor lasers because they have many advantages, such as the small device size, spectral stability to ambient temperature fluctuation, and high reliability.
Polarization-insensitive semiconductor optical amplifier (SOA) arrays are desired for optical parallel interconnection systems as optical loss compensators[1]. The authors have, for the first time, realized four-channel polarization-insensitive SOA arrays with uniform device characteristics, by employing a novel fabrication method with selective MOVPE[2,3]. Uniform gain of more than 20dB at 100mA injection current was achieved for the four-channel array. However, for practical application of multi-channel array, much lower power consumption is required. Reduction of injection current is important because it decreases power consumption of not only SOA itself but also other electronic circuits such as thermo-electric cooler. As for low power consumption SOAs, a discrete SOA with 20dB gain at 40mA injection current have been reported[4]. However, fabrication method of this SOA is not array compatible. Therefore, such a polarization-insensitive SOA haven't been yet reported in an array configuration where low power consumption is actually desired.
Using a new LPE growth technique, an InGaAsP/InP planar buried heterostructure laser diode (PBH-LD) has been realised in 1.3 and 1.5 μm wavelength regions. As a result of the effective carrier confinement, CW threshold currents as low as 8.5 mA and 13 mA have been obtained in 1.3 and 1.5 μm PHB-LDs, respectively, at room temperature.
An optical matrix switch is one of key components for photonic switching systems. So far, several kinds of switch element have been investigated.(1)-(5) Among them, the GaAs/AlGaAs electro-optic directional coupler (EODC) switch has several advantages including (1) the low electric power consumption and fast switching speed inherent to electro-optic effect, and (2) low absorption loss in the long1 wavelength region of 1.3 - 1.5 μm.
We report the development of LiNbO/sub 3/:Ti optical modulators with low resistive Si double slit structure for improving the thermal stability and the long-term reliability for high-speed transmission systems, including submarine transmission systems.
Abstract Considerable research and development have been done on semiconductor photonic integrated circuits in which various components such as a laser diode and other photonic devices were integrated. In this paper, a 1.55‐μm band wavelength division multiplexing (WDM) integrated light source for optical communication is developed and the results of the evaluation are described. Four‐channel laser sources were fabricated by integrating tunable semiconductor lasers and semiconductor optical modulators plus multiplexers, and the possibility of using a 2.5‐Gbit/s high‐density WDM optical transmission system is discussed. After analyzing the problems encountered in the fabrication of these photonic integrated components, the development of a bandgap energy‐controlling technique of quantum well structure using the selective metal oxide vapor‐phase epitaxial (MOVPE) growth, which is a better fabrication technique, is described. By using this technique, the difficult process of combining the waveguide with a different bandgap energy can be accomplished only by a one‐step crystal growing. This simplifies the components fabrication, and a high‐coupling efficiency of the waveguide between the integrated elements can be obtained. As an application example, the integrated light source was fabricated by integrating a tunable laser, distributed feedback (DFB) laser, and semiconductor optical modulator. Then the tunable characteristic and the extinction characteristic were verified. This simplifies the fabrication method of the previously difficult method of semiconductor photonic integrated circuits and clarifies the possibility of developing a high‐density integrated element.
