Katsuyoshi Ito

Microfabrication and characteristics of magnetic thin-film inductors in the ultrahigh frequency region

Thin-film inductors for 1 GHz-drive mobile communication handset application has been demonstrated. This is the possible practical application of soft magnetic films in 1 GHz range. Fe61Al13O26 with Ms=1.2 T, ρ=500 μΩ cm, fr=2 GHz were used for the inductors. L=7.6 nH, R=6.5 Ω, and Q=7.4 were obtained at 1 GHz in a 370 μm×370 μm square four turn spiral of line/space=11 μm/11 μm covered with 0.1-μm-thick slitted Fe61Al13O26 film with Cr underlayer. The L was increased over the flux saturated inductor by 8.6% without any degrade of quality factor.

Interferometric crosstalk-free optical add/drop multiplexer using Mach-Zehnder-based fiber gratings

Mach-Zehnder interferometers with fiber Bragg gratings (MZ-FG) are investigated as promising devices for wavelength-selectable optical add-and-drop multiplexers (OADM). A wavelength reused OADM performance is demonstrated for the first time to our knowledge in a six-channel, 10 Gb/s WDM experiment using a single-stage MZ-FG. We discuss both theoretically and experimentally the interferometric crosstalk induced by imperfect Bragg-reflectivity. Two methods are proposed to solve the interferometric crosstalk issues. The first one is wavelength offset scheme. It is experimentally confirmed that there is no interference when the wavelength of crosstalk is away from that of the signal at least two times of bit-rate. In order to separate each wavelength, the master-slave wavelength control method is proposed with Fabry-Perot interferometer made of a set of fiber gratings. The second one is a cascaded MZ-FG scheme eliminating the crosstalk itself. The calculation indicates that a Bragg-reflectivity of only 93% can suppress the crosstalk to be -35 dB. Cascaded MZ-FGs have been fabricated to show that the interferometric crosstalk can be successfully reduced to -50 dB for the add signal, and -71 dB for the drop signal, respectively. The eight-wavelength 10 Gb/s OADM experiment is carried out to demonstrate the low interferometric crosstalk performance.

Fiber-optic local area passive network using burst TDMA scheme

A fiber-optic loop-configured passive network using burst TDMA scheme which features high reliability and efficient communication capability is presented. The basic analysis for the passive network design including the level diagram, dynamic range, and TDMA burst synchronization are discussed. It is calculated that about 20 stations can be installed if the output peak power of laser diode is +20 dBm and the connector pair loss of optical access coupler is 1 dB. Efficient data transmission of nearly 80 percent with a frame length of 1 ms can be obtained in the TDMA system for 20 stations. The station equipment designs concerning to the burst-mode optical transmission and the unique word detection are also described. An experimental system model with three stations using 51.2-Mbit/s bit rate is constructed, and the feasibility of this passive loop-configured network has been confirmed.

A 980-nm band laser diode pump source with a detuned wavelength of 1000 nm for praseodymium-doped fiber amplifiers

By using practical high-power 980-nm band laser diodes, efficient direct pumping for a praseodymium-doped fiber amplifier (PDFA) is achieved. The lasing wavelength is detuned from 980 to 1000 nm by selective optical feedback from a fiber grating.

Relationship between the Growth Rate of Laser‐Induced Damage in Polyalkylmethacrylates and Their Glass Transition Temperature

The interaction of laser light with the transparent organic high polymers with Q‐switching dye was investigated. Several sorts of polyalkylmethacrylate plates, for which glass transition temperature was a function of composition of copolymers made of methylmethacrylate and n‐butylmethacrylate, were prepared, and the relationship between the growth rate of the laser‐induced damage and the thermal properties was examined. When the ambient temperature of these copolymer plates was 27°C, the growth rate of the damage becomes slower with the decrement of their glass transition temperature. The authors found that the difference (Tg‐T) or the ratio (Tg/T) of glass transition temperature (Tg) and ambient temperature (T) of the organic high polymers exerts predominant influence on the growth rate of laser‐induced damage.