Toshinori Nozawa

Arrayed-waveguide grating multiplexer with loop-back optical paths and its applications

We present a basic configuration of an unique integrated-optic arrayed-waveguide grating (AWG) multiplexer with loop-back optical paths and demonstrate an add-drop multiplexer (ADM), a network access terminal, and a wavelength channel selector for dense-WDM ring or bus networks, as three useful examples of its attractive applications. A key device in these components is a silica-glass based 1.55 /spl mu/m polarization-insensitive 32/spl times/32 AWG multiplexer chip with 0.8 nm channel spacing which is fabricated using planar lightwave circuit (PLC) technologies. Fine operation in their new functional components is achieved by using the AWG multiplexer module having low insertion loss of 3.9 dB and low interchannel crosstalk of less than -28 dB.

Spectral-domain analysis of coplanar waveguide traveling-wave electrodes and their applications to Ti:LiNbO/sub 3/ Mach-Zehnder optical modulators

Hybrid-mode and quasi-TEM analyses are carried out for coplanar waveguide traveling-wave electrodes applicable to z-cut Ti:LiNbO3 optical modulators. The analyses are based on the spectral-domain approach. The microwave effective index and the characteristic impedance are clarified, together with the microwave conductor loss. These are incorporated to accurately predict the modulator characteristics. It is shown that these characteristics can be greatly improved by employing a thicker buffer layer. High-speed and low-driving-power Ti:LiNbO/sub 3/ optical modulators are realized at 1.52 mu m wavelength. Agreement between the calculated and measured results is good. >

A wide-band and low-driving-power phase modulator employing a Ti:LiNbO/sub 3/ optical waveguide at 1.5 mu m

A wide-band and low-driving-power Ti:LiNbO/sub 3/ optical modulator at 1.5- mu m wavelength is described. A relatively thick SiO/sub 2/ buffer layer is effectively utilized to improve phase velocity mismatch between the microwaves and optical waves. A coplanar waveguide is used as an efficient traveling-wave electrode, and is designed utilizing the upper bound calculation in the spectral domain. Wide-band modulation of 12 GHz (3 dB optical and 6 dB electrical cutoff frequency) and small driving-power-to-modulation-bandwidth ratio of 20 mW/GHz are realized.<<ETX>>

A Ti:LiNbO/sub 3/ optical intensity modulator with more than 20 GHz bandwidth and 5.2 V driving voltage

A broadband and low driving-voltage Ti:LiNbO/sub 3/ optical intensity modulator is described. A coplanar waveguide with a shielding plane is used for optical-electrical velocity matching and a confined waveguide is used for lowering the driving voltage. The relationship between the mode size of the guided wave and the driving voltage is shown. This modulator has an electrical 3-dB bandwidth of more than 20 GHz and a driving voltage of 5.2 V at a wavelength of 1.5 mu m.<<ETX>>

Water vapor effects on optical characteristics in Ti:LiNbO 3 channel waveguides

This paper describes experimental studies on propagation loss and crosstalk of TM-polarized light in Ti-diffused Z-cut LiNbO(3) channel waveguides as a function of the water vapor content in the diffusion atmosphere. The dependence of surface roughness and crystal quality on the waveguide fabrication atmosphere is taken into consideration. In this study it is found that waveguides with low propagation loss (<0.2 dB/cm), low crosstalk (<-20 dB), and smooth surfaces can be fabricated by strictly controlling the water vapor content introduced into the oxygen or argon carrier gas.

Reliability of optical components for use in submarine optical fiber transmission systems

This paper presents the reliability test results for LD modules, optical couplers, and APD modules, which are fabricated through methods for achieving and assuring a high degree of reliability for use in 400-Mbit/s submarine optical fiber transmission systems. In particular, the paper presents methods for evaluating the optical component reliability as well as an investigation into the degradation factors in the coupling circuits. From the reliability test results obtained, the paper also discusses the mechanism and test acceleration of wear-out degradation following reliability tests conducted for more than 8000 h on the fabricated optical components. These optical components are consequently confirmed to be highly reliable for a system life of 25 years.

Efficient highly stable laser diode module for single-mode fiber employing a combination of hemispherical ended GRIN rod lens and virtual fiber

An efficient and practical laser diode module is demonstrated for single-mode fiber applications. The module is developed through use of an earlier proposed combination lens method, where a hemispherical ended graded index rod lens and virtual fiber are employed. Since lens and virtual fiber misalignment tolerances are large in this coupling method, the YAG laser welding technique is easily applicable. This laser diode module has not only a simple structure but also high coupling efficiency, excellent reproducibility, and extremely high reliability.