Masato Kawahara

1.5 μm band efficient broadband wavelength conversion by difference frequency generation in a periodically domain‐inverted LiNbO3 channel waveguide

Efficient 1.5 μm band wavelength conversion by difference frequency generation (DFG) in a periodically domain‐inverted LiNbO3 channel waveguide is demonstrated, and DFG efficiency as high as 40% W−1 cm−2 is obtained. Nearly constant wavelength conversion efficiency has been confirmed over a broad wavelength range of 30 nm, which is the largest value ever reported.

Wavelength conversions ∼1.5 μm by difference frequency generation in periodically domain‐inverted LiNbO3 channel waveguides

Wavelength conversions ∼1.5 μm are realized by difference frequency generation in periodically domain‐inverted LiNbO3 channel waveguides for the first time. A wide wavelength conversion bandwidth, which is very important for future wavelength division multiplexing optical communication system, is demonstrated in this kind of devices.

Reflective waveguide array demultiplexer in LiNbO/sub 3/

Wavelength demultiplexer fabricated on electrooptic LiNbO/sub 3/ is demonstrated. Reflection structure was employed to halve the device length. The full width at half maximum of the transmission peak was around 1 nm. The crosstalk was -12 to -25 dB. Polarization independence was attained using a reflective quarter-wave plate.

Widely tunable semiconductor optical fiber ring laser

A wide tunable optical fiber ring laser with a diffraction grating as a tuning element is demonstrated. A wide tuning range over 100 nm is achieved using a high performance traveling‐wave amplifier (TWA) as a gain medium. The TWA with a V‐grooved inner stripe structure on a p substrate (VIPS structure) has a high peak gain over 30 dB and a broad gain width of 100 nm at 16 dB. The effects of the gain of TWA and the total loss of the external ring cavity on the tuning range are also discussed.

Tunable Filters with Extended Tunability

Filters with extended tunability using waveguide devices are proposed. The first and second types of filters are combinations of a filter with a wide tuning range and a filter with narrow passbands. The first type is composed of cascaded filters and the second type is the filter with a wide tuning range embedded in a resonator. The last type of filter uses the Vernier effect which has seldom been applied to nonresonant-type devices. The tunability of these filters can overcome the limitation set by the electrooptic property of the material. The performance of the fabricated multibranch Mach-Zehnder interferometric filter, which is the key component for implementing the proposed filter configuration, is demonstrated.

Pulse broadening in picosecond amplification by a 1.3 μm InGaAsP traveling‐wave amplifier

Pulse broadening is observed for the amplification of a 2.2 ps pulse by a semiconductor laser traveling‐wave amplifier when the input pulse energy is well below the saturation energy of the amplifier. The broadening is found to be much larger than that predicted on the basis of homogeneous gain saturation. It is shown from a traveling‐wave rate equation simulation that the nonlinear gain compression is responsible for such a large temporal broadening.

Multiwavelength highway photonic switches using wavelength-sorting elements-design

We propose multiwavelength highway photonic switch architectures for cross-connects using the wavelength routing function of the waveguide-array-grating demultiplexer. The wavelength router is used as wavelength-sorting elements. The wavelength division multiplexed (WDM) optical signals from multiple input ports are routed to group of output ports with certain combination of wavelengths. This enables multiport WDM systems to be configured using the reduced number of wavelength demultiplexing and multiplexing elements.

Programmable Electro-Optic Waveguide Filter,

Programmable filters with multisection electro‐optic mode converter structures are proposed, with which wavelength tuning without increasing the drive voltage and simultaneous selection of multiple wavelengths can be realized.

Large differences in Ti thermal diffusion caused domain inversion between undoped and MgO‐doped LiNbO3

The periodic modulation of domain polarizations by Ti thermal diffusion on the +c face of LiNbO3 with and without MgO doping was studied systematically. It was shown that the depth of the inverted domain is quite different for these two substrates. Under the same fabrication conditions, the depth of domain inversion in the MgO‐doped substrate is less than one‐tenth that of the undoped substrate. This large difference can be explained by the presence of MgO in LiNbO3, which decreases the Ti diffusion constant and increases the minimum Ti concentration required for domain inversion.

Gain Saturation of a 1.3 µm InGaAsP Traveling-Wave Amplifier in Picosecond Pulse Amplification

Saturation energy of a 1.3 µm semiconductor laser traveling wave amplifier is found to depend both on the input pulsewidth and on the input pulse energy at picosecond regime. Shorter pulses are shown to have less saturation energy than longer pulses, which suggests the nonlinear gain give influence to the response of the amplifier. The simulated pulsewidth dependent energy gain by a set of traveling wave rate equations incorporating the nonlinear gain shows fairly good agreement with the measurements.