Tsutomu Kitoh

An optical FDM-based self-healing ring network employing arrayed waveguide grating filters and EDFA's with level equalizers

An optical frequency-division multiplexing (OFDM) based self-healing unidirectional ring network is designed and its performance is verified. It employs arrayed waveguide grating add/drop multiplexers (ADMs) and erbium-doped fiber amplifiers (EDFAs) with waveguide level equalizers in each remote node. The route diversity configuration is employed to make the network robust and bit loss-free route switching is performed. The level diagram reproducibility for each OFDM channel is guaranteed by the waveguide-level equalizers. Successful transmission performance confirms the effectiveness of the proposed system.

Two-port optical wavelength circuits composed of cascaded Mach-Zehnder interferometers with point-symmetrical configurations

Wavelength circuit characteristics are investigated systematically for a family of two-port optical wavelength circuits composed of cascaded Mach-Zehnder interferometers (MZIs) with point-symmetrical configurations. A novel design method is presented for flattening their cross-port passbands (through-port stopbands). The design principle is based on a consideration of the general relations between wavelength circuit characteristics and circuit configuration symmetries. It is shown that the role of this novel design method is complementary to that of the conventional flattening method which is used for simple wavelength-insensitive couplers (WINCs) with a single-stage MZI configuration. Various optical wavelength circuits are designed by using both the novel and conventional design principles, including fixed and tunable WINCs, a wavelength-insensitive switch (WINS), and a wavelength multi/demultiplexer with a flattened passband and stopband. Measurement results are provided for some of the designed optical circuits which were fabricated using silica-on-silicon planar lightwave circuits (PLCs).

160-Gb/s optical-time-division multiplexing with PPLN hybrid integrated planar lightwave circuit

160-Gb/s (20 Gb/s /spl times/ 8) optical time-division-multiplexing is demonstrated using a multiplexer based on periodically poled lithium niobate hybrid integrated planar lightwave circuits. With this multiplexer, eight 20-Gb/s signals are independently modulated and time division multiplexed all-optically. To confirm the quality of the multiplexed signal, it was demultiplexed and bit error rates were measured. The measured power penalties are less than 2.2 dB.

160-Gb/s OTDM transmission using integrated all-optical MUX/DEMUX with all-channel modulation and demultiplexing

This letter provides the first report of 160-Gb/s optical time-division-multiplexed transmission with all-channel independent modulation and all-channel simultaneous demultiplexing. By using a multiplexer and a demultiplexer based on periodically poled lithium niobate and semiconductor optical amplifier hybrid integrated planar lightwave circuits, 160-km transmission is successfully demonstrated.

Bending loss reduction in silica-based waveguides by using lateral offsets

The excess loss that occurs in waveguide bends can be minimized by offsetting the connecting waveguides so as to reduce the transition loss at the junctions. Such bends were investigated in detail by employing the beam propagation method (BPM) and it was found that they can be optimized with respect to overall loss. In the addition, the S-shaped waveguides and directional couplers with offset junctions were fabricated based on silica-based planar lightwave circuits (PLC) on silicon substrates. The measured insertion losses of these S-shaped waveguides and directional couplers, which are in good agreement with the calculated results, are the lowest thus far reported. >

Optical spotsize converter using narrow laterally tapered waveguide for planar lightwave circuits

We present a full description of the design and fabrication of a compact laterally tapered spotsize converter (SSC) that provides both low-loss coupling and large fabrication tolerances. The SSC is based on a laterally tapered waveguide with a narrow core width that can be fabricated simply by using the usual fabrication process. We discuss the design concept of the SSC in detail and provide a simple design procedure with which to obtain the optimum SSC design parameters. We also investigate the fiber misalignment tolerance and mode field diameter of the SSC and confirm that it is suitable for integration with large-scale optical devices. Furthermore, we examine the performance of the SSC for higher refractive index difference (/spl Delta/) of 2.0% and 2.5% with a smaller bending radius. We fabricated the 2-mm-long SSC using 1.5%-, 2.0%-, and 2.5%-/spl Delta/ silica-based planar lightwave circuits. This enabled us to reduce the single-mode fiber coupling loss to 0.4 dB at a single waveguide junction with a low polarization-dependent loss of 0.05 dB regardless of the /spl Delta/ values, while providing a core width fabrication tolerance of /spl plusmn/0.3 /spl mu/m, and an endface position tolerance of /spl plusmn/0.2 mm.

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. >

Passband-width broadening design for WDM filter with lattice-form interleave filter and arrayed-waveguide gratings

We successfully fabricated a high channel count and flat-top wavelength-division-multiplexing filter by integrating a waveguide-type interleave filter and two arrayed-waveguide grating on one chip. Optimizing the loss ripple of the interleave filter, we realized a 50-GHz spacing, 102-channel ports, a 1-dB passband of 30 GHz, and an insertion loss of 4 dB.

Compact and low-loss interleave filter employing lattice-form structure and silica-based waveguide

This paper describes a compact and practical interleave filter with uniform multi/demultiplexing properties and a wide operational wavelength range realized by using a lattice-form structure and a silica-based waveguide. In the design, we optimized the bandwidth by controlling the lattice stage number and the loss ripple in the spectrum. Moreover, we propose a novel coupler with a large fabrication tolerance, a new tandem configuration that provides uniform characteristics and low dispersion, a polarization dependence compensation method, and a folded configuration, which are effective in realizing a high-performance interleave filter. Based on the above techniques, we fabricated a 50-GHz channel spacing interleave filter by using planar-lightwave-circuit technologies and demonstrated that it performed well throughout the C-band, exhibiting a low insertion loss of about 2 dB, a low chromatic dispersion of within +/-20 ps/nm, a 1-dB passband width of over 34 GHz, and a 30-dB stopband width of over 25 GHz, which are sufficient for a 10-Gbps transmission system.

12.5 GHz spaced 1.28 Tb/s (512-channel x 2.5 Gb/s) super-dense WDM transmission over 320 km SMF using multiwavelength generation technique

We achieve a 512-channel super-dense wavelength-division-multiplexing (WDM) transmission with a 12.5 GHz channel spacing over 320 km (80 km/spl times/4) of standard single-mode fiber in the C+L-bands. Optical carrier supply modules, which are based on a flattened sideband generation scheme, are applied to generate the 512 wavelengths from only 64 distributed-feedback laser diodes with a frequency spacing of 100 GHz. Arrayed-waveguide gratings with a 12.5 GHz spacing are used in this super-dense WDM experiment.