Kazuyuki Moriwaki

Planar lightwave circuit dispersion equalizer

The authors report an integrated-optic dispersion equalizer fabricated on a planar lightwave circuit (PLC). This PLC dispersion equalizer is composed of several asymmetrical Mach-Zehnder interferometers cascaded in series. The dispersion equalizer has a high degree of design flexibility and can compensate for both normal and anomalous fiber dispersions at any center wavelength. Moreover, the equalizer can be applied to WDM transmission systems. This equalizer employing five asymmetrical interferometers is fabricated and its measured dispersion values are +834 and -1006 ps/nm. The effectiveness of the equalizer is demonstrated in a 2.5 Gb/s transmission experiment with a 1.3 /spl mu/m zero-dispersion fiber at 1.55 /spl mu/m. Also, its performance is evaluated theoretically.

Dispersion compensation using a planar lightwave circuit optical equalizer

We successfully demonstrate the effectiveness of a planar lightwave circuit (PLC) optical dispersion equalizer in a 2.5 Gb/s transmission experiment with a 40 km-long 1.3 /spl mu/m zero-dispersion fiber at 1.55 /spl mu/m. The dispersion equalizer consists of 5 Mach-Zehnder interferometers with asymmetrical arm lengths cascaded in series. The total insertion loss is 3.5 dB and the maximum dispersion value is 836 psec/nm in the 1.55 /spl mu/m region.<<ETX>>

Hybrid integration of spot-size converted laser diode on planar lightwave circuit platform by passive alignment technique

An index alignment technique was developed for a planar lightwave circuit platform. The technique was successfully applied to the hybrid integration of a spot-size converted laser diode on the platform. The fabricated modules exhibited an average coupling loss of 4.2 dB and a maximum optical output power of 10 mW at an injection current of 70 mA.

Planar lightwave circuit platform with coplanar waveguide for opto-electronic hybrid integration

We propose a planar lightwave circuit (PLC) platform constructed on a silica-on-terraced-silicon (STS) substrate for opto-electronic hybrid integration. This platform consists of an embedded silica PLC region, a terraced silicon region for optical device assembly, and a high-speed electrical circuit region. In the electrical circuit region, the coplanar waveguides (CPW) are prepared on a thick-silica/silicon substrate. This structure reduces the propagation loss of the CPW drastically to 2.7 dB/cm at 10 GHz, because the loss tangent (tan /spl delta/) of the dielectric constants of silica is much smaller than that of silicon. In order to study the feasibility of this PLC-platform for multi-gigabit operation, we used it to fabricate an LD module in which an LD chip and LD-driver integrated circuits (IC) are assembled on the PLC-platform. A bit error rate measurement of this LD module in a 2.5 Gb/s NRZ showed that this platform is applicable to multi-gigabit optical signal processing.

High frequency electrical circuits on a planar lightwave circuit platform

We investigated the propagation losses and the characteristic impedances Z/sub L/ of coplanar waveguides (CPWs) and microstrip lines (MSLs) on a planar lightwave circuit (PLC)-platform formed on a silica/silicon substrate. The loss of the CPWs was 2.7 dB/cm at 10 GHz on the PLC-platform with 30 /spl mu/m thick silica layer. Thus, a cm-order circuit of this CPW is difficult to fabricate in the 10 Gb/s module. This is because the silicon substrate has a large loss tangent (tan /spl delta/). On the other hand, the loss of the MSLs, where a ground plane shielded the high loss silicon substrate, could be improved to 0.9 dB/cm at 10 GHz with 30 /spl mu/m thick polyimide. These lower loss MSLs on a PLC-platform can be applied to module operation at 10 Gb/s. Furthermore they have the advantage that they are suitable for application to array device circuits or circuits in a module where several devices are integrated because unlike CPWs the ground planes are not divided by signal lines or DC bias lines. The structure of CPWs and MSLs on a PLC-platform with a Z/sub L/ of 50 /spl Omega/ was also studied in detail.

An application of a silica-on-terraced-silicon platform to hybrid Mach-Zehnder interferometric circuits consisting of silica-waveguides and LiNbO/sub 3/ phase-shifters

By using a silica-on-terraced-silicon platform (STS-platform) for optical hybrid integration, we fabricated a hybrid Mach-Zehnder interferometric circuit consisting of silica-waveguide directional couplers and a LiNbO/sub 3/ phase-shifter array. The circuit functioned as an optical switch with an insertion loss of 6.0 dB including input and output fiber coupling loss and an extinction ratio of better than 20 dB. The STS-platform was thus confirmed to incorporate both a high-performance planar lightwave circuit and a silicon optical bench.<<ETX>>

Loss reduction in a coplanar waveguide on a planar lightwave circuit (PLC) platform by quenching

The hybrid integration of semiconductor optoelectronic devices on a silica-based optical circuit is one of the key technologies by which to realize opto-electronic components for high-speed wavelength division multiplexing (WDM). However, a coplanar waveguide (CPW) on a silicon-terraced silica (STS)-type planar lightwave circuit (PLC)-platform has a large propagation loss compared with one on a conventional ceramic substrate. We discuss the reduction of the propagation loss of a CPW on a PLC-platform. First we prove that this CPW loss originates from an increase of the loss tangent (tan /spl delta/) induced by the thermal donors (TDs) which connect with oxygen in the silicon substrate during the silica deposition process. Second we introduce quenching to eliminate the TDs, and drastically reduce the loss of a CPW on a 30 /spl mu/m-thick silica from 2.7 to 0.6 dB/cm at 10 GHz. This loss value is almost the same as that of a CPW on a ceramic substrate. Moreover we fabricated a LD module using a 50 mm-long improved CPW on a PLC-platform. The small signal frequency response characteristics of this module reveal that the improved CPW can be applied as a cm-order electrical circuit in a 10 Gb/s module. This exhibits that an established electronic circuit technology including a multi-chip module (MCM) for a microwave application can be developed on a PLC-platform.