Toshiaki Kagawa

Optical interconnection using VCSELs and polymeric waveguide circuits

We investigated the waveguide loss and transmission characteristics for optical interconnection using vertical-cavity surface-emitting lasers (VCSELs) and multimode polymeric waveguide circuits with crossings. The excess loss with 100 crossings is 2.2 dB when the image magnification from a VCSEL to a waveguide is 2.3. We obtained error-free (i.e., bit error rate <10/sup -11/) optical interconnection at 1.0625 Gbps regardless of the number of crossings or the magnification. These results suggest the practicality of large-scale optical interconnection between VCSEL-based smart-pixel chips using multimode waveguides with more than 100 crossings.

Polarization-controlled 850-nm-wavelength vertical-cavity surface-emitting lasers grown on [311]B substrates by metal-organic chemical vapor deposition

We demonstrate the polarization stability of 850-nm-wavelength vertical cavity surface-emitting lasers (VCSELs) grown on [311]B substrates under continuous-wave (CW) and dynamic operation. To clearly verify the polarization stability of VCSELs on [311]B substrates due to the anisotropic optical gain, the characteristics of both VCSELs on [311]B and [100] substrates were compared experimentally. Under CW operation, very small difference in both orthogonal polarization suppression ratio and the distribution of polarization direction was observed between VCSELs on [311]B and [100] polyimide-buried structures. On the other hand, significantly larger orthogonal polarization suppression ratio was obtained for VCSELs on [311]B substrates than those on [100] substrates under zero-bias modulation. Time-dependent orthogonal polarization suppression ratio measurements also showed that the orthogonal polarization suppression ratios of the VCSEL on [311]B substrates were more stable than those on [100] substrates. The data transmission characteristics also indicate large differences in the dependence of the bit error rate on bias current and the power penalty between polarization resolved and unresolved systems between VCSELs on [311]B and [100] substrates. The beneficial effect of the polarization stability of VCSELs on [311]B substrates due to their anisotropic optical gain is clearly demonstrated.

Investigation of dynamic polarization stability of 850-nm GaAs-based vertical-cavity surface-emitting lasers grown on [311]B and [100] substrates

The polarization stability of 850-nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) under dynamic operation was investigated by comparing the characteristics of VCSELs grown on [311]B and [100] GaAs substrates. Significantly larger suppression ratios of the two orthogonal polarization modes was obtained for VCSELs on [311]B substrates than those on [100] substrates under zero-bias modulation. Time-dependent orthogonal polarization suppression ratio measurements also showed that the polarization direction was more stable in the VCSEL on [311]B substrates than that on [100] substrates. Error-free transmission was realized from VCSELs on [311]B substrates with and without a polarizer in both back-to-back and 100-m multimode fiber transmission.

ParaBIT-1: 60-Gb/s-throughput parallel optical interconnect module

We previously proposed ParaBIT (parallel inter-board optical interconnection technology), and developed a prototype front-end module, called ParaBIT-0, with a total throughput of 28 Gb/s (700 Mb/s/spl times/40 ch). Aiming at higher throughput, lower cost, and further miniaturization, we are now developing a version, called ParaBIT-1, which is designed to achieve a total throughput of 60 Gb/s (1.25 Gbit/s/spl times/480-ch). To achieve a compact and high-throughput module, we developed a new compact high-density packaging structure and cost-effective optical coupling system for ParaBIT-1. This packaging structure enabled us to reduce the volume of ParaBIT-1 to 9 cc, which is about one-third that of ParaBIT-0 (25 cc). The optical coupling system consists of a new structure 24-fiber BF (bare fiber) connector whose main parts are made of molded plastic and a 24-channel optical coupling component using new polymeric optical waveguide film. The optical coupling component is composed of a 24-ch waveguide film with 45/spl deg/ mirrors and the 24-fiber BF connector interface, and can be assembled by passive alignment. The film has high thermal stability to allow soldering reflow processes, and is fabricated by direct photo-patterning. ParaBIT-1 met the design target of 1.25 Gb/s per channel.

Design of Deep Guard Ring for Geiger Mode Operation Avalanche Photodiode

The performance of avalanche photodiodes with deep guard rings for Geiger mode operation is studied. The electric field distribution is calculated using the finite element method and the carrier multiplication characteristic is calculated along typical lines in the device. The nonlinear dependence of the ionization rates on the electric field strength can make a guard ring less effective in Geiger mode operation. The maximum single photon detection efficiency that can be obtained without breakdown at the guard ring is calculated for several structure parameters. It is shown that the single photon detection efficiency strongly depends on the guard ring design.

A 100-Gb/s throughput ATM switch MCM with a 320-channel parallel optical I/O interface

For an ATM switch system, we have developed a 100-Gb/s input/output (I/O) throughput optical I/O interface ATM switch multichip module (MCM) that has 320-ch optical I/O ports. This MCM is fabricated using ceramic (MCM-C) technology and very-small highly-parallel O/E and E/O optical converters. It uses 0.25-/spl mu/m complementary metal oxide semiconductors (CMOS) ATM switch large scale integrations (LSIs) and has a total I/O throughput of up to 160 Gb/s. A prototype module with total I/O throughput of 100 Gb/s has been partially assembled using eight optical I/O interface blocks, each composed of a 40-ch O/E converter and a 40-ch E/O converter; the data rate per channel is from dc to 700 Mb/s. Using this module we developed an optical I/O interface ATM switch system and confirmed the operation of the optical interface.