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As a solution to provide a small-size and low-cost 100-Gb/s optical module, direct optical coupling between a lens-integrated surface-emitting DFB laser (LISEL) array and a single-mode fiber (SMF) array is demonstrated. A very-small far-field angle ( $\sim 2$ °) was obtained by monolithic integration of an InP lens with a laser chip. As a result, each channel of the LISEL array can directly couple to an SMF without any additional external optical components. The measured misalignment tolerance between the LISEL array and an SMF array was sufficiently large, namely, $\pm 5.5~\mu \text{m}$ , at excess loss of 1 dB over all four channels with the maximum coupling efficiency of 8.4 dB. These measurement results are in good agreement with a theoretical calculation based on Gaussian optics. These results demonstrate that high coupling efficiency (−3 dB) can be achieved while large misalignment tolerance ( $\pm 4.5~\mu \text{m}$ ) at excess loss of only 1 dB is maintained.

As a solution to provide small-footprint and low-cost light sources for silicon platforms, light sources using a lens-integrated surface-emitting laser (LISEL), and a grating coupler fabricated on a silicon-on-insulator substrate is proposed. Light emitted from the LISEL (based on an InP distributed feedback laser) has a narrow far-field pattern, so the LISEL can be directly mounted on the silicon platform with no additional external optical components. The alignment tolerance between the LISEL and grating coupler was experimentally measured. This measurement confirmed large alignment tolerance. The excess loss due to misalignment of ±5 μm is only 1.5 dB.

A prototype transceiver composed of a 1.3-μm-range lens-integrated laser diode and photodiode as well as a complementary metal-oxide-semiconductor (CMOS) laser diode driver and a CMOS transimpedance amplifier for high-speed optical interconnections was developed. It demonstrated 25-Gb/s error-free 100-m multimode fiber transmission, with power dissipation of only 9 mW/Gb/s, for the first time.

A high-speed large-capacity optical printed circuit board (OPCB) for next-generation high-capacity routers and servers was developed. This OPCB is composed of a multilayer polymer optical waveguide, a receiver optical input/output (I/O) module (with a lens-integrated photodiode and a SiGe transimpedance amplifier), and a low-power (7.1 mW/Gb/s) transmitter optical I/O module consisting of a lens-integrated surface-emitting laser and complementary metal-oxide-semiconductor (CMOS) driver IC. A 1-Tb/s (20 Gb/s/ch × 48 ch per transmitter or receiver) large-capacity OPCB prototype was fabricated and demonstrated 20-Gb/s/ch operation.