40 Gb/s optical subassembly module for a multi-channel bidirectional optical link.

A 40 Gb/s bidirectional optical link using four-channel optical subassembly (OSA) modules and two different wavelengths for the up- and down-link is demonstrated. Widely separated wavelengths of 850 nm and 1060 nm are used to reduce the optical crosstalk between the up- and down-link signals. Due to the integration capabilities of silicon, the OSA is implemented, all based on silicon: V-grooved silicon substrates to embed fibers and silicon optical benches (SiOBs) to mount optical components. The SiOBs are separately prepared for array chips of photodiodes (PDs), vertical-cavity surface-emitting lasers (VCSELs), and monitoring PDs, which are serially configured on an optical fiber array for direct coupling to the transmission fibers. The separation of the up- and down-link wavelengths is implemented using a wavelength-filtering 45° mirror which is formed in the fiber under the VCSEL. To guide the light signal to the PD another 45° mirror is formed at the end of the fiber. The fabricated bidirectional OSA module shows good performances with a clear eye-diagram and a BER of less than 10(-12) at a data rate of 10 Gb/s for each of the channels with input powers of -8 dBm and -6.5 dBm for the up-link and the down-link, respectively. The measured inter-channel crosstalk of the bidirectional 40 Gb/s optical link is about -22.6 dB, while the full-duplex operation mode demonstrates negligible crosstalk between the up- and down-link.

Low-voltage high-performance silicon photonic devices and photonic integrated circuits operating up to 30 Gb/s.

We present high performance silicon photonic circuits (PICs) defined for off-chip or on-chip photonic interconnects, where PN depletion Mach-Zehnder modulators and evanescent-coupled waveguide Ge-on-Si photodetectors were monolithically integrated on an SOI wafer with CMOS-compatible process. The fabricated silicon PIC(off-chip) for off-chip optical interconnects showed operation up to 30 Gb/s. Under differential drive of low-voltage 1.2 V(pp), the integrated 1 mm-phase-shifter modulator in the PIC(off-chip) demonstrated an extinction ratio (ER) of 10.5dB for 12.5 Gb/s, an ER of 9.1dB for 20 Gb/s, and an ER of 7.2 dB for 30 Gb/s operation, without adoption of travelling-wave electrodes. The device showed the modulation efficiency of V(π)L(π) ~1.59 Vcm, and the phase-shifter loss of 3.2 dB/mm for maximum optical transmission. The Ge photodetector, which allows simpler integration process based on reduced pressure chemical vapor deposition exhibited operation over 30 Gb/s with a low dark current of 700 nA at -1V. The fabricated silicon PIC(intra-chip) for on-chip (intra-chip) photonic interconnects, where the monolithically integrated modulator and Ge photodetector were connected by a silicon waveguide on the same chip, showed on-chip data transmissions up to 20 Gb/s, indicating potential application in future silicon on-chip optical network. We also report the performance of the hybrid silicon electronic-photonic IC (EPIC), where a PIC(intra-chip) chip and 0.13µm CMOS interface IC chips were hybrid-integrated.

High-efficiency and stable optical transmitter using VCSEL-direct-bonded connector for optical interconnection.

A high-efficiency optical transmitter module for PCB (printed circuit board)-based interconnections was fabricated using a bottom-emitting VCSEL. The bottom-emitting VCSEL was directly bonded by an epoxy on a 90 degrees -bent fiber connector which is inserted into the PCB to couple to the fiber layer embedded in the board. A ray trace simulation indicates that close contact between the VCSEL and the connector removes most of the losses due to Fresnel reflection and beam divergence. This tendency was experimentally identified. Thermal dissipation through the epoxy layer and the connector also improves significantly the power characteristics of the VCSEL. The VCSEL after bonding on the connector shows about 40% higher power compared to that of the bare VCSEL at the current showing a peak power before bonding. The results indicate that direct bonding improves both optical and electrical efficiencies. A successful eye diagram at the speed of 5 Gb/s/ch with 850 nm was accomplished from the VCSEL-direct-bonded transmitter module.