Mu Hee Cho

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.

Passively assembled optical interconnection system based on an optical printed-circuit board

We propose a passively assembled chip-to-chip optical interconnection system using fiber-optic technology. To demonstrate the system, three components were prepared: a fiber-embedded optical printed-circuit board (OPCB), optical transmitter/receiver modules, and 90/spl deg/-bent fiber connectors. All components were assembled using precise guide pins and holes so that complete passive alignment was achieved in the OPCB. An optical link of 5-Gb/s/ch signals with a total link loss of -1.5 dB has been successfully demonstrated from the assembled system.

High-coupling-efficiency optical interconnection using a 90/spl deg/-bent fiber array connector in optical printed circuit boards

A high-coupling-efficiency optical interconnection has been demonstrated using a 90/spl deg/-bent fiber array connector to deflect beams between surface-emitting lasers or surface-receiving photodiodes and optical layers embedded in a board. A 90/spl deg/-bent fiber array is mounted in a tetragonal body with a millimeter scale size to make it suitable for passive packaging in the board. The bending radius of silica fibers in the connector was controlled to have 1.5 mm resulting in bending loss of about 0.5 dB. An optical link of 2.5-Gb/s signals with a total interconnection loss of -1.3 dB was demonstrated using the connectors and a fiber-embedded board.

Two-Dimensional Optical Interconnection Based on Two-Layered Optical Printed Circuit Board

The demonstration of an optical platform based on an optical printed circuit board (OPCB) was shown for two-dimensional (2-D) chip-to-chip optical interconnection. The optical platform was designed for 96 Gb/s total throughput which was 2 layers times 4 channels times 4 parallel links times 3 Gb/s/ch and using a passive assembly technology. We fabricated three main components for the 2-D optical interconnection; two-layered six-channel fiber- and connector-embedded OPCB, two-layered six-channel 90deg-bent fiber connectors, and 2-D optical transmitter/receiver (Tx/Rx) modules. The total optical loss from the Tx to the Rx was measured to approximately be -5.3 dB. The optical interconnection using an optical platform was successfully achieved with 3-Gb/s/ch data transmission

Optical interconnection using fiber-embedded boards and connection blocks fabricated by a micro-grooving technique for fiber insertion

We fabricated fiber-embedded boards using a micro-grooving technique for optical interconnects. This approach is quite cost effective and fully compatible with conventional PCB processes. U-shaped grooves were formed on FR-4 plates using a 90? V-shaped diamond blade. Polyimide-coated glass fibers were inserted in the grooves followed by a conventional lamination process. The 12 fibers embedded in the board showed a good uniformity in their position with a fluctuation below ?8 ?m. Optical connection blocks were also fabricated using fiber segments embedded in a grooved silicon wafer piece in order to couple the light between a transmitter/receiver module and a fiber-embedded board. 45? mirrors were formed at the end of the connection blocks by mechanical polishing. An optical link of 2.5 Gb s?1 signals with a high coupling efficiency was demonstrated through the fiber-embedded connection blocks and a board.

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.

10 Gbps Transimpedance Amplifier-Receiver for Optical Interconnects

2with power consumption of 16.9 mW at 1.3 V. The measured input-referred noise of optical TIA-Rx is 20 pA/√Hz with a 3-dB bandwidth of 6.9 GHz. The proposed TIA-Rx achieved a high gain-bandwidth product per DC power figure of merit of 408 GHzΩ /mW.

Optical Interconnection Platform Composed of Fiber-Embedded Board, 90

An architecture of a passively assembled optical platform is suggested for a chip-to-chip optical interconnection system. The platform is constructed using all-fiber media for the optical paths: a fiber-embedded optical printed-circuit board (OPCB) and 90-bent fiber connector. The passive assembling was achieved by employing the guide pins/holes of commercialized ferrules in the optical link between the OPCB, 90-bent fiber connector, and the transmitter/receiver (Tx/Rx) module. From this interconnection scheme, a low total optical loss of was obtained. From an assembled platform with 10 Gb/s/ch 4 ch Tx/Rx modules, a 7-Gb/s/ch data transmission was demonstrated with a bit error rate below , involving the optical and electrical crosstalk arisen in the whole channel operation.

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Passive optical components for optical interconnection using hybrid optical printed-circuit boards (PCBs) where electrical and optical layers are integrated into one board has been studied. We present detailed fabrication processes and optical characteristics of optical PCBs and connectors for optical coupling between vertical and horizontal directions. Two kinds of optical PCBs, polymer-waveguide-embedded and silica-fiber-embedded PCBs, were prepared. For the polymer-waveguide-embedded PCB, the polymer waveguide was formed lithographically on a FR-4 board and its core has 100 μm width and 60 μm thickness. The waveguide-defined board was covered with another FR4 plate and then laminated at 185°C under the pressure of 35 kg/cm2. After lamination the transmission loss of the waveguide was -0.53 dB/cm. For the fiber-embedded PCB, fibers with 100 μm core diameter were inserted in grooves formed on a FR-4 board and they followed a similar lamination processes. The propagation loss of the fiber-embedded board at 850 nm was negligible in board scale. We also prepared 2 types of connectors for optical coupling between the surface mounted transmitter or receiver modules and the optical PCBs; 45°-ended fiber block and 90°-bent fiber connector. The insertion losses of the 2 kinds of connectors were, respectively, -0.15 dB and -0.25 dB. The best combination between the optical PCBs and connectors in view of optical characteristics and packaging is fiber-embedded board and 90°-bent fiber connector. They show successfully optical link of 2.5 Gbps with a very low coupling losses of -4.4 dB and a low optical crosstalk of -53 dB.

-Bent Fiber Block, and 10-Gb/s Optical Module

A simple method for fabricating fiber- and waveguide-embedded boards for optical interconnects is described. It is quite cost effective and fully compatible with conventional PCB processes. On-board optical link of 2.5Gb/s signals between the transmitter and the receiver modules. was demonstrated by placing connecting blocks having 45/spl deg/-mirror planes at the ends of the fiber and waveguide-embedded boards.