Chin-Ta Chen

Optical interconnect transmitter based on guided-wave silicon optical bench

An optical interconnect transmitter based on guided-wave silicon optical bench is demonstrated. The guided-wave silicon optical bench (GW-SiOB) is developed on a silicon-on-insulator (SOI) substrate. The three-dimensional guided-wave optical paths on the silicon optical bench are realized using trapezoidal waveguides monolithically integrated with 45° micro-reflectors. Such three-dimensional guided-w ave optical paths of SiOB would simplify and shrink the intra-chip optical interconnects located on a SOI substrate. The clearly open eye patterns operated at a data rate of 5 Gbps verifies the proposed GW-SiOB is suitable for intra-chip optical interconnects.

Linear Cascade Arrays of GaN-Based Green Light-Emitting Diodes for High-Speed and High-Power Performance

In the following study, we demonstrated linear cascade GaN-based light-emitting-diode (LED) arrays at a wavelength of approximately 520 nm. Experimental LEDs were analyzed with the goal to improve the output power and differential efficiency of a single LED. The study shows that using arrays with up to four LEDs connected in series, we can achieve four times the improvement in output power (differential quantum efficiency) under the same bias current as compared to a single LED apparatus. We have also measured the modulation-speed performance of experimental LEDs, and both devices exhibit similar 3-dB bandwidth (90 MHz) under the same bias currents. Experimental results indicate that the cascade connection offers the advantages of significantly enhanced external differential efficiency and provision of a method to use a constant-voltage power supply. The current crowding problem and resistance-capacitance-limited bandwidth degradation issues in a large active area LED can also be minimized using the connection demonstrated in our experiment.

SOI-based trapezoidal waveguide with 45-degree microreflector for non-coplanar light bending

SOI-based trapezoidal waveguide with 45° reflector for non-coplanar light bending is proposed and demonstrated. The proposed structures include 45° micro-reflector and silicon trapezoidal waveguide. Due to the SOI-based trapezoidal waveguide with 45° reflector, light wave can be coupled into silicon waveguide easily and have higher coupling efficiency. All of structures are fabricated using a single-step wet etching process. The RMS roughness of waveguide sidewall and 45° micro-reflector is about 30 nm. The coupling efficiency of proposed structure is -4.51 dB, and misalignment tolerance are 42 μm at horizontal direction and 41 μm at vertical direction. The multi-channel trapezoidal waveguide is also demonstrated. This device can transfer the light wave at the same time, and its cross talk is about -50 dB.

Linear Cascade GaN-Based Green Light-Emitting Diodes With Invariant High-Speed/Power Performance Under High-Temperature Operation

We demonstrate the performance of linear cascade green light-emitting diode (LED) arrays suited for use in plastic optical fiber (POF) communications in automobiles or harsh environments. With this three-LED array, driven by the constant voltage bias of an in-car battery output (12 V) we obtain high-speed ( ~ 100-Mb/s eye-opening), high-coupling power (0.9 mW), and a very small variation of coupled power versus temperature [- 0.12%degC-1 at room temperature (RT)] for the whole measured temperature range (i.e., RT to 120degC). Even under high bias current (100 mA) operation, our device can sustain a clear 150-Mb/s eye-opening from RT to 120degC. The static and dynamic measurement results indicate that the speed and power performance of this device are less sensitive to variations in ambient temperature than are those of the red resonant-cavity LEDs utilized for POF communication.

Chip-Level Optical Interconnects Using Polymer Waveguide Integrated With Laser/PD on Silicon

In this letter, we demonstrate a chip-level high-speed optical interconnect, where the optical transmitter/receiver, the polymer waveguides, and the silicon-trench 45° microreflectors are integrated on a single silicon platform. The silicon platform with a silicon trench can provide independent photonic and electrical layers, respectively, for high-speed and low-speed (except high-frequency transmission lines) data transmissions. In order to demonstrate the technical capability of chip-level optical interconnects, the vertical-cavity surface-emitting laser (VCSEL)/photodetector (PD) and the driver/amplifier IC as well as the polymer waveguides combined with the 45° microreflectors are integrated on the electrical and photonic layers of the silicon platform, respectively. The total optical transmission (VCSEL-to-waveguide-to-PD via two 45° microreflectors) is -4.7 dB. The high-speed transmission experiment shows the clear eye opening up to 20-Gbit/s data rate. The bit error rate better than 10-12 for the proposed architecture is also successfully demonstrated. It reveals such chip-level optical interconnects based on the proposed silicon platform with the polymer waveguides is suitable for high-speed data transmission.

SOI-based trapezoidal waveguide with 45° microreflector for noncoplanar optical interconnect

A silicon on insulator (SOI)-based trapezoidal waveguide with a 45° reflector for noncoplanar optical interconnect is demonstrated. The proposed waveguide is fabricated on an orientation-defined (100) SOI substrate by using a single-step anisotropic wet-etching process. The optical performances of proposed waveguides are numerically and experimentally studied. Transmittance of -4.51 dB, alignment tolerance of ±20 μm, cross talk of -53 dB, and propagation loss of -0.404 dB/cm are achieved The proposed waveguide would be a basic element and suitable for the future intrachip optical interconnects.

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The 45°-mirror terminated polymer waveguides fabricated on a silicon substrate are demonstrated for on-chip out-of-plane optical interconnects. The silicon 45^° microreflectors are fabricated on an orientation-defined (100) silicon substrate by using anisotropic chemical wet etching. On using a photolithography process, we observe two vertically bending paths at the input and output ports of polymer waveguide on a silicon substrate with 45^° microreflectors. The transmission efficiency of -3.77 dB is measured for a 0.5-cm polymer waveguide combined with the 45^° microreflectors. The optical loss occurring at the 45^°-mirror is -0.27 dB. The channel-to-channel crosstalk for the 250-μm pitch is less than -40 dB. The wider alignment tolerance up to ±15 μm would facilitate the active-device assembly on a silicon substrate.

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We utilize the Zn-diffusion technique to fabricate a single-mode high-speed 850-nm vertical-cavity surface-emitting laser. With this technique, we are able to minimize the thermal effect without greatly scaling down the diameter of the oxide-confined aperture. The demonstrated device has a 9-mum active diameter with which we can attain a bandwidth of 8 GHz, a small differential resistance (~47 Omega), and a maximum output power of 3 mW. The single-mode characteristics can be sustained under dynamic operation for the whole bias current range. The dynamic measurement results indicate that with this single-mode device the damping-limited bandwidth of our multimode control can be eliminated without a Zn-diffusion aperture. A larger intrinsic bandwidth (32 versus 21 GHz) is also obtained due to the minimization of damping. The narrower divergence angle (8deg versus 20deg) means that the device exhibits a larger alignment tolerance and much lower coupling loss (9 dB) when used with the standard multimode fiber than those of the control sample.

-Mirror Terminated Polymer Waveguides on Silicon Substrates

The chip-level 1 × 2 optical interconnects using the polymer vertical splitter developed on a silicon substrate are demonstrated. The 1 × 2 vertical-splitting configuration is realized using a polymer waveguide terminated at three silicon 45 ° reflectors. The high-frequency transmission lines combined with the indium solder bumps are developed to flip-chip assemble a vertical-cavity surface-emitting laser chip at the input port and two photodetector chips at two output ports. Total transmission loss of -3.26 dB with a splitting ratio of 1 : 1 for the proposed splitter is experimentally obtained. A 10-Gbit/s data transmission with bit error rates better than 10-12 for two output ports is achieved. It reveals that such chip-level 1 × 2 optical interconnects using the polymer vertical splitter are suitable for high-speed data transmission with multiple output ports.

Minimization of Damping in the Electrooptic Frequency Response of High-Speed Zn-Diffusion Single-Mode Vertical-Cavity Surface-Emitting Lasers

A polymer-waveguide-based optical circuit with two vertical-transition output ports for the optical interconnects is demonstrated on a silicon substrate. Such a 1 × 2 vertical splitter is realized using a polymer waveguide monolithically integrated with three silicon 45° microreflectors. The vertical-cavity surface-emitting laser chip assembled at the input port and two multimode fibers located at two output ports are arranged to demonstrate a two-port optical proximity coupling of the off-chip optical interconnects based on the proposed splitter. The optical insertion loss of -6.6 dB is experimentally obtained for the proposed 1 × 2 vertical splitter with a splitting ratio of 1.3 : 1. The clearly 10-Gb/s optical eye patterns at both output ports verify that the 1 × 2 vertical splitter is suitable for the optical interconnects with multiple output ports.