Ray T. Chen

Fully embedded board-level guided-wave optoelectronic interconnects

A fully embedded board-level guided-wave optical interconnection is presented to solve the packaging compatibility problem. All elements involved in providing high-speed optical communications within one board are demonstrated. Experimental results on a 12-channel linear array of thin-film polyimide waveguides, vertical-cavity surface-emitting lasers (VCSELs) (42 /spl mu/m), and silicon MSM photodetectors (10 /spl mu/m) suitable for a fully embedded implementation are provided. Two types of waveguide couplers, titled gratings and 45/spl deg/ total internal reflection mirrors, are fabricated within the polyimide waveguides. Thirty-five to near 100% coupling efficiencies are experimentally confirmed. By doing so, all the real estate of the PC board surface are occupied by electronics, and therefore one only observes the performance enhancement due to the employment of optical interconnection but does not worry about the interface problem between electronic and optoelectronic components unlike conventional approaches. A high speed 1-48 optical clock signal distribution network for Cray T-90 super computer is demonstrated. A waveguide propagation loss of 0.21 dB/cm at 850 nm was experimentally confirmed for the 1-48 clock signal distribution and for point-to-point interconnects. The feasibility of using polyimide as the interlayer dielectric material to form hybrid three-dimensional interconnects is also demonstrated. Finally, a waveguide bus architecture is presented, which provides a realistic bidirectional broadcasting transmission of optical signals. Such a structure is equivalent to such IEEE standard bus protocols as VME bus and FutureBus.

80-micron interaction length silicon photonic crystal waveguide modulator

An ultracompact silicon electro-optic modulator was experimentally demonstrated based on silicon photonic crystal (PhC) waveguides for the first time to our knowledge. Modulation operation was demonstrated by carrier injection into an 80μm-long silicon PhC waveguide of a Mach-Zehnder interferometer (MZI) structure. The π phase shift driving current, Iπ, across the active region is as low as 0.15mA, which is equivalent to a Vπ of 7.5mV when a 50Ω impedance-matched structure is applied. The modulation depth is 92% operating at 1567nm.

Flexible optical waveguide film fabrications and optoelectronic devices integration for fully embedded board-level optical interconnects

This paper demonstrates a flexible optical waveguide film with integrated optoelectronic devices (vertical-cavity surface-emitting laser (VCSEL) and p-i-n photodiode arrays) for fully embedded board-level optical interconnects. The optical waveguide circuit with 45/spl deg/ micromirror couplers was fabricated on a thin flexible polymeric substrate by soft molding. The 45/spl deg/ couplers were fabricated by cutting the waveguide with a microtome blade. The waveguide core material was SU-8 photoresist, and the cladding was cycloolefin copolymer. A thin VCSEL and p-i-n photodiode array were directly integrated on the waveguide film. Measured propagation loss of a waveguide was 0.6 dB/cm at 850 nm.

All ink-jet-printed carbon nanotube thin-film transistor on a polyimide substrate with an ultrahigh operating frequency of over 5 GHz

We report a flexible carbon nanotube (CNT) thin-film transistor (TFT) fabricated solely by ink-jet printing technology. The TFT is top gate configured, consisting of source and drain electrodes, a carrier transport layer based on an ultrapure, high-density (>1000 CNTs/μm2) CNT thin film, an ion-gel gate dielectric layer, and a poly(3,4-ethylenedioxythiophene) top gate electrode. All the TFT elements are ink-jet printed at room temperature on a polyimide substrate without involving any photolithography patterning or surface pretreatment steps. This CNT-TFT exhibits a high operating frequency of over 5 GHz and an on-off ratio of over 100. Such an all-ink-jet-printed process eliminates the need for lithography, vacuum processing, and metallization procedures and thus provides a promising technology for low-cost, high-throughput fabrication of large-area high-speed flexible electronic circuits on virtually any desired flexible substrate.

On-chip methane sensing by near-IR absorption signatures in a photonic crystal slot waveguide

We demonstrate a 300 μm long silicon photonic crystal (PC) slot waveguide device for on-chip near-infrared absorption spectroscopy, based on the Beer-Lambert law for the detection of methane gas. The device combines slow light in a PC waveguide with high electric field intensity in a low-index 90 nm wide slot, which effectively increases the optical absorption path length. A methane concentration of 100 ppm (parts per million) in nitrogen was measured.

Recent advances in silicon-based passive and active optical interconnects

Silicon photonics has experienced phenomenal transformations over the last decade. In this paper, we present some of the notable advances in silicon-based passive and active optical interconnect components, and highlight some of our key contributions. Light is also cast on few other parallel technologies that are working in tandem with silicon-based structures, and providing unique functions not achievable with any single system acting alone. With an increasing utilization of CMOS foundries for silicon photonics fabrication, a viable path for realizing extremely low-cost integrated optoelectronics has been paved. These advances are expected to benefit several application domains in the years to come, including communication networks, sensing, and nonlinear systems.

Fabrication of core-shell Au-Pt nanoparticle film and its potential application as catalysis and SERS substrateElectronic supplementary information (ESI) available: AFM image and line scans of core-shell Au-Pt nanoparticle film (colour version of Fig. 4). See http://www.rsc.org/suppdata/jm/b3/b314868h/

In this paper we report the rational design and fabrication of high-quality core-shell Au-Pt nanoparticle film. Such film shows highly efficient catalytic properties and excellent surface-enhanced Raman scattering (SERS) ability.

High speed silicon photonic crystal waveguide modulator for low voltage operation

A high speed compact silicon modulator is experimentally demonstrated to work at a low driving voltage desirable for on-chip applications. As carrier injection is the only practical option for optical modulation in silicon, a lower limit of current density (∼104A∕cm2) exists for achieving gigahertz modulation in the p-i-n diode configuration. Exploiting the slow group velocity of light in photonic crystal waveguides, the interaction length of this Mach-Zehnder interferometer-type silicon modulator is reduced significantly compared to conventional modulators. The required high current density is achieved with a low voltage (2V) by scaling down the interaction length to 80μm.

Effective in-device r 33 of 735 pm/V on electro-optic polymer infiltrated silicon photonic crystal slot waveguides

We design and fabricate a 320 nm slot for an electro-optic (E-O) polymer infiltrated silicon photonic crystal waveguide. Because of the large slot width, the poling efficiency of the infiltrated E-O polymer (AJCKL1/amorphous polycarbonate) is significantly improved. When coupled with the slow light effect from the silicon photonic crystal waveguide, an effective in-device r(33) of 735 pm/V, which to our knowledge is a record high, is demonstrated, which is ten times higher than the E-O coefficient achieved in thin film material. Because of this ultrahigh E-O efficiency, the V(π)L of the device is only 0.44 V mm, which is to our knowledge the best result of all E-O polymer modulators.

Electro-optic polymer infiltrated silicon photonic crystal slot waveguide modulator with 23 dB slow light enhancement

A silicon/organic hybrid modulator integrating photonic crystal (PC) waveguide, 75 nm slot, and electro-optic (EO) polymer is experimentally demonstrated. Slow light in PC waveguide and strong field confinement in slot waveguide enable ultraefficient EO modulation with a record-low Vπ×L of 0.56 V mm and an in-device effective r33 of 132 pm/V. This result makes it the most efficient EO polymer modulator demonstrated to date. The modulated signal shows strong wavelength dependence and peak enhancement of 23 dB near the band edge of defect mode, which confirms the signature of the slow light effect.