Lucie Robitaille

Multifunctional resistive-heating and color-changing monofilaments produced by a single-step coaxial melt-spinning process.

Multifunctional coaxial monofilaments were successfully produced by melt-spinning several polymer composites in a single-step. The external layer of the monofilaments was a thermochromic composite having a color-transition at 40 °C (above the ambient temperature) in order to avoid control interferences by the external temperature. The core layer of the monofilaments was a conductive polymer nanocomposite whose resistive heating properties were used to control the monofilaments temperature and therefore its color using electrical current. The careful selection of the materials and adequate formulation allowed to obtain a trilayer structure with enhanced compatibility between the layers. The mechanical properties of the monofilaments were improved by a solid-state stretching step while also decreasing their diameter. A 64 cm(2) prototype fabric was woven to characterize the resistive-heating and color-changing properties of the monofilaments. Exceptional thermal output levels were reached, with a temperature rising up to over 100 °C at voltages above 110 V. The reversible color change properties were also successfully demonstrated.

Design and fabrication of low-loss polymer waveguide components for on-chip optical interconnection

This paper reports the fabrication and characterization of straight and curved polyimide waveguides for on-chip optical signal distribution in GaAs-based optoelectronic integrated circuits. Polyimide ridge waveguides with propagation losses (at 830 nm) as low as 0.6 dB/cm have been fabricated. S-bends and splitters with low curvature losses and good splitting ratios have also been successfully fabricated and tested. The effects of the material properties and radius of curvature on the optical losses are presented, and the advantages of this polymer technology are discussed.

Integration of optoelectronic switch matrices using metal-semiconductor-metal photodetectors and polyimide waveguide circuitry

The integration of metal-semiconductor-metal (MSM) photodetector arrays with multimode polyimide waveguides has been demonstrated. MSM detectors were fabricated using transparent indium tin oxide (ITO) interdigitated electrodes on semi-insulating GaAs substrates. Light at 830 nm was coupled efficiently from the waveguides into the underlying photodetectors through gaps in the SiO2 buffer layer. Absolute responsivities of the integrated MSM detectors were around 0.5 A/W, and 3-dB bandwidths of 4 to 6 GHz were measured. Division of the input optical signal between four detectors of increasing length integrated along a single waveguide was achieved. Four 1 x4 arrays were used to assemble a prototype hybrid 4x4 optoelectronic switch. Band- widths of around 1.2 GHz, limited by the electronic circuitry, were measured. The isolation was better than 35 dB, and the crosstalk was approximately ?35 dB. The advantages of polyimide waveguides for on- chip interconnection in switch matrices are discussed.

Optical signal distribution to MSM photodetector arrays via integrated polyimide waveguides

The integration of metal-semiconductor-metal (MSM) photodetector arrays with polyimide ridge waveguides is demonstrated. MSM detectors were fabricated using transparent indium tin oxide (ITO) interdigitated electrodes on semi-insulating GaAs substrates. An optical buffer layer of SiO/sub 2/ was deposited and patterned, and then polyimide ridge waveguides were fabricated on top by spin coating and photolithography. The guides were multimode with widths from 10 to 50 /spl mu/m. Light at 830 nm was coupled efficiently from the waveguides through gaps in the SiO/sub 2/ buffer layer into the underlying detector structures. Absolute responsivities of the integrated MSM devices were around 0.5 A/W and the 3 dB bandwidths of 5-6 GHz were measured. Division of the input signal between sets of two and four detectors under a single waveguide has been achieved, highlighting the potential for the fabrication of integrated optoelectronic switches.

Optimization of metal-semiconductor-metal (MSM) photodetector arrays integrated with polyimide waveguides

The integration of MSM photodetector arrays with polyimide ridge waveguides is demonstrated. MSM detectors consisting of two Schottky interdigitated electrodes were fabricated singly and in arrays of two or four, on semi-insulating GaAs substrates. Following deposition and patterning of an SiO2 buffer layer, polyimide ridge waveguides were fabricated on top by spin coating and photolithography. The guides were multimode, with widths from 10 to 50 micrometer, allowing for ease of coupling from an optical fiber. Light from the waveguides was coupled through gaps in the SiO2 buffer layer into the photodetectors. Transparent indium tin oxide (ITO) Schottky electrodes were employed to maximize absorption of light in the detector region. The end-to-end responsivities of the integrated MSM devices were typically 0.1 to 0.16 A/W. Bandwidths were 1 to 1.7 GHz; however these values could be increased substantially by optimization of the etch conditions used in the detector fabrication. Losses due to butt coupling to the multimode waveguides were around 1.5 dB. Division of the input signal between sets of two and four detectors has been demonstrated using a series of optical taps fabricated in an overlying polyimide ridge waveguide. Results indicate that polyimide waveguides could be a practical means of monolithically integrating optical functions such as signal routing and power division on complex optoelectronic integrated circuits (OEICs).

Langmuir-Blodgett processing of conjugated polymers

Abstract Stable monolayers of poly(2-decyloxyaniline) and poly(1,1,1,2,2,3,3,4,4,5,5,6,6,-tridecafluorononylthiophene) have been obtained at an air-water interface. In both cases the presence of alkoxy or fluorinated substituents has improved the stability of these polymeric monolayers compared with their respective alkyl analogues. Successful transfer of multilayers of poly(2-decyloxyaniline) has been achieved, while only a monolayer of the fluorinated polythiophene could be obtained on silanized glass slides. A monolayer of the latter polymer has revealed similar thermochromic properties to those observed with a spin-coated film, indicating that the interchain interactions are not the dominant factor in these thermally induced optical effects.

Assessment of third-order optical nonlinearities in conjugated organic polymers

Third-order nonlinear optical susceptibilities of substituted polythiophenes, polyanilines, and polysilanes have been estimated by third-harmonic generation measurements at 1.053 μm. Values of x3(-3ω,ω,ω,ω) for new polymers-two poly(alkoxyphenylthiophenes), a fluorinated poly(alkylthiophene), and a poly(alkoxyaniline)-were found to be in the range 0.7 x 10-12 to 2.3 x 10-12 esu, similar to those for other substituted polythiophenes and polyanilines. Values of x3(-3ω,ω,ω,ω)) are correlated with the absorption maxima for series of polythiophenes, polysilanes, and polyanilines. Third-order nonlinearities are found to depend strongly on the nature of the polymer backbone and only slightly on substituents.

Polymer waveguide devices for WDM applications

The use of polymer waveguides for the design and fabrication of devices for wavelength division multiplexing (WDM) at 1550 nm is described. Single mode 1 X 2, 1 X 4 and 1 X 8 splitters and combiners have been fabricated using photosensitive polyimide materials on silicon substrates. Good division of light was achieved in the devices, and waveguide facets could be cleaved to allow efficient coupling from optical fibers. The design of phased array wavelength demultiplexers for polymer waveguide technologies is described and compared to competitive technologies. Optimization of the trade-off between device size and waveguide cross-section is discussed and preliminary device designs for different polymer systems are presented.

Use of polymer waveguides for optical interconnection in high-speed communication and signal processing systems

GaAs optoelectronic integrated circuits are having an increasing impact on the development of lightwave communication systems and very high sped digital and analog signal processors. However, cost-effective integration of complex electronic and optoelectronic circuits used in high speed networks or backplane interconnects still presents a significant technological challenge and substantial efforts are being devoted to the development of practical, low-loss integration processes. Photodetector/waveguide integration is a key aspect of the successful packaging of optoelectronic devices. In this work, metal-semiconductor- metal (MSM) photodetectors were integrated with polyimide ridge waveguides, and the processing parameters were varied for optimum performance. The absolute responsivities of the integrated MSM/polyimide waveguide structures were typically 0.5 A/W, and 3 dB bandwidths of 4-6 GHz were measured. Series of 1 X 2 and 1 X 4 photodetector arrays were interconnected, demonstrating a uniform division of the optical signal between the detectors. Results indicate that these arrays offer the potential to fabricate optoelectronic switches that can be used in a variety of high speed and broadband communication systems.

High-speed switching characteristics of integrated optoelectronic crossbar switch

Optoelectronic (OE) switching is a promising approach for routing signals in fiber optic networks. Recently, the integration of a 4 X 4 MSM array with optical surface waveguides has been reported. This technique greatly simplifies the packaging of an OE switch. The on-chip polyimide optical waveguides perform the optical signal distribution to a matrix of MSMs which are responsible for the switching operation itself. Photoresponse bandwidths exceeding 4 GHz have been demonstrated. Another important characteristic of a switch is the switching speed since it determines the reconfiguration time. Mechanical and thermal optical waveguide switches offer switching speeds of the order of milliseconds which is sufficient for network traffic management but too slow for packet switching. We report measurements on the switching characteristics of a 4 X 4 optoelectronic switch performed in both the frequency and time domain. In the time domain, the individual crosspoints exhibit a rise time of 3 ns. However, a sizeable overshoot and ringing settles only after 35 ns. This constitutes the reconfiguration time at present. This is confirmed by measurements in the frequency domain of the electrical transmission from control line to output line. The 3-dB switching bandwidth is a few hundred megahertz. The 35 ns reconfiguration time indicates that it is already suitable for packet switching in a 10 Mb/s network. Switching speed measurements on individual MSMs suggests that modifications to the switch circuit could improve the switching time. The switch could also find application as a component in the wavelength conversion circuit of a WDM fiber optic network.