James T. Yardley

FREE-SPACE ELECTRO-OPTIC DETECTION OF CONTINUOUS-WAVE TERAHERTZ RADIATION

We present a scheme for the coherent detection of freely propagating continuous-wave terahertz radiation using electro-optic detection. The terahertz radiation is generated by photomixing two single-mode laser diodes in an antenna fabricated on low-temperature-grown GaAs. This radiation is detected using the electro-optic effect in 〈110〉 ZnTe. In contrast to typical terahertz detection techniques, this is a frequency-domain measurement that relies on coherent up-conversion of the terahertz field combined with optical homodyning to suppress background noise.

Electro-optic determination of the nonlinear-optical properties of a covalently functionalized Disperse Red 1 copolymer

We report the development of a methodology for the comprehensive characterization of the linear- and nonlinear-optical properties of a model copolymer, Disperse Red 1, covalently functionalized to a methyl methacrylate backbone. From refractive-index and electro-optic measurements, we have evaluated both fundamental macroscopic and microscopic nonlinear-optical properties. We have measured the refractive indices of the copolymer as a function of chromophore concentration, wavelength, and poling field. For the linear-optical properties we find that the wavelength dependence is well described by a single-oscillator Sellmeier equation and that the poling-field dependence is well described by a simple theory related to the order parameter. From the observed refractive-index anisotropy as a function of poling field, we have obtained an effective dipole moment for the Disperse Red chromophore. We have measured the linear electro-optic effect in these systems as a function of poling temperature, film thickness, poling-field strength, wavelength, and concentration. We have found that the electro-optic coefficients may be modeled by an independent-response two-level dispersion model, from which an independent determination of the effective dipole moment, nonresonant second-order susceptibility χ(2), and nonresonant molecular hyperpolarizability β have been obtained.

Affordable WDM components: the polymer solution

An advanced polymeric waveguide technology was developed for affordable WDM components that address the needs of both the Telecom and the Datacom industries. We engineered high- performance organic polymers that can be readily made into both multimode and single-mode optical waveguide structures of controlled numerical aperture and geometry. These materials are formed from highly-crosslinked acrylate monomers with specific linkages that determine properties such as flexibility, toughness, loss, and environmental stability. These monomers are intermiscible, providing for precise adjustment of the refractive index from 1.3 to 1.6. In polymer form, they exhibit state-of-the-art loss values, high thermal stability, high humidity resistance, low dispersion and low birefringence. Waveguides are formed photolithographically, with the liquid monomer mixture polymerizing upon illumination in the UV via either mask exposure or laser direct writing. A wide range of rigid and flexible substrates can be used, including glass, quartz, oxidized silicon, glass-filled epoxy printed circuit board substrate, and flexible polyimide film. Waveguiding structures measuring tens of inches in length can be produced on computer boards, and guides that are meters long can be printed on rolls of plastic. We describe the fabrication of both Bragg gratings and waveguide grating routes in our polymers for filtering and demultiplexing applications in Telecom WDM systems. In Datacom, we describe polymeric components that we produced for aerospace WDM sensor systems. The importance of CAD tools in designing WDM devices is emphasized in this work. We further discuss the low-cost manufacturing of WDM components in an industrial environment.

Photochemical laser writing of polymeric optical waveguides

We report a rapid one‐step laser writing process for forming optical channel waveguides by photochemically lowering the index of refraction in selected areas of thin, highly photosensitive polymeric flims. We have demonstrated the concept by forming single‐ and multimode waveguides in films composed of poly(methylmethacrylate) containing (4‐N‐N‐dimethylaminophenyl)‐N‐phenyl nitrone. The effects of ultraviolet fluence on the refractive index of the films and on channel lightwave confinement were examined. Low loss (1.5 dB/cm) channels were produced with ultraviolet fluences as low as 20 mJ/cm2.

Advanced polymer systems for optoelectronic integrated circuit applications

An advanced versatile low-cost polymeric waveguide technology is proposed for optoelectronic integrated circuit applications. We have developed high-performance organic polymeric materials that can be readily made into both multimode and single-mode optical waveguide structures of controlled numerical aperture (NA) and geometry. These materials are formed from highly crosslinked acrylate monomers with specific linkages that determine properties such as flexibility, toughness, loss, and stability against yellowing and humidity. These monomers are intermiscible, providing for precise adjustment of the refractive index from 1.30 to 1.60. Waveguides are formed photolithographically, with the liquid monomer mixture polymerizing upon illumination in the UV via either mask exposure or laser direct-writing. A wide range of rigid and flexible substrates can be used, including glass, quartz, oxidized silicon, glass-filled epoxy printed circuit board substrate, and flexible polyimide film. We discuss the use of these materials on chips and on multi-chip modules (MCMs), specifically in transceivers where we adaptively produced waveguides on vertical-cavity surface-emitting lasers (VCSELs) embedded in transmitter MCMs and on high- speed photodetector chips in receiver MCMs. Light coupling from and to chips is achieved by cutting 45 degree mirrors using excimer laser ablation. The fabrication of our polymeric structures directly on the modules provides for stability, ruggedness, and hermeticity in packaging.

Robust photopolymers for MCM, board, and backplane optical interconnects

A robust polymeric waveguide technology is proposed for affordable optoelectronic interconnects in massively parallel processing applications. We have developed high-performance organic polymeric materials that can be readily made into both multimode and single-mode optical waveguide structures of controlled numerical aperture and geometry. These materials are formed from highly-crosslinked acrylate monomers with specific linkages that determine properties such as flexibility, toughness, loss, and stability against yellowing. These monomers are intermiscible, providing for precise adjustment of the refractive index from 1.30 to 1.60. Waveguides are formed lithographically, with the liquid monomer mixture polymerizing upon illumination in the UV via either mask exposure or laser direct-writing. A wide range of rigid and flexible substrates can be used, including glass, quartz, oxidized silicon, glass-filled epoxy printed circuit board substrate, and flexible polyimide film. Our waveguides are low loss (0.02 dB/cm at 840 nm) as well as temperature resistant (over 65 years at 100 degree(s)C) and humidity resistant (no effect on unpackaged guides after 600 hours at 85 degree(s)C 85% RH), enabling use in a variety of demanding applications. We discuss the use of these materials on multi-chip modules, boards, and backplanes. Waveguiding structures measuring tens of inches in length can be produced on backplanes, and guides that are meters long can be laser-written on rolls of plastic. We also discuss the fabrication of symmetrically-clad flexible strips of waveguide arrays that are compatible with MT- type connectors.

Femtosecond response of electro‐optic poled polymers

We investigate the ultrafast electro‐optic response and sensitivity of a poled side chain polymer film via the electro‐optic sampling technique. A 760 fs rise‐time electrical transient is observed corresponding to a bandwidth of 460 GHz. We believe this to be device limited and not due to limitations in the speed of response of the polymer.

Integration of polymeric micro-optical elements with planar waveguiding circuits

We report on an advanced polymer technology that enable the low-cost monolithic integration of micro-optical elements with planar waveguiding circuitry. We have developed high- performance organic polymeric materials in which both micro- optical and waveguiding structures can be formed with controlled geometries. These materials are formed form highly-crosslinked acrylate monomers with specific linkages that determine properties such as flexibility, toughness, contrast, loss, and stability against yellowing. Waveguides with microns to tens of microns dimensions as well as micro- optical structures that are up to several hundred microns in thickness are printed photolithographically, withthe liquid monomer mixture polymerizing upon illumination in the UV via either mask exposure or laser direct-writing. Precise control of the photochemical reaction dynamics results in high resolution in the complete thickness range. A variety of rigid and flexible substrates can be utilized, including glass, quartz, silicon, glass-filled epoxy printed circuit board substrate, and flexible polyimide film. We discuss the production of various novel micro-optical elements that we routinely integrate with waveguiding circuits. These elements include fiber grippers for waveguide pigtailing, prisms for coupling of light from VCSELs into waveguides and from guides into photodetector chips, and pedestals for passive alignment of fiber ribbons or waveguide-array strips to waveguides.

Nonlinear optical properties of organic dye dimer-monomer systems

An analysis is provided for the discussion of nonlinear optical properties of aggregated dye systems. The intensity-dependent transmission of fluorescein solutions excited by nanosecond dye laser pulses is shown to fit a monomer-dimer equilibrium shifted towards monomer formation by excitation. The implications for spatial light modulation and other nonlinear optical applications are discussed.

Viewing-angle-enhancement system for LCDs

An enhanced liquid crystal display (LCD) design with minimal contrast ratio or color shift with increased viewing angle and with improved performance in high brightness environments has been developed. Contrast ratios of greater than 50 :1 have been demonstrated at ±60° (vertical and horizontal) on an active matrix LCD. The operating principles of the key components of this new design will be described.