Tony C. Kowalczyk

Synthesis and stability studies of conformationally locked 4-(diarylamino)aryl- and 4-(dialkylamino)phenyl-substituted second-order nonlinear optical polyene chromophores

A series of chromophores with high second-order nonlinearities has been synthesized; the chromphores consist of triarylamine or dialkylarylamine donors linked by a conformationally locked polyene bridge to a dicyanomethylidene acceptor. The use of bridges of this type, combined with the replacement of dialkylarylamine with triarylamine donors, leads to high thermal stability without adverse affects on the nonlinear optical properties of the chromophores.

LOSS MECHANISMS IN POLYIMIDE WAVEGUIDES

Waveguide losses in thin film polyimides using waveguide loss spectroscopy and photothermal deflection spectroscopy as a function of cure cycle and structure were studied. Fluorinated sidegroups on the polyimide backbone lead to decreases in birefringence and absorption. The primary waveguide loss mechanism is absorption, not scattering. Waveguide losses as low as 0.4 dB/cm at 800 nm have been measured. Losses as low as 0.3 dB/cm at 1300 nm can be inferred from the photothermal deflection spectroscopy.

Optical anisotropy in thin films of a blue electroluminescent conjugated polymer

We determined the anisotropic optical constants of thin films of a conjugated polymer, the methyl-substituted ladder-type poly(paraphenylene) (m-LPPP), over a large spectral range between 1.55 and 3.5 eV. In the subgap region the anisotropic refractive indices were obtained via waveguiding experiments at 1.55 eV and 1.95 eV. Propagation loss measurements revealed that the absorption coefficient parallel to the polymer film surface is very small (<12.6 cm−1) in this energy region, due to the high purity of the polymer. In the strongly absorbing energy region of the π–π* electronic transition (2.6–3.5 eV) we performed spectroscopic ellipsometric measurements, in order to determine the anisotropic optical constants parallel (No) and perpendicular (Ne) to the polymer surface. The optical anisotropy in the m-LPPP films can be attributed to a preferential orientation of the polymer chains in the plane of the substrate.

Crosslinked polyimide electro-optic materials

We report studies of the optical and electro‐optic properties of guest–host polymeric nonlinear optical materials based on aromatic, fluorinated, fully imidized, organic soluble, thermally, and photochemically crosslinkable, guest–host polyimides. We have introduced temperature stable nonlinear optical chromophores into these polyimides and studied optical losses, electric field poling, electro‐optic properties, and orientational stability. We measured electro‐optic coefficients of 5.5 and 12.0 pm/V for ((2,6‐Bis(2‐(3‐(9‐(ethyl)carbazolyl))ethenyl)4H‐pyran‐4‐ylidene)propanedinitrile (4‐(Dicyanomethylene)‐2‐methyl‐6‐(p ‐dimethylaminostyryl)‐4H‐pyran) DCM‐doped guest–host systems at 800 nm using a poling field of 1.3 MV/cm. Poling induced nonlinearities in single‐layer films were in agreement with the oriented gas model, but were lower in three‐layer films due to voltage division across the layers.

Anomalous-dispersion phase-matched second-harmonic generation in a polymer waveguide.

We demonstrate phase-matched second-harmonic generation in a poled polymer waveguide, using anomalous-dispersion phase matching. Phase matching was achieved between lowest-order fundamental and harmonic modes, TM0ω to TM02ω, at a fundamental wavelength of 815 nm over a propagation length of 32 μm. The maximum conversion efficiency was ηexp = 39%/W cm2, in good agreement with theory.

Fabrication of low loss polyimide optical waveguides using thin-film multichip module process technology

Polyimides containing fluorine are attractive for integrated optics since the introduction of fluorine increases the optical transparency in the visible and near infrared spectrum. Polyimides are easily integrated with silicon or GaAs optical devices, can be spin-coated on a number of substrates and are resistant to chemical etchants, solvents and package assembly temperatures. Photosensitive polyimides are being widely used as dielectrics in multichip module fabrication because they offer a combination of good electrical and mechanical properties and low cost processing relative to non-photosensitive polyimides. In this paper, a simple, wet chemical patterning process for the fabrication of low loss waveguides using photosensitive polyimides is described. Optically transparent, fluorinated polyimides are modified by copolymerizing a low concentration of photocrosslinking groups into the backbone. The polyimides can then be patterned into channel, ribs, or Y branches by UV exposure through a photomask followed by wet chemical development. Sidewall smoothness and sidewall profiles can be controlled by varying exposure and development conditions. >

Optical polyimides for single-mode waveguides

The synthesis and optical characterization of fluorinated polyimide systems with potential use in passive waveguides and electro-optic devices is reported. The effect of fluorination on optical properties such as refractive index, birefringence, and near-infrared absorbance is reviewed in terms of optical performance requirements. Synthetic methods of tuning the refractive index in order to achieve appropriate core/cladding differentials is discussed. The relation between processing parameters and refractive index for several polyimide structures also is reported. We describe the microlithographic fabrication of a multilayer polyimide rib- type waveguide that is suitable for single mode guiding. The waveguide is fabricated using photosensitive polyimide systems via negative resist imaging. A comparison of wall profiles and resolution limits afforded by the wet-chemical patterning techniques is presented. Results on channel guide coupling, propagation, and loss are described, as well as progress in producing active guides.

Polyimide-based electro-optic materials

The properties of new, high temperature optical materials based on dye-doped Ultradel 9000D polyimides are presented. Ultradel 9000D is a soluble, pre-imidized, fluorinated polymer with properties optimized for integrated optical applications. When thermally or photochemically cross-linked, it has a Tg approaching 400

Molecular to material design for anomalous-dispersion phase-matched second-harmonic generation

DEGC and retains excellent optical transparency as measured by both waveguide loss spectroscopy (WLS) and photothermal deflection spectroscopy (PDS). The agreement between WLS and PDS data indicates that losses in polyimides are due to absorption, not scattering. Two thermally stable, donor-acceptor oxazole-based dyes were designed, synthesized, and doped into the polyimide at concentrations up to 25 percent by weight. The Tg of the doped polymers decreased from the neat polymer, but remained above 300

Anomalous dispersion phase-matched second harmonic generation in poled polymer waveguides

DEGC. The effects of doping on the dielectric constant, refractive index, and coefficient of thermal expansion of the polyimide are presented.