Keith A. Horn

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.

The palladium catalyzed synthesis of substituted phenylethynylpentamethyldisilanes and phenylethynylheptamethyltrisilanes

Abstract Bis(triphenylphosphine)palladium(II) chloride-cuprous iodide or tetrakis(triphenylphosphine)palladium(0)-cuprous iodide catalyze the formation of phenylethynylpentamethyldisilanes from substituted bromo- or iodo-benzenes and ethynylpentamethyldisilane. Concurrent siliconsilicon bond cleavage is not observed. The synthesis of 4-cyanophenylethynylheptamethyltrisilane from 4-bromobenzonitrile and ethynylheptamethyltrisilane was also demonstrated.

Loss measurements in electro-optic polymer waveguides

We report loss measurements in polymer-bound Disperse Red I slab and photodelineated channel waveguides. Losses resulting from electronic charge-transfer and vibrational carbon- hydrogen stretch overtone absorptions, trans to cis isomerization, exposure to visible or ultraviolet (UV) light and changes in dye pendant group number density are investigated. A waveguide absorption spectrometer is described which can measured waveguide losses (alpha) ((lambda) ) from 600 - 1800 nm. Absorption losses are compared to the wavelength dependent electro-optic coefficient r33((lambda) ) and a figure-of-merit r33((lambda) )/(alpha) ((lambda) ) is determined for the material.

Photochemical delineation of waveguides in polymeric thin films

Polymeric materials that exhibit a controlled change in refractive index upon irradiation with UV light are promising candidates for the development of polymeric optical interconnects. We have demonstrated that polymers containing nitrone functional groups can be spatially patterned for single-mode waveguide devices using both laser direct writing and traditional photolithographic techniques.

Polymeric materials for guided wave devices

Organic polymeric materials offer great promise for the creation ofoptical guided-wave structures for use with silicon or gallium arsenide semiconductor devices. We have developed a number of new polymeric materials for which the refractive index may be photochemically controlled. These materials are ifiustrated by solid solutions of novel nitrone compounds in polymer hosts such as PMMA. We have demonstrated the creation of planar guided-wave structures in these materials both with direct laser writing and with traditional photolithographic techniques. We have also developed polymeric materials which are electro-optically active and which provide for the photochemical delineation ofguided-wave structures. We have utilized these materials to create electro-optic devices such as optical modulators.

A new organic electrooptic crystal: 2,6-dibromo-N-methyl-4-nitroaniline (DBNMNA)

A new organic electrooptic crystal, 2,6-dibromo-N-methyl-4-nitroaniline, is reported. The crystal structure was determined by X-ray diffraction (orthorhombic, space group Fdd2, point group mm2, Z=16, a=11.745 AA, b=29.640 AA, c=10.807 AA). The refractive indexes were measured at several wavelengths between 500 and 1100 nm (at 632.8 nm, n/sub a/=1.90, n/sub b/=1.62, and n/sub c/=1.48) and fit the data to a single oscillator Sellmeier equation. A report is presented on measurements of the linear electrooptic effect, yielding the combined coefficients n/sub a//sup 3/r/sub 13/-n/sub c//sup 3/r/sub 33/, as well as the first known measurements of the quadratic electrooptic effect in an organic crystal, yielding the coefficients r/sub 42/ and r/sub 51/ at 514.5, 632.8, and 810 nm. Good agreement is found between the observed dispersion in the electrooptic coefficients and that predicted by the simple two-level dispersion model. >

Polymeric Electro-Optic Materials and Devices: Meeting the Challenges of Practical Applications

Over the past five years, a new class of electro-optic polymeric materials has evolved which provides for the first time the capability to fabricate simple and inexpensive electro-optic devices on a variety of substrates. More importantly, these materials possess optical dielectric constants (or refractive indexes) comparable to radio-frequency dielectric constants allowing for fabrication of devices in which the electric field and the optical field propagate at the same velocity. Finally, the low dielectric constant of these materials relative to inorganic ionic crystals provides for operation of devices at much higher efficiency. Although the above facts have been clear for some time, the practical applications of these materials cannot be realized until materials can be created which satisfy a host of practical requirements and until device architectures and fabrication techniques appropriate for these materials can be developed. We will describe here research directed toward both of these ends.

Photochemical Formation of Polymeric Optical Waveguides and Devices for Optical Interconnection Applications

The formation of both passive and active optical waveguide structures in thin films of organic polymers by a direct one-step photochemical process is reported. A photochemical transformation changes the chemical composition of a polymer of dye/polymer mixture. The reaction modifies the absorption spectrum of the material and thus alters its index of refraction. This technique is used to create waveguide structures both by spatially-selected laser direct writing and contact mask exposure. It is demonstrated that passive and active waveguide structures can be delineated in thin films of organic polymers by photochemically altering the index of refraction of the materials. The formation of single or multimode devices is possible using standard lithographic procedures which are suitable for mass production.

Optical characterization of azo dye-based electro-optic polymer films

We have investigated the photochemistry and optical properties of an azo dye-based electro- optic (EO) copolymer, methacrylate-bound Disperse Red 1/methylmethacrylate (MA1). We present a complete picture of the optical properties of the copolymer at wavelengths ranging from 200 nm to 1800 nm with detection sensitivity over 6 orders of magnitude. We describe intrinsic measurements of absorption loss and also describe how temperature and radiation affect absorption loss. Photochemical investigations reveal details concerning photodelineation of waveguides in MA1. Irreversible photodegradation of the azo chromophore proceeds with both visible and ultra-violet radiation and a quantum yield of 2 X 10-5 is found for 475 nm radiation in MA1.

Optical Waveguides Based On Specialized Organic Polymers

A number of organic polymers have been prepared for use in the fabrication of high performance optical waveguides operating at short optical wavelengths (< 830 nm). Slab optical waveguides have been realized by spin coating the specialized polymers on substrates such as quartz and silicon wafers. Refractive index profiles were measured to be of the step index type, with the refractive index differences ranging from 0.12 to 0.15. Propagation losses and intermodal scattering levels were measured to be about 1.2-4.5 dB/cm and 15-20 dB, respectively. In addition, the electro-optic properties of the specialized polymers have been studied using suitable optical structures. An electro-optic modulator has been built as a demonstration device utilizing a slab polymer waveguide.