Srinath Kalluri

Fabrication and characterization of high-speed polyurethane-disperse red 19 integrated electrooptic modulators for analog system applications

The fabrication and characterization of polymeric electrooptic modulators, made of a thermally crosslinkable polyurethane with Disperse Red 19 side chains, are summarized in this paper. Straight channel and Mach-Zehnder modulators have been fabricated, packaged and tested for the fiber-optic analog transmission system applications. Device performances including halfwave voltage, insertion loss, on-off ratio, and modulation frequency responses were measured. Long-term halfwave voltage stability, dc-bias voltage stability, and optical power handling capability at 1.3-/spl mu/m wavelength were investigated. A carrier-to-noise ratio of 53 dB and 80-channel television transmission have been demonstrated using the packaged polymer modulators.

Monolithic integration of waveguide polymer electrooptic modulators on VLSI circuitry

We demonstrated some of the critical technology that is needed for the monolithic integration of polymer electrooptic modulators and VLSI circuitry by fabricating and testing a phase slab modulator on nonplanar VLSI circuits. We demonstrated the survival of GaAs MESFETs to the high-voltage poling and polymer modulator fabrication procedures. We also implemented an electrical interconnect scheme between the electronics and photonics layers.

Simple two‐slit interference electro‐optic coefficients measurement technique and efficient coplanar electrode poling of polymer thin films

A novel technique using coplanar electrodes for measuring the electro‐optic coefficients of in‐plane poled polymer thin films is presented. This method does not require waveguiding and uses a simple optical setup. In this technique the index across one slit of a two‐slit aperture is modulated by an electric field and the modulated interference pattern of light after it propagates through these slits is detected in the far field. A coplanar electrode pattern was used for both in‐plane poling and for measuring the r coefficients in a two‐arm push–pull configuration. The maximum poling strength achieved was 200 V/μm. An r33 coefficients of 12.5 pm/V at 1.3 μm, the wavelength dispersion of r33 and the r33/r13 ratio as a function of the poling field, were measured for the PURDR19 electro‐optic polymer.

Improved poling and thermal stability of sol‐gel nonlinear optical polymers

An aminosulfone dye chromophore was covalently incorporated into a sol‐gel network for second‐order nonlinear optics applications by functionalizing both ends of the chromophore. Covalent incorporation allows for high chromophore loading densities (∼35%) and locking in both ends of the chromophore improves thermal stability. Short term stability of the nonlinearity at 200 °C and long term stability over 500 h at 100 °C was demonstrated. Two different temperature profiles for corona poling were investigated and one found superior to the other. A second harmonic coefficient, d33 of 27 pm/V at the 1064 nm fundamental wavelength was measured.

Optimized Oxygen Plasma Etching of Polyurethane‐Based Electro‐optic Polymer for Low Loss Optical Waveguide Fabrication

Oxygen plasma etching of thermosetting polyurethane electro-optic polymers containing disperse red 19 side groups was characterized in detail for making low loss optical waveguides and modulators. The effect of varying parameters such as the RF power, oxygen pressure, and flow rate on optical loss, etching rate, and etching selectivity to photoresist etch mask was studied. These parameters were optimized to minimize the surface roughness in etched areas. By properly choosing the etching conditions, scattering loss due to the surface roughness can be reduced from 0.9 dB/cm to less than 0.1 dB/cm at the wavelength of 1.3 μm, which is much smaller than the absorption loss of the polymer.

Photoinduced molecular alignment relaxation in poled electro‐optic polymer thin films

The photoinduced nonlinearity decay in poled nonlinear optical polymer, polyurethane/Disperse Red 19, films was studied at wavelengths from 543 to 1320 nm. Electro‐optic gratings and waveguide modulators were used in measuring and monitoring material’s nonlinearity. No photoinduced nonlinearity decay was detected at near infrared wavelengths. However, the photoinduced relaxation rate increased approximately 5 orders of magnitude from 670 to 543 nm, as the excitation wavelength approaches π‐π* transition of the chromophores. The photoinduced chromophore reorientation was identified as the dominant relaxation mechanism.

Integration of polymer electro-optic devices on nonplanar silicon-integrated circuits

To demonstrate the feasibility of integrating polymer electro-optic devices on Si circuitry, we have vertically integrated a demonstration slab phase modulator on nonplanar VLSI circuitry. Optical loss measurements for waveguides fabricated on planarized circuits demonstrate that more practical devices like channel phase and Mach-Zehnder amplitude modulators can easily be integrated onto the circuits.

Measurement of the electro-optic coefficient dispersion in poled polymer materials

A simple and easy method to study the dispersion of electro-optic coefficients of poled second- order nonlinear optical polymer films is presented. Phase grating type electro-optic modulators were used to measure the relative electro-optic effects at different wavelengths. The grating structures were formed by either etching a grating in the nonlinear polymer thin films or defining a transparent electrode on top of a uniform polymer film. When an AC voltage is applied to the electrodes, the diffraction efficiency of the grating is modulated by the small index modulation. The measurement of the electro-optic response can be carried over a large wavelength range, even deep into the absorption band of the material due to the short interaction length of the optical beam and the polymer thin film. The grating modulation method uses a single optical beam in a transmission arrangement which requires little optical alignment and no polarization optics. With a properly designed electrode, the grating modulator can also be used in measuring the electro-optic coefficient, r13, of the poled polymer films. Other measurement applications such as monitoring temporal, thermal, and photo-excitation stability are discussed.

Nonlinear optical effects in PTCDA crystalline organic thin films

Nonlinear optical properties of 3, 4, 9, 10-perylenetetracarboxylic dianhydride thin films grown by ultra-high vacuum process of organic molecular beam deposition are characterized by self-diffraction method. We observe a large diffraction efficiency (approximately 10-4) from a micron thick film and attribute the nonlinearity to a thermal shift in the excitonic absorption feature or free carrier effects.

Second-Order Nonlinear Optical Polymers With Different Chromophore Arrangements

Second-order nonlinear optical polymers can be divided into four groups regarding arrangements of chromophore dipoles in polymer backbones, namely, side-chain polymers, random, head-to-tail, and head-to-head Main-chain polymers. A variety of polymers with the aforementioned configurations have been designed and synthesized from functionalized amino-nitro azobenzene chromophores. Poling processes of these polymeric materials have been investigated by in-situ poling and second-harmonic generation detection.