Geoffrey A. Lindsay

Second‐order nonlinear optical measurements in guest‐host and side‐chain polymers

The second harmonic generation (SHG) coefficients dij of several corona‐poled guest‐host and side‐chain polymers have been measured and studied over time using a new Maker Fringe analysis. The electro‐optic coefficient r33 and scattering losses have also been measured in thin‐film waveguides, on silicon and glass substrates, made from some of the polymers. Kleinman symmetry (d15=d31) was not valid for near‐resonant SHG in these materials and d15/d31 was determined. Stable values of d33, for a fundamental of 1.064 μm, were as high as 40 pm/V for one of the side‐chain polymers. Optical waveguide losses determined from scattering measurements were as low as 0.4 dB/cm at 1.06 μm.

Second-order nonlinear optical properties of poled coumaromethacrylate copolymers

Second-order nonlinear optical properties of newly designed and synthesized coumaromethacrylate side-chain polymers are reported. The optimum poling conditions were determined experimentally. The optimum poling temperature for these side-chain polymers is well above the glass transition temperature. The second harmonic coefficient of films poled by coronaonset at elevated temperature and the linear electro-optic coefficient of films poled by contact electrodes were measured. The stabilized value of the second harmonic coefficient, d33, at 1064nm fundamental wavelength was found to be 13 pm/V. The linear electro-optic coefficient, r33, exhibits strong dispersion ranging from 2 to 12pm/V in the wavelength range 477 to 1115 nm.

A simplified technique for efficient fiber-polymer-waveguide power coupling using a customized cladding with tunable index of refraction

A novel technique to minimize the mode mismatch between the fiber and waveguide modes in integrating optical fiber to polymer waveguides is presented. The mode fields at the facets of the waveguides were tailored, optimizing the waveguide geometry as well as tuning the index of refraction of the lower cladding near the facets, by chemical composition. No additional processes were required after the core was deposited. The modified lower cladding can be integrated efficiently with any other lower-cladding material used in the remaining portion of the waveguide, resulting in hybrid waveguides. A power-coupling loss as low as 0.46 dB at the fiber-waveguide interfaces was demonstrated with the available fiber

Backscatter Compensation in IFOG Based Inertial Measurement Units With Polymer Phase Modulators

Precision guidance in navigation systems requires highly accurate, compact, and low cost inertial measurement units (IMUs). The key active guided-wave component of the IMU is the phase modulator. In our approach, electro-optic polymers have been utilized in fabricating low loss phase modulators with low half-wave drive voltage using advanced hybrid waveguide fabrication processes and novel optical integration techniques. However, the interference between the primary wave and the backscatter waves generated by the phase modulator and/or the interference between the two counter-propagating backscatter waves at the detector of the IMU has been a major source of error in this approach. A novel technique was introduced in assessing the error caused by backscatter and an offset waveguide design was developed to suppress the interference of backscatter light. The novel design not only preserved the miniaturization, but also improved the insertion loss with the use of a shorter waveguide. The gyro level tests performed with the backscatter compensated modulators showed about 5 times improvement of the average bias uncertainty over gyros integrated with a standard symmetric phase modulator.

Main-chain syndioregic nonlinear optical polymers. II. Extended Pi conjugation and improved thermal properties

Recent results concerning the synthesis of new main-chain syndioregic nonlinear optical polymers are presented. In particular, the synthesis of polymers with extended pi conjugation in the chromophore and chromophores with improved thermal stability are presented. The nonlinear optical coefficient of several of the polymers and the optical loss at 1.3 and 1.55 μm were measured and are discussed.

Components for IFOG based inertial measurement units using active and passive polymer materials

Highly accurate, compact, and low cost inertial measurement units (IMUs) are needed for precision guidance in navigation systems. Active and passive polymer materials have been successfully used in fabricating two of the key guided-wave components, the phase modulator and the optical transceiver, for IMUs based on the interferometric fiber optic gyroscope (IFOG) technology. Advanced hybrid waveguide fabrication processes and novel optical integration techniques have been introduced. Backscatter compensated low loss phase modulators with low half-wave drive voltage (Vπ) have been fabricated with CLD- and FTC- type high performance electro-optic chromophores. A silicon-bench architecture has been used in fabricating high gain low noise transceivers with high optical power while maintaining the spectral quality and long lifetime. Gyro bias stability of less than 0.02 deg/hr has been demonstrated with these components. A review of the novel concepts introduced, fabrication and integration techniques developed and performance achieved are presented.

Second harmonic generation from new dyes in polymer films

One might say this paper is about something old, something new, something borrowed, something blue -- finding chromophoric brides to be wed to polymeric husbands. Several dyes have been synthesized that are red, magenta, or blue in color and have large ground-state dipole moments. Dyes synthesized in our laboratory were characterized by differential scanning calorimetry and UV-VIS spectroscopy. First molecular hyperpolarizabilities ((beta) o) of the dyes were calculated using MOPAC (V6). Some of the dyes were dissolved in poly(methyl methacrylate), corona poled above the glass transition temperature, and cooled to room temperature to freeze in the polar order. Second-order nonlinear optical properties of these guest-host films were compared by optical frequency doubling measurements.

Polyimides with attached chromophores for improved performance in electro-optical devices

A method of chemical synthesis that allows for the facile attachment of a wide variety of chemical compounds, including highly active nonlinear optical chromophores, to polyimides has been developed recently at the Naval Air Warfare Center, Weapons Division. The synthesis of these compounds is presented, along with a discussion of their relevant physical and chemical properties, alone and in comparison to equivalent guest/host materials. Examples of attached chromophores include the well-known Disperse Red 1, along with high-activity chromophores of more recent interest such as FTC and CLD. The synthesis of structures that contain both attached chromophores and chemical functionalities that enable thermal cross-linking of the polyimides is also discussed.

Synthesis and characterization of chiral conjugated polymers for optical waveguides

In the pursuit of new photonic devices, the unique waveguide properties of chiral films made from single-handed helical molecules are under investigation. The synthesis of polymers with a hierarchical structure is the first step. In this paper we present results on the synthesis and characterization of poly(p-phenylenes) (PPPs) and polythiophenes possessing amine and amide chiral side-chains. A regioirregular PPP possessing one chiral side group per repeat unit was prepared. Regioregular PPPs possessing two chiral side groups per repeat unit were also synthesized; however, lower molecular weights were achieved due to steric constraints. The PPPs exhibited total optical rotation that was a function of the concentration of the chiral side group, with 35- per chiral group or 70- per repeat unit. A regioirregular polythiophene was prepared using oxidative polymerization. A molecular structure that leads to helical polymer chains that undergo supramolecular packing in spin-cast films is the goal.

Alternating polyanion/polycation second-order nonlinear optical films by aqueous solution deposition

Alternating polyelectrolyte deposition (APD) in aqueous solutions may be used to process nonlinear optical polymers (NLOPs) into noncentrosymmetric ordered films at ambient temperature. Second-order NLOP films were prepared by alternately dipping a substrate into aqueous solutions of a polycation and a polyanion. Polyepichlorohydrin substituted with stilbazolium side-chain chromophore was used as the cationic NLOP. The inactive polyanion was polystyrene sulfonate. Uniform layer to layer deposition is observed as evidenced by a linear increase of UV-Visible absorbance and quadratic increase of second harmonic generated light intensity as a function of film thickness. Films have been uniformly deposited up to 24 bilayers. Films have been further characterized by contact angle measurements, interferometry, and polarized light microscopy. Work is in progress to deposit thicker films of the same quality and to quantify NLO figures of merit.