Mach-Zehnder optical modulators were fabricated using the CLD and FTC chromophores in polymer-on-silicon optical
waveguides. Up to 17 months of oven-ageing stability are reported for the poled polymer films. Modulators containing
an FTC-polyimide had the best over all aging performance. To model and extrapolate the ageing data, a relaxation
correlation function attributed to A. K. Jonscher was compared to the well-established stretched exponential correlation
function. Both models gave a good fit to the data. The Jonscher model predicted a slower relaxation rate in the out
years. Analysis showed that collecting data for a longer period relative to the relaxation time was more important for
generating useful predictions than the precision with which individual model parameters could be estimated. Thus from
a practical standpoint, time-temperature superposition must be assumed in order to generate meaningful predictions.
For this purpose, Arrhenius-type expressions were found to relate the model time constants to the ageing temperatures.
Progress in the development of a new class of multi-functional polyimides for use in electro-optical devices is reported.
These polyimides contain hydroxymethyl-functional side-groups attached to the polymer backbone, allowing for the
attachment of a wide variety of molecular species. It is shown that multiple types of organic molecules may be attached
to the polymer simultaneously, with a quantitatively controllable distribution, to tailor the physical properties of the
material. Methods for cross-linking the polyimides are presented, based on both modification to the backbone and the
addition of difunctional additives (such as isocyanates) to solutions of the polymer during spin casting. Processing
studies using spectroscopy to track the cross-linking reaction and its effects on organic nonlinear optical materials
indicate that the latter method is compatible with poling processes for polymer guest/host systems with high nonlinear
optical activities. Further studies using a novel thermomechanical analysis method demonstrate that the cross-linking
reactions increase the glass transition temperature and inhibit physical relaxation processes in the cross-linked
Epitaxial single-crystal chemical-vapor-deposited diamond with (100) crystal orientation is obtained from Element Six (Ascot, United Kingdom) and Apollo Diamond (Boston, Massachusetts). Both companies supply 5×5-mm squares with thicknesses of 0.35 to 1.74 mm. Element Six also provides disks with a state of the art diameter of 10 to 11 mm and a thickness of 1.0 mm. The absorption coefficient measured by laser calorimetry at 1.064 µm is 0.003 cm−1 for squares from Element Six and 0.07 cm−1 for squares from Apollo. One Apollo specimen has an absorption coefficient near those of the Element Six material. Absorption coefficients of Element Six disks are 0.008 to 0.03 cm−1. Each square specimen can be rotated between orientations that produce minimum or maximum loss of polarization of a 1.064-µm laser beam transmitted through the diamond. Minimum loss is in the range 0 to 11% (mean=5%) and maximum loss is 8 to 27% (mean=17%). Element Six disks produce a loss of polarization in the range 0 to 4%, depending on the angle of rotation of the disk. Part of the 0.04 to 0.6% total integrated optical scatter in the forward hemisphere at 1.064 µm can be attributed to surface roughness.
Epitaxial single-crystal chemical-vapor-deposited diamond was obtained from Element Six Ltd. (Ascot, UK) and from
Apollo Diamond (Boston, MA). Both companies provided 5 x 5 mm squares with thicknesses ranging from 0.5 to 1.5
mm. In addition, Element Six provided 10-mm-diameter disks with a thickness of 1.0 mm. The absorptance of all
specimens at 1064 nm was measured by laser calorimetry, with good agreement between independent measurements at
the University of Central Florida and at QinetiQ (Malvern, UK). Depolarization at 1064 nm and ultraviolet absorption
properties are also reported.
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.
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.
This is a brief overview of the technology of nonlinear optical polymers (NLOP) and their use in electro-optic (EO) modulators. This paper also covers preliminary results from the authors' laboratories on highly active CLD- and FTC-type chromophores in guest-host films of APC amorphous polycarbonate. Emphasis will be given to thermal stability and long-term EO modulator aging.
The successful development of high-performance polymer optical waveguides depends critically on the stability of the materials during device fabrication. Typically, ensuring the stability of the organic chromophores contained in these materials represents the most difficult challenge. We present an overview of the mainly spectrophotometric techniques recently developed in our laboratory that have served as exceptionally useful tools in materials development. In addition, recent results involving the relative stability of various chromophores under exposure to simulated processing conditions are described. These allow for an improved understanding of the effects of variables such as temperature, oxygen concentration, and radiation intensity during fabrication on the performance of polymer optical waveguides.
Techniques for the rapid evaluation of material properties of interest in the design of polymer integrated optical devices that have recently been developed in our laboratory are described. These include methods for determining optical loss and electrical resistivity. The use of the techniques is demonstrated with polyimide materials as an example. The level of precision that is reasonably attained from each technique is discussed, along with the relative merits of these techniques compared to other potential approaches to obtaining similar information.
New insights into the relationship between film processing conditions and properties for polyimide-based systems of interest in the fabrication of optical waveguides are presented. The critical role of the rate of solvent evaporation to ensuring high-quality films is explored, as are the effects of varying the casting solution concentration, spin casting, and baking conditions. In addition to film quality, the effect of the previously mentioned processing conditions on optical properties is also described.
Methods that successfully predict the refractive index at near-infrared wavelengths of negatively birefringent polymer films for optical waveguide applications are presented. The starting point for these methods is a correlation based on connectivity indexes originally developed by Bicerano for the refractive index of isotropic polymers at visible wavelengths. This correlation is applied to a set of polyimides at near infrared wavelengths with modifications in order to improve its predictive power. The polyimides were synthesized by condensation of monomers to form the precursor poly(amic acid)s followed by imidization in solution. Solutions of the polyimides were then spin coated onto glass substrates and baked to produce films of 2-3 microns in thickness with a variable negative birefringence. The refractive index profiles of these films near 1320 nm were then measured in both the TE- and TM- modes using a prism-coupling technique. The average refractive index of these films was then compared to the prediction generated by the model. The agreement between the predicted and observed values has been sufficient to enable the rapid development of materials for optical waveguides without the need for many rounds of trial-and-error investigation. These techniques facilitate the development of specialized polymers for optical waveguide applications.