Empirical data regarding the radiation induced responses of Mach Zehnder interferometric electro-optic polymer based modulators (PBMs) operating at 1310 and 1550 nm and broadband InP quantum dot (QD) polymer photodetectors (PPDs) operating into the near infrared (NIR) are reported. Modulators composed of spun-on materials and hybrid electostatically self assembled (ESA) and spun-on NLO materials are examined for changes to their half-wave voltage and insertion losses following a gamma-ray total dose of 163 krad(Si) and irradiation by 25.6 MeV protons at a fluence of ~1011 cm-2. Pre- and post- irradiation responses of ESA grown polymer detectors using InP QDs are examined for photovoltage degradation and aging effects. The data indicates and excellent potential for developing polymer based photonic (PBP) devices with increased radiation resistance suitable for transition to photonic space applications.
Recent progress in developing high-performance organic polymers for electro-optics and photonics is reviewed. A highly fluorinated hyperbranched aromatic polymer with the degree of branching around 0.51 was prepared by a mild one-step polyesterification of an AB2 type monomer. Further post-functionalization with and thermally cross-linking by aromatic trifluorovinyl ethers (TFVE) afforded thermally stable, low loss optical polymer with improved solvent resistance. By more precisely controlling the molecular nano-architecture, we have developed a series of highly fluorinated crosslinkable dendrimers. These materials possess most of the desirable properties needed for the fabrication of optical waveguides, such as high solubility in common organic solvents (up to 50 wt%), very low optical loss, and excellent thermal stability. To overcome the “nonlinearity-stability tradeoff,” a facile and reversibly crosslinkable NLO polymer system is developed that combines both advantages of high poling efficiency and good alignment thermal stability. By smartly controlling the poling and crosslinking processes through the reversible Diels-Alder (DA) reactions, it allows highly polarizable chromophores to be efficiently poled at the stage of low viscosity linear thermoplastic polymer. The resulting nonlinear optical polymer exhibits a combination of a very large r33 value (76 pm/V at 1.3 μm) and good temporal stability at 70°C.
Spectral absorption behavior of a series of FTC-like dyes of varying shape incorporated into amorphous polycarbonate (APC) is characterized by photothermal deflection spectroscopy. Previous Monte Carlo calculations by Dalton and Robinson predict a strong dependence of the macroscopic nonlinear optical susceptibility on the chromophore waist:length aspect ratio in electric field-poled films. This dependence arises from London interactions between chromophores, which are expected to influence the absorption characteristics of the composite both by changing the local polarity of the medium and through dipole interactions. It is expected that these interactions will play a role in the absorption characteristics of unpoled films as well. Of particular interest are the spectral characteristics of the red edge of the main dye electronic absorption peak, and the fine structure in the near-IR, dominated by overtones of fundamental C-H stretching and bending modes. The spectral structure in these key regions can be influenced by inter- and intramolecular interactions and conformational changes in the dye. The near-IR structure, in turn, will dictate absorption loss in optical devices prepared from these materials at key transmission wavelengths (1.3 and 1.55 um). In this study, a homologous series of spacer lengths, ranging from ethyl to hexyl, attached to an FTC-like NLO chromophore, LMCO-46M, is characterized by a combination of photothermal deflection spectroscopy (PDS) and UV-Vis spectroscopy to examine the effects of the molecular environment on near-IR loss at 1090 nm, 1300 nm and 1550 nm.
A series of functional and photo-crosslinkable maleate or fumarate type polyesters containing azo-type NLO chromophores were studied. The result demonstrated this is a versatile and convenient method of fabricating crosslinked supramolecular ultra-structure polymer thin films for potential nonlinear optical (NLO) and other photonic applications. The unsaturated PDRMA/PDRFC polyester thin films are capable of crosslinking in air via photo polymerization to form a hardened lattice. A ratio of 1:1 of crosslinker double bonds to polyester double bonds was preferred for optimal crosslinking. Thermal stability of Second Harmonic Generation (SHG) signals for a photo crosslinked polymer thin film reached to about 150°C. Films from photo crosslinking of fumarate or maleate vs. vinyl crosslinkers have the advantages of avoiding NH/OH groups and their vibrational overtones that absorb at telecommunication wavelength of 1550 nm.
A wide variety of aromatic trifluorovinyl ether monomers and highly fluorinated crosslinkable dendrimers have been developed via novel synthetic strategies. Through the thermal dimerization of trifluorovinyl ether moieties on the monomers or on the periphery of dendrimers, these monomers or dendrimers can be melt or solution polymerized to form perfluorocyclobutane(PFCB)-containing prepolymers with good processability for optical waveguide fabrication. By further thermal crosslinking, the resulting thermoset materials possess low optical loss (0.3-0.4 dB/cm at 1310 nm with 1% of DR-1 or DCM doping), high thermal stability (Tg: 100-400 °C), good thermo-optic property, high solvent and humid resistance, and excellent mechanical flexibility. The combination of processability and performance in these PFCB-containing thermoset materials make them as ideal candidates for the fabrication of high-performance polymeric planar lightwave circuit components with the applications in the telecom and datacom optical networks.
Spectral absorption behavior of Disperse Red-1 and Disperse Red-19 dyes incorporated into a series of polymers by covalent attachment, representing various chemical structures, is characterized by photothermal deflection spectroscopy. Of particular interest are the spectral characteristics of the red edge of the main dye electronic absorption peak, and the fine structure in the near-IR, dominated by overtones of fundamental C-H and O-H stretching modes. The spectral structure in these key regions can be influenced by inter- and intramolecular interactions, or conformational or configurational changes in the dye. The NIR structure, in turn, will dictate absorption loss in optical devices prepared from these materials at key transmission wavelengths (1.3 and 1.55 um) for waveguide devices. A well characterized dye-polymer system, DR1-PMMA, is compared with two other polymer systems. Differences in spectral absorption behavior is assessed in terms of polymer host structure and bonding environment.
Encapsulated by highly-fluorinated dendrons, a nonlinear optical chromophore core, which is based on the phenyl-tetracyanobutadienyl (Ph-TCBD) thiophene-stilbene-based NLO chromophore, exhibits a large ~30-40 nm blue shift of the charge-transfer absorption maximum, 20 oC higher decomposition temperature, and most impressively, three times higher E-O coefficient. The combination of these appreciable improvements makes the molecular design of dendritic modification as a very promising molecular-engineering for next generation of E-O materials.