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.
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.
The selection process leading to the development of a guest- host electro-optic material based on an amorphous polycarbonate is described. The optical loss at 1300 nm of this material system is under 2 dB/cm, which is the confidence limit of the slab measurement used. A Mach- Zehnder Modulator fabricated using the push-pull poling technique has a low switching voltage of 1.2V.
Optoelectronic devices based on organic materials are uniquely suited to applications requiring high rf bandwidth. There have been significant advances in lithium niobate technology, but fundamental frequency-sensitivity tradeoffs are generally required in device design. Using a guest-host electro-optic polymer system, we have demonstrated a Mach- Zehnder modulator with a switching voltage of 3.5 V and interaction length of 2.6 cm. Anisotropic V-groove etching for fiber attachment provides a path to low-cost packaging of these devices. Materials and process optimization are expected to enhance device performance, allowing more compact, sensitive devices. Issues related to electro-optic device development are discussed in this paper, and an update on our development of new chromophores for use in electro-optic polymers is given.
Polymer photonic modulators and switches offer several attractive features for space systems, including rf bandwidth of 50 GHz or higher, and the potential for high sensitivity and low cost. We have shown that polymer modulators experience little if any degradation (less than 2%) in the half-wave voltage due to total dose exposure of up to 5 MRad from a Co-60 source. An outgassing test at 125 degrees Celsius in vacuum for 24 hr resulted in a mass loss of less than 0.2% of the polymer material.
Materials to be used for optoelectronic, photorefractive, or frequency doubling applications must have high nonlinearities, good thermal stabilities, and low optical loss (high transparency). Organic compounds synthesized for incorporation into poled nonlinear polymers typically exhibit tradeoffs between nonlinearity and each of the other two qualities. By judicious use of arylamino donor groups and cyano-containing acceptor groups, a small set of chromophores that are both highly nonlinear and stable at high temperatures has been prepared. By selecting delocalized bridging moieties that are either tuned for optimum hyperpolarizability or exhibit two charge-transfer excited states, highly transparent chromopohores with excellent nonlinearities can be prepared. The results suggest that thermal stability and nonlinearity are jointly achieved by modifying donor and acceptor groups, while transparency and nonlinearity are jointly achieved by modifying bridging groups.
Summarized are two project areas: First, the development of a quantitative structure property relationship for analyzing thermal decomposition differential scanning calorimetry data of electro-optic dyes is presented. The QSPR relationship suggest that thermal decomposition can be effectively correlated with structure by considering the kinds of atoms, their hybridization, and their nearest neighbor bonded atoms. Second, the simple preparation of clad plastic optical fibers (POF) is discussed with the intention of use for nonlinear optical applications. We discuss preparation techniques for single core and multiple core POF, and present some recent data on index profiles and the optimization of thermal stability in acrylate-based POF structures.
The electro-optical properties of UltradelR 9000D polyimides doped with DCM and DADC, a bis(carbazole) analog of DCM with improved thermal stability, are reported. Cure temperatures were restricted to 240 degree(s)C or less to minimize potential thermal degradation of these dyes. Low poling fields of 30 V/micrometers were used in these experiments and yielded r13 coefficients in the 0.1 - 0.8 pm/V range. Photothermal deflection measurements of dye-doped Ultradel 9000D samples showed low optical absorption losses in systems cured at 175 degree(s)C, but losses exceeded 20 dB/cm in samples cured at 300 degree(s)C.
An approach to optical interconnect networks at the module level is presented that addresses the requirements imposed by electronic system manufacturing, such as thermal stability, low cost, and compatibility with standard electronic design, fabrication, and assembly processes. Research is presented on poled polyimide electro-optic materials with extended thermal stability, poled polyimide integrated optic switches acting as transmitters, and a demonstration of a CMOS-compatible optical interconnect.
We report the background leading to the development of the first all-polyimide system (cladding/core/cladding) suitable for fabrication of electro-optic waveguide devices on silicon substrates. The cladding layers are spun from a low optical loss, commercially available polyimide that is suitable for multilayer stacks. The electro-optic material consists of this same polyimide as host to a commercially available guest chromophore and is based upon our prior work on thermoplastic polyimides. The synthesis and purification of this chromophore and an analog is discussed. We also present the materials and process development methodology with the results for this polymer system and demonstrate it by fabrication of an all-polyimide Mach- Zehnder modulator operating at 830 nm. CMOS-compatible switching using a device based on the new material has been demonstrated.
The exceptional electro-optic properties of poled polymer films, coupled with the power and flexibility of thin film fabrication and photolithographic processing, may make possible the hybrid integration of electronic and photonic devices, combining the processing power of VLSI with a dense, high bandwidth, photonic interconnection and switching network in a single, large format, package. In this paper, we describe the potential applications and benefits of electro-optic polymers for optical interconnection and present a review of some of the relevant progress to date in electro-optic polymer materials and devices. Development of an all-polyimide electro-optic polymer system (cladding/core/cladding) based entirely on commercially available components is described. An integrated optic Mach-Zehnder modulator was fabricated using this material system and used in a 200 Mbit/sec digital signal transmission optical interconnection demonstration. Lastly, a potential increase in electro-optic polymer integration density was illustrated by a proof of concept demonstration of three levels of waveguide structures on a single substrate.
We report our continuing investigations of the cumulenes, a novel class of compounds proposed for use as the active second- and third-order nonlinear optical component materials for electro-optic and all-optical devices. Unlike conjugated organic nonlinear optical molecules based on alternating multiple and single bonds, these molecules contain a contiguous, or `cumulated' system of double bonds, leading to a highly rigid one-dimensional backbone of polarizable (pi) -electrons. A series of symmetrically- and asymmetrically-substituted tetraphenyl cumulenes has been synthesized and characterized. Direct-current electric field- induced second harmonic generation experiments show significant second-order nonlinear susceptibilities in a series of polar cumulenes. These experiments have been performed at 1.9 micrometers to avoid dispersion effects. Thermogravimetric analysis indicates survival of a butatriene to 300 degree(s)C.
The exceptional electro-optic properties of poled polymer films, coupled with the power and flexibility of thin film fabrication and photolithographic processing, may make possible a new class of integrated optic systems: photonic large scale integration (PLSI). PLSI systems are characterized by the hybrid integration of electronic and photonic devices, combining the processing power of VLSI with a dense, high bandwidth, photonic interconnection and switching network in a single, large format, package. In this paper, we describe the potential applications and benefits of PLSI and present a review of some of the relevant progress to date in electro-optic polymer materials and devices, including the demonstration of polymer switch based 100 Mbit/sec digital signal transmission for optical interconnection and a 20 GHz electro-optic polymer modulator.
Using polyimide as host in a guest-host electro-optic thin film a thermally stable poled electro- optic response is demonstrated at temperatures at 150 degree(s)C and 300 degree(s)C. A coplanar-electrode poling geometry is used so that the guest molecular alignment between the electrodes is coincident with the free volume of the host. Electric field poling during curing process including imidization (170 - 230 degree(s)C) and densification (340 - 380 degree(s)C) accounts for the highly thermally stable electro-optic response.
We report our investigations of the cumulenes, a novel class of compounds proposed for use as the active second- and thirdorder
nonlinear optical component materials for electro-optic and all-optical devices. Unlike conjugated organic nonlinear
optical molecules based on alternating multiple and single bonds, these molecules contain a contiguous, or "cumulated" system
of double bonds, leading to a highly rigid one-dimensional backbone of polarizable ic-electrons. A series of symmetrically- and
asymmetrically-substituted teiraphenyl cumulenes has been synthesized and characterized. D.C. electric field-induced second
harmonic generation experiments show significant second-order nonlinear susceptibilities in a series of polar cumulenes.
Preliminary results showing evidence of resonant and nonresonant third-order nonlinear optical activity are also reported.