Albert S. Ren

From molecules to opto-chips: organic electro-optic materials

Recent advances in polymeric electro-optic materials and device fabrication techniques have significantly increased the potential for incorporation of these materials and devices into modern high bandwidth (fiber and wireless) telecommunication, information processing, and radar systems. Charge transfer π-electron chromophores characterized by molecular first hyperpolarizability (second order optical non-linearity) values approaching 3000×10 –30 esu have been synthesized. Elucidation of the role of intermolecular electrostatic interactions in inhibiting the efficient translation of molecular optical non-linearity to macroscopic electro-optic activity has permitted systematic modification of materials to achieve electro-optic coefficients approaching 100 pm V –1 . Improvements in the optical loss of polymeric materials at wavelengths of 1.3 and 1.55 µm have been effected. Mode matching of passive transmission and active electro-optic waveguides has been addressed, permitting a dramatic reduction in insertion loss. The putative ability of polymeric electro-optic materials to be efficiently integrated with very large scale integration semiconductor electronic circuitry and with passive optical circuitry has been demonstrated. Several devices of varying degrees of complexity have been fabricated and evaluated to operational frequencies as high as 150 GHz. The operational stability of polymeric devices is very competitive with devices fabricated from lithium niobate and gallium arsenide.

The molecular and supramolecular engineering of polymeric electro-optic materials

Abstract A new class of electro-optic chromophores, of which 2-dicyanomethylen-3-cyano-4-{2-[ E -(4- N , N -di(2-acetoxyethyl)-amino)-phenylene-(3,4-dibutyl)thien-5]- E -vinyl}-5,5-dimethyl-2,5-dihydrofuran (denoted FTC) is the prototype, has been prepared, characterized, and used to fabricate electro-optic devices. The molecular hyperpolarizability and thermal stability of these chromophore molecules are exceptional. Strong intermolecular electrostatic interactions inhibit the efficient poling of these molecules. A statistical mechanical theoretical treatment is used to quantitatively predict the competition of poling, intermolecular electrostatic interactions, and thermal effects in defining achievable acentric order and hence macroscopic optical nonlinearity. Theory is used to predict the optimum chromophore structure and material composition (chromophore loading in a polymer matrix) for maximum electro-optic activity and minimum optical loss. Problems associated with lattice hardening to lock-in poling-induced order are discussed briefly.

Polymer electro-optic devices for integrated optics

Abstract Recent advances in polymer electro-optic polymers and in fabrication techniques have made possible advances in polymer optical guided wave devices which bring them much closer to system ready. The processing of a new thermal set FTC polymer and its incorporation into a high-frequency, low-Vπ optical amplitude modulator are reviewed. The design and fabrication of 100 GHz modulators and their integration with rectangular metal waveguides using an anti-podal finline transition with a flexible Mylar substrate is discussed. High-speed polymer modulators with balanced outputs and the in situ trimming of the output coupler is described. More complex guided wave devices using polymers are demonstrated by the photonic rf phase shifter. Techniques for integrating both passive and active polymers into the same optical circuit without the need for mode matching is presented and demonstrated. To reduce the Vπ of a polymer amplitude modulator to 1 V or under, a technique of constant-bias voltage is demonstrated. Finally, a technique to directly laser write electro-optic polymer devices is reviewed.

Polymeric electro-optic modulator based on 1×2 Y-fed directional coupler

We have demonstrated a polymeric electro-optic modulator based on a 1×2 Y-fed directional waveguide coupler. The symmetric geometry of the 1×2 Y-fed directional coupler provided the modulator unique characteristics of intrinsic 3 dB operating point and two complementary output ends. A low switching voltage of 3.6 V and a high extinction ratio of 26 dB were obtained with the modulator operating at a wavelength of 1.34 μm. The modulator was fabricated with a novel electro-optic polymer that was synthesized from polyurethane cross-linking with a chromophore.

EO polymer-based integrated-optical acoustic spectrum analyzer

An acoustic spectrum analyzer based on electrooptic (EO) polymer integrated optics is presented. The device is used in a scanning heterodyne geometry by zero biasing a Michelson interferometer. It is capable of detecting vibrations from DC to GHz range. The novelty of the work is applying EO polymers to high frequency acoustic sensing applications. EO polymers have been extensively used for communication devices. However, their use in high frequency sensing applications remains unexplored. The sensor presented is designed to analyze thin film structure by utilizing high frequency capabilities of EO polymers. The advantage of this approach over existing methods is in its potential to detect vibrations over 100 GHz with low drive voltages (V/sub /spl pi// less than 1 V), using a device that is completely electrically controlled with no mechanical moving parts. Low frequency tests indicate good agreement between experimental results and theoretical predictions. Acoustic vibrations excited by pulsed Nd-YAG laser are detected to frequencies up to 200 MHz using the device presented.

Electroactive polymers including non-linear optical polymers

Abstract Recent advances in design, synthesis, and processing of electroactive polymers promise important commercial applications ranging from improved performance flat panel displays to critical components of the next generation information superhighway. Electroactive polymer research is also providing fundamental new insight into the role of long range electrostatic interactions with consequences for condensed matter theory and the development of nanostructured materials.

Vertically integrated polymer waveguide device minimizing insertion loss and Vπ

We present design and fabrication considerations for a vertically integrated electro-optic polymer modulator. The hybrid design incorporates both passive and active core segments for optimized transmission and modulation of an optical signal. When compared to traditional structures, this vertically integrated modulator potentially reduces fiber coupling and propagation losses by more than 10 dB for a 6 cm structure while maintaining a minimized V(pi ).

Polymetric waveguide beam deflector for electro-optic switching

We fabricated and demonstrated a beam deflector implemented in an electro-optic polymer planar waveguide. An array of prism- shaped electrodes formed on the top of the waveguide induces selective refractive index change in the core polymer layer, which results in the tilt of the propagation direction of the guided beam. Waveguide beam deflectors have potential applications in the emerging photonics technologies such as optical storage systems, optical phased array antenna, and optical switching. The deflection sensitivity of 28 mrad/kV, and the maximum deflection angle of +/- 8.4 mrad at +/- 300 V were obtained for this first demonstrated device.

Three dimensional integration of polymer electro-optic modulators

The proposed structure consists of a vertical power splitter that divides the fiber coupled optical input among the vertical layers. Modulators on each layer share a common intermediate ground plane which provides electrical isolation. We will present preliminary beam propagation simulation, fabrication, and experimental results including the required drive voltages, crosstalk, and insertion losses of the individual modulators.

Beam deflection with electro-optic polymeric waveguide prism array

A beam deflector device has been demonstrated that used thin-film electro-optical polymeric waveguide. Prism cascade was fabricated within a planar waveguide. We report the detail of the design and fabrication of new polymer material beam deflector to operate at 1.3 micrometers .