We added a control electrode to a phase-shifted Bragg grating filter in an electro-optic polymer waveguide to obtained voltage tunability. The waveguide grating transmission spectrum near 1.3 microns featured a 5 GHz passband with a peak transmission of 32% within a 2 nm wide, 12 dB deep blocking band. With the waveguide grating sandwiched between gold layers separated by ~10 microns, we were able to shift the transmission spectrum at a rate of 0.1 GHz/volt. Such filter tunability may be used in ultradense WDM channel selection or to compensate for detuning by environmental factors.
Polymer based electro-optic (EO) modulators and other integrated optic devices have the potential to provide low cost and lightweight alternative for high-speed digital as well as analog RF links. To be truly competitive with existing technologies such as LiNbO<SUB>3</SUB>, EO polymer modulators must also meet the criteria of low loss. There are two major causes of loss in EO modulators: waveguide loss (including material loss, scattering, etc.), and fiber- to-waveguide coupling (butting) loss. Various techniques can be utilized to minimize these coupling losses, however, to maintain low cost of component, we resort to the simplest possible approach which is easy to manufacture. Pigtails using standard single mode fiber produce coupling loss on the order of 3 to 5 dB/connection. In order to improve mode size matching yet maintain low drive voltage we incorporate waveguide and fibers tapers. Waveguide tapers resulted to butting losses as low as 1.5 dB/connection, whereas fiber tapers resulted to 2.5 dB/connection butting losses. Combining both techniques together, it was possible to produce 1.3 dB/connection butting loss, however, tapered waveguide devices were less sensitive to alignment tolerance than tapered fiber devices, and therefore less sensitive to environmental conditions.
Poling induced losses of split-ground plane, push-pull polymeric electro-optic modulators have been investigated. Two sources of loss are found: loss due to the presence of oxygen and loss due to deforming the waveguide structure by large poling fields. Deformation is the most severe at the edges of the electrodes, where the electric field amplitude is largest. Experiments were done by poling waveguides with different architectures and poling in air and in an inert atmosphere. There is an apparent rapid increase in poling induced loss (to the 4<SUP>th</SUP> power) with poling voltage due to the presence of oxygen (up to 6.5 dB/cm for poling field of 170 V/micrometers ), whereas loss due to deformation increases linearly with poling voltage (up to 2.5 dB/cm). Oxygen-induced loss can be minimized by poling in inert atmosphere, while deformation induced loss can be minimized by optimizing device architecture.
Recent developments in electro-optic polymer materials and devices have led to new opportunities for integrated optic devices in space environments. The results of numerous tests have indicated that polymer materials have many properties that are suitable to be used in space. These results coupled with recent advances in device and material technology will allow very large bandwidth modulators and switches with drive voltages less than 1 V. At IPITEK, we have already designed and fabricated new polymeric modulators with halfwave voltages less than 0.8 V and a halfwave voltage-interaction product of 2.2 V-cm. The low drive voltage allows electro-optic modulators and switches to be driven directly by high-speed logic devices without the use of broadband amplifiers.
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<SUB>(pi</SUB> ).
A portable optical processor, specially designed for optical wavelet transforms for target detection, has been developed at JPL. The system architecture, engineering design and packaging are presented. A new algorithm development in wavelet filter design is discussed. Demonstration for objection detection using this new approach also is provided.
A wavelet processing-based automatic target detection technique has been developed at JPL and demonstrated for mine detection applications. In this approach, first, a multiresolution wavelet decomposition method was utilized to remove clutter from the input scene so that the false alarm rate due to background clutter could be greatly reduced. Second, a shape-specific ternary-valued wavelet filter was used to perform mine detection. This ternary-valued wavelet filter was successfully implemented in an optical wavelet processor and real-time mine detection was demonstrated. Theoretical analysis of this wavelet processing method will be provided. Experimental results illustrating mine detection will also be presented.
An all-optical wavelet processor for target detection has been developed and demonstrated at JPL. An innovative 2D Shape-discriminant wavelet filter, encoded with a ternary-valued scheme, was developed and implemented in a Liquid Crystal Television Spatial Light Modulator (LCTV SLM) to enable real-time updatable processing. Applications ranging from flight object discrimination, mine detection, and cancer cell detection have been demonstrated.
A novel optical wavelet processor is introduced. Generic wavelet functions, consisting of both amplitude and phase information can be optically synthesized using two cascaded Liquid Crystal Television Spatial Light Modulators. An innovative ternary-valued shape discriminant wavelet filter and its optical implementation is also introduced. Experimental demonstrations of multitarget classification using both a 2D Morlet wavelet filter and a ternary wavelet filter are also reported. The experimental results show that the wavelet filters are superior in discrimination than that of the conventional correlation technique.
Azo dye polymers have been investigated as polarization holographic recording and all-optical modulating media. The use of azo dye polymers is limited by their intrinsic low response time. Different dyes and fabrication techniques have been utilized to enhance the material's speed. A relatively new modulation technique utilizing the nonlinear Fabry-Perot effect in attenuated total internal reflection (ATR) geometry is compared to the conventional transmission type modulation geometry. In the ATR case, a small change in the index of the polymer causes a shift in the angular spectrum of the Fabry-Perot resonances, thus enabling us to modulate a probe beam with an external pump beam. Both modulation speed and contrast ratio are greatly enhanced using this technique. Experimental results are presented, and the limits of both methods are analyzed. The ATR method is also useful in characterizing thin (less than a few microns) polymer films, for studying photo-induced index changes. Future applications, such as optically addressed spatial light modulators and nonlinear optical processing applications, are discussed.
A new holographic recording medium based on poly-2-Hydroxyethyl Methacrylate (HEMA) and visible light sensitizer is investigated. The holographic recordings are based on photo- induced polymerization of HEMA, using Camphorquinone as a visible light sensitizer. The medium has several advantages. Namely, it does not require extensive processing and survives high humidity conditions, including water immersion. Several experiments have been conducted to analyze the behavior of this medium, including analysis of recording parameters using a real-time holographic recording/playback setup, precuring, swelling, and water survivability tests. Water-immersion survivability of our material is a unique characteristic that can be incorporated in novel holographic and optical systems, such as water immersed holographic optical elements. New possibilities and applications are discussed.