Organic electro-optic material based optical modulators have been fervently pursued over the past two decades. The material properties of organic materials over crystalline electro-optic materials such as LiNbO3 have yielded devices with record low drive voltages and significant promise for high frequency operation that are ideal for implementation in many developing telecommunication technologies. This paper will discuss a TM electro-optic phase modulator based on a recently developed material IKD-1-50. A simple fabrication process that is compatible with wafer scale manufacturability using commercially available cladding materials, spin processing, standard photolithography, and dry etching will be presented. Non-centrosymmetric order is induced in the core material via a thermally enabled poling process that was developed based on work in simple slab waveguide material characterization devices, and optimized for polymer stack waveguide architectures. Basic phase modulators are characterized for half wave voltage and optical loss. In device r33 values are estimated from a combination of measured and simulated values. Additional work will be discussed including amplitude modulation and high frequency applications. The design for a Mach-Zehnder interferometer amplitude modulator that implements a multi mode interference cavity splitter will be presented along with plans for a microstrip transmission line traveling wave modulator.
Silicon slot waveguides leverage the field enhancement provided by the continuity of normal electric flux density across a dielectric boundary to confine an optical mode to a void between two proximal silicon strips. Silicon-organic hybrid slot modulators make use of this mode profile by infiltrating the slot region with a non-linear organic electro-optic material (OEOM) for modulation. The dual slot modulator takes this idea a step further by similarly confining a propagating RF mode to the same slot region to increase modal overlap for improved modulation efficiency. This effect is achieved by aligning a titanium dioxide RF slot along a conventional silicon slot waveguide. The TiO2 has an optical refractive index lower than silicon, but a significantly higher index in the RF regime. As a result of the large modal overlap and high electro-optic activity of the OEOM this design can produce measured phase modulated VπL of less than 1.40 V•cm. Furthermore, as the modulator operates without the introduction of a doping scheme it can potentially realize high operational bandwidth and low loss. We present work towards achieving various working prototypes of the proposed device and progress towards high frequency operation.
Dual vertical slot modulators leverage the field enhancement provided by the continuity of the normal electric flux density across a boundary between two dielectrics to increase modal confinement and overlap for the propagating optical and RF waves. This effect is achieved by aligning a conventional silicon-based optical slot waveguide with a titanium dioxide RF slot. The TiO2 has an optical refractive index lower than silicon, but a significantly higher index in the RF regime. The dual slot design confines both the optical and RF modes to the same void between the silicon ribs of the optical slot waveguide. To obtain modulation of the optical signal, the void is filled with an organic electro optic material (OEOM), which offers a high optical non-linearity. The optical and RF refractive index of the OEOM is lower than silicon and can be deposited through spin processing. This design causes an extremely large mode overlap between the optical field and the RF field within the non-linear OEOM material which can result in a device with a low Vπ and a high operational bandwidth. We present work towards achieving various prototypes of the proposed device, and we discuss the fabrication challenges inherent to its design.
Organic EO materials, sometimes called EO polymers, offer a variety of very promising properties that have improved at remarkable rates over the last decade, and will continue to improve. However, these materials rely on a “poling” process to afford EO activity, which is commonly cited as the bottleneck for the widespread implementation of organic EO material-containing devices. The Solution Phase-Assisted Reorientation of Chromophores (SPARC) is a process that utilizes the mobility of chromophores in the solution phase to afford acentric molecular order during deposition. The electric field can be generated by a corona discharge in a carefully-controlled gas environment. The absence of a poling director during conventional spin deposition forms centric pairs of chromophores which may compromise the efficacy of thermal poling. Direct spectroscopic evidence of linear dichroism in modern organic EO materials has estimated the poling-induced order of the chromophores to be 10-15% of its theoretical maximum, offering the potential for a manyfold enhancement in EO activity if poling is improved. SPARC is designed to overcome these limitations and also to allow the poling of polymeric hosts with temporal thermal (alignment) stabilities greater than the decomposition temperature of the guest chromophore. In this report evidence supporting the theory motivating the SPARC process and the resulting EO activities will be presented. Additionally, the results of trials towards a device demonstration of the SPARC process will be discussed.
As EO phase modulators become more prevalent components in optical and RF applications, the demand increases for high bandwidth and low drive voltage modulators that can easily be integrated into developing photonic technologies. The proposed paper will discuss a device architecture for a phase modulator based on a recently developed organic EO material (OEOM), IKD-1-50 integrated into a PMMA polymer host, using a low-index, photo-curable resin as the cladding layers all on a Si platform. Designs for a TM waveguide and electrode configuration will be presented from theory and modeling, through fabrication to characterization. The EO material serving as the core of the waveguide is poled using a poling stage and monitoring apparatus with same electrodes designed for modulation. Poling procedures have been optimized for this material based on experimentation in simple slab-capacitor characterization devices, and produce in-device r33 values that are comparable with attenuated total internal reflection measurements. The challenges presented by the instability of OEOMs in common processing conditions have been addressed and a very simple fabrication process has been developed using standard photolithography and reactive ion etching to define an inverted ridge waveguide structure, pattern surrounding electrodes, and prepare usable end facets. Phase modulator characterization results for fabricated and poled devices have been quantified and will be presented. The simplicity of this device architecture on a Si handle allows for integration into various photonic applications.
A technique is described for displaying polarization information from passive millimeter-wave (mmW) sensors. This technique uses the hue of an image to display the polarization information and the lightness of an image to provide the unpolarized information. The fusion of both images is done in such a way that minimal information is lost from the unpolarized image while adding polarization information within a single image. The technique is applied to experimental imagery collected in a desert environment with two orthogonal linear polarization states of light and the results are discussed. Several objects such as footprints, ground textures, tire tracks, and shrubs display strong polarization features that are clearly visible with this technique, while materials with low polarization signatures such as metal are also clearly visible in the same image.
An all-polymer high-frequency Mach-Zehnder modulator that can be fabricated using standard UV lithography is
proposed. The optical waveguide structure consists of three polymer layers, two low-index, outer cladding layers and an
organic-electro-optic material in a polymer host as the core. Lateral confinement is provided by a trench that is defined
in the lower cladding layer, resulting in an inverted electro-optic polymer ridge waveguide. The inverted nature of this
trench structure allows for a fabrication process in which the cladding layer is patterned, and the highly sensitive electrooptic
material is simply spun on and cured. Microstrip transmission line electrodes patterned on the outer cladding, over
the optical waveguides provide the modulation field. Similar devices using CLD1 or AJL8, as the electro-optic material
have been numerically analyzed at up to 260GHz, and characterized at frequencies up to 40 GHz, but to date no electrooptic
polymer device has been characterized at such high frequencies. A recently developed material, IKD-1-50, with
electro-optic coefficients up to five times larger than CLD1 and AJL8 will be utilized as the core layer for the optical
waveguide. The greater nonlinearity of these materials will yield a device with a lower Vπ. Additionally, high
frequency characterization up to 300GHz will demonstrate the high bandwidth application possibilities of these new
Modern high frequency applications necessitate the utilization of the millimeter wave band. Slot waveguides have
previously been used for electro optic modulators as the enhancement of the electric field strength in the slot creates a
large overlap with the electro optic material. We present a design that utilizes the field enhancement provided by a slot
waveguide geometry for both the optical field and the RF modulating field. The dual RF and optical slot configuration
maximizes the overlap of the optical field and the modulating field in the electro optic material, creating the maximum
amount of phase change per applied volt of modulating signal. This design presents unique fabrication challenges.
Organic electro-optic materials, or "EO polymers," offer much higher nonlinearities than traditional crystalline
materials, making these materials ideal for next generation electro-optic modulators. These materials require an
additional processing step known as poling, which reorients the chromophores through the application of a high electric
field. This effort will focus on corona poling, where a gas is ionized and the electric field across the sample is applied
through the relocation of charged ions. The proposed technique avoids the need to raise the temperature of the material
by applying the electric field while the material is deposited in solution phase. This process can overcome the thermal
stability tradeoff in many organic electro-optic materials, and preliminary results indicate this process results in an
enhancement in the electro-optic activity of the material.