Dylan D. Ross

Simple Fabrication and Processing of an All-Polymer Electrooptic Modulator

Emerging systems requiring large-scale manufacture and monolithic integration of photonic components have created demand for inexpensive and scalable processes for the production of conformal, low-drive voltage, and high bandwidth EO modulators. This paper discusses a device architecture for a phase modulator based on a recently developed organic EO material, IKD-1-50, using low-index, photocurable cladding layers on a Silicon platform. Theory and modeling for a TM waveguide and electrode configuration are presented, followed by the fabrication process and device characterization. The EO material serving as the core of the waveguide is poled using a poling and monitoring apparatus with procedures that were optimized for this material based on experimentation in simple slab-capacitor characterization devices. The challenges presented by the instability of OEOMs under common processing conditions have been addressed and a simple fabrication process has been developed using standard photolithography and reactive ion etching. The characterization methodology for phase modulators will be presented along with the results for modulators fabricated for this study. This study culminates in a VπL of roughly 3.3 V·cm which is comparable with the record demonstrations in the literature for a TM-mode inverted ridge-waveguide-based EO modulator.

High-Power Photodiode-Integrated-Connected Array Antenna

We present a novel optical feeding technique to achieve efficient excitation of an ultrawideband-connected array (CA) antenna. The passive fiber optic feed allows for preservation of the theoretical bandwidth and low profile of elementary connected dipole elements. In order to improve effective radiated power, high-power charge compensated modified unitravelling carrier photodiodes are integrated into an antenna array for the first time. Circuit and full-wave simulations, which include all required antenna and feed components, are conducted for the optimization of the arrays performance. A 9 × 12 element CA is populated with a 1-D array of four photodiode-integrated active elements to demonstrate the concept. The optically fed array is confirmed experimentally to have a 3-dB bandwidth of approximately 7–17 GHz, in good agreement with simulations.

Optically Upconverted, Spatially Coherent Phased-Array-Antenna Feed Networks for Beam-Space MIMO in 5G Cellular Communications

The densification of cellular networks and their soon-to-increase operational frequency is forcing new topological considerations in 5G networks. In particular, networks that enable extreme spatial discrimination are being considered as a means to significantly increase data capacity by realizing spatial-spectral channels that offer frequency reuse without co-channel or adjacent-channel interference. In this paper, we present a new approach to realizing such a capability based on optically upconverted, spatially coherent phased-array feed networks. The details of our approach, presented herein, include the design and initial demonstration of both transmit (Tx) and receive (Rx) array systems that are used in tandem to form a down-/up-link for the purpose of characterizing both array and link performance. Design parameters and initial link characterization results are presented.

Optically addressed ultra-wideband connected array antenna

Modern RF antenna systems are being asked to address many simultaneous and pressing challenges, e.g., wide operational bandwidth, dynamic gain patterns, and conformal profiles. One way to address these problems is to develop a low profile and ultra-wideband (UWB) phased array antenna. However, the design, fabrication, and integration of such an array using an all-RF feed is exceedingly difficult. Thus, in this paper we present a novel optical feeding technique to achieve efficient excitation of a UWB connected array (CA) antenna. By feeding the array optically, preservation of the theoretical bandwidth and low-profile of elementary connected dipole elements is enabled. Coupling of light to a photodiode merely requires enough space to firmly secure a fiber ferrule, allowing for the population of more densely packed arrays and wider operational bandwidth. Additionally, the optical feeding of the array can provide low noise excitation of the radiating elements, which supports high fidelity beam steering of independent signals over the arrays ultra-wide bandwidth. Currently all of these abilities are unattainable by conventional electronic feeding networks. Previously the main limiting factor for the realization of such an optical system was the low power handling capability of the photodiode at the antenna excitation point. Recently, however, modified uni-travelling carrier (MUTC) photodiodes, flip-chip bonded to high-thermal conductivity aluminum nitride (AlN), have been able to achieve output powers of over 1 W at 10 GHz under CW operation, and over 10 W using pulsed power modulation. A prototype MUTC photodiode-integrated antenna array on AlN with direct fiber feed to each antenna element is discussed and demonstrated that can provide 5-20 GHz bandwidth and a size, weight, and power (SWaP) superior to conventional electronic phased array systems.

Photonic Tightly Coupled Array

We present the first demonstration of a tightly coupled array (TCA) excited by high-power photodiodes directly integrated onto the antenna substrate. As a complex electrical feed network is not required to feed the radiating elements, the design can realize ultra-wide bandwidth while improving upon the size, weight, and power of conventional electronic-based arrays. Circuit and full-wave simulations are conducted for optimization of array performance and compared against all-electronic TCA designs within the literature. A prototype

Processing of organic electro-optic materials: solution-phase assisted reorientation of chromophores

9\times 12

k-Space tomography for spatial-spectral monitoring in cellular networks

element TCA with four photodiode-integrated active elements is characterized to validate the design process. The photonic array exhibits high radiation efficiency between 5 and 20 GHz, and a maximum effective isotropic radiated power of 25 dBm at 13 GHz is measured in the far field.

High-Power, Aperture Coupled Photonic Antenna

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.

Low-Profile High-Power Optically Addressed Phased Array Antenna

A technique for the spatial-spectral analysis of the cellular environment by performing a near real-time imaging of k-space is presented. The system uses a random spatial-spectral dispersion map from an optically-upconverted RF phased array receiver and tomographic reconstruction techniques to recover the cellular source scene. While spatial dispersion is inherent to phased array antennas, temporal dispersion is introduced by randomizing the fiber length for each up-converted antenna element, which contains the received RF signal as a sideband on an optical carrier. Each fiber is routed into a common fiber bundle where the filtered RF-sidebands are launched into free space, expand and overlap. The resulting complex superposition produces an interference pattern unique to a given RF source location and frequency, which is used to recover the spatial direction and frequency of each source in the cellular environment. We present the theory of operation and experimental results of this approach.

Compressive k -Space Tomography

A high-power charge-compensated modified uni-travelling carrier photodetector is directly integrated into an aperture coupled patch antenna. The coupling technique offers not only good isolation between feed and radiating patch substrates but also wide operational bandwidth. The antenna is developed to operate at 22 GHz with 3-dB relative bandwidth of ~20%, over which the measured effective isotropic radiated power approaches 31 dBm. The photonic antenna is integrated with a lightweight, low form factor fiber-optic feed that demonstrates potential for future wireless communications applications. The antenna’s electrical and radiation characteristics are observed to be in good agreement with simulations.