White light spectroscopy has the potential to be used as an optical biopsy method, as backscattered light data can be
related to the cellular nucleus size. In this paper, we compare experimental backscattering results against the general
Mie theory simulations. Our experimental technique obtains results in terms of intensity vs. wavelength. We also use
optical filters, to limit the source spectrum, and when converting the backscattered data into the Fourier domain, we
obtain characteristic frequencies which describe the scatterer size. Phantom tissues, comprised of polystyrene spheres in
a liquid or gel, are used for the experiments.
Early pre-cancerous conditions in tissue can be studied as mixture of cancerous and healthy cells. White light
spectroscopy is a promising technique for determining the size of scattering elements, which, in cells are the nuclei.
However, in a mixture of different sized scatterers, possibly between healthy and cancerous cells, the white light
spectroscopy spatial data is not easily analyzed, making it difficult to determine the individual components that comprise
the mixture. We have previously found by obtaining spatial limited data by using an optical filter and converting this
spatial data into the Fourier domain, we can determine characteristic signature frequencies for individual scatterers. In
this paper, we show analysis of phantom tissues representing esophagus tissue. We examine phantom tissue representing
pre-cancerous conditions, when some of the cell nuclei increase in size. We also experimentally show a relationship
between the particle concentration and the amplitude of the Fourier signature peak. In addition, we discuss the frequency
peak amplitude dependency based on the Tyndall Effect, which describes particles aggregating into clusters.
A great deal of attention in recent years has been given to inkjet printing as an alternative to traditional
lithographic techniques due to its potential for low cost and rapid turnaround fabrication. A Dimatix DMP-2831
materials printer is used to inkjet print polymer waveguides of SU-8 negative photoresist. Several obstacles must
be overcome for the technology to be feasible on a large scale including the development of capable print devices,
suitable materials for printing, and the ability to consistently and precisely print high-aspect-ratio geometries.
We will discuss the inkjet printing fabrication process, explore some of the difficulties encountered through the
method, present several of our first prototype waveguides, and report some preliminary results on waveguide
The study of biological tissue using white light spectroscopy has the potential to be an effective, fast, and inexpensive
method for the detection of size changes in cell nuclei. The relationship between the spherical scatterer size and the
number of oscillation peaks in the optical spectrum (intensity of scattered light versus wavelength) has been observed by
many researchers. To this point, there was not a detailed theoretical model describing this dependence for elliptical
particles, a common shape of cell nuclei at lower tissue layers. In this paper, we report a theoretical model, valid for both
spheres and ellipsoids, detailing the scattering intensity as a function of the wavelength and the scatterer's diameter.
Supporting this theory, we experimentally test mixtures of scatterers of different sizes and provide density analysis.
In this paper, Multiple-Input Multiple-Output (MIMO) technology is applied to diffuse free-space optical (DFSO)
links. We compare the theoretical BER performance of simulated MIMO and Single-Input Single-output (SISO)
optical links in an indoor office environment. An iterative site-based simulation tool is used to determine the
impulse response of wireless infrared (IR) channels for specified locations within a room. For our purposes, we
use a MIMO 4x4 orthogonal space-time block code. Using this scheme a BER calculation is done based on
received signal power and the corresponding channel gains. By setting a BER threshold within which the system
can operate, we are able to see the coverage area provided by MIMO and SISO DFSO system architecture.
We simulate a stationary transmitter while the receiver is moved through 735 different locations in the room,
resulting in a BER contour plot of the system for a specified room. Simulation results show that by using 4-element arrays at both ends of the link, along with space-time block coding techniques, allows the effective coverage area to be increased by approximately 4 times. Also, when operating with a BER threshold of 10-3, the MIMO architecture requires up to 15dB less signal power than the SISO architecture to remain below the threshold. An optical testbed is used to begin hardware validation of our theory, both with and without optical orthogonal frequency division multiplexing (OFDM) techniques. We provide initial measurement results for the proposed optical system.
Currently, free space optical interconnect systems can be severely limited by optical crosstalk that can arise due
to unfocused systems and misalignments between transmitter and receiver elements. To address this limitation,
space-time codes, largely developed for radio frequency channels, are adapted for use in a free space optical
interconnect system. We have extended space-time coding for a 4x4 optical channel based on on-off keying
that uses real intensity-based signals. These codes improve system performance by taking advantage of the
optical crosstalk in a system composed of multiple transmitters and receivers. Data is encoded by space-time
codes based on orthogonal designs and is split into four streams that are simultaneously transmitted using four
transmitters with the same wavelength. The received signal at each of the four optical receivers is a superposition
of the transmitted signals with the addition of noise. Decision metrics are calculated making use of the received
signals and the optical path gains which are determined using channel training. These metrics, in conjunction
with maximum likelihood decoding, decouple the individual signals transmitted from different transmitters. Use
of the modified codes based on orthogonal designs allows for simple maximum likelihood decoding based on
minimum Euclidean distance. Simulated results show that our system can achieve a low BER on the order of
10-6 even in case of a substantial misalignment between the transmitter and receiver.
Enlargement of mammalian cells nuclei due to the cancerous inflammation can be detected early through noninvasive optical techniques. We report on the results of cellular experiments, aimed towards the development of a fiber optic endoscopic probe used for precancerous detection of Barrett's esophagus. We previously presented white light scattering results from tissue phantoms (polystyrene polybead microspheres). In this paper, we discuss light scattering properties of epithelial MDCK (Madine-Darby Canine Kidney) cells and cell nuclei suspensions. A bifurcated optical fiber is used for experimental illumination and signal detection. The resulting scattering spectra from the cells do not exhibit the predicted Mie theory oscillatory behavior inherent to ideally spherical scatterers, such as polystyrene microspheres. However, we are able to demonstrate that the Fourier transform spectra of the cell suspensions are well correlated with the Fourier transform spectra of cell nuclei, concluding that the dominate scatterer in the backscattering region is the nucleus. This correlation experimentally illustrates that in the backscattering region, the cell nuclei are the main scatterer in the cells of the incident light.
In previous work, we proposed a method for imaging using micro optical electromechanical (MOEM) mirrors. Our solution was to introduce into the imaging sensor optics a 2-D micro-mirror array. This device provides high resolution images with a wide field of view. In this paper, we provide further simulations that validate the functionality of our system design. In addition, we present our first system prototype that can produce an image with higher resolution and support a wider field of view than the image sensor employed in the system.
Along with breast and cervical cancer, esophageal adenocarcinoma is one of the most common types of cancers. The characteristic features of pre-cancerous tissues are the increase in cell proliferation rate and cell nuclei enlargement, which both take place in the epithelium of human body surfaces. However, in the early stages of cancer these changes are very small and difficult to detect, even for expert pathologists. The aim of our research is to develop an optical probe for in vivo detection of nuclear size changes using white light scattering from cell nuclei. The probe will be employed through an endoscope and will be used for the medical examination of the esophagus. The proposed method of examination will be noninvasive, cheap, and specific, compared to a biopsy. Before the construction of this probe, we have developed theory to determine the nuclei size from the reflection data. In this first stage of our research, we compare experimental and theoretical scattered light intensities. Our theoretical model includes the values of scatterer size from which we can extract the nuclei size value. We first performed the study of polystyrene microspheres, acting as a tissue phantom. Spectral and angular distributions of scattered white light from tissue phantoms were studied. Experimental results show significant differences between the spectra of microspheres of different sizes and demonstrate almost linear relation between the number of spectral oscillations and the size of microspheres. Best results were achieved when the scattered light spectrum was collected at 30° to the normal of the sample surface. We present these research results in this paper. In ongoing work, normal and cancerous mammalian cell studies are being performed in order to determine cell nuclei size correlation with the size of microspheres through the light scattering spectrum observation.
We present a means for forming images using micromirror arrays. Using an array of 2D tilt mirrors it is possible to create an image
whose resolution is much higher than the number of mirrors. We
present several types of simulations, including images produced by
graphical ray tracing for linear MEMS array of containing 1 and 2
mirrors, and general NxN configurations.
In this paper, we present our most recent theory and the experimental setup to verify our research into an advanced automation technique that yields high performance, low cost optoelectronic alignment and packaging through the use of intelligent control theory and system-level modeling. Our approach is to build an a priori knowledge based model, specific to the assembled package's optical power propagation characteristics. From this model, a piece-wise linear inverse model is created and used in the "feed-forward" loop. If accurate models are determined, perfect tracking can be achieved. In addition to this feed-forward model, our controller is designed with feedback components, along with the inclusion of a built-in optical power sensor. We will also introduce the test bed that we have developed to verify our control loop algorithm and present initial results.
Proc. SPIE. 5346, MOEMS and Miniaturized Systems IV
KEYWORDS: Switches, Waveguides, Microopto electromechanical systems, Vertical cavity surface emitting lasers, Chemical elements, Analog electronics, Digital electronics, Signal detection, Systems modeling, Device simulation
Densely integrated systems in the future will incorporate device and communication technologies that span the domains of digital and analog electronics, optics, micro-mechanics, and micro-fluidics. Given the fundamental differences in substrate materials, feature scale and processing requirements between integrated devices in these domains, it is likely that multi-chip, system-in-package, integration solutions will be required for the foreseeable future. The multi-domain nature of these systems necessitates design tools that span multiple energy domains, time and length scales, as well as abstraction levels. This paper describes a case study of the modeling of a photonic/multi-technology system based on a 3D volumetric packaging technology implemented with Fiber Image Guide (FIG) based technology. It is 64x64 fiber crossbar switch implementation using three Silicon-on-Sapphire mixed signal switch die with flip-chip bonded VCSEL and detector arrays. We show a single end-to-end system simulation of the O/E crossbar working across the domains of free-space and guided wave optical propagation, GaAs O/E and E/O devices, analog drivers and receivers and integrated digital control.
In this paper, we present an automation technique that yields high performance, low cost optoelectronic alignment and packaging through the use of intelligent control theory and system-level modeling. Our control loop design is based on model predictive control, previously popularized in process and other control industries. Our approach is to build an a priori knowledge model, specific to the assembled package’s optical power propagation characteristics, and use this to set the initial "feed-forward" conditions of the automation system. In addition to this feed-forward model, our controller is designed with feedback components, along with the inclusion of a built in optical power sensor. The optical modeling is performed with the rigorous scalar Rayleigh-Sommerfeld formulation, efficiently solved using an angular spectrum technique. One of the benefits of using our knowledge based control technique is that the efficiency of the automation process can be increased, as the number of alignment steps can be greatly reduced. An additional benefit of our technique is that it can reduce the possibility that attachment between optical components will occur at local power maximums, instead of the global maximum of the power distribution. Therefore, our technique improves system performance, while reducing the overall cost of the automation process.
In this paper, we present a system-level simulation and analysis of a diffractive optical MEM Grating Light Valve. The simulations are performed in a system-level multi-domain CAD framework developed at the University of Pittsburgh. Including the electrical, mechanical, and optical domains, this framework allows the user to design micro-optical systems by examining performance measures of the entire system. In this paper, we provide a brief background of the models that are used for signal and device simulation, and use these results for the simulation and analysis of the promising GLV device for applications in a projection system.
To improve productivity and design space exploration in MOEMS design, new high levels specification and validation methodologies are required. These methodologies have to deal with systems heterogeneity. In this paper we present SystemC based cosimulation methodology for the global validation of MOEMS which is starting from a heterogenous specification where the different modules may be described at different abstraction levels or using different specification languages.
Micro-optical-electrical-mechanical systems (MOEMS) present a new set of challenges for systems on a chip (SoC) and mixed- technology designers including the need for mixed-signal multi-domain simulation. We present new modeling techniques for optical and mechanical MEM components and apply these models to the simulations of a MOEMS switch for optical fiber telecommunications applications.
Computer Aided Design (CAD) tools for modeling optical MEM systems must not only model three distinct domains (optical, electrical, and mechanical), these tools must also model the interactions between the signals of these domains. We strive to create system-level models that are applicable for an optical MEM CAD tool using techniques that support accurate results and interactive computation times. This paper discusses our modeling efforts for multi-domain optical MEM systems with the implementation of these models into our CAD framework, Chatoyant. As an example of our mixed-modeling research, we present the simulation and analysis of a 2 X 2 optical cross connect using Chatoyant. The simulations include the dynamic response of a mechanical beam, diffractive optical effects, and the interaction between these domains.
Computer Aided Design (CAD) tools for modeling optical computing systems use a variety of different optical propagation techniques. However, for modeling micro-systems, common optical modeling techniques are not always valid. This paper discusses various optical propagation models for optical micro-systems by examining the requirements imposed by the physical size of the microsystems and the goal of achieving an interactive CAD framework. Based on these constraints, an appropriate optical model is chosen and used in our opto-electro-mechanical CAD tool, Chatoyant, to perform simulations of 2 X 2 micro-optical switch systems.
We employ Modified Nodal Matrix representation, piecewise linear modeling of non-linear devices, and piecewise characterization of signals to accomplish the simulation of mixed technology system. Piecewise simulation modeling for both optoelectronic and mechanical devices is used to decrease the computational task and allow for a trade-off between accuracy and speed. The extraction from device level simulation of circuit models, which characterize high level effects in optoelectronic or mechanical devices, allows for the inclusion of these effects into traditional circuit representations for the device. This technique improves the overall simulation accuracy without compromising the efficiency of the simulator. The additional advantage of using the same technique to characterize electrical and mechanical models allows us to easily merge both technologies in complex devices that interact in mixed domains.
The use of MEMS technology has enabled the fabrication of micro-optical and micro-electro-mechanical systems on a common substrate. This has led to new challenges in computer aided design of optical micro-electro-mechanical systems. We have extended our opto-electronic system DAD tool, Chatoyant, to attempt to meet the needs to optical MEMS designers. This paper present new component models and analysis techniques which extend our tool to support optical MEMS design. We demonstrate these extensions with the analysis of a micro-optical high speed FT engine and a 1 by 2 optical MEM interferometer switch.