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Azad Siahmakoun

Dr. Azad  Siahmakoun

Rose-Hulman Institute of Technology

Physics & Optical Engineering Dept
5500 Wabash Ave

Terre Haute IN 47803-3920
United States

tel: 812 877 8400
fax: 812 877 8670
E-mail: siahmako@rose-hulman.edu

Area of Expertise

Nonlinear optics, Applications of Photorefractive Materials, RF photonics, Optical MEMS, Plasmonics, Optical Beamforming


Azad Siahmakoun received his BS, MS, and PhD all in physics. He completed his PhD at University of Arkansas in 1988 prior to joining Rose-Hulman Institute of Technology (RHIT) where he is now a professor of Physics and Optical Engineering, Associate Dean of Faculty, and the Founding Director of Micro-Nanoscale Devices and Systems (MiNDS) cleanroom facility at RHIT.

Prof. Siahmakoun was the PI of Wideband Optically Multiplexed Beamformer Architecture project in collaboration with NAVSEA-Crane Division, a program that was managed by ONR 2000-2003. Through this funding, he has established the state-of-the-art RF Photonics laboratory at RHIT. He was also the Director of the Center for Applied Optics Studies 2002-2007. Dr. Siahmakoun has published over 200 articles in nonlinear optics, RF photonics, MEMS and micro/nanofabrication. He has 3 US patents to his name. Prof. Siahmakoun is the recipient of the "Rose-Hulman's Board of Trustees Outstanding Scholar Award," in 1999. He is also a Fellow of the International Society of Optical Engineering (SPIE) and Senior Member of the Optical Society of America

Lecture Title(s)

Photonic Data Converters

Optical signal processing offers many benefits such as high speeds, parallel processing, high information capacity, and immunity to electromagnetic interference.  Photonics is ideally suited for where electrical digital-to-analog (D/A) and analog-to-digital (A/D) conversion techniques are reaching their performance limits.

In this paper we describe a photonic system that combines operation of a serial-to-parallel conversion device along with a bit selector, to form a high-speed D/A converter. A fiber-optic D/A converter system is proposed and demonstrated. The operation technique is based on bit-interleaving and cross-gain modulation in a semiconductor optical amplifier (SOA). The fiber-optic 3-bit converter operates at 2 Gb/s, however, the proposed architecture can be easily scaled to operate at 100s of Gb/s.

Additionally, a photonic A/D converter based on the first-order asynchronous delta-sigma modulation (ADSM) is theoretically investigated and experimentally demonstrated. ADSM is a straightforward approach to A/D since it does not require external clocking.  To improve signal-to-noise and effective number of bits, a non-interferometric optical ADSM has been implemented. The ADSM is comprised of three photonic devices:  a photonic integrator, a bistable quantizer, and a corrective feedback.  The photonic integrator which is a recirculating loop performs the oversampling of an analog input using the cross-gain modulation in an SOA. The photonic ADSM produces an inverted non-return-to-zero pulse-density modulated binary output describing the analog input.  We will show that while the fiber-optic ADSM system converts MHz range analog inputs, the integrated photonic system has the potential to operate in GHz range.  

Optical Beamforming of Multiple Independent-Simultaneous RF Beams for Phased-Array Antennas

We propose and demonstrate a novel architecture for processing simultaneous independent RF beams. The proposed optical processor technology employs wavelength division multiplexing (WDM) encoding and technologies that enhances secure communications for a wide bandwidth of operation. In our example of two-channel approach, four adjacent ITU optical WDM channels are used as optical carriers. Each pair of optical carriers directs RF information of one receive/transmit beam. The optical channels feed a 3-bit programmable dispersion matrix (PDM), which performs true-time delay processing. The PDM is based on three optical delay lines, arranged in a binary or ternary configuration. Each delay line consists of four fiber-Bragg gratings (FBG). The separation between FBG increases by multiples of two for each delay line. Beampatterns are characterized in receive and transmit modes for RF signals in 0.5-1.5 GHz range and are obtained for target angles of ± 70o. The measurement results demonstrate the simultaneous processing of two RF-beams and the squint free nature of the beamformer. The scaled up version of beamformer to large array size and its simultaneous multiple-beam processing will be presented.

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