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Optical Software Defined Radio Transmitter Extinction Ratio Enhancement with Differential Pulse CarvingA unique challenge in the development of a deep space optical software defined radio (SDR) transmitter is the optimization of the extinction ratio (ER). For a Mars to Earth optical link, an ER approaching 40dB may be necessary. However, a high ER can be difficult to achieve at the low PPM orders and narrow slot widths required for high data rates. The quality of the digital signal transmitted by the SDR does not meet the amplitude and timing characteristics needed by an analog optical modulator. The conflicting implementation constraints of these two fundamentally different systems, the digital SDR and analog optical modulator, can make achieving the required ER very difficult. In this paper, the causes of fidelity loss at the interface between the SDR and optical modulator are discussed. The SDR signal quality requirements are derived and explored. It is shown that increasing the SDR signal quality enough to meet these requirements is impractical to implement due to bandwidth limitations of electronic components as well as Field Programmable Gate Array (FPGA) clock speed constraints. A novel optical modulation architecture based on low-voltage differential signaling and dual Mach-Zehnder modulators is presented which reduces the signal quality requirements on the SDR and increases the system ER.
Document ID
Document Type
Lantz, Nicholas C.
(NASA Glenn Research Center Cleveland, OH, United States)
Nappier, Jennifer M.
(NASA Glenn Research Center Cleveland, OH, United States)
Vyhnalek, Brian E.
(NASA Glenn Research Center Cleveland, OH, United States)
Tedder, Sarah A.
(NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
February 13, 2019
Publication Date
February 5, 2019
Subject Category
Communications And Radar
Report/Patent Number
Meeting Information
SPIE Photonics West LASE Free-Space Laser Communications XXXI(San Francisco, CA)
Funding Number(s)
WBS: WBS 277985.
Distribution Limits
Work of the US Gov. Public Use Permitted.
Electro-Optic Modulator
Extinction Ratio
Software Defined Radio
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