Impact of Nonlinearity on RF-Modulated Frequency Combs with Different Modulation Depths in an MUTC Photodetector
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Date
2019-11-07
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Citation of Original Publication
S. E. J. Mahabadi, T. F. Carruthers, C. R. Menyuk, M. N. Hutchinson, J. D. McKinney and K. J. Williams, "Impact of Nonlinearity on RF-Modulated Frequency Combs with Different Modulation Depths in an MUTC Photodetector," 2019 International Topical Meeting on Microwave Photonics (MWP), Ottawa, ON, Canada, 2019, pp. 1-4.; https://ieeexplore.ieee.org/document/8892212
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
Public Domain Mark 1.0
This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
We calculate the impact of nonlinearity in a modified uni-traveling carrier (MUTC) photodetector on an RF-modulated frequency comb that is generated using short optical pulses. We take into account bleaching (nonlinear saturation), which plays an important role due to the large peak-to-average power ratio. Nonlinear impairment of an RF-modulated continuous wave is characterized by the second- and third-order intermodulation distortion (IMD2 and IMD3). By contrast, an RF-modulated frequency comb is characterized by a distinct IMD2ₙ and IMD3ₙ for each comb line n. We study the effect of modulation
depth on nonlinearity in frequency combs, comparing modulation depths of 4% and 8%. When we include bleaching, we find that the OIP3ₙ, third-order intercept point for the n-th comb line, increases when the modulation depth increases for comb lines at frequencies above 2 GHz (n >= 40), so that distortion decreases. We show that this effect occurs because bleaching attenuates lower frequencies more than higher frequencies and this preferential attenuation increases as the modulation depth increases.