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Precluding nonlinear ISI in direct detection long-haul fiber optic systemsLong-distance, high-rate fiber optic systems employing directly modulated 1.55-micron single-mode lasers and conventional single-mode fiber suffer severe intersymbol interference (ISI) with a large nonlinear component. A method of reducing the nonlinearity of the ISI, thereby making linear equalization more viable, is investigated. It is shown that the degree of nonlinearity is highly dependent on the choice of laser bias current, and that in some cases the ISI nonlinearity can be significantly reduced by biasing the laser substantially above threshold. Simulation results predict that an increase in signal-to-nonlinear-distortion ratio as high as 25 dB can be achieved for synchronously spaced samples at an optimal sampling phase by increasing the bias current from 1.2 times threshold to 3.5 times threshold. The high SDR indicates that a linear tapped delay line equalizer could be used to mitigate ISI. Furthermore, the shape of the pulse response suggests that partial response precoding and digital feedback equalization would be particularly effective for this channel.
Document ID
19910051296
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Swenson, Norman L.
(Stanford Univ. CA, United States)
Shoop, Barry L.
(Stanford Univ. CA, United States)
Cioffi, John M.
(Stanford University CA, United States)
Date Acquired
August 15, 2013
Publication Date
February 1, 1991
Publication Information
Publication: IEEE Photonics Technology Letters
Volume: 3
ISSN: 1041-1135
Subject Category
Optics
Accession Number
91A35919
Funding Number(s)
CONTRACT_GRANT: NAGW-419
Distribution Limits
Public
Copyright
Other

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