Abstract
In radio-over-fiber systems, optical single-sideband (SSB) modulation signals are preferred to optical double-sideband (DSB) modulation signals for fiber distribution in order to mitigate the microwave power fading effect. However, typically adopted modulation schemes generate DSB signals, making DSB-to-SSB conversion necessary before or after fiber distribution. This study investigates a semiconductor laser at stable locking dynamics for such conversion. The conversion relies solely on the nonlinear dynamical interaction between an input DSB signal and the laser. Only a typical semiconductor laser is therefore required as the key conversion unit, and no pump or probe signal is necessary. The conversion can be achieved for a broad tunable range of microwave frequency up to at least 60 GHz. In addition, the conversion can be carried out even when the microwave frequency, the power of the input DSB signal, or the frequency of the input DSB signal fluctuates over a wide range, leading to high adaptability and stability of the conversion system. After conversion, while the microwave phase quality, such as linewidth and phase noise, is mainly preserved, a bit-error ratio down to 10-9 is achieved for a data rate up to at least 8 Gb/s with a detection sensitivity improvement of more than 1.5 dB.
Highlights
Radio-over-fiber has attracted great attention due to the strong demand in distributing microwave subcarriers over long distances through fibers for broadband wireless access networks [1, 2]
A few remarks are made as follows to compare the stable locking dynamics approach demonstrated here with the period-one dynamics approach proposed in [13]. Different from the former, the latter requires frequency locking between the modulation sidebands of an input DSB signal and the oscillation sidebands of a period-one dynamical state in order to take advantage of the inherent power difference between the oscillation sidebands, typically more than 20 dB
As opposed to the stable locking dynamics approach, the DSB-to-SSB conversion is achieved with a higher SRR value, typically more than 20 dB, and a higher detection sensitivity improvement, up to at least 15 dB, using the period-one dynamics approach
Summary
Radio-over-fiber has attracted great attention due to the strong demand in distributing microwave subcarriers over long distances through fibers for broadband wireless access networks [1, 2]. External or direct modulation of semiconductor lasers is the simplest scheme to superimpose microwave subcarriers onto optical carriers for such radio-over-fiber systems [3]. Owing to the inherent nature of either modulation scheme, an optical double-sideband (DSB) modulation signal is typically generated, in which the power of the two modulation sidebands around the optical carrier is the same. Such a DSB feature leads to severe microwave power fading over fiber distribution of the optical signal [4, 5], which results from a walk-off in the relative phases of the two modulation sidebands to the optical carrier due to fiber chromatic dispersion. Various different conversion approaches and systems have been proposed [6,7,8,9,10,11,12,13,14]
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