Abstract
In coherent optical communication systems, the transmitter usually employs an optical in-phase and quadrature (IQ) modulator to perform electrical-to-optical up-conversion. However, some environmental factors, such as temperature and mechanical stress, strongly influence the stability. To stabilize the quality of the transmitted signal, auto bias control (ABC) is essential to keep modulator in optimum bias. In this paper, we present a novel method of ABC for the optical orthogonal frequency division multiplexing (O-OFDM) signal. In the proposed scheme, a small cosine/sine wave dither signal is added on to the I/Q baseband signal, respectively. Based on the power monitoring of the 1st and 2nd harmonics of the dither signal, the biases of the optical IQ modulator for O-OFDM system can be adjusted very precisely. The simulation and experimental results show good performance on locating the optimum bias voltages for the IQ modulator with high precision.
Highlights
In the last decade, the attention of both academia and industry in high-capacity transmission shifted to coherent optical communication due to rapid advances in semiconductor technology#181329 - $15.00 USD (C) 2013 OSAReceived 7 Dec 2012; revised 25 Jan 2013; accepted 7 Feb 2013; published 1 Mar 2013 11 March 2013 / Vol 21, No 5 / OPTICS EXPRESS 5833 and electronic digital signal processing (DSP) [1,2,3]
In [7,8], the auto bias control (ABC) was based on an asymmetric dithering and has been employed to monitor and control the bias drifting of signal carriers modulated with QPSK and 16-QAM, respectively
Only a few publications on bias controlling for orthogonal frequency division multiplexing (O-OFDM) have been reported, in [10], Cho analyzed the statistics of output optical power to control the bias of OFDM modulated signal
Summary
The attention of both academia and industry in high-capacity transmission shifted to coherent optical communication due to rapid advances in semiconductor technology. In [7,8], the ABC was based on an asymmetric dithering and has been employed to monitor and control the bias drifting of signal carriers modulated with QPSK and 16-QAM, respectively. In [10], within a small range ( ± 10% of Vπ ) close to the optimum DC condition, the statistical analysis only offers a tiny distinguish ratio of the monitored power (< 0.5 dB). This may be a challenge for the practical implementation. Based on the power monitoring of the 1st and 2nd harmonics of the dither signal, the bias of the optical IQ modulator for O-OFDM system can be finely controlled. We will demonstrate that the proposed approach successfully enables us to control the system to the optimum bias condition with only negligible dithering penalty in the back-to-back configuration
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