Automatic bias control technology of IQ modulator for optical QPSK transmitter based on envelope detection

Abstract

The optical in-phase and quadrature (IQ) modulator is a crucial component in coherent optical communication transmitter. An automatic bias control technology of optical IQ modulator for optical quadrature phase-shift keying (QPSK) transmitter based on envelope detection is proposed in this paper. The implementation basis of this method is provided and the feasibility of this method has been demonstrated through experiments. This method applies dither signals to the three direct current (DC) arms of optical IQ modulator in time sharing, and provides envelope detection to the feedback optical-to-electrical signal, and controls the real-time DC bias of the three arms according to the spectrum of the signal that completes envelope detection calculated by Fast Fourier transform (FFT). The described dither signals are all sine single frequency signals and the specific basis refers to the amplitude value of the point corresponding to the frequency of the dither signal on the spectrum. This method has simple judgment basis, and is easy to implement in practice, and does not have high requirements for the feedback photodetectors. The local optimal algorithm can serve this method well. By using this ABC method based on envelope detection, QPSK modulation was completed with an error vector amplitude (EVM) of 8.89%.