Impact of Nonlinear Transfer Function and Imperfect Splitting Ratio of MZM on Optical Up-Conversion Employing Double Sideband With Carrier Suppression Modulation

• Published in: Journal of lightwave technology 2008, Vol.26 (15), p.2449-2459
• Main Authors: Chun-Ting Lin, Chen, J.J., Sheng-Peng Dai, Peng-Chun Peng, Sien Chi
• Format: Article
• Language: English
• Subjects: Amplitude modulation; Application software; Applied sciences; Carriers; Exact sciences and technology; Information, signal and communications theory; Mach-Zehnder modulator (MZM); Microwave photonics; millimeter-wave (mm-wave) generation; Modulation; Modulation, demodulation; Multiplexing; MZM imbalance; MZM nonlinearity; Nonlinear optics; Nonlinearity; Optical communication; Optical fiber communications; Optical fiber networks; Optical modulation; Optical receivers; Optical sensors; Optical telecommunications; radio-over-fiber (RoF); Receiving; Signal and communications theory; Signal generators; Splitting; Spread spectrum; Spreads; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Transfer functions; Transmission and modulation (techniques and equipments); Upconversion; Wireless communications; Wireless sensor networks; Yttrium
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2008.927160

Generation of optical millimeter-wave (mm-wave) signal using a Mach-Zehnder modulator (MZM) based on double-sideband (DSB), single-sideband (SSB), and double-sideband with carrier suppression (DSBCS) modulation schemes have been demonstrated for various applications, such as broadband wireless signals or optical up-conversion for wavelength-division-multiplexing (WDM) radio-over-fiber (RoF) network, wideband surveillance, spread spectrum, and software-defined radio. Among these schemes, DSBCS modulation offers the best receiver sensitivity, lowest spectral occupancy, the least stringent requirement of electrical bandwidth, and the smallest receiving power penalty after long transmission distance. Nonetheless, the inherent nonlinear E/O (electrical/optical) conversion response of a MZM is such that the signal quality of the optical mm-wave suffers. Fabrication tolerances make a balanced 50/50 splitting ratio of the MZM's y-splitter particularly difficult to achieve. As a result, imbalanced MZMs have a finite extinction ratio (ER) and degrade the optical carrier suppression ratio (OCSR) using DSBCS modulation. In this paper, the effect of the MZM nonlinearity and imbalanced y-splitter on optical mm-wave generation by DSBCS modulation is theoretically and experimentally investigated. A novel approach with better performance and greater cost-effectiveness than dual-electrode MZM (DD-MZM) is presented to realize a DSBCS modulation scheme based on a single-electrode MZM (SD-MZM).