Subcarrier multiplexing for high-speed optical transmission

Abstract

Abstract-The performance of high-speed digital fiber-optic transmission using subcarrier multiplexing (SCM) is investigated both analytically and numerically. In order to reduce the impact of fiber chromatic dispersion and increase bandwidth efficiency, optical single-sideband (OSSB) modulation was used. Because frequency spacing between adjacent subcarriers can be much narrower than in a conventional DWDM system, nonlinear crosstalk must be considered. Although chromatic dispersion is not a limiting factor in SCM systems because the data rate at each subcarrier is low, polarization mode dispersion (PMD) has a big impact on the system performance if radiofrequency (RF) phase detection is used in the receiver. In order to optimize the system performance, tradeoffs must be made between data rate per subcarrier, levels of modulation, channel spacing between subcarriers, optical power, and modulation indexes. A 10-Gb/s SCM test bed has been set up in which 4 2.5 Gb/s data streams are combined into one wavelength that occupies a 20-GHz optical bandwidth. OSSB modulation is used in the experiment. The measured results agree well with the analytical prediction.

Calculation of Receiver Sensitivities in (Orthogonal) Subcarrier Multiplexing Microwave-Optical Links

“…The main advantage of SCM with respect to a single channel implementation is the higher tolerance to dispersion [2]. However, standard modulation of an optical carrier produces a double sideband (DSB) spectrum.…”

“…Consequently, optical single side band (SSB) modulation is preferred as it eliminates dispersive fading [9] and achieves the higher tolerance to dispersion expected from SCM. SCM/SSB can be directly obtained without employing optical filters with dual-drive Mach Zehnder modulators (DD-MZM) [2] and with optical IQ modulators [10]. The optical modulators exhibit a nonlinear behaviour that produces intermodulation distortion (IMD) between the electrical subchannels.…”

“…Digital subcarrier multiplexing (SCM) consists of the generation of a multicarrier electrical signal that is then modulated onto an optical carrier and transmitted over fiber [1,2]. The (de)modulation of the electrical digital subchannels can be accomplished by digital signal processing (DSP) [1] and analogue signal processing (ASP) [2].…”

“…However, from a practical perspective, the performance of digital electro-optical transceivers is typically specified in terms of receiver sensitivity, which is the minimum received power at which data can be successfully recovered. Calculations to obtain the best achievable sensitivities in digital broadband SCM links in the presence of optical noise were presented in [2], but did not include the IMD. In contrast, a model that includes IMD was developed in [10] for the case of optical IQ modulators.…”

“…The (de)modulation of the electrical digital subchannels can be accomplished by digital signal processing (DSP) [1] and analogue signal processing (ASP) [2]. Broadband DSP-based SCM schemes can potentially achieve high modulation orders with a high spectral efficiency, but they require expensive analogue-to-digital and digital-to-analogue converters (ADC and DAC) and are also penalised by a high power consumption and latency [3].…”