Spectrally Efficient WDM Nyquist Pulse-Shaped 16-QAM Subcarrier Modulation Transmission With Direct Detection

Abstract

The ability to transmit signals with high information spectral density (ISD) using low-complexity and cost-effective transceivers is essential for short-and medium-haul optical communication systems. Consequently, spectrally efficient direct detection transceiver-based solutions are attractive for such applications. In this paper, we experimentally demonstrate the wavelength-division multiplexed (WDM) transmission of 7×12 GHz-spaced dispersion pre-compensated Nyquist pulse-shaped 16-QAM subcarrier modulated channels operating at a net bit rate of 24 Gb/s per channel, and achieving a net optical ISD of 2.0 b/s/Hz. The direct detection receiver used in our experiment consisted of a single-ended photodiode and a single analog-todigital converter. The carrier-to-signal power ratio at different values of optical signal-to-noise ratio was optimized to maximize the receiver sensitivity performance. The transmission experiments were carried out using a recirculating fiber loop with uncompensated standard single-mode fiber and EDFA-only amplification. The maximum achieved transmission distances for single channel and WDM signals were 727 and 323 km below the bit-error ratio of 3.8 × 10 −3 , respectively. To the best of our knowledge, this is the highest achieved ISD for WDM transmission in direct detection links over such distances.Index Terms-Digital signal processing, direct detection, information spectral density, Nyquist pulse shaping, optical fiber communication, single sideband signaling, subcarrier modulation, transceiver design, wavelength division multiplexing.

Comparison of Optical Single Sideband Techniques for THz-Over-Fiber Systems

“…As can be seen, the AVSSB technique presents lower values of optimum CSPR for the 5.5 GHz and 4.75 GHz GBs. For a certain GB, a lower optimum value of CSPR means the technique suffers from lower optical SNR (OSNR) [22]. These lower values could be due to the quantized nature of the CSPR measurements or due to a decrease in the transmitted THz power (due to fiber-UTC PD misalignments or polarization mismatches).…”

Spectrally-efficient direct-detection WDM transmission systems

“…The DSP scheme to generate and detect dispersion pre-compensated SSB 16QAM N-SCM is shown in Fig. 1, and is described in detail in [8]. The FEC-encoded bits are mapped to 16QAM symbols at a symbol rate of f s , followed by Nyquist pulse shaping with root raised-cosine (RRC) filters, up-conversion to the subcarrier frequency f sc , (where f sc < f s for high ISD), DSB to SSB conversion using a digital sideband filter, and finally electronic pre-distortion (EPD) to mitigate the chromatic dispersion at the targeted distance.…”

“…Finally, the output of the symbol demapper is passed to the HD-FEC decoder. Figure 2 shows the experimental setup, described in detail in [8]. Two IQ-modulators, with inputs from an optical comb generator (OCG), were used to generate odd and even channels carrying decorrelated bit sequences.…”

“…This comparison suggests that N-SCM is a promising technique for future short-and medium-haul direct detection links. [8].…”

“…We recently carried out a comparison of OFDM and N-SCM, showing that the higher tolerance to signal-signal beat interference and the lower optimum CSPR of the N-SCM format results in a lower required OSNR, which translates to an increase in maximum reach [6]. We also experimentally demonstrated single-sideband (SSB) QPSK and 16QAM N-SCM transmission, at net ISDs of up to 2.0 (b/s)/Hz [7], [8].…”