Spectrally efficient terabit optical transmission with Nyquist 64-QAM half-cycle subcarrier modulation and direct detection

Abstract

We demonstrate 1.728 Tb/s(16×108 Gb/s) direct-detection wavelength division multiplexing (WDM) transmission over 80 km standard single mode fiber (SSMF) with Nyquist 64-ary quadrature amplitude modulation (64-QAM) and half-cycle subcarrier modulation. Each channel carries single sideband 18 GBaud 64-QAM signal and the channel spacing is 27 GHz. Considering 20% soft-decision forward error correction and frame redundancy, a net spectral efficiency record of 3.25 b/s/Hz is achieved for 100 G single polarization direct-detection WDM transmission.

Comparison of digital signal-signal beat interference compensation techniques in direct-detection subcarrier modulation systems

“…(2), as the calculation of the signal-signal beating products is based on the received distorted signal, this technique itself introduces extra unwanted beating interference, thus limiting the compensation gain. To further improve the performance of the single-stage linearization filter, an iterative linearization filter was proposed for DD Nyquist-SCM system in [13]. Figure 3 shows the receiver DSP design with this technique, and its working principle is described as follows: the waveform of VDD(n) is stored in memory, and the signal-signal beating products are calculated based on the filtered SSB signal, which are then subtracting from the stored signal waveform, VDD(n), in the memory, to mitigate the SSBI.…”

“…Recently, a number of SSBI compensation techniques have been investigated for singlepolarization DD SCM systems, operating either optically [9][10][11] or digitally [12][13][14][15][16][17][18][19][20][21][22][23][24]. The optical schemes offer superior compensation gain, but have the drawback of increasing the optical transceiver complexity.…”

“…On the other hand, a number of promising digital compensation schemes have been proposed: the single-stage linearization filter first proposed in [12] enables the mitigation of SSBI using a very simple digital signal processing (DSP) architecture. Its compensation performance can be further improved by iteratively repeating the linearization process or adding an extra linearization stage, techniques termed iterative linearization filter [13] and two-stage linearization filter [14], respectively. Alternatively, in order to maximize the potential compensation gain, especially at high values of optical signal-to-noise power ratio (OSNR), combined linearization and SSBI estimation and cancellation was proposed and investigated in [15] in which the SSBI is estimated from the symbol decisions and subtracted from the received signal waveform.…”

Two-Stage Linearization Filter for Direct-Detection Subcarrier Modulation

“…In DD applications, single sideband subcarrier modulation (SSB SCM) can be employed to achieve high information spectral densities (ISDs). Two SCM approaches are being studied for DD systems: optical orthogonal frequency division multiplexing (OFDM) [3] and Nyquist-pulse shaped subcarrier modulation (Nyquist-SCM) [4][5][6][7]. However, a nonlinear effect known as signal-signal beat interference (SSBI) results from the square-law detection and significantly degrades the system performance.…”

“…techniques require multiple iterations, thus significantly increasing the digital signal processing (DSP) complexity. The single-stage linearization filter proposed in [12] can reduce SSBI with a very simple DSP structure, but cannot achieve the maximum compensation gain due to the introduction of extra beating interference by the technique itself; its compensation performance can be improved by repeating the single-stage linearization filter iteratively (four times or more) and using the stored received signal waveform [7]. A single-stage linearization filter combined with single-iteration SSBI cancellation [13,14] avoids the need for multiple iterations but still has the drawback of high dependency on the accuracy of symbol decision making.…”