Comb-based WDM transmission at 10 Tbit/s using a DC-driven quantum-dash mode-locked laser diode

Abstract

Chip-scale frequency comb generators have the potential to become key building blocks of compact wavelength-division multiplexing (WDM) transceivers in future metropolitan or campus-area networks. Among the various comb generator concepts, quantum-dash (QD) mode-locked laser diodes (MLLD) stand out as a particularly promising option, combining small footprint with simple operation by a DC current and offering flat broadband comb spectra. However, the data transmission performance achieved with QD-MLLD was so far limited by strong phase noise of the individual comb tones, restricting experiments to rather simple modulation formats such as quadrature phase shift keying (QPSK) or requiring hard-ware-based compensation schemes. Here we demonstrate that these limitations can be over-come by digital symbol-wise phase tracking algorithms, avoiding any hardware-based phase-noise compensation. We demonstrate 16QAM dualpolarization WDM transmission on 38 channels at an aggregate net data rate of 10.68 Tbit/s over 75 km of standard single-mode fiber. To the best of our knowledge, this corresponds to the highest data rate achieved through a DC-driven chip-scale comb generator without any hardware-based phase-noise reduction schemes.

Coherent WDM transmission using quantum-dash mode-locked laser diodes as multi-wavelength source and local oscillator

“…This indicates that, for the chosen observation time of 0.4 µs, the lineshape is dominated by high-frequency phase noise rather than by low-frequency drift. Since the estimated linewidth of the QD-MLLD tones is relatively high compared to that obtained from benchtop-type continuous-wave (CW) ECL, we use high symbol rates and employ symbol-wise phase tracking as in [9] for the transmission experiments discussed in Section 3.…”

“…Subsequently, carrier phase noise compensation is carried out based on a blind phase search (BPS) algorithm [21]. This technique allows for symbolwise phase tracking and has been shown to effectively cope with the phase noise of QD-MLLD carriers in previous experiments [9]. Figure 4(b) depicts the superposition of the LO comb tones with the WDM signal.…”

“…These links crucially rely on compact WDM transceivers that offer multi-terabit/s aggregate data rates and that can be deployed in large quantities at low cost. In this context, optical frequency combs have emerged as a promising approach towards compact and efficient light sources that provide a multitude of tones for parallel WDM transmission [2][3][4][5][6][7][8][9]. Unlike the carriers derived from a bank of individual lasers, the tones of a comb are intrinsically equidistant in frequency and are defined by just two parameters  the center frequency and the free spectral range (FSR).…”

“…Among the different frequency comb sources, quantum-dash mode-locked laser diodes (QD-MLLD) are particularly interesting due to their technical simplicity: Driven by a DC current, these devices emit broadband frequency combs consisting of tens of optical carriers, spaced by free spectral ranges of, e.g., 25 GHz or 50 GHz, as determined by the cavity length. In previous experiments [6,9], the potential of QD-MLLD has been demonstrated by using the devices as multi-wavelength optical sources for parallel transmission on tens of WDM channels, achieving aggregate lines rates of more than 10 Tbit/s. In these experiments, symbol-wise phasetracking [9] or self-injection locking [6] was used to overcome the limitations imposed by the rather high intrinsic linewidth of the QD-MLLD tones.…”

“…In previous experiments [6,9], the potential of QD-MLLD has been demonstrated by using the devices as multi-wavelength optical sources for parallel transmission on tens of WDM channels, achieving aggregate lines rates of more than 10 Tbit/s. In these experiments, symbol-wise phasetracking [9] or self-injection locking [6] was used to overcome the limitations imposed by the rather high intrinsic linewidth of the QD-MLLD tones. However, while these demonstrations show the great potential of QD-MLLD as multi-wavelength light sources at the WDM transmitter, demodulation of the coherent signals still relied on a single-wavelength external-cavity laser (ECL), which acts as a local oscillator (LO) and needs to be tuned to the respective channel of interest.…”