Abstract
Terabit/s super-channels are likely to become the standard for next-generation optical networks and optical interconnects. A particularly promising approach exploits optical frequency combs for super-channel generation. We show that injection locking of a gain-switched laser diode can be used to generate frequency combs that are particularly well suited for terabit/s super-channel transmission. This approach stands out due to its extraordinary stability and flexibility in tuning both center wavelength and line spacing. We perform a series of transmission experiments using different comb line spacings and modulation formats. Using 9 comb lines and 16QAM signaling, an aggregate line rate (net data rate) of 1.296 Tbit/s (1.109 Tbit/s) is achieved for transmission over 150 km of standard single mode fiber (SSMF) using a spectral bandwidth of 166.5 GHz, which corresponds to a (net) spectral efficiency of 7.8 bit/s/Hz (6.7 bit/s/Hz). The line rate (net data rate) can be boosted to 2.112 Tbit/s (1.867 Tbit/s) for transmission over 300 km of SSMF by using a bandwidth of 300 GHz and QPSK modulation on the weaker carriers. For the reported net data rates and spectral efficiencies, we assume a variable overhead of either 7% or 20% for forward- error correction depending on the individual sub-channel quality after fiber transmission.
Highlights
Interfaces operating at 400 Gbit/s or 1 Tbit/s are foreseen as the standards after 100 Gbit/s Ethernet [1,2,3]
We investigate six different super-channel architectures that are based on three different line spacings, 20 GHz, 18.5 GHz and 12.5 GHz, and two different modulation formats, quadrature phase shift keying (QPSK) and 16QAM
We find that all 15 sub-channels perform better than the threshold for second-generation forward error correction (FEC) with 7% overhead, yielding a total data rate of 1.009 Tbit/s transmitted over 300 km. (c) Measured constellation diagrams for sub-channels 1 and 8 of the polarization division multiplexed (PDM)-QPSK experiment. (d) Spectrum of the super-channel derived from a 18.5 GHz comb with 18 GBd PDM-16QAM (RBW 0.01 nm). (e-f) Measured EVMm and BER for each sub-channel and transmission over different distances
Summary
Interfaces operating at 400 Gbit/s or 1 Tbit/s are foreseen as the standards after 100 Gbit/s Ethernet [1,2,3]. Broadband frequency combs for terabit/s superchannels can be generated by solid-state mode-locked lasers in combination with highly nonlinear fibers [5,9,20], or multi-stage parametric mixers [16,17,18] Both approaches require strong optical pumps and large interaction lengths in delicately arranged sequences of specialized optical fibers. In this work we demonstrate that gain-switched comb sources (GSCS) [21] can be used as an alternative approach to generate terabit/s super-channels These devices exploit injection locking of a gain-switched laser diode and feature both an electrically tunable free spectral range [22] and an electrically tunable center wavelength [23], good spectral flatness, high OCNR, low RIN and low optical linewidth.
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