Fig. 1. (a) Experimental setup for generating a single-soliton microcomb in a high-QSi3N4 microring resonator. EDFA: erbium-doped fiber amplifier; TBPF: tunable bandpass filter; FPC: fiber polarization controller; OSA: optical spectrum analyzer. (b) Microscope photo of a Si3N4 microring resonator with a radius of about 240 μm. (c) Typical transmission spectrum and Q-factor of the resonator resonance mode. (d) Variation of 1 h resonance wavelength with and without temperature control.

Fig. 2. (a) Optical spectra of the single-soliton microcomb. (b) C-band spectra of the single-soliton microcomb before modulation. (c) Respective SSB frequency noise spectra of the 1552 and 1542.4 nm comb line. (d) Distribution of the soliton microcomb linewidth. The error bar stands for the standard deviation of three measurements.

Fig. 3. Experimental setup for soliton microcomb coherent communication. WaveShaper: waveform shaper; Tx-DSP: data signal processing sender port; AWG: arbitrary waveform generator; DAC: digital to analog converter; DP-IQM: dual polarization IQM; OC: optical coupler; Fiber: 40 km of single-mode fiber; PM-EDFA: bias-preserving erbium-doped fiber amplifier; Filter: narrowband optical filter; ICR: coherent optical receiver; OSC: real-time oscilloscope; Rx-DSP: data signal processing receiver port; and LO: local oscillator.

Fig. 4. (a) Optical spectra of 39 channels modulated with 40 Gbaud and DP-16QAM modulation format (measured at OC). The red and blue colors of the carriers represent the parity carriers. (b) Measured bit error ratios of the transmitted channels for the single comb with a received power of −14  dBm and a modulation symbol transmission rate of 40 Gbaud. The red dashed line indicates the soft decision forward error correction (SD-FEC) BER threshold with an overhead of 20%. The 12 lines at the high-frequency edge of the C-band (yellow region) are modulated with quadrature phase-shift keying (QPSK) signals rather than 16QAM owing to the large linewidths of these carriers. (c) Measured bit error ratios versus combs OSNR for QPSK modulated channels and neighboring 16QAM modulated channels. (d) Linewidth distribution of the corresponding channel in (c), and the powder blue background represents the modulation formats DP-QPSK and DP-16QAM used by the carriers in range. (e) Constellation diagrams of soliton coherent communication obtained at carrier wavelengths of 1532, 1548.8, 1549.6, and 1562.4 nm at a received power of −14  dBm.

Fig. 5. (a) Measured bit error ratios of the transmitted channels for each channel at the maximum transmission rate with a received power of −14  dBm. The red dashed line indicates the soft decision forward error correction (SD-FEC) BER threshold with an overhead of 20%. (b) Measured single-wave maximum rate versus OFC OSNR.