Author Affiliations
1Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China2Optics Valley Laboratory, Wuhan 430074, Chinashow less
Fig. 1. Schematic of optical frequency comb generators. (a) Typical self-starting mode-locked fiber laser; (b) On-chip optical frequency comb generation based on Kerr microresonators
Fig. 2. Schematic of an integrated electro-optic frequency comb generator
Fig. 3. Schematic of electro-optic modulators.(a) Single-phase modulator;(b) Dual-drive Mach-Zehnder modulator
Fig. 4. (a) Frequency spectrum of a single-phase modulator;(b) Frequency spectrum of a DD-MZM
Fig. 5. (a) Schematic of an microring intracavity modulator; (b) Schematic of a coupling-modulated modulator
Fig. 6. Flow chart of the smart-cut process for a LNOI wafer
[66] Fig. 7. Integrated EO comb generator and its output spectrum based on LNOI
[67]. (a) Optical micrograph of a fabricated lithium niobate microring resonator; (b) Measured output spectrum of the EO comb generated from the microring resonator, demonstrating a bandwidth exceeding 80 nm and more than 900 comb lines with a slope of 1 dB·nm
−1 Fig. 8. Schematic of mid-infrared frequency combs generator based on LNOI and their corresponding spectrums
[69]. (a) Design 1, the DFG process occurs outside the microring resonator; (b) Power spectrum of the output mid-infrared frequency comb for modulation coefficient
β=1.2π in design 1; (c) Design 2, the DFG process occurs in the microring resonator; (d) Power spectrum of the output mid-infrared frequency comb for modulation coefficient
β=0.4π in design 2
Fig. 9. Schematic of an InP integrated EO comb generator
[48]. (a) Integrated comb generator PIC schematic; (b) Optical micrograph of the fabricated PIC (Photonic integrated chip, PIC) (Footprint: 4.5 mm× 2.5 mm); (c) PIC-PCB assembly
Fig. 10. Schematic of MRM integrated EO comb
[99]. (a) Optical micrograph of a microring resonator modulator (Footprint of the MRM and electrical pads: 0.062 mm
2); (b) Schematic of waveguide cross section; (c) Generated EO frequency comb at 10 GHz line spacing for a 0.22 V forward bias voltage applied
Fig. 11. Schematic of cascaded MRM integrated EO comb
[100]. (a) Schematic of the proposed MRM; (b) Cross-section schematic of the PN junction of the microring; (c) Experimental setup; (d) Comb spectrum demonstrating 5 lines when driving MRM 1 at 20 GHz and MRM 2 at 10 GHz
Fig. 12. Schematic of cascaded MZM integrated EO comb generator
[53]. (a) Schematic of the cascaded MZMs optical frequency comb generation, the inset shows the cross-sectional view of active arms in the MZM; (b) Measured optical spectrum of the 9-line OFC; (c) Measured Nyquist pulses in the time domain; (d) Comparison of the measured single Nyquist pulse (red solid line) with the calculated theoretical pulse (black dashed line)
Fig. 13. Schematic of EOFC for WDM
[111]. (a) Illustration of the dual-drive MZM design; (b) Cross section schematic of MZM phase shifter; (c) Output spectrum of generated 5-line comb with 20 GHz spacing; (d) BER of Nyquist-WDM signals of 5×16 Gbaud 16/32 QAM and 5 × 20 Gbaud 16 QAM
Fig. 14. Schematic of MRM for WDM
[96]. (a) Schematic of a flexible-grid WDM silicon photonic transmitter based on cascaded MRMs; (b) Experimental setup for optical comb generation, data transmission, and characterization; (c) Spectrum after data transmission when MRM1 is aligned at 20 GHz comb line with channel 1 (1554 nm), channel 2 (1554.16 nm), and channel 3 (1553.84 nm)
Fig. 15. Schematic of EOFC based on LNOI for DCS
[116]. (a) Scheme of DCS with integrated EO microrings (AOFS: acousto-optic frequency shifter, BS: beam splitter, BD: balanced detector, DAU: data acquisition Unit); (b) Measured dual comb spectrum with a measurement time of 195 s; (c) Measured absorption spectra of the acetylene
Fig. 16. Schematic of EOFC based on MZM for DCS
[98]. (a) Top-view schematic of the 4-mm long Si single-drive push-pull MZM; (b) Beat notes for
fRF= 1 GHz and Δ
fRF = 4 MHz; (c) Experimentally measured transfer function of optical bandpass filter