With the unabated exponential growth of data traffic and global cloud service, the need for high performance computers with higher processing speed is significantly increased. However, traditional complementary metal oxide semiconductor (CMOS) microprocessors have to face the bottleneck in processing speed, design complexity, power consumption and heat dissipation. An alternative technological solution is to implement high-speed arithmetic operations in the optical domain. Optical nonlinearities are potentially well suited to perform optical signal processing. Graphene has been suggested as a material that might have large χ(3) nonlinearities which have been used to the domain of all optical signal processing. Meanwhile, silicon photonics is now the most active discipline within the field of integrated optics.

Jian Wang’s group at Wuhan National Laboratory for Optoelectronics (WNLO), Multi-Dimensional Photonics Laboratory (MDPL), has been devoted to the research of graphene-based optical nonlinear device/silicon waveguide/ silicon Mach–Zehnder modulator and achieved a series of progress:

  (1)PhD candidate Yun Long from Jian Wang’s group propose and demonstrate on-chip all-optical wavelength conversion and regeneration of 10 Gbit/s PAM-4 signal by exploiting         degenerate four-wave mixing (FWM) in a silicon waveguide. This work was published on Optics Express (vol. 24, no. 7, pp. 7158-7167, 2016).

  (2)PhD candidate Yun Long from Jian Wang’s group proposed and demonstrate a simple yet effective scheme to obtain frequency-multiplicated microwave signals or amplitude coded microwave signals based on a single integrated silicon MZM.  In proof-of-concept experiments, 2-GHz frequency-doubled microwave signal is generated using a 1-GHz driving signal. 750-MHz/1-GHz frequency-tripled/quadrupled microwave signals are obtained with a driving signal of 250 MHz. Moreover, a 50-Mb/s binary amplitude coded 1-GHz microwave signal is also successfully generated in the experiment. This work was published on Scientific Reports (6:20215, 2016).

  (3)PhD candidate Xiao Hu from Jian Wang’s group have presented an innovative scheme to achieve degenerate/non-degenerate FWM based wavelength conversion of a 5 Gbaud Nyquist 16-QAM signal. This work “Phase conjugated and transparent wavelength conversions of Nyquist16-QAM signals employing a single-layer graphene coated fiber device,” has been published on the Scientific Reports 6, 22379 (2016).

  (4)PhD candidate Xiao Hu from Jian Wang’s group have proposed and demonstrated an innovative scheme to demonstrate up and down wavelength conversion of a 10-Gbaud quadrature phase-shift keying (QPSK) signal by exploiting degenerate four-wave mixing (FWM) progress in the fabricated graphene silicon microring resonator. This work “Graphene-silicon microring resonator enhanced all-optical up and down wavelength conversion of QPSK signal,” has been published on the Optics Express 24(7), 7168-7177 (2016).

Fig. 1.  Concept and principle of all-optical wavelength conversion and signal regeneration of PAM-4 signal in a silicon waveguide. Case 1: traditional wavelength conversion; Case 2: signal regeneration.

Fig. 2. Waveforms of (a) the original 50-Mb/s baseband signal with a pattern of “110100101101001011”, ( b) original 1-GHz microwave carrier signal, and ( c) the output microwave ASK signal. 

Fig.3(a) Measured BER versus received OSNR for degenerate FWM wavelength conversion of Nyquist16-QAM signal. (b) Measured BER versus received OSNR for non-degenerate FWM wavelength conversion of Nyquist 16-QAM signal. Insets show constellations of the B-to-B signals and newly converted idlers.

Fig.4 Measured degenerate FWM spectra for (a) up and (b) down wavelength conversion.

These works are supported by the National Natural Science Foundation of China (NSFC) under grant 61222502,11574001,11274131, and 61077051, the Program for New Century Excellent Talents in University (NCET-11-0182), the Wuhan Science and Technology Plan Project under grant 2014070404010201, the Fundamental Research Funds for the Central Universities (HUST) under grants 2012YQ008 and 2013ZZGH003, and the seed project of Wuhan National Laboratory for Optoelectronics (WNLO).

Links of the published papers:

  (5)Yun Long, Andong Wang, Linjie Zhou, and Jian Wang*, “All-optical wavelength conversion and signal regeneration of PAM-4 signal using a silicon waveguide,” Optics Express 24(7), 7158-7167 (2016).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-7-7158

  (6)Yun Long, Linjie Zhou, and Jian Wang*, “Photonic-assisted microwave signal multiplication and modulation using a silicon Mach-Zehnder modulator,” Scientific Reports 6, 20215 (2016).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4735760/

  (7)Xiao Hu, Mengqi Zeng, Yun Long, Jun Liu, Yixiao Zhu, Kaiheng Zou, Fan Zhang, Lei Fu, and Jian Wang*, “Phase conjugated and transparent wavelength conversions of Nyquist 16-QAM signals employing a single-layer graphene coated fiber device,” Scientific Reports 6, 22379 (2016).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4773766/

  (8)Xiao Hu, Yun Long, Mengxi Ji, Andong Wang, Long Zhu, Zhengsen Ruan, Yi Wang, and Jian Wang*, “Graphene-silicon microring resonator enhanced all-optical up and down wavelength conversion of QPSK signal,” Optics Express 24(7), 7168-7177 (2016).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-7-7168