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  • Received: May. 28, 2019

    Accepted: Aug. 26, 2019

    Posted: Sep. 29, 2019

    Published Online: Sep. 29, 2019

    The Author Email: Zhe Kang (, Sai Tak Chu (

    DOI: 10.1364/PRJ.7.001200

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    Yuhua Li, Kun Zhu, Zhe Kang, Wai Lok Ho, Roy Davidson, Chao Lu, Brent E. Little, Sai Tak Chu. CMOS-compatible high-index doped silica waveguide with an embedded silicon-nanocrystal strip for all-optical analog-to-digital conversion[J]. Photonics Research, 2019, 7(10): 10001200

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Photonics Research, Vol. 7, Issue 10, 10001200 (2019)

CMOS-compatible high-index doped silica waveguide with an embedded silicon-nanocrystal strip for all-optical analog-to-digital conversion 

Yuhua Li1,†, Kun Zhu2,†, Zhe Kang2,5,*, Wai Lok Ho1, Roy Davidson3, Chao Lu2, Brent E. Little4, and Sai Tak Chu1,6,*

Author Affiliations

  • 1Department of Physics, City University of Hong Kong, Hong Kong, China
  • 2Photonics Research Centre, Department of Electronic and Information Engineering, The Hong Kong Polytechnic University, Hong Kong, China
  • 3QXP Technology Inc., Xi’an 710119, China
  • 4State Key Laboratory of Transient Optics and Photonics, XIOPM, CAS, Xi’an 710119, China
  • 5e-mail:
  • 6e-mail:


Passive all-optical signal processors that overcome the electronic bottleneck can potentially be the enabling components for the next-generation high-speed and lower power consumption systems. Here, we propose and experimentally demonstrate a CMOS-compatible waveguide and its application to the all-optical analog-to-digital converter (ADC) under the nonlinear spectral splitting and filtering scheme. As the key component of the proposed ADC, a 50 cm long high-index doped silica glass spiral waveguide is composed of a thin silicon-nanocrystal (Si-nc) layer embedded in the core center for enhanced nonlinearity. The device simultaneously possesses low loss (0.16 dB/cm at 1550 nm), large nonlinearity (305 W 1/km at 1550 nm), and negligible nonlinear absorption. A 2-bit ADC basic unit is achieved when pumped by the proposed waveguide structure at the telecom band and without any additional amplification. Simulation results that are consistent with the experimental ones are also demonstrated, which further confirm the feasibility of the proposed scheme for larger quantization resolution. This demonstrated approach enables a fully monolithic solution for all-optical ADC in the future, which can digitize broadband optical signals directly at low power consumption. This has great potential on the applications of high-speed optical communications, networks, and signal processing systems.