Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Waveguide-integrated, ultralow-energy GeSi electro-absorption modulators


Waveguide-integrated photonic modulators are crucial devices when encoding optical signals for electronic–photonic integration on silicon1,2. Silicon photonic modulators based on the free carrier plasma dispersion effect3 have undergone significant development in recent years4,5,6,7,8,9,10, reaching speeds of 40 Gbit s–1 (ref. 7). Some issues yet to be resolved include the large size and the relatively high energy consumption of silicon Mach–Zehnder interferometer modulators, and the susceptibility to fabrication errors as well as a limited operation wavelength range of 1 nm for silicon microring modulators. We demonstrate the first waveguide-integrated GeSi electro-absorption modulator on silicon with a small active device area of 30 µm2, a 10-dB extinction ratio at 1,540 nm, an operating spectrum range of 1,539–1,553 nm, ultralow energy consumption of 50 fJ per bit, and a 3-dB bandwidth of 1.2 GHz. This device offers unique advantages for use in high-performance electronic–photonic integration with complementary metal oxide semiconductor circuits.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Structure of the waveguide-integrated GeSi EA modulator.
Figure 2: Performance of the GeSi EA modulator.
Figure 3: Dynamic EO response of the device in the frequency range of 10 MHz to 10 GHz with a dynamic driving voltage (Vpp) of 3 V.


  1. 1

    Soref, R. A. The past, present and future of silicon photonics. IEEE. J. Sel. Top. Quant. Electron. 12, 1678–1687 (2006).

    ADS  Article  Google Scholar 

  2. 2

    Kimerling, L. C. et al. Electronic–photonic integrated circuits on the CMOS platform. Proc. SPIE 6125, 612502 (2006).

    Article  Google Scholar 

  3. 3

    Soref, R. A. & Bennett, B. R. Electro-optical effects in silicon. IEEE J. Quant. Electron. 23, 123–129 (1987).

    ADS  Article  Google Scholar 

  4. 4

    Liu, A. et al. A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor. Nature 427, 615–618 (2004).

    ADS  Article  Google Scholar 

  5. 5

    Xu, Q., Schmidt B., Pradhan, S. & Lipson M. Micrometre-scale silicon electro-optic modulator. Nature 435, 325–327 (2005).

    ADS  Article  Google Scholar 

  6. 6

    Liu, A. et al. High-speed optical modulation based on carrier depletion in a silicon waveguide. Opt. Express 15, 660–668 (2007).

    ADS  Article  Google Scholar 

  7. 7

    Liao, L. et al. 40 Gbit/s silicon optical modulator for high speed applications. Electron. Lett. 43, 1196–1197 (2007).

    Article  Google Scholar 

  8. 8

    Green, W. M. J., Rooks, M. J., Sekaric, L. & Vlasov, Y. A. Ultra-compact, low RF power, 10 Gb/s silicon Mach–Zehnder modulator. Opt. Express 15, 17106–17113 (2007).

    ADS  Article  Google Scholar 

  9. 9

    Xu, Q., Manipatruni, S., Schmidt, B., Shakya, J. & Lipson, M. 12.5 Gbit/s carrier-injection-based silicon microring silicon modulators. Opt. Express 15, 430–436 (2007).

    ADS  Article  Google Scholar 

  10. 10

    Manipatruni, S., Xu, Q. & Lipson, M. PINIP based high-speed high-extinction ratio micron-size silicon electro-optic modulator. Opt. Express 15, 13035–13042 (2007).

    ADS  Article  Google Scholar 

  11. 11

    Lampin, J. F., Desplanque, L. & Mollot, F. Detection of picosecond electrical pulses using the intrinsic Franz–Keldysh effect. Appl. Phys. Lett. 78, 4103–4105 (2001).

    ADS  Article  Google Scholar 

  12. 12

    Jongthanmmanurak, S. et al. Large electro-optic effect in tensile strained Ge-on-Si films. Appl. Phys. Lett. 89, 161115 (2006).

    ADS  Article  Google Scholar 

  13. 13

    Kuo, Y. H. et al. Strong quantum-confined Stark effect in germanium quantum-well structures on silicon. Nature 437, 1334–1336 (2005).

    ADS  Article  Google Scholar 

  14. 14

    Kuo, Y. H. et al. Quantum-confined stark effect in Ge/SiGe quantum wells on Si for optical modulators. IEEE J. Sel. Top. Quant. Electron. 12, 1503–1513 (2006).

    ADS  Article  Google Scholar 

  15. 15

    Roth, J. E. et al. Optical modulator on silicon employing germanium quantum wells. Opt. Express 15, 5851–5859 (2007).

    ADS  Article  Google Scholar 

  16. 16

    Liu, J. F. et al. Design of monolithically integrated GeSi electro-absorption modulators and photodetectors on an SOI platform. Opt. Express 15, 623–628 (2007).

    ADS  Article  Google Scholar 

  17. 17

    Liu, J. F. et al. Waveguide-integrated Ge p-i-n photodetectors on Si. 3rd IEEE International Conference on Group IV Photonics (IEEE cat. no. 06EX1276C), Ottawa, ON, Canada, 13–15 September 2006, 173–175.

  18. 18

    Beals, M. et al. Process flow innovations for photonic device integration in CMOS. Proc. SPIE 6898, 689804 (2008).

    Article  Google Scholar 

  19. 19

    Frova, A. & Handler, P. Franz–Keldysh effect in the space-charge region of a germanium p-n junction. Phys. Rev. 137, A1857–A1861 (1965).

    ADS  Article  Google Scholar 

  20. 20

    Dash, W. C. & Newman, R. Intrinsic optical absorption in single-crystal germanium and silicon at 77 K and 300 K. Phys. Rev. 99, 1151–1155 (1955).

    ADS  Article  Google Scholar 

  21. 21

    Madelung, O. (ed.) Physics of group IV elements and III–V compounds, in Numerical Data and Functional Relationships in Science and Technology vol. 17a, 88 (Springer, Berlin, 1982).

    Google Scholar 

  22. 22

    Chin, M. K. & Chang, W. S. C. Theoretical design optimization of multiple-quantum-well electroabsorption waveguide modulators. IEEE J. Quant. Electron. 29, 2476–2488 (1993).

    ADS  Article  Google Scholar 

  23. 23

    Chou, H. F. & Bowers, J. E. High-speed OTDM and WDM networks using traveling-wave electroabsorption modulators. IEEE. J. Sel. Top. Quant. Electron. 13, 58–69 (2007).

    ADS  Article  Google Scholar 

  24. 24

    Liu, B. et al. Analog characterization of low-voltage MQW traveling-wave electroabsorption modulators. J. Lightwave Technol. 21, 3011–3019 (2003).

    ADS  Article  Google Scholar 

  25. 25

    Loi, K. K., Hodiak, J. H., Mei, X. B., Tu, C. W. & Chang, W. S. C. Linearization of 1.3-µm MQW electroabsorption modulators using an all-optical frequency-insensitive technique. IEEE Photon. Technol. Lett. 10, 964–966 (1998).

    ADS  Article  Google Scholar 

  26. 26

    Chou, H. F. & Bowers, J. E. Simplified optoelectronic 3R regenerator using nonlinear electro-optical transformation in an electroabsorption modulator. Opt. Express 13, 2742–2746 (2005).

    ADS  Article  Google Scholar 

Download references


This research was sponsored under the Defense Advanced Research Projects Agency's (DARPA) EPIC program supervised by J. Shah in the Microsystems Technology Office (MTO) under contract no. HR0011-05-C-0027. The authors would like to thank K. Wada and D. Pan for their early contributions to this work, and D. Gill from Alcatel-Lucent Bell Laboratories and S. Akiyama from Fujitsu Laboratories for helpful discussions.

Author information



Corresponding author

Correspondence to Jifeng Liu.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Liu, J., Beals, M., Pomerene, A. et al. Waveguide-integrated, ultralow-energy GeSi electro-absorption modulators. Nature Photon 2, 433–437 (2008).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing