Vertical Junction Silicon Microdisk Modulators at 25Gb/s

  • Authors: E. Timurdogan, C. M. Sorace-Agaskar, A. Biberman, M. R. Watts
  • Sponsorship: DARPA, NSF GRFP

High-performance computing systems require high bandwidth, low power, and scalable optical interconnects to maintain balanced communications in future exascale machines. Low-power, low-voltage, high-speed, and compact CMOS-compatible silicon electro-optic modulators are key enablers for next generation optical interconnects. Silicon modulators based on the free-carrier effect in silicon achieve high-speed modulation by injecting or depleting charge, inducing a frequency shift in a Mach-Zehnder interferometer or resonant device that translates the resultant frequency shift into an amplitude response. Resonant modulators confine light in compact high-Q devices, enhancing the interaction of the light with the change in charge distribution. Compact resonant devices also minimize the device capacitance, enabling high-speed and low power modulators. In previous record-setting demonstrations, vertical p-n junction devices have achieved error-free modulation up to 12.5Gb/s with only a 1V drive and while consuming only 3fJ/bit[1].

In our work[2], we experimentally demonstrate the first vertical junction silicon microdisk modulator (Figure 1a-b) to achieve open eye-diagrams at a data rate of 25Gb/s (Figure 1d) and error-free operation up to 20Gb/s. A circular overlapping p+ and n+ doping profile within circularly contacted microdisk modulators (Figure 1a-b) reduce the device resistance and enable high-speed operation while maintaining a hard outer wall for maximizing the optical confinement. Frequency shifts and spectral response is shown in Figure 1c. The device represents the smallest silicon modulator to run at 25Gb/s and achieves the lowest reported power penalty compared to a commercial LiNbO3 modulator [2], important for the overall power budget in a microphotonic link.

Figure 1: a) Top-view of the 6-µm-diameter microdisk modulator, which utilizes circular inner contacts. b) 2D cross-section showing the doping profile with p-n vertical junction, p+and n+ overlapping regions. c) Spectral response of the microdisk modulator with respect to voltage dropped and current passing through the microdisk modulator. d) High-speed measured optical eye diagrams at 10-, 15-, 20-, and 25-Gb/s data rates of the microdisk modulator, driven by AC coupled 1.2Vpp. The eye diagrams are shown with the true zero (gray line) at each data rate.

Figure 1: a) Top-view of the 6-µm-diameter microdisk modulator, which utilizes circular inner contacts. b) 2D cross-section showing the doping profile with p-n vertical junction, p+and n+ overlapping regions. c) Spectral response of the microdisk modulator with respect to voltage dropped and current passing through the microdisk modulator. d) High-speed measured optical eye diagrams at 10-, 15-, 20-, and 25-Gb/s data rates of the microdisk modulator, driven by AC coupled 1.2Vpp. The eye diagrams are shown with the true zero (gray line) at each data rate.

  1. M. R. Watts, W. A. Zortman, D. C. Trotter, R. W. Young, and A. L. Lentine, “Vertical junction silicon microdisk modulators and switches,” Opt. Exp., vol. 19, no. 22, pp. 21989–22003 2011. [↩]
  2. E. Timurdogan, C. M. Sorace-Agaskar, A. Biberman, and M. R. Watts, “Vertical Junction Silicon Microdisk Modulators at 25Gb/s,” in Proc. OFC/NFOEC, paper OTh3H.2 2013. [↩]

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