Ultrafast Photodetection in an All-Silicon Chip Enabled by Two-Photon Absorption


This form of photodetection demonstrates high efficiency at telecommunication wavelengths. It is designed for use in integrated photonic microdevices.

Problem Addressed:

Photodetection can convert optical signals into electrical signals, which is useful for optical telecommunications. In semiconductors, photodetection involves linearly absorbing an optical signal to create an electrical response in the material. This optical absorption relies on the size of the electronic bandgap, a material specific parameter. Past photodetectors have used silicon with a large, indirect bandgap that is too large for linear absorption of the energy of photons in the telecommunication band. Though silicon photodetectors are easily manufactured with conventional CMOS processes, a new system is needed that can absorb optical energy in the correct range for telecommunication.


Si-based ultrafast photodetection provides the basis for a practical implementation of all-silicon integrated photodetectors. This system uses a Si-based microcavity and waveguide photonic crystal to receive an input optical signal. Optical energy is then absorbed by a nonlinear multi-photon absorption process such as two-photon absorption (TPA). This nonlinear process is enhanced by optical microresonators, which enable light confinement for times, orders of magnitude longer than the characteristic period of light, increasing bit-rates to up to 10Gbits/s. The silicon based structure also features electrodes that are responsive to the nonlinear multi-photon absorption process in the microcavity, and are responsible for producing an electronic signal indicative of the optical signal. Since both the microcavity and waveguide are photonic crystals made of silicon, the entire system can be manufactured with established CMOS techniques. Enhanced TPA in these silicon microcavities can yield a 15% increase in efficiency in photodetectors, paving the way for a new class of integrated photonic microdevices.


  • Easily manufactured with established fabrication techniques for silicon
  • Increased bit-rates and energy conversion efficiencies for faster processing