Fig. 1. Cross-sectional view of a p-i-n photodiode integrated with nonperiodic subwavelength gratings.

Fig. 2. Optical microscope pictures of the fabricated nonperiodic S-SWGs and nonperiodic CC-SWGs. The groove width at various locations is shown in scanning electron microscope (SEM) images in the insets.

Fig. 3. Power distribution at the reflection focal plane of the fabricated gratings when the TM-polarized wave is incident.

Fig. 4. Relationship between the input power and the output photocurrent.

Fig. 5. Measured response spectra of different devices, when the reverse bias is 3 V and the input power is 1.46 mW. The black lines correspond to the original PD that is not integrated with a reflector. The red curves and the blue curves represent the PD integrated with S-SWGs and CC-SWGs, respectively.

Fig. 6. Relative frequency response of the PDs.

Fig. 7. Relationship between the efficiency-bandwidth product and the input power for different devices.