Mechanically Flexible Chip-to-Substrate Optical Interconnections Using Optical Pillars

Power delivery, signaling and cooling for 2D and 3D integrated systems

“…Even with perfect alignment during assembly, any lateral misalignment between the mirror and the detector due to either CTE mismatch or other factors may reduce the coupling efficiency and limit the achievable bandwidth. When 30x150 µm pins (optical aperture 30 µm in diameter) were tested, the coupling efficiency improved by 3 to 4.5 dB [33]. This improvement in the optical coupling efficiency is larger than the measured improve-ment from the 50x150 µm pin.…”

“…At distances of ±25 µm away from the center, the optical coupling improvement due to the pin exceeds 4 dB. The 4 dB coupling improvement is significantly larger than the 0.23 dB excess loss of the pins [33,34], which clearly demonstrates the benefits of the pins. Note that the profile of the relative intensity curve of the optical pin is almost flat across the entire endface of the pin and abruptly drops beyond the edges of the pin (X=±25 µm).…”

“…The use of flexible surface-normal optical waveguides, or optical pins, have been proposed as a means of addressing the shortcomings of free-space optical I/O interconnections [33]. The height separation between the chip and the substrate has minimal effect on the optical power received at the photodetector (except for losses through the polymer pin) because the light is tightly confined within the crosssectional area of the pin.…”

“…The height separation between the chip and the substrate has minimal effect on the optical power received at the photodetector (except for losses through the polymer pin) because the light is tightly confined within the crosssectional area of the pin. Although we consider using polymeric materials with relatively high optical absorption losses for the fabrication of the optical pins, due to their very short length (height), the optical transmission losses through the pins are small [33,34]. The optical pins are designed to be mechanically compliant (flexible).…”

“…The top of Figure 2.17 demonstrates that for a given loss budget of, e.g., 1 dB, the 50x150 µm flexible pins double the displacement tolerance from less than 15 µm to approximately 30 µm. The 4 dB pin-assisted loss reduction at the 30 µm displacement can decrease the BER by few orders of magnitude [33,34]. Thus, the optical pins provide a method of reducing optical coupling losses caused by thermomechanically induced misalignment between the CTE mismatched chip and substrate.…”