Low-loss optical interposer with recessed vertical-cavity surface-emitting laser diode and photodiode chips into Si substrate

A new interposer with an optical interconnection called optical interposer has been proposed for a high-performance parallel processor system. The optical interposer is composed of polynorbornene (PNB) optical waveguides with 45° micromirrors and a Si substrate having chip-sized through-Si holes of 150 μm depth. The polymeric waveguides are formed on the Si substrate before forming the through-Si holes by deep reactive ion etching (DRIE). Vertical-cavity surface-emitting laser diode (VCSEL) and photodiode (PD) chips are placed onto the photolithographically defined hole patterns that are 15 μm larger than the size of the chips. In addition, the chips can be precisely aligned and recessed into the holes by passive alignment of self-assembly driven by the surface tension of a lead-free solder. We can fabricate the low-loss optical interposer with an insertion loss of below 0.2 dB measured at the waveguide length of 5 cm and a coupling loss of 0.5 dB measured with a 45° micromirror.