In this paper we propose to eliminate all data and control pads generally present in conventional chips and to replace them with a new type of ultra-compact, low power optical interconnect implemented almost entirely in CMOS. The proposed scheme enables entirely optical through-chip buses that could service hundreds of thinned stacked dies. Very high throughputs and communication density could be achieved even in tight power budgets. The core of the optical interconnect is a single-photon avalanche diode operating in pulse position modulation. We demonstrate how throughputs of several gigabits per second may be achieved. We also show a systematic analysis and trade-offs of such a system and preliminary results to support its suitability in emerging DSM technologies.