Reclaiming Light Dropped During Optical Modulation to Bias Avalanche Photodetectors

Abstract

The introduction of avalanche photodetectors in optical interconnects can extend the unallocated optical budget while unleashing further opportunities to migrate to novel datacenter network architectures. The required high-voltage rail that biases the photodiodes would involve a specialized electronic circuitry but will be instead harvested directly at the optical layer, taking advantage of the dropped power during optical modulation at local transmitters. Rather than dumping light resulting from extinct space bits, we will collect this contribution and convert it to a high-voltage bias by means of a photovoltaic power conversion circuit that is shared among and powered from all constituent data lanes of the optical interconnect. We will experimentally demonstrate that this energy reclamation circuit can sustain the sourced current during avalanche photodetection whilst maintaining a bias rail at ~25V with continuity, as will be proven for up to 64 data lanes. We demonstrate an optical budget of ~30 dB for 10 Gb/s/lane transmission, with a reception penalty as small as 0.2 dB with respect to an electrically biased photoreceiver. We will further elaborate on the limitations linked to the proposed concept, such as in terms of dynamic range.

Turning Zero-Bits of Parallel Interconnects into Optical Budget: Biasing APDs through Dumped Power

“…The feed for this circuit stems from (i) optical zero bits that manifest themselves as power being dropped at the complementary output of an interferometric (eg, micro-ring or Mach-Zehnder) modulator of the local transmitter and (ii) the backfacet of the optical laser source of the same transmitter. We then distribute this optical feed Pfeed equally to a serial stack of 2N photodiodes to generate a high no-load voltage VAPD >20V [4] with a corresponding Sourceable ω short-circuit current given by ISC = RPIN Pfeed / L, where RPIN is the (worst) responsivity of the PIN diodes used in the stack and L is the loss of the 2N×2N distribution splitter. The latter can be space-efficiently realized using inverse design [5].…”