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Photo: Heinz Nixdorf Institut

Ultra-Wideband Photonically Assisted Analog-to-Digital Converters (PACE)

Electronic data conversion has witnessed significant progress over the last decade. Data converters based on the silicon platform operating at sampling rates of tens of GSa/s now exist. While electronic data converters are now running at unprecedented sampling rates, their effective resolution as defined by the effective number of bits (ENOB) and analog bandwidth, has not improved commensurately. A major factor limiting the progress towards higher bandwidth and resolution is aperture jitter, i.e. the inability of ADCs to sample at precisely defined times, which critically limits the analog-bandwidth-resolution-product (ABRP). The best electronic ADCs operate at equivalent aperture jitter levels of around 60fs. Further reduction becomes increasingly difficult, and is limited by the jitter of electronic clocks. Extrapolating past progress, an order of magnitude improvement will take a decade. On the other hand, ultra-stable mode-locked laser (MLL) sources feature jitter levels down to the single attosecond level. Used for sampling, they could improve ADC performance by 5 orders of magnitude. While other limitations may play a role, too, significant progress is expected from substantially lower jitter levels. The potential of the photonic approach has already been demonstrated by sampling a 41 GHz signal with a record 7 ENOB with a discrete-component photonic ADC. This performance is equivalent to a significantly improved 15fs jitter. However, a practical photonic ADC must be integrated, which can be realized using rapidly developing silicon photonics technology. Moreover, suitable MLLs should also fit into compact form factors. We propose to investigate and demonstrate photonically assisted ultra-wideband ADCs with architectures that can be integrated in silicon photonics platforms and show an improvement in ABRP by a factor of 25 over today’s electronic samplers. This would constitute revolutionary progress made possible by the ultralow jitter, large bandwidth, and the possibility of massive spectral parallelization at optical frequencies. Specifically, we aim in a joint effort to demonstrate samplers with an analog bandwidth of 500GHz at an ENOB of 5, as well as 100GHz analog bandwidth at an ENOB of 8. We will further investigate individual subsystem integration (e.g. ultralow jitter integrated MLLs, coherent optical signal analyzer subsystems with optical processing co-integrated with electronics). In particular, we will explore compact, ultralow jitter, integrated MLLs using semiconductor and rare-earth doped glass gain materials, as well as frequency comb stabilization with help of microresonator induced feedback. Further, we will investigate different ADC architectures based on optically frequency-interleaved and optically time-interleaved analog-to-digital conversion, and photonic-electronic sampling. Architectures and comb source capabilities will be harmonized in view of converging towards a complete range of subsystem capabilities.

Professor Dr.-Ing. Christian Koos
Karlsruher Institute of Technology (KIT)
Institute of Photinics and Quantum Electronics (IPQ)

Professor Dr.-Ing. Franz Xaver Kärtner
Universitaet Hamburg
Department of Physics
Institute of Experimental Physics

Professor Dr.-Ing. Christoph Scheytt
Paderborn University
Heinz Nixdorf Institute
Research Group System and Circuit Technology

Professor Dr. Jeremy Witzens, Ph.D.
RWTH Aachen University
Faculty of Electrical Engineering and Information Technology
Institute of Integrated Photonics (IHP)