High speed analog-to-digital conversion with silicon photonics

Abstract

Sampling rates of high-performance electronic analog-to-digital converters (ADC) are fundamentally limited by the timing jitter of the electronic clock. This limit is overcome in photonic ADC's by taking advantage of the ultra-low timing jitter of femtosecond lasers. We have developed designs and strategies for a photonic ADC that is capable of 40 GSa/s at a resolution of 8 bits. This system requires a femtosecond laser with a repetition rate of 2 GHz and timing jitter less than 20 fs. In addition to a femtosecond laser this system calls for the integration of a number of photonic components including: a broadband modulator, optical filter banks, and photodetectors. Using silicon-on-insulator (SOI) as the platform we have fabricated these individual components. The silicon optical modulator is based on a MachZehnder interferometer architecture and achieves a V π L of 2 Vcm. The filter banks comprise 40 second-order microring-resonator filters with a channel spacing of 80 GHz. For the photodetectors we are exploring ion-bombarded silicon waveguide detectors and germanium films epitaxially grown on silicon utilizing a process that minimizes the defect density.

Integrated Photonic Magic-T (with Twice the Magic)

“…The optical magic T device proposed could be used in coherent receivers to provide even splitting and mixing of the signal and local oscillator. We propose as additional applications its use as the output section of a broadband Mach-Zehnder amplitude modulator to provide dual outputs with high extinction ratio for photonic analog-to-digital converter applications [10] and as an alternative approach to polarization diversity, where circular/diagonal polarizations are split by the magic T, rather than vertical/horizontal. Fig.…”

Characterization of SiGe-detector arrays for visible-NIR imaging sensor applications

“…In previous studies, diodes have been made by selectively growing Ge in oxide windows on a Si substrate [8,9,10,11]. The selective-area growth serves to reduce the threading dislocations arising from the lattice mismatch between the Si and Ge, yielding a higher quality Ge film and a lower leakage current.…”

A 16-fs aperture-jitter photonic ADC: 7.0 ENOB at 40 GHz

“…The equivalent aperture jitter of our ADC is 16 fs, which is to the best of our knowledge one order of magnitude better than any electronic RF (GHz frequencies) A/D converter previously reported. Figure 1(a) shows the overall schematic of the ADC system based on optical sampling and wavelength demultiplexing [6][8] [9]. In summary, the output of a mode locked laser is sliced into multiple wavelengths channels, which are delayed by different amounts of time and then multiplexed together.…”