Photonic ADC: overcoming the bottleneck of electronic jitter

Abstract

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels. This work demonstrates that the photonic approach can deliver on its promise by digitizing a 41 GHz signal with 7.0 effective bits using a photonic ADC built from discrete components. This accuracy corresponds to a timing jitter of 15 fs -a 4-5 times improvement over the performance of the best electronic ADCs which exist today. On the way towards an integrated photonic ADC, a silicon photonic chip with core photonic components was fabricated and used to digitize a 10 GHz signal with 3.5 effective bits. In these experiments, two wavelength channels were implemented, providing the overall sampling rate of 2.1 GSa/s. To show that photonic ADCs with larger channel counts are possible, a dual 20-channel silicon filter bank has been demonstrated. 289-296 (1992). 11. J. Kim, J. Chen, J. Cox, and F. X. Kärtner, "Attosecond-resolution timing jitter characterization of free-running mode-locked lasers using balanced optical cross-correlation," Opt. Lett. microwave signals at 40-GHz with higher than 7-ENOB resolution," Opt. ©2012 Optical Society of America

On-Chip Strong Coupling and Efficient Frequency Conversion between Telecom and Visible Optical Modes

“…At the triply resonant condition, the three modes' frequencies approximately fulfill the energy conservation requirement ωa0 + ωc0 = ω b0 . c, Coupled resonator model for the coherent interaction in a χ (2) microring resonator. Here we use two resonators to depict resonant modes supported at two different wavelengths.…”

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Developments in photonic chips have spurred photon based classical and quantum information processing, attributing to the high stability and scalability of integrated photonic devices [1,2]. Optical nonlinearity [3] is indispensable in these complex photonic circuits, because it allows for classical and quantum light sources, all-optical switch, modulation, and non-reciprocity in ambient environments.

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“…However, the manifestations of coherent photon-photon interaction in a cavity, analogous to the electromagnetically induced transparency [5], have never been reported on an integrated platform. Here, we present an experimental demonstration of the coherent photon-photon interaction induced by second order optical nonlinearity (χ (2) ) on an aluminum nitride photonic chip. The non-reciprocal nonlinear optic induced transparency is demonstrated as a result of the coherent interference between photons with different colors: ones in the visible wavelength band and ones in the telecom wavelength band.…”

“…Second order optical nonlinearity (χ (2) ) is one of the most widely explored properties in photonics, utilizing various nonlinear materials [8][9][10][11][12][13]. χ (2) nonlinearity enables the coupling between photons with very different colors, acting as the basis for many important applications such as second harmonic generation, spontaneous parametric down conversion, optical parametric amplification and oscillation. Due to the high quality factor to mode volume ratio, the nonlinear interaction strength is expected to be boosted in optical cavities.…”

“…Preliminary results in millimeter sized optical resonators have already shown such trend, where efficient second harmonic generation [14,15] and sum frequency generation [16] are demonstrated. However, the realized nonlinear interaction strength on an integrated platform is normally weak, hindered by the challenges of fabricating small size, low loss optical circuits with materials featuring high χ (2) nonlinearity.…”