Energy Efficiency Bounds for Photonic Analog to Digital Converters

Many efforts have examined the prospect of photonic based analog to digital converters (ADCs) and shown that they can substantially outperform their electronic counterparts in terms of speed and resolution. In this paper we analyse the power consumption of photonic ADCs, which has not been meaningfully examined in previous literature yet is a critical figure of merit for analog to digital conversion. Firstly, we show that in a quantum noise limited regime photonic based converters cannot exceed the efficiency of conventional electronic designs in any reasonable operating environment. However, we further show that the exceptional performance of photonic ADCs at high frequencies may allow them to outperform high sampling rate electronic ADCs on a Schreier figure of merit basis, whose performance is limited by technological constraints such as clock jitter and the switching speed of the integrated circuit technology

Clock Synchronized Transmission of 51.2GBd Optical Packets for Optically Switched Data Center Interconnects

Optical switching has attracted significant attention in recent research on data center networks (DCNs) as it is a promising viable route for the further scaling of hyper scale data centers, so that DCNs can keep pace with the rapid growth of machine-to-machine traffic. It has been shown that optical clock synchronization enables sub-nanosecond clock and data recovery time and is crucial to high performance optically switched DCN. Moreover, the interconnect data rate is expected to increase from the current 100 Gb/s per fiber to scale to 800 Gb/s and beyond, requiring high baud rate signaling at >50 GBd. Thus, future optically switched DCN should support >50GBd data transmission with optical clock synchronization. Here, we demonstrate the clock- synchronized transmission of 128-byte optical packets at 51.2 GBd and study the impact of reference clock phase noise on system performance, focusing on the tolerance to the clock phase misalignment that affects the system scalability and reliability. By comparing the tolerable sampling clock phase offsets using different reference clocks, we show that a clock phase offset window of about 8ps could be achieved with a <0.2ps source clock. Furthermore, we model and numerically study the de- correlation of clock phase noise. This allows the total jitter to be estimated, and thereby, the estimation of the transmission performance for future generations of high baud rate, clock synchronized DC interconnects

Communications with guaranteed bandwidth and low latency using frequency-referenced multiplexing

Emerging cloud applications such as virtual reality and connected car fleets demand guaranteed connections, as well as low and stable latency, to edge data centres. Currently, user–cloud communications rely on time-scheduled data frames through tree-topology fibre networks, which are incapable of providing guaranteed connections with low or stable latency and cannot be scaled to a larger number of users. Here we show that a frequency-referenced multiplexing method can provide guaranteed bandwidth and low latency for time-critical applications. We use clock and optical frequency synchronization, enabled by frequency comb and signal processing techniques, to provide each user with dedicated optical bandwidth, creating scalable user–cloud upstream communications. As a proof of concept, we demonstrate a frequency-division multiplexing system servicing up to 64 users with an aggregate bandwidth of 160 GHz, exhibiting a data rate of up to 4.3 Gbps per user (240.0 Gbps aggregated capacity considering a 200 GHz wavelength band) with a high receiver sensitivity of –35 dBm

All-fibre heterogeneously-integrated frequency comb generation using silicon core fibre

Originally developed for metrology, optical frequency combs are becoming increasingly pervasive in a wider range of research topics including optical communications, spectroscopy, and radio or microwave signal processing. However, application demands in these fields can be more challenging as they require compact sources with a high tolerance to temperature variations that are capable of delivering flat comb spectra, high power per tone, narrow linewidth and high optical signal-to-noise ratio. This work reports the generation of a flat, high power frequency comb in the telecom band using a 17 mm fully-integrated silicon core fibre as a parametric mixer. Our all-fibre, cavity-free source combines the material benefits of planar waveguide structures with the advantageous properties of fibre platforms to achieve a 30 nm bandwidth comb source containing 143 tones with 30 dB OSNR over the entire spectral region

All-fibre heterogeneously-integrated frequency comb generation using silicon core fibre.

Originally developed for metrology, optical frequency combs are becoming increasingly pervasive in a wider range of research topics including optical communications, spectroscopy, and radio or microwave signal processing. However, application demands in these fields can be more challenging as they require compact sources with a high tolerance to temperature variations that are capable of delivering flat comb spectra, high power per tone, narrow linewidth and high optical signal-to-noise ratio. This work reports the generation of a flat, high power frequency comb in the telecom band using a 17 mm fully-integrated silicon core fibre as a parametric mixer. Our all-fibre, cavity-free source combines the material benefits of planar waveguide structures with the advantageous properties of fibre platforms to achieve a 30 nm bandwidth comb source containing 143 tones with 30 dB OSNR over the entire spectral region

Dual optical frequency comb analog to digital conversion

Analog to digital converters (ADCs) are the fundamental technology that allows the capture and analysis of signals across all scientific and engineering disciplines and underpin the digital links that connect our analog world. Modern communications systems demand high bandwidth, high resolution ADC in order to detect higher order modulation formats at high baud rates and maximise the spectral efficiency of the channel. However, the resolution of high speed (i.e. 1 GHz) electronic ADCs is typically limited by clock jitter and, at especially high frequencies, the speed of the component transistors that results in comparator ambiguity. This presents a trade-off between the frequency of the detected signal and accuracy, defined by the SINAD or ENOB. In a jitter limited ADC, the SINAD decreases quadratically with increasing frequency, giving a 6 dB SINAD penalty for every doubling of the input frequency. This thesis proposes a frequency interleaving photonic front end for analog to digital converters, based on dual optical frequency combs, in order to meet this challenge of high speed, high resolution signal digitisation. Firstly, the dual frequency comb technique is described and modelled, both analytically and through simulations, to establish the potential performance of the dual comb approach in analog to digital conversion and other radio frequency signal processing applications. Secondly, a dual frequency comb prototype is experimentally demonstrated based on phase coherent electro-optic combs. The phase noise characteristics of the architecture are established and the prototype is evaluated using the IEEE ADC testing standard, outperforming any reported electronic ADC. Finally, arbitrary signal detection using the dual comb technique is demonstrated using a novel phase locking approach that efficiently utilises the comb bandwidth, and the impact of possible implementation errors is investigated

Frequency interleaving dual comb photonic ADC with 7 bits ENOB up to 40 GHz

We demonstrate a record high performance of frequency-interleaved analog-to-digital conversion using a phase-noise-engineered dual frequency comb photonic technique, enabling 7 effective number of bits (ENOB) for signals up to 40 GHz

Research data supporting "Encapsulation of methylammonium lead bromide perovskite in nanoporous GaN"

Supporting data for the article titled "Encapsulation of methylammonium lead bromide perovskite in nanoporous GaN". The article was accepted for publication in 2019 in the journal "APL Materials". Supplementary material is available from the publisher (AIP). The data files provided are named according to the specific figures in the article in which they are used. Data for Figure 3: Scanning transmission electron microscopy and energy dispersive X-ray spectroscopy (STEM-EDX) data (.ser) and metadata (.emi), as well as elemental maps of the spatial distribution of Ga, Pb, Br in a perovskite/porous GaN composite (2D arrays of the peak intensity of the respective K-alpha lines extracted from the EDX spectra at each point, in CSV format). Data for Figures 4 and 5: Photoluminescence (PL) emission spectra of perovskite samples presented in a two-column CSV format with one header row. Data for Figure S1: EDX spectra of a perovskite/porous GaN composite measured on a pore and between pores, presented in a two-column CSV format with one header row.This work was supported by funding from EPSRC Grant Nos. EP/L015978/1 (Cambridge NanoDTC), EP/L015455/1 (IPES CDT), and EP/M010589/1, funding from Trinity College, Cambridge (Krishnan-Ang Studentship), and funding from the Royal Society (Grant No. UF130278)