Ultrafast Broadband Research Articles

The Effect of Fibre Broadband on Student Learning

We estimate the impact of ultra-fast broadband on schools’ academic performance using a difference-in-difference study of a new fibre broadband network. We show that fibre broadband increases primary schools’ passing rates in standardised assessments by roughly one percentage point. Estimates are robust to alternative specifications, such as controlling for time-varying covariates. We find no evidence that gender, ethnic minorities or students enrolled in remote schools benefit disproportionately. However, we find some evidence of a larger benefit within schools that have a greater proportion of students from lower socio-economic backgrounds.

Multi-gigahertz, femtosecond Airy beam optical parametric oscillator pumped at 78 MHz

We report a high power ultrafast Airy beam source producing femtosecond pulses at multi-gigahertz (GHz) repetition rate (RR). Based on intra-cavity cubic phase modulation of an optical parametric oscillator (OPO) designed in high harmonic cavity configuration synchronous to a femtosecond Yb-fiber laser operating at 78 MHz, we have produced ultrafast 2D Airy beam at multi-GHz repetition rate through the fractional increment in the cavity length. While small (<1 mm) crystals are used in femtosecond OPOs to take the advantage of broad phase-matching bandwidth, here, we have exploited the extended phase-matching bandwidth of a 50-mm long Magnesium-oxide doped periodically poled LiNbO3 (MgO:PPLN) crystal for efficient generation of ultrafast Airy beam and broadband mid-IR radiation. Pumping the MgO:PPLN crystal of grating period, Λ = 30 μm and crystal temperature, T = 100 °C using a 5-W femtosecond laser centred at 1064 nm, we have produced Airy beam radiation of 684 mW in ~639 fs (transform limited) pulses at 1525 nm at a RR of ~2.5 GHz. Additionally, the source produces broadband idler radiation with maximum power of 510 mW and 94 nm bandwidth at 3548 nm in Gaussian beam profile. Using an indirect method (change in cavity length) we estimate maximum RR of the Airy beam source to be ~100 GHz.

Analyte-induced spectral filtering in femtosecond transient absorption spectroscopy

We discuss the influence of spectral filtering by samples in femtosecond transient absorption measurements. Commercial instruments for transient absorption spectroscopy (TA) have become increasingly available to scientists in recent years and TA is becoming an established technique to measure the dynamics of photoexcited systems. We show that absorption of the excitation pulse by the sample can severely alter the spectrum and consequently the temporal pulse shape. This “spectral self-filtering” effect can lead to systematic errors and misinterpretation of data, most notably in concentration dependent measurements. The combination of narrow absorption peaks in the sample with ultrafast broadband excitation pulses is especially prone to this effect.

Fixed Access Network Sharing

Deep fiber deployments for ultrafast broadband are both technically and economically challenging. Fixed access network sharing (FANS) offers a highly enhanced form of virtual unbundling of broadband access networks, enabling cost sharing and the dynamics of a competitive landscape. Data, control, and management interfaces are automated and harmonized among wholesale infrastructure providers and retail virtual network operators. Standardized FANS interfaces can greatly decrease OPEX while increasing customer satisfaction. When FANS is implemented, network slicing logically partitions and isolates network resources among the VNOs, and such sharing can split the cost of network upgrades among several entities. FANS works with virtualization, where control plane functions are migrated from dedicated network equipment into software running on commodity hardware, with FANS providing network as a service. This article describes the drivers behind FANS, several architectures supporting FANS, and emerging standards supporting FANS.

Cooperative Subunit Refolding of a Light‐Harvesting Protein through a Self‐Chaperone Mechanism

AbstractThe fold of a protein is encoded by its amino acid sequence, but how complex multimeric proteins fold and assemble into functional quaternary structures remains unclear. Here we show that two structurally different phycobiliproteins refold and reassemble in a cooperative manner from their unfolded polypeptide subunits, without biological chaperones. Refolding was confirmed by ultrafast broadband transient absorption and two‐dimensional electronic spectroscopy to probe internal chromophores as a marker of quaternary structure. Our results demonstrate a cooperative, self‐chaperone refolding mechanism, whereby the β‐subunits independently refold, thereby templating the folding of the α‐subunits, which then chaperone the assembly of the native complex, quantitatively returning all coherences. Our results indicate that subunit self‐chaperoning is a robust mechanism for heteromeric protein folding and assembly that could also be applied in self‐assembled synthetic hierarchical systems.

Cooperative Subunit Refolding of a Light-Harvesting Protein through a Self-Chaperone Mechanism.

The fold of a protein is encoded by its amino acid sequence, but how complex multimeric proteins fold and assemble into functional quaternary structures remains unclear. Here we show that two structurally different phycobiliproteins refold and reassemble in a cooperative manner from their unfolded polypeptide subunits, without biological chaperones. Refolding was confirmed by ultrafast broadband transient absorption and two-dimensional electronic spectroscopy to probe internal chromophores as a marker of quaternary structure. Our results demonstrate a cooperative, self-chaperone refolding mechanism, whereby the β-subunits independently refold, thereby templating the folding of the α-subunits, which then chaperone the assembly of the native complex, quantitatively returning all coherences. Our results indicate that subunit self-chaperoning is a robust mechanism for heteromeric protein folding and assembly that could also be applied in self-assembled synthetic hierarchical systems.

Market Evolution and Regulation in the Italian Telecommunications Industry

In this paper we analyse the evolution of the Italian telecommunications market since the beginning of the liberalisation and privatisation process in Italy started in the mid-nineties. The role of competition and regulatory authorities is also considered. We present a survey of the main regulatory interventions in the industry as well as the market structure and its dynamics in the period 2000-2015. We also provide some insights on the current state of the ultra-fast broadband access and the evolution of the so called “next generation networks”. In this regard, the recent Italian government’s plan regarding the deployment of the broadband services is also discussed. Our research can provide helpful information on telecommunications trends in Italy and would help to assess past as well as ongoing policies.

Market Evolution and Regulation in the Italian Telecommunications Industry

In this paper we analyse the evolution of the Italian telecommunications market since the beginning of the liberalisation and privatisation process in Italy started in the mid-nineties. The role of competition and regulatory authorities is also considered. We present a survey of the main regulatory interventions in the industry as well as the market structure and its dynamics in the period 2000-2015. We also provide some insights on the current state of the ultra-fast broadband access and the evolution of the so called “next generation networks”. In this regard, the recent Italian government’s plan regarding the deployment of the broadband services is also discussed. Our research can provide helpful information on telecommunications trends in Italy and would help to assess past as well as ongoing policies.

Clocking the onset of bilayer coherence in a high- Tc cuprate

In cuprates, a precursor state of superconductivity is speculated to exist above the critical temperature $\mathrm{T_C}$. Here we show via a combination of far-infrared ellipsometry and ultrafast broadband optical spectroscopy that signatures of such a state can be obtained via three independent observables in an underdoped sample of NdBa$_2$Cu$_3$O$_{6+\delta}$. The pseudogap correlations were disentangled from the response of laser-broken pairs by clocking their characteristic time-scales. The onset of a superconducting precursor state was found at a temperature $\mathrm{T_{ONS}}$ $>$ $\mathrm{T_C}$, consistent with the temperature scale identified via static optical spectroscopy. Furthermore, the temperature evolution of the coherent vibration of the Ba ion, strongly renormalized by the onset of superconductivity, revealed a pronounced anomaly at the same temperature $\mathrm{T_{ONS}}$. The microscopic nature of such a precursor state is discussed in terms of pre-formed pairs and enhanced bilayer coherence.

Go for Gigabit? First Evidence on Economic Benefits of (Ultra-)Fast Broadband Technologies in Europe

The literature on the effects of telecommunications infrastructure investments find positive macroeconomic effects, however, it is severely constrained because it could hitherto only analyze investment up to broadband but not up to the newer generations of and broadband; in particular there is no such evidence available at the EU level so far. Utilizing a comprehensive panel dataset of EU27 member states for the period from 2003-2015, we estimate a small but significant effect of fiber-based ultra-fast broadband over and above the effects of basic broadband on GDP. Adoption of hybrid-fiber fast broadband is incrementally to basic broadband insignificant. Our cost-benefit analysis implies that policy intervention – as foreseen by the European Commission in its public policy targets – is only justified for coverage and adoption levels of around 50% of fast or ultra-fast broadband, whereas for 100% coverage levels we find net losses to society. Thus, it appears that – for the time being and according to the policy principle of technological neutrality – a combination of basic broadband, fast and ultra-fast broadband entails the largest economic net benefits to society.

Ultrafast Broadband Saturable Absorption in Sb2Se3 Nanowires

Manipulating optical nonlinearity is a very fascinating prospective for both fundamental and technological purpose; offers a potential platform to explore the saturable absorption (SA) to the nanoscale limit. In this manuscript, we have focused on the tunable wavelength and pulse width dependent ultrafast broadband SA of Sb2Se3 nanowires in the resonant and the above bandgap excitations of 120 fs and 7 ns pulses. In this context, we numerically simulated the SA of Sb2Se3 nanowire with a two-level model. The solutions of the coupled rate equations for a Gaussian shaped pulse exactly reproduced the experimental results in both temporal and spatial domains. Our model provides a precise spacio-temporal analysis of carrier populations of each photo-excited state in the system. Moreover, excited state decay time (1.5 ns) and the ratio of excited state absorption cross section (σes) to the ground state absorption cross section (σgs) is less than unity for 1-D Sb2Se3 nanowires. Hence, Sb2Se3 nanowires can be employed as passive mode-lockers and essential photodetectors for ultrashort pulsed laser and can be tuned by wavelength and pulse width. These observations advise a remarkable nonlinear optical response which is expected to be comparable or even better than the graphene and 2D TMDC’s (MX2) like MoSe2, MoS2, WSe2, WS2 etc.

Picking up Speed: Does Ultrafast Broadband Increase Firm Productivity?

UFB alone is not the path to success. Organise, you must. We estimate whether there are productivity gains from ultrafast broadband (UFB) adoption and whether any gains are higher when firms undertake complementary organisational investments. Using an IV strategy based on proximity to schools (that were targeted in the UFB roll-out), we find that the average effect of UFB adoption on employment and (labour and multifactor) productivity is insignificantly different from zero, even for firms in industries where we might expect the returns to UFB to be relatively high. Conversely, we find that firms making concurrent investments in organisational capital specifically for the purpose of getting more from their ICTs appear to experience higher productivity growth, at least in first-difference specifications. Firms making these joint (UFB-organisational) investment decisions are significantly more likely to report other positive outcomes from their ICT investments, consistent with the identified relationship with productivity being causal.

Ultrafast Charge Recombination Dynamics in Ternary Electron Donor-Acceptor Complexes: (Benzene)2-Tetracyanoethylene Complexes.

The charge-transfer (CT) state relaxation dynamics of the binary (1:1) and ternary (2:1) benzene/tetracyanoethylene (BZ/TCNE) complexes are reported. Steady-state and ultrafast time-resolved broadband fluorescence (TRFL) spectra of TCNE dissolved in a series of BZ/CCl4 mixed solvents are measured to elucidate the spectroscopic properties of the BZ/TCNE complexes and their CT-state relaxation dynamics. Both steady-state and TRFL spectra exhibit marked BZ concentration dependences, which can be attributed to the formation of two types of 2:1 complexes in the ground and excited states. By combining with the density functional theory (DFT) calculations, it was concluded that the BZ concentration dependence of the absorption spectra is mainly due to the formation and excitation of the sandwich-type 2:1 ternary complexes, whereas the changes in fluorescence spectra at high BZ concentrations are due to the formation of the asymmetric-type 2:1 ternary complex CT1 state. A unified mechanism involving both direct excitation and secondary formation of the 2:1 complexes CT states are proposed to account for the observations. The equilibrium charge recombination (CR) time constant of the 1:1 CT1 state is determined to be ∼150 ps in CCl4, whereas that of the 2:1 DDA-type CT1 state becomes ∼70 ps in 10% BZ/CCl4 and ∼34 ps in pure BZ. The CR rates and the CT1-S0 energy gap of these complexes in different solvents exhibit a correlation conforming to the Marcus inverted region. It is concluded that partial charge resonance occurring between the two adjacent BZs in the asymmetric-type 2:1 CT1-state reduces the CR reaction exothermicity and increases the CR rate.

Spindle‐Type Conjugated Compounds Containing Twistacene Unit: Synthesis and Ultrafast Broadband Reverse Saturable Absorption

Spindle‐Type Conjugated Compounds Containing Twistacene Unit: Synthesis and Ultrafast Broadband Reverse Saturable Absorption

A versatile setup for ultrafast broadband optical spectroscopy of coherent collective modes in strongly correlated quantum systems.

A femtosecond pump-probe setup is described that is optimised for broadband transient reflectivity experiments on solid samples over a wide temperature range. By combining high temporal resolution and a broad detection window, this apparatus can investigate the interplay between coherent collective modes and high-energy electronic excitations, which is a distinctive characteristic of correlated electron systems. Using a single-shot readout array detector at frame rates of 10 kHz allows resolving coherent oscillations with amplitudes <10−4. We demonstrate its operation on the charge-transfer insulator La2CuO4, revealing coherent phonons with frequencies up to 13 THz and providing access into their Raman matrix elements.

Promoting Consumer Migration to New Communications Technology: Does Regulation Affect the Digital Gap?

This paper provides evidence on the migration of consumers from an “old” (copper-based) to a “new” (fiber-based) communications technology, taking specifically into account the impact of regulatory interventions imposed on the old technology. The analysis has been applied to a sample of EU25 countries using panel data from 2003 to 2014 on the adoption (i.e. the demand of subscriptions by households and firms), and take-up rate of ultra-fast broadband technology (i.e. the ratio between fiber subscribers - “homes connected” - to population covered with fiber connections - “homes passed”). Results show that an increase in the regulated price for accessing the existing old network favours consumer migration to the new technology. However, the access price to old technology negatively affects the take-up rate of the new technology. This implies that access regulation also positively affects broadband coverage but more than demand adoption. Hence, in order to raise broadband take-up rate, other instruments are needed to support ultra-fast broadband subscriptions.

Interplay of Ion-Water and Water-Water Interactions within the Hydration Shells of Nitrate and Carbonate Directly Probed with 2D IR Spectroscopy.

The long-range influence of ions in solution on the water hydrogen-bond (H-bond) network remains a topic of vigorous debate. Recent spectroscopic and theoretical studies have, for the most part, reached the consensus that weakly coordinating ions only affect water molecules in the first hydration shell. Here, we apply ultrafast broadband two-dimensional infrared (2D IR) spectroscopy to aqueous nitrate and carbonate in neat H2O to study the solvation structure and dynamics of ions on opposite ends of the Hofmeister series. By exciting both the water OH stretches and ion stretches and probing the associated cross-peaks between them, we are afforded a comprehensive view into the complex nature of ion hydration. We show in aqueous nitrate that weak ion-water H-bonding leads to water-water interactions in the ion solvation shells dominating the dynamics. In contrast, the carbonate CO stretches show significant mixing with the water OH stretches due to strong ion-water H-bonding such that the water and ion modes are intimately correlated. Further, the excitonic nature of vibrations in neat H2O, which spans multiple water molecules, is an important factor in describing ion hydration. We attribute these complex dynamics to the likely presence of intermediate-range effects influenced by waters beyond the first solvation shell.

Ultrafast broadband Fourier-transform CARS spectroscopy at 50,000 spectra/s enabled by a scanning Fourier-domain delay line

We propose and demonstrate a coherent Raman scattering (CRS) spectroscopy technique capable of acquiring 50,000 broadband Raman spectra/s. This ultrafast spectral acquisition is realized by employing a Fourier-domain delay line based on a rapidly rotating polygonal mirror array as an optical path-length scanner in a broadband Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) spectroscopy platform. We provide a theoretical description of the proposed FT-CARS spectroscopy technique while also presenting its proof-of-concept demonstration on a liquid toluene sample. Our use of a 54-facet polygonal mirror array rotating at 916 rotations/s achieves a record high scan rate of 50,000 CARS spectra/s, covering most of the molecular fingerprint region (200–1430cm−1) with a high resolution of 4.2cm−1. This ultrafast broadband CRS technique is expected to be of great use in applications where high-throughput screening or real-time monitoring of unknown samples with high specificity is required, such as single-cell analysis and biomedical imaging.

Digital technologies: From vision to action

The interest and uptake in utilising digital technologies in education appears to be exponential. With the rollout of ultrafast broadband and the development of the Network for Learning in New Zealand, school leaders face the challenge and opportunity of deciding when, what and how they go about implementing digital technologies in their schools. Based on evidence from an interpretive study involving three school leaders of new schools I explore here alignment of their organisation’s vision for teaching and learning and use of digital technologies. This study suggests that digital technologies have significant potential to enhance learning opportunities within an explicit and shared vision of what a learner needs to be successful in their lives.

Broadband optical transparency in plasmonic nanocomposite polymer films via exciton-plasmon energy transfer.

Inherent absorptive losses affect the performance of all plasmonic devices, limiting their fascinating applications in the visible range. Here, we report on the enhanced optical transparency obtained as a result of the broadband mitigation of optical losses in nanocomposite polymeric films, embedding core-shell quantum dots (CdSe@ZnS QDs) and gold nanoparticles (Au-NPs). Exciton-plasmon coupling enables non-radiative energy transfer processes from QDs to metal NPs, resulting in gain induced transparency of the hybrid flexible systems. Experimental evidences, such as fluorescence quenching and modifications of fluorescence lifetimes confirm the presence of this strong coupling between plexcitonic elements. Measures performed by means of an ultra-fast broadband pump-probe setup demonstrate loss compensation of gold NPs dispersed in plastic network in presence of gain. Furthermore, we compare two films containing different concentrations of gold NPs and same amount of QDs, to investigate the role of acceptor concentration (Au-NPs) in order to promote an effective and efficient energy transfer mechanism. Gain induced transparency in bulk systems represents a promising path towards the realization of loss compensated plasmonic devices.