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ACKNOWLEDGMENTS
Financial support for this work was provided by Bristol-MyersSquibb, the Catalan Government (postdoctoral fellowshipto J.C.), the U.S. Department of Defense (National DefenseScience and Engineering Graduate fellowship to J.T.E.),
NIH (F32GM117816 postdoctoral fellowship to L.R.M.),the China Scholarship Council (postdoctoral fellowship toC.L.), and the National Institute of General Medical Sciences(GM106210). We thank D.-H. Huang and L. Pasternack forassistance with nuclear magnetic resonance spectroscopy;M. Collins for providing samples of atorvastatin, cetirizine,and pregabalin; R. Mills for experimental assistance;A. Rheingold, C. E. Moore, and M. A. Galella for x-raycrystallographic analysis; M. R. Ghadiri for providing accessto preparative HPLC equipment; and K. Chen for helpfuldiscussions. Metrical parameters for the structures of11 and 73 are available free of charge from the CambridgeCrystallographic Data Center under reference nos.CCDC-1457710 and CCDC-1457711, respectively.
SUPPLEMENTARY MATERIALS
www.sciencemag.org/content/352/6287/801/suppl/DC1Materials and MethodsSupplementary TextFigs. S1 to S3Tables S1 to S6References (34–60)
4 March 2016; accepted 11 April 2016Published online 21 April 201610.1126/science.aaf6123
APPLIED PHYSICS
On-chip noninterference angularmomentum multiplexing ofbroadband lightHaoran Ren,1 Xiangping Li,1,2 Qiming Zhang,1,3 Min Gu1,3*
Angular momentum division has emerged as a physically orthogonal multiplexing methodin high-capacity optical information technologies. However, the typical bulky elements usedfor information retrieval from the overall diffracted field, based on the interference method,impose a fundamental limit toward realizing on-chip multiplexing. We demonstratenoninterference angular momentum multiplexing by using a mode-sorting nanoringaperture with a chip-scale footprint as small as 4.2 micrometers by 4.2 micrometers,where nanoring slits exhibit a distinctive outcoupling efficiency on tightly confinedplasmonic modes. The nonresonant mode-sorting sensitivity and scalability of our approachenable on-chip parallel multiplexing over a bandwidth of 150 nanometers in the visiblewavelength range. The results offer the possibility of ultrahigh-capacity and miniaturizednanophotonic devices harnessing angular momentum division.
In the age of information technology, opti-cal multiplexing using physical dimensionsof light, including space (1), frequency (2),brightness (3), color (1, 4), polarization (1, 5,6), mode (7), and lifetime (8), has played a
crucial role in high-definition displaying (3–5),high-capacity data storage (1, 6), high-speed com-munications (7), and highly sensitive biologicalsensing (8). As one of the most fundamentalphysical properties in both classical and quantum
optics, angular momentum (AM) of light—includingspin angular momentum (SAM) possessed bycircularly polarized light and orbital angularmomentum (OAM) manifested by the helicalwavefront of light—has emerged as a physicallyorthogonal multiplexing approach to high-capacityoptical communications ranging from free-space(9) to compact optical fibers (10). However, macro-scale interference-based detection methods throughhologram-coding (9, 10) or phase-shifting (11, 12)of AM-carrying beams have imposed a funda-mental physical limit for realizing such a prin-ciple at a chip-scale footprint.The advance of strong light-confinement
nanophotonic approaches has been a majorpropellant of miniaturized optical circuits toharness AM of light. The chip-scale generationand transmission of AM-carrying beams on
silicon-integrated circuits have been realizedthrough whispering gallery mode resonators(13) and resonant microring fibers (10). How-ever, these approaches are resonant in nature,leading to a narrow bandwidth down to sev-eral nanometers. Surface plasmon polaritons(SPPs) capable of strong light confinementshave long been pursued to overcome the sizelimitation of nanophotonic devices and, hence,potentially facilitate the chip-scale multiplexingof SAM through the SAM-distinguishing nano-structures (14–18). Even though the OAM gen-erators mediated by SPPs have been demonstratedeither through digitalized metasurfaces with ahelical phase (19) or geometric metasurfaces basedon spin-orbit interaction (20), the extrinsic natureof OAM (21) with helical wavefronts restricts itsdetection to a phase-sensitive interference-basedmethod through a holographic metasurface (22),which inevitably degrades the perceptive devicesfor on-chip applications.The concept of our on-chip noninterference
AMmultiplexing of broadband light is illustratedin Fig. 1. Without losing the generality, coaxiallysuperposed AM-carrying beams with four se-lected AM modes [l0 = –4, s = –1 (AM1); l0 = –2,s = –1 (AM2); l0 = +2, s = +1 (AM3); and l0 = +4,s = +1 (AM4); where l0 and s are the modalindices for OAM and SAM, respectively (Fig.1A)] propagate through a nanoring aperture(NRA) multiplexing unit that consists of shal-low nanogrooves and the spatially shifted mode-sorting nanoring slits of different sizes (Fig. 1Band fig. S1A). The nanogroove structures act asthe metal-dielectric interfaces to convert the AMmodes carried by photons into SPPs and to spa-tially route the excited plasmonic AM modesto the locations of the nanoring slits. A set ofAM-carrying beams of l0 = ±1, ±2, ±3, ±4 and s =±1 (fig. S2) can be adopted to excite a range ofplasmonic AMmodes (determined by total AML = l0 + s + ls, where ls is the geometrical topo-logical charge arising from the nanogrooves),with a distinguished spatial separability from
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1Centre for Micro-Photonics and Centre for Ultrahigh BandwidthDevices for Optical Systems (CUDOS), Faculty of Science,Engineering and Technology, Swinburne University ofTechnology, Hawthorn, Victoria 3122, Australia. 2Institute ofPhotonics Technology, Jinan University, Guangzhou, China.3Artificial Intelligence Nanophotonics Laboratory, School ofScience, RMIT University, Melbourne, Victoria 3001, Australia.*Corresponding author. Email: [email protected]
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the structure depicted in fig. S1A. The forma-tion of the spatial separability by nanogroovesprovides a physical ground for AM mode sort-ing. As a result of the distinctive AM mode-sorting sensitivity by nanoring slits, the plasmonicAMmodes can be selectively coupled out throughthe slits that have different sizes and spatialshifts (Fig. 1C). Furthermore, the nonresonantAM mode-sorting sensitivity by the nanoringslits enables the AM multiplexing over a broadbandwidth. As such, a large-scale NRA-structuredAM multiplexing chip (NAMMC) (Fig. 1D) con-sisting of an array of individually addressableNRAs, wherein NRA units are separated by aspacing larger than the diffraction-limit distance,allows for on-chip processing of an AM-multiplexedimage in parallel through a multibeam approach(Fig. 1E).In terms of the operation mechanism, we con-
sidered a nanoring slit enclosed by a concentricnanogroove (ls = 0) in a gold film. Throughout
this paper, the width of the nanoring slit is fixedas 50 nm. We carried out a full vectorial ap-proach for the analysis of the AM mode in thenanoring slit (23). With respect to the cut-offAM mode (fig. S3) of the nanoring slit, the cal-culated effective indices of the eigen-AMmodes ofL = ±1 and ±3 indicate that the lower AMmodeof L = ±1 can be supported by both slits, withinner radii of 75 nm (Rin1) and 200 nm (Rin2), butthe higher AM mode of L = ±3 can only bemaintained by the slit with Rin2 (Fig. 2A). More-over, the effective index differences almost re-main flat in visible wavelengths, which indicatesthe nonresonant nature of AMmodes supportedby nanoring slits and lays the foundation formultiplexing broadband light.The outcoupling (transmittance) efficiency
of nanoring slits can be determined by themode matching between the eigen-AM modesupported by nanoring slits (fig. S4, A to C)and the plasmonic AM mode excited from nano-
grooves (fig. S4, D to F). A mode-matching fac-tor (MF) can be defined (23) so that we intuitivelyunderstand the distinctive AM mode-sortingselectivity by the nanoring slits. The MF can beselectively maximized from its dependence onthe illumination wavelength and the slit radius(fig. S4, G to I). As an example, the black curvesin Fig. 2A reveal that plasmonic modes withtotal AM of L = ±1 and ±3 can be distinctivelycoupled out through nanoring slits with Rin1
and Rin2, respectively. In addition, theoreticalanalysis of the fundamental symmetries in nano-photonics (24, 25) provides physical insight intothe NRA exhibiting the distinctive sensitivity onthe total AM of SPPs, which yields additional flex-ibility in the subsequent chip design operatingby different SAM and OAM combinations withthe given total AM.The distinctive AM mode-sorting selectivity,
as defined in (23), can be experimentally ver-ified for AM modes of L = ±1 and ±3 over a
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Fig. 1. The principle of on-chip noninterference AMmultiplexing of broadband light. (A) Four selected AM beams [l0 = –4, s = –1 (AM1); l0 = –2, s = –1 (AM2);l0 = +2, s = +1 (AM3); and l0 = +4, s = +1 (AM4)] are coaxially overlapped as the AM-superposed beams. (B) Schematic of a NRA multiplexing unit consisting ofnanogroove structures and the mode-sorting nanoring slits. (C) Mechanism for AM mode-sorting by nanoring slits that have different sizes and lateral shifts.(D) NAMMC integrated by an array of 8 NRA units by 8 NRA units. (E) Concept of on-chip processing of AM-multiplexed images over a broadband by theNAMMC. l, wavelength.
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Fig. 2. Distinctive AMmode-sorting selectivity by a nanoring slit of vary-ing size. (A) Theoretically calculated effective index differences (Dneff) (redcurves) andMFs (black curves) for the plasmonicmodeswith total AMof L=±1(solid lines) and L = ±3 (dashed lines) for a nanoring slit with Rin1 = 75 nm (top)and Rin2 = 200 nm (bottom), respectively. (B and C) Scanning electron mi-croscopy (SEM) images of the fabricated NRAs consisting of concentric nano-grooves and nanoring slits with inner radii of Rin1 (see fig. S1B for 45° view) and
Rin2 (see fig. S1C for 45° view), respectively.The insets show enlarged views ofthe nanoring slits (scale bars, 100nm). (D)Numerically calculated (curves) andexperimentally confirmed (triangles) AM mode-sorting selectivity spectra ofthe AMbeams of l0 =–2, s=+1 (L= –1) and l0 = +2, s=+1 (L= +3) for nanoringslits with inner radii of Rin1 (top) and Rin2 (bottom), respectively.The red colorindicates the bandwidths (defined as the selectivity ≥ 0.1) of AMmode-sortingselectivity by nanoring slits.
Fig. 3. Experimental characterization of chip-scale AMmultiplexing basedon double concentric and spatially shifted nanoring slits enclosed by sec-tionsof spatially shifted nanogrooves. (A) SEM image of the double nanoringslits (inset),withRin1 andRin2 enclosedby the two sections of shifted grooveswithls = +2. (B) Simulated total intensity distributions of the AM beams of AM1 (top)andAM2 (bottom) in the longitudinal planesof the nanoringslits. (C) Experimental
far-field intensity distributions of the AM beams of AM1 and AM2 in the transverseplanes. (D) Experimental cross-sectionplots of the far-field intensity distributionsin (C), as labeled by the dashed white lines. A.U., arbitrary units. (E to H) Coun-terparts of (A) to (D), based on the spatially shifted nanoring slits with Rin1 andnanogrooves with ls = +2 (left) and ls = –2 (right). In (F) to (H), top imagescorrespond to AM2 (top); bottom images correspond to AM3.
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broad bandwidth of 150 nm in visible wave-lengths (Fig. 2D). As an illustration, fig. S5 showstransmissive patterns of the AM beams at awavelength of 640 nm. The physical principleof the distinctive AM mode-sorting selectivitycan be extended to other wavelengths, such astelecommunication bands ranging from 1.45 to1.65 mm (fig. S6).The principle of the AM mode-sorting se-
lectivity by nanoring slits of different sizes canbe adopted for chip-scale multiplexing of AM-superposed beams if two nanoring slits withRin1 and Rin2 are used concentrically. As shownin Fig. 3, A to D, two sections of the circularnanogrooves were spatially shifted in oppositedirections, yielding ls = +2. Additionally, AMbeams of AM1 and AM2 can excite plasmonicAM modes corresponding to L = –3 and –1,respectively, leading to the distinctive transmit-tance from the concentrically aligned nanoringslits. The capacity of the AM mode-sorting mul-tiplexing can be increased by laterally shiftingone of the circular nanogroove sections and theenclosed nanoring slit in opposite directions(Fig. 3, E to H). Using this nanogroove-shiftingprinciple, AM beams with OAM modes rangingfrom l0 = –4 to +4 and SAMmodes of s = –1 and+1 can be coupled out by the two spatially shiftednanoring slits that have different locations andsizes, with the smallest footprint of 4.2 mm by4.2 mm (fig. S7).Based on the AM mode-sorting principle,
we can achieve on-chip multiplexing of mul-tiple AM modes (Fig. 4). We used two con-centric double nanoring slits (Fig. 4A and fig.S1D) to selectively couple out the AM beamsof AM1, AM2, AM3, and AM4, which can easily
be evidenced by their distinctive transmissivepatterns in the far-field region (fig. S8). Assuch, chip-scale AM multiplexing by dynami-cally switching on individual AM beams canbe directly observed at different wavelengths(Fig. 4B and fig. S9), with a modal cross-talkas low as –17 dB (Fig. 4C).The broadband feature of the noninterfer-
ence AM multiplexing by the chip-scale NRAcan enable a multiplexing chip constructed byan array of NRAs (i.e., the NAMMC) to carryout both AM- and wavelength-division multi-plexing in parallel. The NAMMC, which con-sists of an array of 8 NRA units by 8 NRAunits, was fabricated (Fig. 4D) and illuminatedby an array of 8 by 8 multibeams carrying well-defined SAM and OAM (23) (figs. S10 and S11).Consequently, Fig. 4E shows the experimen-tally reconstructed AM- and wavelength-codedimages (100 pixels by 100 pixels), which wereconstructed one piece at a time through thedynamic area-by-area coding method (23). Inaddition, we show that the NAMMC is alsocapable of displaying the AM-coded image bysimultaneously addressing the four AM infor-mation channels (fig. S12).In bulky optics, OAM multiplexing is outper-
formed by conventional multiplexing techniques,in terms of multiplexing capacity. However, OAMmultiplexing outperforms other techniques innanoscale systemswith a small space-bandwidthproduct (26). In general, the AM mode-sortingsensitivity of the NRAs can be extended to spiralnanogroove systems with different ls (figs. S13and S14) and to multiple concentric nanoringslits. This generalization can be advantageous forfurther reduction of the NRA footprint while
multiplexing optical beams with a greater num-ber of AMmodes. The noninterference operatingprinciple in NRAs removes the requirement ofbulky interference-based optics, and the asso-ciated nonresonance nature can largely increasethe multiplexing capacity in conjunction withthe wavelength-division multiplexing in a broadband. The large-scale NAMMC can be further in-tegrated with chip-scale AM generators and couldthereby offer compact on-chip AM applicationsin optical communications, information display,data storage, and data encryption.
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Fig. 4. Four-state AM multiplexing through aNRA unit and parallel AM- and wavelength-divisionmultiplexing through the large-scale NAMMC.(A) SEM image of the single NRA (see fig. S1D for45° view) in the NAMMC and the two concentricdouble nanoring slits (inset). (B) Experimental char-acterization of the four-state AM multiplexing bydynamically switchingon theAM-superposed beams.The imagesarepresented inpseudo-colors. (C)Mea-sured modal cross-talk of the four AM modes atdifferentwavelengths. (D) SEM image of theNAMMC.(E) Experimentally reconstructedAM-andwavelength-coded images retrieved from the four AM modes(AM1, AM2, AM3, and AM4) (Fig. 1A) at the threedifferent wavelengths.
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ACKNOWLEDGMENTS
We thank X. Li for help with the ion beam lithography,G. Gervinskas and F. Eftekhari from the Melbourne Centre forNanofabrication for their fabrication efforts, H. Lu for technicalassistance with the waveguide calculation, and J. Storteboomfor assistance with using the Spectra-Physics Inspire lasersystem. This work was supported under the AustralianResearch Council Laureate Fellowship program (grantFL100100099). M.G. acknowledges support from the AustralianResearch Council Centre for Ultrahigh Bandwidth Devices for
Optical Systems (CUDOS) (project CE110001018). X.L.acknowledges support from the Australian Research Council(grant DE150101665). All data related to the experimentsdescribed in this manuscript are archived on a lab computer atSwinburne University of Technology.
SUPPLEMENTARY MATERIALS
www.sciencemag.org/content/352/6287/805/suppl/DC1Materials and MethodsSupplementary TextFigs. S1 to S14References (27–30)
18 December 2015; accepted 9 March 2016Published online 7 April 201610.1126/science.aaf1112
GEOCHEMISTRY
Preservation of Earth-forming eventsin the tungsten isotopic compositionof modern flood basaltsHanika Rizo,1* Richard J. Walker,2 Richard W. Carlson,3 Mary F. Horan,3
Sujoy Mukhopadhyay,4 Vicky Manthos,4 Don Francis,5 Matthew G. Jackson6
How much of Earth's compositional variation dates to processes that occurredduring planet formation remains an unanswered question. High-precision tungstenisotopic data from rocks from two large igneous provinces, the North AtlanticIgneous Province and the Ontong Java Plateau, reveal preservation to thePhanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities,caused by the decay of hafnium-182 in mantle domains with high hafnium/tungstenratios, were created during the first ~50 million years of solar system history,indicating that portions of the mantle that formed during Earth’s primary accretionaryperiod have survived to the present.
Four and a half billion years of geologic ac-tivity have overprintedmuch of the evidencefor the processes involved in Earth’s forma-tion and initial chemical differentiation.High-precision isotopic measurements of
the decay products of short-lived radionuclidesthat were presentwhen Earth formed can providea view of events that occurred during the first tensto hundreds ofmillion years of Earth history. Datafromboth the 146Sm-142Nd (half-life, t1/2 = 103millionyears) and 129I-129Xe (t1/2 = 15.7 million years) sys-tems show the importance of early mantle dif-ferentiation and outgassing events but provideconflicting evidence about the preservation ofearly-formed mantle reservoirs to the presentday (1–4). Of the short-lived systems, the 182Hf-182W (t1/2 = 8.9 million years) system is distinc-tively sensitive to metal-silicate separation andhas been used effectively to trace the timing and
processes of core formation (5), which is arguablythe most important chemical differentiation eventto occur on a rocky planet. Only recently, however,have measurement techniques improved to the
point of resolving 182W/184W variability in an-cient (>2.7 billion years old) terrestrial rocks;such variability reflects the preservation of com-positionally distinct domains in Earth’s interiorthat were probably created during Earth’s for-mation (6–10). Young mantle-derived rocks ex-amined to date have shown neither 142Nd nor182W isotopic heterogeneity, suggesting that theearly-formed compositional domains in Earth’sinterior were largely destroyed bymantle-mixingprocesses during the first half of Earth history(1–4, 6–10). Here we report 182W/184W ratios inPhanerozoic flood basalts from Baffin Bay andthe Ontong Java Plateau, some of which areamong the highest ever measured in terrestrialrocks. These results document the preservationof regions within Earth’s interior whose compo-sitions were established by events that occurredwithin the first ~50 million years of solar systemhistory. This study, consequently, provides newinsights into the processes at work during planetformation, the chemical structure of Earth’s in-terior, and the interior dynamics that allowedthe preservation of chemical heterogeneities for4.5 billion years.Flood basalts are the largest volcanic eruptions
identified in the geological record. These typesof eruptions created both the North Atlantic
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Fig. 1. m182W values measuredfor the Baffin Bay and OntongJava Plateau samples, thegeological reference materialsVE-32 and BHVO-1, and theAlfa Aesar W standard.Thevalues are expressed as devia-tions, in parts per million (ppm),from the average valuemeasured for the W standard.The gray shaded area represents2s for the average W standardvalue. Errors for each data pointare 2s.
1Geotop, Département des Sciences de la Terre et del’Atmosphère, Université du Québec à Montréal, Montreal, Canada.2Department of Geology, University of Maryland, College Park, MD,USA. 3Carnegie Institution for Science, Washington, DC, USA.4Department of Earth and Planetary Sciences, University ofCalifornia–Davis, Davis, CA, USA. 5Department of Earth andPlanetary Sciences, McGill University, Montreal, Canada.6Department of Earth Science, University of California–SantaBarbara, Santa Barbara, CA, USA.*Corresponding author. Email: [email protected]
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On-chip noninterference angular momentum multiplexing of broadband lightHaoran Ren, Xiangping Li, Qiming Zhang and Min Gu
originally published online April 7, 2016DOI: 10.1126/science.aaf1112 (6287), 805-809.352Science
, this issue p. 805; see also p. 774Scienceprocessing of optical signals.states of angular momentum (see the Perspective by Molina-Terriza). The approach is promising for on-chip multiplex
take a nanophotonics approach to measure and sort light co-propagating with differentet al.on-chip processing. Ren further. Typically, however, the bulk optical elements used to determine the angular momentum of light limit possible communications, and biological sensing. Angular momentum is another degree of freedom that could increase capacitypolarization have played crucial roles in information technologies, high-capacity data storage, high-speed
Information can be encoded using various properties of light. Optical multiplexing frequency, brightness, andA twist on optical multiplexing
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REFERENCES
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