Strongly Enhanced Molecular Fluorescence inside a Nanoscale Waveguide Gap

Sorger, Volker J.; Pholchai, Nitipat; Cubukcu, Ertugrul; Oulton, Rupert F.; Kolchin, Pavel; Borschel, Christian; Gnauck, M.; Ronning, Carsten; Zhang, Xiang

doi:10.1021/nl202825s

Cited by 94 publications

(91 citation statements)

References 27 publications

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“…This measure of spontaneous emission rate is complementary to lifetime measurements. Lifetime can be influenced by emitters coupling to surface plasmons or optical cavities, which may not radiate, the energy still being lost as heat (21,27), whereas the intensity method demands a knowledge of relative pump efficiency, relative emission pattern, and possible difference in internal quantum efficiency near the antenna.…”

Section: Methodsmentioning

confidence: 99%

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Optical antenna enhanced spontaneous emission

Eggleston

Messer

Zhang³

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

142

157

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Atoms and molecules are too small to act as efficient antennas for their own emission wavelengths. By providing an external optical antenna, the balance can be shifted; spontaneous emission could become faster than stimulated emission, which is handicapped by practically achievable pump intensities. In our experiments, InGaAsP nanorods emitting at ∼200 THz optical frequency show a spontaneous emission intensity enhancement of 35× corresponding to a spontaneous emission rate speedup ∼115×, for antenna gap spacing, d = 40 nm. Classical antenna theory predicts ∼2,500× spontaneous emission speedup at d ∼ 10 nm, proportional to 1/d 2 . Unfortunately, at d < 10 nm, antenna efficiency drops below 50%, owing to optical spreading resistance, exacerbated by the anomalous skin effect (electron surface collisions). Quantum dipole oscillations in the emitter excited state produce an optical ac equivalent circuit current, I o = qωjx o j/d, feeding the antenna-enhanced spontaneous emission, where qjx o j is the dipole matrix element. Despite the quantum-mechanical origin of the drive current, antenna theory makes no reference to the Purcell effect nor to local density of states models. Moreover, plasmonic effects are minor at 200 THz, producing only a small shift of antenna resonance frequency.A ntennas emerged at the dawn of radio, concentrating electromagnetic energy within a small volume <<λ 3 , enabling nonlinear radio detection. Such coherent detection is essential for radio receivers and has been used since the time of Hertz (1). Conversely, an antenna can efficiently extract radiation from a subwavelength source, such as a small cellphone. Despite the importance of radio antennas, 100 y went by before optical antennas began to be used to help extract optical frequency radiation from very small sources such as dye molecules (2-10) and quantum dots (11)(12)(13)(14).In optics, spontaneous emission is caused by dipole oscillations in the excited state of atoms, molecules, or quantum dots. The main problem is that a molecule is far too small to act as an efficient antenna for its own electromagnetic radiation. Antenna length, l, makes a huge difference in radiation rate. An ideal antenna would preferably be λ/2, a half-wavelength in size. To the degree that an atomic dipole of length l is smaller than λ/2, the antenna radiation rate Δω is proportional to ω(l/λ) 3 , as given by the Wheeler limit (15). Spontaneous emission from molecular-sized radiators is thus slowed by many orders of magnitude, because radiation wavelengths are much larger than the atoms themselves. Therefore, the key to speeding up spontaneous emission is to couple the radiating molecule to a proper antenna of sufficient size.Since the emergence of lasers in 1960, stimulated emission has been faster than spontaneous emission. Now the opposite is possible. In the right circumstances, antenna-enhanced spontaneous emission could become faster than stimulated emission. Theoretically, very large bandwidth >100 GHz or >1 THz is possible when the light emitter is ...

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Section: Methodsmentioning

confidence: 99%

“…Metal structures have also been used to enhance the spontaneous emission rate, such as by coupling excited material to flat surface plasmon waves (21)(22)(23)(24)(25)(26)(27)(28). Flat metal surfaces are far from ideal antennas, resulting in low radiation efficiencies and large ohmic losses.…”

Section: Nanophotonics | Metal Optics | Plasmonics | Ultrafast Devicesmentioning

confidence: 99%

Optical antenna enhanced spontaneous emission

Eggleston

Messer

Zhang³

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

142

157

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“…Thus, resonator-based electro-optic modulators require painstaking fabrication tolerances of the high-Q cavity and are temperature-prone calling for sophisticated athermal designs and operation requirements [6] . Both the footprint and bandwidth constrains can be simultaneously overcome by (i) enhancing the optical mode overlap with the actively index-modulated region (geometric effect) [7][8][9], and (ii) increasing the light-matter-interaction of the optical mode with the actively index-modulated material via enhancing the electromagnetic-fi eld strength (absorptive effect) [9][10][11] . We achieve both of these desired effects by deploying a plasmonic metal-oxide-semiconductor (MOS) type optical mode which concentrates part of the propagating mode ' s fi eld into a nanometer-thin region overlapping with the actively index-modulated material [7 -9] .…”

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confidence: 99%

Ultra-compact silicon nanophotonic modulator with broadband response

et al. 2012

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Electro-optic modulators have been identifi ed as the key drivers for optical communication and signal processing. With an ongoing miniaturization of photonic circuitries, an outstanding aim is to demonstrate an on-chip, ultra-compact, electro-optic modulator without sacrifi cing bandwidth and modulation strength. While silicon-based electro-optic modulators have been demonstrated, they require large device footprints of the order of millimeters as a result of weak non-linear electro-optical properties. The modulation strength can be increased by deploying a high-Q resonator, however with the trade-off of signifi cantly sacrifi cing bandwidth. Furthermore, design challenges and temperature tuning limit the deployment of such resonance-based modulators. Recently, novel materials like graphene have been investigated for electro-optic modulation applications with a 0.1 dB per micrometer modulation strength, while showing an improvement over pure silicon devices, this design still requires device lengths of tens of micrometers due to the ineffi cient overlap between the thin graphene layer, and the optical mode of the silicon waveguide. Here we experimentally demonstrate an ultra-compact, silicon-based, electro-optic modulator with a record-high 1 dB per micrometer extinction ratio over a wide bandwidth range of 1 μm in ambient conditions. The device is based on a plasmonic metal-oxide-semiconductor (MOS) waveguide, which efficiently concentrates the optical modes ' electric fi eld into a nanometer thin region comprised of an absorption coefficient-tuneable indium-tin-oxide (ITO) layer. The modulation mechanism originates from electrically changing the free carrier concentration of the ITO layer which dramatically increases the loss of this MOS mode. The seamless integration of such a strong optical beam modulation into an existing silicon-on-insulator platform bears signifi cant potential towards broadband, compact and effi cient communication links and circuits.Keywords: Modulator; silicon-on-insulator; ultra-compact.A waveguide-integrated electro-optical modulator can be perceived as a transistor with an optical source and drain and an electrical gate [1]. This waveguide receiving a continuous wave laser beam converts electrical data arriving at the gate electrode into an optical encoded data stream. A widely used modulation mechanism is to change the free carrier concentration of the material overlapping with the propagating optical mode, which leads to a shift of the plasma frequency of the dispersion relation [2]. This modifi es both the real and imaginary parts of the refractive index of the material, and henceforth alters the index and loss of the optical propagating mode. While a Mach-Zehnder type modulator utilized a refractive index change in the real part [3], an electro-absorption type modulator deploys the altered loss of the optical mode [4]. With the promise of silicon-on-insulator (SOI) technology [5] for on-chip integrated photonics, the Intel team demonstrated a Mach-Zehnder modulator by c...

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“…Under an applied bias, the carrier concentration is changed from 1 × 10 19 cm −3 to 6.8 × 10 20 cm −3 , and the propagation length is varied from 1.3 to 43 µm. Also, the total insertion loss comprising of both the SOI-to-MOS coupling (−0.25 dB/coupler) and plasmonic MOS mode propagation (−0.14 dB/µm) were fairly low, which could achieve a total insertion loss as low as only about −1 dB for a 5 µm long modulator due to the good impedance match between the SOI and MOS mode and low ohmic losses from the plasmonic MOS mode [20,[67][68][69]. Recently, another characteristic of the SPP EOM deploying ITO as an active material was demonstrated by the Leuthold's team (2014); the hysteresis of the gate current and the optical transmission displays characteristics of a resistive random access memory (RRAM) (Fig.…”

Section: Eom Devices Based On Itomentioning

confidence: 99%

Indium-Tin-Oxide for High-performance Electro-optic Modulation

et al. 2015

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Advances in opto-electronics are often led by discovery and development of materials featuring unique properties. Recently, the material class of transparent conductive oxides (TCO) has attracted attention for active photonic devices on-chip. In particular, indium tin oxide (ITO) is found to have refractive index changes on the order of unity. This property makes it possible to achieve electrooptic modulation of sub-wavelength device scales, when thin ITO films are interfaced with optical light confinement techniques such as found in plasmonics; optical modes are compressed to nanometer scale to create strong light-matter interactions. Here we review efforts towards utilizing this novel material for high performance and ultra-compact modulation. While high performance metrics are achieved experimentally, there are open questions pertaining to the permittivity modulation mechanism of ITO. Finally, we review a variety of optical and electrical properties of ITO for different processing conditions, and show that ITO-based plasmonic electro-optic modulators have the potential to significantly outperform diffractionlimited devices.

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Strongly Enhanced Molecular Fluorescence inside a Nanoscale Waveguide Gap

Cited by 94 publications

References 27 publications

Optical antenna enhanced spontaneous emission

Optical antenna enhanced spontaneous emission

Ultra-compact silicon nanophotonic modulator with broadband response

Indium-Tin-Oxide for High-performance Electro-optic Modulation

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