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Debnath K, Welna K, Ferrera M, Deasy K, Lidzey DG, O'Faolain L. Highly efficient optical filter based on vertically coupled photonic crystal cavity and bus waveguide. OPTICS LETTERS 2013; 38:154-6. [PMID: 23454946 DOI: 10.1364/ol.38.000154] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We experimentally demonstrate a new optical filter design based on a vertically coupled photonic crystal (PhC) cavity and a bus waveguide monolithically integrated on the silicon-on-insulator platform. The use of a vertically coupled waveguide gives flexibility in the choice of the waveguide material and dimensions, dramatically lowering the insertion loss while achieving very high coupling efficiencies to wavelength scale resonators and thus allows the creation of PhC-based optical filters with very high extinction ratio (>10 dB).
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Reimer C, Nedeljkovic M, Stothard DJM, Esnault MOS, Reardon C, O'Faolain L, Dunn M, Mashanovich GZ, Krauss TF. Mid-infrared photonic crystal waveguides in silicon. OPTICS EXPRESS 2012; 20:29361-29368. [PMID: 23388763 DOI: 10.1364/oe.20.029361] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We demonstrate the design, fabrication and characterization of mid-infrared photonic crystal waveguides on a silicon-on-insulator platform, showing guided modes in the wavelength regime between 2.9 and 3.9 µm. The characterization is performed with a proprietary intra-cavity Optical Parametric Oscillator in a free space optical setup and with a fibre coupled setup using a commercial Quantum Cascade Laser. We discuss the use of an integrated Mach-Zehnder interferometer for dispersion measurements and report a measured group velocity of up to a value of n(g) = 12, and determine the propagation loss to be 20 dB/cm.
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Debnath K, O'Faolain L, Gardes FY, Steffan AG, Reed GT, Krauss TF. Cascaded modulator architecture for WDM applications. OPTICS EXPRESS 2012; 20:27420-8. [PMID: 23262692 DOI: 10.1364/oe.20.027420] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Integration density, channel scalability, low switching energy and low insertion loss are the major prerequisites for on-chip WDM systems. A number of device geometries have already been demonstrated that fulfill these criteria, at least in part, but combining all of the requirements is still a difficult challenge. Here, we propose and demonstrate a novel architecture consisting of an array of photonic crystal modulators connected by a dielectric bus waveguide. The device architecture features very high scalability and the modulators operate with an AC energy consumption of less than 1fJ/bit. Furthermore, we demonstrate cascadeability and multichannel operation by using a comb laser as the source that simultaneously drives 5 channels.
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Reardon CP, Rey IH, Welna K, O'Faolain L, Krauss TF. Fabrication and characterization of photonic crystal slow light waveguides and cavities. J Vis Exp 2012:e50216. [PMID: 23222804 DOI: 10.3791/50216] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals(1-4) and the enhancement of both linear(5-7) and nonlinear devices.(8-11) Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically(12) and electrically(13) pumped ultra-low threshold lasers and the enhancement of nonlinear effects.(14-16) Furthermore, passive filters(17) and modulators(18-19) have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption. To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues. The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum(20-21) and interferometric techniques.(22-25) Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.(26) Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans. When characterising photonic crystal cavities, techniques involving internal sources(21) or external waveguides directly coupled to the cavity(27) impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.(28) and further developed by Galli et al.(29).
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Li J, O'Faolain L, Krauss TF. Four-wave mixing in slow light photonic crystal waveguides with very high group index. OPTICS EXPRESS 2012; 20:17474-17479. [PMID: 23038300 DOI: 10.1364/oe.20.017474] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We report efficient four-wave mixing in dispersion engineered slow light silicon photonic crystal waveguides with a flat band group index of n(g) = 60. Using only 15 mW continuous wave coupled input power, we observe a conversion efficiency of -28 dB. This efficiency represents a 30 dB enhancement compared to a silicon nanowire of the same length. At higher powers, thermal redshifting due to linear absorption was found to detune the slow light regime preventing the expected improvement in efficiency. We then overcome this thermal limitation by using oxide-clad waveguides, which we demonstrate for group indices of ng = 30. Higher group indices may be achieved with oxide clad-waveguides, and we predict conversion efficiencies approaching -10 dB, which is equivalent to that already achieved in silicon nanowires but for a 50x shorter length.
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Xiong C, Monat C, Clark AS, Grillet C, Marshall GD, Steel MJ, Li J, O'Faolain L, Krauss TF, Rarity JG, Eggleton BJ. Slow-light enhanced correlated photon pair generation in a silicon photonic crystal waveguide. OPTICS LETTERS 2011; 36:3413-3415. [PMID: 21886228 DOI: 10.1364/ol.36.003413] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We report the generation of correlated photon pairs in the telecom C-band at room temperature from a dispersion-engineered silicon photonic crystal waveguide. The spontaneous four-wave mixing process producing the photon pairs is enhanced by slow-light propagation enabling an active device length of less than 100 μm. With a coincidence to accidental ratio of 12.8 at a pair generation rate of 0.006 per pulse, this ultracompact photon pair source paves the way toward scalable quantum information processing realized on-chip.
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Kotlyar VV, Stafeev SS, O'Faolain L, Soifer VA. Tight focusing with a binary microaxicon. OPTICS LETTERS 2011; 36:3100-3102. [PMID: 21847173 DOI: 10.1364/ol.36.003100] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Using a near-field scanning microscope (NT-MDT) with a 100 nm aperture cantilever held 1 μm apart from a microaxicon of diameter 14 μm and period 800 nm, we measure a focal spot resulting from the illumination by a linearly polarized laser light of wavelength λ=532 nm, with its FWHM being equal to 0.58λ, and the depth of focus being 5.6λ. The rms deviation of the focal spot intensity from the calculated value is 6%. The focus intensity is five times larger than the maximal illumination beam intensity.
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Monat C, Spurny M, Grillet C, O'Faolain L, Krauss TF, Eggleton BJ, Bulla D, Madden S, Luther-Davies B. Third-harmonic generation in slow-light chalcogenide glass photonic crystal waveguides. OPTICS LETTERS 2011; 36:2818-2820. [PMID: 21808323 DOI: 10.1364/ol.36.002818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We demonstrate third-harmonic generation (THG) in a dispersion-engineered slow-light photonic crystal waveguide fabricated in AMTIR-1 chalcogenide glass. Owing to the relatively low loss and low dispersion in the slow-light (c/30) regime, combined with the high nonlinear figure of merit of the material (∼2), we obtain a relatively large conversion efficiency (1.4×10(-8)/W(2)), which is 30× higher than in comparable silicon waveguides, and observe a uniform visible light pattern along the waveguide. These results widen the number of applications underpinned by THG in slow-light platforms, such as the direct observation of the spatial evolution of the propagating mode.
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Corcoran B, Pelusi MD, Monat C, Li J, O'Faolain L, Krauss TF, Eggleton BJ. Ultracompact 160 Gbaud all-optical demultiplexing exploiting slow light in an engineered silicon photonic crystal waveguide. OPTICS LETTERS 2011; 36:1728-1730. [PMID: 21540983 DOI: 10.1364/ol.36.001728] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We demonstrate all-optical demultiplexing of a high-bandwidth, time-division multiplexed 160 Gbit/s signal to 10 Gbit/s channels, exploiting slow light enhanced four-wave mixing in a dispersion engineered, 96 μm long planar photonic crystal waveguide. We report error-free (bit error rate<10⁻⁹) operation of all 16 demultiplexed channels, with a power penalty of 2.2-2.4 dB, highlighting the potential of these structures as a platform for ultracompact all-optical nonlinear processes.
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Li J, O'Faolain L, Rey IH, Krauss TF. Four-wave mixing in photonic crystal waveguides: slow light enhancement and limitations. OPTICS EXPRESS 2011; 19:4458-4463. [PMID: 21369277 DOI: 10.1364/oe.19.004458] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We demonstrate continuous wave four-wave mixing in silicon photonic crystal waveguides of 396 μm length with a group index of ng=30. The highest observed conversion efficiency is -24 dB for 90 mW coupled input pump power. The key question we address is whether the predicted fourth power dependence of the conversion efficiency on the slowdown factor (η≈S4) can indeed be observed in this system, and how the conversion efficiency depends on device length in the presence of propagation losses. We find that the expected dependencies hold as long as both realistic losses and the variation of mode shape with slowdown factor are taken into account. Having achieved a good agreement between a simple analytical model and the experiment, we also predict structures that can achieve the same conversion efficiency as already observed in nanowires for the same input power, yet for a device length that is 50 times shorter.
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36
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Spurny M, O'Faolain L, Bulla DAP, Luther-Davies B, Krauss TF. Fabrication of low loss dispersion engineered chalcogenide photonic crystals. OPTICS EXPRESS 2011; 19:1991-1996. [PMID: 21369015 DOI: 10.1364/oe.19.001991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We demonstrate low loss photonic crystal waveguides in chalcogenide (Ge(33)As(12)Se(55)) glasses. The measured losses are as low as 21 dB/cm. We experimentally determine the refractive index of the thin film chalcogenide glass to be n = 2.6 and demonstrate that dispersion engineering can be performed up to a group index of ng = 40 in this relatively low refractive index contrast system.
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37
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O'Faolain L, Schulz SA, Beggs DM, White TP, Spasenović M, Kuipers L, Morichetti F, Melloni A, Mazoyer S, Hugonin JP, Lalanne P, Krauss TF. Loss engineered slow light waveguides. OPTICS EXPRESS 2010; 18:27627-27638. [PMID: 21197037 DOI: 10.1364/oe.18.027627] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Slow light devices such as photonic crystal waveguides (PhCW) and coupled resonator optical waveguides (CROW) have much promise for optical signal processing applications and a number of successful demonstrations underpinning this promise have already been made. Most of these applications are limited by propagation losses, especially for higher group indices. These losses are caused by technological imperfections ("extrinsic loss") that cause scattering of light from the waveguide mode. The relationship between this loss and the group velocity is complex and until now has not been fully understood. Here, we present a comprehensive explanation of the extrinsic loss mechanisms in PhC waveguides and address some misconceptions surrounding loss and slow light that have arisen in recent years. We develop a theoretical model that accurately describes the loss spectra of PhC waveguides. One of the key insights of the model is that the entire hole contributes coherently to the scattering process, in contrast to previous models that added up the scattering from short sections incoherently. As a result, we have already realised waveguides with significantly lower losses than comparable photonic crystal waveguides as well as achieving propagation losses, in units of loss per unit time (dB/ns) that are even lower than those of state-of-the-art coupled resonator optical waveguides based on silicon photonic wires. The model will enable more advanced designs with further loss reduction within existing technological constraints.
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Galli M, Gerace D, Welna K, Krauss TF, O'Faolain L, Guizzetti G, Andreani LC. Low-power continuous-wave generation of visible harmonics in silicon photonic crystal nanocavities. OPTICS EXPRESS 2010; 18:26613-26624. [PMID: 21165010 DOI: 10.1364/oe.18.026613] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We present the first demonstration of frequency conversion by simultaneous second- and third-harmonic generation in a silicon photonic crystal nanocavity using continuous-wave optical excitation. We observe a bright dual wavelength emission in the blue/green (450-525 nm) and red (675-790 nm) visible windows with pump powers as low as few microwatts in the telecom bands, with conversion efficiencies of ∼ 10 (-5) /W and ∼ 10/ W(2) for the second- and third-harmonic, respectively. Scaling behaviors as a function of pump power and cavity quality-factor are demonstrated for both second- and third order processes. Successful comparison of measured and calculated emission patterns indicates that third-harmonic is a bulk effect while second-harmonic is a surface-related effect at the sidewall holes boundaries. Our results are promising for obtaining practical low-power, continuous-wave and widely tunable multiple harmonic generation on a silicon chip.
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Monat C, Ebnali-Heidari M, Grillet C, Corcoran B, Eggleton BJ, White TP, O'Faolain L, Li J, Krauss TF. Four-wave mixing in slow light engineered silicon photonic crystal waveguides. OPTICS EXPRESS 2010; 18:22915-22927. [PMID: 21164630 DOI: 10.1364/oe.18.022915] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We experimentally investigate four-wave mixing (FWM) in short (80 μm) dispersion-engineered slow light silicon photonic crystal waveguides. The pump, probe and idler signals all lie in a 14 nm wide low dispersion region with a near-constant group velocity of c/30. We measure an instantaneous conversion efficiency of up to -9dB between the idler and the continuous-wave probe, with 1W peak pump power and 6 nm pump-probe detuning. This conversion efficiency is found to be considerably higher (>10 × ) than that of a Si nanowire with a group velocity ten times larger. In addition, we estimate the FWM bandwidth to be at least that of the flat band slow light window. These results, supported by numerical simulations, emphasize the importance of engineering the dispersion of PhC waveguides to exploit the slow light enhancement of FWM efficiency, even for short device lengths.
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40
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Portalupi SL, Galli M, Reardon C, Krauss TF, O'Faolain L, Andreani LC, Gerace D. Planar photonic crystal cavities with far-field optimization for high coupling efficiency and quality factor. OPTICS EXPRESS 2010; 18:16064-73. [PMID: 20720991 DOI: 10.1364/oe.18.016064] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Different types of planar photonic crystal cavities aimed at optimizing the far-field emission pattern are designed and experimentally assessed by resonant scattering measurements. We systematically investigate the interplay between achieving the highest possible quality (Q) factor and maximizing the in- and out-coupling efficiency into a narrow emission cone. Cavities operate at telecommunications wavelengths, i.e. around approximately 1.55 microm, and are realized in silicon membranes. A strong modification of the far-field emission pattern, and therefore a substantial increase of the coupling efficiency in the vertical direction, is obtained by properly modifying the holes around L3, L5 and L7 type PhC cavities, as we predict theoretically and show experimentally. An optimal compromise yielding simultaneously a high Q-factor and a large coupling to the fundamental cavity mode is found for a L7-type cavity with a measured Q congruent with 62000, whose resonant scattering efficiency is improved by about two orders of magnitude with respect to the unmodified structure. These results are especially useful for prospective applications in light emitting devices, such as nano-lasers or single-photon sources, in which vertical in- and out-coupling of the electromagnetic field is necessarily required.
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41
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Li J, Liang B, Liu Y, Zhang P, Zhou J, Klimonsky SO, Slesarev AS, Tretyakov YD, O'Faolain L, Krauss TF. Photonic crystal formed by the imaginary part of the refractive index. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2010; 22:2676-2679. [PMID: 20446300 DOI: 10.1002/adma.200903938] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
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42
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Corcoran B, Monat C, Pelusi M, Grillet C, White TP, O'Faolain L, Krauss TF, Eggleton BJ, Moss DJ. Optical signal processing on a silicon chip at 640Gb/s using slow-light. OPTICS EXPRESS 2010; 18:7770-7781. [PMID: 20588618 DOI: 10.1364/oe.18.007770] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We demonstrate optical performance monitoring of in-band optical signal to noise ratio (OSNR) and residual dispersion, at bit rates of 40Gb/s, 160Gb/s and 640Gb/s, using slow-light enhanced optical third harmonic generation (THG) in a compact (80microm) dispersion engineered 2D silicon photonic crystal waveguide. We show that there is no intrinsic degradation in the enhancement of the signal processing at 640Gb/s relative to that at 40Gb/s, and that this device should operate well above 1Tb/s. This work represents a record 16-fold increase in processing speed for a silicon device, and opens the door for slow light to play a key role in ultra-high bandwidth telecommunications systems.
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43
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Corcoran B, Monat C, Pudo D, Eggleton BJ, Krauss TF, Moss DJ, O'Faolain L, Pelusi M, White TP. Nonlinear loss dynamics in a silicon slow-light photonic crystal waveguide. OPTICS LETTERS 2010; 35:1073-1075. [PMID: 20364221 DOI: 10.1364/ol.35.001073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We directly investigate both experimentally and numerically the influence of optical nonlinear loss dynamics on a silicon waveguide based all-optical device. The dynamics of these nonlinear losses are explored through the analysis of optical limiting of an amplitude distorted 10 Gbit/s signal in a slow-light silicon photonic crystal waveguide. As the frequency of the distortion approaches the free-carrier recombination rate, free-carrier absorption reaches a steady state, leaving two-photon absorption the dominant dynamic nonlinear loss. Our results highlight the importance of engineering the free-carrier lifetime in silicon waveguides for high speed all-optical processing applications.
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Loiacono R, Reed GT, Gwilliam R, Mashanovich GZ, O'Faolain L, Krauss T, Lulli G, Jeynes C, Jones R. Germanium implanted Bragg gratings in silicon on insulator waveguides. ACTA ACUST UNITED AC 2010. [DOI: 10.1117/12.839502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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45
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Gardes FY, Brimont A, Sanchis P, Rasigade G, Marris-Morini D, O'Faolain L, Dong F, Fedeli JM, Dumon P, Vivien L, Krauss TF, Reed GT, Martí J. High-speed modulation of a compact silicon ring resonator based on a reverse-biased pn diode. OPTICS EXPRESS 2009; 17:21986-21991. [PMID: 19997443 DOI: 10.1364/oe.17.021986] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
High speed modulation based on a compact silicon ring resonator operating in depletion mode is demonstrated. The device exhibits an electrical small signal bandwidth of 19 GHz. The device is therefore a candidate for highly compact, wide bandwidth modulators for a variety of applications.
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46
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Grande M, O'Faolain L, White TP, Spurny M, D'Orazio A, Krauss TF. Optical filter with very large stopband (approximately 300 nm) based on a photonic-crystal vertical-directional coupler. OPTICS LETTERS 2009; 34:3292-3294. [PMID: 19881571 DOI: 10.1364/ol.34.003292] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We have designed, fabricated, and demonstrated a vertical directional coupler based on the coupling between a polymer waveguide and a W1 photonic crystal waveguide. The filters have a bandwidth of approximately 2 nm within a stopband of Delta lambda approximately 300 nm and an on-chip insertion loss of 1 dB. This is the first (to our knowledge) demonstration of a filter with such a large stopband that overcomes the bandwidth limitation of existing filters.
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47
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Kotlyar MI, Triandaphilov YR, Kovalev AA, Soifer VA, Kotlyar MV, O'Faolain L. Photonic crystal lens for coupling two waveguides. APPLIED OPTICS 2009; 48:3722-3730. [PMID: 19571929 DOI: 10.1364/ao.48.003722] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report the design, fabrication, and characterization of a new nanophotonic device comprising a two-dimensional photonic crystal (PhC) lens of size 3x4 microm fabricated in silicon-on-insulator. The PhC lens is put at the output of a planar waveguide of width 4.5 microm to couple light into a planar waveguide of width 1 microm, with two waveguides being of length 5 mm. A 1 microm off-axis displacement of the smaller waveguide leads to an 8-fold reduction of output light intensity, which means that the focal spot size at output of the PhC lens in silicon is less than 1 microm. The simulation has shown that the PhC lens has maximal transmittance at 1.55 microm, with the coupling efficiency being 73%. The focal spot size of the lens in air calculated at the FWHM is 0.32lambda (where lambda is the wavelength).
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48
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Monat C, Corcoran B, Ebnali-Heidari M, Grillet C, Eggleton BJ, White TP, O'Faolain L, Krauss TF. Slow light enhancement of nonlinear effects in silicon engineered photonic crystal waveguides. OPTICS EXPRESS 2009; 17:2944-2953. [PMID: 19219198 DOI: 10.1364/oe.17.002944] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We report nonlinear measurements on 80microm silicon photonic crystal waveguides that are designed to support dispersionless slow light with group velocities between c/20 and c/50. By launching picoseconds pulses into the waveguides and comparing their output spectral signatures, we show how self phase modulation induced spectral broadening is enhanced due to slow light. Comparison of the measurements and numerical simulations of the pulse propagation elucidates the contribution of the various effects that determine the output pulse shape and the waveguide transfer function. In particular, both experimental and simulated results highlight the significant role of two photon absorption and free carriers in the silicon waveguides and their reinforcement in the slow light regime.
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White TP, O'Faolain L, Li J, Andreani LC, Krauss TF. Silica-embedded silicon photonic crystal waveguides. OPTICS EXPRESS 2008; 16:17076-17081. [PMID: 18852818 DOI: 10.1364/oe.16.017076] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We report on the fabrication and characterization of silicon photonic crystal waveguides completely embedded in silica. These waveguides offer a robust alternative to air-membranes and are fully compatible with monolithic integration. Despite the reduced refractive index contrast compared to the air-membranes, these waveguides offer a considerable operating range of approximately 10 nm in the 1550 nm window. While the reduced index contrast weakens the perturbations due to surface roughness, we measure losses of 35 +/- 3dB/cm compared to 12 +/- 3 dB/cm for nominally identical air-membranes. Numerical analysis reveals that the difference in loss results from the different mode distribution and group index of the respective waveguide modes. Radius disorder is used as a fitting parameter in the numerical simulations with the best fits found for disorder levels of 1.4 - 1.7 nm RMS, which attest to the high quality of our structures.
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50
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Bog U, Smith CLC, Lee MW, Tomljenovic-Hanic S, Grillet C, Monat C, O'Faolain L, Karnutsch C, Krauss TF, McPhedran RC, Eggleton BJ. High-Q microfluidic cavities in silicon-based two-dimensional photonic crystal structures. OPTICS LETTERS 2008; 33:2206-2208. [PMID: 18830353 DOI: 10.1364/ol.33.002206] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We demonstrate postprocessed microfluidic double-heterostructure cavities in silicon-based photonic crystal slab waveguides. The cavity structure is realized by selective fluid infiltration of air holes using a glass microtip, resulting in a local change of the average refractive index of the photonic crystal. The microcavities are probed by evanescent coupling from a silica nanowire. An intrinsic quality factor of 57,000 has been derived from our measurements, representing what we believe to be the largest value observed in microfluidic photonic crystal cavities to date.
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