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Photonic integrated circuits (PICs) are revolutionizing nanotechnology, with far-reaching applications in telecommunications, molecular sensing, and quantum information. PIC designs rely on mature nanofabrication processes and readily available and optimised photonic components (gratings, splitters, couplers). Hybrid plasmonic elements can enhance PIC functionality (e.g., wavelength-scale polarization rotation, nanoscale optical volumes, and enhanced nonlinearities), but most PIC-compatible designs use single plasmonic elements, with more complex circuits typically requiring ab initio designs. Here we demonstrate a modular approach to post-processes off-the-shelf silicon-on-insulator (SOI) waveguides into hybrid plasmonic integrated circuits. These consist of a plasmonic rotator and a nanofocusser, which generate the second harmonic frequency of the incoming light. We characterize each component’s performance on the SOI waveguide, experimentally demonstrating intensity enhancements of more than 200 in an inferred mode area of 100 nm2, at a pump wavelength of 1320 nm. This modular approach to plasmonic circuitry makes the applications of this technology more practical., Chip-scale modular components are important for nanophotonic applications. Here, the authors demonstrate post-processing of a silicon-on-insulator waveguide into an integrated hybrid plasmonic circuit, consisting of a plasmonic rotator and a nanofocusser module, which together result in nanoscale nonlinear wavelength conversion.

We review our recent work on the generation of novel optical solitons arising from different, high orders of dispersion and combinations thereof. By incorporating a spectral pulse-shaper in a mode-locked laser cavity, we can tailor the net-cavity dispersion, allowing us to access a wide range of new operating regimes corresponding to previously unobserved soliton pulses. We demonstrate the generation of solitons arising between self-phase modulation and any pure, negative even order of dispersion, as well as soliton molecules consisting of multiple solitons with different frequencies but that are temporally coincident.

The authors demonstrate the existence of optical solitons arising from the balance between self-phase modulation and negative, pure, even high-order dispersion using a fiber laser incorporating a spectral pulse shaper.

We report the generation and characterization of soliton-molecules in dispersion-managed fiber lasers. Solitons at two different frequencies, with common (negative) dispersion, have identical group velocities; these solitons form a bound state with temporal beat fringes.

We report a continuum of pulse-like soliton solutions to the generalized nonlinear Schr ̈odinger equation with both quadratic and quartic dispersion and a Kerr nonlinearity. We show that the well-known nonlinear Schr ̈odinger solitons, which occur in the presence of only negative (anomalous) quadratic dispersion, and pure-quartic solitons, which occur in the presence of only negative quartic dispersion, are members of a large superfamily, encompassing both. The members of this family, none of which are unstable, have exponentially decaying tails, which can exhibit oscillations. We find new analytic solutions for positive quadratic dispersion and negative quartic dispersion and investigate the soliton dynamics. We also find evidence that a combination of the quadratic and quartic dispersion, rather than exclusively quadratic dispersion, is likely to improve the performance of soliton lasers.

We report the first laser emitting pure-quartic solitons, temporal optical solitons arising from the balance of Kerr nonlinearity and fourth-order dispersion. We demonstrate that these pulses follow new energy-width scaling.

We study nonlinear pulse propagation in an optical fiber with positive quartic dispersion and gain, and find an exact asymptotic solution. Our solution is confirmed by numerical simulations based on the nonlinear Schrödinger equation.

In optical fibre resonators, the balance between anomalous quadratic dispersion and self-phase modulation (SPM) gives rise to optical solitons [1]. These pulses have made a significant impact in a wide range of photonic applications including telecommunications and lasers. However, these conventional soliton-based lasers can only deliver modest pulse energy due to the appearance of Kelly sidebands arising from periodical perturbations in the cavity [2] and a fixed energy-width scaling. Recently, a new class of soliton, arising from the balance of anomalous quartic dispersion and SPM, called pure-quartic soliton (PQS), were observed in a dispersion engineered photonic crystal waveguide [3]. PQSs have huge potential for generating ultrashort pulses with high energy due to their generalized area theorem (E ∼ 1/Δτ3), however they are yet to be observed in fibre platforms [4]. Here we report on the generation of PQS pulses from a passively mode-locked fibre laser incorporating a programmable spectral pulse-shaper that induces a dominant quartic net cavity dispersion. We find that the spectral profile of the generated pulses are in good agreement with the spectral shape of PQSs [3]. We also observe spectral sidebands in this quartic-dispersion cavity, in analogy to the conventional soliton case [2], and find that their positions are in excellent agreement with analytic predictions. These are strong evidences of a novel type of mode-locked laser, the PQS laser, which has the potential to reach dramatically higher energies at short pulse durations than its conventional soliton counterpart [3,4].

We report the generation of pure-quartic solitons from a fiber laser. Quartic cavity dispersion is achieved by an intracavity pulse-shaper. The pulses are characterized through spectral and temporal phase-resolved measurements and resonant dispersive wave analysis.

Plasmonic waveguides are promising in many applications because of their subwavelength field confinement, which can strongly enhance light-matter interactions. Nevertheless, how to efficiently evaluate their Kerr nonlinear performance is still an open question because of the presence of relatively large linear losses. Here a simple and versatile figure of merit (FOM) is proposed for Kerr nonlinear waveguides with linear losses. To derive the FOM, a generalized full-vectorial nonlinear Schrodinger equation governing nonlinear pulse propagation in a lossy waveguide is developed, and an approximate analytic solution of the degenerate four wave mixing conversion efficiency is derived and validated. The effectiveness of the FOM is verified with an all-plasmonic and a hybrid-plasmonic waveguide configuration. Rigorous results show that the optimal waveguide length for the highest conversion efficiency is ln 3 times the attenuation length. At this length, the upper limits of the conversion efficiency and the nonlinear phase shift are determined by the FOM. These results provide fundamental theory and useful guidance in exploring plasmonic waveguides for nonlinear optical applications.

We study the propagation of ultrashort pulses in optical fiber with gain and positive (or normal) quartic dispersion by self-similarity analysis of the modified nonlinear Schrödinger equation. We find an exact asymptotic solution, corresponding to a triangle-like T 4 / 3 intensity profile, with a T 1 / 3 chirp, which is confirmed by numerical simulations. This solution follows different amplitude and width scaling compared to the conventional case with quadratic dispersion. We also suggest, and numerically investigate, a fiber laser consisting of components with positive quartic dispersion that emits quartic self-similar pulses.

The recently discovered pure-quartic solitons, arising from the interaction of quartic dispersion and Kerr nonlinearity, open the door to unexplored soliton regimes and ultrafast laser science. Here, we report a general analysis of the dispersion and nonlinear properties necessary to observe pure-quartic solitons in optical platforms. We apply this analysis, in combination with numerical calculations, to the design of pure-quartic soliton supporting microstructured optical fibers. The designs presented here, which have realistic fabrication tolerances, support unperturbed pure-quartic soliton propagation providing access to an unmatched platform to study novel soliton physics. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

The European Union has launched the Blue growth concept as a strategy for stimulating economic growth in European seas. It is accompanying the core principles of the Green growth paradigm that seek to stimulate smart, sustainable and inclusive growth of economic activities. Focusing on Blue growth, this article examines its adequacy to enable social innovation as a strategy for the use and management of marine resources. Social innovation is interpreted as the changing behaviour of a group of actors joined in a network, leading to new and improved ways of collaborative action within the group and beyond. Social innovation can contribute to changing behaviour across different institutional settings, across markets and public sectors, and to enhancing bottom-up responsible inventiveness towards integration of social, economic and environmental objectives. Based on case-study research it is concluded that, to secure long-term sustainable development over short-term benefits, a social innovation perspective in the maritime domain will depend on cooperation, inclusiveness and trust.

We determine, experimentally and numerically, the electric and magnetic Purcell factors in a fishnet metamaterial in the frequency range 5--15 GHz by measuring the impedance of a dipole antenna. We compare measurements and numerical simulations of the Purcell factor for transverse electric (${\mathrm{TE}}_{\mathrm{z}}$) and transverse magnetic (${\mathrm{TM}}_{\mathrm{z}}$) polarizations. For ${\mathrm{TM}}_{\mathrm{z}}$ polarization, the dispersion relation of the structure is hyperbolic and enhances the Purcell factor. For ${\mathrm{TE}}_{\mathrm{z}}$ polarization, the dispersion relation does not allow any propagating solutions and decreases the Purcell factor below the effective plasma frequency. Eigenmode calculations of the periodic unit cell of the metamaterial are used to obtain the band structure and confirm the presence of hyperbolic isofrequency surfaces. The isofrequency surfaces are used to calculate the density of states (DOS). We also use the impedance method to obtain the DOS by averaging the Purcell factor obtained at different locations over the periodic unit cell and find good agreement with DOS calculated from eigenmode calculations.

We report total absorption of unpolarized, wide bandwidth (800-1550 nm) light in 90 nm thick graphene-based metamaterial. Grooves in the metamaterial couple incoming light into the absorber’s guided modes. Fabrication is low-cost and scalable.

Through numerical simulations and analytical developments we show the propagation behaviour, stability, and energy scaling of the recently discovered pure quartic solitons, indicating excellent potential for pure-quartic solitons in ultrafast lasers.

Silicon is an ideal material for on-chip applications, however its poor acoustic properties limit its performance for important optoacoustic applications, particularly for Stimulated Brillouin Scattering (SBS). We theoretically show that silicon inverse opals exhibit a strongly improved acoustic performance that enhances the bulk SBS gain coefficient by more than two orders of magnitude. We also design a waveguide that incorporates silicon inverse opals and which has SBS gain values that are comparable with chalcogenide glass waveguides. This research opens new directions for opto-acoustic applications in on-chip material systems., Comment: 4 pages, 6 figures

© 2015 Optical Society of America. The guided mode resonances (GMRs) of diffraction gratings surrounded by low index materials can be designed to produce broadband regions of near perfect reflection and near perfect transmission. These have many applications, including in optical isolators, in hybrid lasers cavities and in photovoltaics. The excitation of rapid GMRs occurs in a background of slowly varying Fabry-Perot oscillation, which produces Fano resonances.We demonstrate the critical role of the polarity of adjacent Fano resonances in the formation of the broadband features. We design gratings for photovoltaic applications that operate at wavelengths where material absorption must be considered and where light is incident at non-normal angles.

We theoretically investigate a nonlinear all-optical switching scheme based on a long period grating written in a highly nonlinear chalcogenide fiber. We investigate the impact of two-photon absorption on the device and show that the influence of a modest amount of two photon absorption is actually beneficial to device performance as quantified by the power transfer function and improvement of the Q-factor of an incident signal. © 2007 Elsevier B.V. All rights reserved.

The usual technique for calculating the mesoscopic conductance of materials is based on Pichard's transfer matrix method [J.L. Pichard, Thesis, University of Paris, Orsay, 1984]. The essential ideas of the theory of conductance for electronic systems also extend to electromagnetic systems such as waveguides and photonic devices. In the standard formulation of Pichard's treatment, there is an explicit assumption that the number of channels (or “leads”) in the input and output media is identical. In this paper, we extend the theory to handle the general situation when the input and output media may support different numbers of (propagating) channels, as is needed to study the photon conductance of semi-infinite waveguides. We show that the pivotal conclusions of Pichard's original derivation, including the existence of the key polar decomposition of the transfer matrix, continue to hold, even though the premise on which the original formulation was based (i.e., that the matrices involved are square and invertible) no longer hold. We also demonstrate this generalisation by calculating the conductance ladder for a photonic crystal waveguide terminated in free space.

Temporal optical solitons have been the subject of intense research due to their intriguing physics and applications in ultrafast optics and supercontinuum generation. Conventional bright optical solitons result from the interaction of anomalous group-velocity dispersion and self-phase modulation. Here we experimentally demonstrate a class of bright soliton arising purely from the interaction of negative fourth-order dispersion and self-phase modulation, which can occur even for normal group-velocity dispersion. We provide experimental and numerical evidence of shape-preserving propagation and flat temporal phase for the fundamental pure-quartic soliton and periodically modulated propagation for the higher-order pure-quartic solitons. We derive the approximate shape of the fundamental pure-quartic soliton and discover that is surprisingly Gaussian, exhibiting excellent agreement with our experimental observations. Our discovery, enabled by precise dispersion engineering, could find applications in communications, frequency combs and ultrafast lasers., Optical solitons are pulses that propagate undistorted. Here, the authors demonstrate a class of soliton arising from the interaction of self-phase modulation with quartic dispersion, rather than with quadratic dispersion as occurs in conventional solitons.

We compare coupling between parallel waveguides within one-dimensional photonic crystals and coupling between conventional waveguides. We consider the situation in which coupling between the waveguides is minimized, so that light in the waveguides propagates essentially independently. Subject to this condition, we compare the minimum mutual distance between conventional planar waveguides and waveguides in one-dimensional photonic crystals. We find that the packing densities of the conventional and periodic structures are comparable.

Nanowire arrays exhibit efficient light coupling and strong light trapping, making them well suited to solar cell applications. The processes that contribute to their absorption are interrelated and highly dispersive, so the only current method of optimizing the absorption is by intensive numerical calculations. We present an efficient alternative which depends solely on the wavelength-dependent refractive indices of the constituent materials. We choose each array parameter such that the number of modes propagating away from the absorber is minimized while the number of resonant modes within the absorber is maximized. From this we develop a semi-analytic method that quantitatively identifies the small range of parameters where arrays achieve maximum short circuit currents. This provides a fast route to optimizing NW array cell efficiencies by greatly reducing the geometries to study with full device models. Our approach is general and applies to a variety of materials and to a large range of array thicknesses., Comment: Accepted by ACS Photonics

We present a novel method to manipulate mode coupling by using tilted gratings written in standard fiber that is rotated during the writing process. We show theoretically that such gratings exhibit significantly reduced transmission losses in the 15-nm wavelength range below the main core-to-core reflection peak. By combining with existing methods, cladding mode losses can be further reduced.

Using a systematic approach based on a Bloch function expansion and the method of multiple scales, we present a rigorous derivation of the coupled-mode equations for light propagation through deep quadratically nonlinear gratings. The coupled-mode equations for deep gratings differ from those derived previously for shallow gratings in that the coefficients have different values and additional nonlinear terms appear. In the shallow grating limit these equations reduce to the standard coupled-mode equations. Our results show that deep grating effects can be significant in GaAs–AlAs thin film stacks, while in glass optical fibers these effects are too small to play a role. Using a standard shooting technique, bright soliton solutions to the new equations are obtained.

Light propagation through nonuniform gratings with slowly varying parameters is studied using a Schrodinger-like equation. This treatment is intuitively pleasing when applied to uniform gratings as the results are then expressed in terms of the dispersion of the grating. It is shown here that when applied to nonuniform gratings, this method leads to an additional and potentially significant contribution to the dispersion that is not included in naive treatments. It is found that the magnitude of this dispersion can be larger than the total dispersion of the structure. An approximate expression for the reflectivity is also given.

We demonstrate all-optical switching in rocking filters which are externally written in photosensitive fiber using ultra-violet irradiation. This fabrication technique allows considerable flexibility in the design of the rocking filter and lets one tailor the switching characteristics. Using 2 ps pulses from a Ti:sapphire laser and a 0.889 m rocking filter, we measure a switching power of 300 W, corresponding to a switching energy of about 600 pJ.

We study experimentally modulational instability and multiple-soliton generation in apodized Bragg gratings. We confirm earlier theoretical predictions that the parameters of the instability are widely tunable: a strain variation of 0.003% on the fiber grating leads to a variation in the repetition rate of the generated pulse train by a factor of 2. The results are in qualitative agreement with numerical simulations, and with the results of a simple analysis based on the nonlinear Schrodinger equation.

We have fabricated superstructure rocking filters which operate on the principle of linear polarization rotation through the twisting of the birefringent axes of photosensitive elliptical-core fibers by UV radiation. The polarization coupling spectrum of these filters consists of a series of narrow resonances which are roughly equally spaced in frequency. This can result in a comb-like response extending over the entire single-mode frequency range of the fiber. Applications of such structures are also discussed.

We develop the theory of linear and nonlinear grating superstructures, gratings in which the parameters vary periodically with position on the scale of typically about 1 mm. Following earlier work in semiconductors, these have now been written in optical fibers. We develop the theory by introducing a set of 'super envelopes': envelopes of the usual envelope functions of the grating structure. We show that under very general conditions these super envelopes satisfy a set of super coupled mode equations, and that these equations have solitary wave solutions.

We show that light trapped in an optical cavity can be extracted from that cavity in an ultrashort burst by means of a trigger pulse. We find a simple analytic description of this process and show that while the extracted pulse inherits its pulse length from that of the trigger pulse, its wavelength can be completely different. Cavity Optical Pulse Extraction is thus well suited for the development of ultrashort laser sources in new wavelength ranges. We discuss similarities between this process and the generation of Hawking radiation at the optical analogue of an event horizon with extremely high Hawking temperature. Our analytic predictions are confirmed by thorough numerical simulations.

We identify a family of unusual slow-light modes occurring in lossy multimode grating waveguides, for which either the forward or backward mode components, or both, are degenerate. In the fully degenerate case, the response can be modulated between coherent perfect absorption (zero reflection) and perfect reflection by varying the wave amplitudes in a uniform input waveguide. The perfectly absorbed wave has anomalously short absorption length, scaling as the inverse one-third power of the absorptivity. Published version

We discuss two aspects of nonlinear propagation of fiber gratings. The first of these is grating solitons, which were recently observed experimentally. Grating solitons exist because of the balancing of nonlinearity and grating dispersion. The second is the nonlinear interaction occuring when a strong pump pulse and a weak signal pulse copropagate through a grating. This is predicted to lead to pulse compression and enhanced parametric amplification of the signal pulse. Although these latter effects have not yet been observed experimentally, the required parameters are comparable to those for observing grating solitons.

We study pulse formation in a laser containing a frequency shifting element, but without dispersion, and find simple approximate expressions for the pulse parameters. The operation of such lasers can be understood without reference to soliton-like effects.

We show that a waveguide with multiple gratings can have a modal dispersion relation which supports frozen light. This means that light can be coupled efficiently to low group velocity modes of an optical waveguide or can even have finite coupling to zero group velocity modes. These effects are associated with stationary points in the dispersion of the form ω-ω o ⊃(k⊃-k o⊃)m, for integer order m>1, around a center frequency ω o and wave number k o. Stationary points of any order can be created, not only regular band edges (m=2), but also degenerate band edges (m>2 and even) and stationary inflection points (m odd). Using the perturbation theory of matrices in Jordan normal form, the modes and their properties are calculated analytically. Efficient coupling is shown to stem from evanescent modes which must accompany the presence of high-order stationary points with m>2. © 2012 American Physical Society.

We present a semi-analytical formulation for calculating the supermodes and corresponding Bloch factors of light in hexagonal lattice photonic crystal waveguide arrays. We then use this formulation to easily calculate dispersion curves and predict propagation in systems too large to calculate using standard numerical methods., Comment: Accepted by J. Opt. Soc. Am. B, DocID:160522. http://www.opticsinfobase.org/abstract.cfm?msid=160522

Most dielectric waveguides depend for guidance on total internal reflection within a region of elevated refractive index. A little‐explored alternative to this is Bragg reflection. Here we consider a ‘‘Bragg’’ optical fiber in which a cylindrical Bragg grating is used to inhibit radial power flow. We find that such Bragg fibers can be guaranteed to be effectively single‐moded, with no polarization degeneracy; the electric field in this fundamental mode is purely azimuthal (transverse electric polarized).

Degenerate band edges (DBEs) of a photonic bandgap have the form (ω- ωD)∝k2m for integers m > 1, with ωD the frequency at the band edge. We show theoretically that DBEs lead to efficient coupling into slow-light modes without a transition region, and that the field strength in the slow mode can far exceed that in the incoming medium. A method is proposed to create a DBE of arbitrary ordermby couplingmoptical modes with multiple superimposed gratings. The enhanced coupling near a DBE occurs because of the presence of one or more evanescent modes, which are absent at conventional quadratic band edges. We furthermore show that the coupling can be increased or suppressed by varying the number of excited evanescent waves. © 2011 Optical Society of America.

Stationary Inflection Points (SIPs) around a frequency ω 0 are of the form ω-ω 0 ∝ km for any positive odd integer. We show theoretically that SIPs of order m can be created in optical waveguides such as optical fiber gratings or periodic nanobeam waveguides by coupling between m modes. Remarkably, we find that at the SIP frequency significant incident energy can be coupled into the waveguide even though the group velocity of the associated mode is zero. Here we demonstrate this frozen light for cubic (k3) and quintic (k5) SIPs and relate it to the existence of evanescent modes at the interface and demonstrate it.

We report on the generation of 2.04 μm light from an 801 nm Ti:Sapphire source via soliton self-frequency shift and resonant dispersive wave emission in a PCF with low OH loss and broad anomalous dispersion region.

We report the first experimental demonstration of Bragg grating-based nonlinear switching in a bismuth-oxide single-mode fiber. Exploiting the strong χ3-nonlinearity of this fiber in a cross-phase modulation scheme, we change the transmission of a probe near the grating stop band from 90 % to 20 %, a 6.5 dB extinction ratio, at powers as low as 55 W. This is an 18-fold improvement in the switching power compared to the best demonstrations in silica. The experimental results agree well with numerical simulations.

We present a systematic theoretical method to design PC waveguides with low or zero group velocities. Our method is based on separating the PC mirror from the waveguide, which enabled us to derive an analytical expression for the group velocity.

We experimentally demonstrate solid-core photonic crystal fibers that guide via the inhibited coupling mechanism. We measure an overall transmission window of more than an octave, as well as an uninterrupted width of almost one octave. The fiber is fabricated in polymer, with high-index ring-shaped inclusions. This type of fiber was conceived based on a simple model which shows that the cutoffs of the modes of a thin ring cluster around the cutoffs of planar waveguide modes. The model shows that such ring based fibers are closely related to kagome and square lattice hollow core fibers, and have transmission bandwidths that could in principle reach 1.6 octaves. Measured transmission properties are in good agreement with rigorous modelling.

Many nonlinear systems exhibiting wave propagation, support solitons, nonlinear excitations that propagate unchanged, due to a balance of nonlinearity and dispersion. Of particular interest, both as a subject within photonics, as well as a topic of basic research, is their interaction with periodic structures, such as photonic crystals or gratings. Optical fibers and fiber gratings are rich experimental environments for nonlinear physics. The propagation of light in such a fiber is described approximately by the nonlinear Schrodinger equation. Here we demonstrate, both in experiment and simulation, that the process of soliton excitation, which is inherently discrete, profoundly changes the high power transmission properties of pulses through a Fiber Bragg grating for frequencies close to the band-edge. The quantization manifests itself in a characteristic staircase shape of the transmission spectrum at high powers. This behaviour is analyzed by a systematic study of the temporally resolved transmission spectra, which allows us to identify gap solitons as causing the transmission quantization. They act as discrete, self-induced transmission channels, because only solitons are able to propagate through the otherwise "forbidden" band-gap.

We study numerically nonlinear pulse propagation in a phase-shifted Bragg grating with a π phase-shift. The phase-shift acts as a cavity, accumulating the field inside the grating, and hence improving the switching efficiency. Due to material nonlinearity such cavity can operate in a bistable regime, enabling all-optical switching between high and low transmission states. We give optimization criteria for grating design that reduce the switching threshold and minimize the response time of the device. We demonstrate that if the grating and the pulse parameters are chosen carefully, a temporal reshaping of the transmitted pulse occurs. An asymmetric shape of the output pulse is an indication of the pulse self-switching between the two states of a bistable Bragg cavity.

Photonic crystal fibers often consist of rotationally symmetric inclusions in an otherwise uniform background medium. The band diagrams and modes of such structures can be efficiently calculated using geometry-specific methods that exploit this rotational symmetry. Until now, these have only been applied to fibers in which the inclusions are circular and have a uniform refractive index. Here, we generalize this to arbitrary rotationally symmetric inclusions using a transfer matrix approach, and we implement this approach in an approximate scalar method, which is valid for low-index contrasts and in the rigorous Rayleigh multipole method. We apply the methods to structures incorporating inclusions with graded refractive indices and to structures incorporating metal rings. © 2009 Optical Society of America.

Solid core photonic bandgap fibers (SC-PBGFs) consisting of an array of high index cylinders in a low index background and a low index defect core have been treated as a cylindrical analog of the planar anti-resonant reflecting optical waveguide (ARROW). We consider a limiting case of this model in which the cylinders in the SC-PBGF cladding are widely spaced apart, so that the SC-PBGF modal loss characteristics should resemble the antiresonant scattering properties of a single cylinder. We find that for glancing incidence, the single cylinder scattering resonances are Fano resonances, and these Fano resonances do in fact appear in the loss spectra of SC-PBGFs. We apply our analysis to enhance the core design of SC-PBGFs, specifically with an eye towards improving the mode confinement in the fundamental bandgap.

We characterize the spontaneous emission of dye that is introduced into the central core of a tapered photonic crystal fiber. Since the photonic crystal period in the fibre cladding varies along the taper, the transmission and spontaneous emission spectra over a wide range of relative frequencies can be observed. The spontaneous emission spectra of the fibre transverse to the fiber axis show suppression due to partial band-gaps of the structure, and also enhancement of spontaneous emission near the band edges. We associate these with van Hove features, as well as finite cluster size effects.