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Photonic crystal waveguides can support polarisation singularities, which are predicted to be useful in future quantum information applications. For example, C-points possess local chirality, allowing spin-photon entanglement when a quantum dot is placed at its location. Photonic crystal waveguides also support slow-light modes, and we have studied the enhancement of this coupling in the slow-light regime. We have also studied the practicalities of using such C-points in real world waveguides with disorder.

We use slow-light photonic crystals to enhance optical switching and modulation in silicon. By using dispersion-engineered designs, a switch as short as 5 ¿m was achieved, in which we have demonstrated rerouting of optical pulses on a 3-ps time scale through the absorption of a femtosecond pulse. We additionally demonstrate a modulator with a Mach-Zehnder interferometer (MZI) configuration with flat-band slow-light photonic crystal phase shifters that is designed to give a large group-index-bandwidth product. An extinction ratio in excess of 15 dB is obtained over the entire 11-nm bandwidth of the modulator.

We demonstrate a silicon photonic crystal (PhC) directional coupler optical switch. By engineering the supermodes of the coupled system to provide a slow-light region, the switch has a total length of just 4.9 μm. Thermo-optic switching with a 20 μs response time via an integrated nickel microheater is shown. The proposed switch uses a silica overlayer and infilling of the etched silicon PhC, rather than the more usual membrane slab geometry. The silica infilling and overlayer provides a vertically symmetric structure and is a more robust solution compared to the membrane geometry. We also show that there is no apparent increase in optical loss due to the silica overlayer, despite operating above the lightline; the insertion loss for the air-bridge and silica-embedded structures are comparable (at 1–2 dB).

Control and repeatability in the fabrication of two-dimensional photonic crystal (PhC) slabs is becoming increasingly important as the technology matures towards practical applications. A key problem in this respect is the determination of the actual hole size in finished devices. We have developed an optical method for measuring the hole size in PhC slabs as an alternative to the inspection of scanning electron microscope (SEM) images. The optical method relies on determining the cut-off frequency of W1 PhC waveguides, which is easily measured and compared to calculations as a function of hole size. We show that the typical error in the measurement of hole diameter is approximately 2%, or 5 nm. This level of accuracy is a significant improvement over current methods, which rely on the inspection by SEM. SEM inspection can introduce large systematic errors because different electron detectors, and even different settings of the same detector, will provide differing contrasts between a hole and its edge. Such errors can be of the order of 20 nm, or as much as 5–10% of the absolute hole diameter. Furthermore, our method provides thefunctional or effective hole size, which determines the photonic function of the device, and which may be different from the physical hole size. # 2008 Elsevier B.V. All rights reserved.

We measure polarization- and wavelength-resolved spectra and spatial emission intensity distributions from silicon photonic crystal waveguides in the near-infrared spectral range using spectroscopic cathodoluminescence imaging polarimetry. A 30 keV electron beam, incident along the surface normal of the sample, acts as an ultrabroadband and deeply subwavelength excitation source. For photonic crystal waveguides with a broad range of design parameters, we observe a dominant emission intensity distribution that is strongly confined to the waveguide. For a period of 420 nm and a hole radius of 120 nm, this occurs at a wavelength of 1425 nm. The polarization-resolved measurements demonstrate that this feature is fully linearly polarized along the waveguide axis. Comparing the modal pattern and polarization to calculations of the electric field profiles confirms that we measure the odd TE waveguide mode of the system. This result demonstrates that the electron beam can couple to modes dominated by in-plane field components in addition to the more commonly observed modes dominated by out-of-plane field components. From the emission directionality, we conclude that we sample a leaky portion of the odd waveguide mode.

A dual waveguide heterostructure device that couples light from single mode optical fibres into nanophotonic devices with an overall modelled efficiency of 81% has been investigated. A four-stage taper design for the ridge waveguide which allows for a total device length of [email protected] is described. The fabrication of the ridge waveguide using chemically-assisted ion-beam etching has been optimised.

The first solid state structures for cavity quantum electrodynamic studies were realized analog to established designs from the field of trapped atom or ions: Single emitters (e.g. semiconductor quantum dots) were place in optical resonators with small mode volumes and a large quality factors. These devices have allowed the demonstration of effects that were already observed for atom/ion systems, like the strong coupling of a single emitter to an optical cavity mode [1,2]. However, a solid state platform offers much more control over the optical density of states than the open resonators used in quantum optics experiments with atoms or ions. Modern nano-fabrication tools can be used to pattern the dielectric environment of the emitters with nanometer precision, opening completely new possibility to tailor their photonic environment. This has led to the development of alternative structures, e.g. for single photon sources. Cavity based single photon sources rely on the Purcell effect to direct the spontaneous emission into a defined optical mode. However, it is also possible to collect a large fraction of the emitted photons in a single mode when the emission into other modes is suppressed. This can be achieved by embedding the quantum dots in photonic crystal waveguides [3] or nanowires [4]. A big advantage of these structures is their broadband operation that is not limited by the bandwidth of a cavity resonance.

Propagation of electromagnetic waves through a system of randomly placed cylinders has been modelled. It was found that there is a dip in the ballistic transmission spectra for both the E and H polarizations, which is associated with scattering of the partial wave with angular momentum equal to zero by a single cylinder.

The bandstructures of two-dimensional photonic crystals with octagonal quasicrystalline unit cells have been calculated. The existence of photonic band-gaps in such structures is demonstrated, and results showing the variation of the spectral position and width of the photonic band-gaps with the size of the unit cell and filling fraction within the unit cell are presented.

Transmission and reflection of light in disordered two-dimensional photonic crystals with an incomplete photonic band-gap have been modelled for various levels of disorder. It is found that ballistic and scattered light display different behaviours as a function of the disorder parameter. For ballistic light, the dependence of the transmission coefficient on the disorder parameter exhibits a threshold-like behaviour, whereas the transmission of scattered light increases rapidly for small disorder. Unlike for photonic crystals with a complete band-gap, the minimum of the transmission for scattered light does not coincide with the centre of the photonic band-gap, and Fabry–Perot-type oscillations can be seen within the photonic band-gap.

We have studied GaAs/oxidized AlAs (AlOx) Bragg reflectors with etched air grooves running parallel to the growth direction. Such structures possess periodic modulation of the refractive index in two dimensions, and we have found that they have a photonic band gap for E-polarized modes over a large range of parameters of the structure, and can support complete photonic band-gaps for both E- and H-polarizations for a more restricted range of values of the parameters. Also, for certain parameter values of the etched Bragg reflector, the total density of states in a wide spectral region is reduced by factor of up to 20 compared to an effective medium characterized by the mean dielectric constant.

An approach using simple analytical theory has been developed for the design of multilayered spectral optical filters based on coupled microcavities. The method has been applied to find the parameters of the optimal structure, providing a near square-shaped transmission band. The case of normal and oblique incident light has been considered. It is shown that the situation corresponding to the weak coupling-strong coupling threshold for coupled cavity modes is optimal for achieving a square-shaped transmission band.

Control and repeatability in fabrication of two-dimensional photonic crystal (PhC) slabs will become increasingly important as the technology matures into real device applications. A related problem is the determination of hole sizes in final etched devices. We have developed an optical method of measuring the hole size in PhC slabs as an alternative to the inspection of scanning electron microscope (SEM) images. The optical method relies on W1 PhC waveguides by patterning and fabricating reference W1 waveguides, the cut-off frequency of the waveguiding defect state can be measured and compared to calculations of this frequency as a function of hole size. Such calculations are relatively straightforward, and such in-situ transmission measurements are relatively cheap and fast. We show that the typical error in the measurement of hole radius is approximately 2%, or just 2–3 nm, and that this error is dominated by the uncertainty in the silicon slab thickness. Such performance is a significant improvement on current methods, which rely on the inspection via SEM. Not only is this slow and expensive, but there can be a large systematic error involved in the measurement. Different detectors, and even different settings of the same detector, will provide different contrasts between a hole and its edge, leading to different apparent hole sizes. Such errors in the absolute hole size can be of the order of 10 nm, which is as much as 5–10% for a PhC.

We demonstrate a silicon photonic crystal (PhC) optical switch with a 20-mus response time controlled by a thermo-optic microheater. The switch consists of a dispersion engineered PhC directional coupler that is only 4.9 mum long. Optical and electrical isolation is provided by backfilling the holes and embedding the PhC in a silica cladding to produce a vertically symmetric structure that is more robust than a membrane geometry. No increase in optical loss is observed due to the silica cladding, despite operating above the lightline; the insertion loss for airbridge and silica embedded structures are comparable at 1-2 dB.

We demonstrate nanoscale photonic point-to-point measurements characterizing a single component inside an all-optical signal-processing chip. We perform spectrally resolved near-field scanning optical microscopy on ultrashort pulses propagating inside a slow light photonic crystal waveguide, which is part of a composite sample. A power study reveals a reshaping of the pulse’s spectral density, which we model using the nonlinear Schrodinger equation. With the model, we are able to identify the various physical processes governing the nonlinear pulse propagation. Finally, we contrast the near-field measurements with transmission measurements of the complete composite sample to elucidate the importance of gaining local information about the evolution of the spectral density.

Using a silicon slow-light photonic crystal waveguide, we demonstrate the operation of a dynamic delay line based on an ultrafast indirect photonic transition to alter the group velocity of a pulse. We show continuously tuneable delays of up to 20 ps, using a waveguide just 300 μm in length. Our approach is scalable, in that both the maximum delay and capacity of the buffer are proportional to the length of the waveguide, and flexible, in that individual pulses in a pulse stream can be controlled independently, which we demonstrate by operating on pulses separated by just 30 ps.

This paper reports on experimental investigations of the evolution of the spectral density of an ultrashort laser pulse as it propagates through a composite sample consisting of a slow-light photonic crystal (PhC) waveguide and polymer access waveguides. A novel method of near-field scanning optical microscopy was used to measure the spectrum at different locations, and for different powers, only inside the PhC waveguide. This is in contrast to traditional transmission measurements where the evolution of the spectrum due to the entire system is observed.

This paper discusses the consequences of exploiting the phase degree-of-freedom in multi-pathway resonant coupling. As a test system, the simplest available structure, a plasmonic grating coupler, was chosen. Rigorous electromagnetic modeling was used to study how the geometry of a two component grating coupler, , controls the resonant plasmonic coupling. The coupling characteristics, in this case the amplitude and phase of the excited surface plasmon polariton (SPP), of each channel are determined by its corresponding amplitude and phase. And, as shown, adding a single second-order pathway, allows to completely turn off the plasmonic coupling.

In this work we use ultrafast pump-probe measurements to demonstrate a slow light photonic crystal (PhC) optical modulator that is based on free-carrier dispersion, and which operates in transmission.

We demonstrate, by theory and experiment, the ultrafast tilting of the dispersion curve of a photonic-crystal waveguide following the absorption of a femtosecond pump pulse. By shaping the pump-beam cross section with a nanometric shadow mask, different waveguide eigenmodes acquire different spatial overlap with the perturbing pump, leading to a local flattening of the dispersion by up to 11%. We find that such partial mode perturbation can be used to adiabatically compress the spectrum of a light pulse traveling through the waveguide. Publisher PDF

We demonstrate the ultrafast tilting of the dispersion curve of a photonic crystal waveguide following the absorption of a femtosecond pump pulse. By shaping the pump cross section with a shadow mask, different waveguide eigenmodes have different spatial overlaps with the perturbation, leading to a local flattening of the dispersion by up to 11%. Such partial mode perturbation can be used to adiabatically compress the spectrum of a light pulse in the waveguide.

We introduce the concept of an indirect photonic transition and demonstrate its use in a dynamic delay line to alter the group velocity of an optical pulse. Operating on an ultrafast time scale, we show continuously tuneable delays of up to 20 ps, using a slow light photonic crystal waveguide only 300 $\mu$m in length. Our approach is flexible, in that individual pulses in a pulse stream can be controlled independently, which we demonstrate by operating on pulses separated by just 30 ps. The two-step indirect transition is demonstrated here with a 30% conversion efficiency., Comment: "Copyright (2012) by the American Physical Society."

Through a fully analytical model [Phys. Rev. B 78, 245108 (2008)], we investigate the impact of several disorder models on backscattering losses in photonic crystal waveguides. To evaluate their relative relevance, we compare the predictions with loss measurements. The comparison suggests that a long-range disorder at the scale of every hole has to be considered in disorder model, in addition to the more classical hole surface roughness.

We use an indirect photonic transition to alter the group velocity of a pulse in a silicon photonic crystal waveguide. Delays of up to 20ps, with efficiencies of 30%, are achievable in a 300μm waveguide.

We propose a new design for compact tunable optical delay lines, based on adiabatic wavelength conversion and group velocity dispersion, in engineered silicon slow light photonic crystal waveguides. Actuation is performed over a small fraction of the device area, allowing for efficient operation in terms of switching power. We report on the experimental demonstration of variable delays up to 15 ps in a 300 µm long waveguide using this scheme, thus realising an ultrafast tunable delay line in an integrated format.

By performing ultrafast pump-probe experiments, we show the 0.3THz adiabatic frequency conversion of pulses in a slow-light photonic crystal waveguide with 80% efficiency. We demonstrate the use of this conversion scheme in a delay line.

We show a direct comparison between silicon reconfigurable delay lines based on coupled resonator optical waveguides and photonic crystal waveguides. The structures are used to selectively delay the two orthogonally polarized channels of a RZ-PolDM-DQPSK format at 100 Gbit/s.

We report statistical fluctuations for the transmissions of a series of photonic-crystal waveguides (PhCWs) that are supposedly identical and that only differ because of statistical structural fabrication-induced imperfections. For practical PhCW lengths offering tolerable -3dB attenuation with moderate group indices (n(g) approximately 60), the transmission spectra contains very narrow peaks (Q approximately 20,000) that vary from one waveguide to another. The physical origin of the peaks is explained by calculating the actual electromagnetic-field pattern inside the waveguide. The peaks that are observed in an intermediate regime between the ballistic and localization transports are responsible for a smearing of the local density of states, for a rapid broadening of the probability density function of the transmission, and bring a severe constraint on the effective use of slow light for on-chip optical information processing. The experimental results are quantitatively supported by theoretical results obtained with a coupled-Bloch-mode approach that takes into account multiple scattering and localization effects.

By performing an ultrafast pump-probe experiment, we demonstrate the adiabatic frequency conversion of a telecommunications pulse in a silicon photonic crystal waveguide. By using slow-light modes to spatially compress the pulse, a 1.3 ps long pulse is blue-shifted by 0.3 THz with 80% efficiency in a waveguide just 19 μm long. We also present the results of an adiabatic model of the process, which agrees excellently with the experimentally measured data.

All photonic crystal slab designs rely on the accurate control of the sizes of the holes during fabrication - a small error of just a few nanometers can mean a shift of tens of nanometers in the operating wavelength of the device. A key problem is the measurement of the hole size. We have developed an optical method which determines the functional hole diameter with a typical accuracy of 5 nm. We also suggest a way for the nanometre control of the hole diameter.

We demonstrate by experiment and theory that a light pulse propagating through a Si-based photonic-crystal waveguide is adiabatically blueshifted when the refractive index of the Si is reduced on a femtosecond time scale. Thanks to the use of slow-light modes, we are able to shift a 1.3-ps pulse at telecom frequencies by 0.3 THz with an efficiency as high as 80% in a waveguide as short as 19 mu m. An analytic theory reproduces the experimental data excellently, which shows that adiabatic dynamics are possible even on the femtosecond time scale as long as the external stimulus conserves the spatial symmetry of the system. Publisher PDF

We discuss the performance of slow-light enhanced optical switches and modulators fabricated in silicon. The switch is based on photonic crystal waveguides in a directional coupler geometry, and the dispersion of the device is engineered to allow a switching length as short as 5 μm and rerouting of optical signals within 3 ps. The 3 ps switching time is demonstrated using free carriers in the silicon generated by the absorption of a femtosecond pump pulse. The modulator is based on a Mach-Zehnder interferometer configuration, with photonic crystal waveguides in each arm to act as phase-shifters. A flat-band slow-light region has been engineered in the phase-shifters to provide an extinction ratio in excess of 15 dB over the entire 11 nm bandwidth of the modulator device.

Through a combined theoretical and experimental study of disorder-induced incoherent scattering losses in slow-light photonic crystal slab waveguides, we show the importance of Bloch mode reshaping and multiple scattering. We describe a convenient and fully three-dimensional theoretical treatment of disorder-induced extrinsic scattering, including the calculation of backscatter and out-of-plane losses per unit cell, and the extrapolation of the unit-cell loss to the loss for an entire disordered waveguide. The theoretical predictions, which are also compared with recent measurements on dispersion engineered silicon waveguides, demonstrate the failure of the Beer-Lambert law due to multiple scattering. We also explain why the previously assumed group velocity scalings of disorder-induced loss break down in general.

We present a method to fully characterize linear photonic devices that change their properties on ultrashort time scales. When we feed the device with a broadband input pulse and detect the resulting output field for a sufficient number of arrival times of the input, the device response to any other input with smaller bandwidth can be extracted numerically, without the need for additional measurements. Our approach is based on the formalism of linear time-varying systems, and we experimentally demonstrate its feasibility for the example of an ultrafast nanophotonic switch.

We demonstrate a silicon optical switch that can reroute optical signals within a switching time of just 3 ps. The switch is based on photonic crystal waveguides in a directional coupler geometry. The dispersion of the device has been engineered to provide slow-light enhancement, which allows the switching length of the device to be just 5 μm. The 3 ps switching time is demonstrated using free-carriers in the silicon generated by the absorption of a femtosecond laser pulse.

We report on a study of propagation losses in engineered slow light photonic crystal (PhC) waveguides. By modifying the rows of holes adjacent to the defect (see figure 1), it has been shown that dispersion can be reduced to manageable levels [1], enabling promising applications, such as optical buffers and for increasing light matter interactions. Loss then remains as the key issue facing slow light photonic crystals.

We observe light localization in a two-dimensional geometry, induced by residual disorder at a photonic band edge located below the light cone. The combination of a spectrally selective illumination and a grating assisted k-space imaging technique allows us to image the equifrequency surfaces associated with such a photonic band, with high accuracy and without aberrations. Thanks to this approach, the impact of the nonideal nature of real planar photonic crystals on the propagation properties of the Bloch wave at the band edge is decorrelated from the contribution of the intrinsic out-of-plane losses. As a by-product, our result demonstrates an immersion free effective numerical aperture as high as 3.5 in k space.

We demonstrate that we can switch the transmission of a directional coupler from one output port to another within a time as short as 3ps with laser pulse energies of less than 10pJ.

Photonic crystal slow light waveguides enable modulators with high speed and large bandwidth. Group indices of 30-40 are achieved with low loss and we demonstrate modulators of

The phenomenon of slow light in photonic crystal waveguides is used for miniaturized (5µm long) optical switches as well as the broadband (5-10 nm) enhancement of nonlinear effects such as self-phase modulation.

We present the design, fabrication, and operation of a polarization converter based on angled waveguides in the InP/InGaAsP material system. By combining design elements from mode evolution and birefringent devices, the total device length is kept short (less than 50 microm) and the insertion efficiency high at 81%+/-19%, which corresponds to an insertion loss of 1 dB. Devices operate broadband, i.e., the polarization conversion exceeds 15 dB over a 100 nm wavelength range. A polarization rotator with these specifications is a prime candidate for use in an integrated polarization diversity scheme.

A new mathematical method, the Phase Distribution Model, is devised for the calculation of attenuation and scattering of THz radiation in random materials. The accuracy of the approximation is tested by comparison with exact calculations and with experimental measurements on textiles and specially constructed phantoms.

Nature Photonics 8, 43–46 (2014); published online: 15 December 2013; corrected after print: 30 January 2014 The reference section in the print version of this Letter contained the following errors: For ref. 3, the volume number should have been 4 rather than 3. For ref. 17, “15, 1289–1295” should have been “http://dx.

We review the different types of dispersion engineered photonic crystal waveguides that have been developed for slow light applications. We introduce the group index bandwidth product (GBP) and the loss per delay in terms of dB ns −1 as two key figures of merit to describe such structures and compare the different experimental realizations based on these figures. A key outcome of the comparison is that slow light based on photonic crystals performs as well or better than slow light based on coupled ring resonators.

We use a Fourier-space imaging technique relying on outcoupling grating probes to study the coupled mode interaction and dispersion properties of guided modes in silicon-on-insulator codirectional couplers. Our approach allows us to measure the mode splitting inherent to coupled systems, determine the mode symmetry, and locally probe the coupling length with an accuracy of +/- 50 nm. A systematic study of directional couplers with different waveguide widths, coupling gaps, and e-beam exposure doses is reported in order to verify the results across a wider parameter space. (C) 2008 American Institute of Physics.

Switching light is one of the most fundamental functions of an optical circuit. As such, optical switches are a major research topic in photonics, and many types of switches have been realized. Most optical switches operate by imposing a phase shift between two sections of the device to direct light from one port to another, or to switch it on and off, the major constraint being that typical refractive index changes are very small. Conventional solutions address this issue by making long devices, thus increasing the footprint, or by using resonant enhancement, thus reducing the bandwidth. We present a slow-light-enhanced optical switch that is 36 times shorter than a conventional device for the same refractive index change and has a switching length of 5.2 microm.

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. (C) 2010 Optical Society of America Publisher PDF

Backscattering and its dependence on group index is experimentally studied in ring-resonators and photonic crystals. Independently of the structure, the behavior of optical devices can be dramatically modified as backscattered power increases with group index.

We experimentally investigate the effect of residual disorder on the dispersion curve of light near a band edge. A Fourier space imaging technique accurately distinguishes the propagating regime from evanescent regime in planar photonic crystal. (C) 2009 Optical Society of America

Near-field scanning optical microscopy (NSOM) using the aperture probe (AP) has helped to uncover exciting phenomena such as single molecule excitation [1], optical polarization singularities [2] and slow light [3]. However, the interpretations of these measurements have all been based on the assumption that what is collected is the in-plane electric near-field [2,3,4]. And, until the recent advent of metamaterials [5] this view has remained unchallenged. Interestingly, the AP has been recently reported yield information on the in-plane magnetic field [6]. In this study we show that contrary to both, the originally held assumption and the assertion of the new study, a typical AP (as shown in Fig. 1a) is sensitive to both electric and magnetic fields. Specifically, we show that the AP collects radiation from the four in-plane components of the near-field.We collect the near-field with a NSOM (shown in in Fig. 1b). We use /2(2) to orient the fields such that Ly detects light from an electric field along y (Ey), and a magnetic field along x (Hx). To identify the APs sensitivity to the in-plane electric (E//) and magnetic field (H//), we measure on a photonic crystal waveguide that has distinctly different electric and magnetic near-fields. In Fig 1c we show how the computed spatial distribution of Ey and Hx evolve with increasing height (the blue arrows in Fig. 1c highlight the differences). At a height of 20 nm above the sample, the measured signal on Ly (shown in Fig 1d, Lx not shown) neatly matches both Ey and Hx. Surprisingly, at increasing heights the signal matches neither purely Ey, nor only Hx. Hence, we investigate the possibility that the AP collects both E// and H//. To find the relative contribution of each of field we fit the measurements with a superposition of the calculated E// and H//. The fits, shown in the right column of Fig. 1d, excellently match the data, when using only the sensitivity to E// and H// on each detector to fit scans at 9 heights simultaneously (only 5 are shown). For 8 probes, with diameters ranging from 130 nm to 370 nm we find that the sensitivity of a coated probe to E// and H// is within a factor three. Based on the excellent agreement between the measurements and the fitted fields, we conclude that we detect all in-plane fields and no vertical field components. This creates a new possibility for a full map of the EM near-field. Moreover the ability to measure the magnetic as well as the electric near-field, opens up new avenues towards a better understanding of light matter interactions on the nanoscale, as well as facilitate the development of magnetically active structures.