No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Integrated Spectral Filters Consisting of Several Dielectric Ridges on the Surface of a Slab Waveguide
ResearchGate has not been able to resolve any citations for this publication.
The theoretical analysis and experimental demonstration of a waveguide resonator are presented based on bound states in the continuum in an integrated photonic chip platform. The continuum has the form of a collimated beam of light which is confined vertically in a transverse electric (TE) mode of a silicon slab. The bound state is a discrete transverse‐magnetic (TM)‐like mode of a ridge on the silicon slab. The coupling between the slab and ridge modes results in a single sharp resonance at the wavelength where they phase match. This phenomenon is experimentally demonstrated on a silicon photonic chip using foundry‐compatible parameters and it is interfaced on‐chip to standard single‐mode silicon nanowire waveguides. The fabricated chip exhibits a single sharp resonance near 1550 nm with a line width of a few nanometers, an extinction ratio of 25 dB, and a thermal stability of 19.5 pm °C−1. It is believed that the demonstration of a resonance operating near a bound state in the continuum realized using guided wave components will form the basis of a new approach to on‐chip wavelength filtering and sensing applications. The first experimental demonstration of waveguide resonance based on bound state in the continuum in silicon photonics is presented. This is achieved by coupling between a continuum of transverse‐electric (TE) slab modes to a discrete quasi‐transverse‐magnetic (quasi‐TM) mode of a silicon ridge to create a single sharp resonance. A theoretical description of the phenomenon and experimental results are presented.
In the present work, we numerically study the performance (reflectance and scattering /absorption losses) of dielectric Bragg gratings for surface plasmon polaritons using a rigorous coupled-wave analysis technique. We demonstrate that the main reason behind the low efficiency of such Bragg reflectors is the parasitic out-of-plane scattering of SPP at the grating ridges. As efficient approaches for scattering suppression, we propose an increase in the grating period at a fixed aspect ratio and the utilization of a two-layer geometry of the grating ridge. We show that these two approaches enable increasing the efficiency of the SPP Bragg grating by 15-35%. The obtained results may find applications in the design of high-efficiency plasmonic elements. © 2018, Institution of Russian Academy of Sciences. All rights reserved.
We show that a very simple structure consisting of a single subwavelength dielectric ridge on the surface of a slab waveguide enables spatial integration and differentiation of the profile of optical beams propagating in the waveguide. The integration and differentiation operations are performed in reflection and in transmission, respectively, at oblique incidence of the beam impinging on the ridge. The implementation of these operations is associated with the resonant excitation of a cross-polarized eigenmode of the ridge. We demonstrate that the quality factor of the resonances strongly varies along the dispersion curves and allows one to achieve the required tradeoff between the integration (or differentiation) quality and the amplitude of the resulting beam. The presented rigorous numerical simulation results confirm high-quality integration and differentiation. The proposed integrated structure may find application in ultrafast all-optical analog computing and signal processing systems.
We consider the derivation of a dispersion relation of Bloch surface waves supported by interfaces between a semi-infinite one-dimensional photonic crystal and a homogeneous medium. From the derived dispersion relation, we obtain an explicit analytical expression that defines the relationship between the propagation constant and the thickness of the upper layer of the photonic crystal. © 2018, Institution of Russian Academy of Sciences. All rights reserved.
Narrow bandpass filters are applied in laser systems, imaging, telecommunications, and astronomy. Traditionally implemented with thin-film stacks, there is recent interest in alternative means incorporating photonic resonance effects. Here, we demonstrate a new approach to bandpass filters that engages the guided-mode resonance effect working with a cavity-based Fabry–Perot resonance to flatten and steepen the pass band. Both of these resonance mechanisms are native to simple resonant bandpass filters placed in a cascade. Numerical examples provide quantitative spectral properties including pass-band shape and sideband levels. Thus, we compare the spectra of single-layer 1D and 2D resonant gratings with the dual-cascade design incorporating identical gratings. Two- and three-cavity designs are measured against a classic multi-cavity thin-film filter with 151 layers. Whereas these initial results show comparable and improved results achieved with sparse structures, the challenge remains of developing a suitable fabrication technology to capitalize on this promise.
Bound states in the continuum (BICs) are waves that remain localized even though they coexist with a continuous spectrum of radiating waves that can carry energy away. Their very existence defies conventional wisdom. Although BICs were first proposed in quantum mechanics, they are a general wave phenomenon and have since been identified in electromagnetic waves, acoustic waves in air, water waves and elastic waves in solids. These states have been studied in a wide range of material systems, such as piezoelectric materials, dielectric photonic crystals, optical waveguides and fibres, quantum dots, graphene and topological insulators. In this Review, we describe recent developments in this field with an emphasis on the physical mechanisms that lead to BICs across seemingly very different materials and types of waves. We also discuss experimental realizations, existing applications and directions for future work.
Computer-generated planar holograms are a powerful approach for designing planar lightwave circuits with unique properties. Digital planar holograms in particular can encode any optical transfer function with high customizability and is compatible with semiconductor lithography techniques and nanoimprint lithography. Here, we demonstrate that the integration of multiple holograms on a single device increases the overall spectral range of the spectrometer and offsets any performance decrement resulting from miniaturization. The validation of a high-resolution spectrometer-on-chip based on digital planar holograms shows performance comparable with that of a macrospectrometer. While maintaining the total device footprint below 2 cm2, the newly developed spectrometer achieved a spectral resolution of 0.15 nm in the red and near infrared range, over a 148 nm spectral range and 926 channels. This approach lays the groundwork for future on-chip spectroscopy and lab-on-chip sensing.
Recently [Opt. Lett. 25, 1092 (2000)], two of the present authors proposed extending the domain of applicability of grating theories to aperiodic structures, especially the diffraction structures that are encountered in integrated optics. This extension was achieved by introduction of virtual periodicity and incorporation of artificial absorbers at the boundaries of the elementary cells of periodic structures. Refinements and extensions of that previous research are presented. Included is a thorough discussion of the effect of the absorber quality on the accuracy of the computational results, with highly accurate computational results being achieved with perfectly matched layer absorbers. The extensions are concerned with the diversity of diffraction waveguide problems to which the method is applied. These problems include two-dimensional classical problems such as those involving Bragg mirrors and grating couplers that may be difficult to model because of the length of the components and three-dimensional problems such as those involving integrated diffraction gratings, photonic crystal waveguides, and waveguide airbridge microcavities. Rigorous coupled-wave analysis (also called the Fourier modal method) is used to support the analysis, but we believe that the approach is applicable to other grating theories. The method is tested both against available numerical data obtained with finite-difference techniques and against experimental data. Excellent agreement is obtained. A comparison in terms of convergence speed with the finite-difference modal method that is widely used in waveguide theory confirms the relevancy of the approach. Consequently, a simple, efficient, and stable method that may also be applied to waveguide and grating diffraction problems is proposed.
Time-domain optical processing implemented through linear spectral filtering offers unique potential for future high-bandwidth communications systems. One key to realization of this potential is the development of robust, cost-effective, fully integrated filtering devices. A new spectral filtering device concept, derived from the unique properties of index holograms stamped or otherwise written in thin planar waveguide slabs, is described. The holograms that are described provide for high-resolution spectral filtering while at the same time mapping general input spatial waveforms to desired output waveforms.
We propose and theoretically and numerically investigate narrowband integrated filters consisting of identical resonant dielectric ridges on the surface of a single-mode dielectric slab waveguide. The proposed composite structures operate near a bound state in the continuum (BIC) and enable spectral filtering of transverse-electric-polarized guided modes propagating in the waveguide. We demonstrate that by proper choice of the distances between the ridges, flat-top reflectance profiles with steep slopes and virtually no sidelobes can be obtained using just a few ridges. In particular, the structure consisting of two ridges can optically implement the second-order Butterworth filter, whereas at a larger number of ridges, excellent approximations to higher-order Butterworth filters can be achieved. Owing to the BIC supported by the ridges constituting the composite structure, the flat-top reflection band can be made arbitrarily narrow without increasing structure size. In addition to the filtering properties, the investigated structures support another type of BIC—the Fabry–Perot BIC—arising when the distances between adjacent ridges meet the Fabry–Perot resonance condition. In the vicinity of the Fabry–Perot BIC, an effect similar to electromagnetically induced transparency is observed, namely, sharp transmittance peaks against the background of a wide transmittance dip.
We investigate the diffraction of the guided modes of a dielectric slab waveguide on a simple integrated structure consisting of a single dielectric ridge on the surface of the waveguide. Numerical simulations based on aperiodic rigorous coupled-wave analysis demonstrate the existence of sharp resonant features and bound states in the continuum (BICs) in the reflectance and transmittance spectra occurring at the oblique incidence of a transverse-electric (TE)-polarized guided mode on the ridge. Using the effective index method, we explain the resonances by the excitation of cross-polarized modes of the ridge. Formation of the BICs are confirmed using a theoretical model based on coupled-wave theory. The model suggests that the BICs occur due to the coupling of quasi-TE and quasi-transverse-magnetic modes of the structure. Simple analytical expressions for the angle of incidence and the ridge width predicting the location of the BICs are obtained. The existence of high-Q resonances and BICs enables using the considered integrated structure for sensing, transformation of optical signals, and enhancing nonlinear light–matter interactions. Due to the Lorentzian line shape of the resonances near the BICs, the struc-ture is also promising for filtering applications.
We propose a simple integrated narrowband filter consisting of two grooves on the surface of a slab waveguide. Spectral filtering is performed in transmission at oblique incidence due to excitation of an eigenmode of the structure localized at a ridge cavity between the grooves. For the considered parameters, strictly zero reflectance and unity transmittance are achieved at resonant conditions. Width and location of the transmittance peak can be controlled by changing the widths of the grooves and of the ridge, respectively. The proposed filter may find application in waveguide-integrated spectrometers.
Criteria and tolerances are discussed for realizing grating filters with bandwidths as narrow as 0.1 Å. Techniques are presented for minimizing the adverse effect of film thickness variations which broaden filter response and raise out of band ripple. Using these techniques a grating filter fabricated on a glass thin‐film waveguide is demonstrated which has 73% reflectivity and a 3‐dB bandwidth of 0.15 Å.
Broad‐band grating filters have been fabricated on glass thin‐film waveguides and evaluated with a tunable dye laser. Measured and calculated filter responses were found to be in good agreement. Grating filters with bandwidths of 300 and 150 Å, and reflectivities of 18 and 40%, respectively, are reported.
Standard Bragg filters (dielectric waveguides with a grating
overlay) show a stopband only in reflection. Filters with
quarter-wave-shifted gratings have an extremely narrow transmission peak
the center of the stopband but its shape (a sharp triangle with a broad
bottom) is not suitable for system design. Using standard coupled-mode
theory together with transfer-matrix formalism, we show that by
introducing several phase-shift regions and properly choosing their
locations and magnitudes the transmission spectrum can be tailored into
a nearly rectangular shape. For InP-InGaAsP based Bragg-grating filters
estimates are made of achievable channel spacings in wavelength-division
multiplexing systems