Diamond Photonic Crystals Research Articles

Strongly Confining Light with Air-Mode Cavities in Inverse Rod-Connected Diamond Photonic Crystals

Three-dimensional dielectric optical crystals with a high index show a complete photonic bandgap (PBG), blocking light propagation in all directions. We show that this bandgap can be used to trap light in low-index defect cavities, leading to strongly enhanced local fields. We compute the band structure and optimize the bandgap of an inverse 3D rod-connected diamond (RCD) structure, using the plane-wave expansion (PWE) method. Selecting a structure with wide bandgap parameters, we then add air defects at the center of one of the high-index rods of the crystal and study the resulting cavity modes by exciting them with a broadband dipole source, using the finite-difference time-domain (FDTD) method. Various defect shapes were studied and showed extremely small normalized mode volumes (Veff) with long cavity storage times (quality factor Q). For an air-filled spherical cavity of radius 0.1 unit-cell, a record small-cavity mode volume of Veff~2.2 × 10−3 cubic wavelengths was obtained with Q~3.5 × 106.

Colloidal cubic diamond photonic crystals through cooperative self-assembly.

Colloidal cubic diamond crystals with low-coordinated and staggered structures could display a wide photonic bandgap at low refractive index contrasts, which makes them extremely valuable for photonic applications. However, self-assembly of cubic diamond crystals using simple colloidal building blocks is still considerably challenging, due to their low packing fraction and mechanical instability. Here we propose a new strategy for constructing colloidal cubic diamond crystals through cooperative self-assembly of surface-anisotropic triblock Janus colloids and isotropic colloidal spheres into superlattices. In self-assembly, cooperativity is achieved by tuning the interaction and particle size ratio of colloidal building blocks. The pyrochlore lattice formed by self-assembly of triblock Janus colloids acts as a soft template to direct the packing of colloidal spheres into cubic diamond lattices. Numerical simulations show that this cooperative self-assembly strategy works well in a large range of particle size ratio of these two species. Moreover, photonic band structure calculations reveal that the resulting cubic diamond lattices exhibit wide and complete photonic bandgaps and the width and frequency of the bandgaps can also be easily adjusted by tuning the particle size ratio. Our work will open up a promising avenue toward photonic bandgap materials by cooperative self-assembly employing surface-anisotropic Janus or patchy colloids as a soft template.

Spectral tuning of diamond photonic crystal slabs by deposition of a thin layer with silicon vacancy centers

Abstract The controlled extraction of light from diamond optical color centers is essential for their practical prospective applications as single photon sources in quantum communications and as biomedical sensors in biosensing. Photonic crystal (PhC) structures can be employed to enhance the collection efficiency from these centers by directing the extracted light towards the detector. However, PhCs must be fabricated with nanoscale precision, which is extremely challenging to achieve for current materials and nanostructuring technologies. Imperfections inherently lead to spectral mismatch of the extraction (leaky) modes with color center emission lines. Here, we demonstrate a new and simple two-step method for fabricating diamond PhC slabs with leaky modes overlapping the emission line of the silicon vacancy (SiV) centers. In the first step, the PhC structure with leaky modes blue shifted from the SiV emission line is fabricated in a nanocrystalline diamond without SiV centers. A thin layer of SiV-rich diamond is then deposited over the PhC slab so that the spectral position of the PhC leaky modes is adjusted to the emission line of the SiV centers, thereby avoiding the need for nanoscale precision of the structuring method. An intensity enhancement of the zero-phonon line of the SiV centers by a factor of nine is achieved. The color centers in the thin surface layer are beneficial for sensing applications and their properties can also be further controlled by the diamond surface chemistry. The demonstrated PhC tuning method can also be easily adapted to other optical centers and photonic structures of different types in diamond and other materials.

Diamond photonic crystal mirror with a partial bandgap by two 2D photonic crystal layers

In this study, photonic crystals with a partial bandgap are demonstrated in the visible region using single-crystal diamonds. Quasi-three-dimensional photonic crystal structures are fabricated in the surface of the single-crystal diamonds using a tetrahedron Faraday cage that enables angled dry etching in three directions simultaneously. The reflection spectra can be controlled by varying the lattice constant of the photonic crystals. In addition, nitrogen-vacancy center single-photon sources are implanted on top of the diamond photonic crystals, and doubled collection efficiency from the light sources is achieved.

Strong light confinement in rod-connected diamond photonic crystals.

We show that it is possible to confine light in a volume of order 10-3 cubic wavelengths using only dielectric material. Low-index (air) cavities are simulated in high-index rod-connected diamond photonic crystals. These cavities show long storage times (Q-factors >106) even at the lowest volumes. Fabrication of such structures could open a new field of photon-level interactions.

Microsphere lithography for scalable polycrystalline diamond-based near-infrared photonic crystals fabrication

We demonstrate the fabrication of a polycrystalline diamond-based two-dimensional photonic crystal (PhC) slab using microsphere lithography (MSL). First, the essential issues of MSL on rough diamond surfaces are demonstrated. The peak-to-valley value of the rough surfaces is shown as the most important parameter in choosing the appropriate sphere size for the MSL technique. Second, we fabricate a diamond-based PhC composed of a hexagonal lattice of air holes and tuned to have a leaky mode in the near-infrared wavelength region at 1.31μm which is an important telecommunication window. A monolayer of plasma-treated polystyrene microspheres with controllable size and periodicity, combined with a metal mask, are utilised as templates in the fabrication process. The prepared diamond films and photonic crystal are characterised using scanning electron microscopy, atomic force microscopy, Raman spectroscopy, reflection, and transmission measurements. In order to investigate the optical properties of the PhC, the experimental measurements are compared with simulation outputs. The successful employment of MSL on rough diamond films with their unique properties opens the road to the large scale fabrication of highly durable and chemically inert scalable structures.

Direct wide-angle measurement of a photonic band structure in a three-dimensional photonic crystal using infrared Fourier imaging spectroscopy.

We propose a method to directly visualize the photonic band-structure of micrometer-sized photonic crystals using wide-angle spectroscopy. By extending Fourier imaging spectroscopy sensitivity into the infrared range, we have obtained accurate measurements of the band structures along the high-symmetry directions (X-W-K-L-U) of polymeric three-dimensional, rod-connected diamond photonic crystals. Our implementation also allows us to record single-wavelength reflectance far-field patterns showing very good agreement with simulations of the same designs. This technique is suitable for the characterization of photonic structures working in the infrared and, in particular, to obtain band-structure information of complete photonic band gap materials.

Enhanced Extraction of Silicon-Vacancy Centers Light Emission Using Bottom-Up Engineered Polycrystalline Diamond Photonic Crystal Slabs

Silicon vacancy (SiV) centers are optically active defects in diamond. The SiV centers, in contrast to nitrogen vacancy (NV) centers, possess narrow and efficient luminescence spectrum (centered at ≈738 nm) even at room temperature, which can be utilized for quantum photonics and sensing applications. However, most of light generated in diamond is trapped in the material due to the phenomenon of total internal reflection. In order to overcome this issue, we have prepared two-dimensional photonic crystal slabs from polycrystalline diamond thin layers with high density of SiV centers employing bottom-up growth on quartz templates. We have shown that the spectral overlap between the narrow light emission of the SiV centers and the leaky modes extracting the emission into almost vertical direction (where it can be easily detected) can be obtained by controlling the deposition time. More than 14-fold extraction enhancement of the SiV centers photoluminescence was achieved compared to an uncorrugated sample. Computer simulation confirmed that the extraction enhancement originates from the efficient light-matter interaction between light emitted from the SiV centers and the photonic crystal slab.

Modelling defect cavities formed in inverse three-dimensional rod-connected diamond photonic crystals

Defect cavities in 3D photonic crystal can trap and store light in the smallest volumes allowable in dielectric materials, enhancing non-linearities and cavity QED effects. Here, we study inverse rod-connected diamond (RCD) crystals containing point defect cavities using plane-wave expansion and finite-difference time domain methods. By optimizing the dimensions of the crystal, wide photonic bandgaps are obtained. Mid-bandgap resonances can then be engineered by introducing point defects in the crystal. We investigate a variety of single spherical defects at different locations in the unit cell focusing on high-refractive-index-contrast (3.3:1) inverse RCD structures; quality factors (Q-factors) and mode volumes of the resonant cavity modes are calculated. By choosing a symmetric arrangement, consisting of a single sphere defect located at the center of a tetrahedral arrangement, mode volumes < 0.06 cubic wavelengths are obtained, a record for high-index cavities.

2D inverse periodic opal structures in single crystal diamond with incorporated silicon-vacancy color centers

Well-ordered opal-diamond composite and inverted opal structure in single crystal (SC) diamond have been prepared by microwave plasma CVD. The process is based on epitaxial diamond growth through a monolayer of densely packed SiO2 spheres placed on a (100) HPHT diamond substrate. Finally, the opal monolayer with ≈600nm sphere diameter was completely embedded in SC CVD diamond forming a new type of ordered diamond composite. In addition, the inverse opal structures (air cavities in diamond) were produced by SiO2 etching. The XRD analysis confirmed the single crystal nature of the deposit. The photoluminescence spectrum exhibits a strong peak at 738nm wavelength of silicon-vacancy defects in diamond, indicating Si doping during the CVD process. The optical properties of the diamond structures were evaluated also with Raman spectroscopy and optical reflection spectrometry. The developed epitaxy-through-mask approach is considered as a potential strategy to fabricate multilayered (3D) SC diamond photonic crystals.

Surface-sensitive diamond photonic crystals for high-performance gas detection.

Diamond slotted photonic crystal (PhC) cavities were fabricated and used for gas detection. They exhibit wavelength sensitivity reaching a 350 nm per unit change of the refractive index of the gaseous environment of the PhC. With a simple oxidized surface termination, diamond PhCs display an ultrahigh sensitivity to the surface adsorption of polar molecules. Gaseous concentrations as low as 80 parts per million (ppm) of hexanol vapor in nitrogen are probed, and a detection limit in the ppm range is inferred, demonstrating a high interest of such devices for trace sensing.

Stereolithographic Additive Manufacturing of Diamond Photonic Crystal Composed of Titania and Alumina Micro Lattices

Three dimensional micro photonic crystals with a diamond structure made of a dense titania and alumina were fabricated successfully by using stereolithographic additive manufacturing. Photonic band gap properties were investigated in gigahertz and terahertz wave frequency ranges. Acrylic diamond lattice structures with nanometer sized particles of titania and alumina dispersion at 40 vol. % were fabricated by the stereolithography. The forming accuracy was 10 μm. After dewaxing and sintering process, the titania and alumina diamond lattice structures were obtained. The relative density reached above 98 %. Electromagnetic wave transmittances were measured by using a W-band millimeter waveguide connected with a network analyzer and a terahertz wave time domain spectroscopy. In the transmission spectra for the Γ-X &amp;lt;100&amp;gt; direction, a forbidden band was observed at 90 – 110 GHz and 0.4 – 0.6 THz. The band gap frequencies well agreed with calculated results by plane wave expansion (PWE) method. Additionally, simulated results by transmission line modeling (TLM) method indicated that a localized mode can be obtained by introducing a plane defect between twinned diamond lattice structures.

Cryptic iridescence in a fossil weevil generated by single diamond photonic crystals.

Nature's most spectacular colours originate in integumentary tissue architectures that scatter light via nanoscale modulations of the refractive index. The most intricate biophotonic nanostructures are three-dimensional crystals with opal, single diamond or single gyroid lattices. Despite intense interest in their optical and structural properties, the evolution of such nanostructures is poorly understood, due in part to a lack of data from the fossil record. Here, we report preservation of single diamond (Fd-3m) three-dimensional photonic crystals in scales of a 735,000 year old specimen of the brown Nearctic weevil Hypera diversipunctata from Gold Run, Canada, and in extant conspecifics. The preserved red to green structural colours exhibit near-field brilliancy yet are inconspicuous from afar; they most likely had cryptic functions in substrate matching. The discovery of pristine fossil examples indicates that the fossil record is likely to yield further data on the evolution of three-dimensional photonic nanostructures and their biological functions.

Study on Band Gap Varying of Diamond Photonic Crystals by Fabricating to Bring the Error of Dielectric Volume Fraction

To avoid the effect of the error of dielectric volume fraction brought by fabricating process on band gap, the diamond crystals with different the error of dielectric volume fraction were designed and fabricated to investigate the fluctuation of band gaps. Theses photonic crystals with a diamond structure were fabricated using alumina by stereolithography, gel-casting and sintering. The photonic band gaps were observed along &lt;100&gt; direction and the photonic band gaps were formed in different frequency range. Increasing the radius from 4.2mm to 4.32mm and changing band width from 0.8 to 1.39GHz, the radius is increased by 2.86%, and corresponding band width increased by 73.75%. Therefore, the fabrication error in mold and fabrication process including injecting mold, sintering should be maintained under the same conditions, which can retain the error of band gap.

Fabrication of Diamond Photonic Crystals with Oxide and Metallic Glasses Lattices for Terahertz Wave Control by Micro Pattering Stereolithography

Diamond lattice type photonic crystals with periodic arranged magnetic and dielectric materials can reflect the terahertz waves through Bragg diffraction. The fine diffraction lattices were fabricated successfully by using micro patterning stereolithography of computer aided designing and manufacturing methods. In this process, the photo sensitive acrylic resin paste mixed with micrometer sized metallic glass and oxide glass particles was spread on a glass substrate with 10 μm in layer thickness by using a mechanical knife edge, and cross sectional images of ultra violet ray were exposed with 2 μm in part accuracy. The high resolution exposure could be realized by using a digital micro-mirror device. The micro mirrors of 14 μm in edge length were tilted individually by piezoelectric actuators. Through the layer by layer stacking, the micrometer order metallic glass and oxide glass composite structure was formed. The magnetic and dielectric composite lattices could be obtained through the dewaxing and sintering process with the lower temperature of 400 ºC under the transition point of metallic glass and above the melting point of oxide glass. The amorphous structure formation after the heat treatment was verified by a X-ray diffraction analysis. A transmission spectrum of electromagnetic wave in terahertz frequency ranges for the formed magnetic and dielectric crystals with a diamond lattice structure was measured by using a terahertz time domain spectroscopy.

Robust flow of light in three-dimensional dielectric photonic crystals

Chiral defect waveguides and waveguide bend geometry were designed in diamond photonic crystal to mold the flow of light in three dimensions. Propagations of electromagnetic waves in chiral waveguides are robust against isotropic obstacles, which would suppress backscattering in waveguides or integrated devices. Finite-difference time-domain simulations demonstrate that high coupling efficiency through the bend corner is preserved in the polarization gap, as it provides an additional constraint on the polarization state of the backscattered wave. Transport robustness is also demonstrated by inserting two metallic slabs into the waveguide bend.

Tunable three-dimensional diamond photonic crystal made of a liquid medium

A three-dimensional diamond photonic crystal with an ultra-wide tunable bandgap and resonant mode has been proposed based on a liquid medium approach. A bandgap tuning range of up to 12.8% is achieved in the microwave regime. The liquid-infiltrated photonic crystal is realized by using a low-loss liquid medium of which a large refractive index variation from 1.58 to 6.32 is achieved. The weak-dispersion and non-resonant nature of the liquid ensure a broadband and low-loss performance from 12 to 18 GHz. The flexibly tunable bandgap and resonant mode of the proposed photonic crystal were demonstrated by simulation and experimental results.

Bandpass waveguide in 3D diamond-structure EBG fabricated by stereolithography and gel casting

A waveguide located in a diamond photonic crystal (PC) is presented in this article. The alumina-based three-dimensional electromagnetic band gap crystal has been designed, optimized, and fabricated by the stereolithography combined with gel-casting, which experimentally exhibited a large bandgap between 13.8 and 16.3 GHz with a relative width of 16.7%. Meanwhile, a waveguide located in such diamond structure has been designed and fabricated, which shows obvious bandpass between 13.8 and 15.5 GHz. Transmission properties of PCs waveguide will achieve their integration applications in standard microwave devices. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1145–1149, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27478

Exploiting Nanoroughness on Holographically Patterned Three‐Dimensional Photonic Crystals

AbstractThe fabrication of three‐dimensional (3D) diamond photonic crystals with controllable nanoroughness (≤120 nm) on the surface from epoxy‐functionalized cyclohexyl polyhedral oligomeric silsesquioxanes (POSS) is reported. The nanoroughness is generated on the 3D network due to microphase separation of the polymer chain segments in a nonsolvent during the rinsing step in holographic lithography process. The degree of roughness can be tuned by the crosslinking density of the polymer network, which is dependent on the loading of photoacid generators, the exposure dosage, and the choice of developer and rinsing solvent. Because the nanoroughness size is small, it does not affect the photonic band gap position of the photonic crystal in the infrared region. The combination of periodic microstructure and nanoroughness, however, offers new opportunities to realize superhydrophobicity and enhanced dye adsorption in addition to the photon management in the 3D photonic crystal.

Efficient light amplification in low gain materials due to a photonic band edge effect

One of the possibilities of increasing optical gain of a light emitting source is by embedding it into a photonic crystal (PhC). If the properties of the PhC are tuned so that the emission wavelength of the light source with gain falls close to the photonic band edge of the PhC, then due to low group velocity of the light modes near the band edge caused by many multiple reflections of light on the photonic structure, the stimulated emission can be significantly enhanced. Here, we perform simulation of the photonic band edge effect on the light intensity of spectrally broad source interacting with a diamond PhC with low optical gain. We show that even for the case of low gain, up to 10-fold increase of light intensity output can be obtained for the two-dimensional PhC consisting of only 19 periodic layers of infinitely high diamond rods ordered into a square lattice. Moreover, considering the experimentally feasible structure composed of diamond rods of finite height - PhC slab - we show that the gain enhancement, even if reduced compared to the ideal case of infinite rods, still remains relatively high. For this particular structure, we show that up to 3.5-fold enhancement of light intensity can be achieved.