Photonic Bandgap Structures Research Articles

Graphene load for harmonic rejection and increasing the bandwidth in Quasi Yagi–Uda array THz antenna for the 6G wireless communication

The THz array antenna is necessary for many applications such as the 6G satellite communication for the next generation of cell phone services. In this type of antenna increasing the bandwidth and harmonic rejection is vital. In this paper, a novel substrate integrated waveguide (SIW) Quasi Yagi–Uda antenna is suggested with a high Q-factor of 573 for 0.482 THz, and the photonic band-gap structure is also added for amending the antenna Q-factor and reduces the side-lobe level. Basic studies show the effect of SIW formation and PBG on the Q-factor and gain of this antenna. However, arraying and adding a power divider can impact the antenna return loss and increasing the harmonic or resonance in other frequencies which is not interesting in real antennas. Therefore, a THz filter based on the graphene load is added between the power divider and the array antenna to reduce the return loss in harmonic and increasing the bandwidth of the antenna to 15.2 % and the total gain of the antenna is 9.07 dB with a directive pattern and side-lobe level of −5 dB. As a result, the graphene load in the power dividers can be used for omitting unwilling harmonic in the array structure.

Influence of a cylindrical waveguide with a concentric photonic band-gap wall on interatomic resonance energy transfer

We consider how the rate of resonance energy transfer (RET) between an excited atom and a ground-state one is affected by the presence of a cylindrical photonic band-gap waveguide by using the Green’s function approach. Both positions inside and outside the wall and three types of atomic dipole moment orientations, namely radial, azimuthal and axial orientations, are examined. Results for the photonic band-gap structure and those for the perfectly reflecting one are compared. Differences between the two are found to be significant near the surfaces. Frequency dependence of the rate, which is beyond the perfectly reflecting wall model, is investigated. It is shown that when the waveguide is located in between two atoms which have transition dipole moments parallel with the axis and transition frequency falling within the gap region, the RET is suppressed.

Photonic band gap structure microstrip patch antenna for WiMAX and Wi-Fi application

Photonic band gap structure microstrip patch antenna for WiMAX and Wi-Fi application

Video-Rate Identification of High-Capacity Low-Cost Tags in the Terahertz Domain.

In this article, we report on video-rate identification of very low-cost tags in the terahertz (THz) domain. Contrary to barcodes, Radio Frequency Identification (RFID) tags, or even chipless RFID tags, operate in the Ultra-Wide Band (UWB). These THz labels are not based on a planar surface pattern but are instead embedded, thus hidden, in the volume of the product to identify. The tag is entirely made of dielectric materials and is based on a 1D photonic bandgap structure, made of a quasi-periodic stack of two different polyethylene-based materials presenting different refractive indices. The thickness of each layer is of the order of the THz wavelength, leading to an overall tag thickness in the millimetre range. More particularly, we show in this article that the binary information coded within these tags can be rapidly and reliably identified using a commercial terahertz Time Domain Spectroscopy (THz-TDS) system as a reader. More precisely, a bit error rate smaller than 1% is experimentally reached for a reading duration as short as a few tens of milliseconds on an 8 bits (~40 bits/cm2) THID tag. The performance limits of such a tag structure are explored in terms of both dielectric material properties (losses) and angular acceptance. Finally, realistic coding capacities of about 60 bits (~300 bits/cm2) can be envisaged with such tags.

Enhanced circular dichroism of sparse nanoobjects by localized superchiral optical field

The spectroscopic methods of circular dichroism (CD) is commonly used in analysing the chirality of molecules, which plays an important role in pharmaceutical compounds. However, the current methods require high sample density due to the weak CD effect of natural material, making it challenging to detect the signal of individual chiral molecule. In this work, we propose a technique to enhance CD signal of individual chiral molecule with the use of superchiral optical field, which is acquired by focusing a twisted radially polarized vortex onto a one-dimensional photonic band gap structure. Through adjusting the topological charge and the focusing angle of the illumination, a deep subwavelength optical field with full width at half maxima (FWHM) of 0.02λ and 22.4-fold superchirality factor enhancement can be generated. In addition, we demonstrate that up to 20-fold CD enhancement can be obtained by introducing 2 nm on-resonant chiral molecule into the superchiral optical field. This finding will have widely potential applications in CD spectroscopy and superresolution imaging for sparse subdiffraction chiral objects.

Multicolored absorbing nickel oxide films based on anodic electrochromism and structural coloration

Inorganic electrochromic materials are promising for applications in color-based chromogenic technologies. Limited color control in these materials has, however, hitherto hampered their applications. Here, we show that multicolored nickel oxide (NiO) films can be obtained due to the combined effect of the intrinsic color of NiO and the structural color of the inverse opal structures by tailoring anodic oxide NiO films, exhibiting an absorption tail in the visible region into three-dimensional ordered macroporous inverse opal photonic bandgap structures. Various colors were achieved by the synergistic mechanism of structural and electrochromic coloration, thus realizing a wide spectrum of blue, green, yellow, orange, and brown colors depending on pore size, wall thickness, and viewing angle. Importantly, it is shown that the depth of color can be varied by applying an external potential. The electrochromic coloring of the inverse opal NiO films is found to be very different from the typical optical switching of non-structural NiO films. Thus, our work brings insights into the development of inorganic colored electrochromic materials.

Stability of moving Bragg solitons in a semilinear coupled system with cubic–quintic nonlinearity

We investigate the photonic bandgap structure, soliton properties and their stability in a semilinear coupled system where one core has cubic–quintic nonlinearity and is equipped with a Bragg grating, while the other one is uniform and linear. The investigation reveals that three distinct bandgaps, namely the upper, lower and central gaps, exist in the model. It is shown that the model supports two disjoint soliton families which are designated as Type 1 and Type 2 solitons. The soliton families exist only in the upper and lower bandgaps and are separated by a boundary at which no soliton solutions exist. A systematic numerical stability analysis is performed. It is found that vast regions in both the upper and lower bandgaps exist where Type 1 solitons are stable. However, Type 2 solitons are found to be always unstable. The effects of system parameters such as group velocity mismatch between the cores, velocity of solitons, and the coupling coefficient on the stability of solitons are analysed.

Electro-optic/metamaterial/electro-optic heterostructure defect induced resonant modes in reflectance spectrum of a band gap structure based on TiO2/SiO2 multilayers

Extremely tunable one dimensional photonic band gap structures are proposed for optical integrated circuit (OIC) applications. Ideal crystal is made of alternating layers of TiO2 and SiO2 dielectric slabs. Two defective crystals are also considered by inserting composite defects of electro-optic and metamaterial slabs in the ideal structure. Optical characteristics of the proposed structures are tailored by using 4 × 4 transfer matrix method at the wavelength range of 410‒480 nm. Dependence of the crystals’ reflectance on the structural characteristics is systematically extracted by not only discussing the crystals reflectivity at various thicknesses of the layers qualitatively but also by extracting the values of the resonant modes' reflectivity amount and Q-factors quantitatively. Furthermore, the effect of the light incident angle, defect layers’ optical axis orientation and externally applied voltages to the ends of the electro-optic layers are considered. Results clearly reflect how easily the response of the proposed crystals could be tuned in practice. So that stop band gaps of as large as ~ 45 nm width and shifts of more than 35 nm might take place in the reflectance spectrum of the crystals by controlling the layers' size. But it is shown that the low size of the metamaterial layer does not play a serious role on the optical features of the crystals. Similarly it comes out that at least 100 V bias is needed to be applied to the ends of the electro-optic layer to see somewhat observable changes at resonant modes. Instead, by changing the incident angle from 0 to 80°, significant changes of the gap width as well as ~ > 30 nm shift in resonant modes are realized.

Millimeter-Wave Frequency-Reconfigurable Metasurface Antenna Based on Vanadium Dioxide Films

A novel frequency-reconfigurable method using vanadium dioxide (VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) is proposed. VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is one kind of phase change material (PCM) which can be electrically switched between the states of insulator and metal. By integrating the VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film into a uniplanar compact photonic-bandgap (UC-PBG) structure, a frequency-reconfigurable metasurface (FRMS) structure with frequency ratio of 1.78 is constructed accordingly. Moreover, the active VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based FRMS is used as radiation element to design a high-gain millimeter-wave frequency-reconfigurable metasurface antenna (FRMSA), which is excited by a stepped waveguide through two slots of different lengths. In order to electrically activate the VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films of the antenna, a simple dc bias co-planarly localized with the FRMS is well designed. Benefiting from the convenient connection of the UC-PBG, only simple connection with two sides of the antenna is required for the dc bias, thus causing little impact on radiation due to far from the radiation region. One prototype is fabricated and measured for demonstration. When the VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film is activated to insulating state, the measured results show that the proposed FRMSA can operate in 23.25-24.3 GHz with the maximum gain of ~8.7 dBi, while it can work in 37-39.8 GHz with a peak gain of ~7.6 dBi when driven to metallic state. The ratio of two frequencies is about 1:1.61. Compared with other reported VO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based antennas, the proposed antenna exhibits a larger frequency ratio and higher gain in millimeter-wave bands.

Electrically Tunable Plasmonic Biosensors Based on Cavity-Coupled Structure With Graphene

In this research, we proposed a highly tunable hybrid plasmonic biosensor for identifying molecule fingerprints of proteins in the infrared range. The device is composed of a photonic band-gap structure and a cavity. The plasmonic energy is confined inside the cavity to enhance the light-analyte interactions. A layer of graphene is placed on the bottom surface of the cavity that is filled with analytes for detection. Our device has a high value of effective sensitivity that is defined as the ratio of the resonant frequency shift to the change of effective refractive index when the cavity is loaded with an analyte. The effective refractive index takes into account the effects of both the cavity structure and the optical property of the analyte. Another feature of our device is that a wide-ranging electrical tunability can be realized by applying various values of bias voltage to the graphene. The resonant frequency can be tuned for sensing different analytes without redesigning and refabricating the device. In addition, the graphene tunability can improve the sensitivity in detecting the non-targeted analytes. A prototype was designed based on photonic theory and fabricated via bottom-up lithography techniques. The research results are expected to be beneficial for nanometer-range bio-identifications and infrared optical sensors.

Far-field optical imaging of surface plasmons with a subdiffraction limited separation.

When an ultrathin silver nanowire with a diameter less than 100 nm is placed on a photonic band gap structure, surface plasmons can be excited and propagate along two side-walls of the silver nanowire. Although the diameter of the silver nanowire is far below the diffraction limit, two bright lines can be clearly observed at the image plane by a standard wide-field optical microscope. Simulations suggest that the two bright lines in the far-field are caused by the unique phase distribution of plasmons on the two side-walls of the silver nanowire. Combining with the sensing ability of surface plasmons to its environment, the configuration reported in this work is capable of functioning as a sensing platform to monitor environmental changes in the near-field region of this ultrathin nanowire.

Polarization-selective modulation of supercavity resonances originating from bound states in the continuum

Bound states in the continuum (BICs) are widely studied for their ability to confine light, produce sharp resonances for sensing applications and serve as avenues for lasing action with topological characteristics. Primarily, the formation of BICs in periodic photonic band gap structures are driven by symmetry incompatibility; structural manipulation or variation of incidence angle from incoming light. In this work, we report two modalities for driving the formation of BICs in terahertz metasurfaces. At normal incidence, we experimentally confirm polarization driven symmetry-protected BICs by the variation of the linear polarization state of light. In addition, we demonstrate through strong coupling of two radiative modes the formation of capacitively-driven Freidrich-Wintgen BICs, exotic modes which occur in off-Γ points not accessible by symmetry-protected BICs. The capacitance-mediated strong coupling at 0° polarization is verified to have a normalized coupling strength ratio of 4.17% obtained by the Jaynes-Cummings model. Furthermore, when the polarization angle is varied from 0° to 90° (0° ≤ ϕ < 90°), the Freidrich-Wintgen BIC is modulated until it is completely switched off at 90°.

Silicon waveguide as virtual photonic bandgap structure array for realizing compact optical filters

ABSTRACT An engineered silicon rib waveguide on Silicon-On-Insulator platform which can act as virtual photonic bandgap structure is proposed. Selective periodic etching of materials from a rib waveguide is done to create a periodic rib-ridge structure. Each of the rib-ridge sections will therefore have different effective refractive indices and will act as virtual multilayered periodic structure or one-dimensional photonic bandgap structure. Their spatial positions and widths can be controlled to realize different type of photonic filters for integrated photonics applications. Realization of narrowband, multi-band and band-pass filter are shown here. These types of waveguide based monomaterial optical filters avoid the challenges generally faced while fabricating multilayer structures of different heterogeneous materials having different refractive indices. Moreover, as the device is waveguide based, its size is very small and will be useful for compact integrated photonics.

Propagating multi-channel four-wave mixing process in the modulated moving photonic band gap.

Three and four electromagnetically induced transparency windows generate the multi-channel four-wave mixing (FWM) process are observed in a four-level atomic system. The transmission of the probe field and the reflection of the FWM are investigated in the modulated moving photonic band gap structures which are caused by the coupling fields with a relative small detuning offset when scanning detuning frequency of the probe field and the dressing field, respectively. The experimental results show that the more channels spectrum signal of the FWM process can be modulated and the generated multi-channel can be further modulated by adding a dressing field. We have also explained theoretically these experimental results which may have applications in the design of photonic crystal and optical signal amplifiers.

Photonic Bandgap Hepta-Band Stacked Microstrip Antenna for L, S and C Band Applications

This paper proposed a novel design of hepta-band microstrip patch antenna which is realized by a rectangular patch. The proposed patch antenna resonates between 1 and 9 GHz at seven distinct frequencies which covers L-, S- and C-band. The proposed microstrip patch antenna was designed using IE3D v. 15.00 simulation tool and have to achieve seven distinct band by using the combination of photonic band-gap (PBG) structure and stacking. The reflected power and resonating frequency of each bands are − 28.43 dB, − 14.57 dB, − 14.47 dB, − 21.53 dB, − 14.32 dB, − 29.47 dB and − 12.20 dB at 1.72 GHz, 2.36 GHz, 3.08 GHz, 3.64 GHz, 5 GHz, 6.16 GHz and 7.32 GHz respectively. And also, have shown its performance improvement by the use of the PBG structure and stacking.

Improving the performance of a patch antenna array by using photonic bandgap structures at X-band

A proposed three-layered patch antenna array combined with Uniplanar Compact Photonic Bandgap structures (UC-PBG) is presented to avoid non-desired radiations from the feeding structure and to mitigate the surface propagation modes, increasing the radiation efficiency, and reducing the parasitic lobes. The array is fed by electromagnetic proximity, implemented by a stripline network below the radiators. The array is designed to operate at of 10 GHz and is surrounded by UC-PBG structures. This configuration also helps to increase the bandwidth by keeping the electric field and the surface current stable around the radiators, reducing the variations of the impedance on a wider bandwidth. Also, the UC-PBG structures attenuate the surface propagation modes, lowering the parasitic lobes by almost 7 dB and reaching measured radiation efficiency higher than 80%. The patch array gets an operational bandwidth of 2.5 GHz, with a measured gain of 24 dB. The fractional bandwidth is 25%.

Tunable resonant Bragg photonic bandgap structures based on active quantum dot layers; crystals with applications in all-optical switches manufacturing

Novel tunable photonic bandgap structures are proposed in this paper. Alternately placed slabs of GaAs (as barriers) and layers containing InAs/InGaAs quantum dots (active dipole elements) are considered as the main building blocks of the proposed crystals. The common transfer matrix method is utilized for characterization of the optical features of the structures. However, to take more physical phenomena into considerations, effective excitonic susceptibility is defined in a way that includes all the homogeneous and non-homogeneous broadenings. Dependences of the optical responses to the structural parameters such as the number of periods, uniformity of the quantum dots, and the size of the barrier/dots are investigated at the first step. Extracting the optimum values, tunability of the optical features of the structures by changing the crystal temperature, light incident angle and also illuminating an external pump laser is investigated then. To study the potential of the proposed structures to be used as all-optical switches, the response of the crystals to the square wave pulse series of 50 ps duration and data sequences of 10101 is studied by turning the pump pulse on and off. Results are notable for less quantum dot size fluctuations and low temperatures.

Design and Analysis of Microstrip Antenna on Periodic and Non-Periodic Photonic Band Gap Substrate

This paper describes the investigation of a microstrip patch antenna with periodic and non-periodic Photonic Band Gap structure (PBG) as a substrate. The proposed antenna is designed to operate at 5.9 GHz. The problem of surface wave leakage in the conventional antenna is controlled by producing dielectric periodicity with the help of photonic crystal as a substrate. Parametric analysis of the proposed antenna is carried out by including the photonic crystal substrate with an optimized air hole diameter as 1, 1.5, and 2.5 mm. It is observed that the gain, directivity, and the S parameters of the proposed microstrip patch antenna are improved compared to the conventional patch antenna.

Project and Analysis of Quasi-Periodic PBG for Microstrip Antenna

Abstract In this work the influence of quasi-periodic distributions of air holes with 6, 12 and 6-fold modified symmetries, applied to the substrate of a rectangular microstrip patch antenna are analyzed. To validate the study, parameters such as S11 parameter, bandwidth, total gain, radiation pattern and electric field were investigated through computational simulations. The results obtained for all the PBG structures were compared to each other and to a reference antenna without PBG. In addition, we analyzed the resonating modes of each structure and it was observed improvements in bandwidth and gain for all modified structures when compared with the reference antenna, as well as reduction of the dielectric constant that is also recalculated. Some prototypes were built to compare the computational results to the measured results. It was verified that the measured and simulated results of return loss are in agreement and the antenna with 6-fold modified symmetry presented better performance than the others analyzed PBG structures.

Electrically tunable photonic band gap structure in monodomain blue-phase liquid crystals

Photonic band gap materials have the ability to modulate light. When they can be dynamically controlled beyond static modulation, their versatility improves and they become very useful in scientific and industrial applications. The quality of photonic band gap materials depends on the tunable wavelength range, dynamic controllability, and wavelength selectivity in response to external cues. In this paper, we demonstrate an electrically tunable photonic band gap material that covers a wide range (241 nm) in the visible spectrum and is based on a monodomain blue-phase liquid crystal stabilized by nonmesogenic and chiral mesogenic monomers. With this approach, we can accurately tune a reflection wavelength that possesses a narrow bandwidth (27 nm) even under a high electric field. The switching is fully reversible owing to a relatively small hysteresis with a fast response time, and it also shows a wider viewing angle than that of cholesteric liquid crystals. We believe that the proposed material has the potential to tune color filters and bandpass filters.