Photonic Crystal Defect Research Articles

Tunable reflectance characteristics of magnetized cold plasma based one-dimensional defective photonic crystal

In this work, we analyze the reflectance property of a MCP based 1DPC with symmetrically introduced defect layer of air. The reflectance spectra of the defective PC are obtained by employing TMM with variation in the thickness of the defect. It is reported that the PC with the defect thickness of zero having the form, (AB)N/2(BA)N/2, exhibits two adjacent completely reflected bands separated by a defect mode with reflectance zero. The conventional extrinsic PC offers a single completely reflected band lying in the range 4–6 GHz that splits into two parts by defect mode when we operate the PC in defective mode. By increasing the defect thickness up to 15 mm, the low frequency band becomes narrower and the defect mode frequency is shifted towards a lower value, whereas the second band becomes wider. The defect mode frequency shows a similar decreasing behavior with increase in the thickness of air defect below and above its particular value of 20 mm. In this investigation, the disappearance of defect mode at a critical thickness and reappearance of new defect mode at higher frequency with further increase in defect thickness, are considered as important features of this defective PC. Such kind of tunability in the reflected band, defect mode frequency, and reappearance of new defect mode, all are in a good agreement with the computed results reported by the researchers. The insights of the analysis can be employed in design of optical filters, waveguides, detectors, and similar tunable microwave and switching devices.

Local density of states in a one-dimensional photonic crystal with a semiconducting cavity

In this paper, we calculate the local density of states using dyadic Green’s functions for a defective one-dimensional photonic crystal of finite size composed of alternating air and semiconductor layers. Herein, spatial periodicity is broken as one of the semiconductor layers increases its layers. In this study, we consider that the refractive index of semiconductor materials, such as GaAs, Si, and SiO2, changes with the amount of the applied pressure. We determined the existence of a confined mode within the cavity with a maximum value of the local density of states. The results show that, as pressure increases, the local density of states decreases within the confined mode. However, for the GaAs cavity, the results reveal that increased pressure favors the appearance of a larger number of confined modes at frequencies within the second photonic band gaps.

Thermal and Layer Thickness Dependence of Defect and Band Edge Transmissions in 1D PCs Based on ZnS/CaF2 Multilayers

Alternating layers of different materials with sub wavelength thickness in one dimension are used for controlling the propagation of electromagnetic waves owing to their ability to selectively transfer and confine photons of specific wavelengths, called photonic band gap (PBG). Temperature independent large PBG in the visible wavelength range is highly desired for many applications and we have theoretically investigated the thermal and layer thickness dependence on PBG and proposed a novel strategy to choose materials based on their coefficients of thermal expansion and thermo optic effect. The thermal dependence of PBG can be eliminated by making the spectral shift due to thermo optic effect equal and opposite to that of the thermal expansion effect. We have chosen ZnS/CaF2 multilayers for the design of 1D photonic crystal (PC) and our calculations have shown that the spectral shift due to thermal fluctuations could be significantly reduced by the negative thermo optic coefficient of these materials compensated by the positive thermal expansion coefficient. The proposed 1D PC shows a temperature dependent spectral shift of ∼14 pm/oC in the visible range.

Properties of Defect Modes of One-Dimensional Quaternary Defective Photonic Crystal Nanostructure

Properties of Defect Modes of One-Dimensional Quaternary Defective Photonic Crystal Nanostructure

High-Q slow light and its localization in a photonic crystal microring

We introduce a photonic crystal ring cavity that resembles an internal gear and unites photonic crystal (PhC) and whispering gallery mode (WGM) concepts. This `microgear' photonic crystal ring (MPhCR) is created by applying a periodic modulation to the inside boundary of a microring resonator to open a large bandgap, as in a PhC cavity, while maintaining the ring's circularly symmetric outside boundary and high quality factor ($Q$), as in a WGM cavity. The MPhCR targets a specific WGM to open a large PhC bandgap up to tens of free spectral ranges, compressing the mode spectrum while maintaining the high-$Q$, angular momenta, and waveguide coupling properties of the WGM modes. In particular, near the dielectric band-edge, we observe modes whose group velocity is slowed down by 10 times relative to conventional microring modes while supporting $Q~=~(1.1\pm0.1)\times10^6$. This $Q$ is $\approx$50$\times$ that of the previous record in slow light devices. Using the slow light design as a starting point, we further demonstrate the ability to localize WGMs into photonic crystal defect (dPhC) modes for the first time, enabling a more than 10$\times$ reduction of mode volume compared to conventional WGMs while maintaining high-$Q$ up to (5.6$\pm$0.1)$\times$10$^5$. Importantly, this additional dPhC localization is achievable without requiring detailed electromagnetic design. Moreover, controlling their frequencies and waveguide coupling is straightforward in the MPhCR, thanks to its WGM heritage. By using a PhC to strongly modify fundamental properties of WGMs, such as group velocity and localization, the MPhCR provides an exciting platform for a broad range of photonics applications, including sensing/metrology, nonlinear optics, and cavity quantum electrodynamics.

Defective 1D quinary photonic crystal sensors for the detection of cancerous blood cells

We introduce structures of sensors based on defective one-dimensional quinary photonic crystals. The unit cell of the structure is composed of five layers of N-BAF10 / KNbO3 / TiO2 / KNbO3 / N-BAF10, whereas blood cells under investigation are supposed to construct a defective layer in the middle of the structure. The basic principle of detection of the proposed sensor is based on the existence of the resonant mode, within the photonic bandgap of the transmittance spectrum, due to the presence of blood cells in the defect layer. We found that the characteristics of the resonant mode are dependent on the type of blood cells used, thickness of the defect layer, and the angle of incidence of radiation. The average values of sensitivity, quality factor, and figure of merit for all types of cancerous blood cells are found to be about 623 nm / RIU, 129,560, and 73,950, respectively, at normal incidence. These values increased to 717 nm / RIU, 426,000, and 318,600, respectively, as the angle of incident increased from 0 deg to 45 deg with a low limit of detection of 1.998 × 10 − 7 at 45 deg. Our results indicate that the proposed structures are very efficient in sensing and identifying the type of cancerous blood cells.

Correction to: Theoretical study of one‑dimensional defect photonic crystal as a high‑performance sensor for water‑borne bacteria

Correction to: Theoretical study of one‑dimensional defect photonic crystal as a high‑performance sensor for water‑borne bacteria

Tunable dual-wavelength saturable absorber based on dual defective photonic crystal by MoS2 monolayer

Dual-wavelength Q-switched lasers have currently received extensive attention due to their wide applications in nonlinear optoelectronic devices. Their main mechanism can be based on the integration of laser with devices such as dual defective photonic crystals (DPCs). Nonetheless, DPCs with a high modulation depth is still demanding in this field. Toward this goal, in this paper, we have designed a dual DPC with MoS2 monolayers as defects in this structure. Defect modes helped adjust the wavelength by the distance between the two defects, and finally, a tunable wavelength was created by changing the intensity, incident angle, and polarization. Using the dual DPC, modulation depth was increased to 97% and 85% in the dual defect modes and a wide range of light intensities was achieved with over 80% of absorption, which helps accomplish a tunable dual Q-switching operation.

Spectral statistics of a 1D photonic crystal containing an anisotropic graphene-based hyperbolic metamaterial defect layer

A simple photonic crystal is a periodic and regular nanostructure. Breaking the periodicity of a photonic crystal by a defect layer can be an interesting pattern. We study the spectral statistics of eigenfrequency spacings (the so-called level spacing statistics) for TM-polarized waves in the one-dimensional (1D) defective photonic crystal containing graphene-based hyperbolic metamaterial as a defect layer. The localization of light in the proposed structure has been investigated using the transfer matrix method. Moreover, the effects of different parameters, such as the number of graphene cells and the defect layer's optical axis orientation, are discussed. The performance of the ratios of nearest neighbor level spacings has become a Wigner distribution at the localized phases which are introduced by inserting a defect layer. The spectral statistics are found to approach the Wigner distribution for different repeat numbers of graphene layers. In contrast, in the absence of graphene layers, the level spacing statistics follow the Poisson distribution.

Theoretical study of one-dimensional defect photonic crystal as a high-performance sensor for water-borne bacteria

Theoretical study of one-dimensional defect photonic crystal as a high-performance sensor for water-borne bacteria

Defective Microwave Photonic Crystals for Salinity Detection

In this paper, defective microwave photonic crystals (MPCs) are designed to sense the salinity of aqueous solutions. The defective MPC sensors are constructed by two kinds of microwave dielectric layers and one defective salt solution layer. Transfer matrix method (TMM) for lossy medium is developed to calculate the transmittance spectra of the sensors. It is found that the peak transmittance of both the defective resonance within the microwave band gap (MBG) and transmitting modes outside the MBG monotonously decrease with the increase of salinity, while the resonant and transmitting mode frequencies remain unchanged. By comparing the four MPC sensor structures, the first transmitting mode in the upper frequency band outside the MBG of the 15-layer MPC sensor has the largest salinity sensing range from 0 to 40‰ with relative stable detecting sensitivity. The sensing principle is based on the fact that the dielectric loss factor of saline solution is much more sensitive to salinity than the dielectric constant in the microwave frequency band. The sensitivity, quality factor, and salinity detection range of the MPC sensors are calculated and compared. The reported defective MPC sensors are suitable to be used for non-contact salinity detection.

Photonic Crystal Enhanced by Metamaterial for Measuring Electric Permittivity in GHz Range

The rise of broadband cellular networks and 5G networks enable new rates of data transfer. This paper introduces a new design to measure the permittivity in the GHz range of non-magnetic materials. We tested the proposed design with a wide range of materials such as wood, glass, dry concrete, and limestone. The newly proposed design structure has a maximum sensitivity of 0.496 GHz/RIU. Moreover, it can measure permittivities in the range from 1 up to 9. The main component of the designed structure is a defective one-dimensional photonic crystal with a unit cell consisting of metamaterial and silicon. In addition, we demonstrate the role of the metamaterial in enhancing the proposed design and examine the impact of the defect layer thickness on the proposed structure.

Bistable absorption in a 1D photonic crystal with a nanocomposite defect layer.

We investigate the nonlinear absorption properties of a defective one-dimensional photonic crystal at the near-infrared range using the nonlinear transfer matrix method. The defect is a nanocomposite layer containing vanadium dioxide nanoparticles sandwiched between two nonlinear dielectric layers. The linear absorption spectrum of the designed structure has three resonant absorption lines at the bandgap region of the photonic crystal. We can reconfigure the structure in the linear regime from nearly transparent to absorbent or vice versa in multiple resonant wavelengths by adjusting the temperature. Moreover, the system shows absorptive bistability by adjusting the intensity and incident angle of the input light. We discuss the tunability of the nonlinear absorption in detail. In the nonlinear regime, we show that, besides the temperature, the structure can be reconfigured from absorbent to transparent and vice versa by adjusting the incident optical power and the incident angle. We validate the results by examining the electric field distribution throughout the structure.

Angular-adjustable single-channel narrow-band filter based on one-dimensional photonic crystal heterostructure

In this work, we designed a narrow-band filter based on a one-dimensional photonic crystal heterostructure featuring an angle-adjustable single-channel. The design presented here is based on a quarter-wave reflector with a mirror defect layer in the middle of the structure. By combining two defective one-dimensional photonic crystals (PCs), we obtained a heterostructure in which the two sub-PCs had the wavelengths of their defect modes, that is, the same at one incident angle and different at all other incident angles. This structure possessed the single-channel resonant peak in the transmission spectrum under either a normal or an oblique incident angle, and the angle-adjustability was related to the two modifying parameters. The filter based on this heterostructure possessed not only a narrow passband but also a sharp angular pass breadth. These properties have potential applications in angular tunable, single-channel narrow-band filters.

Light localization in one-dimensional photonic crystal heterostructures

Effects of both metamaterial inclusion and lack of inversion symmetry on the localized modes in one-dimensional photonic heterostructures under normal incidence are investigated. Each structure consists of two semi-infinite photonic crystals separated by an interface or by several layers. A general condition for light localization between semi-infinite crystals is given by parallelism between two-dimensional vectors in the electromagnetic (H, E) space. The case of a defective photonic crystal is recovered by joining crystals having the same unit cell. The defect modes display leftward and rightward damped oscillations with the same ratio, even when the unit cell lacks inversion symmetry. Their frequencies are found in good agreement with peaks of the transmittance through truncated structures. In heterostructures including metamaterials, an anomalous exponential decay of the magnetic field is found near one edge of the zero-〈n〉 gap.

Two-dimensional photonic crystals with insertion of circular and triangular defects

In this work, we calculate photonic band structure for a defective two-dimensional photonic crystal using plane wave expansion method and supercell technique. The photonic crystal comprises circular GaAs cylinders arranged in a two-dimensional hexagonal lattice embedded in an air background in which circular and triangular GaAs defects are inserted. Within the photonic band gap, we can observe a defect mode, whose electric field intensity exhibits a bipolar pattern confined around the defect. If we increase pressure while keeping the GaAs dielectric constant at a constant temperature, we observe that the defective modes shift toward higher frequencies without changing the width of the photonic band gap. Moreover, increasing the radius of the circular GaAs defect favors the appearance of a new defective mode within the photonic band gap. However, if we increase the length of the triangular defect, only a single defect mode may be observed at frequencies close to the air band. We hope that these findings can be considered for the development of new photonic devices.

Investigation of transmission properties in defective one dimensional superconductive photonic crystal for ultralow level bioethanol detection

The present study exhibits design and analysis of a superconductor-based defective 1D photonic crystal (PhC) to envisage an ultra-high sensitive ethanol sensor. The proposed structure is realized with alternate layers of high temperature superconductor (YBa2Cu3O7) and dielectric (SrF2) material, whereas the central defect layer is designed with porous silicon (P-Si) material. Transmittance and absorption spectrum are explored theoretically by employing transfer matrix method and two-fluid model. The mainstay of this work is to investigate the shift in wavelength of the resonant mode, which is created within the band gap, in the transmittance spectrum. The position of the defect mode wavelength is assayed by varying the incidence angle, thickness of superconductor layer and operating temperature. An ultra-high wavelength sensitivity of 8.53×105 nm/RIU and temperature sensitivity of 6.673 nm/K are achieved by the proposed sensor, which open up an avenue for effective sensing of different % volume of ethanol with minute refractive index contrast. Besides sensitivity, other sensing parameters like figure of merit, quality factor and detection limit are thoroughly studied and compared with the recently published works. On top of that, the simple structure, easy analysis, and available fabrication techniques make the proposed design a suitable candidate for biosensing applications.

Compact Magnetless Optical Isolator using Two Coupled Microcavities with Time-Modulation

It is shown how time-modulating the refractive index of two coupled microcavities with a 90 degree phase shift between them leads to non-reciprocal wave propagation. The cavities are implemented as defects in a one-dimensional photonic crystal. The ratio of forward to backward power transmission can be as high as 25 dB with experimentally realizable modulation frequencies and amplitudes. Further, it is demonstrated how a simple passive filter can remove modulation sidebands.

Faraday rotator made of conjugated magneto active photonic crystal heterostructures

Two defective conjugated magneto active photonic crystals are proposed in this paper for fabrication of Faraday rotators. Optical features of the suggested structures are studied using 4 × 4 transfer matrix method and taking into consideration of the couplings of polarization states. Band structure of the crystals including generation of stop bands and resonant modes localizations are studied by exploring the dependence of the crystals' transmittance on the period number of the layers. It is shown that desirable responses are obtained by just very low number of periods. Furthermore, optical anisotropy of the crystals is considered to be purely magnetic field-induced. Then in addition to studying the dependencies on structural parameters, connection between wave incident angle and magneto-optical effects (Faraday rotations and changes of the ellipticity angle) are discussed in detail. Results clearly show the ease of tunability of the structures' responses in this way which is of prime importance from experimental point of view. Furthermore, the proposed structures offer remarkable Faraday rotation angles when transmittance amounts remain high enough simultaneously. Thus it seems that these crystals might be useful for fabrication of polarization dependent sensor/transducers based on Faraday rotators which are vital elements in development of integrated circuits as well as imaging systems.

Point-Defect-Localized Bound States in the Continuum in Photonic Crystals and Structured Fibers.

We show that point defects in two-dimensional photonic crystals can support bound states in the continuum (BICs). The mechanism of confinement is a symmetry mismatch between the defect mode and the Bloch modes of the photonic crystal. These BICs occur in the absence of band gaps and therefore provide an alternative mechanism to confine light. Furthermore, we show that such BICs can propagate in a fiber geometry and exhibit arbitrarily small group velocity which could serve as a platform for enhancing nonlinear effects and light-matter interactions in structured fibers.