Asymmetric Photonic Crystal Research Articles

Effect of angle of incidence on defect modes of symmetric and asymmetric one-dimensional photonic crystals

The impact of the angle of incidence on defect modes within a one-dimensional photonic crystal (PC) containing a central defect has been thoroughly examined. We have considered two distinct types of photonic crystals, each featuring a solitary defect: symmetric PCs and asymmetric PCs. Our findings reveal that in the case of asymmetric PCs, a defect mode emerges precisely at the central wavelength. Conversely, for symmetric PCs, two distinct defect modes appear in the proximity of the central wavelength. By widening the defect layer, these two defect modes can be merged into a single central defect mode. However, it's worth noting that the intensities of these merged defect modes differ from those observed in the asymmetric case. We have analyzed the propagation characteristics of the proposed structure using the transfer matrix method.

Near-IR unidirectional absorption in a tunable asymmetric one-dimensional photonic crystal with VO2 defect layers

In this paper, a dynamically modulated Near-IR asymmetric composite photonic crystal (PC) is proposed, which constitutes by a one-dimensional PC (1-D PC) with vanadium dioxide (VO2) phase transition defect layers. By combining asymmetric composite PC with VO2 phase material, which will undergo the semiconductor-metal transition (SMT) under thermal stimulation, to realize the controllable unidirectional multi-channel absorber under temperature control. Based on a relatively simple 1-D stacked thin film model, the model is investigated and optimized in terms of the structure, number of periods, and the thickness of defect layers, with the result of 20 nm for VO2 defect layers and seven circles for the post-defect period. By using the pre-defect period number of 3, an average absorbance of 0.19 can be achieved when VO2 is in the semiconductor phase at low temperature. With the rise in temperature, VO2 transitions to metal phase, where the structure absorption reaches 0.99. In addition, changing the per-defect period number to 5, the average absorption at semiconductor and metal VO2 is 0.73 and 0.10, respectively. The differential absorption around the SMT enables the tunability of single photonic devices. During the simulation, the effects of electric field and incidence angle on the structure are also analyzed. Meanwhile, the Bruggeman approximation effective medium theory is introduced in this work, and the changes of the absorption during the phase transition from semiconductor to metal in the VO2 defect layers are also given. These characteristics are applicable to controllable multispectral absorbers, infrared detectors, limiter, and optical switchers.

Design of Temperature Sensor Based on One-Dimensional Photonic Crystal Containing Si–BGO Layer

This paper describes the theoretical investigation of enhancement in temperature sensitivity using one-dimensional (1D) symmetric defective photonic crystal (PC) containing Si (Silicon) and Bi4Ge3O[Formula: see text] (Bismuth Germanate, BGO) material. The proposed sensor consists of a defect layer (air defect) sandwiched between two 1D-PCs with a symmetrical and asymmetrical structure composed of Si and BGO, respectively. Sensor performance has been evaluated by calculating the transmittance spectra of the proposed structure. In order to obtain the transmittance spectra, a transfer matrix method (TMM) is employed. The principle of temperature sensing is based on the shift in the resonant wavelength (or peak) of the transmission mode with a change in temperature. This is due to the temperature-dependent refractive index of the Si and BGO layers. Analysis of the transmittance spectra shows that temperature sensitivity of 1D-PC structure can be enhanced by using a symmetric defective PC with and without an external defect layer over asymmetric defective PC. It is found that symmetric defective PC with and without defect shows sensitivity equal to 0.173[Formula: see text]nm/[Formula: see text]C and 0.140[Formula: see text]nm/[Formula: see text]C, whereas asymmetric defective PC shows 0.125[Formula: see text]nm/[Formula: see text]C, for the same parameters. Further, the results show that symmetric defective 1D-PC (without the presence of any external defect layer) gives a higher [Formula: see text]-factor than a symmetric and asymmetric defective 1D-PC with an external defect layer. The proposed structure is cost-effective, easy to fabricate and compact in size.

Wavelength-control of multi-narrowband high absorbers using symmetric and asymmetric photonic crystals with two MoS2-based defects

Wavelength control of multi-narrowband absorbers plays a pivotal role in photonic devices. Such absorbers have been designed and constructed using highly absorbent layers. Ultra-thin layers of two-dimensional (2D) nanomaterials, such as MoS2, which are highly absorbent materials, have found attractive applications in photonics. In this study, defective photonic crystals (DPC) with two defects were formed by DMD with M and D indicating MoS2 and SiO2 layers, respectively. The calculation method used in this paper is the transfer matrix method (TMM). This paper proposes that symmetric and asymmetric DPCs with respect to each defect layer affect the number of defect modes, which ranges from one to four. Furthermore, changing the number of MoS2, defect positions, and thickness significantly impact the absorption, wavelength, and quality factor of the defect modes. In addition, changing the polarization and incident angle causes the wavelength of the defect modes to shift towards blue and changes the peak-to-peak distance. The distance between the defects provides wavelength adjustability, and the polarization and incident angle provide wavelength turnability. Moreover, changing the thickness of the D layer provides a redshift in the wavelength of the defect modes. The location of the defect layer, symmetry or asymmetry of DPCs affect the number and wavelength of defect modes. Increasing of distance between defects provides the same mechanism as a DPC with one defect. Also, photonic band gap does not depend on the thickness of the defect layer, the symmetry or asymmetry of the structure, periodicity of the top, middle, and bottom defect layer of DMD. This controllable design of multi-narrowband defect modes is likely to find numerous applications in multi-channel absorbers and sensors.

Gigahertz femtosecond laser-by a novel asymmetric one-dimensional photonic crystal saturable absorber device with defect layer

Abstract High repetition frequency (HRF) ultrashort pulse fiber laser has been widely used in laser cold processing. The technical solutions such as short cavity length fiber laser have been proposed to achieve HRF ultrashort pulse output recently. However, the application of material-based saturable absorbers in this field has been astricted due to the low modulation depth, low damage resistance threshold, and high saturation fluence. Here, we designed a one-dimensional asymmetric photonic crystal with defect layer (1D-APCDL) as a novel saturable absorber, where the defect layer is Bi1.6Sb0.4Te3 with high modulation depth. The harmonic pulse with 3.82 GHz repetition frequency is achieved at the wavelength of 1562 nm, which is the highest repetition frequency of the topological insulator-based ring fiber laser so far to the best of our knowledge. The research provides a new saturable absorber solution, and provides a new idea for the application of material-based nonlinear optical chip in high-repetition frequency ultrashort pulse fiber lasers.

Electromagnetic diode based on asymmetric microwave photonic crystal

A subwavelength electromagnetic diode scheme in a microwave waveguide system is proposed by using an asymmetric photonic crystal (PC) cavity side-coupled with electromagnetically induced transparency like (EIT-like) metamaterials. It is found that the composite PC-EIT configuration can generate tenfold <i>Q</i>-factor enlargement, accompanied with enhanced nonreciprocal electromagnetic localization simultaneously. Further study of the measured one-way response exhibits excellent electromagnetic diode performance including 19.7 dB transmission contrast and 7 dBm operating power at a working frequency of 1.329 GHz. We emphasize that such high-contrast transmission and low-threshold diode actions are not at costs of greatly increasing volume and drastically reducing transmission. Our findings may benefit the design of compact nonreciprocal devices in the integrated optical nanocircuits.

Tunable Faraday rotation of light from symmetric and asymmetric photonic crystals containing a plasma layer

Tunable Faraday rotation of light from symmetric and asymmetric photonic crystals containing a plasma layer

Nonlinear optical absorption switching behavior of BaTiO3 in asymmetric microcavity

In this paper, an asymmetric 1-D photonic microcavity with BaTiO3 as defect has been fabricated using RF magnetron sputtering technique. Open aperture Z-scan shows enhancement in nonlinear absorption of BaTiO3 due to strong field confinement around the defect layer. We further report the switching behavior in nonlinear absorption from reverse saturable absorption to saturable absorption in response to the angle tuning of the sample. The transfer matrix simulation results further support the cavity defect in asymmetric photonic crystal confine the photon and thereby enhancing nonlinear optical phenomena.

Magneto-optical effects on the properties of the photonic spin Hall effect owing to the defect mode in photonic crystals with plasma

In this study, we have demonstrated a multi-layered structure to examine how the magneto-optical effects affect the behavior of the photonic spin Hall effect (PSHE). The Faraday and Voigt effects are taken into account. The multi-layered structure is one-dimensional (1D) photonic crystal (PC) with a defective plasma layer. The properties of the PSHE in both symmetric and asymmetric defective PCs are explored. The numerical results show that the applied magnetic field and the geometries of the structures have significantly changed the characteristics of the PSHE. The transverse displacements of the H-polarization can be easily enhanced by more than ten times, while the transverse displacement of the V-polarization can be easily suppressed by a few percent based the manipulating of the external magnetic field. Moreover, the magneto-optical effects can change the optimal incident angle for the assessment of the peak transverse displacements of the PSHE. In addition, the numerical results also show that the plasma frequency, defective plasma thickness, and the geometry of the structure have greatly influenced the behavior of the PSHE. The parameter dependencies of theses effects are also calculated and discussed.

Tunable modulation of photonic spin Hall effect owing to the defect mode in one-dimensional photonic crystal with plasma

We have investigated theoretically the properties of the photonic spin Hall effect (PSHE) when light propagates through a one-dimensional (1D) photonic crystal (PC) with a plasma defect layer. The properties of the PSHE in both asymmetric and symmetric defective PCs are explored. The effects of the defect layer thickness, plasma frequency, and geometry of the structure on the properties of the PSHE are examined in detail. The results show that these factors significantly influence the behavior of the PSHE, which can be enhanced or suppressed by adjusting the plasma layer thickness and plasma frequency or manipulating the geometry of the 1D PC. Moreover, optimal angles for huge transverse displacements are also discussed in detail. These results indicate that the simple structure proposed in this study enables us to realize a tunable PSHE device that can be used to yield meaningful results in the studies of more complex systems related to the PSHE.

Optical Fano resonance sensing of bilayer asymmetric photonic crystal slabs as biosensors.

A bilayer asymmetric photonic crystal slab made of porous Si3N4/SiO2 is designed as a biosensor by considering the optical performance of this photonic crystal slab with a square lattice based on rigorous coupled-wave analysis theory and wavelength interrogation methods. The results show that this bilayer asymmetric photonic crystal can be used as a biosensor according to its excellent linearity relationship between the guided resonance peak shift and refractive index of aqueous solution with or without glycerol. The theoretical sensitivity value of the bilayer asymmetric photonic crystal biosensor is achieved as (S>286 nm/RIU) in the wavelength range from 1400nm to 1600nm. These results also indicate that the asymmetry bilayer structure has an important influence on its optical characteristic and sensitivity of the bilayer photonic crystal biosensor, and hence, it can be modified by changing the lattice constant and slab thickness. This research paper is very useful for understanding the application and design of biosensors based on porous structures.

Non-reciprocal Transmission of Electromagnetic Waves in Asymmetric Photonic Crystals

Abstract The non-reciprocal transmission properties of transverse electric (TE) mode waves are investigated for two asymmetric, complex photonic crystals composed of magnetic gyrotropic and normal media. Three pairs of non-reciprocal transmission peaks in three different bandgaps for forward and backward waves occur because of optical Tamm states (OTSs) at the interface between the photonic crystals. Numerical results indicate that the non-reciprocal transmission properties are influenced by the incident angles, gyrotropic permeability, and number of layers of the photonic crystals. The asymmetric structure with multiple non-reciprocal transmission peaks at a certain incident angle can provide promising opportunities for the design of multichannel isolators.

Investigation of one-way absorption properties in an asymmetric photonic crystal containing a semiconductor defect.

We theoretically study the one-way absorption in two 1D defective asymmetric photonic crystals, air/(DB)NA(BD)M/air and air/(DB)NA(BD)MA(DB)NA(BD)M/air, where A and B are dielectrics, D is the semiconductor, n-InSb, and N, M are stack numbers with N≠M. It is revealed that their absorption spectra exhibit one-way properties. We also find that the number of one-way absorption peaks depends on the symmetry and number of defect layers, which are similar to the defect modes in the transmittance spectra of the usual symmetry photonic crystals. Additionally, effects of the incident angles for both TE and TM waves on the one-way feature are also presented. At a large incident angle, the TE wave is almost reflected, whereas the TM wave can have a partial absorption.

Wave properties in asymmetric single-negative-base photonic crystals.

We theoretically study wave properties for one-dimensional defective asymmetric photonic crystals, air/(AB)MG(BA)N/air, air/(AQ)MG(QA)N/air, and air/(BQ)MG(QB)N/air, where A is a lossy epsilon-negative material, B is a lossy mu-negative material, G and Q are dielectrics with different refractive indexes, and M and N are stack numbers with M≠N. Special attention has been paid to their absorption spectra. It is found that at certain frequencies the absorption can exhibit unidirectional properties. Our calculated results show two kinds of unidirectional absorption peaks. One is a single absorption peak whose frequency depends on the thickness of defect layer G. For the other peaks, its frequency does not change when the defect layer's thickness changes. In addition, in the second kind of peaks, the peak numbers for forward and backward propagation are different, that is, there are (M-1) absorption peaks for forward propagation, while there are (N-1) absorption peaks for backward propagation. When the two kinds of unidirectional absorption peaks are merged, some new peaks appear, and both forward and backward propagation will have (M+N-1) absorption peaks.

Achieving Large Band Gaps in 2D Symmetric and Asymmetric Photonic Crystals

This paper systematically studies the influence of symmetry on photonic band gaps (PBGs) of two-dimensional photonic crystals (PhCs) by using the finite-element analysis and topology optimization methods. Optimal designs of symmetric and asymmetric PhCs of square and hexagonal lattices with PBGs of both transverse electric (TE) and transverse magnetic (TM) modes are designed and analyzed. The results show that the band gap sizes of asymmetric designs are larger than those of symmetric ones. More importantly, we found that the largest TM band gap of the square lattice PhCs is comparable to that of the hexagonal lattice PhCs, which extends the state-of-the-art understanding. Physically, forming orthogonal patterns of electric or magnetic fields is critical for maximizing TE or TM band gaps. Our unique design method opens new possibility of generating novel PhCs with properties on demand.

A thermally tunable narrowband selector based on a chiral nematic containing a binary thermosensitive chiral dopant mixture

ABSTRACTWe employed a thermosensitive chiral dopant (CD), characterized by its thermoinduced change in helical twisting power (HTP) in terms of the handedness and strength, to shift the Bragg reflection band of a CLC. A thermally tunable photonic bandgap (PBG) device was demonstrated using a one-dimensional asymmetric photonic crystal (PC) infiltrated with the CLC as a defect layer. With a temperature controller to shift the PBG of the CLC, two narrow transmission bands can be tuned in the spectrum dominated by the asymmetric PC structure. This optical device can find applications as a tunable narrowband wavelength selector or an intensity controller.

Elevation-azimuth angular selectivity and angle-frequency filtering in asymmetric photonic crystal.

Asymmetric photonic crystal (APC) has been proposed and investigated, which only allows the transmission of the incidence at a certain incident plane and angle. Simulation results show that the proposed structure exhibits both azimuth- and elevation- angular selectivity within a broad waveband under p-polarized illumination. Consequently, functional devices such as angle-frequency filter operating in the visible range can be achieved by combining the azimuth-elevation-angular selectivity and frequency selectivity. Our scheme may find potential applications in communication and imaging systems.

Tunable multichannel absorber composed of graphene and doped periodic structures

A new design for a tunable multichannel compact absorber, which is achieved by using an asymmetric photonic crystal with graphene monolayers, is theoretically proposed. The graphene monolayers are periodically embedded into the first and last dielectric layers. The absorption, reflection, and transmission spectra of the absorber are studied numerically. A perfect absorption channel is achieved because of impedance matching, and channel number can be modulated by changing periodic number. The characteristic properties of the absorption channel depend on graphene conductivity, which can be controlled via the gate voltage. The proposed structure works as a perfect absorber that is independent from polarization. It has potential applications in the design of multichannel filters, thermal detectors, and electromagnetic wave energy collectors.

Reflection phase characteristics and their applications based on one-dimensional coupled-cavity photonic crystals with gradually changed thickness ofsurface layer

In this paper, we first improve the traditional transfer matrix method to adapt to one-dimensional photonic crystal consisting of arbitrary materials, and then use it to study the reflection phase characteristics of two kinds of photonic crystals, i.e., a simple periodic photonic crystal structure and a coupled-cavity asymmetric photonic crystal with gradually changed thickness of surface layer. For both of the structures, the reflectivity within photonic band gap is above 98% and hardly affected by the thickness of the surface layer. However, their reflection phases exhibit distinctly different properties. For the simple photonic crystal structure, the reflection phases of both TE and TM polarizations are sensitively dependent on the thickness of surface layer, but their phase difference is almost the same as the thickness of surface layer varies, which cannot change the polarization of reflected light. While for the coupled-cavity asymmetric photonic crystal structure, studies show that the degenerate defect modes within photonic band gap will split as the thickness of the surface layer varies. Moreover, around the splitting defect modes the reflection phases of both TE and TM polarizations, as well as their phase difference, are sensitively dependent on the thickness of surface layer, resulting in sensitive polarization change of reflected light. The physical reason is attributed to the dramatic phase change caused by the splitting of degenerate defect modes. The above reflection phase characteristics of coupled-cavity asymmetric photonic crystals have potential in lowering or even eliminating the coherence of lasers in some special application cases. As an example, we design a one-dimensional photonic crystal structure with two-dimensional periodic varying thickness of surface layer. After an oblique incident narrowband laser beam is reflected from this structure and then focused by a lens, various polarized light beams (including linear polarized light beams along different directions, left-hand (or right-hand) circular (or elliptical) polarized light beams) will exist simultaneously, whose superposition will produce optical field with random phase and polarizations in the focal region. These results can effectively reduce the coherence of lasers, which holds promise in many fields such as laser nuclear fusion.

Tunable narrow-bandpass filter based on an asymmetric photonic bandgap structure with a dual-mode liquid crystal.

A one-dimensional asymmetric photonic crystal with dual-frequency liquid crystal as a central defect layer was demonstrated. Such asymmetric structure was characterized by the dramatic increase in intensity of the electric field of light localized at the overlapped photonic bandgap edges, thereby enhancing the observed transmittance of the spectral windows originating from the defect layer. The defect layer was made of a dual-mode liquid crystal that exhibited not only electrical tunability and switchability but also optical bistability. Consequently, tunable and bistable defect modes can be realized in the photonic structure. This asymmetric photonic crystal structure is promising and should be further explored for photonic device applications.