One-dimensional Photonic Band Gap Structures Research Articles

Weyl semimetal assisted nonreciprocal modification of Flat-top optical pulses via defective photonic band-gap structures

We study the non-reciprocal modification of flat-top optical pulses via a one-dimensional photonic band-gap structure with Weyl semimetal-based defect layers due to their wide range of applications, such as high-speed communication, nonlinear optical switching, and ultrafast pump–probe experiments. We apply the transfer matrix method to obtain the transmission spectrum of the structure. Also, the Fourier transform technique is used to investigate the effect of the propagation direction of the incoming pulse on the time profile of the outgoing pulse. Then we examine the effect of the carrier frequency and duration of the incoming pulse on the length, energy, and magnetic field distribution of the outgoing pulse. It is shown that the time profile of an incoming flat-top pulse may modify to a nearly flat-top, single-peak, or oscillatory multi-peak time profile depending on the carrier frequency, length, and propagation direction of the incoming pulse.

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.

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.

Innovative fiber Bragg grating filter based on a graphene photonic crystal microcavity.

We propose a new model for a fiber Bragg grating (FBG) filter based on one-dimensional defective photonic bandgap structures, which operates within telecom windows. The device is realized in an asymmetric $ {{\rm SiO}_2}/{{\rm TiO}_2} $SiO2/TiO2 photonic crystal (PC) microcavity with the defect layer of the graphene disk placed in the center of the structure. The theoretical analysis of the optical properties of the narrowband FBG filter is given based on the combination of the density matrix approach with the transfer matrix method. The effect of the incident angle and the polarization of the probe field on the transmittance spectra is calculated. Also, tuning the filtering wavelength and the number of guided modes is performed by changing the properties of PC's defect layer. It is shown that depending on the ratio of the coupling fields' intensity, the probe field absorption can be minimized and even be amplified in $ {\lambda _0} = 1550\;{\rm nm} $λ0=1550nm. The results show very promising potential for fabrication of FBG filters operating in the near-infrared regime for light wave communications.

Optimized optical nonreciprocal transmission in defective one-dimensional photonic bandgap structures with weak asymmetry

A novel and compact one-dimensional (1D) geometry for optical nonreciprocal transmission was proposed in this paper. Different from previous designs with high spatial asymmetry, by simply introducing a few dielectric periods of (BA) and (AB) into a typical nonlinear Fabry–Perot resonator with symmetric Bragg mirrors (AB)ND(BA)N, excellent optical nonreciprocal transmission properties can be achieved in the optical communication wavelength range. The optimized structure can be generally expressed as: (AB)ND(BA)M(AB)L, where M=N+1, L=1; M=N+2, L=2; M=N+3, L=3;…… and N≥6. The relationship between the bistability and the local field distribution of the Kerr defect layer D and the optical nonreciprocal transmission of the whole 1D system was analyzed theoretically. The direction- and incident wavelength-dependent shift of defect mode are confirmed to be responsible for the optimized optical nonreciprocity. The proposed optimized structures (AB)6D(BA)8(AB)2 and (AB)7D(BA)8(AB)1 are shown to have advantages over previously reported 1D designs with wide unidirectional transmission range (UTR) width (>3.1nm), high transmission for the forward incidence (>88%) and low transmission for the backward incidence (<1.22%) at lower input intensity (10 MW/cm2) with fewer layers (33 layers). Interestingly, the asymmetry degree of the proposed structures can be as low as 11.12%, which is only 1/4 or less of that of previous designs. The effects of the incident angle and polarization on the nonreciprocal transmission properties were also discussed for practical applications. These results are of great importance to the design of high-performance optical nonreciprocal devices, such as all-optical diodes, isolators and limiters.

Enhancement in sensitivity of blood glucose sensor by using 1D defect ternary photonic band gap structures

This paper demonstrates a novel way to enhance sensitivity of a blood glucose sensor made up of one-dimensional (1D) defect binary photonic band gap (PBG) structure by converting it to 1D defect ternary PBG structure. On conversion of the structure from binary to ternary, the glucose concentration sensitive output transmission spectrum shift in the structure enhances by 25% and the sensitivity enhancement is 4.71 nm/RIU. Due to high sensitivity of 1D defect ternary PBG structure, fast and more accurate determination of concentration of glucose in blood can be achieved.

Band-edge field enhanced nonlinear cross-polarized wave generation in photonic band-gap structure.

We report on the enhancement of nonlinear cross-polarized wave (XPW) generation in a one-dimensional photonic band-gap structure, which is composed of two periodic arrangements of barium-fluoride and silicon-dioxide through numerical simulations. By detuning the pump-field wavelength to the band-edge position of the photonic band-gap spectrum, the electric field at this wavelength would be resonant and then the field enhancement mechanism arises immediately. Under band-edge field enhancement condition, we found that the conversion efficiencies of XPW generation was implicitly enhanced even without phase-matched condition from the exact angle of crystallographic axis orientation.

Effect of Excitation Beam Divergence on the Goos–Hänchen Shift Enhanced by Bloch Surface Waves

The Goos–Hänchen (GH) shift is simulated and experimentally studied when the Bloch surface wave is excited in the forbidden band of a one-dimensional photonic band-gap structure for an excitation beam with different divergence. By changing the beam waist radius, a correspondingly changed Goos–Hänchen shift curve can be observed, where with a larger waist radius and the corresponding less divergence of the excitation beam, a greater GH shift that is closer to the Artmann estimation is obtained. The experimental demonstration of this phenomenon agrees well with the theoretical simulation.

Photonic band-gap resonators for high-field/high-frequency EPR of microliter-volume liquid aqueous samples

High-field EPR provides significant advantages for studying structure and dynamics of molecular systems possessing an unpaired electronic spin. However, routine use of high-field EPR in biophysical research, especially for aqueous biological samples, is still facing substantial technical difficulties stemming from high dielectric millimeter wave (mmW) losses associated with non-resonant absorption by water and other polar molecules. The strong absorbance of mmW’s by water also limits the penetration depth to just fractions of mm or even less, thus making fabrication of suitable sample containers rather challenging. Here we describe a radically new line of high Q-factor mmW resonators that are based on forming lattice defects in one-dimensional photonic band-gap (PBG) structures composed of low-loss ceramic discs of λ/4 in thickness and having alternating dielectric constants. A sample (either liquid or solid) is placed within the E = 0 node of the standing mm wave confined within the defect. A resonator prototype has been built and tested at 94.3 GHz. The resonator performance is enhanced by employing ceramic nanoporous membranes as flat sample holders of controllable thickness and tunable effective dielectric constant. The experimental Q-factor of an empty resonator was ≈ 420. The Q-factor decreased slightly to ≈ 370 when loaded with a water-containing nanoporous disc of 50 μm in thickness. The resonator has been tested with a number of liquid biological samples and demonstrated about tenfold gain in concentration sensitivity vs. a high-Q cylindrical TE012-type cavity. Detailed HFSS Ansys simulations have shown that the resonator structure could be further optimized by properly choosing the thickness of the aqueous sample and employing metallized surfaces. The PBG resonator design is readily scalable to higher mmW frequencies and is capable of accommodating significantly larger sample volumes than previously achieved with either Fabry-Perot or cylindrical resonators.

Temperature control of the ultra-short laser pulse compression in a one-dimensional photonic band gap structure with nematic liquid crystal as a defect layer

We investigate numerically the controllable chirped pulse compression in a one-dimensional photonic structure containing a nematic liquid crystal defect layer using the temperature dependent refractive index of the liquid crystal. We consider the structure under irradiation by near-infrared ultra-short laser pulses polarized parallel to the liquid crystal director at a normal angle of incidence. It is found that the dispersion behaviour and consequently the compression ability of the system can be changed in a controlled manner due to the variation in the defect temperature. When the temperature increased from 290 to 305 K, the transmitted pulse duration decreased from 75 to 42 fs in the middle of the structure, correspondingly. As a result, a novel low-loss tunable pulse compressor with a really compact size and high compression factor is achieved. The so-called transfer matrix method is utilized for numerical simulations of the band structure and reflection/transmission spectra of the structure under investigation.

Design and analysis of concave diffraction grating with one-dimensional photonic bandgap structure

Matching one-dimensional photonic bandgap theory with the grating condition, a novel design approach of the etched diffraction grating for the demultiplexer was proposed. With a stack of eight alternating dielectric layers per grating tooth, a computed reflection efficiency of 98% around the central wavelength was achieved by this method. The grating efficiency approached −0.78 dB with a channel uniformity of 0.06 dB over 120 nm bandwidth, and the neighbor channel crosstalk was better than −20 dB. An analysis of etching deviation suggests that the diffraction grating designed by this approach is very tolerant concerning fabrication imperfections.

Photonic bandgap structure with plasmonic inclusions for refractive index sensing in optofluidics at terahertz frequencies.

We propose a refractive index sensor in the terahertz domain for optofluidics comprising a one-dimensional photonic bandgap structure with plasmonic inclusions. The central defect layer of the photonic bandgap structure is the fluid channel and acts as the sensing region wherein the embedded plasmonic inclusions provide the enhanced fields. The simultaneous excitation of the plasmonic resonances within the photonic bandgap defect mode results in an enhanced fluid-field interaction. The effective medium parameters of this composite sensing region become extremely sensitive to refractive index variations of the fluid within the channel and lead to significant spectral shifts. The sensitivity of this sensor increases with the volume fraction of the plasmonic inclusions and also provides self-referenced spectral measurement. This is an improved alternative to conventional refractive index sensors, which are based exclusively on either photonic or plasmonic effects.

Design and fabrication of energy efficient film based on one-dimensional photonic band gap structures

A photonic band gap structure of (SiO2/TiO2)5 with Ag system for energy efficient film was proposed theoretically and experimentally. The calculated transmittance spectra show high transmittance in the visible range, but ultra-low transmittance in the wavelength ranges of ultraviolet and infrared. Besides, the effects of the incident angle and two opposite directions on the optical characteristics were studied. The results demonstrate that the structure can simultaneously satisfy the demands of lighting and heat insulating as energy efficient window film. The cross-section morphology indicates that the sample has good periodicity in accordance with the design, whereas the experimentally measured transmittance spectra are well matched with the theoretical calculation.

Highly Sensitive, Bloch Surface Wave D-Type Fiber Sensor

A novel sensor based on a D-type optical fiber coated with a specially designed dielectric multilayer forming a one-dimensional photonic bandgap structure is proposed. The characteristics of its propagation modes are numerically analyzed at a wavelength of 785 nm to evaluate the sensor's performance. The results show that its sensitivity can drastically exceed that of its metal-coated, surface plasmon resonance counterpart, due to the sharp resonance and low wave-propagation loss of its Bloch surface wave. The novel sensor can also be easily adapted for all kinds of aqueous analytes of different refractive indices by modifying the photonic bandgap structure. This could lead to the development of compact, ultra-sensitive biochemical sensing devices.

Application of transfer matrix method to second-harmonic generation in nonlinear photonic bandgap structures: oblique incidence

Generalization of the transfer matrix method is developed to analyze Type I second-harmonic generation in linear&#x2013;nonlinear multilayer one-dimensional photonic bandgap structures for oblique incidence of a nondepleted fundamental. The advantage of the transfer matrix method is that it takes into account reflections and interferences between all forward and backward propagating fundamental and second-harmonic waves. The conversion efficiency is calculated as a function of the incident angle of the fundamental and the thicknesses of the linear and nonlinear layers. Specific incident angles and thicknesses may generate relatively high conversion efficiency inside nonlinear material. Our analytical and numerical analyses show that the conversion efficiency of second-harmonic generation depends on the fundamental pump power, second-order susceptibility, and field enhancement in the photonic bandgap structure. Upper bounds on pump intensity can be found for a given incidence angle and sample thickness where the nondepleted pump approximation can be used to model such a nonlinear structure.

Enhancing and inhibiting stimulated Brillouin scattering in photonic integrated circuits.

On-chip nonlinear optics is a thriving research field, which creates transformative opportunities for manipulating classical or quantum signals in small-footprint integrated devices. Since the length scales are short, nonlinear interactions need to be enhanced by exploiting materials with large nonlinearity in combination with high-Q resonators or slow-light structures. This, however, often results in simultaneous enhancement of competing nonlinear processes, which limit the efficiency and can cause signal distortion. Here, we exploit the frequency dependence of the optical density-of-states near the edge of a photonic bandgap to selectively enhance or inhibit nonlinear interactions on a chip. We demonstrate this concept for one of the strongest nonlinear effects, stimulated Brillouin scattering using a narrow-band one-dimensional photonic bandgap structure: a Bragg grating. The stimulated Brillouin scattering enhancement enables the generation of a 15-line Brillouin frequency comb. In the inhibition case, we achieve stimulated Brillouin scattering free operation at a power level twice the threshold.

Ultralow-threshold single-mode lasing based on a one-dimensional asymmetric photonic bandgap structure with liquid crystal as a defect layer.

In this Letter, we propose defect-mode lasing from a one-dimensional asymmetric photonic structure with dye-doped nematic liquid crystal as a central defect layer. The local field intensity of the distinguished single defect mode at the overlapped photonic band edges is drastically enhanced by the asymmetric structure consisting of two distinct multilayer photonic crystals. With high density of states of photons, effective output lasing emission and maximum input excitation are ensured. As a result, the single-mode lasing with a low excitation threshold of 0.2 μJ/pulse is achieved due to the combination of the defect layer and the photonic band edge effect.

Asymmetric one-dimensional photonic crystal for optical sensing in the visible spectral range

A gas sensor based on an asymmetric one-dimensional (1D) photonic band gap structure with one defect layer was designed and fabricated through layer-by-layer deposition of spin-coated poly methyl methacrylate (PMMA) and vacuum-deposited As2S3. Initially, the thickness variations, Δd, were determined of the thin films resulting from the poly methyl methacrylate exposure to chloroform vapor in the concentration range 100 – 9000 ppm. It was found that the value of Δd depends on the gas concentration and the exposure time. A two-layer structure was prepared consisting of PMMA and vacuum-deposited As2S3. Further, the permeability of thin As2S3 films to chloroform vapors was investigated. The asymmetric photonic structure consisted of 11 alternating layers of As2S3 and PMMA. The defect PMMA layer was located before the last high-refractive-index film of chalcogenide glass. The thickness of the defect layer of PMMA was pre-calculated so that the pass band be centered at the wavelength of 550 nm. An offset was observed of the position of the pass band to the larger wavelengths after exposure to chloroform vapor. The multilayered structure proposed is promising for optical sensor applications.

High-sensitivity sensing based on intensity-interrogated Bloch surface wave sensors

A high-sensitivity sensing scheme based on Bloch surface wave is presented with the simple intensity interrogation configuration. The p-polarized electromagnetic surface wave is designed to be excited in a one-dimensional photonic crystal band-gap structure, and support a rather steep resonance dip, much sharper than that of the well-known surface plasmon resonance (SPR). Although the angular shift of this Bloch-surface-wave-based sensor is not as sensitive, the intensity measurement proves to be a more suitable scheme for Bloch surface wave based sensors, thanks to the sharpness of their resonance. Through detection of glycerol in water solution for different concentrations, the intensity sensitivity of our Bloch-surface-wave-based sensor significantly surpasses that of the conventional SPR-based sensors. Experimental results show that the sensor could achieve a detection limit as low as 7.5×10−7 refractive index units in a simple lab setup, which is much simpler than many of the much more complicated SPR-based platforms.

Optical parametric amplification in one-dimensional photonic bandgap structures

In this paper, optical parametric amplification based on the degenerate four-wave mixing principle in a one-dimensional photonic bandgap (PBG) structure has been numerically studied. First, the multiple scale method was introduced to derive a complete set of nonlinear coupled-mode equations for a finite structure with different inhomogeneous nonlinear coefficients than those used in previous works. This finite structure is composed of 680 dielectric layers, which are alternating half-wave/eight-wave films. The wavelengths of the pump, signal, and idler pulses have been determined from the transmission spectrum, which was illustrated by using the transfer matrix method. The parametric interaction of the pump, signal, and idler pulses inside PBG structure has been numerically simulated by using the split-step Fourier transform method. The results of the simulation have shown that the intensities of the signal and idler have exponential growth with respect to the number of layers in the medium. Meanwhile, pump wavevector detuning directly affects the intensities of both pulses due to a band-edge phase-matching condition that might be achieved from only one optimal detuning parameter. Moreover, both the amplification gain and the conversion efficiency of the idler pulse have been shown to be dependent on the bandwidth of the pump pulse spectrum. A very narrow pulse, with a bandwidth much less than the relevant transmission peak, enables the highest amplification and conversion efficiency in this medium because the most efficient phase-matched condition occurs in this situation. Finally, the conversion efficiency grows exponentially with input pump intensity for several input signal intensities. Furthermore, the maximum conversion efficiencies directly vary with input signal intensity.