2D Photonic Crystal Waveguide Research Articles

2D FDTD Electromagnetic Simulation of an Ultracompact All Optical Logic Gate Based on 2D Photonic Crystal for Ultrafast Applications

In this paper, the concept of photonic crystals (PhCs) is fundamental to designing and simulating an all-optical logic gate device. We proposed an all-optical switch composed of two-dimensional (2D) photonic crystal waveguides with a central photonic crystal ring resonator (PCRR). The new all-optical NAND logic gate device comprises two linear waveguides coupled to each other through a single compact PCRR. The plane wave expansion (PWE) and finite-difference time-domain (FDTD) methods are applied to simulate the properties of the system. The structure is implemented on the operational wavelength of 1700 nm on an air wafer of only 12 μm × 12 μm. Indeed, the simulation results show that the proposed all-optical NAND gate is a strong candidate for ultrafast photonic integrated circuits (PICs) for applications in optical communications, being advantageous with high transmitting power, with simple design, and without the use of optical amplifiers and nonlinear materials.

Slow-light-enhanced on-chip 1D and 2D photonic crystal waveguide gas sensing in near-IR with an ultrahigh interaction factor

Nanophotonic waveguides hold great promise to achieve chip-scale gas sensors. However, their performance is limited by a short light path and small light–analyte overlap. To address this challenge, silicon-based, slow-light-enhanced gas-sensing techniques offer a promising approach. In this study, we experimentally investigated the slow light characteristics and gas-sensing performance of 1D and 2D photonic crystal waveguides (PCWs) in the near-IR (NIR) region. The proposed 2D PCW exhibited a high group index of up to 114, albeit with a high propagation loss. The limit of detection (LoD) for acetylene (C2H2) was 277 parts per million (ppm) for a 1 mm waveguide length and an averaging time of 0.4 s. The 1D PCW shows greater application potential compared to the 2D PCW waveguide, with an interaction factor reaching up to 288%, a comparably low propagation loss of 10 dB/cm, and an LoD of 706 ppm at 0.4 s. The measured group indices of the 2D and 1D waveguides are 104 and 16, respectively, which agree well with the simulation results.

Topology Optimization of Low-Loss Z-Bend 2D Photonic Crystal Waveguide

In this article, we design a low-loss, high-bandwidth Z-bend photonic silicon crystal waveguide bending in a triangular lattice through topology optimization. Based on the topological optimization method, we change the relative position of air holes in the global scope to maximize the transmittance and bandwidth of the waveguide. The simulation results indicate that the transmission characteristics can be effectively improved with our method. After the optimization, the loss of the waveguide can be reduced to −5 dB and the bandwidth can increase to 160 nm. Our research has great significance for further optimizing the propagation of light in photonic crystals.

Design and analysis of all-optical 1 × 4 demultiplexer based on 2D photonic crystal

Abstract In this paper, an all-optical 1 × 4 demultiplexer (DEMUX) has been designed by employing 2D photonic crystal (PhC) waveguides for use in optical networking and signal processing. The proposed structures consist of four T-shaped and one Y-shaped waveguide using 15a × 15a rectangular lattice silicon rods in ambient air. All-optical DEMUX has been simulated using the finite-difference-time-domain (FDTD) method and the results have been verified by distributing the optical field at a wavelength of 1.90 μm. Analysis of the device has been carried out for distinctive crystal and lattice designs with the achievement of a transmission ratio of more than 2.05 in presence of select input.

Design and analysis of an optical three-input AND gate using a photonic crystal fiber.

In this paper, a three-input AND logic gate is employed using a 2D photonic crystal T-shaped waveguide using a silicon in an air medium. In contrast to other gates, the key functions of employing an AND gate are recognition, error correction, code conversion, data encryption/decryption, and arithmetic operations. The proposed footprint is 8.4µm×5.4µm, which is a modest size. The performance of the proposed AND gate is investigated by employing the finite-difference time-domain approach, and the outputs are validated at wavelength (λ) of 1.55 µm. The outcomes clearly show the higher contrast ratio (CR) of 24.533 dB, and the worst case CR of is 8.6 dB; transmission efficiency values for minimum and maximum values are 19.6% and 142%; reaction time is 26 fs; insertion loss is 1.52 dB; and bit rate is 38.4 Tbps, which can be used in high-speed optical signal processing. The suggested circuit's primary objective is to consume minimal space and possess high CR.

Photonic Crystal Based Bio-Sensor Detection in Nanophotonic Structure Using FEM Method

Background & Objective: In this article, a nano-cell coupled 2D photonic crystal waveguide bio- detection platform is proposed for the detection of organic liquids such as water, ethanol, glycerol, benzene and bromine for different refractive indices (n). Methods: The detection characteristics are analyzed and obtained for the band diagram, before and after change of radius (r) as well as after the injection of liquids into the heart of the nanostructure cell at the resonant wavelength (λ res). Also, we extracted variations from the power flow norm (P) to the resonance and the transmission (T) for each material. This nanostructure for different (n) materials used, gives (P) at different levels to the resonance. This explains the importance of the refractive index parameter (n) which plays a crucial role in the detection of materials. Results & Conclusion: The proposed biosensor enables the detection of liquids. This is shown through the numerical results obtained. These results give a good observation of the different behavior of the signal in the presence of the liquids used which depend on their refractive indices 'n'. This parameter 'n' is very important for detection when it varies from material to material. The proposed biosensor can be used in several research areas, particularly in medical and environmental applications.

Slow light in rod type 2D photonic crystal waveguide comprising of cavity: Optimization and analysis

Structure comprising of 2D photonic crystal waveguide and cavity (PhCWC) is designed in this paper and propagation of slow light through it is investigated for its potential application as optical delay device. Rod type 2D photonic crystal structure has been considered here. Two-dimensional finite difference time domain (2DFDTD) method has been used in the present investigations. The proposed PhCWC structure is optimized in two steps. In the first step, Q factor is optimized by varying the number of rods of the cavity. In the second step, number of rods are kept fixed (as optimized for Q in the first step), and the delay is maximized by varying radius of the cavity rods. The resultant structure thus obtained is further investigated for (i) dispersion and group velocity, (ii) variation of optical delay with input pulse width, (iii) variation of optical delay with wavelength and (iv) variation of optical transmission with wavelength.The present paper proposes optical delay in the one cavity structure that could be manipulated by manipulating the number of cavity rods in the waveguide and radius of the central rod of the cavity. Further, the structure can be designed to operate at a desired wavelength.

Ultracompact gas-sensor based on a 2D photonic crystal waveguide incorporating with tapered microcavity

In this study, a new ultra compact gas-sensor, based on a 2D photonic crystal waveguide incorporating with tapered microcavity, is designed to detect small refractive index changes. The refractive index (RI) sensor is formed by a point-defect resonant cavity in the sandwiched waveguide on Si slab with triangular lattice. The properties of the sensor are simulated by using the plane wave expansion (PWE) method and the finite-difference time-domain (FDTD) algorithm. The transmission spectra of the sensor with different ambient refractive indices ranging from n = 1.0 to n = 1.01 are calculated. The calculation results show that a change in ambient refractive index of Δn=1×10−4is apparent. The proposed sensor achieves a sensitivity (Δλ/Δn) of 523.2 nm/RIU. It was found that the resonance wavelength is a linear function of the refractive index in under study range. The sensor is appropriate for detecting homogeneous media.

The Integration of Photonic Crystal Waveguides with Atom Arrays in Optical Tweezers

AbstractIntegrating nanophotonics and cold atoms has drawn increasing interest in recent years due to diverse applications in quantum information science and the exploration of quantum many‐body physics. For example, dispersion‐engineered photonic crystal waveguides (PCWs) permit not only stable trapping and probing of ultracold neutral atoms via interactions with guided‐mode light, but also the possibility to explore the physics of strong, photon‐mediated interactions between atoms, as well as atom‐mediated interactions between photons. While diverse theoretical opportunities involving atoms and photons in 1D and 2D nanophotonic lattices have been analyzed, a grand challenge remains the experimental integration of PCWs with ultracold atoms. Here, an advanced apparatus that overcomes several significant barriers to current experimental progress is described, with the goal of achieving strong quantum interactions of light and matter by way of single‐atom tweezer arrays strongly coupled to photons in 1D and 2D PCWs. Principal technical advances relate to efficient free‐space coupling of light to and from guided modes of PCWs, silicate bonding of silicon chips within small glass vacuum cells, and deterministic, mechanical delivery of single‐atom tweezer arrays to the near fields of photonic crystal waveguides.

Second-harmonic generation from 2D photonic crystal waveguide with simultaneous near-flat dispersions at fundamental frequency and second harmonic

Photonic crystal waveguides (PCW) have shown great potential to generate second harmonic (SH), but the available schemes with cavity or defect suffer from a lack of multiple wavelengths operation and excessive phase-matching requirement. Here we propose a 2D PCW structure comprised of a modulated single line defect, which is capable of independently controlling the fundamental frequency (FF) and SH modes. Therefore, two near-flat group velocity dispersions can be achieved for these modes, and they simultaneously satisfy phase matching conditions. Based on multiply scattering method, we theoretically demonstrate that the SH resonant modes originated from the nonradiative near-flat dispersion have high quality factors (nearly 6.5×104 for the maximum value). And the maximum SH conversion efficiency for these resonant modes are 2 orders of magnitude higher than that of off-resonant modes. In addition, benefitting from the matching of the group velocities of the second harmonic and the fundamental, the central wavelength of SH can be modulated within wavelength range ∼3nm. These results can provide potential applications in on-chip integration of photonics and quantum optics.

Pulse optimization for all-optical switching engineered in photonic crystal waveguide with micro-resonator

We have investigated switching properties and especially pulse shape preservation in the process of all-optical switching. To this end, we made two different designs of all-optical switches based on two-dimensional (2D) photonic crystal (PC) waveguides with different dispersive properties and micro-resonators with different quality factors. We realized numerically that all-optical switching without or with marginal temporal pulse distortion can be obtained under precisely chosen conditions on pulse duration and detuning. In particular, the former has to be approximately 2.5 times longer than cavity buildup time and the latter has to be equal to one full width at half maximum of the cavity transmission spectrum.

Unidirectional light propagation photonic crystal waveguide incorporating modified defects

In this paper, we have proposed a design of an Optical Diode-like in two-dimensional (2D) Photonic Crystal (PC) waveguide. The proposed device consists of 2D square-lattice PC structures, and it is based on two PC waveguides with different symmetric guiding modes, where various configurations of defects, including elliptic or/and semi-circular defects have been incorporated. The proposed one-way light propagation Optical Diode has been designed and optimized by employing in-house 2D Finite Difference Time Domain (FDTD) numerical method. We have reported that the unidirectional light propagation depends strongly on the coupling region between the introduced defects and the adjacent waveguides, and it also depends on the matching and mismatching between the defects and waveguide modes. It has been shown also that owing to its tunable features, the proposed Optical Diode can be potentially applied as a building block in future complex optical integrated circuits.

General method for eliminating wave reflection in 2D photonic crystal waveguides by introducing extra scatterers based on interference cancellation of waves

We propose a general method for eliminating the reflection of waves in 2 dimensional photonic crystal waveguides (2D-PCWs), a kind of 2D material, by introducing extra scatterers inside the 2D-PCWs. The intrinsic reflection in 2D-PCWs is compensated by the backward-scattered waves from these scatterers, so that the overall reflection is greatly reduced and the insertion loss is improved accordingly. We first present the basic theory for the compensation method. Then, as a demonstration, we give four examples of extremely-low-reflection and high-transmission 90°bent 2D-PCWs created according to the method proposed. In the four examples, it is demonstrated by plane-wave expansion method and finite-difference time-domain method that the 90°bent 2D-PCWs can have high transmission ratio greater than 90% in a wide range of operating frequency, and the highest transmission ratio can be greater than 99.95% with a return loss higher than 43 dB, better than that in other typical 90°bent 2D-PCWs. With our method, the bent 2D-PCWs can be optimized to obtain high transmission ratio at different operating wavelengths. As a further application of this method, a waveguide-based optical bridge for light crossing is presented, showing an optimum return loss of 46.85 dB, transmission ratio of 99.95%, and isolation rates greater than 41.77 dB. The method proposed provides also a useful way for improving conventional waveguides made of cables, fibers, or metal walls in the optical, infrared, terahertz, and microwave bands.

Frequency generation in moving photonic crystals

In this paper, we discuss experimental feasibility and present several system designs that could be potentially used for generation of new frequencies by light waves interacting with moving photonic crystals. In particular, we first theoretically analyze multiple frequency generation when incident light is reflected or diffracted by the moving infinite 1D photonic crystals of different orientations. We then demonstrate frequency harmonics generation via leaky waves of a moving finite-size 1D photonic crystal. Finally, we study dispersion relations of modes guided in the hollow core of a moving waveguide. In particular, we demonstrate frequency comb generation inside of the hollow core of a moving 2D photonic crystal waveguide.

Temperature-independent strain sensing characteristics of coupled photonic crystal waveguides

A highly sensitive strain sensor based on coupled two-dimensional (2D) photonic crystal waveguides consisting of dielectric rods array immersed in air is designed. The effective side-coupling between directional coupled waveguides and surrounding defect cavities gives flexibility in the choice of the sensing monitoring band. The coupling process and transmission spectral properties are analyzed by the finite difference time domain (FDTD) method. The influence of strain and temperature on the transmission spectrum is investigated by monitoring the wavelength shift in the loss peaks. The dual-channel sensing method is proposed to eliminate the cross sensitivity effect between the strain and ambient temperature, and render a new category of temperature-independent strain sensing devices.

Air-Suspended Fast Transient Tunable Silicon Photonic Crystal Waveguide

We report an air-suspended ultracompact (30 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm m}\times\,$</tex></formula> 40 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm m})$</tex></formula> fast transient thermo-optic silicon (Si) 2D photonic crystal (PhC) waveguide (WG) operated at around telecommunication <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$S$</tex></formula> -band. A line defect triangular lattice PhC WG was fabricated on a silicon-on-insulator substrate with a 220-nm-thick Si layer on 2- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm m}$</tex> </formula> -thick buried oxide. The oxide layer was partially removed to air-suspend the 2D slab Si PhC to shift cutoff wavelength by localized heating through integrated NiCr microheaters. The cutoff wavelength of the PhC light modulator was 1465 nm at room temperature, but it was shifted 17 nm when 120 mA was applied. The transient time was estimated to 6.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm s}$</tex></formula> in rising time and falling time.

FROZEN MODE IN PHOTONIC CRYSTAL WAVEGUIDE

We propose a structure of 2D photonic crystal waveguide composed of hexagonal lattices of air holes in high index materials. Frozen mode regime can be observed within the photonic band gap. Light incident into the waveguide is coupled into two modes. One mode has enhanced amplitude and the other one has slow group velocity. Finite-different time-domain (FDTD) simulation is used to demonstrate the propagation of the slow mode.

Design of Photonic Crystals Waveguide Using Microfluidic Infiltration

The use of photonic crystals (PCS) in biosensor applications has lead to the development of highly sensitive and selective microfluidic sensor elements. Two main advantages of these devices for sensing applications are their high sensitivity and their reduced size, which makes it possible, in one hand, to detect very small analytes without the need of markers (label-free detection), and to integrate many of these devices on a single chip to perform a multi-parameter detection on the other hand. In the present paper, we analyze the design of a highly sensitive microfluidic sensors based on 2D photonic crystal slab waveguide formed by increasing the radii of air holes localized at each side of the line defect and filling with homogenous de-ionized water (nc =1.33). The transmission spectrum of the sensor has been obtained with the use of Finite Difference Time Domain (FDTD) method and it has been observed that a 306 nm wavelength position of the lower band edge shift was observed corresponding to a sensitivity of more than 927 nm per refractive index unit (RIU). Development of microfluidic sensor designs that enhance sensitivity is especially important because it allows detection of lower concentrations of analytes.

Design and analysis of slow light regime in silicon carbide 2D photonic crystal waveguides

We theoretically demonstrate the slow light capabilities of 2D silicon carbide based photonic crystal W1 waveguides (SiC-PhC-W1Ws) with numerical simulations. The PhC is assumed to be created by devising air-holes with hexagonal lattice in a standard SiC substrate having oscillator type ordinary refractive index. Numerical simulations show that by means of selective optofluidic infiltration and varying the air-holes radii, SiC-PhC-W1Ws are capable of slowing light down by about 473 times while their group velocity dispersions are tailored to near zero values. Our numerical study also suggests the possibility of slow-light guiding with ng×Δλ/λc values as high as 0.42 in SiC-PhC-W1Ws at optical telecommunications wavelengths.

Modeling of spectral dependences for 2D photonic crystal waveguide systems

A numerical algorithm is designed and implemented based on the joint application of the finite-difference time-domain (FDTD) method with absorbing boundary conditions (a combination of the perfectly matched layer (PML) and Mur first-order conditions) and the total-field/scattered-field technique (TF/SF). A complete formulation of the algorithm is given. The results of computing the spectral characteristics of the 2D photonic crystal with defects in the form of waveguides are presented. They demonstrate that it is possible to conduct calculations in a wide range of frequencies.