Ultracompact photonic coupling splitters twisted by PTT nanowires

We report a series of ultracompact photonic coupling splitters with multi-input/output ports assembled by twisting flexible polymer nanowires, which were fabricated by one-step drawing method from poly(trimethylene terephthalate) (PTT). Experimental demonstration shows that the properties of the splitters are dependent on the operation wavelength and the input branch of the optical signal launched. For a fixed operation wavelength and the input branch, desirable splitting ratio can be tuned by controlling the input/output branching angle. The excess loss of these splitters is less than 1 dB, and the intrinsic loss is less than 0.4 dB. They are desirable for high density photonic integrated circuits (PICs) and nanonetworks, while the twisting technology will be useful in constructing other wire-based photonic devices.     

All optical active high decoder using integrated 2D square lattice photonic crystals

The paper introduces a novel all optical active high 2 × 4 decoder based on 2D photonic crystals (PhC) of silicon rods with permittivity of ε = 10.1 × 10^?11 farad/m. The main structure of optical decoder is designed using a combination of five nonlinear photonic crystal ring resonator, set of T-type waveguide, and line defect of Y and T branch splitters. The proposed structure has two logic input ports, four output ports, and one bias input port. The total size of the proposed 2 × 4 decoder is equal to 40 μm × 38 μm. The PhC structure has a square lattice of silicon rod with refractive index of 3.39 in air. The overall design and the results are discussed through the realization and the numerically simulation to confirm its operation and feasibility.     

Tunable electro-optical 2 × 2 photonic crystal beam splitter

A tunable electro-optical 2?×?2 beam splitter based on two-dimensional rod-type photonic crystals is presented. The beam splitter consists of two orthogonally crossed linear waveguides and a single center rod in square lattice photonic crystals. In order to create a linear waveguide, the radius of a line of rods is reduced. A single center rod is positioned at the intersection of the linear waveguides to divide the input lightwave into output ports. The switching mechanism is a change in the conductance of the waveguide region and hence modulating the guided modes. The tunable beam splitter can be applied to photonic integrated circuits.     

Study the role of non-linear resonant cavities in photonic crystal-based decoder switches

In this paper, we are going to design and propose a novel structure for all optical decoder. The proposed structure is composed of optical power splitters and a four-port optical switch. The four-port optical switch simply is a non-linear optical demulitiplexer. For achieving non-linear behaviour for the demultiplexer, we will employ defect rods made of doped glass which has high Kerr coefficient. The final structure has three input ports and four output ports. Port E acts as enable port, which will be used activating or deactivating the total structure. A and B are the control ports, by which one can control when the structure is active, which port of the structure to be active. The optical intensity of the input ports required appropriate operation of the structure is about 20 W/μm². The maximum switching frequency of the proposed structure is 2 GHz. Reduced input optical intensity is the main characteristics of the present work. Numerical methods such as plane wave expansion and finite difference time domain were used for performing the required calculations.     

A 2*4 all optical decoder switch based on photonic crystal ring resonators

Based on photonic crystal ring resonators and nonlinear Kerr effect in this paper, we proposed a 2*4 all optical decoder switch. Our proposed structure has two logic input ports and one bias input port. This decoder switch has four output ports. Via these two logic input ports, we control the bias signal to transfer toward which output port. We employed numerical methods such as plane wave expansion and finite difference time domain methods for analyzing the proposed structure.     

Design, fabrication, and characterization of Si-based ARROW photonic crystal bend waveguides and power splitters

Silicon-based (Si-based) photonic crystal waveguide based on antiresonant reflecting optical waveguide (ARROW PCW) structures consisting of 60° bends and Y-branch power splitters were designed and first efficiently fabricated and characterized. The ARROW structure has a relatively large core size suitable for efficient coupling with a single-mode fiber. Simple capsule-shaped topography defects at 60° photonic crystal (PC) bend corners and Y-branch PC power splitters were used for increasing the broadband light transmission. In the preliminary measurements, the propagation losses of the ARROW PC straight waveguides lower than 2 dB/mm with a long length of 1500?μm were achieved. The average bend loss of 60° PC bend waveguides was lower than 3 dB/bend. For the Y-branch PC power splitters, the average power imbalance was lower than 0.6?dB. The results show that our fabricated Si-based ARROW PCWs with 60° bends and Y-branch structures can provide good light transmission and power-splitting ability.     

Beam splitter and beam bends based on self-collimation effect in two-dimensional photonic crystals

Basing on the self-collimation effect of photonic crystals, one-to-two beam splitter, beam bend and one-to-three beam splitter are, respectively, designed by introducing a different line defect along the same direction. From the equal-frequency contour plot which is calculated by the plane wave expansion method, we obtain the frequency and the propagate direction of the self-collimated beam. The self-collimated beam propagation in photonic crystals with different line defects is simulated by the two-dimensional finite-difference time-domain method with perfectly matched layer absorbing boundary conditions. The simulation results show that one-to-two beam splitter, beam bend and one-to-three beam splitter can be realized by appropriately arranging the line defect along the proper direction. Such devices can greatly enhance photonic crystals for use in high-density optical integrated circuits.     

A 1 × 4 optical splitter for TE modes based on a silicon photonic crystal self-collimation ring resonator

A 1?×?4 optical splitter (OS) is proposed for TE modes based on a self-collimation (SC) effect ring resonator (SCRR) in an air-hole type silicon photonic crystal. A 1?×?4 OS consists of four beam splitters formed by varying the radii of the air holes. Utilizing multiple-beam interference theory, the theoretical transmission spectra at each port in the OS were analyzed. By forming four splitters in a SCRR properly, self-collimation light can come out from four ports with the light-intensity ratio we set. OSs were investigated using the two-dimensional finite-difference time-domain (FDTD) simulation technique. The simulation results have good agreement with the theoretical prediction. Because of its small dimensions, whole silicon material, and air-hole type, this structure may have an important role in photonic integrated circuits.     

Three-dimensional power splitter based on self-imaging effect in multimode layer-by-layer photonic crystal waveguides

The self-imaging effect based on symmetrical interference in multimode layer-by-layer photonic crystal waveguides (PhCWs), is numerically studied with finite-difference time-domain simulations. With the properties of twofold images, a kind of three-dimensional (3D) PhCW-based power splitters with an ultracompact size using complete photonic bandgaps is proposed, calculated, and analyzed. The presented structure can be extended for the design of M×N power splitters for 3D photonic integrated circuits applications.     

Ultrahigh-Q nanocavities written with a nanoprobe

High-Q nanocavities have been extensively studied recently because they are considered key elements in low-power photonic devices and integrated circuits. Here we demonstrate that ultrahigh-Q (>10(6)) nanocavities can be created by employing scanning probe lithography on a prepatterned line defect in a silicon photonic crystal. This is the first realization of ultrahigh-Q nanocavities by the postprocess modification of photonic crystals. With this method, we can form an ultrahigh-Q nanocavity with controllable cavity parameters at an arbitrary position along a line defect. Furthermore, the fabricated nanocavity achieves ultralow power all-optical bistable operation owing to its large cavity enhancement effect. This demonstration indicates the possibility of realizing photonic integrated circuits on demand, where various circuit patterns are written with a nanoprobe on a universal photonic crystal substrate.     

Temporal coupled-mode theory for the Fano resonance in optical resonators

We present a theory of the Fano resonance for optical resonators, based on a temporal coupled-mode formalism. This theory is applicable to the general scheme of a single optical resonance coupled with multiple input and output ports. We show that the coupling constants in such a theory are strongly constrained by energy-conservation and time-reversal symmetry considerations. In particular, for a two-port symmetric structure, Fano-resonant line shape can be derived by using only these symmetry considerations. We validate the analysis by comparing the theoretical predictions with three-dimensional finite-difference time-domain simulations of guided resonance in photonic crystal slabs. Such a theory may prove to be useful for response-function synthesis in filter and sensor applications.     

All-optical digital 4 × 2 encoder based on 2D photonic crystal ring resonators

The photonic crystals draw significant attention to build all-optical logic devices and are considered one of the solutions for the opto-electronic bottleneck via speed and size. The paper presents a novel optical 4 × 2 encoder based on 2D square lattice photonic crystals of silicon rods. The main realization of optical encoder is based on the photonic crystal ring resonator NOR gates. The proposed structure has four logic input ports, two output ports, and two bias input port. The photonic crystal structure has a square lattice of silicon rods with a refractive index of 3.39 in air. The structure has lattice constant ‘a’ equal to 630 nm and bandgap range from 0.32 to 044. The total size of the proposed 4 × 2 encoder is equal to 35 μm × 35 μm. The simulation results using the dimensional finite difference time domain and Plane Wave Expansion methods confirm the operation and the feasibility of the proposed optical encoder for ultrafast optical digital circuits.     

A novel proposal for all optical 3 to 8 decoder based on nonlinear ring resonators

In this paper, a 3 to 8 optical decoder was proposed using nonlinear photonic crystal ring resonators. For realizing the 3 to 8 decoder, we combined seven 1 to 2 optical decoders. In the proposed structure, X, Y and Z serve as input ports. By combination of these ports, one can control which output port to be ON. The maximum time delay of the proposed structure is about 6?ps.     

A compact optical wavelength splitter in one-dimensional photonic crystal waveguides

A fundamental T-branch in one-dimensional photonic crystal waveguides based on the omnidirectional reflection is constructed. Numerical simulations of this T-branch indicate that without any structural optimization, four high reflectance peaks and three high transmittance peaks appear alternately within a wide enough frequency band. The T-branch with the unique transmission characteristics can be used as a wavelength splitter. Combining the fundamental T-branch with flexible bends of one-dimensional photonic crystal waveguides, we construct simple and compact wavelength splitters with arbitrary branching angles. Those wavelength splitters are expected to be applied to high density photonic integrated circuits.     

Polarization beam splitter based on honeycomb-lattice photonic crystal ring resonators

A new polarization beam splitter is proposed based on a photonic crystal ring resonator (PCRR) composed of honeycomb-lattice cylindrical silicon rods in air. By shrinking the width of the bus waveguide and adjusting the radii of two nearest-neighbor center rods of the PCRR, an unpolarized beam can be separated well into TE and TM polarization states, respectively, at the backward and forward output ports. Simulation results obtained by the two-dimensional finite-difference time-domain technique show that the insertion losses are 3.58 dB and 3.08 dB, and the polarization extinction ratios are 21.42 dB and 28.53 dB for TE and TM polarization, respectively, at a 1566.7 nm center wavelength. The excess loss is less than 0.34 dB and its dimensions are roughly 43.2 μm × 27.52 μm. These findings offer potential practical applications in high-density photonic integrated circuits.     

Nonreciprocal optical divider based on two-dimensional photonic crystal and magneto-optical cavity

We suggest and analyze a new nonreciprocal optical device based on two-dimensional photonic crystal and a magneto-optical cavity that simultaneously fulfills two functions: division of the input signal and isolation of the input port from two output ones. At the central frequency, the division of the signal between the output ports is -3 dB and the isolation of the input port from the output ones is about -25 dB. For the level -20 dB of this isolation, the calculated bandwidth is around 100?GHz at the wavelength 1.5?μm.     

Ultracompact 1×4 TM-polarized beam splitter based on photonic crystal surface mode

We provide an improved surface-mode photonic crystal (PhC) T-junction waveguide, combine it with an improved PhC bandgap T-junction waveguide, and then provide an ultracompact 1×4 TM-polarized beam splitter. The energy is split equally into the four output waveguides. The maximal transmission ratio of each output waveguide branch equals 24.7%, and the corresponding total transmission ratio of the ultracompact 1×4 beam splitter equals 98.8%. The normalized frequency of maximal transmission ratio is 0.397(2πc/a), and the bandwidth of the ultracompact 1×4 TM-polarized beam splitter is 0.0106(2πc/a). To the best of our knowledge, this is the first time such a high-efficiency 1×4 beam splitter exploiting the nonradiative surface mode as a guided mode has been proposed. Although we only employed a 1×4 beam splitter, our design can easily be extended to other 1×n beam splitters.     

Manipulating wavelength-selective emission with heterogeneous photonic crystals

The usual near-field radiation profile of a light beam emanating from a photonic crystal waveguide (PCW) has a main lobe at the center line of the waveguide. However, a centrally symmetric profile for the emission pattern with two sidelobes can be required in some applications, e.g., Y-type power dividers, wavelength multiplexers, and semiconductor lasers. With such motivations in mind, we present the design of a compact structure that deflects the beam propagation direction in this manner. The idea utilizes the manipulation of the dispersion diagram of cascaded photonic crystals by exploiting the bandgap and self-collimation properties. The waveguide mode in the PCW can be transformed from a propagating mode into a diffusive one by altering the filling factor, which, in turn, leads to off-axis light emission. By using the finite-difference time-domain method, we show that the emission takes place into free space at the inclined output surfaces of the PCW with deviation angles of ±45°.     

A simple scheme with coupled down converters with type-I phase matching as resource for conditional preparation of macroscopic entangled states

It is shown that macroscopic entangled states can be generated using an experimental arrangement consisting of coupled spontaneous parametric down-converters with type-I phase matching (SPDCI) pumped simultaneously by optical fields in coherent state and two beam splitters. Two beam splitters in auxiliary generated modes are used to conditionally prepare macroscopic entangled states in output pumping modes of the studied system. Identification of two macroscopic entangled states is produced by use of photon number resolving detection. In contrast to all previous schemes, our scheme does not need Kerr-type nonlinear interaction and is purely based on second-order susceptibility of the crystal which is stronger for the Kerr nonlinearity. We calculate concurrence of the states as a measure of the amount of entanglement stored in the states and present analysis concerning ‘separation’ between components forming studied entangled states.     

Multi-channel terahertz wavelength division demultiplexer with defects-coupled photonic crystal waveguide

Abstract

Terahertz (THz) wavelength division demultiplexer based on a compact defects-coupled photonic crystal waveguide is proposed and demonstrated numerically. This device consists of an input waveguide that perpendicularly coupled with a series of defects cavities, each of which captures the resonance frequency from the input waveguide. Coupled-mode theory and finite element method are used to analyze the transmission properties of the structure. It is found that the transmission wavelength centered around 1 THz can be adjusted by changing the geometrical parameters of defects cavities, which equals to THz waves generated by optical methods such as difference frequency generation and optical rectification. Applications in this frequency range are urgently needed. Furthermore, the highest transmission efficiency of 0.94 can be achieved when a perfect wavelength-selective mirror is set in the output waveguide.