Lattice Photonic Crystal Waveguide Research Articles

Slow light-based refractive index sensor in single mode photonic crystal waveguide

Here, a slow light-based refractive index sensor has been presented in a hole-type 2D hexagonal lattice photonic crystal waveguide by insertion of only four defect holes inside the channel. The width of the channel has been optimized to provide single mode operation and large free spectral range. Also, the performance of the sensor with and without introducing the central cavity inside the channel have been regarded for different radii of defects. The proposed sensor presents the highest sensitivity and detection range of 126 nm/RIU and 1–2.2, respectively for the detection based on band edge shift. The defects inside the channel have been introduced to obtain high Q-factor by defect radii tailoring. The highest average Q-factor and sensitivity of 1570 and 249.5 have been obtained for defect hole with radius of rc = 0.34a. The study has been carried out by plane wave expansion and finite difference time domain analysis. There is a good agreement between the results and the study proves the effect of slow light on the enhancement of light-matter interaction and sensitivity. The proposed structures can find potential applications in gas or liquid detection in medical and biochemical fields.

Photonic Crystal-Based All-Optical Half Adder with High Contrast Ratio

Abstract Photonic crystal waveguides provide a way to manipulate the performance of an optical signal in an ultra-small volume and are quite viable in designing chip-based components that will work all-optically. Here, in this article an all-optical half adder is proposed. It is based on a square lattice photonic crystal waveguide in which silicon rods are arranged periodically. The photonic crystal offers a wide photonic band-gap in the desired region of telecommunication wavelength (i. e. near λ = 1550 nm. The performance of half Adder is measured using the contrast ratio and response time. The contrast ratio for sum and carry is 5.2 dB and 16.7 dB, respectively. The proposed half adder is miniaturized in size and having a footprint of 49 µm2 only. The total response time of the proposed adder is 1.4 picoseconds only. So, the device offers a high bit rate of 0.714 Tb/sec. The proposed half adder is an optimum choice for its application in on-chip optical integrated circuits.

Symmetry-engineered waveguide dispersion in $ {\cal P}{\cal T} $PT symmetric photonic crystal waveguides

This work demonstrates how the crystal symmetry of photonic crystal defect waveguides interacts with simple, experimentally realizable parity-time ( P T ) symmetric regions of chip-scale absorption and amplification to control the existence and location of exceptional points in the first Brillouin zone. Our analysis is based on Heesh–Shubnikov group theory and is generalizable to a large class of devices for which the symmetry groups can be identified. Transverse, longitudinal, and transverse–longitudinal hybrid P T symmetries are considered, and for each, a triangular lattice photonic crystal waveguide with lattice-aligned and lattice-shifted cladding orientations is analyzed. We find that various symmetry combinations produce either strictly real-valued or strictly complex-valued eigenfrequencies at the Brillouin zone boundary. We also show how symmetry can be used to predict P T transitions at accidental degeneracies in the waveguide bands. It is shown how symmetry can be used to design single-mode waveguides, and we discovered exceptional points whose propagation constants are highly sensitive to the non-Hermiticity factor.

High efficiency all-optical diode based on hexagonal lattice photonic crystal waveguide

A high efficiency all-optical diode based on 2D hexagonal lattice photonic crystal (PC) waveguide is proposed. The structure is asymmetrically coupled by a high Q factor micro-cavity-containing nonlinear Kerr medium and a F-P cavity in PC waveguide. The transmission properties are numerically investigated by finite-difference time-domain (FDTD) method. Because of interference between the two cavities, the structure can achieve the function of forward transmission and backward cut-off under a suitable light intensity. For light incidence close to the direction of micro-cavity, nonlinear Kerr effect of micro-cavity can be excited by a certain light intensity. Then the resonant frequency of Fano cavity will change and forward incidence becomes transmission from reflective state. But for light incidence away from the direction of micro-cavity, the field distribution is asymmetric due to the asymmetric structure, so backward incidence needs stronger incidence light to excite Kerr effect and keeps reflective state. This design of all-optical diode has many advantages, including high maximum transmittance, high transmittance contrast ratio, low power threshold, and ease of integration, and so on.

Supermodes of hexagonal lattice waveguide arrays

We present a semi-analytical formulation for calculating the supermodes and corresponding Bloch factors of light in hexagonal lattice photonic crystal waveguide arrays. We then use this formulation to easily calculate dispersion curves and predict propagation in systems too large to calculate using standard numerical methods.

Wideband slow light and dispersion control in oblique lattice photonic crystal waveguides

We find that the angle between elementary lattice vectors obviously affects the bandwidth and dispersion of slow light in photonic crystal line-defect waveguides. When the fluctuation of group index is strictly limited in a +/-1% range, the oblique lattice structures with the angle between elementary lattice vectors slightly larger than 60 degrees have broader available bandwidth of flat band slow light than triangular lattice structures. For example, for the angle 66 degrees , there are increases of the available bandwidth from 20% to 68% for several different structures. For the same angle and a +/-10% variation in group velocity, when group indices are nearly constants of 30, 48.5, 80 and 130, their corresponding bandwidths of flat band reach 20 nm, 11.8 nm, 7.3 nm and 3.9 nm around 1550 nm, respectively. The increasing of bandwidth is related to the shift of the anticrossing point towards smaller wave numbers.

Distributed feedback regime of photonic crystal waveguide lasers at 1.5μm

Lasing of W3 and W2∕3 triangular lattice photonic crystal waveguides on InP substrate is investigated around 1.5μm by optical pumping. The lattice period of the fabricated structures is varied from 320 to 540nm by steps of 20nm, thereby leading to a detailed exploration of the lasing mechanism over a large frequency range. A distributed-feedback-laser- (DFB-) like-emission is observed above the gap (W3), while a genuine DFB laser emission is obtained in the gap (W2∕3). Side-mode suppression ratios can reach 40dB when an antireflecting coating is used on the cleaved output facet. Experimental results including light–light characteristics are analyzed in the framework of two-dimensional plane-wave calculations.

Investigation of physical mechanisms in coupling photonic crystal waveguiding structures

We explain the fundamental physical mechanisms involved in coupling triangular lattice photonic crystal waveguides to conventional dielectric slab waveguides. We show that the two waveguides can be efficiently coupled outside the mode gap frequencies. We especially focus on the coupling of the two structures within the mode gap frequencies and show for the first time that the diffraction from the main photonic crystal structure plays an important role on the reflection of power back into the slab waveguide. The practical importance of this effect and possible strategies to modify it are also discussed.