Single-mode 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.

High transmission through a 90° bend in a polarization-independent single-mode photonic crystal waveguide.

We propose a polarization-independent single-mode waveguide, using a two-dimensional square photonic crystal with a complete band gap. The waveguide is tuned such that both TE and TM modes have the same group velocity and zero group velocity dispersion at the centergap frequency. We also present results for a 90° bend with transmission values of 98% for both modes.

Compact wavelength de-multiplexer design using slow light regime of photonic crystal waveguides

We demonstrate the operation of a compact wavelength de-multiplexer using cascaded single-mode photonic crystal waveguides utilizing the slow light regime. By altering the dielectric filling factors of each waveguide segment, we numerically and experimentally show that different frequencies are separated at different locations along the waveguide. In other words, the beams of different wavelengths are spatially dropped along the transverse to the propagation direction. We numerically verified the spatial shifts of certain wavelengths by using the two-dimensional finite-difference time-domain method. The presented design can be extended to de-multiplex more wavelengths by concatenating additional photonic crystal waveguides with different filling factors.

Slow pulses in disordered photonic-crystal waveguides

Using a 3D fully-vectorial coupled Bloch-mode method, we present a systematic study of the transport of slow-light pulses in single-mode photonic-crystal waveguides (PhCW) with a realistic disorder model. For the intermediate regime corresponding to waveguide lengths of the order of the mean-free path (3 dB attenuation), we show that the group-velocity has a strong impact on the pulse broadening and distortion, limiting the practical use of PhCW to group indices below ≈50. For smaller group velocities, the pulse experiences an additional delay and the group-velocity is no longer a meaningful quantity.

Slow light in tapered slot photonic crystal waveguide

A slotted single-mode photonic crystal waveguide with a linear tapered slot is presented to realize slow light, whose dispersion curve is shifted by changing the slot width. When the slot width is reduced, the band curve shifts in the tapered structure, and the group velocity of light approach zero at the cut-off frequency. Therefore, different frequency components of the guided light are slowed down even localized along the propagation direction inside a tapered slot photonic crystal waveguide. Furthermore, this structure can confine slow light-wave in a narrow slot waveguide, which may effectively enhance the interaction between slow light and the low-index wave-guiding materials filled in the slot. In addition, this tapered slot structure can be used to compensate group velocity dispersion of slow light by modifying the structure, thus opening the opportunity for ultra-wide bandwidth slow light.

Light Coupling Between Photonic Crystal and Standard Photonic Waveguides in a Compact Photonic Integrated Circuitry Using 2D FDTD

Finite difference time domain (FDTD) analysis was used to design a photonic integrated circuitry (PIC) based on a Silicon-on-Insulator (SOI) structure. Light coupling efficiency from a single mode photonic crystal waveguide (PCW) into a single mode fibre (SMF) through adiabatic tapered waveguide and microrings based on resonance acting as spot-size converters (SSCs), is demonstrated. Optimisation of each component and their integration into a single optical chip is presented. SSCs are optimised in order to reduce back reflection and increased coupling efficiency between all devices constituting the optical chip. Significant reduction of back-reflections, insertion losses and the Fabry-Perrot noise are obtained by optimising each component and when mode and impedance matching conditions are achieved. The transmission characteristics of each component are investigated and low propagation losses in the PIC are reported.

Enhancing the emission efficiency in photonic crystal waveguide with coupled waveguide arrays

We propose a system of enhanced emission efficiency by employing coupled waveguide arrays to a single-mode photonic crystal waveguide. The FDTD simulation results show that, when the coupled waveguide arrays are placed properly at the exit plane of the single-mode photonic crystal waveguide, the output light can be split into many light beams, and the interference of these light beams can produce a focusing emission beam, which greatly enhances the emission efficiency. In addition, when the row number of the waveguide arrays is larger than a certain value (2N=8), the state of the emission is nearly steady and the most compact structure can be obtained. This type of photonic crystal has potential applications in near-field optics or integrated optics.

Light Localization in Slot Photonic Crystal Waveguide

A single-mode photonic crystal waveguide with a linear tapered slot is presented, which can localize light spatially by changing the slot width. Its effective bandwidth is 52nm, from 1500nm to 1552 nm. Along the tapered structure, the slot width is reduced, and the corresponding band curve shifts. The group velocity of light becomes zero at the band edge. Therefore, different frequency components of the guided light are slowed down and finally localized at correspondingly different widths inside a tapered slot photonic crystal waveguide. Furthermore, this structure can confine light wave in a narrow slot waveguide, which may effectively enhance the interaction between light and the low-index wave-guiding materials filled in the slot.

Photonic Crystal Fiber and Waveguide-Based Surface Plasmon Resonance Sensors for Application in the Visible and Near-IR

In the proposed photonic crystal waveguide-based surface plasmon resonance (SPR) sensor, a plasmon wave on the surface of a thin metal film is excited by a Gaussian-like leaky mode of an effectively single-mode photonic crystal waveguide. By judicious design of a photonic crystal waveguide, the effective refractive index of a core mode can be made considerably smaller than that of the core material, thus enabling efficient phase-matching with a plasmon, high sensitivity, and high coupling efficiency from an external Gaussian source, at any wavelength of choice from the visible to near infrared (IR), which is, to our knowledge, not achievable by any other design. Moreover, unlike the case of total internal reflection (TIR) waveguide-based sensors, a wide variety of material combinations can be used to design photonic crystal waveguide-based sensors as there is no limitation on the value of the waveguide core refractive index. This sensor design concept was implemented using planar multilayer photonic crystal waveguides, solid and hollow core Bragg fibers, as well as microstructured photonic crystal fibers. Amplitude and spectral-based methodologies for the detection of changes in the analyte refractive index were devised. Sensor resolution as low as 8.3·10−6 refractive-index unit (RIU) was found for aqueous analyte.

Ultracompact and wideband power splitter based on triple photonic crystal waveguides directional coupler

Three single-mode photonic crystal waveguides (PCWs) are put together closely to construct three PCWs directional coupler (3PCWDC). It is found that the coupling coefficient of two even modes excited by the input field symmetrically entering 3PCWDC may be increased dramatically by reducing the size scales of dielectric rods between the neighbouring PCWs. The coupling length in this structure can be much shorter than that in conventional PCWs within the frequency range of interest. The application of this feature to an ultracompact, wide bandwidth and high-transmission power splitter is addressed. The simulation results by using the finite-difference time-domain method show that the structure exhibits new interesting characteristics.

Photon crystal waveguide-based surface plasmon resonance biosensor

The concept of a photonic crystal waveguide-based surface plasmon resonance sensor is proposed, in which plasmons on a surface of a thin metal film are excited by a Gaussian-like leaky mode of an effectively single mode photonic crystal waveguide. The authors demonstrate that effective refractive index of a waveguide core mode can be designed to be considerably smaller than that of a core material, enabling efficient phase matching with plasmons at any wavelength of choice, while retaining highly sensitive response to changes in the refractive index of an analyte layer. This is attractive for the development of portable surface plasmon resonance biochemical sensors.

Tailoring holes for improving the efficiency of single-mode photonic crystal waveguide lasers on InP substrate

The authors show that the use of triangular lattice photonic crystals (PhCs) with wide holes can significantly improve the lasing performances of PhC waveguides in the InP substrate approach. The study is carried out on W2-3 waveguides made in PhCs whose air filling factor is varied from ∼25% to 55%. Intrinsically single-mode laser emissions with reduced threshold (/2) are obtained when the laser mode folds deeply into the gap. Concurrently, the slope of the light-light characteristic is increased by a factor of 14. The laser spectral behavior and threshold evolution are explained from three-dimensional finite difference time domain calculations.

Light coupling for single-mode photonic crystal waveguides

We use a transfer-matrix method (TMM) to investigate light coupling into and out of single-end single-mode photonic crystal waveguides. Without multi-reflection complexity, we give clearly the unambiguous quantitative determination of the coupling efficiency of external light into guided mode and the transition among guided modes. It is shown that the waveguide with a line defect along Γ J direction exhibits a much better coupling efficiency than that with a line-defect orientation along Γ M direction.

Waveguide mode converter based on two-dimensional photonic crystals

We propose and numerically analyze a novel mode converter based on two-dimensional photonic crystal waveguides with square arrays of cylindrical dielectric rods in air. The mode converter uses small perturbation defects to decouple various modes in the multimode waveguide, thereby permitting propagation of only one mode at any given frequency, which permits one-to-one mode conversion without exciting unwanted modes. The mode converter can efficiently convert a TM0 mode supported in a single-mode photonic crystal waveguide into a TM2 mode supported in the multimode waveguide that is laterally coupled to the single-mode waveguide section for a wide wavelength range. Influences of different sizes and positions of perturbation rods on the band structure of the multimode waveguide are studied.

General methods for designing single-mode planar photonic crystal waveguides in hexagonal lattice structures

We systematically investigate and compare general methods of designing single mode photonic crystal waveguides in a two-dimensional hexagonal lattice of air holes in a dielectric material. We apply the rather general methods to dielectric-core hexagonal lattice photonic crystals since they have not been widely explored before. We show that it is possible to obtain single mode guiding in a limited portion of the photonic bandgap of hexagonal lattice structures. We also compare the potentials of different photonic crystal lattices for designing single-mode waveguides and conclude that triangular lattice structures are the best choice.