Ultrasmall-V high-Q photonic crystal nanobeam microcavities based on slot and hollow-core waveguides

Photonic crystal nanobeam microcavities based on slot and hollow-core waveguides were proposed and analyzed. Three-dimensional finite-difference time-domain simulations show that both an ultrasmall modal volume (V) and a high quality (Q) factor can be obtained simultaneously in hollow-core-nanobeam mirocavities (HCNMs) due to the strong confinement of fields in the two lateral directions. For a 6.5-μm-long HCNM, the Q factor and V are on the order of 10? and 10?2(λ/2n)3, respectively. With compactness, lower fabrication requirements as well as ultrahigh Q/V, the proposed microcavities would be very promising in a variety of applications.     

Ion detection with photonic crystal microcavities

We have experimentally demonstrated a cation and anion sensor by using short linear photonic crystal microcavities with an embedded quantum dot active region. The photonic crystal microcavity covered with an ion-selective polymer forms a submicrometer optical detection system sensitive to small changes of perchlorate anion (ClO4(-)) and calcium cation (Ca2+) concentrations.     

Silicon nano-membrane based photonic crystal microcavities for high sensitivity bio-sensing

We experimentally demonstrated photonic crystal microcavity based resonant sensors coupled to photonic crystal waveguides in silicon nano-membrane on insulator for chemical and bio-sensing. Linear L-type microcavities are considered. In contrast to cavities with small mode volumes, but low quality factors for bio-sensing, we showed increasing the length of the microcavity enhances the quality factor of the resonance by an order of magnitude and increases the resonance wavelength shift while retaining compact device characteristics. Q~26760 and sensitivity down to 15 ng/ml and ~110 pg/mm2 in bio-sensing was experimentally demonstrated on silicon-on-insulator devices.     

Highly sensitive photonic crystal fiber biosensor based on titanium nitride

A highly sensitive surface plasmon resonance photonic crystal fiber (PCF) biosensor based on Titanium Nitride (TiN) as a new alternative plasmonic material is proposed and analyzed. The TiN has high stability, high conductivity, and corrosion resistance which make it an ideal material for nanofabrication. The suggested biosensor is analyzed by full vectorial finite element method with perfectly matched layer as boundary conditions. In this paper, the biosensor geometrical parameters are studied to achieve high sensitivity for both polarized modes. A refractive index sensitivity of 7700 and 3600 nm/RIU for quasi-transverse electric and quasi transverse magnetic modes, respectively, are obtained. Additionally, the reported biosensor could be used for detecting an unknown analyte refractive index ranging from 1.32 to 1.34 with a high linearity. Further, the proposed biosensor structure is easy for fabrication using standard PCF fabrication current technologies.     

Fast-response terahertz wave switch based on T-shaped photonic crystal waveguide

We design an ultra-fast terahertz wave switch based on T-shape photonic crystal waveguide. The polymer rod is added in the junction as a point defect, the refractive index of which can be varied by adjusting the external pump laser intensity. The transmission spectrum is calculated by finite-difference time-domain method, which shows that the output energy of the two output ports is closely related to the refractive index of the polymer rod. By continuous wave excitation of the guided mode, the simulation results show that the T-shaped photonic crystal waveguide can flexibly tune the power in two output ports. The tuning rate of the device is about 0.3 ns. These results provide a useful guide and a theoretical basis for the developments of terahertz wave functional components.     

The study of electro-optical sensor based on slotted photonic crystal waveguide

A compact and sensitive electro-optical sensor based on slotted photonic crystal waveguide (S-PhCW) is demonstrated. The electro-optical sensor can be realized in photonic crystal (PhC) slabs of silicon in Silicon-on-Insulator (SOI). Nonlinear optical polymer is used as infiltration. By applying three-dimensional finite difference time domain (3D-FDTD), the sensitivity and quality factor of electro-optical sensor with different slotted waveguide width are calculated. In addition, sensitivity and the optical properties such as transmission spectrum and field distributions are compared between electro-optical sensor based on line defect photonic crystal waveguide (W1-PhCW) and that based on slotted photonic crystal waveguide (S-PhCW). Simulation results demonstrate that, compared with electro-optical sensor based on line defect photonic crystal waveguide, the sensitivity and quality factor is improved by 30 times and 6.6 times respectively in sensor based on slotted photonic crystal waveguide. Besides, the proposed PhC sensor devices have the advantage of a compact structure with the potential for monolithic integration with optical-to-electrical on-chip conversion and detection.     

Ultra-compact variable optical attenuator based on slow light photonic crystal waveguide

An ultra-compact variable optical attenuator based on slow light photonic crystal waveguide with thermooptic effect is demonstrated. Along with power consumption of as low as 30.7 mW, a variable attenuation range of 10 dB is experimentally achieved by shifting the transmission spectrum at about 4.6 nm. The length of the proposed device is only 20 μm.     

T-shaped polarization beam splitter based on two-dimensional photonic crystal waveguide structures

A T-shaped polarization beam splitter based on two-dimensional photonic crystal is proposed, which is composed of three waveguides: one input and two output. Unpolarized beams incident from the input port will be separated into two different polarization modes and outputted individually by two different coupling structures. Simulation results can be obtained by the finite-difference time-domain (FDTD) method. In the normalized frequency range of 0.3456 < \(\omega \alpha /2\pi {}c\) < 0.37, multiple frequencies can obtain high transmission efficiency simultaneously for both TE and TM modes. And the degree of polarization is very closed to 1 for both output ports at this frequency range. When the normalized frequency \(f=0.3534 \omega \alpha /2\pi {}c\), the transmission efficiency, respectively, is 88 % and \(91\) % for TE modes and TM modes. The extinction ratio is all 30dB for both modes. The polarization beam splitter attains the requirement we expected by analyzing simulation results.     

A photonic crystal side-coupled waveguide based on a high-quality-factor resonator array

Based on the present coupled mode theory of the photonic crystal resonator array in this paper,we propose a novel side-coupled waveguide to achieve highly efficient coupling of photonic crystal devices.It is found that the coupling efficiency is sensitive to the interval,the total number and the quality factor of the resonator.Considering the coupling efficiency and the coupling region,we select five resonators with an interval of six lattice periods.By optimizing the structure parameters of the waveguide and resonator,the quality factors of the resonator can be modulated and the coupling efficiency of the side-coupled waveguide reaches 95.47% in theory.Compared with other coupling methods,the side-coupled waveguide can realize efficient coupling with a compact structure,a high level of integration and a low degree of operational difficulties.     

Anisotropic photonic crystals and microcavities based on mesoporous silicon

A technique to prepare one-dimensional anisotropic photonic crystals and microcavities based on anisotropic porous silicon exhibiting optical birefringence has been developed. Reflectance spectra demonstrate the existence of a photonic band gap and of an allowed microcavity mode at the photonic band gap center. The spectral position of these bands changes under rotation of the sample about its normal and/or under rotation of the plane of polarization of the incident radiation. The dependence of the shift of the spectral position of the photonic band gap edges and of the microcavity mode on the orientation of the polarization vector of incident electromagnetic wave with respect to the optical axis of the photonic crystals and microcavities was studied.     

High sensitivity photonic crystal waveguide sensors

A theoretical investigation of the sensitivity of an optical liquid sensor, based on photonic crystal waveguide, is carried out. The sensing principle is based on the variation of the effective index of the waveguide induced by analyte refractive index change. The sensor modelling is carried out by using the 3D finite element method. The influence of geometrical parameters on the sensor sensitivity has been investigated. The results show that the sensitivity can be optimized by an appropriate choice of the geometrical parameters and a sensitivity superior to 20 has been achieved, near the cut-off in the slow light region, which is several times higher than that can be achieved with conventional waveguides.     

New version of seven wavelengths demultiplexer based on the microcavities in a two-dimensional photonic crystal

A new two dimensional photonic crystal demultiplexer of wavelength (WDM) is designed by exploiting two Fabry–Pérot reflectors at the end of the bus waveguides. The results show that the light with different wavelengths can be successfully filtered to different ports by setting different radius of the center defect rods in the drop waveguides and high drop efficiency can be achieved by means of reflection feedbacks. The proposed filter has a cross section equal to 9.7 μm × 5.8 μm. In the designed filter, an improvement of the number of channels has been achieved. The normalized transmission spectra of this component have been studied using finite difference time domain (FDTD) method. The important parameters consider for this studies are radius of rods used in Fabry–Pérot reflectors, and radius of center defect rods in the drop waveguides. The demultiplexer we designed can easily separate the light with seven different wavelengths simultaneously. The scope of this paper lies on demultiplexer for communication systems around 1.55-μm wavelength.     

High-Q microcavities realized in a circular photonic crystal slab

A series of microcavities in circular photonic crystal slabs are studied in this paper. It is shown that high quality factors can be obtained for such microcavities. For a cavity with three inner layers of air holes missing, Q factor larger than 10⁵ can be obtained. It is also worth noting there exists resonant modes with high quality factors, even for the defect-free circular photonic crystal slab, due to gradual change of the average effective index.     

Impedance matching in photonic crystal microcavities for second-harmonic generation

By numerically integrating the three-dimensional Maxwell equations in the time domain with reference to a dispersive quadratically nonlinear material, we study second-harmonic generation in planar photonic crystal microresonators. The proposed scheme allows efficient coupling of the pump radiation to the defect resonant mode. The outcoupled generated second harmonic is maximized by impedance matching the photonic crystal cavity to the output waveguide.     

Multiwavelength ultralow-threshold lasing in quantum dot photonic crystal microcavities

We demonstrate multiwavelength lasing of resonant modes in linear (L3) microcavities in a triangular-lattice 2D photonic crystal (PC) slab. The broad spontaneous emission spectrum from coupled quantum dots, modified by the PC microcavity, is studied as a function of the intensity of incident optical excitation. We observe lasing with an ultralow-threshold power of approximately 600 nW and an output efficiency of approximately 3% at threshold. Two other resonant modes exhibit weaker turnon characteristics and thresholds of approximately 2.5 and 200 microW, respectively.     

Multi-channel drop filters using photonic crystal ring resonators

In this paper, we propose a photonic crystal multi-channel drop filter based on ring resonators and investigate its properties numerically by using the finite-difference time-domain (FDTD) method. This structure is constructed in a two-dimensional square lattice. Our multi-channel drop filter is composed of three waveguides and three ring resonators. These ring resonators are located in two different regions (heterostructure) which each region has specific dielectric constant. At resonance of each ring resonator, the power with certain wavelength transferred to one of the three drop waveguides is found to be more than 81%.     

Liquid refractive index sensor based on slow light in slotted photonic crystal waveguide

A high sensitive and compact refractive index sensor based on slotted photonic crystal waveguide (S-PhCW) is demonstrated. This design is worked on a Mach–Zehnder interferometer (MZI) configuration with S-PhCW as the measuring arm, which can be used to detect any changes in refractive index that correspond to different concentration of the measuring liquid. Combining the slow light enhancement in photonic crystal waveguide (PhCW) with the advantage of excellent optical confinement in slot waveguide, the sensitivity of this simple scheme can reach to 2.3 × 10⁹ nm/RIU with the active region of only 1 mm long.     

1-to-N beam splitter based on photonic crystal branched waveguide structure

A novel beam splitter is proposed based on a two-dimensional (2D) photonic crystal (PC) branched waveguide structure. The beam splitter structure comprises branched waveguide channels and extra dielectric columns. These branched waveguide channels are used to obtain secondary sources and the introduced extra dielectric columns are used to control the phase difference of the secondary point sources. The field distributions of the beam are investigated using the finite-difference time-domain (FDTD). It is found that the number of beams is sensitive to the distance of the waveguide channels ports and extra dielectric columns. By adjusting the positions of the waveguide channels and the parameters of the extra dielectric columns, 1-to-N beam splitters can be realized. These simple, easily fabricated and controllable structures have important potential applications in integrated optical circuits.     

Purcell effect of GaAs quantum dots by photonic crystal microcavities

We fabricate photonic crystal slab microcavities embedded with GaAs quantum dots by electron beam lithography and droplet epitaxy. The Purcell effect of exciton emission of the quantum dots is confirmed by the micro photoluminescence measurement. The resonance wavelengths, widths, and polarization are consistent with numerical simulation results.     

Terahertz two-dimensional high-Q photonic crystal waveguide cavities

Numerical simulations were used to design a variety of high-Q resonant cavities for integration into a terahertz 2D photonic crystal waveguide. After fabrication, the transmission characteristics of each integrated cavity were explored. These photonic waveguide-coupled cavities demonstrate resonances with linewidths approaching 10 GHz. The results compare favorably to previous observations of rectangular waveguide cavities. Good agreement between the experimental results and the numerical simulations was obtained.