Tunable Photonic Crystal Mach--Zehnder Interferometer Based on Self-collimation Effect

A theoretical model for tunable Mach--Zehnder interferometers (TMZIs) constructed in a two-dimensional photonic crystal (2D PhC) is proposed. The 2D PhC consists of a square lattice of cylindric air holes in silicon. The TMZI includes two mirrors and two splitters. Light propagates between them employing a self-collimation effect. The two interferometer branches have different path lengths. Parts of the longer branch are infiltrated with a kind of liquid crystal (LC) with ordinary and extraordinary refractive indices 1.522 and 1.706, respectively. The transmission spectra at two TMZI output ports are in the shape of sinusoidal curves and have a uniform peak spacing 0.0017c/a in the frequency range from 0.26c/a to 0.27c/a. When the effective refractive index n_eff of the liquid crystal is increased from 1.522 to 1.706, the peaks shift to the lower frequencies over 0.0017c/a while the peak spacing is almost kept unchanged. Thus this TMZI can work as a tunable power splitter or an optical switch. For the central operating wavelength around 1550nm, its dimensions are only about tens of micron. Thus this device may be applied to photonic integrated circuits.     

Absorption Spectra of a Three-Level Atom Embedded in a PBG Reservoir

We introduce the ‘decay rate＇ terms into the density matrix equations of an atom embedded in a photonic band gap （PBG） reservoir successfully. By utilizing the master equations, the probe absorption spectra and the refractivity properties of a three-level atom in the PBG reservoir are obtained. The interaction between the atom and the PBG reservoir as well as the effects of the quantum interference on the absorption of the atom has also been taken into account. It is interesting that two different types of the anomalous dispersion relations of refractivity are exhibited in one dispersion line. The methodology used here can be applied to theoretical investigation of quantum interference effects of other atomic models embedded in a PBG reservoir.     

Probe absorption spectra of a V-type atom embedded in PBG reservoir

In this paper, the probe absorption spectra of a V-type atom embedded in photonic band gap (PBG) reservoir have been investigated under conditions that quantum interference among decay channels is important. The effect of the probe polarization on the absorption amplitude and spectral structure is investigated in detail. Comparing with similar models located in vacuum reservoir studied earlier, the study here shows that the probe polarization has some different effects on the absorption spectra in PBG reservoir.     

Zero-Dispersion Slow Light with Wide Bandwidth in Photonic Crystal Coupled Waveguides

By introducing an adjustment waveguide besides the incident waveguide, zero-dispersion slow light with wide bandwidth can be realized due to anticrossing of the incident waveguide mode and the adjustment waveguide mode. The width of the adjustment waveguide （W2） and the hole radii of the coupling region （r＇） will change the dispersion of incident waveguide mode. Theoretical investigation reveals that zero dispersion at various low group velocity vg in incident waveguide can be achieved. In particular, proper W2 and r＇ can lead to the lowest vg of 0.0085c at 1550 nm with wide bandwidth of 202 GHz for zero dispersion.     

An Array of One-Dimensional Porous Silicon Photonic Crystal Reflector Islands for a Far-Infrared Image Detector

With the aid of photolithography, an array of one-dimensional porous silicon photonic crystai reflector islands for a far infrared image detector ranging from 10 μm to 14 μm is successfully fabricated. Silicon nitride formed by low pressure chemical vapor deposition （LPCVD） was used as the masking layer for the island array formation. After etching, the microstructures were examined by a scanning electron microscope and the optical properties were studied by Fourier transform infrared spectroscopy, the result indicates that the multilayer structure could be obtained in the perpendicular direction via periodically alternative etching current in each pre-pattern. At the same time, the island array has a well-proportioned lateral etching effect, which is very useful for the thermal isolation in lateral orientation of the application in devices. It is concluded that regardless of the absorption of the deposition layer on the substrate, the localized photonic crystalline islands have higher reflectivity. The designed islands structure not only prevents the cracking of the porous silicon layers but is also useful for the application in the cold part for the sensor devices and the iliterconnection of each pixel.     

Spontaneous emission of a three-level lambda-type atom coupled to separate reservoirs

Considering the anisotropic dispersion model, the upper state population and spontaneous emission spectrum of three-level lambda-type atom with two transitions coupled to separate reservoirs are investigated using the resolvent operator. The upper state population reaches to a steady state value after a weak oscillation when the decay rate is zero and one transition frequency is inside the bandgap. The spectrum associated with each transition was given. Compared with results that were obtained by using isotropic dispersion model, the shape of spectrum changes significantly, and no dark line appears in the spectra.     

A Defect Effect to Light Transmission through Acute Bending Coupled Cavity Waveguide in a Two-Dimensional Photonic Crystal

Light propagation through a coupled-defect waveguide with a 63.5° bend in a two-dimensional （2D） photonic crystal is investigated. The waveguide modes are non-degenerate monopole state and dipole defect state of a square lattice for two different branches. To increaze the transmission in the bending waveguide, we propose a method to rotate the localized state by introducing a cavity. The higher coupling efficiency and transmission shift. new type defect with a sheared square rod into coupled in the bending waveguide are obtained with proper shear     

A Novel Woodpile Three-Dimensional Terahertz Photonic Crystal

A novel woodpile lattice structure is proposed. Based on plane wave expansion （PWE） method, the complete photonic band gaps （PBGs） of the novel woodpile three~dimensional （3D） terahertz （THz） photonic crystal （PC） with a decreasing symmetry relative to a face-centred-tetragonal （fct） symmetry are optimized by varying some structural parameters and the highest band gap ratio can reach 27.61%. Compared to the traditional woodpile lattice, the novel woodpile lattice has a wider range of the filling ratios to gain high quality PBGs, which provides greater convenience for the manufacturing process. The novel woodpile 3D PC will be very promising for materials of THz Junctional components.     

High Polarization Single Mode Photonic Crystal Microlaser

Generally, dipole mode is a doubly degenerate mode. Theoretical calculations have indicated that the single dipole mode of two-dimensional photonic crystal single point defect cavity shows high polarization property. We present a structure with elongated lattice, which only supports a single y-dipole mode. With this structure we can eliminate the degeneracy, control the lasing action of the cavity and demonstrate the high polarization property of the single dipole mode. In our experiment, the polarization extinction ratio of the y-dipole mode is as high as 51：1.     

Nonperturbative analysis of spontaneous emission in one dimensional special photonic crystals

The retarded spontaneous emission (SpE) process of a two-level atom embedded in realistic one dimensional photonic crystals (1DPC) is investigated with the quantum nonperturbative theory. The atomic transient decay is divided into two processes: the first comes from the natural decay to free space and the second is induced by the reflected field emitted from the atom itself. Due to the multi-reflection in the multi-layer structure, the correct delay time of the induced decay process is hard to calculate in the usual ways. However with the special but practical 1DPC provided, we give the analytic result of the atomic dynamic decay in 1DPC. Our result gives a clear picture to show the process which the atom feels the surrounding.     

Single-Photon Emission from a Single InAs Quantum Dot

Excitation power-dependent micro-photoluminescence spectra and photon-correlation measurement are used to study the optical properties and photon statistics of single InAs quantum dots. Exciton and biexciton emissions, whose photoluminescence intensities have linear and quadratic excitation power dependences, respectively, are identified. Under pulsed laser excitation, the zero time delay peak of second order correlation function corresponding to exciton emission is well suppressed, which is a clear evidence of single photon emission.     

Controllable Photonic Band Gap and Defect Mode in a 1D CO2-Laser Optical Lattice

We propose a new method to form a novel controfiable photonic crystal with cold atoms and study the photonic band gap （PBG） of an infinite 1D CO2-laser optical lattice of SSRb atoms under the condition of quantum coherence. A significant gap generated near the resonant frequency of the atom is founded and its dependence on physical parameters is also discussed. Using the eigenquation of defect mode, we calculate the defect mode when a defect is introduced into such a lattice. Our study shows that the proposed new method can be used to optically probe optical lattice in situ and to design some novel and controllable photonic crystals.     

Structure Tuning of Line-Defect Waveguides Based on Silicon-on-Insulator Photonic Crystal Slabs

We present fabrication and experimental measurement of a series of photonic crystal waveguides. The complete devices consist of an injector taper down from 3 μm into a triangular-lattice air-hole single-line-defect waveguide with lattice constant from 410nm to 470nm and normalized radius 0.31. We fabricate these devices on a silicon- on-insulator substrate and characterize them using a t unable laser source over a wavelength range from 1510 nm to 1640nm. A sharp attenuation at photonic crystal waveguide mode edge is observed for most structures. The edge of guided band is shifted about 30nm with the 10nm increase of the lattice constant, We obtain high-efficiency light propagation and broad flat spectrum response of the photonic crystal waveguides.     

TM-like and TE-like Modes Coupling in a Two-Dimensional Photonic Crystal Slab Composed of Truncated Cone Silicon Rods

We numerically investigate the coupling of TE-like modes and TM-like modes in a two-dimensional （2D） photonic crystal （PC） slab composed of truncated cone silicon rods. In such structures, the classification of TE-like modes and TM-like modes is generally impossible and the coupling occurs due to vertical structural asymmetries. The frequency and wavevector dependences of the mode coupling are discussed by investigating the photonic band structures, and the coupling efficiency is studied by examining the transmittance. The results show that the efficiency of mode conversion is strengthened by the vertical asymmetry and weakened by the clear sinall gap. These structures could be used as polarization conversion devices in integrated optics.     

Carrier-envelope phase-dependent electron tunneling in a coupled double-quantum-dot system driven by a few-cycle laser pulse

We theoretically investigate the dependence of the electron tunneling on the carrier-envelope phase of a few-cycle laser pulse in a coupled double-quantum-dot system, and we show that the electron tunneling between coupled quantum dots is very sensitive to the carrier-envelope phase under a change of the parameters of the system. This in turn provides an additional means to measure the carrier-envelope phase of a laser pulse at lower laser intensity regime in the solid-state nanostructure.     

Transmission Properties of W3 Y-Branch Filters in Two-Dimensional Photonic Crystal Slabs

A highly efficient W3 Y-branch filter in a two-dimensional photonic crystal slab with triangular lattice of air holes is designed and fabricated, and its transmission properties are measured. By accurately adjusting the size of the resonant cavities, the minimum wavelength spacing of 7 nm between two channels is realized. The corresponding resonant wavelengths of the two cavities agree well with the calculated ones. This implies that this kind of fiIter may be promising in integrated wavelength division multiplexing system.     

New Configuration of Ring Resonator in Photonic Crystal Based on Self-Collimation

We propose a novel ring resonator configuration in a channelless photonic crystal. The proposed ring resonator utilizes the self-collimation effect and the bending and splitting mechanisms of line defects to route the propagation of light, instead of conventional indexed-guided waveguides or photonic crystal band gap waveguides. The finite-difference time-domain method (FDTD) is used to investigate the characteristics of the ring resonator. The new design exhibits an ON--OFF contrast with an extinction ratio of more than 12dB, and has an ultra-compact footprint of 3.3×3.3μm² when it operates at the optical communication wavelength λ=1.55μm. The design presented may find applications in the areas including ultra-compact optical switch and wavelength filer in integrated optical circuits.     

Focusing Properties in Photonic Crystal Structure Formed by Air Holes in Dielectric Background with Concave Interface

We investigate the focusing properties of photonic crystal structures with a concavo-concave as the photonic crystal boundary. The photonic crystal is constituted by air holes parallelly distributed in a uniform dielectric. A good-quality focus of a plane wave can appear out of the photonic crystal structure, and a strong far field focus is also formed from the photonic crystal interface. A negative-refractive beam at the frequency 0.195 （2πc/α） for the excited Bloch wave mode near the Brillouin zone edges under all incident angles are obtained by simulation.     

An Integrative Biosensor Based on Contra-Directional Coupling Two-dimensional Photonic Crystal Waveguides

We propose an integrative biochemical sensor utilizing the dip in the transmission spectrum of a normal singleline defect photonic crystal （PC） waveguide, which has a eontra-directional coupling with another PC waveguide. When the air holes in the PC slab are filled with a liquid analyte with different refractive indices, the dip has a wavelength shift. By detecting the output power variation at a certain fixed wavelength, a sensitivity of 1.2 × 10^-4 is feasible. This structure is easy for integration due to its plane waveguide structure and omissible pump source. In addition, high signal to noise ratio can be expected because signal transmits via a normal single-line defect PC waveguide instead of the PC hole area or analyte.     

Optical Tamm States in Dielectric Photonic Crystal Heterostructure

We investigate one-dimensional dielectric photonic crystal and optical Tamm modes formed by superposition of two band gaps and find that this kind of mode can be explained by the single negative materials tunnelling effect. A finite-size dielectric photonic band gap can mimic one kind of effective single negative material and this property sensitively depends on the frequency location in stop-band regions and surface termination and so on. The effective impedance match and effective phase match give the precise position of the optical Tamm mode. Complete transparency via tunnelling is achieved by two opaque media and demonstrates the validity of our approach.