Light transmission by a three-level emitter embedded in a waveguide-coupled two-mode photonic crystal nanocavity

We investigate light transmission obtained from a three-level V-type emitter embedded in a waveguide-coupled two-mode photonic crystal nanocavity operating in the weak-coupling regime. It is shown that the composite system exhibits double electromagnetically-induced-transparency-like characteristics and a π phase shift while not suffering from absorption in the experimentally available parameter range. The double-frequency transparency of the input light expands the frequency range of EIT and may improve the controllability of EIT. The proposed scheme also provides a way to achieve integrated photonic devices on a chip for applications requiring multiple EIT effect.     

A cheap and practical FBG temperature sensor utilizing a long-period grating in a photonic crystal fiber

A whole temperature sensor in one package utilizing a fiber Bragg grating (FBG) made in a conventional single-mode fiber and which uses a long-period grating (LPG) made in a photonic crystal fiber is proposed and experimentally demonstrated. The function of the interrogation is that the wavelength change of the FBG with environmental temperature is transferred to the intensity of the output via the LPG. Utilizing the temperature-insensitivity of the LPG in the PCF, the interrogation is stable and enables a cheap and practical temperature measurement system with a wide dynamic range.     

共轴环光子晶体的缺陷微腔特性

采用数值计算方法,模拟了共轴环光子晶体缺陷微腔的谐振模式场分布,计算了此微腔的品质因数和功率损耗,并分析其几何参数对谐振特性的影响。以此缺陷微腔为基础构建周期性慢波系统,讨论了该系统的色散特性。结果表明,微腔中能够存在单一的谐振模式,微腔的纵向长度和介质环介电常数对谐振特性影响较大。所构建的慢波系统有较宽的慢波频域,且慢波比曲线较为平坦。增大电子注开孔半径和减小周期长度对于提高工作频率及增加带宽较为有效。     

Ultrahigh-Q of the L3 photonic crystal microcavity

In this paper, we theoretically investigate the L3 cavity with three missing holes in the center. They are of great interest for the realization of low threshold laser nanosources and for a strong interaction between the cavity and sources. In order to improve the transmission and Q factor simultaneously of these structure, by reducing unwanted reflection due to mismatch and through minimization of propagation losses, we modified L3 geometry: three missing holes in a line where both lateral displacement of the first hole adjacent to the cavity, d, and their radius, r, were changed. A photonic microcavity with a high Q factor of 1.8741 × 10⁷ and a modal volume V of 0.351 is demonstrated. We demonstrate that the calculated Q factor for the designed cavity increases by a factor of 49 relative to that for a cavity without displaced and reduced air holes, while the modal volume remains almost constant.     

Double-state controllable optical switching through three tunnel-coupled quantum dots inside waveguide coupled photonic crystal microcavity

We study optical transmission properties of a combined system which is composed of a photonic crystal (PC) microcavity with low quality factor Q, a triple quantum dot (QD) embedded in cavity and two parallel waveguides. We demonstrate that low coupling strength (i.e., the weak coupling regime) between a cavity and a dot, by means of electron tunnel-induced coupling, can lead to a type of double-state controllable optical switching under the experimentally available parameter conditions.     

Influence of two-photon absorption on bistable switching in a silicon photonic crystal microcavity

By employing a simplified nonlinear coupled mode theory, we discuss the influence of two-photon absorption (TPA) on the characteristics of bistable switching. It is revealed that the critical value of frequency detuning for bistability rises linearly with increasing TPA coefficient k (when k is less than 30), and eventually access to a saturated value. It is also found that TPA effect will be enhanced for a greater frequency detuning, especially when transmission reaches its peak value. As a result, the peak transmission will decrease monotonously with the increasing frequency detuning. Based on this simplified model, the TPA-induced temperature rise in microcavity is also estimated. The theoretical predictions show good agreement with the simultaneous results, as well as the proposed experimental phenomena.     

Optimization of long-period grating inscribed in large mode area photonic crystal fiber for design of bandstop filter

By inscribing long period grating (LPG) in a photonic crystal fiber (PCF), optical filters for communication wavelengths can be fabricated. In this paper, by utilizing coupled-mode theory and enhanced improved vectorial effective index method, a design of bandstop filter based on optimal LPG parameters is presented where the optimized full-width half-maximum (FWHM), the number (N) and total length of gratings of LPGs (L) are determined. As a result, by the determination of optimized LPG parameters with an optimum length of L_opt=6.5 mm and optimum number of grating N_opt=27 inscribed in the PCF, a bandstop optical filter with FWHM=1 nm is designed.     

Ultracompact refractive index sensor based on microcavity in the sandwiched photonic crystal waveguide structure

A refractive index (RI) sensor based on the two-dimensional photonic crystal is presented. The sensor is formed by a point-defect resonant cavity in the sandwiched waveguide structure. The transmission spectrums of the sensor with different ambient refractive indices ranging from n = 1.0 to n = 1.6 are calculated. The calculation results show that a change in ambient RI of Δn = 0.001 is apparent, the sensitivity of the sensor (Δλ/Δn) is achieved with 330 nm/RIU (when lattice constant a = 440 nm), where RIU means the refractive index unit; and the transmission efficiency in the RI range of 1.0-1.6 can reach about 40% to 70%, that make the detection of spectrum easy and feasible. The properties of the sensor are analyzed and calculated using the plane-wave expansion (PWE) method and simulated using the finite-difference time-domain (FDTD) method.     

Simultaneous strain and temperature measurement using a highly birefringence fiber loop mirror and a long-period grating written in a photonic crystal fiber

We present a new design for simultaneous strain and temperature measurement using a high-birefringence fiber loop mirror (HiBi-FLM) concatenated with a temperature-insensitive long-period grating (LPG) written in a photonic crystal fiber (PCF). The FLM acts as a sensor head, while the LPG in PCF serves as a filter to convert wavelength variation to optical power change. By measuring the wavelength variation and the power difference of two near peaks in the spectral response of this configuration, simultaneous strain and temperature measurement is obtained.     

Simultaneous strain and temperature measurement based on a photonic crystal fiber modal-interference interacting with a long period fiber grating

An alternative all-fiber sensor for simultaneous strain and temperature measurement based on a photonic crystal fiber (PCF) spliced between single-mode fibers cascaded with a long period grating (LPG) is proposed. By collapsing the air holes at two splicing regions along the PCF, a simple but effective modal-interference (MI) is occurred between the core and cladding modes of the PCF. Due to the different responses on the changes of strain and temperature on the MI and the cascaded LPG, the strain and temperature can be measured simultaneously. Experimental results show that the sensing resolution of 9.1 με in strain measurement is experimentally achieved over a range of 2640 με, while the temperature sensing resolution is 0.27 °C within a range of 30-100 °C.     

Numerical analysis of a temperature sensor based on the photonic band gap effect in a photonic crystal fiber

In this paper we investigate, by the plane wave expansion method and an analytical model, the temperature effect on the photonic band gap fiber, and we report on a numerical demonstration of a temperature sensor based on the photonic band gap (PBG) shift in a solid core photonic crystal fiber (PCF) infiltrated with a high refractive index oil. The bandwidth and the position of the central wavelength of the band gap are the parameters of interests for our temperature sensing purpose. Simulation results were found to be in excellent agreement with the refractive index scaling law and the highest sensitivity of 3.21?nm/°C was achieved, and it will be even higher than the grating based sensors written in PCFs with similar structure.     

Design of electro-optic switching via a photonic crystal cavity coupled to a quantum-dot molecule and waveguides

We demonstrate the possibility to realize an electro-optic switching operation in a weak-excitation limit, where one can control the path of an optical field propagating in a waveguide by suitably varying the applied bias voltage to tune the electron tunnel coupling.     

Enhancement of extraction efficiency by metallic photonic crystal embedding in light-emitting diode

The bandgap effect of photonic crystals (PCs) and the effect of grating diffraction can be used to improve the extraction efficiency of light from the light-emitting diode (LED). The transmission of light at certain wavelength through periodic sub-wavelength hole arrays in metal films is extraordinary, surface plasmon (SP) effects effectively. In this letter, silver metallic photonic crystals with square lattice of cylinder unit cells are fabricated in GaN layer of GaN-based blue LED. We use the finite-difference time-domain (FDTD) method to investigate the optical transmission, the results show that the light extraction efficiency is enhanced by more than four times. Then we use the surface plasmon dispersion relation to analyze the mechanism of antireflection.     

Intersecting veins effects of a two-dimensional photonic crystal with a large two-dimensional complete bandgap

Optimal design of a two-dimensional photonic crystal with a square lattice of dielectric rods with intersecting veins in GaAs is investigated numerically using plane wave expansion method. It is shown how a maximum complete two-dimensional bandgap is obtained by optimally connecting the dielectric rods with intersecting veins. The complete two-dimensional photonic bandgap (PBG) of our optimal design reaches Δω = 0.10664(2πc/a) (where a is the lattice constant and c is the speed of light in vacuum) when the radius of dielectric rod is 280.1 nm and the half-vein width is 60 nm. Our result shows 40% the width of PBG higher than that obtained from Ref. [M. Qiu, S. He, J. Opt. Soc. Am. B 17 (2000) 1027] (Δω = 0.0762(2πc/a)). In addition, we found that the complete bandgap can be obtained in a large range of radius R of dielectric rod when the half width of intersecting veins d is larger than 65 nm.     

光子晶体理论应用于取样光纤光栅的研究

将取样光纤光栅近似为引入多个有规律的大尺寸缺陷的一维二元光子晶体,运用光子晶体传输矩阵理论分析了其长度L、周期LA、折射率调制量δneff和采样率p等参量对其反射谱的影响规律,并将所得结果与用取样光纤光栅传输矩阵法计算所得结果进行了比较,得出了用光子晶体理论分析与用传统的模耦合理论分析相吻合的特性。在分析取样光纤光栅的其它性质以及将其应用于实际时都可借鉴此理论,以达到工程实际应用的最佳效果。     

光子晶体光纤长周期光栅的谐振波长特性研究

利用有限差分法和耦合模理论分析了光子晶体光纤结构参数等因素对光栅周期调节长周期光栅谐振波长作用的影响,结果表明:对于同种光纤,可通过增大或减小光栅周期来减小或增大谐振波长;若占空比f增大或减小,可通过减小或增大光栅周期来保持谐振波长不变;若比例系数M增大或减小,可以成正比增大或减小光栅周期来保持谐振波长不变;在只是空气孔层数增加的系列光纤中,在长波处,为取得同一谐振波长,光栅周期需要增大数个m,但在短波处则正好相反;内层气孔对光栅周期调节谐振波长的作用影响较大,而第5层以外各层的影响十分微弱。综合利用这些规律,可以快捷地选择合适的光栅周期,高效率地制备有合适谐振波长的光子晶体光纤长周期光栅。     

Large range of omni-directional reflection in 1D photonic crystal heterostructures

A simple design of one-dimensional omni-directional reflector based on photonic crystal heterostructures structure has been proposed. The proposed structure consists of a periodic array of alternate layers of SiO₂ and Te as the materials of low and high refractive indices, respectively. The structure considered here has three stacks of periodic structures having five layers each. The lattice period of successive stack is increased by a certain multiple (say gradual constant, δ) of the lattice period of the just preceding stack. For numerical computation, the method of transfer matrix method (TMM) has been employed. It is found that such a structure has wider reflection bands in comparison to a conventional dielectric PC structure and the width of the omni-directional reflection (ODR) bands can be enlarged by increasing the value of the gradual constant δ.     

一维Al/SrF2低温超导体-电介质光子晶体能带结构

基于二流体电子模型和平面波展开法,计算了一维Al/SrF2超导体-电介质光子晶体的能带结构.结果表明:随着超导层厚度的增加,第一光子带隙中心频率和截止频率均发生蓝移,且第一带隙宽度逐渐增加到一个峰值后又逐渐变窄.更重要的是,在低于临界温度的超低温环境中,温度的微小变化,对该类光子晶体的带隙宽度、中心频率以及截止频率均有...     

Photonic band gap failure in photonic crystal devices

The photonic crystal is an artificial material with periodic dielectric constant and the key factor to preserve their band features is its periodicity. When the number of periods of photonic crystal is decreased the photonic band gap cannot prevent the light of the corresponding frequencies from propagating in photonic crystal, in another word, photonic band gap will be failure. The minimum periods of photonic crystal device which can keep photonic band gap effective in miniaturization process is analyzed, the transmittance spectrum is calculated by the Finite-difference time-domain algorithm (FDTD) [1], the minimum periods is got in the simulation and the reason which affects the minimum periods is analyzed in this paper.     

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.