Giant Goos–Hnchen shifts of waveguide coupled long-range surface plasmon resonance mode

A hybrid structure based on a planar waveguide(PWG) mode coupling a long-range surface plasmon resonance(LRSPR) mode is proposed to enhance the GH shift. Both the PWG mode and LRSPR mode can be in strong resonance, and these two modes can be coupled together due to the normal-mode splitting. The largest GH shift of PWG-coupled LRSPR structure is 4156 times that of the incident beam, which is 23 times and 3.6 times that of the surface plasmon resonance(SPR) structure and the LRSPR structure, respectively. As a GH shift sensor, the highest sensitivity of 4.68 × 10~7λ is realized in the coupled structure. Compared with the sensitivity of the traditional SPR structure, the sensitivity of our structure is increased by more than 2 orders, which theoretically indicates that the proposed configuration can be applied to the field of high-sensitivity sensors in the future.     

Reducing Insertion Loss of Photonic Crystal Couplers by Suppressing the Remained Power

We find that the increasing coupling strength can lead to a decreasing density of power inside the waveguide of a photonic crystal waveguide （PC-WG） directional coupler, which is called the mode power remaining phenomenon. This phenomenon is detrimental to achieving low insertion loss of the coupler. An improved structure of the PC- WG directional coupler is proposed by simply increasing the radii of air holes in the post coupling region. The simulation results demonstrate that the insertion loss can be reduced dramatically by suppressing the remained power, and therefore both the short coupling length （8μm） and low insertion loss （lower than 0.5dB） can be obtained.     

Different optical properties in different periodic slot cavity geometrical morphologies

In this paper,optical properties of two-dimensional periodic annular slot cavity arrays in hexagonal close-packing on a silica substrate are theoretically characterized by finite difference time domain(FDTD) simulation method.By simulating reflectance spectra,electric field distribution,and charge distribution,we confirm that multiple cylindrical surface plasmon resonances can be excited in annular inclined slot cavities by linearly polarized light,in which the four reflectance dips are attributed to Fabry–Perot cavity resonances in the coaxial cavity.A coaxial waveguide mode TE11 will exist in these annular cavities,and the wavelengths of these reflectance dips are effectively tailored by changing the geometrical pattern of slot cavity and the dielectric materials filled in the cavities.These resonant wavelengths are localized in annular cavities with large electric field enhancement and dissipate gradually due to metal loss.The formation of an absorption peak can be explained from the aspect of phase matching conditions.We observed that the proposed structure can be tuned over the broad spectral range of 600–4000 nm by changing the outer and inner radii of the annular gaps,gap surface topography.Meanwhile,different lengths of the cavity may cause the shift of resonance dips.Also,we study the field enhancement at different vertical locations of the slit.In addition,dielectric materials filling in the annular gaps will result in a shift of the resonance wavelengths,which make the annular cavities good candidates for refractive index sensors.The refractive index sensitivity of annular cavities can also be tuned by the geometry size and the media around the cavity.Annular cavities with novel applications can be implied as surface enhanced Raman spectra substrates,refractive index sensors,nano-lasers,and optical trappers.     

Measurement of absolute phase Shift on reflection of thin films using white-light spectral interferometry

A novel method to measure the absolute phase shift on reflection of thin film is presented utilizing a white-light interferometer in spectral domain. By applying Fourier transformation to the recorded spectral interference signal, we retrieve the spectral phase function Ф, which is induced by three parts： the path length difference in air L, the effective thickness of slightly dispersive cube beam splitter Teff and the nonlinear phase function due to multi-reflection of the thin film structure. We utilize the fact that the overall optical path difference （OPD） is linearly dependent on the refractive index of the beam splitter to determine both L and Teff. The spectral phase shift on reflection of thin film structure can be obtained by subtracting these two parts from Ф. We show theoretically and experimentally that our new method can provide a simple and fast solution in calculating the absolute spectral phase function of optical thin films, while still maintaining high accuracy.     

A monolithic distributed phase shifter based on right-handed nonlinear transmission lines at 30 GHz

The epitaxial material, device structure, and corresponding equivalent large signal circuit model of GaAs planar Schottky varactor diode are successfully developed to design and fabricate a monolithic phase shifter, which is based on right-handed nonlinear transmission lines and consists of a coplanar waveguide transmission line and periodically distributed GaAs planar Schottky varactor diode. The distributed-Schottky transmission-line-type phase shifter at a bias voltage greater than 1.5 V presents a continuous 0°–360° differential phase shift over a frequency range from 0 to 33 GHz. It is demonstrated that the minimum insertion loss is about 0.5 dB and that the return loss is less than-10 dB over the frequency band of 0–33 GHz at a reverse bias voltage less than 4.5 V. These excellent characteristics, such as broad differential phase shift, low insertion loss, and return loss, indicate that the proposed phase shifter can entirely be integrated into a phased array radar circuit.     

Multiple optical trapping based on high-order axially symmetric polarized beams

Multiple optical trapping with high-order axially symmetric polarized beams(ASPBs) is studied theoretically,and a scheme based on far-field optical trapping with ASPBs is first proposed.The focused fields and the corresponding gradient forces on Rayleigh dielectric particles are calculated for the scheme.The calculated results indicate that multiple ultra-small focused spots can be achieved,and multiple nanometer-sized particles with refractive index higher than the ambient can be trapped simultaneously near these focused spots,which are expected to enhance the capabilities of traditional optical trapping systems and provide a solution for massive multiple optical trapping of nanometer-sized particles.     

Intensity detecting refractive index sensors with long-period fiber gratings written in STS structure

A refractive index intensity detecting sensor with long-period grating written in the single-mode–thin-core–single-mode fiber(STS) structure is proposed and optimized theoretically. The sensor is composed of two single-mode fibers connected by a section of long-period fiber grating fabricated on thin-core fiber. After optimization and benefitting from the phase matching point, the loss peak of the structure can reach 62.8 d B theoretically. The wavelength of the characteristic peak is fixed at the phase matching point, so intensity detection can be achieved. The sensitivity can reach 272.5 d B/RIU. The structural optimization in this Letter provides a reference for the fabrication of an easy-made all-fiber sensor without extra cladding.     

Triple plasmon-induced transparency and outstanding slow-light in quasi-continuous monolayer graphene structure

We propose a simple quasi-continuous monolayer graphene structure and achieve a dynamically tunable triple plasmon-induced transparency(PIT)effect in the proposed structure.Additional analyses indicate that the proposed structure contains a selfconstructed bright-dark-dark mode system.A uniform theoretical model is introduced to investigate the spectral response characteristics and slow light-effects in the proposed system,and the theoretical and the simulated results exhibit high consistency.In addition,the influences of the Fermi level and the carrier mobility of graphene on transmission spectra are discussed.It is found that each PIT window exhibits an independent dynamical adjustability owing to the quasi-continuity of the proposed structure.Finally,the slow-light effects are investigated based on the calculation of the group refractive index and phase shift.It is found that the structure displays excellent slow-light effects near the PIT windows with high-group indices,and the maximum group index of each PIT window exceeds 1000 when the carrier mobility of graphene increases to 3.5 m^2 V^-1s^-1.The proposed structure has potential to be used in multichannel filters,optical switches,modulators,and slow-light devices.Additionally,the established theoretical model lays a theoretical basis for research on multimode coupling effects.     

Phase-controlled gain, phase shift, and group velocity using a room-temperature active-Raman-gain medium

A four-level tripod active-Raman-gain scheme is analyzed for obtaining phase-controlled gain, phase shift, and group velocity at room temperature. The scheme can be used to eliminate significant probe field atten- uation or distortion which is unavoidable in the scheme based on electromagnetically induced transparency. It is shown that the intensity gain, phase shift, and group velocity of a probe field can be simultaneously manipulated by changing the relative phase of two pump fields. The scheme is also different from that proposed recently by Deng et al. where a probe-field gain always exists. New features of the scheme presented here raise the possibility of designing rapidly responding optical switches and gates for optical information processing.     

Coupled resonator-induced transparency on a three-ring resonator

The coupled resonator-induced transparency(CRIT) phenomenon, which is analogous to electromagnetically induced transparency in atomic systems, can occur in an original integrated optical resonator system due to the coherent interference of the coupled optical resonators. The system was composed of three ring resonators on silicon, each with the same cavity size, and the optical coupling to the input and output ports was achieved using grating with a power coupling efficiency of 36%. A CRIT resonance whose spectrum shows a narrow transparency peak with a low group velocity was demonstrated.The quality factor of the ring resonator can attain a value up to 6×10~4, and the harmonic wavelength can be controlled by adjusting the temperature. The through and drop transmission spectra of the resonator are reconciled well with each other and also consistent well with the theoretical analysis.     

环中环结构谐振腔中的耦合谐振透明特性研究

在考虑耦合器插入损耗的情况下,理论分析了环中环结构谐振腔的耦合谐振透明效应.利用迭代法推导了整个结构的透过系数和有效相移,从而得到考虑了插入损耗的该结构的色散.研究表明,整个结构的有效相移,群速度和带宽,可通过耦合器的插入损耗、环中环结构中环与环周长之间的倍数以及环的个数来控制,这在旋转传感、光学时延线、光缓存、滤波等方面的应用有重要意义. 关键词： 环中环结构 耦合谐振透明 色散 慢光     

基于新型三环谐振器的诱导透明效应分析

针对谐振式微腔的应用需求, 提出了一种新型三环谐振式微腔结构, 类似于原子系统中的电磁诱导透明, 耦合诱导透明(CRIT)效应在一个新的光学微腔系统中已被实验证明. 该结构在硅基上由三个尺寸完全一样的微环腔组成, 通过理论分析、制备和实验测试, 能够观察到CRIT现象, 其频谱具有低群速的狭窄透明峰, 与光栅耦合器的耦合效率为34%, 并且谐振器的品质因数达到了0.65×10⁵, 同时, 失谐的谐振波长可以通过温度变化来控制, 这在旋转传感、光滤波器、光存储器等方面的应用有重要意义.     

平面环形谐振腔微光学陀螺结构设计与优化

提出具有高群有效折射率的双环级联作为核心元件的谐振式平面光波导陀螺结构, 基于光学Sagnac原理得到了双微环耦合谐振式光学陀螺理论灵敏度与群有效折射率的一般表达式和双环与单环陀螺系统的灵敏度关系, 并由耦合模理论方法得到了双环系统耦合器的两个透射系数对应的群有效折射率变化情况. 在环腔半径R₁=R₂=100 μm、环腔传输损耗系数t₁=t₂=0.95的情况下, 针对环与环之间耦合器和环与波导之间耦合器透射系数对群有效折射率的不同影响, 得到了最大群有效折射率的产生条件. 采用文中参数(R=100 μm, t=0.95)计算的单环谐振式陀螺灵敏度为(10⁴-10⁵)°/h, 而双环级联谐振系统理论灵敏度能够达到10 °/h. 该研究对微环耦合谐振腔在角速度检测上的应用有重要的意义.     

光学谐振系统中慢光特性研究

针对两环形腔与直波导耦合的系统,考虑光纤耦合器的插入损耗,发现两个耦合器反射值的不同匹配,却可以在谐振处得到相同的透过率峰值,因此可以不必限定某两个具体反射值,通过数值模拟得到中心频率处透过率峰值与群折射率的反比关系.由于群延迟与群折射率相对应,所以群延迟的增加势要以牺牲峰值透过率为代价.将增益介质加入到三环形腔与直波导耦合的系统中,可以使结构的色散响应由反常色散转化为正常色散,同样体现出慢光的特性.在频域和时域范围内分别对群延迟做了定量的分析. 关键词： 慢光 透过率 有效相移 群延迟     

Coupled-resonator-induced transparency in two microspheres as the element of angular velocity sensing

We proposed a two-coupled microsphere resonator structure as the element of angular velocity sensing under the Sagnac effect.We analyzed the theoretical model of the two coupled microspheres,and derived the coupled-resonatorinduced transparency(CRIT) transfer function,the effective phase shift,and the group delay.Experiments were also carried out to demonstrate the CRIT phenomenon in the two-coupled microsphere resonator structure.We calculated that the group index of the two-coupled sphere reaches n_g = 180.46,while the input light at a wavelength of 1550 nm.     

Design and analysis of all-optical 4–2 binary encoder based on photonic crystal

In this paper we theoretically propose combining optical waveguides with nonlinear photonic crystal based ring resonators for realizing an all optical 4–2 encoder. Nonlinear resonant rings are constructed from GaAs as the material used for dielectric rods. By application of optical beam to input ports of the structure the on/off states are realized and the resulting truth table confirms functionality of proposed device. The switching threshold and time delay of the device are about 1 kW/µm² and 1 ps, respectively. The normalized power at the output ports for all the ports in ON states is the same and equal to 60%.     

两腔级联纠缠增强的理论分析

高纠缠度的纠缠源是实现高保真度量子信息传输与处理的保障,因为受到光学元器件自身性能不完美的限制,通过有效的操控手段来提高光场的纠缠度是十分必要的.连续变量Einstein-Podolsky-Rosen纠缠态光场可以利用工作在阈值以下的非简并光学参量放大器来获得.将两个非简并光学参量放大器级联,可以利用第二个光学腔来操控第一个光学腔输出的纠缠态光场,在一定条件下实现光场的纠缠增强.本文通过理论分析设计出两种光学腔级联的实验系统,其中,纠缠产生装置采用具有三共振结构的半整块驻波腔,输出到目前为止世界上单腔获得两组份纠缠态光场纠缠度的最高值,操控光学腔采用驻波腔或四镜环形腔的结构.详细对比分析了不同结构的操控腔对纠缠增强效果的影响,得出利用不同腔形作为操控腔的最佳实验方案.同时分析了级联腔输出光场的纠缠度随不同物理参量的变化关系,得出进一步优化的最佳实验系统参量,为实验获得更高纠缠度的纠缠态光场提供了依据.     

X-两环结构的光学特性研究

提出了一种X-两环的金属周期性阵列结构,该结构由两个同心圆环包围中心X型构成.利用时域有限差分算法研究了该结构的光学特性.计算表明,当光入射到金属表面时,能够在结构中产生法诺共振现象,并在不同的位置下产生共振谷.同时,共振谷的出现又明显依赖于结构的相对参数(X的臂长、内外环的距离、内外环宽度、周期、环数、X所呈的角度),从而可以通过调节结构的相对参数来实现对结构的共振强度及共振谷位置的调控.另外,进一步分析了在不同环境折射率条件下该结构共振谷的变化规律,可以得出该结构也对周围的环境折射率有着较高的敏感度,最高可达1300 nm/RIU.结果表明,该结构在环境折射率传感器及某些光子器件的应用方面有着潜在的价值.     

Control of dispersion in fiber coupled resonator-induced transparency structure

Induced transparency phenomena and strong dispersion can be produced in a coupled resonator induced transparency(CRIT) structure.In this paper,we investigate the influences of structure parameters,such as amplitude reflection coefficient and loss,on transmission spectrum and dispersion of CRIT structure,and further study the control of dispersion in the structure.The results show that in the CRIT structure,adjusting the loss of resonators is an effective method of controlling dispersion and producing simultaneous normal and abnormal dispersion.When we choose approximate amplitude reflection coefficients of the two couplers,the decrease of transmittance due to loss could be effectively made up.In the experiment,we achieve the control of dispersion and simultaneous strong normal and abnormal dispersion in the CRIT structure comprised of fiber.The results indicate the CRIT structure has potential applications in optical signal processing and optical communication.     

All optical NOR and NAND gate based on nonlinear photonic crystal ring resonators

In this paper we proposed optical NOR and NAND gates. By combining nonlinear Kerr effect with photonic crystal ring resonators first we designed a structure, whose optical behavior can be controlled via input power intensity. The switching power threshold obtained for this structure equal to 2 kW/μm². For designing the proposed optical logic gates we employed two resonant rings with the same structures, both rings at the logic gates were designed such that their resonant wavelength be at λ = 1550 nm. Every proposed logic gate has one bias and two logic input ports. We used plane wave expansion and finite difference time domain methods for analyzing the proposed structures.