Design and analysis of two-dimensional photonic crystals channel filter

A novel three-port channel add/drop filter consisting of two waveguides and two cavities is proposed. One is used for a resonant tunneling-based channel add/drop operation from the bus waveguide to the add/drop waveguide, while the other is used to realize the wavelength-selective reflection feedback in the bus waveguide. By means of coupled mode theory in time, the conditions to achieve 100% add efficiency are derived thoroughly. Based on these theoretical analysis, the channel add filter and some other multi-channel filters are designed in two-dimensional photonic crystals (2D PCs) with square lattice of dielectric rods in air. The numerical results by using the finite-difference time-domain (FDTD) method demonstrate almost complete channel add/drop tunneling at resonance via the three-port systems.     

A channel drop filter in hetero-woodpile-structure

By finite difference time domain method, a channel drop filter with four-port is designed, analyzed, and theoretically simulated in the hetero-woodpile-structure. Hetero-woodpile-structure includes three parts namely, along the propagation direction, the constant lattice in the core woodpile is different from two cladding woodpiles. This channel drop filter is comprised of two straight waveguides separated by an air-cavity in the same layer. Through simulations, we found that adjustment of the resonant-mode in heterostructure can be achieved in various ways, such as only changing the lattice constants, or changing both lattice constants, and the cavity size. The results also show that this structure can realize the energy transfer between bus and drop waveguides.     

A novel polarization channel drop filter based on two-dimensional photonic crystals

<正>A novel polarization channel drop filter(PCDF) based on two-dimensional(2D) photonic crystals(PCs) is presented.It consists of two line defect waveguides and two point defect micro-cavities.In the line-defect waveguides,the transverse-electric(TE) and transverse-magnetic(TM) polarization lights are guided using photonic band-gap and total internal reflection effect,respectively.The light at the resonant frequency for TE polarization can be transferred from one waveguide to the other using the proposed system.Compared with the existing four-port PCDF based on PCs,the three-port structure can realize a multi-channel wavelength system of PCDF more easily and can be an essential device in future polarization wavelength division multiplexing(PWDM) systems.     

Photonic crystal channel drop filters with mirror cavities

In this paper, a new channel drop filter in two dimensional photonic crystals with mirror cavities is proposed. In the structure, three cavities are used. One is used for a resonant tunneling-based channel drop filter. The others are used to realize reflection feedback in the bus waveguide, which consists of a point defect micro-cavity side-coupled to a waveguide. The simulation results by using the finite-difference time-domain method conclude 98% output efficiency.     

Vertically coupled photonic crystal optical filters

A novel design of optical filters, based on the vertical coupling between channel waveguides and photonic crystal microcavities, is proposed. The choice of channel waveguides can be arbitrary because of the flexibility of the device geometry, which makes it possible to utilize conventional low-loss waveguides. The separation between waveguides and microcavities, which determines filter bandwidths and drop efficiencies, can be accurately controlled by material growth (or deposition). The filters might also be switchable, e.g., by mechanical movements of microcavities. An example of a reflection-type optical filter is demonstrated in numerical experiments using the finite-difference time-domain method.     

A compact in-plane photonic crystal channel drop filter

This paper presents a novel in-plane photonic crystal channel drop filter.The device is composed of a resonant cavity sandwiched by two parallel waveguides.The cavity has two resonant modes with opposite symmetries.Tuning these two modes into degeneracy causes destructive interference in bus waveguide,which results in high forward drop efficiency at the resonant wavelength.From the result of numerical analysis by using two-dimensional finite-difference time-domain method,the channel drop filter has a drop efficiency of 96% and a Q value of over 3000,which can be used in dense wavelength division multiplexing systems.     

Woodpile结构三维光子晶体中的四端口通道下载滤波器

基于三维光子晶体空间完全带隙的特性,本文在实验上构建了一种由非共面的两个波导和一个立体微腔组成的四端口通道下载滤波器。讨论了球体、正方体、长方体微腔滤波器的选频特性,以及连续旋转长方体微腔时,其输出频率的变化。研究结果表明,无论是对称型还是非对称型微腔,都可以较好地实现选频。提高微腔的不对称性,共振输出频率随之发生移动,说明改变微腔的对称性,可以有效调节滤波器的选频特性。连续旋转非对称型长方体微腔,输出频率会随之发生明显的移动,如果引入有效调节机制,可以产生连续调节输出频率的效果。该研究结果给多端口选择性输出空间滤波器的设计提供了新的思路,为光学器件集成化的设计提供了重要的理论参考。     

Integrated all-optical nonlinear device for re- configurable add/drop and wavelength shifting of WDM signals

A novel configuration is proposed for an all-optical device performing two key functionalities in a communication network based on wavelength-division-multiplexing (WDM): reconfigurable add/drop and wavelength shifting of single channels. The device is based on guided second-order nonlinear interactions, such as sum-frequency generation and difference-frequency generation, between the WDM channels and a suitable pump beam. A directional coupler and two parallel waveguides allow the spatial separation between the main WDM signal and the dropped or wavelength-shifted channel for a subsequent routing in the desired path. A first numerical simulation provided a cross-talk level in the dropped channel lower than -41 dB and a wavelength-shifting range of more than 40 nm. Received: 18 May 2001 / Published online: 30 October 2001     

Improved photonic crystal directional coupler with short length

We investigate a photonic crystal (PC) waveguide coupler which is formed by two closely spaced linear waveguides in a two-dimensional triangular lattice of air holes. Our study shows that shifting one row of the air holes between the waveguides affects the dispersion curves of the guided modes and if the triangular lattice of air holes between the waveguides is replaced by a rectangular lattice, this modification results in an ultra-short coupling structure with coupling length less than 3a, where a is the lattice constant. Also, we investigate the effect of changing the radii of air holes that are adjacent to or between the waveguides on the coupling length and show that increasing the radius of air holes between the waveguides decreases the coupling length. We analyze the output spectrum of an ultra-short channel drop filter designed based on this structure.     

Theoretical Analysis of Resonant Cavities Loaded with Lossy Material

Theoretical analysis of abrupt cavities loaded with lossy material has been described in detail. Dispersion equation for waveguides with lossy material and hybrid modes (HEM) matching equations for abrupt structure were derived. Further, the equations have been solved by numerical calculation to study waveguides and abrupt cavities loaded with lossy material. The theoretical analysis is available for designing and analysis RF devices. It was used to design the RF system for Ka band gyroklystron amplifier, the calculation results accord with the cold test.     

Prediction and suppression of strong dispersive coupling in microracetrack channel drop filters

For a four-port microracetrack channel drop filter, unexpected transmission characteristics due to strong dispersive coupling are demonstrated by the light tunneling between the input-output waveguides and the resonator, where a large dropping transmission at off-resonance wavelengths is observed by finite-difference time-domain simulation. It causes a severe decline of the extinction ratio and finesse. An appropriate decrease of the coupling strength is found to suppress the dispersive coupling and greately increase the extinction ratio and finesse, a decreased coupling strength can be realized by the application of an asymmetrical coupling waveguide structure. In addition, the profile of the coupling dispersion in the transmission spectra can be predicted based on a coupled mode theory analysis of an equivalent system consisting of two coupling straight waveguides. The effects of structure parameters on the transmission spectra obtained by this method agree well with the numerical results. It is useful to avoid the strong dispersive coupling region in the filter design.     

Photonic crystal channel drop filter based on ring-shaped defects for DWDM systems

This paper presents a novel configuration of channel drop filters based on two-dimensional photonic crystal slabs in silicon-on-insulator platforms. The structure is composed of two photonic crystal line-defect waveguides as input and output ports, along with an L3 cavity with ring-shaped border holes. The effects of structural parameters and fabrication errors on resonance frequency and drop efficiency are investigated. Band structure and propagation of electromagnetic field through device are calculated by plane wave expansion and finite-difference time-domain methods. The results show that the quality factor and line-width of output signal are ~5690 and 0.27 nm, respectively, indicating that the proposed filter can be properly used in dense wavelength division multiplexing systems with 0.8 nm channel spacing.     

二维异质结光子晶体中含近邻点缺陷的弯曲波导的可调谐滤波特性

应用时域有限差分(FDTD)法,对光在二维异质结光子晶体中含两个近邻点缺陷直角弯曲波导的传输特性进行了数值模拟研究。计算结果表明,具有特定本征共振频率的光子晶体微腔(点缺陷),可将在其邻近波导中传播的相同频率成分的光波"引入"到微腔中。"引入"的频率依赖于异质结光子晶体弯曲波导和微腔的参量,从而能够实现调变"引入"频率。通过改变点缺陷周围介质材料(液晶)的折射率或相关介质柱半径,可分别实现约31 nm或12 nm的波长调谐范围。计算结果为光通信中的调谐、上/下载滤波器,提供了一条新的设计思路和依据。     

Wavelength demultiplexing structure based on arrayed plasmonic slot cavities

A compact wavelength demultiplexing structure based on arrayed metal-insulator-metal (MIM) slot cavities is proposed and demonstrated numerically. The structure consists of a bus waveguide perpendicularly coupled with a series of slot cavities, each of which captures SPPs at the resonance frequency from the bus waveguide and tunes the transmission wavelength by changing its geometrical parameters. A cavity theory model is used to design the operating wavelengths of the structure. Moreover, single band transmission of each channel and the adjustable transmission bandwidth can be obtained by altering the drop waveguide positions and the coupling distance. The proposed arrayed slot cavity-based structure could be utilized to develop ultracompact optical wavelength demultiplexing device for large-scale photonic integration.     

Magnetically controllable resonance splitting in a unidirectional waveguide system with coupled cavities

A resonance splitting effect is investigated in a system composed of two cavities coupled by two unidirectional waveguides. Both theoretical analysis and numerical calculations demonstrate that the resonance splitting (indicating a coupling between the cavities) is independent of the phase shift between the cavities, which is in contrast to previous research where reciprocal waveguides are used. Moreover, this splitting can be tunable by an external magnetic field. Our findings offer a possibility to realize effective coupling between remote on‐chip resonators, which is highly demanded in the next‐generation photonic circuits.

     

Three-dimensional polymer optical waveguide interleaver with selectable channel spacing

A polymer optical waveguide interleaver with selectable channel spacing and adjustable flat top based on a three-dimensional structure is reported. This interleaver is made of two waveguides laid in two different but parallel layers. These two waveguides cross-over each other three times, with an electrode heater deposited on top of each crossing point to adjust the coupling ratio between the guides. This 3D structure has many advantages over the corresponding 2D counterpart such as the ease of fabrication and the adjustment of coupling ratio between the two waveguides. The channel spacing can be selected to be either 1.6 nm, 0.8 nm or 0.53 nm simply by changing the power supplied to each heater; also at the 1.6 nm channel spacing it is possible to create a flat-top spectral response (0.6 dB ripple over 0.5 nm), again by tuning the coupling ratios using the electrical heaters.     

二维硅基平板光子晶体器件

硅材料在红外通讯波段具有低损耗和高折射率的特性,使得其成为集成光学领域中应用最广的材料之一.主要介绍了本课题组在二维硅基平板光子晶体中实现微纳尺度上光调控的研究进展,讨论了利用光子晶体的缺陷态实现各种集成光学器件,包括光子晶体波导、微腔和利用光子晶体波导和微腔形成的滤波器.还介绍了光子晶体中特殊的光折射现象,包括红外波...     

Directional coupler wavelength selective filter based on dispersive Bragg reflection waveguide

A new type of wavelength selective filter, based on high differential dispersion between two coupled waveguides, is presented. The Bragg Reflection Waveguide displays high effective refractive index dispersion, due to the interaction of the guided mode with the two confining Bragg reflectors. When coupled with a weakly guided buried channel silica waveguide, a very narrow bandwidth filter (<1 nm) can be easily produced, in a shorter length, with respect to directional couplers made with standard step index channel waveguides. The complete design methodology, fabrication and characterization are presented.     

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.     

Coupling constant of microcavity waveguides based on coupled mode theory

We analyze the microcavity waveguides and derive the coupling constant based on the coupled mode theory. The formula contains only two parameters with clear physical meanings, the quality factor of the cavity modes and the phase shift that the lightwave acquires when tunnelling between two cavities. It provides an easy way to express and modulate the properties of the waveguides. Our analytical results are supported by the simulations using the transfer matrix method.