一种新型无色散慢光光子晶体薄板波导

利用椭圆形孔替代传统光子晶体薄板波导中邻接波导的最内层两排圆孔构成一种新型低损耗光子晶体薄板光波导.该波导的群速度和群速度色散特性强烈依赖于波导中这两排邻接波导的椭圆孔的特性.借助波导导模展开方法,计算得到波导的能带结构和群指数,并分析了它们与椭圆孔的参数关系.通过优化这些椭圆孔的参数,可以增加光子晶体光波导导模在光锥以下的无固有传输损耗带宽,在2—45 nm 的带宽上实现无色散的常数群速度.这些理论结果将为低损耗低色散慢光波导的设计制造提供理论基础. 关键词： 光子晶体薄板波导 群速度 群指数 群速度色散     

一种新型无色散慢光光子晶体薄板波导

利用椭圆形孔替代传统光子晶体薄板波导中邻接波导的最内层两排圆孔构成一种新型低损耗光子晶体薄板光波导.该波导的群速度和群速度色散特性强烈依赖于波导中这两排邻接波导的椭圆孔的特性.借助波导导模展开方法,计算得到波导的能带结构和群指数,并分析了它们与椭圆孔的参数关系.通过优化这些椭圆孔的参数,可以增加光子晶体光波导导模在光锥以下的无固有传输损耗带宽,在2—45 nm 的带宽上实现无色散的常数群速度.这些理论结果将为低损耗低色散慢光波导的设计制造提供理论基础.     

A systematic analysis of hole size,hole-type and rows shifting on slow light characteristics of photonic crystal waveguides with ring-shaped holes

A photonic crystal waveguide embedded in silica is proposed and the effects of number of defect rows adjacent to the line-defect, number of rows shifted in transverse direction to the light propagation and the types of holes in these rows on slow light properties are investigated without changing the line-width by plane-wave expansion method. We observe that the structure with one row of ring-shaped holes exhibits better slow light properties than the structure with two and three innermost rows of ring-shaped holes when outer and inner radius of the holes are considered as free parameters. Shifting the second innermost rows of holes is found to be preferable than shifting the second innermost rows of rings. Besides, shifting the second and third innermost rows together does not make considerable enhancement on the slow light properties as shifting only the second innermost rows, no matter the shifting holes are ring-shaped holes or only holes.     

Nonlinear performance in silicon nitride slow light photonic crystal waveguides with elliptical holes

We propose a slow-light photonic crystal waveguide, which uses a combination of circular and elliptical air holes arranged in a hexagonal lattice with the background material of silicon nitride (refractive index n = 2.06). Large value of normalized delay bandwidth product (NDBP = 0.3708) is obtained. We have analyzed nonlinear performance of the structure. With our proposed geometry strong SPM is observed at moderate peak power levels. Proposed photonic crystal waveguide has slow light applications such as reduction in length and power consumption of all-optical and electro-optic switches at optical frequency.     

Wideband and low dispersion slow light in slotted photonic crystal waveguide

We present a procedure to generate wideband and low dispersion slow light in slotted photonic crystal waveguide. By shifting the first and second rows of air holes of slotted photonic crystal waveguide, the bandwidth of slow light can be increased, with small group velocity dispersion. Using 2D plane wave expansion method, we numerically demonstrate slow light with the nearly constant group indices of 23, 42, and 54 over 17.6 nm, 6.7 nm and 3.3 nm bandwidth, respectively. The maximal normalized delay-bandwidth product is 0.26. From the fabrication's point of review, shifting the position of holes is easier to be controlled technically than changing the diameters of air holes. In addition, our simulations suggest this design is tolerant to deviation for positions of the first two rows of air holes. Therefore, the proposed approach decreases the dependence on the fabrication accuracy.     

高透射率慢光速的光子晶体耦合腔波导的研究

将二维三角晶格光子晶体波导和微腔结构结合,优化设计了一种二维三角晶格光子晶体共振耦合腔波导,运用时域有限差分法(FDTD)模拟共振耦合腔波导TE偏振光的透射谱,通过透射谱得到传输光的透射率和群速度。结果表明,合适参数的二维三角晶格共振耦合腔波导在波长1.551μm处的群速度为c/130、透射率为20.1%,在波长1.502μm处的群速度为c/50、透射率为29.2%。运用平面波展开法(PWE)计算的该波导的能带结构对慢光特性进行了分析。这种慢光特性的光子晶体波导将在光存储、光延迟及光子集成等方面有潜在的应用价值。     

Dispersion optimization of slow light in slotted photonic crystal waveguide by selective air holes infiltration

This work proposed a methodology based on the liquid infiltration of slotted photonic crystal waveguide (SPCW). By choosing the refractive index that infiltrated in the first and second rows of air holes adjacent to the slot, respectively, SPCW was optimized to possess wideband slow light with large group index and low dispersion. The properties of SPCW were numerically simulated by plane wave expansion (PWE) method and finite-difference time-domain (FDTD) method. Simulation results showed that the designed SPCW could control the group index for the same SPCW with the nearly constant group index of 50, 68, 81, 150, and 200 over 7.5 nm, 5.5 nm, 3.1 nm, 1.65 nm, and 1.15 nm. In addition, we demonstrated that this post-fabrication liquid infiltrated technology has the potential for realizing reconfigurable and tunable SPCW, in which the flexible wavelength range of SPCW can also be controlled by different liquid infiltration.     

Numerical demonstration of slow light tuning in slotted photonic crystal waveguide using microfluidic infiltration

Tuning of the operating wavelength of slow light in the slotted photonic crystal waveguide using microfluidic infiltration has been investigated. Using 2D plane wave expansion method, we numerically demonstrate that the operating wavelength can be shifted from the C to L band, simply by choosing the refractive index of the infiltrated fluid. It is also found that, as the refractive index of the infiltrated fluid changes, the group velocity dispersion has slight variation at different operating wavelength. This design opens the possibility for post-fabrication scheme of tuning the operating wavelength of slow light in slotted photonic crystal waveguide, and allows the device to be optimized for different applications.     

Slow light performance enhancement of graphene-based photonic crystal waveguide

We propose a graphene-based photonic crystal (PC) slow light waveguide, which is realized by creating periodical air holes in a silicon layer to achieve spatially varying chemical potentials of graphene. The structure is optimized around 30 THz, and a large group index of 166.6 is obtained, with a very low propagation loss of ?2.1 dB/um. The corresponding normalized delay-bandwidth product reaches as high as 4.00. Furthermore, the slow light performance can be dynamically tuned by changing a bias voltage. The center frequency of the slow light waveguide can be tuned between 19.1 THz and 27.4 THz. Our results suggest that graphene-based PC structures are very promising for slow light devices.     

Influences of supercell termination and lateral row number on the determination of slow light properties of photonic crystal waveguides

We systematically analyze the effects of the use of an inaccurate supercell termination and an insufficient supercell size of plane-wave expansion method on the dispersion and the slow light properties of the photonic crystal waveguides. The inattentive use of supercells of photonic crystal waveguides appeared in the literature is found to be yielding errors in the dispersion and slow light characteristics of the fundamental guided mode of photonic crystal waveguides. In addition, extra modes appear in the photonic band gap of the photonic crystal waveguide due to inaccurate supercell termination. By examining the field distribution of the modes, the extra modes can be determined and removed from the band diagram. The dispersion, group index and bandwidth characteristics are observed to be less affecting from inaccurate supercell termination as the number of rows adjacent to the waveguide increases. Moreover, the dispersion and the group index-frequency curves of the fundamental guided mode of correctly terminated supercells are found to be converging as the lateral row number along the line-defect is increased.     

二维平板光子晶体直波导的制备和光传输特性的测量

利用聚焦离子束刻蚀的方法在SOI(silicon on insulator)基片上制备了W3型二维光子晶体直波导.观察并测量了近红外激光通过光子晶体波导的散射图形和透过谱.实验结果说明，激光在有引入引出脊形波导的光子晶体直波导中具有很好的传输特性. 关键词： 光子晶体波导 光子带隙 脊型波导     

Slow light engineering in polyatomic photonic crystal waveguides based on square lattice

In this paper, the slow light properties of the polyatomic Photonic Crystal (PhC) which has multiple different air holes in each primitive cell are investigated. A slow light waveguide with “U-type” group index-frequency curve, which results in nearly constant group index over large bandwidth, is achieved using this new photonic crystal geometry based on the square lattice. Also, the radius and position of the innermost rows of small air holes have been modified to investigate the feasibility of controlling the dispersion relation by subtle structural modification. Numerical results demonstrate that decreasing the group velocity effectively and meanwhile maintaining a large Normalized Delay-Bandwidth Product (NDBP) can be achieved by only modifying the radius of the innermost rows of small air holes. Shifting the innermost rows of small air holes toward the waveguide core is highly beneficial to enlarge the slow light bandwidth, but it contributes nothing to the promotion of NDBP. Our results provide important theoretical basis for the potential application offered by the polyatomic photonic crystal in future optical networks.     

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.     

Theory and method for enhancing sensitivity of multi-gas sensing based on slow light photonic crystal waveguide

A novel harmonic detection theory and method for multi-component gas sensing based on photonic crystal waveguide (PCW) slow light is proposed. The PCW is used as gas chamber, and harmonic detection method was adopted for signal processing. This system could real-time and remote monitoring multi-component gases simultaneously with sensitivities increased by 10,278, 8650 and 6282 times respectively compared with system PCW not used. The proposed theory and method possesses powerful practicability and favorable application prospects. It could be also applied to other fluid concentration detection system, thus providing a new idea for expanding applications of slow light in sensing fields.     

慢光在光子晶体弯折波导中的高透射传播

研究了慢光模式在SOI(silicon-on-insulator)材料光子晶体线缺陷弯折波导中的传输特性. 通过优化波导弯折处的结构参数,慢光模式在光子晶体60°与120°弯折波导中的透射率提高10倍以上,归一化透射率分别达到80%和60%以上. 为了进一步减慢光速,设计了新颖的高Q值耦合腔弯折波导结构,在归一化透射率达到75%的基础上,光波群速度低至c/170(c为真空光速). 研究结果对于增强光子晶体的慢光效应,提高光子晶体慢光器件的微型化和集成化都有一定的积 关键词： 光子晶体 慢光 弯折波导 透射率     

Photonic crystal optical switch using a new slow light waveguide and heterostructure Y-junctions

In this paper we propose a photonic crystal Mach-Zehnder interferometer (MZI) based on a new coupled-cavity waveguide, where its advantage over the previous type of photonic crystal coupled-cavity waveguide is discussed. A heterostructure Y-junction is comprised of square and hexagonal lattices of the new coupled-cavity waveguide. It is designed by applying the temporal coupled-mode theory and is optimized, where an overall throughput efficiency of more than 90% is achieved at the wavelength of 1.55 μm. The design of the Y-junction is performed using finite-difference time-domain method. The designed heterostructure Y-junction is used in the structure of a MZI, where its arms are approximately as short as 24 μm. Finally, the transient response of the proposed optical switch is investigated.     

Optical interleaver based on directional coupler in a 2D photonic crystal slab with triangular lattice of air holes

A small-size optical interleaver based on directional coupler in a 2D photonic crystal slab with triangular lattice of air holes is designed and theoretically simulated using plane wave expansion and finite-difference time-domain method. The interleaver is formed by two parallel and identical photonic crystal slab waveguides which are separated by three rows of air holes. The coupling region is designed below the light line to avoid vertical radiation. The simulated results show that the coupling coefficient is increased and the final length of the interleaver is decreased by enlarging the radius of the middle row of air holes. The transmission properties are analyzed after the interleaver’s structure is optimized, and around 100 GHz channel spacing can be got when the length of the interleaver is chosen as 40.5 μm.     

Slow light in photonic crystal with combinations of gradient dielectric constant

A line defect waveguide formed by a new kind of two-dimensional photonic crystal with combinations of gradient varied dielectric was designed and the properties of slow light will been studied by using the Plane Wave expansion Method (PWM). The result shows that the group velocity is slower when the corresponding combination of gradient dielectric constants are with higher dielectric constant and lower interval. In our new structure of photonic crystal, the corresponding group velocity can reach as low as 0.06c (c: light velocity in vacuum), two orders magnitude lower than light velocity. Meanwhile, the group velocity dispersion effect is relatively small.     

Transmission characteristics simulation of an erbium-doped lithium niobate film photonic crystal slab

A photonic crystal slab (PhC slab) which was constructed as a 2D hexagonal lattice with a finite depth was etched into an Er:LiNbO₃ film waveguide. The band diagrams and transmission spectra were simulated by plane wave expansion (PWE) and the finite-difference time-domain (FDTD) method. A high refractive index contrast of 0.5 enables strong light confinement in the vertical direction and a broad band gap. The simulated transmittance spectra indicate that the stop band is determined by lattice constant. The transmission spectra along ΓM of the PhC slab with a lattice constant 500 nm show a 250-nm broad stop band in the wavelength range from 1.33 to 1.58 μm and sharp band edge.     

Simplified design of low-loss and flat dispersion photonic crystal waveguide on SOI

A low-loss and flat dispersion line-defect photonic crystal waveguide is proposed with a simplified waveguide-design on silicon-on-insulator (SOI) based on hexagonal lattice of 2D photonic crystals. A propagation loss of 3.6 dB/mm and flat dispersion over a large wavelength band is reported with an easy-to-implement design without disturbing the periodicity (keeping lattice constant and hole diameter fixed) in the line-defect photonic crystals. The combined effect of photonic crystals (in-plane periodicity) and the vertical layers on SOI results in efficient waveguiding and dispersion characteristics.