Group velocity dependence of propagation losses in single-line-defect photonic crystal waveguides on GaAs membranes

Group velocity, v/sub g/, dependence of propagation loss in single-line-defect photonic crystal waveguides on GaAs membranes, and minimum loss as low as 2.5 dB/mm, are presented. When v/sub g/ is reduced by a factor of 7, an additional loss is found to be only 5 dB/mm, thus proving a feasible usage of low v/sub g/.     

Low-loss propagation in photonic crystal waveguides

The fabrication and characterisation of high-quality silicon membrane photonic crystals are reported. The etching process was carefully optimised to give holes with very smooth and vertical sidewalls, resulting in propagation, with a minimum loss of 4.1plusmn0.9 dB/cm in a single line defect (W1) waveguide     

Out-of-plane losses of line-defect photonic crystal waveguides

A numerical model is presented for computing the out-of-plane losses of a general class of two-dimensional photonic crystals superimposed. onto a slab confinement structure. The usefulness of this model is demonstrated by calculating the propagation loss of a single-row-defect waveguide composed of hexagonal air holes etched into two different slab structures. The results are interpreted in terms of a simple coupled-mode-theory picture in which loss is due to resonant coupling between the fundamental and certain radiative slab modes. These calculations show that low-loss photonic crystal waveguides should be possible by carefully designing the slab waveguide     

光子晶体波导传输特性的计算和模拟

应用时域有限差分法研究了在空气孔-介质光子晶体波导中引入一空气柱后对光学传输特性的影响.结果表明:引入空气柱后,通过改变空气柱的半径及其在波导中的位置,能使其透射特性产生显著的变化.在归一化频率＞0.26的高频段,透射率迅速降低;空气柱半径越大、越靠近入射源,透射率越小.通过数值模拟对计算结果进行了验证.     

光子晶体薄板波导导模的固有损耗特性研究

利用波导模展开法计算了强介质比光子晶体薄板波导中的固有损耗。在导模高群速度的频段中,辐射损耗随着晶体中空气比的增加而增加,随着波导宽度的增加或薄板厚度的增加而减小,而且可以计算得到在靠近模式色散中微小带隙处的损耗与复频率的关系,计算得到的损耗与si薄板中所测的结果十分吻合。     

Low-loss silicon-on-insulator photonic crystal waveguides

Silicon-on-insulator-based 2D photonic crystal waveguides have been optically characterised. The measured total insertion loss is below 19 dB in the waveguides with unpolarised light. With the length mask technique, it is found that the photonic crystal waveguides show propagation losses below 4 dB/mm     

Coupling between photonic crystal waveguides

A calculation procedure for evaluation of the coupling length of two parallel coupled channel waveguides in a planar photonic crystal is proposed. The first step of the calculation is evaluation of the band structure of a photonic crystal containing two coupled linear defects. The eigenvalue corresponding to eigenstates localized in the linear defect (the waveguide) is split due to the coupling. This splitting is treated within the coupled-mode theory that yields a simple relation between the splitting and the coupling length. The MIT photonic bands code is used to evaluate the coupling between channel waveguides in silicon./sup 1/ These calculations show that in contrast to the finite-difference time-domain approach, the method is effective for three-dimensional light propagation.     

Bend losses in GaAs/AlGaAs optical waveguides

Circular bends with low excess bend loss (? l dB) and radii of a few millimetres were fabricated using GaAs/AlGaAs single-heterostructure rib waveguides with propagation loss ? 1 dB/cm. The effect of rib geometry and roughness due to bend pattern quantisation on the excess bend loss at 1.52/?i was investigated.     

Multiple-scales analysis of photonic crystal waveguides

The multiple-scales method is used to derive a scalar differential equation that describes the envelopes of photonic crystal waveguide modes. For a photonic crystal heterostructure waveguide and an air core photonic crystal waveguide, the mode frequencies calculated from the envelope approximation and full numerical simulations agree to 9% in the worst case when compared to the frequency difference of the band edges. The single-mode and cutoff width conditions for a photonic crystal waveguide are predicted and verified.     

Light propagation characteristics through the annular coupled-cavity waveguides based on the two-dimensional square-lattice photonic crystal

The light propagation characteristics through the annular coupled-resonator cavity waveguides are systematically analyzed by the finite-difference time-domain (FDTD) method. It is found that this kind of waveguide has more minbands owing to the increasing of the cavity’s size, compared with the traditional line-typed coupled-resonator waveguide. The group velocity of light propagation can be reduced for a further degree when the adjacent annular cavities are interlaced in the perpendicular direction, and a group velocity about 0.00067c (c is the light speed in vacuum) can be obtained.     

Low loss GaAs optical waveguides

To realize an optical integrated circuit, various losses in the semiconductor waveguide such as absorption loss, waveguide loss, bending loss, and coupling loss, have to be minimized. Theoretical and experimental considerations for the reduction of these losses have been presented. A propagation loss of less than 0.5 dB/cm has been observed for a well-designed GaAs ridge waveguide. Moreover its coupling loss with a polarization-maintaining optical fiber decreased below 1.5 dB.     

Low loss GaAs optical waveguides

To realize an optical integrated circuit, various losses in the semiconductor waveguide such as absorption loss, waveguide loss, bending loss, and coupling loss, have to be minimized. Theoretical and experimental considerations for the reduction of these losses have been presented. A propagation loss of less than 0.5 dB/cm has been observed for a well-designed GaAs ridge waveguide. Moreover its coupling loss with a polarization-maintaining optical fiber decreased below 1.5 dB.     

Low transition losses in bent rib waveguides

We reduce the transition losses that occur between curved and straight rib waveguides, by offsetting the guides and placing isolation trenches. Using a three-dimensional (3-D) semivectorial beam propagation program, we also can investigate more novel effects such as rib heights and sidewall slopes. Our consideration of all these effects results in an optimized design     

Dispersion compensation with photonic crystal line-defect waveguides

A concept for dispersion compensation in transmission is proposed, based on modes anti-crossing in photonic crystal (PC) line-defect waveguides. Quasi-constant positive and negative dispersion is possible in order of 100 ps/nm/mm on the bandwidth of 100 GHz. An adiabatic taper is proposed for efficient coupling into PC structure.     

光子晶体波导中慢光的实现

首先指出实现慢光的两种不同途径--改变材料色散和波导结构色散,并对利用结构色散产生慢光的光子晶体波导的原理、结构和特征作了说明.然后综述了目前光子晶体波导中产生慢光的新型结构和方法:啁啾结构、耦合结构和优化参数方法,并对它们做了比较.最后简要说明了慢光的研究意义和发展前景.     

Accurate modeling of line-defect photonic crystal waveguides

An accurate three-dimensional method to calculate the Bloch modes of photonic crystal (PhC) waveguides is proposed. Good agreement with available experimental and numerical data is obtained. The originality of the method lies in the fact that the Bloch modes are seen as the electromagnetic fields associated to the complex poles of an in-plane transversal scattering matrix. In comparison with previous approaches, the computational domain discretized is smaller and a higher accuracy for the losses of PhC waveguides is achieved.     

GaAs acoustic-surface-wave propagation losses at 1 GHz

Measurements of acoustic-surface wave propagation losses in air have yielded the following for GaAs at 1 GHz: 3.62 dB/?s for the [211] cut, [111] propagating orientation, and 4.22 dB/?s for the [110] cut, [100] propagating orientation. Air loading for these two cuts is 0.27 and 0.40 dB/?s, respectively. These results are independent of surface quality for defects up to 0.04 wavelengths in size.     

Singlemode transmission within photonic bandgap of width-variedsingle-line-defect photonic crystal waveguides on SOI substrates

It is demonstrated experimentally that a single missing-hole line defect photonic crystal waveguide fabricated on a silicon-on-insulator substrate can support a single waveguiding mode within the photonic bandgap if the waveguide width is properly tuned     

Time-delay measurement in singlemode, low-loss photonic crystal waveguides

The group delay in low-loss, singlemode, 1 mm-long photonic crystal slab waveguides is measured using the phase shift technique for the first time. Low group velocities (相似文献   

一种实现超微光子晶体型定向耦合器的方法

在光子晶体定向耦合器中,通过减小两耦合波导之间介电柱的折射率来增大耦合系数,从而获得更短的拍长,形成超微的器件尺寸。耦合器的奇模场随调制折射率的减小变化不敏感,偶模场向更高频率的方向移动。在同一频率范围内,调制折射率减小,导致拍长随频率变化的函数曲线的斜率随频率增加而增大,这一特性可以在波分复用器中用来减小相邻信号频率差,在相同的器件长度下,可获得更多的信道。采用时域有限差分法验证了拍长随调制折射率减小而减小的变化规律。