Numerical characterization of nanopillar photonic crystal waveguides and directional couplers

We numerically characterize a novel type of a photonic crystal waveguide, which consists of several rows of periodically arranged dielectric cylinders. In such a nanopillar photonic crystal waveguide, light confinement is due to the total internal reflection. A nanopillar waveguide is a multimode waveguide, where the number of modes is equal to the number of rows building the waveguide. The strong coupling between individual waveguides leads to the proposal of an ultrashort directional coupler based on nanopillar waveguides. We present a systematic analysis of the dispersion and transmission efficiency of nanopillar photonic crystal waveguides and directional couplers. Plane wave expansion and finite difference time domain methods were used to characterize numerically nanopillar photonic crystal structures both in two- and three-dimensional spaces.     

Design of short length and C+L-band mismatched optical coupler with waveguide weighted by the Blackman function

A mismatched optical coupler with waveguide weighted by the Blackman function is numerically investigated in the demand of short length, C+L-band, and low crosstalk. Utilizing the full factorial design, the structure parameters of coupling waveguide are obtained by beam propagation method. In the condition of crosstalk of −35 dB, the mismatched optical coupler with proper selected waveguide structure parameters is found to have a coupling length of 3.60 mm in the transmission wavelength ranges of C+L-band (1.53-1.61 μm). Obviously, the selection and design of waveguide structure are very important to satisfy the qualities of a mismatched optical coupler for the demand of short length, broad bandwidth, and low crosstalk.     

多模干涉耦合器一般成像位置分析

自映像效应是多模波导的一个重要特性,利用多模波导自映像效应制成的多模干涉耦合器被广泛地应用于集成光学回路中。然而根据以往的文献要得出多模干涉耦合器的成像位置要经过一系列复杂的计算。根据多模干涉耦合器的自映像原理,对多模干涉耦合器的成像位置进行分析。成像位置与输入场位置和位置数密切相关,给出了成像位置的解析表达式,得出奇数、偶数的位置数的成像位置分别对应相同,并且奇、偶数的位置数所对应的成像位置之和为多模波导宽度的成像规律。用导模传输分析法验证了表达式和成像规律的正确性。根据成像位置的表达式和成像规律可以直接得出任意输入场位置和位置数所对应的成像位置。为一维和二维限制的多模干涉耦合器的设计提供了理论基础。     

Apodized grating coupler using fully-etched nanostructures

A two-dimensional apodized grating coupler for interfacing between single-mode fiber and photonic circuit is demonstrated in order to bridge the mode gap between the grating coupler and optical fiber. The grating grooves of the grating couplers are realized by columns of fully etched nanostructures, which are utilized to digitally tailor the effective refractive index of each groove in order to obtain the Gaussian-like output diffractive mode and then enhance the coupling efficiency.Compared with that of the uniform grating coupler, the coupling efficiency of the apodized grating coupler is increased by 4.3% and 5.7%, respectively, for the nanoholes and nanorectangles as refractive index tunes layer.     

具有波长不敏感特性的全光纤时分复用器

分析了熔锥型非对称单模光纤耦合器的宽带特性,介绍了采用２×２宽带光纤耦合器进行级联实现的８×２．５Ｇｂ／ｓ时分复用器,信号源采用增益开关量子阱ＤＦＢ激光器,脉冲宽度为４０ｐｓ,周期为４００ｐｓ。实验结果表明,采用这种方案制作的时分复用器,插入脉冲的间隔均匀,脉冲的波动小且损耗低,同时,这种时分复用器具有对波长响应不敏感的特性     

Reversing multistrip coupler

A theory of a reversing multistrip coupler (RMSC) is presented based on a previously developed spectral theory of IDTs. It shows that the frequency dependence of the track-changing reflection of a SAW taking place in a RMSC, and the dependence of the reflection of the SAW from a periodic grating reflector are described by the same functions. The reflection of the SAW to the other channel is complete in a narrow frequency band of relative width (2/3) Δv/v if the RMSC is sufficiently long. Several expected applications of RMSCs are discussed, among them SAW dispersive filters, resonators, and low-loss filters.     

Recent advances in optical bistability

In this paper, recent advances in optical bistability and gating of semiconductors will be reviewed. Nonlinear mechanisms responsible for switching will be described. The advantages of nonlinear etalons for massive parallelism and current problems in performing such operations will be mentioned.     

Three‐dimensional ultra‐broadband integrated tapered mode multiplexers

The demonstration of a three‐dimensional tapered mode‐selective coupler in a photonic chip is reported. This waveguide‐based, ultra‐broadband mode multiplexer was fabricated using the femtosecond laser direct‐write technique in a boro‐aluminosilicate glass chip. A three‐core coupler has been shown to enable the multiplexing of the LP₀₁, LP and LP spatial modes of a multimode waveguide, across an extremely wide bandwidth exceeding 400 nm, with low loss, high mode extinction ratios and negligible mode crosstalk. Linear cascades of such devices on a single photonic chip have the potential to become a definitive technology in the realization of broadband mode‐division multiplexing for increasing optical fiber capacity.     

Optical‐fiber microcoil waveguides and resonators and their applications for interferometry and sensing

In this work, recent progress in the theoretical and experimental studies of optical‐fiber microcoil waveguides and resonators, as well as their various applications are reviewed. In particular, the focus is set on sensing and interferometry applications. It is shown that due to its inherently low propagation and fiber‐coupling losses, fiber‐microcoil based sensors and interferometers offer substantial enhancement of sensitivity and compactness compared to other types of devices. Recent progress in the realization and experimental characterization of such structures is presented and the theoretical tools to analyze the impact of real‐world nonuniformities on the characteristics of fiber‐microcoil structures are provided.     

自陡对光纤耦合器调制不稳定性的影响

当考虑自陡效应时,从光纤耦合器的耦合模方程出发,用偶奇超模对其进行了重写。讨论了当输入条件使奇偶超模的其中之一被单独激发时光纤耦合器中的自陡效应对调制不稳定性的影响。结果表明:在光纤耦合器中不论是正常色散区还是反常色散区,当输入功率一定时,随着自陡参数的增大,调制不稳定性增益谱较多地显示出了强度变弱和宽度变窄,最终导致光纤耦合器的超模发生畸变。