Properties of a 1 × 4 optical power splitter made of photonic crystal waveguides

Optical power splitters made of photonic crystal waveguides are believed to become essential components for compact photonic integrated circuits used in fiber optic networks. We design a 1 × 4 optical power splitter made of linear-defect waveguides in photonic crystals, and analyze its properties using the finite-difference time-domain method. Our simulation results show that the transmission properties vary with wave frequency and branch geometry, and that an incident wave is divided equally into four output ports. To reduce the reflections at the three branching regions in the 1 × 4 splitter, we place the defects of extra rods in the branching region, and achieve high transmission in each output waveguide.     

Selective modes excitation in multimode photonic crystal waveguides

We investigate modes excitation with the input field of different positions in two-dimensional multimode photonic crystal waveguides. Odd modes can be selectively excited by the input field of odd symmetry. The input field with different positions can excite different modes due to the field intensity distribution of modes. When the input field locates at the position of the zero field, intensity of waveguide modes is zero and the modes are not excited. The finite-difference time-domain method is used to obtain the excited field distributions.     

Ultra-compact polarization beam splitter based on photonic crystal waveguides

The authors design an ultra-compact all-PC-integrated polarization beam splitter which is only composed of three waveguides: one input waveguide and two output waveguides. The input waveguide can support both TM and TE modes, but one of the two output waveguides can only support TM modes while the other can only support TE modes. So an incident beam will be separated into two different polarization beams which emerge from different output waveguides. By the simulation of finite-difference time-domain method, we know that the polarization beam splitter really works the way as we predict.     

A three-channels WDM based on MMI in photonic crystal

A photonic crystal waveguide coupling structure can be constructed by putting three adjacent photonic crystal waveguides in parallel. Guided mode propagation method is employed to analyze the interference behavior of the approximate solution in such a coupling and the self-image phenomenon in multi-mode waveguides. A three-channel multimode interference wavelength division multiplexing can be obtained. The presented device has a high transmission rate as well as the advantage of multi-wavelength selection, thus it may have a potentially practical application in future photonic integrated circuit.     

A novel optical beam splitter based on photonic crystal with hybrid lattices

A novel optical beam splitter constructed on the basis of photonic crystal(PC) with hybrid lattices is proposed in this paper.The band gap of square-lattice PC is so designed that the incident light is divided into several branch beams.Triangular-lattice graded-index PCs are combined for focusing each branch.Computational calculations are carried out on the basis of finite-different time-domain algorithm to prove the feasibility of our design.The waveguide is unnecessary in the design.Thus the device has functions of both splitting and focusing beams.Size of the divided beam at site of full-width at half-maximum is of the order of λ/2.The designed splitter has the advantages that it has a small volume and can be integrated by conventional semiconductor manufacturing process.     

Contra-directional coupling between two-dimensional photonic crystal waveguides

The contra-directional coupling between two photonic crystal (PC) waveguides is studied, using the finite-difference time-domain (FDTD) method. A design of contra-directional coupler is presented and its transmission properties are investigated. The device can be used as an add/drop filter. It is also shown that the coupled mode theory is suitable to study the photonic crystal waveguide coupler.     

Multimode interference effect in plasmonic subwavelength waveguides and an ultra-compact power splitter

The real part of the effective index is enhanced in a metal-insulator-metal (MIM) surface plasmon waveguide when the thickness of the insulator is quite small and this mechanism can be utilized to achieve some ultra-compact photonic devices. The mode properties of an index-guided multimode plasmonic waveguide of subwavelength size are analyzed and the multimode interference (MMI) effect is investigated. A novel ultra-compact MMI power splitter, with the transverse size less than 1/3 of the free space wavelength, is proposed.     

带有环形谐振器的1×2光子晶体功率分配器传输性能

 利用正方格2维光子晶体设计了带有环形谐振器的1×2光子晶体功率分配器结构,该结构具有1个输入端口和2个输出端口。采用时域有限差分法研究了该功率分配器对电磁波的传输性能,结果表明：其结构在第三通信窗口(1 550 nm波长)实现了电磁波的高效传输,同时具有优良的电磁波通频带功率二等均分性,以及电磁波传输转向设计灵活、损耗低、结构紧凑等优点。     

Analysis of multiple reflections in hybrid photonic crystal multimode interference coupler

In this paper the analysis of multiple reflections in photonic crystal (PhC) multimode interference (MMI) couplers using eigen-mode expansion method is presented. The analysis is conducted on a hybrid PhC structure which consisted of 1-D PhC multimode waveguide sandwiched between 2-D PhC input/output waveguides. In PhC multimode waveguide, where the mechanism of wave confinement is not due to total internal reflection but due to photonic bandgap properties, the reflectivity at 2-D PhC facet wall would be very large for all the guided modes in the waveguide when ever the image formed due to MMI effect does not coincides with the output access waveguide.     

基于自映像的光子晶体波导分束器的设计

通过研究2维正方晶格光子晶体波导多模干涉的自映像效应,优化设计了一种新型1×2光子晶体波导分束器,采用时域有限差分法对其传输特性进行模拟分析。设计过程中,根据多模干涉耦合区中周期出现的双重像的位置确定两个单模输出波导的位置,通过在分束器输入和输出耦合区的连结处设置介质柱,改变输入和输出耦合区中的模场分布,实现模式匹配,从而明显减小分束器的反射损耗。计算结果表明:设置的介质柱归一化半径分别为0.08和0.177时,对于波长为1.55 μm的入射光,该分束器的透射率可高达93%。     

Terahertz polarization splitter based on an asymmetric dual-core photonic crystal fiber

By employing the liquid crystal refractive index changes induced by applied electric field, a novel terahertz polarization splitter with tunable the operating frequency and bandwidths has been proposed and theoretically analyzed. It possesses an extinction ratio as high as the polarization splitters based on the two-dimensional photonic crystal waveguides. These distinguished features ensure its important applications in the integrated optical systems.     

High-Q microcavities realized in a circular photonic crystal slab

A series of microcavities in circular photonic crystal slabs are studied in this paper. It is shown that high quality factors can be obtained for such microcavities. For a cavity with three inner layers of air holes missing, Q factor larger than 10⁵ can be obtained. It is also worth noting there exists resonant modes with high quality factors, even for the defect-free circular photonic crystal slab, due to gradual change of the average effective index.     

Slow light transmission in a photonic crystal power splitter with parallel outputs

In this paper, we investigate coupling of light to slow modes in a photonic crystal power splitter composed of a Y-junction and two 60° bends. First, a combination of two cascaded bends which is commonly used in integrated photonic crystal circuits is studied in slow light frequency regime. We propose a structure that its transmission spectrum covers the high group-index frequencies near the band edge. Also, by structural modifications, high transmission near to 95% is achieved in slow light bandwidth. Next, we study the complete structure of a photonic crystal power splitter with parallel outputs based on a Y-junction integrated with two 60° bends. Using modified bends and reducing sharpness of Y-junction, the efficiency of splitting increases in both high and low group-index frequency bands. The optimized structure has an average efficiency of 82% in slow mode regime. This structure can be used in photonic crystal based slow light devices, such as Mach-Zehnder interferometers.     

1-to-N beam splitter based on photonic crystal branched waveguide structure

A novel beam splitter is proposed based on a two-dimensional (2D) photonic crystal (PC) branched waveguide structure. The beam splitter structure comprises branched waveguide channels and extra dielectric columns. These branched waveguide channels are used to obtain secondary sources and the introduced extra dielectric columns are used to control the phase difference of the secondary point sources. The field distributions of the beam are investigated using the finite-difference time-domain (FDTD). It is found that the number of beams is sensitive to the distance of the waveguide channels ports and extra dielectric columns. By adjusting the positions of the waveguide channels and the parameters of the extra dielectric columns, 1-to-N beam splitters can be realized. These simple, easily fabricated and controllable structures have important potential applications in integrated optical circuits.     

Terahertz power splitter based on ferrite photonic crystal

In this paper, we design a novel Y-junction power splitter which is optimized according to coupled mode theory. Two rods are added in the junction. One rod is a silicon rod and another one is a ferrite rod, the refractive index of which can be varied by adjusting the external magnetic field. So, it not only can split the power, but also controls the output energy of the two branches automatically. The transmission spectrum is calculated by finite difference time domain (FDTD) method, which shows that the output energy of the two branches is closely related to the frequency of the incident terahertz (THz) wave and the refractive index of the ferrite rod. The device is a good candidate for integrated optical circuit, the tuning rate of which is about a few microseconds.     

基于表面波的新型光子晶体分束器

通过激发光子晶体-光子晶体表面波的方法,设计出了一种由表面修饰光子晶体组成的新型复合结构。利用平面波展开法结合超原胞技术对该结构的耦合表面波色散关系进行了研究,在此基础上利用时域有限差分法对光束在该结构中的传输特性进行了数值模拟,并分析了其物理机制。研究结果表明,所提出的新型结构,对一定频率范围内的传输光,能够实现输出光的分束,此特征可以用来制作光束分束器。     

基于表面波的新型光子晶体分束器

通过激发光子晶体-光子晶体表面波的方法,设计出了一种由表面修饰光子晶体组成的新型复合结构。利用平面波展开法结合超原胞技术对该结构的耦合表面波色散关系进行了研究,在此基础上利用时域有限差分法对光束在该结构中的传输特性进行了数值模拟,并分析了其物理机制。研究结果表明,所提出的新型结构,对一定频率范围内的传输光,能够实现输出光的分束,此特征可以用来制作光束分束器。     

Polarization beam splitter based on photonic crystal self-collimation Mach-Zehnder interferometer

A polarization beam splitter based on a self-collimation Mach-Zehnder interferometer (SMZI) in a hole-type silicon photonic crystal was proposed and numerically demonstrated. Utilizing polarization dependence of the transmission spectra of the SMZI and polarization peak matching (PPM) method, the SMZI can work as a polarization beam splitter (PBS) by selecting appropriate path length difference in the structure. Because of its intrinsic operating principle, the PBS possesses high polarization extinction ratios (PERs). As its dimensions are only several operating wavelengths, the PBS may have practical applications in photonic integrated circuits.     

Splitting-on-demand optical power splitters using multimode interference (MMI) waveguide with programmed modulations

Reconfigurable multi-channel optical power splitter is proposed and its optical properties are calculated. The device can dynamically reconfigure the number of splitting channels by providing programmed refractive index modulations on a multimode interference (MMI) waveguide. A reconfigurable 3-channel optical power splitter is designed to work as 1 × 1, 1 × 2 or 1 × 3 optical power splitter depending on the state of the heat electrodes using thermo-optic modulation, and the input light can be distributed to three output channels with sequential orders. The device can work in the whole C-band (1530-1565 nm) with extinction ratio better than −29.0 dB, excess loss better than −0.45 dB, imbalance better than 0.08 dB and polarization dependent loss (PDL) better than 0.14 dB. The design conception is scalable to a multi-channel splitting-on-demand optical power splitter which can divide input light to 1, 2, …, N output channels equally by using the 3-channel reconfigurable optical power splitter as a building block.     

Design of a compact polarization splitter based on the dual-elliptical-core photonic crystal fiber

We propose a compact polarization splitter based on dual-elliptical-core photonic crystal fiber. Two elliptical cores are introduced to increase the difference of effective index between x-polarized and y-polarized mode and three elliptical modulation air holes are used to control the power transfer between the two cores. By optimizing the structure parameters, the length of the polarization splitter is distinctly shortened. Numerical results demonstrate that the compact splitter has the length of 775 μm and up to 50 dB extinction ratio at the central wavelength of 1.55 μm. The corresponding bandwidth of 32 nm could be achieved from the wavelength of 1.534–1.566 μm with the extinction ratio over 20 dB