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     

Multimode interference photonic switches (MIPS)

The switching characteristics of multimode interference photonic switches (MIPS) are analyzed by wide-angle finite difference beam propagation method (FD-BPM). As a result, it is found that the MIPS with a multimode interference (MMI) length of 599 μm can switch the output light polarization insensitively with a crosstalk of less than -20 dB for a wavelength range of 70 nm. These analyses show that the MIPS can also have a 3-dB coupler function. Experimentally, an InGaAsP/InP 1×2 MIPS with a thicker InP cladding layer was fabricated and exhibited switching operation with crosstalks of -8 dB and -10 dB at 0 and 20 mA current injections, respectively. For a 2×2 MIPS with a thinner InP cladding layer, better switching characteristics with a crosstalk of -13 dB and an extinction ratio of 17 dB were realized     

Topology optimised broadband photonic crystal Y-splitter

A planar photonic crystal waveguide Y-splitter that exhibits large-bandwidth low-loss 3 dB splitting for TE-polarised light has been fabricated in silicon-on-insulator material. The high performance is achieved by utilising topology optimisation to design the Y-junction and by using topology optimised low-loss 60/spl deg/ bends. The average excess loss of the entire component is found to be 0.44/spl plusmn/0.29 dB for a 100 nm bandwidth, and the excess loss due to the Y-junction is found to be 0.34/spl plusmn/0.30 dB in a 175 nm bandwidth.     

Y-junction power divider in InGaAsP-InP photonic integratedcircuits

A demonstration is presented of an InGaAsP-InP asymmetric waveguide Y junction with a power dividing ratio which is independent of the polarization of the input light. The Y junction is monolithically integrated with an active optical gain section by metalorganic chemical vapor deposition (MOCVD). The integrated chip represents a fundamental building block for photonic integrated circuits. Experimental results are in agreement with a theoretical analysis of the Y junction. The theory shows a low radiation loss (0.4 dB) and negligible power reflection (-63 dB) at the Y junction, which is ideal for monolithic integration with active devices. They also report on an integrated optical amplifier Y-junction-monitoring detector chip as an example of a photonic integrated circuit that employs the new Y-junction design. The estimated excess loss of the Y junction was 1.4 dB for the integrated chip, and the Y-junction reflectivity was found to be negligible     

MEMS-actuated photonic crystal switches

A compact guided-wave optical switch is realized by integrating one-dimensional photonic crystals with microelectromechanical systems (MEMS) actuators. The ON-OFF switching is achieved by physically moving a photonic crystal defect. Experimental results show an extinction ratio of 11 dB at 1.56-/spl mu/m wavelength and a 0.5-ms time constant of the step response.     

Transmission characteristics of metallodielectric photonic crystalsand resonators

K_u band Fabry-Perot type resonances have been observed in the stop band of a metallodielectric photonic crystal by transmission measurements at microwave frequencies. The metallodielectric photonic crystal has a face centered cubic Bravais lattice structure with a lattice constant of 15 mm. Metallic spheres with 6.35 mm diameter are placed at the lattice sites. The metallodielectric photonic crystal displayed a directional bandgap with a lower band edge of 13.0 GHz, an upper band edge of 21.5 GHz and a center frequency of 17.25 GHz, corresponding to a stop bandwidth center frequency ratio of 50%. The maximum rejection at the band center is 35 dB, corresponding to a 7 dB per unit cell rejection ratio. The Fabry-Perot type resonance in the K _u band has a quality factor of 200, with a maximum transmission peak of -5 dB     

Metal-assisted coupling to hollow-core photonic crystal fibres

Selective coupling to the fundamental mode of short hollow-core photonic bandgap fibres without exciting cladding modes is improved by gold-coated fibre end facets. Cladding modes are suppressed by 20-30 dB for single-and multimode fibre launch, respectively, while in-band power loss is 3-8 dB.     

太赫兹光子晶体光纤与天线设计

以聚甲基丙烯酸甲酯(PMMA)材料为基质,设计了一种空芯多孔包层结构的太赫兹光纤,中心的大孔缺陷用于传输太赫兹波,周围四层小孔可以将太赫兹波的传播限制在缺陷内部。利用COMSOL软件对光纤的损耗特性进行仿真分析发现,光纤在0.6 THz的泄露损耗低于0.1 dB/m,具有良好的传输特性。和金属波导口可以当作天线辐射电磁波的原理相似,光纤的端面也可以作为天线将内部传输的太赫兹波向外辐射,通过仿真分析,天线在0.59~0.61 THz的回波损耗低于-25 dB,方向性系数大于20 dB,半功率波束宽度约为13。     

Suppressed modal interference switches with integrated curvedamplifiers for scaleable photonic crossconnects

A novel, compact optical switch that incorporates two 1×2 suppressed modal interference (SMI) switches with an integrated curved amplifier is demonstrated as a basic component for scaleable, lossless photonic crossconnects. The basic operation of the switch is described and measured on/off ratios of 22 dB (16 dB) are reported for the cross (bar) state with switching currents of less than 25 mA per section. Lossless switching was attained in the amplified cross state, while only 0.5 dB of excess loss was measured in the unamplified bar state. Cascading of these elements should lead to N×N lossless, optical crossconnects with crosstalk levels near 40 dB     

双矩形纤芯光子晶体光纤偏振分束器

基于双折射效应设计了一种新颖的纤芯为椭圆空气孔,包层为圆形空气孔的矩形双芯光子晶体光纤偏振分束器。用半矢量光束传播法(BPM)数值模拟了基模情形下该偏振分束器的性能,结果表明:在工作波长为1.55μm,光纤长度为1659μm时,两个纤芯在X、Y方向偏振光的隔离度分别达到了-41.3 dB和-39.1 dB,隔离度小于-10 dB的带宽超过了80 nm,达到了良好的偏振分束性能。同时,模拟了实际加工误差对所设计的偏振分束器的影响,得出在1.55μm的工作波长下,误差达到±7%时,隔离度仍能小于-10 dB,具有较高的实际应用价值。     

Digitally linearized wide-band photonic link

A photonic analog-to-digital (A/D) link with third-order distortion suppression is proposed and demonstrated. Experimental results with single-and two-tone analog input signals and a one giga-sample per second (GSPS) photonic A/D system with 500-MHz instantaneous bandwidth are presented. The application of a simple time-domain linearization scheme results in distortion suppression approaching 30 dB and allows optical modulation depths over 80%     

A wide-band microwave photonic phase and frequency shifter

Advanced radar deception systems require wide-band devices which perform microwave processing of frequency and phase information. A wide-band microwave photonic phase shifter was constructed which is capable of imposing greater than 2π phase shift to microwave signals in the 2-18-GHz frequency range. The maximum standard deviation from the phase setting was 10° (7° typical). The phase shifter was then incorporated into a frequency translation architecture. The carrier suppression obtained was 50 dB with a spurious harmonic suppression of 23 dB     

Microstructure fibre array for RF photonic signal processing applications

A novel microstructure fibre array (MFA), comprising multiple singlemode fibre waveguides reduced to an overall diameter of approximately 30 /spl mu/m is reported. When used in conjunction with a single photodetector, the array facilitates the efficient and stable electrical summation of a number of RF-modulated optical signals with minimal optical interference effects. The reported MFA has optical insertion loss less than 0.1 dB. An RF filter based on the array exhibits less than 0.4 dB optical insertion loss and excellent temporal stability.     

混合导光双芯光子晶体光纤及分束器

设计了一种基于全内反射和光子带隙效应两种导光机制的混合导光双芯光子晶体光纤,以耦合模式理论为基础,利用全矢量有限元法和平面波展开法分析了其有效折射率和耦合长度特性。数值分析结果表明:通过改变光纤中大空气孔直径及孔间距,可以调节耦合长度的大小,通过改变高折射率柱直径以及高折射率柱的有效折射率,可以调节耦合长度大小及耦合长度极大值的位置。利用所设计的混合导光双芯光子晶体光纤制作的偏振分束器,其长度为5.2 mm,在31 nm带宽范围内,分光比小于-30 dB;在60 nm带宽范围内,分光比小于-20 dB。     

Cascadability of large-scale 3-D MEMS-based low-loss photonic cross-connects

The performance of cascaded low-loss (<3.5 dB) 256/spl times/256 three-dimensional microelectromechanical system (3-D MEMS) photonic cross-connects (PXCs) is experimentally investigated in a recirculating loop. After 60 transitions through the PXC, a power penalty of 1.7 dB is observed, which is attributed to the accumulation of the low polarization-dependent loss in the optical switch. The use of 3-D MEMS PXCs as a wavelength-selective switch (WSPXC) for transparent all-optical networks is also demonstrated. Measured Q-factors for all 16 100-GHz-spaced wavelengths at 10 Gb/s over eight spans of 75-km single-mode fiber and eight transitions through the WSPXC nodes are better than 17 dB.     

Single-polarization single-mode photonic crystal fibers

A new structure of single-polarization single-mode (SPSM) photonic crystal fiber (PCF) is proposed and analyzed by using a full-vector finite element method with anisotropic perfectly matched layers. From the numerical results it is confirmed that the proposed fiber is low-loss SPSM-PCF within the wavelengths ranging from 1.48 to 1.6 /spl mu/m, where only the slow-axis mode exists and the confinement loss is less than 0.1 dB/km.     

A WDM receiver photonic integrated circuit with net on-chip gain

We demonstrate a photonic circuit with an optical preamplifier, a WDM filter and a fast photodetector integrated on the same chip. The passive integrated filter is formed by an aspheric waveguide lens and a planar Bragg grating. This arrangements yields narrow filter response (8 Å width at -3 dB is demonstrated) and high rejection ratio of 24 dB. The optical preamplifier consisting of strained multi-quantum well layers provides sufficient amplification to overcome the passive losses. Response curves demonstrate net on-chip gain with low ripple     

Ultralow loss and long length photonic crystal fiber

We have succeeded in fabricating a low-loss and long length photonic crystal fiber (PCF) by improvement of fabrication process. The fiber is 10 km long and has a lowest loss of 0.37 dB/km at 1550 nm ever reported. We also succeeded in reducing the OH absorption loss to 3 dB/km. This is almost the half of the value ever reported. Using the low-loss PCF, we performed the first DWDM transmission experiment. DWDM signal of 8/spl times/10 Gbit/s is successfully transmitted through the PCF.     

基于磁光子晶体的三通道太赫兹波选路开关

在完整的二维正方晶格硅(Si )中,引入线缺 陷(波导)和磁光子晶体点缺陷(微腔),利用磁性 材料的磁导率随磁场的变化,通过波导和微腔的耦合,提出了一种基于磁光子晶 体的三通道太赫兹(THz)波选路开关。利用平面波展开法(PWM)和时域有限差分法(FDTD) ,对基于磁光子晶体的三通道THz 波选路开关进行了仿真研究。结果表明,选路开关通道1的消光比(EXT) 为12.74dB,通道2和通道3的EXT〖W T BZ〗都为28.05dB,响应速度可达ps量级。利用本方案实现的THz 波选路开关,在未来的集成光路中具有很好的应用前景。     

Silicon-based Fano resonance devices based on photonic crystal nanobeams

To address the driving power and density of wavelength-division-multiplexing (WDM) computing architectures, a Fano resonator based on a photonic crystal nanobeam is proposed. The Fano resonator comprises a T-shaped waveguide, introducing an additional phase shift in the continuous propagation mode, and a photonic crystal nanobeam with a discrete mode. The device has one resonance peak within wavelength ranging from 1 500 nm to 1 600 nm, with a maximum extinction ratio of 8.7 dB and a transmission spectrum slope of up to 11.30 dB/nm. The device has good reusability, extinction ratio, and spectral resolution. It is expected to provide essential photonic components for low-energy consumption and high-density photonic computing to meet the requirements of future convolutional neural network (CNN) acceleration computing.