A study on an active square-law combining method for apolarization-diversity coherent optical receiver

A polarization-diversity coherent optical receiver which realizes ideal square-law combining with active gain control is described. This receiver can suppress the additional power penalty due to the demodulator dynamic range limitation by equivalently expanding the demodulator dynamic range. A low-power penalty less than 1 dB was attained with a 400-Mb/s FSK (frequency-shift keyed) single-filter detection system. Throughout a 25-h 183-km transmission experiment, the stable operation of this receiver was confirmed     

波导微环共振滤波器的滤波特性分析

根据波导耦合模理论详细研究了微环共振滤波器的滤波特性,分析了单环、串联双环、串联三环结构等波导微环共振滤波器的滤波特点。通过模拟计算发现,滤波带宽平坦化程度和信道串扰大小主要依赖于由波导构成的各方向耦合器之间的功率耦合比k,同时微环波导的损耗是器件滤波特性劣化的重要原因。在一定优化参数条件下,多环结构的滤波效果优于传统单环结构,并且各方向耦合器功率耦合比k值的优化取值范围扩大,降低了器件工艺实现难度。     

太赫兹硅基微环谐振器的设计与分析

设计了一个工作频率在太赫兹大气传输第一窗口的硅基波导型微环谐振器。利用传输矩阵法和耦合模理论计算微环谐振器的传输函数,并对波导耦合系数进行分析,获得微环谐振器的临界耦合条件。采用时域有限差分法分析微环谐振器的性能参数,并与串联双环谐振器性能参数相比较。结果表明：单环谐振器的自由谱宽范围为27 GHz,插入损耗为0.3 dB。单环与双环谐振器的响应谱线形状因子分别为0.16和0.52,即串联双环谐振器使谐振谱线顶端更平坦,滚降度增高。Abstract：关键词：     

Temperature insensitive vertically coupled microring resonatoradd/drop filters by means of a polymer overlay

The temperature dependence of vertically coupled glass microring resonator add/drop filters is investigated. Measurements show that the passband of the air-clad microring resonator filter increases with temperature at a rate of 0.0137 mm/°C. Using a PMMA-TFMA polymer that has an opposite refractive index temperature gradient than glass as the overlay of the microring resonator, the temperature dependence of the filter is compensated to -0.0025 nm/°C in the operation range of 25°C to 55°C     

Wavelength-Tunable Microring Resonator on Lithium Niobate

A wavelength-tunable microring resonator with integrated microheater on lithium niobate is presented. Ridge structure on lithium niobate is formed by a wet-etching technique for enhancing the lateral index contrast of the waveguide. The resonant wavelength of the microring resonator is tuned through thermooptic effect by injecting current into the integrated microheater. The tuning characteristics of through port and drop port are measured and the tuning rates in the microring resonator with a radius of 100 mum for transverse-magnetic and transverse-electric polarizations are 2.54 x 10^-2 nm/mA and 3.40 x 10^-3 nm/mA.     

Proposal for a High-Speed Optical Dark-Soliton Detector Using a Microring Resonator

This letter presents a theoretical study of a novel application of a simple waveguide-based microring resonator as a high-speed optical dark-soliton detector. The microring resonator is described by a z-transform transfer function that consists of one zero and one pole. When the resonator has a zero equal to unity (or is at resonance) and a pole equal to 0.81, it can convert a dark-soliton signal into a Gaussian-like return-to-zero signal with a power level that is ~20 dB greater than that of the existing interferometer-based scheme. The proposed scheme also has a simpler structure than the integrator-based method     

微环共振器光开关在高速互连中的应用

在高性能计算机系统中, 极低延迟高吞吐量的光交换网络具有很多优势, 而光开关作为全光交换网络中的关键器件, 它的性能直接影响到光交换网络的交换能力, 是近年光通信领域的研究热点。半导体微环共振器作为近年提出的一种新的光开关解决方案, 在功耗、延迟、体积等方面具有优势, 目前吸引了越来越多研究机构的注意, 并先后提出了一些比较有价值的微环共振器光开关设计方案。结合目前国内外微环共振器光开关的最新进展, 分析了微环共振器光开关在高性能计算机和光交换网络中的应用, 需要进一步改进的研究重点, 以及微环共振器作为低延迟光开关的发展前景。     

Reduction of AM-induced penalty in DPSK receivers by sum-squaredemodulation

A DPSK (differential phase shift keying) demodulator which is insensitive to the amplitude modulation induced by semiconductor optical amplifier phase modulators is proposed. The demodulator consists of only two additional power dividers/combiners, compared to a traditional DPSK demodulator. Analysis shows that the receiver penalty caused by amplitude modulation can be reduced from 2-4 dB to zero. The demodulator is demonstrated in a 2.5-Gb/s DPSK system experiment using an optical amplifier as phase modulator     

Ultrasmall Thermally Tunable Microring Resonator With a Submicrometer Heater on Si Nanowires

An ultracompact widely tunable thermooptical (TO) microring resonator (MRR) filter based on Si nanowires is presented. The Si nanowire waveguide has a insulator, Si core, a up-cladding, and a thin metal film at the top. The metal circuit along the microring is used as a submicrometer heater which has the same width as the Si nanowire waveguide. The up-cladding is optimized to reduce the light absorption of the metal as well as to have a good heat-conduction from the heater to the Si core. Two pads used as the contact points for the probes connecting to the electrical power are perpendicularly connected to the microring by using optimized T-junctions (with a low excess loss of about 0.06 dB per T-junction). With such a design, the present thermally tunable microring resonator (MRR) can be fabricated by using a standard fabrication process with a single lithography process, which is much simpler than the fabrication with double lithography processes used for the conventional TO components. Finally, the simulation results show that the designed MRR has a wide tuning range of about 20 nm with a low heating power of 5 mW.     

双层介质加载等离子体微环的高灵敏生物传感

为了提高介质加载表面等离子体的传输距离,提出了基于双层介质加载的表面等离子体波导结构。利用有限元方法研究了介质加载的表面等离子体波导的模场分布及传输特性,并对其传感应用的波导灵敏度进行了分析。研究表明, 当低折射率介质厚度占波导总厚度的33%时,传输距离是单层介质加载表面等离子体波导的2.4倍。利用该波导结构组成的微环谐振腔被用于生物传感研究,其传感特性分析表明,传感灵敏度为411 nm/RIU,检测极限为1.210-5 RIU。双层混合介质加载表面等离子体波导的设计和研究为其进行无标记生物传感应用提供了有价值的指导。     

High-performance all-optical silicon microswitch

An integrated micron-size all-optical Si switch capable of 94.7 GHz operation frequency is presented. The device consists of a microring resonator formed by Si/SiO/sub 2/ slot-waveguides with a low-index nonlinear optical material in the slot region. Strong optical confinement in the slot permits an achievement of low switching power of 6.2 mW.     

微环谐振器中各参数对光速控制输出脉冲畸变的影响仿真分析

利用微环谐振器进行光速控制时,各参数对光脉冲传输的影响是不可忽略的,它除了导致光脉冲展宽,还引起脉冲的畸变。基于微环谐振器的传输特性,推导了单环谐振器的二阶色散和三阶色散表达式,针对无损耗/增益情形,分析了利用微环谐振器进行光速控制时,高阶色散和输入脉冲中心波长对输出脉冲畸变的影响,分析了损耗/增益对单环谐振器输出脉冲畸变的影响。结果表明,二阶色散导致脉冲展宽,三阶色散导致脉冲畸变,输入脉冲中心波长位置影响脉冲分裂谷底的深浅,而损耗和增益影响脉冲畸变情况。为利用微环谐振器实现光速控制的应用提供了设计优化依据。     

Compact Thermally Tunable Silicon Wavelength Switch: Modeling and Characterization

A wavelength-selective photonic switch is developed based on a Si microring resonator using thermooptic effect. The 10-mum-diameter microring resonator uses single-mode strip Si waveguides of dimension 0.25 mum times 0.45 mum operating at 1.5 mum. Full-width at half-maximum are in the range 0.1-0.2 nm. The ultrawide tunable range (>6.4 nm) and wide free spectral range (~18 nm) of the switch element enables wavelength reconflgurable multichannel matrix switch by wavelength multiplexing/demultiplexing. Average rise delay time of 14 mus with low switching power of 3.15 mW has been achieved with 0.2-nm wavelength tuning and 78 mus, 104 mW for 6.4-nm tuning. Fall delay times are usually less than 10 mus. Thermal simulations show 10%-20% agreement with the measurements up to 3.2-nm tuning. The compact size of the switch shows its potential as an active element in photonic integrated circuits.     

Ultra-small microring resonator based on sub-micrometer fiber

The transfer function of the microring resonator is deduced,and the effects of the normalized loss,coupling coefficient and surrounding media on the resonance performance are investigated thoroughly.Utilizing the improved fused tapering tech-nique and ingenious self-coiling coupling method,a high-quality microring resonator(radius of about 500μm)with larger extinction ratio(>10 dB)and sharper resonance is designed and fabricated by a segment of continuous sub-micrometer fiber.The microring resonator constructed in this way demonstrates extremely small connection loss with communication fiber in contrast to the planar waveguide technology.     

微环谐振器的弯曲损耗

通过解弯曲波导的正规模的方法,从理论上分析了微环谐振器的弯曲损耗与微环的直径、宽度和厚度间的对应关系,给出了微环谐振器的弯曲损耗与微环芯和周围介质折射率对比间的关系.将上述的计算结果与保角变换方法的计算结果进行了比较.设计了微环谐振器的特征参数.     

氮化硅微腔中的光学频率梳(特邀)

具有高品质因子（Q 值）的光学谐振腔能够长时间将光束缚在较小的模式体积内,极大地增强了光与物质的相互作用,成为集成光学器件中具有重大潜力的重要组成部分。聚焦于目前广泛应用于集成非线性光学领域的氮化硅材料平台,为了解决大尺寸氮化硅微环腔由拼接误差、表面粗糙等因素导致的散射损耗较大的问题,进行了一系列的工艺改进以提高大尺寸氮化硅微环腔的品质因子。结果表明:通过薄膜再沉积工艺可以有效降低氮化硅波导的散射损耗,半径为560 μm的大尺寸氮化硅微环腔的本征Q值得到了平均26% 的提升。得益于提高的微腔Q 值,在氮化硅微环腔中实现了重复频率40 GHz 的光学频率梳。     

硅基槽型微环谐振器及其调谐特性研究

仿真和实验研究了含槽型(slot)光波导的反馈波导型微环谐振器的特性,将槽型光波导集成到Si基微环谐振器中,丰富Si基光波导的功能,为新型光电子器件的实现提供途径。通过锥形波导结构实现从传统波导到槽型波导的模式转换,减小传输损耗,采用时域有限差分法(FDTD)研究了光功率的分布和模式转换过程。结果显示,光功率逐渐转移到锥形结构两侧的槽型波导中并最终形成槽型波导中的传输模式,通过优化锥形结构能实现较高的模式转换效率,可以达到90%以上。采用电子束刻写技术和等离子刻蚀技术制备了反馈波导型槽型微环谐振器。实验显示,锥形波导能够实现模式的转换,光传输过程良好。通过在槽型波导中填充电光聚合物来改变槽型光波导的折射率,测量结果显示,传输谱谐振峰发生了明显移动,移动幅度达到5.6nm,器件具备很好的可调谐性。     

Linearized microring-loaded Mach-Zehnder modulator with RF gain

A linearized modulator based on the Mach-Zehnder interferometer (MZI) loaded with a second-order allpass microring resonator is proposed and analyzed. The device is shown to exhibit much smaller intermodulation distortion than standard Mach-Zehnder modulators, thus greatly enhancing the device dynamic range. Gain effect associated with the microring resonance results in a modulator transfer function with high slope efficiency and large RF gain. Moreover, combined with the use of a highly electrooptic polymer, the high slope efficiency allows for the possibility of realizing modulators with subvolt drive voltage. The detrimental effect of loss in the microring resonators on device performance is also investigated and a design approach to mitigate its effect is presented. The proposed modulator can be linearized to any arbitrary nth order by loading the MZI with a higher order allpass microring resonator.     

聚合物10环并联微环阵列谐振滤波器的设计

设计了聚合物硅基并联10环阵列微环谐振滤波器,优化了并联多环谐振器的环数,并给出了光强传递函数的通用公式。根据数值模拟结果,优化了波导尺寸、谐振级数、相邻微环的圆心间距、耦合比率等相关参数。     

基于光学微环的化学传感器

以SiN为材料,采用与CMOS工艺相兼容的技术,制备了波导宽度为1μm,半径为400μm的SiN光学微环。经测量,其品质因数(Q值)高达20 000,自由光谱范围(FSR)为0.5 nm。提出了采用光学微环传感器、单波长光源和光功率计对待测物进行测量的方案。实验证明,该方案与传统的采用光谱仪测量谐振峰值漂移的方法相比,可以取得更高的系统探测灵敏度。最后,利用微环传感器对葡萄糖溶液浓度进行测量,灵敏度高达10-4折射率单元(RIU),证明了该传感器可以应用于溶液检测领域。