Switchable microwave photonic filter using a phase modulator and a silicon-on-insulator micro-ring resonator

A switchable microwave photonic filter(MPF) using a phase modulator(PM) and a silicon-on-insulator microring resonator(MRR) is proposed and demonstrated. By adjusting the polarization controller between the PM and the MRR, the filtering function of the MPF can be switched between a band-stop filter and a band-pass filter. In a proof-of-concept experiment, an MPF with a rejection ratio of 30 dB(or 15 dB) for the band-stop(or band-pass) response and a frequency tuning range from 9.6 to 20.5 GHz is achieved.     

Arbitrary response design for incoherent microwave photonic filters based on basic filtering cell combination

An arbitrary response designing method for incoherent microwave photonic filter (MPF) is proposed and experimentally verified. By decomposing the response function of incoherent MPFs into basic filtering cells, arbitrary responses can be designed by simply choosing and recombining proper filtering cells. With the proposed method, required implementing parameters for arbitrary responses can be determined easily, which will bring great convenience for realistic MPF implementation based on existing structures. A simple band-pass MPF is designed as an example and a verification experiment is set up to testify the designing results. Good accordance between the theoretical and the experimental results are obtained.     

A spurious frequencies suppression method for optical frequency comb based microwave photonic filter

The traditional optical frequency comb (OFC) based microwave photonic filters (MPFs) are rigidly restricted to be operated in a single “Nyquist zone”, as varieties of spurious frequencies signals coexist in the output. Here, a method for spurious frequencies suppression in the OFC‐based MPF is proposed and experimentally demonstrated. The method is achieved by applying group velocity dispersion on the carrier combs to separate the filter transfer functions of the spurious frequencies from that of the input radio frequency signal. It is fairly simple and effective, and has no effect on the filter characteristic. With this method, the filter pass band can be freely tuned without the limitation of the “Nyquist zone”. It can be considered as a step forward for the practical application of the OFC‐based MPF.     

Characteristic analysis of series-cascaded microring resonator arrays

In terms of the coupled mode theory, novel formulations of the transfer functions are presented for a series-cascaded microring resonator (MRR) array. Using these formulas, transmission characteristics are analyzed and some parameters are optimised for such a polymer device. Simulation results show that when several microrings are serially cascaded to form a MRR array, the passband becomes steep, and the nonresonant light and the crosstalk become weak.     

双微环谐振腔耦合的双波长半导体激光器（英）

提出一种新颖的单片集成双微环耦合的双波长半导体激光器结构。集成于激光腔内的2个微环谐振腔作为模式选择滤波器,通过游标效应选择谐振模式,同时还可作为等效的反射镜面以形成行波腔。这种无需解理的行波激光腔代替了需要解理面的法布里-珀罗驻波腔。理论仿真表明,跟驻波腔结构相比,行波腔双微环激光器结构简单,可获得约34 mA的较低的阈值电流和大于31 dB的边模抑制比。合理地控制有源区的增益峰值和谐振模式分布,该激光器能提供一致性和稳定性较好的双波长激光输出。     

Highly sensitive Si nanowire-based optical sensor using a Mach-Zehnder interferometer coupled microring

A Mach-Zehnder interferometer (MZI) coupled microring is demonstrated experimentally to obtain a high sensitivity as well as a large range for measuring change in refractive index. For the present MZI-coupled microring, there is a major resonance wavelength with a high extinction ratio (16-36 dB) in a very large wavelength span. Consequently, a very large quasi-free spectral range (>120 nm) is achieved, which helps to obtain a large measurement range. The MZI-coupled microring sensor is used for measuring the change of the ambient refractive index ranging from 1.0 to 1.538, and the sensitivity is as high as 111 nm/refractive index unit.     

Sensitivity and detection limit of dual-waveguide coupled microring resonator biosensors

We show that a linear relation exists between the device sensitivity and the quality （Q） factor of a dual- waveguide coupled microring resonator optical biosensor when the optimal conditions are satisfied. We also show that the detection limit depends on the loss coefficient and signal-to-nosie ratio （SNR） of the overall system, rather than the circumference of the ring. For a microring resonator sensor whose Q factor is 20000, the detection limit is found to be about 10-7 with 30-dB SNR, which is in good agreement with reported experimental data. These results indicate that loss reduction is the top priority in the design and fabrication of highly sensitive microring resonator optical biosensors.     

SNR improvement by intergranular exchange coupling in CGC perpendicular magnetic recording media

Effect of intergranular exchange coupling in coupled granular and continuous (CGC) perpendicular media was investigated in terms of improvement of signal-to-noise ratio (SNR). The exchange coupling improves SNR and byte error rate (BER); however, it tended to widen the magnetic track width (MWW) of a track. That degradation is of concern for the CGC media. This paper discusses intergranular exchange coupling in CGC media to optimize track density and linear density to achieve high areal density.     

Single-photon all-optical switching using coupled microring resonators

We study the nonlinear phase response of a microring resonator coupled to a bus waveguide and the use of this nonlinear phase shift to store information in the microring resonator and enhance the switching characteristics of a Mach-Zehnder interferometer (MZI). By introducing coupling between adjacent microring resonators, the switching characteristics of the MZI can be exponentially enhanced as a function of the number of microring resonators, when compared to the linear enhancement for uncoupled resonators. With only a few moderate-finesse microring resonators, the switching power can be reduced to attowatt level, allowing for photonic switching devices that operate at single-photon level in ordinary optical waveguides.      

Effect of ring spacing on spectral response of parallel-cascaded microring resonator arrays

In terms of the coupled mode theory and transfer matrix technique, novel formulas of the amplitude coupling ratio and transfer functions are presented for a parallel-cascaded microring resonator array (PCMRR). By using these formulas, effects of structural parameters, especially the ring spacing, on the spectral response are analyzed for this kind of polymer device. The box-like spectral response is successfully obtained due to the proper selection of the ring spacing, amplitude coupling ratio and the number of rings.     

Group delay and dispersion analysis of compound high order microring resonator all-pass filter

In this paper, we propose a novel compound high order microring resonator all-pass filter employing two cascaded microrings and an assistant microring. It improves the dispersion compensation ability and provides a wide bandwidth. The group delay range is effectively extended, which provides flexibility in choosing the geometrical parameters of the microring for technical convenience and bend loss improvement. The careful design of coupling coefficients can optimize the group delay response. This device is able to provide dispersion compensation to systems such as the high speed dense wavelength division multiplexer (DWDM) optical fiber links.     

A novel accelerometer based on microring resonator

A novel microring resonator accelerometer is proposed. It is realized by a suspended straight waveguide coupled with a microring resonator. Under the external acceleration, the coupling coefficient is a function of gap spacing between the two waveguides. The mathematical model of the sensing element is established. Both the finite element method and coupled mode theory are adopted to analyze and optimize the proposed structure. Simulation results show that the mechanical sensitivity is 0.015 μm/g with the working frequency below 500 Hz and cross-axis sensitivity less than 0.001%, which is promising in seismic related applications.     

Resonant modal conversion in a two-mode waveguide

We characterize a system consisting of a two-mode waveguide coupled to a single-mode microring resonator possibly presenting a nonlinear response of Kerr type. By using the scattering parameter formalism extended to the multimode domain, we show that in the linear regime and for an ideally transparent medium, each resonance of the system can be exploited to perform complete even-to-odd (respectively, odd-to-even) modal conversion. Moreover, when the Kerr nonlinearity is effective, the microring enables a power-dependent modal switching mediated by phase bistability. Thanks to its mode-processing capabilities, this configuration is suitable to find application as a functional building-block in mode-division multiplexing (MDM) photonic integrated circuits.     

Experimental investigation on submicron rib waveguide microring/racetrack resonators in silicon-on-insulator

In experiment, characteristics of silicon microring/racetrack resonators in submicron rib waveguides have been systematically investigated. It is demonstrated that only a transverse-electric mode is guided for a ratio of slab height to rib height h/H = 0.5. Thus, these microring/racetrack resonators can only function for quasi-transverse-electric mode, while they get rid of transverse-magnetic polarization. Electron beam lithography and inductively coupled plasma etching were employed and improved to reduce sidewall roughness for low propagation loss and high performance resonators. Then, the effects of waveguide dimensions, coupling region design, waveguide roughness, and oxide cladding for the resonators have been considered and analyzed.     

单片集成微环反射器可调谐半导体环形激光器理论和数值模型(英)

设计了一种新颖的快速可调谐激光器。这种激光器在恒定电流泵浦的有源微环组成的半导体环形激光器腔外部集成一个可调谐的无源微环反射器,其结构将决定激光器激射腔模的有源腔和无源可调谐部分分离,有助于提高调谐速度。与光栅结构的激光器相比,该激光器结构简单,具有强烈的选模功能,不需要相位匹配部分,输出波长不受调谐部分热效应的影响。基于多模速率方程建立了激光器的理论和数值模型,数值仿真结果表明该激光器能在选取的15个腔模范围内完成数字调谐,且具有40 mA的较低阈值电流和适中的边模抑制比。     

用于光纤无线通讯的微环相位辅助型马赫-曾德尔调制器

针对光纤无线通信(ROF)系统对光强调制器线性度的特殊要求,设计了一种新型的集成光学器件——微环相位辅助型马赫-曾德尔调制器(RPAMZM)。将一个微环谐振器和一个相位调制器分别加载到马赫-曾德尔调制器的两臂,可以补偿普通马赫-曾德尔调制器的亚线性,得到线性度良好的响应特性。建立了该种器件的理论分析模型,计算了不同条件下的传输特性和无毛刺动态范围(SFDR)。分析结果表明,在不计损耗的情况下,器件的非线性主要来源于传输函数泰勒展式的三次项,通过控制透射系数,可以使该项等于零,无毛刺动态范围获得19.68 dB的提高;在损耗存在的情况下,通过控制透射系数和偏压因子,可以同时抑制掉二次和三次这两个主要的非线性项,无毛刺动态范围获得15.74 dB的相对改善。     

Predistortion techniques for synthesizing coupled microring filters with loss

A general method based on the predistortion technique is presented for determining the optimum coupling parameters of multiple-coupled microring filters in the presence of known uniform resonator loss. The technique involves predistorting the filter transfer function by shifting its poles and zeros to compensate for loss in the microring resonators due to material absorption, surface roughness scattering, coupling loss and bending loss. It is shown that by sacrificing some in-band insertion loss, both the amplitude and group delay responses of the filter can be recovered when loss is present. Application of the method to synthesizing lossy microring filters in both the digital z-domain and analog s-domain will be presented. The proposed technique is general in that it can be applied to both amplitude and phase filters constructed of coupled microresonators in the most general two-dimensional coupling topology.     

聚合物串联耦合双环电光开关的优化

利用耦合模理论、电光调制理论和微环谐振理论,提出一个聚合物串联耦合双环电光开关器件模型,在1.55 μm谐振波长下对该器件进行了模拟和优化.结果为：微环波导芯截面尺寸为1.6×1.6 μm2,波导芯与电极间的限制层厚度为1.6 μm,电极厚度为0.15 μm,微环半径为15.2 μm,微环与信道间的耦合间距为0.14 μm,微环与微环间的耦合间距为0.6 μm,输出光谱的3 dB带宽约为0.06 nm,开关电压约为6 V左右,插入损耗约为2.2 dB,串扰约为－20 dB.所设计的双环电光开关较单环型电光开关不仅输出光谱更加平坦陡峭,非谐振光更弱,而且开关电压更低.     

Optimization and analysis of series-coupled microring resonator arrays

In terms of the coupled mode theory and transfer matrix technique, novel formulas of the amplitude coupling ratios and transfer functions are presented for a series-coupled microring resonator (MRR) array. By using these formulas, parameters are optimized, and transmission characteristics including the transmission spectrum and the insertion loss are analyzed for a SiN/SiO₂ series-coupled MRR array on Si substrate. The box-like spectral response is successfully obtained owing to the proper selection of the amplitude coupling ratio between the channel and the ring, and that between adjacent rings, as well as the number of series-coupled rings.     

Application of Turbo codes in optical OFDM multimode fiber communication system

In this paper, Turbo Code is proposed in optical OFDM multimode fiber communication system in order to decrease the bit error rate (BER) of the system, which is mainly affected by the deep nulls of the magnitude response of multimode fiber in the high frequency region (above 3 dB). A simulation system in SIMULINK is established. Based on the system, the BER of the system with Turbo Code is compare to the systems with another two typical coding schemes including convolutional code (CC) and serially concatenated code (SCC) which uses a concatenation of convolutional and RS codes when transmitting 10 Gbps data over various length multimode fibers. Different transmitting rate is also considered. The results show that Turbo coded system has a lower BER than the other two systems and the Turbo coded system can transmit 10 Gbps data to the distance of 300 m with BER below 1e−6.