Optimization design of optical waveguide in Mach-Zehnder electro-optical polymer modulator

In order to reduce transmission loss of the optical waveguide in Mach-Zehnder (M-Z) electro-optical (EO) polymer modulator,the basic iterative formula of semi-vector finite-difference beam propagation method (FD-BPM) is obtained from the scalar wave equation. The transition waveguide is combined with S-type bend branch waveguide for the M-Z EO modulator in the branch waveguide. The effects of structure parameters such as ridge width,length of the branch waveguide and interferometer spacing on the transmission loss are systematically studied by using the semi-vector FD-BPM method. The structure is optimized as an S-sine bend branch waveguide,with rib width w=7μm,length of branch waveguide L=1200μm and interferometer spacing G=22 μm. The results show that the optimized structure can reduce transmission loss to 0.083 dB,which have a certain reference value to the design of optical waveguide in M-Z polymer modulator.     

Influence on Multimode Rectangular Optical Waveguide Propagation Loss by Surface Roughness

Optical scattering loss coefficient of muhimode rectangular waveguide is analyzed in this work. First, the effective refrac tive index and the mode field distribution of waveguide modes are obtained using the Marcatili method. The influence on scattering loss coefficient by waveguide surface roughness is then analyzed. Finally, the mode coupling efficiency for the SMFOpticalWaveguide （SOW） structure and MMFOptical Waveguide （MOW） structure are presented. The total scatter ing loss coefficient depends on modes scattering loss coeffi cients and the mode coupling efficiency between fiber and waveguide. The simulation results show that the total scatter ing loss coefficient for the MOW structure is affected more strongly by surface roughness than that for the SOW struc ture. The total scattering loss coefficient of waveguide decreas es from 3.97 x 10^-2 dB/cm to 2.96 x 10^-4 dB/cm for the SOW structure and from 5.24 - 10^-2 dB/cm to 4.7 x 10^-4 dB/ cm for the MOW structure when surface roughness is from 300nm to 20nm and waveguide length is 100cm.     

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.     

1.3-μm 1 × 4 MMI coupler based on shallow-etched InP ridge waveguides

1.3-μm 1 × 4 MM1 coupler is designed and fabricated on an InP substrate based on a shallow etched waveguide structure. Tapered input/output waveguides and a bending waveguide design are adopted and applied in the device to optimize the performance. The average excess losses of the 1 × 4 MMI coupler per channel are 2.8, 1.7, 2.9, and 2.9 dB, respectively. The smallest excess loss can be lower than 0.5 dB in the 40-nm spectrum bandwidth. The average uniformity between the four channels of the MMI coupler is 1.3 dB, while the smallest uniformity is only 0.4 dB.     

A novel loss compensation technique analysis and design for 60 GHz CMOS SPDT switch

A novel loss compensation technique for a series-shunt single-pole double-throw (SPDT) switch is presented operating in the 60 GHz. The feed-forward compensation network which is composed of an NMOS, a couple capacitance and a shunt inductance can reduce the impact of the feed forward capacitance to reduce the insertion loss and improve the isolation of the SPDT switch. The measured insertion loss and isolation characteristics of the switch somewhat deviating from the 60 GHz are analyzed revealing that the inaccuracy of the MOS model can greatly degrade the performance of the switch. The switch is implemented in TSMC 90-nm CMOS process and exhibits an isolation of above 27 dB at transmitter mode, and the insertion loss of 1.8-3 dB at 30-65 GHz by layout simulation. The measured insertion loss is 2.45 dB at 52 GHz and keeps<4 dB at 30-64 GHz. The measured isolation is better than 25 dB at 30-64 GHz and the measured return loss is better than 10 dB at 30-65 GHz. A measured input 1 dB gain compression point of the switch is 13 dBm at 52 GHz and 15 dBm at 60 GHz. The simulated switching speed with rise time and fall time are 720 and 520 ps, respectively. The active chip size of the proposed switch is 0.5×0.95 mm².     

High-Q micro-ring resonators and grating couplers for silicon-on-insulator integrated photonic circuits

An ultra-small integrated photonic circuit has been proposed,which incorporates a high-quality-factor passive micro-ring resonator(MR) linked to a vertical grating coupler on a standard silicon-on-insulator(SOI) substrate.The experimental results demonstrate that the MR propagation loss is 0.532 dB/cm with a 10μm radius ring resonator,the intrinsic quality factor is as high as 202.000,the waveguide grating wavelength response curve is a 1 dB bandwidth of 40 nm at 1540 nm telecommunication wavelengths,and the measured fiber-to-fiber coupling loss is 10 dB.Furthermore,the resonator wavelength temperature dependence of the 450 nm wide micro-ring resonator is 54.1 pm/℃.Such vertical grating coupler and low loss MR-integrated components greatly promote a key element in biosensors and high-speed interconnect communication applications.     

Study of WDM polymer planar curved waveguide couplers

A wavelength division multiplexer based on curved polymer planar waveguide is proposed. According to the coupled modetheory and the waveguide structure, the performance of the curved waveguide coupler (CWC) is analyzed. The results showthat CWC can accommodate wider multiplexing bandwidth than parallel straight waveguide coupler (SWC) due to thecompensation effect of the effective coupling length. The two variables, curvature radius and minimum spacing, increasethe design flexibility of the waveguide device. A 4-channel wavelength division multiplexing (WDM) system based onCWC is designed. The deviation of the center wavelength, due to the errors of curvature radius and minimum spacingduring fabrication process, is investigated. The smaller the curvature radius and the minimum spacing are, the larger thecentral wavelength deviation caused by the error of the curvature radius and the minimum spacing is, which provides someuseful theoretical basis for the design and the fabrication of polymer waveguide devices.     

纳米锥SiGe-SOI光波导与光纤的耦合分析

Based on a submicrometer-sized SiGe-SOI waveguide, the coupling loss mechanism is analyzed between the submicrometer-sized SiGe-SOI waveguide and the fiber. The main sources of coupling loss are analyzed, and the mismatch loss of the mode field is the mainly lost during connection between the submicrometer-sized waveguide and the fiber. In order to reduce the mismatch loss of the mode field, the structure ofa nanotaper SiGeSOI waveguide with a nanometer-sized tip is adopted. By reducing the waveguide dimensions to increase the mode field size, coupling loss could be reduced between the waveguide and the fiber. Different mode field dimensions ofnanotaper SiGe-SOI waveguides and fiber are quantitatively analyzed, and the quantitative relationship between nanotaper SiGe-SOI waveguide dimensions and mode field dimensions are obtained. Finally, nanotaper SiGe-SOI waveguides are made, and the test and analysis have been done. The final experimental results accord well with the theoretical analysis. When the waveguide width is 0.5 μm, the minimum coupling loss of the SiGe-SOI waveguide is 0.56 dB/facet, and also the correctness of the design method and theoretical analysis are verified.     

Study and Design of Spiral Bent Waveguide Configuration

A new version of the scalar transverse electric（TE） wave equation in the bent waveguide is introduced. Then. TE polarized field in curved single-mode waveguides is analyzed by using the finite- difference beam propagation method（FD-BPM）. The bending loss in bent waveguides is gotten for the optical fields obtained from BPM and comparisons are made among losses of the waveguides with various curvature radiuses, refractive index differences and cross sections. Based on the results, the design of spiral bent waveguide configuration is proposed as follows： refractive index difference being of 0. 007, both width and thickness of waveguides being of 6 μm, the curvature radius in the spiral centre being of 4 mm, and the bending loss coefficient of the designed spiral bent waveguide being of 0. 302 3 dB/cm.     

Four-way radial waveguide power divider with high power-handling capacity

In this paper,a novel four-way radial waveguide power divider with low insertion loss and high power-handling capacity is proposed.This power divider consists of an input coaxial waveguide,a central probe,a radial waveguide,four equispaced identical coupling probes,four equispaced identical adjusting posts and four output coaxial waveguides.The novel coupling probes and the adjusting posts are used to realize favorable uniform power division.A power divider with the center frequency of 4.1 GHz is designed,fabricated and measured.Good agreement between simulation and experiment is noted.The measured 15 dB return-loss bandwidth of the power divider is about 600 MHz.The measured 0.5 dB insertion loss bandwidth is wider than 700 MHz.The differences and isolations between the output ports are also discussed.The power-handling capacity of the power divider is analyzed through simulation,and the result proves its usability in high power applications.     

Diffusion-limited etching for compact, low-loss semiconductor integrated optics

It is shown that diffusion-limited wet chemical etching can be used to fabricated single-mode GaAs/AlGaAs rib waveguides suitable for compact circular waveguide bends (300- mu m radius). The waveguides exhibit lower propagation losses (1-4 dB/cm at 1.52- mu m wavelength) than previously reported guides fabricated for compact bend applications by dry etching. To study the radius dependence of waveguide bend loss, a set of nested 90 degrees circular bends was fabricated simultaneously on a single chip.<>     

Reduction of bend losses in Ti:LiNbO3 waveguides through MgO double diffusion

A significant reduction in bend losses in Y-cut Ti: LiNbO3waveguides by means of a double-diffusion technique is reported. Compared to pure Ti: LiNbO3 waveguide bends, MgO: Ti: LiNbO3 waveguide bends offer a reduction in the necessary bend radius by a factor as large as eight, if a total bend excess loss of 1 dB is allowable.     

TE01 attenuation of 90° sharp bend in reduced diameter circular waveguide

The transmission characteristics of a TE01-mode waveguide sharp bend, of 1m equivalent radius, are presented. The attenuation is less than 0.25 dB across the frequency band 30?110 GHz.     

SOI波导弯曲损耗改善方法的研究

采用有效折射率方法EIM(Effective Index Method)和二维束传播算法(2D-BPM)对SOI(Sillcon-on—insulator)波导弯曲损耗的改善方法进行了模拟分析．模拟发现，在波导连接处引入偏移量和在波导外侧刻槽等两种不同方法都能有效减小弯曲损耗，并且后者的效果更明显．同时通过实验获得了验证．对R=16mm、横向位移为70μm的弯曲波导，通过刻槽方法将插入损耗降低了5dB，基本消除了弯曲所带来的附加损耗.     

Less than 1 dB per meter propagation loss of silica waveguidesmeasured using a ring resonator

Phosphorus doped silica on silicon waveguide propagation loss, bend loss and their polarization dependence have been measured using a set of different radii ring resonators. For a 30 mm ring radius a finesse of 132 was measured and the inferred propagation loss was 0.85 dB/m, the lowest value yet reported. To characterize the finesse of the high Q resonator we proposed and used for the first time a stable Er⁺³ fiber grating laser source which was thermally tuned. This configuration provides improved and accurate measurements capability for finesse values in the range well beyond 100     

Topology design and fabrication of an efficient double 90/spl deg/ photonic Crystal waveguide bend

We have designed and fabricated a novel 90/spl deg/ bend in a photonic crystal waveguide. The design was obtained using topology optimization and the fabricated waveguide displays a bend loss for transverse-electric-polarized light of less than 1 dB per bend in a 200-nm wavelength range.     

Low-loss near-infrared passive optical waveguide components formedby electron beam irradiation of silica-on-silicon

Results are presented for a range of near infrared single-mode passive channel waveguide optical components fabricated in PECVD silica-on-silicon by electron beam irradiation. The devices include S-bends, Mach-Zehnder interferometers, Y-junction tree-structured splitters, and directional couplers. It is shown that low loss may be obtained through appropriate choice of waveguide bend radius and fabrication parameters; fiber-device insertion losses of ≈2 dB and ≈1 dB are achieved for 1×8 splitters and 3-dB directional couplers, respectively, at λ=1.525 μm     

Low-loss Ti:LiNbO3-waveguide bends prepared by MgOindiffusion

A significant bend loss reduction for z-cut Ti:LiNbO₃ waveguides was achieved with a single and very efficient technique. The refractive index on the outer sides of an S bend was decreased through indiffusion of a double-MgO layer for reducing the radiation losses, and a broadening of the bent waveguide sections was used for further decreasing of the radiation losses and additionally reducing the transition losses. The acceptable bend radius for an allowed excess loss of 1 dB could thus be reduced from 24 mm down to 5 mm for TM polarization and from 26 mm down to 10 mm for TE polarization     

Variable optical attenuator for large-scale integration

A polymer thermooptic variable optical attenuator (VOA) was designed and demonstrated for dense waveguide device integration. The waveguide bend design is compatible with photolithography fabrication techniques and operates by controlling waveguide bend radiation loss. The design optimizes the compromise between integration capability, integration cost, and attenuation efficiency. For a 5 mm bend length, optical attenuation of >40 dB has been achieved with an applied electrical power of 250 mW. The fiber-to-fiber insertion loss was 1.5 dB for a 20-mm total waveguide length. The design's compact size makes it practical for both VOA arrays and dense integrated optical circuits     

Estimation of polarization crosstalk at a micro-bend in Si-photonic wire waveguide

The singlemode Si-photonic wire waveguide allows sharp bends, which significantly expands the design flexibility of optical devices and circuits. Here, the suppression of the polarization crosstalk at a sharp bend will be an important issue, since a large crosstalk affects the performance of devices and circuits. In this study, the three-dimensional (3-D) finite-difference time-domain (FDTD) simulation showed that the crosstalk at a 90/spl deg/-bend with a radius of 0.35-1.75 /spl mu/m is less than -25 dB at a wavelength of 1.55 /spl mu/m. In the experiment, the crosstalk from TE-like to TM-like polarization was evaluated to be -13 dB to -10 dB. This large value was explained by a small tilt of waveguide sidewalls, which seriously increased the crosstalk. In addition, it was found in the calculation that some combinations of bends increase or decrease the crosstalk, and that a U-shape bend is the most effective for the suppression of the crosstalk.