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     

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.     

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     

Integrated AlGaAs waveguide components for optical phase differencemeasurement and correction

A Y-junction interferometer phase measurement technique has been developed that is independent of the power or power ratio in the input arms. This technique was incorporated into a proof-of-concept AlGaAs guided-wave Mach-Zehnder interferometer to demonstrate the measurement and correction of a phase difference between the arms. In the first part of this paper, we describe the design, fabrication, and characterization of the individual AlGaAs dielectric-loaded rib waveguide components that were chosen to fabricate the proof-of-concept interferometer. These components include passive waveguides, bends and Y-junctions, and reverse-biased phase modulators. The composition of the waveguide layer was chosen so that these modulators would have low loss at the applied voltage required for maximum phase correction. The choice was based on electroabsorption measurements on test modulators as a function of the energy difference between the bandgap of the waveguide layer and the operating wavelength. The average propagation loss at 862 nm of the passive single-mode guides used was 1.1 dB/cm. The abrupt bend insertion loss was ~0.20 dB/bend for a 0.5° bend angle, and the Y-junction insertion loss was ~0.37 dB for 1.0° full angle. Two-mm-long p⁺ -n^--n⁺ phase modulators typically had V_π voltages of ~6.8 V. On a slightly modified structure, V _π voltages as low as 2.65 V were measured. In the last part of the paper, the proof-of-concept interferometer and test setup are described and recent phase difference measurement and correction data with intentional power imbalances greater than 90% between the interferometer arms are presented. These results demonstrate conclusively that the phase difference measurement and correction performance of the Y-junction interferometer technique are independent of the power ratio in the interferometer input arms for power ratios >10:1     

High-silica single-mode optical reflection bending and intersecting waveguides

Single-mode high-silica optical reflection bending and intersecting waveguides are examined under conditions of large bending and intersecting angles (5?90 degrees). The reflection bending waveguide shows a loss of 2 dB at the bending angle of less than 50 degrees. When the intersecting angle was 30 degrees or more, a small intersecting loss (less than 0.1 dB) and a low crosstalk (less than ?20 dB) were attained.     

Low Loss and Low Crosstalk Waveguide Crossings Designed by Wavefront Matching Method

We designed waveguide crossings with small angles by the wavefront matching method to reduce excess loss and crosstalk. The designed waveguide crossings were fabricated using silica-based planar lightwave circuit (PLC) technology. We experimentally obtained excess loss and crosstalk values of less than 0.3 and$-$30 dB, respectively, for a crossing angle of 5$^circ$, and of less than 0.1 and$-$38 dB, respectively, for an angle of 20$^circ$, in the 1530–1565-nm wavelength range. The designed waveguide crossings are promising as basic circuit elements for realizing more compact PLC devices.     

Design and Analysis of Refractometer Based on Bend Waveguide Structure with Air Trench for Optical Sensor Applications

This study proposes a novel optical sensor structure based on a refractometer combining a bend waveguide with an air trench. The optical sensor is a splitter structure with a reference channel and a sensing channel. The reference channel has a straight waveguide. The sensing channel consists of a U‐bend waveguide connecting four C‐bends, and a trench structure to partially expose the core layer. The U‐bend waveguide consists of one C‐bend with the maximum optical loss and three C‐bends with minimum losses. A trench provides a quantitative measurement environment and is aligned with the sidewall of the C‐bend having the maximum loss. The intensity of the output power depends on the change in the refractive index of the measured material. The insertion loss of the proposed optical sensor changes from 3.7 dB to 59.1 dB when the refractive index changes from 1.3852 to 1.4452.     

不同切型质子交换弯曲波导的弯曲损耗研究

退火质子交换铌酸锂光波导是一类重要的光波导。对2种不同切型的3种常用S形弯曲质子交换光波导,利用宽角有限差分光束传播法进行了分析。结果表明,3种弯曲波导的弯曲损耗,随波导结构参数的变化基本上是相同的,而在相同的波导结构参数下,X切型的质子交换光波导的弯曲损耗总体上都要小于Z切型的质子交换光波导。数值计算结果为相应波导器件的设计和制备提供了一定的参考。     

Low propagation losses in single-line-defect photonic crystal waveguides on GaAs membranes

We have fabricated and characterized straight single-line-defect two-dimensional photonic-crystal waveguides on GaAs films with lengths of 1, 4, and 10 mm. By optimizing key processes for smooth top and bottom waveguide-surface, as well as fine patterning process of the air holes, extremely low propagation loss was achieved. The optimization includes wet etching process of a sacrificial AlGaAs clad layer and oxygen plasma process for complete resist removal. AFM measurement resulted that the surface roughness is less than 1 nm at the top surface of the line-defect waveguide. From the transmittance spectra for different-length samples, the propagation loss is estimated as small as 0.76/spl plusmn/0.5 dB/mm. Besides the loss for the straight waveguide, the loss per bend for the 60/spl deg/ bend waveguide was estimated as 0.3 dB/bent with the bandwidth of broader than 40 nm. The present results are promising for key passive elements such as photonic-crystal symmetric Mach-Zehnder switches needed in future optical communication applications.     

E- and H-Plane Bends for High-Power Oversized Rectangular Waveguide

A study is presented of theoretical and experimental results of E- and H-plane bends for high-power oversized rectangular waveguide having cross-section dimensions in the range between 1..5 and 2.5 free space wavelengths. It is expected that waveguides having these dimensions will be able to transmit 50 to 100 kW of average power at X-band without water cooling. The transmission of at least 5.0 MW of peak power at X-band without pressurization is also a design objective. Dimensions for bends having low-mode conversion loss were determined by numerical integration of the coupled transmission line equations. The dominant TE/sub 10//spl square/ mode and four spurious modes were considered in these calculations. The results obtained for both constant curvature and sinusoidally shaped E- and H-plane bends are presented. A compact H-plane constant curvature bend is described for which the ratio of centerline radius to waveguide width is equal to 1.48. The measured mode conversion loss to the TE/sub 20//spl square/, TE/sub 30//spl square/, and TE/sub 40//spl square/ modes for an experimental model having a width equal to 2.25 inches was less than -20 dB in the frequency range from 7.0 to 11.0 Gc/s.     

一种新型毫米波差分线和基片集成波导结构转换设计

差分线和基片集成波导(Substrate Integrated Waveguide,SIW)结构由于各自显著的优势,在毫米波系统中得到广泛研究和应用。为了实现毫米波系统高度集成化,提出一种新型毫米波段差分线转基片集成波导结构。为实现工程系统中的通用性,差分线的输入端与射频前端的输出端呈一定夹角,这将导致共模噪声增大,插损恶化,结构体积增大,匹配结构的设计难度增大。通过差分线的过渡结构转角设计以及SIW结构的模式转换设计,在结构上实现了45°夹角的差分传输线输入、射频前端垂直输出,在性能上实现了转换结构的高共模噪声抑制比。对该转换结构进行了建模分析和加工测试,在68~80 GHz频段内,输入、输出端口的回波损耗高于10 dB,插入损耗低于3.39 dB。     

Characteristics of S-shaped waveguide structures by the annealedproton exchange process in LiNbO3

The loss of S-shaped waveguide bends in annealed proton-exchanged LiNbO₃ integrated optical devices is found to be dependent on the length of thermal annealing time. The minimum transition length required in order to have losses as low as 0.2 dB is 2.0 mm for a 0.1-mm lateral offset. Intersecting waveguides based on S-shaped structures have been characterized for passive crossovers. An angle greater than 6° is required to provide a crosstalk of less than -30 dB. At a particular angle, intersecting waveguides offer the possibility of making a 3-dB coupler if an insertion loss of 1.2 dB is not a big concern. Zero-gap couplers based on S-shaped structures have been characterized for applications as 3-dB couplers as well. This type of 3-dB coupler has a much lower insertion loss of roughly 0.4-0.5 dB. Both 3-dB intersecting waveguides and 3-dB zero-gap couplers are less sensitive to wavelength variations     

S-band single-stage EDFA with 25-dB gain using distributed ASE suppression

We propose a novel compact design for a single-stage S-band erbium-doped fiber amplifier, wherein distributed suppression of C-band amplified spontaneous emission is provided by optimized bend loss in a coaxial core fiber. Simulations show that /spl sim/25-dB unsaturated gain over 30-nm bandwidth (1495-1525) nm is achievable with the designed module, using a nominal pump power of 500 mW. The noise figure of the amplifier varies between 4.5 and 8 dB from 1495 to 1525 nm. By proper designing, we have also ensured that the gain ripple over the entire 30-nm bandwidth is 相似文献