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.<>     

Mode Analysis and Design of a Low-Loss Photonic Crystal 60$^{circ}$ Waveguide Bend

The guided modes of a two-dimensional photonic crystal straight waveguide and a waveguide bend are studied in order to find the high transmission mechanism for the waveguide bend. We find that high transmission occurs when the mode patterns and wave numbers match, while the single-mode condition in the waveguide bend is not necessarily required. According to the mechanism, a simply modified bend structure with broad high transmission band is proposed. The bandwidth is significantly increased from 19 to 116 nm with transmission above 90%, and covers the entire C band of optical communication.      

Curved waveguides for spatial mode filters in semiconductor lasers

Curved waveguides are used as a lateral spatial mode filter to increase the threshold for the first-order mode in high-power narrow stripe semiconductor lasers. Beam propagation analysis is used to determine optimal waveguide geometries and radii of curvature to establish appropriate amounts of bend loss. Curved waveguide devices are fabricated and compared against conventional devices. Use of a curved waveguide increases the current level at which lateral beam instabilities occur from /spl sim/400 to /spl sim/700 mA with no decline in slope efficiency.     

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。     

Experimental woodpile EBG waveguides, bends and power dividers at microwave frequencies

Experimental waveguides, bends and power dividers in the woodpile electromagnetic bandgap (EBG) material at Ku-band are demonstrated. Prototypes are fabricated from alumina, and use an efficient waveguide transition to enable high quality measurements. Low-loss transmission is demonstrated for a waveguide and a 90/spl deg/ bend, and near equal power division shown for a woodpile EBG waveguide power divider. The components have the potential to be scaled for applications at millimetre-wave and terahertz frequencies     

Analysis of Optical Waveguide Consisting of a Square-Law Lenslike Medium and its Analogies to Circular TE/sub 01/ waveguide

Propagation behavior of light beams along sinusoidal and serpentine bends as well as circular bends and linearly tapered bends of optical waveguides consisting of a square-law Ienslike medium is investigated in detail, both theoretically and numerically, on the basis of the approximate wave theory. A new design method of the circular bend for removing the effects of the bend is proposed and numerical results are presented. The divergence phenomena of the beam trajectory in both the sinusoidal and serpentine bends of the optical waveguide are discussed in comparison with mode-conversion phenomena occurring in the circular TE/sub 01/ waveguide with the same bends. Several design conditions to eliminate undulations of the beam trajectory and/or the spot size which would occur at a circnlar bend of the optical waveguide are also studied, and interesting analogies to the design conditions proposed so far to prevent mode-conversion losses at a circular bend of the TE/sub 01/ waveguide are shown.     

可调谐氮化硅波导微环谐振腔滤波器研究

设计并制备了一种基于热光效应的集成可调谐氮化 硅(Si₃N₄)波导微环谐振腔滤波器,通过采用马赫-曾德干涉仪(MZI)构成的可调谐 耦合器控制耦合区耦合比,以实现滤波器消光比的调谐。设计并优化了微环谐振 腔的波导截面尺寸、弯曲半径和耦合区波导间隔等参数,并通过光刻、反应离子刻蚀(RIE )等工艺制备 了两种不同弯曲半径的Si₃N₄波导微环谐振腔。实验结果表明,本文器件在波长1550nm附近处的自由光谱 范围(FSR)为68pm,3dB带宽约为16pm,品质因子Q达到了9.68×10 4,消光比可调范围约为17dB。     

High efficiency 90/spl deg/ silica waveguide bend using an air hole photonic crystal region

We propose the hybrid integration of an air hole photonic crystal (PhC) structure with a high /spl Delta/ (0.75%) single-mode silica waveguide to achieve an ultracompact high efficiency 90/spl deg/ bend for transverse-magnetic polarized light. Diffraction from the periodic boundary between the PhC and silica waveguide regions is shown to seriously degrade the optical efficiency of the bend. A microgenetic algorithm (/spl mu/GA) combined with a two-dimensional finite-difference time-domain method is used to modify the PhC and its boundary layer to suppress this diffraction which in turn maximizes bend efficiency. The final optimized structure has a 99.4% bend efficiency at a wavelength of 1.55 /spl mu/m and occupies an area of only 27 /spl times/ 27 /spl mu/m.     

Compact Bends for Achieving Higher Integration Densities for LiNbO$_{3}$ Waveguides

A new waveguide platform is demonstrated that allows the bend radii to be substantially decreased for titanium-diffused lithium-niobate (LiNbO₃) waveguides using vertically integrated arsenic-trisulfide (As₂S₃) overlay waveguides. Power is transferred from a Ti-diffused waveguide into the overlay waveguide using tapers, guided by the As₂S₃ waveguide through the S-bend region and transferred back into another Ti-diffused waveguide. This structure also behaves like a polarization beam splitter. We present simulation results as well as measurements to show the feasibility of achieving low loss and reduced bend radii for electrooptic waveguides.     

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.     

TE/sub 01/ Mode Components in the 3-mm Region

In the 3-mm region (94 Gc) it is desirable to use waveguide components operating in the low loss TE/sub 01/ mode in circular waveguide rather than in fundamental-mode rectangular waveguide. Because this is a higher mode, mode purity is of major concern. A method of identifying undesired modes and their amplitudes is by means of radiation patterns from the end of the waveguide. Components developed to operate in this mode include a transition from rectangular to circular waveguide, standing wave detector, variable attenuator, directional coupler, flexible waveguide, fixed 90/spl deg/ bend and rotary joint.     

Ultrashort optical pulse generation with a mode-locked long-wavelength (1075-1085 nm) InGaAs-GaAs semiconductor laser

Optical pulses are generated by passive and hybrid mode-locking of a long wavelength (1075-1085 nm) InGaAs-GaAs ridge waveguide laser grown by gas source molecular beam epitaxy. The devices are fabricated with two sections, one of which contains a bend in the waveguide for coupling to an external linear cavity. Pulses 2-5 ps in duration have been generated with average powers ranging from 750 /spl mu/W to 1.8 mW. Pulse compression yields durations as short as 570 fs. Post amplification with a narrow stripe InGaAs-GaAs semiconductor optical amplifier increases the average output power up to 13 mW.     

Low-loss CaxBa1−xNb2O6 ridge waveguide for electro-optic devices

Optical ridge waveguide using calcium barium niobate (CBN) on silicon substrate for the first time is designed, fabricated and characterized for future integrated electro-optic devices. To obtain single-mode propagation, the CBN thin strip is designed to be surrounded by thick silicon dioxide layer forming a ridge waveguide. Deposition of CBN film on profiled silicon dioxide introduces spatial separation which solves the CBN etching problem. Fabrication, edge polishing and near-field mode profile measurement of the waveguide are carried out. The measurement is in good agreement with the simulation and an exact loss as low as 2.15 dB/cm was obtained for the fabricated waveguide.     

Bend losses in GaAs/AlGaAs optical waveguides

Circular bends with low excess bend loss (? l dB) and radii of a few millimetres were fabricated using GaAs/AlGaAs single-heterostructure rib waveguides with propagation loss ? 1 dB/cm. The effect of rib geometry and roughness due to bend pattern quantisation on the excess bend loss at 1.52/?i was investigated.     

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 polyimide-Ta2O5-SiO2hybrid ARROW waveguides

A low-loss polyimide-Ta₂O₅-SiO₂ hybrid antiresonant reflecting optical waveguide (ARROW) is presented. The ARROW device was fabricated using both the organic and dielectric thin-film technologies. It consists of the fluorinated polyimide, tantalum pentoxide (Ta₂O₅), and silicon dioxide (SiO₂) hybrid layers deposited on a Si substrate. For transverse electric polarized light, the propagation loss of the waveguide as low as 0.4 dB/cm was obtained at 1.31 μm. The propagation loss for transverse magnetic polarized light is 1.5 dB/cm. An ARROW waveguide fabricated using the polyimide-Ta₂O₅ -polyimide material system is also presented for comparison     

Design and performance of an erbium-doped silicon waveguide detector operating at 1.5 /spl mu/m

A new concept for an infrared waveguide detector based on silicon is introduced. It is fabricated using silicon-on-insulator material, and consists of an erbium-doped p-n junction located in the core of a silicon ridge waveguide. The detection scheme relies on the optical absorption of 1.5-/spl mu/m light by Er/sup 3+/ ions in the waveguide core, followed by electron-hole pair generation by the excited Er and subsequent carrier separation by the electric field of the p-n junction. By performing optical mode calculations and including realistic doping profiles, we show that an external quantum efficiency of 10/sup -3/ can be achieved in a 4-cm-long waveguide detector fabricated using standard silicon processing. It is found that the quantum efficiency of the detector is mainly limited by free carrier absorption in the waveguide core, and may be further enhanced by optimizing the electrical doping profiles. Preliminary photocurrent measurements on an erbium-doped Si waveguide detector at room temperature show a clear erbium related photocurrent at 1.5 /spl mu/m.     

Low-loss electrooptic BaTiO/sub 3/ thin film waveguide modulator

A strip-loaded electrooptic waveguide modulator based on an epitaxial BaTiO/sub 3/ thin film was fabricated and characterized for the first time. The strip-loaded waveguide structure greatly improves waveguide propagation and polarization-dependent loss performance. A propagation loss of 1.1 dB/cm and polarization dependent loss of 0.1 dB/cm were measured. The electrooptic waveguide modulator exhibited a half-wave voltage-interaction length product of 4.5 V /spl middot/ cm at a wavelength of 1542 nm. The measured effective electrooptic coefficient of the as-grown BaTiO/sub 3/ waveguide modulator was 38 pm/V. The experimental results indicate that a strip-loaded thin film waveguide modulator is suitable for photonic applications.     

Two-step laterally tapered spot-size converter 1.55-/spl mu/m DFB laser diode having a high slope efficiency

We demonstrate a two-step lateral tapered 1.55-/spl mu/m spot-size converter distributed feedback laser diode (SSC DFB LD) having slope efficiencies as high as 0.457 and 0.319 mW/mA measured at 25 /spl deg/C and 85 /spl deg/C, respectively. The SSC DFB LD fabricated by using a nonselective grating process has a double core waveguide structure including a planar buried heterostructure type active waveguide and a ridge type passive waveguide. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far-field pattern in horizontal and vertical directions of 7.3/spl deg/ and 11.6/spl deg/, respectively.     

SOI波导弯曲损耗影响因素的分析

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 (silicon-on-insulator）波导弯曲损耗的几种影响因素进行了分析. 通过模拟发现弯曲损耗随弯曲半径的增大、波导宽度的增加及内外脊高比的减小而减小. 同时，改进波导结构，例如在弯曲波导外侧刻槽可以减小SOI脊形波导的弯曲损耗.