Mode Converters for Coupling to High Aspect Ratio Silicon-on-Insulator Channel Waveguides

The design, simulation, and experimental performance of mode converters for coupling from single-mode silicon-on-insulator ridge waveguides to high aspect ratio channel waveguides are described. The converters consist of a two-level adiabatic taper structure. The final channel waveguide is 1.5 mum high by 0.8 mum wide. Simulations predict that for total coupler lengths longer than 20 mum, the coupling loss from the fundamental ridge mode to the slit mode is better than -0.2 dB. The couplers and waveguides were fabricated using a two-step self-aligned process. The measured coupling loss for fabricated mode converters is -0.4 dB     

Improved coupled-mode formulation based on composite modes forparallel grating-assisted co-directional couplers

An improved coupled-mode formulation based on the ideal modes of the coupled waveguides (ideal composite modes) is presented. In comparison with the formulation based on the ideal modes of the individual waveguides (ideal waveguide modes), the formulation in terms of composite modes is more rigorous and yields a more accurate grating period and coupling lengths. In addition, the radiation loss due to input and output junctions can in the composite-mode formulation. A new to the coupled-mode equations is derived in which all the spatial harmonics generated by the periodic grating are taken into account. The power exchange between the waveguides is examined by considering the input and the output conditions. The phase-matching conditions and the coupling lengths are calculated and compared with the analysis in terms of the waveguide modes. The grating period predicted by the waveguide-mode formulation agrees very well with that by the composite-mode formulation; however, dramatically different coupling lengths are predicted by the two formulations     

True-time-delay element in lossy environment using EO waveguides

We investigate a photonic true time delay element in a lossy environment using electrooptic waveguides. Its principle is based on the ring resonator and the all-pass filter. In the lossy environment, it is known that the insertion loss depends on the delay time when using the conventional ring resonator. We add a by-pass waveguide to the ring resonator in order to compensate the resonant-dependent loss. As a result, we have a voltage-controlled photonic true time delay element with its insertion loss independent of the delay time.     

Passive integrated-optical waveguide structures by Ge-diffusion insilicon

The realization of low loss optical channel waveguides and passive waveguide structures by a germanium indiffusion process into silicon will be discussed. Employing relatively simple technological processing like standard lithography, e-beam evaporation and diffusion, single-mode waveguides could be produced exhibiting polarization independent losses of as low as 0.3 dB/cm at wavelengths of λ=1.3 μm and λ=1.55 μm. S-bends fabricated with the same technology offered an excess loss of 1 dB at a radius of around 5 mm without any optimization. For a Y-junction designed with S-bends the maximum opening angle was determined to be 1.8° if an excess loss of 1 dB is allowed. The examination of directional couplers with various coupling lengths and distances revealed an excellent agreement between measurement and theory     

Optical Interconnects on and in Printed Circuit Boards

Two types of short distance optical interconnects for on-board applications are presented: Small diameter plastic optical fibre (POF) links and multimode polymer waveguide layers integrated in multilayer printed circuit boards (PCB). POF links with fibre numbers up to 128 and link lengths up to 50 cm are realized with total transmission loss values below 2 dB at 660 nm. First tests of 10 cm long temperature stable multimode polymer waveguides laminated into standard multilayer PCBs demonstrate the capabilities of combined electrical-optical circuit boards.     

Automated Attenuation Test in Multimodal Waveguides by Resonance Return-Loss or Insertion-Loss Measurements

Two methods for testing short lengths of multimodal circular waveguides, working in the TE/sub 01/ mode accompanied by many spurious modes are described. One method is based on the measurement of the return loss of a resonant one-port cavity; the second one measures the insertion loss of a cavity coupled to the rectangular main waveguide. Automatic data selection and manipulation are emphasized.     

串联微环谐振器的光学特性

根据波导耦合方程,导出了串联微环谐振器的传输矩阵,并分析了环数、环间耦合系数以及损耗对串联微环谐振器输出特性的影响。数值模拟表明,串联微环谐振器具有光子带隙的特征。当环数增加时,通带内满足谐振条件的波长数增加;当环间耦合系数增加时,可使通带带宽加宽;通过适当选择环数和环间耦合系数,可以实现滤波和波分复用(WDM)的功能。选用脉冲宽度为50 ps的高斯型激光脉冲注入微环谐振器,发现当环间耦合系数较小时,出射脉冲相对于入射脉冲具有光学延迟的效果,并且随着环数的增加,延迟时间逐渐增大,而当环间耦合系数较大时,光学延迟效果不明显。     

Transverse Electric Field Distributions in Ferrite Loaded Waveguides (Correspondence)

The transverse electric field distribution in dielectric and ferrite loaded waveguides has been measured by several investigators. Knowledge of the actual field distribution within the waveguide is needed in the design of field displacement isolators, phase-shifters, and similar microwave devices. In making such measurements, care must be taken to choose lengths of samples of ferrites or dielectrics sufficiently long enough so that the distribution in one transverse plane will he the same (except for an attenuation effect) as in another transverse plane.     

Integration of a laser diode with a polymer-based waveguide forphotonic integrated circuits

The fabrication and characterization of BRS lasers monolithically integrated with butt-coupled polymer-based buried strip waveguides is presented. Threshold currents of lasers with one cleaved and one etched mirror facets are 15-18 mA and waveguide output powers are in excess of 5 mW at 100 mA laser driving currents and for 600 μm long waveguides. The device exhibits a total waveguide insertion loss less than 5 dB. The integrated device is potentially suitable as a building-block for photonic integrated circuits     

渐变截面多模干涉器件中MMI区长度的计算

从渐变截面波导与强导近似的阶跃截面波导之间的区别入手,推导出了渐变截面ＭＭＩ区长度的精确表达式,并对成像的振幅和相位关系进行了研究。结果表明,在相同ＭＭＩ区宽度条件下渐变截面器件中ＭＭＩ区最短长度为阶跃截面的两倍,但它的设计灵活性却是阶路截面器件所无法比拟的。     

Design of a single-mode tapered waveguide for low-losschip-to-fiber coupling

The novel waveguide structures described in this paper have nonlinearly tapered shapes that result in low radiation losses despite their relatively short lengths. The core at the waveguide endface connected with the fiber has a very small cross section and an expanded mode field with a non-Gaussian shape. The taper structures are analyzed by using an improved step-transition method. This method is a based on the theory of enclosing a waveguide within electrical walls and that can therefore treat the radiation modes in a tapered waveguide as discrete mode spectra. Analyzing the relationships between the lengths and shapes of the tapers and the radiation loss due to the tapers show that appropriately tapered semiconductor waveguides operating at an optical wavelength of 1.55 μm and having a taper length of less than 0.7 mm can have a radiation loss of only 0.1 dB and a coupling loss with a conventional single-mode fiber of less than 0.5 dB     

Performance Evaluation of Single-Wavelength Fiber Delay Line Buffer With Finite Waiting Places

The performance of single-wavelength fiber delay line buffer with finite waiting places is evaluated in this paper. For Poisson arriving packets with arbitrarily distributed lengths, the generating function of delay time distribution can be derived from the quantized delay buffer model. Then queue length distributions, loss probability, and other important performance measures can be figured out. Specifically, two important cases of negative-exponentially distributed packet lengths and fixed packet lengths are considered and compared. The accuracy of the proposed approach is verified through simulation. It is also observed that the buffer system performs more effectively for the fixed-length packets.     

Thermal Aging Reliability of Package-Level Polymer Optical Waveguides

Polymer optical waveguides are viewed as a potential interconnect solution in board-level optoelectronic systems. In this paper, the optical loss changes in siloxane polymer waveguides during thermal aging conditions are studied for the wavelengths of 850 and 1310 nm. The optical loss in waveguides during intended operation and temperature exposure can increase due to factors such as oxidation of waveguides, increased absorption, and scattering. In addition to these inherent changes in the optical properties of the waveguides, physical failures such as delamination and cracking of waveguides will also increase the optical loss. This paper focuses on the first set of parameters that affects the optical loss and as a first step; the optical absorption of the polymer material is characterized through spectroscopy experiments. The thermal-aging dependent optical loss is determined for waveguide samples at several different accelerated temperature conditions. The temperature contours in a polymer waveguide with an embedded laser are determined from experiments as well as finite-element modeling. Using experimental data, analytical models have been developed that relate the optical loss with temperature and time, and provide a practical way of determining the reliability of the optical waveguides during field-use conditions.     

Optical-fibre coupling to high-silica channel waveguides with fibre-guiding grooves

A practical coupling technique between high-silica multimode channel waveguides and optical fibres has been demonstrated using guiding grooves formed simultaneously with waveguides on a substrate. The fibre-waveguide (15 mm long)-fibre insertion loss was 1.23 dB.     

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.     

Spectral Loss Characterization of Femtosecond Laser Written Waveguides in Glass With Application to Demultiplexing of 1300 and 1550 nm Wavelengths

Femtosecond laser written waveguides in glass were characterized across the full telecom spectrum to gain insight into waveguide loss mechanisms, and to aid in the design of a low-loss 1300/1550 nm wavelength demultiplexer. A lambda^-4 wavelength scaling of propagation loss confirms Rayleigh scattering as a principal loss mechanism. Laser exposure was optimized for generating low-loss directional couplers with high isolation between the 1300 and 1550 nm bands. Dispersive coupling in the straight and curved wavelength regions was balanced with a 1.5-fold difference in 1300 and 1550 nm beat lengths, leading to the first demonstration of 1300/1550 nm demultiplexer written with a laser. A minimum interaction length of 3.2 mm, ~2 dB insertion loss and channel isolations of 16.7 and 18.8 dB are reported.     

Rectangular Ring Lasers Based on Total Reflection Mirrors and Three Waveguide Couplers

Novel rectangular ring lasers containing active and passive sections are fabricated and characterized. The rectangular laser cavity is formed using four low-loss total internal reflection (TIR) mirrors and an output coupler made out of passive three coupled waveguides. The fabrication process is exactly the same as for other active and passive devices except for one deep etch step for TIR mirror fabrication. Two different lasers having active section lengths of 250 and 350 mum and total cavity lengths of 580 and 780 mum are fabricated. For both devices, lasing thresholds of 38mA are obtained at room temperature and under continuous-wave operation. Lasing is predominantly single-mode with a sidemode suppression ratio better than 20 dB. The power loss of a single TIR mirror is also determined to be about 0.5 dB. Such low-loss TIR mirrors enabled lasers with very small footprints     

A novel proposal for all-optical Galois field adder based on photonic crystals

In this paper we are going to propose an all-optical structure for implementing Galois field adder. To do so, we will use four optical XOR gates. The working principle of the proposed structure is based on destructive interference of optical waves. By choosing different lengths for the input waveguides, 180\(^\circ \) of phase difference will be generated between the optical waves. In the final structure, the normalized power for logic 0 and 1 at the output ports was 1 and 45%. Time delay of the proposed structure is about 1.5 ps.     

Two-step purely thermal ion-exchange technique for single-modewaveguide devices in glass

Two-step purely thermal ion-exchange technique using two monovalent ions for single-mode waveguides is proposed. Experiments show embedded waveguide structure below the surface of the glass, as computer simulation predicted. The insertion loss of the straight waveguide was less than 1 dB for 19 mm long samples, at both λ=1.3 μm and 1.55 μm     

Splicing losses between dissimilar optical waveguides

A simple computational formalism has been derived for the analysis of splicing and return losses between different optical waveguides. It has been found that the splicing loss can be approximated by the overlap integral method as long as total reflectance is negligible. The reciprocity of splicing loss between two single-mode waveguide is theoretically confirmed while return loss is found nonreciprocal. The return loss can be tolerably approximated by simple Fresnel formula except near the resonance. When close to the resonance, the deviation from Fresnel approximation is found to be strongly dependent on the structure of the waveguide and the refractive index difference between the core and clad