MMI Devices with Weak Guiding Designed in Three Dimensions Using a Genetic Algorithm

We discuss the design of weakly guided multimode interference (MMI) devices using a genetic algorithm. For devices exhibiting a nonnegligible vertical waveguide offset, such as those produced using ion exchange in glass, three-dimensional modeling is required to properly evaluate the device performance. A combination of semivectorial finite difference modeling in two transverse dimensions and mode propagation analysis (MPA) in the propagation direction is used to evaluate the merit of each trial design. An example is provided of a 1 x 4 power splitter designed for ion exchange, which shows considerable improvement over that obtained by self-imaging theory

Determination of Ion Exchange Parameters by a Genetic Algorithm

Modeling the process of ion exchange in glass requires accurate knowledge of the self-diffusion coefficients of the incoming and outgoing ions. Furthermore, correlating the concentration profile of the incoming ions to a change in refractive index requires knowledge of the correlation coefficient. We present a method by which these three parameters can be quickly determined experimentally, using a genetic algorithm. Comparison with published data is presented

Bilateral Contracts

The basic form of economic exchange is a bilateral relationship between buyer and seller. If economic conditions are common knowledge there is no problem in principle to determine the efficient quantity to trade. But if benefits are known only to the buyer and costs are known only to the seller a situation of bargaining under incomplete information results. Instead of relying on the vagaries of a bargaining outcome, which might be quite costly to implement, economic inefficiency is likely to be improved by a contractual arrangement that could be agreed upon in advance. In such contracts various aspects of the exchange could be allocated to the two parties involved. For example, a price per unit might be fixed in advance and the buyer might be allowed to name his quantity in the light of the information he has about benefits. A more complex version would present the buyer with a non-linear price schedule. Alternatively the supplies might be given control. While these solutions are fairly well understood, there are other types of arrangements in which control is mutual. This paper studies contracts of this nature. We examine the feasibility of implementing various agreements and the nature of optimal bilateral contracts under these informational circumstances. When the random influences impact both parties significantly, full efficiency is not attainable. We show that contracts involving mutual control might sometimes be superior to the best contract giving one side or the other exclusive dominance.

Ion-Exchanged Glass Waveguide Technology: A Review

We review the history and current status of ion exchanged glass waveguide technology. The background of ion exchange in glass and key developments in the first years of research are briefly described. An overview of fabrication, characterization and modeling of waveguides is given and the most important waveguide devices and their applications are discussed. Ion exchanged waveguide technology has served as an available platform for studies of general waveguide properties, integrated optics structures and devices, as well as applications. It is also a commercial fabrication technology for both passive and active waveguide components

Ion-Exchanged Glass Waveguides with Low Birefringence for a Broad Range of Waveguide Widths

Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by use of silica-on-silicon waveguides or buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. We present experimental results on waveguide birefringence for buried silver–sodium ion-exchanged glass waveguides. We show that the waveguide birefringence of the order of 106 for waveguide mask opening widths ranging from 2 to 10 μm can be obtained by postprocessing the sample through annealing at an elevated temperature. The measured values are in agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization independent operation

Fabrication and Comprehensive Modeling of Ion-Exchanged Bragg Opitcal Add-Drop Multiplexers

Optical add–drop multiplexers (OADMs) based on asymmetric Y branches and tilted gratings offer excellent-performance in wavelength-division multiplexed systems. To simplify waveguide fabrication, ion-exchange techniques appear to be an important option in photosensitive glasses. Optimum OADM performance depends on how accurately the waveguide fabrication process and tilted Bragg grating operation are understood and modeled. Results from fabrication and comprehensive modeling are compared for ion-exchange processes that use different angles of the tilted grating. The transmission and reflection spectra for the fabricated and simulated OADMs show excellent agreement. The OADM’s performance is evaluated in terms of the measured characteristics of the Y branches and tilted gratings

The cave spider Meta menardi (Araneae, Tetragnathidae) – occurrence in Finland and notes on its biology

Fifteen years ago the cave spider Meta menardi (Latreille, 1804) was known in Finland in two locations only. Partly due to extensive search it is to date known from 20 sites, all however located in the south-westernmost parts of the country. M. menardi is known to prefer stable and relatively warm subterranean habitats. Our temperature data from a cave on the Åland Islands in Finland indicates that the populations of M. menardi on the northern limit of its distribution could be more cold tolerant than the previously studied populations in Central Europe. In this paper all known locations in Finland are mapped and presented in a table with habitat data. A note on the strategy for catching mosquitoes with the orb web is given and the possible importance of the prey-catching function of the orb web is briefly discussed

Buried Ion-Exchanged Glass Wavelengths: Burial-Depth Dependence on Waveguide Width

A detailed theoretical and experimental study of the depth dependence of buried ion-exchanged waveguides on waveguide width is reported. Modeling, which includes the effect of nonhomogeneous time-dependent electric field distribution, agrees well with our experiments showing that burial depth increases linearly with waveguide width. These results may be used in the proper design of integrated optical circuits that need waveguides of different widths at different sections, such as arrayed waveguide gratings

Ion-Exchanged Glass Waveguides with Low Birefringence for a Broad Range of Waveguide Widths

Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by use of silica-on-silicon waveguides or buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. We present experimental results on waveguide birefringence for buried silver–sodium ion-exchanged glass waveguides. We show that the waveguide birefringence of the order of 106 for waveguide mask opening widths ranging from 2 to 10 μm can be obtained by postprocessing the sample through annealing at an elevated temperature. The measured values are in agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization independent operation