Mixed data rate and format transmission (40-Gbit/s non-return-to-zero, 40-Gbit/s duobinary, and 10-Gbit/s non-return-to-zero) by mid-link spectral inversion.

A polarization-diverse subsystem based on periodically poled lithium niobate waveguides is used as an optical phase conjugator for compensation for linear and nonlinear distortion. We show successful transmission formats of 13 x 40 Gbit/s non-return-to-zero mixed with 6 x 10 Gbit/s non-return-to-zero and 40-Gbit/s duobinary over 8 x 100 km of standard single-mode fiber. A single phase conjugator is used to conjugate all data formats, including the alternative duobinary format, simultaneously.

Strong self-phase modulation in planar chalcogenide glass waveguides.

Single-mode planar waveguides were fabricated from chalcogenide glass compounds with large Kerr nonlinearities. Strong self-phase modulation of subpicosecond pulses along with low linear and nonlinear absorption losses demonstrates the potential for ultrafast, low-power, all-optical processing applications.

Large Kerr effect in bulk Se-based chalcogenide glasses.

High-speed optical communication requires ultrafast all-optical processing and switching capabilities. The Kerr nonlinearity, an ultrafast optical nonlinearity, is often used as the basic switching mechanism. A practical, small device that can be switched with ~1-pJ energies requires a large Kerr effect with minimal losses (both linear and nonlinear). We have investigated theoretically and experimentally a number of Se-based chalcogenide glasses. We have found a number of compounds with a Kerr nonlinearity hundreds of times larger than silica, making them excellent candidates for ultrafast all-optical devices.

Bragg-grating-enhanced polarization instabilities.

Experiments demonstrate a dramatic decrease in polarization-instability threshold as an optical pulse is tuned near the short-wavelength edge of the photonic bandgap formed by a fiber Bragg grating. These enhanced nonlinear interactions and birefringent effects are modeled with coupled-mode numerical simulations. Nonlinearities are shown to increase much more rapidly than the effective birefringence as the pulse wavelength approaches the bandgap edge.

Normal human serum contains natural antibodies reactive with autologous ABO blood group antigens.

It is widely accepted that the serum of healthy individuals contains natural antibodies only against those blood group A or B antigens that are not expressed on the individual's red blood cells. The mechanisms involved in tolerance to autologous blood group antigens remain unclear. In the present study, we show that IgM and IgG antibodies reactive with autologous blood group antigens are present in the immunoglobulin fraction of normal human serum. Natural IgG anti-A antibodies purified by affinity chromatography from IgG of individuals of blood group A exhibited an affinity for A trisaccharide antigen in the micromolar range and agglutinated A red cells at sixfold higher concentrations than those required for agglutination with affinity-purified anti-A IgG of individuals of blood group B. Whereas autoantibodies reactive with self A and B antigens are readily detected in purified IgG and IgM fractions, their expression is restricted in whole serum as a result of complementary interactions between variable regions of antibodies. These observations suggest that tolerance to autologous ABO blood group antigens is dependent on peripheral control of antibody autoreactivity.

Grating resonances in air-silica microstructured optical fibers.

We report what is believed to be the first demonstration of optical fiber gratings written in photonic crystal fibers. The fiber consists of a germanium-doped photosensitive core surrounded by a hexagonal periodic air-hole lattice in a silica matrix. The spectra of these gratings allow for a detailed characterization of the fiber. In particular, the gratings facilitate coupling to higher-order leaky modes. We show that the spatial distribution and the effective index of these modes are determined largely by the design of the lattice and that the grating spectra are unaffected by the refractive index surrounding the fiber. We describe these measurements and corresponding simulations and discuss their implications for the understanding of such air-hole structures.

Mechanisms of action of intravenous immune globulin in immune-mediated diseases.

Intravenous immune globulin (IVIG) exhibits a number of immunomodulatory properties that are mediated by the Fe portion of IgG and by the spectrum of variable (V) regions contained in the immune globulin preparations. Five predominant and non-exclusive mechanisms of action have been proposed to account for the immunomodulatory effects of IVIG in immune-mediated diseases: (i) functional blockade of Fc receptors on splenic macrophages; (ii) inhibition of complement-mediated damage, an effect that is dependent on the ability of IgG to bind C3b and C4b and thus reduce the number of activated complement fragments that may deposit on target surfaces of complement activation; (iii) modulation of the production of cytokines and cytokine antagonists; (iv) neutralization of circulating autoantibodies by complementary (e.g. anti-idiotypic) antibodies in IVIG, a mechanism that accounts for the rapid decrease in titre of circulating autoantibodies that is often observed within hours following the infusion of IVIG; (v) selection of immune repertoires, a complex set of effects that may be observed in individuals receiving IVIG far beyond the half-life of the infused immunoglobulin and that is directly relevant to the ability of IVIG to, for example, suppress autoantibody-producing clones in patients with antibody-mediated autoimmune disease and modulate graft versus host disease (GVHD). IVIG has been shown to downregulate or activate B-cell clones expressing surface IgG that is complementary (anti-idiotypic) to V regions of antibodies present in IVIG. IVIG has been shown also to interact with surface molecules of T cells that are essential to immune regulation, such as the alpha beta TCR, CD5, CD4, non-polymorphic determinants of MHC class I molecules and adhesion molecules of T and B cells. The complex interactions of IVIG with functional molecules of cells of the immune system are relevant to its therapeutic effects in T cell- as well as B cell-mediated diseases and indeed, to our understanding of the physiological role of normal IgG and antibody networks in controlling autoreactivity in healthy individuals.

Immunoglobulins and the regulation of autoimmunity through the immune network.

Beneficial effects of the administration of intravenous immunoglobulins (IVIg) have now been reported in a large number of autoimmune diseases, whether mediated by autoantibodies or by autoaggressive T cells. We have proposed that the immunoregulatory effect of IVIg in autoimmune disease is dependent on the selection of the recipient's immune repertoires by the variable (V) region reactivities of infused immunoglobulins. Thus IVIg contains antibodies reactive with idiotypes of natural and disease-related autoantibodies and surface immunoglobulins of B cells; IVIg also contains antibodies reactive with the idiotype, framework and constant regions of the beta chain of the alpha beta T cell receptor. Infusion of IVIg results in transient or long lasting suppression of specific autoantibody clones in vivo and in stimulation of a distinct subset of B cells reactive with the F(ab')2 fragments of IVIg Infusion of IVIg alters the general "architecture" of the network as assessed by studying the kinetic patterns of spontaneous fluctuations of natural autoantibodies in serum. Infusion of normal mouse Ig in healthy adult mice selects expressed immune repertoire by removing late pre-B and B cells in the bone marrow, mostly those expressing D proximal Vh genes, and by activating distinct subsets of B cells and CD4+ T cells in the spleen. Although dependent on the V region reactivities (composition) or injected preparations, these effects probably also require that the infused immunoglobulin contains an intact Fc moiety. If one considers the effect of IVIg on the structure, function and dynamics of the immune network IVIg may be viewed as a substitutive therapy for the quantitative/qualitative defects in network regulation that are associated with autoimmune diseases.