60 dB high-extinction auto-configured Mach-Zehnder interferometer.

Imperfections in integrated photonics manufacturing have a detrimental effect on the maximal achievable visibility in interferometric architectures. These limits have profound implications for further technological developments in photonics and in particular for quantum photonic technologies. Active optimization approaches, together with reconfigurable photonics, have been proposed as a solution to overcome this. In this Letter, we demonstrate an ultrahigh (>60 dB) extinction ratio in a silicon photonic device consisting of cascaded Mach-Zehnder interferometers, in which additional interferometers function as variable beamsplitters. The imperfections of fabricated beamsplitters are compensated using an automated progressive optimization algorithm with no requirement for pre-calibration. This work shows the possibility of integrating and accurately controlling linear-optical components for large-scale quantum information processing and other applications.

The isolation and partial characterization of chondronectin, an attachment factor for chondrocytes.

We have previously demonstrated that the adhesion of embryonic chick sternal chondrocytes to a type II-collagen substrate is not mediated by fibronectin but rather by a distinct attachment factor which we have named chondronectin. Here we describe the isolation, properties, and biological activity of chondronectin prepared from chicken serum. Chondronectin is shown to be a glycoprotein with an estimated Mr = 180,000. After reduction, it migrates as subunits of Mr = 70,000. Antibodies directed against chondronectin inhibited the attachment of chondrocytes to type II collagen. Chondronectin is immunologically distinct from either fibronectin or laminin. Immunofluorescence studies on frozen sections of embryonic chick sternal cartilage and of cultured sternal chondrocytes showed that chondronectin is cell-associated rather than a major matrix component.

Interaction of fibronectin with collagen fibrils.

The interaction of fibronectin with native collagen during collagen fibril formation was investigated. Fibronectin prepared from serum, or from the cell surface, bound to the forming collagen fibrils while less fibronectin bound to preformed fibers. Denatured collagen competed with native collagen in binding fibronectin. Fibronectin delayed the precipitation of collagen fibrils but did not alter the total amount of fibrils formed. Fibronectin which was heated to 30 degrees C for 30 min did not promote cell adhesion but still bound to native collagen and delayed fiber formation. The collagen-binding fragment of fibronectin produced by digestion either with chymotrypsin or with neutrophil elastase had a similar effect in delaying fibril formation, but the cell-binding fragment was not active. These studies indicate that fibronectin can bind to aggregating collagen fibers probably at the same site shown previously to bind to denatured collagen. Since fibronectin inhibits the rate of collagen fibrillogenesis, it may regulate the size of collagen fibers.