Non-paraxial design and fabrication of a compact OAM sorter in the telecom infrared.

A novel optical device is designed and fabricated in order to overcome the limits of the traditional sorter based on log-pol optical transformation for the demultiplexing of optical beams carrying orbital angular momentum (OAM). The proposed configuration simplifies the alignment procedure and significantly improves the compactness and miniaturization level of the optical architecture. Since the device requires to operate beyond the paraxial approximation, a rigorous formulation of transformation optics in the non-paraxial regime has been developed and applied. The sample has been fabricated as 256-level phase-only diffractive optics with high-resolution electron-beam lithography, and tested for the demultiplexing of OAM beams at the telecom wavelength of 1310 nm. The designed sorter can find promising applications in next-generation optical platforms for mode-division multiplexing based on OAM modes both for free-space and multi-mode fiber transmission.

Total angular momentum sorting in the telecom infrared with silicon Pancharatnam-Berry transformation optics.

Parallel sorting of orbital angular momentum (OAM) and polarization has recently acquired paramount importance and interest in a wide range of fields ranging from telecommunications to high-dimensional quantum cryptography. Due to their inherently polarization-sensitive optical response, optical elements acting on the geometric phase prove to be useful for processing structured light beams with orthogonal polarization states by means of a single optical platform. In this work, we present the design, fabrication and test of a Pancharatnam-Berry optical element in silicon implementing a log-pol optical transformation at 1310 nm for the realization of an OAM sorter based on the conformal mapping between angular and linear momentum states. The metasurface is realized in the form of continuously variant subwavelength gratings, providing high-resolution in the definition of the phase pattern. A hybrid device is fabricated assembling the metasurface for the geometric-phase control with multi-level diffractive optics for the polarization-independent manipulation of the dynamic phase. The optical characterization confirms the capability to sort orbital angular momentum and circular polarization at the same time.

A surface acoustic wave (SAW)-enhanced grating-coupling phase-interrogation surface plasmon resonance (SPR) microfluidic biosensor.

A surface acoustic wave (SAW)-enhanced, surface plasmon resonance (SPR) microfluidic biosensor in which SAW-induced mixing and phase-interrogation grating-coupling SPR are combined in a single lithium niobate lab-on-a-chip is demonstrated. Thiol-polyethylene glycol adsorption and avidin/biotin binding kinetics were monitored by exploiting the high sensitivity of grating-coupling SPR under azimuthal control. A time saturation binding kinetics reduction of 82% and 24% for polyethylene and avidin adsorption was obtained, respectively, due to the fluid mixing enhancement by means of the SAW-generated chaotic advection. These results represent the first implementation of a nanostructured SAW-SPR microfluidic biochip capable of significantly improving the molecule binding kinetics on a single, portable device. In addition, the biochip here proposed is suitable for a great variety of biosensing applications.

Generation of high-order Laguerre-Gaussian modes by means of spiral phase plates.

Spiral phase plates for the generation of Laguerre-Gaussian (LG) beam with non-null radial index were designed and fabricated by electron beam lithography on polymethylmethacrylate over glass substrates. The optical response of these phase optical elements was theoretically considered and experimentally measured, and the purity of the experimental beams was investigated in terms of LG modes contributions. The far-field intensity pattern was compared with theoretical models and numerical simulations, whereas interferometric analyses confirmed the expected phase features of the generated beams. The high quality of the output beams confirms the applicability of these phase plates for the generation of high-order LG beams.

Grating-coupled surface plasmon resonance in conical mounting with polarization modulation.

A grating-coupled surface plasmon resonance (GCSPR) technique based on polarization modulation in conical mounting is presented. A metallic grating is azimuthally rotated to support double-surface plasmon polariton excitation and exploit the consequent sensitivity enhancement. Corresponding to the resonance polar angle, a polarization scan of incident light is performed, and reflectivity data are collected before and after functionalization with a dodecanethiol self-assembled monolayer. The output signal exhibits a harmonic dependence on polarization, and the phase term is used as a parameter for sensing. This technique offers the possibility of designing extremely compact, fast, and cheap high-resolution plasmonic sensors based on GCSPR.

Nanoporous gold plasmonic structures for sensing applications.

The fabrication, characterization and functionalization of periodically patterned nanoporous gold layers is presented. The material shows plasmonic properties in the near infrared range, with excitation and propagation of surface plasmon polaritons. Functionalization shows a marked enhancement in the optical response in comparison with evaporated gold gratings, due to a great increase of the active surface. Due to its superior response, nanoporous gold patterns appear promising for the realization of compact plasmonic platforms for sensing purposes.

Sensitivity enhancement in grating coupled surface plasmon resonance by azimuthal control.

We present a method for improving the sensing capability of grating coupled surface plasmon resonance (GCSPR) sensors. The grating is rotated azimuthally (phi) until the excitation of double surface plasmon polaritions (SPPs) by a single wavelength is possible. Close to this condition, further tuning of the incident wavelength will merge the double SPPs into a multi-SPP resonance which is angularly broad but spectrally sharp. This is the condition where the momentum vector of the propagating SPP is perpendicular to the incident light momentum. We demonstrate this sensitivity enhancement on a Au grating surface using a dodecanethiol (C12) self-assembled monolayer (SAM). Using this method, a shift in resonance angle as large as 3 degrees can be observed. The simulated sensitivity of this method shows that a sensitivity up to 800 degrees /RIU is achievable, which is one order of magnitude greater than that in a conventional fixed grating (phi = 0 degrees ) as well as the prism-coupled Kretschmann configuration.

The use of laser-nephelometry in evaluating fibrinogenaemia in patients with hepatocarcinoma and cirrhosis.

In the present study fibrinogen was assayed by the immunonephelometric method in 19 patients afflicted with hepatocarcinoma and 24 patients afflicted with cirrhosis. The two groups were similar in age, sex and presence of HbsAg. The incidence of values above the norm was significantly greater in patients with hepatocarcinoma (p less than 0.05). Then, the concentration of fibrinogen was measured in all using two other immunological methods (Laurell and Mancini) and two coagulative methods (Clauss and Ratnoff). A dysfibrinogenemia (an excess of fibrinogen assayed by immunological methods to be greater than 100 mg/dl with respect to biological methods). is more frequent using the Nephelometer-Clauss (p less than 0.01) and Mancini-Clauss (p less than 0.01) methods in patients with hepatocarcinoma with respect to those with cirrhosis. The study of the kinetics of antifibrinogen antigen-antibody reaction failed to show differences between patients with hepatocarcinoma or cirrhosis and normal subjects.

Clotting changes in Cushing's syndrome: elevated factor VIII activity.

Thirteen women and 2 men affected by Cushing's syndrome were investigated. The following parameters were used: plasma and urinary cortisol levels, factor VIII assay (antigen, activity and von Willebrand factor) together with other coagulative assays. Samples were taken before surgery or before medical and/or radiation therapy and every 30-50 days after treatment and continued for 11 months. Cortisol and factor VIII were increased before treatment and decreased slowly after treatment to become normal in 3-4 months. Other clotting tests did not show any significant changes. High plasma cortisol levels seem to stimulate the production of factor VIII. Patients with Cushing's syndrome often exhibit thromboembolic complications after surgery. The clotting abnormalities responsible for such complications may be due to increased factor VIII activities.

Prothrombin antigen evaluation by means of laser nephelometry in health and disease.

Prothrombin antigen concentration was evaluated by means of laser nephelometry in 10 patients on coumarin therapy, in 17 patients with cirrhosis of the liver, and in four patients with congenital hypo- or dysprothrombinemias. The average values obtained were 46.4, 37.7, and 35.6%, respectively, for anticoagulated, cirrhotic, and congenitally abnormal patients. These values correlated well with those obtained by means of electroimmunoassay (Laurell) and immunodiffusion (Mancini) methods. Similarly, satisfactory results were obtained in eight normal subjects. Multiple evaluations at different incubation times, also allowed the authors to construct kinetic curves of the interaction between antigen and antibody. However, an abnormal kinetic curve was demonstrated only for coumarin-treated patients.

Factor VII Padua defect: the heterozygote population.

14 heterozygote patients, belonging to three families with factor VII Padua defect were investigated. All patients were asymptomatic but presented a mild prolongation of prothrombin time. Factor VII activity varied between 45 and 61% of normal and no overlap was found with the homozygous or the normal populations. On the contrary, factor VII cross-reacting material was normal. A good negative correlation was found between factor VII level and prothrombin times. All patients came from the same valley of northeastern Italy. This valley, the Piave river valley, is not far from the valley where the factor X Friuli defect was found. The significance of this peculiar geographical distribution of the two abnormalities is unknown.

Differences between normal antithrombin III and antithrombin III Padua as determined by laser nephelometry.

Laser nephelometry was used to characterize an abnormal antithrombin III (AT III Padua) in comparison with normal antithrombin. Heparinized (0.2 IU/ml) or non-heparinized AT III Padua plasma reacts with Laser nephelometry antithrombin III antiserum in a different way compared with pooled normal plasma. There is in fact a slower antigen-antibody reaction during the first 40-45 min both in AT III Padua heparinized and non-heparinized plasmas, compared with pooled normal plasma; then the kinetics overlap. On the contrary the concentrations of antithrombin III Padua in percent correlate well with those obtained by Mancini's and Laurell's methods. These data indicate that Laser nephelometry is suitable for AT III antigen determinations and may also supply useful information for the characterization of abnormal clotting factors.