A Novel Approach to Fiber-Optic Tweezers: Numerical Analysis of the Trapping Efficiency

We present a novel all-fiber optical tweezer (OT) for biological applications. The tweezer is based on a new approach relying on total internal reflection in an annular core fiber or into a fiber bundle. The proposed device, whose trapping efficacy has been recently demonstrated experimentally, is extremely promising, also because optical manipulation and analysis functions can be easily added to the tweezer basic structure, leading to the realization of a powerful biotool. In this paper, a detailed numerical analysis of the structure properties and of its efficiency is carried out in the Mie regime. Moreover, by defining a new parameter to evaluate the trapping efficiency, we perform a comparison between the proposed tweezer structure and a standard OT based on a strongly focused Gaussian beam.     

Minimally invasive surgery with the Port-Access method. Preliminary experience

METHODS: Data from the initial experience of 40 patients operated on with the Port-Access technique are reported. Indication to surgery was mitral disease in 24 patients and coronary stenosis in 16 patients. Mean age was 52 years (range 32-75). Operations performed were: 8 mitral valvuloplasties, 16 valve replacements, 9 single CABG (associated with an MVR in one case), 1 double CABG, 6 triple CABG and one quadruple CABG. Coronary endarterectomy was performed in 5 patients and left atrial isolation was associated with MV surgery in 5 cases. RESULTS: There were no operative deaths and every patient was discharged after a mean postoperative stay of 5.5 days (range 3-30). Postoperative course was complicated in 7 patients: surgical revision was necessary in 4 patients due to bleeding (through the mini-thoracotomy incision in 3 cases), 1 pacemaker was implanted for A-V block, one retained pulmonary catheter was removed through the mini-thoracotomy without the aid of cardiopulmonary bypass and in one case, there was an emergency conversion to median sternotomy due to a ventricular fibrillation unresponsive to usual resuscitative maneuvers a few hours after surgery. Some of these complications can be ascribed to the learning phase of this new technique and should disappear as experience is increased. CONCLUSIONS: Port-Access surgery is a new minimally invasive technique that utilizes a cardiopulmonary bypass with femoral access and a specialized catheter system that provides endoaortic clamping, pulmonary artery venting and myocardial preservation with infusion of cardioplegic solution in the aortic bulb or in the coronary sinus. Major contraindications to this technique are iliac-femoral disease or severe dilatation of ascending aorta. The aim of the Port-Access technique is to combine the aesthetic and functional advantages of the minimally invasive surgery with the wide range of surgical options that cardiopulmonary bypass can afford (to operate on atrioventricular valves and perform all the CABG that the patient need), without the limitations characteristic of the classic minimally invasive direct coronary artery bypass (MIDCAB) technique.     

Acoustofluidic separation: impact of microfluidic system design and of sample properties

We describe the results of a numerical study about the separation of fluid-suspended microsamples (as microbeads and cells) by acoustophoresis. A microfluidic channel with rectangular cross section is considered, and we investigate the impact on particle separation of many different parameters, dividing them in two groups: sample’s intrinsic factors (own properties of the sample) and extrinsic factors (related to the microfluidic system design and operation). Differently from what is usually done, we include in our study the impact of the initial sample position, which always has a certain variability in real experiments, and we introduce several new parameters allowing to assess system performance and to optimize the microchip separation efficiency. The obtained results show the importance of two design parameters that are generally overlooked: the channel width and the offset between the channel border and the input of the target samples in the microchannel. Additionally, the analysis method we describe and the new parameters we introduce to study the system can be beneficially used in almost any study of acoustophoretic-based separation system.     

Field demonstration of in-line all-optical wavelength conversion in a WDM dispersion managed 40-Gbit/s link

The development of wavelength-division multiplexing (WDM) all-optical transport networks is an interesting solution to increase the capacity of long-haul transmission systems and to solve the route-exhaust problems of metropolitan networks, driving down the cost of that traffic. Routing can be achieved using a transparent device able to select and interchange wavelengths, such as an all-optical wavelength converter. In this paper, an optical transport network over an embedded link located between Rome and Pomezia in Italy is emulated. The transmission has been realized along a WDM, 5/spl times/100 km long, dispersion managed link at 40 Gb/s. The in-line rerouting process has been controlled by means of an all-optical wavelength converter realized with a periodically poled lithium niobate waveguide. Moreover, a polarization-independent scheme for the converter has been exploited to allow the in-line signal processing. This scheme is based on the counterpropagation of TE and TM signal components along the same guide and results extremely compact. In this paper it is demonstrated that wavelength conversion and rerouting add no penalty with respect to the simple transmission along the embedded cable. This result seems to be another step toward the feasibility of true all-optical networks.     

Experimental demonstration of nonlinearity and dispersion compensation in an embedded link by optical phase conjugation

We report in this letter, the experimental demonstration of simultaneous dispersion and nonlinearity compensation in an embedded link characterized by strongly asymmetrical power profiles. This result is obtained by using a highly efficient optical phase conjugator based on a periodically poled lithium-niobate waveguide, combined with two small dispersion-compensating elements properly inserted in the link.     

Techniques for nonlinearity cancellation into embedded links by optical phase conjugation

One of the main causes of signal degradation in high-bit-rate transmission systems is the interplay between fiber nonlinear effects and dispersion. Different techniques to compensate nonlinear effects in transmission systems, by using an optical phase conjugator, have been proposed in the literature. In this paper, two different innovative setups allowing nonlinearity cancellation in an embedded link are disclosed. The proposed schemes are simpler than those previously described and strongly improve systems performances. The physical mechanism allowing nonlinearity compensation is depicted, and the effectiveness of the proposed solutions is numerically demonstrated. Moreover a new practical method, useful for performance optimization of systems including a phase conjugator, is presented. Results apply to any bit-rate and modulation format.     

All-Optical Wavelength Conversion of a Chaos Masked Signal

Wavelength conversion in the transmission of a message masked by optical chaos is experimentally demonstrated. In our setup, chaos is generated by a distributed-feedback laser subject to delayed optical feedback, and hides a message by additive chaos masking. The optical wavelength is converted, along the transmission line, by four-wave mixing in a semiconductor optical amplifier. At the receiver, the message is extracted by master-slave synchronization. Our experiments demonstrate that secure communications based on chaos are compatible with channel switching as required in reconfigurable optical networks.