Spliced-fiber mode filter for 1060-nm single-mode transmission

We present a novel mode filter operating for the 1060-nm band, which selectively removes the power of the high-order mode (HOM) from a conventional single-mode fiber (C-SMF) that supports two modes at the short-wavelength band. Our mode filter is fabricated very easily by fusion-splicing a short section of short-wavelength single-mode fiber in the middle of the C-SMF link. By using our spliced-fiber mode filter (SF-MF), a high HOM suppression performance of > 18 dB has been achieved with a low insertion loss of < 0.3 dB over the full band of optical communications from 1050 nm to 1650 nm. We have also developed a new mode power measurement scheme that takes advantage of the bending sensitivity of the HOM guidance. This measurement scheme enabled us to evaluate accurately the performance factors of the fabricated mode filter.     

A CTRW-based model of time-resolved fluorescence lifetime imaging in a turbid medium

We develop an analytic model of time-resolved fluorescent imaging of photons migrating through a semi-infinite turbid medium bounded by an infinite plane in the presence of a single stationary point fluorophore embedded in the medium. In contrast to earlier models of fluorescent imaging in which photon motion is assumed to be some form of continuous diffusion process, the present analysis is based on a continuous-time random walk (CTRW) on a simple cubic lattice, the objective being to estimate the position and lifetime of the fluorophore. This can provide information related to local variations in pH and temperature with potential medical significance. Aspects of the theory were tested using time-resolved measurements of the fluorescence from small inclusions inside tissue-like phantoms. The experimental results were found to be in good agreement with theoretical predictions provided that the fluorophore was not located too close to the planar boundary, a common problem in many diffusive systems.     

A novel technique for measurement of self-generated magnetic fields and the plasma density in laser produced plasmas from the Faraday rotation using two color probes

Diagnostic information about the self-generated magnetic fields (SGMF) generated in laser produced plasmas is normally obtained by measuring the Faraday rotation angle (FRA) of a linearly polarized laser probe beam passing through the plasma. Simultaneous recording of the corresponding interferogram is required to get the density information necessary for estimating the magnetic field. The problem with this method is that the visibility of the fringes in the interferogram can be poor, and the SGMF cannot be calculated in the regions where the interference fringes are not observable. In this paper, we propose a new method to obtain the density distribution and the SGMF from two simultaneous measurements of FRA using two probe beams of different colors, which allows one to calculate the SGMF without the need of interferometry.     

Gradient echo memory in a tripod-like dense atomic medium

We analyze the storage and retrieval of a weak light pulse, having two orthogonally (circularly) polarized components, onto an atomic ensemble of four-level atoms of the tripod type driven by a far detuned coupling field. The atoms are subject to a longitudinal magnetic field which produces a spatially varying Zeeman splitting of the lower levels along the medium and allows for a spatial encoding of the different angular frequencies of the input pulse during the storage phase. A single reversion of the external magnetic field results in a rephasing of the dipoles and leads to the release of the stored signals. The shape of the recovered pulse is a time-reversal copy of the input pulse. The application of an additional reversion of the magnetic field during the storage phase allows the release of a copy of the input pulse without time reversal. We also show that the system may operate like an all-optical multiplexer when considering two impinging optical fields which have orthogonal components. The proposal has potential applications in quantum information processing.     

Lateral diffusion of the topological charge density in stochastic optical fields

Stochastic (i.e. random and quasi-random) optical fields may contain distributions of optical vortices that are represented by non-uniform topological charge densities. Numerical simulations are used to investigate the evolution under free-space propagation of topological charge densities that are inhomogeneous along one dimension. It is shown that this evolution is described by a diffusion process that has a diffusion parameter which depends on the propagation distance.     

Dipole solitons in an optical lattice with longitudinal modulation

In this paper, we numerically demonstrate the (1+1)-dimensional dipole solitons can exist in a new Kerr-type optical lattice with longitudinal modulation that fades away and boosts up alternately. The solitons whose two dipoles simultaneously located at one lattice site and at two adjacent lattice sites are investigated, respectively. The results show that, in the two cases, the dipole solitons can be stably trapped in this kind of lattice by properly adjusting lattice parameters and soliton parameters when the repulsive force of dipoles balances the centripetal force resulting from the lattice potential effect on dipole solitons. In addition, the trapping of dipole solitons with an incident angle or the initial center position is discussed.     

Implementing minimal clock skew Directed Logic

Although the physics of computing allows the possibility of logic operations with no energy dissipation, over 40 years of work by brilliant scientists in many fields has not achieved it. The solution described here required breaking from the tacit assumptions that logic gates had to be electronic. The system is implemented entirely with passive optical components. Also needed was a logic that could utilize those passive components. Hardy and Shamir showed how to map a Boolean logic problem into a form suitable to be implemented by light flowing through various paths and cascaded as needed. This paper examines a modular approach to implementing their approach (called Directed Logic) in an integrated optical system. We start from unit cells, implementing a dynamic flip-flop principle and combine the cells in a network or “logic fabric.” Contrary to proofs by the founders of this field, speed is limited only by the message bandwidth of the optical signal, and, of course, no energy is dissipated. There are still aspects that need additional work on issues like accuracy using analog components and size relative to electronics. But the basic problem is solved at last and paths toward solving the remaining problems have been identified.     

Fast and slow light generated simultaneously for up-down-link frequency converter applications

We firstly propose a new system for simultaneous fast and slow light generation using a soliton pulse propagating within the nonlinear micro-ring resonators. The nonlinear Kerr effect induces the spreading frequency bands within the micro-ring device, where the chaotic filtering characteristics can be employed using the appropriate micro-ring parameters. Results obtained have shown that the wide spreading of frequency bands can be generated and selected to form the optical wireless communication links. In this work, the selected down-link and up-link frequency bands are 500 MHz and 2 GHz, respectively. The proposed system can be implemented within the mobile telephone hand set, where the two different frequency carriers within the same frequency bands can be selected to form the up-down-link converters, which means that the frequency converter can be performed within a single system.     

The position independence of heterostructure coupled waveguides in photonic-crystal switch

Based on studying the propagation states of electromagnetic waves in heterostructure coupled waveguides produced by appropriately modulating the refractive index of rods, the realization of photonic-crystal switch is analyzed and the position effect of the heterostructure coupled waveguides on the switch function is investigated. The simulation results show that the output state is the result of the integral effect of different coupling regions; therefore, the switch function is independent on the distribution of heterostructure coupled waveguides. This property will bring great flexibility to fabricate photonic-crystal switch in practice.