Monitoring and control of polarization-related impairments in optical fiber systems

Polarization-related impairments have become a critical issue for high-data-rate optical systems, particularly when considering polarization-mode dispersion (PMD) and polarization-dependent loss (PDL). In general, polarization effects are stochastic processes and can occur on short or long time scales. Therefore, control and monitoring of these effects may be crucial in any systems-level mitigation. This tutorial will highlight the following key issues: PMD and PDL, monitoring schemes, emulation of proper statistics, interaction, and applications of polarization scrambling.     

Amplified chemiluminescence surface detection of DNA and telomerase activity using catalytic nucleic acid labels

A G-rich nucleic acid sequence binds hemin and yields a biocatalytic complex (DNAzyme) of peroxidase activity, namely, the biocatalyzed generation of chemiluminescence in the presence of H(2)O(2) and luminol. The DNAzyme is used as a label for the amplified detection of DNA, or for the analysis of telomerase activity in cancer cells, using chemiluminescence as an output signal. In one configuration, the analyzed DNA is hybridized with a primer nucleic acid that is associated with a Au surface, and the DNAzyme label is hybridized with the surface-confined analyte DNA. The DNA is analyzed with a detection limit of approximately 1 x 10(-)(9) M. In the second system, telomerase from HeLa cancer cells induces telomerization of a primer associated with a Au surface and the complementary DNAzyme units are hybridized with the telomere to yield the chemiluminescence. The detection limit of the system corresponds to 1000 HeLa cells in the analyzed sample.     

Actin-based metallic nanowires as bio-nanotransporters

The synthesis of conductive nanowires or patterned conductive nanoelements is a challenging goal for the future fabrication of nanoscale circuitry. Similarly, the realization of nanoscale mechanics might introduce a new facet to the area of nanobiotechnology. Here we report on the design of conductive and patterned actin-based gold nanowires, and on the ATP-driven motility of the nano-objects. The polymerization of G-actin labelled with Au nanoparticles, followed by the catalytic enlargement of the nanoparticles, yields gold wires (1-4 microm long and 80-200 nm high) exhibiting high electrical conductivity. The polymerization of the Au nanoparticle/G-actin monomer followed by the polymerization of free G-actin, or alternatively the polymerization of the Au-nanoparticle-labelled G-actin on polymerized F-actin followed by the catalytic enlargement of the particles, yields patterned actin-Au wire-actin or Au wire-actin-Au wire nanostructures, respectively. We demonstrate the ATP-fuelled motility of the actin-Au wire-actin filaments on a myosin interface. These actin-based metallic wires and their nanotransporting funcionality introduce new concepts for developing biological/inorganic hybrid devices.     

Time and frequency domain characteristics of polarization-modedispersion emulators

We investigate both experimentally and theoretically a new technique to realistically emulate polarization-mode dispersion (PMD). We propose and demonstrate a PMD emulator using rotatable connectors between sections of polarization-maintaining fibers that generates an ensemble of high PMD fiber realizations by randomly rotating the connectors. It is shown that: (1) the DGD of this emulator is Maxwellian-distributed over an ensemble of fiber realizations at any fixed optical frequency; and (2) the frequency autocorrelation function of the PMD emulator resembles that in a real fiber when averaged over an ensemble of fiber realizations. A realistic autocorrelation function is required for proper emulation of higher order PMD and indicates the feasibility of using this emulator for wavelength-division-multiplexing (WDM) systems     

A Shape Memory Acrylamide/DNA Hydrogel Exhibiting Switchable Dual pH‐Responsiveness

Shape memory acrylamide/DNA hydrogels include two different crosslinkers as stabilizing elements. The triggered dissociation of one of the crosslinking elements transforms the shaped hydrogel into an arbitrarily shaped (or shapeless) quasi‐liquid state. The remaining crosslinking element, present in the quasi‐liquid, provides an internal memory that restores the original shaped hydrogel upon the stimulus‐triggered regeneration of the second crosslinking element. Two pH‐sensitive shape memory hydrogels, forming Hoogsten‐type triplex DNA structures, are described. In one system, the shaped hydrogel is stabilized at pH = 7.0 by two different duplex crosslinkers, and the transition of the hydrogel into the shapeless quasi‐liquid proceeds at pH = 5.0 by separating one of the crosslinking units into a protonated cytosine–guanine–cytosine (C–G·C⁺ ) triplex. The second shaped hydrogel is stabilized at pH = 7.0, by cooperative duplex and thymine–adenine–thymine triplex (T–A·T) bridges. At pH = 10.0, the triplex units separate, leading to the dissociation of the hydrogel into the quasi‐liquid state. The cyclic, pH‐stimulated transitions of the two systems between shaped hydrogels and shapeless states are demonstrated. Integrating the two hydrogels into a shaped “two‐arrowhead” hybrid structure allows the pH‐stimulated cyclic transitions of addressable domains of the hybrid between shaped and quasi‐liquid states.     

Compensation for I/Q Imbalances and Bias Deviation of the Mach–Zehnder Modulators in Direct-Detected Optical OFDM Systems

We demonstrate an equalization technique to simultaneously compensate for the fiber chromatic dispersion and the distortions induced by the in-phase/quadrature-phase (I/Q) imbalances and bias deviation in the Mach-Zehnder modulators (MZMs). With this technique, the requirement for the monitoring circuits at the transmitter could be relaxed or even eliminated, and thus simplifies the system design and reduces the system cost. The system exhibits a good performance with our proposal over a broad range of imbalances and bias deviation in the MZM. With deliberately introducing I/Q imbalances and bias deviation, we have observed a 2- and 4-dB optical signal-to-noise ratio improvement, for the back-to-back and 800 km of uncompensated standard single-mode fiber transmission, respectively, with our proposed scheme.     

Light-Stimulated Formation and Dissociation of Supramolecular Donor–Acceptor Complexes between Eosin and Bipyridinium Azobenzenes: Design of Molecular Electronic Devices for the Piezoelectrical Transduction of Recorded Optical Signals

The photoisomerizable electron acceptors, trans-4,4′-bis(N-methylpyridinium)azobenzene, ( 1t ), and trans-3,3′-bis(N-methylpyridinium)azobenzene, ( 2t ), exhibit photoswitchable binding affinities to eosin. While the trans isomers, ( 1t ) or ( 2t ) exhibit high association affinities (K_a = 8.3 × 10³ M⁻¹ and 3.8 × 10⁴ M⁻¹, respectively), the cis isomers ( 1c ) or ( 2c ) reveal lower binding affinities (K_a = 3.4 × 10³ M⁻¹ and 1.4 × 10⁴ M⁻¹, respectively). The formation of the supramolecular donor–acceptor complexes between the eosin and the electron acceptors is associated with an absorbance change of the chromophore. This enables the cyclic spectroscopic transduction of the optically-induced formation and dissociation of the complexes upon photoisomerization between the respective trans and cis states. An eosin monolayer was assembled onto the Au-electrodes associated with a quartz piezoelectric crystal. The eosin-functionalized crystal was employed for the microgravimetric, quartz-crystal-microbalance analyses of the association of ( 1t ), ( 2t ), ( 1c ), or ( 2c ) to the crystal interface. The microgravimetric analyses allowed the characterization of the kinetics of association of the electron acceptors to the monolayer and the association constants between the isomers ( 1t ), ( 2t ), ( 1c ), and ( 2c ) with the eosin monolayer. By cyclic photoisomerization of the electron-acceptor between the trans and cis states, reversible piezoelectric transduction of the formation of the complexes with ( 1t ) or ( 2t ) at the monolayer interface, and their dissociation upon photoisomerization to ( 1c ) or ( 2c ) was accomplished.     

Limitations in 10 Gb/s WDM optical-fiber transmission when using avariety of fiber types to manage dispersion and nonlinearities

We analyze the system limitations of WDM transmission when using various types of optical fiber to manage dispersion and nonlinearities. In our model, from two to eight 10 Gb/s WDM channels are transmitted through a cascade of EDFA's experiencing dispersion, stimulated Raman scattering, and self- and cross-phase modulation. The fiber types modeled include: conventional single-mode fiber, dispersion shifted fiber, and dispersion-compensating fiber. These fibers have different dispersion spectral profiles and are combined to manage dispersion to produce a total zero dispersion for a certain fiber span while eliminating four-wave mixing. We find that a system using dispersion-shifted fiber and conventional single-mode fiber exhibits the best performance, with the combination of dispersion and cross-phase modulation as the dominant effects. Furthermore, conventional single-mode fiber combined with dispersion-compensating fiber system exhibits the worst performance, with the combination of dispersion and self-phase modulation as the dominant effects     

Transmission of many WDM channels through a cascade of EDFA's inlong-distance links and ring networks

We analyze the transmission of many wavelength-division-multiplexed (WDM) channels through a cascade of erbium-doped fiber amplifiers (EDFA) in both long-distance links and ring-based networks. For a megameter long-distance system, optimal operating conditions are found for achieving a high signal-to-noise ratio (SNR) per channel with as small an SNR differential as possible between 20 WDM channels spaced 0.5 nm apart. Critical issues addressed in this paper include: (a) the non-uniformity of the EDFA gain with wavelength: (b) the link loss between amplifiers; (c) the small-signal gain per amplifier; and (d) the input signal power