Spectrum of the Intensity of Modulated Noisy Light After Propagation in Dispersive Fiber

The spectral density of the optical intensity which results after modulated noisy light is propagated in dispersive single-mode fiber is investigated theoretically and experimentally. An exact general result is obtained for the case of lowest-order-only group velocity dispersion and is applied to light from a 1550-nm distributed-feedback semiconductor laser which is large-signal phase modulated and then propagated through 50 km of standard single-mode fiber. Experimental results demonstrate the effect of dispersion on the intensity spectrum (and thus, on lightwave system characteristics such as modulation response, relative intensity noise, carrier-to-noise ratio, and harmonic distortion) in this situation and provide confirmation of the theoretical results

Laser phase noise to intensity noise conversion by lowest-order group-velocity dispersion in optical fiber: exact theory

An exact result for the spectral density of intensity variations that occur after propagation of ergodic light in a medium having lowest-order-only group-velocity dispersion is obtained and applied to the problem of semiconductor laser phase noise to intensity noise conversion in a single-mode optical fiber. It is shown that the intensity spectrum after propagation formally approaches, for a large laser linewidth or a long (or high-dispersion) fiber, the intensity spectrum of a thermal source having the same line shape as the laser

Representation of second-order polarisation mode dispersion

A new expansion for the Jones matrix of a transmission medium is used to describe high-order polarisation dispersion. Each term in the expansion is characterised by a pair of principal states and the corresponding dispersion parameters. With these descriptors, a new expression for pulse deformation is derived and confirmed by simulation

Reduction of relative intensity noise of the output field of semiconductor lasers due to propagation in dispersive optical fiber

The effect of dispersive, linear propagation (e.g., in single-mode optical fiber) on the intensity noise from semiconductor lasers is investigated. Relations between the frequency and amplitude noise variations of semiconductor lasers are obtained from the laser rate equations and used to calculate the change in the relative intensity noise (RIN) spectrum that occurs during dispersive propagation. Propagation in fiber with positive dispersion (D>0) over moderate distances (several km for standard single-mode fiber at 1.55 mu m) is found to reduce the RIN over a wide range of frequencies. Measurements with a 1.56 mu m distributed feedback laser confirm the main theoretical results and demonstrate reductions in RIN of up to II dB with 4 km of standard fiber

Statistical determination of the length dependence of high-order polarization mode dispersion

We describe a method of characterizing high-order polarization mode dispersion (PMD).Using a new expansion to approximate the Jones matrix of a polarization-dispersive medium, we study the length dependence of high-order PMD to the fourth order. A simple rule for the asymptotic behavior of PMD for short and long fibers is found. It is also shown that, in long fibers (~1000 km), at 40 Gbits/s the third- and fourth-order PMD may become comparable to the second-order PMD

Discovery of a Spin-Down State Change in the LMC Pulsar B0540-69

We report the discovery of a large, sudden, and persistent increase in the spin-down rate of B0540-69, a young pulsar in the Large Magellanic Cloud, using observations from the Swift and RXTE satellites. The relative increase in the spin-down rate of 36% is unprecedented for B0540-69. No accompanying change in the spin rate is seen, and no change is seen in the pulsed X-ray emission from B0540-69 following the change in the spin-down rate. Such large relative changes in the spin-down rate are seen in the recently discovered class of 'intermittent pulsars', and we compare the properties of B0540-69 to such pulsars. We consider possible changes in the magnetosphere of the pulsar that could cause such a large change in the spin-down rate.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter

Numerical Studies of the Compressible Ising Spin Glass

We study a two-dimensional compressible Ising spin glass at constant volume. The spin interactions are coupled to the distance between neighboring particles in the Edwards-Anderson model with +/- J interactions. We find that the energy of a given spin configuration is shifted from its incompressible value, E_0, by an amount quadratic in E_0 and proportional to the coupling strength. We then construct a simple model expressed only in terms of spin variables that predicts the existence of a critical value of the coupling above which the spin-glass transition disappears.Comment: REVTeX, 4 pages, 4 figures. Submitted to Phys. Rev. Let

New East African Curculionidae Part I

Volume: XVI

Is FeedForward the way forward? A comparison of the effects of FeedForward coaching and Feedback.

Objectives: The FeedForward Interview (FFI) is a means of structuring conversations (Kluger & Nir, 2006), such as performance appraisals, or indeed coaching in organisations. Conceptually situated in a positive psychological paradigm, FFI techniques build on appreciative inquiry (Cooperrider & Srivastva, 1987), positive psychology (Seligman & Csikszentmihalyi, 2002) and Feedback Intervention Theory (Kluger & DeNisi, 1996). The objective of this research was to investigate how FFI affects individual outcomes compared to traditional feedback as part of a coaching session. Design: We conducted a quasi-experimental longitudinal study allocating 54 participants randomly to either a FFI or Feedback-based coaching intervention. Methods: We measured self-efficacy, mood and strengths-confidence as well goal attainment before and after each intervention. Results: Self-efficacy significantly increased following FFI compared to feedback; participants were more likely to obtain their goals in the FFI condition. There were no significant differences for mood; and no main effects for strengths-knowledge but a significant interaction by treatment condition. Conclusions: The results indicate that FFI appears a valid intervention to facilitate positive psychological change as part of a coaching session. We discuss the potential for further research including the evaluation of transfer of learning arising from FFI in experimental paradigms as well as behavioural observations