Frank P. Payne

Modification of the physical and optical properties of the frustule of the diatom Coscinodiscus wailesii by nickel sulfate

In this paper we demonstrate how the photonic properties of a diatom can be altered by growth with a metal pollutant. Both the optical and physical properties of the silica frustule of the diatom Coscinodiscus wailesii were affected by the presence of nickel sulfate in sea water. It was found that a sublethal concentration of the metal both significantly modified the size of the pores of the valves and quenched the intrinsic PL of the amorphous silica. Since cytoplasmic structures may be involved in determining the frustule architecture, we also present TEMs of nickel-grown diatoms and show the affected organelles. The ability to modify the properties of the frustule shows that mechanisms exist for the alteration of existing structures in nature to optimize specific characteristics for exploitation in biotechnological applications.

Derivation of an Analytical Expression for the Power Coupling Coefficient for Offset Launch Into Multimode Fiber

The demand for higher bandwidth in local area networks (LANs) has fuelled considerable research in techniques for mitigating modal dispersion in multimode fiber (MMF). These techniques include selective mode excitation, offset launching, angular multiplexing and electronic dispersion compensation, all of which strive to optimize the channel impulse response of a MMF. To obtain the optimal bandwidth-enhancement results from these techniques, knowledge of the distribution of power coupling coefficients given an arbitrary offset launch in a MMF is important. In this paper, an analytical expression for the power coupling coefficient for an incident Gaussian beam launched with a radial offset into a MMF having an infinite parabolic refractive index profile is derived. This expression is useful in understanding the parameters which may affect the power coupling coefficient and how they may enhance the MMF bandwidth. The power coupling coefficients obtained from the derived analytical expression are compared with numerical results and are in excellent agreement. The analytical expression may be extended to manufactured MMF.

The generation of 68 Gbps quantum random number by measuring laser phase fluctuations.

The speed of a quantum random number generator is essential for practical applications, such as high-speed quantum key distribution systems. Here, we push the speed of a quantum random number generator to 68 Gbps by operating a laser around its threshold level. To achieve the rate, not only high-speed photodetector and high sampling rate are needed but also a very stable interferometer is required. A practical interferometer with active feedback instead of common temperature control is developed to meet the requirement of stability. Phase fluctuations of the laser are measured by the interferometer with a photodetector and then digitalized to raw random numbers with a rate of 80 Gbps. The min-entropy of the raw data is evaluated by modeling the system and is used to quantify the quantum randomness of the raw data. The bias of the raw data caused by other signals, such as classical and detection noises, can be removed by Toeplitz-matrix hashing randomness extraction. The final random numbers can pass through the standard randomness tests. Our demonstration shows that high-speed quantum random number generators are ready for practical usage.The speed of a quantum random number generator is essential for practical applications, such as high-speed quantum key distribution systems. Here, we push the speed of a quantum random number generator to 68 Gbps by operating a laser around its threshold level. To achieve the rate, not only high-speed photodetector and high sampling rate are needed, but also a very stable interferometer is required. A practical interferometer with active feedback instead of common temperature control is developed to meet requirement of stability. Phase fluctuations of the laser are measured by the interferometer with a photodetector, and then digitalized to raw random numbers with a rate of 80 Gbps. The min-entropy of the raw data is evaluated by modeling the system and is used to quantify the quantum randomness of the raw data. The bias of the raw data caused by other signals, such as classical and detection noises, can be removed by Toeplitz-matrix hashing randomness extraction. The final random numbers can pass through the standard randomness tests. Our demonstration shows that high-speed quantum random number generators are ready for practical usage.

Pulse propagation in fibers with polarization-mode dispersion

The propagation of pulses in optical fibers with polarization mode dispersion (PMD) is considered. The approach taken differs from those previously used, adapting Marcuses perturbation method to analyze pulse dispersion rather than using Jones matrices or Stokes parameters. This allows the complex stochastic partial differential equations to be reduced to a simple propagation equation for the pulse power. This may be solved to obtain the transfer function of the fiber. The impact of PMD on optical fiber communications systems is considered, with the effect on pulsewidth and eye closure calculated. Finally, the statistical behavior of the phenomenon is considered to calculate the system outage probability due to PMD.

A General Framework for the Finite-Difference Time-Domain Simulation of Real Metals

We present an efficient framework for the finite-difference time-domain simulation of real metals. The complex permittivity function of a metal is fitted to experimental data in the frequency domain using a non-linear least squares algorithm. A memory-efficient finite-difference time-domain (FDTD) scheme is presented for the simulation of the dispersive behavior of a metal in the frequency domain. The stability limit for the proposed scheme is determined and compared to the Courant limit. Excellent agreement between our FDTD formulation and the analytical solution for reflections from a thin metal sheet is found

A Finite-Difference Time-Domain Method for the Simulation of Gain Materials With Carrier Diffusion in Photonic Crystals

In this paper, we present a finite-difference time-domain formulation for active gain materials. Our scheme is based on a frequency-dependent conductivity. Experimental material gain is fitted with high accuracy to a multipole Lorentzian model using a semideterministic fitting algorithm. Because our model is an approximation to the full vectorial Maxwells system of equations, we include carrier diffusion into the rate equations for a two-level system. The material gain is included into the standard set of Maxwells equations by linking the frequency-dependent conductivity to the rate equations. Lasing is demonstrated for a vertical-cavity-surface-emitting-laser structure and photonic crystal lasers.

Theory and Design of Adiabatically Tapered Multimode Interference Couplers

Tapered-multimode-interference (MMI) splitters and couplers result in more compact designs than conventional MMI devices. In this paper, we analyze the adiabatic limit of the tapered MMI and present new designs that are both compact and result in minimal loss

Estimating Outages Due to Polarization Mode Dispersion Using Extreme Value Statistics

Polarization mode dispersion (PMD) is a time varying phenomenon, which in a network can result in system outages. In this paper, it is demonstrated that the method of extreme value statistics can be used to model the occurrence of these rare events. The extreme value behavior of the bit error rate (BER) due to PMD is analyzed both theoretically and experimentally, revealing that the logarithm of the BER follows a Gumbel distribution

Gain equalization of a six-mode-group ring core multimode EDFA

We propose a 6-mode-group ring core multimode erbium doped fiber amplifier (RC-MM-EDFA) capable of providing almost identical gain among the six mode groups within the C band using either core- or cladding-pumped implementations.

Linearly polarized mode division multiplexed transmission over ring-index multimode fibres

LP modes in ring-index multimode fibres (RI-MMFs) are proposed to carry parallel-data for spatial multiplexing systems with low-complexity MIMO processing. Simulation shows that, with 3×3MIMO, 6×20Gb/s NRZ error-free transmission is achieved over 1km-RI-MMFs using IMDD.