Design of a flat-top fiber Bragg filter via quasi-random modulation of the refractive index

The statistics of the reflection spectrum of a short-correlated disordered fiber Bragg grating are studied. The averaged spectrum appears to be flat inside the bandgap and has significantly suppressed sidelobes compared to the uniform grating of the same bandwidth. This is due to the Anderson localization of the modes of a disordered grating. This observation prompts a new algorithm for designing passband reflection gratings. Using the stochastic invariant imbedding approach it is possible to obtain the probability distribution function for the random reflection coefficient inside the bandgap and obtain both the variance of the averaged reflectivity as well as the distribution of the time delay of the grating.

Multiwavelength fiber laser with fine adjustment, based on nonlinear polarization rotation and birefringence fiber filter

We have proposed and demonstrated a multiwavelength fiber laser based on nonlinear polarization rotation (NPR). The mechanism for stable room-temperature multiwavelength operation contributes to the ability of the intensity-dependent loss in NPR to effectively alleviate mode competition. In addition, through tuning the birefringence fiber filter, the lasing wavelength can be accurately tuned in the free spectrum range of the in-line periodic filter.

A network coding based interference cancelation scheme for wireless ad hoc networks

The performance of wireless networks is limited by multiple access interference (MAI) in the traditional communication approach where the interfered signals of the concurrent transmissions are treated as noise. In this paper, we treat the interfered signals from a new perspective on the basis of additive electromagnetic (EM) waves and propose a network coding based interference cancelation (NCIC) scheme. In the proposed scheme, adjacent nodes can transmit simultaneously with careful scheduling; therefore, network performance will not be limited by the MAI. Additionally we design a space segmentation method for general wireless ad hoc networks, which organizes network into clusters with regular shapes (e.g., square and hexagon) to reduce the number of relay nodes. The segmentation methodworks with the scheduling scheme and can help achieve better scalability and reduced complexity. We derive accurate analytic models for the probability of connectivity between two adjacent cluster heads which is important for successful information relay. We proved that with the proposed NCIC scheme, the transmission efficiency can be improved by at least 50% for general wireless networks as compared to the traditional interference avoidance schemes. Numeric results also show the space segmentation is feasible and effective. Finally we propose and discuss a method to implement the NCIC scheme in a practical orthogonal frequency division multiplexing (OFDM) communications networks. Copyright © 2009 John Wiley & Sons, Ltd.

MAP detection for impairment compensation in coherent WDM systems

We propose a novel recursive-algorithm based maximum a posteriori probability (MAP) detector in spectrally-efficient coherent wavelength division multiplexing (CoWDM) systems, and investigate its performance in a 1-bit/s/Hz on-off keyed (OOK) system limited by optical-signal-to-noise ratio. The proposed method decodes each sub-channel using the signal levels not only of the particular sub-channel but also of its adjacent sub-channels, and therefore can effectively compensate deterministic inter-sub-channel crosstalk as well as inter-symbol interference arising from narrow-band filtering and chromatic dispersion (CD). Numerical simulation of a five-channel OOK-based CoWDM system with 10Gbit/s per channel using either direct or coherent detection shows that the MAP decoder can eliminate the need for phase control of each optical carrier (which is necessarily required in a conventional CoWDM system), and greatly relaxes the spectral design of the demultiplexing filter at the receiver. It also significantly improves back-to-back sensitivity and CD tolerance of the system.

Filter assisted wavelength conversion with quantum-dot SOAs

The nonlinear operation regimes of quantum-dot semiconductor optical amplifiers (QD-SOAs) are investigated and the ideal filter providing the best all-optical wavelength conversion efficiency is derived theoretically. Results are confirmed by experiments with Q2-factors amounting to 16 dB.

All-fiber-integrated soliton-similariton laser with in-line fiber filter

We demonstrate an all-fiber-integrated Er-doped fiber laser operating in the soliton-similariton mode-locking regime. In the similariton part of the cavity, a self-similarly evolving parabolic pulse with highly linear chirp propagates in the presence of normal dispersion. Following an in-line fiber-based birefringent filter, the pulse evolves into a soliton in the part of the cavity with anomalous dispersion. The similariton and the soliton pulses are dechirped to 75.5 and 167.2 fs, respectively, outside of the cavity. Mode-locked operation is very robust, owing to the influence of the two similariton and soliton attractors that predominate each half of the laser cavity. The experimental results are supported with numerical simulations, which provide good agreement.

Chromatic dispersion effect in a microwave photonic filter using superstructured fiber Bragg grating and dispersive fiber

In this paper a microwave photonic filter using superstructured fiber Bragg grating and dispersive fiber is investigated. A theoretical model to describe the transfer function of the filter taking into consideration the spectral width of light source is established. Experiments are carried out to verify the theoretical analysis. Both theoretical and experimental results indicate that due to chromatic dispersion the source spectral width introduces an additional power penalty to the microwave photonic response of the filter.

Studying membrane trafficking in the worm C. elegans by RNA interference

A powerful approach to gain understanding of molecular machinery responsible for membrane trafficking is through inactivation of gene function by RNA interference (RNAi). RNAi-mediated gene silencing occurs when a double-stranded RNA is introduced into cells and targets a complementary mRNA for degradation. The subsequent lack of mRNA prevents the synthesis of the corresponding protein and ultimately causes depletion of a particular gene product from the cell. The effects of such depletion can then by analyzed by functional, morphological, and biochemical assays. RNAi-mediated knockdowns of numerous gene products in cultured cells of mammalian and other species origins have provided significant new insight into traffic regulation and represent standard approaches in current cell biology. However, RNAi in the multicellular nematode Caenorhabditis elegans model allows RNAi studies within the context of a whole organism, and thus provides an unprecedented opportunity to explore effects of specific trafficking regulators within the context of distinct developmental stages and diverse cell types. In addition, various transgenic C. elegans strains have been developed that express marker proteins tagged with fluorescent proteins to facilitate the analysis of trafficking within the secretory and endocytic pathways. This chapter provides a detailed description of a basic RNAi approach that can be used to analyze the function of any gene of interest in secretory and endosomal trafficking in C. elegans. © 2013 Elsevier Inc.

The embodied nature of spatial perspective taking:embodied transformation versus sensorimotor interference

Humans are able to mentally adopt the spatial perspective of others and understand the world from their point of view. We propose that spatial perspective taking (SPT) could have developed from the physical alignment of perspectives. This would support the notion that others have put forward claiming that SPT is an embodied cognitive process. We investigated this issue by contrasting several accounts in terms of the assumed processes and the nature of the embodiment. In a series of four experiments we found substantial evidence that the transformations during SPT comprise large parts of the body schema, which we did not observe for object rotation. We further conclude that the embodiment of SPT is best conceptualised as the self-initiated emulation of a body movement, supporting the notion of endogenous motoric embodiment. Overall our results are much more in agreement with an ‘embodied’ transformation account than with the notion of sensorimotor interference. Finally we discuss our findings in terms of SPT as a possible evolutionary stepping stone towards more complex alignments of socio-cognitive perspectives.

Bragg grating fast tunable filter for wavelength division multiplexing

A Bragg grating fast tunable filter prototype working over a linear tuning range of 45 nm with a maximum tuning speed of 21 nm/ms has been realized. The tunable filter system is based on two piezoelectric stack actuators moving a mechanical device thus compressing an apodized fiber Bragg grating. The filter allows both traction and compression and can work in transmission and in reflection. It is designed to work with a channel spacing of 100 GHz according to the ITU specifications for wavelength division multiplexing systems.

Fibre Bragg grating sensor interrogation using an acousto-optic tunable filter and low-coherence interferometry

We describe how an acousto-optic tunable filter can be used to both demultiplex the signals from multiple fibre Bragg grating sensors and simultaneously provide wide bandwidth signal demodulation in a system using interferometric wavelength shift detection. In an experimental demonstration, the approach provided a noise limited strain resolution of 24.9 nε Hz -1/2 at 15 Hz. © 2007 IOP Publishing Ltd.

Development of an electrically tuneable Bragg grating filter in polymer optical fibre operating at 1.55 νm

We present a thorough study on the development of a polymer optical fibre-based tuneable filter utilizing an intra-core Bragg grating that is electrically tuneable, operating at 1.55 νm. The Bragg grating is made tuneable using a thin-film resistive heater deposited on the surface of the fibre. The polymer fibre was coated via the photochemical deposition of a Pd/Cu metallic layer with the procedure induced by VUV radiation at room temperature. The resulting device, when wavelength tuned via Joule heating, underwent a wavelength shift of 2 nm for a moderate input power of 160 mW, a wavelength to input power coefficient of -13.4 pm mW-1 and time constant of 1.7 s-1. A basic theoretical study verified that for this fibre type one can treat the device as a one-dimensional system. The model was extended to include the effect of input electrical power changes on the refractive index of the fibre and subsequently to changes in the Bragg wavelength of the grating, showing excellent agreement with the experimental measurements. © 2007 IOP Publishing Ltd.

Multiwavelength fiber laser with fine adjustment, based on nonlinear polarization rotation and birefringence fiber filter

We have proposed and demonstrated a multiwavelength fiber laser based on nonlinear polarization rotation (NPR). The mechanism for stable room-temperature multiwavelength operation contributes to the ability of the intensity-dependent loss in NPR to effectively alleviate mode competition. In addition, through tuning the birefringence fiber filter, the lasing wavelength can be accurately tuned in the free spectrum range of the in-line periodic filter.

A novel tunable all-optical incoherent negative-tap fiber-optic transversal filter based on a DFB laser diode and fiber Bragg grating

We demonstrate experimentally a novel and simple tunable all-optical incoherent negative-tap fiber-optic transversal filter based on a distribution feedback laser diode and high reflection fiber Bragg gratings (FBGs). In this filter, variable time delay is provided by cascaded high reflection fiber Bragg gratings (FBGs), and the tuning of the filter is realized by tuning different FBG to match the fixed carrier wavelength, or adjusting the carrier wavelength to fit different FBG. The incoherent negative tapping is realized by using the carrier depletion effect in a distribution feedback laser diode.

Novel design of FBG-based composite double notch VSB filter for DWDM systems

This paper proposes a novel design of optical filters based on a cascade of tailored fiber Bragg gratings (FBGs) operating in the transmission regime. As an example of the application of the proposed general technique, ultranarrow optical vestigial sideband (VSB) filtering based on two FBGs operating in the transmission regime was examined. This design can be easily implemented by writing FBG-based filters for each wavelengthdivision-multiplexing channel before multiplexing. © 2006 IEEE.