Engineering

Publication Search Results

Now showing 1 - 10 of 13
  • (2001) Malomed, Boris; Peng, Gang-Ding; Chu, Pak; Towers, Isaac; Buryak, Alexander; Sammut, Rowland
    Journal Article
    We present a review of new results which suggest the existence of fully stable spinning solitons (self-supporting localised objects with an internal vorticity) in optical fibres with selffocusing Kerr (cubic) nonlinearity, and in bulk media featuring a combination of the cubic selfdefocusing and quadratic nonlinearities. Their distinctive difference from other optical solitons with an internal vorticity, which were recently studied in various optical media, theoretically and also experimentally, is that all the spinning solitons considered thus far have been found to be unstable against azimuthal perturbations. In the first part of the paper, we consider solitons in a nonlinear optical fibre in a region of parameters where the fibre carries exactly two distinct modes, viz., the fundamental one and the first-order helical mode. From the viewpoint of application to communication systems, this opens the way to doubling the number of channels carried by a fibre. Besides that, these solitons are objects of fundamental interest. To fully examine their stability, it is crucially important to consider collisions between them, and their collisions with fundamental solitons, in (ordinary or hollow) optical fibres. We introduce a system of coupled nonlinear Schr¨ odinger equations for the fundamental and helical modes with nonstandard values of the cross-phase-modulation coupling constants, and show, in analytical and numerical forms, results of collisions between solitons carried by the two modes. In the second part of the paper, we demonstrate that the interaction of the fundamental beam with its second harmonic in bulk media, in the presence of self-defocusing Kerr nonlinearity, gives rise to the first ever example of completely stable spatial ring-shaped solitons with intrinsic vorticity. The stability is demonstrated both by direct simulations and by analysis of linearized equations.

  • (2006) Childs, Paul; Wong, Allan; Peng, Gang-Ding
    Journal Article
    The performance of a strain sensor system based on the use of carrier-modulated gratings and Fourier-domain decoding is analyzed. For three sensors, Young`s modulus is measured as 69.98 ± 0.27, 69.15 ± 0.81, and 70.65 ± 0.58 GPa. Crosstalk is shown to exist only when two sensors are designed with an overlap of the carrier band in the Fourier domain. Improving the data processing shows it is possible to limit this crosstalk to a value below that of the system error. © 2006 IEEE.

  • (2004) Kaalund, Christopher; Peng, Gang-Ding
    Journal Article
    The pole-zero diagram is a tool that has been widely employed in digital and electronic filter design. It greatly facilitates filter design by producing a simple and direct visualization of parametrical behaviors and general spectral characteristics. In this paper, we propose new methods of applying pole-zero diagrams to photonic filter design, aimed at tailoring spectral characteristics. In particular, we demonstrate the effectiveness of this method in designing ring resonator-based filters for application to optical wavelength interleavers; and deinterleavers. We show that there exist close relations between the pole-zero diagram of an optical filter and its wavelength response, and derive pole-zero diagrams for filters with various ring resonator configurations. Further, we propose a novel graphical technique using pole-zero diagrams for optimizing filter performance. As a practical example to demonstrate the effectiveness of the pole-zero approach, we present a new wavelength interleaver design with low crosstalk. This design was realized by superimposing the pole-zero diagrams of parallel and series-coupled ring resonator arrays.

  • (1999) Xiong, Zhengjun; Peng, Gang-Ding; Wu, B; Chu, Pak
    Journal Article
    The effects of the zeroth-order diffraction of a phase mask on the creation of Bragg gratings using the mask technique were theoretically and experimentally investigated. Experimental results showed that the zeroth-order diffraction of 1% total power, while in interference with the first-order diffraction of 44% each, dramatically affected the structure of the gratings in a polymer optical preform, including their period. Theoretical analysis by taking the zeroth-order diffraction into account predicted that a very small part of the zeroth-order component (0.1%) would have substantial effects on the gratings, which will be no longer uniform along both the directions of the incident laser beam propagation and the groove array. Theoretical calculation agrees well with the experimental results

  • (2008) Liu, K; Jing, W; Peng, Gang-Ding; Zhang, Jianzhong; Wang, Y; Liu, T; Jia, D; Zhang, H; Zhang, Y
    Journal Article
    Wavelength sweep technique (WST) is introduced into intracavity fiber laser (ICFL) for low concentration gas detection. The limitation induced by noise can be eliminated using this method, and the performance of the system is improved. The sensitivity of the system is reduced to less than 200 ppm. With WST, the sweeping characteristic of the ICFL can be described according to known gas absorption spectra.

  • (2001) Liu, H.; Peng, Gang-Ding; Chu, Pak
    Journal Article
    Bragg gratings in polymethyl methacrylate (PMMA)-based polymer fibers were created and were tuned thermally. It is found that the tuning range is more than 18 nm over a temperature variation of 50°C. More importantly, no hysteresis effect was observed as the gratings were heated up and cooled down .

  • (2007) Zhang, Jianzhong; Peng, Gang-Ding; yuan, l; Sun, W; Jin, W
    Journal Article
    A novel fiber-optic sensor unit by combining fiber-optic white-light interferometry and fiber Bragg gratings is proposed for simultaneous long- and short-gauge strain measurements. A new demodulation scheme based on spectral coherence theory for fiber-optic white-light interferometric sensors is proposed. This makes it possible that two quite different types of sensors in one unit can be simultaneously demodulated in the spectral domain. An experimental sensor unit has been built and tested. The results demonstrated that the spectral demodulation of the sensor unit is readily realized and that the sensor scheme is feasible.

  • (2002) Liu, Huiyong; Peng, Gang-Ding; Chu, Pak
    Journal Article
    Polymer fiber Bragg gratings (FBGs) with 28-dB transmission rejection and a line width less than 0.5 nm has been achieved for the first time. This result is achieved based on the systematic investigation of growth dynamics of polymer FBGs. We have observed that the growth of polymer FBGs bears some similarities to that of silica FBGs. This work links the mechanism of polymer fiber gratings formation to silica fiber grating and helps to gain better understanding of polymer fiber grating formation process

  • (2004) Liu, Hongbo; Peng, Gang-Ding; Chu, Pak; Liu, Huiyong
    Journal Article
    Some novel behaviors in fiber Bragg gratings (FBGs) growth have been observed when the polymer optical fiber are exposed to low-power level of ultraviolet (UV) irradiation. For the first time, we observed the growing and erasing of polymer FBGs under UV exposure, and regrowing after the UV exposure is OFF. The growth behaviors are quite different in contrast with the previously reported Type I and Type II polymer optical FBGs behaviors. This discloses that polymer FBG growth is a writing-power-dependent process.

  • (1999) Xiong, Zhengjun; Peng, Gang-Ding; Wu, B; Chu, Pak
    Journal Article
    A Bragg grating in a single-mode polymer optical fiber (POF) has been created. The novel grating has a length of 1 cm with a reflectivity of 80% and a linewidth of about 0.5 nm. The wavelength tunability of the POF grating by stretching was investigated and a wavelength tunable range of 20 nm has been achieved. Based on the properties of the polymer, we believe that this kind of grating has a wavelength tuning potential of more than 100 nm