Alan L. Steele

Analysis of optical instabilities and bistability in a nonlinear optical fibre loop mirror with feedback

Abstract The dynamics of a nonlinear optical fibre loop mirror with feedback and a CW input is examined. The device, first investigated by Shi, Optics Comm. 107 (1994) 276, using a graphical technique, is re-examined using linear stability analysis and iterative methods. Results show that the known bistable behaviour of the device can be affected by Ikeda instabilities. We also report that more than one method of analysis is required to fully classify the dynamical behaviour of the device.

Low-cost, rapid prototyping of IMU and pressure monitoring system using an open source hardware design

Open source hardware is a type of hardware where the schematics and designs are made unrestricted and available to all. They are often accompanied by open source software. This can bring reliability, ease of debugging, and modular development for rapid prototyping using pre-written libraries. Merits of using open source hardware are discussed and then applied to a portable sensor system based on the open hardware Arduino-derived Jeenode microcontroller board. The system uses an inertial measurement unit (IMU) and seamless integration of other sensors, including a piezo-resistive pressure sensor. It is shown that open source hardware can help to increase rapid development, reduce costs, and encourage further development.

Nonlinear optical loop mirror constructed from dispersion decreasing fibre

The performance of a nonlinear optical loop mirror (NOLM) composed of a fibre with axially varying dispersion profile is investigated numerically. Results show a departure from the standard NOLM behaviour, including self-switching when a symmetric coupler is used. Furthermore, if there is an asymmetric coupler then results show that the energy transfer characteristics vary depending on which of the two input ports is used.

Controlling chaos in nonlinear optical resonators

Abstract This article presents an analytical method for controlling the chaos in two nonlinear bistable optical resonators. The devices are a bulk cavity ring oscillator and a nonlinear simple fibre ring resonator. It is shown that there is a trade-off between flexibility and controllability in such devices. For the first time, as far as the authors are aware, theoretical studies have shown that by controlling the chaos within a bistable region it becomes possible to use a previously unstable device as a bistable resonator.

Corrections To And Comments On "Dynamic Behavior Of Re Ection Optical Bistability In A Nonlinear Fiber Ring Resonator"

In the above paper on a transient analysis based on the multiplebeam interference method [1], some errors have been discovered. In this note, we detail corrections and discuss the validity of the multiple-beam interference method by comparison with another numerical method. Initially, we correct the mistakes in the analysis. The problem lies in the calculation of the total nonlinear phase shift of the partial wave entering the ring resonator at time t m R and leaving it at time t after the mth circulation. In the text, the nonlinear phase change suffered during each circulation was calculated using the intracavity field at the exit (port 3, see Fig. 1(a) of the above paper) of the ring resonator. The integration of the last circulation (corresponding to time interval from t R to t) was carelessly omitted. As a corrected formula becomes implicit, i.e., the phase change suffered during the last circulation is expressed in terms of the output field, itself to be determined, this formulation is not advantageous. A more adequate procedure is to use the intracavity field at the input (port 4) of the resonator, in which case the output field is computed by using previously determined values. In such a formulation, Eq. (10) on p. 1538 should be replaced by

Resonance conditions of long-period gratings in temperature sensitive polymer ring optical fibers

Recently a novel optical fiber with a temperature sensitive polymer ring and long-period grating has been experimentally produced and studied. We present here results from a finite-element based simulation of such a structure. The numerically determined resonance conditions for varying temperature show similar behavior to previously reported experimental results. We predict for the first time, as far as the authors are aware, that it is possible for this type of fiber to exhibit dual resonance conditions and as a consequence suffer band rejection broadening.

Nonlinear Optical Fibre Resonators with Applications in Electrical Engineering and Computing

In 1969, Szoke et al. reported their first experiments on optical bistability [39] and Seidel filed his patent [29] on a bistable optical circuit. Both reported optical hysteresis and suggested applications. The two essential ingredients for bistability are nonlinearity and feedback. Bistability is a phenomenon where a given optical device can have two possible output powers for a given input power. In 1976, Gibbs [10] demonstrated bistability using a sodium-filled Fabry-Perot interferometer. Bistability is a hysteresis effect that is dependent upon the history of the system. There are two stable steady-states within a bistable region and the path followed is dependent upon whether the input power is increasing or decreasing. Consider Fig. 3.1 , the power is increased from zero and the output power follows the route A, B, C. The input power is then decreased back down to zero and the output power follows the route C, D, A, giving a counterclockwise bistable region. For an input power, x, say, there are two possible outputs depending on whether the input power is increasing or decreasing. This bistable behavior can be introduced through an absorption process or a dispersion process. With the first process a saturable absorber could be contained within a cavity [29].

Stride time estimation: Realtime peak detection implemented on an 8-bit, portable microcontroller

Falls are a threat of great magnitude for the aging population. Methods, and the pursuit thereof to improve anticipatory prediction of falls, could reduce incidence of injury thereby lowering associated costs of healthcare. Gait monitoring is seen as a reliable area to help decipher potential warning signs as precursors to falls. Stride time is one such parameter, in particular to monitor a patient and recognize variation between stride times. Demographic trends show increasing numbers of older adults. Prevention and avoidance of injurious falls is a key area to impact sustained vigour and quality of life for seniors. Couple this with prolonged ability to maintain autonomy and remain living at home. This combination can profoundly extend distribution of healthcare resources. A portable, inexpensive, low power 8-bit microcontroller in conjunction with an accelerometer and gyroscope is used to implement an algorithm on the microcontroller board to perform peak detection and calculate the gait parameter, stride time, of a patient in real time. This information then transmits via Bluetooth®.

Nonlinear Dynamics of a Passively Mode-Locked Fiber Laser Containing a Long-Period Fiber Grating

We report on a numerical investigation of the nonlinear dynamics of a passively mode-locked fiber laser containing a long period fiber grating. The model is based on the normalized complex Ginzburg-Landau equation and the nonlinear coupled mode equations of the grating. The numerical results indicate the existence of passive mode-locking and autosoliton generation in the cavity of the laser. Both single and bound soliton pulse trains exhibit period doubling bifurcations and a route to chaos as the normalized saturated gain is increased. Furthermore, we show the presence of long period pulsation, soliton sidebands and possible coexisting attractors excited by multisoliton formation and soliton energy quantization.

Impact of Self-Steepening on the Dynamics of a Passively Modelocked Fiber Laser containing a Long Period Fiber Grating

We report on a numerical investigation of the effect of self-steepening on the dynamics of a passively modelocked fiber laser containing a long period fiber grating. The numerical model is based on the normalized complex Ginzburg-Landau equation and the nonlinear coupled mode equations of the grating. The nonlinear dynamics of the laser are observed through plotting the pulse energy against the linearly increasing gain so obtaining bifurcation diagrams. The inclusion of self-steepening was found to result in a temporal walk-off with no significant pulse width or energy alternations, while exhibiting different regions of period doubling bifurcation.