1,720,984 research outputs found
Slow light propagation through a Moire grating at the zero dispersion wavelength
No full textThe reduction in the group velocity of a light pulse, or ‘slow light’, has many practical applications including optical switching and buffers. We investigate slow light propagating near the band edge of a Bragg grating. At the Bragg wavelength a resonance occurs in the reflection spectrum creating a photonic band gap. At wavelengths close to the band edge light is transmitted through the grating and a reduction in group velocity is observed, but also an increase in group velocity dispersion (GVD) leading to large pulse broadening preventing any practical use. We present a possible resolution to this problem.We analyse single period Bragg gratings using coupled mode theory. For a pulse with a given carrier frequency and desired group velocity, there exist two grating periods for a chosen AC grating modulation which produce a band gap above and below the carrier frequency respectively. In both cases, as the group velocity tends to zero the GVD diverges causing substantial pulse broadening. One grating period produces normal and the other anomalous GVD, suggesting that a Moiré grating that superimposes both grating periods could be used to create a zero dispersion wavelength at the carrier frequency. To simulate pulse propagation through such a grating, we employ matrix transfer methods and numerical optimisation to find the grating parameters which produce the smallest group velocity and GVD for a given pulse bandwidth.Our initial results demonstrate a group velocity reduction by a factor of 4 with negligible pulse broadening. We are currently examining the use of apodisation which will provide an improvement in the grating transmission spectrum and increase the allowable pulse bandwidth. With this we expect to achieve group velocity reduction by a further two orders of magnitude whilst minimising pulse broadening
Slow and stopped light in dynamic Moiré gratings
No full textWe investigate a theoretical model for a dynamic Moiré grating which is capable of producing slow and stopped light with improved performance when compared with a static Moiré grating. A Moiré grating superimposes two grating periods, which creates a narrow slow light resonance between two band gaps. A Moiré grating can be made dynamic by varying its coupling strength in time. By increasing the coupling strength the reduction in group velocity in the slow light resonance can be improved by many orders of magnitude while still maintaining the wide bandwidth of the initial, weak grating. We show that for a pulse propagating through the grating this is a consequence of altering the pulse spectrum, and therefore the grating can also perform bandwidth modulation. Finally we present a possible realization of the system via an electro-optic grating by applying a quasistatic electric field to a poled χ(2) nonlinear medium.</p
Slow-light enhanced second-harmonic generation using a π-phase shifted Moiré grating in a quasi-phased-matched medium
No full textSlow light is the phenomenon of a large reduction in group velocity, normally due to a material resonance. Slow light causes spatial compression and consequently large field enhancement which has been suggested as a method for increasing nonlinear optical effects. Here we investigate the use of a Moiré grating for enhancing second-harmonic generation (SHG) in a χ(2) medium.&more...<br/
Grating-induced slow-light enhancement of second-harmonic generation in periodically poled crystals
No full textDataset for paper 'Grating-induced slow-light enhancement of second-harmonic generation in periodically poled crystals' published in Physical Review A (PRA) </span
Grating-induced slow-light enhancement of second harmonic generation in periodically poled crystals
No full textThe effect of slow light on second-harmonic generation in a periodically poled χ(2) nonlinear medium is investigated theoretically. A linear π phase-shifted grating is used to slow the group velocity of the fundamental frequency, and the resulting field enhancement greatly increases the second-harmonic conversion efficiency. A second linear grating at the input end ensures that all output is in the forward direction. We show that almost 100% conversion efficiency can be achieved for continuous wave pumping at low intensities that generate negligible conversion in the absence of the slow-light grating.</p
Integrated quantum photonics
No full textThis chapter will only be concerned with quantum photonics; systems where the photons themselves act as carriers of quantum informatio
Dataset for: Short single-frequency self-pulsing Brillouin-Raman distributed feedback fiber laser
No full textDataset for the paper: 'Short single-frequency self-pulsing Brillouin-Raman distributed feedback fiber laser' accepted in Optics Express.
Dataset contains raw data for all the optical/eletronic spectra and oscioscope graphs presented in the paper.</span
Improving the functionality of a laser writing system using software
No full textLaser writing is a method of fabricating ‘pipes’ inside glass that confine light, known as optical waveguides. This confinement allows interactions between individual photons to be controlled, an important feature for quantum optics experiments. For such experiments, the total optical loss in the system should be below 1.7dB[1]; minimising the total loss in these structures is very important for scalability. Waveguides can be created by translating a photosensitive glass sample under a focussed laser at a precise speed. 2D structures allow spatial control of how photons interact. Additionally periodic structures known as Bragg gratings cause light within a narrow predefined wavelength range to be reflected, allowing filtering and trapping of light. Creating devices of a high enough standard to be useful requires a great deal of computational control. Currently this consists of a PC uploading code to an FPGA, which is connected to an air-bearing stage, which moves samples through a fixed laser beam. Complex coordinate transforms are difficult to implement and test in the current system due its use of AeroBasic (a CNC language modified from G-Code); as a result this work follows an upgrade to control the system using a custom library written in C++
Self-pulsing of Brillouin-Raman distributed feedback fiber lasers
No full textWe report on self-pulsing in distributed-feedback single-frequency Raman fibre lasers. We see a periodic reduction in intra-cavity power associated with each pulse and propose that this self-pulsing arises from parasitic Brilluoin scattering cavity dumping the Raman
Highly-chirped Bragg gratings for integrated silica spectrometers
No full textA blazed chirped Bragg grating in a planar silica waveguide device was used to create an integrated diffractive element for a spectrometer. The grating diffracts light from a waveguide and creates a wavelength dependent focus in a manner similar to a bulk diffraction grating spectrometer. An external imaging system is used to analyse the light, later device iterations plan to integrate detectors to make a fully integrated spectrometer. Devices were fabricated with grating period chirp rates in excess of 100nm/mm, achieving a focal length of 5.5 mm. Correction of coma aberrations resulted in a device with a footprint of 20 mm x 10mm, a peak FWHM resolution of 1.8 nm, a typical FWHM resolution of 2.6 nm and operating with a 160 nm bandwidth centered at 1550 nm.<br/
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