Adenowo Gbadebo

We propose a return-to-zero on-off keying (RZ-OOK) to non-return-to-zero (NRZ) OOK conversion scheme based on a transmissive phase-modulated fiber Bragg grating (PM-FBG). The PM-FBG has a spectrum similar to the combination of a delay line interferometer and a narrow band optical filter, which is designed and synthesized using numerical optimization algorithm. The coupling strength of the PM-FBG is almost uniform and the grating period varies along the fiber length according to the optimization method. The designed PM-FBG has been fabricated using advanced ultraviolet laser inscription technique. Experimental results show that such a PM-FBG can perform RZ-OOK to NRZ-OOK format conversion successfully.

State of the art fibre optic sensors based on fibre Bragg gratings (FBGs) are robust sensing platforms widely used in real-world applications [1]. Interrogation of such FBGs are typically facilitated using broadband sources in combination with linear detector arrays, or swept-wavelength sources. Here, for the first time to the best of our knowledge, we demonstrate a compressed sensing approach to FBG sensor interrogation. Optical source and detector complexity are reduced by employing a broadband ASE source and a single-pixel detector respectively. Reconstruction is aided by convex optimisation, which provides the sampling compression, offering a modality to increase sensor readout rates in the process.

We demonstrate a multichannel fiber Bragg grating (MC-FBG) based distributed temperature field sensor with millimeter-order spatial resolution. The MC-FBG was designed by using the layer peeling (LP) algorithm with a tailored group delay characteristic and fabricated using seamless UV-inscription. We have achieved a 21-channel MC-FBG with 0.2 nm bandwidth of each channel and 0.5 nm channel gap. The sensor was tested by using a temperature field distribution. Experimental results show that the sensor had a spatial resolution of 3 mm and could measure a maximum temperature gradient of 7.85 °C/mm.

We demonstrate the design and fabrication of multichannel fibre Bragg gratings (FBGs) with aperiodic channel spacings. These will be suitable for the suppression of specific spectral lines such as OH emission lines in the near infrared (NIR) which degrade ground based astronomical imaging. We discuss the design process used to meet a given specification and the fabrication challenges that can give rise to errors in the final manufactured device. We propose and demonstrate solutions to meet these challenges.

Customized ultrahigh repetition rate pulse bursts are demonstrated with phase-modulated fiber Bragg gratings (PM-FBGs) in transmission for the first time. Examples of three, four and eight replicas with a repetition rate of 100GHz in one period of the input pulse are designed and numerically simulated.

We use phase-diverse ensemble-averaged homodyne detection to characterize spectral widths and strengths of disorder induced resonances in fiber Bragg gratings with 16 fm (2 MHz) resolution. Spectral widths as narrow as 187 fm (56 MHz) are observed.

We demonstrated a multichannel FBG based temperature field sensor, in which the grating was designed by pre-compensation layer peeling method. Such system could achieve a real time temperature field monitoring with 3mm high spatial resolution.

Disorder offers rich possibilities for manipulating the phase and intensity of light and designing photonic devices for various applications including random lasers, light storage, and speckle-free imaging. Disorder-based optical systems can be implemented in one-dimensional structures based on random or pseudo-random alternating layers with different refractive indices. Such structures can be treated as sequences of scatterers, in which spatial light localization is characterized by random sets of spectral transmission resonances, each accompanied by a relatively high-intensity concentration. The control and manipulation of resonances is the key element in designing disorder-based photonic systems. In this work, we introduce a method of controlling disorder-induced resonances by using the established non-trivial interconnection between the symmetry of bi-directional light propagation properties and the features of the resonant transmissions. Considering a fiber with resonant Bragg gratings as an example, the mechanism of enhancing or suppressing the resonant transmission of polychromatic light and the effectiveness of the method have been demonstrated both theoretically and experimentally. The proposed algorithm of controlling disorder-induced resonances is general and applicable to classical waves and quantum particles, for disordered systems both with and without gain.

Light localisation in one-dimensional (1D) randomly disordered medium is usually characterized by randomly distributed resonances with fluctuating transmission values, instead of selectively distributed resonances with close-to-unity transmission values that are needed in real application fields. By a resonance tuning scheme developed recently, opening of favorable resonances or closing of unfavorable resonances are achieved by disorder micro-modification, both on the layered medium and the fibre Bragg grating (FBG) array. And furthermore, it is shown that those disorder-induced resonances are independently tunable. Therefore, selected resonances and arranged light localisation can be achieved via artificial disorder, and thus meet the demand of various application fields.

An all-optical first-order temporal differentiator is demonstrated with transmissive phase-modulated fiber Bragg grating (PM-FBG) for the first time. A novel two-step nonlinear optimization method is proposed to design the transmissive PM-FBG.