Photonics is a broad research area that underpins many different areas of science and engineering. The future of the United Kingdom (UK) photonics industry depends on training the next generation of photonic engineers and scientists to lead research and innovation across a wide range of industrial applications. In 2018, the UK government invested £446 million through the Engineering and Physical Sciences Research Council (EPSRC) in 75 Centres for Doctoral Training (CDT), of which one is focused on industry inspired Photonics, Imaging, Sensing and Analysis (CDT in Applied Photonics). A key element of these CDTs is the increase in formal taught components to enhance technical interdisciplinary knowledge and broaden the postgraduate research student’s skills and knowledge base. This paper presents the development, implementation and evaluation of a new taught course for the CDT in Applied Photonics to broaden the skills of photonics researchers to integrate analogue and programmable digital electronics in to photonic systems. The course builds fundamental theoretical knowledge in digital and analogue electronics and provides practical laboratories using accessible programmable digital hardware. It also provides the opportunity to apply this knowledge through a practical group project developing an integrated photonic system, culminating in an assessed practical presentation and demonstration of the working systems. The course uses National Instrument’s myRIO, designed to allow access to industry-grade embedded system technology combining LabVIEW’s graphical programming environment with a processor, reconfigurable field programmable gate array (FPGA) and convenient hardware interfaces. This facilitates access to the technology for postgraduate students from a range of undergraduate backgrounds, yet also provides a pathway to develop similar technology used in industrial photonic research.
The spatial sensitivity of an erbium doped optical fibre distributed feedback (DFB) laser to an external magnetic field is
reported. Intrinsic birefringence of the laser cavity allows lasing in two orthogonal modes. The polarisation beat frequency
between these modes is sensitive to magnetic fields aligned along the axis of the optical fibre due to the Faraday effect. The
interaction of magnetic field, generated by a permanent magnet, with the spatial mode profile of the laser is investigated.
Experimental measurements show a 3.82 MHz change in the beat frequency when a permanent magnet is scanned along
the fibre laser.
Near-field ultrasonic response (50-2000 kHz) of an underwater 1-3 piezocomposite transducer is experimentally
investigated using a polarimetric polarization maintaining fiber sensor. Measured outputs from our sensor and a
reference hydrophone are observed to be comparable.
The interaction of fibre Bragg grating sensors with ultrasonic acoustic waves in water is investigated in the near field
region of a 1-3 piezocomposite transducer. Longitudinal and transverse strain coupling is studied using two different
grating designs and high fidelity measurement of the emitted field was demonstrated.
An optically powered DFB fiber laser based magnetometer free from hysteresis, incorporating drift compensation is
demonstrated. Optical power is delivered through a dedicated fiber to provide the required dither current yielding an
electrically passive sensor.
The DFB fiber laser strain sensor is shown to provide an improvement in the minimum detectable length
change by a factor of 275 at 2 kHz for an applied strain when compared with an interferometric sensor interrogated by an
equivalent DFB laser. This corresponds to a strain resolution enhancement by a factor of 18, if the strain is applied over a
10cm length of fiber. The ability of the fiber laser sensor to operate in its thermodynamic noise limit is shown to be the
primary reason for this enhanced sensitivity. Thermodynamically limited noise performance is demonstrated with three
interrogation methods.
Fiber Bragg gratings have been demonstrated as a versatile sensor for structural health monitoring. We present an
efficient and cost effective multiplexing method for fiber Bragg grating and fiber Fabry-Perot sensors based on a
broadband mode-locked fiber laser source and interferometric interrogation. The broadband, pulsed laser source permits
time and wavelength division multiplexing to be employed to achieve very high sensor counts. Interferometric
interrogation also permits high strain resolutions over large frequency ranges to be achieved. The proposed system has
the capability to interrogate several hundred fiber Bragg gratings or fiber Fabry-Perot sensors on a single fiber, whilst
achieving sub-microstrain resolution over bandwidths greater than 100 kHz. Strain resolutions of 30nε /Hz1/2 and 2
nε/Hz1/2 are demonstrated with the fiber Bragg grating and fiber Fabry-Perot sensor respectively. The fiber Fabry-Perot
sensor provides an increase in the strain resolution over the fiber Bragg grating sensor of greater than a factor of 10. The
fiber Bragg gratings are low reflectivity and could be fabricated during the fiber draw process providing a cost effective
method for array fabrication. This system would find applications in several health monitoring applications where large
sensor counts are necessary, in particular acoustic emission.
We report interferometric interrogation of fiber Bragg gratings in separate cores of a multicore fiber for high resolution quasi-static and dynamic bend measurements. Two axis curvature measurements are made by measuring the differential strain between three FBG sensors formed in a singlemode four-core fiber using a common interrogating interferometer.
Therefore a measurement of the differential phase from each FBG yields the differential strain and compensates for the common-mode random drift of the interrogating interferometer. A DC curvature accuracy of 3.4×10-3m-1, and an AC
curvature resolution of 1.2×10-4m-1 / Hz1/2 are reported.
An efficient multiplexing method for fiber Bragg grating sensors based on a broadband mode-locked laser source and interferometric interrogation is described. The system has the capability to interrogate several hundred fiber Bragg grating sensors on a single fiber, whilst achieving sub-microstrain resolution over bandwidths greater than 100 kHz. A demonstration system with 8 sensors is presented, which achieves strain resolutions less than 213 nε/Hz1/2 up to 100 Hz.
We report experimental measurements of the reflection spectra of Bragg gratings inscribed in 4-core fibers under transverse loading. Broadening and splitting of the Bragg peaks from each core are observed as a function of load and fiber orientation.
We report measurements of the strain and temperature coefficients of optical fibre Bragg gratings with ~1pm wavelength resolution using Fourier transform spectroscopy and Hubert transform signal processing.
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