Introduction In this special issue of Photonic Sensors the research activities of some of the （ex） members of the Applied Optics Group （AOG） at the University of Kent （UoK） will present brief details of their re...Introduction In this special issue of Photonic Sensors the research activities of some of the （ex） members of the Applied Optics Group （AOG） at the University of Kent （UoK） will present brief details of their research in AOG and then describe in greater lengthdetails of their careers since leaving the University. The research group has made significant contributions to many areas of ＂Fiber Optic Sensors＂ （FOS） as indicated in the ＂star diagram＂ below. This review is in recognition of the important advances made at AOG in the field of FOS and I was asked by Professor Y. Rao to organize it.展开更多
The practical development of compact modern nanophotonic devices relies on the availability of fast and low-cost fabrication techniques applicable to a wide variety of materials and designs.We have engraved a split gr...The practical development of compact modern nanophotonic devices relies on the availability of fast and low-cost fabrication techniques applicable to a wide variety of materials and designs.We have engraved a split grating geometry on stainless steel using femtosecond laser processing.This structure serves as a template to fabricate efficient plasmonic sensors,where a thick gold layer is grown conformally on it.The scanning electron microscope(SEM)images confirm the generation of the split laser-induced periodic spatial structures.The optical reflectance of our sensors shows two dips corresponding to the excitation of surface plasmon resonances(SPRs)at two different wavelengths.Furthermore,the asymmetric shape of these spectral responses reveals a strong and narrow Fano resonance.Our computational electromagnetism models accurately reproduce the reflectivity of the fabricated structure.The spectral responses of both the simulated and fabricated structures are fitted to the Fano model that coherently combines the narrow SPRs with the broad continuum background caused by diffraction.The parameters extracted from the fitting,such as the resonance wavelengths and line widths,are used to evaluate the performance of our device as a refractometric sensor for liquids.The maximum sensitivity and figure of merit are 880 nm/RIU and 80 RIU-1,respectively.Besides the compact design of our sensing device,its performance exceeds the theoretical maximum sensitivity of a classical Kretschmann setup.展开更多
The potential for improving the penetration depth of optical coherence tomography systems by using light sources with longer wavelengths has been known since the inception of the technique in the early 1990s.Neverthel...The potential for improving the penetration depth of optical coherence tomography systems by using light sources with longer wavelengths has been known since the inception of the technique in the early 1990s.Nevertheless,the development of mid-infrared optical coherence tomography has long been challenged by the maturity and fidelity of optical components in this spectral region,resulting in slow acquisition,low sensitivity,and poor axial resolution.In this work,a mid-infrared spectral-domain optical coherence tomography system operating at a central wavelength of 4μm and an axial resolution of 8.6μm is demonstrated.The system produces two-dimensional cross-sectional images in real time enabled by a high-brightness 0.9-to 4.7-μm mid-infrared supercontinuum source with a pulse repetition rate of 1 MHz for illumination and broadband upconversion of more than 1-μm bandwidth from 3.58–4.63μm to 820–865 nm,where a standard 800-nm spectrometer can be used for fast detection.The images produced by the mid-infrared system are compared with those delivered by a state-of-the-art ultra-high-resolution near-infrared optical coherence tomography system operating at 1.3μm,and the potential applications and samples suited for this technology are discussed.In doing so,the first practical mid-infrared optical coherence tomography system is demonstrated,with immediate applications in real-time non-destructive testing for the inspection of defects and thickness measurements in samples that exhibit strong scattering at shorter wavelengths.展开更多
A multichannel heterodyne fiber optic vibrometer is demonstrated which can be operated at ranges in excess of 50m. The system is designed to measure periodic signals, impacts, rotation, 3D strain, and vibration mappin...A multichannel heterodyne fiber optic vibrometer is demonstrated which can be operated at ranges in excess of 50m. The system is designed to measure periodic signals, impacts, rotation, 3D strain, and vibration mapping. The displacement resolution of each channel exceeds 1 nm. The outputs from all channels are simultaneous, and the number of channels can be increased by using optical switches.展开更多
A conceptual coaxial Pitot tube （PT） has been developed using fiber optic sensors combined with actuators to monitor and maintain its correct operation under different environmental conditions. Experiments were perf...A conceptual coaxial Pitot tube （PT） has been developed using fiber optic sensors combined with actuators to monitor and maintain its correct operation under different environmental conditions. Experiments were performed showing that the dynamic and static tubes can be cleared of ice. It was also demonstrated that the dynamic tube could be cleared of dust and sand which was not the case for the static tube in the coaxial configuration. An approach was proposed to overcome this problem involving a conventional configuration where the static tube was operated independently orthogonal to the dynamic tube, and a second set of sensors and actuators was used. Sensors and associated actuators were developed for temperature and intensity for a linear PT. The aim of this work is to propose a solution for a problem that has caused the loss of the lives of many passengers and crew of aircraft. Resources were not available to test a full implementation of a PT incorporating the proposed modifications.展开更多
The aim of this project was to develop non-contact fiber optic based displacement sensors to operate in the harsh environment of a ＂light gas gun＂ （LGG）, which can ＂fire＂ small particles at velocities ranging fr...The aim of this project was to develop non-contact fiber optic based displacement sensors to operate in the harsh environment of a ＂light gas gun＂ （LGG）, which can ＂fire＂ small particles at velocities ranging from 1 km/s-8.4km/s. The LGG is used extensively for research in aerospace to analyze the effects of high speed impacts on materials. Ideally the measurement should be made close to the center of the impact to minimize corruption of the data from edge effects and survive the impact. We chose to develop a non-contact ＂pseudo＂ confocal intensity sensor, which demonstrated resolution comparable with conventional polyvinylidene fluoride （PVDF） sensors combined with high survivability and low cost. A second sensor was developed based on ＂fiber Bragg gratings＂ （FBG） to enable a more detailed analysis of the effects of the impact, although requiring contact with the target the low weight and very small contact area of the FBG had minimal effect on the dynamics of the target. The FBG was mounted either on the surface of the target or tangentially between a fixed location. The output signals from the FBG were interrogated in time by a new method. Measurements were made on carbon fiber composite plates in the LGG and on low velocity impact tests. The particle momentum for the low velocity impact tests was chosen to be similar to that of the particles used in the LGG.展开更多
An optical akinetic swept source （AKSS） at 1060nm, comprising a 5m length fiber ring cavity, a semiconductor optical amplifier （SOA） as gain medium, and a 98% reflective chirped fiber Bragg grating as a dispersive...An optical akinetic swept source （AKSS） at 1060nm, comprising a 5m length fiber ring cavity, a semiconductor optical amplifier （SOA） as gain medium, and a 98% reflective chirped fiber Bragg grating as a dispersive element, is described. Active mode-locking was achieved by directly modulating the current of the SOA with sinusoidal signal of frequency equal to 10 times and 20 times the cavity resonance frequency. In the static regime, linewidths as narrow as 60pm and a tuning bandwidth of 30nm were achieved, while a 2roW output power, without any optical booster, was measured dynamically at a sweep speed of 100kHz. The axial range of the AKSS was evaluated by scanning through the channeled spectrum of a Mach-Zehnder interferometer.展开更多
A review is presented of several technical solutions developed by the Applied Optics Group （AOG） in the field of low coherence interferometry applied to optical fiber sensors （OFS） that subsequently allowed AOG to...A review is presented of several technical solutions developed by the Applied Optics Group （AOG） in the field of low coherence interferometry applied to optical fiber sensors （OFS） that subsequently allowed AOG to quickly progress in the field of optical coherence tomography （OCT）.展开更多
Differences in physical and structural characteristics of seeds may indicate variability within and between plant populations.In the present study,we performed a close characterization of dimension,shape,and tegument ...Differences in physical and structural characteristics of seeds may indicate variability within and between plant populations.In the present study,we performed a close characterization of dimension,shape,and tegument delayed chlorophyll fluorescence in seeds obtained from three species of the genus Annona(Annonaceae),i.e.,Annona coriacea,A.montana,A.squamosa.Results showed that studied seeds may be sorted as scalene ellipsoids expressing low values for the seed sphericity.The morphological estimates suggested differences in seed shape for all species.A high correlation was observed between surface area and volume(r^2>99%)for all the three species suggesting that in addition to structural shape.In addition,we also observed very high positive correlations(Rho=1.000,p<0.001)between surface area and arithmetic mean diameterof the seeds for all species.The first principal component(PCA1)of elliptical Fourier descriptors explained most of the variations in morphological structure of the seeds in the three species.Additionally,a less intense tegument delayed chlorophyll fluorescence was observed for A.montana while the highest intensity was recorded for A.squamosa,revealing the potential use of fluorescence spectroscopy in discrimination at the species level by analyzing the frequency domain by means of Fourier Transform spectra as well as the relationship time-frequency of chlorophyll fluorescence.展开更多
文摘Introduction In this special issue of Photonic Sensors the research activities of some of the （ex） members of the Applied Optics Group （AOG） at the University of Kent （UoK） will present brief details of their research in AOG and then describe in greater lengthdetails of their careers since leaving the University. The research group has made significant contributions to many areas of ＂Fiber Optic Sensors＂ （FOS） as indicated in the ＂star diagram＂ below. This review is in recognition of the important advances made at AOG in the field of FOS and I was asked by Professor Y. Rao to organize it.
文摘The practical development of compact modern nanophotonic devices relies on the availability of fast and low-cost fabrication techniques applicable to a wide variety of materials and designs.We have engraved a split grating geometry on stainless steel using femtosecond laser processing.This structure serves as a template to fabricate efficient plasmonic sensors,where a thick gold layer is grown conformally on it.The scanning electron microscope(SEM)images confirm the generation of the split laser-induced periodic spatial structures.The optical reflectance of our sensors shows two dips corresponding to the excitation of surface plasmon resonances(SPRs)at two different wavelengths.Furthermore,the asymmetric shape of these spectral responses reveals a strong and narrow Fano resonance.Our computational electromagnetism models accurately reproduce the reflectivity of the fabricated structure.The spectral responses of both the simulated and fabricated structures are fitted to the Fano model that coherently combines the narrow SPRs with the broad continuum background caused by diffraction.The parameters extracted from the fitting,such as the resonance wavelengths and line widths,are used to evaluate the performance of our device as a refractometric sensor for liquids.The maximum sensitivity and figure of merit are 880 nm/RIU and 80 RIU-1,respectively.Besides the compact design of our sensing device,its performance exceeds the theoretical maximum sensitivity of a classical Kretschmann setup.
基金the financial support from Innovation Fund Denmark through ShapeOCT Grant No.4107-00011Athe NIHR Biomedical Research Center at Moorfields Eye Hospital NHS Foundation Trust+3 种基金the UCL Institute of Ophthalmologythe Royal Society Wolfson Research Merit Award.the support from H.C.Orsted COFUNDED Marie-Curie action fellowshipfinancial support from H.C.Orsted for the running cost.
文摘The potential for improving the penetration depth of optical coherence tomography systems by using light sources with longer wavelengths has been known since the inception of the technique in the early 1990s.Nevertheless,the development of mid-infrared optical coherence tomography has long been challenged by the maturity and fidelity of optical components in this spectral region,resulting in slow acquisition,low sensitivity,and poor axial resolution.In this work,a mid-infrared spectral-domain optical coherence tomography system operating at a central wavelength of 4μm and an axial resolution of 8.6μm is demonstrated.The system produces two-dimensional cross-sectional images in real time enabled by a high-brightness 0.9-to 4.7-μm mid-infrared supercontinuum source with a pulse repetition rate of 1 MHz for illumination and broadband upconversion of more than 1-μm bandwidth from 3.58–4.63μm to 820–865 nm,where a standard 800-nm spectrometer can be used for fast detection.The images produced by the mid-infrared system are compared with those delivered by a state-of-the-art ultra-high-resolution near-infrared optical coherence tomography system operating at 1.3μm,and the potential applications and samples suited for this technology are discussed.In doing so,the first practical mid-infrared optical coherence tomography system is demonstrated,with immediate applications in real-time non-destructive testing for the inspection of defects and thickness measurements in samples that exhibit strong scattering at shorter wavelengths.
文摘A multichannel heterodyne fiber optic vibrometer is demonstrated which can be operated at ranges in excess of 50m. The system is designed to measure periodic signals, impacts, rotation, 3D strain, and vibration mapping. The displacement resolution of each channel exceeds 1 nm. The outputs from all channels are simultaneous, and the number of channels can be increased by using optical switches.
文摘A conceptual coaxial Pitot tube （PT） has been developed using fiber optic sensors combined with actuators to monitor and maintain its correct operation under different environmental conditions. Experiments were performed showing that the dynamic and static tubes can be cleared of ice. It was also demonstrated that the dynamic tube could be cleared of dust and sand which was not the case for the static tube in the coaxial configuration. An approach was proposed to overcome this problem involving a conventional configuration where the static tube was operated independently orthogonal to the dynamic tube, and a second set of sensors and actuators was used. Sensors and associated actuators were developed for temperature and intensity for a linear PT. The aim of this work is to propose a solution for a problem that has caused the loss of the lives of many passengers and crew of aircraft. Resources were not available to test a full implementation of a PT incorporating the proposed modifications.
文摘The aim of this project was to develop non-contact fiber optic based displacement sensors to operate in the harsh environment of a ＂light gas gun＂ （LGG）, which can ＂fire＂ small particles at velocities ranging from 1 km/s-8.4km/s. The LGG is used extensively for research in aerospace to analyze the effects of high speed impacts on materials. Ideally the measurement should be made close to the center of the impact to minimize corruption of the data from edge effects and survive the impact. We chose to develop a non-contact ＂pseudo＂ confocal intensity sensor, which demonstrated resolution comparable with conventional polyvinylidene fluoride （PVDF） sensors combined with high survivability and low cost. A second sensor was developed based on ＂fiber Bragg gratings＂ （FBG） to enable a more detailed analysis of the effects of the impact, although requiring contact with the target the low weight and very small contact area of the FBG had minimal effect on the dynamics of the target. The FBG was mounted either on the surface of the target or tangentially between a fixed location. The output signals from the FBG were interrogated in time by a new method. Measurements were made on carbon fiber composite plates in the LGG and on low velocity impact tests. The particle momentum for the low velocity impact tests was chosen to be similar to that of the particles used in the LGG.
文摘An optical akinetic swept source （AKSS） at 1060nm, comprising a 5m length fiber ring cavity, a semiconductor optical amplifier （SOA） as gain medium, and a 98% reflective chirped fiber Bragg grating as a dispersive element, is described. Active mode-locking was achieved by directly modulating the current of the SOA with sinusoidal signal of frequency equal to 10 times and 20 times the cavity resonance frequency. In the static regime, linewidths as narrow as 60pm and a tuning bandwidth of 30nm were achieved, while a 2roW output power, without any optical booster, was measured dynamically at a sweep speed of 100kHz. The axial range of the AKSS was evaluated by scanning through the channeled spectrum of a Mach-Zehnder interferometer.
文摘A review is presented of several technical solutions developed by the Applied Optics Group （AOG） in the field of low coherence interferometry applied to optical fiber sensors （OFS） that subsequently allowed AOG to quickly progress in the field of optical coherence tomography （OCT）.
文摘Differences in physical and structural characteristics of seeds may indicate variability within and between plant populations.In the present study,we performed a close characterization of dimension,shape,and tegument delayed chlorophyll fluorescence in seeds obtained from three species of the genus Annona(Annonaceae),i.e.,Annona coriacea,A.montana,A.squamosa.Results showed that studied seeds may be sorted as scalene ellipsoids expressing low values for the seed sphericity.The morphological estimates suggested differences in seed shape for all species.A high correlation was observed between surface area and volume(r^2>99%)for all the three species suggesting that in addition to structural shape.In addition,we also observed very high positive correlations(Rho=1.000,p<0.001)between surface area and arithmetic mean diameterof the seeds for all species.The first principal component(PCA1)of elliptical Fourier descriptors explained most of the variations in morphological structure of the seeds in the three species.Additionally,a less intense tegument delayed chlorophyll fluorescence was observed for A.montana while the highest intensity was recorded for A.squamosa,revealing the potential use of fluorescence spectroscopy in discrimination at the species level by analyzing the frequency domain by means of Fourier Transform spectra as well as the relationship time-frequency of chlorophyll fluorescence.
