Classical ghost imaging with opto-electronic light sources: novel and highly incoherent concepts

In conventional imaging systems, the emitted light from a source interacts with an object and the intensity of the transmitted or reflected light is captured by a spatially resolving detector. In this thesis, a fundamentally different imaging principle has been studied, known as ghost imaging (GI). In contrast to conventional imaging, GI exploits the intensity correlations of light to form an image of an object. A ghost image is obtained by measuring the total intensity of the transmitted or reflected light of an illuminated object and the spatially resolved intensity of a highly-correlated reference beam which itself has never interacted with the object. The information of both intensities alone is not enough to form an image of the object. However, image reconstruction can be achieved by correlating the two intensities. Intriguingly, the spatial resolution of the ghost image is provided by the non-interacting reference beam. The work presented in this thesis joins into the continuous strive for making GI applicable to real-world sensing and imaging fields. The title: Classical ghost imaging with opto-electronic emitters, reflects one of the approaches to this objective. The second approach is what rather sets this thesis apart from other ongoing work on GI. Instead of utilizing state-of-the-art detection systems, novel GI configurations are developed

The application of low coherence interferometry to the micron scale imaging of the living human retina

Current optical and ultrasound techniques for high resolution in vivo retinal imaging cannot provide the depth accuracy required to enable sensitive ophthalmologic diagnosis to be carried out on the basis of images of retinal microstructures. The axial depth resolution of one of the recently introduced retinal imaging instruments, the scanning laser ophthalmoscope, is restricted by the combined effect of the depth of focus achievable through the eye pupil and aberrations to about 300 pm. A new imaging technique, based on low coherence interferometry, providing improved depth resolution figures of the order of a few microns, is demonstrated here. Non-invasive topographic and tomographic measurements can be performed with an instrument based on this technique. A novel path modulation procedure, the Newton rings sampling function, is presented together with experimental results obtained in its application to the imaging of various objects including human in vivo retina. The advantages and disadvantages of novel and more conventional imaging modes, their associated techniques and the overall importance and likely impact of the novel Newton rings modulation method are considered. The measurement of 3-dimensional profiles of various targets, including tomographic images of in vivo human retinas from volunteers’ eyes, is presented. The utility of OCT measurements in the high-resolution mapping of in vivo tissue and its potential usage alongside scanning laser ophthalmoscopy in identifying features in the human eye are discussed

Two applications of the Fabry-Perot interferometric sensor

Two important applications of the fiber Fabry-Perot Interferometer (FFPI) sensor are investigated: (1) an optical binary switch for aerospace application, and (2) an FFPI weigh-in-motion sensor for measuring the weight of trucks traveling down a highway. In the fiber optical switch, the FFPI sensor is bonded to a copper cantilever to sense the elongation of cavity length induced by force applied to the end of the cantilever via a pushed button. Light from a superluminescent diode light source passes through a scanned Michelson interferometer and is reflected from a sensing FFPI and a reference FFPI to produce a fringe pattern. A secondary interferometer uses a distributed feedback laser light source to compensate for irregularities in the mechanical scanning rate of the moving stage to achieve precision measurement of the optical path difference. The system is calibrated by applying known weights to the cantilever. The elongation measured by the FFPI sensor shows excellent linearity as a function of the force applied, and little hysteresis was observed. By comparing the measured force to a threshold, the system produces a binary signal that indicates the state of the pilotactuated system; i. e., whether or not the button has been pushed. In FFPI weigh-in-motion sensors system, the FFPI sensors are installed in metal bars so that they will experience the strain induced by applied loads and are connected to the Signal Conditioning Unit (SCU). The SCU determines the induced phase shift in the FFPI and produces voltage outputs proportional to the phase shifts. Laboratory Material Testing System tests show that the fiber optic sensor response is a fairly linear function of the axial displacement. In highway tests the FFPI sensors showed strong responses and consistently reproduced the expected characteristics of truck wheel crossings. A falling weight deflectometer was used to calibrate the sensor response and predict unknown loads. All sensors in steel bars and aluminum bars showed excellent repeatability and accurate predictions, with an average relative percentage error within 2%. The study on sensor response variation with applied load positions shows a bell shaped distribution. Truck tests on the road sensors indicate that the repeatability of wheel crossings at similar position is good. The sensor can accurately measure axle spacing, speed, and truck class

Development of high-performance quantum dot mode-locked optical frequency comb

This PhD thesis focus on the development of high-performance optical frequency combs (OFCs) generated by two-section passively mode-locked lasers (MLLs) based on novel optimised InAs quantum dot (QD) structures grown on GaAs substrates. Throughout the thesis, several important aspects are covered: the epitaxial structures, the device designs, the fabrication process, the characterisation of the fabricated laser devices and the evaluation of their performance. To gain a deep level comprehension of the mode-locking mechanisms in two-section QD MLLs, a detailed study is presented on a series of QD MLLs with different saturable absorber (SA) to gain section length ratios (from 1: 3 to 1: 7) in either ridged-waveguide structure or tapered waveguide structure. The effect of temperature on different device configurations is experimentally examined. And the data transmission capability of the QD MLLs is systematically investigated in different scenarios. In this thesis, an ultra-stable 25.5 GHz QD mode-locked OFC source emitted solely from the QD ground state from 20 °C to a world record 120 °C with only 0.07 GHz tone spacing variation has been demonstrated. Meanwhile, a passively QD MLL with 100 GHz fundamental repetition rate is developed for the first time, enabling 128 Gbit s−1 λ−1 PAM4 optical transmission and 64 Gbit s−1 λ−1 NRZ optical transmission through 5-km SSMF and 2-m free-space, respectively. All of the studies aim to prove that our two-section passively InAs QD MLLs can be used as simple, compact, easy-to-operate, and power-efficient multi-wavelength OFC sources for future high-speed and large-capacity optical communications

Electro-optic architecture for servicing sensors and actuators in advanced aircraft propulsion systems

A detailed design of a fiber optic propulsion control system, integrating favored sensors and electro-optics architecture is presented. Layouts, schematics, and sensor lists describe an advanced fighter engine system model. Components and attributes of candidate fiber optic sensors are identified, and evaluation criteria are used in a trade study resulting in favored sensors for each measurand. System architectural ground rules were applied to accomplish an electro-optics architecture for the favored sensors. A key result was a considerable reduction in signal conductors. Drawings, schematics, specifications, and printed circuit board layouts describe the detailed system design, including application of a planar optical waveguide interface

Performance of a Distributed Simultaneous Strain and Temperature Sensor Based on a Fabry-Perot Laser Diode and a Dual-Stage FBG Optical Demultiplexer

A simultaneous strain and temperature measurement method using a Fabry-Perot laser diode (FP-LD) and a dual-stage fiber Bragg grating (FBG) optical demultiplexer was applied to a distributed sensor system based on Brillouin optical time domain reflectometry (BOTDR). By using a Kalman filter, we improved the performance of the FP-LD based OTDR, and decreased the noise using the dual-stage FBG optical demultiplexer. Applying the two developed components to the BOTDR system and using a temperature compensating algorithm, we successfully demonstrated the simultaneous measurement of strain and temperature distributions under various experimental conditions. The observed errors in the temperature and strain measured using the developed sensing system were 0.6 °C and 50 με, and the spatial resolution was 1 m, respectively

Self-Mixing Diode Laser Interferometry

Self-mixing interferometry in a laser diode is a very powerful tool in measurement science. The Self-mixing interferometer is a very robust and low cost interferometer with extreme simplicity in alignment and setup. In this thesis, a self-mixing interferometer is analysed and developed. The measurements of the self-mixing interferometer are verified using a Michelson interferometer. It is then followed by the signal processing of the detected signal. Three different methods are developed to retrieve the movement of the target. Results obtained by applying these methods to different experimental data sets are presented. In the later part of the thesis, a phase locked self-mixing interferometer is developed. This slightly modified interferometer follows the target movement. As a result no additional circuitry or signal processing is necessary for the recovery of the target movement. Phase locked interferometer developed in this thesis was able to measure down to 1 nm of vibration. It is then followed by a novel method to detect cracks in eggshells using the phase locked vibrometer. The proposed method is tested and proved to be capable of differentiating between the intact and cracked eggs