Master of Science (M.S.), University of Dayton, 2024, Electro-Optics

Light Detection And Ranging (LiDAR) technology continues to gain significance across various industries, including autonomous vehicles, surveying, mapping, and defense. The demand for precise 3D spatial data necessitates active sensing methods. Flash imaging and scanning LiDAR are two ways of achieving direct-detection LiDAR. Flash imaging LiDAR captures the entire scene instantaneously by emitting a single pulse and measuring the return. Scanning LiDAR, on the other hand, operates by directing a focused laser pulse in a controlled pattern, typically through mechanically steered mirrors, and measures the reflected signals at each point. Due to the losses in the optical system and light propagation in the atmosphere, the received light is at a much lower intensity than the emitted. This calls for the demand of sensitive detectors that are able to convert the returned light into a measurable electrical signal. Traditionally, low-light sensing has been achieved using linear mode or Geiger mode avalanche photodiodes (APDs). While linear mode APDs offer amplification akin to low-noise amplifiers, their gain values are often limited, and higher gain variants like those in HgCdTe are costly. Geiger mode APDs, despite their increased sensitivity, operate as switches with a notable dead time. In contrast, the discrete amplification photon detector (DAPD) offers a promising alternative by aiming to achieve single-photon detection without the drawbacks associated with APDs. This study gives comparison between flash and scanning LiDAR systems then focuses on the performance of the DAPD, evaluating the viability of the DAPD for LiDAR applications. As detector technology advances, it not only enhances LiDAR system performance but also broadens its applicability across diverse domains. This research contributes to advancing LiDAR technology, unlocking its potential for even broader adoption and innovation.

Committee: Paul McManamon (Advisor); Andrew Sarangan (Committee Member); David Rabb (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Optics; Physics

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

Contactless, nondestructive measurements of minority carrier lifetime by transient microwave reflectance (TMR) and photoluminescence are used to study the carrier dynamics of several ternary materials: InGaAs, GaAsSb, and InAsSb. As contactless measurements, TMR and photoluminescence can determine quality of as-grown wafers. The minority carrier lifetime is inversely proportional to the diffusion component of the dark current and can be used as an indicator of device performance, without the need for full device fabrication. The ability to yield useful information about wafer quality without the time and cost used for fabrication allows for quick feedback to growers. GaAsSb and InGaAs lattice-matched to InP are candidates for short-wave infrared (SWIR) detection at 1.5 μm, a wavelength used for eye safety and optical communication. The high speed or low signal applications at this wavelength benefit from the use of separate absorber, charge, and multiplier (SACM) avalanche photodiodes (APDs). In these devices, the absorber is optimized for detection at the wavelength of interest, and the multiplier is optimized for gain through impact ionization. InGaAs-based SACM APDs are a mature technology and are available commercially. The multipliers paired with InGaAs, however, typically have high noise. Research into low-noise multipliers has resulted in the demonstration of AlGaAsSb as a low noise material. When AlGaAsSb is paired with InGaAs, the grading material AlInGaAs creates a conduction band offset with AlGaAsSb, limiting bandwidth. GaAsSb lattice-matched to InP has similar properties to InGaAs and could be implemented without a conduction band offset due to the grading material being AlGaAsSb. When a GaAsSb/AlGaAsSb SACM APD was demonstrated, it was found to have higher dark current than commercial InGaAs-based devices. Because these materials are so similar, this was unexpected. As mentioned, the diffusion component of the dark current is inversely proportio (open full item for complete abstract)

Committee: Sanjay Krishna (Advisor); Steve Ringel (Committee Member); Preston Webster (Committee Member); Anant Agarwal (Committee Member); Shamsul Arafin (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

The increasing concentration of greenhouse gases, particularly methane (CH4) and carbon dioxide (CO2), has driven global temperature rises, intensifying concerns regarding the prevailing climate crisis. Effectively monitoring these gases requires a detector spanning the short-wavelength infrared (~2400 nm) range, covering wavelengths of CH4 (1650 nm) and CO2 (2050 nm). The state-of-the-art (SOA) HgCdTe avalanche photodetectors (APDs) offer outstanding performance metrics, including high gain (M) and low excess noise (F(M)). However, their widespread adoption is prevented by inherent challenges such as manufacturability, reproducibility, and cost consideration. Moreover, their reliance on cryogenic cooling adds to the cost, size, weight, and power (SWaP-c) of the system. Commercially available SWIR APDs are demonstrated on cost-effective InP substrates using a separate absorption, charge, and multiplication (SACM) structure. These SACM APDs, featuring a mature In0.53Ga0.47As (InGaAs) absorber, exhibit high material quality, ease of manufacturability, and low dark current. However, the multipliers employed in these commercial APDs, either InP or In0.52Al0.48As, display high excess noise (k~0.5 and k~0.2, respectively), limiting their sensitivity and speed. Recent research on the Al0.85Ga0.15AsSb(AlGaAsSb) multiplier on InP substrates has shown extremely low excess noise, comparable to Si APDs, with F(M) < 3 up to M = 70. In this dissertation, SWIR APDs were developed using AlGaAsSb multipliers on InP substrates to achieve high sensitivity and low SWaP-C. Through iterative optimization of design and demonstration, the AlGaAsSb SACM APD with GaAs0.5Sb0.5 (GaAsSb) absorber for 1650 nm wavelength detection achieved a remarkably high gain of M ~ 1,212, setting a record among III-V based SACM APDs at room temperature (RT). Furthermore, the GaAsSb-based APD exhibited a minimal temperature-dependent breakdown coefficient (~11 mV/K), indicating high reliability and accuracy (open full item for complete abstract)

Committee: Sanjay Krishna (Advisor); John P. R. David (Committee Member); Shamsul Arafin (Committee Member); Betty Lise Anderson (Committee Member) Subjects: Electrical Engineering; Engineering

Doctor of Philosophy (PhD), Wright State University, 2021, Engineering PhD

Measuring cerebral blood flow (CBF) is a crucial element in monitoring a vast variety of human brain disorders. Current imaging modalities used for measuring CBF has various limitations that restricts its usefulness especially in the neuroscience intensive care unit (NSICU). Here, the use of Time-gated DCS (TG-DCS) which has significant advantages compared to its predecessor, CW-DCS, was proposed as the solution. However, this technology is still in its infancy and its clinical capability has yet to be established. To show the feasibility of deploying TG-DCS in NSICU settings, the time-domain analytical model for TG-DCS was expanded for multi-layered cases. Next, CW-DCS was validated in humans and in NSICU settings on patients suffering from Traumatic Brain Injury (TBI). A prototype 1064nm TG-DCS system was built and validated on several in-vivo experiments. Finally, the feasibility of the system was shown by deploying it in NSICU settings for measuring CBF in TBI patients. Lastly, deep learning was used to show the feasibility of obtaining real-time results.

Committee: Ulas Sunar Ph.D. (Advisor); Sherif Elbasiouny Ph.D. (Committee Member); Robert Lober M.D., Ph.D. (Committee Member); Brandon Foreman M.D. (Committee Member); Jonathan Lovell Ph.D. (Committee Member) Subjects: Artificial Intelligence; Biomedical Engineering; Biomedical Research; Biophysics; Medical Imaging; Neurosciences; Optics

Master of Science (M.S.), University of Dayton, 2018, Electro-Optics

In this thesis, Electro-Optic (EO) range signatures are obtained with a Short-Wave Infrared Super-Continuum Laser (SWIR-SCL) source. 3D printed canonical targets of interest are illuminated by the SWIR-SCL pulsed laser. The scattered laser light from the target is directly detected in mono-static and bi-static configurations with a fast, high bandwidth Indium Gallium Arsenide (InGaAs) PIN photodiode. Temporal pulse returns provide target shape, orientation, and surface roughness information. Spatial and temporal analysis of the collected intensity distribution is performed in MATLAB. Macro and micro surface properties are identified from the collected data by correlating pulse amplitude variations with known range scenes. Finally, range resolution improvement is investigated by means of Tomographic Reconstruction using Radon Transforms and by image processing techniques such as Deconvolution.

Committee: Edward Watson Ph.D. (Advisor); Paul McManamon Ph.D. (Committee Member); Joe Haus Ph.D. (Committee Member) Subjects: Computer Engineering; Electrical Engineering; Engineering; Experiments; Optics; Physics; Scientific Imaging