Optical Signal Processing For Data Compression In Ultrafast Measurement

Today the world is filled with continuous deluge of digital information which are ever increasing by every fraction of second. Real-time analog information such as images, RF signals needs to be sampled and quantized to represent in digital domain with help of measurement systems for information analysis, further post processing and storage. Photonics offers various advantages in terms of high bandwidth, security, immunity to electromagnetic interference, reduction in frequency dependant loss as compared to conventional electronic measurement systems. However the large bandwidth data needs to be acquired as per Nyquist principle requiring high bandwidth electronic sampler and digitizer. To address this problem, Photonic Time Stretch has been introduced to reduce the need for high speed electronic measurement equipment by significantly slowing down the speed of sampling signal. However, this generates massive data volume. Photonics-assisted methods such as Anamorphic Stretch Transform, Compressed Sensing and Fourier spectrum acquisition sensing have been addressed to achieve data compression while sampling the information. In this thesis, novel photonic implementations of each of these methods have been investigated through numerical and experimental demonstrations. The main contribution of this thesis include (1) Application of photonic implementation of compressed sensing for Optical Coherence Tomography, Fiber Bragg Grating enabled signal sensing and blind spectrum sensing applications (2) Photonic compressed sensing enabled ultra-fast imaging system (3) Fourier spectrum acquisition for RF spectrum sensing with all-optical approach (4) Adaptive non-uniform photonic time stretch methods using anamorphic stretch transform to reduce the the number of samples to be measured

Optical Signal Processing For Data Compression In Ultrafast Measurement

Today the world is filled with continuous deluge of digital information which are ever increasing by every fraction of second. Real-time analog information such as images, RF signals needs to be sampled and quantized to represent in digital domain with help of measurement systems for information analysis, further post processing and storage. Photonics offers various advantages in terms of high bandwidth, security, immunity to electromagnetic interference, reduction in frequency dependant loss as compared to conventional electronic measurement systems. However the large bandwidth data needs to be acquired as per Nyquist principle requiring high bandwidth electronic sampler and digitizer. To address this problem, Photonic Time Stretch has been introduced to reduce the need for high speed electronic measurement equipment by significantly slowing down the speed of sampling signal. However, this generates massive data volume. Photonics-assisted methods such as Anamorphic Stretch Transform, Compressed Sensing and Fourier spectrum acquisition sensing have been addressed to achieve data compression while sampling the information. In this thesis, novel photonic implementations of each of these methods have been investigated through numerical and experimental demonstrations. The main contribution of this thesis include (1) Application of photonic implementation of compressed sensing for Optical Coherence Tomography, Fiber Bragg Grating enabled signal sensing and blind spectrum sensing applications (2) Photonic compressed sensing enabled ultra-fast imaging system (3) Fourier spectrum acquisition for RF spectrum sensing with all-optical approach (4) Adaptive non-uniform photonic time stretch methods using anamorphic stretch transform to reduce the the number of samples to be measured

Interferometry-based Free Space Communication And Information Processing

This dissertation studies, analyzes, and experimentally demonstrates the innovative use of interference phenomenon in the field of opto-electronic information processing and optical communications. A number of optical systems using interferometric techniques both in the optical and the electronic domains has been demonstrated in the filed of signal transmission and processing, optical metrology, defense, and physical sensors. Specifically it has been shown that the interference of waves in the form of holography can be exploited to realize a novel optical scanner called Code Multiplexed Optical Scanner (C-MOS). The C-MOS features large aperture, wide scan angles, 3-D beam control, no moving parts, and high beam scanning resolution. A C-MOS based free space optical transceiver for bi-directional communication has also been experimentally demonstrated. For high speed, large bandwidth, and high frequency operation, an optically implemented reconfigurable RF transversal filter design is presented that implements wide range of filtering algorithms. A number of techniques using heterodyne interferometry via acousto-optic device for optical path length measurements have been described. Finally, a whole new class of interferometric sensors for optical metrology and sensing applications is presented. A non-traditional interferometric output signal processing scheme has been developed. Applications include, for example, temperature sensors for harsh environments for a wide temperature range from room temperature to 1000 degree C

Commissioning of a Compton camera for medical imaging

The interest of using hadron-therapy in cancer treatment, particularly for tumors in the vicinity of critical organs-at-risk, is continuously growing due the ability of this treatment modality to provide high precision dose delivery. In order to fully exploit this beneficial property, it is mandatory to ensure that the well-localized dose deposition (Bragg peak) is located in the tumor volume. This calls for a precise in-vivo monitoring of the particle (proton, ion) beam stopping range. Therefore, the purpose of our project is to develop an in-vivo imaging system based on a Compton camera to verify the particle beam range by detecting (multi-MeV) prompt γ rays, generated as a result of nuclear reactions between the particle beam and biological tissue. In the context of this thesis the prototype of the LMU Compton camera was considerably improved and upgraded, and characterized both in the laboratory as well as under online conditions with particle beams at various accelerator facilities. The Compton camera consists of two main components: a scatterer (tracker), formed by a stack of six double-sided Si-strip detectors (DSSSD), and a monolithic LaBr 3 :Ce scintillation detector (5x5x3 cm 3 ), acting as absorber. The highly segmented DSSSD detectors, each with 128 strips per side (strip pitch: 0.39 mm), is processed by a compact ASIC-based electronics (1536 signal channels), while the scintillation detector is read out by a 256-fold segmented, position-sensitive multi-anode photomultiplier tube, providing energy and time information for each PMT segment. The stacked design of the LMU Compton camera scatter detector allows not only to reconstruct the incident photon origin, but it also allows to track Compton scattered electrons, thus enhancing the reconstruction efficiency compared to the conventional design. The Compton camera absorber (LaBr 3 :Ce scintillator crystal) was characterized in two different side-surface wrapping scenarios, absorptive and reflective. (Position-dependent) energy resolution and time resolution were determined for both coating scenarios, revealing the superior properties of the advanced scintillator material in case of the reflectively coated crystal, providing excellent energy (position independent: ∆E/E =3.8 % at 662 keV) and time resolution (273(6) ps FWHM). In addition, the impact of the crystal wrapping options on the scintillation light distribution was studied by extracting the Light Spread Function (LSF) from the crystal irradiation with a collimated 137 Cs source. Here, as can be expected, the absorptively coated crystal reveals a slightly better FWHM value of the LSF compared to the reflectively coated detector. Nevertheless, the drastic improvement of the other properties with reflective coating motivated this choice for the Compton camera absorber. The capability of the monolithic LaBr 3 :Ce scintillator to provide the γ-ray interaction position, which is a mandatory prerequisite for the targeted photon source reconstruction based on Compton scattering, was determined by applying two specific algorithms (’k-nearest neighbor’(k-NN) and ’Categorical Average Pattern’ (CAP)). These algorithms require a large reference data base of 2D scintillation light amplitude distributions, acquired by perpendicularly irradiating the scintillator front surface with a tightly (1 mm diameter) collimated photon source on a fine grid (0.5 mm step size). Two γ-ray sources, 137 Cs and 60 Co, were used to generate the required reference libraries in order to study the energy-dependent spatial resolution of the LaBr 3 :Ce scintillator. Systematic parameter studies were performed as a function of the photon energy, PMT granularity, irradiation grid size and number of photopeak events acquired in each of the 10 4 irradiation positions. Optimum values for the spatial resolution were achieved with 4.8(1) mm (FWHM) at 662 keV and 3.7(1) mm (FWHM) at 1.3 MeV using the CAP algorithm,thus almost reaching the final design goal of 3 mm envisaged for the prompt-γ energy region of 4-6 MeV. With the observed trend of improving spatial resolution with increasing photon energy, it will be interesting to study this property beyond the realm of γ-ray calibration sources in the higher energy region beyond 4 MeV, provided the availablility of an intense, monoenergetic and collimated photon beam. Furthermore, the Compton camera has been commissioned at different particle beam facilities. The camera components were first calibrated and characterized with monoenergetic 4.44 MeV γ rays generated via the nuclear 15 N(p,αγ) 12 C ∗ reaction at the Helmholtz-Zentrum Dresden Rossendorf (HZDR). The response of both the scatter and absorber detectors was found in good agreement with Monte-Carlo simulations. Moreover, the time-of-flight (TOF) measurement capability of the absorbing scintillator was studied at the Garching Tandem accelerator, using a 20 MeV pulsed (400 ns) deuteron beam hitting a water phantom, showing prompt γ rays well separated from the slower neutron background. The camera was finally commissioned with different clinical proton beams (100 MeV, 160 MeV and 225 MeV) at the research area of the Universitäts Protonen Therapie Dresden, stopping either in a water or a PMMA phantom. Energy spectra were acquired and separated into their prompt and delayed components, extracting the prompt photon contribution via TOF. The Compton electron energy deposit in each DSSSD layer was determined and found in very good agreement with simulation expectations. Hit multiplicities and the correlated electron tracking capability of the scatter/tracker array were investigated and limitations imposed by the present ASIC-based readout electronics, as well as options for further improvements, were identified

Modern Applications in Optics and Photonics: From Sensing and Analytics to Communication

Optics and photonics are among the key technologies of the 21st century, and offer potential for novel applications in areas such as sensing and spectroscopy, analytics, monitoring, biomedical imaging/diagnostics, and optical communication technology. The high degree of control over light fields, together with the capabilities of modern processing and integration technology, enables new optical measurement systems with enhanced functionality and sensitivity. They are attractive for a range of applications that were previously inaccessible. This Special Issue aims to provide an overview of some of the most advanced application areas in optics and photonics and indicate the broad potential for the future

Commissioning of a Compton camera for medical imaging

The interest of using hadron-therapy in cancer treatment, particularly for tumors in the vicinity of critical organs-at-risk, is continuously growing due the ability of this treatment modality to provide high precision dose delivery. In order to fully exploit this beneficial property, it is mandatory to ensure that the well-localized dose deposition (Bragg peak) is located in the tumor volume. This calls for a precise in-vivo monitoring of the particle (proton, ion) beam stopping range. Therefore, the purpose of our project is to develop an in-vivo imaging system based on a Compton camera to verify the particle beam range by detecting (multi-MeV) prompt γ rays, generated as a result of nuclear reactions between the particle beam and biological tissue. In the context of this thesis the prototype of the LMU Compton camera was considerably improved and upgraded, and characterized both in the laboratory as well as under online conditions with particle beams at various accelerator facilities. The Compton camera consists of two main components: a scatterer (tracker), formed by a stack of six double-sided Si-strip detectors (DSSSD), and a monolithic LaBr 3 :Ce scintillation detector (5x5x3 cm 3 ), acting as absorber. The highly segmented DSSSD detectors, each with 128 strips per side (strip pitch: 0.39 mm), is processed by a compact ASIC-based electronics (1536 signal channels), while the scintillation detector is read out by a 256-fold segmented, position-sensitive multi-anode photomultiplier tube, providing energy and time information for each PMT segment. The stacked design of the LMU Compton camera scatter detector allows not only to reconstruct the incident photon origin, but it also allows to track Compton scattered electrons, thus enhancing the reconstruction efficiency compared to the conventional design. The Compton camera absorber (LaBr 3 :Ce scintillator crystal) was characterized in two different side-surface wrapping scenarios, absorptive and reflective. (Position-dependent) energy resolution and time resolution were determined for both coating scenarios, revealing the superior properties of the advanced scintillator material in case of the reflectively coated crystal, providing excellent energy (position independent: ∆E/E =3.8 % at 662 keV) and time resolution (273(6) ps FWHM). In addition, the impact of the crystal wrapping options on the scintillation light distribution was studied by extracting the Light Spread Function (LSF) from the crystal irradiation with a collimated 137 Cs source. Here, as can be expected, the absorptively coated crystal reveals a slightly better FWHM value of the LSF compared to the reflectively coated detector. Nevertheless, the drastic improvement of the other properties with reflective coating motivated this choice for the Compton camera absorber. The capability of the monolithic LaBr 3 :Ce scintillator to provide the γ-ray interaction position, which is a mandatory prerequisite for the targeted photon source reconstruction based on Compton scattering, was determined by applying two specific algorithms (’k-nearest neighbor’(k-NN) and ’Categorical Average Pattern’ (CAP)). These algorithms require a large reference data base of 2D scintillation light amplitude distributions, acquired by perpendicularly irradiating the scintillator front surface with a tightly (1 mm diameter) collimated photon source on a fine grid (0.5 mm step size). Two γ-ray sources, 137 Cs and 60 Co, were used to generate the required reference libraries in order to study the energy-dependent spatial resolution of the LaBr 3 :Ce scintillator. Systematic parameter studies were performed as a function of the photon energy, PMT granularity, irradiation grid size and number of photopeak events acquired in each of the 10 4 irradiation positions. Optimum values for the spatial resolution were achieved with 4.8(1) mm (FWHM) at 662 keV and 3.7(1) mm (FWHM) at 1.3 MeV using the CAP algorithm,thus almost reaching the final design goal of 3 mm envisaged for the prompt-γ energy region of 4-6 MeV. With the observed trend of improving spatial resolution with increasing photon energy, it will be interesting to study this property beyond the realm of γ-ray calibration sources in the higher energy region beyond 4 MeV, provided the availablility of an intense, monoenergetic and collimated photon beam. Furthermore, the Compton camera has been commissioned at different particle beam facilities. The camera components were first calibrated and characterized with monoenergetic 4.44 MeV γ rays generated via the nuclear 15 N(p,αγ) 12 C ∗ reaction at the Helmholtz-Zentrum Dresden Rossendorf (HZDR). The response of both the scatter and absorber detectors was found in good agreement with Monte-Carlo simulations. Moreover, the time-of-flight (TOF) measurement capability of the absorbing scintillator was studied at the Garching Tandem accelerator, using a 20 MeV pulsed (400 ns) deuteron beam hitting a water phantom, showing prompt γ rays well separated from the slower neutron background. The camera was finally commissioned with different clinical proton beams (100 MeV, 160 MeV and 225 MeV) at the research area of the Universitäts Protonen Therapie Dresden, stopping either in a water or a PMMA phantom. Energy spectra were acquired and separated into their prompt and delayed components, extracting the prompt photon contribution via TOF. The Compton electron energy deposit in each DSSSD layer was determined and found in very good agreement with simulation expectations. Hit multiplicities and the correlated electron tracking capability of the scatter/tracker array were investigated and limitations imposed by the present ASIC-based readout electronics, as well as options for further improvements, were identified

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Conformable transistors for bioelectronics

The diversity of network disruptions that occur in patients with neuropsychiatric disorders creates a strong demand for personalized medicine. Such approaches often take the form of implantable bioelectronic devices that are capable of monitoring pathophysiological activity for identifying biomarkers to allow for local and responsive delivery of intervention. They are also required to transmit this data outside of the body for evaluation of the treatment’s efficacy. However, the ability to perform these demanding electronic functions in the complex physiological environment with minimum disruption to the biological tissue remains a big challenge. An optimal fully implantable bioelectronic device would require each component from the front-end to the data transmission to be conformable and biocompatible. For this reason, organic material-based conformable electronics are ideal candidates for components of bioelectronic circuits due to their inherent flexibility, and soft nature. In this work, first an organic mixed-conducting particulate composite material (MCP) able to form functional electronic components and non-invasively acquire high–spatiotemporal resolution electrophysiological signals by directly interfacing human skin is presented. Secondly, we introduce organic electrochemical internal ion-gated transistors (IGTs) as a high-density, high-amplification sensing component as well as a low leakage, high-speed processing unit. Finally, a novel wireless, battery-free strategy for electrophysiological signal acquisition, processing, and transmission that employs IGTs and an ionic communication circuit (IC) is introduced. We show that the wirelessly-powered IGTs are able to acquire and modulate neurophysiological data in-vivo and transmit them transdermally, eliminating the need for any hard Si-based electronics in the implant

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium