Scaling Optical Phased Arrays

Optical phased array (OPA) technology can improve the useful capabilities of lasers by controlling the relative optical phase of an array of emitting apertures. Combining lasers in this way can produce a beam with increased optical intensity, rapid beam pointing and the potential to perform adaptive optics to correct for atmospheric turbulence. Future applications of optical phased arrays, particularly ground-to-space laser transmission, require both the ability to combine individual high power optical sources and emitter counts greater than in existing implementations. Breakthrough Starshot proposes the ambitious goal of accelerating a light sail to 20% of the speed of light to reach the nearest solar system within a human lifespan, which may require upwards of 100 GW total power from 100 million emitters in a ground-to-space array. At a reduced scale, improved tracking and eventual manoeuvring of orbital space debris could be also improved through the use of a ground-to-space OPA. The research in this thesis presents improvements and techniques for internally-sensed optical phased array designs to allow the scaling to greater numbers of combined optical sources. While primarily motivated by enabling large scale ground-to-space optical phased arrays, consideration is given to more conventional systems and benefits to non-optical phased array applications. A thorough investigation of the limits of digitally enhanced heterodyne interferometry (DEHI), a technique which allows the simultaneous measure of multiple optical phase signals, forms the first major component of this work. In addition to optical phased arrays, this technique has potential applications in acoustic sensing, wavefront sensing, satellite interferometry and fibre frequency references. A combination of analytical, simulation and experimental work was performed to better predict crosstalk between optical phase measurements and establish a set of robust parameters to improve phase measurement performance. Recommendations for requirement dependent parameter choices when using this technique are presented. The optical phased array underpinning this work is internally sensed, implying the ability to measure differential emitter paths without the need for external beam sampling. However, a lingering challenge in previous implementations arose from the double-pass of internal optical pathlengths, resulting in a pi-phase ambiguity in the sensing. The second key challenge addressed in this thesis is a proof-of-concept experimental solution to resolve this ambiguity, demonstrated with a novel waveguide optical head created using three-dimensional laser inscription. In culmination, this research presents a conceptual design for a ground-to-space optical phased array to act as the "photon engine" component of the Breakthrough Starshot program. This design involves a system to interferometrically link multiple sub-arrays in a scalable hierarchy. The active control of differential pathlengths in the hierarchy are enabled using a combination of wavelength division multiplexing and DEHI. Internal array measurements in this design are partnered with measurements of a satellite mounted laser beacon for atmospheric phase sensing and to account for unevenness of the array surface across a kilometre scale. The satellite laser beacon is designed to operate at a different wavelength from the arrays outgoing beam, allowing weak beacon light to be distinguished from high powered emitter scattering. An associated technique established and modelled in this work is how phase measurements can be accurately mapped between wavelengths. Multiple variations of the complete array are modelled to assess fundamental performance limits of the sensing system with realistic system parameters for the combination of 100 million emitters

Recruitment of Gr-1+ monocytes is essential for control of acute toxoplasmosis

Circulating murine monocytes comprise two largely exclusive subpopulations that are responsible for seeding normal tissues (Gr-1−/CCR2−/CX3CR1high) or responding to sites of inflammation (Gr-1+/CCR2+/CX3CR1lo). Gr-1+ monocytes are recruited to the site of infection during the early stages of immune response to the intracellular pathogen Toxoplasma gondii. A murine model of toxoplasmosis was thus used to examine the importance of Gr-1+ monocytes in the control of disseminated parasitic infection in vivo. The recruitment of Gr-1+ monocytes was intimately associated with the ability to suppress early parasite replication at the site of inoculation. Infection of CCR2−/− and MCP-1−/− mice with typically nonlethal, low doses of T. gondii resulted in the abrogated recruitment of Gr-1+ monocytes. The failure to recruit Gr-1+ monocytes resulted in greatly enhanced mortality despite the induction of normal Th1 cell responses leading to high levels of IL-12, TNF-α, and IFN-γ. The profound susceptibility of CCR2−/− mice establishes Gr-1+ monocytes as necessary effector cells in the resistance to acute toxoplasmosis and suggests that the CCR2-dependent recruitment of Gr-1+ monocytes may be an important general mechanism for resistance to intracellular pathogens

Towards solid-state beam steering using a 7-emitter 1550 nm optical phased array

We present the preliminary design and experimental results of a 1550 nm solid-state beam pointing system based on an optical phased array (OPA) architecture. OPAs manipulate the distribution of optical power in the far-field by controlling the phase of individual emitters in an array. This allows OPAs to steer the beam in the far field without any mechanical components (e.g., steering mirrors). The beam-steering system presented here uses waveguide electro-optic modulators to actuate the phase of each element in a 7-emitter OPA, enabling kHz bandwidth steering with sub-milliradian pointing precision. The control system used to stabilize and control the phase of each emitter in the OPA exploits a technique called digitally enhanced heterodyne interferometry, allowing the phase of each emitter to be measured simultaneously at a single photodetector, dramatically simplifying the optical system. All digital signal processing is performed using a field-programmable gate-array. Applications of this technology include free-space link acquisition and tracking for satellite-to-satellite laser communications and light detection and ranging (LiDAR).This work was partially funded by the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav) (project ID CE170100004) and the Australian Research Council Centre of Excellence for Engineered Quantum Systems (EQUS) (project ID CE170100009)

Type, Content, and Source of Social Support Perceived by Women during Pregnancy: Evidence from Matlab, Bangladesh

Specific and contextualized data on social support during distinct health events are needed to improve social support interventions. This study identified the type, content, and source of social support perceived by women during pregnancy. In-depth interviews with 25 women, aged 18-49 years, living in Matlab, Bangladesh, were conducted. The findings demonstrated that women perceived, the receipt of eight distinct types of support. The four most frequently-mentioned types included: practical help with routine activities, information/advice, emotional support and assurance, as well as the provision of resources and material goods. Sources varied by type of support and most frequently included-\u2014mothers, mothers-in-law, sistersin-law, and husbands. Examples depicting the content of each type of support revealed culturally-specific issues that can inform community-based social support interventions

Cultural Theories of Postpartum Bleeding in Matlab, Bangladesh: Implications for Community Health Intervention

Early recognition can reduce maternal disability and deaths due to postpartum haemorrhage. This study identified cultural theories of postpartum bleeding that may lead to inappropriate recognition and delayed care-seeking. Qualitative and quantitative data obtained through structured interviews with 149 participants living in Matlab, Bangladesh, including women aged 18-49 years, women aged 50+ years, traditional birth attendants (TBAs), and skilled birth attendants (SBAs), were subjected to cultural domain. General consensus existed among the TBAs and lay women regarding signs, causes, and treatments of postpartum bleeding (eigenvalue ratio 5.9, mean competence 0.59, and standard deviation 0.15). Excessive bleeding appeared to be distinguished by flow characteristics, not colour or quantity. Yet, the TBAs and lay women differed significantly from the SBAs in beliefs about normalcy of blood loss, causal role of the retained placenta and malevolent spirits, and care practices critical to survival. Cultural domain analysis captures variation in theories with specificity and representativeness necessary to inform community health intervention

Evolution of Bacterial Phosphoglycerate Mutases: Non-Homologous Isofunctional Enzymes Undergoing Gene Losses, Gains and Lateral Transfers

The glycolytic phosphoglycerate mutases exist as non-homologous isofunctional enzymes (NISE) having independent evolutionary origins and no similarity in primary sequence, 3D structure, or catalytic mechanism. Cofactor-dependent PGM (dPGM) requires 2,3-bisphosphoglycerate for activity; cofactor-independent PGM (iPGM) does not. The PGM profile of any given bacterium is unpredictable and some organisms such as Escherichia coli encode both forms.To examine the distribution of PGM NISE throughout the Bacteria, and gain insight into the evolutionary processes that shape their phyletic profiles, we searched bacterial genome sequences for the presence of dPGM and iPGM. Both forms exhibited patchy distributions throughout the bacterial domain. Species within the same genus, or even strains of the same species, frequently differ in their PGM repertoire. The distribution is further complicated by the common occurrence of dPGM paralogs, while iPGM paralogs are rare. Larger genomes are more likely to accommodate PGM paralogs or both NISE forms. Lateral gene transfers have shaped the PGM profiles with intradomain and interdomain transfers apparent. Archaeal-type iPGM was identified in many bacteria, often as the sole PGM. To address the function of PGM NISE in an organism encoding both forms, we analyzed recombinant enzymes from E. coli. Both NISE were active mutases, but the specific activity of dPGM greatly exceeded that of iPGM, which showed highest activity in the presence of manganese. We created PGM null mutants in E. coli and discovered the ΔdPGM mutant grew slowly due to a delay in exiting stationary phase. Overexpression of dPGM or iPGM overcame this defect.Our biochemical and genetic analyses in E. coli firmly establish dPGM and iPGM as NISE. Metabolic redundancy is indicated since only larger genomes encode both forms. Non-orthologous gene displacement can fully account for the non-uniform PGM distribution we report across the bacterial domain

Crosstalk reduction for multi-channel optical phase metrology

Digitally enhanced heterodyne interferometry (DEHI) combines the sub-wavelength displacement measurements of conventional laser interferometry with the multiplexing capabilities of spread-spectrum modulation techniques to discriminate between multiple electric fields at a single photodetector. Technologies that benefit from DEHI include optical phased arrays, which require the simultaneous phase measurement of a large number of electric fields. A consequence of measuring the phase of multiple electric fields is the introduction of crosstalk, which can degrade measurement precision. This work analytically and experimentally investigates the crosstalk when using DEHI to measure the phase of an arbitrarily large number of electric fields at a single photodetector. Also considered is the practical limit the dynamic range of the photodetector and shot noise imposes on the number of electric fields that can be discriminated. We describe how to minimize crosstalk by design. Experimental results demonstrate up to 55 dB suppression of crosstalk between two electric fields with a phase measurement bandwidth of 20 kHz and 1-10 pm/Hz displacement sensitivity for audio frequencies. Additionally, we demonstrate scaling of crosstalk proportional to the square-root of the number of electric fields when using an M-sequence modulation. Based on this analysis, we estimate that digitally enhanced heterodyne interferometry should be capable of measuring the phase of several hundreds of electric fields at a single photodetector while maintaining the same measurement bandwidth.AustralianResearch Council Centre of Excellence for GravitationalWave Discovery (CE170100004); AustralianResearch Council Centre of Excellence for Engineered Quantum Systems (CE170100009). P. Sibley would also like to acknowledge the support of the Cooperative Research Centre for Space Environment Management (SERC Limited) through the Australian Government’s Cooperative Research Centre Programme and is supported by an Australian Government Research Training Program (RTP Scholarship)