Thesis (Ph. D.)--Boston University This item was digitized by the Internet Archive.

viii, 184 leaves : graphs, tables ; 30 cm / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Mawson Institute, 1978

This thesis describes my work on the project to connect the James Clerk Maxwell Telescope (JCMT) and the Caltech Submillimeter Observatory (CSO) to form the world's first astronomical interferometer operating at submillimetre wavelengths. Included are my contributions to the technical design and construction of the instrument and to the subsequent debugging and calibration, and my analysis of the data that was obtained from a number of astronomical objects. I was responsible for much of the system that brings the signals from the receivers at each antenna to the digital correlator at the JCMT. A key feature is that the signals are carried extensively in single-mode optical fibre. The design of the delay line system is presented; this helps to equalize the travel times from the source to the correlator by inserting different lengths of optical fibre into the two signal paths. Also described is the use of a microcomputer to control a pair of oscillators, where accurate timing is necessary to ensure that a source is tracked correctly as the Earth rotates. Careful calibration is needed to remove the effects of the instrument from the data. For an interferometer this requires a precise knowledge of many aspects of the system, including, the lengths of the baseline components, thermal drift in the fibre and other components, the deformation of the dishes under gravity, the contribution of the Earth's atmosphere and the complex passband. The techniques used to make these measurements on the JCMT -CSO Interferometer are described. There is also an explanation of how software that I have written processes the raw data from the correlator to give spectra and fluxes.<br> After four rather brief observing sessions, the interferometer is working well and has been used successfully to observe several astronomical sources. Brief descriptions are given of observations and their interpretation for three sources: the recombination-line maser source MWC 349, the black-hole candidate Sagittarius A* at the centre of our galaxy, and the nearby radio-galaxy Centaurus A. This is followed by a more detailed analysis of data for the evolved star VY CMa and observations of discs around young stars. Spectra of the 321 GHz H20 line from VY CMa confirm that maser amplification is responsible for the emission. Continuum emission, spatially offset from the masers, was also detected with the interferometer, as was the CO (3-2) line. These data, particularly the offset continuum, are shown to be incompatible with single-star models for VY CMa. Instead, a binary model is proposed. This also helps to account for many previous observational results. Many protostars are suspected of having accretion discs. The JCMT-CSO Interferometer has resolved the dust continuum emission on scales of < 100 AU for the sources HL Tau and L1551-IRS 5. An analysis of the visibility curves is presented, showing that the emission is extended perpendicular to the outflow direction in each case; radii to half-maximum brightness are determined to be 60 AU and 80 AU respectively. A lower limit to the disc masses of ~0.02 M. is also derived.

The interferometeric optical fiber sensor has high sensitivity for sound signal. This characteristic is used to design hydrophones. The sound pressure causes the optical fiber to change its shape. So as to induce phase difference between sensing and reference arms. Using the demodulation system, we can get the signal we want. In this thesis, we plan to analyze three different kinds of optic configurations, such as Michelson, compensating Mach-Zehnder, hybrid configuration of Mach-Zehnder and Sagnac interferometers. The mathematical methods are used to compare their characters. We also use software to simulate the relation among sensitivity, delay fiber and frequency character of the Sagnac interferometer. In our experiment, we use PGC modulation technology and compare the results with a standard hydrophone B&K 8103 for calibration. We also measure the dynamic range of proposed three interferometers. The measurement result of this paper is as following: Michelson and compensating type Mach-Zehnder interferometer dynamic range were about 24.90 dB and 13.98 dB, the acoustic signal sensitivity was -201.67 dB re V/1uPa and -205.97 dB re V/Pa, respectively. The dynamic range of the hybrid of Mach-Zehnder and Sagnac type interferometer was 33.67 dB and acoustic signal sensitivity was -212.47 dB re V/1uPa.

Because the acoustic wave is capable of propagating at a long-distance in water, the hydrophone plays a key role in the underwater acoustic sensing all the time. The hydrophone based on fiber optic interferometry has an extremely high sensitivity and large dynamic range. In addition, the electrically passive, immunity to electromagnetic interference, and multiplexing properties of fiber optic sensor offer great advantages over traditional piezoelectric hydrophone. Due to the complete path-balance between the two counterpropagating waves, a Sagnac interferometric configuration can employ a low-coherent light source to reduce the cost. This configuration can easily route optical paths and replace sensor heads to compare with each other. But, the sensitivity varying with frequency and the polarization-induced signal fading problem make it unsuitable for applications in need of detecting correct amplitude of signals. The Michelson interferometric configuration with Farady rotator mirror (FRM) has a constant sensitivity and solves the polarization-induced signal fading problem. But, this configuration uses a high-coherent light source and expensive FRMs, and be difficult to route. In this paper, we use the polarization-insensitive Michelson fiber optic sensor to adjust the demodulation circuits we design. In this paper, we establish the interferometric hydrophones. The fiber optic coil of the sensor head is embedded with the special materials in order to acoustic impedance matching and waterproofing. We employ phase generated carrier demodulation technology to get the acoustic signal of interest from the output of the interferometer. In our experiment, the dual Sagnac configuration has a dynamic range of 23 dB and a sensitivity of -226 dB re V/1uPa, the Michelson configuration with FRMs has a dynamic range of 25 dB and a sensitivity of -204 dB re V/1uPa.

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We propose a PCF-based interferometer by the misaligned splicing method. The PCF-based interferometers are composed of a photonic crystal fiber (PCF) and single-mode fibers (SMFs) which are spliced with lateral offsets. As the wave propagates at the first splicing point, the lateral offset will excite the cladding mode and the core mode simultaneously. As the two modes reach the other splicing point, they are recombined and coupled into another SMF. Thus, we can observe the interference pattern resulted from the phase difference between the two modes. In addition, as the length of PCF is increased, the average splicing of the interference fringes become smaller in the same measured range. We demonstrate the applications of the PCF-based interferometer as temperature, bending, and the surrounding refractive index sensors. The temperature sensitivity for the 2-cm and 4-cm PCF-based-interferometer is 3.9.~4.3pm/¢XC and 3.5~4.3pm/¢XC, respectively. As we increase the surrounding refractive index, the curves move toward longer wavelengths. Besides, the measured bending sensitivity of the PCF-based interferometer is 3.8~4.2nm/m-1. We also fabricated the liquid-filled-PCF-based interferometers by using the vacuum filling method. The measured bending sensitivity of the liquid-filled-PCF-based interferometer is 8.5nm/m-1 which is higher than that of the PCF-based interferometer. The measured surrounding refractive index sensitivity is insensitive. Thus, this liquid-filled-PCF-based interferometer can also be utilized as a sensor.

iii, 119 leaves : ill. ; 30 cm / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1976) from the Mawson Institute for Antarctic Research, University of Adelaide