Optical Coherence Tomography(OCT) is a popular, rapidly growing imaging technique with an increasing number of bio-medical applications due to its noninvasive nature. However, there are three major challenges in understanding and improving an OCT system: (1) Obtaining an OCT image is not easy. It either takes a real medical experiment or requires days of computer simulation. Without much data, it is difficult to study the physical processes underlying OCT imaging of different objects simply because there aren't many imaged objects. (2) Interpretation of an OCT image is also hard. This challenge is more profound than it appears. For instance, it would require a trained expert to tell from an OCT image of human skin whether there is a lesion or not. This is expensive in its own right, but even the expert cannot be sure about the exact size of the lesion or the width of the various skin layers. The take-away message is that analyzing an OCT image even from a high level would usually require a trained expert, and pixel-level interpretation is simply unrealistic. The reason is simple: we have OCT images but not their underlying ground-truth structure, so there is nothing to learn from. (3) The imaging depth of OCT is very limited (millimeter or sub-millimeter on human tissues). While OCT utilizes infrared light for illumination to stay noninvasive, the downside of this is that photons at such long wavelengths can only penetrate a limited depth into the tissue before getting back-scattered. To image a particular region of a tissue, photons first need to reach that region. As a result, OCT signals from deeper regions of the tissue are both weak (since few photons reached there) and distorted (due to multiple scatterings of the contributing photons). This fact alone makes OCT images very hard to interpret.
\r\n\r\nThis thesis addresses the above challenges by successfully developing an advanced Monte Carlo simulation platform which is 10000 times faster than the state-of-the-art simulator in the literature, bringing down the simulation time from 360 hours to a single minute. This powerful simulation tool not only enables us to efficiently generate as many OCT images of objects with arbitrary structure and shape as we want on a common desktop computer, but it also provides us the underlying ground-truth of the simulated images at the same time because we dictate them at the beginning of the simulation. This is one of the key contributions of this thesis. What allows us to build such a powerful simulation tool includes a thorough understanding of the signal formation process, clever implementation of the importance sampling/photon splitting procedure, efficient use of a voxel-based mesh system in determining photon-mesh interception, and a parallel computation of different A-scans that consist a full OCT image, among other programming and mathematical tricks, which will be explained in detail later in the thesis.
\r\n\r\nNext we aim at the inverse problem: given an OCT image, predict/reconstruct its ground-truth structure on a pixel level. By solving this problem we would be able to interpret an OCT image completely and precisely without the help from a trained expert. It turns out that we can do much better. For simple structures we are able to reconstruct the ground-truth of an OCT image more than 98% correctly, and for more complicated structures (e.g., a multi-layered brain structure) we are looking at 93%. We achieved this through extensive uses of Machine Learning. The success of the Monte Carlo simulation already puts us in a great position by providing us with a great deal of data (effectively unlimited), in the form of (image, truth) pairs. Through a transformation of the high-dimensional response variable, we convert the learning task into a multi-output multi-class classification problem and a multi-output regression problem. We then build a hierarchy architecture of machine learning models (committee of experts) and train different parts of the architecture with specifically designed data sets. In prediction, an unseen OCT image first goes through a classification model to determine its structure (e.g., the number and the types of layers present in the image); then the image is handed to a regression model that is trained specifically for that particular structure to predict the length of the different layers and by doing so reconstruct the ground-truth of the image. We also demonstrate that ideas from Deep Learning can be useful to further improve the performance.
\r\n\r\nIt is worth pointing out that solving the inverse problem automatically improves the imaging depth, since previously the lower half of an OCT image (i.e., greater depth) can be hardly seen but now becomes fully resolved. Interestingly, although OCT signals consisting the lower half of the image are weak, messy, and uninterpretable to human eyes, they still carry enough information which when fed into a well-trained machine learning model spits out precisely the true structure of the object being imaged. This is just another case where Artificial Intelligence (AI) outperforms human. To the best knowledge of the author, this thesis is not only a success but also the first attempt to reconstruct an OCT image at a pixel level. To even give a try on this kind of task, it would require fully annotated OCT images and a lot of them (hundreds or even thousands). This is clearly impossible without a powerful simulation tool like the one developed in this thesis.
", "doi": "10.7907/Z9X63JVM", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:8254", "collection": "thesis", "collection_id": "8254", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05212014-113511509", "primary_object_url": { "basename": "Steger-S-T-electronic-updated.pdf", "content": "final", "filesize": 4202621, "license": "other", "mime_type": "application/pdf", "url": "/8254/1/Steger-S-T-electronic-updated.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "A Fundamental Approach to Phase Noise Reduction in Hybrid Si/III-V Lasers", "author": [ { "family_name": "Steger", "given_name": "Scott Tiedeman", "clpid": "Steger-Scott-Tiedeman" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Choo", "given_name": "Hyuck", "clpid": "Choo-Hyuck" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" }, { "family_name": "Painter", "given_name": "Oskar J.", "clpid": "Painter-O" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Spontaneous emission into the lasing mode fundamentally limits laser linewidths. Reducing cavity losses provides two benefits to linewidth: (1) fewer excited carriers are needed to reach threshold, resulting in less phase-corrupting spontaneous emission into the laser mode, and (2) more photons are stored in the laser cavity, such that each individual spontaneous emission event disturbs the phase of the field less. Strong optical absorption in III-V materials causes high losses, preventing currently-available semiconductor lasers from achieving ultra-narrow linewidths. This absorption is a natural consequence of the compromise between efficient electrical and efficient optical performance in a semiconductor laser. Some of the III-V layers must be heavily doped in order to funnel excited carriers into the active region, which has the side effect of making the material strongly absorbing.
\r\n\r\nThis thesis presents a new technique, called modal engineering, to remove modal energy from the lossy region and store it in an adjacent low-loss material, thereby reducing overall optical absorption. A quantum mechanical analysis of modal engineering shows that modal gain and spontaneous emission rate into the laser mode are both proportional to the normalized intensity of that mode at the active region. If optical absorption near the active region dominates the total losses of the laser cavity, shifting modal energy from the lossy region to the low-loss region will reduce modal gain, total loss, and the spontaneous emission rate into the mode by the same factor, so that linewidth decreases while the threshold inversion remains constant. The total spontaneous emission rate into all other modes is unchanged.
\r\n\r\nModal engineering is demonstrated using the Si/III-V platform, in which light is generated in the III-V material and stored in the low-loss silicon material. The silicon is patterned as a high-Q resonator to minimize all sources of loss. Fabricated lasers employing modal engineering to concentrate light in silicon demonstrate linewidths at least 5 times smaller than lasers without modal engineering at the same pump level above threshold, while maintaining the same thresholds.
", "doi": "10.7907/91CD-6H86", "publication_date": "2014", "thesis_type": "phd", "thesis_year": "2014" }, { "id": "thesis:7820", "collection": "thesis", "collection_id": "7820", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06032013-060508409", "primary_object_url": { "basename": "Arseny_Vasilyev_Thesis_CompleteThesis.pdf", "content": "", "filesize": 10762891, "license": "other", "mime_type": "application/pdf", "url": "/7820/1/Arseny_Vasilyev_Thesis_CompleteThesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Optoelectronic Swept-Frequency Laser and Its Applications in Ranging, Three-Dimensional Imaging, and Coherent Beam Combining of Chirped-Seed Amplifiers", "author": [ { "family_name": "Vasilyev", "given_name": "Arseny", "clpid": "Vasilyev-Arseny" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" }, { "family_name": "Schwab", "given_name": "Keith C.", "clpid": "Schwab-K-C" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis explores the design, construction, and applications of the optoelectronic swept-frequency laser (SFL). The optoelectronic SFL is a feedback loop designed around a swept-frequency (chirped) semiconductor laser (SCL) to control its instantaneous optical frequency, such that the chirp characteristics are determined solely by a reference electronic oscillator. The resultant system generates precisely controlled optical frequency sweeps. In particular, we focus on linear chirps because of their numerous applications. We demonstrate optoelectronic SFLs based on vertical-cavity surface-emitting lasers (VCSELs) and distributed-feedback lasers (DFBs) at wavelengths of 1550 nm and 1060 nm. We develop an iterative bias current predistortion procedure that enables SFL operation at very high chirp rates, up to 10^16 Hz/sec. We describe commercialization efforts and implementation of the predistortion algorithm in a stand-alone embedded environment, undertaken as part of our collaboration with Telaris, Inc. We demonstrate frequency-modulated continuous-wave (FMCW) ranging and three-dimensional (3-D) imaging using a 1550 nm optoelectronic SFL.
\r\n\r\nWe develop the technique of multiple source FMCW (MS-FMCW) reflectometry, in which the frequency sweeps of multiple SFLs are \"stitched\" together in order to increase the optical bandwidth, and hence improve the axial resolution, of an FMCW ranging measurement. We demonstrate computer-aided stitching of DFB and VCSEL sweeps at 1550 nm. We also develop and demonstrate hardware stitching, which enables MS-FMCW ranging without additional signal processing. The culmination of this work is the hardware stitching of four VCSELs at 1550 nm for a total optical bandwidth of 2 THz, and a free-space axial resolution of 75 microns.
\r\n\r\nWe describe our work on the tomographic imaging camera (TomICam), a 3-D imaging system based on FMCW ranging that features non-mechanical acquisition of transverse pixels. Our approach uses a combination of electronically tuned optical sources and low-cost full-field detector arrays, completely eliminating the need for moving parts traditionally employed in 3-D imaging. We describe the basic TomICam principle, and demonstrate single-pixel TomICam ranging in a proof-of-concept experiment. We also discuss the application of compressive sensing (CS) to the TomICam platform, and perform a series of numerical simulations. These simulations show that tenfold compression is feasible in CS TomICam, which effectively improves the volume acquisition speed by a factor ten.
\r\n\r\nWe develop chirped-wave phase-locking techniques, and apply them to coherent beam combining (CBC) of chirped-seed amplifiers (CSAs) in a master oscillator power amplifier configuration. The precise chirp linearity of the optoelectronic SFL enables non-mechanical compensation of optical delays using acousto-optic frequency shifters, and its high chirp rate simultaneously increases the stimulated Brillouin scattering (SBS) threshold of the active fiber. We characterize a 1550 nm chirped-seed amplifier coherent-combining system. We use a chirp rate of 5*10^14 Hz/sec to increase the amplifier SBS threshold threefold, when compared to a single-frequency seed. We demonstrate efficient phase-locking and electronic beam steering of two 3 W erbium-doped fiber amplifier channels, achieving temporal phase noise levels corresponding to interferometric fringe visibilities exceeding 98%.
", "doi": "10.7907/YD38-BT07", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7800", "collection": "thesis", "collection_id": "7800", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-151934307", "primary_object_url": { "basename": "Thesis.pdf", "content": "final", "filesize": 9140424, "license": "other", "mime_type": "application/pdf", "url": "/7800/1/Thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "High-Coherence Hybrid Si/III-V Semiconductor Lasers", "author": [ { "family_name": "Santis", "given_name": "Christos Theodoros", "orcid": "0000-0001-8636-1613", "clpid": "Santis-Christos-Theodoros" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Painter", "given_name": "Oskar J.", "clpid": "Painter-O" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" }, { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The relentlessly increasing demand for network bandwidth, driven primarily by Internet-based services such as mobile computing, cloud storage and video-on-demand, calls for more efficient utilization of the available communication spectrum, as that afforded by the resurging DSP-powered coherent optical communications. Encoding information in the phase of the optical carrier, using multilevel phase modulationformats, and employing coherent detection at the receiver allows for enhanced spectral efficiency and thus enables increased network capacity. The distributed feedback semiconductor laser (DFB) has served as the near exclusive light source powering the fiber optic, long-haul network for over 30 years. The transition to coherent communication systems is pushing the DFB laser to the limits of its abilities. This is due to its limited temporal coherence that directly translates into the number of different phases that can be imparted to a single optical pulse and thus to the data capacity. Temporal coherence, most commonly quantified in the spectral linewidth \u0394\u03bd, is limited by phase noise, result of quantum-mandated spontaneous emission of photons due to random recombination of carriers in the active region of the laser.
\r\n\r\nIn this work we develop a generically new type of semiconductor laser with the requisite coherence properties. We demonstrate electrically driven lasers characterized by a quantum noise-limited spectral linewidth as low as 18 kHz. This narrow linewidth is result of a fundamentally new laser design philosophy that separates the functions of photon generation and storage and is enabled by a hybrid Si/III-V integration platform. Photons generated in the active region of the III-V material are readily stored away in the low loss Si that hosts the bulk of the laser field, thereby enabling high-Q photon storage. The storage of a large number of coherent quanta acts as an optical flywheel, which by its inertia reduces the effect of the spontaneous emission-mandated phase perturbations on the laser field, while the enhanced photon lifetime effectively reduces the emission rate of incoherent quanta into the lasing mode. Narrow linewidths are obtained over a wavelength bandwidth spanning the entire optical communication C-band (1530-1575nm) at only a fraction of the input power required by conventional DFB lasers. The results presented in this thesis hold great promise for the large scale integration of lithographically tuned, high-coherence laser arrays for use in coherent communications, that will enable Tb/s-scale data capacities.
", "doi": "10.7907/M4KJ-8H56", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7812", "collection": "thesis", "collection_id": "7812", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-213433052", "primary_object_url": { "basename": "JS_Thesis.pdf", "content": "final", "filesize": 8183664, "license": "other", "mime_type": "application/pdf", "url": "/7812/1/JS_Thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "On-Chip Integrated Label-Free Optical Biosensing", "author": [ { "family_name": "Sendowski", "given_name": "Jacob Benjamin", "clpid": "Sendowski-Jacob-Benjamin" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis investigates the design and implementation of a label-free optical biosensing system utilizing a robust on-chip integrated platform. The goal has been to transition optical micro-resonator based label-free biosensing from a laborious and delicate laboratory demonstration to a tool for the analytical life scientist. This has been pursued along four avenues: (1) the design and fabrication of high-$Q$ integrated planar microdisk optical resonators in silicon nitride on silica, (2) the demonstration of a high speed optoelectronic swept frequency laser source, (3) the development and integration of a microfluidic analyte delivery system, and (4) the introduction of a novel differential measurement technique for the reduction of environmental noise.
\r\n\r\nThe optical part of this system combines the results of two major recent developments in the field of optical and laser physics: the high-$Q$ optical resonator and the phase-locked electronically controlled swept-frequency semiconductor laser. The laser operates at a wavelength relevant for aqueous sensing, and replaces expensive and fragile mechanically-tuned laser sources whose frequency sweeps have limited speed, accuracy and reliability. The high-$Q$ optical resonator is part of a monolithic unit with an integrated optical waveguide, and is fabricated using standard semiconductor lithography methods. Monolithic integration makes the system significantly more robust and flexible compared to current, fragile embodiments that rely on the precarious coupling of fragile optical fibers to resonators. The silicon nitride on silica material system allows for future manifestations at shorter wavelengths. The sensor also includes an integrated microfluidic flow cell for precise and low volume delivery of analytes to the resonator surface. We demonstrate the refractive index sensing action of the system as well as the specific and nonspecific adsorption of proteins onto the resonator surface with high sensitivity. Measurement challenges due to environmental noise that hamper system performance are discussed and a differential sensing measurement is proposed, implemented, and demonstrated resulting in the restoration of a high performance sensing measurement.
\r\n\r\nThe instrument developed in this work represents an adaptable and cost-effective platform capable of various sensitive, label-free measurements relevant to the study of biophysics, biomolecular interactions, cell signaling, and a wide range of other life science fields. Further development is necessary for it to be capable of binding assays, or thermodynamic and kinetics measurements; however, this work has laid the foundation for the demonstration of these applications.
", "doi": "10.7907/2H9Y-AB63", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7074", "collection": "thesis", "collection_id": "7074", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05242012-174045229", "primary_object_url": { "basename": "Thesis_HsiChunLiu.pdf", "content": "final", "filesize": 2427683, "license": "other", "mime_type": "application/pdf", "url": "/7074/1/Thesis_HsiChunLiu.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Theory and Experiment of Slow-Light Coupled-Resonator Structures", "author": [ { "family_name": "Liu", "given_name": "Hsi-Chun", "clpid": "Liu-Hsi-Chun" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" }, { "family_name": "Vaidyanathan", "given_name": "P. P.", "clpid": "Vaidyanathan-P-P" }, { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Slow light has been an inter-disciplinary topic and a rapidly growing area, especially over the last decade with the improvement of fabrication technology. The ability to slow down and control the group velocity of light may find applications such as optical buffers, optical delay lines, and enhanced light-matter interaction in optical modulator, amplifier, detectors, lasers, and nonlinear optics. The spirit of slow light is to replace a bulky device with a much shorter, compact structure.
\r\n\r\nThis thesis explores the design and experiment of coupled-resonator optical waveguides (CROWs), which consist of arrays of optical resonators in which light propagates through the coupling between resonators. The group velocity of light is dictated by the inter-resonator coupling strength. Light can be significantly slowed down if the inter-resonator coupling is weak. CROWs can be realized with various types of resonators. This thesis focuses on grating resonators in silicon waveguides, including grating-defect resonators and bandgap-modulated resonators. With the strong gratings, the grating resonators are only a few microns long. We control the inter-resonator coupling via the number of holes between adjacent resonators.
\r\n\r\nThe major limitations in the realization of CROWs have been various kinds of transmission losses, including the resonator losses, the discontinuity between CROWs and the coupling waveguides, and the fabrication disorder. These transmission losses limit the achievable group velocity and the maximum number of resonators. We address these transmission losses throughout this thesis. The resonator losses are overcome with the design and optimized fabrication of tapered grating-defect resonators and bandgap-modulated resonators. The discontinuity between CROWs and waveguides is reduced by tailoring the coupling along the CROW for adiabatic conversion. The optimization of the CROW response leads to the study of filter design based on CROW. Filter design formalism based on coupled-mode theory is presented. The effect of fabrication disorder on CROWs is analyzed, and the Butterworth filters are shown to be more robust against fabrication disorder. The fabrication and measurement of grating CROWs are presented, featuring high-Q (Q=105) grating resonators, coupling of up to 50 resonators, control of group velocity between c/13 and c/49, and Butterworth filters.
\r\n\r\nFinally, an optical analog of electromagnetically induced transparency is presented. The structure consists of two co-spatial gratings imposed on a three-mode waveguide. One of the supermodes, the Dark mode, possesses a group velocity which depends on the ratio of the grating strengths. The group velocity can be nearly zero if the two grating strengths are nearly identical.
\r\n", "doi": "10.7907/GVBF-4T29", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" }, { "id": "thesis:6364", "collection": "thesis", "collection_id": "6364", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04292011-221312708", "type": "thesis", "title": "Optoelectronic Control of the Phase and Frequency of Semiconductor Lasers", "author": [ { "family_name": "Satyan", "given_name": "Naresh", "clpid": "Satyan-Naresh" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Hajimiri", "given_name": "Ali", "clpid": "Hajimiri-A" }, { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis explores the precise control of the phase and frequency of the output of semiconductor lasers (SCLs), which are the basic building blocks of most modern optical communication networks. Phase and frequency control is achieved by purely electronic means, using SCLs in optoelectronic feedback systems, such as optical phase-locked loops (OPLLs) and optoelectronic swept-frequency laser (SFL) sources. Architectures and applications of these systems are studied.
\r\n\r\nOPLLs with single-section SCLs have limited bandwidths due to the nonuniform SCL frequency modulation (FM) response. To overcome this limitation, two novel OPLL architectures are designed and demonstrated, viz. (i) the sideband-locked OPLL, where the feedback into the SCL is shifted to a frequency range where the FM response is uniform, and (ii) composite OPLL systems, where an external optical phase modulator corrects excess phase noise. It is shown, theoretically and experimentally, and in the time and frequency domains, that the coherence of the master laser is \u201ccloned\u201d onto the slave SCL in an OPLL. An array of SCLs, phase-locked to a common master, therefore forms a coherent aperture, where the phase of each emitter is electronically controlled by the OPLL. Applications of phase-controlled apertures in coherent power-combining and all-electronic beam-steering are demonstrated.
\r\n\r\nAn optoelectronic SFL source that generates precisely linear, broadband, and rapid frequency chirps (several 100 GHz in 0.1 ms) is developed and demonstrated using a novel OPLL-like feedback system, where the frequency chirp characteristics are determined solely by a reference electronic oscillator. Results from high-sensitivity biomolecular sensing experiments utilizing the precise frequency control are reported. Techniques are developed to increase the tuning range of SFLs, which is the primary requirement in high-resolution three-dimensional imaging applications. These include (i) the synthesis of a larger effective bandwidth for imaging by \"stitching\" measurements taken using SFLs chirping over different regions of the optical spectrum; and (ii) the generation of a chirped wave with twice the chirp bandwidth and the same chirp characteristics by nonlinear four-wave mixing of the SFL output and a reference monochromatic wave. A quasi-phase-matching scheme to overcome dispersion in the nonlinear medium is described and implemented.
\r\n", "doi": "10.7907/24DM-VW62", "publication_date": "2011", "thesis_type": "phd", "thesis_year": "2011" }, { "id": "thesis:5780", "collection": "thesis", "collection_id": "5780", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05072010-002329705", "primary_object_url": { "basename": "Xiankai.Sun_thesis_simplex_printing.pdf", "content": "final", "filesize": 1974789, "license": "other", "mime_type": "application/pdf", "url": "/5780/1/Xiankai.Sun_thesis_simplex_printing.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Supermode Si/III-V Lasers and Circular Bragg Lasers", "author": [ { "family_name": "Sun", "given_name": "Xiankai", "orcid": "0000-0002-9137-0298", "clpid": "Sun-Xiankai" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Atwater", "given_name": "Harry Albert", "clpid": "Atwater-H-A" }, { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" }, { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Semiconductor lasers are arguably the most important component in optical communications. This thesis investigates two types of semiconductor lasers that are useful in integrated optics. Part I focuses on supermode Si/III\u2013V lasers and Part II discusses circular Bragg lasers for the application as surface-emitting lasers.
\r\n\r\nJust as optical fibers have largely replaced the traditional copper wires in long-distance applications, people started to consider incorporating optical communication onto chips, primarily because the increased ohmic heating and RC delay associated with the metal interconnection prevent further increase in the data-processing rate. Si is well known to be the integration platform for electronics, and III\u2013V materials (GaAs, InP, etc.) are efficient light emitters. It is natural to bring them together to realize the on-chip optical communication. Among various Si/III\u2013V integration schemes the most promising is the hybrid Si evanescent platform in which a wafer-bonding technique that is compatible with current CMOS processing is used to bring Si and III\u2013V materials together. Part I of this thesis focuses on the application of a novel mode-control method to such hybrid waveguide system to enhance the modal gain, which makes for more efficient and, most importantly, shorter devices that may hold the key to the photonics/electronics integration. The supermode theory is derived, the shortest adiabatic mode transformer is theoretically and numerically studied, and the device design and fabrication are presented, followed by the experimental demonstration of the performance enhancement in the mode-controlled Si/InGaAsP laser devices.
\r\n\r\nVertical cavity surface emitting lasers are a commercial light source for optical communications, but their single-modedness and good emission pattern are guaranteed only over a very small mode area (diameter of several microns) thus they have limitations in high-power applications. As an alternative, circular Bragg lasers can be designed as a superior surface emitting laser that produces high output power with good beam quality. Part II of this thesis presents a comprehensive and systematic theoretical study on the surface-emitting Hankel-phased circular Bragg lasers in various geometries. The analytical and numerical mode-solving methods will be described, followed by near- and above-threshold modal analyses.
", "doi": "10.7907/6797-0136", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:2284", "collection": "thesis", "collection_id": "2284", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05292009-172708", "primary_object_url": { "basename": "08_Thesis_Ostby.pdf", "content": "final", "filesize": 44426206, "license": "other", "mime_type": "application/pdf", "url": "/2284/9/08_Thesis_Ostby.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Photonic Whispering-Gallery Resonators in New Environments", "author": [ { "family_name": "Ostby", "given_name": "Eric Paul", "clpid": "Ostby-Eric-Paul" } ], "thesis_advisor": [ { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" } ], "thesis_committee": [ { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" }, { "family_name": "Atwater", "given_name": "Harry Albert", "clpid": "Atwater-H-A" }, { "family_name": "Painter", "given_name": "Oskar J.", "clpid": "Painter-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Optical whispering-gallery devices, like the microtoroid or microdisk, confine light at resonant frequencies and in ultra-small volumes for long periods of time. Such ultra-low loss resonators have been applied in diverse areas of scientific research, including low-threshold lasers on-chip, biological sensing, and quantum computing. In this thesis, novel ultra-low loss microstructures are studied for their unique characteristics and utility. The author investigates the interaction between microcavities and various environments in order to quantify the results and lay the foundation for future applications.
\r\n\r\nThe first optical cavity studied is the microtoroid, which possesses ultra-high quality factor (Q) on account of its nearly atomic smooth surface, produced by surface-tension induced laser reflow. Ytterbium-doped silica microtoroids are fabricated by a sol-gel technique. The ytterbium microtoroid laser achieves record-low laser threshold (2 \u00b5W) in air, and produces the first laser output for a solid-state laser in water. This laser in water can be developed as an ultra-sensitive biological sensor, with potentially record sensitivity enabled by gain-narrowed linewidth. Also, a novel CO2 laser reflow and microtoroid testing vacuum system is demonstrated. Fabrication and testing of microtoroids is performed in a vacuum chamber to study the effect of atmospheric water and upper limit of Q in microtoroids.
\r\n\r\nThe selective reflow of microtoroids presents difficulties for integration of on-chip optical waveguides. As an alternative, dimension-preserving low-loss optical structures are researched for their unique applications. A gold-coated silica microdisk is fabricated, and demonstrates record and nearly-ideal quality factor (1,376) as a surface-plasmon polariton resonator. The hybrid optical-plasmonic mode structure is studied in simulation and experiment. The plasmonic resonator has ultra-low mode volume and high field confinement, making it suitable for short-range optical communication or sensing. Finally, a novel whispering-gallery optical delay line in a spiral geometry is designed and experimentally demonstrated. The center transition region of the spiral is optimized for low transmission loss by beam propagation simulation. A 1.4 m long spiral waveguide within a 1 cm^2 area is presented. The spiral waveguide structure is being developed as a real-time optical delay line with fiber-like loss, important for optical communication and signal processing.
", "doi": "10.7907/ER2J-WT93", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:1184", "collection": "thesis", "collection_id": "1184", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03272008-143400", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 3825487, "license": "other", "mime_type": "application/pdf", "url": "/1184/16/thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Study of Optical Phase Lock Loops and the Applications in Coherent Beam Combining and Coherence Cloning", "author": [ { "family_name": "Liang", "given_name": "Wei", "clpid": "Liang-Wei" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Optical Phase-Lock loops (OPLLs) have potential applications in phase coherent optics including frequency synthesis, clock distribution and recovery, jitter and noise reduction, etc. However, most implemented OPLLs are based on solid state lasers, fiber lasers, or specially designed semiconductor lasers, whose bulky size and high cost inhibit the applications of OPLLs.
\r\n\r\nSemiconductor lasers have the advantages of low cost, small size, and high efficiency. In this thesis, I report on a study of OPLLs using commercial SCLs, and explore their novel applications in coherent beam combining and coherence cloning.
\r\n\r\nIn chapter 1-3, I will first introduce the theory of OPLLs and presents the experimental study of OPLLs made of different commercial SCLs. To improve the performance of OPLLs, electronic compensations using filter designs are also discussed and studied.
\r\n\r\nIn chapter 4-5, I will study the application of OPLLs in coherent beam combining. Using OPLLs, an array of slave lasers can be phase locked to the same master laser at the same frequency, their outputs can then be coherently combined. The phase variations of the element beams due to the optical path-length variations in fibers can be further corrected for by using multi-level OPLLs. This approach eliminates the use of the optical phase/frequency shifters conventionally required in a coherent beam combining system. In the proof of principle experiment, we have combined two lasers with a combining efficiency of 94% using the filled-aperture combining configuration. Furthermore, I will discuss the scalability of a cascaded filled-aperture combining system for the combination of a large number of lasers.
\r\n\r\nOPLLs can also be used to reduce the phase noise of SCLs by locking them to a low noise master laser. In chapter 6, I will describe the theory of coherence cloning using OPLLs and present the experimental measurements of the linewidths and frequency noises of a low noise fiber laser, a free-running and locked slave lasers.
\r\n\r\nIn chapter 7, the thesis concludes by proposing a novel OPLL configuration of large loop bandwidth and identifying future works that need to be done to advance the development of this technology.
", "doi": "10.7907/YHBF-KW11", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:2215", "collection": "thesis", "collection_id": "2215", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05282008-162123", "primary_object_url": { "basename": "linzhu_thesis.pdf", "content": "final", "filesize": 5368793, "license": "other", "mime_type": "application/pdf", "url": "/2215/1/linzhu_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Photonic Crystal Bragg Lasers: Design, Fabrication, and Characterization", "author": [ { "family_name": "Zhu", "given_name": "Lin", "clpid": "Zhu-Lin" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" }, { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "On-chip, single mode semiconductor lasers are usually fabricated using conventional distributed feedback (DFB) structures. Due to the limitation of index guiding in the transverse direction, the width of these lasers has to be less than a few microns. Meanwhile, the laser output power is limited by catastrophic optical damage (COD) at the facets and thus large optical cavities are necessary for high power semiconductor lasers. Therefore, high power, single mode applications are challenging, due to the conflicting requirements for large modal volume (to prevent COD by reducing optical power density) and narrow width (to obtain the single mode operation). Increasing the width of single mode semiconductor lasers is fundamentally important for obtaining high spectral and spatial optical power densities.
\r\n\r\nThis thesis reports on achieving the single mode operation of large area, edge emitting semiconductor lasers, using the photonic crystal Bragg structure (two dimensional distributed feedback structure). Both theoretical and experimental results are presented. Two dimensional coupled mode approaches and transfer matrix methods are developed to analyze and design the photonic crystal Bragg structure. It is shown that the single mode lasing can be obtained by satisfying both the transverse and longitudinal Bragg conditions and a single lobe, diffraction limited far field can be obtained by optimizing the coupling coefficient of the photonic crystal.
\r\n\r\nElectrically pumped, large-area (100 um x 500 um), single mode semiconductor photonic crystal Bragg lasers are experimentally demonstrated in pulsed and continuous wave conditions with single lobe, diffraction limited far fields. Two dimensional lasing wavelength tuning is demonstrated, which proves that the lasing mode is truly defined by the photonic crystal lattice. Furthermore, a wavelength tuning sensitivity about 80 times smaller than a conventional DFB laser is also achieved, allowing for more accurate control of the lasing wavelength.
\r\n\r\nPhotonic crystal lasers based on effective index guiding are also studied. Single mode operation is achieved by combining the transverse confinement provided by an effective index guiding mechanism with the longitudinal mode selection provided by the Bragg reflection from the photonic crystal cladding. These devices represent an important first step toward using photonic crystals in a different way for the modal control of semiconductor lasers in planar optical circuits.
\r\n\r\n\r\n", "doi": "10.7907/7MMN-7Q15", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:636", "collection": "thesis", "collection_id": "636", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02142007-151137", "primary_object_url": { "basename": "Choi_jm_2007.pdf", "content": "final", "filesize": 2712042, "license": "other", "mime_type": "application/pdf", "url": "/636/1/Choi_jm_2007.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Design, Fabrication, and Characterization of Semiconductor Transverse Bragg Resonance Lasers", "author": [ { "family_name": "Choi", "given_name": "John Myun", "clpid": "Choi-John-Myun" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" } ], "thesis_committee": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" }, { "family_name": "Bockrath", "given_name": "Marc William", "clpid": "Bockrath-M-W" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Controlling the spatial modes of a laser cavity is fundamental for improving the beam quality of a laser and achieving highly efficient coupling of power into an optical system. High-power applications are particularly challenging due to the conflicting requirements for large modal volume, to prevent facet damage by reducing energy density, and narrow width, for single-mode operation of an index-guided waveguide. By replacing traditional index confinement with Bragg reflection in the transverse direction, single-mode operation can be achieved even for large modal volumes. These grating confined structures, transverse Bragg resonance (TBR) waveguides, have the unique ability to support localized modes above the light line. Such modes normally couple to radiation modes of the cladding when the confinement mechanism is total-internal-reflection and are too lossy to be considered guided modes. However, for Bragg resonance confined modes, the modal loss can be designed by careful optical mode engineering to introduce a large loss discrimination that can favor a single spatial, low-loss mode. Semiconductor TBR lasers in an InP/InGaAsP/InGaAs material system were designed, fabricated, and characterized to investigate this property. Two regions of operation are identified for TBR waveguides, and, while transverse mode selection is provided by a grating, longitudinal mode control is found to be also necessary to restrict operation to the region that supports modes above the light line.", "doi": "10.7907/NG25-BN55", "publication_date": "2007", "thesis_type": "phd", "thesis_year": "2007" }, { "id": "thesis:2020", "collection": "thesis", "collection_id": "2020", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05242007-105741", "primary_object_url": { "basename": "PoonThesis.pdf", "content": "final", "filesize": 3158864, "license": "other", "mime_type": "application/pdf", "url": "/2020/1/PoonThesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Active and Passive Coupled-Resonator Optical Waveguides", "author": [ { "family_name": "Poon", "given_name": "Joyce Kai See", "clpid": "Poon-Joyce-Kai-See" } ], "thesis_advisor": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" } ], "thesis_committee": [ { "family_name": "Yariv", "given_name": "Amnon", "clpid": "Yariv-A" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" }, { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" }, { "family_name": "Bockrath", "given_name": "Marc William", "clpid": "Bockrath-M-W" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Coupled-Resonator Optical Waveguides (CROWs) are chains of resonators in which light propagates by virtue of the coupling between the resonators. The dispersive properties of these waveguides are controllable by the inter-resonator coupling and the geometry of the resonators. If the inter-resonator coupling is weak, light can be engineered to propagate slowly in these structures. The small group velocities possible in CROWs may enable applications in and technologies for optical delay lines, interferometers, buffers, nonlinear optics, and lasers.
\r\n\r\nThis thesis reports on achieving and controlling the optical delay in passive and active CROWs. Both theoretical and experimental results are presented. Transfer matrices, tight-binding models, and coupled-mode approaches are developed to analyze and design a variety of coupled resonator systems in the space, frequency, and time domains. Although each analytical method is fundamentally different, in the limit of weak inter-resonator coupling these approaches are consistent with each other. From these formalisms, simple expressions for the delay, loss, bandwidth, and a figure of merit are derived to compare the performance of CROW delay lines. Using a time-domain tight-binding model, we examine the resonant gain enhancement and spontaneous emission noise in amplifying CROWs to find that the net amplification of a propagating wave does not always vary with the group velocity but instead depends on the termination and excitation of the CROW.
\r\n\r\nCROWs in the form of high-order (> 10) weakly coupled passive polymer microring resonators were fabricated and measured. The measured transmission, group delay, and dispersive properties of the CROWs agreed with the theoretical results. Delays in excess of 100 ps and slowing factors of about 25 over bandwidths of about 20 GHz were observed. The main limitation of the passive CROWs was the optical losses. To overcome the losses and to enable electrical integration, we demonstrated active CROWs in the form of current injection InP-InGaAsP Fabry-Perot laser arrays. Even though the losses could be completely compensated, the transmission spectra and signal-to-noise ratio depended strongly on the injection current and resonator position. The signal-to-noise ratio degraded rapidly away from the input. Our results highlight possible avenues to operate laser arrays as loss-compensated or amplifying CROWs.
", "doi": "10.7907/MX8K-9V82", "publication_date": "2007", "thesis_type": "phd", "thesis_year": "2007" }, { "id": "thesis:5237", "collection": "thesis", "collection_id": "5237", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07062006-135109", "primary_object_url": { "basename": "ThesisBumkiMin.pdf", "content": "final", "filesize": 23482231, "license": "other", "mime_type": "application/pdf", "url": "/5237/1/ThesisBumkiMin.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Ultrahigh\u2013Q Microtoroid On-Chip Resonators for Low Threshold Microlasers", "author": [ { "family_name": "Min", "given_name": "Bumki", "orcid": "0000-0002-4639-3423", "clpid": "Min-Bumki" } ], "thesis_advisor": [ { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" } ], "thesis_committee": [ { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Atwater", "given_name": "Harry Albert", "clpid": "Atwater-H-A" }, { "family_name": "Painter", "given_name": "Oskar J.", "clpid": "Painter-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Recently demonstrated silica toroidal microcavities, as on-chip resonant cavities, become one of the most promising laser resonators due to their exceptional ability to confine optical energy temporarily and spatially (high Q-factor and small mode volume) while being integrated on a silicon substrate.
\r\n\r\nIn the first part of this thesis, semianalytic theory is presented for an in-depth understanding of the high-Q toroidal microcavity coupled to a tapered fiber waveguide. Basic properties of toroidal microcavities such as cavity mode field, resonance wavelength, cavity mode volume, radiative Q-factor, and phase-matching condition are described within the limit of an iterative perturbation expansion method. With this theoretical background, various laser systems with different gain media, utilizing the high-Q toroidal microcavity as a laser resonator, are demonstrated in the latter parts.
\r\n\r\nAs a first example, II-VI semiconductor nanocrystal, CdSe/ZnS (core/shell), quantum dots are coated on the surface of ultrahigh-Q toroidal microcavities. By pulsed excitation of quantum dots on the surface, either through tapered fiber waveguides or free-space, lasing is observed at both room and liquid nitrogen temperature. Use of a tapered fiber coupling substantially lowered the threshold energy when compared to the case of free-space excitation. Further threshold reduction down to 9.9 fJ was made possible by quantum dot density control.
\r\n\r\nLasing from an erbium-implanted high-Q silica toroidal microcavity is demonstrated and analyzed in the next chapter. A minimum threshold power as low as 4.5 uW and a maximum output lasing power as high as 39.4 uW are obtained. Control of lasing wavelength is demonstrated by changing the cavity loading. Analytic formulas predicting threshold power, differential slope efficiency are derived and their dependence on cavity loading, erbium ion concentration and Q-factor is found and compared with the experimental results.
\r\n\r\nThe nonlinear oscillation in an ultrahigh-Q silica toroidal microcavity is investigated in the last chapter. A controllable and reversible transition between parametric and Raman oscillation is experimentally demonstrated and theoretically analyzed. By direct change of cavity loading and indirect adjustment of frequency detuning, parametric and/or Raman oscillation can be accessed selectively without modification of cavity geometry in a toroidal microcavity with large enough aspect ratio. Based on an effective cavity gain theory, this transition is analyzed in terms of cavity loading and frequency detuning leading to a better understanding of the combined effects of parametric and Raman processes in silica microcavities.
", "doi": "10.7907/KGE9-J792", "publication_date": "2006", "thesis_type": "phd", "thesis_year": "2006" }, { "id": "thesis:4457", "collection": "thesis", "collection_id": "4457", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11082005-204747", "primary_object_url": { "basename": "Title.pdf", "content": "final", "filesize": 26939, "license": "other", "mime_type": "application/pdf", "url": "/4457/3/Title.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "High-Q Microcavities: Optomechanical Nonlinearities, Measurement Techniques and Applications", "author": [ { "family_name": "Rokhsari Azar", "given_name": "Hossein", "clpid": "Rokhsari-Azar-Hossein" } ], "thesis_advisor": [ { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" } ], "thesis_committee": [ { "family_name": "Vahala", "given_name": "Kerry J.", "clpid": "Vahala-K-J" }, { "family_name": "Crosignani", "given_name": "Bruno", "clpid": "Crosignani-B" }, { "family_name": "Rutledge", "given_name": "David B.", "clpid": "Rutledge-D-B" }, { "family_name": "Psaltis", "given_name": "Demetri", "clpid": "Psaltis-D" }, { "family_name": "Pickar", "given_name": "Kenneth A.", "clpid": "Pickar-K-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Optical microresonators have historically been perceived as structures that could efficiently confine optical energies. This is due to their exceedingly low losses at optical frequencies. This thesis has, for the first time, explored these structures in a starkly different frequency range. Optical microcavities like any other structure have mechanical eigenmodes or resonant modes of vibration with quality-factors representing the efficiency of energy storage at mechanical frequencies. It is shown here that micron size of these structures results in vibrations at radio frequencies (~1-100 MH), about seven orders of magnitude apart from the optical frequencies (~100 THz). Mechanical quality factors in excess of 5,000 are measured for toroidal microcavities revealing a heretofore unknown potential of these structures in storing energy at frequencies remarkably distant from their optical resonant modes. \r\n\r\nThis thesis describes how radiation-pressure or the force due to impact of photons could result in exceptionally strong couplings between the mechanical and optical resonators collocated within the same device. The discovered optomechanical coupling present in toroid microcavities is shown to reach such a high level that regenerative mechanical oscillations of the cavity structure are initiated with only micro-Watts of optical power. This is the first demonstration of radiation-pressure-induced mechanical oscillations in any type of optomechanical system. Embodied within a microscale, chip-based device, this mechanism can benefit both research into macroscale quantum mechanical phenomena and improve the understanding of the mechanism within the context of Laser interferometer gravitational-wave observatory (LIGO). It also suggests that new technologies are possible that will leverage the phenomenon within photonics.\r\n\r\nDifferent physical functionalities are also realized in this thesis by a combination of ultra-high-Q microtoroids and extremely low-loss tapered optical fibers for efficient delivery of optical power to these structures. Using these tools an almost ideal optical band-pass filter is designed with efficiencies solely limited by intrinsic losses of the optical resonator. These intrinsic loss mechanisms are experimentally studied and differentiated by a powerful technique based on thermal nonlinearities of the microcavity material. By taking advantage of slow response times of thermal effects, an innovative pump and probe technique is also developed to unveil and measure the Kerr nonlinearity in microcavities, for the first time, at room temperature.", "doi": "10.7907/CVT6-8J70", "publication_date": "2006", "thesis_type": "phd", "thesis_year": "2006" } ]