Dissertations / Theses on the topic 'Electrical-optical modulator'

The Silicon Wafer Integrated Fiber Technology, SWIFT, is a novel platform for the development of photonic devices. SWIFT is comprised of an optical fiber, specifically a D-fiber in this work, embedded into a V-groove etched into a silicon wafer. This provides a method to secure the fiber and allows the use of standard semiconductor industry equipment and techniques in latter processing for device fabrication. The SWIFT platform is used as the basis for the development of a polarimetric in-fiber electro-optic modulator. The modulator is based on the application of a nonlinear optical polymer, NLOP, film into the evanescent field of a D-fiber. In this way electric fields applied to the NLOP can be used to influence the light propagating through the fiber. The two initial processes in fabricating the modulator are accessing the evanescent field of the D-fiber and making a nonlinear optical polymer (NLOP) thin film. To expose the evanescent field the fiber is chemically etched using hydrofluoric acid. During the etching, light transmitted through the fiber is monitored for changes in power and polarization. The measured optical changes are correlated to scanning electron microscope images of the etched fibers to relate the etch depth to the changes in power and polarization. This provides an etching process that is controllable and repeatable. The NLOP films are made from a simple guest-host system based poly(methyl methacrylate) (PMMA) and dispersed red 1 azo dye (DR1), a nonlinear optical dye. The films are poled to align the dye molecules so that the polymer will exhibit nonlinear optical properties. The poled polymers are tested for second harmonic generation, SHG, to insure that they are nonlinearly optically active. Utilizing the SWIFT platform and the monitored etching process, fibers were etched to a desired 0.2 microns from the core on a repeatable basis. A nonlinear optical polymer was synthesized, formed into thin films, and poled. Nonlinear optical activity in the films was verified by SHG testing.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 125-127).
Analog RF phase modulation of optical signals has been a topic of interest for many years, mainly focusing on Intensity Modulation Direct Detection (IMDD). The virtues of coherent detection combined with the advantages of Frequency Modulation, however, have not been explored thoroughly. By employing Frequency Modulation Coherent Detection (FMCD), the wide optical transmission bandwidth of optical fiber can be traded for higher signal-to-noise performance. In this thesis, we derive the FM gain over AM modulation -- the maximum achievable signal-to-noise ratio (by spreading the signal's spectrum) for specific carrier-to-noise ratio. We then employ FMCD for a scheme of remote antennas for which we use optical components and subsystem to perform signal processing such as nulling of interfering signals. The performance of optical processing on different modulation schemes are compared, and some important conclusions are reported relating to the use of conventional FMCD, FMCD with optical discriminator (FMCD O-D), and IMDD. Specifically, the superiority of conventional FMCD is shown; and, on the other hand, the inferiority of FMCD O-D is shown (same performance as IMDD) because of the use of an O-D. Finally, the remote antenna scheme is generalized for N antennas and N users.
by Nikolas I. Andrikogiannopoulos.
S.M.

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 209-214).
This thesis presents the operational theory and engineering numerical models for the operation of a schlieren-like Fourier optical system, used to read out a phase-only spatial light modulator (SLM) for phase to intensity conversion. The computational model, based on discrete cosine transforms, is lightweight enough to be run on standard desktop computers, and flexible enough to allow engineering simulations of arbitrary pixel phase profiles, including empirical datasets. We apply these models to case studies of the design and simulation of pixel geometries and readout system designs for a MEMS-based membrane mirror spatial light modulator (MMSLM), for use as a projection display at a range of visible and infrared wavelengths. Output images, contrast curves and pixel uniformities are simulated for each case study. Simulation results indicate the use of a zero-order blocking spatial filter when high contrast is prioritized, while a zero-order passing spatial filter provides enhanced uniformity of arrays of many pixels. Key engineering rules of thumb and a sample design flow are provided for the design of future phase-contrast projection systems.
by Michael J. Whitson.
M. Eng.

La spectroscopie dans la plage de longueurs d'onde du moyen infrarouge (2-20 µm) est une technique cruciale pour détecter et identifier des substances chimiques et biologiques. Dans ce contexte, les circuits photoniques intégrés à base de silicium (Si) opérant dans cette plage spectrale sont hautement attractifs pour développer des systèmes de spectroscopie moyen infrarouge compacts, qui pourront avoir des applications dans la surveillance environnementale, le diagnostic médical et les communications spatiales. L'intégration de composants photoniques actifs, tels que des modulateurs électro-optiques et des photodétecteurs, est essentielle pour ces systèmes de détection.La première partie de cette thèse explore le développement et la caractérisation des modulateurs électro-optiques moyen infrarouge en utilisant des circuits photoniques SiGe, en mettant l'accent sur les configurations à diodes Schottky et PIN. L'objectif principal était d'exploiter l'effet de dispersion du plasma de porteurs libres pour une modulation optique large bande sur toute la plage spectrale du moyen infrarouge.Tout d'abord, j'ai développé un modèle de simulation prenant en compte à la fois les propriétés optiques et électriques du dispositif pour optimiser l'efficacité de modulation et la conception des électrodes pour la transmission de signaux RF à grande vitesse. Le dispositif a ensuite été fabriqué dans la centrale de technologie du C2N, en utilisant des croissances épitaxiales SiGe du laboratoire L-Ness. Au final, j'ai réussi à démontrer une modulation optique sur une large bande spectrale, allant de 5 µm à 9 µm de longueur d'onde, avec un taux d'extinction de plus de 1 dB à une longueur d'onde de 9 µm et un fonctionnement à haute vitesse jusqu'à 1.5 GHz.De plus, ce travail présente une démonstration expérimentale du premier modulateur SiGe intégré à un guide d'ondes utilisant une diode PIN fonctionnant de 5 à 10 µm de longueur d'onde. À 10 µm, un taux d'extinction de 10 dB est obtenu en injection, alors qu'il atteint 3.2 dB en régime de déplétion. Un fonctionnement à haute vitesse est également obtenu, jusqu'à 1.5 GHz.De manière intéressante, j'ai également mis en évidence, à température ambiante, la présence d'un photocourant généré dans les diodes Schottky et PIN intégrées dans des guides d'ondes SiGe. La photodétection dans le dispositif Schottky est mise en évidence sur une large plage spectrale de 5 à 8 µm, avec une responsivité pouvant atteindre 0,1 mA/W. Par ailleurs, l'utilisation d'impulsions laser entre 50 et 200 ns a indiqué un fonctionnement à une fréquence RF supérieure à 20 MHz. D'autre part, la photodétection dans le dispositif PIN a été caractérisée de 5.2 µm à 10 µm de longueur d'onde, montrant une responsivité interne d'environ 1.6 mA/W et une bande passante électro-optique à 3 dB de 3.2 MHz. Diverses stratégies sont proposées et étudiées pour comprendre l'origine du photocourant. Il est suggéré que l'absorption sub-bande interdite médiée par les dislocations pourrait être responsable de cette photo-réponse dans les photodétecteurs SiGe. Les performances obtenues indiquent que ces dispositifs sont déjà adaptés pour le contrôle du couplage optique sur circuit photonique.En conclusion, ces résultats représentent une avancée significative dans les photodétecteurs intégrés et les modulateurs électro-optiques pour la spectroscopie du moyen infrarouge, ouvrant la voie vers des systèmes spectroscopiques avancés, compacts et entièrement intégrés fonctionnant dans les régions de l'infrarouge lointain
Spectroscopy in the mid-infrared wavelength range (2-20 µm) is a crucial technique for detecting and identifying chemical and biological substances. In this context, silicon (Si)-based integrated photonic circuits operating in this spectral range are highly attractive for developing on-chip mid-infrared spectroscopy systems, which have applications in environmental monitoring, medical diagnosis, and free-space communications. Integrating active photonic components, such as electro-optical modulators and photodetectors, is essential for these sensing systems. The first part of this thesis explores the development and characterization of mid-IR electro-optical modulators using SiGe photonic circuits, with a focus on Schottky and PIN diode configurations. The primary goal was to leverage the free-carrier plasma dispersion effect for broadband optical modulation across the mid-infrared spectral range. First, I developed a simulation model considering both optical and electrical properties of the device to optimize modulation efficiency and the design of traveling electrodes for driving RF signals at high speeds. The device was then fabricated at C2N cleanroom facilities, employing SiGe epitaxial growths from L-Ness lab. In the end, I have successfully demonstrated broadband optical modulation from 5 µm to 9 µm wavelengths, with the highest extinction ratio of over 1 dB at 9 µm wavelength and high-speed operation up to 1.5 GHz. In addition, this work presents an experimental demonstration of the first waveguide-integrated SiGe modulator using a PIN diode operating across a wide spectral range of the mid-infrared region (5-10 µm). At a wavelength of 10 µm, an extinction ratio of up to 10 dB is achieved in injection mode, and 3.2 dB in depletion mode. High-speed operation is also obtained, reaching up to 1.5 GHz. Interestingly, I have shown that the Schottky and PIN diodes embedded in SiGe waveguides also act as photodetectors at room temperature. Photodetection in the Schottky device is achieved over a wide spectral range from 5 to 8 µm, with responsivity up to 0.1 mA/W. Photodetection in pulse regime with laser pulse widths between 50 and 200 ns indicates operation beyond 20 MHz. On the other hand, photodetection in the PIN device has been characterized from 5.2 µm to 10 µm wavelengths, showing an internal responsivity around 1.6 mA/W and a 3 dB electro-optical bandwidth of 32 MHz. Various strategies are proposed and investigated to understand the origin of the photocurrent. It is suggested that sub-bandgap absorption mediated by dislocations could be responsible for this photoresponse in SiGe photodetectors. The achieved performances indicate that these devices are already suitable for on-chip signal monitoring. In conclusion, these results represent a significant advancement in integrated photodetectors and electro-optical modulators for mid-infrared spectroscopy, paving the way toward advanced, compact, and fully integrated spectroscopic systems operating in the long-wave infrared regions

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.
Includes bibliographical references (leaves 74-75).
A wideband optical frequency comb generator can be built using an electro-optic modulator that is driven at a frequency of several GHz and that is enclosed in an optical cavity. When light is circulated within the optical cavity, multiple passes through the modulator produce a spectrum centered at the carrier frequency with hundreds of sidebands spaced at the modulation frequency, with a comb span limited only by the material dispersion of the modulator. We present the design, construction, and testing of an optical frequency comb generator using lithium tantalate as a modulator substrate.
by Elisa C. Pasquali González.
M.Eng.

A high contrast, low intensity GaAlInAs/AlInAs multiple quantum well asymmetric Fabry-Perot reflection modulator for operation at 1.3 μm has been demonstrated. The reflection modulator takes advantage of the large absorptive and refractive nonlinearities associated with saturating the heavy-hole exciton resonance. We achieve an on/off contrast ratio in excess of 1000:1 (30 dB) and an insertion loss of 2.2 dB at a pump intensity of 30 kW/cm², corresponding to a carrier density of 4.5 x 10¹⁷ cm⁻³ The modulator was demonstrated to have a large operating bandwidth, achieving an on/off contrast ratio of greater than 100:1 over a 5 nm optical band. The operating speed of the modulator was measured and found to approach 1 GHz.

A large interest has been devoted to the use of optical interconnections in digital computer and digital telecommunication systems over the last few years. This interest is motivated by the promise of a greatly increased connectivity, lower power dissipation, and the compactness of interconnections that can be achieved with the use of this technology.
This thesis examines the design and the implementation of a modular spot-array generator for a modulator-based free-space optical interconnect. Two cascaded diffractive optical elements produce 4 x 8 clusters on a 1600 mum x 800 mum pitch, where each cluster is a 4 x 4 array of (1/e 2) 13.1-mum-radius spots on a 90-mum pitch. The spot-array generator is kinematically aligned to the interconnect system in such a way that it can be removed and reinserted without realignment. Characterization results are presented.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.
In title on t.p., [Sigma] and [Delta] appear as the upper-case Greek letters.
Includes bibliographical references (p. 87-89).
This thesis describes the design and implementation of an optical-electrical sub-sampling down-conversion receiver that employs [Sigma] [Delta] modulation. Accurate sub-sampling of an electrical RF signal in the optical domain is achieved by using a low-jitter mode-locked-laser and a high-bandwidth interferometer. The sub-sampled information is then digitized by an optical-electrical continuous-time (CT) [Sigma] [Delta] analog- to-digital converter (ADC). Here, photodiodes and low-jitter pulses from the mode- locked-laser are leveraged to perform signal clocking and quantizer pre-amplification, overcoming digital-to-analog converter (DAC) clock jitter and quantizer metastability issues that plague traditional electronic implementations. The optical-electrical converter achieves 76.5 dB of SNR (12.4 ENOB) with a 1 MHz signal bandwidth and a sampling rate of 780 MHz. The chip was implemented using a standard bulk 0.18 [mu]m CMOS process from National Semiconductor, occupies a total area of 3 mm2, and consumes 45 mW of power.
by Matthew Park.
M.Eng.

With the requirement to store and transmit information efficiently, an ever increasing number of uses of data compression techniques have been generated in diverse fields such as television, surveillance, remote sensing, medical processing, office automation, and robotics. Rapid increases in processing capabilities and the speed of complex integrated circuits make data compression techniques a prime candidate for application in the areas mentioned above. This report addresses, from a theoretical viewpoint, three major data compression techniques, Pixel Coding, Predictive Coding, and Transform Coding. It begins with a project description and continues with data compression techniques, focusing on Differential Pulse Code Modulation.

In the recent years, the exponential Internet traffic growth projections place enormous transmission rate demand on the underlying information infrastructure at every level, from the long haul submarine transmission to optical metro networks. In recent years, optical transmission at 100 Gb/s Ethernet date rate has been standardized by ITU-T and IEEE forums and 400Gb/s and 1Tb/s rates per DWDM channel systems has been under intensive investigation which are expected to be standardized within next couple of years.To facilitate the implementation of 400GbE and 1TbE technologies, the new advanced modulation scheme combined with advanced forward error correction code should be proposed. Instead of using traditional QAM, we prefer to use some other modulation techniques, which are more suitable for current coherent optical transmission systems and can also deal with the channel impairments. In this dissertation, we target at improving the channel capacity by designing the new modulation formats. For the first part of the dissertation, we first describe the optimal signal constellation design algorithm (OSCD), which is designed by placing constellation points onto a two dimensional space. Then, we expand the OSCD onto multidimensional space and design its corresponding mapping rule. At last, we also develop the OSCD algorithm for different channel scenario in order to make the constellation more tolerant to different channel impairments. We propose the LLR-OSCD for linear phase noise dominated channel and NL-OSCD for nonlinear phase noise dominated channel including both self-phase modulation (SPM) and cross-phase modulation (XPM) cases. For the second part of the dissertation, we target at probability shaping of the constellation sets (non-uniform signaling). In the conventional data transmission schemes, the probability of each point in a given constellation is transmitted equally likely and the number of constellation sets is set to 2!. If the points with low energy are transmitted with larger probability then the others with large energy, the non- uniform scheme can achieve higher energy efficiency. Meanwhile, this scheme may be more suitable for optical communication because the transmitted points with large probabilities, which have small energy, suffer less nonlinearity. Both the Monte Carlo simulations and experiment demonstration of both OSCD and non-uniform signaling schemes indicate that our proposed signal constellation significantly outperforms QAM, IPQ, and sphere-packing based signal constellations.

The Internet has fundamentally changed the way of modern communication. Current trends indicate that high-capacity demands are not going to be saturated anytime soon. From Shannon's theory, we know that information capacity is a logarithmic function of signal-to-noise ratio (SNR), but a linear function of the number of dimensions. Ideally, we can increase the capacity by increasing the launch power, however, due to the nonlinear characteristics of silica optical fibers that imposes a constraint on the maximum achievable optical-signal-to-noise ratio (OSNR). So there exists a nonlinear capacity limit on the standard single mode fiber (SSMF). In order to satisfy never ending capacity demands, there are several attempts to employ additional degrees of freedom in transmission system, such as few-mode fibers (FMFs), which can dramatically improve the spectral efficiency. On the other hand, for the given physical links and network equipment, an effective solution to relax the OSNR requirement is based on forward error correction (FEC), as the response to the demands of high speed reliable transmission. In this dissertation, we first discuss the model of FMF with nonlinear effects considered. Secondly, we simulate the FMF based OFDM system with various compensation and modulation schemes. Thirdly, we propose tandem-turbo-product nonbinary byte-interleaved coded modulation (BICM) for next-generation high-speed optical transmission systems. Fourthly, we study the Q factor and mutual information as threshold in BICM scheme. Lastly, an experimental study of the limits of nonlinearity compensation with digital signal processing has been conducted.

In the emerging industry of small unmanned vehicles, pioneered by small businesses and research institutions, a suitable combat system test platform is needed. Computer simulations are useful, but do not provide the definitive proof of effective operation necessary for deployment of a combat system. What is needed is an affordable simulated weapons system that enables live flight testing without the used of live weaponry. A framework is developed here for the construction of a simulated weapon using Free Space Optical (FSO) infrared communication. It is developed in such a way to ensure compatibility with a variety of platforms including ground and aerial vehicles, so that identical but configurable modules can be used on any vehicle that is to take place in a live combat simulation. A proof-of-concept implementation of this modular laser combat system framework is also presented and tested. The implemented system shows the value of such a simulated weapons system and future areas of improvement are also explored.

Etude des proprietes electriques et optiques a basse temperature dans inp de haute purete. Observation de l'effet hall quantique par etude detaillee de proprietes de transport des porteurs bidimensionnels a l'heterojoncion, a dopage module de type p ou n dans inp/ga::(0,47) in::(0,53) as et inp/ga::(0,25) in::(0,75) as::(0,5) p::(0,5). Etude des proprietes structurelles et optiques des puits quantiques multiples inp/ga::(0,47) in::(0,53) as

碩士
國立中山大學
光電工程研究所
95
Semiconductor Electroabosortion Modualtor (EAM) has become an important element in optical fiber communications because of its capability to integrate with other semiconductor devices, high-speed and low driving voltage. However, high optical insertion loss and low tolerance in optical power coupling are main general problems to be solved in order to get high electro-optical (EO) efficiency. Monolithically integrating EAM with optical spot-size converter (SSC) can lead to high-efficiency single-mode fiber coupling, but the price is on the complex fabrication methods. In this paper, based on previous work, the selective undercut etching active region (UEAR) and the whole wet-etching techniques are employed to fabricate the integration of laterally tapered SSC and EAM. Also, by applying the ion-implantation in SSC region, the reliable transfer efficiency and also high-speed performance are obtained based on the high resistance and low parasitic capacitance in SSC. The active region containing 10 strain compensated multiple-quantum-wells (MQWs) sandwiched by n-InP (bottom) and p-InP (top) for the electroabsorption region of EAM and also the top region of lateral tapered SSC. The converted waveguide in SSC consists of alternating InGaAsP and InP layers. An HBr-base etching solution is first used to define the top p-cladding with the widths of from 6um to 8um. An H2O2-base solution is then utilized to selectively undercut-etch the MQWs from InP material. The active waveguide p-cladding in EAM is set as 8um. After defining EAM and SSC, the converted waveguide is fabricated by aligning the top SSC and then wet-etched. By using an e-beam evaporator, Ti/Pt/Au and Ni/AuGe/Ni/Au are deposited as p- and n-type metallization, respectively. PMGI is spun serving as the passivation, planarization and bridging. The microwave coplanar waveguide (CPW) line is finally defined by depositing Ti/Au for microwave load- and feed- lines and connecting EAM. The length of SSC is 350um. The Spot-Size Converter monolithically integrated with Electroabsortion Modulator using whole wet-etching technique is demonstrated. –12.5dB of fiber-to-fiber insertion loss and 10dB (TE) 10dB(TM) extinction ration in 1V(1570nm excitation) is obtained in this device. Using Fabry-Perot method, the average optical transfer loss in SSC is extracted to be 2dB, quite consistent with simulation results. By applying ion-implantation on SSC, the broadband EO performance 45GHz of –3dB bandwidth is achieved for 100um long device due to the low capacitance and the high resistivity in SSC.

Optical communication has transformed information technology and enabled the present-day data explosion. The new era of data centric society is primarily driven by the ability to communicate data at high-speed. Migration from copper cables to optical fibres has created basic infrastructure for the revolution of optical interconnect. One of the important functionalities in an optical communication network is light modulation that imprints electrical signal information on to an optical carrier. Optical modulators are the devices that do the conversion. Optical modulator changes either the phase or intensity of the carrier light in accordance with the electrical signal. Broadly, modulators are classi fied as electro-refractive; where the phase of light is changed and electro-absorptive; where the intensity is changed based on the electrical signal. Both types of modulators rely on the refractive index of the optical material. The research work in this thesis is primarily focused on the design, fabrication and characterization of an electro-optic (EO) modulator in Silicon and electro-optic materials on Silicon-on-Insulator (SOI) platform for the implementation of high-performance electro-optic functionalities. The dominance of silicon in commercial CMOS for electronic applications led to the investigation of silicon photonic integrated circuits and enabled the implementation of photonic integrated circuit in silicon for many applications, including, high-speed communication and on-chip sensing. In addition, high-index contrast of silicon-silicon dioxide structures enabled the fabrication of complex and compact integrated circuits. Since silicon has a very-poor linear electro-optic coefficient, modulation is achieved through plasma dispersion effect, where the concentration of free carriers alters the real and imaginary part of the refractive index. The modulation speed of silicon optical modulators is limited by carrier mobility. In this research work, we demonstrated for the fi rst time carrier-injection based electro-optic modulation using a diffusion doped electro-optic modulator. In order to develop high-speed modulation, ion implanted EO modulators are developed and demonstrated with an electro-optic bandwidth of 25-50 GHz. Using the high-speed silicon modulators, we have demonstrated various applications including, 4-channel silicon photonics-based transceiver with 200 Gbps capacity, frequency doubling, pulsed-RF signal generation and an integrated approach of single sideband generation from double sideband signal. Though the high-index contrast platform of SOI offers compact device and circuit platform, the power density in a submicron waveguide result in undesirable two-photon absorption. A detailed study of non-linearity due to higher optical power and the ways of mitigating the non-linearity in silicon waveguides are also analyzed with possible trade-offs. The electro-optic bandwidth of a silicon modulator is limited by the carrier dynamics and associated electronics. Hence we investigated electro-optic materials compatible with silicon photonics. For the purpose of developing small footprint electro-optic switching and modulation (few GHz), devices with phase change materials (PCM) can be used. Of all the PCMS, vanadium dioxide is chosen because of its ability to transit from optically transparent monoclinic insulating phase to optically opaque tetragonal rutile phase. Pulsed laser deposited vanadium dioxide (VO2) on silicon-on-insulator is studied for material, electrical and optical properties. Electro-optic modulation using VO2 tab on silicon waveguides is also demonstrated by thermally tuning the phase of VO2. Furthermore, to achieve a high-speed phase modulation and overcome the bandwidth limit of silicon, we attempt to develop an electro-refractive type modulator using complex oxide such as barium titanate (BaTiO3) on SOI platform. Of all the complex oxides, BaTiO3 has the highest Pockels coefficient (1000 pm/V). To reduce the lattice mismatch with silicon, magnesium oxide (MgO) is used as the buffer layer, and BaTiO3/MgO/Si stack is characterized for material and electrical properties. Second-harmonic generation experiments are conducted on the material to characterize electro-optic characteristics of BaTiO3. Preliminary transmission measurements of BaTiO3-silicon waveguides were also demonstrated, and possible solutions to reduce the loss in the devices are also discussed.

Silicon photonics is emerging as a promising platform for manufacturing and integrating photonic devices for light generation, modulation, switching and detection. The compatibility with existing CMOS microelectronic foundries and high index contrast in silicon could enable low cost and high performance photonic systems, which find many applications in optical communication, data center networking and photonic network-on-chip. This thesis first develops and demonstrates several experimental work on high speed silicon modulators and switches with record performance and novel functionality. A 8x40 Gb/s transmitter based on silicon microrings is first presented. Then an end-to-end link using microrings for Binary Phase Shift Keying (BPSK) modulation and demodulation is shown, and its performance with conventional BPSK modulation/ demodulation techniques is compared. Next, a silicon traveling-wave Mach- Zehnder modulator is demonstrated at data rate up to 56 Gb/s for OOK modulation and 48 Gb/s for BPSK modulation, showing its capability at high speed communication systems. Then a single silicon microring is shown with 2x2 full crossbar switching functionality, enabling optical interconnects with ultra small footprint. Then several other experiments in the silicon platform are presented, including a fully integrated in-band Optical Signal to Noise Ratio (OSNR) monitor, characterization of optical power upper bound in a silicon microring modulator, and wavelength conversion in a dispersion-engineered waveguide. The last part of this thesis is on network-level application of photonics, specically a broadcast-and-select network based on star coupler is introduced, and its scalability performance is studied. Finally a novel switch architecture for data center networks is discussed, and its benefits as a disaggregated network are presented.

Inter-chip input-output (I/O) communication bandwidth demand, which rapidly scaled with integrated circuit scaling, has leveraged equalization techniques to operate reliably on band-limited channels at additional power and area complexity. High-bandwidth inter-chip optical interconnect architectures have the potential to address this increasing I/O bandwidth. Considering future tera-scale systems, power dissipation of the high-speed I/O link becomes a significant concern. This work presents a design flow for the power optimization and comparison of high-speed electrical and optical links at a given data rate and channel type in 90 nm and 45 nm CMOS technologies. The electrical I/O design framework combines statistical link analysis techniques, which are used to determine the link margins at a given bit-error rate (BER), with circuit power estimates based on normalized transistor parameters extracted with a constant current density methodology to predict the power-optimum equalization architecture, circuit style, and transmit swing at a given data rate and process node for three different channels. The transmitter output swing is scaled to operate the link at optimal power efficiency. Under consideration for optical links are a near-term architecture consisting of discrete vertical-cavity surface-emitting lasers (VCSEL) with p-i-n photodetectors (PD) and three long-term integrated photonic architectures that use waveguide metal-semiconductor-metal (MSM) photodetectors and either electro-absorption modulator (EAM), ring resonator modulator (RRM), or Mach-Zehnder modulator (MZM) sources. The normalized transistor parameters are applied to jointly optimize the transmitter and receiver circuitry to minimize total optical link power dissipation for a specified data rate and process technology at a given BER. Analysis results shows that low loss channel characteristics and minimal circuit complexity, together with scaling of transmitter output swing, allows electrical links to achieve excellent power efficiency at high data rates. While the high-loss channel is primarily limited by severe frequency dependent losses to 12 Gb/s, the critical timing path of the first tap of the decision feedback equalizer (DFE) limits the operation of low-loss channels above 20 Gb/s. Among the optical links, the VCSEL-based link is limited by its bandwidth and maximum power levels to a data rate of 24 Gb/s whereas EAM and RRM are both attractive integrated photonic technologies capable of scaling data rates past 30 Gb/s achieving excellent power efficiency in the 45 nm node and are primarily limited by coupling and device insertion losses. While MZM offers robust operation due to its wide optical bandwidth, significant improvements in power efficiency must be achieved to become applicable for high density applications.

Indoor positioning is an enabling technology primed to impact the indoor application space as Global Navigation Satellite Systems (GNSS) did for the outdoor space. Amongst the competing positioning technologies are methods of different mediums: light, radio frequency and ultra-wideband, ultrasonic, and imaging; methods of different modalities: received signal strength, angle-of-arrival, time-of-flight; and methods of different mathematics: trilateration, triangulation, machine learning, and signal processing. Light-based positioning compared to other positioning schemes exploits fixed-location directional luminaires placed regularly throughout a space as anchor points -- there is an efficiency argument for multi-purpose lighting and a cost-share argument for infrastructure-based positioning. Similar to the satellite infrastructure with GNSS, with anchor points and models for light propagation and construction, position is estimated based on received signals at active photodiode-equipped target devices. Received signal strength, a common first order attribute, alone is not noise resilient enough for centimeter-level 3D positioning. Methods using angle diversity produce better results particularly in 3D but with more complex hardware. For this dissertation, we exploit angle diversity and modulated optical sources in light-based positioning systems to estimate position to centimeter-level accuracy in 3D. We propose, analyze, and contribute two novel positioning schemes that use these concepts. One of the proposed schemes is a new hybrid 3D indoor positioning technique, Ray-Surface Positioning (RSP), which incorporates a narrow field-of-view (FOV) optical source (Ray) with wide diffuse optical sources (Surfaces) to position active devices in 3D. The second scheme, a Zone-based Positioning Service (ZPS), is a positioning scheme and architecture that incorporates an angle diverse narrow FOV optical source at the positioned device. This unique design decision allows the active device to position itself directly with respect to photovoltaic anchor points but also to position other devices in its FOV called transitive positioning. Along with these contributions, we also investigate several other related topics. Concisely, as part of the dissertation, we contribute (a) review of the state-of-the-art, (b) analysis for steering Lambertian sources, (c) method of creating angle diversity from a narrow FOV optical source, (d) novel positioning approaches in (1) RSP and (2) ZPS, (e) proof of concept prototypes for (1) RSP and (2) ZPS, and (f) architectures for indoor positioning applications.

The increasing integration of digital information with our daily lives has led to the rise of big data, cloud computing, and the internet of things. The growth in these categories will lead to an exponential increase in the required capacity for data centers and high performance computation. Meanwhile, due to bottlenecks in data access caused by the limited energy and bandwidth scalability of electrical interconnects, computational speedup can no longer scale with demand. A better solution is necessary in order to increase computational performance and reduce the carbon footprint of our digital future. People have long thought of photonic interconnects, which can offer higher bandwidth, greater energy efficiency, and orders-of-magnitude distance scalability compared to electrical interconnects, as a solution to the data access bottleneck in chip, board, and datacenter scale networks. Over the past three decades we have seen impressive growth of photonic technology from theoretical predictions to high-performance commercially available devices. However, the dream of an all-optical interconnection network for use in CPU, Memory, and rack-to-rack datacenter interconnects is not yet realized. Many challenges and obstacles still have to be addressed. This work investigates these challenges and describe some of the ways to overcome them. First we will first examine the pattern sensitivity of microring modulators, which are likely to be found as the first element in an optical interconnect. My work will illustrate the advantage of using depletion mode modulators compared to injection mode modulators as the number of consecutive symbols in the data pattern increases. Next we will look at the problem of thermal initialization for microring demultiplexers near the output of the optical interconnect. My work demonstrates the fastest achieved initialization speed to-date for a microring based demultiplexer. I will also explore an thermal initialization and control method for microrings based on temperature measurement using a pn-junction. Finally, we will look at how to control and initialize microring and MZI based optical switch fabrics, which is the second element found in a optical interconnect. Work here will show the possibility of switching high-speed WDM datastreams through microring based switches, as well as methods to deal with the complexities inherent in control and initialization of high-radix switch topologies. Through these demonstrations I hope to show that the challenges facing optical interconnects, although very real, are surmountable using reasonable engineering efforts.

The atmospheric lightwave propagation is considerably influenced by the random variations in the refractive index of air pockets due to turbulence. This undesired effect significantly degrades the performance of free-space optical (FSO) communication systems. Interestingly, the severity of such random degradations is highly related to the range of atmospheric propagation. In this thesis, we introduce relay-assisted FSO communications as a very promising technique to combat the degradation effects of atmospheric turbulence. Considering different configurations of the relays, we quantify the outage behavior of the relay-assisted system and identify the optimum relaying scheme. We further optimize the performance of the relay-assisted FSO system subject to some power constraints and provide optimal power control strategies for different scenarios under consideration. Moreover, an application of FSO relaying technique in quantum communications is investigated. The results demonstrate impressive performance improvements for the proposed relay-assisted FSO systems with respect to the conventional direct transmission whether applied in a classical or a quantum communication channel.