The Photonic Crystal (PC) is a potential candidate for a compact optical integrated circuit on a solid state platform. The fabrication process of a PC is compatible with CMOS technology; thus, it could be potentially employed in hybrid optical and electrical integrated circuits. One of the main obstacles in the implementation of an integrated optical circuit is the polarization dependence of wave propagation. Our goal is to overcome this obstacle by implementing PC based polarization controlling devices. One of the crucial elements of polarization controlling devices is the polarization rotator. The polarization rotator is utilized to manipulate and rotate the polarization of light. In this thesis, we have proposed, designed and implemented an ultra-compact passive PC based polarization rotator. Passive polarization rotator structures are mostly composed of geometrically asymmetric structures. The polarization rotator structure consists of a single defect line PC slab waveguide. The geometrical asymmetry has been introduced on top of the defect line as an asymmetric loaded layer. The top loaded layer is asymmetric with respect to the z-axis propagation direction. To synchronize the power conversion and avoid power conversion reversal, the top loaded layer is alternated around the z-axis periodically. The structure is called periodic asymmetric loaded PC slab waveguide. Due to the compactness of the proposed structure, a rigorous numerical method, 3D-FDTD can be employed to analyze and simulate the final designed structure. For the quick preliminary design, an analytical method that provides good approximate values of the structural parameters is preferred. Coupled-mode theory is a robust and well-known method for such analyses of perturbed waveguide structures. Thus, a coupled-mode theory based on semi-vectorial modes was developed for propagation modeling on square hole PC structures. In essence, we wish to develop a simple yet closed form method to carry out the initial design of the device of interest. In the next step, we refined the design by using rigorous but numerically expensive 3D-FDTD simulations. We believe this approach leads to optimization of the device parameters easily, if desired. To extend the design to a more general shape PC based polarization rotator, a design methodology based on hybrid modes of asymmetric loaded PC slab waveguide was introduced. The hybrid modes of the structure were calculated utilizing the 3D-FDTD method combined with the Spatial Fourier Transform (SFT). The propagation constants and profile of the slow and fast modes of an asymmetric loaded PC slab waveguide were extracted from the 3D-FDTD simulation results. The half-beat length, which is the length of each loaded layer, and total number of the loaded layers are calculated using the aforementioned data. This method provides the exact values of the polarization rotator structure’s parameter. The square hole PC based polarization rotator was designed employing both coupled-mode theory and normal modal analysis for THz frequency applications. Both design methods led to the same results. The design was verified by the 3D-FDTD simulation of the polarization rotator structure. For a square hole PC polarization rotator, a polarization conversion efficiency higher than 90% over the propagation distance of 12 λ was achieved within the frequency band of 586.4-604.5 GHz corresponding to the normalized frequency of 0.258-0.267. The design was extended to a circular hole PC based polarization rotator. A polarization conversion efficiency higher than 75% was achieved within the frequency band of 600-604.5 GHz. The circular hole PC polarization rotator is more compact than the square-hole PC structure. On the other hand, the circular hole PC polarization rotator is narrow band in comparison with the square hole PC polarization rotator. In a circular hole PC slab structure, the Bloch modes (fast and slow modes) couple energy to the TM-like PC slab modes. In both square and circular hole PC slab structures with finite number of rows, and the TM-like PC slab modes are extended to the lower edge of the bandgap. In bandgap calculation using PWEM, it is assumed that the PC structure is extended to infinity, however in practice the number of rows is limited, which is the source of discrepancy between the bandgap calculation using PWEM and 3D-FDTD. In an asymmetric loaded circular hole PC slab waveguide, the leaky TM-like PC slab modes are extended deep inside the bandgap and overlapped with both the slow and fast Bloch modes; whereas, in an asymmetric loaded square hole PC slab waveguide, the leaky TM-like PC slab modes are below the frequency band of slow and fast modes. Therefore, TM-like PC slab modes have significantly more adverse effect on the performance of the circular-hole based polarization rotator leading to a narrow band structure. SOI based PC membrane technology for THz application was developed. The device layer is made of highly resistive silicon to maintain low loss propagation for THz wave. The PC slab waveguide and polarization rotators were fabricated employing this technology. Finally, an a-SiON PC slab waveguide structures were also fabricated at low temperature for optical applications. This technology has the potential to be implemented on any substrate or CMOS chips.

Superconducting nanowire single-photon detectors (SNSPDs) are nanodevices usually made from thin niobium nitride (NbN) films. Operated at liquid helium temperature, they can exhibit high detection efficiency with low dark-counts associated with a fast response time and a low timing jitter. Covering a broad detection range from ultraviolet to mid-infrared, SNSPDs are a very attractive alternative to silicon or gallium arsenide based semiconductor detectors for fiber based telecommunication when single-photon sensitivity and high counting rates are necessary. Efficient packaging and fiber coupling of a SNSPD is in itself a real challenge and is often a limiting factor in reaching high system quantum efficiency. Our approach makes use of a controlled expansion alloy which has been adequately heat treated to enhance its characteristics for cryogenic operation. This insures the integrity of the optical coupling at cryogenic temperatures while done at room temperature. It also provides a good attenuation for electromagnetic interference due to the high relative permeability of the nickel-iron alloy. The small form factor of this pigtailed optical fiber package makes it versatile and could be easily integrated with a commercial cryogen-free system or simply dipped into a standard helium transport Dewar. We report on our theoretical and experimental methodology to evaluate the optical coupling quality and present the optoelectronic characterization of two devices packaged in this way. Electrical simulation is studied to understand the speed limitation factor inherent to these devices and preliminary speed and jitter measurements are reported.

This thesis describes the fabrication and testing of electroluminescent diodes made from silicon subjected to plasma ion implantation. A silicon-compatible, electrically driven light source is desired to increase the speed and efficiency of short-range data transfer in the communications and computing industries. As it is an indirect band gap material, ordinary silicon is too inefficient a light source to be useful for these applications. Past experiments have demonstrated that modifying the structural properties of the crystal can enhance its luminescence properties, and that light ion implantation is capable of achieving this effect. This research investigates the relationship between the ion implantation processing parameters, the post-implantation annealing temperature, and the observable electroluminescence from the resulting silicon diodes.<p> Prior to the creation of electroluminescent devices, much work was done to improve the efficiency and reliability of the fabrication procedure. A numerical algorithm was devised to analyze Langmuir probe data in order to improve estimates of implanted ion fluence. A new sweeping power supply to drive current to the probe was designed, built, and tested. A custom software package was developed to improve the speed and reliability of plasma ion implantation experiments, and another piece of software was made to facilitate the viewing and analysis of spectra measured from the finished silicon LEDs.<p> Several dozen silicon diodes were produced from wafers implanted with hydrogen, helium, and deuterium, using a variety of implanted ion doses and post-implantation annealing conditions. One additional device was fabricated out of unimplanted, unannealed silicon. Most devices, including the unimplanted device, were electroluminescent at visible wavelengths to some degree. The intensity and spectrum of light emission from each device were measured. The results suggest that the observed luminescence originated from the native oxide layer on the surface of the ion-implanted silicon, but that the intensity of luminescence could be enhanced with a carefully chosen ion implantation and annealing procedure.</p>

Perylene-based materials, including charge-transport discotic liquid crystals and charge-transfer long-wavelength absorbing chromophores, for potential organic electronic and optoelectronic applications, were designed, synthesized and characterized. Two types of discotic liquid crystals, perylene diimides and coronene diimides, can form columnar liquid crystalline phases over a wide temperature range; many of them can have room-temperature liquid crystalline phases after cooling from isotropic liquid. Their charge transport properties were studied by space-charge limited current method; high charge carrier mobilities, with the highest being up to 6.6 cm2/Vs, were found in liquid crystalline phases of these materials under ambient conditions. Structural variables, including aromatic cores and side groups, were examined to get a certain degree of understanding of charge transport properties in these discotic liquid crystals. It was found that mesophase order can have an important effect on charge carrier mobilities. The discotic liquid crystals with high charge carrier mobilities are serious candidates for use in large-area low-cost applications such as solar cells. Long-wavelength, highly absorbing chromophores, featuring donor-substituted perylene diimides, were generated by a combination of charge-transfer process and conjugation extension. The charge-transfer chromophores are expected to lead to further investigation on their potentials as sensitizers in Grtzel solar cells.

Indium tin oxide (ITO) thin films have been used as transparent electrodes in many technological applications such as display panels, solar cells, touch screens and electrochromic devices. Commercial grade ITO thin films are usually deposited by sputtering. Solution-based coating methods, such as sol-gel however, can be simple and economic alternative method for obtaining oxide films and also ITO. In this thesis, &ldquo / ITO sols&rdquo / and &ldquo / ITO nanoparticle-incorporated hybrid ITO coating sols&rdquo / were prepared using indium chloride (InCl3

The work presented in this thesis is primarily concerned with the synthesis and characterization of large, linear heteroacenes and their derivatives. We have been able to significantly expand on the types of materials available for application in organic electronic device architectures. In particular, the work focused on solution processible and novel derivatives of thiadiazoles, diazatetracenes, diazapentacenes, tetrazapentacences, and N,N-dihydrotetraazaheptacene. Extensive computational studies have been performed in order to better understand the optoelectronic properties of these materials. Although no devices have been fabricated that show appreciable hole or electron mobility, the properties of these materials are very promising. Besides our work on organic electronic materials for application in optoelectronic devices, we have also been able to develop, via the Click reaction, a series of aqueous metal sensors for copper (II), nickel (II), and silver (I) based upon fluorescence quenching. The use of a modified Stern-Volmer equation was necessary to fit the data in order to obtain binding constants. The exploration of new materials and their properties in the area of organic electronics is an exciting field for the synthetic organic chemist, as the goals associated with this work strive to impact humanity in a positive manner by reducing energy costs.

Most neutral atom quantum computing experiments rely on destructive state detection techniques that eject the detected qubits from the trap. These techniques limit the repetition rate of these experiments due to the necessity of reloading a new quantum register for each operation. We address this problem by developing reusable neutral atom qubits. Individual Rubidium 87 atoms are trapped in an optical lattice and are held for upwards of 300 s. Each atom is prepared in an initial quantum state and then the state is subsequently detected with 95% fidelity with less than a 1% probability of losing it from the trap. This combination of long storage times and nondestructive state detection will facilitate the development of faster and more complex quantum systems that will enable future advancements in the field of quantum information.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

The classical structure of an Opto-Electronic Oscillator (OEO) is based on a long fiber loop acting as a delay line and leading to the high spectral purity, or very low phase noise, of the oscillator. Such an OEO has been developed in SATIE/LPQM laboratory at ENS Cachan, operating at 8 GHz frequency. However, this system has some main disadvantages such as a bulky size, the difficulty to control temperature and a wide range of peaks among which it is difficult to select only one mode. In order to eliminate these disadvantages, high quality factor optical resonator can be used instead of the optical fiber loop. In this thesis, two resonator structures are produced and investigated. Microspheres are fabricated based on optical single mode fiber. Whispering gallery modes of these resonators are characterized by tapered fiber -resonator coupling. The experimental results show that the quality factor of the microsphere is up to 106 and FSR depends on the diameter of the resonator. A microsphere with a diameter of 300 µm, presents a FSR of 0.2 nm corresponding to a frequency of 25 GHz. However, for an OEO system which should work at 8 GHz, microsphere with a smaller FSR or with diameter of some millimeters should be fabricated- that is really difficult to obtain. Another add/drop racetrack resonator is designed and investigated. Optical experimental behavior of racetrack is characterized via fiber micro-lens coupling. The transmission spectrum shows resonance dips with average quality factor of 105 and a small FSR of 0.050 ± 0.003 nm (actually corresponding to 6 GHz) for a scanning wavelength range from 1534 nm to 1610 nm. The most promising features of the racetrack resonator are its high quality factor, and its free spectral range, which give it the high suitability for being used in the OEO system. Nevertheless the coupling with fiber lens leads to high losses and it is not possible to fulfill the oscillation conditions. Future work should be conducted for improving the coupling and for controlling the resonance dips position in agreement with the wavelength of the laser used in the OEO.

Microelectronics has enjoyed great success in the past century. As the technology node progresses, the complementary metal-oxide-semiconductor scaling has already reached a wall, and serious challenges in high-bandwidth interconnects and fast-speed signal processing arise. The incorporation of photonics to microelectronics provides potential solutions. The theme of this thesis is focused on the novel applications of travelling-wave microresonators such as microdisks and microrings for the on-chip optical interconnects and signal processing. Challenges arising from these applications including theoretical and experimental ones are addressed. On the theoretical aspect, a modified version of coupled mode theory is offered for the TM-polarization in high index contrast material systems. Through numerical comparisons, it is shown that our modified coupled mode theory is more accurate than all the existing ones. The coupling-induced phase responses are also studied, which is of critical importance to coupled-resonator structures. Different coupling structures are studied by a customized numerical code, revealing that the phase response of symmetric couplers with the symmetry about the wave propagating direction can be simply estimated while the one of asymmetric couplers is more complicated. Mode splitting and scattering loss, which are two important features commonly observed in the spectrum of high-Q microresonators, are also investigated. Our review of the existing analytical approaches shows that they have only achieved partial success. Especially, different models have been proposed for several distinct regimes and cannot be reconciled. In this thesis, a unified approach is developed for the general case to achieve a complete understanding of these two effects. On the experimental aspect, we first develop a new fabrication recipe with a focus on the accurate dimensional control and low-loss performance. HSQ is employed as the electron-beam resist, and the lithography and plasma etching steps are both optimized to achieve vertical and smooth sidewalls. A third-order temperature-insensitive coupled-resonator filter is designed and demonstrated in the silicon-on-insulator (SOI) platform, which serves as a critical building block element in terabit/s on-chip networks. Two design challenges, i.e., a broadband flat-band response and a temperature-insensitive design, are coherently addressed by employing the redundant bandwidth of the filter channel caused by the dispersion as thermal guard band. As a result, the filter can accommodate 21 WDM channels with a data rate up to 100 gigabit/s per wavelength channel, while providing a sufficient thermal guard band to tolerate more than ±15°C temperature fluctuations in the on-chip environment. In this thesis, high-Q microdisk resonators are also proposed to be used as low-loss delay lines for narrowband filters. Pulley coupling scheme is used to selectively couple to one of the radial modes of the microdisk and also to achieve a strong coupling. A first-order tunable narrowband filter based on the microdisk-based delay line is experimentally demonstrated in an SOI platform, which shows a tunable bandwidth from 4.1 GHz to 0.47 GHz with an overall size of 0.05 mm². Finally, to address the challenges for the resonator-based delay lines encountered in the SOI platform, we propose to vertically integrate silicon nitride to the SOI platform, which can potentially have significantly lower propagation loss and higher power handling capability. High-Q silicon nitride microresonators are demonstrated; especially, microresonators with a 16 million intrinsic Q and a moderate size of 240 µm radius are realized, which is one order of magnitude improvement compared to what can be achieved in the SOI platform using the same fabrication technology. We have also successfully grown silicon nitride on top of SOI and a good coupling has been achieved between the silicon nitride and the silicon layers.