The integration of hollow anti-resonant reflecting optical waveguides (ARROWs) with vapor cells on silicon chips provides a compact platform for a number of optical applications, including the study of quantum coherence effects such as electromagnetically induced transparency and single-photon nonlinearities, as well as frequency stabilization standards. The use of hollow waveguides allows for light propagation in low index (vapor) media with compact mode areas. ARROWs make particularly attractive waveguides for this purpose because they can be interfaced with solid core waveguides, microfabricated on a planar substrate, and are effectively single mode. ARROW fabrication utilizes an acidremoved sacrificial core surrounded by alternating plasma deposited dielectric layers, which act as Fabry-Perot reflectors. A demonstration platform consisting of solid and hollow core waveguides integrated with rubidium vapor cells has been constructed. Rubidium was used because it is of particular interest for studying quantum coherence effects. Liquefied rubidium was transferred from a bulk supply into an on-chip vapor cell in an anaerobic atmosphere glovebox. Optical absorption measurements confirmed the presence of rubidium vapor within the hollow waveguide platform. Coherence dephasing in the small dimensions of the ARROW (quantum coherence effect) can be addressed by adding a buffer gas and passivation coatings to the ARROW walls.
The integration of hollow anti-resonant reflecting optical waveguides (ARROWs) with vapor cells on silicon chips provides a compact platform for a number of optical applications, including the study of quantum coherence effects such as electromagnetically induced transparency and single-photon nonlinearities, as well as frequency stabilization standards. The use of hollow waveguides allows for light propagation in low index (vapor) media with compact mode areas. ARROWs make particularly attractive waveguides for this purpose because they can be interfaced with solid core waveguides, microfabricated on a planar substrate, and are effectively single mode. ARROW fabrication utilizes an acidremoved sacrificial core surrounded by alternating plasma deposited dielectric layers, which act as Fabry-Perot reflectors. A demonstration platform consisting of solid and hollow core waveguides integrated with rubidium vapor cells has been constructed. Rubidium was used because it is of particular interest for studying quantum coherence effects. Liquefied rubidium was transferred from a bulk supply into an on-chip vapor cell in an anaerobic atmosphere glovebox. Optical absorption measurements confirmed the presence of rubidium vapor within the hollow waveguide platform. Coherence dephasing in the small dimensions of the ARROW (quantum coherence effect) can be addressed by adding a buffer gas and passivation coatings to the ARROW walls.
This thesis presents the integration of atomic vapor cells with anti-resonant reflecting optical waveguides (ARROWs) fabricated on silicon chips. These potentially provide a compact platform for a number of optical applications, including the study of quantum coherence effects such as electromagnetically induced transparency and single-photon nonlinearities, as well as frequency stabilization standards. The use of hollow waveguides allows for light propagation in low index (vapor) media with compact mode areas. ARROWs make particularly attractive waveguides for this purpose because they can be interfaced with solid core waveguides, microfabricated on a planar substrate, and are effectively single mode. ARROW fabrication utilizes an acid-removed sacrificial core surrounded by alternating plasma deposited dielectric layers, which act as Fabry-Perot reflectors. To demonstrate the effectiveness of the ARROW as a vapor cell, a platform consisting of solid and hollow core waveguides integrated with rubidium vapor cells was developed. A variety of sealing techniques were tested for vapor cell integration with the ARROW chip and for compatibility with rubidium. Rubidium was used because it is of particular interest for studying quantum coherence effects. Liquefied rubidium was transferred from a bulk supply into an on-chip vapor cell in an anaerobic atmosphere glovebox. Optical absorption measurements confirmed the presence of rubidium vapor within the hollow waveguide platform. Further analysis of the measurements revealed high optical density of rubidium atoms in the hollow core. Saturated absorption spectroscopy measurements verified that the on-chip integrated vapor cell was suitable for common precision spectroscopy applications.
We review the current status of integrating optical quantum interference effects such as electromagnetically induced transparency (EIT), slow light, and highly efficient nonlinear processes on a semiconductor chip. A necessary prerequisite for combining effects such as slow light and related phenomena with the convenience of integrated optics is the development of integrated alkali vapor cells. Here, we describe the development of integrated rubidium cells based on hollow-core antiresonant reflecting optical waveguides (ARROWs). Hollow-core waveguides were fabricated on a silicon platform using conventional microfabrication and filled with rubidium vapor using different methods. Rubidium absorption through the waveguides was successfully observed which opens the way to integrated atomic and molecular on a chip. The realization of quantum coherence effects requires additional surface treatment of the waveguide walls, and the effects of the surface coating on the waveguide properties are presented.
The author presents the successful development of an on-chip, monolithic, integrated rubidium vapor-cell. These vapor-cells integrate ridge waveguide techniques with hollow-core waveguiding technology known as Anti-Resonant Reflecting Optical Waveguides (ARROWs). These devices are manufactured on-site in BYU's Integrated Microelectronic Laboratory (IML) using common silicon wafer microfabrication techniques. The ARROW platform fabrication is outlined, but the bulk of the dissertation focuses on novel packaging techniques that allow for the successful introduction and sealing of rubidium vapor into these micro-sized vapor-cells. The unique geometries and materials utilized in the ARROW platform render common vapor-cell sealing techniques unusable. The development of three generations of successful vapor-cells is chronicled. The sealing techniques represented in these three generations of vapor-cells include high-temperature epoxy seals, cold-weld copper crimping, variable pressure vacuum capabilities, indium solder seals, and electroplated passivation coatings. The performance of these seals are quantified using accelerated lifetime tests combined with optical spectroscopy. Finally, the successful probing of the rubidium absorption spectrum, electromagnetically induced transparency, and slow light on the ARROW-based vapor-cell platform is reported.
The demonstration of slow, fast, and stopped light1 has helped generate considerable interest in quantum interference effects. In addition to producing intriguing physical phenomena, these effects will be valuable for future optical communications. Buffers using slow-light modules will be important elements in alloptical data networks. Cryptography systems may also be expected to use quantum interference effects for photon creation and detection. But if slow-light buffers and quantum cryptography are to be practical in real-world applications, wemust create miniaturized, stand-alone quantum interference modules. This is the aim of research involving on-chip atomic vapor cells integrated with optical waveguides Slow-light effects are a product of a medium with large, frequency-dependent gain or absorption features that then give rise to large dispersion characteristics. Our work employs quantum interference effects in atomic vapor to create large dispersion. At present, atomic vapor can provide excellent dispersion characteristics, but it usually requires a large system footprint. In classical optical setups, which beam a laser through a transparent vapor cell, there is also a constant trade-off between focal depth and beamwidth. By using on-chip hollow-core optical antiresonant reflecting optical waveguides (ARROWs), we are able to direct light down vapor-filled cores, maintaining large optical intensities over long distances. This is particularly beneficial for nonlinear optical effects that can be exploited for single-photon generation and detection. In addition, ARROW-based platforms also require only a small footprint (1×1cm). ARROWs are constructed by growing alternating layers of silicon oxide and silicon nitride around a sacrificial core on a silicon wafer. The alternating dielectric materials with specific thicknesses confine and guide light through antiresonance. After etching out the sacrificial core, we are left with a hollow channel into which we can introduce various gases and liquids for optical experiments. Solid waveguides etched into the silicon on Figure 1. A rubidium (Rb)-loaded ARROW atomic vapor cell.
The focus of this work is the integration of alkali vapor atomic vapor cells into common silicon wafer microfabrication processes. Such integrated platforms enable the study of quantum coherence effects such as electromagnetically induced transparency, which can in turn be used to demonstrate slow light. Slow and stopped light devices have applications in the optical communications and quantum computing fields. This project uses hollow core anti-resonant reflecting optical waveguides (ARROWs) to build such slow light devices. An explanation of light-matter interactions and the physics of slow light is first provided, as well as a detailed overview of the fabrication process. Following the discovery of a vapor transport issue, a custom capillary-based testing platform is developed to quantify the effect of confinement, temperature, and wall coatings on rubidium transport. A mathematical model is derived from the experimental results and predicts long transport times. A new design methodology is presented that addresses the transport problem by increasing the number of rubidium entry points. This design also improves chip durability and decreases environmental susceptibility through the use of a single copper reservoir and buried channel waveguides (BCWs). New chips are successfully fabricated, loaded, and monitored for rubidium spectra. Absorption is observed in several chips and absorption peaks depths in excess of 10% are reported. The chip lifetime remains comparable to previous designs. This new design can be expanded to a multi-core platform suitable for slow and stopped light experimentation.
Atomic spectroscopy relies on photons to probe the energy states of atoms, typically in a gas state. In addition to providing fundamental scientific information, this technique can be applied to a number of photonic devices including atomic clocks, laser stabilization references, slow light elements, and eventually quantum communications components. Atomic spectroscopy has classically been done using bulk optics and evacuated transparent vapor cells. Recently, a number of methods have been introduced to dramatically decrease the size of atomic spectroscopy systems by integrating optical functionality. We review three of these techniques including: 1) photonic crystal fiber based experiments, 2) wafer bonded mini-cells containing atomic vapors and integrated with lasers and detectors, and 3) hollow waveguides containing atomic vapors fabricated on silicon substrates. In the context of silicon photonics, we will emphasize the hollow waveguide platform. At the heart of these devices is the anti-resonant reflecting optical waveguide (ARROW). ARROW fabrication techniques will be described for both hollow and solid core designs. Solid-core waveguides are necessary to direct light on and off the silicon chip while confining atomic vapors to hollow-core waveguides. We will also discuss the methods and challenges of attaching rubidium vapor reservoirs to the chip. Experimental results for optical spectroscopy of rubidium atoms on a chip will be presented.