For the 1D photonic crystal waveguide devices, enhanced atom-light coupling between localized cesium atoms in the vicinity of the devices, and also atom-atom interaction between cesium atoms mediated by the guided mode of the photonic crystal waveguide, have been observed. My work for these experiments was mostly with the building of the devices, and perhaps a minor contribution to the day-to-day work in the optics laboratory.
LIST OF TABLES
MOTIVATION
- Nanophotnics and Optical Property Engineering
- Light Interaction with Quantum Emitters
- Interfacing Hybrid Systems
- Thesis Outline
In an intuitive picture, the incoming light is reflected multiple times inside the cavity, allowing the interaction between the light and the quantum object to accumulate. This can be done using cavity systems where quantum emitters interact together with a common cavity mode, with the interaction strength varying with the local intensity determined by the cavity mode profile as reported in [11].
SUPPORT STRUCTURE DESIGN
- Design Targets for Atom-Nanophotonics Hybrid System
- High-Stress Silicon Nitride and Mechanical Stress Handling
- Thermal Conductance Structures
- Connecting Waveguides to Outside World
- Anti-Reflection Designs on Highly Evanescent Waveguides
- shaped free-space coupling tether design
- Assembly of Fiber-Coupled Chip
- Coupling into Free-Space Lens-Coupled Chip
The core of the optical fiber must then be precisely aligned with the completed coupling waveguide. Also, the adhesion to the chip holder material (aluminum or Macor) is significantly stronger than to the silicon chip.
FABRICATION OF DEVICES
Fabrication Requirements
The chip should be placed in a configuration that avoids the accumulation of bubbles on both sides of the edges of the chip to avoid local masking. Accumulation of bubbles can prevent the etching solution from contacting the silicon substrate, which.
Substrate Selection and Preparation
We pattern a 2 mm x 6 mm rectangle on the back of the chips, to allow the etching of the through window to proceed from both sides. The UV exposure is performed using a chrome-on-glass mask that references the edges of the precut chips.
Electron Beam Lithography with Large Device Footprint
Exposing just a 1 µm wide grid, rather than filling the entire area of the groove, improves exposure quality and also reduces exposure time. The program to convert our CAD file into a pattern file for our lithography machine (GenISys BEAMER) allows control over the placement on the main field.
Etching
In this configuration, any patterns etched into the Silicon Nitride layer will expose fast etch directions of the Silicon substrate, and the substrate will etch until only the <1,1,1> planes remain. The angle between the chip normal and the <1,1,1> direction of the substrate provides a way.
Applications of Silicon Anisotropic Etching
Place the chip on the glass slide and then move it to the edge of the slide using tweezers. Using tweezers, apply force to the chip substrate, away from the device patterns, on both sides of the chip.
Wet-Chemistry Processing
Due to the large amount of bubbles generated by the KOH etching, it is necessary to hold the chip firmly in the holder to prevent it from floating out. After the chips are placed in the pockets of the holder, Teflon spacers are wedged between the chip and the holder. Near the end of the etch, we visually observe to confirm that the through-window is free of all chips in the holder before the process ends.
Post-Release Plasma Cleaning
This image shows the mechanical separation of an early hole-based double-beam device in SEM, taken at 15 kV accelerating voltage. This image shows one of the cooling tether arrays on our chip after baking on our thermal curing adhesive processing step. We believe that this material is organic as it can be removed by Oxygen plasma treatment and the stuck units are then repaired using the SEM charging technique.
Characterization using photonic crystal cavities
Plasma processes, as they are dry processes, can be performed after initial optical test, and also after ALD coating. Suitable plasma etching recipes can be used to tune the devices with optical measurement feedback; for more information, please refer to the thesis [49]. A longer taper is built on the inside (right side in this image) of the cavity mirror to reduce scattering loss.
Metal Deposition for Potential Electrostatic Tuning
The metal is deposited using electron beam evaporation, where a reservoir of pure metal is struck with a high-energy electron beam in a vacuum, locally heating the metal to create metal vapor that is emitted from the reservoir and deposited on the chip. The metal pattern is defined by exposed areas on the chip that are not covered by the resist. When the metal deposition is complete, the resist is lifted from the substrate in solvents (trichlorethylene at room temperature) with the metal layer, leaving the metal pattern only where it was directly deposited on the chip itself.
Device Fine-Tuning Using Atomic Layer Deposition
Although it is typically preferred to deposit the metal layer first and include metal markers, our resist thickness and Silicon-under-Nitride negative-tone marker appear to allow sufficient alignment precision for our investigative capacitors. With metal wiring, we have preliminary capacitive tuning results for the double-beam photonic crystal, which will be covered in Chapter 8.
Experiments with High-Temperature Annealing
Cracks in the <1,1,1> surfaces, as shown in this image, and the irregular shape of where this surface meets the edge of the V-grooves were believed to be hidden damage to the crystalline structure of the surface . We suspect that the possible causes are loss of stoichiometry of the ALD material, similar to that observed in [51], or mechanical problems related to increased stress due to annealing of Al2O3, as reported in [52].
ENGINEERING OPTICAL PROPERTIES WITH APCW
- Engineering Atom-Light Coupling Using Photonic Crystal
- Placement of Photonic Crystal Frequency
- Tapering Photonic Crystal Waveguides
- Cesium Dual-Frequency Operation
- Additional Engineering Options
A similar calculation, but with the injected frequency set in the band gap of the crystal. The probe mode operates at the other edge of the photonic bandgap for maximum coupling. For our photonic crystal waveguide, this can be made for devices operating inside the Brillouin zone.
OPTICAL CHARACTERIZATION OF DEVICES
- Reflection and Transmission Measurement
- Features of Measured Spectra
- Interaction Enhancement Estimation
- Power Handling Capability Test in Vacuum
- Precision shifting to Cs frequencies using optical measurement feedback We make the last stage of device band adjustment using the atomic layer depositionWe make the last stage of device band adjustment using the atomic layer deposition
- Characterization of Single-Beam Fabry-Perot-Type Cavity
Propagation loss and device scattering loss would also result in non-ideal characteristics of band edge resonances. Using this simple model and assuming that the resonances correspond to βn = nπL, the group index can be estimated from the position of the resonances at the band edge; see Figure 5.6. The spreader profile should be calibrated away using the baseline average of a device that spreads far away from the edge of the lane.
ATOM-LIGHT INTERACTION MEASUREMENT
- Vacuum System Adaption for Photonic Devices
- Vacuum System Design and Atom Delivery
- Methods for Measurement of Atom-Light Interaction
- Observation of Enhanced Single-Atom Decay Rate
- Observation of Light-Mediated Atom-Atom Interaction
The cloud slows down and captures a small MOT and restricts it to near devices. The dashed line is the unchanged decay rate of the atom in free space as a reference. It is hoped that in the near future it will be possible to achieve efficient loading of water traps.
ENGINEERING OPTICAL PROPERTIES WITH 2D PHOTONIC CRYSTAL SLABS
- Adaptation of Support Structures to Photonic Crystal Slabs
- Optical Properties of 2D PhC Modes
- Optical Properties of 2D PhC with Defects
- Atom-Light Interaction Parameters of the Slot Waveguide
- Characterization and Tuning of 2D-Based Devices
By suitable perturbation of the hole shape (which preserves 3-fold rotational symmetry) this degeneracy can be overcome; see [71]. We investigate the features that can be created by local modification of a 2D photonic crystal lattice. We observe up to 8dB suppression of the two orientations of the TE dipole (blue and green traces) in the band frequencies from 320THz to 355THz.
OUTLOOK
- Migration Toward Free-Space Coupled Devices
- Deterministic Loading and Positioning with Optical Tweezers
- Electro-capacitive dynamic tuning of slot waveguide
- Potential Future Development
We can use the mechanically malleable nature of the nanostring geometry to fabricate devices that can be dynamically deformed by capacitive actuation. This technology can be applied to our slot waveguide devices in the following way: The slot wave channel propagates in the K direction of the 2D background lattice, while the 2D modes are easily coupled in the M direction, perpendicular to K. Then, each atom can be individually addressed by a coordinate system defined by the indices of both orthogonal sets of device ports.
BIBLIOGRAPHY
Single Quantum Dot Spontaneous Emission in a Finite-Size Photonic Crystal Waveguide: Proposal for an Efficient "On Chip" Single Photon Gun. An out-of-plane grating coupler for efficient bat coupling between compact planar waveguides and single-mode fibers”. Two-dimensional photonic crystals with large complete photonic bandgaps in both TE and TM polarizations”.
FEM SIMULATION METHODS
Optical Band Structures
In addition to the Bloch surfaces, a symmetry plane is placed parallel to the device plane at half the thickness of the material. This can be done by meshing one of the Bloch surfaces and then copying it to the other surface. The program can be requested to output electric and magnetic fields interpolated at any given set of coordinates in the simulation volume.
Mechanical stress and resonance frequency
Many of the structures simulated here have a very large aspect ratio, because our devices are very thin and tall. First, the static solver is called to calculate the steady state equilibrium configuration of the structures due to intrinsic stresses. When the 'large deformation' is turned on, the program treats the system as non-linear, and performs several iterations of the solver linearizing the system around the previous run to achieve convergence.
FDTD SIMULATION METHODS
Transmission and Reflection
Second are the field profile monitors that we typically place on the symmetry planes of the simulation volume. To begin with, we use the excitation source's eigenmode solver to calculate the guided mode profile inside the Lumerical program, which we record and save the field profile. The measured power at the power monitors is then projected into the guided state of interest using the inner product of the measured state profile with the stored guided state profile.
Green’s Function Calculation
It is also useful to calculate the sensitivity of these values to the different geometry parameters and potential misalignment between parts of the optical path. It is also useful to keep track of the field patterns generated by the source as a function of frequency and dipole orientation, since the propagation of a photonic crystal structure can be highly anisotropic. The 'improvement' of the Green's function imaginary component is calculated from the ratio of the dipole power measured to reference dipole power function.
DIMENSIONS FOR CHEMISTRY PROCESSING HOLDER
TYPICAL DESIGN AND FABRICATION PROCESS FLOW
- Optical Functionality
- Simulation
- Simulation
- Write-File Processing
- Electron Beam Lithography
- Pattern Transfer
- Wet-Chemistry Release Process
- Optical Characterization
This is most easily done by comparing the distance from the surface of the fiber to the edge of the V-groove on both sides of the fiber. Use the hand tool described above to apply more glue to the back side of the attached fiber where it touches the Macor holder. Gently apply tension to the attached fiber again to confirm that the glue has completely dried. j) Unload the back of the already attached fiber from the translation stage.
