Proc. SPIE. 10096, Free-Space Laser Communication and Atmospheric Propagation XXIX
KEYWORDS: Receivers, Control systems, Telecommunications, Free space optics, Acquisition tracking and pointing, Data communications, Stratosphere, Optics manufacturing, Prototyping, Free space optical communications
Internet connectivity is limited and in some cases non-existent for a significant part of the world's population. Project Loon aims to address this with a network of high-altitude balloons traveling in the stratosphere, at an altitude of approximately 20 km. The balloons navigate by using the stratified wind layers at different altitudes, adjusting the balloon's altitude to catch winds in a desired direction. Data transfer is achieved by 1) uplinking a signal from an Internet-connected ground station to a balloon terminal, 2) crosslinking the signal through the balloon network to reach the geographic area of the users, and 3) downlinking the signal directly to the end-users' phones or other LTE-enabled devices. We describe Loon's progress on utilizing free-space optical communications (FSOC) for the inter-balloon crosslinks. FSOC, offering high data rates and long communication ranges, is well-suited for communication between high-altitude platforms. A stratospheric link is sufficiently high to be above weather events (clouds, fog, rain, etc.), and the impact of atmospheric turbulence is significantly weaker than at ground level. In addition, being in the stratosphere as opposed to space helps avoid the typical challenges faced by space-based systems, namely operation in a vacuum environment with significant radiation. Finally, the angular pointing disturbances introduced by a floating balloon-based platform are notably less than any propelled platform, which simplifies the disturbance rejection requirements on the FSOC system. We summarize results from Project Loon's early-phase experimental inter-balloon links at 20 km altitude, demonstrating full duplex 130 Mbps throughput at distances in excess of 100 km over the course of several-day flights. The terminals utilize a monostatic design, with dual wavelengths for communication and a dedicated wide-angle beacon for pointing, acquisition, and tracking. We summarize the constraints on the terminal design, and the key design trades that led to our initial system. We illustrate measured performance during flight tests: received signal power variations with range, pointing system performance, and data throughput.
We developed a new type of optical lens device that can change its curvature like crystalline lens in human eye. The
curvature changing capability of the lens allows for a tremendous tuning range in its optical power and subsequently
enables miniaturized imaging systems that can perform autofocus, optical zoom, and other advanced functions. In this
paper, we study the physical properties of bio-inspired fluidic lenses and demonstrate the optical functionality through
miniaturized optical systems constructed with such lenses. We report an auto-focusing optical system that can turn from
a camera to a microscope, and demonstrate more than 4X optical zoom with a very short total track length. Finally, we
demonstrate the benefits of fluidic lens zoom camera through minimally invasive gallbladder removal surgery.
Miniaturized imaging systems have become ubiquitous as they are found in an ever-increasing number of devices, such
as cellular phones, personal digital assistants, and web cameras. Until now, the design and fabrication methodology of
such systems have not been significantly different from conventional cameras. The only established method to achieve
focusing is by varying the lens distance. On the other hand, the variable-shape crystalline lens found in animal eyes
offers inspiration for a more natural way of achieving an optical system with high functionality.
Learning from the working concepts of the optics in the animal kingdom, we developed bio-inspired fluidic lenses for a
miniature universal imager with auto-focusing, macro, and super-macro capabilities. Because of the enormous dynamic
range of fluidic lenses, the miniature camera can even function as a microscope. To compensate for the image quality
difference between the central vision and peripheral vision and the shape difference between a solid-state image sensor
and a curved retina, we adopted a hybrid design consisting of fluidic lenses for tunability and fixed lenses for aberration
and color dispersion correction. A design of the world's smallest surgical camera with 3X optical zoom capabilities is
also demonstrated using the approach of hybrid lenses.
Monolithic multi-layer optical disks have been recorded with single-beam two-photon absorption using a high-repetition- rate laser. The recorded bit shape and signal readout will be discussed. It will also present some initial experimental results in cross talk and signal quality measurements.
Two-photon 3D optical data storage techniques can achieve hundreds of GB data capacity per disk by storing data in multi-layer volumetric media. This approach can also provide fast data transfer rates by using parallel access techniques. It is a promising solution for the high data capacity demands in imaging and video applications, and the high-speed data access requirements in large-scale high- speed data processing. Development of this technology integrates and leverages developments in parallel sensors, spatial light modulators, novel optics, parallel signal processing, and micro-optic packaging.
Three-dimensional parallel readout of 2-photon multilayer optical disks can simultaneously offer high capacities (greater than 100 GB/disk) and high data transfer rates (greater than 1 Gb/s). The robust system tolerances should enable cost effective storage systems with capacities and transfer rates that are scaleable to match various application requirements.
The generation and application of information is rapidly evolving from text and graphics based to multimedia based, and it will shortly continue to evolve to virtual reality. The evolution between these stages introduces dramatic increases in the amount of data associated with the applications. For example, where text-based meeting notes have given way to emailed copies of vugraphs, future meeting documentation may require storing and communicating an entire collaborative virtual reality session. Even in the near term, the need to store, search for, and edit large numbers of images and digital video clips will drive data storage requirements forward in home, office, and network arenas, as shown in Fre 1 .
Three layer data recording has been demonstrated in monolithic disk media using two-photon absorption. Two dimensional data arrays have been recorded and retrieved in parallel. The recording process has been modeled and simulated. Fluorescence has been detected from a disk spinning at 1500 rpm with a signal to noise ratio of 10.