Multiplexed optical scanner technology

Details Multiplexed optical scanner technology Multiplexed optical scanner technology

2001-11-05

2004-02-03

Juba, John (Department: 2872)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S578000, C359S615000, C359S298000, C250S550000, C348S036000

Reexamination Certificate

active

06687036

ABSTRACT:

FIELD OF THE INVENTION
Applications using scanned or agile laser beams are wide spread in both the commercial and military sectors. First several applications and their scanner requirements are described to put the proposed scanner inventions in perspective.
Military applications such as for infrared countermeasures, target designation, and laser communications presently require substantial improvements in laser beam steering technology. Specifically, there is a need to realize small, low power consumption, lightweight, low cost, rapidly (e.g., a few microseconds or less) reconfigured laser beam scanners for steering, pointing, and tracking. Other useful features of these scanners include the ability to generate multiple simultaneous laser beams in space, eye safe operation, wide scan angles (e.g., ±45 deg.), low sidelobes (e.g., <−30 dB), large apertures (e.g., 10 cm diameter) to provide high resolution scans, and true rapid three dimensional (3-D) beamforming to accurately control beam position, power and shape. This application proposes scanners that can meet the military scanner requirements.
An important commercial application is freespace optical wireless. The need for more information bandwidth with a global emphasis has given a new technological challenge for wireless information network designers. This increased bandwidth will be gobbled up by both improved present and completely new wireless information services such as worldwide internet services, data communications, multi-media, virtual navigation, and telemedicine, wideband indoor wireless, to name a few. Over the last few years, a number of approaches have been taken to implement both terrestrial and satellite wireless services with an increased bandwidth. Methods include using efficient signal coding and modulation schemes, the use of spatial processing using microwave phased array antennas, and the transfer to higher radio frequencies (e.g., into the millimeter band) for the carrier. More recently, a bold and potentially high payoff approach of pushing the carrier all the way up to the optical frequency has been chosen to get the ultimate jump in information bandwidth into the several gigabits per second (Gb/s) regime. Specifically, commercial communication companies are making strides to deploy freespace optical communications for ultrawideband (e.g., upto 10 Gb/s) wireless links. One application is long range intersatellite links, while another focus is short haul (e.g., <5 km) terrestrial links in air. Another application being considered using freespace optical communications is indoor wireless. Free-space optics technology is expected to deliver unprecedented wide bandwidths, massive carrier reuse, ultra-low interchannel interference, and cost savings where electrical wires and optical fibers are too expensive to deploy and maintain.
With this initial driving motivation in mind, the next natural step in freespace optical communications for wireless is the use of inertialess optical scanners as the agile free space light routing method within a multi-user free-space optical wireless network to realize all-optical advanced wireless networking. This would lead to a wireless network essentially transparent to the information bandwidth, implying ultra-wideband operation. Depending on the wireless scenario, the impact and benefits are different yet highly significant. For instance, optical intersatellite links can use the highly accurate and fast beam pointing capabilities of the scanner to enhance the tradeoff between link distance and data rates. Similarly, indoor optical wireless can be greatly more power efficient and eye safe when using a scanner coupled with the optical link.
Freespace optical wireless links for satellite and outdoor terrestrial applications currently under development mainly use large and costly mechanically actuated mirrors and lenses to focus and direct light to the remote optical transceiver to maximize signal-to-noise ratio and hence bandwidth. This alignment process is slow and power consuming and requires precise mechanical motion of optics that are prone to misalignments due to vibrations and other environmental effects. Furthermore, the mounting mechanics can occupy a large fraction of the transceiver frontend, restricting overall head size, weight, and volume. For low earth orbit satellite systems, this is particularly a major problem from a payload point of view as short (<1 min.) acquisition times are required. Thus, as recently pointed out, the pointing, acquisition and tracking subsystems in an optical intersatellite link terminal presently pose key technical and economic problems. Hence, one objective in this patent application is to invent and develop new low cost, compact, and high performance (including microseconds domain high speed) optical scanner technology that can be applied for inertialess beam pointing, acquisition and tracking for both satellite and ground-based optical wireless links. Another objective is to show by example how the proposed scanners can solve the problems facing current indoor optical wireless links. Over the past decade, indoor optical wireless has developed concentrating on a technique called diffused infrared radiation (DFIR) technology. In DFIR wireless, the roof of a room has an optical data source whose light is diffused and scattered in the room volume so any wide angle optical receiver in any location of the room can pick up the signal. Although this method lends itself to receiver portability, it requires high optical power and suffers from bandwidth limits due to multipath effects. In addition, DFIR can suffer from eye safety issues as the room is permeated with IR radiation. To solve most of these problems, the directed-beam IR (DBIR) technique was developed that uses a single directed beam from the optical satellite on the room roof. Here, the eye safe 1550 nm wavelength beam direction is fixed such that it points to the fixed receiver. This technique requires accurate beam alignment and suffers from catastrophic failure when the beam might be temporally blocked by some moving object or person. Hence, DBIR has found limited commercial use as it is not appropriate for moving platforms. In this application, we propose a scanner use that using a combination of DBIR and DFIR implemented through the use of our proposed scanner technology is able to retain the best attributes of both DBIR and DFIR, leading to wideband, efficient power consumption, wireless optical links that do require fixed and no-mobile status of the transceivers.
Another important application for optical scanners is in data storage and retrieval whether it is personal computers (PCs), main frames or some other database system. The ever-increasing processing power and ultra fast fiber-optic networks have put enormous pressure on shared/distributed data storage devices for fast and efficient handling of massive data. So far, only mechanical systems have been devised to access different locations of a storage device for data storage and retrieval. For instance, a compact disc (CD) drive rotates the CD whereas the laser head scans in a radial direction to access different locations on the CD. Accessing different locations of a storage device at a fast speed for data handling is limited due to the mechanical inertia associated with these systems. Very high speed optical scanning can be used for rapidly accessing these storage devices to handle data at exceedingly fast rates. In this application, scanners are proposed that can be used to form high speed fiber-optic scanning systems for data handling in 2D and 3D data storage devices. The proposed architectures produce fast, e.g., less than a microsecond per scan spot beams. The potential speed of the proposed scanners is in the GigaHertz rates using present-day state-of-the-art nanosecond tuning speed lasers.
High speed optical scanners are also needed in numerous other applications. The proposed scanners in this patent application can benefit other applications such as optically coupled ultrasonics, b

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