Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2001-05-16
2002-12-03
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06490067
ABSTRACT:
FIELD OF THE INVENTION
The present application relates to optical transceiver technology, for example, as used in a wireless optical network (WON).
BACKGROUND
Wireless optical networks (WONs) are becoming increasingly popular in the telecommunications market as a strategy to meet last-mile demand, enabling reliable high-bandwidth connectivity previous available only to customers directly connected to fiber or cable. An example of a WON is Airfiber's OptiMesh system, which is described generally in U.S. Pat. No. 6,049,593, and co-pending U.S. patent application Ser. No. 09/181,043, entitled “Wireless Communication Network.”
Historically used by military and aerospace industry, WON technology has evolved into systems with backup and redundant optical links, providing high reliability and fiber-like bandwidth to customers located up to a kilometer away from buried fiber. Such systems are being deployed to commercial buildings in urban area, breaking the so-called “last-mile” bottleneck. These WONs provide higher bandwidth than Radio Frequency (RF) wireless systems and are considerably less expensive to deploy than laying fiber.
FIG. 1
illustrates an example of a WON application. As shown therein, facilities
104
(e.g., commercial office buildings) can be linked to a high bandwidth network
102
(e.g., a fiber-based network) by means of optical transceivers
106
and
107
, which use “open-air” or “free-space” laser beams to maintain wireless, high bandwith communication links
108
among each other. The central, or main, optical transceiver
107
can have a communication link
110
(e.g., either wired or wireless) to the network
102
, and thereby serve as a hub for the other optical transceivers
106
.
FIG. 2
shows an example of a conventional wireless optical transceiver
106
. As shown therein, the transceiver
106
is composed of two basic elements: an output channel
200
for transmitting a laser beam (modulated or otherwise impressed with data) to another transceiver in the WON, and input channel
202
for receiving a modulated laser beam from another transceiver in the WON. Each of the input and output channels is composed of three basic components. The output channel
200
includes a laser diode (LD), which emits a laser beam of a predetermined wavelength (in this example,
785
nanometers) that passes through a diffuser
206
and which is focused by optics
204
(e.g., a plano aspheric lens). An incoming beam, for example, from another transceiver in the WON, is received by optics
204
of the input channel
202
, passed through a bandpass filter
210
and ultimately received by a photodetector (PD), e.g., an avalanche photodiode.
The open-air laser beams used by WONs to transmit and receive data pose a potential threat to human eye safety. The collimated, beam-like quality of a laser results in very high irradiance (also known as “power density” or “flux”), which can damage tissues in the human eye causing serious conditions such as photokeratitus (“welder's flash”) and cataracts.
Accordingly, several laser safety standards have come into existence that specify and regulate the parameters of lasers operating in environments that may expose the human eye to laser radiation. In general, three main aspects of regulations exist for lasers and their usage: Class definitions, Accessible Emission Limits (AEL), and Maximum Permissible Exposure (MPE). The class definitions provide non-technical descriptions understandable to lay-persons, AELs define the classification breakpoints, and MPEs are based on biophysical data and indicate actual tissue damage thresholds.
Class definitions—for example, Class 1, 2, 3, or 4—provide an abbreviated way to readily communicate a hazard level to a user. Class 1 represents lasers that are safe under reasonably foreseeable conditions, including the possibility of a human eye being exposed, either aided (e.g., through binoculars) or unaided, to a laser beam. At the other end of the spectrum, a Class 4 laser is capable of producing hazardous diffuse reflections that may pose skin and fire hazards. As an example, to meet the most stringent standard—class 1—a laser operating at 785 nm must be limited in power density such that the power collected by a human eye exposed to the laser is no greater than 0.56 milliwatts (the class 1 AEL for 785 nm lasers). Various factors such as the distance from the eye to the laser during exposure, and whether the viewing is aided or not, have a significant impact on how much power is collected by the eye.
The present inventors recognized that, while increased demand for WON bandwidth and link range generally would require the power densities of lasers used in WON transceivers to be increased, eye safety standards and concerns for human ocular safety represent strict limits on increasing such power densities. For example, the optical transceiver shown in
FIG. 2
uses 622 megabits per second in both directions. However, beyond some level—for example, 1.2 gigabits per second—more power would be required to sustain the data rate. Accordingly, the present inventors developed systems and techniques that, among other advantages, enable laser output devices such as WON transceivers to transmit and receive data at increased bandwidths but without exceeding existing safety standards and without increasing risks to humans.
SUMMARY
Implementations of the systems and techniques described here may include various combinations of the following features.
In one aspect, an optical transceiver such as used, for example, in a wireless optical network (WON), may include multiple laser sources including a first laser source configured to transmit a first output channel beam having a first optical characteristic and at least a second laser source configured to transmit a second output channel beam having a second optical characteristic; multiple detectors including a first detector configured to detect a first input channel beam having the first optical characteristic and at least a second detector configured to detect a second input channel beam having the second optical characteristic; and multiple apertures including a first aperture through which the first output channel beam and the second input channel beam pass and a second aperture through which the second output channel beam and the first input channel beam pass.
In an embodiment, the first optical characteristic may be a first wavelength (e.g., 830 nm) and the second optical characteristic may be a second wavelength different from the first wavelength (e.g., 785 nm). A difference between the first wavelength and the second wavelength is about 50 nanometers or greater. One or more of the wavelengths may be between 1530 and 1570 nanometers.
In another embodiment, the first optical characteristic may be a first polarization (e.g., transverse electric polarization) and the second optical characteristic may be a second polarization different from the first polarization (e.g., transverse magnetic polarization).
Laser sources that may be used include laser diodes, gas lasers, fiber lasers, and/or diode-pumped solid state (DPSS) lasers. In an embodiment, a laser diode is used that emits an output field that is either substantially transverse electric or substantially transverse magnetic.
Detectors that may be used includes an avalanche photodiode with a bandpass filter or an avalanche diode with a polarizer, for example, a transverse electric polarizer or a transverse magnetic polarizer.
The aperatures may include a lens, for example, a plano aspheric lens having a diameter of about 75 mm.
In an embodiment, the transceiver further may include multiple beamsplitters, including a first beamsplitter associated with the first aperture and a second beamsplitter associated with the second beamsplitter, which differentiate between the first and second optical characteristics. At least one of the beamsplitters may be an optical highpass filter such as a dichroic mirror. At least one of the beamsplitters may be a polarizing beamsplitter. One or more of the beamsplitters may pass
Alwan Jim
Bloom Scott H.
Chan Victor J.
Airfiber, Inc.
Knobbe Martens Olson & Bear LLP
Pascal Leslie
Phan Hanh
LandOfFree
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