OPTICAL COMMUNICATION SYSTEM AND METHOD
FIELD OF THE INVENTION
The present invention is directed towards communication systems, and
more particularly, to so-called "wireless" communication systems.
BACKGROUND OF THE INVENTION
The ever increasing processing speed and popularity of computing
systems, along with increasing population densities in urban areas, has created a need
for communication systems capable of quickly transmitting ever-increasing amounts of
data. Currently, demand has bypassed the bit rate capabilities of conventional telephone
line technology, which is limited to less than 64,000 bits per second of data
transmission. Other technologies with higher bit rate capabilities are known, but
typically require either the laying of new cables, such as is required for coaxial cable
systems or fiber optic systems, or the licensing of an electromagnetic spectrum, such as
is required for wireless cellular systems and microwave link systems. These
requirements may tend to decrease the commercial viability of such systems.
Additionally, with the exception of fiber optic systems, many of the known technologies
are limited to 40 million bits per second, or less, transmission rates whereas
requirements for up to several billion bits per second of data transmission are anticipated.
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The present invention is directed, at least in part, toward overcoming one
or more of the problems discussed above.
SUMMARY OF THE INVENTION
In one aspect of the present invention, an optical communication system
is provided for use with a communication network. The system includes a fixed site
base station linkable to the communication network, and a plurality of fixed site
subscriber units spaced from the base station. The base station includes a plurality of
optical transmitters for transmitting communication signals through the atmosphere in
the form of laser pulses, and a plurality of optical receivers for receiving communication
signals through the atmosphere in the form of laser pulses. Each of the subscriber units
includes an optical transmitter in optical alignment with one of the base station optical
receivers for transmitting communication signals thereto through the atmosphere in the
form of laser pulses, and an optical receiver in optical alignment with one of the base
station optical transmitters for receiving communication signals therefrom through the
atmosphere in the form of laser pulses. The laser pulses have wavelengths in the visible
spectrum covering the wavelength range of 0.3 μm to 30.0μm.
In another aspect of the invention, a communication system is provided
that includes at least two fixed site communication units spaced from each other. Each
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unit includes an optical transmitter and an optical receiver. The optical receiver of each
unit is optically aligned with an optical transmitter of another unit for receiving
communication signals through the atmosphere in the form of laser pulses transmitted
from the optical transmitter of said another unit. The laser pulses have wavelengths in
the visible spectrum covering the wavelength range of 0.3 μm to 30.0μm.
In another aspect of the invention, at least one of the optical transmitters
includes an active laser diode configured to convert electrical communication signals
into the laser pulses.
In yet another aspect of the invention, at least one of the receivers
includes a photovoltaic screen and a telescopic lens system for concentrating the laser
pulses from at least one of the optical transmitters onto the photovoltaic screen.
In one aspect of the invention, at least one of the receivers includes an
optical filter, an optical repeater, and a telescopic lens system for concentrating the laser
pulses from at least one of the optical transmitters onto the optical filter.
In accordance with one aspect of the invention, a method of
communicating is provided and includes the step of transmitting communication signals
through the atmosphere in the form of laser pulses between a plurality of optical
transmitters and optical receivers in a fixed site base station and a plurality of fixed site
subscriber units which are spaced from the base station. Each of the subscriber units
includes an optical transmitter in optical alignment with one of the base station optical
receivers and an optical receiver in optical alignment with one of the base station optical
transmitters. The laser pulses have wavelengths in the visible spectrum covering the
wavelength range of 0.3 μm to 30.0μm.
In accordance with another aspect of the invention, a method of
communicating is provided that includes the step of transmitting communication signals
through the atmosphere in the form of laser pulses between an optical transmitter and
optical receiver in a first communications unit and an optical transmitter and optical
receiver in a second communications unit. Each of the optical receivers is in optical
alignment with the optical transmitter of the other communications unit for receiving the
communication signals transmitted from the optical transmitter. The laser pulses have
wavelengths in the visible spectrum covering the wavelength range of 0.3μm to 30.0μm.
In one aspect of the invention, the transmitting step comprises the step
of converting electrical communication signals into the laser pulses through an active
laser diode.
In another aspect of the invention, the transmitting step comprises the
step of concentrating the laser pulses through a telescopic lens system.
In yet another aspect of the invention, the transmitting step comprises the
step of passing the laser pulses through an optical filter.
In one aspect of the invention, the method further includes the step of
converting the laser pulses into electrical communication signals through a photovoltaic
screen.
In another aspect of the invention, the method further includes the step
of retransmitting the laser pulses through an optical repeater.
It is the principle object of the invention to provide a new and improved
optical communication system and method.
It is another object of the invention to provide a communication system
and method that does not require the laying of new transmission cables.
It is yet another object of the present invention to provide a
communication system that is capable of several bidirectional billion bits per second
transmission rates.
Numerous other features and advantages of the present invention will
become readily apparent from the following detailed description of the invention, the
accompanying figures, and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic representation of an optical communication
system embodying the present invention;
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FIG. 2 is a diagrammatic representation of an optical transmitter for use in the system of Fig. 1;
FIG. 3 is a diagrammatic representation of an optical receiver for use in the system of Fig. 1; and
FIG. 4 is a diagrammatic representation of another optical receiver for
use in the system of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Although this invention is susceptible to embodiment in many different
forms, the preferred embodiments of the invention are shown. It should be understood,
however, that the present disclosure is to be considered as an exemplification of the
principles of this invention and is not intended to limit the invention to the embodiments
illustrated.
Fig. 1 illustrates an optical communication system 10 that is capable of
several billion bits per second of transmission rates without requiring extensive laying
of transmission lines or cables. The system 10 is linkable to communication network
12, such as a public switched telephone network, a private branch exchange, a public
land mobile telecommunication system, a microcellular communication network, a
universal mobile telecommunication system, a satellite communication system,
networked cellular telephone base station, or a plurality of networked optical communication systems 10.
The system 10 includes a fixed site base station 14 and a plurality of
fixed site subscriber units 16 located within a service area 17. The base station 14
includes a plurality of optical transmitters 18 for transmitting communication signals
through the atmosphere in the form of laser pulses 20, and a plurality of optical receivers
22 for receiving communication signals through the atmosphere in the form of laser
pulses 20. Each of the subscriber units 16 includes an optical transmitter 24 in optical
alignment with one of the base station optical receivers 22 for transmitting
communication signals thereto through the atmosphere in the form of laser pulses 20,
and an optical receiver 26 in optical alignment with one of the base station optical
transmitters 18 for receiving communication signals therefrom through the atmosphere
in the form of laser pulses 20.
As seen in Fig. 2, each of the transmitters 18, 24 includes an active or
injection laser diode 30, or other similar device currently used in optical
communications, for nano/peco second optical pulsing. The laser diode 30 converts
electrical communication 31 signals into laser pulses. Such laser diodes 30 are
conventionally used in fiber optic systems for generating low power optical laser pulses
for transmission through an optical fiber. Many types of such laser diodes 30, or other
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similar devices used in optical communications today, are well-known in the art and
may be utilized to practice the invention. The laser diode 30 is optically aligned with
its respective optical receiver 22, 26 for transmitting laser pulses 20 in the visible
spectrum through the earth's atmosphere.
The laser pulses 20 have wavelengths in the visible spectrum from
ultraviolet to infrared. Preferably, the laser pulses 20 have wavelengths in the visible
spectrum within the wavelength range of 0.3μm to 30.0μm, and in the highly preferred
embodiment, within the wavelength range of 0.4μm to 0.7μm. Further, the laser pulses
20 can be transmitted from the transmitters 18, 24 at any discrete frequency within the
aforementioned wavelength ranges. Thus, the laser pulses 20 from a transmitter 18 to
a receiver 22 of a subscriber unit 16 may have a wavelength of 0.3 μm, while the laser
pulses 20 from the transmitter 24 of the subscriber unit 16 to a receiver 22 of the base
station 14 may have a wavelength of lOμm. Further, some or all of the transmitters 18,
24 may transmit monochromatic laser pulses 20 having a specific fixed frequency.
Alternatively, some or all of the transmitters 18, 24 may use wavelength division
multiplexing (WDM) where a multitude of light wavelengths can be used for the laser
pulses 20.
Each of the optical receivers 22, 26 includes a laser sensitive photovoltaic
screen or a semiconductor laser detector 32, as seen in Fig. 3, or an optical filter 34 and
optical repeater 35, as seen in Fig. 4. Because the laser pulses 20 are travelling through
the atmosphere, which is not a bounded wave guide, some scattering of the laser pulses
occurs and the laser intensity will decrease at a rate proportional to the square of the
transmission distance between each transmitter 18, 24 and receiver 22, 26 pair.
Accordingly, as seen in Figs. 3 and 4, each of the optical receivers 22, 26 further
preferably includes a telescopic lens system or optical concentrator 36 for gathering and
focusing the laser pulses 20 onto the photovoltaic screen 32 or the optical filter 34. The
telescopic lens system 36 preferably includes a suitable micro controller or computer
controlled focal point adjustment system 38 to maintain a proper focus and alignment
of the laser pulses 20 onto the photovoltaic screen 32 or optical filter 34. The power of
the transmitters 18, 24 and the magnification power of the optical concentrator 36 will
vary depending on the transmission distance and the desired transmission rate.
As seen in Fig. 3, the photovoltaic screen 32 converts the laser pulses 20
into electrical communication signals 40 for continued transmission through the system
10. As seen in Fig. 4, after the laser pulses pass through the filter 34, the repeater 35
reconfigures the laser pulses 20 into optical communication signals 42 for continued
transmission through the system 10. Because many types of photovoltaic screens 32,
optical filters 34, optical repeaters 35, telescopic lens systems 36, and focal point
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adjustment systems 38 are well-known in the art and may be utilized to practice the
invention, a more detailed description of these components is not required.
As seen at 44 in Figs. 1-4, conventional communications circuitry may
be provided to amplify, reshape, retime, recreate, multiplex, and/or demultiplex the
communication signals 31, 40, 42 as they are transmitted to the laser diode 30 and
transmitted from the photovoltaic screen 32 or optical repeater 35. Such circuitry is
well-known in the art and further description is not required herein.
Returning to Fig. 1, a communications link 46 is provided between the
network 12 and the base station 14. Preferably, the base station 14 is linked to the
network 12 by a very high bandwidth or wavelength division multiplexed optical fiber
cable, or through optical transmitters 18, 24 and receivers 22, 26 as described herein.
In operation, communication signals from the network 12 are transmitted
through the link 46 to the base station 14 where they are demultiplexed and otherwise
reconfigured before being fed to the respective transmitters 18 which will convert the
communication signals 31 into the laser pulses 20 for downlinking to the subscriber
units 16. Each of the subscriber units 16 will have its telescopic lens system 36
optically aligned and focused at one of the transmitters 18 for receiving the laser pulses
20 therefrom. Each subscriber unit 16 could be tuned to the same or different
wavelengths. The photovoltaic screen 32 or optical filter 34 and repeater 35 will then
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convert the laser pulses 20 into communication signals 40, 42 corresponding to the
output received from the base station 14.
For the uplink from the subscriber units 16 to the base station 14,
communication signals 31 are input into a subscriber unit 14 for conversion by the laser
diode 30 of the transmitter 24 into laser pulses 20. One of the optical receivers 22 in the
base station 14 will have its telescopic lens system 36 optically aligned and focused at
the transmitter 24 for receiving the laser pulses 20 therefrom. The photovoltaic screen
32 or optical filter 34 and repeater 35 of the optical receiver 22 will then convert the
laser pulses 20 into communication signals 40, 42 for continued transmission to the
network 12 via the link 46 after passing through the circuitry 44. Alternatively, rather
than passing to the network 12, signals intended for another subscriber unit 16 in the
system 10 may be directly sent thereto by the base station 14 through local switching
circuits in the base station 14. Preferably, the communication signals 40, 42 will be
multiplexed and transmitted through a higher bandwidth system to the network 12, or
to another subscriber unit 16. Preferably, the switching or connection between
subscribers of different base station 14 is governed by a switching center in the network
12, while limited local switching function may be programmed into each base station
14 for connecting two subscriber units 16 within the same service area 17.
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It should be understood that the bit rate in the uplink and/or downlink can
be adjusted by adjusting the pulse width of the laser pulses 20 and by adjusting the
power of the transmitters 18, 24. Further, the bit rate for the uplink may be different
than the bit rate for the downlink, which is advantageous in a number of situations. For
example, if a subscriber unit 16 is being utilized for "surfing" the internet, a very large
bit rate may be provided for the downlink, without requiring an equally large bit rate for
the uplink.
As previously noted, because the atmosphere is not about a wave guide,
the signal strength of the laser pulses will decrease with distance. However,
communication between distances at least on the order of 100s of meters would be
sustainable between the base stations 14 and the subscriber units 16. Further, while the
system 10 will not be as error-free as an optical fiber cable, a single bit simple error
correction scheme can overcome most of the error situations.
It should also be understood that, while the system 10 is shown in the
form of a hierarchal and centralized star network, other network topologies, including
decentralized topologies, may also be used for the system 10. For example, the system
10 could be configured so that the laser pulses 20 are transmitted between a pair of
subscriber units 16, or all of the subscriber units 16.
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It should also be understood that a plurality of the systems 10 may be
provided to cover a plurality of service areas 17, as is conventionally done in current
wireless cellular systems and networks, such as a cellular style tree network.
It should be appreciated that the laser pulses in the visible spectrum can
easily deliver several billion bits per second of data transmission. In this regard, it
should be appreciated that the wide bandwidth of the laser pulses provides an
opportunity for dynamic allocation within the bandwidth. Additionally, the bandwidth
for the uplink from each subscriber unit 16 is independent of the bandwidth for the
downlink to each subscriber unit 16. This allows for each of the uplink and downlink
to be of gigabit bandwidth. Further, as previously noted, this allows for the bandwidth
of the uplink to be different from the bandwidth of the downlink. Additionally, because
the laser pulses 20 are a relatively focused transmission, issues of electromagnetic wave
interference between subscriber units 16 are reduced or completely eliminated. In this
regard, it should also be appreciated that other electromagnetic frequency radiation
should not effect the system 10. Further, because of the fine tune focusing of the
telescopic lens system 36, external visible spectrum light, such as general atmospheric
light should not effect the system 10. Optical filters and/or waveform reshaping
repeaters can also be used to prevent interference by screening out selected wavelengths
of visible spectrum light.
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It should further be appreciated that the system 10 does not require
extensive laying of transmission cables between units, thereby avoiding not only the
cost involved in laying such cables but also avoiding right-of-way concerns as to where
the cables could be placed and time lost in establishing a communication system while
waiting on such cables to be laid. Thus, not only are infrastructure costs minimized, but
the system 10 of the present invention may be quickly established in new locations.
It should also be appreciated that laser pulses 20 such as used with the
present invention can be narrowly focused with substantially all of the pulses
transmitted directly at the receiver and without broad emanation of the signal as
commonly found with radio signals. Accordingly, the energy of transmission may be
substantially utilized (with little of the energy being wasted by being sent off in a wide
range of directions). Moreover, it is significant that no license to use the laser pulses 20
of the present invention would be required, nor is there any likelihood that any would
be required in the future. While licenses are required in the United States and many
other countries to use radio signals in various ranges (in large part because of the limited
number of such ranges available and the problem with interference between signals if
no such control is exercised), the narrow focus of laser pulses eliminates interference
between such pulses as a concern. Of course, the ability to operate systems 10
according to the present invention without licensing not only avoids the cost of such
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licenses and the associated delays which could result in establishing the system 10 while
awaiting such a license, but the lack of any limitations on use of the pulses in the
identified range provide the potential for unlimited use of such systems 10.
Still other aspects, objects, and advantages of the present invention can
be obtained from a study of the specification, the drawings, and the appended
claims.