Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-02-12
2003-03-18
Chan, Jason (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C372S101000, C372S102000, C372S103000
Reexamination Certificate
active
06535308
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and apparatus for communicating over a single optical fiber communications channel, and more specifically, to methods and apparatus for converting electrical signals to optical signals and optical signals to electrical signals by a single laser diode which acts as both a light-emitting diode and a photodetection diode.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The telecommunications industry is using more and more optical or light fibers in lieu of copper wire. Optical fibers have a extremely high bandwidth, thereby allowing significantly more information to be carried than can be carried by a copper wire.
Of course, modern communication systems require bidirectional communications, where each station on a communications channel can both transmit and receive. This is true, of course, whether using electrical wiring or optical fibers as the transmission medium. Early telephone communication systems solved this need simply by providing separate copper wires for carrying the communications in each direction. Some early attempts at using optical fibers as a transmission medium followed this example and also used two different optical fibers
10
and
10
A for carrying the communications in each direction as illustrated in the prior art FIG.
1
. As shown, fiber
10
is connected by an optical coupler
12
to an LED (light-emitting diode)
14
at one end and by optical coupler
16
to a PD (photodetection diode)
18
at the other end. Similarly, but in reverse, fiber
10
A is connected by an optical coupler
16
A to PD
18
at one end and by optical coupler
12
A to LED
14
at the other end.
However, because of the extremely high bandwidth available for use by an optical fiber a single fiber is quite capable of carrying communications in both directions. In fact, as will be appreciated by those skilled in the art, by using modern multiplexing techniques a single fiber has sufficient bandwidth to carry a large number of different communications by different customers in both directions at the same time. One such technique is (WDM) (wavelength divisional multiplexing) which is shown in the prior art FIG.
2
and uses different wavelengths for each direction of travel. Components in FIG.
2
and subsequent figures which operate the same as shown in
FIG. 1
carry the same reference numbers. In the embodiment shown in
FIG. 2
, a central office
20
is connected to an RDT (remote digital terminal)
22
by a single optical fiber
10
B. As shown, the central office includes a light-emitting diode
14
optically connected to fiber optics
10
by optical coupler
12
for converting electrical signals to optical signals and a photodetection diode
18
optically connected to optical fiber
10
B by coupler
16
A for converting optical signals to electrical signals. The fiber optics
10
and fiber optics
10
B are each connected to a wavelength division multiplexor
24
which in turn is connected by optical coupler
26
to optical fiber
10
B. This arrangement is duplicated at the RDT
22
by light-emitting diode
14
A, photodetection diode
18
A, and wavelength division multiplexor
24
A. It will, of course, be appreciated that although the figure is shown as providing communications between a central office
20
(station
1
) and a remote terminal office
22
(station
2
), the communications system could be used for providing communications between any two types of stations such as, for example, two central offices, two remote terminal offices, or between a remote office and an individual user's location etc. A typical communication system using an LED and a PD with a single optical fiber is disclosed in U.S. Pat. No. 5,075,791 entitled “Method and Apparatus for Achieving Two-Way Long Range Communication over an Optical Fiber”, issued to Mark W. Hastings, and incorporated in its entirety hereby by reference.
Yet another technique for using a single optical fiber
10
B is illustrated in the prior art FIG.
3
. The illustrated figure is referred to as TCM (time compression multiplexing) and is sometimes referred to as a “ping-pong” system. The system uses a single optical fiber
10
and a single diode
30
and
30
A at each end connected by optical coupler
32
and
32
A, respectively, for both converting electrical signals to optical signals and for receiving optical signals and converting those optical signals to electrical signals. TCM systems have the obvious advantage of requiring fewer components. Unfortunately, diodes presently available for such dual use while having a high efficiency of converting electrical signals to optical signal for transmission in one direction down the optical fiber, are not as efficient at receiving the very low-level optical or light signal from the fiber and converting that optical signal to an electrical signal. This is especially true after the significant attenuation the optical signal will experience as it travels down the optical fiber. Consequently, present systems using a signal diode for both transmitting and receiving are often noisy and ineffective.
Thus, it would be advantageous to provide a signal diode system which can receive the low amplitude optical signal and make the conversion to an equivalent electrical signal amplifying the electrical signal and still maintain a low signal-to-noise ratio.
SUMMARY OF THE INVENTION
The present invention addresses the above concerns and disadvantages of prior art systems for using a signal diode for both transmitting and receiving optical signals.
The circuitry of a preferred embodiment of the invention for using a signal diode connected to an optical fiber for both receiving and transmitting digital signals provided by a drive unit connected to the diode and making up a part of the circuitry of this invention is described. The drive unit receives electrical digital input signals such as PWM (pulse-width modulated) signals from a suitable digital source and then stabilizes parameters of these signals such as the voltage level and the duty cycle of the PWM signal before providing the signal to a current amplification device which then provides the amplified current signal to drive the diode. A preferred embodiment of the invention further includes a temperature compensation circuit for maintaining the output level of the drive circuit within acceptable limits even with temperature variations. The optical fiber connected to the circuitry is, of course, suitable for transmitting digital light signals in both directions. The diode is optically coupled to the optical fiber and is controlled by the inventive circuitry so as to have a receiving mode and a transmitting mode. In the receiving mode, the diode receives the digital light signals from the optical fiber and generates electrical digital signals representative of the received digital light signals. In the transmitting mode, the diode is electrically connected to the electrical digital signal source and receives the electrical digital signals and generates optical or light digital signals representative of the electrical digital signals for transmission by the optical fiber. A preferred diode for both receiving and transmitting is an ELED (edge-emitting light-emitting diode). The electrical signals generated by the diode in response to receiving the optical digital signals are provided to a receiver circuit which is connected to the diode electrical outputs. The receiver circuit amplifies and conditions the electrical signals from the diode in a manner such that the signals are suitable for being provided as electrical digital output signals for communication purposes. In a preferred embodiment, a receiver circuit has amplifying circuitry which includes an automatic gain control amplifier and further includes a slicing comparator for calculating the slicing level of the output signal. Since the diode includes a single set of input/output leads, it will be appreciated that the drive circuit and the receive circ
BuAbbud George H.
Hastings Mark W.
Kimbrough Mahlon D.
Chan Jason
Jones Day Reavis & Pogue
Marconi Communications Inc.
Payne David
LandOfFree
Method and apparatus for converting electrical signals and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for converting electrical signals and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for converting electrical signals and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3043449