Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2001-11-20
2003-09-30
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C359S199200
Reexamination Certificate
active
06627867
ABSTRACT:
FIELD OF THE INVENTION
The invention is generally related to laser transceivers and fiber optic communication links. More specifically, the invention is related to monitoring operational performance of fiber optic communication links.
BACKGROUND OF THE INVENTION
Today, optical fibers form the backbone of a global telecommunication system. These strands of glass, each thinner than a human hair, are designed to carry huge amounts of data transmitted by tightly focused laser beams. Together, optical fibers and lasers have dramatically increased the capacity of the telephone and data systems. With equal improvements in computing, mankind has become dependant on this communication technology.
Thus, maintaining the integrity of a fiber optic communications link has become critical, particularly in these high capacity telephone and data systems. Failure to properly maintain a link can result in severed communications as well as data disruptions since both voice and data may be carried on the same fiber. This can lead to lost revenues since people often do not reestablish calls once they have been interrupted or “dropped.” Further, reestablished calls and data links must be rerouted by the host system over another link. This results in delays as well as the additional time and effort required for rerouting, not to mention reduced system capacity.
Often, breaks in these links can be traced to failures of laser diodes that transmit data over these fibers. These laser diodes function to transmit voice and data through modulation of their photonic emission. Laser diodes are “biased” by a DC current which causes them to emit radiation at a particular frequency. This emission frequency is then varied, or “modulated,” by an AC current in response to voice or data which is desired to be transmitted. Experience has shown that most laser diodes do not fail catastrophically but rather slowly deteriorate in performance, drawing more and more bias and modulation current to generate the amount of output power necessary to maintain the link. At some point, the amount of current required becomes so burdensome to the electronic driver that the link is broken.
Once a link breaks, a technician must be dispatched to diagnose and repair the broken link. Oftentimes, the technician must disconnect the optical fiber from the transceiver located at the opposite end of the link from the laser diode and connect it to an optical power meter in order to measure the emitted optical power from the transceiver. Based on the measured power, a diagnosis is made by the host system. Optical power transmitted from the laser diode must pass through an optical system of complex interconnections before reaching a transceiver. Many times, the optical output power is too low due to a failure of the laser diode in the laser module. Other times, the break in the link is due to a failure of a connection in the link itself. Optical fibers can be up to 10 km in length and can be spliced and optically switched as well. Optical attenuation along this path is a reality. Lasers experience optical attenuation along the network due to damaged or dirty optical interconnects. In either case, the end result is reduced modulated optical power reaching the transceiver disposed at the opposite end of the link.
This process of measuring the optical power incident on a transceiver can also be performed in an effort to predict potential failures in the future. However, the skill of the technicians which perform the measurements becomes paramount as the orientation of the fiber in relation to the optical power meter can significantly effect the amount of power measured. This along with the amount of time, effort, and manpower, as well as the reduced system capacity, that accompany this approach make service providers which use fiber optic links reluctant to use this process.
Therefore, a significant need exists in the art for a manner of monitoring the optical power incident on a transceiver in a fiber optical link without breaking the link.
SUMMARY OF THE INVENTION
The invention addresses these and other problems associated with the prior art by providing an apparatus, circuit arrangement, and method that monitor the optical power received by a transceiver in a fiber optical link without having to break the link. The optical power incident on a photo-detector configured to receive an optical from an optical fiber is monitored in part through the use of a receiver circuit coupled to the photo-detector and configured to generate a data signal representative of information encoded in the received optical signal and a monitor signal that is proportional to the peak-to-peak optical power of the received optical signal. By providing a signal which is proportional to incident peak-to-peak optical power, a host system such as a computer or other data processing system has the ability to read a signal and calculate, as desired, the peak-to-peak optical power received by a transceiver in a fiber optic link without breaking the link. Thereby, the host system is further able to determine laser performance and preempt laser failure of a laser disposed in another transceiver at the other end of a link that may not be detected by an average power meter.
In one embodiment consistent with the invention, a monitor voltage is presented directly to an analog-to-digital converter within the host system. In another embodiment of the invention, the monitor signal is digitized in a receiver circuit and delivered to the host system via a digital interconnect. In the embodiments, the host system is operative, using coefficients located in the transceiver nonvolatile memory, to calculate the optical power by reading the monitor signal. As such, the host system is capable of monitoring the peak-to-peak optical power received by a transceiver in a fiber optic link without disrupting the link.
These and other advantages and features, which characterize the invention, are set forth in the claims annexed hereto and forming a further part hereof. However, for a better understanding of the invention, and of the advantages and objectives attained through its use, reference should be made to the Drawings, and to the accompanying descriptive matter, in which there are described exemplary embodiments of the invention.
REFERENCES:
patent: 5920438 (1999-07-01), Christensen et al.
patent: 5956168 (1999-09-01), Levinson et al.
patent: 6528777 (2003-03-01), Ames et al.
U.S. patent application Ser. No. 09/955,545, entitled “Laser Diode Monitoring Via Current Mirroring”, filed on Sep. 18, 2001 by Stephen John Ames et al. (ROC920000318US1).
U.S. patent application Ser. No. 09/761,526, entitled “Transimpedance Amplifier With an In-Situ Optical Power Meter”, filed on Nov. 16, 2000 by Stephen J. Ames et al. (ROC920000245US1), Now U.S. patent No. 6,528,777.
Ames Stephen John
Marlowe Michael William
White Christopher K.
Le Que T.
Wood Herron & Evans LLP
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