Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
1998-07-09
2001-05-08
Davie, James W. (Department: 2881)
Coherent light generators
Particular beam control device
Optical output stabilization
C327S337000, C372S038100
Reexamination Certificate
active
06229830
ABSTRACT:
TECHNICAL FIELD
This invention relates to the art of controlling generated signals, and more particularly, to controlling the output power of a laser used for burst mode transmission in a passive optical network (PON).
BACKGROUND OF THE INVENTION
In prior art passive optical networks using a bursty signal format power control for the laser requires high speed circuitry, because the power of each light pulse is measured and controlled. Such high speed circuitry is expensive, and consumes substantial power.
SUMMARY OF THE INVENTION
We have recognized that when using a bursty signal format power control for the laser may be performed on at least a per-packet basis, rather than a per-pulse basis, and that end-of-life detection may similarly be performed. This is achieved by accumulating the current generated by a photodiode in response to the light signal generated by the laser, subtracting therefrom a preset threshold current which is similarly modulated in response to the data signal used to drive the laser, and comparing the resulting difference to the value prior to having begun accumulating and subtracting. The result of the comparison, which may be filtered, is used to control the driver of the laser.
Computationally, this is similar to integrating the current generated by the photodiode in response to the signal generated by the laser; dividing by the number of bits which drove the laser to generate light and further dividing by the length of one bit, so as to find the average peak magnitude of the bits over a packet; and comparing this average peak magnitude with a preset threshold which is set to the current level which would be generated by the photodiode when the laser is supplying the desired power level for typical use, e.g., as specified by a user. Advantageously, because the average peak magnitude over a packet is used, slower components may be employed, reducing both cost and power consumption.
Additionally, by using a different threshold current, e.g., one-half of the current level which would be generated by the photodiode when the laser is supplying the desired power level for typical use, end-of-life detection for the laser may be achieved.
REFERENCES:
patent: 5936986 (1999-08-01), Cantatore et al.
T. Inoue et al: “Burst-mode CMOS LD driver IC for 156 Mbit/s transmission”, Electronics Letters: vol. 33, No. 9, Apr. 24, 1997.
N. Ishihara et al: “3.3V, 50Mb/s CMOS Transceiver for Optical Burst-Mode Communication”, 1997 IEEE International Solid-State Circuits Conference Feb. 1997 Digest of Technical Papers, vol. 40, ISSN 0193-6530/Paper FP 15.4.
Ota Yusuke
Sackinger Eduard
Agere Systems Optoelectronics Guardian Corp.
Davie James W.
Rosenthal Eugene J.
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