Coherent light generators – Particular resonant cavity – Specified cavity component
Reexamination Certificate
1999-03-03
2001-08-21
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular resonant cavity
Specified cavity component
C372S032000
Reexamination Certificate
active
06278721
ABSTRACT:
TECHNICAL FIELD
The present invention relates to laser modules and, more particularly, to laser modules which employ external gratings to stabilize lasing.
BACKGROUND OF THE INVENTION
Lightwave communication systems strive for maximum transmission capacity by spacing optical channels as closely as possible, typically a few nanometers or less. However, any drift in the lasing wavelength readily causes the signals from one optical channel to cross into another. As such, lightwave communication systems typically use laser modules which employ external gratings to stabilize the lasing wavelength at a desired value. In this latter case, although the laser housed in the module resonates over a range of wavelengths, the external grating confines or so-called “locks” the laser to operate at a single desired wavelength. This arrangement has the additional benefit that the linewidth of the laser's output is narrowed considerably after passing through the grating.
The above locking mechanism, however, only works over a particular range in temperatures, known as the laser module's “locking range.” Traditionally, this locking range is designed to match the span in temperatures for the desired application. It has been observed that the locking range, however, varies from one module to another. Accordingly, it would be desirable to provide for a method to eliminate, or at least minimize, the variations in the locking range of such laser modules.
SUMMARY OF THE INVENTION
The present invention discloses a method for eliminating, or at least minimizing, the locking range variability of laser modules which employ external gratings, such as fiber bragg gratings. It has been observed that the coupling efficiency between the laser and its output fiber is a highly variable property of the laser module, causing variations in the laser module's locking range. The laser module's locking range, however, can be readily reset to or near its nominal value by measuring the laser module's coupling efficiency, and then judiciously choosing a grating having a peak reflectivity which compensates for variations in the coupling efficiency by maintaining constant the effective reflectivity R
eff
of the fiber/grating combination. In this latter manner, the fraction of the light coupled back into the laser cavity is substantially maintained constant from module to module, minimizing locking range variability. Preferably, fiber bragg gratings of different known peak reflectivity values can be readily fabricated, kept in inventory, and then judiciously chosen depending on the measured coupling efficiency, C.
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Arroyo Teresa M.
De La Rosa J.
Inzirillo Gioacchino
Lucent Technologies - Inc.
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