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To: ahhaha who wrote (281)	3/5/1999 8:05:00 PM
From: Frank A. Coluccio	Respond to of 626

I've just unpacked the patent pdf file. The drawings bring things into better focus, but I see I've got my work cut out here.

To: ahhaha who wrote (281)	3/5/1999 8:43:00 PM
From: ahhaha	Respond to of 626

For completeness I include the patent's Background and summary: STABILIZED DFB LASER FIELD OF THE INVENTION The field of the invention relates to lasers and in particular to the stabilization of lasers used for cable television transmissions. BACKGROUND OF THE INVENTION The use of lasers for the transmission of information in communication systems is known. Such use has tv typically been limited to amplitude modulated systems that in use often attain a speed of several megabytes. Laser systems in current use for communications are typically amplitude modulated because of certain inherent limitations in a laser's ability to change frequency. Lasers, in fact. are often limited to a single frequency, or a narrow range of frequencies. The tendency of a laser to operate within narrow ranges is inherent in the resonant cavity used in the generation of laser signals. A resonant cavity of a laser is designed to amplify, optical signal, of a desired frequency and attenuate signals of an undesired frequency. The cavity amplifies desired frequency through use of a laser cavity dimensioned in one quarter wavelength increments. The closer the cavity dimensions are to a desired tolerance, the narrower the range of frequencies within which the laser will operate the line width, The narrower the line width, the less inherent noise will be transmitted in a laser signal. Further, the narrower the line width, the more power is focused into a desired center frequency, While gas lasers have been developed with extremely narrow line widths, solid state lasers, do not perform nearly as well. Distributed feedback (DFB) semiconductor lasers. in fact, are known to have relatively wide line widths. As the junction current of a DFB laser is changed (or the cavity temperature changes), the operating frequency of the laser also changes. The linewidth may also vary. Static variations in the inside cavity dimensions may cause the cavity to inherently resonate at a number of frequencies. Variations in the junction current may cause a center frequency to shift (i.e., hop) from one resonant regime to another. Changes in cavity dimension caused by temperature may have the same effect. Because of their inherent low cost and reliability, DFB lasers have an enormous potential in laser communication systems. Consequently, a need exists for a method of controlling the line width of DFB lasers. SUMMARY A method and apparatus are provided for stabilizing a distributed feedback semiconductor laser. The method includes the steps of comparing an optical output of a first oscillating mode of the semiconductor laser at a first polarization angle with an optical output of a second oscillating mode of the semiconductor laser at a second polarization angle orthogonal to the first polarization angle. A first feedback signal is provided to a cavity temperature control of the semiconductor laser in response to detected differences of the compared first and second oscillating modes. The method further includes the step of comparing an output of the reference laser with an output of the semiconductor laser and providing a difference signal as a second feedback signal to the temperature controller of the semiconductor laser in response to detected differences between the reference laser and semiconductor laser.