Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
1999-06-08
2001-02-06
Lee, John D. (Department: 2874)
Coherent light generators
Particular beam control device
Optical output stabilization
C372S029011, C372S029015, C372S029020, C372S038010, C372S038020
Reexamination Certificate
active
06185233
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a wavelength stabilizing system. In particular, this invention relates to a system and method for minimizing the wavelength variation at the output of a laser diode.
BACKGROUND OF THE INVENTION
A wavelength optical transmitter is an optical amplifier which amplifies light having a required wavelength band. Multiple wavelength optical transmitters are typically used in a system to transmit several laser signal lights over a single fiber. Each laser signal light represents a separate channel. It is critical that each laser signal light transmitted over a single fiber be on wavelength, otherwise they will interfere with each other. When two or more laser signal lights interfere with each other the light becomes a noise component and degrades the signal to noise ratio of the laser signal light. An optical wavelength filter is conventionally provided on the post-stage of the wavelength optical amplifier to prevent any laser signal lights from interfering with each other.
Another method used to stabilize the wavelength of the laser signal light is to improve the accuracy of the laser diode. However, improving the accuracy of the laser diode can be very expensive. To avoid these high costs, other methods for stabilizing the wavelength of a laser signal light are used. In one such method, a laser is first mounted to a thermoelectric cooler. A feedback control loop is then used to keep the thermister resistance of a thermoelectric cooler constant, thus holding the temperature of the laser transmitter constant. Since the laser transmitter temperature constant, the laser wavelength is stabilized. The above technique works well for optical transmitters requiring relatively constant output power, however, if the output power is varied, a simultaneous shift in the laser signal wavelength occurs causing interference with an adjoining channel.
SUMMARY OF THE INVENTION
The present invention provides a wavelength stabilizing system and method that substantially eliminates or reduces disadvantages and problems associated with previously developed wavelengths stabilizing systems and methods.
More specifically the present invention provides a system for minimizing the wavelength variation of the light output by a laser diode. The output power controlled stabilizing system and method includes a wavelength limiter which minimizes the wavelength variation of a laser signal light. The wavelength limiter comprises a first and second clamping circuit. The first clamping circuit receives an offset voltage, compares the offset voltage to a first predetermined reference voltage, and outputs the voltage difference between the offset voltage and the first predetermined reference voltage. If the offset voltage rises higher than the first predetermined reference voltage, the first clamping circuit clamps and keeps the output power of the output power controlled wavelength stabilizing system from increasing. The second clamping circuit also receives the offset voltage, compares the offset voltage to a second predetermined reference voltage, and outputs the voltage difference between the offset voltage and the second predetermined reference voltage. If the offset voltage drops below the second predetermined reference voltage, the second clamping circuit clamps and keeps the output power of the output power controlled wavelength stabilizing system from decreasing.
The present invention provides an important technical advantage by providing an output power controlled wavelength stabilizing system and method that reduces variation in output wavelength from a laser source due to changes in laser output power.
The present invention provides another important technical advantage by providing an output power controlled wavelength stabilizing system and method wherein the laser current can be prevented from changing faster than the thermoelectric cooler can compensate for changes in the output wavelength of a laser light signal. This can be done with minimal response time penalty by allowing the wavelength to drift within a pre-defined acceptable limit while temperature control changes are underway.
The present invention provides another important technical advantage by providing an output power controlled wavelength stabilizing system and method by providing a way to vary the output power and thus eliminate the need for a motor driven optical attenuator.
The present invention provides another important technical advantage by providing a system and method where the variation in wavelength is kept to a minimum even when the output power is varied over a large range.
REFERENCES:
patent: 4689795 (1987-08-01), Yoshimoto et al.
patent: 4733398 (1988-03-01), Shibagaki et al.
patent: 4924470 (1990-05-01), Ries
patent: 5867514 (1999-02-01), Anderson
Dugan John M.
Moothart Michael R.
Alcatel
Gary Cary Ware & Freidenrich LLP
Lee John D.
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