Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-06-17
2001-07-10
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S042000, C385S039000, C385S140000, C385S147000
Reexamination Certificate
active
06259842
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to an optical monitoring system and, more particularly, to monitoring apparatus for a high power light source, such as a fiber amplifier or fiber laser or other such fiber resonator providing light output on a fiber medium.
BACKGROUND OF THE INVENTION
It is common practice to have an optical monitoring system coupled to the output of a light source to monitor its output power and adjust system parameters as may be required in operation of the source. For example, a light source may be comprised of a fiber gain medium or a semiconductor gain medium and the output power is monitored to control of the pump power supplied to the gain medium. In order to monitor the output power of the light source, a small portion of the output power can be tapped off and provided to a suitable photodetector. Common beamsplitters or optical taps may be employed for this function in the output fiber of the light source. Only a small amount of light is needed and the goal is to effect as little as possible the output power provided to an application. The taped monitoring power should be as low as possible so that all of the power available can be provided to the application. This permits the employment of smaller capacity photodetectors having low saturation levels which translates into lower cost and smaller package requirements or package space. Down to about 1% power taping with a beamsplitter or tap is possible before it becomes polarization sensitive. Thus, if the output power being monitored is in the range of 300 mW to several watts, a 1% polarization tap provides several tens of milliwatts of power that is split off, which easily exceeds the saturation power level of a desired small capacity photodetector, which may have a saturation level of 10 mW of less. If the tap or beamsplitter is then made to split-off power below 1%, it becomes polarization sensitive. The lower the split-off power, the more polarization sensitive the device becomes. If the device is polarization sensitive, continuous variations in the power level of the split-off light will occur which, of course, is not acceptable for use in monitoring the real time output power on a fiber medium. Attempts to make these devices polarization insensitive is costly and not reliable from a reproducibility standpoint. Therefore, there is a need to provide a way for providing a tap or beamsplitter which provides a polarization insensitive tapped power level which can be handled by a lower cost, smaller saturation capacity photodetector.
SUMMARY OF THE INVENTION
According to this invention, a monitoring apparatus for a high power light source comprises a fiber medium containing a high power output for an application with a first monitoring tap optically coupled to the fiber medium for removing a small portion of light from the output to monitor the output power level. A photodetector is optically coupled to receive the light portion to monitor the output power level. The photodetector, however, has a predetermined saturation level below the power level provided from the first monitoring tap. Therefore, at least one light attenuator is provided between the first monitoring tap and the photodetector to provide a level of monitoring power within a range below the saturation level of the photodetector to accurately monitor changes in the output power present on the fiber medium. The attenuator may be employed in the application of this invention may be comprised of an optical tap; a beamsplitter, such as a fiber beamsplitter; a WDM splitter; a fused coupler; a bulk optical filter or other micro-optic filter; misaligned, coupled optical fibers; or a fiber bound into a tight loop or coil to provide for optical dispersion loss from the fiber.
This invention further provides for a fiber optic beamsplitter configuration capable of less than 0.25% power splitting and which is used to split off light from power levels of greater than 300 mW from a fiber medium having high reliability under high power operation as well as being polarization insensitive. The configuration comprises a first fused fiber coupler with a splitting level of less than about 5% for splitting a small portion of light and at least one additional fused fiber coupler coupled to receive the small light portion from the first fused fiber coupler and splitting off an additional amount at a ratio of at least 20:1 such that an overall power level reduction of at least 400 times less than the original power level is achieved at the output of the second fiber coupler.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.
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Carothers, Jr. W. Douglas
Healy Brian
SDL Inc.
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