Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1998-10-14
2001-04-03
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Input/output coupler
C385S001000
Reexamination Certificate
active
06212316
ABSTRACT:
FIELD OF THE INVENTION
The present invention is an improvement in the field of fiber optics and more specifically it is a generic device for achieving low reflection fiber optic interfaces. This invention reduces troublesome optical reflections that occur when an optical waveguide (including optical fibers) is interfaced to a bulk media of significantly differing refractive index.
BACKGROUND OF THE INVENTION
Methods of interfacing to match fiber optic waveguides of differing refractive indexes is well known in the art but the typical mechanically angled optical interface has many complications associated with their use. Along with effecting wavelength and polarization they are difficult to fabricate, hard to align, and generate transmission losses. This invention uses a simple 90 degree interface with a stand-off and avoids these problems.
Reflections in fiberoptic systems degrade performance. They can lead to temporal dispersion, background noise, losses, crosstalk, laser instabilities and other problems. Reflections can arise from many sources such as switch and device interfaces, receiver termination, and other connections. Reflection requirements are becoming more and more demanding given such products as dense LAN's and test equipment. Return loss is one of the most important specifications in many optical devices. Traditional fixes are relatively complex and expensive. For example, a large refractive index discontinuity occurs between a fiber and a gradient index (GRIN) lens. This discontinuity can create a return loss of 30 dB. The standard industry method to fix this problem is to angle both the fiber and the GRIN lens. This can create a return loss of greater the 50 dB. Using the approach of this invention with parts that are easy to fabricate and assemble return losses of greater then 40 dB can be achieved.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problems described above. It reduces optical reflections thereby increasing return losses that occur when an optical waveguide, including optical fibers, is interfaced to a bulk media of significantly differing refractive index. A small spacer material, or stand-off, is placed between the waveguide and the media. The stand-off is index-matched to the waveguide thereby eliminating reflections from this interface. The length of the stand-off is chosen so the reflections from the stand-off/media interface are weakly coupled back to the waveguide due to diffraction and attenuation losses within the stand-off. This invention can be used in most situations where an optical fiber must be interfaced to a material of significantly different refractive index and is applicable to both multi-mode and single-mode fibers. And, it is generally applicable to any focal plane in an optical system that coincides with a refractive index discontinuity which results in troublesome back reflections. The general Stand-off Matched Index approach is also extendible to waveguides other than fibers, and even unguided light beams, independent of wavelength.
REFERENCES:
patent: 4153331 (1979-05-01), Cross
patent: 4732450 (1988-03-01), Lee
patent: 4783137 (1988-11-01), Kosman et al.
patent: 4872180 (1989-10-01), Rideout et al.
patent: 5892868 (1999-04-01), Peck, Jr. et al.
Cook Dennis L.
Font Frank G.
Lauchman Layla
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