Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-03-29
2001-03-27
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S027000, C385S115000
Reexamination Certificate
active
06208783
ABSTRACT:
TECHNICAL FIELD
This invention relates to the filtering of light propagating within waveguides, including optical fibers.
BACKGROUND OF THE INVENTION
The term “waveguide” is used herein to refer to an optical structure having the ability to transmit light in a bound propagation mode along a path parallel to its axis, and to contain the energy within or adjacent to its surface. In many optical applications it is desirable to filter light that is propagating within a waveguide, perhaps an optical fiber, in order to eliminate or redirect light of certain wavelengths or to pass only light of certain wavelengths. Many types of filters, including interference filters, are commonly used for this filtering. However, there are a number of difficulties associated with the use of many types of filters, including interference filters.
First, in some applications the power density of light propagating within a waveguide may be unacceptably high for the filter, having detrimental effects that may include damage to the filter material or reduced filter performance.
Also, filters are typically employed by means of bulky, multiple-optical-element assemblies inserted between waveguides, which produces a variety of detrimental effects. Separate optical elements can be difficult to align in an assembly and it can be difficult to maintain the alignment in operation as well. Each element often must be separately mounted with great precision and the alignment maintained. Also, an increase in the number of pieces in an optical assembly tends to reduce the robustness of the assembly; the components may be jarred out of alignment or may break. In addition, interfaces between optical elements often result in significant signal losses and performance deterioration, especially when an air gap is present in the interfaces. The materials of which the additional elements are composed may also introduce fluorescence or other undesirable optical interference into the assembly.
The size of filtering assemblies is often a problem as well. Not only can it be difficult to manufacture a filter on a small surface area, but also filtering assemblies usually contain bulky light-collimating, alignment and mounting components in addition to the filtering element. However, space is often at a premium in optical assemblies.
In addition, the filtering characteristics of interference filters change depending upon the angle at which light is incident on the filter, and interference filters are generally designed for the filtration of normally incident light. As illustrated in
FIG. 1
, for many purposes light can be envisioned as numerous light rays
101
simultaneously traveling down the length of a waveguide
102
at different angles. As illustrated in
FIG. 1
, when an optical filter
103
is placed in the path of light
101
that is propagating within a waveguide
102
, much of the light
101
strikes the filter
103
at angles departing significantly from normal to the filter surface
103
, adversely affecting filter performance. Therefore, prior to incidence of light upon an interference filter that is normal to the longitudinal axis of a waveguide, it is desirable to reduce the angle between the path of travel of light traveling within the waveguide and the longitudinal axis of the waveguide, referred to herein as the “angular orientation” of the light. Various means have been used for reducing the angular orientation of light traveling within a waveguide for the purpose of interaction with an interference filter, including the construction of elaborate optical assemblies (see U.S. Pat. No. 5,112,127 to Carrabba et al.), the insertion of “ball lenses” or “microlenses” (see U.S. Pat. No. 4,358,851 to Scifres et al.) into the optical path and spot-size enlarging a portion of an optical fiber (see U.S. Pat. No. 4,958,897 to Hisaharu et al.). However, these means for reducing the divergence of light typically involve the addition of multiple, bulky optical elements to an assembly, which introduces a variety of problems as described above.
The angular orientation of light propagating within a waveguide can have detrimental effects in optical assemblies that include filters other than impairment of filter performance.
FIG. 2
depicts an optical assembly that includes three optical fibers, one of which has a filter
201
applied to its end face
202
. In this optical assembly, light
203
propagating in a first fiber
204
crosses a junction between the optical fibers
205
before impinging upon the filter
201
applied to the end face
202
of the second optical fiber
206
. As illustrated in
FIG. 2
, because of the gap
205
between the first optical fiber
204
and the second optical fiber
206
, light having a significant orientation misses the second optical fiber
206
and is lost. Approaches to addressing this problem in the prior art include the use of separate optical elements such as lenses and the fusing of optical fiber end faces to spherical lenses (see U.S. Pat. No. 4,867,520 to Weidel). The same phenomenon can also occur in optical assemblies in which there is no air gap between optical fibers due to materials, such as the filter itself, that are located between waveguide sections and do not provide totally internally reflective surfaces to contain the light.
A long-standing challenge with optical architectures incorporating single mode optical fibers is associated with the small percentage of the fiber end face that is active. Not only is the optically active core extremely small, but a large radial distance separates the optically active core and surrounding region from the optical fiber end face's outer circumference. This characteristic of optical fibers, especially single mode optical fibers, makes alignment of optical fibers extremely difficult when a filter is interposed between them.
Therefore, there is a need in the art for a compact, robust, easily manufactured and high-performance device for filtering light propagating within a waveguide that addresses these difficulties.
SUMMARY OF THE INVENTION
As will be seen, the instant invention satisfies the foregoing needs.
The invention includes an optical filter, a first section of waveguide and a second section of waveguide positioned between the first section of waveguide and the optical filter. The diameter of the second waveguide section is greater on the end proximate to the optical filter than on the end opposite the optical filter. The first waveguide section and second waveguide section can either be separate optical components or can be fabricated as separate regions of the same waveguide.
The shape of the second waveguide section can vary depending upon manufacturing and performance considerations. The diameter of the second waveguide may change at a constant taper, or the degree of the taper may vary over the length of the second waveguide section. In one embodiment, the degree of taper is constant throughout the second waveguide section, which is relatively easy to manufacture. In another embodiment, the second waveguide section is designed so that at each point over the length of the second waveguide section the slope of the taper varies so as to optimize the overall effect of the second waveguide section given manufacturing and design constraints. In yet another embodiment the section waveguide section has a finite number of distinct longitudinal sections having varying angles of taper. Those skilled in the art will appreciate that any number of combinations and variations of the above themes can be formulated and that the second waveguide section may also include non-tapered sections.
A relatively lengthy second waveguide section can be used to optimize the collimation of light for filtering. Alternatively, the second waveguide section may be truncated or the shape of the second waveguide section designed so as to optimize collimation within the constraint of having a specified maximum length.
Material of varying refractive index can be incorporated into the second waveguide section in order to achieve a number of effects that may be
CIRREX Corp.
King & Spalding
Palmer Phan T. H.
LandOfFree
Optical filtering device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical filtering device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical filtering device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2510270