Precision optical filter with a ball-end joint

Details Precision optical filter with a ball-end joint Precision optical filter with a ball-end joint

2000-11-14

2003-09-16

Nasri, Javaid H. (Department: 2839)

Optical waveguides

With optical coupler

Input/output coupler

Reexamination Certificate

active

06621954

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to fiber optics. In particular, the present invention relates to a precision optical filter with a ball-end joint.
2. The Prior Art
Background
Fiber optic communication systems are largely responsible for the recent expansion of bandwidth in communications systems such as the Internet. Much of this bandwidth expansion is being accomplished through the multiplexing of many. channel of optical signals onto a single optical fiber. In typical applications today, as many as
128
semiconductor lasers may share a single fiber through a process known as “wavelength division multiplexing” (WDM). A Wavelength Division Multiplexer (WDM) used to accomplish this process is typically a passive optical device configured to combine multiple channels of optical information onto a single optical fiber (multiplexing), or to separate multiple channels of optical information contained in a single optical fiber onto separate optical fibers (demultiplexing).
Much attention today is being given to Dense Wavelength Division Multiplexers (DWDM) because of the requirement to divide signals that are spaced very close together in wavelength. Current International Telecommunications Union (ITU) specifications call for channel separations of approximately 0.4 nm. Using such channel separations, a single fiber may carry as many as 128 channels.
Because of this close channel separation, it is desirable to fabricate DWDMs with excellent stability over both time and temperature. It is desirable, among other things, that the insertion loss of a DWDM may not vary more than +/−0.5 dB over the temperature range of 0°-70° C. Additionally, since a DWDM usually comprises many filters cascaded together. For example, an 8-channel DWDM may comprise 8 cascaded filters. Thus, at the final stage of such an 8-channel DWDM, any variation introduced by a particular channel may be multiplied by as much as eight times. Accordingly, it is desirable to keep any such variations to a minimum. However, it is a challenge for typical DWDMs produced today to meet such standards.
FIG. 1
shows a DWDM
100
of the prior art. DWDM
100
includes a first collimator
102
which further includes a ferrule
104
and a lens
106
. Ferrule
104
further includes an incident fiber
110
and a reflecting fiber
112
. Typically, lens
106
comprises a GRIN lens standard in the art. DWDM
100
further includes a thin-film filter
114
standard in the art. Additionally, DWDM
100
includes a second collimator
116
, which also includes a lens
118
and a ferrule
120
having a transmitting fiber
122
. During fabrication, first collimator
102
, thin film filter
114
, and second collimator
116
must be precisely aligned about an axis
106
to function properly. A finished DWDM as shown in
FIG. 1
is typically 5 mm in diameter and 40 mm in length.
FIGS. 2A
,
2
B, and
2
C are diagrams which provide a brief overview of the operation of a DWDM.
FIGS. 2A-2C
are graphical diagrams having a transmission axis T versus wavelength &lgr;.
FIG. 2A
shows a plurality of channels incident to a DWDM in which it is desired to isolate channel &lgr;
0
. By way of example, the signals of
FIG. 2A
may be applied to incident fiber
110
of DWDM
100
of FIG.
1
. If the DWDM
100
of
FIG. 1
is aligned properly, the incident signals will be optically coupled through lens
106
to the filter
114
. Filter
114
is coated with a multi-layer coating standard in the art to reflect all of the incident signal into the reflecting fiber
112
, except for the channel &lgr;
0
, as is shown in FIG.
2
B. Furthermore, filter
114
will transmit the channel &lgr;
0
through lens
118
and ultimately to transmitting fiber
122
, as shown in FIG.
2
C.
However, as mentioned above, the DWDM must be properly aligned for the results of
FIGS. 2A-2C
to occur. The position of the thin-film filter is critical to the proper operation of the DWDM, with acceptable errors in orientation being in the order of 1 milliradian or 1 micrometers. Two challenges face manufacturers of DWDMs: first, the DWDM must be precisely aligned and secured during manufacturing; and, secondly, the DWDM must be able to tolerate the temperature ranges imposed by environmental and operational conditions and tested through the Bellcore process.
FIG. 3
is a detail diagram of a prior art diagram of a prior art DWDM.
FIG. 3
focuses on how the thin film filter
114
of DWDM
100
shown in
FIG. 1
is secured in prior art devices. During fabrication, the filter
114
is aligned such that the incident signals are properly reflected and transmitted as described above. When the desired location of the filter
114
is determined, it is typically secured with epoxy (shown as spots of epoxy
300
) to the collimator
102
. It should be noted that
FIG. 3
is not drawn to scale and the tilt of the filter is exaggerated for illustrative purposes.
However, the process of securing the filter with epoxy as shown in
FIG. 3
has been shown to introduce certain deficiencies in the operation of the DWDM. Often, when the filter is secured in place, there is a significant gap between the filter and the collimator, and when the epoxy is applied to the filter, the epoxy spreads and dries in an uneven manner. This uneven distribution of epoxy can lead to deficiencies in the final product. For example, epoxy has been shown to expand and contract with temperature changes, thus causing the DWDM to shift operationally with temperature. Naturally, any temperature deviations will reflect negatively in the Bellcore tests and performance in the field. These deviations can be exaggerated if the epoxy is distributed nonuniformly. Additionally, it has been shown that when epoxy makes contact with the delicate surface of a thin-film filter, the areas proximate to the epoxy may suffer performance degradations.
Hence, there is a need for a method and apparatus for aligning and securing a thin-film filter within an optical device which overcomes the problems of the prior art.
BRIEF DESCRIPTION OF THE INVENTION
The invention satisfies the above needs. The present invention relates generally to fiber optics. In particular, the present invention relates to a precision optical filter with a ball-end joint.
A portion of an optical device is disclosed. In one aspect of the present invention, the device comprises a cylinder formed about an axis having first and second ends, the second being formed so as to define a segment of an inward-facing concave spherical surface;
a module defining a cylinder formed about the axis and having first and second ends, the module having an optical element disposed therein about the axis, the first end of the module being formed so as to define a segment of an outward-facing convex spherical surface, the convex surface being complimentary in shape to the concave surface; and
wherein the complimentary concave and convex surfaces of the cylinder and the module being mated so as to allow the optical element to be aligned about a plane forming a predetermined angle with the axis.
Additional aspects of the present invention include the use of the present invention in optical devices such as DWDMs.
A method for aligning an optical element is disclosed. In a preferred embodiment, the method comprises: providing a cylinder formed about an axis having first and second ends, the second end being formed so as to define a segment of an inward-facing concave spherical surface;
providing a module defining a cylinder formed about the axis and having first and second ends, the module having an optical element disposed therein between the first and second ends of the module about the axis, the first end of the module being formed so as to define a segment of an outward-facing convex spherical surface, the convex surface being complimentary in shape to the concave surface;
mating the complimentary concave and convex surfaces of the cylinder and the module; and
wherein the optical element may be aligned about a plane forming a predeter

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