Optical waveguides – Accessories – External retainer/clamp
Reexamination Certificate
2002-07-08
2004-11-30
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Accessories
External retainer/clamp
C385S083000
Reexamination Certificate
active
06826347
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a two-dimensional optical element array and a two-dimensional waveguide apparatus. Specifically, this invention relates to a two-dimensional optical element array with a high alignment precision of optical elements (optical fiber, lens, for example) on a substrate and a high long-term reliability, and a two-dimensional waveguide apparatus having high density and capacity and allowing the number of steps in packaging or connection to be reduced.
Recently, with the increased communications data capacity, a demand for an optical cross-connect switch technique that provides a higher throughput of communications data has increased. For example, there has been used an optical switch that is manufactured using the MEMS (micro-electro-mechanical-system) for conducting fine machining in a semiconductor process including silicon etching, which is used for micro-machining and the like. Additionally, with the increased demand for reliability, as well as the demand for the higher throughput, a surface-emitting laser enabling communications with high definition and stability has come into common use.
In such an optical switch or surface-emitting laser, an optical element array is used (optical fiber array, lens array, waveguide (PLC) array, semiconductor laser (LD) array, photo diode (PD) array, for example). In the description hereinafter, the “optical fiber array” is taken as an example of the optical element array. In consideration of requirements for increased throughput and space-saving, the optical fiber array is a so-called two-dimensional optical fiber array (occasionally abbreviated as 2DFA hereinafter) whose cross-section taken along a plane perpendicular to central axes of the aligned optical fibers has a two-dimensional (hierarchical) configuration.
For example, as shown in
FIG. 16
, there has been proposed a conventional two-dimensional optical fiber array
100
with a pitch in a thickness direction determined by controlling a thickness of a substrate
102
with V-shaped grooves with high precision, arranging optical fibers
101
between the substrates
102
with V-shaped grooves and between the uppermost substrate
102
with V-shaped grooves and the fixing member
103
, and stacking the substrates in such a manner that a front surface of each substrate
102
with V-shaped grooves is brought into contact with a back surface of the adjacent substrate
102
with V-shaped groove (for example, JP-A-56-113114).
A waveguide substrate (unit)
205
having one or more waveguides
201
patterned near a surface thereof, shown in
FIG. 17
, has been used in a splitter, AWG or waveguide modulator, for example. FIG.
17
(
a
) is a schematic plan view of a splitter with one channel input and eight channel outputs, and FIG.
17
(
b
) is a cross-sectional view taken along a line X—X in FIG.
17
(
a
).
However, the conventional two-dimensional optical fiber arrays have problems as described below.
(1) It is difficult to control the thickness of a substrate having V-shaped grooves on a surface thereof (substrate with V-shaped grooves, simply referred to as a substrate occasionally hereinafter) with a precision of the order of submicrons, and the industrial limit of error for the entire surface of the substrate is approximately ±1 &mgr;m. For example, if eight substrates each having a thickness error of +1 &mgr;m are stacked, the resulting 2DFA has a thickness error of +7 &mgr;m at the maximum. Thus, the alignment precision of the optical fibers is inevitably low.
(2) Since the substrates abut on each other, the thickness of an adhesive layer therebetween is substantially 0. This is unfavorable for adhesion for most adhesives. In particular, if the substrates abut on each other over the substantially entire surface, the long-term reliability thereof is not always sufficiently assured.
(3) In the case where the upper substrate of adjacent two substrates serves as a fixing member for the lower substrate, including the case where it serves as a lid, it is inevitably required to adopt a method of “optical fiber array formation (FA formation) after stacking”, in which the substrates are stacked and ferruled, and then the optical fibers are inserted, or a method of “FA formation simultaneous with stacking”, in which the optical fibers are placed in the V-shaped grooves of the lowermost substrate before the second lowest substrate is positioned and placed on the lowermost substrate, the optical fibers are placed in the V-shaped grooves of the second lowest substrate before the third lowest substrate is positioned and placed on the second lowest substrate, and such a process is successively carried out. In the case of the former method of “FA formation after stacking,” in order to assure precision, a hole, into which the optical fiber is to be inserted, has to be designed to minimize a clearance from the optical fiber. Thus, the hole is so small that it is extremely difficult to assemble the optical fibers without cutting. For example, in the case of the 2DFA comprising eight stacked substrates each having eight optical fibers aligned thereon, the number of optical fibers to be inserted is 64. Also in the case of the latter method of “FA formation simultaneous with stacking”, the process is complicated and it is difficult to assemble the optical fibers without cutting. In addition, it is extremely difficult to simultaneously conduct positioning of the substrate and alignment of optical axes in each substrate including parallelization.
(4) In order to solve the above problem (3), there has been proposed an optical fiber array having, between the substrates with V-shaped grooves stacked one on another, an accommodation section for accommodating an optical fiber presser member (equivalent to the fixing member in this invention) in a state where the tops of the optical fibers protrude slightly from the V-shaped grooves and the optical fiber presser member on one substrate is kept from contact with the other substrate with V-shaped grooves (Japanese Patent No. 3108241). This optical fiber array is superior in that it has enhanced workability and alignment precision because a procedure of stacking after FA formation can be adopted. However, the above-described problems (1) and (2) associated with the alignment precision and the long-term reliability, respectively, has not been solved yet.
(5) As another approach for solving the above problem (3), there has been proposed an optical fiber multicore connector having a groove for an optical fiber and a rod for aligning axes of connector terminals (JP-A-55-45051). With the optical fiber multicore connector, although the procedure of FA formation simultaneous with stacking is involved, the workability is enhanced because the positioning is accomplished automatically by the action of the V-shaped grooves and the optical fibers. And, the above problem (2) of the long-term reliability can be solved depending on the setting of the depth of the groove. However, the above problem (1) of the alignment precision remains, and it is difficult to align the V-shaped grooves on both surfaces of a substrate with those on another substrate in the width direction. Thus, an additional problem of misalignment in the width direction has arisen.
(6) An optical communication network involving the two-dimensional optical fiber arrays described above has various connection points therein. The connection points each reflect light passing therethrough, and when the reflected light is launched again into its original fiber, a laser or the like is disadvantageously affected (a noise occurs, for example). In particular, in the case of the 2DFA mainly used for the MEMS switch or the like, since lens coupling is often adopted, and a space is provided immediately after the 2DFA, the reflected light, which is launched into the original fiber again, has a significant influence.
(7) To eliminate the disadvantage described above, in the past, reflection from an end face has been suppressed by prov
Fukuyama Masashi
Ide Akiyoshi
Matsumoto Akira
Burr & Brown
NGK Insulators Ltd.
Palmer Phan T. H.
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