Optical waveguides – Optical fiber bundle
Reexamination Certificate
1999-01-22
2001-03-27
Font, Frank G. (Department: 2877)
Optical waveguides
Optical fiber bundle
C385S114000
Reexamination Certificate
active
06208786
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to manufacturing arrays of optical fibers, in particular monomode fibers.
II. Description of the Related Art
The availability of arrays of monomode optical fibers represents a major factor in developing optical technologies and in making them widespread, essentially in the following two fields: firstly optical switching and cross-connection systems using high interconnection density in free space; and secondly motherboard links and integrating components with arrays of fibers. Monomode fiber arrays are key components that are essential for these two fields of activity and that perform the following functions:
inlet and outlet ports for free space optical switches and cross-connection fields;
making arrays of collimated beams in association with arrays of microlenses;
making high density 2D connectors for optical buses; and
coupling arrays of vertical cavity surface emitting lasers (VCSELs) with monomode fiber arrays.
Interconnecting monomode fibers with the required specifications, i.e. positioning accuracy of &mgr;m order between fibers, can be achieved for fibers presented in the form of strips. The fibers are placed in respective V-grooves etched in a silicon substrate or machined in a glass or zirconium support. Commercial products are presently available.
Nevertheless, when it comes to interconnecting arrays of fibers, manufacture remains difficult and certain problems have not yet been solved. The solution of stacking strips cannot be used because of the impossibility of controlling the thickness of such strips with &mgr;m order accuracy.
Two lines are presently being investigated. The first lies in using a piezoelectric micropositioner to position fibers dynamically in an array of holes that can be made using various methods such as etching a silicon substrate, precision drilling, or ablating metal by means of a laser. Nevertheless, that technique which consists in individually and dynamically aligning and sticking fibers in an array of holes is difficult, lengthy, and very expensive. Furthermore, it does not provide sufficient guarantee that the fibers will be properly positioned angularly in the support so that the axes of the fibers are exactly parallel. The precision with which the fibers are positioned is determined by the regularity of the pitch and the diameter of the holes in the array, and also by the performance of the micropositioner. On this topic, reference can be made in particular to the following documents:
A) N. Basavanhally et al., “Evaluation of fiber arrays for free space interconnect applications”, International Topical Meeting on Optical Computing, Salt Lake City, Utah, U.S.A., Mar. 15-17, 1995, Vol. 12, PFB2-1, pp. 124-128;
B) Geoff M. Proudley, C. Stace, H. White, “Fabrication of two-dimensional fiber optic arrays for an optical crossbar switch”, Optical Engineering, February 1994, Vol. 33, No. 2, pp. 627-635;
C) J. M. Sassian et al., “Fabrication of fiber bundle arrays for free-space photonic switching systems”, Optical Engineering, September 1994, Vol. 33, NO. 9, pp. 2979-2985.
In a second technique, fibers that are bare or that are positioned in microferrules are stacked in a U-shaped support. That technique, which consists in stacking fiber-containing ferrules in a rigid U-shaped frame structure, constitutes a collective assembly method which gives good angular positioning, but which suffers from poor perpendicularity in the array of ferrules, and therefore from excessive positioning errors relative to a reference grid for fibers situated in the corners. Reference can be made in particular to document D) K. Koyabu, F. Ohira, T. Yamamoto, “Fabrication of two-dimensional PANDA fiber array digital free-space photonic switch module”, International Topical Meeting on Optical Computing, Sandai, Japan, Apr. 21-25, 1996, Technical Digest Vol. 1, PWC26, pp. 136-137.
BRIEF SUMMARY OF THE INVENTION
An object of the invention is to provide a method of manufacturing fiber arrays that is simple, fast, and inexpensive to implement, and that makes it possible to manufacture a fiber array having rows and columns that are accurately perpendicular, together with good parallelism between the axes of the fibers.
In order to achieve this object, the invention provides a method of manufacturing optical fiber arrays, the method comprising the step consisting in:
placing optical fibers in an enclosure in the form of a deformable parallelogram, the fibers being in an array of rows and of columns that are at an angle relative to the rows; and
deforming the enclosure so as to vary the angle.
Thus, the method makes it possible to optimize the perpendicularity of the sides of the array. The method of the invention makes it possible to make fiber arrays in which the position of each fiber core is less than ±2.5 &mgr;m relative to a predetermined grid as a function of the selected pitch, and to provide angular misalignment that does not exceed ±5 milliradians. These tolerances make it possible to obtain coupling losses between monomode fibers that are less than 3 dB. By means of this method, it becomes extremely simple to make arrays of fibers, and in particular monomode fibers. The adjustment is collective and is performed merely by observation.
The juxtaposition and stacking method is validated by relying on the fact that during assembly, the fibers, and for example the ferrules, are placed in random manner. Equilibrium is thus produced in the distribution between the ferrules which have a maximum diameter and those which have a minimum diameter. Thus, each fiber core is located at a position that is very close to the grid defined as a function of the pitch. A simulation on five thousand reconfigurations of an 8×8 array (sixty-four fibers) has verified this analysis. Under the least favorable assembly conditions, the mean error relative to a reference grid is only 2.06 &mgr;m.
Advantageously, the method includes the step of fixing the fibers to one another.
Advantageously, the fixing step comprises molding by means of a resin.
Advantageously, the method includes the step of pressing the array in at least one direction selected from the row direction and the column direction.
Thus, in addition to adjusting perpendicularity, the dimensions of the array are also adjusted.
The invention also provides a device for manufacturing optical fiber arrays, the device having four faces defining an enclosure suitable for receiving optical fibers disposed in an array, the faces giving the enclosure the shape of a parallelogram with non-parallel faces forming an angle between one another, wherein the enclosure is deformable so as to vary the angle.
This device can be used to implement the method of the invention.
Advantageously, the device includes means for adjusting the angle.
Advantageously, the device includes two elements forming two mutually parallel faces of the enclosure, a frame structure, and at least one actuator movable relative to the frame structure and connected to the elements so that displacing the actuator causes the angle to vary.
The actuator makes it possible to modify the perpendicularity of the parallelogram accurately.
Advantageously, the actuator is hinged to the frame structure.
Advantageously, the actuator is hinged by means of a flexible portion.
Advantageously, the device has two actuators connected to two respective elements and interconnected to each other.
Advantageously, the device includes adjustment means for adjusting the distance between mutually parallel faces of the enclosure.
Advantageously, the adjustment means comprise a drive member, a pusher for pushing one of the faces under the effect of urging from the drive member, and a ball interposed between the drive member and the pusher.
This prevents rotation being applied to the array at the same time as force is applied thereto for the purpose of adjusting its size.
Advantageously, the device includes zirconium elements forming the faces.
Advantageously, the elements comprise blocks.
The inventi
Audibert Georges
Bonnel Léon
Gravey Philippe
Blakely & Sokoloff, Taylor & Zafman
Font Frank G.
France Telecom
Stafira Michael P.
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