Method of making an optical fiber array by overlapping stripped portions of ribbon fibers

Two ribbon cables are partially stripped of their covering to reveal a window of optical fibers. The bare optical fibers are slightly bent and overlapped so that they define an interior channel. A rod is passed through the interior channel to temporarily hold the bare fibers in place. The bare fibers are placed on a v-groove substrate and a cover is pressed on top of the substrate. Adhesives are applied to hold the ribbon cables and bare fibers in place. The bare fibers are cleaved to form a half-pitch optical fiber array.

BACKGROUND OF THE INVENTION

In order to meet the demand of high-density and high-transmission rate, reduction in component size, and high production scalability, the deployment of Planar Lightwave Circuits (PLC) and related waveguide packaging is undoubtedly the trend in the optical networking industry. An optical fiber array is used for the connection of light input/output ends of optical fibers to a waveguide substrate. Since the alignment accuracy for such a connection requires tolerances at the submicron level, the method of fabrication of the optical fiber array is crucial to achieve and maintain high-product yields of PLC devices. Moreover, to increase the density and reduce the size of the waveguide, efforts are being made to reduce the waveguide pitch and thus the inter-fiber pitch of a fiber array down to 127 μm, which is approximately half of the standard waveguide pitch of 250 μm.

In order to obtain an accurate pitch in an optical fiber array, a v-groove substrate commonly are made by using: (1) wet etching of a Si substrate; (2) slicing of a glass substrate; or (3) molding of a plastic substrate. However, the operation of arranging the bare optical fibers and setting them into the predetermined v-grooves is a very difficult task. For example, FIGS.1(a)-(b) show the setting of bare fibers33into the predetermined v-grooves of substrate30for a half-pitch optical array. FIG.1(a) shows ribbon fibers31and32. Each include four optical fibers33surrounded by a coating34. After removing the coating34, bare fibers33′ are exposed. However, it is difficult to keep the same inter-fiber pitch without the coating as the fibers tend to separate and spread out. As shown in FIG.1(b), as the bare fibers33′ are pressed against the substrate30, the bare fibers33″ do not align with the v-grooves. In other words, some of the bare fibers33″ are positioned outside the v-grooves. In order to guide these loose, bare fibers after removal of the coating, the conventional method is to adopt a positioning guide fixture to arrange the bare fibers so that the inter-fiber pitch is approximately the same as the v-groove pitch of the substrate30. Unfortunately, however, the positioning guide fixture can require very accurate and sophisticated machinery, which adds extra cost to the manufacturing costs associated with an optical fiber array product.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a method of making an optical fiber array comprising begins by stripping a first middle portion of a first coated optical ribbon fiber so that the first middle portion includes only bare optical fibers that are bounded on each side of the first middle portion by a coated portion of the first coated optical ribbon fiber. A second middle portion of a second coated optical ribbon fiber is stripped so that the second middle portion includes only bare optical fibers that are bounded on each side of the second middle portion by a coated portion of the second coated optical ribbon fiber. The first middle portion of the first coated optical ribbon fiber is overlapped with the second middle portion of the second coated optical ribbon fiber so that the overlapping bare optical fibers of the first and second middle portions alternate between strands of the first coated optical ribbon fiber and strands of the second coated optical ribbon fiber. The first and the second middle portions define an interior channel bounded by the overlapping bare optical fibers. A bar is passed through the interior channel. Then, the overlapping bare optical fibers are positioned on a substrate having a plurality of parallel grooves. A cover is positioned over the overlapping bare optical fibers so that the overlapping bare optical fibers are held in place between the cover and the substrate. The overlapping bare optical fibers are cleaved along an end of the cover and the substrate.

According to another aspect of the invention, a method of making an optical fiber array begins by providing a first ribbon fiber and a second ribbon fiber each having a plurality of optical fibers enclosed within a coating. A portion of the coating is stripped from the first ribbon fiber and the second ribbon fiber to expose the optical fibers. The stripped portion of the first ribbon fiber is overlapped with the stripped portion of the second ribbon fiber so that the optical fibers of the first ribbon fiber intermingle with the optical fibers of the second ribbon fiber. A substrate having a base and an elevated step with a plurality of grooves is provided. The first ribbon fiber and the second ribbon fiber are placed on the substrate so that the exposed optical fibers rest on the plurality of grooves. More specifically, the coated portion of the first ribbon fiber rests on the base of the substrate and the coated portion of the second ribbon fiber rests on the first ribbon fiber. A spacer is placed between the intermingled optical fibers of the first ribbon fiber and the optical fibers of the second ribbon fiber.

According to further aspects of the invention, a cover is provided. The cover is placed on the substrate to hold the plurality of optical fibers in place. The cover and the substrate form an interior passage through which the optical fibers pass and an end at which the interior passage terminates. The bare optical fibers are cleaved at the end formed by the substrate and the cover. The number of fibers and inter-fiber spacing (or pitch) is the same for both optical fibers.

According to further aspects of the invention, a middle portion of the optical fibers is stripped leaving a window exposing bare optical fibers. The first ribbon fiber is flexed in an upward direction so that the first ribbon fiber forms an upward arch and the second ribbon fiber is flexed in a downward direction so that second ribbon fiber forms a downward arch. The portion of the upward arch intersects with and extends above a portion of the downward arch so that the bare optical fibers overlap to define an interior channel. The spacer (a rod) is passed through the interior channel.

According to still another aspect of the invention, a method of making an optical array comprising begins by stripping a middle portion of two ribbon fibers to expose a window of bare optical fibers. The two ribbon fibers have a matching inter-fiber pitch. The bare optical fibers are bent and overlapped to form an interior channel. The overlapping portion of the bare optical fibers have a pitch approximately equal to one half of the matching inter-fiber pitch. A rod is passed through the interior channel. A portion of the bare optical fibers is placed on a substrate having a plurality of parallel grooves that receive the bare optical fibers. The inter-groove pitch is approximately equal to one half of the matching inter-fiber pitch. A cover is placed over the portion of the bare optical fibers on the substrate. An adhesive is applied to hold the bare optical fibers in place. The rod is removed from the interior channel. The bare optical fibers are cleaved along a plane defined by an end of the cover and the substrate.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of this invention are described below in detail with reference to the drawings. Referring to FIGS.2(a)-(g), a preferred method of making a half-pitch optical fiber array is explained.

Preferably, a half-pitch optical fiber array includes a lower v-groove substrate having a base and a step portion. The step portion has v-shaped grooves formed in its surface. The half-pitch optical fiber array also includes a cover that is located above the v-shaped grooves. Bare fibers from a ribbon cable (or ribbon fibers) are placed in the v-shaped grooves. An adhesive fixes the bare fibers in place and holds the ribbon fibers to the base of the substrate.

Turning to FIG.2(a), two ribbon fibers r1and r2are shown. These are window-stripped to expose the bare optical fibers b1and b2. Although the ribbon fibers r1and r2as shown include four bare optical fibers each, other ribbon fibers could be used, for example ones with eight, twelve, sixteen, etc. The method for window stripping of the ribbon fibers r1and r2can be laser stripping, thermal and mechanical stripping, or chemical etching. The advantage of the window-stripping is that it keeps the inter-fiber pitch p constant. For example, the inter-fiber pitch p as shown is 250 μm. By stripping a middle portion of the ribbon fibers r1and r2, the bare fibers b1and b2remain fixed at 250 μm on each end of the bare window.

Turning to FIG.2(b), the ribbon fibers are mutually overlapped and purposely bent so as to array the bare fibers b1and b2shown in FIG.2(b). Specifically, the lower ribbon fiber r2is bent to form an upward arch and the upper ribbon fiber r1is bent to form a downward arch. The bare portion of the ribbon fibers r1and r2are mutually overlapped so that the upward arch of ribbon fiber r1extends above the downward arch of ribbon fiber r2and consequently forms an interior channel20. In this way, the bare optical fibers alternate between strands from ribbon fiber r1and ribbon fiber r2and in the overlapped portion the pitch p′ is half of the pitch p of a single ribbon fiber. Thus, the inter-fiber pitch is approximately 125 μm, which is approximately the same as the v-groove pitch of a preferred v-groove substrate.

Turning to FIG.2(c), a rigid circular bar3, such as a fiber, is put into the interior channel20between bare fibers b1and b2. Consequently, the bar3runs perpendicular to the axis of the bare fibers b1and b1. This temporarily holds and guides the intermixed array of bare fibers. Consequently, it is not necessary to use a positioning guide to hold and array the bare fibers. This helps to reduce the manufacturing costs of a half-pitch fiber array and greatly simplifies the manufacturing process.

Turning to FIG.2(d), the arrayed bare fibers b1and b2are arranged on a substrate5. The substrate has a base21and a step portion22. The v-shaped grooves are formed in the step portion22. As the overlapping bare fibers b1and b2are positioned in the v-shaped grooves, the covered ribbon fibers r1and r2are placed on the base21. The upper ribbon fiber r1rests on the lower ribbon fiber r2and the lower ribbon fiber r2rests on the base21. Then, the cover4, which aligns with the step portion22, is installed above the v-shaped grooves. The cover is pressed in place and fixes the bare optical fibers b1and b2in place. To avoid breaking the fibers, excessive force should not be used.

After the bare fibers b1and b1have been inserted and located in the v-shaped grooves and the ribbon fibers r1and r2have been fixed, the circular bar3is removed as shown in2(e). Adhesive6is applied to fill the gap in between the cover lid4and the v-groove lower substrate5by capillary action. The ribbon fibers r1and r2are then fixed using adhesive7as shown in FIG.2(f). Then, the optical fiber array20is irradiated with UV rays to harden the adhesive. An UV-curable silicon adhesive9fills the gap between cover lid4and adhesive7to protect the exposed bare fibers b1and b2.

After hardening of adhesives, the bare fibers b1and b2are cleaved as shown in FIG.2(f). Specifically, the outer end of the array20is formed by the step potion22and the cover4. This outer end defines a plane and the bare fibers b1and b2are cleaved along this plane. Turning to FIG.2(g) a perspective view of the arrayed bare optical fibers is shown positioned between the substrate5and the cover4. The rod3temporarily holds the array in position.

By using the above-described method of making optical fiber arrays, the bare fibers are easily arranged into the predetermined v-grooves with excellent reproduceablity but without the use of positioning guides or other fixtures. This achieves ease of manufacturing and helps reduce costs associated with making optical fiber arrays. Although the invention has been described above with reference to specific preferred embodiments, those skilled in the art will appreciate that many modifications and variations can be made without departing from the teachings of the invention. All such modification and variation are intended to be encompassed within the scope of the following claims.