Multilayer optical fiber coupler

Abstract

A multilayer optical fiber coupler for coupling optical radiation between an optical device and an optical fiber, including a first layer that has a fiber socket formed by photolithographic masking and etching to extend through said first layer, and a second layer bonded to the first layer. The first layer may comprise substantially single-crystal silicon. An optical fiber is inserted into the fiber socket to align the optical fiber precisely within the fiber socket. In one embodiment the optical fiber is a single mode fiber, and an optical focusing element formed on the second layer is aligned with the core of the single mode fiber. The second layer may comprise glass having an index of refraction that approximately matches the index of the optical fiber, and an optical epoxy is used to affix the optical fiber into the fiber socket and fill the gaps between the end face of the fiber and the second layer. Embodiments are disclosed in which an optical device such as a VCSEL or photodetector is bonded to the second layer. Alternative embodiments are disclosed in which the optical device is incorporated into the second layer. Advantages include reduced cost due to batch fabrication techniques, and passive alignment of the optical fiber.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]Priority is hereby claimed to U.S. Provisional Application No. 60 / 088,374, filed Jun. 8, 1998 entitled LOW COST OPTICAL FIBER TRANSMITTER AND RECEIVER and U.S. Provisional Application No. 60 / 098,932, filed Sep. 3, 1998 entitled LOW COST OPTICAL FIBER COMPONENTS.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention generally relates to couplers for coupling optical radiation into and out of an optical fiber.[0004]2. Description of Related Art[0005]Optical fibers have by far the greatest transmission bandwidth of any conventional transmission medium, and therefore optical fibers provide an excellent transmission medium. An optical fiber is a thin filament of drawn or extruded glass or plastic having a central core and a surrounding cladding of lower index material to promote internal reflection. Optical radiation (i.e. light) is coupled (i.e. launched) into the end face of an optical fiber by focusing the lig...

AI Technical Summary

Benefits of technology

[0012]In order to overcome the limitations of prior art optical fiber couplers, the present invention provides a multilayer optical fiber coupler for coupling optical radiation between an optical device and an optical fiber, including a first layer that has a fiber socket formed by photolithographic masking and etching to extend through said first layer, and a second layer bonded to the first layer. A multilayer optical fiber coupler is described that has a vertical through hole (a “fiber socket”) in a first layer that precisely aligns an optical fiber with an optical focusing element formed in the second layer. A method for forming the fiber couplers is described herein that can advantageously utilize semiconductor processing techniques including photolithography and dry etching to fabricate the couplers. The precision of the fiber socket structure allows single mode optical fibers to be passively aligned, and is also useful for aligning multimode optical fibers.

[0014]In order to provide precise, passive alignment of the optical fiber within the fiber socket, the fiber socket is formed to be only slightly larger than the fiber diameter. Single-crystal silicon is particularly useful to form the fiber sockets because silicon DRIE techniques have been developed recently as a result of advances in microelectromechanical system (MEMS) research, which allow vertical holes to be etched at high speeds (up to 10 micron / minute at present) with less than 1 micron vertical variation in hole diameter (i.e. ±0.5 micron). In one embodiment, the deep-etching process uses high definition photolithography and an appropriate high etch selectivity mask to create precisely-dimensioned fiber sockets. These fiber sockets then receive precisely-dimensioned optical fibers, thereby accurately aligning the optical fibers within the fiber socket. The fibers are held in place by epoxy or another suitable adhesive.

[0015]In one embodiment the second layer comprises borosilicate glass such as PYREX, which is advantageous for several reasons. The glass can be strongly and conveniently bonded to silicon by anodic bonding, which is a dry bonding process. The thermal expansion coefficient of borosilicate glass matches well with that of silicon, which provides a durable and reliable structure. Furthermore, the index of refraction of borosilicate glass approximately matches the index of refraction of the core of the optical fiber, which is the light transmitting section of the fiber, and therefore an optical epoxy can be used that also approximately matches the index of refraction of the optical fiber. In such an embodiment, the glass, epoxy, and optical fiber form a natural index-matched system, eliminating the need for polishing and anti-reflection coating the end face of the optical fiber which are current fiber optical industry practices, and resulting in further cost savings. Due to the index matching in some embodiments, optical radiation advantageously propagates substantially loss-free through the fiber end face, epoxy, and the adjacent surface of the second layer.

[0016]Due to the fiber sockets formed to extend through the silicon layer, a large number of single mode optical fiber couplers can be made on the wafer level with very low cost. One cost advantage is attributed to the batch microfabrication process and the elimination of the need to actively align the fiber. For example, assuming a 4-inch integrated wafer and a 1 mm×1 mm die size, about 7800 fully-integrated chips can be obtained by dicing the wafer. This approach allows optical couplers as well as other devices disclosed herein to be manufactured with the same kind of economies of scale as the silicon electronics industry, since the cost of the processing steps are shared by all the individual chips.

Problems solved by technology

For effective coupling, light must be directed within a cone of acceptance angle and inside the core of an optical fiber; however, any light incident upon the surrounding cladding or outside of the acceptance angle will not be effectively coupled into the optical fiber.

It is a difficult task to couple light into the central core of an optical fiber due to its small size and acceptance angle, particularly if the optical fiber is a single mode optical fiber.

This manual assembly procedure is time consuming, labor intensive, and expensive.

The high cost of aligning optical fiber presents a large technological barrier to cost reduction and widespread deployment of optical fiber modules.

For example, in a splice connection between two optical fibers, a large loss in the transmitted signal can occur if the two inner cores fail to align precisely with each other.

The large core diameter of multi-mode fibers (e.g. 50 microns) allows this approach to be suitable for coupling light into multi-mode fibers; however the lack of a light-focusing mechanism prevents use of this method with single-mode fibers.

If the substrate material is fused silica (or glass), the fiber guide etch rate is very slow (typically 0.3 micron per minute or less) and as a result it is impossible to obtain fiber guides of sufficient etch depth, which is necessary to obtain precise angular alignment to single mode fibers.

The device disclosed by Stegmueller is subject to the same problems as the device disclosed in the Basavanhally patent.

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