Optical fiber termination

[0002] The invention relates to optical fiber terminations, and in particular to a termination which provides an output of a light beam in a direction traverse to the direction of the beam propagation.

[0003] Existing optical fiber terminations are designed so as to reduce backward reflections of light into the fiber and/or to provide optimal coupling between two co-axial fibers. These functions are rather limited and do not solve a problem that has arisen recently because of the constant demand of reducing the size of optoelectronic components and increasing the density of optoelectronic packaging. The problem is concerned with utilizing a three dimensional space in a package more efficiently while using optoelectronic components of a smaller size. For example, it is preferred to mount semiconductor devices such as detectors parallel to the package base with the active area facing up. Also it is preferred to pass optical feedthrough fibers through the package sidewalls. Accordingly, it generates a requirement for the fiber to provide an output of the laser light in a flexible manner while ensuring enhanced functionality of the fiber and the use of minimal optical elements. Discrete optical components are costly-and difficult to align and therefore should be avoided. Additional requirements for the fiber or fiber termination of this kind would be simple design and manufacturing along with an easy alignment with other elements in a package.

[0004] None of the existing fiber terminations have addressed the above-mentioned problems so far.

[0005] It is therefore an object of the invention to provide an optical fiber termination which would provide enhanced functionality of the fiber while providing output of laser light in a flexible manner.

[0006] According to one aspect of the invention there is provided an optical fiber having an optical element formed at an end of the fiber,

[0007] the element providing an output of a light beam, propagating through the fiber, in a direction traverse to the direction of the beam propagation while reshaping the beam into a spot of a required shape and size,

[0008] the element being an integral part of the fiber.

[0009] Conveniently, the optical element is an angled ball, the angle of the angled surface of which is chosen so as to provide a total internal reflection of the beam. Depending on the requirements for the fiber, the diameter of the ball may be either substantially equal the diameter of the fiber or greater than the diameter of the fiber at a joint with the ball. Alternatively, the optical element may comprise an angled fiber end and a lens, the lens being disposed so as to receive the beam reflected from the angled fiber end. The lens may be replaced with a cylindrical or tapered multimode fiber section having a lens at its lens, or any other optical element which would provide a similar function. Conveniently, the fiber comprises a groove for receiving the lens.

[0010] Conveniently, the optical element provides the output of the light beam in a direction substantially perpendicular or perpendicular to the direction of the beam propagation within the fiber. Alternatively, it may provide output of the light beam in a direction forming an acute angle or obtuse angle with the direction of the beam propagation.

[0011] According to another aspect of the invention there is provided an optical fiber termination, comprising an optical element formed at one end thereof,

[0012] the element being designed so that, when the termination is being coupled to a fiber, to provide an output of a light beam, propagating through the fiber, in a direction traverse to the direction of the beam propagation while reshaping the beam into a spot of a required shape and size,

[0013] the element being an integral part of the termination.

[0014] Conveniently, the optical element is an angled ball, the angle of the angled surface of which is chosen so as to provide a total internal reflection of the beam. The diameter of the ball may be substantially equal the diameter of the fiber or greater than the diameter of the fiber at a joint with the ball depending on the requirement for the fiber termination. Alternatively, the optical element of the termination may be formed by an angled fiber end and a lens, the lens being disposed so as to receive the beam reflected from the angled fiber end. In other embodiments of the invention the lens is replaced with a cylindrical or tapered multimode section, having a lens at the end of the taper, which a provide similar function.

[0015] Conveniently, the termination provides the output of the light beam in a direction perpendicular or substantially perpendicular to the direction of the beam propagation. Alternatively, the termination may provide output of the light beam in a direction forming an acute or obtuse angle with the direction of the beam propagation. Additionally, an assembly of an optical fiber and the termination described above is provided, thus forming a combined optical fiber, wherein the other end of the termination is appended, e.g. spliced, to the optical fiber.

[0016] Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

[0017] FIG. 1ais an isometric view of an optical fiber termination according to a first embodiment of the invention;

[0018] FIG. 1bis an enlarged end portion of the fiber termination of FIG. 1a;

[0019] FIG. 2 is a cross sectional view of the fiber termination of FIG. 1a;

[0020] FIG. 3 is an isometric view of an optical fiber termination according to a second embodiment of the invention; and

[0021] FIG. 4 is an isometric view of an optical fiber termination according to a third embodiment of the invention.

[0022] As shown in FIGS. 1aand 1b, the optical fiber termination 10 according to the first embodiment of the invention comprises a short fiber stub 12 which has a section tapered to one of its ends as designated by reference numeral 14, and has an optical element 16 formed at that end. The optical element 16 provides reflection of a light beam 18, propagating along the fiber axis 20 (shown in FIG. 2), in a direction traverse to the direction of the beam propagation and focuses it into a small spot 22 onto an active area of a semiconductor detector 24. The other end of the fiber termination 10 is appended, preferably spliced, to an optical fiber 26 to form a combined optical fiber 28.

[0023] As shown in more detail in FIG. 2, the optical element 16 includes an angled ball which has a diameter greater than the diameter of the tapered section at a joint 30 with the ball. The angle 32 of the angled surface of the ball 34 is about 45 degrees to the fiber axis 20, the angle being chosen so as to provide a total internal reflection of the beam 18 propagating through the fiber. The mode field diameter increases in the taper section. Therefore, as the beam 18 propagating down the core of the fiber enters the tapered section 14, the beam diameter expands. The expanded beam is reflected at about 90 degrees by the polished angled surface 34 of the ball 16. As the light exits the fiber, it is focused by the spherical surface of the ball into the spot 22.

[0024] The fiber termination 10 is manufactured in the following manner. An optical fiber is heated by flame or electric arc and pulled to form a tapered section. The tapering continues until the fiber is severed. The pointed fiber end is then carefully melted so that the surface tension in the melted fiber forms a ball at the end of the fiber. Part of the ball is then ground away, and the flat surface polished so as to provide total internal reflection of the light propagating through the fiber. The diameter of the ball would be typically about 60 micron, the taper diameter about 15 micron where it joins the ball, and the taper length of about 2 millimeters. It is understood for those skilled in the art that these dimensions may vary depending upon the application.

[0025] Thus, the termination 10 provides a dual functionality by simultaneously reflecting the beam in a required direction and changing the shape of the beam by focusing it into a small spot.

[0026] In modifications to the above embodiment, the termination may or may not include the tapered section, and the diameter of the ball may vary from being smaller than the diameter of the fiber to being substantially equal to the diameter of the fiber. The optical element may provide output of the light beam in a required direction relative to the direction of the beam propagation (fiber axis), e.g. in a direction which would form an acute, obtuse, perpendicular or substantially perpendicular angle with the fiber axis. The fiber termination 10 described above may be formed either as a separate item or as an end section of an optical fiber.

[0027] An optical fiber termination 100 according to the second embodiment of the invention is illustrated in FIG. 3. It comprises a short fiber stub 102 having an angled end 104 which reflects a light beam, travelling along the fiber, in a traverse direction relative to the fiber axis, and a GRIN lens 106 disposed so as to receive the reflected light and to focus it into a small spot 108 onto an area of a photodetector 110 or any other optical element (as required). Conveniently, the laser rod 102 has a groove 112 for receiving the lens 106. The lens 106 is made integral with the fiber rod by using an index matching adhesive so as to form the termination 100 as an integral component.

[0028] Conveniently, in modifications to the second embodiment, the GRIN lens may be replaced with a multimode fiber section of a similar shape or any other optical element which would provide a similar function.

[0029] The fiber termination of the third embodiment of the invention is illustrated in FIG. 4. It is similar to that of the second embodiment of FIG. 3 except for the GRIN lens 106 being replaced with a tapered multimode fiber stub 206 whose end is rounded so as to form a lens 214 which focuses a light beam in a similar manner. Similar elements in FIGS. 3 and 4 are referred to by the same reference numerals incremented by 100.

[0030] The terminations 100 and 200 of the second and third embodiments can be made as separate items (to be further appended to optical fibers, e.g. spliced) or as end sections of optical fibers.

[0031] Thus, it will be appreciated that, while specific embodiments of the invention are described in detail above, numerous variations, modifications and combinations of these embodiments fall within the scope of the invention as defined in the following claims.