1. Field of the Invention
The present invention relates to a wedged and lensed optical fiber in which the tip end of the optical fiber is formed into a wedge shape in order that a light beam generated from a laser diode light source is effectively coupled into the optical fiber utilized in an optical fiber communication system. The tip end of the optical fiber is formed into a shape such that a reflection beam or a multiple reflection beam returning from the optical fiber end face to the laser diode light source can be reduced.
2. Description of the Related Art
As has been well known, a laser diode light source 7, as shown in FIG. 8 has an active layer 7a with a light emitting end face such that the dimension in the longitudinal direction (YY-direction) is made relatively small while the dimension in the lateral direction (XX-direction) is relatively large. That is, the end face has an aspect ratio in which the dimension in the longitudinal direction and the dimension in the lateral direction are different from each other. Thus, the light emission pattern of the laser diode becomes an ellipse such that the radiating angle in the longitudinal direction (YY-direction) is relatively large while the radiating angle in the lateral direction (XX-direction) is relatively small.
U.S. Pat. No. 3,910,677 discloses a proposal in which irradiated light having an elliptical cross-section from the above-described laser diode light source is effectively collected into an optical fiber core having a circular cross-section. A configuration of the tip end of the above-introduced proposal will be described with reference to FIGS. 6A to 6C and FIG. 7B. FIG. 6A is a front view of-an optical fiber having a wedged shape according to the conventional technique, and FIGS. 6B, 6C, and 7B are a side view, a plan view, and an oblique view of the wedged and lensed optical fiber shown in FIG. 6A. The optical fiber has an optical fiber core 1 provided at the center of an optical fiber cladding 6. The tip end of the optical fiber is ground to form inclined surfaces 3 and 4 constituting a wedge shape so that the longitudinal direction (YY-direction) of the incident-end surface 2 of the optical fiber is symmetrical with respect to the optical axis (ZZ-direction) and the lateral direction (XX-direction) of the same extends in the direction perpendicular to the optical axis (ZZ-direction). Further, a ridge portion 5 resulting from formation of the wedge shape is formed to have a semi-cylindrical surface. According to the wedged and lensed optical fiber of an experimental trial manufacture using a single-mode optical fiber by the applicant et al. based on the present example, it was confirmed that a coupling efficiency of 80% or more was achieved.
According to the conventional wedged and lensed optical fiber, as shown in FIG. 2B, the ridge of the wedge-shaped portion extends in the lateral direction (XX-direction) in a plane perpendicular to the optical axis (ZZ-direction). Therefore, light P incident along the optical axis (ZZ) of the optical fiber end face (ridge portion) 5 is partly reflected at right angle to become reflected light BR1, which then becomes incident on the active layer of the light-emitting end face of the laser diode light source 7. At the same time, the reflected light BR1 becomes multiple reflection light repeatedly reflecting between the optical fiber end face 5 and the light-emitting end face of the laser diode light source 7. Furthermore, reflected returning light BR2 from a connecting surface (not shown) of an optical fiber circuit is similarly incident on the active layer of the light-emitting end face of the laser diode light source 7.
In this case, if the optical fiber end face 5 is given an antireflection coating (AR coating), the light reflectivity of the reflected light BR1 is about 2%. On the other hand, the reflected returning light BR2 returning from the connecting surface of the optical fiber circuit varies depending on the condition of the connecting surface of the optical fiber circuit. However, a reflectivity of 1.6% at most can be expected. The reflected light BR1 and the reflected returning light BR2 incident on the active layer of the light-emitting end surface of the laser diode light source 7 will negatively influence stable operation of the laser diode light source 7. Therefore, it is necessary to reduce the influence of the reflected light BR1 and the reflected returning light BR2 as far as possible.
Accordingly, it is an object of the present invention to provide a wedged and lensed optical fiber which can reduce the above-described negative influence caused by the reflected light BR1 and the reflected returning light BR2 on the stable operation of the laser diode light source.
Accordingly the present invention is provided with a wedged and lensed optical fiber in which the optical fiber is ground so that the ridge of the wedge-shaped optical fiber is formed into an inclined surface with an inclination angle of (xcex2) with respect to a plane perpendicular to the optical axis (ZZ) of the optical fiber.
Further, it is another object of the present invention to provide an arrangement of an optical fiber in which the wedged and lensed optical fiber is supported in a ferrule.
In order to achieve the above objects, according to one aspect of the present invention, there is provided an optical fiber comprising a wedge-shaped lens at the tip end thereof, wherein a ridge of the optical fiber is formed such that the center tip end of a core lies in the ridge and the ridge is inclined to have an inclination angle (xcex2) with respect to a plane perpendicular to an optical axis of the optical fiber, and the ridge is formed into one of a semi-cylindrical surface and a conical surface.
In an optical fiber comprising a wedge-shaped lens, if a Z-axis is introduced so as to be coincident with the optical axis of the optical fiber and an XZ-plane is defined so that the ridge of the wedge-shaped lens lies in the XZ-plane, the optical fiber is supported so that the ridge is in parallel with a grinding surface and thereafter the optical fiber is tilted, whereby a pair of inclined surfaces are formed so that each of the surfaces has an inclination angle (xcex1) with respect to a plane perpendicular to the XZ-plane, and the ridge is formed into one of a semi-cylindrical surface and a conical surface by the grinding.
According to the above arrangement, the tip end side of the ridge can be cut away to form a flat surface up to the vicinity of the outer periphery of the core. Thus, the tip end of the optical fiber can be brought close to the light source.
According to another aspect of the present invention, there is provided an optical fiber comprising a wedge-shaped lens having a tip end thereof supported in a ferrule with a conical shape at the tip end thereof, and formed into a rooftop shape together with the tip end of the ferrule, wherein a ridge of the optical fiber is formed so as to include the center of a core at the tip end and to be inclined to have an inclination angle (xcex2) with respect to a plane perpendicular to an optical axis of the optical fiber, and the ridge is formed into one of a semi-cylindrical surface and a conical surface together with the conical surface of the ferrule.
If a Z-axis is introduced so as to be coincident with the optical axis of the optical fiber supported in the ferrule and an XZ-plane is defined so that the ridge of the wedge-shaped lens lies in the XZ-plane, the wedged and lensed optical fiber is supported together with the ferrule so that the ridge is in parallel with a grinding surface and thereafter the optical fiber is tilted, whereby a pair of inclined surfaces are formed on the tip end of a conical surface of the optical fiber and the ferrule so that each of the surfaces has an inclination angle (xcex1) with respect to a plane perpendicular to the XZ-plane, and the ridge is formed into one of a semi-cylindrical surface and a conical surface on the optical fiber together with the conical surface of the ferrule by the grinding.
The inclination of the generatrix of the cone of the ferrule at the tip end of the optical fiber is made substantially equal to the inclination angle a of the inclined surfaces.
The ferrule may be provided with an index determining the direction in which the ridge extends. The index may be formed by partly changing the columnar surface of the ferrule into some shape. Alternatively, the index may be implemented by providing a machined part fixed to the ferrule.
One of the semi-cylindrical surface and the conical surface formed on the ridge serves as a positive lens in the YZ-plane.
The inclination angle (xcex2) of the ridge at the tip end of the optical fiber is set so that xcex2xe2x89xa71xc2x0.