Single mode polarization maintaining (SMPM) optical fibers are used in order to transmit polarized light and polarized coherent light, while maintaining the polarization of the light. Such fibers typically consist of a single strand core surrounded by cladding material. Within the cladding material are stress rods which help maintain polarization. One application for such SMPM fibers is in fiber optic gyroscopes. Fiber optic gyroscopes detect interference patterns in light transmitted through an optical fiber.
FIG. 1 shows a cross-section of a single mode optical transmission fiber 11. Light is transmitted through a core 13 which is approximately 5 .mu.m (microns) (5.times.10.sup.-6 M) in diameter. The core 13 is surrounded by a cladding material 15 which is typically 75 to 125 .mu.m in diameter. The cladding 15 has a different index of refraction from the core 15, facilitating transmission of light through the core 13. Cladding 15 also provides structural strength to the fiber 11. FIG. 2 shows a cross-section of single mode polarization maintaining (SMPM) optical transmission fiber 21. The SMPM fiber includes a core 23 surrounded by cladding 25 in a manner similar to that of the conventional single mode fiber 11 of FIG. 1. In order to enable the SMPM fiber 21 to maintain polarization of light transmitted through it, a pair of stress rods 27, 29 are located in the cladding 25. It is believed that the stress rods 27, 29 induce stress in the cladding 25 and/or core 23 so that the fiber 21 maintains the desired polarization.
Optical fibers hve been spliced with mechanical connectors, with gluing techniques and by arc plasma bonding. In the case of single mode fibers, two fiber ends are brought into alignment by relative movement of a pair of platforms. At least one of the platforms is finely moveable along three orthogonal axes. The output light from a light source is injected into one of the fibers to be joined. The incident light passes through the one fiber to the other fiber and is received by an optical detector associated with the other fiber. Core alignment is effected by monitoring the optical power transmitted to the optical detector through the fibers while, at the same time, moving the moveable platform to a point at which optical power indicated by the optical detector reaches its maximum. When such alignment has been completed, a plasma arc is used to effect a splice in the manner described by Smith in U.S. Pat. No. 4,049,414. This technique results in a firmly bonded joint which has good structural integrity and optical transmission qualities. Unfortunately, when used with SMPM fiber, the arc plasma results in damage to the fiber and loss of the ability for the spliced fiber to maintain polarization. Apparently when attempting to use a plasma arc on SMPM fibers, small explosions occur. Consequently, glue bonding is attempted.
In order for glue bonding to work, the glue joint must be relatively large in order to maintain mechanical strength of the fiber at the joint. This results in a corresponding loss of optical transmission capacity. Furthermore, adjustable platforms use a vacuum in order to hold the fiber ends in position on the platforms until the splice is complete. This vacuum results in a certain amount of vibration and instability at the fiber ends at the time of adjusting the positions of the fiber ends and at the time of bonding.
Fiber splices often include fibers from different manufacturers often have different dimensions. Therefore, a splicing technique must accomodate such differences.
It is therefore desired to provide a fiber splice which may be applied to SMPM fibers without damaging the fiber ends. It is desirable to provide a splice that is capable of maintaining polarization of light transmitted through SMPM fiber. It is also important to maintain structural rigidity of the fiber and to provide an inexpensive splice in a non-complicated manner.