Abstract: Fusion-splicing polarization maintaining optical fibers includes the steps of: observing a polarization maintaining optical fiber containing stress applying members in a predetermined direction, using a core direct monitoring method to obtain a reference image; aligning the pair of polarization maintaining optical fibers to be fusion-spliced; automatically rotating the fibers while observing them with the core direct monitoring method until the images of the pair coincide with the reference image; and fusion splicing the pair together.

Abstract: In a method for estimating a splice loss of a spliced portion of a fusion-spliced optical fiber, an amount of axial deviation attained prior to or immediately after heating a pair of optical fibers and an amount of axial deviation attained upon completion of heat treatment on the optical fibers are first detected to provide a difference between the axial deviations, and a splice loss originated from an opposite-phase core distortion is estimated based on the difference between the axial distortions.

Abstract: In a method of testing a spliced portion of exposed fiber portions of optical fibers, the optical fibers are arranged with each other in line so that ends of the exposed fiber portions are spaced apart from each other by a predetermined distance. The ends of the exposed fiber portions are heated and melted by discharge heating. The optical fibers are then moved in the abutment or closing directions by a predetermined distance, so that the ends of the exposed fiber portions abut against each other to form a spliced portion. The minimum outer diameter value d of the spliced portion is measured. Ratio d/D of minimum value d to value D of the outer diameter of exposed fiber portion is calculated. Spliced portions having splicing defects can be detected by detecting of spliced portions having ratio d/D of less than 1 (d/D<1). That is, spliced portions having ratio d/D of less than 1 (d/D<1) are regarded as splicing defects.

Abstract: .theta.-clamp also serves as a jacket clamp. The clamp comprises a cover mounted on an arm by a hinge and kept closed by a magnet, so that a pusher provided in the cover is urged against a jacketed portion of an optical fiber by a spring. In this state, the fiber is rotated in a .theta. direction by rotating a dial. .theta.-clamp also serves as a jacket clamp. Therefore, 1. The .theta.-clamp can be positioned close to a fiber clamp. For this reason, the optical fiber is not twisted during .theta.-axes alignment, and a follow-up property of rotation of the optical fiber with respect to rotation of the .theta. axis is improved. In addition, the apparatus need not be adjusted so as not to twist the optical fiber. 2. The distance between fiber clamp and .theta.-clamp is shortened. Therefore, when the optical fiber is clamped and moved in the z direction, the jacketed portion is not flexed.