In the previous section, we gave the following three points required of a fusion splicer for it to make a low-loss connection with high precision, and talked about the advantages of direct core monitoring splicers.
- 1. The ability to accurately identify the location of the core
- 2. A mechanism by which to align the cores of two opposing optical fibres
- 3. A function that creates an arc discharge in the correct position and the correct temperature
In this section, we will introduce the advantages of a fixed V-groove fusion splicer.
A fixed V-groove splicer is a fusion splicer in which the V-grooves, which are mobile in a direct core monitoring splicer, are fixed in place. The ends of the optical fibres are aligned by setting them in two V-grooves facing one another and moved towards each other, along their longitudinal axis, for splicing.
A fixed V-groove splicer satisfies three points in the following ways.
(1) The ability to accurately identify the location of the core
It presupposes that the core is exactly in the center of the cladding and that the cladding is perfectly circular: i.e. the fibre has zero 'core to cladding concentricity error' and zero ellipticity.
The optics used in fixed V-groove splicers don’t allow for direct observation of the core, so the achievable splice loss is inferior to that of direct core monitoring splicers.
The geometry of optical fibre produced today is very accurate and well controlled. Typical values of core to cladding concentricity error for fibre currently made by major manufacturers lie in the range 0.1~0.2um. With such high quality fibre comes improvement in the viability of this alignment method and the splice losses that can be obtained.
(2) A mechanism by which to align the cores of the facing optical fibres
It employs two high precision V-grooves to accurately align the fibres cladding edge to cladding edge.
Prior to splicing, a fixed V-groove splicer checks the alignment of the cladding centers of the two fibres and, if this exceeds a pre-set limit, displays an alert, warning the user that any splice made could be compromised by dirt or debris in the V-groove or on the fibres. The user can remove the fibres, rectify the anomaly and restart the splice cycle. Thus, minimizing the possibility of creating poor splices which must later be broken and remade.
In a fixed V-groove splicer, when the arc is active and the glass within the arc-zone is liquid the splicer takes advantage of the "surface tension self-centering effect". Surface tension tries to minimize the surface area of the liquid glass in the arc-zone, consequently pulling the cladding edges of the two fibres into alignment. If the fibre has good geometry, with low ellipticity and low core to cladding concentricity error, aligning the cladding edges aligns the cladding centers and aligns the core centers with reasonable precision.
(3) A function that creates conditions for an appropriate arc discharge
A fixed V-groove splicer uses an electric arc fired between two electrodes orthogonal to the longitudinal axis of two fibres to melt their ends and fuse them together.
To achieve a low loss splice with good mechanical strength the splicer must use the correct temperature for fusion.
However, the current flowing in the arc, and hence the temperature in the melt zone, is affected by environmental parameters such as ambient temperature, atmospheric pressure and humidity. Also, with repeated use, silica soot debris accumulates on the electrode tips, increasing the arc gap impedance and reducing the current.
Sumitomo fusion splicers use a variety of techniques to compensate for these factors. Our Arc Test utility optimizes the arc power & the position of the fibre ends relative to the arc center. In AUTO mode Sumitomo splicers also use image processing techniques to estimate the temperature of the glass during fusion.
Combining these techniques ensures the arc temperature is optimized for the specific fibres in use, the environmental conditions present and any contamination on the electrodes.
A fixed V-groove splicer is optimal for applications that allow a certain amount of loss, such as the last-mile connection in a FTTH installation. In our lineup, we have the TYPE-201e, which is ideal for working in narrow or high places, and the TYPE-71M, which makes possible multicore splicing.