JP2003270472A - System and method for connecting optical fiber having high-concentrated fluorine to optical fiber of different type with low loss - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and a method for low-loss connection of an optical fiber having high-concentrated fluorine with an optical fiber of a different type. <P>SOLUTION: Disclosed are a technique and a system for connecting both 1st and 2nd optical fibers together. Provided are a chassis, a fiber holding block which holds the couple of optical fibers connected together at a connection point and includes a cut part for exposing the connection point and a torch, and the fiber holding block and torch are fitted to the chassis so that the connection point and the position of the torch can mutually be adjusted to put the connection point in a flame. Disclosed is a heat treatment station. Further, the optical fibers are connected together by using a fusion splicer and heat- treated by arranging the connection point in a flame while connection loss is monitored. Disclosed the technique for connecting two optical fibers together. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates generally to improvements in techniques used for splicing optical fibers, and more particularly, for low loss splicing of optical fibers having a high concentration of fluorine to other types of optical fibers. System and method of the present invention.

[0002]

BACKGROUND OF THE INVENTION A new type of optical fiber has been recently developed and is known as a dispersion compensating fiber (DCF) which has a steep negative slope dispersion characteristic. One use of DCF is standard single mode fiber (SSM
To optimize the dispersion characteristics of existing fiber optic links manufactured from F) to operate at different wavelengths. This technique is described in US patent application Ser. No. 09/09, filed June 19, 2000 and assigned to the assignee of the present application.
No. 596454, which is hereby incorporated by reference in its entirety.

An important parameter of DCF is that DCF is S
It is the excessive loss that occurs when connecting to the SMF. To obtain a high negative variance, the DCF uses the SSMF 1550
A small core with high index of refraction is used with a mode field diameter of about 5.0 μm at 1550 nm compared to a mode field diameter of about 10.5 μm at nm.
The different core diameters result in significant signal loss when connecting the DCF to the SSMF using the fusion splicing technique. The amount of signal loss can be reduced by choosing connection parameters that spread the core of the DCF, thereby tapering the mode field diameter of the DCF core outward, providing a focusing effect. However, the amount and duration of heat required to create the focusing effect results in unwanted diffusion of fluorine dopants within the cladding around the DCF core. This fluorine diffusion limits the amount of splice loss reduction that can be obtained using the mode field extension technique.

[0004]

Therefore, there is a need for an improved technique for connecting a DCF to an SSMF that reduces splice losses below current limits.

[0005]

SUMMARY OF THE INVENTION The foregoing and other problems are solved by the present invention, and aspects of the present invention provide a method and system for connecting together first and second optical fibers. One aspect of the present invention is a chassis,
A heat treatment station is provided that includes a fiber holding block that holds a pair of optical fibers that are connected together at a connection point and that includes a notch that exposes the connection point, and a torch. The fiber holding block and torch are preferably mounted to the chassis so that the position of the splice and torch can be adjusted relative to each other so that the splice is in the flame. A further aspect of the invention is that two optical fibers are heat treated by first splicing them together using a fusion splicer and then placing the splice point in a flame while monitoring splice loss. A method for connecting fibers together is provided.

Further features and advantages of the present invention will be apparent with reference to the following detailed description and accompanying drawings.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The first aspect of the present invention provides a technique for connecting fibers having a relatively high concentration of fluorine to other types of optical fibers. The preferred application of this technology is to use dispersion compensating fiber (DCF) as standard single
Reducing splice loss when splicing to other types of optical fiber that have a larger spot size than DCF, such as mode fiber (SSMF). According to one aspect of the present technology, mode field expansion of DCF using electric arc heating is combined with thermally induced diffusion of DCF dopants using a flame, furnace, or other suitable heating source. This thermally induced diffusion of photodopants is also known as "Thermal Diffusion Expanded Core" (TEC) technology.

DCFs are generally difficult to connect due to their refractive index (RI) distribution. Figure 1A shows a typical DC
FIG. 1B is a cross-sectional view of the example of F10, and FIG.
It is a figure which shows the refractive index (RI) distribution 20 corresponding to CF10. As shown in FIG. 1A, the DCF includes a core 12,
The core 12 is surrounded by a clad including the first, second and third clad regions 14, 16 and 18. Figure 1B
As shown in FIG. 5, the RI distribution has a central spike 22 corresponding to the DCF core 10, grooves 24 on both sides of the spike 22 corresponding to the first cladding region 14, and each groove 24 corresponding to the second cladding region 16. 26 on both sides of the ridge 26 and the flat portions 2 on both sides of each ridge 26 corresponding to the third cladding region 18.
8 and.

DCF is typically a silicon dioxide (Si
Manufactured from O ₂ ) based glass. The desired RI distribution is achieved by doping core 12 and cladding regions 14, 16, 18 with appropriate dopants. 1
In two DCF designs, the core 12 is germanium (Ge)
The first cladding region is doped with fluorine (F), the second cladding region is doped with germanium and fluorine (G / F), and the third cladding region is doped with
Is doped with a lower concentration of fluorine than the cladding region.
Alternatively, some DCF designs do not dope the third cladding region.

Grooves 24 of sufficient depth on either side of spike 22
In order to obtain the first cladding region 14, the first cladding region 14 is doped with a relatively high concentration of fluorine dopant. Since fluorine begins to diffuse at temperatures much lower than the typical temperatures reached during weld splices, a significant amount of fluorine diffusion occurs during typical weld splice operations. This diffusion results in relatively high splice losses unless very short deposition times are used.

In one optical transmission link design, the DCF is
It needs to be connected to other types of fiber such as MF.
In these designs, both the core 22 and the recessed region 24 within the DCF generally must be modified to provide low loss conversion of the DCF light distribution to a distribution having a spot size similar to that of other fibers. I have to. Since the fluorine and the core dopant, which is typically germanium, begin to diffuse at different temperatures, diffusion of the core and recessed regions can occur in a two step process.
First, the DCF is spliced to another fiber by standard fusion splicing using a splicing program optimized to properly expand the germanium core. At the same time, much of the fluorine that diffuses at lower temperatures than germanium diffuses. Therefore, at this point in the process, diffusion of the fluorine dopant results in very high splice loss.

The splice is heated using either a flame or a furnace. The temperature is adjusted so that fluorine diffusion begins, but no significant germanium diffusion occurs, ie the DCF core expansion is maintained. At the same time, no significant changes in the RI distribution of the second fiber will occur unless the second fiber is doped with as much fluorine as DCF. The heat treatment smoothes the fluorine distribution of the DCF and reduces splice losses to values below those obtained only with the use of a welding splicer.

In the following, the above steps are carried out in one DCF.
Will be described in more detail in connection with connecting one SSMF together. Splices are made while monitoring the loss and the heating arc is kept on until the target splice loss value, which is the point at which the arc is turned off, is reached. The target splice loss value, as well as splice program parameters such as arc current, are determined by optimizing for the actual DCF and SSMF used. The details of implementing this method depend on the splicer actually used.

For example, Ericsson FSU925
With respect to, a highly reproducible result can be obtained by the following method. DCF has a relatively short deposition time, eg 0.
Connected to SSMF using 3 seconds. After this connection, the service can be turned on and off manually.
Enter the mode. A low arc current of, for example, 11 mA is used to ensure that the splice loss assessment can be manually observed because the process is so slow. The arc is then turned off when the desired value is reached. Optimal splice loss after splice is typically 3-6 dB
Is the range.

The splice is now ready for heat treatment. A furnace or torch as described in the examples below can be used. FIG. 2 illustrates an embodiment of a heat treatment station 30 used to heat a connected optical fiber 32 according to a further aspect of the invention. Optical fiber 3
The second connection point 34 is located above the flame 36 of the gas torch 37. A mass flow controller 40 is provided in the torch gas supply 38 for accurate adjustment of the torch 36. A chimney 42 is arranged above the torch 36 to stabilize the flame during heating. The optical fiber 32 and the chimney 42 have a cutout portion 45 for exposing the connection point 34.
It is held in place by a plate 44 containing That is, the optical fiber 32 is held at a fixed position on the plate 44 by the first and second clamps 46 and 48 arranged on both sides of the cutout portion 45, and the chimney 42 is fixed by the arm 50 that holds the chimney 42. It is held in place on 44.

A weight removably attached to one end of the fiber maintains a slight tension on the optical fiber 32 during the heating process. This tension prevents the optical fiber 32 from moving relative to the flame during the heating process. Care must be taken in determining the proper weight to avoid stretching the fiber as it is heated. In this example, 0.
Use a 7g weight. The first clamp 46 holds the optical fiber 32 with sufficient slack so that the tension in the fiber is controlled in this manner and functions more as a guide than as a clamp. To prevent bending damage to the fiber, curved guides are provided on which the weight portion of the fiber is placed during the heating process. Plate 44 is moveable relative to torch 36 using a translation stage 58 on which plate 44 is mounted, as described further below. Plate 44
Position reading device 60 that provides accurate information about the placement of the
Is provided.

When the spliced optical fiber 32 is installed in the heat treatment station 30, the plate 44 is positioned well above the flame. After installation, translation stage 5
Using 8, the connection point 34 is moved into the flame. Position reader 60 is used to monitor the position of translation stage 58 for reproducible results. Once the optimum position of the connection point 34 with respect to the torch 36 is determined, this position is used for the next heat treatment.

In this embodiment, the torch 37 is manufactured from a quartz tube having an inner diameter of about 4 mm. As the temperature required to diffuse fluorine is estimated to be 1200 to 1300 ° C., gases such as propane or hydrogen without additional oxygen supply can be used. The mass flow controller 40 is used to maintain the gas flow at the proper value. A typical flow is about 10 ml / min (for propane). Again, this value must be optimized for the particular fiber used.

Splice loss is monitored as splice point 34 is in flame 36. When the minimum connection loss is reached in about 10 minutes,
The translation stage 58 is used to remove the splice 34 from the flame 36. The splice 34 can now be removed from the heat treatment station 30. The heat treatment station design shown in FIG. 2 requires only 1 cm of bare fiber at splice point 34. This is useful for small splice protection.

FIG. 3 is a flow chart illustrating a method 70 for implementing the above techniques. In step 72, the first
And the second fiber is spliced together using a fusion splicer. As mentioned above, in order to reduce splice losses resulting from core size mismatches of the first and second fibers, fusion splicing parameters are selected to achieve optimal mode field expansion of the first fiber core. To do. In step 74, the spliced fibers are loaded into a heat treatment station such as the station shown in FIG. At step 76, the connection point is placed in the flame.
This can be accomplished either by moving the connection point, moving the torch, or moving both the connection point and the torch. In step 78, splice is monitored in the flame for splice loss. In step 80, the splice is removed from the flame once the desired minimum splice loss is achieved. Finally, in step 82, the heat treated fiber is removed from the heat treatment station.

FIG. 4 is a graph 90 illustrating a typical behavior of splice loss as a function of heat treatment time. As a comparison, the minimum splice loss obtained for a real DCF design is about 0.8 dB using only the weld splicer.
Is. One feature of the present technology is that it can be performed in a relatively short time. The time required to splice two fibers together using a fusion splicer to produce the desired core expansion is typically only a few minutes. The time required to produce the desired diffusion of the fluorine dopant using heat treatment is typically only about 10 minutes to reach the minimum splice loss value.

FIG. 5 illustrates a further embodiment of the heat treatment station 100 used in performing the TEC technique described above. As shown in FIG. 5, in the heat treatment station 100, a fiber holding block 102 having a series of clamps 104 for holding an optical fiber to be heat treated, and a torch 106 for applying a flame to the fiber are provided above a chassis 101.
And a chimney 108 for stabilizing the torch flame. The gas supply includes a pair of gas lines 110 for carrying flammable gas and oxygen, respectively. The gas flow through each line is regulated by the flow controller 112. In addition, each gas line has a filter 114 and a valve 11
6 and both lines are routed through a gas alarm 118. As will be described in more detail below, the heat treatment station 100 provides for translational movement of the fiber held within the fiber holding block 102 relative to the torch 106 along the x, y, and z axes. First, the fiber holding block 102 is manually pulled along the y-axis, i.e. towards the station operator, and then pushed back into place. Second
In addition, translation stage 120 provides for accurate translational movement of torch 106 along the x, y, and z axes. The exact position of the torch 106 is determined by the translation stage 120.
It can be monitored by three screws 122 projecting from each, each screw corresponding to an axis of translation. The heat treatment station 100 is provided with a lamp 124 or other device to provide suitable illumination of the connection points. Further embodiments of the invention include a laser or other suitable device attached to the connection point that can be used to aid in aligning the splice with respect to the flame.

FIG. 6A is an exploded perspective view showing the heat treatment station 100 shown in FIG. 5 with the gas supply line removed for the sake of explanation. FIG. 6B is an assembled perspective view of the heat treatment station 100. As shown in FIGS. 6A and 6B, the heat treatment station 100 includes a chimney holder 130 and a torch holder 132 that hold the chimney 108 in place above the flame. Further, as shown in FIG. 6A, the heat treatment station 100 includes a small mounting block 134 used to hold the heating wire assembly used to ensure that the torch flame is not inadvertently extinguished. The heating wire assembly is shown in FIG. 10 described below. The chimney holder 130, torch holder 132, and mounting block 134 are all translation stage 12
0, so the fiber holding block 102
Can be moved as a single unit.

The chimney holder 130 ensures that the chimney is placed immediately around the flame to stabilize the flame. With proper chimney placement, a relatively short bare fiber is required to avoid flame burning of the fiber coating near the splice point. This is useful when the final product packaging requires very short splice protection.

FIG. 6A further shows the side support 136 with the fiber holding block 102 placed thereon. As mentioned above, the fiber holding block 102 is slidably disposed on the upper surface of the side support 136 to allow the station operator to move the fiber holding block along the y-axis. In FIGS. 6A and 6B, it can be seen that the fiber holding block 102 includes a pair of legs that closely span the outer surface of the side support 136. With this configuration, the fiber holding block 102 is
Off-axis sliding is prevented when moved back and forth by the operator. It can further be seen in FIG. 6A that each side support 136 includes an upwardly projecting member 138 at the rear of its upper surface that functions as an anti-reversal device to establish the working position of the fiber block. Thus, when placing the fiber holding block 102 above the torch, the station operator need only push the fiber holding block 102 forward until it abuts the pair of upper protruding members 138.

FIG. 6C is a perspective view of translation stage 120 shown in FIGS. 5, 6A, and 6B. FIG. 6C shows a screw 1
3 shows three axes of movement controlled by turning 22.
Movement along the x-axis is left and right, movement along the y-axis is inside and outside, z
The movement along the axis is up and down.

FIG. 7 is a diagrammatic view of the components of the gas supply line and the oxygen supply line as the single element 110 shown in FIG. To illustrate the present invention, two supply lines are provided, a first gas line 110a for supplying a flammable gas or mixture of gases to the torch 106 and an oxygen torch 1.
Separately labeled as a second gas line 110b feeding 06. As shown in FIG. 7, each supply line includes a flashback arrester 140a, 140b, a mass flow controller 112a, 112b, and a filter 11.
4a, 114b and valves 116a, 116b. trout·
The flow controllers 112a, 112b are separately controlled to precisely control the flow of gas or oxygen, each with a delivery rate of 0-20 millimeters per minute. The use of oxygen can raise the temperature of the flame if desired.

FIG. 8A is a cross-sectional view of a modified single jet torch 106, which is suitable for use with the heat treatment station 100 shown in FIG. 5, and FIG. 8B is a front view. Torch 106 is an upper conduit 150 connected to an oxygen source.
And a lower conduit 152 connected to a gas source. The upper conduit 150 ends in a jacket 154 that surrounds the end of the lower conduit 152. Thus, as shown in FIG. 8B, the flame end of torch 106 has a central jet of gas supplied by lower conduit 152 and a ring of oxygen supplied by jacket 154 around the gas jet.
Including jet. In this embodiment of torch 106, the torch length is 80 mm, the jacket length is 55 mm, and the conduit center-to-center distance is 20 mm. The conduit has an inner diameter of 4 mm and an outer diameter of 6 mm. The jacket is
It has an inner diameter of 9 mm and an outer diameter of 11 mm.

FIG. 9A shows the leg portion 10 shown in FIGS. 6A and 6B.
9 is a perspective view of the fiber holding block 102, without FIG.
B is a plan view. The fiber holding block 102 includes channels 160 that receive the optical fibers to be processed. In addition, three clamps 16 that hold the optical fiber in place.
There are 2, 164, 166. The first and third clamps 162, 166 are of the type that hold the fiber in a fixed position. The second clamp 164 is of a type that operates as a guide, but does not fix its position. The reason for combining clamps in this way is
When the connection point is placed in a flame for heat treatment, connection point 1
This is because at 68 an exact amount of tension in the fiber occurs.
As shown in FIG. 9B, the first and second clamps 16
2, 164 are arranged on both sides of the first notch 169 exposing the connection point 168.

Since the position of the fiber is not fixed with respect to the second clamp 164, the fiber itself is sufficiently weighted within the "weight region 170" to create the correct amount of tension at the splice point 168. As shown in FIG. 9B, the weight region 170
Is a second notch portion of sufficient length such that the length of the optical fiber that overhangs this weight region 170 has sufficient weight to create the desired tension at the connection point 168. It has been found that a weight region 170 having a length of about 200 mm provides sufficient tension at the connection point to ensure that the fiber is not bent by the flame. However, at the same time, this tension is so low that the heated fiber does not taper or stretch.

FIG. 10 is a perspective view of a heating wire assembly 180 used to ensure that the torch 106 is flame free. The heating wire assembly 180 is made of ceramic
It includes a block 182 and a wire 184. In this embodiment of the invention, the heating wire 184 has a diameter of about 0.3 mm.
Of platinum (Pt). The wire is heated by applying an electric current. When the heat treatment station 100 is started, the heated wire turns on the flame, ensuring that the flame is always on during operation of the device. The heating wire assembly 180 is useful because the gas flow is often very small and the flame is inadvertently extinguished.

FIG. 11A is a plan view of the fiber holding block 102 with the visible laser source 190 placed in close proximity.
The laser 190 can be used to ensure that the splices are accurately aligned within the fiber holding block 102 along the x-axis after the spliced fibers have moved from the weld splicer to the heat treatment station 100. it can. Accurate placement of the splice in the center of the torch flame is desirable.

The visible laser source 190 is mounted on the fiber holding block 102. As shown in FIG. 11B, the laser beam is at the connection point 1 of the connected optical fiber 192.
As it passes through 94, the result is a characteristic linear interference pattern 198 with the laser beam spot 196. By referring to this linear interference pattern,
The translation stage 120 can be used to position the torch relative to the connection point.

FIG. 12 is a flow chart illustrating a method 200 for using the heat treatment station shown in FIGS. In step 202, the flame is turned on by opening the gas source and applying an electric current to the heating wire. In step 204, the fiber holding block is pulled slightly along the y-axis towards the station operator to ensure that the splice is not in the flame as it is loaded into the fiber holding block. At step 206, a pair of fibers connected together using a fusion splicer is loaded into a fiber holding block. The position of the connected fibers is fixed by closing the fiber holding clamp. In step 208, the torch is aligned along the x-axis so that the connection point is in the center of the flame. As mentioned above, this is
This can be accomplished by using a laser and observing the resulting interference pattern. Step 210
Then, the torch is lowered to the lowest position along the z axis.
At step 212, the fiber holding block is moved inward so that the splice is located just above the center of the torch. In step 214, the torch is raised to its final position. The final position can be controlled by taking the position read by the z-axis translation screw on the translation stage. In step 216, splice loss is continuously monitored during the heat treatment process. At step 218, the splice is removed once the minimum splice loss is obtained. Fiber removal is accomplished by first lowering the torch down to the lowest position along the z-axis and then moving the fiber holding block away from the torch along the y-axis. The splice can be removed by releasing the clamp.

FIG. 13 shows one connected to one SSMF.
Resulting from applying the above technique to a book's DCF,
FIG. 21 is a table 220 showing typical loss values at 1550 nm. DCF used for splicing is Lucent T
Standard Dispersion C manufactured by technologies Denmark I / S
It was an opening fiber. SSM
F can be, for example, Corning SMF28 fiber. These splice losses were obtained using a combination of propane-butane and oxygen. Further, by applying the above technique, a splice having sufficient strength can be obtained. FIG. 14 shows 1550 nm with some of the optimal breaking loads obtained for splices made with a high strength splice setup and subsequently heat treated according to the invention.
It is the table 230 which shows the connection data in. Again, a combination of propane butane and oxygen was used.

While the above description contains details that enable those skilled in the art to practice the invention, it is of an exemplary nature and many modifications and variations are possible. It should be understood that it will be apparent to those skilled in the art having the benefit of these teachings. Accordingly, the invention herein is defined only by the claims appended hereto, which are to be broadly construed, as permitted by the prior art.

[Brief description of drawings]

FIG. 1A is a cross-sectional view of a typical dispersion compensating fiber.

FIG. 1B is a diagram showing a refractive index distribution of the dispersion compensating fiber shown in FIG. 1A.

FIG. 2 is a perspective view of a heat treatment station according to an aspect of the invention.

FIG. 3 is a flow chart of a method according to a further aspect of the invention.

FIG. 4 is a graph illustrating the relationship between heat treatment time and connection loss.

FIG. 5 is a perspective view of a further embodiment of a heat treatment station according to the present invention.

FIG. 6A is an exploded perspective view showing the heat treatment station shown in FIG. 5 with a gas supply line removed for explanation.

FIG. 6B is an assembled perspective view of the heat treatment station shown in FIG. 5 with the gas supply line removed for purposes of illustration.

6C is a perspective view of a translation stage suitable for use in the heat treatment station shown in FIG.

7 is a diagrammatic view of gas and oxygen supply lines suitable for use in the heat treatment station shown in FIG.

8A is a cross-sectional view of a torch suitable for use in the heat treatment station shown in FIG.

8B is a front view of a torch suitable for use in the heat treatment station shown in FIG.

9A is a perspective view of a fiber holding block used in the heat treatment station shown in FIG. 5. FIG.

9B is a plan view of a fiber holding block used in the heat treatment station shown in FIG.

FIG. 10 is a perspective view of a heating wire assembly positioned in proximity to a torch head according to a further aspect of the present invention.

FIG. 11A is a plan view of the fiber holding block shown in FIG. 9A with a visible laser source in close proximity, according to a further aspect of the invention.

11B is a perspective view of the visible laser source shown in FIG. 11A, showing the characteristic interference pattern that occurs when the visible laser beam is directed through the splice point of the optical fiber.

FIG. 12 uses the heat treatment station shown in FIG.
6 is a flow chart of a method according to a further aspect of the invention.

13 is a table showing results of splice loss obtained using the heat treatment station shown in FIG.

FIG. 14 is a table showing splice loss and failure load for high strength splices processed using the heat treatment station shown in FIG.

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[Procedure amendment]

[Submission date] September 24, 2002 (2002.9.2)
4)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tony Sorensen             Denmark DK-2765 Snell             Mu, lutter care 73 (72) Inventor Torben Erik Weng             Denmark 2605 Blendby, Sol             K-33 second floor F-term (reference) 2H036 MA12 MA17 NA12

Claims (10)

[Claims] 1. A heat treatment station (30,100) for holding a pair of optical fibers connected together at a connection point (34,168) with a chassis (58,101) and exposing the connection point. 1 notch (4
5, 169), including fiber holding blocks (44, 1)
02) (30, 100) and a torch (37, 106) that allows the fiber holding block and torch to adjust the position of the splice point and the torch relative to each other so that the splice point is in the flame. A heat treatment station, characterized in that it is attached to a heat treatment station. 2. The fiber holding block can be moved back and forth from a first position for loading the connected fiber into the fiber holding block to a second position where the connection point is above the flame. The heat treatment station of claim 1, wherein the fiber retention block is mounted to the chassis so that it can. 3. A pair of side supports (136) attached to the chassis so that the fiber retention block can move back and forth along a path defined by the side supports (136). ), The fiber holding block comprises a pair of legs spanning the side support such that the inner surface of the leg abuts the outer surface of the side support. 4. The upper surface of each side support includes an upwardly projecting member that defines a second position of the fiber holding block.
The heat treatment station according to claim 3. 5. The fiber holding block includes a first clamp that holds a pair of connected optical fibers in place,
A second clamp functioning as a guide to allow the optical fiber to move therethrough, the first and second clamps being disposed on the fiber holding block on opposite sides of the notch. Item 1. The heat treatment station according to Item 1. 6. The fiber retention block includes a second notch region, wherein the second notch region is positioned such that there is a second clamp between the first notch region and the second notch region. The notch region is provided with a pair of connected optical fibers when the second optical fiber is inserted into the fiber holding block in a state in which a part of the optical fiber is arranged so as to cover the second notch region. 6. The heat treatment station of claim 5, wherein a portion of the optical fiber that spans the notch region is of sufficient length to provide a desired level of tension at the splice point. 7. A laser source mounted to the fiber holding block further comprising a laser source mounted to the fiber holding block such that a characteristic interference pattern is produced when the spliced optical fiber is loaded into the fiber holding block. The heat treatment station according to claim 1, which indicates a location. 8. A method for splicing together first and second optical fibers comprising: (a) splicing the first and second fibers together at a splice point using a fusion splicer. , (B) placing the splice point in the flame, (c) monitoring the spliced first and second fibers for splice loss, and (d) the desired minimum level of splice loss. Once accomplished, removing the spliced first and second fibers from the flame. 9. The method of claim 8, wherein step (a) further comprises the step of producing a desired level of mode field diffusion in the first fiber using optimized fusion splice parameters. . 10. The method further comprises the step of loading the connected fibers into a fiber holding block of the heat treatment station before step (b) and the step of removing the connection point from the heat treatment station after step (d). 9. The method of claim 8 including.