KR101179645B1 - variable optical attenuator - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable optical attenuator, comprising: a main portion comprising a first core and a first clad, a thermal expansion portion comprising a second core extended from the first core by heating between the main portion, The thermally expanded core optical fiber having an auxiliary coating layer formed on the outside of the second clad opposing the second core, and the thermally expanded core optical fiber may interfere with the thermally expandable core optical fiber so that the bend radius can be varied while the thermally extended portion of the thermally expanded core optical fiber is curved. And a bending adjustment guide portion provided so as to interfere with the bending deformation guide portion and varying a bending radius of the thermal expansion core optical fiber. Such a variable optical attenuator provides the advantages of a simple structure, easy connection in an inline form, low insertion loss, and a large attenuation range.

Description

Variable optical attenuator

The present invention relates to a variable optical attenuator, and more particularly, to a variable optical attenuator using a thermal diffusion core optical fiber.

Recently, optical communication systems using optical fibers have been actively developed and spread to effectively transmit a variety of types of information.

Such an optical communication system converts an electrical signal into an optical signal in an optical transmission module of a transmitter and transmits the optical signal through an optical fiber, and receives and processes an optical signal transmitted through the optical fiber as an electrical signal.

In the optical communication system, an optical amplifier is used in the middle of the transmission in consideration of the attenuation of the optical signal to transmit the optical signal over a long distance. Since the gain of the optical amplifier varies depending on the wavelength, the optical output for each wavelength is different from each other. Accordingly, when the optical power transmitted through the optical fiber is input too high at the receiving end, the optical attenuator is used to adjust the received optical power to an appropriate level because normal signal reception processing is not performed.

Such optical attenuators are known in various ways, but suffer from problems such as complex structure, low variable range of attenuation rate, and poor in-line coupling.

In particular, in-line structures require interface problems between the attenuator and single-mode fiber, low insertion loss, negligible retroreflection, mechanical stability, and ease of assembly.

SUMMARY OF THE INVENTION The present invention has been made to improve the above problems, and in particular, it is easy to connect in an in-line form with an optical fiber for transmitting an optical signal and has a simple structure and a variable attenuation variable range having a large attenuation variable range. There is this.

In order to achieve the above object, the variable optical attenuator according to the present invention includes a main portion composed of a first core and a first clad, and a thermal expansion having a second core extended from the first core by heating between the main portions. A thermal expansion core optical fiber having a portion and an auxiliary coating layer formed on an outer side of the second clad opposite the second core of the thermal expansion portion; A bending deformation guide part installed to interfere with the thermal expansion core optical fiber such that the thermal expansion portion of the thermal expansion core optical fiber is curved in an arc shape and the bending radius is variable; And a bend adjusting unit that interferes with the bend guide unit to vary the bend radius of the thermally expanding core optical fiber.

Preferably, the bending deformation guide portion has an inner space and a housing in which the first and second through holes through which the thermal expansion core optical fiber enters and exits are opposed to each other; It is installed in the inner space of the housing so as to be inserted through the first and second through holes in the center of the first base portion so as to interfere downwardly the thermal expansion portion of the thermal expansion core optical fiber installed in the housing A moving block having a first protruding portion protruding downward and second and third protruding portions protruding downward at positions spaced apart from each other in the first and second through-hole directions with respect to the first protruding portion; A fourth protrusion part spaced apart from the moving block in the inner space of the housing and opposed to the movable block, the fourth protrusion part protruding from the second base part toward the area between the first protrusion part and the second protrusion part; A fixed block having a fifth protrusion protruding toward an area between the third protrusions; And a first elastic bias member coupled between the housing and the movable block to apply the elastic bias in a direction away from the fixed block with respect to the movable block. A retraction screw is screwed into and retracted from a screw hole formed along a direction opposite to the first base portion of the movable block outside the housing so as to interfere with the first base portion by the retraction.

In addition, an outline connecting the second and third protrusions from the first protrusion of the moving block is formed to have an arc-shaped curvature drawn upward, and the fourth protrusion and the fifth of the fixed block. The contour connecting the protrusions is formed to have an arc-shaped curvature drawn downward.

More preferably, the first through hole and the second through hole are coupled between the thermally expanding core optical fiber and the housing to allow movement of the thermally expanding core optical fiber but to elastically bias to a restoring position when the external force is released. It further comprises a bias member.

It is preferable that the refractive index of the auxiliary coating layer is 0.001 to 0.006 larger than that of the second clad.

According to the variable optical attenuator according to the present invention, the structure is simple, the connection in the inline form is easy, the insertion loss is low, and the attenuation range is large.

1 is a view showing a variable optical attenuator according to the present invention,
FIG. 2 is an enlarged view of the thermal expansion core optical fiber of FIG. 1;
3 is a view illustrating a process of forming a thermal expansion portion of the thermal expansion core optical fiber of FIG.
Figure 4 is a graph showing the bending loss according to the core radius of the thermal expansion core optical fiber,
5 and 6 are graphs showing simulation results of mode propagation (left graph) and guided mode optical power (right graph) for a single mode optical fiber before heat treatment and a thermal diffusion core optical fiber subjected to heat treatment.
FIG. 7 is a graph showing the results of measuring the excess loss due to thermal expansion of a core while applying heat to a single mode optical fiber over a wavelength range of 1250 nm to 1650 nm.
FIG. 8 is an image of a standard single mode optical fiber and white diffracted samples A and B irradiated with fiber.
Figure 9 is a graph showing the results of measuring the bending loss while moving the micrometer to bend the thermal expansion core optical fiber while differently applying the refractive index of the protective coating layer.
FIG. 10 is a graph illustrating bending losses measured while varying the advancing length of the adjusting screw after insertion of the protective coating layers A and B and the single mode optical fiber into the housing of FIG. 1.

Hereinafter, a variable light attenuator according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing a variable optical attenuator according to the present invention, Figure 2 is a view showing a process of forming a thermal expansion portion of the thermal expansion core optical fiber of Figure 1, Figure 3 is a thermal expansion portion of Figure 2 After the formation is an enlarged view of the thermal expansion core optical fiber of FIG.

1 to 3, the variable optical attenuator 100 includes a thermal expansion core optical fiber 110, a bending deformation guide part 140, and a bending adjusting part 160.

As shown in FIG. 2, the thermal expansion core optical fiber 110 has a structure having a main portion 120 and a thermal expansion portion 130.

The main part 120 refers to a part having a general single mode optical fiber structure, and includes a first core 121 and a first clad 122.

As shown in FIG. 3, the second core 131 extended from the first core 121 by heating to about 1300 ° C. between the main parts 120 using the microtorch 210 as shown in FIG. 3. The auxiliary coating layer 135 is formed outside the second clad 132 facing the second core 131 while surrounding the second core 131.

When the main portion 120 is a single mode optical fiber is applied to the outer diameter of the second core 131 is formed to be two to three times the outer diameter of the first core 121.

The thermally expanding core optical fiber 110 may be formed by applying heat to a general single mode optical fiber to form an extended second core 131 and then forming an auxiliary coating layer 135 outside the second clad.

On the other hand, the main portion 120 of the thermal expansion core optical fiber 110 is covered with a conventional tube 124 outside the first clad 122, and the main portion 120 of the main portion 120 adjacent to the thermal expansion portion 130 Of course, some of the first clad 122 may be exposed or covered.

The bending deformation guide part 140 interferes with the thermally expanding core optical fiber 110 so that the bending radius of the thermally expanding portion 130 can be varied while the thermally expanding portion 130 of the thermally expanding core optical fiber 110 is curved in an arc shape. It is installed so that it can be done.

The bending deformation guide part 140 includes a housing 141, a moving block 143, a fixed block 151, and a first spring 158.

The housing 141 has an inner space 141a having a rectangular shape, and the first and second through holes 142a and 142b through which the thermal expansion core optical fiber 110 enters and exit from each other.

The moving block 143 is movably installed in the inner space 141a of the housing 141, and is inserted through the first and second through holes 142a and 142b to be installed in the housing 141. The first protruding portion 145 protruding downward in the center of the first base portion 144 and the first protruding portion 145 so as to interfere downwardly with the thermal expansion portion 130 of the first base portion 144. The first and second through holes 142a and 142b are integrally formed with the second and third protruding portions 146 and 147 protruding downward from positions spaced apart from each other.

The contour connecting the second and third protrusions 146 and 147 from the first protrusion 145 of the moving block 143 is formed to have an arc-shaped curvature drawn upward.

The fixing block 151 is fixedly installed to face the moving block 143 in the inner space 141a of the housing 141 so as to face the first protrusion 145 and the second protrusion 152 from the second base portion 152. (146) in a shape having a fourth protrusion 153 protruding toward the interregion and a fifth protrusion 154 protruding toward the region between the first protruding portion 145 and the third protruding portion 147. Formed.

The first spring 158 is applied as the first elastic bias member, and the housing 141 and the moving block 143 can apply the elastic bias to the moving block 143 in a direction away from the fixed block 151. It is coupled between the first base portion 144 of the).

Meanwhile, when the thermal expansion core optical fiber 110 having the thermal expansion portion 130 mounted in the housing 141 is bent by the retraction of the moving block 143 is allowed to move, the external expansion core 130 may return to the initial position when the external force is released. The first through hole 142a and the second through hole 142b are coupled between the thermal expansion core optical fiber 110 and the housing 141 to allow the movement of the thermal expansion core optical fiber 110 to be restored when the external force is released. A second spring 105, which is a second elastic bias member that elastically biases in position, is provided.

The bend adjuster 160 faces the first base portion 144 of the movable block 143 outside the housing 141 to interfere with the first base portion 144 of the movable block 143 by advancing and retreating. Retreating screw 161 is screwed into the screw hole (141b) formed along the back was applied.

In this structure, the thermal expansion core optical fiber 110 is supported by one side by the second protrusion 146 and the fourth protrusion 153, and is supported by the third protrusion 147 and the fifth protrusion 154. The first projecting portion 145 interferes with the center of the thermally expanding portion 130 of the thermally expanding core optical fiber 110 to change the bending radius by advancing and retracting the screw 161 while the other side is supported.

Unlike the illustrated example, the advance screw 161 may be combined with a motor (not shown) to advance and retreat by electric energy.

Hereinafter, the characteristics of the variable optical attenuator will be described.

The mode field diameter of single mode optical fibers expands when heated to high temperatures above 1300 ° C.

The bending loss is required to increase continuously with respect to the bending rate of the thermal expansion core optical fiber 110. However, the bending loss of the thermal expansion core optical fiber 110 depends on the refractive index of the auxiliary coating layer 135 and the vibration of the bending rate is not uniform. Therefore, it should be structurally complemented to have a single value for the change in the bending rate. For this purpose, the auxiliary coating layer 135 is larger than the refractive index of the second cladding 132 but has a refractive index of 0.001 to 0.006 larger than the second cladding 132. Apply.

GeO ₂ dopant added to the core of silica single-mode fiber is thermally diffused when the fiber is heated above 1300 ℃, and the difference in refractive index between core and clad is attenuated by thermally diffused GeO ₂ dopant, resulting in core expansion. .

Despite changes in the core structure, the normalization frequency remains constant after diffusion of the dopant. Therefore, the thermal diffusion core optical fiber maintains a single mode even after heat treatment.

The normalized frequency (V) of a single mode optical fiber can be expressed by Equation 1 below.

Here, λ is the wavelength, a ₀ is the radius of the first core 121, n _CO is the refractive index of the first core 121, Δ ₀ is between the first core 121 and the first clad 122 before the heat treatment Normalized refractive index difference.

Assuming that the normalization frequency of a single mode optical fiber does not change, the following equation (2) is obtained.

Here, a is the radius of the second core 131 after the heat treatment, Δ Is the refractive index of the second core 131 after heat treatment.

The thermal diffusion core optical fiber 110 has a characteristic that bending loss is very sensitive by a reduction in the normalized refractive index difference.

The bending loss with respect to the step refractive index of the single mode optical fiber can be expressed as Equation 3 below.

Where a is the radius of the second core 131, R is the bending radius, K1 is the second type of primary Bessel function, Δ Is the normalized refractive index difference between the second core 131 and the second clad 132.

U is a propagation constant for the cross direction of the second core 131, W is a propagation constant for the cross direction of the second clad 132, and V is a normalized frequency.

4 is a graph showing the results of calculating the bending loss for the case where the difference between the core radius and the normalized refractive index difference is different for the normalized frequency of 1550 nm. Here, the refractive index of the second clad 132 is assumed to be 1.444. As can be seen from FIG. 4, the attenuation decreases exponentially as the bending radius increases. In addition, as the second core 132 is expanded, the attenuation further increases. Therefore, it can be seen that the bending loss of the thermal expansion core optical fiber 110 is more sensitive to the change in curvature than the conventional single mode optical fiber.

On the other hand, if the diameter of the second clad 132 is optically finite in Equation 3, the diameter of the second clad 132 is no longer applicable, and since the diameter of the second clad 132 is finite, the bending loss is influenced by the refractive index of the surrounding material. Receive.

5 and 6 are graphs showing simulation results of mode propagation (left graph) and guided mode optical power (right graph) of a single mode optical fiber before heat treatment and a thermal diffusion core optical fiber subjected to heat treatment. Here, it is assumed that the second core 131 is adiabaticly extended 1.0 mm in the mode propagation direction, and the normalized frequency is maintained in the mode propagation direction. In addition, the core radius (a ₀ ) and the normalized refractive index difference (Δ ₀ ) Were assumed to be 4.0 μm and 0.344%, respectively, before the heat treatment. Core radius a ₀ and normalized refractive index difference Δ ₀ of the thermally expanding portion 130 of the thermally expanding core optical fiber 110. Was assumed to be 8.0 μm, 0.086%. When the core of the optical fiber is adiabaticly extended along the longitudinal direction of the optical fiber, the coupling loss and reverse reflection between the single mode optical fiber region and the thermal expansion region 130 are gradually changed due to the mode evolution effect. Can be ignored.

It can be seen that a standard single fiber has a small bending loss of less than 5% as shown in FIG. 5, while a thermally expanding core fiber has a high bending loss of more than 85% as shown in FIG. Can be.

<Production example>

SMF28, a standard single mode optical fiber, was prepared and stripped 20 mm of the coating, and then heat-treated while reciprocating with respect to the stripped portion with the microtorch 210 as described with reference to FIG. 3. The heat treatment part was 12mm, and the heating time was differently produced by 15 minutes and 30 minutes, respectively. In the following description, the sample applied with the heating time for 15 minutes is referred to as A, and the sample applied with the heating time for 30 minutes is described as B. FIG.

The excess loss due to thermal expansion of the core while applying heat was measured over a wide wavelength range of 1250 nm to 1650 nm and the results are shown in FIG. 7.

As can be seen from FIG. 7, the measured excess loss was less than 0.4 dB in all wavelength bands. In addition, a small peak was found at 1390 nm. The optical loss due to OH absorption was increased by the heating process, and the insertion loss of the thermal expansion core optical fiber was less than 0.2dB at 1550nm.

8 is an image of a standard single mode optical fiber, and sample A and sample B irradiated with white light through a fiber. Samples A and B have core sizes that are two to three times larger than single-mode fiber. In addition, the diameter of the second clad of the thermal expansion portion of the thermal expansion core optical fiber after heating is reduced by about 2 to 3㎛.

On the other hand, as a result of examining the influence of the protective coating layer 135 on the thermal expansion portion, if the refractive index of the protective coating layer 135 is smaller than the refractive index of the second cladding 132 serves as a new cladding, the cladding mode is a protective coating layer ( 135).

Figure 9 is a graph showing the results of measuring the bending loss while moving the micrometer to bend the thermal expansion core optical fiber while differently applying the refractive index of the protective coating layer.

9, if the refractive index of the protective coating layer 135 is different from that of the second clad 132, the bending loss vibrates without having a single value, but the refractive index difference between the second clad 132 and the second clad 132 is very small. The protective coating layer 135 having a refractive index of 1.446 has a single value. As a result, when the refractive index of the protective coating layer 135 is slightly higher than the refractive index of the second clad 132 and the difference is 0.001 to 0.006 or less, the clad mode does not exist, thereby providing a characteristic having a single attenuation value with respect to the bending radius change. do.

Preferably, when the protective coating layer 135 is formed of a polymer material by curing, it also provides an effect of suppressing breakage due to bending.

FIG. 10 is a graph illustrating bending losses measured while varying the advancing length of the adjusting screw after insertion of the protective coating layers A and B and the single mode optical fiber into the housing of FIG. 1. As can be seen from FIG. 10, it can be seen that the loss change due to the bending of the thermal expansion core fiber changes exponentially much more rapidly than the single mode fiber.

As described above, the variable optical attenuator 100 forms a single-mode optical fiber having the thermal expansion portion 130 to adjust the bending radius of the thermal expansion portion 130 so that the wide attenuation region exceeds 55 dB and 0.2 dB at 1550 nm. It is possible to provide a variable madness with lower losses.

110: thermal expansion core optical fiber 130: thermal expansion portion
141: housing 143: moving block
151: fixed block 161: retraction screw

Claims (5)

delete A main portion comprising a first core and a first clad, a thermal expansion portion comprising a second core extended from the first core by heating between the main portion, and a second core facing the second core of the thermal expansion portion; A thermal expansion core optical fiber having an auxiliary coating layer formed on the outside of the second clad;
A bending deformation guide part installed to interfere with the thermal expansion core optical fiber such that the thermal expansion portion of the thermal expansion core optical fiber is curved in an arc shape and the bending radius is variable;
And a bend adjusting unit for varying a bend radius of the thermally expanded core optical fiber by interfering with the bent deformation guide part.
The bending deformation guide portion
A housing having an inner space, the first and second through-holes of which the thermal expansion core optical fiber is introduced and opposed to each other on both sides thereof;
It is installed in the inner space of the housing so as to be inserted through the first and second through holes in the center of the first base portion so as to interfere downwardly the thermal expansion portion of the thermal expansion core optical fiber installed in the housing A moving block having a first protruding portion protruding downward and second and third protruding portions protruding downward at positions spaced apart from each other in the first and second through-hole directions with respect to the first protruding portion;
A fourth protrusion part spaced apart from the moving block in the inner space of the housing and opposed to the movable block, the fourth protrusion part protruding from the second base part toward the area between the first protrusion part and the second protrusion part; A fixed block having a fifth protrusion protruding toward an area between the third protrusions;
And a first elastic bias member coupled between the housing and the movable block to apply the elastic bias to the movable block in a direction away from the fixed block.
The bend adjusting unit is a retraction screw that is screwed into the screw hole formed along the direction opposite to the first base portion of the movable block from the outside of the housing so as to interfere with the first base portion of the movable block by the retreat; Variable light attenuator, characterized in that. 3. The contour of claim 2, wherein an outline connecting the second and third protrusions from the first protrusion of the moving block is formed to have an arc-shaped curvature drawn upward.
The contour connecting the fourth protrusion and the fifth protrusion of the fixing block is formed with an arc-shaped curvature drawn downward. The method of claim 3, wherein the first through the second through-hole is coupled between the thermal expansion core optical fiber and the housing allowing the movement of the thermal expansion core optical fiber to elastically bias to a restoring position when the external force is released 2. An elastic attenuator further comprising: an elastic bias member. The variable light attenuator of claim 4, wherein a refractive index of the auxiliary coating layer is 0.001 to 0.006 larger than that of the second clad.

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