KR20210120701A - Optical fiber device for removing cladding light - Google Patents

Abstract

The present invention relates to an optical fiber device for removing cladding light, which efficiently emits extra light. According to the present invention, the optical fiber device for removing the cladding light includes: a first to Nth optical fiber sections which sequentially are connected along a direction in which light travels; and a first tapered connection section connecting any two adjacent ones of the first to Nth optical fiber sections. Therefore, it is possible to efficiently emit the extra light by repeatedly disposing a tapered connection section.

Description

Optical fiber device for cladding light removal

The present invention relates to an optical fiber device for removing cladding light, and more particularly, to an optical fiber device for removing cladding light that efficiently emits excess light.

Conventionally, a high-power laser generating device has been implemented using a solid state laser, but recently, there is a trend to implement a high-power laser generating device using an optical fiber.

A high-power laser generating device using an optical fiber has the following advantages over a solid-state laser.

First, since the diameter of the optical fiber is about several hundred micrometers, it is possible to easily implement a high-power laser generating device having a small footprint compared to a solid-state laser.

In the case of optical fibers, the gain medium can be lengthened, so that more surfaces are in contact with air per unit active volume. Therefore, heat dissipation is easy and cooling is easy compared to a solid-state laser. Due to this characteristic, fiber lasers are receiving more attention than high-power lasers, which have limitations in realizing higher power due to difficulty in dissipating heat.

Fiber optics are also much smaller and more flexible than solid-state lasers, so they have a spatial advantage when used in high-power lasers. In addition, the solid-state laser implements the laser through alignment using a lens, but this alignment has the disadvantage of being easily changed by an external impact. On the other hand, fiber laser has the advantage of being portable due to its high structural stability because it can be implemented without alignment.

Finally, fiber lasers can produce high-quality beams at higher power than solid-state lasers. Using this characteristic, it is possible to realize a more sophisticated and effective high-power laser.

1 is a cross-sectional view showing an optical fiber according to the prior art and the propagation of light therein.

Referring to FIG. 1 , a conventional optical fiber (double-clad fiber) surrounds a core ( 20 ) and a core ( 20 ) as a path of signal light, and an inner cladding ( 30 ) as a path of pump light and and an outer cladding 40 surrounding the inner cladding 30 .

The pump light is totally reflected at the boundary between the inner cladding 30 and the outer cladding 40 to amplify the signal light traveling along the core 20 .

The excess pump light remaining after amplifying the signal light should be removed from the output stage of the laser generating device. In addition to the extra pump light, light due to a small amount of loss occurring in the connection portion (spliced portion) of the optical fiber and light leaking from the core 20 must also be removed.

A device for removing such excess light is called a cladding light stripper (CLS). If the excess light is not removed, the excess light not only interferes with the propagation of the signal light, but may also cause damage to the optical fiber due to heat. Therefore, the excess light must be removed.

Therefore, a CLS that removes excess light with high efficiency is absolutely necessary for manufacturing a high-power laser generating device using an optical fiber.

1. U.S. Patent No. 8,537,871 2. US Patent No. 9,880,355 3. US Patent No. 10,090,631

1. A Combined method for the fabrication of high-power cladding light stripper using buffered oxide etchant, Elif Yapar Yildirim et al., Applied Optics Vol. 58 No. 25, pp. 6926-6933 (2019). 2. High power cladding light stripper using segmented corrosion method: theoretical and experimental studies, Lu Yin et al., Optics Express Vol. 25, Issue 8, pp. 8760-8776 (2017).

An object of the present invention is to provide an optical fiber device for removing cladding light that efficiently emits excess light.

An optical fiber device for removing cladding light according to the present invention includes: first to Nth optical fiber sections sequentially connected along a direction in which light travels; and a first tapered connection section connecting two adjacent ones of the first to Nth optical fiber sections, wherein each of the first to Nth optical fiber sections alternates along a direction in which the light travels. a first subsection and a second subsection that are closely connected; and at least one second tapered connection section connecting the first subsection and the second subsection, wherein the first optical fiber section included in the Kth optical fiber section which is any one of the first to Nth optical fiber sections. The diameter (D _2K-1 ) and length (L _2K-1 ) of the subsection and the diameter (D _2K ) and length (L _2K ) of the second subsection, the (K+1)th adjacent to the Kth optical fiber section _{The diameter (D 2K+1} ) and length (L _2K+1 ) of the first subsection included in the optical fiber section and the diameter (D _2K+2 ) and length (L _2K+2 ) of the second subsection are [ D _2K-1 > D _2K ] and [D _2K+1 > D _2K+2 ], [L _2K-1 > L _2K+1 ], [L _2K > L _2K+2 ] and [D _2K-1 = D _2K+1 ], [D _2K > D _2K+2 ] when K is odd, and [D _2K < D _2K+2 ] when K is even (N is natural number, K is a natural number greater than or equal to 1 (N-1) or less).

It is preferable to satisfy [L _2K-1 < L _{2K ] for any K.}

It is preferable to satisfy [L _2K+1 < L _{2K+2 ] for any K.}

The optical fiber device for removing cladding light includes first to fourth optical fiber sections and three first tapered connection sections, each of the first to fourth optical fiber sections sequentially in the direction in which the light travels. connected first and second subsections; and a second tapered connection section connecting the first subsection and the second subsection, wherein diameters of the first subsections of the first to fourth optical fiber sections (D ₁ , D ₃ , D _{5 )} , D ₇ ) and length (L ₁ , L ₃ , L ₅ , L ₇ ) and diameter (D ₂ , D ₄ , D ₆ , D ₈ ) and length (L ₂ , L ₄ , L _{6 ) of the second subsection} , L ₈ ) is [L ₁ > L ₃ > L ₅ > L ₆ ], [L ₂ > L ₄ > L ₆ > L ₈ ], [L ₁ < L ₂ ], [L ₃ < L ₄ ], [ L ₅ < L ₆ ], [L ₇ < L ₈ ], [D ₁ = D ₃ = D ₅ = D ₇ ] and [D ₂ = D ₆ > D ₄ = D ₈ ] are satisfied.

The optical fiber element for removing cladding light includes first to fourth optical fiber sections and three first tapered connection sections, each of the first to fourth optical fiber sections having a first optical fiber section along a direction in which the light travels. two first subsections and two second subsections connected in an order of a subsection, a second subsection, a first subsection and a second subsection; and three second tapered connecting sections connecting the first subsection and the second subsection, wherein the diameters of the first subsections of the first to fourth optical fiber sections (D ₁ , D ₃ , D ₅ , D ₇ ) and length (L ₁ , L ₃ , L ₅ , L ₇ ) and diameter (D ₂ , D ₄ , D ₆ , D ₈ ) and length (L ₂ , L _{4 ) of the second subsection} L ₆ , L ₈ ) is [L ₁ > L ₃ > L ₅ > L ₆ ], [L ₂ > L ₄ > L ₆ > L ₈ ], [L ₁ < L ₂ ], [L ₃ < L ₄ ] , [L ₅ < L ₆ ], [L ₇ < L ₈ ], [D ₁ = D ₃ = D ₅ = D ₇ ] and [D ₂ = D ₆ > D ₄ = D ₈ ] are satisfied.

The optical fiber device for removing cladding light according to the present invention has the following advantages.

(1) By repeatedly arranging the tapered connecting section, it is possible to efficiently emit the extra light.

(2) By appropriately adjusting the lengths of the first subsection and the second subsection, heat loss can be prevented.

(3) By appropriately adjusting the diameters of the first subsection and the second subsection, the surface area of the tapered connecting section can be increased, so that the extra light can be emitted more efficiently.

1 is a cross-sectional view showing an optical fiber according to the prior art and the propagation of light therein.
2 is a cross-sectional view schematically illustrating an optical fiber device for removing cladding light according to the present invention.
3 is a cross-sectional view schematically showing a first embodiment of an optical fiber device for removing cladding light according to the present invention.
4 is a cross-sectional view schematically showing a second embodiment of an optical fiber device for removing cladding light according to the present invention.

Hereinafter, an optical fiber device for removing cladding light according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a cross-sectional view schematically illustrating an optical fiber device for removing cladding light according to the present invention. In FIG. 2 , the optical fiber device for removing cladding light is divided into upper and lower parts, but it is divided on the paper for convenience of illustration. The optical fiber device for removing cladding light shown in FIGS. 3 and 4 is also the same. In addition, in the present specification, the first optical fiber section, the second optical fiber section, the first section, the second section, the tapered connection section, and the like are conceptually divided and not physically separated.

Referring to FIG. 2 , the optical fiber device 1000 for removing cladding light according to the present invention is one of a first optical fiber section to an Nth optical fiber section and a first optical fiber section to an Nth optical fiber section sequentially connected along a direction in which light travels. and a first tapered connecting section 250 connecting any two adjacent ones (N is a natural number).

Specifically. The optical fiber device 1000 for removing cladding light according to the present invention includes a first optical fiber section on which light is incident, a second optical fiber section connected to the first optical fiber section, ... , an Nth optical fiber section connected to the (N-1)th optical fiber section. Also, two adjacent optical fiber sections are connected by a first tapered connection section 250 . For example, the first optical fiber section and the second optical fiber section are connected by the first tapered connection section 250 , and the (N-1)th optical fiber section and the Nth optical fiber section are connected to the first tapered connection section 250 . connected by (N-1) first tapered connection sections 250 are provided to connect the N optical fiber sections.

Each of the first to Nth optical fiber sections includes a first subsection and a second subsection. The first subsection and the second subsection are alternately connected along a direction in which the light travels. For example, n first subsections and n second subsections include a first subsection, a second subsection, . , the first subsection and the second subsection may be connected in the order (n is a natural number).

Each of the first to Nth optical fiber sections includes one or more second tapered connecting sections 150 connecting the first and second subsections. For example, as shown in FIG. 2 , the neighboring first subsection and the second subsection are connected by a second tapered connecting section 150 , and the second subsection and the first subsection are connected to another second subsection 2 connected by a tapered connecting section 150 . Accordingly, (2n−1) second tapered connecting sections 150 are provided to connect the n first subsections and the n second subsections.

Hereinafter, the first subsection and the second subsection will be described in more detail.

As shown in FIG. 2 , if any one of the first to Nth optical fiber sections is referred to as a Kth optical fiber section, and an optical fiber section adjacent to the Kth optical fiber section is referred to as a (K+1)th optical fiber section, the Kth optical fiber section A first subsection included in the optical fiber section has a diameter (D _2K-1 ) and a length (L _2K-1 ) and a second subsection has a diameter (D _2K ) and a length (L _2K ). Likewise, the first subsection included in the (K+1)th optical fiber section has a diameter (D _2K+1 ) and a length (L _2K+1 ), and the second subsection has a diameter (D _2K+2 ) and a length (D 2K+2 ) and length (L _2K+2 ).

For example, as shown in FIG. 2 , when K=1, the first subsection included in the first optical fiber section has a diameter (D ₁ ) and a length (L ₁ ) and the second subsection has a diameter ( D ₂ ) and a length (L ₂ ). Similarly, a first subsection included in a second optical fiber section neighboring the first optical fiber section has a diameter (D ₃ ) and a length (L ₃ ), and the second subsection has a diameter (D ₄ ) and a length (L _{4 )} ) has

When K=2, the first subsection included in the second optical fiber section has a diameter (D ₃ ) and a length (L ₃ ), the second subsection has a diameter (D ₄ ) and a length (L ₄ ), , a first subsection included in a third optical fiber section neighboring the second optical fiber section has a diameter (D ₅ ) and a length (L ₅ ), and the second subsection has a diameter (D ₆ ) and a length (L ₆ ) have

When K=3, the first subsection included in the third optical fiber section has a diameter (D ₅ ) and a length (L ₅ ), the second subsection has a diameter (D ₆ ) and a length (L ₆ ), , a first subsection included in a fourth optical fiber section neighboring the third optical fiber section has a diameter (D ₇ ) and a length (L ₇ ), and the second subsection has a diameter (D ₈ ) and a length (L ₈ ) have

The inventors of the present invention designed the first and second subsections of the Kth optical fiber section and the first and second subsections of the (K+1)th optical fiber section as follows.

(1) diameter and length of the first subsection

The diameter of the first subsection is constant regardless of K. That is, [D _2K-1 = D _2K+1 ].

For example, D ₁ = D ₃ = D ₅ = D ₇ = … am.

According to this configuration, the diameters D ₁ , D ₃ , D ₅ , and D ₇ of the first subsection may each be 120 μm.

The length (L _2K-1 ) of the first subsection included in the Kth optical fiber section is longer than _{the length (L 2K+1} ) of the first subsection included in the (K+1)th optical fiber section. That is, [L _2K-1 > L _2K+1 ].

For example, L ₁ > L ₃ > L ₅ > L ₇ > … am.

According to this configuration, the lengths (L ₁ , L ₃ , L ₅ , and L ₇ ) of the first subsection may be 1300um, 1030um, 770um, and 610um, respectively.

(2) the diameter and length of the second subsection

The diameter of the second subsection depends on K.

Specifically, when K is an odd number, the diameter (D _2K ) of the second subsection included in the Kth optical fiber section is the diameter (D _2K+2 ) of the second subsection included in the (K+1)th optical fiber section. bigger than That is, [D _2K > D _2K+2 ].

For example, when K=1, [D ₂ > D ₄ ], and when K=3, [D ₆ > D ₈ ].

When K is an even number, the diameter (D _2K ) of the second subsection included in the Kth optical fiber section is smaller than _{the diameter (D 2K+2} ) of the second subsection included in the (K+1)th optical fiber section. That is, [D _2K < D _2K+2 ]. For example, when K=2, [D ₄ < D ₆ ], and when K=4, [D ₈ < D ₁₀ ].

According to this configuration, the diameter of the second subsection repeats “large”, “small”, “large”, and “small” as K increases. For example, the diameters D ₂ , D ₄ , D ₆ , and D ₈ of the second subsection may be 95um, 90um, 95um, and 90um, respectively.

_{The length (L 2K} ) of the second subsection included in the Kth optical fiber section is longer than _{the length (L 2K+2} ) of the second subsection included in the (K+1)th optical fiber section. That is, [L _2K > L _2K+2 ].

For example, L ₂ > L ₄ > L ₆ > L ₈ > … am.

According to this configuration, the lengths (L ₂ , L ₄ , L ₆ , and L ₈ ) of the second subsection may be 1500 μm, 1250 μm, 940 μm, and 810 μm, respectively.

(3) the relationship between the diameter of the first subsection and the diameter of the second subsection

The first subsection and the second subsection are connected by a second tapered connecting section 150 having a decreasing diameter shape. _{That is, the diameter D 2K-1} of the first subsection included in the Kth optical fiber section is greater than _{the diameter D 2K} of the second subsection. That is, [D _2K-1 > D _2K ]. _{Similarly, the diameter (D 2K+1} ) of the first subsection included in the (K+1)th optical fiber section is greater than the diameter (D _{2K+2 ) of the second subsection.} That is, [D _2K+1 > D _2K+2 ].

In the above-described example, the diameters D ₁ , D ₃ , D ₅ , and D _{7 of} the first subsection are each 120 μm, and the diameters of the second subsection D ₂ , D ₄ , D ₆ , D ₈ ) are respectively If it is 95um, 90um, 95um, or 90um, this condition is satisfied.

The rougher the surface of the optical fiber, the more back-scattering of light occurs on the surface. The smaller the diameter of the subsection, the more likely the surface will be rough when fabricated using the etching method, and thus more backscattering may occur. The effect of backscattering was reduced by making the diameter of the second subsection in the first optical fiber section larger than the diameter of the second subsection of the second optical fiber section. That is, if backscattering occurs in the first optical fiber section, it may cause a loss in the laser system, so the second subsection D2 having a relatively large diameter is disposed in the first optical fiber section.

(4) the relationship between the length of the first subsection and the length of the second subsection

_{The length (L 2K-1} ) of the first subsection included in the Kth optical fiber section is smaller than the length (L _{2K) of the second subsection.} That is, [L _2K-1 < L _2K ]. _{Similarly, the length (L 2K+1} ) of the first subsection included in the (K+1)th optical fiber section is smaller than the length (L _{2K+2 ) of the second subsection.} That is, [L _2K+1 < L _2K+2 ].

The extra light is emitted through the second tapered connecting section 150 connecting the first and second subsections. In particular, by setting the diameter and length of the first subsection and the second subsection as described above and repeatedly arranging the second tapered connection section 150 , it is possible to efficiently emit excess light. As the light passes through the tapered connection section 150 , the number of total reflections of light increases, and at the same time, light of low NA is changed to light of high NA, which is relatively easy to be removed, so that light can be efficiently emitted.

The properties of the second tapered connecting section 150 are determined by the relationship between the diameter of the first subsection and the diameter of the second subsection. As the difference between the two diameters increases, the slope of the second tapered connection section 150 increases. As the slope increases, light of a smaller NA can be converted into light of a high NA that can be removed. When the inclination in the first optical fiber section is larger than the inclination in the second optical fiber section, the light not emitted by the first optical fiber section may be emitted in the second optical fiber section. In addition, arranging a relatively gentle slope in the first optical fiber section can prevent light from being emitted all at once, thereby eliminating light evenly throughout the optical fiber.

Hereinafter, a first embodiment and a second embodiment according to the present invention will be described in detail with reference to FIGS. 3 and 4 .

3 is a cross-sectional view schematically showing a first embodiment of an optical fiber device for removing cladding light according to the present invention, where N=4 in the optical fiber device for removing cladding light shown in FIG. This case includes one subsection and one second subsection.

Referring to FIG. 3 , the optical fiber device 1100 for removing cladding light according to the first embodiment of the present invention includes first to fourth optical fiber sections and three first tapered connection sections 250 .

Each of the first to fourth optical fiber sections includes a first subsection and a second subsection sequentially connected along a direction in which light travels, and a second tapered connection section connecting the first subsection and the second subsection ( 150).

According to (1) to (4) described above, the diameters (D ₁ , D ₃ , D ₅ , D ₇ ) and lengths (L ₁ , L _{3 ) of the first subsections of the first to fourth optical fiber sections} L ₅ , L ₇ ) and the diameter (D ₂ , D ₄ , D ₆ , D ₈ ) and length (L ₂ , L ₄ , L ₆ , L ₈ ) of the second subsection are [L ₁ > L ₃ > L ₅ > L ₆ ], [L ₂ > L ₄ > L ₆ > L ₈ ], [L ₁ < L ₂ ], [L ₃ < L ₄ ], [L ₅ < L ₆ ], [L ₇ < L _{8 ]} ], [D ₁ = D ₃ = D ₅ = D ₇ ] and [D ₂ = D ₆ > D ₄ = D ₈ ] are satisfied.

That is, the diameters of the first subsection (D ₁ , D ₃ , D ₅ , D ₇ ) are constant and the diameters of the second subsection (D ₂ , D ₄ , D ₆ , D ₈ ) are Repeat the cow ([D ₂ = D ₆ > D ₄ = D ₈ ]). Also, the lengths L ₁ , L ₃ , L ₅ , and L ₇ of the first subsection and the lengths L ₂ , L ₄ , L ₆ , and L ₈ of the second subsection gradually decrease. The length of the second subsection of each fiber section is longer than the length of the first subsection ([L ₁ < L ₂ ], [L ₃ < L ₄ ], [L ₅ < L ₆ ], [L ₇ < L _{8 ]} ]).

4 is a cross-sectional view schematically showing a second embodiment of an optical fiber device for removing cladding light according to the present invention, where N=4 in the optical fiber device for removing cladding light shown in FIG. This case includes one subsection and two second subsections.

Referring to FIG. 4 , the optical fiber device 1200 for removing cladding light according to the second embodiment of the present invention includes first to fourth optical fiber sections and three first tapered connection sections 250 .

Each of the first to fourth optical fiber sections includes two first subsections and two second subsections alternately connected along a direction in which light travels, and a second subsection connecting the first and second subsections. two tapered connecting sections 150 .

According to (1) to (4) described above, the diameters (D ₁ , D ₃ , D ₅ , D ₇ ) and lengths (L ₁ , L _{3 ) of the first subsections of the first to fourth optical fiber sections} L ₅ , L ₇ ) and the diameter (D ₂ , D ₄ , D ₆ , D ₈ ) and length (L ₂ , L ₄ , L ₆ , L ₈ ) of the second subsection are [L ₁ > L ₃ > L ₅ > L ₆ ], [L ₂ > L ₄ > L ₆ > L ₈ ], [L ₁ < L ₂ ], [L ₃ < L ₄ ], [L ₅ < L ₆ ], [L ₇ < L _{8 ]} ], [D ₁ = D ₃ = D ₅ = D ₇ ] and [D ₂ = D ₆ > D ₄ = D ₈ ] are satisfied.

That is, the diameters of the first subsection (D ₁ , D ₃ , D ₅ , D ₇ ) are constant and the diameters of the second subsection (D ₂ , D ₄ , D ₆ , D ₈ ) are Repeat the cow ([D ₂ = D ₆ > D ₄ = D ₈ ]). Also, the lengths L ₁ , L ₃ , L ₅ , and L ₇ of the first subsection and the lengths L ₂ , L ₄ , L ₆ , and L ₈ of the second subsection gradually decrease. The length of the second subsection of each fiber section is longer than the length of the first subsection ([L ₁ < L ₂ ], [L ₃ < L ₄ ], [L ₅ < L ₆ ], [L ₇ < L _{8 ]} ]).

1000, 1100, 1200: Optical fiber device for cladding light removal
150: second tapered connection section 250: first tapered connection section

Claims (5)

a first optical fiber section to an Nth optical fiber section sequentially connected along a direction in which light travels; and
A first tapered connection section connecting any two adjacent ones of the first optical fiber section to the Nth optical fiber section
including,
Each of the first to Nth optical fiber sections is
first and second subsections alternately connected along a direction in which the light travels; and
at least one second tapered connecting section connecting the first subsection and the second subsection
includes,
_{A diameter (D 2K-1} ) and a length (L _2K-1 ) and a diameter of the second subsection included in a Kth optical fiber section that is any one of the first to Nth optical fiber sections (D _2K ) and length (L _{2K ), diameter (D 2K+1} ) and length (L _2K+1 ) of the first subsection included in the (K+1)th optical fiber section adjacent to the Kth optical fiber section and the diameter (D _2K+2 ) and length (L _2K+2 ) of the second subsection are [D _2K-1 > D _2K ] and [D _2K+1 > D _2K+2 ], [L _2K-1 > L _2K+1 ], [L _2K > L _2K+2 ] and [D _2K-1 = D _2K+1 ],
When K is odd, [D _2K > D _2K+2 ] is satisfied, and when K is even, [D _2K < D _2K+2 ] is satisfied. K is a natural number of 1 or more (N-1) or less). According to claim 1,
An optical fiber device for removing cladding light, characterized in that it satisfies [L _2K-1 < L _{2K] for any K.} 3. The method of claim 2,
An optical fiber device for removing cladding light, characterized in that it satisfies [L _2K+1 < L _{2K+2] for any K.} According to claim 1,
first to fourth optical fiber sections and three first tapered connecting sections;
Each of the first to fourth optical fiber sections is
a first subsection and a second subsection sequentially connected in a direction in which the light travels; and
a second tapered connecting section connecting the first subsection and the second subsection
includes,
_{The diameter (D 1} , D ₃ , D ₅ , D ₇ ) and length (L ₁ , L ₃ , L ₅ , L ₇ ) of the first subsection of the first to fourth optical fiber sections and the second subsection The diameter (D ₂ , D ₄ , D ₆ , D ₈ ) and length (L ₂ , L ₄ , L ₆ , L ₈ ) of [L ₁ > L ₃ > L ₅ > L ₆ ], [L ₂ > L ₄ > L ₆ > L ₈ ], [L ₁ < L ₂ ], [L ₃ < L ₄ ], [L ₅ < L ₆ ], [L ₇ < L ₈ ], [D ₁ = D ₃ = D ₅ = D ₇ ] and [D ₂ = D ₆ > D ₄ = D ₈ ] An optical fiber device for removing cladding light, characterized in that it satisfies. According to claim 1,
first to fourth optical fiber sections and three first tapered connecting sections;
Each of the first to fourth optical fiber sections is
two first subsections and two second subsections connected in the order of a first subsection, a second subsection, a first subsection and a second subsection along a direction in which the light travels; and
three second tapered connecting sections connecting the first subsection and the second subsection
includes,
_{The diameter (D 1} , D ₃ , D ₅ , D ₇ ) and length (L ₁ , L ₃ , L ₅ , L ₇ ) of the first subsection of the first to fourth optical fiber sections and the second subsection The diameter (D ₂ , D ₄ , D ₆ , D ₈ ) and length (L ₂ , L ₄ , L ₆ , L ₈ ) of [L ₁ > L ₃ > L ₅ > L ₆ ], [L ₂ > L ₄ > L ₆ > L ₈ ], [L ₁ < L ₂ ], [L ₃ < L ₄ ], [L ₅ < L ₆ ], [L ₇ < L ₈ ], [D ₁ = D ₃ = D ₅ = D ₇ ] and [D ₂ = D ₆ > D ₄ = D ₈ ] An optical fiber device for removing cladding light, characterized in that it satisfies.

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