JPH04317013A - Optical fiber coupler - Google Patents

Abstract

PURPOSE:To make an intercepting area wider and to easily produce a coupler by heating and drawing the middle part of an optical fiber. CONSTITUTION:In an optical fiber coupler consisting of a coupling part which is constituted by making the middle parts 6 of the optical fibers 4 and 5 having a core and a clad tightly contact and heating and drawing them, at least one of plural optical fibers has two or more cores 9 and 9' in a single clad 8. Then, one core 9 out of the plural cores 9 and 9' in the single clad 8 exists in the center of the clad 6. In this optical fiber coupler, light made incident on one core 4-1 is firstly transmitted to the core 5-1' while it passes through the coupling part, and transmitted to the core 5-1 while it advances further. In the case that coupling still continues, the light returns to the core 5-1' from the core 5-1 again. Therefore, the intercepting area is made wider by causing the coupling among three or more cores.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coupler used in optical fiber communications and optical fiber sensors.

0002

2. Description of the Related Art The structure of a conventional optical fiber coupler is shown in FIG. Reference numeral 1 indicates a first optical fiber, and reference numeral 2 indicates a second optical fiber. After removing the coating at the intermediate portion of the optical fibers 1 and 2, the optical fibers 1 and 2 are brought into close contact with each other and heated and stretched to form a joint portion 3. A, B
are the input end and output end of the first optical fiber, C,
D is an input end and an output end of the second optical fiber, respectively. FIG. 6 is a sectional view taken along the line aa' of the joint 3 in FIG.
2-1 are the cores of the first and second optical fibers, 2-1,
2-2 are claddings of the first and second optical fibers, respectively.

The coupling coefficient of the coupling section 3 at the wavelength input is C(
If the length of the coupling part 3 is L, then the optical power transfer coefficient T1 (input) from the input end A to the output end B of the first optical fiber is
And the optical power transfer coefficient T2 (input) to the second optical fiber is expressed by the following equation. T1 (in) = -10 log [ co
s C (in)・L ]2...(1) T2
(in) = -10 log [ sim C (in)・L
]2...(2) FIG. 7 shows optical power transfer coefficients T1 and T2 for C (on) and L.

From equations (1) and (2), C (in)・L=n
When π (n is a positive integer), T1=0(dB), T2=∞(dB),

[0005]

[Math 1]

Therefore, by selecting C (input) and L to a predetermined value, for example by setting the spacing between cores 1-1 and 2-1 or the value of the coupling length L, it is possible to connect the first optical fiber to the second optical fiber. An optical fiber coupler can be formed that transmits all the light to the optical fiber.

[0007]

[Problems to be solved by the invention] In the conventional optical fiber coupler, the transmission range is the region where T1, T2≦0.5 (dB): △in 0.5, T1, T2≧25 (dB) The cutoff area is △input 25, and T1 and T2 are from 0 to ∞
If the area that changes to △0-∞ is △in0.5/△0-∞=0.428...(3) △in2
5/Δ0−∞=0.072 (4).

[0008] Conventional optical fiber couplers have a narrow cutoff range, so in order to create a coupler with a predetermined cutoff value, manufacturing conditions such as the length of the optical fiber, fusion, and heating must be controlled with high precision. I needed to. Here, if sufficient performance could not be obtained, a separate cutoff filter was used.

[0009]

[Means for Solving the Problems] The present invention solves the above problems by widening the cut-off range of an optical fiber coupler, and FIG. 1 shows an example thereof. 4 is a first optical fiber;
5 is a second optical fiber, and after removing the coating at the intermediate portion of the optical fibers 4 and 5, the optical fibers 4 and 5 are brought into close contact with each other and heated and stretched.
E and F forming the coupling part 6 are the input end and output end of the first optical fiber 4, respectively, and G and H are the input end and output end of the second optical fiber 5, respectively.

FIG. 2 is a 6-6' sectional view of the coupling part 6 in FIG. The core of the second optical fiber, 5-2, is the cladding of the second optical fiber.

More specifically, the structure of the present invention is shown in FIGS. 1 to 3. A plurality of optical fibers 4 and 5 having a core and a cladding are brought into close contact with an intermediate portion 6 of the optical fibers, and this is heated and stretched. The optical fiber coupler is characterized in that at least one of the plurality of optical fibers has two or more cores 9, 9' in a single cladding 8. Yes, one core 9 of a plurality of cores 9, 9' in a single cladding 8
is composed of an optical fiber located at the center of the cladding 8.

0012

[Operation] In the optical fiber coupler of the present invention shown in FIGS. 1 and 2, the light incident on one core 4-1 is first transmitted to the core 5-1' while passing through the coupling part, and when further traveling, the light is transmitted to the core 5-1'. 5
-1. If the bonding continues, the core 5-1 returns to the core 5-1' again. Therefore, the present invention attempts to widen the cutoff range by causing bonding between three or more cores.

In a waveguide in which the three cores 4-1, 5-1', and 5-1 have the same core diameter and refractive index, and the core spacing is the same, the optical power transfer coefficient T from the input end E to the output end F is
3 (input) and the optical power transfer coefficient T4 (input) of the output end H to the core 5-1 is expressed by Equation 1 and Equation 2. However, C' (in) is between core 4-1 and core 5-1' and between core 5-1' and core 5.
-1 is the coupling coefficient.

[0014]

[Math 2]

[0015]

[Math 3]

[0016] Here, when determining the cutoff region and the transmission region, they are respectively △
'Enter 25 /△'0-∞=0.304...(7)△'
Input 0.5/Δ'0-∞=0.304 (8), and it can be seen that the cutoff area (7) is significantly expanded compared to (4). If the number of cores is further increased using the same method, the cutoff band becomes wider than the transmission band, which becomes the characteristic of a bandpass filter.

[0017]

[Example] A SiO2 glass rod was produced by the VAD method, holes were made at the center and periphery of the circular cross section, a GeO2-doped SiO2 glass rod was introduced, and this was heated and drawn to form the cladding shown in Figure 3. 2 cores 9 in 8
, 9' was fabricated. On the other hand, an optical fiber having the core 10 only at the center of the cladding 7 shown in FIG. 4 was produced in a similar manner. In each case, the refractive index difference between the core and the cladding was 0.32%, the core diameter was 10 μmφ, and the cladding diameter was 125 μmφ. As shown in FIG. 4, these two optical fibers are connected to three cores 4-1, 5-1'5-
The optical fiber couplers shown in FIGS. 1 and 2 were obtained by observing and setting the optical fibers under a microscope so that the fibers 1 were lined up on the same line, and then fused and drawn.

[0018] An ordinary optical fiber having one core is fused to both ends of the two-core optical fiber, and light can enter only the central core of the two cores. Only the emitted light can be measured. Output ends F and H for the input from the E end of the obtained optical fiber coupler
When we measured the optical power transfer coefficient to and found the cut-off region and transmission region, we found that △′-included 25/△′0-∞: 0.32 △′-included 0.5/△′0-∞: 0.30 Met.

[0019]

[Effects of the Invention] The structure of the present invention enables an optical fiber coupler with a wide cutoff range.

[Brief explanation of drawings]

[Fig. 1] Configuration diagram of one embodiment of the present invention

[Figure 2] Cross-sectional view of the joint in Figure 1

[Figure 3] Cross-sectional view of an optical fiber with two cores in a single cladding

[Figure 4] Diagram showing the relative positional relationship between optical fiber cores

[Figure 5] Configuration diagram of a conventional optical fiber coupler

[Figure 6] Cross-sectional view of the joint in Figure 5

[Figure 7] Characteristic diagram of conventional optical fiber coupler

[Explanation of symbols]

1: First optical fiber 1-1: Core 1-2: Clad 2: Second optical fiber 2-1: Core 2-2: Clad 3: Joint part 4: First optical fiber 4-1: Core 4-2: Clad 5: Second optical fiber 5-1: Core 5-1': Core 5-2: Clad 6: Joint part 7: Clad 8: Clad 9: Core 9': Core 10: Core

Claims (2)

[Claims] 1. An optical fiber coupler comprising a plurality of optical fibers each having a core and a cladding, and a coupling portion formed by closely bonding the intermediate portions of the optical fibers and heating and stretching the fibers. An optical fiber coupler characterized in that at least one of the fibers has two or more cores in a single cladding. 2. The optical fiber coupler of claim 1, wherein one core of the plurality of cores within a single cladding is at the center of the cladding.