JP2003307632A - Photonic crystal optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photonic crystal optical fiber durable against bending from the viewpoint of transmission loss, strength and reliability and usable for connecting parts of conventional optical fibers. <P>SOLUTION: Tensile strain due to bending can be decreased by using quartz for the core 3 and a clad 2 and by making the outer diameter of the clad 2 smaller than the outer diameter (125 μm) of a standard optical fiber. For example, by controlling the outer diameter of the clad 2 comprising quartz to 60 μm, the tensile strain is 0.002 even when the bending radius is decreased as small as 15 mm, which suppresses the strain to an almost equal level to that of conventional optical fibers. By forming resin coating layers 5 to 7 around the clad 2 to make the outer diameter of 125 μm, connecting parts such as connectors and mechanical splice for conventional optical fibers can be used. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a photonic crystal optical fiber.

[0002]

2. Description of the Related Art A conventional optical fiber has a two-layer structure including a core and a clad which covers the core and has a refractive index lower than that of the core. The material of the core and the clad is based on quartz, and the core has a composition in which an additive such as germanium is added to the quartz in order to make the refractive index higher than that of the clad.

In this type of optical fiber, the refractive index of the core of the optical fiber is higher than that of the cladding,
Due to this refractive index difference, the light incident on the optical fiber can be confined in the core and propagate in the optical fiber. When light propagates in an optical fiber, in order to satisfy the single mode condition of the propagating light, the diameter of the core should be 5 μm.
It is necessary to set the thickness to about 10 μm.

However, in recent years, due to the development of optical amplification technology and wavelength division multiplexing (WDM) technology, the power of light incident on an optical fiber has increased, and various nonlinear effect phenomena are likely to occur. For example, when the self-phase modulation phenomenon, which is one of the nonlinear effect phenomena, occurs, the pulse signal waveform propagating in the optical fiber is distorted and the transmission capacity is limited. In addition, the Brillouin scattering phenomenon, which is one of the same non-linear phenomena, is likely to occur. When this Brillouin scattering phenomenon occurs, the incident power of the optical fiber is saturated.

When such a non-linear effect phenomenon occurs, the transmission characteristics propagating in the optical fiber are deteriorated.
Further, the transmission loss of the current optical fiber is about 0.16 dB / km even at the best, and the main factor is the Rayleigh scattering loss due to the fluctuation of the composition density in the vicinity of the core where the light propagates and the clad core. Further reduction of loss is desired for optical fibers used for long-distance transmission between continents.

By the way, as an optical fiber that solves the above-mentioned problems of the optical fiber, a photonic crystal optical fiber (PCF: Photonic Crystal) is used.
Fiber), which is attracting attention. This PCF
Is an optical fiber having a photonic crystal structure formed in the cladding. The photonic crystal structure is a periodic structure with a refractive index, and specifically, a space having a honeycomb structure such as a honeycomb is formed in a clad. With such a honeycomb structure, a photonic band gap (PBG: Photonic) which is a light forbidden band is formed.
Band Gap) occurs. For example, Knight
Et al. Science 282, 1476, (1998)
Reported a PBF structure using PCG as a guiding principle.

[0007] Also, Cregan et al.
285, 1573, (1999) reported a hollow core PCF having a PCG structure as a guiding principle.
Since the hollow core PCF has no quartz medium in the core through which light propagates, it shows the possibility of an ultra-low-loss optical fiber in which Rayleigh scattering, which is the main cause of loss, becomes extremely small.

Furthermore, Japanese Patent No. 3072842 discloses a PCF having a hollow core.
It is described that a low loss of about 01 dB / km can be expected.

However, in order to propagate light in these PCFs, it is necessary to construct a precise PBG structure. Therefore, if there is a slight structural fluctuation, the light propagation condition cannot be maintained, and so-called structure. Generate fraudulent losses.

Recently, although it is not an optical fiber having a perfect PBG structure, pores are formed in the vicinity of the core of the optical fiber having a relative refractive index difference due to the difference in the conventional glass composition to form an effective refractive index of the clad. Lower the core /
It has been reported that by expanding the relative refractive index difference between the clads, an optical fiber having characteristics that could not be obtained conventionally. For example, Hasegawa et al. Is a hole-added holey optical fiber in which four holes are formed in the vicinity of the core of the cladding of an optical fiber having a normal single-mode optical fiber structure in OFC2001PD-1, and between the core and the cladding. We have reported that by expanding the effective relative refractive index difference, we have realized an optical fiber with zero dispersion and single mode operation in the 0.8 μm wavelength band.

As described above, the photonic crystal optical fiber has various possibilities because it can increase the effective refractive index as compared with the conventional optical fiber, but it can reduce the bending loss. One feature is that loss increase can be suppressed even with a small bending radius.

The inventors of the present invention prototyped a photonic crystal optical fiber having four pores formed in the vicinity of the core and obtained a very good result of a loss of 0.01 dB when wound around a mandrel having a diameter of 15 mm for 1 m. There is.

Here, FTTH (Fiber To T
(He Home) is considered to be the ultimate form of broadband, and is becoming popular. The number of optical fibers installed in homes such as existing houses will also increase, but because optical fibers have a limited bending diameter unlike copper wires, installation is more difficult than installation of copper wires, There are problems in use, such as having to use special parts that limit bending. In such a case, if the photonic crystal optical fiber described above is used, it is considered that there is no deterioration in transmission loss, the bending radius can be reduced, special components are not required, and installation is easy.

[0014]

By the way, in the conventional silica-based optical fiber, when the bending diameter is reduced, tensile strain occurs on the glass surface which is outside the curved portion. Therefore, it is known that static fatigue fracture occurs when left for a long period of time. Generally, considering the use for about 25 years, it is necessary to maintain the bending radius at 30 mm or more. in this case,
Since the glass diameter of the silica-based optical fiber is Φ125 μm, the strain is 0.002 or less.

Since the photonic crystal optical fiber is also made of quartz, the deterioration of transmission loss due to bending can be suppressed, but the problem of static fatigue remains.

Therefore, an object of the present invention is to solve the above problems and provide a photonic crystal optical fiber which is resistant to bending in terms of transmission loss, strength, and reliability and which can be used as a conventional connecting component for optical fibers. To do.

[0017]

In order to achieve the above object, the invention according to claim 1 is to provide a large number of holes in the clad in order to expand the effective relative refractive index difference between the core and the clad. In the photonic crystal optical fiber that we have,
Only the core and the clad are made of quartz, and the outer diameter of the portion made of quartz is smaller than 125 μm.

According to a second aspect of the present invention, in addition to the structure of the first aspect, the coating layer that covers the outer periphery of the clad is composed of two or more resin coating layers, and the innermost layer is harder than the second coating layer. It is preferable that the outer diameter is 125 μm and the resin is large.

According to the present invention, quartz is used for the core and the clad, and the outer diameter of the clad is set to the outer diameter (12) of the standard optical fiber.
By making it smaller than 5 μm, the tensile strain due to bending can be reduced. For example, by setting the outer diameter of the clad to be 60 μm, the bending radius is 15 mm.
Even if it is made smaller, the tensile strain becomes 0.002, and it is possible to suppress the strain to the same level as that of the conventional optical fiber, that is, the standard optical fiber.

On the other hand, if the optical fibers are made thin, the connection between the optical fibers becomes a problem. When it is used as wiring at home, it is important that it can be implemented at low cost with simple connections such as connectors and mechanical splices.
All of these connecting parts are intended for a standard optical fiber having an outer diameter of 125 μm, and if these connecting parts are manufactured for a small diameter, they will be expensive. Therefore,
By forming a resin coating layer having an outer diameter of 125 μm on the outer circumference of the clad, a conventional connector for optical fiber or a connecting component such as a mechanical splice can be used.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an embodiment of the photonic crystal optical fiber of the present invention.

In the photonic crystal optical fiber 1 shown in the figure, a large number of holes 4 (only four are shown in the figure, but not limited to them) are formed in the vicinity of the core 3 of the clad 2. Thus, a photonic crystal optical fiber in which the effective relative refractive index difference between the core 3 and the clad 2 is expanded, and only the clad 2 and the core 3 are made of quartz, and the outer diameter of the clad 2 is a standard optical fiber. It is smaller than the outer diameter (125 μm) of the fiber. In addition, two or more (three layers in the figure, but not limited to) resin coating layers 5, 6, and 7 are formed on the outer periphery of the clad 2, and the innermost layer 5 of the resin coating layers 5 to 7 is the second coating. It is made of a resin having a hardness higher than that of the layer 6, and the outermost layer 7 is smaller than the outer diameter of the standard optical fiber.

As described above, quartz is used for the core 3 and the clad 2, and the outer diameter of the clad 2 is set to the outer diameter (1) of the standard optical fiber.
By making it smaller than 25 μm), tensile strain due to bending can be reduced. Also, clad 2
Since the hard resin coating layers 5 to 7 having an outer diameter of 125 μm are formed on the outer circumference of the above, the conventional connecting parts such as the connector for the optical fiber and the mechanical splice can be used as they are.

[0025]

EXAMPLES The following are specific numerical values, but the present invention is not limited thereto.

When the photonic crystal optical fiber 1 was manufactured with the outer diameter of the clad 2 being 60 μm, the tensile strain was 0.002 at a bending radius of 15 mm, which was the same as the conventional one, and static fatigue has no practical problem. Also, the loss is 0.0
Low loss of 1 dB or less.

Further, the first, second and third coating layers 5 to 7 are coated with an ultraviolet curable resin. The Young's moduli of the second and third coating layers 6 and 7 are set to 1 Mpa and 800 Mpa, respectively.
The Young's modulus of the coating layer 5 is sufficiently larger than the Young's modulus of the second and third coating layers 6 and 7.

As described above, according to the present invention, it is possible to obtain an optical fiber having good transmission loss, strength and reliability even if it is bent with a small diameter. In addition, the connection can be made inexpensively using the conventional optical fiber connecting component. Furthermore, by manufacturing an optical cord using the present optical fiber, wiring in a house is easy and inexpensive.

[0029]

In summary, according to the present invention, it is possible to provide a photonic crystal optical fiber which is resistant to bending in terms of transmission loss, strength and reliability and which can be used as a conventional connecting component for optical fibers. You can

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a photonic crystal optical fiber of the present invention.

[Explanation of symbols]

1 Photonic crystal optical fiber 2 clad 3 core 4 holes 5 Resin coating layer (first coating layer) 6 Resin coating layer (second coating layer) 7 Resin coating layer (third coating layer)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuya Murakami             1-6-1, Otemachi, Chiyoda-ku, Tokyo             Standing Wire Co., Ltd. F-term (reference) 2H050 AC62 BA32 BB33 BC04                 4G060 AA01 AC02

Claims (2)

[Claims] 1. In a photonic crystal optical fiber having a large number of holes in the clad for expanding an effective relative refractive index difference between the core and the clad, only the core and the clad are made of quartz, A photonic crystal optical fiber, wherein the outer diameter of the quartz portion is smaller than 125 μm. 2. The coating layer covering the outer periphery of the clad is made of two or more resin coating layers, the innermost layer is made of a resin having a hardness higher than that of the second coating layer, and the outer diameter is 125 μm.
The photonic crystal optical fiber according to claim 1, wherein m is m.