DE2360951A1 - Coupling between optical fibre and terminal device - with max signal utilization in multi-mode operation - Google Patents

Abstract

The coupling is for information transmission systems with an optical fibre coupled to a terminal device having a larger aperture angle than the fibre. A self-focusing gradient fibre portion is located between the optical fibre and the terminal device. The length X of this portion satisfies the expression 0.5xopt X 1.5x opt where xopt is the optimum length determined from the refractive index gradient of the gradient fibre, the radius of the optical fibre core and the aperture angle of the optical fibre. A preferred use is to couple a multi-mode optical fibre to a luminescence diode.

Description

Coupling device for an optical communication transmission system "\,

The invention relates to a contactless coupling device in optical communication systems between a glass fiber with a first aperture angle and a terminal with different aperture angles from the first aperture angle.

With optical communication over many kilometers by means of optical fibers, these must be connected to optical transmitters, possibly intermediate amplifiers and optical receivers in in some cases can be coupled without contact. TJm a high one To obtain coupling efficiency, the signals emitted by the transmitters must be as completely as possible into the optical fiber and as completely as possible into the optical fiber at its end Receiver are coupled. In addition, there are space-consuming imaging systems with cumbersome assembly and adjustment work necessary.

One way out is offered in Appl. Phys. Vol. 44, 6, 1975, p 2756 to 2758 described core sheath fiber with spherically curved End faces. The resulting lens effect increases the aperture angle of the fiber.

The manufacturing process of an optically flawless, spherically curved end face on a glass fiber is, however, very complex. _: ·.

The lens effect of gradient fibers is also known. These are approximately parabolic radially outwards Refractive index gradient in such a way that there is a to be conducted

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Wave energy in them in periodic around the axis of the Fibers oscillating paths spreads out, as a beam directed obliquely to the axis from the optically thin to the optically denser area is steered into it. 'T.

From the DOS 2 12? 916 is known to be this self-focusing Use gradient fibers in optical communication. By a given gradient of the refractive index such aperture angles are possible that Mchtsigaale with can be coupled with end devices with greater effectiveness.

A disadvantage of these fibers, however, is their high level of absorption. Just one ppm of contaminants, like Iron ions as well as copper and chromium ions cause attenuations in the wavelength range between 400 and 1000 nm 20 dB / km. Added to this is the difficulty of producing the parabolic refractive index profile as a prerequisite for a transmission mechanics of the fiber.

As a result of the higher costs involved in production the fibers in message transmission mostly in device construction, data processing and the like, but not used in the transmission of messages over many kilometers. Instead, core sheath fibers are in discussion.

The object of the invention is to provide a low-attenuation, optical Signal transmission over many Kir-lometer with as complete as possible To enable signal utilization when coupling between core sheath fibers and end devices. The expense should be low.

According to the invention, this object is achieved by a self-fo

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Kissing gradient fiber section, the length χ of which _{satisfies the inequality 0.5 x opt} <x < ¹ »5 ^x _opt , where x _{opt is} the optimal length of the gradient fiber section, which is derived from the refractive index gradient a of the gradient fiber, the radius y of the core of the core cladding fiber and the aperture angle λ). _{λ of} the core sheath fiber is determined by:

where a is the refractive index gradient of the gradient fiber and y _{Q is} the radius of the core of the core cladding fiber.

The gradient fiber section is attached to an end face of the core cladding fiber directly or via an immersion layer.

The optimal length x _Q _. can be obtained for given components from the data of the core cladding fiber and the gradient fiber section. The following relationship was calculated between the aperture angle a ^ of a gradient fiber section attached to a core cladding fiber, the angle of incidence Vl _{1 of} a light beam on the light exit surface of the gradient fiber section, the refractive index n. At this location of the gradient fiber section and the refractive index η ■ in the outer space

- «,. \ n-ft, «-xy.
The angle \ contained therein is obtained from the relationship

where v _a - means the angle of incidence of the light beam into the gradient fiber section from the core cladding fiber. _;

This angle ^ is finally obtained directly from the data of the gradient fiber section, namely from the above

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Refractive index η-, the gradient number a and from the data of the core clad fiber, namely from the refractive index of the core n, the refractive index of the clad n _m and the core radius J ₀ according to the relationship

4th ^κ ι - ¹ V,

When using a light emitting diode Light signals with better efficiency in a multimodal Coupling in the core sheath fiber, since the aperture of the fiber line can be expanded by an order of magnitude.

The invention is based on the following exemplary embodiments explained in more detail in the description of the figures.

Figure 1 shows a coupling device with components with the same diameter,

Figure 2 the same with different diameters.

Figure 1 shows an optical fiber with a core 1, a coat 2, aa? Gradient fiber 3 with an approximately parabolic refractive index profile and the cross section of the Light exit surface 4 of a luminescent diode. The light emitting diode is at a short distance from the gradient fiber piece 3 arranged. The luminescent diode has the directional characteristic 5. In direction 6 there is a small, in directions 7 and 8 ^ a high proportion of the intensity of the emitted light. Because of the low intensity components of the emitted light can be dispensed with in the direction and these light components under one If the very large aperture angle of the fiber would enter this and would be radiated outwards, an immediate attachment is required the gradient fiber with its sensitive end face

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on the light emitting diode is not an advantage. ¹ A light beam hitting the gradient fiber section at the angle - ^ is crawled into the gradient fiber section at the interface 9 at the angle and continues along a sinusoidal path along a path of optimal length so that it strikes the interface at _{the angle -§ "& 1} and is broken into the core sheath fiber at the angle &'*.

Given the given data for the core cladding fiber and the gradient fiber section, its length x _Q + is optimized in such a way that all beam directions emitted by the luminescent diode and recorded by the fiber lie in the directional range after the sinusoidal course of the rays within the gradient fiber section when entering the core cladding fiber, in which light rays are conducted without loss. The length x _QX) ^ must neither be too large nor too small, since otherwise the aperture angle of the arrangement will be small. In a gradient fiber, a light beam has a sinusoidal course that oscillates along the optical axis 11.

In Figure 2, an optical fiber 12 is shown which into a gradient fiber section 13 with a larger diameter than that of the Liahtleitfaser is attached. Through this an optically direct and mechanically firm connection between the core cladding fiber 1.2 and the gradient fiber section 13 is ensured; . ,,;

In the following, a refraction example is used to show how much the aperture angle of a core cladding fiber increases when a segment of a gradient fiber is inserted: The aperture of a core fiber is n ^^ y ^ ^ _a =. I ^ .- * - vfj .

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where η = refractive index in the outer space, n ,. = Refractive index of the core and η = refractive index of the cladding. For one fiber with n = 1.5422 and η = 1.54H with η = 1, the value V _a1 = 2.85 results. If one places a gradient fiber section with the refractive index gradient a = J3ÖÖ ¹ mm ~ and a refractive index n ₁ = 1.542 at position 9 in front of this core _{sheath fiber with a core radius y Q} = 0.035 mm, then the calculation results in an optimal length of the gradient fiber section x ". =

α / η ^Ο Φ ^τ

5.072 mm. The aperture angle · o7 = 53 11 '18' ''. This is the 18.68 times the aperture angle of the core fiber of 2.85 °.

2 figures

3 claims

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Claims (3)

- -, - .- .. "-, ■■ ..-: -." 236P95T ~ ^r ~ "■ -". '. ■■ ' ^% . ■. "■" ■ "■, - ■■ ■■:' .: ■ Claims Coupling device in optical communication transmission ring systems between a core cladding fiber and a terminal which has a larger: aperture angle than the glass fiber, geke η η ζ eich η et; by a self-focussing gradient fiber part arranged between the core cladding fiber and the terminal device ^ whose length χ the inequality 0.5x _ ^. - ~ x ^ ^ »5 ^x ₀ -pt is sufficient, where χ _οό ^ the optimal length of the gradient fiber part, which is derived from the refractive index gradient a of the gradient fiber, the radius j _{Q of} the core of the core cladding fiber and the aperture angle -v" ^ the core sheath fiber determined to: TT i f "t .r- CUtt-fft-vt- 2. A coupling device according to claim 1, characterized ζ marked in e ic II-II et that a Gradientenfaserteilstück is placed on the to be coupled brews of the sheath-core fiber. 3. Coupling device according to claim 1 and 2, ge characterizes net by its use for coupling a light emitting diode with a multimodal core cladding fiber ^: i TBk 9/710/3144 50 9 82 4/0473 Blank page