JPH049288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises at least three optical waveguides, the optical axes of which are located on the end face of at least one exit-side optical waveguide that is next to the transmitting optical waveguide in the direction of the light flux. An optical branching unit having a structure in which the optical waveguides are arranged such that they intersect at the points where the optical waveguides exist, and a reflective film is provided on the end face to partially reflect and partially transmit the light coming from the transmitting optical waveguide. Regarding.

Branching units of this type are, for example, HF Mahlein and all: interference filters as fibers, directional couplers, fours, WDMs, etc.
(Interference filter as fiber directional
coupler for WDM) [Electronic Letters 16, 1980, 584-589
page] and E. Miyanchi et all:
Compact Wavelength Multiplexer Using Optical Fiber
pieces (compact wavelength multiplexer)
using optical fiber pieces) [Oprics Letters 5 , 1980, 321~
322 pages].

In this type of device, the end face of the optical fiber section is such that the light is split from one fiber into several fibers by a partially transparent or wavelength-dependent mirror surface on the obliquely polished fiber surface. They are interconnected by as short a distance as possible to ensure that they can reach each other. In all of the above devices, index matching materials are used between the fiber ends. Since in all said devices a dielectric mirror coating is used in each case, it is difficult or impossible to weld the fiber ends and other optical components. A known simple index matching means is to fill the space between the fiber ends with a transparent plastic, such as an epoxy resin. This is just an experimental solution. However, it is questionable whether devices of this type have the long-term stability required for devices used in industry. This is because the light intensity normally present in fiber optics is extremely high. 50μ
For a graded fiber with a core diameter of m and a light power of 2 mw conducted in the core, an intensity of 100 W/cm ² is calculated. The intensity of this light is extremely high. The question therefore arises as to whether, in the case of constant irradiation with such high light intensities, organic adhesives (e.g. epoxy resins) will not succumb to aging processes, resulting in, for example, clouding or absorption of transparent adhesives. be done.

The basis of the invention is the problem of improving a light branching unit of this kind in such a way that it is possible to avoid refractive index adaptation and to obtain good long-term stability.

This problem is solved in the optical branching unit described at the beginning: (a) each end face of at least three optical waveguides forms a space containing no solid or liquid, and (b) the exit side optical waveguide has a reflective film. the optical axis is inclined with respect to the optical axis of the transmitting optical waveguide, and (c) an end face of the exit side optical waveguide having a reflective film comes from the transmitting optical waveguide, and light incident on this end face is , tilted at an angle γ with respect to the optical axis of the exit optical waveguide such that the light is coupled into the exit optical waveguide having a reflective film, and the light reflected from the reflective film is coupled into another exit optical waveguide. The problem is solved by a light branching unit characterized by the fact that

An advantageous embodiment according to the invention is obtained when the space is filled with air.

Advantageously, the reflective coating and/or the angle (γ) are formed in such a way that the incident light is polarized.

at least one space forming space and into which light is incident;
At least one photodetector may be arranged on one side.

According to the invention, the transmission optical waveguide is designed as an optical fiber with a core and a jacket or as a single-mode optical fiber. The at least two optical waveguides may be constructed in one optical component.

The membrane provided on at least one end face is preferably designed as a dichroic membrane, an optical fiber membrane or an edge filter.

At least one end face of the at least one optical waveguide may be fused to form an optical lens (FIG. 3). It is also advantageous if at least two optical waveguides are present, the ends of which are fused to form an optical lens, and an optical distance (s) existing between both lenses is provided via which It is chosen such that the transmitted light has a minimum coupling loss (FIG. 5).

Furthermore, the outer diameter of the at least one optical waveguide can be reduced to a value lying between the core diameter and the jacket diameter of the optical waveguide in the region of the end face, which may be designed as a lens. Figure 4).

The optical lens is generally spherically formed, and a lens so formed can have a lens radius equal to half the outer diameter of the optical waveguide (FIG. 3).

At least one end face, which may be designed as a lens, is preferably provided with an antireflection coating for the light used.

An advantage of the invention is that the optical branching unit can be used as a maintenance-free optical component.

The invention will now be explained in more detail with reference to illustrative embodiments.

The structure of the optical branching unit will be explained with reference to FIG. The light (arrow) entering the optical fiber having core 16 and jacket 17 should be split into optical fibers 20 and 30. End face 1 of optical fiber 10
3 exists at an angle of 90° with respect to the optical axis 11,
The light emitted from the optical fiber 10 into the space 40 is not refracted and travels further in the direction of the optical axis 11 to reach the optical film 2.
4. For example, incident on a dielectric half-mirror. A portion of this light is reflected below the reflection angle and coupled into the optical fiber 30. In the case of the illustrated embodiment, 3
The optical fibers 10 , 20 and 30 are arranged in such a way that their optical axes 11 , 21 , 31 have a common point 22 located on the optical axis membrane 24 . The other part of the light is refracted through an angle β=sin ⁻¹ (1/n _K sin α) and enters the optical fiber 20. Here, n _K is the effective refractive index of the core 26, and α is the angle of incidence and reflection of light. Furthermore, for the angle γ, γ=90°−β must apply.

The data used in the example is α = 45°; n _K =
1.46;β=sin ^-1 1/1.46sin 45゜=29゜;γ=90゜-
β=61°.

Also, regarding the angle of incidence α, other angles, preferably between 20 and 45°, can be selected instead of this angle.
β and γ corresponding to this are obtained.

Optical fiber 20 depending on the type of dielectric film 24
and the division of light into the optical fibers 30 is determined. A 1:1 split ratio or a different ratio can be selected depending on equipment requirements. It is also possible to select the division independently or wavelength-dependently with respect to the wavelengths involved. In the case of wavelength dependence, for example, the dielectric film 24 allows the light of wavelengths λ ₁ and λ ₂ to pass through the optical fiber 10, the light of wavelength λ ₁ being introduced into the optical fiber 20 with high coupling efficiency, and the light of wavelength λ Optical fiber 30 has a high coupling efficiency for light with ₂
It is designed to be implemented in Such a device takes advantage of the dichroic properties of membrane 24 and can be used, for example, in an optical demultiplexer.

The direction of the light beam can be at least partially reversed.
That is, for example, a structural part for so-called simultaneous transmitting and receiving operation (using two-way transmission) is important, and in this part, light having a wavelength λ ₁ entering the optical fiber 10 is not completely incident on the optical fiber 30, for example. On the other hand, the light of wavelength λ ₂ entering the optical fiber 20 (opposite the direction of the arrow) is incident as completely as possible into the optical fiber 10 (opposite the direction of the arrow). A structural part of this type allows intercommunication between two subscribers.

Another significant advantage of the design according to the invention over the solutions mentioned at the outset is that, besides the avoidance of adhesive materials, membranes 24 with more advantageous properties can be used. With known solutions, the angle α between the surface normal of the membrane 24 and the fiber axis 11 of the incoming light is
When using a lens, light enters the film 24 from the glass side (refractive index = 1.5). In contrast, in the branching unit according to the invention, the light enters the membrane 24 from the glass side at an angle β. It is known that the edge gradient (optical filter effect) of a dielectric light splitting film can be increased the smaller the deviation of the angle of incidence of light on the film from normal incidence in the wavelength range. In the case of deviations from normal incidence, different polarization directions of the light are reflected or transmitted with different reflectivities and different wavelength dependencies. Similarly, in the case of a diverging beam, the edge gradient becomes all the more the smaller the deviation of the angle of incidence from normal incidence increases. If the optical adhesive layer is abandoned, the angle β is important for the optical filter effect for the same angle α as in the known adhesive solutions. On the other hand, in the case of gluing, angle α is the decisive angle. If the angle α is reduced to 20°, for example, then the angle β=13.5°. In the case of such devices, light splitting membranes with pronounced edge gradients can be used, and the solution according to the invention therefore makes it possible to separate closely adjacent wavelengths.

All kinds of optical fibers can be used as optical fibers, for example single mode or multimode optical fibers with a stepped or graded index cross section.

The branching device according to the invention is susceptible to losses, since the light travels in the space 40 through a section of air without waveguides. In this region without a waveguide, the light beam spreads out due to diffraction and light divergence (multimode optical fiber), and part of the light is no longer coupled into the core of the fiber. To reduce this loss, the jacket of the fibers, preferably optical fibers 10 and 30, can be partially removed, for example by etching. Therefore, the optical path is shortened in the space without the waveguide, and the loss is reduced.

The fiber ends can be closed air-tight to protect the surface from damage or moisture adhesion.

3 and 4 show another embodiment, the method of operation of which will be explained in more detail with reference to FIG. FIG. 5 is an example of a graph showing the optical coupling loss V (dB) depending on the standardized distance s/d. According to the coupling arrangement shown in FIG. 5, s represents the distance (optical distance) between the two end faces of a coaxially arranged optical waveguide having a core and a jacket. Curves 51 and 52 are, for example, each approximately
It concerns a glass fiber optical waveguide with a jacket having an outer diameter of 130 μm and a core diameter d of approximately 50 μm. Curve 51 shows the coupling loss as a function of the distance s between the end faces of a plane with air as the coupling medium between them. According to the curve 51, the coupling loss V increases as the distance s (optical distance) increases. In the case of the coupling arrangement underlying curve 52, the end face of the optical waveguide is fused to form a spherical lens with a radius of curvature approximately equal to half the diameter of the envelope. Curve 52 shows a clear minimum value of the coupling loss V which lies approximately at the normalized distance s/d=2.4.

In the case of the optical branching unit according to FIG. 1, the optical distance between the plane end faces 13 and 33 is the standardized distance s/d.
=1.2 is not possible for structural reasons. According to FIG. 5, for said values curve 51 results in a coupling loss of approximately 0.9 dB. On the other hand, when the end face is melted to form a spherical lens, according to the curve 52, the standardized distance s/
It is advantageous to choose d=2.4, in which case the coupling loss is only 0.6 dB. This results in a doubled optical distance, which in the case of a branching unit constructed according to FIG. 3 considerably simplifies the mechanical construction and optical adjustment. Furthermore, axes 11 and 31
It is also possible to choose the angle 2α between Such an arrangement also has the advantage that the interference filters used operate more selectively, since in the case of interference filters it is advantageous to select the angle of incidence of the light as small as possible. .

Also, according to FIG. 4, the angle 2α is the lens 131
Further reductions can also be made by reducing the outer diameter of the optical waveguide jacket in the range . and 331, for example by etching.

Optical waveguides with fused lenses can likewise be used advantageously in the branching unit according to FIG.

In order to further reduce coupling losses, it is advantageous to cover the end faces and/or the lenses defining the space 40 with a so-called anti-reflection coating for the light used.

In another embodiment, not shown, the at least one optical fiber delimiting the space 40 is replaced by at least one photoelectric detector, for example a photodiode. Using such a device, it is possible, for example, to measure and/or adjust the intensity of the light coupled into the optical fiber.

[Brief explanation of drawings]

1 to 4 are cross-sectional views of the optical branching unit according to the present invention, and FIG. 5 is a graph showing the optical coupling loss V (dB) as a function of the standardized distance s/d. 10, 20, 30... optical waveguide, 11, 21,
31... Optical axis, 13, 23, 33... End surface, 22
... common point that optical axes have, 16, 26 ... core,
24... Dielectric film, 40... Space formed by end face, 131, 331... Lens.

Claims (1)

[Claims] 1. Consists of at least three optical waveguides, in that their optical axes are located above the end face of at least one exit-side optical waveguide that is next to the transmission optical waveguide in the direction of the light flux. In an optical branching unit having a structure in which the optical branching unit has a structure such that the optical waveguides intersect with each other, and a reflective film is provided on the end face to partially reflect and partially transmit the light coming from the transmitting optical waveguide, (a ) each end face of at least three optical waveguides forms a space containing no solid or liquid, and (b) the optical axis of the exit side optical waveguide having a reflective film is relative to the optical axis of the transmission optical waveguide. (c) an end face of the exit optical waveguide having a reflective film comes from the transmitting optical waveguide, and light incident on this end face is coupled into the exit optical waveguide having a reflective film; 1. An optical branching unit which is inclined at an angle γ with respect to its optical axis so that the optical branching unit is inclined at an angle γ with respect to the optical axis thereof, and the light reflected from the reflective film enters another optical waveguide on the exit side. 2. The unit according to claim 1, wherein the space is filled with air. 3. The unit according to claim 1 or 2, wherein the reflective film and/or the angle γ are formed so that the incident light is polarized. 4. The unit according to any one of claims 1 to 3, wherein one photoelectric detector is arranged on at least one surface forming the space and onto which light is incident. 5. The unit according to claim 1, wherein the optical waveguide is formed as an optical fiber having a core and a jacket. 6. A unit according to claim 5, wherein the optical waveguide is formed as a single mode optical fiber. 7. The unit according to claim 1, wherein the at least two optical waveguides are constructed in a single optical component. 8. The unit according to any one of claims 1 to 7, wherein the reflective film is formed as a dichroic film. 9. The unit according to claim 8, wherein the reflective film is formed as an optical filter film. 10. The unit according to claim 9, wherein the reflective film is formed as an edge filter film. 11. The unit according to any one of claims 1 to 10, wherein one end face of the optical waveguide is melted to form an optical lens. 12 At least two optical waveguides are present whose ends are fused to form an optical lens and an optical distance (s) existing between these lenses is transmitted through it. 12. A unit as claimed in claim 11, in which the light transmitted has a minimum coupling loss. 13. The outer diameter of at least one optical waveguide is reduced to a value lying between the core diameter and the jacket diameter of the optical waveguide in the region of the end face, which may be formed as an optical lens. A unit according to range 11 or 12. 14. A unit according to any one of claims 11 to 13, wherein the optical lens is of substantially spherical design. 15. The unit according to claim 14, wherein the spherically formed lens has a lens radius equal to half the outer diameter of the optical waveguide. 16. Claims 1 to 1, wherein at least one end surface, which may be formed as a lens, is provided with an antireflection coating for the light used.
A unit described in any one of items up to item 5.