DE2830095A1 - OPTICAL RECEIVER FOR FIBER OPTICAL TRANSMISSION SYSTEMS WITH MANY PARTICIPANT STATIONS - Google Patents

Description

R.E. Epworth-13

Optical receiver for fiber optic transmission systems with many participant stations

The invention relates to an optical receiver with a tapping device for decoupling light from a glass fiber light guide of an optical transmission system.

In fiber optic transmission systems with many subscriber stations there is a major problem in coupling the subscriber stations to the optical fiber without excessive To cause attenuation of the light transmitted on the optical fiber. Such a fiber optic transmission system has a tapping device for decoupling light for each subscriber station from the fiberglass. Each tap is set so that the light intensity in each subscriber station of the system is roughly the same. This is disadvantageous for everyone Tapping point of the optical fiber a measurement of the signal level is necessary, and means must also be available to adjust the coupling factor of each tapping device to the fiber. In addition, this system only works satisfactorily if the optical losses and the coupling factors remain constant. Hence it is not possible to do that Modify the system by adding or removing one or more taps without having to recreate the entire system to have to adjust.

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R.E. Epworth-13

task

It is the object of the invention to provide an optical receiver for such a system which has those listed Avoids disadvantages.

5 solution

The object is achieved with the means specified in claim 1. Further developments are the subclaims removable.

description

The invention will now be explained in more detail with reference to the drawings, for example. Show it:

Fig.1 is a block diagram of a receiver for a

optical transmission system with several subscriber stations;

2 and 3 alternative embodiments of the tapping device of the receiver according to Fig. 1.

The fiber optic transmission link in FIG. 1 has a large number of tapping points T1, T2, etc., at each of which a receiving station is provided. Each receiving station has a photodetector 11, an amplifier 12, an amplitude or Noise detector 13 and a comparison circuit 14.

In the receiver there is an automatic gain control, in which the output or noise amplitude of the amplifier is measured and compared with a reference signal with a uniform level. One that depends on this signal comparison

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electrical control signal is sent to the associated tapping device The fiber is fed back to the strength of the light emerging from the fiber at the tap is decoupled to control. In this way it is possible to ensure that there is only so much power over the tapping device is decoupled, like the associated one optical receiver required.

An example of an adjustable tapping device is shown in FIG. The tapping device is jacketed to a Glass fiber 21 made of silicon dioxide with a fiber core 22 and a cladding 23 adapted over a short section the jacket 23 is removed, and the thereby exposed fiber core 22 is electrically conductive with a light-permeable Material 24, such as tin oxide coated. A translucent one Tube 25, for example made of silicon dioxide, the inner surface of which is also covered with the translucent electrically conductive material 24 is coated, is adapted to the exposed portion of the fiber core in such a way that that an annular cavity 26 is formed which is filled with a liquid crystal material. A photodetector is arranged adjacent to the tube.

The control signal from the comparator 14 (Fig.1) is over Lines 28 applied to the electrically conductive surface 24 of the fiber core 22 and the tube 25, and polarized the liquid crystal material in the cavity 26. By

- this polarization changes the refractive index of the liquid crystal material, and higher order modes can be used

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R.E. Epworth-13

exit from the fiber core 22 in the direction of the photodetector 27. The strength of the light emitted from this glass fiber, i.e. the power loss caused by the tapping device corresponds to the amplitude of the over the Liquid crystal material applied electrical signal. To ensure a long life of the liquid crystal material To ensure this, an AC signal should be used as the control signal instead of a DC signal.

3 shows an alternative tapping device. One Sheathed glass fiber 31, via which the message transmission takes place, is let into a holder body 32 and is U-shaped bent. A part of the fiber cladding has been removed in the middle part 33 of the U, and the fiber core thus exposed is coated with a translucent .electrically conductive material 24. A glass plate 34 that too is coated with the electrically conductive material 24, the middle part 33 of the glass fiber is arranged opposite, and the space therebetween is filled with a liquid crystal material. Conductive connections 35 serve to apply the control signal to the fiber and to the plate 34 to determine the index of refraction in between to change lying liquid crystal material and thus the light exit in the direction of the photodetector 36 to steer.

In an optical communication system with many subscriber stations, their tapping devices and thus connected optical receivers as previously described

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are designed, each subscriber station automatically adjusts itself in such a way that it decouples the minimum signal from the transmission line in order to operate the receiver. Changes in the attenuation of the optical fiber and / or of the receiving stations can easily be compensated for, and subscriber stations can be added and / or removed without unbalancing the system
comes.

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Claims (7)

Patent attorney Dipl.-Phys.Leo Thul Kurz StL 8 7 Stuttgart 30 R.E.Epworth-13 INTERNATIONAL STANDARD ELECTRIC CORPORATION, NEW YORK Patent claims 1.jOptical receiver with a tapping device for decoupling light from a glass fiber light guide of an optical transmission system, characterized in that a control circuit (12, 13,14) is provided which compares the intensity of the decoupled light with a reference value (14) and, depending on the comparison result, regulates the coupling factor of the tapping device (T1) and thus the intensity of the decoupled light (FIG. 1). 2. Optical receiver according to claim 1, characterized in that the tapping device (T1) consists of: a stripped area of the glass fiber light guide (22; 31), a photodetector arranged opposite this area and means which contain a liquid crystal material (26) and cause an optical coupling between the glass fiber light guide (22) and the photodetector (27), and means (24, 28; 24, 35) for applying an electric field to the liquid crystal material (26) such that its refractive index and Consequently Kg / Sch
07/06/78 909807/0723 ORIGINAL INSPECTED R.E. Epworth-13 the optical coupling between the glass fiber light guide (22; 31) and the photodetector (27; 36) is adjustable (Fig.2, Fig.3). 3. Optical receiver, characterized in that the liquid crystal material (26) is contained in a transparent glass sleeve (25) arranged coaxially with the stripped area of the glass fiber light guide (22) (FIG. 2). 4. Optical receiver according to claim 2, characterized in that the glass fiber light guide (31) is embedded in a holding body (32) in the region of the tapping device (Figure 3). 5. Optical receiver according to claim 4, characterized in that the glass fiber light guide (31) bent in a U-shape and the liquid crystal material is arranged at the bend (Fig.3). 6. Optical receiver according to claim 2, characterized in that that for applying an electric field to the liquid crystal material (26) a transparent electrically conductive layer (24) is present, which is part of the stripped Area of the glass fiber light guide (22; 31) covered (Fig.2, Fig. 3). 7. Optical receiver according to claim 6, characterized in that the layer (24) consists of tin oxide. 909807/0723