DE1916226A1 - Optical transmission system - Google Patents

Description

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Nippon Selfoc Company 7-151 Shiba Gochome, Minato-ku, Tokyo, Japan

Optical transmission system

The invention relates to an optical transmission system for transmitting a light beam from a transmitter via a transmitting and receiving antenna to a recipient. In the usual optical transmission systems, these are light transceivers and the transmitting and receiving antennas by direct radiation from the atmosphere without assistance any light guide means coupled. In the usual optical transmission system, the Propagation of light through the atmosphere. The antennas must be installed on buildings or on antenna masts, with the transceivers in the vicinity of the Antennas are arranged. Because of this, in most cases the transceivers are outside the building arranged. However, it is often desirable to have the transceivers inside the building are arranged so that they can be easily serviced and operated. A combination of lenses, prisms and reflectors may possibly be such a requirement

-Z- 9 09884/1121

D3Lrtc.:iit? .-an '* AC3 Korito no. 58/3 »531, Postscheck Münchsjr, MS) If,

meet to some extent. In order to be able to implement such an optical transmission system, however, an elongated space is required for the optical path between the transceiver, for example in a relay station, inside the building and the antenna located outside the building. It must be arranged between the Sende ^ Srapfangsgerät and the antenna optical; transmission system can withstand mechanical vibrations. In addition, a precise setting and overall * must be möglieh gensei term direction of the optical elements ^?:: ■ "" ■ "·"'' ■ ■ ■■■■ - "

In order to meet this problem, the above-mentioned optical system can be replaced by so-called optical Fiber elements are replaced. However-is the usual "■ * - Fiberglass material unable to produce a beam of light to be transmitted by a broadband multiplex ■ Information signal is modulated. In particular, white> 'The light beam that is to be transmitted consists of a pulse train, -as e.g. = the modulated laser output signal, can the time division multiplex method 'not' -:, more be sufficiently high «This is attributable to the" fact that in common optical fiber materials the light transmission takes place by means of repeated total reflection, which occurs on the inner surface thin, cylindrical fiberglass material. as The practical consequence is that the usual fiberglass material is only able to transmit the luminance of a picture element, which is a very narrow one Occupies frequency bandwidth. . - - ■

The invention is therefore based on the object of a improved optical line coupling between Sönde receivers and to create antennas.

9 0988471121

BATH ORIGINAL

According to the invention, the object is achieved in such a way that the couplings each consist of a transparent fiber element that has a refractive index distribution across its cross-section that runs along the longitudinal axis is greatest and towards its surface essentially with the square of the distance decreases from the axis.

According to the teaching of the invention can largely solve all the problems with the usual optical Transmission systems, such as the optical lens / prism systems or the usual fiberglass materials for ■ ™ Coupling between transceivers and antennas appear. In other words, the improved fiberglass works like a coaxial cable or a Waveguide used for coupling between a microwave transceiver and the antenna is used.

Because the fiberglass material is flexible and completely free one of the difficulties is encountered with a light guide occur with lens / prism combinations, the present system is sufficiently resistant to Vibrations and thus facilitates the choice of the j

Installation site of the optical transmission system.

In Figures 1 to 3 of the drawings, the subject the invention is shown only schematically on the basis of exemplary embodiments and explained in more detail below. It shows:

1 shows an optical transmission system according to the invention;

Fig. 2 and .3 details of the coupling of the opti- -. .schen transfer, gungε sys t ems.

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BATH

1.81-S 22 §

In Fig. I _1. is. 1 denotes a special fiber-like transparent light guide element, which can be made of glass, plastic or another transparent material, due to the inventive design of the fiber element 1. a light beam runs through the element along its longitudinal axis. The refractive index of the fiber element 1 in a cross-section perpendicular to its longitudinal axis is greatest on the axis and nfjnmt to the surface in relation to the square of the distance; off the axis. In this fiber element, a light beam of a particular spot size that falls on one of the end faces of the fiber element 1 in the direction parallel to the axis or in the direction that includes a certain angle with the axis is not reflected on the side wall of the fiber element 1 , but rather broken due to the converging function of the fiber element 1 and thereby passes through the element essentially without divergence, with an oscillation occurring around the longitudinal axis of the fiber element. In the DW Berreman article in The Bell System Technical Journal, vol. 43, no. 4, part 1, (July 1964), pages 1469 to 1479, a so-called gas lens is described. The gas lens .will have the above-mentioned distribution of the refractive index. imparted over their cross-section by heating the gas filled in a cylindrical housing. It is stated in the article that the light beam is transmitted through the "gas lens" with practically no divergence.

2 with a transmitter is designated, which consists of a laser oscillator, an optical modulator, ■ etnemo.ptisehen Insulator and other elements. The-exit-, The light beam of the transmitter is directed to the entrance area before 3 of the element 1 bundled. To the optical; ; .si; "s

909884/1121.

Adjustment between the incident light beam and to be able to realize the element 1, the spot size of the light beam * that hits the surface 3 meets, optimally adapted to the refractive index distribution be.

According to the article by SE Miller in The Bell System Technical Journal, vol. 44, no. 9 (November 1965), pages 2017 to 2064, the basic spot size W ₀ matched to the element 1 by the relationship

1
"2 1

w _r 2T - n _fl ν ~ 4 Wo = (r ° -) a

given, where the refractive index η, which is at a distance X is measured from the axis of element 1, by the expression

= n _a (1 - J aX ² )

is determined. Ao is the wavelength of light in free space, na is the refractive index on the X-axis of element 1 and a is a positive constant.

Assuming that the entry and exit surfaces 3 and 4 of the element 1 are perpendicular to the Run the axis of the element 1, a light beam is incident on the entrance surface perpendicular to this hits, transferred along the longitudinal axis and occurs at the exit surface 4 perpendicular to this. The light beam that hits the entrance surface perpendicular to this from an off-axis Point or the beam of light that obliquely .auf

909884/1121

the entry surface * is indicated by the Element 1, in which he has a sine wave-like light path takes, transmitted oscillating about the longitudinal axis and finally occurs at the exit surface 4- a point perpendicular to it or at an angle. The last mentioned place and the angle are punctures of the entry angle, the entry point on the entry surface and the length and the refractive index distribution of the transparent Element 1.

In the optical transmission system according to the invention, the light-guiding element 1 made of fiber material has a suitable length and its entrance and exit surfaces, which are perpendicular to the central axis, are polished smooth. The light beam that strikes the entrance surface is converged on the surface 3. The spot size of the converged beam is chosen to be coincident with the basic spot size W ₀ of the light beam transmitted through the element Λ. In addition, the light beam is designed so that it falls on the center of the entrance surface 3 in the direction of the longitudinal axis, so that it emerges at the exit surface 4 perpendicular to the latter. It is then transmitted via an antenna system or a telescope, which consists of the elements 5 and 6, which are each shown in the drawing as mere lenses. On the light path beyond the telescope, the diameter of the light beam can be increased.

The light beam emitted by the receiving antenna system which consists of the elements 7 and 8 is formed so that it is received on the element 1 x am Receiving device after it has converged,

909884 / 1121- ... ~ ⁷ ~

in order to meet the above-mentioned condition, at the exit end 4 'of element 1' lets the light beam fall on light detector 9, which is the first stage of the receiving device,

Fig. 2 shows the type of coupling of the element 1 _; with the * detector 9 »which is particularly suitable for the Pail, -, - in which the. Receiving surface 10 of the light detector is large compared to the exit surface 3 'of the element 1'. In particular, a part of the receiving surface 10 which is not connected to the surface 3 \ is covered with a non-transparent film .11. covered. "-. . .

Fig. 3 · illustrates another type of coupling of the element 1 'to the detector 9, which .is suitable for the case in which the receiving surface 10 is separated from the element 1 ¹ through a transparent lens element 12. In this case, the light beam emerging from the exit surface 3 'diverges and is bundled onto the receiving surface 10 by means of an auxiliary lens 13. , ■

As can be seen from the embodiment, a precise setting for an optical axial alignment between the transmitting and receiving telescope 5.6 and 7.8, the transmitter 2 and the entrance surface 3, the exit surface 4 and the transmitting telescope and the receiving telescope and the entrance ^{surface 3 1 can be} made. Once the alignment is achieved, the elements are fixed against each other, with the fiber elements 1 and 1 ^f outside of a section with the entry and exit surface. 3? 3 ^f can remain mobile.

Since the light-guiding part between the entrance and

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BATH ORIGINAL

the exit surfaces 3 and 4 of the element "I ₁ and correspondingly the part between the surface 3 'and the surface 4' of the element 1 'cannot remain stationary with respect to the other elements of the system, the system is overall more resistant to vibrations; this makes the Selection of the installation site for the transmitting and receiving antennas and the transceiver is made easier.

"9-9 098 8-4 / 1 121" '

Claims (5)

Patent claims Μ.J Optical transmission system for transmission a light beam from a transmitter via a transmitting and receiving antenna to a receiver, consisting of an optical coupling between the transmitter and the transmitting antenna and / or an optical coupling between the receiving antenna and the receiver, characterized that the couplings each consist of a transparent fiber element (1, V) consist of a refractive index distribution has over its cross section, which is greatest along the longitudinal axis, and to its surface towards essentially the square of the distance from the axis decreases. 2. Optical transmission system according to claim 1, characterized in z. ei chnet that Means are provided through which the light beam to be transmitted to the center of the Eintri.ttsoberflache (3) of the fiber element (1) occurs in the direction of its longitudinal axis, the light spot size equal to the size of the base spot adapted to the fiber element Λ -j Where = () in which X _{0 is} the wavelength of the light in the free tree, n _{a is} the refractive index on the X-axis of the fiber element (1) and a is a constant. -10-903884 / 1121. 3. Optical transmission system according to claim. 1, characterized in that the surface of the receiving ^{detector as the first stage of the receiving device (9) adjoins the exit surface (3 1} ) of the fiber element (1 ¹ ) and that the surface of the receiving detector which is not connected to the exit surface (3 ¹ ) , is covered with a transparent film (11). . 4. Optical transmission system according to. Claim. 1, characterized in that a lens system (12, 13) is arranged between the receiving detector as the first stage of the receiving ^{device (9) and the exit surface (3 1} ) of the fiber element (1 ^f). 5. Optical transmission system according to the claims 1 to 4, marked thereby, that adjusting devices are provided with which end portions of the fiber elements (1, 1 ') in the Area of their entry and exit surfaces (3, 3 '»4» 4-') versus sending, transmission and Receiving devices (2; 5 »6; 7,8; 9) are adjustable. 909884/1121