GB2437316A

GB2437316A - Telescope for optical free space communication

Info

Publication number: GB2437316A
Application number: GB0707646A
Authority: GB
Inventors: Thomas Petasch; Helmut Erdl; Hans-Joachim Juranek
Original assignee: Carl Zeiss Optronics GmbH
Current assignee: Hensoldt Optronics GmbH
Priority date: 2006-04-22
Filing date: 2007-04-20
Publication date: 2007-10-24
Also published as: GB0707646D0; DE102006018743A1

Abstract

A telescope 1 for optical free space telecommunication comprises a primary mirror 3, a secondary mirror 4, an eyepiece 6 and a detector 7. The secondary mirror 4 is connected to a barrel wall 2 via holding members 5. On the side facing the eyepiece 6 the holding members 5 are provided with a material 12 that absorbs the transmitted beams 9. Such an arrangement may reduce parasitic light (back reflected light and scattered light). The holding members 5 may extend radially in spoke form (i.e. spiders) from the secondary mirror 4 to the barrel wall 2. The holding members 5 may be wedge shaped; they may be coated with Wood's glass.

Description

TELESCOPE FOR OPTICAL FREE SPACE

TELECOMMUNICATION

The invention relates to a telescope for optical free space telecommunication, comprising a primary mirror, and a secondary mirror which is connected to a barrel wall via holding members, comprising an eyepiece and a detector for transmitted and received light.

Telescopes of this type are simultaneously used as a transmitting and receiving telescope in optical free space telecommunication, for example in space. An optical unit in which the beams are detected is situated in the detector unit, which is arranged behind the eyepiece, the received beams being filtered Out. Information which is to be sent via the transmitted beams is also modulated in the detector, passes as parallel beams up to the eyepiece and after passing through the eyepiece is then reflected at the secondary mirror and subsequently outwardly radiated via the primary mirror, past the secondary mirror, for example into space in the direction of a different telescope.

One problem with these telescopes, however, is parasitic light generated by the high-energy transmitted light in the telescope. The parasitic light is additively made up of back-reflected light which is produced for example on lenses, and scattered light on optical surfaces as well as mechanical surfaces. This parasitic light has to be minimised since the received light entering the telescope from outside is a relatively weak light signal, in particular if it has to overcome great distances in space. The arriving, weak received light signals are accordingly affected by the parasitic light and sometimes cannot be exactly separated therefrom, whereby the receiving power of the telescope is impaired.

One of the causes of scattered light are the holding members for the secondary mirror. These generally extend radially in spoke form from a barrel wall of the telescope and hold the secondary mirror centrally in the interior of the telescope. To avoid vibrations the holding members have to be relatively rigid and therefore cannot fall below a certain material thickness. Reflections therefore occur at the sides of the holding members facing the eyepiece and these lead to the adverse scattered light.

It is therefore known to construct the holding members so as to be wedge-shaped, viewed in cross-section, with a wedge angle through which the transmitted light is reflected or scattered in the direction of the barrel wall at a correspondingly suitable angle. The barrel wall can thus absorb some of the scattered light. There are limits to this method, however, since not all scattered light can be sufficiently suppressed in this way, such that the suppression requirement necessary for the required telescope powers is attained for coherent methods.

The object underlying the present invention is therefore to provide a telescope in which occurring parasitic light is more strongly suppressed or is eliminated.

According to the invention, this object is achieved in that on the side facing the eyepiece the holding members are provided with a material that absorbs the transmitted light.

According to the invention, the transmitted light striking the holding members is accordingly no longer simply deflected but absorbed directly in or by the material and is therefore destroyed as early as at the point of origin. Scattered light may thus be reduced by a factor of 102 to 10g.

In a development of the invention according to the invention it may be provided that the absorbent material is applied to the holding members as an additional volume, whereby very high absorption is achieved according to the volume or thickness of the material.

Alternatively, the holding members themselves can be made from highly absorbent material in place of an additional material layer that is to be applied to the holding members in each case.

If the surface of the holding members or the material layer is also highly polished and antireflection coated on the side facing the eyepiece a further improvement in the absorbing capacity is achieved and reflections are avoided.

If, moreover, on their side facing the eyepiece the holding members also have a wedge shape -known per se -with a wedge angle though which the striking transmitted beams are deflected in the direction of the barrel wall, in addition to absorption, transmitted beams that have potentially not yet been absorbed are also deflected to the barrel wall at which they may also be absorbed.

Wood's glass has proven to be particularly suitable material for absorption.

Advantageous developments and embodiments emerge from the following embodiment described in terms of principle with reference to the drawings, in which: Fig. 1 shows a longitudinal section through a telescope according to the invention, comprising a detector, along the line I-I in Fig. 2; Fig. 2 shows a cross-section through the telescope according to Fig. 1, along the line 11-11 in Fig. 1, and Fig. 3 shows an enlargement of a detail through a cross-section of a holding member.

A telescope 1 with a barrel wall 2 is only described in terms of principle hereinafter since the construction and function thereof are basically generally known.

A primary mirror 3 and a secondary mirror 4 are arranged in the telescope 1. The secondary mirror 4 is connected to the barrel wall 2 via radially extending holding members 5 in spoke form (called spiders). In the illustrated embodiment three holding members 5, arranged so as to be uniformly distributed over the circumference, are provided. The holding members 5 are also called spiders.

An eyepiece 6 is accommodated in the central region of the primary mirror 3. In the beam direction in front of the eyepiece 6 there is arranged a detector 7 from which transmitted beams issue as parallel beams and after deflection by way of a deflecting mirror 8 pass through the eyepiece 6. The transmitted beams formed in the detector 7 then strike the secondary mirror 4 from where they are reflected back to the primary mirror 3 and from there into space as parallel beams 9. En route from the primary mirror 3 through the telescope 1 the transmitted beams 9 inevitably strike the spiders or holding members 5 (see enlarged view in Fig. 3). As may also be seen in Fig. 1 from the arrows 10, reflections would occur at the leading end faces 11 of the holding members 5 facing the eyepiece 6. To avoid this, Wood's glass 12 is in each case arranged at the end faces 11 of the holding members 5. The striking transmitted beams 9 are absorbed in the Wood's glass 12 through the Wood's glass.

The absorption effect is determined in this case by the thickness or strength of the Wood's glass 12.

In addition, on its side facing the eyepiece 6 the Wood's glass 12 can also be wedge-shaped (see Fig. 3) with a wedge angle through which transmitted light that has possibly not been absorbed is reflected in the direction of the barrel wall 2 and can be absorbed there.

The occurrence of scattered light is largely avoided as a result of absorption of transmitted beams 9 which strike the holding members 5.

The weak received light signals 13, which enter the telescope 1 and which after passage through the telescope 1 are detected in the detector 7 and then filtered out as signals, are thus not adversely affected.

Claims

CLAIMS

1. Telescope for optical free space telecommunication, comprising a primary mirror, and a secondary mirror which is connected to a barrel wall via holding members, comprising an eyepiece and a detector for transmitted and received light, characterised in that on the side facing the eyepiece the holding members are provided with a material that absorbs the transmitted light.

2. Telescope according to Claim 1, characterised in that the material is introduced into the volume of the holding members.

3. Telescope according to Claim 1, characterised in that the material is applied to the holding members in the form of a layer.

4. Telescope according to any one of Claims 1 to 3, characterised in that the holding members extend at least approximately radially in spoke form to the barrel wall.

5. Telescope according to any one of Claims 1 to 4, characterised in that on the side facing the eyepiece, viewed in cross-section in each case, the holding members have a wedge shape with a deflection angle directed to the barrel wall for the transmitted light.

6. Telescope according to any one of Claims 1 to 5, characterised in that the sides of the holding members facing the eyepiece are polished and antireflection coated with the material.

7. Telescope according to any one of Claims 1 to 6, characterised in that the material is Wood's glass.

8. Telescope substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.