WO2000025452A1

WO2000025452A1 - Device and method for optical free space transmission

Info

Publication number: WO2000025452A1
Application number: PCT/CH1998/000454
Authority: WO
Inventors: Robert O. Renfer
Original assignee: Renfer Robert O
Priority date: 1998-10-22
Filing date: 1998-10-22
Publication date: 2000-05-04
Also published as: EP1046248A1

Abstract

The inventive device for the free space optical transmission of data, speech, sound and image information comprises a transmitting module (2) with a laser diode, a transmitting optical device (4), and a receiving module (1) having an avalanche photodiode. The inventive device also comprises a navigation assistance unit and/or a sighting device (5), one or more contact wafer(s) and/or one or more hybrid unit(s). In addition, the inventive device is provided with one or more adjusting device(s) and a connection (6) for admitting both current and control pulses. According to the inventive method, modulated light pulses are transmitted at 904 nm or 267 nm. For a bi-directional transmission, the transmitting module (2), the receiving module (1) and a telescopic sight (5) are fastened to a common base plate, and they can, in part, be separately adjusted. The device is very simple to install. It is especially suited for optically communicating over a number of kilometers during bad atmospheric conditions and visibility.

Description

Device and method for wireless optical transmission

The present invention relates to an apparatus and a method for wireless free-space optical transmission.

In the free-space optical transmission of data, voice, sound and image information known in the prior art, two transmitter units and two receiver units are generally used. So a total of 4 devices are required. This type of transmission is very cumbersome because a transmitting unit and a receiving unit are required in pairs for both the forward transmission and the back transmission. Thus, two transmission links must be adjusted independently of one another.

Experience has shown that the known devices only work in good to very good weather and visibility conditions. As soon as light fog or heavy rain appears, the transmission mentioned is negatively affected or impossible. With the known devices, transmissions over distances of approximately 1 km are possible. With the known devices, transmissions over distances of more than 2.5 km are not possible in the best weather and visibility conditions. These devices generally have a large power consumption of several amperes / hour. In addition, unsuitable modulation methods are used in the known devices, for example those modulation methods as described in "Laser Technology", 2nd edition, 1984, Hüthig Verlag Heidelberg, pages 429 to 441, and in "Laser" 4th edition, 1979, Vogel-Verlag Würzburg, pages 91 to 99 are described.

So far, insufficient or extremely complex measures have been taken to improve the transmission in bad weather. For example, it is known from DE 1 268 528 to choose a wavelength with minimal absorption at atmospheric moisture for optical information transmission and, moreover, to clean the atmosphere with a high-energy laser beam. The aim of the present invention is to provide an improved device for free-space optical transmission, with which the disadvantages mentioned above can be overcome.

It is an important goal of the present invention to enable transmissions even in bad weather conditions and visibility. In particular, transmissions should be made possible even in bad weather over distances of more than 2.5 km.

The present invention is also intended to provide a device for free-space optical transmission, which also requires only two devices for bidirectional transmission.

A device for free-space optical transmission is also to be created, in which only one transmission path has to be adjusted.

It is a further purpose of the present invention to enable quick mutual alignment by means of a triaxial structure of the transmitting and receiving units.

These new devices should also have a low power consumption, for example 0.5 amperes at 12 V DC and in continuous operation.

The free-space optical transmission should take place by means of a light pulse edge modulation, a light pulse phase modulation, a light pulse frequency modulation or further modulation methods derived therefrom.

It has now been found, completely surprisingly, that the above objectives can be achieved with the device according to the invention according to independent claim 1 and the method according to the invention according to independent claim 11.

The essence of the invention is namely to create a device for free-space optical information transmission, which has a pulsed laser or a pulsed laser diode with a wavelength in a transmission window at 905 nm or 267 nm. In a particularly preferred embodiment, the device according to the invention for the free optical transmission of data, voice, sound or image information comprises at least one transmitter module 2 with a laser diode, transmitter optics 4, preferably a navigation aid and / or a target device 5, one or more circuit boards (n ) and / or one or more hybrid unit (s), one or more adjustment device (s), a connection 6 for the common inlet of current and control pulses, and optionally one or more operating and / or measuring device (s) and / or control signal connections. Advantageously, a longitudinal axis of the receiving module 1 and a longitudinal axis of the transmitting module 2 are arranged parallel to one another and in a plane Ei, the transmitting module 2 is mounted in a holder 7, which is rigidly connected to a base plate 8, and the receiving module 1 is in a holder 9 mounted, which is rigidly connected to a base plate 8.

Preferably, the transmitter module 2 can be moved forwards and backwards with respect to its position in a first holder 7 and the receiver module 1 can be moved forwards and backwards with respect to its position in a second holder 9, part of the second holder in its vertical and horizontal Position to the base plate 8 is movable. The transmitter module 2 is particularly preferably rotatable about its longitudinal axis within its holder 7 and / or the receiver module in its holder 9 and contains the laser diode in the transmitter module 2 and / or the avalanche photodiode in the receiver module 1 in a conically tapered holder.

Further advantageous embodiments of the device according to the invention are defined in the dependent claims and result from the following description with reference to the figures.

Show it

FIG. 1 shows a possible arrangement of the device according to the invention,

FIG. 2 shows a front view of a preferred embodiment of the device according to the invention, FIG. 3 shows a side view of a preferred embodiment of the device according to the invention,

FIG. 4 shows a rear view of a preferred embodiment of the device according to the invention,

Some exemplary embodiments of the present invention are described below. Reference is generally made to FIGS. 1-4.

A preferred embodiment for the transmission of voice, sound, image and / or data information comprises the following 4 basic elements: a transmitting and receiving unit, comprising the inventive one

Device, a power supply unit, a headset with cable and plug, and a connecting cable with plug and coupling.

The above-mentioned transmission and reception unit comprises the following parts: at least one preferably cylindrical transmission module 2, at least one preferably cylindrical reception module 1, a target device 5 or a navigation aid (not shown), a transmission optics 4, a reception optics 3, a stable housing with a base plate 8, a housing cover, a front plate, a rear plate, a holder 10 with an adjusting device 11 for horizontal adjustment of the above-mentioned transmission

and receiving unit, as well as with an adjusting device 12 for vertical adjustment of the above-mentioned transmitting and receiving unit, a transmitting board, a receiving board, an analog / digital and control board, an operating element 13, a connection 6 for the common inlet of current and control pulses, one Signal socket 14 for the input of data signals, a measuring socket 15 for measuring the received signal, and a measuring socket 16 for measuring the transmission signals.

As an alternative to the circuit boards, one or more hybrid units can also be provided.

The above-mentioned power supply unit comprises the following parts: a battery, in particular a Ni / Cd battery, a mains supply 110/230 VAC,

Signal and power supply sockets, as well as a measuring instrument for measuring the current consumption of the transmit and

Receiver unit, as well as for measuring the charging current of the battery.

The cylindrical transmitter module 2 comprises a laser diode for the transmission of optical light pulses. It is essential to the invention that the laser diode either has a wavelength in a range between 898 nm and 912 nm, preferably 901 nm - 909 nm, particularly preferably 904 nm - 906 nm, in particular a wavelength of 905 nm, or a wavelength in a range between 260 nm and 274 nm, preferably 263 nm - 271 nm, particularly preferably 266 nm - 268 nm, in particular a wavelength of 267 nm, and is operated in pulsed mode. A light pulse edge modulation, a light pulse phase modulation, a light pulse frequency modulation or further modulation methods derived therefrom are particularly suitable as the modulation method. The laser diode is preferably mounted in a tapered holder. The tapered holder is preferred because it enables the greatest possible number of adjustments.

The transmitter module 2 preferably also comprises a multi-stage amplifier unit and the impedance converters required for this. It is preferred to use extremely low-noise transistors, for example gallium arsenide transistors.

The transmitter module 2 also includes sockets for the current and signal supply and for measuring the transmit signals.

The cylindrical receiving module 1 comprises a photodiode, in particular an avalanche photodiode, for receiving optical light pulses. Light pulses of the type mentioned above are preferred. The receiving optics 3 are preferably equipped with a light filter which limits the bandwidth of the light frequency spectrum in favor of better utilization of the preferred light frequency of 905 nm or 267 nm and is in particular a bandpass filter.

The photodiode is in turn mounted in a tapered holder according to the above information.

The laser diode and the avalanche photodiode are preferably adjusted and possibly fixed such that the laser diode is in the focal point of the transmitting optics 4 and the avalanche photodiode is in the focal point of the receiving optics 3.

The receiving module 1 preferably also comprises a low-noise, broadband video signal amplifier unit and the control loops required for this to optimally adjust the amplifier intensity of the video signal amplifier unit.

The receiving module 1 also includes sockets for the current and signal supply and for measuring the received signals.

The target device 5 is connected to the base plate 8, movable in its longitudinal axis and arranged between the receiving optics 3 and the transmitting optics 4. The receiving module 1 and the transmitting module 2 are preferably arranged in a horizontal plane Ei, the target device 5 is arranged above or below the plane Ei and the target device 5 is a telescopic sight of the conventional type.

The transmission optics 4 can be a commercially available lens for cameras; for example a lens with a focal length of 135 mm and a light width of 55 mm. The aperture of the objective is preferably opened as far as possible so that as much light as possible can be emitted through the objective lenses.

The receiving optics 3 can in turn be a commercially available lens for cameras; for example a lens with a focal length of 135 mm and with a light width of 55 mm of the type described above. The diaphragm of the lens is preferably opened as far as possible so that as much light as possible can be captured through the objective lenses.

The stable housing mentioned above can be made from a suitable metal, a suitable alloy or from a plastic reinforced with carbon fibers. The base plate 8 and a housing are advantageously connected to such a carrying device that both the base plate 8 and the housing can be moved in the horizontal and vertical directions, in particular pivoted horizontally and tilted vertically.

The transmitter board, the receiver board and the analog / digital and control board each have all the necessary electronic, signal-processing components in the form of passive and active components of the conventional type.

The control loops mentioned above can be adjusted in the receiving module 1 using the operating element 13. The device according to the invention is suitable for unidirectional or bidirectional transmission. In simplex, semiduplex or full duplex operation of the two transmitting and receiving units, no immobile solid objects, such as a wall, may interrupt the line of sight.

According to the current state of the art, passive or active interference and / or interception and / or targeting of the device according to the invention is practically impossible.

The power consumption when operating the transmitting and receiving units is so low, about 0.5 amperes at 12 V DC and in continuous operation, because a low transmitting power is sufficient to maintain the connection between the two transmitting and receiving units mentioned.

The radiation opening angle of the transmission module 2 is usually only about 2 milliradians.

The two transmitting and receiving units can be used permanently, temporarily stationary or mobile.

The two transmitting and receiving units can also be used, for example, as a connecting link between two glass fiber connections.

In order to overcome a fixed obstacle in the line of sight of two transmitting and receiving units, one or more relay stations can be set up. One or more relay station (s) can also be used to extend the transmission distance.

Spreading tests with a device according to FIGS. 1 to 4 were carried out in Felde in the greater Zurich area under different weather conditions and over different distances. For this purpose, a laser diode with an emission wavelength of 904.8 nm, an average transmission power of 10 mW and a peak power of 10 W was used as well as an avalanche photodiode and a bandpass filter with a spectral transmission window of 904 nm ± 7 nm. Trial A

Weather: sunny, windless, temperature 20 ° C, relative humidity 70%. Distance: 5.1 km.

Attempt B

Weather: hazy, estimated visibility 3 - 4 km, temperature 16 ° C, relative humidity 82%.

Distance: 6 km.

Attempt C

Weather: hazy, estimated visibility 1 km, temperature 22 ° C, relative humidity 85%.

Distance: 2.5 km.

Attempt D

Weather: heavy snow, estimated visibility 200 m, temperature O ° C, relative humidity 87%.

Distance: 3 km.

A station stood behind a double-glazed window.

Tries

Weather: heavy rain, measured visibility 20 m, temperature 18 ° C, relative

Air humidity 90%.

Distance: 2.7 km.

A station stood behind a window, which was covered with condensation.

In all 5 test arrangements, the transmission of voice and sound information was flawless. The power consumption is 0.5 amperes at 12 V DC and in continuous operation. These measurement results show that the invention enables transmission to be achieved even in difficult visibility conditions, in particular in the case of transmission distance / visibility range ratios of 40% ... 60% in haze, 7% in snow and 1% in heavy rain. This effect is all the more surprising since the chosen wavelength is not in a minimum of the absorption spectrum of water, but in a flank of a weak absorption peak. Similar good transmission ratios can be expected for the previously mentioned wavelength window at 267 nm. The reason for this extremely advantageous behavior of the light beam lies in the reduced light scattering in the atmosphere with the white lengths according to the invention. In addition, the light beam even self-focuses on vapor droplets and especially on raindrops.

It is a further aspect of the invention to provide a method for free laser communication which is particularly suitable for the optical transmission of data, voice, sound and image information. Signals between two stations are transmitted unidirectionally or bidirectionally through the atmosphere with the help of light beams. According to the invention, light beams are used which either have a wavelength in a range between 898 nm and 912 nm, preferably 901 nm - 909 nm, particularly preferably 904 nm - 906 nm, in particular a wavelength of 905 nm, or a wavelength in a range between 260 nm and 274 nm, preferably 263 nm - 271 nm, particularly preferably 266 nm - 268 nm, in particular a wavelength of 267 nm. The signals are encoded by pulse modulation of the light beams. The signals are preferably encoded by a light pulse edge modulation, a light pulse phase modulation, a light pulse frequency modulation or further modulation methods derived therefrom

Overall, the invention discloses a free communication device which is characterized by extensive weather independence and thus a large range and high transmission rate with low laser power. Other advantages relate to the high level of security against interference, eavesdropping and sighting. Possible areas of application include civil and military radio relay (mobile and / or stationary), the mobile network and telephony in the general. The device according to the invention and the method according to the invention for open-space laser communication is also useful as an alternative to laying optical fibers, in particular for bridging difficult terrain.

Claims

PATEN TA NS PRÜC HE

Device for free-space optical transmission of data and voice. Sound and image information, the device having at least one transmission module

(2) with a laser or a laser diode, a transmitting optics (4), preferably a navigation aid and/or a targeting device (5), as well as one or more circuit board(s) and/or one or more hybrid unit(s), one or more Adjusting device(s), a connection (6) for the common inlet of current and control pulses, and possibly one or more operating and/or measuring device(s) and/or control signal connections, characterized in that a) the laser has either a wavelength in a range between 898 nm and 912 nm, preferably 901 nm - 909 nm, particularly preferably 904 nm - 906 nm, in particular a wavelength of 905 nm, or a wavelength in a range between 260 nm and 274 nm, preferably 263 nm - 271 nm , particularly preferably 266 nm - 268 nm, in particular a wavelength of 267 nm, and b) a pulse modulation, in particular a light pulse edge modulation, a light pulse phase modulation, a light pulse frequency modulation or further modulation methods derived therefrom, is provided for the laser is.

Device according to claim 1, characterized in that a) at least one receiving module (1) with an avalanche photodiode and receiving optics (3) are provided and b) the receiving optics (3) is equipped with a light filter which increases the bandwidth of the light frequency spectrum in favor of a better utilization of the preferred light frequency of 904 nm or 267 nm and in particular is a bandpass filter.

3. Device according to claim 2, characterized in that a) a longitudinal axis of the receiving module (1) and a longitudinal axis of the transmitting module (2) are arranged parallel to one another and in one plane (Ei), b) the transmitting module (2) in a holder (7) is mounted, which is rigidly connected to a base plate (8) and c) the receiving module (1) is mounted in a holder (9), which is rigidly connected to the base plate (8).

4. Device according to claim 3, characterized in that a) the transmitting module (2) can be moved forwards and backwards with respect to its position in the holder (7), b) the receiving module (1) with respect to its position in the holder (9 ) can be moved forwards and backwards, with part of the holder being movable in its vertical and horizontal position relative to the base plate (8).

5. Device according to claim 4, characterized in that a) the transmitter module (2) is rotatable within its holder (7) about its longitudinal axis, b) in the transmitter module (2) the laser diode is contained in a conically tapered holder and c) in particular the transmitter module (2) is cylindrical.

6. Device according to claim 4, characterized in that a) the receiving module (1) is rotatable within its holder (9) about its longitudinal axis, b) in the receiving module (1) the avalanche photodiode is contained in a conically tapered holder and c) in particular the receiving module (1) is cylindrical.

7. Device according to one of claims 2 to 6, characterized in that a) the laser diode is located in the focal point of the transmitting optics (4) and b) the avalanche photodiode is located in the focal point of the receiving optics (3).

8. Device according to claim 7, characterized in that the aiming device (5) is connected to the base plate (8), is movable in its longitudinal axis and is arranged between the receiving optics (3) and the transmitting optics (4).

9. Device according to claim 8, characterized in that a) the receiving module (1) and the transmitting module (2) are arranged in a horizontal plane (Ei), b) the aiming device (5) is arranged above or below the plane (Ei). is and c) the aiming device (5) is a telescope.

10. The device according to claim 9, characterized in that the base plate (8) and a housing are connected to a support device such that both the base plate (8) and the housing are movable in horizontal and vertical directions.

11. Method for free-space laser communication, particularly suitable for the optical transmission of data, voice, sound and image information, whereby signals between two stations are transmitted unidirectionally or bidirectionally through the atmosphere using light beams, characterized in that a) the light beams either a wavelength in a range between 898 nm and 912 nm, preferably 901 nm - 909 nm, particularly preferably 904 nm - 906 nm, in particular a wavelength of 905 nm, or a wavelength in a range between 260 nm and 274 nm, preferred 263 nm - 271 nm, particularly preferably 266 nm - 268 nm, in particular a wavelength of 267 nm, and b) the signals are encoded by pulse modulation of the light beams.

12. A method for free-space laser communication according to claim 11, characterized in that the signals are encoded by a light pulse edge modulation, a light pulse phase modulation, a light pulse frequency modulation or further modulation methods derived therefrom.