RU2526207C2 - Underwater optical communication apparatus - Google Patents

Abstract

FIELD: physics, communications.

SUBSTANCE: invention relates to electrical communication engineering and can be used in two-way optical communication systems. An underwater wireless optical communication apparatus, having an optical receiver and a transmitter with control circuits therefor, further includes a rotating device, a position-sensitive element and a master controller, wherein all optical subsystems are rigidly joined to each other, are mounted on the rotating device and angle apertures thereof are linked by the relationship θ_t<θ_R<θ_p, where θ_t is the angle of divergence of the radiation of the transmitter; θ_R is the angular field of view of the receiver; θ_p is the angular field of view of the position-sensitive element.

EFFECT: broader functional capabilities of the apparatus for two-way optical communication in an underwater environment.

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Description

The invention relates to techniques for electrical communication and can be used in two-way optical communication systems.

The prior art system and method for underwater optical communication (US Patent No. 7953326 B2, 05/31/2011). The system comprises an optical transmitter made in the form of an array of light wave emitters located on a hemispherical surface and providing omnidirectional radiation in a large aperture angle, a photodetector having a hemispherical shape and providing reception of electromagnetic waves from any direction within the hemisphere. The receiver and transmitter are physically separated from each other. The operating wavelength of the system lies in the range from 300 to 800 nm. The disadvantages of this underwater communication system include the low communication range due to the wide angle of the transmitter radiation, the limitation of the transmission rate due to the need to simultaneously modulate a large number of high power emitters, as well as the mutual influence of various communication channels formed by such systems on each other at close their location.

The closest in technical essence is the method and equipment for underwater wireless optical communication (Patent application publication US 2005/02326338 A1, 20.10.2005), which is selected as a prototype. The equipment includes an optical converter, which includes one or more light emitting diodes that provide radiation in the range 400-700 nm, one or more optical photo detectors that provide signal reception in the specified range, a front panel with lenses mounted on it in front of photo detectors, waterproof a casing with electronic units installed inside it, ensuring the operation of the transmitter and receiver, as well as a controller, ensuring the operation of the system in the selected protocol communication, such as IRDA. This system has a large angle of light emission and, accordingly, a large angular field of view of the receiver. This leads to large transmitter power losses during radiation propagation in the wireless channel. Another drawback of the equipment is that when using several such systems, their mutual influence on each other occurs due to the large aperture angles of the receiver and transmitter.

The technical result of the invention is to improve the functionality of the underwater optical communication system.

The technical result is achieved due to the fact that the underwater optical communication equipment consists of a waterproof casing with a front panel, with an optical transmitter installed inside the casing operating in the spectral range 400-700 nm, an optical receiver providing signal reception in the specified range, as well as an electronics unit providing the operation of the receiver and transmitter. At the same time, the receiver and the transmitter are installed inside the housing on a rotary device, which ensures their angular movement in two orthogonal coordinates and with a position-sensitive element fixed to it and rigidly connected to the transmitter, the coordinates and control controller, the input of which is connected to position-sensitive element, and the output with a rotary device, while the angular apertures of the optical devices obey the ratio:

θ _t <θ _R <θ _p ,

where θ _t is the angle of divergence of the radiation of the transmitter;

θ _R is the angular field of view of the receiver;

θ _p is the angular field of view of the position-sensitive element. In this case, the front panel of the casing is made of a transparent material and may be shaped as part of a sphere. In this case, the rotation axes of the rotary device intersect at the geometric center of the sphere. The position-sensitive element can be made in the form of a matrix photodetector with a focusing system installed in front of it.

Device device

Figure 1 shows the device apparatus for an underwater wireless communication line, where:

1 - waterproof casing;

2 - rotary device;

3 - optical transmitter;

4 - an electronics unit that ensures the operation of the receiver and transmitter;

5 - position-sensitive element;

6 - optical receiver;

7 - bracket for rigid connection between the receiver and the position-sensitive element;

8 - front panel;

9 - controller for determining coordinates and controlling the rotary device.

The optical wireless underwater communications equipment consists of an optical transmitter 3 and an optical receiver 6, which are electrically connected to an electronics unit 4, which enables the transmitter and receiver to operate over a selected communication protocol, such as Ethernet. The receiver and the transmitter are fixed on the carrier bracket 7. A position-sensitive element 5, which can be made in the form of a matrix receiver with an optical system, is rigidly fixed to the same bracket.

In this case, the optical angular apertures of the receiver, transmitter and positionally sensitive photodetector obey the ratio:

θ _t <θ _R <θ _p ,

where θ _t is the angle of divergence of the radiation of the transmitter;

θ _R is the angular field of view of the receiver;

θ _p is the angular field of view of the position-sensitive photodetector, and their optical axes are made parallel.

In turn, the bracket is installed in the rotary device 2. The rotary device provides angular movement of the bracket, and hence the entire optical system in two orthogonal planes. In Fig. 1, this corresponds to rotation about a vertical axis and about a horizontal axis. The rotary device is electrically connected to the output of the coordinate determination and control controller, which provides angular movements around the indicated axes according to the built-in algorithm. Data on the current position of the target is received at the controller input from a position-sensitive element.

All components of the underwater communication equipment are placed and fixed inside the waterproof sealed casing 1. On one of the casing walls, opposite the optical system, is the front panel 8. It is made of transparent material for the radiation wavelength range of 400-700 nm. Figure 1 shows a variant with a flat panel. In another embodiment, the shape of the panel may be performed as part of a sphere. In this case, the axis of rotation of the rotary device pass through the geometric center of the sphere.

Device operation

To ensure communication, two sets of equipment are used, which are located at different ends of the communication line.

The optical transmitter sends to the channel collimated light pulses of radiation from the communication signals at a wavelength in the range from 400 to 700 nm. This range lies in the window of transparency of the aquatic environment. The optical system of the optical radiation receiver collects the radiation transmitted through the channel to the corresponding photosensitive devices.

When light propagates along a distance, it attenuates both due to the geometric expansion of the beam and due to scattering and absorption of radiation. An optical channel for the propagation of radiation in an aqueous medium, in comparison with, for example, atmospheric, is a channel with very strong scattering. The main attenuation of radiation occurs precisely for this reason. However, the scattering indicatrix has a strongly elongated forward shape, which is confirmed by the measurements. Figure 2 shows photographs of operating underwater communications equipment at a distance of about 10 meters in underwater conditions. Figure 2 shows that the beam of light as a whole retains its shape as it propagates, although strong scattering is noticeable. The beam is clearly visible from the side. In addition, in the photographs, you can notice that the center of the spot radiation is well fixed and determined. This means that using a position-sensitive photodetector and a controller for determining coordinates and controlling the drive, you can always point your transmitter at the glow point of the remote transmitter. To do this, the controller, using the primary data from the position-sensitive element, determines the glow point, selects its coordinates and issues control signals to the rotary device. Since the position-sensitive element is rigidly connected to the transmitter, its radiation always accurately hits the opposite communication terminal. Photo 6 in figure 2 illustrates the case when the remote transmitter directed its radiation almost exactly to the receiving aperture of the near receiver.

Thus, by introducing into the equipment a position-sensitive photodetector that is rigidly connected to the transmitter of the information channel, a two-axis rotary device and a controller that supports the guidance of the transmitter at the glow point of the remote transmitter, it is possible to provide effective spatial target selection by narrowing the radiation pattern of the transmitter. In addition, reducing the angular width of the radiation beam of the transmitter provides an increase in the energy reserve of the equipment and increases the communication range. The use of narrow beams also allows you to work with a single laser-type radiation source, which means that you can significantly increase the speed of information transfer, because in this case, modulation of an array of powerful omnidirectional light sources based on LEDs is not required, as indicated in the prototype and analogue.

For maximum realization of these advantages in the proposed equipment for underwater optical wireless communications, the transmitter has a minimum angular aperture. The angular field of view of the receiver of the information channel is of greater importance. Due to this, the requirements to the accuracy of mutual maintaining parallelism of the optical axes of the receiver and transmitter are reduced and the share of received power increases, because the receiver begins to perceive a part of the scattered light rays. The angular field of view of a position-sensitive photodetector should be even wider, because he must “see” the remote source during the guidance process, i.e. at a time when the equipment has not yet been aimed exactly at each other - at the moments of search and capture (figure 2, photo 1-5). The specific values of the aperture angles are determined by many operational, technical, economic factors, but in practice they range from 0.1 angular degrees to 3-5 degrees. A decrease in these values leads to a sharp increase in the requirements for the accuracy of the system, which are not always justified under conditions of work in a strongly scattering medium. An increase in aperture angles also leads to large losses in geometric attenuation and a decrease in the efficiency of spatial selection. In addition, the background illumination of the receivers increases, which reduces their sensitivity.

Working with small angles requires special measures for optical systems. In order to increase the viewing angles of the equipment, which is especially important when installing it on moving underwater objects, the use of a flat front panel becomes irrational. The dimensions of the panel increase dramatically. Using a spherical panel solves this problem. But the panel is the interface between an aqueous medium with a refractive index of about 1.35 and air inside the casing with a refractive index of about 1. In this situation, a convex curved surface is a negative lens. If the rotation axis of the rotary device does not coincide with the geometric center of the sphere, then during rotation the angle of incidence of the beams on the interface and their deviation from the original direction will change. This causes a violation of the parallelism of the beams, which in the far zone can lead to a sharp decrease in the level of the received signal. When the optical system rotates around the geometric center, the angle of incidence at any position will be approximately the same and the channel energy will not decrease.

Practical implementation

Figure 3 shows a photograph of the practical implementation of the proposed equipment with the protective cover removed.

The transmitter 1 is based on a semiconductor laser with a wavelength of 455 nm. The average radiation power is 150 mW. The transmitter emits modulated light and provides a channel data rate of 131 Mbps. The divergence angle of the transmitter is 3 milliradians or about 0.2 angular degrees.

The receiver 2 is made on the basis of a silicon PIN photodiode with a pad size of 400 microns and an angular field of view of 8 miliradians. The receiver and transmitter are connected to the electronics unit 3, which ensures their operation, and also matches the waveform representation of the signal in the wireless channel with the standard Fast Ethernet interface via IEEE802.3u protocol, i.e. performs the functions of an encoder-decoder.

Between the receiver and the transmitter, a position-sensitive element 5 is placed on the rigid bracket 4. It is made on the basis of a CCD matrix with the number of pixels 640x480. An optical system with a variable focal length, which provides a change in the angular field of view from 17 to 2 angular degrees, is installed in front of the matrix.

All optical subsystems are fixed in the rotary device 6. It provides angular movement around the horizontal axis by 60 degrees, and around the vertical axis by 180 degrees. The signals from the position-sensitive photodetector are processed on the controller board 7. The drivers for the drives of the rotary device are also installed there. At the top of the equipment, power supplies and connectors for connecting to the cable are installed.

Tests of the prototype underwater optical wireless equipment confirmed its high performance. The energy budget was more than 47 dB, the data transfer rate was 125 Mbps in full duplex mode with a digital error level of 10 ^-9 and a range of 50 meters, the viewing angle was +/- 15 degrees and was limited only by the size of the flat front panel. The equipment supports two operating modes - search mode and hold mode. In CCD search mode, the matrix works as an image sensor and provides video transmission to the recording equipment. The control of the rotary device in this mode is carried out manually by the operator. In the hold mode, the matrix enters the state of the angular coordinate sensor. Data from the matrix is processed in the controller, target designations are allocated, which are then sent to the drivers of the drives of the rotary device. In this mode, the equipment in automatic mode keeps pointing to the opposite communication terminal with an accuracy of 0.2 mrad. At the same time, mutual angular displacement of the terminals is allowed at a speed of up to 1 deg / s.

Claims (4)

1. Underwater optical communication equipment, comprising a waterproof casing with a front panel, with an optical transmitter installed inside the casing operating in the spectral range 400-700 nm, an optical receiver providing signal reception in the specified range, as well as an electronics unit providing the operation of the receiver and transmitter ,
characterized in that
the receiver and the transmitter are installed inside the housing on a rotary device that provides movement along two angular orthogonal coordinates and with a position-sensitive element fixed to it and rigidly connected to the transmitter, the coordinates and control controller, the input of which is connected to the position-sensitive, is introduced into the electronic blocks element, and the output with a rotary device, while the angular apertures of the optical subsystems obey the relation:
θ _t <θ _R <0 _p ,
where θ _t is the angle of divergence of the radiation of the transmitter;
θ _R is the angular field of view of the receiver;
θ _p is the angular field of view of the position-sensitive photodetector. 2. The equipment according to claim 1, in which the front panel is made of transparent material. 3. The equipment according to claim 1, in which the front panel is made in the form of part of a sphere made of transparent material, while the axis of rotation of the rotary device intersect in the geometric center of the sphere. 4. The equipment according to claim 1, in which the position-sensitive element is made in the form of a matrix photodetector with a focusing system installed in front of it.

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