WO2002041533A2 - Unite de reception de communication en espace libre avec attenuateur de puissance reglable - Google Patents
Unite de reception de communication en espace libre avec attenuateur de puissance reglable Download PDFInfo
- Publication number
- WO2002041533A2 WO2002041533A2 PCT/HU2001/000114 HU0100114W WO0241533A2 WO 2002041533 A2 WO2002041533 A2 WO 2002041533A2 HU 0100114 W HU0100114 W HU 0100114W WO 0241533 A2 WO0241533 A2 WO 0241533A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- photo
- detector
- aperture
- optical axis
- receiver unit
- Prior art date
Links
- 230000003287 optical effect Effects 0.000 claims abstract description 87
- 238000000034 method Methods 0.000 claims 1
- 230000001276 controlling effect Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 3
- 235000008331 Pinus X rigitaeda Nutrition 0.000 description 2
- 235000011613 Pinus brutia Nutrition 0.000 description 2
- 241000018646 Pinus brutia Species 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
- H04B10/112—Line-of-sight transmission over an extended range
- H04B10/1121—One-way transmission
Definitions
- the invention concerns a free space communication receiver unit, which is normally used for providing a wireless data transfer facility between two sites.
- Most known free-space receivers have a photo-detector for detecting the light intensity of an incoming light beam.
- the receivers further comprise an optical lens system for focusing the incoming light beam onto the photo-detector.
- variable optical power attenuation means between the lens system and the photo-detector.
- These attenuation means serve for the attenuation of the optical power incident on the photo- detector.
- US Patent No. 4,307,294 mentions the possibility to insert a motorised iris, i. e. a variable diameter aperture between the focusing lens and the photo-detector.
- the object of the invention is to provide an improved attenuation system, mainly for such free-space communication receivers.
- a free space communication receiver unit which comprises a photo-detector for detecting the light intensity of an incoming light beam.
- the receiver unit also comprises an optical lens system for focusing the incoming light beam onto the photo-detector.
- the variable optical power attenuation means are positioned between the lens system and the photo-detector, and during the operation of the receiver, serve for attenuating the optical power incident on the photo-detector. It is foreseen that the variable optical power attenuation means comprises an aperture, which is positioned on the optical axis between the lens system and the photo-detector.
- the aperture is positioned in a region where the effective diameter of the incoming light beam is varying as a function of the position along the optical axis, i. e. where the effective area of the cross section of the beam is not constant. Typically, such regions are found between focal points and the optics which generate the focal points on the beam.
- the receiver unit further comprises a power control circuit connected to the photo-detector. The power control unit serves for controlling the variable optical power attenuator means, and thereby controlling the optical power level incident on the photo-detector.
- the aperture may be a fixed aperture, and the moving means for translating the aperture need not be very sophisticated, and may be easily constructed in a very rugged fashion.
- the proposed attenuation system may be readily constructed from commercially available, low- cost components.
- Fig. 1 is a schematic figure illustrating the application of the invention
- Fig. 2 is a schematic drawing of a sender unit and a receiver unit of a free-space communication link
- Fig. 3 is a schematic cross-section of a receiver unit with a power attenuation system embodying the present invention, with the aperture in a first position,
- Fig. 4 is a schematic cross section of the receiver unit of Fig. 3, with the aperture in a second position
- Fig. 5 is a front view of a variable aperture applied in a further embodiment of the invention, J -
- Fig. 6 is a schematic cross section of a receiver unit similar to that of Fig. 3, but with a different layout of the control circuitry
- Fig. 7 illustrates the relation between the output signal of the photo-detector and the position of the aperture
- Fig. 8 illustrates the relation between the output signal of the photo-detector and the output signal of the control circuit of the moving means in an embodiment of the invention
- Fig. 9 illustrates the relation between the total optical power passing through the lens system and the position of the aperture.
- the free space receiver unit embodying the invention is particularly used in a communication link 10, which is shown schematically in Fig. 1.
- the communication link 10 consist of a transmitter unit 12 and a receiver unit 14, which are placed in the shown example on the roof of two buildings 16,17.
- a laser beam 18 emitted by the transmitter unit 12 and directed towards the receiver unit 14 will be received by the latter.
- the laser beam 18 is modulated with signals carrying data from a computer 21, usually forwarded to the transmitter unit via an optical cable 22.
- the modulated laser beam 18 is detected by a photo-detector in a manner described below, and the data are extracted from the optical signal by signal decoding circuitry known per se.
- the extracted data are forwarded from the receiver unit 14 via the optical cable 23 to another computer 24. This arrangement is well known in the art, and need not be discussed in more detail.
- the transmitter unit 12 comprises a laser 31 and collimating optics 32.
- the laser 31 is controlled by the laser driver 33, which in turn receives the modulating signal from an input source, e. g. the optical cable 22.
- the collimating optics 32 produces a substantially parallel laser beam 18 from the divergent radiation pattern of the laser 31, which is typically a diode laser operating in the near infrared range.
- the laser beam 18 has normally expanded in diameter when it reaches the aperture 34 of the receiver unit 14, so it may be safely assumed that the complete aperture 34 is illuminated. Due to the expansion or widening of the laser beam 18, the aperture 34 is made as large as possible, to be able to trap a large portion of the optical power of the laser beam 18.
- the receiver unit 14 of the communication link 10 comprises a photo-detector 41 for detecting the light intensity of the incoming laser beam 18.
- the optical lens system 42 consists of two lenses 43,44, but other suitable focusing optics may be used as well.
- the output of the photo-detector 41 is connected to the receiver circuit 45, and the obtained data signal is forwarded to an output line 64, which may be embodied by the optical cable 23.
- the power loss between the transmitter unit 12 and the receiver unit 14 may be substantial.
- the output power of the laser 31, and therewith the power transmitted by the laser beam 18 is set to a relatively high level, even to the extent so that the power substantially surpasses the saturation threshold of the photo-detector 41. If the weather is clear, the power loss in the air may be relatively small, and the power falling on the photo-detector 41 may be too high. For this reason, variable optical power attenuation means is provided before the photo-detector 41, with the purpose of attenuating the excess optical power incident on the photo-detector 41.
- Fig. 3 illustrates the structure of a variable power attenuation means embodying the invention.
- the variable optical power attenuation means in the receiver unit 14 comprises an aperture 46, which is positioned on the optical axis A between the lens system 42 and the photo-detector 41.
- the aperture 46 is placed in a region r where the effective diameter of the incoming laser beam 18 is varying as a function of the position x along the optical axis A.
- a region r may be found between focusing optics and the corresponding focal point (focus), but other regions along the optical axis A may also exhibit this property.
- the diameter d of the aperture 46 is smaller than the largest diameter of the laser beam 18 within the region r, so that the area of the aperture 46 is also smaller than the largest area of the cross section of the laser beam 18. Consequently, in the shown embodiment the largest cross-sectional area of the laser beam 18 within the region r will be immediately adjacent to the rear surface of the lens 44 in the lens system 42.
- the receiver unit 14 also comprises a power control circuit 47 connected to the photo-detector 41.
- This power control circuit 47 serves the potpose of controlling the variable optical power attenuator means, and thereby controlling the optical power level incident on the photo-detector 41.
- the power control circuit 47 is a simple regulating circuit, and its input 48 is connected to the output of the photo-detector 41. The functioning of this circuit will be explained with reference to Fig. 8.
- the moving means in the receiver unit 14 comprises an electric motor, namely a stepper motor 49 and a screw drive 50.
- the aperture 46 is connected to the screw drive 50 by means of an appropriate support 51.
- the support 51 will move along the optical axis A.
- the moving means may comprise a linear motor (not shown), where the aperture 46 or the support 51 is connected directly to the linear motor.
- the receiver unit of a communication link would also comprise a variable gain control circuit for controlling the gain of the photo-detector, typically a so-called automatic gain control circuit (hereafter referred to as AGC).
- AGC automatic gain control circuit
- FIG. 3 and 4 Such an embodiment is shown in Fig. 3 and 4, where the AGC 60 is connected to the output 61 of the photo- detector 41.
- the operating voltage to the photo-detector 41 is provided by the power supply 62.
- the AGC 60 is an automatic control circuit which regulates the power supply 62 of the detector 41, or the signal amplifier 63, or both, in order to provide an output signal with a constant peak amplitude on the output line 64 of the receiver unit 14.
- the aperture 46 is a fixed aperture.
- the diameter d of the aperture opening 66 (and therewith its area in practice) is constant.
- This embodiment allows a very simple attenuator mechanics, because there are no sensitive mechanical parts, like variable shutter apertures. This embodiment is shown in Figs. 3, 4 and 6.
- the aperture is a variable aperture, i. e. the diameter d of the aperture opening 66 may be changed.
- Such an aperture 146 is shown in Fig. 5.
- the aperture 146 is operated by the motor 147, which in turn is activated by the power control circuit 47 and/or by the AGC 60 via the input 148.
- This embodiment has the advantage of providing even greater operating range for the attenuator means. In practice, it is enough if the variable aperture is variable between two states only, as will be explained below.
- the input of the power control circuit 47 in the receiver unit 14 may be connected to an output 65 of the gain control circuit, e. g. an AGC 70, as shown in Fig. 6.
- the gain control circuit e. g. an AGC 70
- an output signal of the AGC 70 which is either proportional or inversely proportional to the output signal of the photo-detector 41 will be used for this purpose.
- the power control circuit 47 need not be realised as a separate circuit, but its role may be performed directly by the AGC 70 as well.
- the AGC 70 and the power control circuit 47 may be an analogue or digital circuit, depending on the specific application.
- Fig. 7 shows the operating curve of the attenuator means, with the incident power Pi ne on the horizontal axis, and the position X of the aperture along the optical axis A being shown on the vertical axis.
- the variable Pj nc denotes the optical power incident on the photo-detector 41, i. e. the total optical power passing through the optical aperture 46 or 146.
- the output signal S out of the photo-detector 41 is practically linearly proportional to the incident power Pj nc .
- This operating range may be determined by the sensitivity of the photo-detector 41 or by the input range of the AGC 60.
- the incident power Pj nc is in the operating range defined by Pi and P 2 , and therewith the value of the output signal S ou t is in the input range of the AGC 60, then the AGC 60 will be able to correct the signal amplitude fluctuations caused by the power fluctuations of the laser beam 18.
- the relevant parameters of receiver unit 14, i. e. the incident power P; nc and the position X of the aperture 46 will define a horizontal section, e. g. the section m in Fig. 7.
- the power control circuit 47 is activated.
- the operating curve of the power control circuit is shown in Fig. 8.
- the incident power Pj nc (and the proportional output signal S out ) is on the horizontal axis, while the output signal Y appearing on the output line 66 of the power control circuit 47 is on the vertical axis.
- control function of the power control circuit 47 need not exhibit the large hysteresis which is shown in Fig. 7.
- the aperture 46 provides only a coarse regulation of the incident power, and the continuous operation of the stepper motor 49 is avoided. Instead, the amplitude of the output signal on the output line 64 is held constant in the fine range by the AGC 60 or 70.
- the attenuator means will greatly enhance the overall working range of the receiver unit 14, as it is illustrated with the operating curve X(Ptot) shown in Fig. 9.
- the total incident power P tot i. e. the total optical power entering the aperture 34 of the receiver
- the position X of the aperture 46 along the optical axis A is shown on the vertical axis.
- the receiver 14 would only have a working range corresponding to a small interval, e. g.
- Fig. 9 also shows the attenuator factor F(x) of the attenuating means in the receiver unit 14, as a function of the x position of the aperture 46.
- the receiver unit 14 can sustain a laser beam 18 which have a power range between Pt ot , ⁇ and P tot ,2, much larger than the power range ⁇ P.
- the operation of the attenuation means may be improved, and its attenuation range extended, if the effective area of the aperture may be varied at least between two states.
- a first state the aperture 146 may have a very small opening. This state is used when a large portion of the laser beam should be blocked, and the aperture 46 is close to the optical lens system 42. With a very small opening, only a very small fraction of the optical power will pass tlirough the aperture.
- the small opening may be a disadvantage, if it is not possible to move the aperture close enough to the photo-detector, or particularly, when the area of the photo-detector is larger than the opening of the aperture 146.
- the attenuator means in the receiver unit may be realised with numerous modifications, without depaiting from the scope or the spirit of the invention.
- the operating curve or other characteristics of the power control circuit may have various, different forms, e. g. to take into account the variable diameter of the aperture.
- Such modifications are within the ordinary knowledge of the person skilled in the art.
- the operating principle of the attenuation means is essentially the same with a controlled power supply. As above, this fact may be considered in the design of the power control circuit.
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optical Communication System (AREA)
Abstract
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU2002218424A AU2002218424A1 (en) | 2000-11-17 | 2001-11-15 | Free space communication receiver unit with controllable power attenuator |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
HU0004568A HU0004568D0 (fr) | 2000-11-17 | 2000-11-17 | |
HUP0004568 | 2000-11-17 |
Publications (2)
Publication Number | Publication Date |
---|---|
WO2002041533A2 true WO2002041533A2 (fr) | 2002-05-23 |
WO2002041533A3 WO2002041533A3 (fr) | 2002-08-15 |
Family
ID=89978769
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/HU2001/000114 WO2002041533A2 (fr) | 2000-11-17 | 2001-11-15 | Unite de reception de communication en espace libre avec attenuateur de puissance reglable |
Country Status (3)
Country | Link |
---|---|
AU (1) | AU2002218424A1 (fr) |
HU (1) | HU0004568D0 (fr) |
WO (1) | WO2002041533A2 (fr) |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4307294A (en) * | 1980-03-04 | 1981-12-22 | Campbell Duncan B | Electro-mechanical control means for space communication receiver |
US4330870A (en) * | 1980-09-05 | 1982-05-18 | Datapoint Corporation | Optical data link |
US5065455A (en) * | 1988-05-20 | 1991-11-12 | Sony Corporation | Optical atmospheric link system |
-
2000
- 2000-11-17 HU HU0004568A patent/HU0004568D0/hu unknown
-
2001
- 2001-11-15 AU AU2002218424A patent/AU2002218424A1/en not_active Abandoned
- 2001-11-15 WO PCT/HU2001/000114 patent/WO2002041533A2/fr not_active Application Discontinuation
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4307294A (en) * | 1980-03-04 | 1981-12-22 | Campbell Duncan B | Electro-mechanical control means for space communication receiver |
US4330870A (en) * | 1980-09-05 | 1982-05-18 | Datapoint Corporation | Optical data link |
US5065455A (en) * | 1988-05-20 | 1991-11-12 | Sony Corporation | Optical atmospheric link system |
Also Published As
Publication number | Publication date |
---|---|
HU0004568D0 (fr) | 2001-02-28 |
WO2002041533A3 (fr) | 2002-08-15 |
AU2002218424A1 (en) | 2002-05-27 |
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