JP2004312698A - Optical space transmission equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive optical space transmission capable of reducing an optical axis deviation correction error due to micro-fluctuations in the atmosphere and having a non-uniform intensity distribution in received light and performing stable communication. Providing equipment.
SOLUTION: The transmission unit converts the electric signal into an optical signal and transmits the electric signal, and the reception unit converts the received optical signal into an electric signal to perform bidirectional information transmission. Regarding the optical space transmission apparatus, the apparatus has a plurality of position detecting light receiving elements for detecting the incident direction of the light beam emitted from the opponent transmitting unit in its own apparatus, and the plurality of position detecting light receiving elements have an optical path in the optical axis direction. The lengths are almost equivalent, but they are installed in a space where the optical axes of the respective position detecting light receiving elements do not coincide.
[Selection diagram] Fig. 1

Description

  The present invention relates to a space optical transmission device that is arranged to face each other at a predetermined distance and that performs bidirectional information transmission.

  Conventionally, as an optical space transmission device having a so-called optical axis correcting means for detecting the incident direction of a light beam from an opposing device and emitting the light beam emitted from the device in the incident direction, as shown in FIG. It is disclosed in Patent Literature 1, and two similar devices are arranged to face each other with a space therebetween to perform two-way communication.

  The laser light emitted from the laser diode 101 and converted into linearly polarized light in the direction perpendicular to the paper is converted into a substantially parallel light beam by a lens group 102 having a positive power, reflected at the boundary surface of the polarizing beam splitter 103, and further moved along the optical axis. The light is reflected by the angle-variable total reflection mirror 104a, and is emitted from the device A to a device B (not shown) as transmission light LA.

  The reception light LB from the device B enters the device A, is reflected by the angle-variable total reflection mirror 104a, passes through the polarization beam splitter 103, and reaches the reception light splitting element 105. At this time, about 90% of the received light LB passes through the light receiving / branching element 105, and is condensed by the lens group 107 having a positive power to the signal detecting light receiving element 106, and about 10% of the remaining 10% is received. The light is reflected by 105 and received by the position detecting light-receiving element 108 by the lens group 109 having positive power.

  As the polarization beam splitter 103, an optical element in which a multilayer thin film is deposited on the bonding surface is used. This multilayer thin film reflects, for example, S-polarized light and transmits P-polarized light. In order to perform the most efficient light emission and reception using the polarization beam splitter 103, the relationship may be such that when the transmission light LA is S-polarized light, the reception light LB is P-polarized light. Further, in order to transmit and receive light with the highest efficiency by making the transmitting and receiving apparatuses having the same configuration face each other, the beam splitter side optical axis 112, which is a common optical axis for transmission and reception, is tilted backward in the drawing. It is preferable to arrange the light LB so that the polarization directions of the light LB are orthogonal to each other.

  Further, in order to perform large-capacity communication with a large amount of information to be transmitted, a small element having an effective light receiving area less than 1 mm in diameter, such as an avalanche photodiode, must be used as the signal detecting light receiving element 106. Therefore, the positions of the main signal detection light receiving element 106 and the position detection light receiving element 108 are matched so that the reception light LB does not deviate from the effective light receiving area of the main signal detection light receiving element 106, and the position signal detection light receiving element 108 The angle of the angle-variable total reflection mirror 104a is adjusted so that the optical axis of the received light LB is substantially at the center of the mirror.

  At this time, in order for the transmission light LA to be efficiently projected toward the partner apparatus B, the optical axis of the transmission light LA may be made to coincide with the center of the position signal detecting light receiving element 108. The positional deviation information of the spot SP created by the received light LB on the light receiving surface of the position detecting light receiving element 108 is sent to the mirror driving control unit 111 as an optical axis deviation correction signal via the signal processing unit 110, and is transmitted to the mirror driving control unit 111. An optical axis direction change signal is sent from the control unit 111 to the optical axis direction movable unit 104. Based on this signal, the angle of the variable mirror 104a is changed to match the optical axes of the transmission light LA and the reception light LB.

  Such control is continuously performed during communication, and the two-way optical communication devices facing each other with a space therebetween are corrected so that the optical axis of the received light LB coming from the partner device becomes the center of the position detecting light receiving element. Is performed, the optical axes of the transmission light LB and the reception light LA can be matched with each other.

  As the position detecting light-receiving element 108 in such a conventional example, a four-split sensor divided into four elements 121 as shown in FIG. 6 is generally used. When used as a light receiving element for detection, the output changes abruptly when the spot of the received light LB crosses the separation band 122 between the divided elements. In addition, because the divider crosses through the center of the sensor, if the spot falls into the center of the sensor, no output from the sensor can be obtained. In order to prevent these, it is desirable that the spot SP of the reception light LB has an appropriate area. For this reason, the position of the light receiving surface of the four-divided sensor is generally set at a position defocused from the focal point.

In addition, it is possible to avoid intentional defocusing by using a sensor without a separation band typified by a two-dimensional PSD (semiconductor image position detecting element). However, there is a weak point that the accuracy of position detection is greatly inferior to that of a four-divided sensor, and the present situation is that a four-divided sensor must be used.
JP-A-5-133716

  However, in the optical space transmission apparatus that transmits and receives light in the air, the above-described conventional example is affected by a phenomenon in which the transmission beam fluctuates due to the vibration of the installation place of the apparatus or the fluctuation of the atmosphere. The fluctuation of the atmosphere is roughly classified into a macro fluctuation in which the entire transmitted light fluctuates and a micro fluctuation in which the intensity distribution of the transmitted light fluctuates. Atmospheric macro-fluctuations can be thought of in the same way as vibrations at the installation site, but micro-fluctuations require different thinking.

  FIG. 7 is an explanatory diagram of a modeled microscopic fluctuation of the atmosphere. W indicates the spread of the transmission light LA emitted from the partner device B at a point (position) where the receiving device A is located. The atmosphere is a non-uniform medium in which convection occurs due to different pressures and temperatures, and the refractive index varies spatially and temporally. Therefore, a portion W1 having a high intensity and a portion W2 having a low intensity are generated in the spread W of the transmission light LA. Since this intensity distribution changes with time, it is observed that W2 is shaking in the spread W of the transmission light LA. This is called microscopic fluctuation of the atmosphere, and the fluctuation is random. In the conventional optical space transmission device, the light-receiving surface of the position detecting light-receiving element 108 is set at a position defocused from the converging point. The spot SP having an appropriate area on the surface does not have a uniform intensity distribution, and the light intensity distribution at the beam inlet M of the device corresponding to the entrance pupil is projected as it is as shown in FIG. FIG. 8 shows a spot SP having an appropriate area of.

  Therefore, as shown in FIG. 9, a high intensity portion P1 and a low intensity portion P2 indicated by oblique lines occur in the spot SP having the diameter T, and the light intensity center PC different from the light flux center BC is determined to be the optical axis. Then, a shift occurs in the optical axis direction of the transmission light LA by an angle corresponding to the positional shift amount S, and as a result, the transmission light LA is detached from the partner apparatus B, and a problem that communication becomes impossible occurs.

  An object of the present invention is to solve the above-described problems, reduce the optical axis deviation correction error due to the occurrence of micro-fluctuations in the atmosphere, even if the received light has an uneven intensity distribution, and achieve stable operation. It is an object of the present invention to provide an inexpensive optical space transmission device capable of performing communication.

An optical space transmission apparatus according to the present invention for achieving the above object has a plurality of light receiving sections divided by a separation band for detecting an incident direction of a light beam emitted from a transmitting section of an opposing partner apparatus. It has at least two light receiving elements,
The optical axes of the optical systems of the at least two position detecting light-receiving elements are shifted from each other, and the amount of the shift is determined by a separation band of the position detecting light-receiving elements with respect to a plane perpendicular to the optical axis of the optical system. It is characterized in that it is larger than the width.

  Furthermore, the optical space transmission apparatus according to the present invention for achieving the above object is characterized in that the optical systems of the optical systems of the at least two position detecting light receiving elements have equivalent optical path lengths in the optical axis direction.

  The light beams incident on the at least two position detecting light receiving elements are separated by a light beam splitting element, and a light collecting element is provided in front of the light beam splitting element. The optical axis of one of the at least two position detecting light receiving elements coincides with the optical axis of the at least two position detecting light receiving elements.

  With the above-described configuration, in the present system, the position detection light is not lost even if the separation band exists in the position detection second light receiving element, and the influence of the micro-fluctuation of the atmosphere is completely eliminated. Stable communication can be performed.

  FIG. 1 is a configuration diagram of an optical space transmission apparatus according to an embodiment of the present invention. The laser beam emitted from the laser diode 1 and converted into linearly polarized light in a direction perpendicular to the paper surface becomes a substantially parallel light beam by the lens group 2 having a positive power, is reflected at the boundary surface of the polarization beam splitter 3, and is further moved in the optical axis direction. The light is reflected by the variable mirror 4a of FIG. 4 and is emitted from the device M to a device N (not shown) as transmission light LA.

  The received light LB from the device N, which is nearly linearly polarized light substantially parallel to the paper, enters the device M, is reflected by the angle-variable total reflection mirror 4a, passes through the polarization beam splitter 3, and reaches the light receiving / branching element 5. At this time, most of the received light LB passes through the light receiving / branching element 5 and is focused on the signal detecting light receiving element 6 by the lens group 7 having a positive power. The remaining received light LBb reflected by the light receiving / branching element 5 is condensed by a lens group 9 having a positive power, passes through a light beam splitting element 13 represented by a half mirror or a prism, and a part of the light beam is used for position detection. The light is received by the first light receiving element 8a, and the remaining light beam is received by the second light receiving element 8b for position detection. At this time, the optical path lengths to the position detecting first light receiving element 8a and the position detecting second light receiving element 8b are substantially the same.

  The optical axis of the position detecting first light receiving element 8a is orthogonal to the optical axis of the position detecting second light receiving element 8b.

  As shown in FIG. 2, the first light-receiving element 8a for position detection is arranged such that the intersection of the separation band (= dead zone) of the light-receiving element coincides with the optical axis of the optical system for light-receiving element for position detection. On the other hand, as shown in FIG. 3, the second light-receiving element 8b for position detection is displaced by more than the separation band width L of the light-receiving element both in the vertical and horizontal directions with respect to the optical axis of the optical system for position detection light-receiving element. D.

  In the present embodiment, the separation band width L of the light receiving element is 0.02 mm.

  By arranging the light receiving elements for position detection at such positions, when the two light receiving elements are considered on the same optical axis, the dead zone is formed by the combined action of the two elements as shown in the black portion of FIG. Is only two points where the separation widths cross each other, and the area of the separation band of the light receiving element is substantially zero. That is, since the detection signals of the two elements can correct each other, even if the spot of the reception light LBb falls to the center of the separation band of the first light-receiving element 8a for position detection which is actually the best position, the position detection signal Detection can be performed by the two light receiving elements 8b. For this reason, the control unit can recognize that the actual optical axis exists at the center of the position 8a by the signal from the position detecting second light receiving element 8b without the signal from the position detecting first light receiving element 8a. it can.

  Further, when the LBb spot moves along the separation band, it is impossible to detect the direction when the LBb spot moves along the separation band with the configuration having one position detecting light receiving element as in the conventional example. On the other hand, in the configuration of the present embodiment, even when the LBb spot falls at two points (intersection of the separation zones of the two elements), which are the remaining dead zones, the line when the number of the position detection light-receiving elements is one is small. Unlike the shape, since the spot has a small area, if the spot moves even slightly, the direction can be detected, and the function of the system is hardly impaired.

  The difference in light intensity detected by each sensor on the position detecting light-receiving element 8a or 8b is sent to the mirror drive control unit 11 as position shift information via the signal processing unit 10. In the normal mode in which the received light emitted from the other party's transmitting unit can be detected without losing the position, the signal processing unit 10 processes the positional deviation information from the first light receiving element 8a for position detection. On the other hand, in the mode in which the reception light emitted from the other party's transmission unit enters the separation band of the first light detecting element 8a for position detection and falls into the undetectable state, the light from the second light receiving element 8b for position detection is used. The signal is checked to recognize that the spot is at the center of 8a.

  With this configuration, the need for the above-described conscious defocusing of the received light is eliminated, and the beam can be narrowed down more than the conventional technology, so that the influence of the microscopic fluctuation of the atmosphere is minimized. It becomes possible.

  Further, when the signal processing unit 10 processes the positional deviation information from the position detecting second light receiving element 8b in the mode in which the position detecting first light receiving element 8a cannot detect the signal, in the present embodiment, The separation zone intersection of the sensor is shifted by a predetermined amount D in the vertical and horizontal directions from the ideal optical axis. D assumes that the spot is larger than the separator width so that neither sensor falls into the separator. However, for example, when one sensor stops sensing and the other sensor is used in chronological order, chattering may occur and the sensor may not be switched properly. In order to avoid such a situation, it is desirable that D is 1.2 times or more the width of the separation band. Further, as indicated by an arrow Ce in FIG. 4, there is an overlapping portion at the center of the sensor. The sensors are more sensitive in the central part where the separators converge, but if this part (Ce) is too large, the sensitive part of the two sensors cannot be used when the spot is located here, which is inefficient. Therefore, it is not desirable that D is less than 10 times the width of the separator.

  That is, it is preferable to satisfy 1.2 × L ≦ D <10 × L. Actually, the distance from the ideal optical axis is shifted by √2 × D, so that it is necessary to perform optical axis direction detection processing in which the distance and the direction from the ideal optical axis are corrected.

  If the correction regarding the distance and the direction from the ideal optical axis is not performed, an error occurs in the detection direction at the time of mode switching, and the system will not function. The amount of correction in the distance and direction from the ideal optical axis is determined by the amount of shift in the vertical and horizontal directions with respect to the optical axis of the second light-receiving element 8b for position detection.

  The mirror driving control section 11 sends an optical axis direction change signal to the optical axis direction movable section 4 based on the positional deviation information. The optical axis direction movable section 4 changes the angle of the angle variable total reflection mirror 4a based on the optical axis direction change signal, and adjusts the optical axis.

  As described above, they are arranged facing each other at a predetermined distance, the transmitting unit converts the electric signal to an optical signal and transmits it, and the receiving unit converts the received optical signal to an electric signal and An optical space transmission apparatus for transmitting information of the type, having incident direction detecting means for detecting an incident direction of a light beam emitted from a counterpart transmitting unit, and emitting a light beam emitted by the own device in the incident direction of the light beam. In the optical space transmission device, it is possible to provide an optical space transmission device that is lower in cost than the above-described technology such as the diffractive optical element and can perform stable communication.

  In this embodiment, the position detecting light receiving elements are the first position detecting light receiving element 8a and the position detecting second light receiving element 8b, but are not limited thereto. If the optical systems are larger than the width of the separation band, three or more light receiving elements for position detection may be used.

Configuration diagram of an optical space transmission device according to an embodiment Arrangement state of first light-receiving element for position detection in embodiment Arrangement state of second light receiving element for position detection in embodiment Image of detectable area in Example Configuration diagram of conventional optical space transmission equipment Front view of photodetector for position detection Illustration of modeled atmospheric micro-fluctuations Diagram showing light receiving state on position detecting light receiving element in conventional optical space transmission device Beam spot diagram on photodetector for position detection in conventional optical space transmission equipment

Explanation of reference numerals

1, 101 Laser diode 2, 7, 9, 102, 107, 109 Lens group 3, 103 Polarization beam splitter 4, 104 Optical axis direction movable part 5, 105 Received light splitting element 6, 106 This signal detection light receiving element 8a, 108a Position detecting first light receiving element 8b, 108b Position detecting second light receiving element 10, 110 Signal processing unit 11, 111 Mirror drive control unit 12, 112 Beam splitter side optical axis 13 Beam splitting element 21 Position detecting light receiving element Upper cross pattern 121 Sensor part on light receiving element for position detection 122 Division line dividing sensor LA Received light LB Transmitted light LBa Signal light LBb Position detection light W Spread of signal light LA at a certain point W1 Signal light LA at a certain point Part where the light intensity is locally high within the spread of W2 Spread of the signal light LA at a certain point Locally weak light intensity in the beam M Beam taking-in diameter of the device SP Beam spot on the position detecting light receiving element BC Center of light flux PC Center of light intensity P1 Local light intensity in the beam spot on the position detecting light receiving element Part where the light intensity is strong P2 Part where the light intensity is locally low in the beam spot on the light receiving element for position detection

Claims (3)

A transmitting unit that converts an electric signal into an optical signal, and a receiving unit that converts a received optical signal into an electric signal, comprising:
At least two position detecting light receiving elements having a plurality of light receiving units divided by a separation band for detecting the incident direction of the light beam emitted from the transmitting unit of the opposing partner device,
The optical axes of the optical systems of the at least two position detecting light-receiving elements are shifted from each other, and the amount of the shift is determined by a separation band of the position detecting light-receiving elements with respect to a plane perpendicular to the optical axis of the optical system. An optical space transmission device characterized by being larger than the width of   The optical space transmission apparatus according to claim 1, wherein the optical path lengths of the optical systems of the at least two position detecting light receiving elements in the optical axis direction are equivalent.   The light beams incident on the at least two position detecting light receiving elements are separated by a light beam splitting element, and a light collecting element is provided in front of the light beam splitting element, and the optical axis of the light collecting element and the at least The optical space transmission apparatus according to claim 1, wherein an optical axis of one of the two light receiving elements for position detection coincides with an optical axis of the light receiving element for position detection.

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