WO2018107452A1 - 自由空间通信系统中的光通信装置和方法以及发射天线 - Google Patents

自由空间通信系统中的光通信装置和方法以及发射天线 Download PDF

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Publication number
WO2018107452A1
WO2018107452A1 PCT/CN2016/110296 CN2016110296W WO2018107452A1 WO 2018107452 A1 WO2018107452 A1 WO 2018107452A1 CN 2016110296 W CN2016110296 W CN 2016110296W WO 2018107452 A1 WO2018107452 A1 WO 2018107452A1
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Prior art keywords
optical signal
optical
unit
light
communication device
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PCT/CN2016/110296
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English (en)
French (fr)
Inventor
赵平
石晓钟
叶亚斌
格尔杰格洛特
刘宁
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华为技术有限公司
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Priority to CN201680091490.8A priority Critical patent/CN110050416B/zh
Priority to PCT/CN2016/110296 priority patent/WO2018107452A1/zh
Publication of WO2018107452A1 publication Critical patent/WO2018107452A1/zh

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    • 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

Definitions

  • Embodiments of the present invention relate to the field of communications, and more particularly, to an optical communication apparatus and method and a transmit antenna in a free space communication system.
  • OWC Optical Wireless Communication
  • High-speed outdoor OWC usually uses 1550nm infrared light wave as the carrier wave, and uses a beam with a very small divergence angle to transmit the signal.
  • the beam divergence angle is less than 0.1 degree.
  • factors such as external jitter tend to cause the beam to deviate from the receiving antenna, causing the optical path to be interrupted. Therefore, the use of tracking technology to perform antenna alignment to ensure that the power of the received optical signal is above the sensitivity required by the photodetector is an important research direction in the field.
  • Embodiments of the present invention provide an optical communication apparatus and method and a transmitting antenna in a free space communication system, which are advantageous for achieving antenna alignment in a free space communication system by signal tracking.
  • an optical communication device in a free space communication system comprising: a light emitting unit for transmitting a first optical signal having a first wavelength; and a light converting unit configured to receive the first light emitted by the light emitting unit An optical signal, the first partial optical signal of the first optical signal is converted into a second optical signal having a second wavelength, and the second partial optical signal and the second optical signal of the first optical signal are output, wherein And the second optical signal is used as beacon light for performing signal tracking, the second partial optical signal is used as communication light for carrying customer data, and the transmitting unit is configured to send the optical conversion unit to the first opposite communication device. The second partial optical signal and the second optical signal are output.
  • the first peer communication device and the optical communication device may be disposed at two spaced locations and may be at respective distal ends of the other party.
  • the second partial optical signal can be used as communication light, wherein the communication light can be an optical signal carrying customer data.
  • the second optical signal can be used as beacon light, wherein the beacon light can be used to track communication light for antenna alignment.
  • the first peer communication device can be based on the beacon light, The transmission direction of the communication light is tracked, and then the spot position of the communication light is controlled to be at the center of the fiber.
  • the optical communication device transmits a first optical signal having a first wavelength by the light emitting unit, and the optical conversion unit performs a frequency conversion conversion process on the first partial optical signal of the first optical signal to obtain a second optical signal.
  • a second optical signal of a wavelength the transmitting unit transmitting the second optical signal and the second partial optical signal of the first optical signal to the first peer communication device, so that the first peer communication device can be according to the second Part of the optical signal is antenna aligned to improve signal transmission performance.
  • the second optical signal and the second partial optical signal can be transmitted to the free space through the same optical path, no additional setting is needed for transmitting the signal.
  • the light-emitting unit of the light source and the light path for transmitting the beacon light thereby saving equipment cost and size and design complexity.
  • the second wavelength is less than the first wavelength.
  • the first wavelength is an integer multiple of the second wavelength;
  • the light conversion unit comprises: a light frequency doubling crystal.
  • the first optical signal may be subjected to frequency conversion processing using a light frequency doubling crystal to convert the first partial optical signal of the first optical signal into the second optical signal.
  • the first optical signal is incident on the optical frequency doubling crystal from the first surface, and is reflected from the third surface by the second surface of the at least one second surface of the optical frequency doubling crystal.
  • a light frequency doubling crystal wherein the first surface and the third surface are plated with an anti-reflection film, and the at least one second surface is plated with a reflective film.
  • the first optical signal may be incident on the first frequency doubling crystal perpendicular to the first surface, and the light doubling crystal may be emitted perpendicular to the third surface.
  • first surface and the third surface may be perpendicular to each other, and an angle between the second surface and the first surface and the third surface may be 45 degrees.
  • the first surface, the second surface, and the third surface may both be sides of the optical frequency doubling crystal, and the thickness h of the light doubling crystal may be greater than the first optical signal incident on the optical frequency doubling
  • the beam diameter at the time of the crystal is 2w 1 to reduce the loss of the first optical signal.
  • the first optical signal can be transmitted in the optical frequency doubling crystal for a sufficiently long distance to improve conversion efficiency.
  • the photomultiplying crystal has at least one chamfer, and the at least one second surface includes the at least one chamfered surface.
  • the chamfer angle may be a 45-degree chamfer.
  • the photo-doubling crystal may be obtained by cutting a crystal having a square shape into three right angles.
  • the chamfered surface can serve as a reflective surface for the first optical signal.
  • the distance L eff transmitted by the first optical signal in the optical frequency doubling crystal satisfies the following conditions:
  • P T, C S C + M C + P R, C + L Rx, C + L A, C + L G, C + L Tx, C ,
  • P T, B S B + M B + P R, B + L Rx, B + L A, B + L G, B + L Tx, B ,
  • P T, C is the power of the second partial optical signal when incident on the optical frequency doubling crystal
  • S C is the sensitivity of the first detector for receiving the second partial optical signal in the first peer communication device
  • P R, C is the power when the second partial optical signal reaches the first detector
  • L Tx, C is the loss of the second partial optical signal in the first peer communication device
  • L G, C is the first The divergence loss of the two partial optical signals
  • L G, C is the atmospheric absorption loss of the second partial optical signal
  • L Rx, C is the loss of the second partial optical signal in the opposite communication device
  • M C is the first two link margin portion of the optical signal
  • P T, B for the second optical signal incident to the optical power when the frequency doubling crystal
  • the sensitivity of the second detector, P R, B is the power when the second optical signal reaches the second detector
  • L Tx, B is the loss of the second optical signal in the optical conversion unit
  • the optical path can be designed based on the actual link power budget and the appropriate device parameters can be selected.
  • the optical conversion unit further includes: a width conversion unit, configured to receive the first optical signal transmitted by the illumination unit, and receive the The beam width of the first optical signal is converted from the first width to the second width; the optical frequency doubling crystal is specifically configured to receive the first optical signal having the second width output by the width conversion unit, and the received A first partial optical signal of the first optical signal having the second width is converted into the second optical signal, and the second partial optical signal and the second optical signal are output.
  • the width conversion unit includes: a first convex lens and a concave through the optical path a mirror, wherein a focus of the first convex lens coincides with a focus of the concave lens.
  • the focal length f 1 of the first convex lens and the focal length f 2 of the concave lens satisfy the following relationship:
  • D 1 is the beam width when the first optical signal is incident on the first convex lens
  • 2w 1 is the beam width when the first optical signal is emitted from the concave lens
  • the sending unit is configured to: send, to the first peer communication device, a first light beam including the second partial optical signal and the second optical signal, where a beamwidth and/or a beam width of the first beam The divergence angle satisfies the preset condition.
  • the transmitting unit includes: a second convex lens and a third convex lens disposed in sequence along the optical path, wherein a focal length f 3 of the second convex lens The focal length f 4 of the third convex lens satisfies the following relationship:
  • D 2 is the beam diameter of the first beam.
  • the optical communications apparatus further includes: an optical amplifying unit, configured to receive the first optical signal that is sent by the illuminating unit, the first The optical signal is amplified, and the amplified first optical signal is output; the optical conversion unit is specifically configured to receive the amplified first optical signal output by the optical amplifying unit.
  • the optical communication device further includes: a receiving unit, a rotatable optical system, a light separating unit, a light detecting unit, and a control unit, where The receiving unit is configured to receive a second light beam sent by the second peer communication device, where the second light beam includes a third optical signal having a first wavelength and a fourth optical signal having a second wavelength; And guiding the transmission direction of the second light beam received by the receiving unit; the light separating unit is configured to receive the second light beam guided by the rotatable optical system, and separate the third optical signal in the second light beam and the a fourth optical signal; the light detecting unit is configured to receive a third optical signal of the second light beam transmitted by the optical separating unit, and perform demodulation processing on the data modulated in the third optical signal; the control unit is configured to: Receiving a fourth optical signal of the second light beam transmitted by the optical separating unit, and controlling an angle of the rotatable optical system
  • the third optical signal can be used as communication light, and the fourth optical signal can be used as beacon light.
  • the light separating unit comprises a splitter plate for separating the optical signals of the first wavelength and the second wavelength.
  • the control unit includes: a location detecting unit and an adjusting unit, where the location detecting unit is configured to receive the optical component Determining, by the unit, the fourth optical signal, determining a position of the optical center of the fourth optical signal, and transmitting information of the optical center position to the adjusting unit; the adjusting unit is configured to receive the optical center position transmitted by the position detecting unit Information and, depending on the information, adjust the angle of the rotatable light system.
  • the position detecting unit comprises: a silicon four quadrant detector.
  • the use of a silicon four-quadrant detector can reduce device cost compared to the use of an infrared four-quadrant detector or other device.
  • a second aspect provides a transmit antenna in a free space communication system, including: a receiving unit configured to receive a first optical signal transmitted by an optical transmitter; and a light converting unit configured to receive the first received by the receiving unit A first portion of the optical signal in the optical signal is converted to a second optical signal having a second wavelength, wherein the second optical signal acts as beacon light for signal tracking, and the second portion of the optical signal serves as carrier data for carrying
  • the communication unit is configured to send, to the first peer communication device, the second partial optical signal of the first optical signal and the second optical signal obtained by the optical conversion unit.
  • the receiving unit may comprise a receiving lens.
  • a receiving lens For example, a convex lens.
  • the first wavelength is an integer multiple of the second wavelength;
  • the light conversion unit comprises: a light frequency doubling crystal.
  • the optical conversion unit further includes: a width conversion unit, configured to receive the first optical signal transmitted by the optical transmitter, and convert the received beam width of the first optical signal from a first width to a first width a second width; the optical frequency doubling crystal is specifically configured to receive the first optical signal having the second width output by the width converting unit, and receive the first portion of the first optical signal having the second width The signal is converted into the second optical signal, and the second partial optical signal and the second optical signal are output.
  • a width conversion unit configured to receive the first optical signal transmitted by the optical transmitter, and convert the received beam width of the first optical signal from a first width to a first width a second width
  • the optical frequency doubling crystal is specifically configured to receive the first optical signal having the second width output by the width converting unit, and receive the first portion of the first optical signal having the second width The signal is converted into the second optical signal, and the second partial optical signal and the second optical signal are output.
  • the width conversion unit comprises: a first convex lens and a concave lens arranged in sequence along the optical path, wherein a focus of the first convex lens coincides with a focus of the concave lens.
  • the sending unit is configured to receive the second partial optical signal and the second optical signal output by the optical frequency doubling crystal, and send the second partial optical signal to the first peer communication device and the a first beam of the second optical signal, wherein a beamwidth and/or a divergence angle of the first beam satisfy a predetermined condition.
  • the sending unit includes: a second convex lens and a third convex lens disposed in sequence along the optical path, wherein a focal length f 3 of the second convex lens and a focal length f 4 of the third convex lens satisfy the following relationship:
  • D 2 is the beam diameter of the first beam.
  • the transmit antenna can be used to implement the functions of the optical conversion unit and the transmit unit in the first aspect or any possible implementation of the first aspect.
  • an optical communication device in a free space communication system comprising an optical transmitter and a transmit antenna in any of the possible implementations of the second aspect or the second aspect.
  • a fourth aspect provides an optical communication method in a free space communication system, including: transmitting a first optical signal having a first wavelength; performing a conversion process on the first optical signal to cause the first optical signal to be The first portion of the optical signal is converted to a second optical signal having a second wavelength; and the second portion of the first optical signal and the second optical signal are transmitted to the first peer communication device.
  • the first wavelength is an integer multiple of the second wavelength; the first optical signal is converted to convert the first partial optical signal in the first optical signal into a second optical signal
  • the optical signal includes: converting the first optical signal by using a light frequency doubling crystal to convert the first portion of the first optical signal into a second optical signal having the second wavelength.
  • the method before the converting the first optical signal by using the optical frequency doubling crystal, the method further includes: performing a width conversion process on the first optical signal, so that the beam width of the first optical signal is The width is changed to the second width; the converting the first optical signal by using the optical frequency doubling crystal comprises: converting, by the optical frequency doubling crystal, the first optical signal having the second width of the beam width.
  • the optical communication method can be performed by the optical communication device of the first aspect or any possible implementation of the first aspect.
  • the optical communication method may be performed by the optical communication device of the third aspect or any possible implementation of the third aspect.
  • FIG. 1 is a schematic block diagram of a typical optical communication device having a tracking function in a free space communication system.
  • FIG. 2 is a schematic block diagram of an optical communication apparatus according to an embodiment of the present invention.
  • FIG. 3a is a schematic perspective view of a light doubling crystal in an optical communication device according to an embodiment of the present invention.
  • Figure 3b is a top plan view of the optical frequency doubling crystal shown in Figure 3a.
  • FIG. 4 is a schematic diagram of an optical path of an optical communication device according to an embodiment of the present invention.
  • FIG. 5 is another schematic block diagram of an optical communication apparatus according to an embodiment of the present invention.
  • FIG. 6 is another schematic block diagram of an optical communication apparatus according to an embodiment of the present invention.
  • FIG. 7 is a schematic block diagram of another optical communication apparatus according to an embodiment of the present invention.
  • FIG. 8 is a schematic block diagram of a free space communication system according to an embodiment of the present invention.
  • FIG. 9 is a schematic diagram of an optical path example of a free space communication system according to an embodiment of the present invention.
  • FIG. 10 is a schematic flowchart of an optical communication method according to an embodiment of the present invention.
  • Figure 1 shows an example of a typical optical communication device with a tracking function in a free space communication system.
  • the optical communication device 100 includes a lens 1 for receiving an illumination signal, and a lens 2 and a movable mirror 3 behind the lens 1 on the optical path.
  • the polarization beam splitter 4 The lens 5 and the illuminating device 6 are placed in the incident direction of the movable mirror 3, and the beam splitting mirror 7, the lens 8 and the position detector 9 are placed in the reflection direction of the polarizing beam splitter 4, and the lens 10 and the light receiving element 11 It is placed in the reflection direction of the beam splitting mirror 7.
  • the output of the multiplexer 12 is connected to the illuminating device 6, and the output of the transmitting signal input terminal 13 is connected to the multiplexer 12 via an amplifier 14, and the output of the oscillator 15 is also connected to the multiplexer 12.
  • the output of the light receiving element 11 is connected to the received signal output terminal 17 via an amplifier 16.
  • the output of the position detector 9 is connected to a tracking control circuit 18, and the output of the tracking control circuit 18 is connected to the movable mirror 3 by means of drivers 19 and 20 for adjusting the angle of the movable mirror 3.
  • the scope 21 for the observer to inspect the aiming axis is approximately parallel to the optical axis of the movable mirror 3.
  • the transmission signal is input through the transmission signal input terminal 13, amplified by the amplifier 14, multiplexed with the signal from the oscillator 15 in the multiplexer 12, and then output to the illuminating device 6.
  • the illuminating device 6 modulates the emitted light according to the input signal to convert the input signal into an optical signal.
  • the light beam output from the light-emitting device 6 reaches the polarization beam splitter 4 via the collimation processing of the lens 5, and since the polarization of the light beam is parallel to the drawing plane, the polarization beam splitter 4 transmits the light beam as it is.
  • the beam is reflected by the movable mirror 3 to the left and then transmitted through the lenses 2 and 1 to the opposite end device.
  • the light beam from the opposite end device Upon receiving the optical signal, the light beam from the opposite end device is incident on the left side of the lens 1, is reflected by the lens 2 to the movable mirror 3, and then reaches the polarized beam splitter 4. Since the direction of polarization of the beam is perpendicular to the plane of the drawing, the beam is reflected by the polarizing beam splitter 4 to the right and then separated by the beam splitting mirror 7 into two directions.
  • the light beam reflected by the beam splitting mirror 7 passes through the lens 10 to the light receiving element 11, and is converted into an electrical signal, which is then amplified by the amplifier 16 to an appropriate level, and then the amplified signal is The received signal output terminal 17 outputs.
  • the light beam projected by the beam splitting mirror 7 is concentrated by the lens 8, and then received as a point image by the position detector 9.
  • the position detector 9 detects the position of the point image S and outputs the position to the tracking control circuit 18 in the form of a position signal.
  • the tracking control circuit 18 calculates an angle of the light beam from the opposite end device with respect to the optical path of the optical communication device 100 based on the position signal, and transmits a drive signal to the drivers 19 and 20.
  • the drivers 19 and 20 adjust the angle of the movable mirror 3 such that the point image S falls at the center of the position detector 9. By this adjustment, the position of the illumination device 6 is also adjusted so that the optical path of the emitted beam coincides with the optical path of the incident beam, and the beam is accurately transmitted to the opposite end device.
  • the position detector 9 selectively detects an AC beacon signal of a specific frequency.
  • the beacon signal is generated by the oscillator 15 and is multiplexed with the transmission signal in the multiplexer 12 as an input signal of the illumination device 6, the illumination device 6 generating an optical signal of a specific wavelength according to the input signal and transmitting it to the pair End device.
  • the optical signal is separated into two parts, one for tracking and the other for transmission to the light receiving element 11. Since the optical transmission power in the free space communication system is limited, the signal for tracking partially causes power loss of the transmitted optical signal, so that the transmission power of the communication light is lower than the maximum transmission power, thereby reducing the communication quality and limiting the communication distance.
  • the maximum transmission power of the communication light can be improved while achieving antenna alignment, thereby improving communication quality and increasing communication distance. Improve system margin and overall performance.
  • FIG. 2 exemplarily shows an optical communication device 200 provided by an embodiment of the present invention.
  • the optical communication device 200 can be adapted to a free space communication system in which the optical communication device 200 and the first peer communication device can be separately located at two relative positions and can communicate by transmitting optical signals to free space.
  • the optical communication device 200 includes:
  • a light emitting unit 210 configured to emit a first optical signal having a first wavelength
  • the light conversion unit 220 is configured to receive the first optical signal emitted by the light emitting unit 210, convert the first partial optical signal of the first optical signal into a second optical signal having a second wavelength, and output the first optical signal. a second partial optical signal and the second optical signal, wherein the second optical signal serves as beacon light for performing signal tracking, and the second partial optical signal serves as communication light for carrying customer data;
  • the sending unit 230 is configured to send the second partial optical signal and the second optical signal output by the optical converting unit 220 to the first peer communication device.
  • the light emitting unit 210 can emit the first optical signal and transmit the first optical signal to the light converting unit 220, wherein the wavelength of the first optical signal is the first wavelength.
  • the illuminating unit 210 may include a laser, but the embodiment of the present invention does not limit this.
  • the optical converting unit 220 may perform frequency conversion processing on a part of the optical signals in the first optical signal to obtain a second optical signal, where the wavelength of the second optical signal is different from the first a second wavelength of one wavelength, and outputting another portion of the optical signal and the second optical signal of the first optical signal.
  • the sending unit 230 may send a first light beam to the first peer communication device by using a free space, where the first light beam may include the second optical signal and a second partial optical signal of the first optical signal.
  • the second optical signal can be used for signal tracking by the first peer communication device, that is, the second optical signal can be used as beacon light, and the second partial optical signal can be modulated with data, that is, the second portion.
  • the light signal can be used as communication light.
  • the first optical signal having the first wavelength is emitted by the light emitting unit, and the optical conversion unit performs a frequency conversion conversion process on the first partial optical signal of the first optical signal to obtain a second optical signal having the second wavelength, and the transmitting unit
  • the first peer communication device transmits the second optical signal and the second partial optical signal of the first optical signal, and the first peer communication device can use the second partial optical signal to perform antenna alignment, which is beneficial to improving the signal. Transmission performance.
  • the second optical signal and the second partial optical signal can be transmitted to the free space through the same optical path, no additional setting is needed for transmitting the signal.
  • the light-emitting unit of the light source and the light path for transmitting the beacon light save equipment cost and design complexity.
  • the optical converting unit 220 may perform up-conversion processing on the first partial optical signal in the first optical signal to obtain the second optical signal.
  • the wavelength of the second optical signal may be smaller than the wavelength of the first optical signal, that is, the second wavelength may be smaller than the first wavelength, but the relationship between the first wavelength and the second wavelength is not in the embodiment of the present invention. Make a limit.
  • the first wavelength may be an integer multiple of the second wavelength.
  • the first wavelength may be an even multiple of the second wavelength, for example, the first wavelength is 1550 nm, and the second wavelength is 775 nm.
  • the light conversion unit 220 may include one or more optical frequency doubling crystals, which may double the frequency of at least a part of the optical signals incident thereon, that is, at least a part of the optical signals The wavelength becomes one third of the original wavelength.
  • the first wavelength may be an odd multiple of the second wavelength.
  • the light conversion unit 220 may include one or more triple frequency crystals, and the triple frequency crystal The frequency of at least a portion of the optical signals incident thereon may be changed to three times the initial frequency, that is, the wavelength of at least a portion of the optical signals becomes one-third of the initial wavelength, but the embodiment of the present invention is not limited thereto.
  • the following description is made by taking the light conversion unit 220 including a light frequency doubling crystal as an example, but those skilled in the art should understand that the description is merely exemplary and not restrictive, and the light conversion unit in the embodiment of the present invention 220 may also have other implementations.
  • the photomultiplying crystal may have a shape such as a cube, a rectangular parallelepiped or a hexahedron.
  • the first optical signal may be incident on the optical frequency doubling crystal from the first surface, wherein the first surface may be a certain side of the optical frequency doubling crystal, and the first optical signal is at least one of the optical doubling crystals
  • the light frequency doubling crystal is emitted from the third surface, wherein the third surface may be a certain side of the light frequency doubling crystal, and is convenient for optical path design
  • the third surface may be different from the first surface, but embodiments of the invention are not limited thereto.
  • the first surface and the third surface may be plated with an anti-reflection film, and each of the at least one second surface may be plated with Reflective film.
  • the reflectance of the reflective film to the optical signals of the first wavelength and the second wavelength may be higher than 99.9%, and the transmittance of the antireflection film to the optical signals of the first wavelength and the second wavelength may be higher than 99.9%.
  • this embodiment of the present invention does not limit this.
  • the first optical signal may be incident on the optical frequency doubling crystal in the form of a parallel beam.
  • the first optical signal can propagate a sufficiently long distance within the optical frequency doubling crystal to convert the first portion of the first optical signal into a second optical signal.
  • the second optical signal and the second partial optical signal may exit the optical frequency doubling crystal in the form of a parallel beam.
  • the thickness of the optical frequency doubling crystal may be much larger than the incident beam diameter of the first optical signal.
  • the optical doubling crystal may have a thickness greater than 5 times the incident beam diameter of the first optical signal.
  • the at least one second surface may be the side of the light frequency doubling crystal, but the embodiment of the invention is not limited thereto.
  • the optical frequency doubling crystal may be processed.
  • the light frequency doubling crystal may be formed by cutting three right angles of a rectangular parallelepiped having an upper surface, wherein the square has a side length L, and the corner angle may be For a 45 degree cut angle, the chamfered surface (ie, the cut surface) may serve as a reflective surface of the optical signal, that is, the at least one second surface may include a cut surface, but the embodiment of the present invention is not limited thereto.
  • a reflective film may be plated on each of the three cut faces, and a transmissive film may be plated on both of the remaining right angle sides, but the embodiment of the invention is not limited thereto.
  • the beam diameter of the first optical signal may be transformed to meet the frequency conversion requirement.
  • the optical conversion unit 220 may further include: a width conversion unit, configured to receive the first optical signal transmitted by the illumination unit 210, and receive the received beam width of the first optical signal. Converting from the first width to the second width, and outputting the first optical signal having the second width of the beam width.
  • the optical frequency conversion crystal may be specifically configured to receive the first optical signal whose beam width is the second width of the width conversion unit, and perform frequency conversion processing on the received first optical signal having the second width. Obtaining the second optical signal and the second partial optical signal.
  • the second optical signal and the second partial optical signal may form a parallel beam, and a beam width of the parallel beam may be maintained at a second width, but the embodiment of the present invention Not limited to this.
  • the width transform unit may have multiple implementations.
  • the width conversion unit may include a first convex lens 222 and a concave lens 223 which are sequentially disposed along the optical path, wherein a focus of the first convex lens coincides with a focus of the concave lens.
  • the width D of the parallel beam incident on a convex lens 222 after the first can be emitted and enters the concave lens 223 in the form of a converging beam, since the The true focus of the first convex lens 222 coincides with the virtual focus of the concave lens 223, and the concentrated light beam can be converted into a parallel light beam having a width of 2w 1 after being refracted by the concave lens 223.
  • the focal length f 1 of the first convex lens 222 and the focal length f 2 of the concave lens 223 can satisfy the formula (1).
  • the optical frequency doubling crystal 221 can also have other forms of chamfering, and the optical path of the first optical signal in the optical doubling crystal 221 can be designed according to specific requirements. This example does not limit this.
  • the optical communication device 200 further includes a sending unit 230, configured to Receiving the second partial optical signal and the second optical signal output by the optical conversion unit 220, and transmitting, to the first peer communication device, a first light beam including the second partial optical signal and the second optical signal, where The beam width and/or the divergence angle of the first beam satisfy a preset condition.
  • the first light beam may be a parallel light beam or an approximately parallel light beam, wherein the first light beam may have a divergence angle of 0.2 to 1.5 mrad, but the embodiment of the present invention is not limited thereto.
  • the transmitting unit 230 can transmit the second partial optical signal and the second optical signal in the same light beam. Alternatively, the transmitting unit 230 can transmit the second optical signal and the second portion in an approximately parallel beam form. Optical signal, but embodiments of the invention are not limited thereto.
  • the sending unit 230 may send the second optical signal and the second partial optical signal through a convex lens.
  • the sending unit 230 may include: a second convex lens 231 and a third convex lens 232 which are sequentially disposed along the optical path, wherein the focal length f 3 and the third of the second convex lens 231 The focal length f 4 of the convex lens 232 satisfies the formula (2).
  • D 2 is the beam diameter of the first beam.
  • D 2 may be less than or equal to the diameter of the third convex lens
  • the focal points of the second convex lens 231 and the third convex lens 232 overlap on the optical path, but the embodiment of the present invention is not limited thereto.
  • the second convex lens 231 may be a self-focusing lens, wherein the self-focusing lens may be a cylindrical lens, and the length L G may be an odd multiple of the focal length f 3 , which is not limited in the embodiment of the present invention.
  • the distance between the optical doubling crystal 221 and the concave lens 223 and the distance between the optical doubling crystal 221 and the second convex lens 231 may be as short as possible, optionally, by the concave lens.
  • the optical path length L' of the 223 exit surface reaching the second convex lens 231 may satisfy the formula (3), but the embodiment of the invention is not limited thereto.
  • FIG. 4 is intended to help those skilled in the art to better understand the embodiments of the present invention and not to limit the scope of the embodiments of the present invention.
  • a person skilled in the art will be able to make various modifications or changes in the form of the embodiment of FIG. 4, and such modifications or variations are also within the scope of the embodiments of the present invention.
  • the proportion of the first partial optical signal in the first optical signal and the ratio of the first optical signal may be determined according to a power budget of the OWC link between the optical communication device 200 and the first peer communication device.
  • the parameters of the light doubling crystal For example, as shown in FIG. 5, in order to cause the second optical signal and the second partial optical signal transmitted by the optical communication device 200 through the OWC link to reach the first peer communication device, the power is at the first opposite end.
  • the transmission power P T of the second partial optical signal and the second optical signal may satisfy Equations (4) and (5), respectively, wherein the subscript B indicates as a beacon.
  • the relevant parameter of the second optical signal of light, subscript C represents the relevant parameter of the second part of the optical signal as communication light.
  • P T,C S C +M C +P R,C +L Rx,C +L A,C +L G,C +L Tx,C (4)
  • P T, B S B + M B + P R, B + L Rx, B + L A, B + L G, B + L Tx, B (5)
  • P T represents the transmission power of the optical signal, that is, the power when the optical signal is incident on the optical doubling crystal
  • S C represents the sensitivity of the corresponding detector of the optical signal, that is, the first pair of communication devices are used to receive the light.
  • the sensitivity of the detector of the signal P R represents the received power of the optical signal, that is, the power when the optical signal reaches the corresponding detector, and L Tx represents the transmit antenna loss of the optical signal, that is, the loss of the optical signal in the optical communication device 200, L G represents the divergence loss of the optical signal, L A represents the atmospheric absorption loss of the optical signal, L Rx represents the receiving antenna loss of the optical signal, that is, the loss of the optical signal in the first peer communication device, and M C represents the optical signal.
  • Link margin can be used to combat random attenuation caused by uncertainties such as rain and fog in the channel.
  • L G, C L G, B , and can be determined by equation (6):
  • ⁇ represents the divergence angle of the light beam in free space
  • the unit is millirad (mrad)
  • R represents the communication distance between the optical communication device 200 and the first peer communication device, and the unit is kilometer
  • D R represents the first The size of the receiving lens of the one-end communication device, in meters.
  • the parameters of the optical frequency doubling crystal may be determined according to equations (7) to (9).
  • n is the refractive index of the photomultiplying crystal
  • C is the vacuum light speed
  • ⁇ is the circular frequency of the first optical signal
  • d eff is the second-order nonlinear coefficient of the optical doubling crystal
  • ⁇ 0 is the vacuum dielectric constant
  • the effective length L eff of the optical frequency doubling crystal and the beam radius w 1 when the first optical signal enters the optical doubling crystal can be determined according to the power budget requirement, and the design is accordingly The optical path of the first optical signal.
  • Table 1 shows an example of the power budget of the OWC link, in which the transmission power of the communication light is 26.5 dBm (ie, 446 mW), and the transmission power of the beacon light is 15.8 dBm (ie, 38 mW), which is obtained by solving the above equation.
  • the relevant device parameters on the optical path can be determined according to the above L eff and w 1 , and a suitable device can be selected accordingly.
  • Table 2 shows parameter examples of the respective devices in the optical conversion unit 220 and the transmission unit 230 corresponding to the power budget example of Table 1, in which the unit of length is mm.
  • the optical communication device 200 may further include: an optical amplifying unit 240, configured to receive the first optical signal emitted by the lighting unit 210, and perform the first optical signal. The amplification process is performed, and the first optical signal after the amplification process is output.
  • the light conversion unit 220 may be specifically configured to receive the first light after the amplification process output by the optical amplifying unit 240. signal.
  • the optical amplifying unit 240 may be specifically an Erbium Doped Fiber Amplifier (EDFA), but the embodiment of the present invention is not limited thereto.
  • EDFA Erbium Doped Fiber Amplifier
  • the optical communication device 200 may further include: a first collimating unit 250 located before the optical switching unit 220 on the optical path, configured to perform collimation processing on the first optical signal, and output The first optical signal after the collimation process, wherein the first optical signal after the collimation process may be a parallel beam.
  • the optical conversion unit 220 may be specifically configured to receive the collimated first optical signal output by the first collimating unit 250.
  • the first collimating unit 250 can be disposed between the light emitting unit 210 and the light converting unit 220 on the optical path, specifically for receiving the first optical signal output by the light emitting unit 210, and illuminating the first light signal.
  • the first optical signal output by unit 210 is subjected to a collimation process.
  • the first collimating unit 250 may be disposed between the optical amplifying unit 240 and the optical converting unit 220 on the optical path, specifically for receiving the amplified processing output by the optical amplifying unit 240.
  • An optical signal is subjected to collimation processing on the amplified first optical signal output from the optical amplifying unit 240, but the embodiment of the present invention is not limited thereto.
  • the first collimating unit 250 may include a convex lens, but the embodiment of the invention is not limited thereto.
  • the optical communication device 200 can also be used to receive optical signals transmitted by other communication devices.
  • 6 shows functional units related to reception of optical signals in the optical communication device 200: a receiving unit 260, a rotatable optical system 265, a light separating unit 270, a light detecting unit 275, and a control unit 280.
  • the receiving unit 260 is configured to receive a second light beam sent by the second peer communication device, wherein the second light beam comprises a third optical signal having a first wavelength and a fourth optical signal having a second wavelength.
  • the receiving unit 260 may include a convex lens, and the second light beam may be specifically a parallel beam or an approximately parallel beam.
  • the second peer communication device may be the same or different device as the first peer communication device, which is not limited in this embodiment of the present invention.
  • the wavelength of the third optical signal is a first wavelength, and can be used as communication light for modulating data.
  • the wavelength of the fourth optical signal is a second wavelength, which can be used as beacon light for signal tracking.
  • the rotatable light system 265 is used to guide the transmission direction of the second light beam received by the receiving unit 260.
  • the optical communication device may further include a second collimating unit, which may be used to receive the receipt The optical signal received by element 260 is collimated to obtain a parallel beam.
  • the rotatable optical system 265 can be specifically configured to guide the transmission direction of the parallel beams output by the second collimating unit.
  • the second collimating unit may be located between the receiving unit 260 and the rotatable optical system 265 on the optical path, but the embodiment of the invention is not limited thereto.
  • the rotatable optical system can direct the direction of transmission of the second beam by refracting and/or reflecting the second beam.
  • the rotatable optical system 265 may include a rotatable mirror, such as a Fast Spin Mirror (FSM), which is not limited by the embodiment of the present invention.
  • FSM Fast Spin Mirror
  • the light separating unit 270 is configured to receive the second light beam guided by the rotatable optical system 265, separate the third optical signal and the fourth optical signal, and output the separated third optical signal and the first Four light signals.
  • the light separating unit 270 may be a splitter plate for separating optical signals of the first wavelength and the second wavelength.
  • the first wavelength and the second wavelength are 1550 nm and 775 nm, respectively
  • the light separating unit 270 may include a 1550 nm/775 nm partial wave plate, but the embodiment of the invention is not limited thereto.
  • the light detecting unit 275 is configured to receive the third optical signal of the second light beam transmitted by the light separating unit 270, and perform demodulation processing on the data modulated in the third optical signal.
  • the control unit 280 is configured to receive a fourth optical signal of the second light beam transmitted by the light separating unit 270, and control an angle of the rotatable optical system 265 according to the received fourth optical signal.
  • the optical path direction between the light separating unit 270 and the light detecting unit 275 and the optical path direction between the light separating unit 270 and the control unit 280 may be symmetric with respect to the light separating unit.
  • the third optical signal can pass through the splitter and enter the light detecting unit 275
  • the fourth optical signal can be reflected by the splitter and enter the control unit 280, if the splitter is 45.
  • the optical path direction between the light separating unit 270 and the light detecting unit 275 and the optical path direction between the light separating unit 270 and the control unit 280 may be perpendicular, but the embodiment of the present invention is not limited thereto.
  • control unit 280 may include: a position detecting unit and an adjusting unit, wherein the position detecting unit may be configured to receive the fourth optical signal output by the light separating unit 270, and determine an optical center of the fourth optical signal. Positioning and transmitting information of the position of the optical center to the adjusting unit; the adjusting unit may be configured to receive information of the position of the optical center transmitted by the position detecting unit, and adjust an angle of the rotatable optical system 265 according to the information.
  • the position detecting unit may include a four-quadrant detector, such as an infrared four-quadrant detector or a silicon four-quadrant detector, but the embodiment of the invention is not limited thereto.
  • a four-quadrant detector such as an infrared four-quadrant detector or a silicon four-quadrant detector
  • the optical communication device 200 may further include a focusing lens unit configured to receive the fourth optical signal output by the optical separating unit 270, and focus the fourth optical signal on the position detecting unit, wherein the focusing
  • the lens unit may include a fourth convex lens, but the embodiment of the invention is not limited thereto.
  • the optical communication device 200 may further include a filtering unit located between the focusing lens unit and the position detecting unit on the optical path, and filtering the optical signal of the fourth optical signal except the wavelength of the second wavelength. Signals other than, for example, filtering out optical signals of the first wavelength that have not been separated, and the like.
  • the filtering unit may include the bandpass filter of the second wavelength, but the embodiment of the present invention does not limit this.
  • the adjusting unit may specifically adjust the angle of the rotatable optical system 265 such that the optical center position of the fourth optical signal is at the center of the position detecting unit, and due to the optical separation unit 270 and the light detecting unit 275
  • the optical path direction and the optical path direction between the light separating unit 270 and the control unit 280 may be symmetric with respect to the light separating unit, and the adjusting may be such that the optical center position of the fourth optical signal is located at the center of the light detecting unit 275, but Embodiments of the invention are not limited thereto.
  • FIG. 7 shows another optical communication device 300 provided by an embodiment of the present invention.
  • the optical communication device 300 can include an optical transmitter 310 and a light transmitting antenna 320, where
  • the optical transmitter 310 is configured to transmit a first optical signal having a first wavelength
  • the light emitting antenna 320 is configured to receive the first optical signal emitted by the optical transmitter 310, convert the first partial optical signal in the first optical signal into a second optical signal having a second wavelength, and The communication device transmits the second partial optical signal and the second optical signal of the first optical signal.
  • the second optical signal may serve as beacon light for performing signal tracking
  • the second partial optical signal may serve as communication light for carrying customer data
  • the optical communication device 300 may include one or more optical transmitting antennas 320, which are not limited in this embodiment of the present invention.
  • the optical transmitting antenna 320 may include a receiving unit, a light converting unit, and a sending unit, where the receiving unit may be configured to receive the first optical signal emitted by the optical transmitter 310, where the optical converting unit The first partial optical signal of the first optical signal received by the receiving unit may be converted into a second optical signal having a second wavelength, and the transmitting unit may be configured to send the first light to the first peer communication device. a second portion of the optical signal in the signal and the second optical signal obtained by the optical conversion unit.
  • the receiving unit in the light emitting antenna 320 may include a receiving lens.
  • the optical converting unit and the sending unit in the optical transmitting antenna 320 may be specifically the optical converting unit and the sending unit in the foregoing embodiment, and the specific implementation of the optical converting unit and the sending unit may be described above, in order to Concise, no more details here.
  • the optical transmitting antenna 320 may further include a first collimating unit, configured to receive the first optical signal emitted by the optical transmitter 310, and perform collimation processing on the first optical signal to obtain The first optical signal after collimation processing.
  • the optical conversion unit may be specifically configured to receive the collimated first optical signal output by the first collimating unit.
  • the optical communication device 300 may further include an optical amplifier 330, configured to receive the first optical signal emitted by the optical transmitter 310, perform amplification processing on the first optical signal, and output the amplification process.
  • the first optical signal At this time, the light emitting antenna 320 can be specifically configured to receive the amplified first optical signal output by the optical amplifier 330.
  • the optical communication device 300 may further include a photodetector and a light receiving antenna, wherein the light receiving antenna is configured to receive the second light beam sent by the second peer communication device, wherein the second light beam comprises a third optical signal having a first wavelength and a fourth optical signal having a second wavelength, separating the third optical signal and the fourth optical signal of the second optical beam, and according to the fourth optical signal, the third optical signal The center of the optical signal is adjusted to the center of the receiving fiber, and the third optical signal is output to the photodetector.
  • the photodetector can be configured to receive the third optical signal output by the optical receiving antenna, and perform demodulation processing on the data modulated by the third optical signal.
  • the light receiving antenna may include a receiving unit, a rotatable optical system, a light separating unit, and a control unit, or may further include a second collimating unit.
  • a receiving unit a rotatable optical system
  • a light separating unit a light separating unit
  • a control unit or may further include a second collimating unit.
  • FIG. 8 shows a free space communication system 400 provided by an embodiment of the present invention.
  • the free space communication system includes a first optical communication device 410 and a second optical communication device 420, and an OWC link may exist between the first optical communication device 410 and the second optical communication device 420.
  • the first optical communication device 410 may include a light emitting unit, a light converting unit, and a transmitting unit
  • the second optical communication device 420 may include a receiving unit, a rotatable optical system, a light separating unit, and a light detecting unit. And control unit.
  • the portion of the optical communication device 200 related to the transmission of the optical signal in the foregoing embodiment reference may be made to the portion of the optical communication device 200 related to the transmission of the optical signal in the foregoing embodiment.
  • the second optical communication device 420 reference may be made to the foregoing embodiment.
  • the portion of the optical communication device 200 related to the reception of the optical signal will not be described herein for the sake of brevity.
  • the first optical communication device 410 can include an optical transmitter and a transmit antenna
  • the second optical communication device 420 can include a receive antenna and a photodetector.
  • the first optical communication device 410 refers to the portion of the optical communication device 300 in the foregoing embodiment that is related to the transmission of the optical signal.
  • the second optical communication device 420 refer to the foregoing embodiment.
  • the portion of the optical communication device 300 related to the reception of the optical signal will not be described herein for the sake of brevity.
  • FIG. 9 shows an architectural example of the free space communication system 400 in which it is assumed that the first wavelength is 1550 nm and the second wavelength is 775 nm.
  • the first optical communication device 410 may include a transmitter 411, an EFDA 412, and a transmitting antenna including a convex lens 413, a light converting unit 414, and a convex lens 415.
  • the second optical communication device 420 may include a receiving antenna, a photodetector (PD), and a receiver, wherein the receiving antenna may include a convex lens 421, a convex lens 422, a rotatable mirror 423, a demultiplexing plate 424, and a convex lens 425.
  • QD silicon four quadrant detector
  • the transmitter 411 can emit a light beam having a wavelength of ⁇ (ie, 1550 nm), which is amplified by the EDFA 412 and incident on the convex lens 413 of the transmitting antenna, and the convex lens 413 collimates the received light beam into a parallel light beam, and the light conversion Unit 414 converts a portion of the optical signal in the parallel beam into beacon light having a wavelength of ⁇ /2 (ie, 775 nm) for tracking alignment, with the remaining optical signal of wavelength ⁇ remaining as the communication light.
  • the convex lens 415 transmits a light beam including communication light of a wavelength ⁇ and beacon light of a wavelength of ⁇ /2.
  • the convex lens 421 can receive a light beam including the communication light of the wavelength ⁇ and the beacon light of the wavelength ⁇ /2 transmitted by the convex lens 415, and the light beam is collimated by the convex lens 422 and transmitted to the rotatable mirror 423.
  • the rotatable mirror reflects the beam to the demultiplexing plate 424.
  • the branching wave plate 424 separates the communication light of the wavelength ⁇ in the light beam from the beacon light of the wavelength ⁇ /2, wherein the communication light of the wavelength ⁇ passes through the branching wave plate 424 and reaches the convex lens 4291, and is then focused.
  • the PD 4292 converts the received communication light into an electrical signal and transmits it to the receiver 4293.
  • the beacon light having a wavelength of ⁇ /2 is reflected by the demultiplexing plate 424 to the convex lens 425, and after filtering processing by 426, reaches the QD 427, and the QD 427 can determine the beacon light having the wavelength of ⁇ /2.
  • the center position and the information of the center position is reported to the controller 428, and the controller 428 can adjust the angle of the rotatable mirror 423 according to the information of the center position such that the center position of the beacon light is at the center of the QD .
  • the center position of the beacon light can be located at the center of the PD.
  • FIG. 9 is intended to help those skilled in the art to better understand the embodiments of the present invention and not to limit the scope of the embodiments of the present invention.
  • a person skilled in the art will be able to make various modifications and changes in the embodiments according to the example of FIG. 9. The modifications or variations are also within the scope of the embodiments of the present invention.
  • optical communication device and the free space communication system provided by the embodiments of the present invention are described in detail above with reference to FIG. 2 to FIG. 9.
  • optical communication method provided by the embodiment of the present invention will be described in detail below with reference to FIG.
  • FIG. 10 shows an optical communication method 500 in a free space communication system provided by an embodiment of the present invention.
  • the second wavelength is different from the first wavelength.
  • the first partial optical signal may be up-converted to obtain a second optical signal.
  • the second wavelength is smaller than the first wavelength.
  • embodiments of the invention are not limited thereto.
  • the second partial optical signal may be a portion of the first optical signal other than the first partial optical signal, but the embodiment of the present invention is not limited thereto.
  • the second optical signal and the second partial optical signal may be sent to the first peer communication device in the form of a parallel beam or an approximately parallel beam, wherein the divergence angle of the approximately parallel beam may be
  • the preset condition is satisfied, for example, between 0.2 mrad and 1.5 mrad, but the embodiment of the invention is not limited thereto.
  • the first wavelength may be an even multiple of the second wavelength.
  • S520 may include: performing frequency conversion processing on the first optical signal by using a light frequency doubling crystal, so that the first partial optical signal in the first optical signal is converted into the second optical signal.
  • the distance that the first optical signal is transmitted in the optical frequency conversion crystal can satisfy the above formulas (5) to (9), and is not described herein for brevity.
  • the first optical signal is frequency-converted using a light doubling crystal
  • the method 500 can also include:
  • the first optical signal is subjected to width conversion processing such that the beam width of the first optical signal is changed from the first width to the second width.
  • the frequency converting the first optical signal by using the optical frequency doubling crystal may include: performing frequency conversion processing on the first optical signal of the second width by using the optical frequency doubling crystal.
  • the second width may satisfy the above formulas (7) to (9), and for brevity, no further details are provided herein.
  • S530 may be specifically: sending a first light beam to the first peer communication device, where the first light beam includes the second optical signal and the second partial optical signal.
  • the first light beam may be a parallel light beam or an approximately parallel light beam, which is not limited in this embodiment of the present invention.
  • the method 500 may further include:
  • the first optical signal is subjected to a collimation process to obtain the first optical signal after the collimation process.
  • the first optical signal after the collimation process may be a parallel beam.
  • the method 500 may be performed by the optical communication device 200 or the optical communication device 300 in the above device embodiment, and for brevity, no further details are provided herein.
  • system and “network” are used interchangeably herein.
  • the term “and/or” in this context is merely an association describing the associated object, indicating that there may be three relationships, for example, A and / or B, which may indicate that A exists separately, and both A and B exist, respectively. B these three situations.
  • the character "/" in this article generally indicates that the contextual object is an "or" relationship.
  • the disclosed systems, devices, and methods may be implemented in other manners.
  • the device embodiments described above are merely illustrative.
  • the division of the unit is only a logical function division.
  • there may be another division manner for example, multiple units or components may be combined or Can be integrated into another system, or some features can be ignored or not executed.
  • the mutual coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interface, device or unit, or an electrical, mechanical or other form of connection.
  • the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the embodiments of the present invention.
  • each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.
  • the above integrated unit can be implemented in the form of hardware or in the form of a software functional unit.
  • the integrated unit if implemented in the form of a software functional unit and sold or used as a standalone product, may be stored in a computer readable storage medium.
  • the technical solution of the present invention contributes in essence or to the prior art, or all or part of the technical solution may be embodied in the form of a software product stored in a storage medium.
  • a number of instructions are included to cause a computer device (which may be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention.
  • the foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, and the like, which can store program codes. .

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Abstract

一种自由空间通信系统中的光通信装置和方法以及发射天线，有利于实现天线对准。该光通信装置包括：发光单元，用于发射具有第一波长的第一光信号；光转换单元，用于接收该发光单元发射的该第一光信号，将该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，并输出该第一光信号中的第二部分光信号和该第二光信号，其中，该第二光信号作为用于进行信号跟踪的信标光，该第二部分光信号作为用于承载客户数据的通信光；发送单元，用于向第一对端通信装置发送该光转换单元输出的该第二部分光信号和该第二光信号。

Description

自由空间通信系统中的光通信装置和方法以及发射天线 技术领域
本发明实施例涉及通信领域，并且更具体地，涉及自由空间通信系统中的光通信装置和方法以及发射天线。
背景技术
光无线通信(Optical Wireless Communication，OWC)利用自由空间进行光信号的传输。由于具有安装灵活、抗电磁辐射、无需频段申请等优点，OWC得到广泛应用。
高速室外OWC通常采用1550nm的红外光波作为载波，并采用具有极小发散角的光束进行信号的传输，一般来说，光束的发散角小于0.1度。然而，外界的抖动等因素容易造成光束偏离接收天线，引起光路中断。因此，采用跟踪技术来进行天线对准，以保证接收光信号的功率在光探测器所需要的灵敏度以上，是本领域的重要研究方向。
发明内容
本发明实施例提供一种自由空间通信系统中的光通信装置和方法以及发射天线，有利于通过信号跟踪实现自由空间通信系统中的天线对准。
第一方面，提供了一种自由空间通信系统中的光通信装置，包括：发光单元，用于发射具有第一波长的第一光信号；光转换单元，用于接收该发光单元发射的该第一光信号，将该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，并输出该第一光信号中的第二部分光信号和该第二光信号，其中，该第二光信号作为用于进行信号跟踪的信标光，该第二部分光信号作为用于承载客户数据的通信光；发送单元，用于向第一对端通信装置发送该光转换单元输出的该第二部分光信号和该第二光信号。
该第一对端通信装置与该光通信装置可以设置在分隔的两个位置，并且可以分别处于对方的远端。
该第二部分光信号可以作为通信光，其中，通信光可以为承载客户数据的光信号。该第二光信号可以作为信标光，其中，该信标光可以用于跟踪通信光，进而进行天线对准。具体地，该第一对端通信装置可以根据该信标光， 跟踪该通信光的传输方向，进而控制该通信光的光斑位置处于光纤中心。
因此，根据本发明实施例的光通信装置，通过发光单元发射具有第一波长的第一光信号，光转换单元对该第一光信号中的第一部分光信号进行变频转换处理，得到具有第二波长的第二光信号，发送单元向第一对端通信装置发送该第二光信号和该第一光信号中的第二部分光信号，以使得该第一对端通信装置可以根据该第二部分光信号进行天线对准，从而提高信号传输性能。
此外，通过将发光单元210发射的第一部分光信号转换为第二光信号，并且该第二光信号和该第二部分光信号可以通过相同的光路传输到自由空间，无需额外设置用于发射信标光的发光单元以及用于传输信标光的光路，从而节约设备成本和大小以及设计复杂度。
可选地，该第二波长小于该第一波长。
可选地，该第一波长为该第二波长的整数倍；该光转换单元包括：光倍频晶体。
具体地，可以利用光倍频晶体对该第一光信号进行变频转换处理，以使得该第一光信号中的第一部分光信号转换为第二光信号。
可选地，该第一光信号从第一表面入射该光倍频晶体，经由该光倍频晶体的至少一个第二表面中的每个第二表面反射至少一次后，从第三表面射出该光倍频晶体，其中，该第一表面和该第三表面镀有增透膜，该至少一个第二表面镀有反射膜。
可选地，该第一光信号可以垂直该第一表面入射该光倍频晶体，并且可以垂直该第三表面出射该光倍频晶体。
可选地，该第一表面和该第三表面可以相互垂直，该第二表面与该第一表面和该第三表面之间的夹角可以均为45度。
可选地，该第一表面、该第二表面和该第三表面可以均为该光倍频晶体的侧面，该光倍频晶体的厚度h可以远大于该第一光信号入射该光倍频晶体时的光束直径2w1，以减少该第一光信号的损耗。
具体地，可以使得该第一光信号在该光倍频晶体中传输足够长的距离，以提高转换效率。
可选地，该光倍频晶体具有至少一个切角，该至少一个第二表面包括该至少一个切角的表面。
该切角可以为45度切角，例如，该光倍频晶体可以是通过将形状为正方体的晶体切掉三个直角后得到的。切角的表面可以作为第一光信号的反射面。
在第一方面的第一种可能的实现方式中，该第一光信号在该光倍频晶体中传输的距离Leff满足以下条件：
PT,C＝SC+MC+PR,C+LRx,C+LA,C+LG,C+LTx,C，
PT,B＝SB+MB+PR,B+LRx,B+LA,B+LG,B+LTx,B，
PT,C＝(PT,C+PT,B)sech2(ΓLeff)，
PT,B＝(PT,C+PT,B)tanh2(ΓLeff)，
其中，
Figure PCTCN2016110296-appb-000001
PT,C为该第二部分光信号入射到该光倍频晶体时的功率，SC该第一对端通信装置中用于接收该第二部分光信号的第一探测器的灵敏度，PR,C为该第二部分光信号到达该第一探测器时的功率，LTx,C为该第二部分光信号在该第一对端通信装置中的损耗，LG,C为该第二部分光信号的发散损耗，LG,C为该第二部分光信号的大气吸收损耗，LRx,C为该第二部分光信号在该对端通信装置中的损耗，MC为该第二部分光信号的链路裕量，PT,B为该第二光信号入射到该光倍频晶体时的功率，SB该第一对端通信装置中用于接收该第二光信号的第二探测器的灵敏度，PR,B为该第二光信号到达该第二探测器时的功率，LTx,B为该第二光信号在该光转换单元中的损耗，LG,B为该第二光信号的发散损耗，LG,B为该第二光信号的大气吸收损耗，LRx,B为该第二光信号在该第一对端通信装置中的损耗，MB为该第二光信号的链路裕量，n为该光倍频晶体的折射率，C为真空光速，ω为该第一光信号的圆频率，deff为该光倍频晶体的二阶非线性系数，ε0为真空介电常数，w1为该第一光信号入射到该光倍频晶体时的光束半径，Leff为该第一光信号在该光倍频晶体中传输的距离。
此时，可以根据实际的链路功率预算来设计光路并选择合适的器件参数。
结合上述可能的实现方式，在第一方面的第二种可能的实现方式中，该光转换单元还包括：宽度变换单元，用于接收该发光单元传输的该第一光信号，并将接收到的该第一光信号的光束宽度由第一宽度变换为第二宽度；该光倍频晶体具体用于接收该宽度变换单元输出的具有该第二宽度的该第一光信号，将接收到的具有该第二宽度的该第一光信号中的第一部分光信号转换为该第二光信号，并输出该第二部分光信号和该第二光信号。
可选地，该宽度变换单元包括：沿着光路依次设置的第一凸透镜和凹透 镜，其中，该第一凸透镜的焦点与该凹透镜的焦点重合。
可选地，该第一凸透镜的焦距f1和该凹透镜的焦距f2满足以下关系：
Figure PCTCN2016110296-appb-000002
其中，D1为该第一光信号入射该第一凸透镜时的光束宽度，2w1为该第一光信号出射该凹透镜时的光束宽度。
可选地，该发送单元具体用于：向该第一对端通信装置发送包括该第二部分光信号和该第二光信号的第一光束，其中，该第一光束的波束宽度和/或发散角满足预设条件。
结合上述可能的实现方式，在第一方面的第三种可能的实现方式中，该发送单元包括：沿着光路依次设置的第二凸透镜和第三凸透镜，其中，该第二凸透镜的焦距f3和该第三凸透镜的焦距f4满足以下关系：
Figure PCTCN2016110296-appb-000003
其中，D2为该第一光束的光束直径。
结合上述可能的实现方式，在第一方面的第四种可能的实现方式中，该光通信装置还包括：光放大单元，用于接收该发光单元发射的该第一光信号，对该第一光信号进行放大处理，并输出放大处理后的该第一光信号；该光转换单元具体用于接收该光放大单元输出的放大处理后的该第一光信号。
结合上述可能的实现方式，在第一方面的第五种可能的实现方式中，该光通信装置还包括：接收单元、可旋转光系统、光分离单元、光探测单元和控制单元，其中，该接收单元用于接收第二对端通信装置发送的第二光束，其中，该第二光束包括具有第一波长的第三光信号和具有第二波长的第四光信号；该可旋转光系统用于引导该接收单元接收到的该第二光束的传输方向；该光分离单元用于接收该可旋转光系统引导的该第二光束，并且分离该第二光束中的该第三光信号和该第四光信号；该光探测单元用于接收该光分离单元传输的该第二光束中的第三光信号，并对该第三光信号中调制的数据进行解调处理；该控制单元用于接收该光分离单元传输的该第二光束中的第四光信号，并根据接收到的该第四光信号，控制该可旋转光系统的角度。
该第三光信号可以作为通信光，该第四光信号可以作为信标光。
可选地，该光分离单元包括用于分离该第一波长和该第二波长的光信号的分波片。
结合上述可能的实现方式，在第一方面的第六种可能的实现方式中，该控制单元包括：位置检测单元和调整单元，该位置检测单元用于接收该光分 离单元输出的该第四光信号，确定该第四光信号的光心位置，并向该调节单元传输该光心位置的信息；该调整单元用于接收该位置检测单元传输的该光心位置的信息，并根据该信息，调整该可旋转光系统的角度。
可选地，该位置检测单元包括：硅四象限探测器。
这样，与采用红外四象限探测器或其它器件相比，采用硅四象限探测器可以降低器件成本。
第二方面，提供了一种自由空间通信系统中的发射天线，包括：接收单元，用于接收光发射机发射的第一光信号；光转换单元，用于将该接收单元接收的该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，其中，该第二光信号作为用于进行信号跟踪的信标光，该第二部分光信号作为用于承载客户数据的通信光；发送单元，用于向第一对端通信装置发送该第一光信号中的第二部分光信号和该光转换单元得到的该第二光信号。
可选地，该接收单元可以包括接收透镜。例如，凸透镜。
可选地，该第一波长为该第二波长的整数倍；该光转换单元包括：光倍频晶体。
可选地，该光转换单元还包括：宽度变换单元，用于接收该光发射机传输的该第一光信号，并将接收到的该第一光信号的光束宽度由第一宽度变换为第二宽度；该光倍频晶体具体用于接收该宽度变换单元输出的具有该第二宽度的该第一光信号，将接收到的具有该第二宽度的该第一光信号中的第一部分光信号转换为该第二光信号，并输出该第二部分光信号和该第二光信号。
可选地，该宽度变换单元包括：沿着光路依次设置的第一凸透镜和凹透镜，其中，该第一凸透镜的焦点与该凹透镜的焦点重合。
可选地，该发送单元具体用于接收该光倍频晶体输出的该第二部分光信号和该第二光信号，并向该第一对端通信装置发送包括该第二部分光信号和该第二光信号的第一光束，其中，该第一光束的波束宽度和/或发散角满足预设条件。
可选地，该发送单元包括：沿着光路依次设置的第二凸透镜和第三凸透镜，其中，该第二凸透镜的焦距f3和该第三凸透镜的焦距f4满足以下关系：
Figure PCTCN2016110296-appb-000004
其中，D2为该第一光束的光束直径。
该发射天线可以用于实现第一方面或第一方面的任意可能的实现方式中的光转换单元和发射单元的功能。
第三方面，提供了一种自由空间通信系统中的光通信装置，包括光发射机和第二方面或第二方面的任意可能的实现方式中的发射天线。
第四方面，提供了一种自由空间通信系统中的光通信方法，包括：发射具有第一波长的第一光信号；对该第一光信号进行转换处理，以使得该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号；向第一对端通信装置发送该第一光信号中的第二部分光信号和该第二光信号。
可选地，该第一波长为该第二波长的整数倍；该将该第一光信号进行转换处理，以使得该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，包括：利用光倍频晶体对该第一光信号进行转换处理，以使得该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号。
可选地，在该利用光倍频晶体对该第一光信号进行转换处理之前，该方法还包括：对该第一光信号进行宽度变换处理，以将该第一光信号的光束宽度由第一宽度变为第二宽度；该利用光倍频晶体对该第一光信号进行转换处理，包括：利用光倍频晶体对光束宽度为该第二宽度的该第一光信号进行转换处理。
该光通信方法可以由第一方面或第一方面的任意可能的实现方式中的光通信装置执行。或者，该光通信方法可以由第三方面或第三方面的任意可能的实现方式中的光通信装置执行。
附图说明
图1为自由空间通信系统中具有跟踪功能的典型光通信装置的示意性框图。
图2为本发明实施例提供的光通信装置的示意性框图。
图3a为本发明实施例提供的光通信装置中的光倍频晶体的立体示意图。
图3b为图3a所示的光倍频晶体的俯视图。
图4为本发明实施例提供的光通信装置的光路示例示意图。
图5为本发明实施例提供的光通信装置的另一示意性框图。
图6为本发明实施例提供的光通信装置的另一示意性框图。
图7为本发明实施例提供的另一光通信装置的示意性框图。
图8为本发明实施例提供的自由空间通信系统的示意性框图。
图9为本发明实施例提供的自由空间通信系统的光路示例的示意图。
图10为本发明实施例提供的光通信方法的示意性流程图。
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行描述。
图1示出了自由空间通信系统中具有跟踪功能的典型光通信装置示例。结合图1中箭头所示的光路可知，光通信装置100包括：用于收发光信号的透镜1、以及在光路上位于透镜1之后的透镜2和可移动反射镜3，极化光束分离器4、透镜5和发光设备6置于可移动反射镜3的入射方向，光束分离镜7、透镜8和位置检测器9置于该极化光束分离器4的反射方向上，透镜10和光接收元件11置于光束分离镜7的反射方向。复用器12的输出端与发光设备6连接，发射信号输入端13的输出通过放大器14与复用器12连接，振荡器15的输出也与复用器12连接。光接收元件11的输出通过放大器16与接收信号输出端17连接。位置检测器9的输出连接至跟踪控制电路18，跟踪控制电路18的输出通过用于调整可移动反射镜3的角度的驱动器19和20与可移动反射镜3连接。用于观察者检验瞄准轴的瞄准镜21与可移动反射镜3的光轴近似平行。
在发射光信号时，发射信号通过发射信号输入端13输入，经由放大器14放大，在复用器12中与来自振荡器15的信号复用，随后输出至发光设备6。发光设备6根据输入信号调制发射光，以将输入信号转换为光信号。发光设备6输出的光束经由透镜5的准直处理到达极化光束分离器4，由于该光束的极化与绘画平面平行，极化光束分离器4按原样传输该光束。该光束被可移动反射镜3反射至左边，随后经过透镜2和1被发射至对端装置。
在接收光信号时，来自对端装置的光束由透镜1的左边入射，经过透镜2被反射至可移动反射镜3，随后到达极化光束分离器4。由于该光束的极化方向与绘画平面垂直，该光束被极化光束分离器4反射至右边，然后被光束分离镜7分离成两个方向。
被光束分离镜7反射的光束经过透镜10到达光接收元件11，被转换为电信号，该电信号随后被放大器16放大至合适的电平，随后该放大信号从 接收信号输出端17输出。
被光束分离镜7投射的光束被透镜8汇聚，然后作为点像被位置检测器9接收。位置检测器9检测点像S的位置，并以位置信号的形式向跟踪控制电路18输出该位置。跟踪控制电路18根据该位置信号，计算来自对端装置的光束相对于光通信装置100的光路的角度，并向驱动器19和20传输驱动信号。驱动器19和20调整可移动反射镜3的角度，以使得点像S落在位置检测器9的中心。通过该调整，发光设备6的位置也调整了，从而使得发射光束的光路与入射光束的光路相符合，光束被精确地发射到对端装置。
由上可知，在光通信装置100中，位置检测器9选择性地检测特定频率的交流信标信号。该信标信号由振荡器15生成，并且在复用器12中与传输信号复用之后作为发光设备6的输入信号，该发光设备6根据输入信号生成特定波长的光信号并将其发送至对端装置。在对端装置中，该光信号被分离成两部分，一部分用于跟踪，另一部分传输至光接收元件11。由于自由空间通信系统中的光发射功率受限，该用于跟踪的信号部分会造成发射光信号的功率损耗，使得通信光的发射功率低于最大发射功率，从而降低通信质量，限制通信距离。
本发明实施例通过向对端通信装置发送具有不同的波长的信标光和通信光，能够在实现天线对准的同时提高通信光的最大发射功率，从而有利于提高通信质量，增大通信距离，提高系统裕量和整体性能。
图2示例性地示出了本发明实施例提供的光通信装置200。该光通信装置200可以适用于自由空间通信系统，其中，该光通信装置200和第一对端通信装置可以分离地位于两个相对位置，并且可以通过向自由空间传输光信号进行通信。如图2所示，该光通信装置200包括：
发光单元210，用于发射具有第一波长的第一光信号；
光转换单元220，用于接收该发光单元210发射的该第一光信号，将该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，并输出第一光信号中的第二部分光信号和该第二光信号，其中，该第二光信号作为用于进行信号跟踪的信标光，该第二部分光信号作为用于承载客户数据的通信光；
发送单元230，用于向第一对端通信装置发送该光转换单元220输出的该第二部分光信号和该第二光信号。
发光单元210可以发射第一光信号，并向光转换单元220传输该第一光信号，其中，该第一光信号的波长为第一波长。可选地，该发光单元210可以包括激光器，但本发明实施例对此不做限定。
光转换单元220在接收到该第一光信号之后，可以对该第一光信号中的一部分光信号进行变频处理，得到第二光信号，其中，该第二光信号的波长为不同于该第一波长的第二波长，并输出该第一光信号中的另一部分光信号和该第二光信号。可选地，该发送单元230可以通过自由空间向该第一对端通信装置发送第一光束，该第一光束可以包括该第二光信号和该第一光信号中的第二部分光信号，其中，该第二光信号可以用于该第一对端通信装置进行信号跟踪，即该第二光信号可以作为信标光，而该第二部分光信号可以调制有数据，即该第二部分光信号可以作为通信光。
因此，通过发光单元发射具有第一波长的第一光信号，光转换单元对该第一光信号中的第一部分光信号进行变频转换处理，得到具有第二波长的第二光信号，发送单元向第一对端通信装置发送该第二光信号和该第一光信号中的第二部分光信号，该第一对端通信装置可以利用该第二部分光信号进行天线对准，有利于提高信号传输性能。
此外，通过将发光单元210发射的第一部分光信号转换为第二光信号，并且该第二光信号和该第二部分光信号可以通过相同的光路传输到自由空间，无需额外设置用于发射信标光的发光单元以及用于传输信标光的光路，从而节约设备成本和设计复杂度。
可选地，在本发明实施例中，该光转换单元220可以对该第一光信号中的第一部分光信号进行上变频转换处理，得到该第二光信号。此时，该第二光信号的波长可以小于该第一光信号的波长，即该第二波长可以小于该第一波长，但本发明实施例对第一波长和该第二波长的大小关系不做限定。
作为一个可选实施例，在本发明实施例中，该第一波长可以为该第二波长的整数倍。可选地，该第一波长可以为该第二波长的偶数倍，例如，该第一波长为1550nm，该第二波长为775nm。此时，可选地，该光转换单元220可以包括一个或多个光倍频晶体，该光倍频晶体可以将入射其中的光束中的至少一部分光信号的频率翻倍，即将至少一部分光信号的波长变为初始波长的三分之一。可选地，该第一波长可以为该第二波长的奇数倍，此时，可选地，该光转换单元220可以包括一个或多个三倍频晶体，该三倍频晶体 可以将入射其中的光束中的至少一部分光信号的频率变成初始频率的三倍，即将至少一部分光信号的波长变为初始波长的三分之一，但本发明实施例不限于此。
为了便于理解，下面以该光转换单元220包括光倍频晶体为例进行描述，但本领域技术人员应理解，该描述仅为示例性而非限制性地，本发明实施例中的光转换单元220还可以具有其它实现方式。
可选地，该光倍频晶体可以具有立方体、长方体或六面体等形状。该第一光信号可以从第一表面入射该光倍频晶体，其中，该第一表面可以为该光倍频晶体的某个侧面，该第一光信号在被该光倍频晶体的至少一个第二表面中的每个第二表面反射至少一次后，从第三表面出射该光倍频晶体，其中，该第三表面可以为该光倍频晶体的某个侧面，并且为了光路设计的方便，该第三表面可以不同于第一表面，但本发明实施例不限于此。
可选地，为了降低光信号在该光倍频晶体中的损耗，该第一表面和该第三表面可以镀有增透膜，该至少一个第二表面中的每个第二表面可以镀有反射膜。该反射膜对第一波长和第二波长的光信号的反射率可以高于99.9％，该增透膜对该第一波长和该第二波长的光信号的透过率可以高于99.9％，但本发明实施例对此不做限定。
可选地，该第一光信号可以以平行光束的形式入射该光倍频晶体。该第一光信号可以在该光倍频晶体内传播足够长的距离，以将该第一光信号中的第一部分光信号转换为第二光信号。该第二光信号和该第二部分光信号可以以平行光束的形式出射该光倍频晶体。作为一个可选示例，该光倍频晶体的厚度可以远大于该第一光信号的入射光束直径，例如，该光倍频晶体的厚度可以为该第一光信号的入射光束直径的5倍以上，此时，可选地，该至少一个第二表面可以均为该光倍频晶体的侧面，但本发明实施例不限于此。
可选地，为了使得该第一光信号在该光倍频晶体中传输足够长的距离，可以对该光倍频晶体进行加工处理。作为一个可选示例，如图3a和3b所示，光倍频晶体可以是通过将上表面为正方形的长方体切掉三个直角形成的，其中，该正方形的边长为L，该切角可以为45度切角，切角的表面(即切面)可以作为光信号的反射面，即该至少一个第二表面可以包括切面，但本发明实施例不限于此。可选地，可以在该三个切面中的每个切面镀上反射膜，并且在剩余的一个直角两面镀上透射膜，但本发明实施例不限于此。
在本发明实施例中，可选地，在对该第一光信号进行变频处理之前，可以对该第一光信号的光束直径进行变换处理，以满足变频需求。相应地，作为一个可选实施例，该光转换单元220还可以包括：宽度变换单元，用于接收该发光单元210传输的该第一光信号，将接收到的该第一光信号的光束宽度由第一宽度变换为第二宽度，并输出光束宽度为第二宽度的第一光信号。此时，该光变频晶体可以具体用于接收该宽度变换单元输出的光束宽度为第二宽度的第一光信号，并对接收到的光束宽度为该第二宽度的第一光信号进行变频处理，得到该第二光信号和该第二部分光信号。可选地，在出射该光倍频晶体时，该第二光信号和该第二部分光信号可以组成平行光束，并且该平行光束的光束宽度可以保持第二宽度不变，但本发明实施例不限于此。
在本发明实施例中，该宽度变换单元可以具有多种实现方式。作为一个可选实施例，如图4所示，该宽度变换单元可以包括沿着光路依次设置的第一凸透镜222和凹透镜223，其中，该第一凸透镜的焦点与该凹透镜的焦点重合。假设该第一宽度为D1，该第二宽度为2w1，则宽度为D1的平行光束入射到该第一凸透镜222之后，可以以汇聚光束的形式射出并且入射到该凹透镜223，由于该第一凸透镜222的真实焦点与该凹透镜223的虚拟焦点重合，则该汇聚光束经由该凹透镜223的折射之后可以变成宽度为2w1的平行光束。假设该第一凸透镜222和该凹透镜223均为薄透镜，则该第一凸透镜222的焦距f1和该凹透镜223的焦距f2可以满足式(1)。
Figure PCTCN2016110296-appb-000005
应理解，在图4所示的例子中，光束宽度为2w1的第一光信号入射到该光变频晶体221之后，经由该光变频晶体221的三个切面中的每个切面的一次反射之后出射，但本发明实施例不限于此。假设Leff表示该第一光信号在光倍频晶体中传输的距离，即光倍频晶体的有效长度，则由图4可知，该光倍频晶体的L和l可以满足以下约束条件：2.5L+1.5l＝Leff。应理解，在本发明实施例中，该光倍频晶体221还可以具有其它形式的切角，并且该第一光信号在该光倍频晶体221中的光路可以根据具体需求设计，本发明实施例对此不做限定。
作为另一个可选实施例，该光通信装置200还包括发送单元230，用于 接收该光转换单元220输出的该第二部分光信号和该第二光信号，并向该第一对端通信装置发送包括该第二部分光信号和该第二光信号的第一光束，其中，该第一光束的波束宽度和/或发散角满足预设条件。可选地，该第一光束可以为平行光束或近似平行光束，其中，该第一光束的发散角可以为0.2～1.5mrad，但本发明实施例不限于此。
该发送单元230可以在同一个光束中发送该第二部分光信号和该第二光信号，可选地，该发送单元230可以以近似平行光束的形式发送该第二光信号和该第二部分光信号，但本发明实施例不限于此。
在本发明实施例中，该发送单元230可以通过凸透镜发送该第二光信号和该第二部分光信号。作为一个可选例子，如图4所示，该发送单元230可以包括：沿着光路依次设置的第二凸透镜231和第三凸透镜232，其中，该第二凸透镜231的焦距f3和该第三凸透镜232的焦距f4满足式(2)。
Figure PCTCN2016110296-appb-000006
其中，D2为该第一光束的光束直径。可选地，D2可以小于或等于该第三凸透镜的直径
Figure PCTCN2016110296-appb-000007
在图4所示的例子中，该第二凸透镜231和第三凸透镜232的焦点在光路上重合，但本发明实施例不限于此。该第二凸透镜231可以为自聚焦透镜，其中，该自聚焦透镜可以是圆柱体透镜，其长度LG可以为焦距f3的奇数倍，但本发明实施例对此不做限定。
在本发明实施例中，该光倍频晶体221与凹透镜223之间的距离以及该光倍频晶体221与该第二凸透镜231之间的距离可以尽可能的短，可选地，由该凹透镜223出射面到达该第二凸透镜231的光路长度L'可以满足式(3)，但本发明实施例不限于此。
L'<1.5Leff            (3)
应注意，图4的这个例子是为了帮助本领域技术人员更好地理解本发明实施例，而非要限制本发明实施例的范围。本领域技术人员根据所给出的图4的例子，显然可以进行各种等价的修改或变化，这样的修改或变化也落入本发明实施例的范围内。
在本发明实施例中，可以根据该光通信装置200与第一对端通信装置之间的OWC链路的功率预算来确定该第一部分光信号在该第一光信号中所占的比例以及该光倍频晶体的参数。例如，如图5所示，为了使得该光通信装置200通过OWC链路传输的第二光信号和该第二部分光信号到达该第一对端通信装置时，其功率处于该第一对端通信装置的接收器的探测灵敏度以 上，第二部分光信号和第二光信号的发射功率PT可以分别满足式(4)和式(5)，其中，下标B表示作为信标(Beacon)光的第二光信号的相关参数，下标C表示作为通信(Communication)光的第二部分光信号的相关参数。
PT,C＝SC+MC+PR,C+LRx,C+LA,C+LG,C+LTx,C       (4)
PT,B＝SB+MB+PR,B+LRx,B+LA,B+LG,B+LTx,B       (5)
其中，PT表示光信号的发射功率，即光信号入射到光倍频晶体时的功率，SC表示光信号的相应探测器的灵敏度，即该第一对端通信装置中用于接收该光信号的探测器的灵敏度，PR表示光信号的接收功率，即光信号到达相应探测器时的功率，LTx表示光信号的发射天线损耗，即光信号在该光通信装置200中的损耗，LG表示光信号的发散损耗，LA表示光信号的大气吸收损耗，LRx表示光信号的接收天线损耗，即光信号在该第一对端通信装置中的损耗，MC表示光信号的链路裕量，可以用于对抗信道中的雨、雾等不确定因素引起的随机衰减。
可选地，LG,C＝LG,B，并且可以由式(6)确定：
LG,C＝20×log10(θ×R/DR)            (6)
其中，θ表示光束在自由空间的发散角，单位为毫弧(mrad)，R表示光通信装置200与该第一对端通信装置之间的通信距离，单位为千米，DR表示该第一对端通信装置的接收透镜的尺寸，单位为米。
在分别确定了该第二部分光信号和第二光信号的发射功率之后，可以根据式(7)～(9)确定该光倍频晶体的参数。
PT,C＝(PT,C+PT,B)sech2(ΓLeff)          (7)
PT,B＝(PT,C+PT,B)tanh2(ΓLeff)          (8)
Figure PCTCN2016110296-appb-000008
其中，n为该光倍频晶体的折射率，C为真空光速，ω为该第一光信号的圆频率，deff为该光倍频晶体的二阶非线性系数，ε0为真空介电常数。
通过上述式(4)至式(9)，可以根据功率预算需求确定该光倍频晶体的有效长度Leff以及第一光信号进入光倍频晶体时的光束半径w1，并据此设计该第一光信号的光路。表1示出了OWC链路的功率预算示例，其中，通信光的发射功率为26.5dBm(即446mW)，信标光的发射功率为15.8dBm(即38mW)，通过求解上述等式，可得出Leff＝74mm，光束半径w1＝135μm。
表1 OWC链路的功率预算示例
Figure PCTCN2016110296-appb-000009
可选地，可以根据上述Leff和w1确定光路上的相关器件参数，并且据此选择合适的器件。表2示出了与表1的功率预算示例对应的光转换单元220和发送单元230中的各个器件的参数示例，其中，长度单位为mm。
表2 光转换单元220和发送单元230的器件参数示例
2w1 Leff DTx D1 f1 f2 f3 LG f4 L l h
0.27 74 40 1 18 4.9 1 3 148.1 21.5 13.5 5
作为另一个可选实施例，如图5所示，该光通信装置200还可以包括：光放大单元240，用于接收该发光单元210发射的该第一光信号，对该第一光信号进行放大处理，并输出放大处理后的该第一光信号。此时，该光转换单元220可以具体用于接收该光放大单元240输出的放大处理后的该第一光 信号。
可选地，该光放大单元240可以具体为掺饵光纤放大器(Erbium Doped Fiber Amplifier，EDFA)，但本发明实施例不限于此。
作为另一个可选实施例，该光通信装置200还可以包括：在光路上位于该光转换单元220之前的第一准直单元250，用于对该第一光信号进行准直处理，并输出准直处理后的该第一光信号，其中，该准直处理后的该第一光信号可以为平行光束。此时，该光转换单元220可以具体用于接收该第一准直单元250输出的准直处理后的第一光信号。
可选地，该第一准直单元250可以在光路上置于该发光单元210和该光转换单元220之间，具体用于接收该发光单元210输出的该第一光信号，并对该发光单元210输出的第一光信号进行准直处理。或者，如图5所示，该第一准直单元250可以在光路上置于光放大单元240和该光转换单元220之间，具体用于接收该光放大单元240输出的放大处理后的第一光信号，并对该光放大单元240输出的放大处理后的第一光信号进行准直处理，但本发明实施例不限于此。
可选地，该第一准直单元250可以包括凸透镜，但本发明实施例不限于此。
作为另一个可选实施例，该光通信装置200还可以用于接收其它通信装置发送的光信号。图6示出了该光通信装置200中与光信号的接收相关的功能单元：接收单元260、可旋转光系统265、光分离单元270、光探测单元275和控制单元280。
接收单元260用于接收第二对端通信装置发送的第二光束，其中，该第二光束包括具有第一波长的第三光信号和具有第二波长的第四光信号。
可选地，该接收单元260可以包括凸透镜，该第二光束可以具体为平行光束或近似平行光束。该第二对端通信装置可以与该第一对端通信装置为相同或不同的装置，本发明实施例对此不做限定。
该第三光信号的波长为第一波长，可以作为通信光，用于调制有数据。该第四光信号的波长为第二波长，可以作为信标光，用于进行信号跟踪。
可旋转光系统265用于引导该接收单元260接收到的第二光束的传输方向。
可选地，该光通信装置还可以包括第二准直单元，可以用于对该接收单 元260接收到的光信号进行准直处理，得到平行光束。此时，该可旋转光系统265可以具体用于引导该第二准直单元输出的平行光束的传输方向。可选地，该第二准直单元可以在光路上位于该接收单元260和可旋转光系统265之间，但本发明实施例不限于此。
具体地，该可旋转光系统可以通过折射和/或反射该第二光束，来引导该第二光束的传输方向。可选地，该可旋转光系统265可以包括可旋转反射镜，例如快速旋转反射镜(Fast Spin Mirror，FSM)，但本发明实施例对此不做限定。
光分离单元270用于接收可旋转光系统265引导的该第二光束，分离该第二光束中的该第三光信号和该第四光信号，并输出分离的该第三光信号和该第四光信号。
可选地，该光分离单元270可以为用于分离第一波长和第二波长的光信号的分波片。例如，假设该第一波长和该第二波长分别为1550nm和775nm，则该光分离单元270可以包括1550nm/775nm分波片，但本发明实施例不限于此。
光探测单元275用于接收该光分离单元270传输的该第二光束中的第三光信号，并对该第三光信号中调制的数据进行解调处理。
控制单元280用于接收该光分离单元270传输的该第二光束中的第四光信号，并根据接收到的该第四光信号，控制该可旋转光系统265的角度。
可选地，该光分离单元270与该光探测单元275之间的光路方向和该光分离单元270与该控制单元280之间的光路方向可以关于该光分离单元对称。例如，该第三光信号可以穿出该分波片后进入该光探测单元275，而该第四光信号可以被该分波片反射后进入该控制单元280，如果该分波片具体为45度分波片，则该光分离单元270与该光探测单元275之间的光路方向和该光分离单元270与该控制单元280之间的光路方向可以垂直，但本发明实施例不限于此。
可选地，该控制单元280可以包括：位置检测单元和调整单元，其中，该位置检测单元可以用于接收该光分离单元270输出的该第四光信号，确定该第四光信号的光心位置，并向该调节单元传输该光心位置的信息；该调整单元可以用于接收该位置检测单元传输的该光心位置的信息，并根据该信息，调整该可旋转光系统265的角度。
可选地，该位置检测单元可以包括四象限探测器，例如红外四象限探测器或硅四象限探测器，但本发明实施例不限于此。
可选地，该光通信装置200还可以包括聚焦透镜单元，用于接收该光分离单元270输出的该第四光信号，并将该第四光信号聚焦在该位置检测单元，其中，该聚焦透镜单元可以包括第四凸透镜，但本发明实施例不限于此。
可选地，该光通信装置200还可以包括在光路上位于该聚焦透镜单元和该位置检测单元之间的滤波单元，用于过滤该第四光信号中除波长为该第二波长的光信号之外的信号，例如滤除尚未分离的该第一波长的光信号，等等。可选地，该滤波单元可以包括该第二波长的带通滤波器，但本发明实施例对此不做限定。
该调整单元具体可以调整该可旋转光系统265的角度，以使得该第四光信号的光心位置处于该位置检测单元的中心，而由于该光分离单元270与该光探测单元275之间的光路方向和该光分离单元270与该控制单元280之间的光路方向可以关于该光分离单元对称，则该调整可以使得该第四光信号的光心位置位于该光探测单元275的中心，但本发明实施例不限于此。
图7示出了本发明实施例提供的另一光通信装置300。该光通信装置300可以包括光发射机310和光发射天线320，其中，
该光发射机310用于发射具有第一波长的第一光信号；
光发射天线320用于接收该光发射机310发射的该第一光信号，将该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，并向第一对端通信装置发送该第一光信号中的第二部分光信号和该第二光信号。
在本发明实施例中，该第二光信号可以作为用于进行信号跟踪的信标光，该第二部分光信号可以作为用于承载客户数据的通信光。
可选地，该光通信装置300可以包括一个或多个光发射天线320，本发明实施例对此不做限定。
作为一个可选实施例，该光发射天线320可以包括接收单元、光转换单元和发送单元，其中，该接收单元可以用于接收该光发射机310发射的该第一光信号，该光转换单元可以用于将该接收单元接收的该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，该发送单元可以用于向第一对端通信装置发送该第一光信号中的第二部分光信号和该光转换单元得到的该第二光信号。
可选地，该光发射天线320中的接收单元可以包括接收透镜。
可选地，该光发射天线320中的光转换单元和发送单元可以具体为上述实施例中的光转换单元和发送单元，该光转换单元和该发送单元的具体实现可以参见上文描述，为了简洁，这里不再赘述。
作为另一个可选实施例，该光发射天线320还可以包括第一准直单元，用于接收该光发射机310发射的第一光信号，并对该第一光信号进行准直处理，得到准直处理后的第一光信号。相应地，该光转换单元可以具体用于接收该第一准直单元输出的准直处理后的第一光信号。
作为另一个可选实施例，该光通信装置300还可以包括光放大器330，用于接收该光发射机310发射的第一光信号，对该第一光信号进行放大处理，并输出放大处理后的该第一光信号。此时，该光发射天线320可以具体用于接收光放大器330输出的放大处理后的第一光信号。
作为另一个可选实施例，该光通信装置300还可以包括光探测器和光接收天线，其中，光接收天线用于接收第二对端通信装置发送的第二光束，其中，该第二光束包括具有第一波长的第三光信号和具有第二波长的第四光信号，分离该第二光束中的该第三光信号和该第四光信号，根据该第四光信号，将该第三光信号的中心调整至接收光纤中心，并向该光探测器输出该第三光信号。该光探测器可以用于接收该光接收天线输出的该第三光信号，并对该第三光信号调制的数据进行解调处理。
作为一个可选实施例，该光接收天线可以包括接收单元、可旋转光系统、光分离单元和控制单元，或者还可以进一步包括第二准直单元，具体可以参见上文描述，为了简洁，这里不再赘述。
图8示出了本发明实施例提供的自由空间通信系统400。该自由空间通信系统包括第一光通信装置410和第二光通信装置420，该第一光通信装置410和第二光通信装置420之间可以存在OWC链路。
作为一个可选实施例，该第一光通信装置410可以包括发光单元、光转换单元和发送单元，该第二光通信装置420可以包括接收单元、可旋转光系统、光分离单元、光探测单元和控制单元。具体地，该第一光通信装置410的具体实现可以参照上述实施例中的光通信装置200的与光信号的发送相关的部分，该第二光通信装置420的具体实现可以参照上述实施例中光通信装置200的与光信号的接收相关的部分，为了简洁，这里不再赘述。
作为另一个可选实施例，该第一光通信装置410可以包括光发射机和发射天线，该第二光通信装置420可以包括接收天线和光探测器。具体地，该第一光通信装置410的具体实现可以参照上述实施例中的光通信装置300的与光信号的发送相关的部分，该第二光通信装置420的具体实现可以参照上述实施例中光通信装置300的与光信号的接收相关的部分，为了简洁，这里不再赘述。
图9示出了该自由空间通信系统400的一个架构示例，其中假设第一波长为1550nm，该第二波长为775nm。如图9所示，该第一光通信装置410可以包括发射机411、EFDA 412和发射天线，该发射天线包括凸透镜413、光转换单元414和凸透镜415。该第二光通信装置420可以包括接收天线、光电探测器(PhotoDetector，PD)和接收机，其中，接收天线可以包括凸透镜421、凸透镜422、可旋转反射镜423、分波片424、凸透镜425、滤波片426、硅四象限探测器(QD)427、控制器428、凸透镜4291、光探测器(PD)4292和接收机4293。
具体地，该发射机411可以发射波长为λ(即1550nm)的光束，该光束被EDFA 412放大后入射到发射天线的凸透镜413，凸透镜413将接收到的光束准直为平行光束，该光转换单元414将该平行光束中的一部分光信号转换为波长为λ/2(即775nm)的信标光，用于跟踪对准，该平行光束中剩余的波长为λ的光信号作为通信光。凸透镜415发送包括波长为λ的通信光和波长为λ/2的信标光的光束。
凸透镜421可以接收凸透镜415发送的包括波长为λ的通信光和波长为λ/2的信标光的光束，该光束被凸透镜422准直后传输至可旋转反射镜423。可旋转反射镜将该光束反射至分波片424。分波片424将该光束中的波长为λ的通信光和波长为λ/2的信标光分离，其中，波长为λ的通信光穿过该分波片424之后到达凸透镜4291，然后被聚焦到PD 4292，该PD 4292将接收到的通信光转换为电信号并将其传输至接收机4293。另一方面，波长为λ/2的信标光被该分波片424反射至凸透镜425，并经过426的滤波处理后到达QD 427，QD 427可以确定该波长为λ/2的信标光的中心位置，并将该中心位置的信息上报至控制器428，该控制器428可以根据该中心位置的信息调整该可旋转反射镜423的角度，以使得该信标光的中心位置位于QD的中心。由于通信光的光路I和的信标光的光路II垂直并关于波分片424对称，则当 信标光的中心位置位于QD的中心时，通信光的中心位置可以位于PD的中心。
应注意，图9的这个例子是为了帮助本领域技术人员更好地理解本发明实施例，而非要限制本发明实施例的范围。本领域技术人员根据所给出的图9的例子，显然可以进行各种等价的修改或变化，这样的修改或变化也落入本发明实施例的范围内。
上文中结合图2至图9，详细描述了本发明实施例提供的光通信装置和自由空间通信系统，下面将结合图10，详细描述本发明实施例提供的光通信方法。
图10示出了本发明实施例提供的自由空间通信系统中的光通信方法500。
S510，发射具有第一波长的第一光信号。
S520，对该第一光信号进行转换处理，以使得该第一光信号中的第一部分光信号转换为具有第二波长的第二光信号。
该第二波长不同于该第一波长，可选地，在S520中，可以对该第一部分光信号进行上变频处理，得到第二光信号，相应地，该第二波长小于该第一波长，但本发明实施例不限于此。
S530，向第一对端通信装置发送该第一光信号中的第二部分光信号和该第二光信号。
可选地，该第二部分光信号可以为该第一光信号中除该第一部分光信号之外的部分，但本发明实施例不限于此。
可选地，在S530中，可以以平行光束或近似平行光束的形式向该第一对端通信装置发送该第二光信号和该第二部分光信号，其中，该近似平行光束的发散角可以满足预设条件，例如，在0.2mrad～1.5mrad之间，但本发明实施例不限于此。
作为一个可选实施例，该第一波长可以为该第二波长的偶数倍。此时，S520可以包括：利用光倍频晶体对该第一光信号进行变频处理，以使得该第一光信号中的第一部分光信号转换为第二光信号。
可选地，该第一光信号在该光变频晶体中传输的距离可以满足上述式(5)至式(9)，为了简洁，这里不再赘述。
作为另一个可选实施例，在利用光倍频晶体对该第一光信号进行变频处 理之前，该方法500还可以包括：
对该第一光信号进行宽度变换处理，以使得该第一光信号的光束宽度由第一宽度变为第二宽度。
相应地，该利用光倍频晶体对该第一光信号进行变频处理可以包括：利用光倍频晶体对第二宽度的该第一光信号进行变频处理。
可选地，该第二宽度可以满足上述式(7)至式(9)，为了简洁，这里不再赘述。
可选地，S530可以具体为：向第一对端通信装置发送第一光束，该第一光束包括该第二光信号和第二部分光信号。具体地，该第一光束可以为平行光束或近似平行光束，本发明实施例对此不做限定。
作为另一个可选实施例，在对该第一光信号进行宽度变换处理之前，该方法500还可以包括：
对该第一光信号进行准直处理，得到准直处理后的该第一光信号。其中，该准直处理后的该第一光信号可以为平行光束。
应理解，上述各过程的序号的大小并不意味着执行顺序的先后，各过程的执行顺序应以其功能和内在逻辑确定，而不应对本发明实施例的实施过程构成任何限定。
还应理解，方法500可以由上述装置实施例中的光通信装置200或光通信装置300执行，为了简洁，这里不再赘述。
还应理解，本文中术语“系统”和“网络”在本文中常被可互换使用。本文中术语“和/或”，仅仅是一种描述关联对象的关联关系，表示可以存在三种关系，例如，A和/或B，可以表示：单独存在A，同时存在A和B，单独存在B这三种情况。另外，本文中字符“/”，一般表示前后关联对象是一种“或”的关系。
本领域普通技术人员可以意识到，结合本文中所公开的实施例中描述的各方法步骤和单元，能够以电子硬件、计算机软件或者二者的结合来实现，为了清楚地说明硬件和软件的可互换性，在上述说明中已经按照功能一般性地描述了各实施例的步骤及组成。这些功能究竟以硬件还是软件方式来执行，取决于技术方案的特定应用和设计约束条件。本领域普通技术人员可以对每个特定的应用来使用不同方法来实现所描述的功能，但是这种实现不应认为超出本发明的范围。
所属领域的技术人员可以清楚地了解到，为了描述的方便和简洁，上述描述的系统、装置和单元的具体工作过程，可以参考前述方法实施例中的对应过程，在此不再赘述。
在本申请所提供的几个实施例中，应该理解到，所揭露的系统、装置和方法，可以通过其它的方式实现。例如，以上所描述的装置实施例仅仅是示意性的，例如，所述单元的划分，仅仅为一种逻辑功能划分，实际实现时可以有另外的划分方式，例如多个单元或组件可以结合或者可以集成到另一个系统，或一些特征可以忽略，或不执行。另外，所显示或讨论的相互之间的耦合或直接耦合或通信连接可以是通过一些接口、装置或单元的间接耦合或通信连接，也可以是电的，机械的或其它的形式连接。
所述作为分离部件说明的单元可以是或者也可以不是物理上分开的，作为单元显示的部件可以是或者也可以不是物理单元，即可以位于一个地方，或者也可以分布到多个网络单元上。可以根据实际的需要选择其中的部分或者全部单元来实现本发明实施例方案的目的。
另外，在本发明各个实施例中的各功能单元可以集成在一个处理单元中，也可以是各个单元单独物理存在，也可以是两个或两个以上单元集成在一个单元中。上述集成的单元既可以采用硬件的形式实现，也可以采用软件功能单元的形式实现。
所述集成的单元如果以软件功能单元的形式实现并作为独立的产品销售或使用时，可以存储在一个计算机可读取存储介质中。基于这样的理解，本发明的技术方案本质上或者说对现有技术做出贡献的部分，或者该技术方案的全部或部分可以以软件产品的形式体现出来，该计算机软件产品存储在一个存储介质中，包括若干指令用以使得一台计算机设备(可以是个人计算机，服务器，或者网络设备等)执行本发明各个实施例所述方法的全部或部分步骤。而前述的存储介质包括：U盘、移动硬盘、只读存储器(Read-Only Memory，ROM)、随机存取存储器(Random Access Memory，RAM)、磁碟或者光盘等各种可以存储程序代码的介质。
以上所述，仅为本发明的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应以权利要求的保护范围为准。

Claims (30)

  1. 一种自由空间通信系统中的光通信装置，其特征在于，包括：
    发光单元，用于发射具有第一波长的第一光信号；
    光转换单元，用于接收所述发光单元发射的所述第一光信号，将所述第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，并输出所述第一光信号中的第二部分光信号和所述第二光信号，其中，所述第二光信号作为用于进行信号跟踪的信标光，所述第二部分光信号作为用于承载客户数据的通信光；
    发送单元，用于向第一对端通信装置发送所述光转换单元输出的所述第二部分光信号和所述第二光信号。
  2. 根据权利要求1所述的光通信装置，其特征在于，所述第二波长小于所述第一波长。
  3. 根据权利要求1或2所述的光通信装置，其特征在于，所述第一波长为所述第二波长的整数倍；
    所述光转换单元包括：光倍频晶体。
  4. 根据权利要求3所述的光通信装置，其特征在于，所述第一光信号从第一表面入射所述光倍频晶体，经由所述光倍频晶体的至少一个第二表面中的每个第二表面反射至少一次后，从第三表面射出所述光倍频晶体，其中，所述第一表面和所述第三表面镀有增透膜，所述至少一个第二表面镀有反射膜。
  5. 根据权利要求4所述的光通信装置，其特征在于，所述光倍频晶体具有至少一个切角，所述至少一个第二表面包括所述至少一个切角的表面。
  6. 根据权利要求3至5中任一项所述的光通信装置，其特征在于，所述光转换单元还包括：宽度变换单元，用于接收所述发光单元传输的所述第一光信号，并将接收到的所述第一光信号的光束宽度由第一宽度变换为第二宽度；
    所述光倍频晶体具体用于接收所述宽度变换单元输出的具有所述第二宽度的所述第一光信号，将接收到的具有所述第二宽度的所述第一光信号中的第一部分光信号转换为所述第二光信号，并输出所述第二部分光信号和所述第二光信号。
  7. 根据权利要求3至6中任一项所述的光通信装置，其特征在于，所 述第一光信号在所述光倍频晶体中传输的距离Leff满足以下条件：
    PT,C＝SC+MC+PR,C+LRx,C+LA,C+LG,C+LTx,C，
    PT,B＝SB+MB+PR,B+LRx,B+LA,B+LG,B+LTx,B，
    PT,C＝(PT,C+PT,B)sech2(ΓLeff)，
    PT,B＝(PT,C+PT,B)tanh2(ΓLeff)，
    其中，
    Figure PCTCN2016110296-appb-100001
    PT,C为所述第二部分光信号入射到所述光倍频晶体时的功率，SC所述第一对端通信装置中用于接收所述第二部分光信号的第一探测器的灵敏度，PR,C为所述第二部分光信号到达所述第一探测器时的功率，LTx,C为所述第二部分光信号在所述第一对端通信装置中的损耗，LG,C为所述第二部分光信号的发散损耗，LG,C为所述第二部分光信号的大气吸收损耗，LRx,C为所述第二部分光信号在所述对端通信装置中的损耗，MC为所述第二部分光信号的链路裕量，PT,B为所述第二光信号入射到所述光倍频晶体时的功率，SB所述第一对端通信装置中用于接收所述第二光信号的第二探测器的灵敏度，PR,B为所述第二光信号到达所述第二探测器时的功率，LTx,B为所述第二光信号在所述光转换单元中的损耗，LG,B为所述第二光信号的发散损耗，LG,B为所述第二光信号的大气吸收损耗，LRx,B为所述第二光信号在所述第一对端通信装置中的损耗，MB为所述第二光信号的链路裕量，n为所述光倍频晶体的折射率，C为真空光速，ω为所述第一光信号的圆频率，deff为所述光倍频晶体的二阶非线性系数，ε0为真空介电常数，w1为所述第一光信号入射到所述光倍频晶体时的光束半径，Leff为所述第一光信号在所述光倍频晶体中传输的距离。
  8. 根据权利要求7所述的光通信装置，其特征在于，所述宽度变换单元包括：沿着光路依次设置的第一凸透镜和凹透镜，其中，所述第一凸透镜的焦点与所述凹透镜的焦点重合。
  9. 根据权利要求8所述的光通信装置，其特征在于，所述第一凸透镜的焦距f1和所述凹透镜的焦距f2满足以下关系：
    Figure PCTCN2016110296-appb-100002
    其中，D1为所述第一光信号入射所述第一凸透镜时的光束宽度，2w1为所述第一光信号出射所述凹透镜时的光束宽度。
  10. 根据权利要求1至9中任一项所述的光通信装置，其特征在于，所述发送单元具体用于：向所述第一对端通信装置发送包括所述第二部分光信号和所述第二光信号的第一光束，其中，所述第一光束的波束宽度和/或发散角满足预设条件。
  11. 根据权利要求10所述的光通信装置，其特征在于，所述发送单元包括：
    沿着光路依次设置的第二凸透镜和第三凸透镜，其中，所述第二凸透镜的焦距f3和所述第三凸透镜的焦距f4满足以下关系：
    Figure PCTCN2016110296-appb-100003
    其中，D2为所述第一光束的光束直径。
  12. 根据权利要求1至11中任一项所述的光通信装置，其特征在于，所述光通信装置还包括：
    光放大单元，用于接收所述发光单元发射的所述第一光信号，对所述第一光信号进行放大处理，并输出放大处理后的所述第一光信号；
    所述光转换单元具体用于接收所述光放大单元输出的放大处理后的所述第一光信号。
  13. 根据权利要求11或12所述的光通信装置，其特征在于，所述光通信装置还包括：接收单元、可旋转光系统、光分离单元、光探测单元和控制单元，其中，
    所述接收单元用于接收第二对端通信装置发送的第二光束，其中，所述第二光束包括具有第一波长的第三光信号和具有第二波长的第四光信号；
    所述可旋转光系统用于引导所述接收单元接收到的所述第二光束的传输方向；
    所述光分离单元用于接收所述可旋转光系统引导的所述第二光束，并且分离所述第二光束中的所述第三光信号和所述第四光信号；
    所述光探测单元用于接收所述光分离单元传输的所述第二光束中的第三光信号，并对所述第三光信号中调制的数据进行解调处理；
    所述控制单元用于接收所述光分离单元传输的所述第二光束中的第四光信号，并根据接收到的所述第四光信号，控制所述可旋转光系统的角度。
  14. 根据权利要求13所述的光通信装置，其特征在于，所述光分离单元包括用于分离所述第一波长和所述第二波长的光信号的分波片。
  15. 根据权利要求13或14所述的光通信装置，其特征在于，所述控制单元包括：位置检测单元和调整单元，
    所述位置检测单元用于接收所述光分离单元输出的所述第四光信号，确 定所述第四光信号的光心位置，并向所述调节单元传输所述光心位置的信息；
    所述调整单元用于接收所述位置检测单元传输的所述光心位置的信息，并根据所述信息，调整所述可旋转光系统的角度。
  16. 根据权利要求15所述的光通信装置，其特征在于，所述位置检测单元包括：硅四象限探测器。
  17. 一种自由空间通信系统中的发射天线，其特征在于，包括：
    接收单元，用于接收光发射机发射的第一光信号；
    光转换单元，用于将所述接收单元接收的所述第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，其中，所述第二光信号作为用于进行信号跟踪的信标光，所述第二部分光信号作为用于承载客户数据的通信光；
    发送单元，用于向第一对端通信装置发送所述第一光信号中的第二部分光信号和所述光转换单元得到的所述第二光信号。
  18. 根据权利要求17所述的发射天线，其特征在于，所述第一波长为所述第二波长的整数倍；
    所述光转换单元包括：光倍频晶体。
  19. 根据权利要求18所述的发射天线，其特征在于，所述光转换单元还包括：宽度变换单元，用于接收所述光发射机传输的所述第一光信号，并将接收到的所述第一光信号的光束宽度由第一宽度变换为第二宽度；
    所述光倍频晶体具体用于接收所述宽度变换单元输出的具有所述第二宽度的所述第一光信号，将接收到的具有所述第二宽度的所述第一光信号中的第一部分光信号转换为所述第二光信号，并输出所述第二部分光信号和所述第二光信号。
  20. 根据权利要求19所述的发射天线，其特征在于，所述宽度变换单元包括：沿着光路依次设置的第一凸透镜和凹透镜，其中，所述第一凸透镜的焦点与所述凹透镜的焦点重合。
  21. 根据权利要求18至20中任一项所述的发射天线，其特征在于，所述发送单元具体用于接收所述光倍频晶体输出的所述第二部分光信号和所述第二光信号，并向所述第一对端通信装置发送包括所述第二部分光信号和所述第二光信号的第一光束，其中，所述第一光束的波束宽度和/或发散角满 足预设条件。
  22. 根据权利要求21所述的发射天线，其特征在于，所述发送单元包括：
    沿着光路依次设置的第二凸透镜和第三凸透镜，其中，所述第二凸透镜的焦距f3和所述第三凸透镜的焦距f4满足以下关系：
    Figure PCTCN2016110296-appb-100004
    其中，D2为所述第一光束的光束直径。
  23. 一种自由空间通信系统中的光通信装置，其特征在于，包括光发射机和权利要求17至22中任一项所述的发射天线。
  24. 一种自由空间通信系统中的光通信方法，其特征在于，包括：
    发射具有第一波长的第一光信号；
    对所述第一光信号进行转换处理，以使得所述第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，其中，所述第二光信号作为用于进行信号跟踪的信标光，所述第二部分光信号作为用于承载客户数据的通信光；
    向第一对端通信装置发送所述第一光信号中的第二部分光信号和所述第二光信号。
  25. 根据权利要求24所述的光通信方法，其特征在于，所述第二波长小于所述第一波长。
  26. 根据权利要求24或25所述的光通信方法，其特征在于，所述第一波长为所述第二波长的整数倍；
    所述将所述第一光信号进行转换处理，以使得所述第一光信号中的第一部分光信号转换为具有第二波长的第二光信号，包括：
    利用光倍频晶体对所述第一光信号进行转换处理，以使得所述第一光信号中的第一部分光信号转换为具有第二波长的第二光信号。
  27. 根据权利要求26所述的光通信方法，其特征在于，所述第一光信号从第一表面入射所述光倍频晶体，经由所述光倍频晶体的至少一个第二表面反射至少一次后，从第三表面射出所述光倍频晶体，其中，所述第一表面和所述第三表面镀有增透膜，所述至少一个第二表面镀有反射膜。
  28. 根据权利要求27所述的光通信方法，其特征在于，所述光倍频晶 体具有至少一个切角，所述至少一个第二表面包括所述至少一个切角的表面。
  29. 根据权利要求26至28中任一项所述的光通信方法，其特征在于，在所述利用光倍频晶体对所述第一光信号进行转换处理之前，所述方法还包括：
    对所述第一光信号进行宽度变换处理，以将所述第一光信号的光束宽度由第一宽度变为第二宽度；
    所述利用光倍频晶体对所述第一光信号进行转换处理，包括：
    利用光倍频晶体对光束宽度为所述第二宽度的所述第一光信号进行转换处理。
  30. 根据权利要求26至29中任一项所述的光通信方法，其特征在于，所述第一光信号在所述光倍频晶体中传输的距离Leff满足以下条件：
    PT,C＝SC+MC+PR,C+LRx,C+LA,C+LG,C+LTx,C，
    PT,B＝SB+MB+PR,B+LRx,B+LA,B+LG,B+LTx,B，
    PT,C＝(PT,C+PT,B)sech2(ΓLeff)，
    PT,B＝(PT,C+PT,B)tanh2(ΓLeff)，
    其中，
    Figure PCTCN2016110296-appb-100005
    PT,C为所述第二部分光信号入射到所述光倍频晶体时的功率，SC所述第一对端通信装置中用于接收所述第二部分光信号的第一探测器的灵敏度，PR,C为所述第二部分光信号到达所述第一探测器时的功率，LTx,C为所述第二部分光信号在所述第一对端通信装置中的损耗，LG,C为所述第二部分光信号的发散损耗，LG,C为所述第二部分光信号的大气吸收损耗，LRx,C为所述第二部分光信号在所述对端通信装置中的损耗，MC为所述第二部分光信号的链路裕量，PT,B为所述第二光信号入射到所述光倍频晶体时的功率，SB所述第一对端通信装置中用于接收所述第二光信号的第二探测器的灵敏度，PR,B为所述第二光信号到达所述第二探测器时的功率，LTx,B为所述第二光信号在所述光转换单元中的损耗，LG,B为所述第二光信号的发散损耗，LG,B为所述第二光信号的大气吸收损耗，LRx,B为所述第二光信号在所述第一对端通信装置中的损耗，MB为所述第二光信号的链路裕量，n为所述光倍频晶体的折射率，C为真空光速，ω为所述第一光信号的圆频率，deff为所述光倍频晶体的二阶非线性系数，ε0为真空介电常数，w1为所述第一光信号入射到所述光倍频晶体时的光束半径。
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