CN104779996A - Free space laser communication optical denoising method based on polarization mark - Google Patents
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Abstract
The invention provides a free space laser communication optical denoising method based on polarization marks. The method comprises the steps that firstly, a communication transmitting terminal carries out polarization marking on a laser communication signal, so that the polarization state of the laser communication signal is left-handed circular polarization or right-handed circular polarization; then, the optical signal with the polarization mark is identified at the communication receiving terminal, and background light noise in the received signal is eliminated. The invention can effectively remove background light noise in the free space laser communication signal, has mature devices and simple structure, and reduces the popularization difficulty.
Description
Technical field
The invention belongs to laser space communication field.Specifically, the optics denoising method of laser space communication, launch terminal and receiving terminal is related to.
Background technology
Good directionality, message capacity are large owing to having for free space laser communication, the important subject of volume and advantage become the wireless communication field such as power consumption is little.Owing to being subject to the impact of the background noise light such as daylight, moonlight, starlight, in communications reception end-probing signal, be mingled with very strong background noise.This will increase the error rate of communication, reduces communication quality.The normal impact adopting the method for optically filtering to eliminate background noise in prior art, namely only allows the light signal in Communication ray wave-length coverage to enter the Photodetection system of receiving terminal.At present, common in engineering optically filtering device has filter, interference filter and Birefringent Filter etc.
Filter is a kind of optical mirror slip, has very high transmitance at communication band, but lower for the transmitance of other wave band.Interference filter commonly uses Fabry-Perot interferometer as filter structure, utilizes the principle filter out background noise of multiple-beam interference.Birefringent Filter mainly utilizes polarization interference principle to carry out filtering, can be divided into Lyot-Ohman filter and Solc filter according to the difference of structure.
Although above three kinds of optically filtering methods to a certain extent can the filtering background noise different from communication band wavelength, the bias light identical with filter center wavelength for wavelength cannot filtering.In addition, the transmission bandwidth of optical filter is narrower, and light wave transmitance is less, and this is unfavorable for the detection of free-space communication light signal under long range propagation, strong background noise.
Summary of the invention
The object of the invention is to the deficiency overcoming above-mentioned optics denoising method, a kind of free space laser communication optics denoising method based on marking of polarization, launch terminal and receiving terminal are provided.
The present invention is achieved in that
1. know-why
Only a kind of electromagnetic wave.Communication light wave generally has the feature that coherence is good, degree of polarization is high; And the bias light in free space has the feature of coherence's difference, its degree of polarization is generally 0.In addition, when light wave transmits in free space, polarization state changes hardly.
Therefore, for free space laser communication, in the polarization state of communications transmit terminal control emergent light, make it have specific polarization state feature, such as Left-hand circular polarization state or right-hand circular polarization state.Like this, the Communication ray arriving communications reception terminal will have and will be different from background noise polarisation of light marker characteristic, so just can pass through from strong background noise, detect communicating light signal to polarization knowledge method for distinguishing.
Polarization identifying can be realized by the mode of polarization beam splitting and Differential Detection.First the flashlight with specific polarization marker characteristic is converted to linear polarization marking signal light by quarter-wave plate specifically, then utilizes polarization beam splitting device that the reception light of communications reception terminal is divided into two bundles.The Communication ray of linear polarization mark be only present in wherein a branch of in the middle of, this bundle light can be expressed as (flashlight+background noise light/2), its light intensity I
acan be expressed as:
I in formula
flashlightand I
background noise lightbe respectively the light intensity of flashlight and background noise light.
Meanwhile, signal of communication is not comprised in another light beam, light intensity I
bcan be expressed as:
Like this by utilizing the method for Differential Detection to subtract each other two-beam, the light intensity I obtained is:
Thus the background noise eliminated in signal.
2. technical scheme
Based on a free space laser communication optics denoising method for marking of polarization, its special character is: comprise the following steps:
1] communicating light signal is produced;
2] by step 1] polarization state of communicating light signal that produces is converted to linear polarization, makes communicating light signal have linear polarization feature;
3] by step 2] communicating light signal with linear polarization feature that produces is converted to the communicating light signal with circular polarization feature;
4] communicating light signal with circular polarization feature is transmitted in free space channel;
The communicating light signal 5] with circular polarization feature transmits in free space channel;
6] communicating light signal with circular polarization feature is received;
7] communicating light signal with circular polarization feature received is converted to the communicating light signal of linear polarization feature;
8] communicating light signal of linear polarization feature is separated into the orthogonal two-beam in polarization direction, wherein light beam comprises communicating light signal and background noise light, and another bundle only comprises background noise light, and in two-beam, the light intensity of background noise light is equal;
9] to step 8] be separated the two-beam that obtains and carry out opto-electronic conversion respectively, and calculus of differences is carried out to the signal of telecommunication be converted to, in the signal of telecommunication that difference obtains, background noise is by filtering.
Preferably, above-mentioned steps 3] in the communicating light signal with linear polarization feature is converted to the communicating light signal with circular polarization feature, be by accessing launch terminal quarter-wave plate after the communicating light signal with linear polarization feature, and make launch terminal quarter-wave plate intrinsic direction of principal axis and linear polarization angle be 45 ° to realize.
Preferably, above-mentioned steps 7] communicating light signal with circular polarization feature received is converted to the communicating light signal of linear polarization feature, be realize by accessing receiving terminal quarter-wave plate after the communicating light signal having circular polarization feature.
Preferably, above-mentioned steps 8] communicating light signal of linear polarization feature is separated into the orthogonal two-beam in polarization direction, be by accessing polarized light splitting device after receiving terminal quarter-wave plate, and make the intrinsic axle of receiving terminal quarter-wave plate and polarized light splitting device intrinsic axle clamp angle be 45 ° to realize.
Preferably, above-mentioned steps 9] to step 8] be separated the two-beam obtained and carry out opto-electronic conversion respectively, and calculus of differences is carried out to the signal of telecommunication be converted to, in the signal of telecommunication that difference obtains, background noise is by filtering, is realized by balance photodetector.
Preferably, above-mentioned steps 2] be utilize the polarizer to be linear polarization by communicating light signal polarization converted.
Preferably, above-mentioned steps 1] produce the detailed process of communicating light signal and be: utilize the communication data signal of telecommunication to control electrooptic modulator, the light intensity that laser exports is modulated, when the signal of telecommunication is high level, electrooptic modulator has Laser output, corresponding communication logic " 1 ", when the signal of telecommunication is low level, electrooptic modulator without Laser output, corresponding communication logic " 0 "; Vice versa.
Based on the free space laser communication launch terminal of marking of polarization, its special character is: comprise laser and be successively set on electrooptic modulator, the polarizer, launch terminal quarter-wave plate and the optical transmitting antenna on laser output light path.Laser exports light and vertically injects electrooptic modulator, and the output light of electrooptic modulator vertically injects the polarizer, and the polarizer exports light and vertically injects launch terminal quarter-wave plate.
Based on the free space laser communication receiving terminal of marking of polarization, its special character is: comprise optical receiver antenna and be successively set on receiving terminal quarter-wave plate, polarized light splitting device and the balance photodetector on optical receiver antenna output light path.Optical receiver antenna exports light and vertically injects receiving terminal quarter-wave plate, the output light of receiving terminal quarter-wave plate vertically injects polarized light splitting device, and the two-beam that polarized light splitting device exports vertically injects two receiving planes of balance photodetector respectively.
The present invention has the following advantages:
1. owing to having carried out circular polarization mark to communicating light signal, make it have the feature being different from background noise light, be conducive to from strong background noise, filter out useful light signal.
2. circular polarization labeling method of the present invention, communications transmit and receiving terminal rise partially and the polarization direction of analyzing device without the need to aiming at, greatly reduce system complexity and use difficulty.
3., owing to adopting balance photodetector to detect the receiving optical signals after polarization beam splitting, all background noises comprising the noise light identical with communication band all can be filtered out.
4. structure is simple, is easy to realize.The present invention's device used all has matured product, and it is simple to transmit and receive terminal structure, is easy to realize and promote.
Accompanying drawing explanation
Fig. 1 is principle schematic of the present invention;
Fig. 2 .1 is communications transmit terminal schematic diagram;
Fig. 2 .2 is communications transmit terminal references coordinate system;
Fig. 3 .1 is communications reception terminal schematic diagram;
Fig. 3 .2 is communications reception terminal references coordinate system;
Fig. 4 is balance photodetector principle schematic.
Embodiment
The present invention can be described by following examples:
Embodiment: based on the 1550nm wave band free-space communication of Left-hand circular polarization mark.
With reference to Fig. 1.Complete the 1550nm wave band free-space communication based on Left-hand circular polarization mark in accordance with the following steps.
1] communicating light signal is produced.With reference to Fig. 2 .1, the electrooptic modulator of communication data signal of telecommunication control 1550nm wave band is utilized to modulate the light intensity that laser exports in communications transmit terminal, laser exports light and vertically injects electrooptic modulator, when the signal of telecommunication is high level, electrooptic modulator has Laser output, corresponding communication logic " 1 ", when the signal of telecommunication is low level, electrooptic modulator without Laser output, corresponding communication logic " 0 "; Or when the signal of telecommunication is high level, electrooptic modulator is without Laser output, and corresponding communication logic " 0 ", when the signal of telecommunication is low level, electrooptic modulator has Laser output, corresponding communication logic " 1 ".
2] by step 1] polarization state of communicating light signal that produces is converted to linear polarization, makes communicating light signal have linear polarization feature.With reference to Fig. 2 .1, after electrooptic modulator, access a polarizer, the output light of electrooptic modulator vertically injects the polarizer, and the laser polarization state that electrooptic modulator is exported is converted to linear polarization.With reference to Fig. 2 .2, in the plane vertical with linearly polarized light transmission direction, set up communications transmit terminal references coordinate system xOy, make linear polarization and communications transmit terminal references coordinate system x-axis forward angle be 45 °.Along communications transmit terminal references coordinate system x-axis and y-axis direction, linearly polarized light is decomposed, light field
be expressed as with Jones matrix:
I in formula
0represent light intensity.
3] by step 2] communicating light signal with linear polarization feature that produces is converted to the communicating light signal with Left-hand circular polarization feature.With reference to Fig. 2 .1, access the launch terminal quarter-wave plate of a 1550nm wave band after the polarizer, the polarizer exports light and vertically injects launch terminal quarter-wave plate.With reference to Fig. 2 .2, in launch terminal quarter-wave plate, two eigen polarization mold component o light and e polarisation of light direction are consistent with the x-axis of communications reception terminal references coordinate system and y-axis direction respectively.And the phase delay of e light and o light is
like this, the Left-hand circular polarization mark of flashlight is completed.Light field under communications transmit terminal references coordinate system
be expressed as:
4] communicating light signal with Left-hand circular polarization feature is transmitted in free space channel.With reference to Fig. 1, after launch terminal quarter-wave plate, access optical transmitting antenna, the communication light wave marked with Left-hand circular polarization is transmitted in free space channel.
The communicating light signal 5] with circular polarization feature transmits in free space channel.With reference to Fig. 1, transmit free space channel from the communicating light signal of optical transmitting antenna outgoing.
6] communicating light signal with circular polarization feature is received.With reference to Fig. 1, communicating light signal arrives communications reception terminal after free space transmission, utilizes optical receiver antenna collection communication light signal.By the impact of free space channel, flashlight light intensity reduces, and mixes noise light of having powerful connections in reception light.Therefore receiving light power I can be expressed as:
I=I
noise+ I
signal
I in formula
noiseand I
signalrepresent the light intensity of noise light component and flashlight component respectively.And flashlight is still left circularly polarized light, and background noise light is natural daylight.
I
signal=α I
0
Signal light intensity in formula in α sign reception light and the ratio of communications transmit terminal output intensity, and 0< α <1.
7] conversion of Communication ray polarization state.With reference to Fig. 3 .1, access the receiving terminal quarter-wave plate of 1550nm wave band after optical receiver antenna, optical receiver antenna output light-wave impinges perpendicularly on receiving terminal quarter-wave plate.With reference to Fig. 3 .2, communications reception end coordinates system x ' Oy ' is set up in the plane of receiving terminal quarter-wave plate place, make two of receiving terminal quarter-wave plate eigen polarization mold component o light and e light and communications reception terminal references coordinate system x ' axle forward angle be respectively 45 ° and 135 °, and the phase-delay difference of e light and o light is
Under communications reception terminal references coordinate system, the flashlight component Jones matrix incided in the reception light on receiving terminal quarter-wave plate can be expressed as:
Under receiving terminal reference frame, after receiving terminal quarter-wave plate, the flashlight representation in components received in light is:
The background noise light component received in light remains unchanged through receiving terminal quarter-wave plate rear polarizer characteristic, is still natural daylight.
8] communicating light signal of linear polarization feature is separated into the orthogonal two-beam in polarization direction, wherein light beam comprises communicating light signal and background noise light, and another bundle only comprises background noise light, and in two-beam, the light intensity of background noise light is equal.With reference to Fig. 3 .1, after receiving terminal quarter-wave plate, access polarized light splitting device.The intrinsic axle clamp angle of receiving terminal quarter-wave plate and polarized light splitting device is 45 °, and the output light of receiving terminal quarter-wave plate vertically injects polarized light splitting device.In Communication ray a two orhtogonal linear polarizaiton component is separated into linear polarization A light and linear polarization B light.With reference to Fig. 3 .2, linear polarization A polarisation of light direction is consistent with communications reception terminal references coordinate system y ' direction of principal axis, and linear polarization B polarisation of light direction is consistent with communications reception terminal references coordinate system x ' direction of principal axis.The then light intensity I of linear polarization A light and linear polarization B light
aand I
bbe respectively
9] to step 8] be separated the two-beam that obtains and carry out opto-electronic conversion respectively, and calculus of differences is carried out to the signal of telecommunication be converted to, in the signal of telecommunication that difference obtains, background noise is by filtering.With reference to Fig. 3 .1, access balance photodetector after polarized light splitting device.With reference to Fig. 4, in balance photodetector, first photodetector A and photodetector B carries out opto-electronic conversion to linearly polarized light A and linearly polarized light B respectively, obtains voltage U
1and U
2; Then to voltage U
1and U
2do difference, obtain exporting signal of telecommunication U=U
1-U
2.Namely
In formula, R is the voltage response degree of balance photodetector, and therefore voltage U is consistent with the Changing Pattern of communications transmit terminal emergent light signal, is the communication data signal of telecommunication that receiving terminal exports, wherein not containing background noise.
Above-mentioned steps 3] described in launch terminal quarter-wave plate in the phase delay of two eigen polarization mold component o light and e light also can be
it is now right-hand circular polarization mark.
In above-mentioned communication process, required device all has matured product.Therefore above-described embodiment shows, the free space laser communication optics denoising method based on marking of polarization provided by the present invention is feasible, and effectively can remove the background noise in free space laser communication Received signal strength.
Claims (9)
1., based on a free space laser communication optics denoising method for marking of polarization, it is characterized in that: comprise the following steps:
1] communicating light signal is produced;
2] by step 1] polarization state of communicating light signal that produces is converted to linear polarization, makes communicating light signal have linear polarization feature;
3] by step 2] communicating light signal with linear polarization feature that produces is converted to the communicating light signal with circular polarization feature;
4] communicating light signal with circular polarization feature is transmitted in free space channel;
The communicating light signal 5] with circular polarization feature transmits in free space channel;
6] communicating light signal with circular polarization feature is received;
7] communicating light signal with circular polarization feature received is converted to the communicating light signal of linear polarization feature;
8] communicating light signal of linear polarization feature is separated into the orthogonal two-beam in polarization direction, wherein light beam comprises communicating light signal and background noise light, and another bundle only comprises background noise light, and in two-beam, the light intensity of background noise light is equal;
9] to step 8] be separated the two-beam that obtains and carry out opto-electronic conversion respectively, and calculus of differences is carried out to the signal of telecommunication be converted to, in the signal of telecommunication that difference obtains, background noise is by filtering.
2. the free space laser communication optics denoising method based on marking of polarization according to claim 1, it is characterized in that: step 3] in the communicating light signal with linear polarization feature is converted to the communicating light signal with circular polarization feature, be by accessing launch terminal quarter-wave plate after the communicating light signal with linear polarization feature, and make launch terminal quarter-wave plate intrinsic direction of principal axis and linear polarization angle be 45 ° to realize.
3. the free space laser communication optics denoising method based on marking of polarization according to claim 1, it is characterized in that: step 7] communicating light signal with circular polarization feature received is converted to the communicating light signal of linear polarization feature, be realize by accessing receiving terminal quarter-wave plate after the communicating light signal having circular polarization feature.
4. the free space laser communication optics denoising method based on marking of polarization according to claim 3, it is characterized in that: step 8] communicating light signal of linear polarization feature is separated into the orthogonal two-beam in polarization direction, be by accessing polarized light splitting device after receiving terminal quarter-wave plate, and make the intrinsic axle of receiving terminal quarter-wave plate and polarized light splitting device intrinsic axle clamp angle be 45 ° to realize.
5. the free space laser communication optics denoising method based on marking of polarization according to claim 4, it is characterized in that: step 9] in, carry out opto-electronic conversion, and calculus of differences is carried out to the signal of telecommunication be converted to, in the signal of telecommunication that difference obtains, background noise is by filtering, is realized by balance photodetector.
6. the free space laser communication optics denoising method based on marking of polarization according to claim 1, is characterized in that: step 2] be utilize the polarizer to be linear polarization by communicating light signal polarization converted.
7. the free space laser communication optics denoising method based on marking of polarization according to claim 1, it is characterized in that: step 1] produce the detailed process of communicating light signal and be: utilize the communication data signal of telecommunication to control electrooptic modulator, the light intensity that laser exports is modulated, when the signal of telecommunication is high level, electrooptic modulator has Laser output, corresponding communication logic " 1 ", when the signal of telecommunication is low level, electrooptic modulator without Laser output, corresponding communication logic " 0 ".
8. based on the free space laser communication launch terminal of marking of polarization, it is characterized in that: comprise laser and be successively set on electrooptic modulator, the polarizer, launch terminal quarter-wave plate and the optical transmitting antenna on laser output light path, laser exports light and vertically injects electrooptic modulator, the output light of electrooptic modulator vertically injects the polarizer, and the polarizer exports light and vertically injects launch terminal quarter-wave plate.
9. based on the free space laser communication receiving terminal of marking of polarization, it is characterized in that: comprise optical receiver antenna and be successively set on receiving terminal quarter-wave plate, polarized light splitting device and the balance photodetector on optical receiver antenna output light path, optical receiver antenna exports light and vertically injects receiving terminal quarter-wave plate, the output light of receiving terminal quarter-wave plate vertically injects polarized light splitting device, and the two-beam that polarized light splitting device exports vertically injects two receiving planes of balance photodetector respectively.
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| CN110462466A (en) * | 2017-03-24 | 2019-11-15 | 日东电工株式会社 | Optical filter and optical communication apparatus |
| CN114374434A (en) * | 2022-01-10 | 2022-04-19 | 北京理工大学 | One-to-many free space laser communication device based on polarized light field and method thereof |
| CN114826399A (en) * | 2022-05-03 | 2022-07-29 | 浙江大学湖州研究院 | Circular polarization shift keying optical communication system based on partially coherent light |
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| CN103401610A (en) * | 2013-08-06 | 2013-11-20 | 中国科学院长春光学精密机械与物理研究所 | Differential-type circularly-polarized laser carrier communication system |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110462466A (en) * | 2017-03-24 | 2019-11-15 | 日东电工株式会社 | Optical filter and optical communication apparatus |
| CN114374434A (en) * | 2022-01-10 | 2022-04-19 | 北京理工大学 | One-to-many free space laser communication device based on polarized light field and method thereof |
| CN114826399A (en) * | 2022-05-03 | 2022-07-29 | 浙江大学湖州研究院 | Circular polarization shift keying optical communication system based on partially coherent light |
| CN114826399B (en) * | 2022-05-03 | 2023-09-12 | 浙江大学湖州研究院 | Circular polarization shift keying optical communication system based on partially coherent light |
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