CN110855368A - High-isolation same-frequency space laser communication optical path for transmitting and receiving with same polarization state - Google Patents
High-isolation same-frequency space laser communication optical path for transmitting and receiving with same polarization state Download PDFInfo
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Abstract
The invention provides a high-isolation common-frequency space laser communication optical path for transmitting and receiving laser light in the same polarization state. The space laser communication optical path is composed of components such as a lambda/4 wave plate, a polarization beam splitter, an energy beam splitter, a signal communication receiving channel, a signal tracking and capturing channel, a signal light emitting channel, a magneto-optical rotator, an optical trap and the like. The light path realizes the same polarization state of the received and transmitted light beams through the matching of the magneto-optical rotator, the wave plate and other components, and ensures that the polarization state of the stray light after primary backscattering/reflection is different from the polarization state of the received light, thereby reducing the energy of the stray light by using a polarization light splitting technology; emission of stray light towards the mechanical wall is suppressed by using light traps.
Description
Technical Field
The invention relates to the field of space laser communication, in particular to a high-isolation same-frequency space laser communication optical path for receiving and transmitting with the same polarization state.
Background
Space laser communication (laser communication link between satellites, between the earth or between the foundations) is a long-distance weak energy detection system, the intensity of signals received by communication is very weak, the energy of emitted light beams is very strong, and the power difference between the two can reach more than 90 dB. Therefore, high isolation between transmission and reception is required, otherwise the transmitted light will reach the communication or capture receiver after being reflected or scattered by the optical element, which will have a serious influence on the signal and even directly annihilate the received signal, resulting in the system not working properly. The impact between transmission and reception is usually measured by the isolation, which is the total loss of energy from the interfering transmitter to the interfered receiver.
At present, two main schemes for solving the problem of isolation of transmitting and receiving are available, namely a wavelength splitting scheme and a polarization splitting scheme.
The wavelength light splitting scheme is that the light of the two receiving and transmitting beams is separated by an interference light splitter according to the difference of the wavelengths of the receiving and transmitting beams. At present, the method is mostly adopted in a space laser communication system, for example, two publications of beacon detection technology of a free space optical communication APT system and research of efficient polarization beam splitting technology of a multipoint simultaneous space laser communication system have related technical records.
However, the wavelength splitting scheme has great limitations, mainly represented by:
1. the wavelength characteristics of the device and the laser are difficult to change, so that the communication terminal can only communicate with the corresponding terminal, and the flexibility among communication links is greatly limited;
2. some modem technologies require communication in a specific frequency band with narrow wavelength intervals, which is difficult to use wavelength division, for example, BPSK modem technologies generally work in the 1550nm band (1530nm to 1570nm), which is only 40nm wide, and are difficult to use wavelength division for isolation.
The other is a polarization splitting scheme, the polarization states of the transmitting and receiving light beams are orthogonal, and the transmitting and receiving light beams can be separated by using a polarization beam splitter. Based on the above reasons, polarization splitting is the only solution for solving the problem of transmit-receive isolation, but the current polarization splitting solution is difficult to realize higher transmit-receive isolation (generally lower than 60dB), for example, chinese patent, with the application numbers: 201710443937.X, the patent name "a method for high-precision separation of light beams with the same frequency as the light receiving and transmitting of space laser communication signals", provides an isolation scheme which can only reach 60dB, but the difference of the receiving and transmitting energy can reach more than 100dB during remote communication, the stray light energy is 40dB higher than the signal energy, and the requirement of remote communication cannot be met.
At present, the same-frequency laser communication light path for receiving and transmitting almost adopts a light path similar to the patent, and two main stray light in the light path are difficult to remove. As shown in fig. 1, the optical path includes a retro-reflection surface 101 of the front optical system, a λ/4 wave plate 102, a polarization splitting plate 103, an energy splitting plate 104, a signal communication receiving branch 105, a signal tracking capturing branch 106, a signal light emitting branch 107 and a laser communication terminal structure frame 108.
Fig. 1 and 2 show two main stray light paths of a space laser communication transceiving optical path using polarization splitting, where fig. 1 shows a primary backscattering/reflecting stray light path of a front-mounted optical system after passing through a λ/4 wave plate 102, and the polarization state of the primary scattering/reflecting stray light is the same as that of received light, resulting in no polarization isolation effect; fig. 2 shows a back scattering path generated by the emitted light passing through the polarization splitter 103 and striking the mechanical wall of the frame 108 of the laser communication terminal, where the two paths greatly reduce the isolation between transmission and reception.
In addition, the existing transmitting-receiving same-frequency laser communication optical path also has the problem that the working mode needs to be switched on track during networking communication. The satellite common-frequency laser communication terminal is in point-to-point communication, and one terminal needs to perform networking communication with a plurality of terminals. The polarization states of the receiving and transmitting light beams of the existing receiving and transmitting common-frequency laser communication light path are different, two working modes are generally set, namely, mode A: transmit left-handed circular polarization, receive right-handed circularly polarized light, mode B: and transmitting right-handed circularly polarized light and receiving left-handed circularly polarized light. As shown in fig. 3, assuming that four spatial laser communication terminals 1, 2, 3, and 4 are networked, the terminal 1 and the terminal 2 operate in mode a, and the terminal 3 and the terminal 4 operate in mode B. At this time, the terminal 1 can perform networking communication with the terminals 3 and 4, but networking communication between the terminals 1 and 2 and between the terminals 3 and 4 is not possible. When the terminal 3 needs to communicate with the terminal 4, the operation mode needs to be switched, and the on-track rotation 1/4 wave plate realizes the exchange of the polarization states of the transmitting and receiving light beams, and the networking communication method increases the risk of on-track operation and the consumption of resources.
Disclosure of Invention
The invention provides a high-isolation transceiving same-polarization-state same-frequency space laser communication light path, which aims to solve the problems that the existing space laser communication light path is not high in transceiving isolation and is greatly influenced by stray light.
The basic design principle of the invention is as follows:
the space laser communication light path is used for absorbing main stray light hitting a mechanical wall through the light trap, so that scattering of the mechanical wall is reduced; the magneto-optical rotator is used for changing the polarization state of the primary back scattering/reflection stray light, so that the polarization state of the primary back scattering/reflection stray light is converted from P light of an original light path into S light, and the polarization state of the primary back scattering/reflection stray light is different from that of the received light, thereby increasing the polarization isolation effect.
The specific technical scheme of the invention is as follows:
the invention provides a high-isolation transceiving same-frequency space laser communication light path in the same polarization state, which comprises a laser communication terminal structure frame, a back reflection surface of a front optical system, a lambda/4 wave plate, a polarization beam splitter, an energy beam splitter, a signal communication receiving channel, a signal tracking and capturing channel and a signal light emitting branch; the improvement is that:
a magneto-optical rotator and a light trap;
the magneto-optical rotator is arranged between the lambda/4 wave plate and the polarization beam splitting plate, wherein the lambda/4 wave plate is a 0-degree lambda/4 wave plate or a 90-degree lambda/4 wave plate, and the magneto-optical rotator can deflect the polarization angle of linearly polarized light, and the deflection angle β is 45 degrees;
the light trap is arranged on the laser communication terminal structure frame body and is opposite to the transmission light path of the polarization beam splitter.
Further, the magneto-optical rotator is composed of a magnetic field generating device and a magneto-optical medium, and the specific technical formula of the deflection angle β is as follows:
β＝VBL＝45°
where V is the Verdet constant of the magneto-optical medium material, B is the magnetic flux, and L is the length of the magneto-optical medium.
Furthermore, the optical trap comprises a reflector, wherein a reflecting cavity with a conical section is formed in the reflector; the absorptivity epsilon of the reflector to incident light per time is more than 95 percent;
the taper of the reflecting cavity is 2 α, wherein, the angle is more than 8 degrees and less than or equal to α degrees and less than or equal to 16.36 degrees;
the stray light suppression ratio of the reflector is as follows:
nmaxis the maximum number of reflections of light by the reflective cavity.
Further, the reflective cavity has two forms:
the first is that: the reflecting cavity is a conical cavity.
Secondly, the reflecting cavity is formed by two crossed inclined planes with the same inclination angle, the inclination angle of the inclined planes is α, and the reflector is formed by splicing two wedges.
Furthermore, the maximum number of reflection times n of the light by the reflection cavitymaxThe specific calculation formula of (A) is as follows: n ismaxRoundup (90/α -0.5), where roundup () is a ceiling function.
Further, the optical trap has two types of configurations:
1. the reflector is made of a metal aluminum material, the surface of a reflecting cavity of the reflector is polished into a mirror surface, and the root mean square value of the roughness of the mirror surface is less than 3 nm; the surface of the reflecting cavity is plated with an absorbing film layer which is a chromium and medium antireflection film.
2. The reflector is made of colored absorption glass, and the transmittance of the colored absorption glass in each millimeter of the working wavelength is less than 0.01 percent; the surface of a reflecting cavity of the reflector is polished into a mirror surface, and the roughness root mean square value of the mirror surface is less than 3 nm; the surface of the reflection cavity is plated with an antireflection film.
Furthermore, the polarization beam splitter is realized by plating a polarization beam splitting film on plate glass, and the extinction ratio of the polarization beam splitter is more than 800: 1; the energy light splitting sheet is realized by plating an energy light splitting film on the flat glass, and the light splitting ratio of the energy light splitting sheet is determined by the plating film.
Furthermore, the signal communication receiving channel is composed of a receiving lens and a receiving optical fiber assembly; the signal tracking and capturing channel consists of a receiving lens and a capturing detector, and the capturing detector is a CMOS (complementary metal oxide semiconductor) or CCD (charge coupled device) or four-quadrant photoelectric device; the signal light emission branch is composed of a collimating lens and a transmitting laser component and emits linear polarized signal light with the polarization state S.
Further, the laser communication terminal structure frame body is processed by adopting a titanium alloy or aluminum-based silicon carbide material, the surface of the laser communication terminal structure frame body is subjected to black anodization treatment, and the absorptivity of the black anodization surface at a 1550nm near infrared communication waveband is not lower than 80%.
The invention has the beneficial effects that:
1. according to the space laser communication light path provided by the invention, the magneto-optical rotator is arranged, the polarization angle of the lambda/4 wave plate is changed, and the two polarization components are skillfully matched, so that backward stray light is S light at one time and is different from the polarization state of received light (P light), and the polarization isolation effect is improved.
2. According to the space laser communication light path provided by the invention, light scattering caused by the transmission of the emergent light of the signal light emitting branch on the mechanical wall through the polarization beam splitter is greatly inhibited through the light trap, and the interference of stray light is avoided.
3. Any two laser communication terminals adopting the space laser communication light path can directly communicate, compared with the existing light path, the receiving polarization state and the transmitting polarization state are different, the receiving polarization state and the transmitting polarization state of the space laser communication light path are the same (simultaneously, left-handed circular polarized light or right-handed circular polarized light), any two laser communication terminals using the light path can directly communicate without switching the polarization states, and networking communication is easier to realize.
Drawings
Fig. 1 is a schematic diagram of a situation that once backscattered stray light enters an existing transmitting and receiving common-frequency space laser communication optical path.
Fig. 2 is a schematic diagram of backward scattering stray light generated by the transmission light of the existing transmitting and receiving common-frequency space laser communication optical path after passing through a polarization beam splitter and striking on a mechanical wall;
fig. 3 is a schematic diagram of the existing network communication of the transmitting and receiving common-frequency space laser communication optical path.
The reference numbers are as follows:
101, a back reflection surface of a front optical system, a 102-lambda/4 wave plate, a 103-polarization beam splitter, a 104-energy beam splitter, a 105-signal communication receiving branch, a 106-signal tracking capturing branch, a 107-signal light emitting branch and a 108-are laser communication terminal structural frame bodies;
FIG. 4 is a light path diagram of the present invention;
FIG. 5 is a schematic diagram of the structure of the optical trap when the reflective cavity is a conical cavity in the present invention;
FIG. 6 is a schematic diagram of the structure of the optical trap when the reflective cavity is two inclined planes according to the present invention;
FIG. 7 is an absorption curve of an absorbent film of the present invention;
FIG. 8 is a schematic diagram of the present invention for suppressing the primary backscattered stray light;
fig. 9 is a schematic diagram of stray light suppression of the optical trap.
Fig. 10 is a schematic diagram of optical path networking communication according to the present invention.
The reference numbers are as follows:
201-a retro-reflection surface of a front optical system, 202-a/4 wave plates, 203-polarization beam splitters, 204-energy beam splitters, 205-a signal communication receiving channel, 206-a signal tracking and capturing channel, 207-a signal light emitting branch, 208-a laser communication terminal structure frame, 209-a magneto-optical rotator and 210-a light trap;
301-reflector, 302-conical cavity, 303-bevel, 304-wedge.
Detailed Description
In order to make the objects, advantages and features of the present invention clearer, the following describes in detail a high-isolation common-frequency spatial laser communication optical path for transmitting and receiving laser beams with the same polarization state, with reference to the accompanying drawings and specific embodiments. Advantages and features of the present invention will become apparent from the following description and from the claims. It should be noted that: the drawings are in simplified form and are not to precise scale, the intention being solely for the convenience and clarity of illustrating embodiments of the invention; second, the structures shown in the drawings are often part of actual structures.
As shown in fig. 4, the optical path of the present invention includes a laser communication terminal structural frame 208, a retro-reflection surface 201 of a front optical system disposed inside the laser communication terminal structural frame 208, a λ/4 wave plate 202, a polarization beam splitter 203, an energy beam splitter 204, a signal communication receiving channel 205, a signal tracking capturing channel 206, a signal light emitting branch 207, a magneto-optical rotator 209, and an optical trap 210;
each optical device in the optical path is described below:
the retro-reflecting surface 201 of the front optical system comprises a plurality of surfaces, for example, the telescopic eyepiece consists of four lenses, which then comprises 8 reflecting surfaces. The reflection matrix of the retro-reflecting surface 201 of the front optical system can be expressed as:
the lambda/4 wave plate 202 is a 0 deg. lambda/4 wave plate or a 90 deg. lambda/4 wave plate, i.e. the fast axis direction of the lambda/4 wave plate is required to be parallel to or perpendicular to the paper (specifically: the fast axis direction corresponding to the 0 deg. lambda/4 wave plate is parallel to the paper, and the fast axis direction corresponding to the 90 deg. lambda/4 wave plate is perpendicular to the paper); (ii) a When the fast axis direction is perpendicular to the paper, the jones transmission matrix can be expressed as:
the polarization beam splitter 203 is realized by plating a polarization beam splitting film on plate glass, the extinction ratio can reach more than 800:1, and the ideal reflection and transmission matrixes of the polarization beam splitter 203 are respectively as follows:
the energy beam splitter 204 is realized by plating an energy beam splitting film on a flat glass, the beam splitting ratio is determined by the plating film, and the beam splitting ratio determines the energy ratio of signal tracking capture and signal communication receiving in practical application.
And the signal communication receiving channel 205 is composed of a receiving lens and a receiving optical fiber assembly, the channel receives the light beam of the opposite laser communication terminal and couples the light beam into the optical fiber, and the optical fiber transmits the light signal into a demodulator demodulation signal.
The signal tracking and capturing channel 206 is composed of a receiving lens and a capturing detector, and the capturing detector may be a detector such as a CMOS, a CCD, or a four-quadrant photoelectric device for detecting the position information of the light spot. The channel receives the light beam facing the laser communication terminal and images the light beam on the capturing detector, and the capturing detector acquires the position information of the light spot and transmits the position information to the capturing and tracking processing system of the laser communication terminal.
The signal light emitting branch 207 is composed of a collimating lens and a transmitting laser component, and emits linearly polarized signal light with a polarization state S, and a transmission matrix of the signal light is:
the laser communication terminal structural frame 208 is a structural frame processed by titanium alloy, aluminum-based silicon carbide and other materials, and the surface of the structural frame is subjected to black anodization treatment, but the absorptivity of the black anodization surface at near-infrared communication bands such as 1550nm is not high and is generally lower than 80%.
The magneto-optical rotator 209 consists of a magnetic field generating device and a magneto-optical medium, the magneto-optical rotator can deflect the polarization angle of linearly polarized light, and the deflection angle β is 45 degrees:
β＝VBL＝45°
where V is the Verdet constant of the magneto-optical medium material, B is the magnetic flux, and L is the length of the magneto-optical medium. The angle of deflection is ensured to be 45 ° by the cooperation of the three parameters. The physical properties of the magneto-optical rotator are such that the changes in the direction of rotation of the light from left to right and from right to left are opposite, and therefore their transmission matrices are different, respectively:
as shown in FIGS. 5 and 6, the optical trap 201 comprises a reflector 301, a reflecting cavity 302 with a conical section is arranged on the reflector, the taper of the reflecting cavity 302 is 2 α, wherein, 8 degrees is more than α degrees and less than or equal to 16.36 degrees, the absorption rate epsilon of the reflector 301 to incident light each time is more than 95 percent, the reflecting cavity 302 has two forms, 1 is an integral conical cavity of the reflecting cavity 302, 2 is composed of two crossed inclined planes 303 with the same inclination angle, the inclination angle of the inclined plane 303 is α, the form 1 is more in line with the requirements of optical devices, and the form 2 is more convenient to process and manufacture.
The light trap absorbs part of the light energy when the light enters each time, and after multiple reflections, the light energy is absorbed multiple times in the reflection cavity 302 of the light trap, and finally the emergent light energy is far smaller than the incident light energy. (in the figure, the reflector 301 is formed by two wedge-shaped members 304, and a reflective cavity 302 is formed by splicing the two wedge-shaped members 304, as shown in fig. 6, or a reflective cavity 302 can be directly machined on one reflector 301, as shown in fig. 5.
There are two implementations of the reflector:
first, the reflector 301 is made of a metallic aluminum material, the surface of the reflective cavity 302 is polished to a mirror surface (roughness rms should be less than 3nm), an absorption film (not shown) is plated on the surface of the reflective cavity 302 for the laser wavelength, and the absorption rate of the absorption film at the working wavelength is greater than 90%. When laser is incident on the surface of the reflection cavity, part of laser energy is absorbed by the absorption film layer, and the absorptivity epsilon of the absorption film layer at single wavelength can reach more than 95%. For example, the reflector is made of polished aluminum material, and the absorption film layer with the inner surface of the reflective cavity plated with chrome and a medium antireflection film has an absorption rate as shown in fig. 7.
Secondly, the reflector 301 is made of coloured absorbing glass having an internal transmission per millimetre at the operating wavelength of less than 0.01%. The surface of the reflecting cavity 302 is polished to be a mirror surface (the roughness root mean square value should be less than 3 nm); the surface of the reflection cavity 302 is plated with a medium antireflection film aiming at the working wavelength, the antireflection film has the function of reducing reflection on the surface of a reflection surface, so that more light enters the colored absorption glass and is absorbed by the colored absorption glass, and the transmittance of the antireflection film at the working wavelength is more than 99.5%. For example, for laser with a wavelength of 1550nm, the reflector is made of schottky KG5 colored absorption glass, the surface of the KG5 colored absorption glass reflector is coated with an antireflection film, the reflectivity of the surface of the reflector in the wavelength of 1550nm is less than 0.5%, the rest 99.5% of energy enters the KG5 glass, the internal transmittance of the 1550nm laser in the KG5 glass is only 4.25e-5/mm, and almost all light energy entering the glass is absorbed.
The two solutions of the reflector have advantages, the first solution adopts the metallic aluminum material with strong machinability; the second solution has higher absorptivity and stronger stray light inhibition capability.
The light beam is reflected in the reflective cavity 302 for multiple times, and the incident angles of the 1 st, 2 nd, 3 rd, … … th and n th times are respectively:
A1＝90°-α (1)
A2＝180°-(90°-A1)-2α-90°＝90°-3α (2)
A3＝180°-(90°-A2)-2α-90°＝90°-5α (3)
……
An＝180°-(90°-An-1)-2α-90°＝90°-(2n-1)α (4)
wherein, when An>At 0, i.e. n<(45/α +0.5) the beam propagates into the reflective cavity 302 of the optical trap when An<At 0, i.e. n>(45/α +0.5), the beam begins to propagate out of the reflective cavity 302 of the optical trap.
When 90 degrees + AnWhen the reflection frequency is less than or equal to 2 α, namely (2n +1) α is more than or equal to 180 degrees, the reflected light beam does not intersect with the opposite reflection surface any more, and the light beam is emergent from the light trap, so that the maximum reflection frequency can be calculated as follows:
nmax＝roundup(90/α-0.5) (5)
where roundup () is a ceiling function.
The emergent angle is:
γ＝180°-2nmaxα (6)
the wedge angle α of the optical trap should be designed to satisfy 1, as many reflection times as possible to absorb more light energy, generally more than 6 reflection times, 2, the angle of the emergent ray deviates from the receiving field of view theta of the receiving optical path, 3, to satisfy a certain opening size, α cannot be too small, which would cause the length of the optical trap to be too long, generally α should be more than 8 deg., therefore, the limiting condition for obtaining α is:
the receive field of view of the receive optical path is typically within 3 ° and the design constraints imposed by the achievable wedge angle α of the above equation are:
8°＜α≤16.36° (8)
defining the stray light suppression ratio of the optical trap as the ratio of the light energy of the emergent optical trap to the light energy of the incident optical trap, and then the stray light suppression ratio of the optical trap is as follows:
based on the introduction of the above optical path and components of the optical path, the operation principle of the optical path will now be described:
1. emission light path implementation process and principle of the invention
Signal emitting laserThe S-shaped linear polarized light is emitted by the device 207, firstly reflected by the polarization beam splitter 203, then converted into-45-degree linear polarized light by rotating the polarization state through the magneto-optical rotator 209, converted into left-handed circular polarized light by the polarization state through the lambda/4 wave plate 202, and finally emitted through the telescopic system. The emitted light can also be made to be right-handed circularly polarized by changing the direction of the fast axis of the lambda/4 plate to be perpendicular to the cross section. The light path laser emits S light (vertical) and finally emits light ETIs left-handed circularly polarized light. The calculation proves that the process is as follows:
2. the receiving light path of the invention is realized as follows:
system receiving light ERThe left-handed circularly polarized light enters a lambda/4 wave plate 202 after passing through a telescopic system, the polarization state of the left-handed circularly polarized light is changed into 45-degree linearly polarized light, the polarization state of the left-handed circularly polarized light is changed into P light through a magneto-optical rotator 209, the P light passes through a polarization beam splitting plate 203 and is split through an energy beam splitter 204, wherein 90% of the energy reaches a signal communication receiving channel 205 for signal demodulation, and 10% of the energy reaches a signal tracking and capturing channel 206 for capturing and tracking of the signal light. Right-handed circularly polarized light can also be received by changing the fast axis direction of the a/4 plate 202 perpendicular to the cross-section. System receiving light ERLeft-handed circularly polarized light to signal communication receiving channel EFThe polarization state of the light is P light, and the calculation proves that the process is as follows:
3. the invention relates to a method and a principle for inhibiting two stray light paths of a light path
A. For the primary backscatter/reflection stray light, as shown in fig. 8, the present optical path structure cooperates with the λ/4 plate 202 through the magneto-optical rotator 209 so that the stray light for the primary backscatter/reflection is finally changed into S light. The process method comprises the following steps: the emitted left-handed (right-handed) circularly polarized light is changed into right-handed (left-handed) circularly polarized light after being subjected to one-time back scattering/reflection, is changed into 45-degree linearly polarized light after passing through a lambda/4 wave plate 202, and is subjected to magnetic rotationThe light becomes S light, and is finally reflected back to the signal light emission branch 207 through the polarization beam splitter. The S-ray transmittance of the polarization splitter 203 is very low, so that the polarization splitter has a very high isolation effect (generally better than 30dB), and can greatly reduce the first backward stray light received by the receiving optical components such as the signal communication receiving channel 205, the signal tracking capturing channel 206, and the like, thereby improving the receiving and transmitting isolation. Backward stray light EZIs S light, the polarization states are demonstrated as follows:
B. for a backscattering path generated by the emitted light after passing through the polarization beam splitter 203 and striking on the mechanical wall, as shown in fig. 9, a light ray tracing diagram is shown after the light enters the light trap, the light rays strike the light trap for multiple times, more than 90% of energy can be absorbed when the light strikes the light trap for each time, the light energy emitted after multiple absorption is greatly attenuated, and the angle between the emitted light and the incident light can be controlled so that the emitted light can not enter a receiving field any more, and the stray light of the part is greatly inhibited.
4. Implementation principle of networking communication
As shown in fig. 10, the receiving polarization state and the transmitting polarization state of the present invention are the same (both left-handed circularly polarized light and right-handed circularly polarized light), and any two laser communication terminals using the optical path can directly communicate without switching the polarization state, thereby facilitating the implementation of networking communication.
Claims (10)
1. A high-isolation common-frequency space laser communication light path for receiving and transmitting with the same polarization state comprises a laser communication terminal structure frame body, a back reflection surface of a front optical system, a lambda/4 wave plate, a polarization beam splitter, an energy beam splitter, a signal communication receiving channel, a signal tracking and capturing channel and a signal light emitting branch, wherein the back reflection surface is arranged in the laser communication terminal structure frame body;
the method is characterized in that:
a magneto-optical rotator and a light trap;
the magneto-optical rotator is arranged between the lambda/4 wave plate and the polarization beam splitting plate, wherein the lambda/4 wave plate is a 0-degree lambda/4 wave plate or a 90-degree lambda/4 wave plate, and the magneto-optical rotator can deflect the polarization angle of linearly polarized light, and the deflection angle β is 45 degrees;
the light trap is arranged on the laser communication terminal structure frame body and is opposite to the transmission light path of the polarization beam splitter.
2. The high-isolation transceiving same-polarization-state same-frequency space laser communication optical path according to claim 1, wherein the magneto-optical rotator comprises a magnetic field generating device and a magneto-optical medium, and the specific calculation formula of the deflection angle β is as follows:
β＝VBL＝45°
where V is the Verdet constant of the magneto-optical medium material, B is the magnetic flux, and L is the length of the magneto-optical medium.
3. The high-isolation transceiving same-polarization-state same-frequency space laser communication optical path according to claim 2, characterized in that: the light trap comprises a reflector, and a reflecting cavity with a conical section is formed in the reflector; the absorptivity epsilon of the reflector to incident light per time is more than 95 percent;
the taper of the reflecting cavity is 2 α, wherein, the angle is more than 8 degrees and less than or equal to α degrees and less than or equal to 16.36 degrees;
the stray light suppression ratio of the reflector is as follows:
nmaxis the maximum number of reflections of light by the reflective cavity.
4. The high-isolation transceiving same-polarization-state same-frequency space laser communication optical path according to claim 3, characterized in that: the reflecting cavity is a conical cavity.
5. The high-isolation co-frequency space laser communication optical path for transceiving with the same polarization state according to claim 3, wherein the reflection cavity is formed by two crossed inclined planes with the same inclination angle, and the inclination angle of the inclined planes is α.
6. The high-isolation co-frequency space laser communication optical path for transceiving with the same polarization state according to claim 3, 4 or 5, wherein: the maximum reflection number n of the reflection cavity to the lightmaxThe specific calculation formula of (A) is as follows: n ismaxRoundup (90/α -0.5), where roundup () is a ceiling function.
7. The high-isolation co-frequency space laser communication optical path for transceiving with the same polarization state according to claim 3, 4 or 5, wherein: the reflector is made of a metal aluminum material, the surface of a reflecting cavity of the reflector is polished into a mirror surface, and the root mean square value of the roughness of the mirror surface is less than 3 nm; the surface of the reflecting cavity is plated with an absorbing film layer which is a chromium and medium antireflection film.
8. The high-isolation co-frequency space laser communication optical path for transceiving with the same polarization state according to claim 3, 4 or 5, wherein: the reflector is made of colored absorption glass, and the transmittance of the colored absorption glass in each millimeter of the working wavelength is less than 0.01 percent; the surface of a reflecting cavity of the reflector is polished into a mirror surface, and the roughness root mean square value of the mirror surface is less than 3 nm; the surface of the reflection cavity is plated with an antireflection film.
9. The high-isolation transceiving same-polarization-state same-frequency space laser communication optical path according to claim 1, characterized in that: the polarization beam splitter is realized by plating a polarization beam splitting film on plate glass, and the extinction ratio of the polarization beam splitter is more than 800: 1; the energy beam splitter is realized by plating an energy beam splitting film on the flat glass, and the beam splitting ratio is determined by the plated film;
the signal communication receiving channel consists of a receiving lens and a receiving optical fiber component; the signal tracking and capturing channel consists of a receiving lens and a capturing detector, and the capturing detector is a CMOS (complementary metal oxide semiconductor) or CCD (charge coupled device) or four-quadrant photoelectric device; the signal light emission branch is composed of a collimating lens and a transmitting laser component and emits linear polarized signal light with the polarization state S.
10. The high-isolation transceiving same-polarization-state same-frequency space laser communication optical path according to claim 1, characterized in that: the laser communication terminal structure frame body is processed by adopting a titanium alloy or aluminum-based silicon carbide material, the surface of the laser communication terminal structure frame body is subjected to black anodization treatment, and the absorptivity of the black anodization surface at a 1550nm near infrared communication waveband is not lower than 80%.
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