CN111371554A - Intrinsic stable coding device and method for automatically calibrating input polarization state - Google Patents
Intrinsic stable coding device and method for automatically calibrating input polarization state Download PDFInfo
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- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
- H04L9/0852—Quantum cryptography
- H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding
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- G02B27/286—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another
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Abstract
The coding device and the coding method for automatically calibrating the input polarization state provided by the invention realize the stabilization of the input coding device in a new mode, namely, a beam splitter is used for splitting a light beam output by the polarization beam splitter into two beams, wherein one beam is used for feedback. The input polarization state of the coding device is stable in a required state, and the coding device cannot form codes without the compensation, so that the coding device can reduce the error rate. The invention ensures that the input polarization state of the encoder is stable and can be automatically calibrated, can improve the universality and the stability of the encoder, and solves the limitation existing in the prior technical method.
Description
Technical Field
The present application relates to the field of quantum communication, and in particular, to an encoding apparatus and method for automatically calibrating intrinsic stability of input polarization state.
Background
Quantum Key Distribution (QKD) systems are a new generation of Key Distribution schemes whose security is guaranteed by physical principles rather than algorithmic strength, which is unconditionally secure in theory. In recent years, quantum cryptography has made great progress both in theoretical and experimental research. Over thirty years of continuous development, QKD systems have emerged as a commercial product.
The encoding scheme commonly employed in QKD systems is either phase encoding or polarization encoding. Polarization encoded QKD is an advantageous choice for free space (including ground-to-ground and satellite-to-ground) secure communications and is not affected by phase drift common in interferometers in phase encoded systems, and is suitable for implementing decoy state protocols that are considered ideal single photon sources, ensuring unconditional security of QKD. Polarization encoding currently implemented schemes are the four-state protocol, the six-state protocol and the measurement-independent QKD scheme, all of which require polarization encoders, and therefore a stable and reliable polarization encoder is necessary, and most existing encoders change the polarization state of a photon by decomposing the photon into two components with polarization states orthogonal to each other and then modulating the phase difference between the two orthogonal modes, which requires that the two orthogonal mode components have the same intensity. At present, the aim is achieved by mainly utilizing 45-degree alignment of a slow axis of a polarization-maintaining fiber and a main axis of a phase modulator (or a polarization beam splitter) in experiments, but the method cannot be kept stable for a long time, and due to the technical limitation of a polarization-maintaining device, the highest extinction ratio of the polarization-maintaining fiber used for a tail fiber of an optical fiber circulator (or a coupler) incident to the phase modulator (or the polarization beam splitter) can only reach about 20 dB. In practical experiments, the polarization state of the optical fiber can be changed greatly even if the optical fiber is slightly vibrated, and the input polarization state of the encoder can be kept stable after the device is used.
Disclosure of Invention
The present invention provides an inherently stable encoding device and method for automatically calibrating input polarization state, which uses a beam splitter to divide the light beam output by the polarization beam splitter into two beams, wherein one beam is used for feedback, and the input polarization state of the encoding device is stabilized in a required state, thereby realizing 45 ° alignment of the main shaft, and further reducing the error rate.
In order to solve the technical problems, the technical scheme of the invention is as follows:
the present invention firstly provides an intrinsic stable encoding device for automatically calibrating input polarization state, comprising: the device comprises an electric control polarization controller, an optical circulator, a polarization beam splitter, a first beam splitter, a second beam splitter, a phase modulator, a first Faraday rotator mirror, a second Faraday rotator mirror, a third Faraday rotator mirror and a deviation feedback controller;
the input end of the electric control polarization controller receives light output by the laser, the electric control polarization controller is used for changing the polarization state of the light on the optical fiber channel, and the output end of the electric control polarization controller is connected with the optical circulator;
the light circulator comprises a first port, a second port and a third port, wherein the first port is used for receiving light output by the electric control polarization controller, the second port is connected with the polarization beam splitter, and the third port is used as an output end of the intrinsic stable coding device for automatically calibrating and inputting the polarization state;
the polarization beam splitter comprises a first port, a second port, a third port and a fourth port, the first port of the polarization beam splitter receives light output by the second port of the light circulator, and the light is divided into two horizontal beams and two vertical beams according to the polarization state and then is output from the second port and the third port of the polarization beam splitter respectively; the second port of the polarization beam splitter is connected with the input end of the first beam splitter; the third port of the polarization beam splitter is connected with the input end of the second beam splitter; the fourth port of the polarization beam splitter is connected with a first Faraday rotator mirror, and the first Faraday rotator mirror is used for rotating the polarization state by 90 degrees and reflecting the light beam;
the first beam splitter comprises two output ends, one output end of the first beam splitter is connected with a second Faraday rotator mirror, and the second Faraday rotator mirror is used for rotating the polarization state by 90 degrees and reflecting the light beam;
the second beam splitter comprises two output ends, one output end of the second beam splitter is connected with one end of the phase modulator, the other end of the phase modulator is connected with a third normal-pulling first rotating mirror, and the third normal-pulling first rotating mirror is used for rotating the polarization state by 90 degrees and reflecting the light beam; the phase modulator is used for applying different phases to different light beams passing through the two times;
and the other output end of the first beam splitter and the other output end of the second beam splitter are both connected to a deviation feedback controller, and the deviation feedback controller is used for calculating a control signal required by the electric control polarization controller and transmitting the control signal to the electric control polarization controller, so that the polarization state of light output by the electric control polarization controller is within a preset range.
Preferably, the deviation feedback controller comprises a balanced light detector, an analog-to-digital conversion module and a field programmable gate array module;
the other output end of the first beam splitter and the other output end of the second beam splitter are both connected to the input end of the balanced light detector; the balance light detector is used for performing photoelectric conversion on light intensity received from the first beam splitter and the second beam splitter as feedback quantity and outputting an analog signal to the analog-to-digital conversion module;
the analog-to-digital conversion module is used for converting the analog signal output by the balanced light detector into a digital signal and outputting the digital signal to the field programmable gate array module;
the field programmable gate array module is used for calculating a control signal required by the electric control polarization controller by using a PID algorithm according to the detected digital signal corresponding to the polarization state and transmitting the control signal to the electric control polarization controller, so that the polarization state of light output by the electric control polarization controller is within a preset range.
Preferably, the electrically-controlled polarization controller keeps the polarization state of the control light at 45 °
Preferably, the first beam splitter and the second beam splitter are 50:50 beam splitters for splitting light into two beams of equal light intensity.
Preferably, an optical isolator is arranged between the output end of the laser and the input end of the electrically-controlled polarization controller, and the optical isolator only allows one-way light to pass through.
Preferably, the analog-to-digital conversion module comprises an attenuation circuit and an operational amplifier, wherein the attenuation circuit controls the signal within the range borne by the analog-to-digital conversion module, and then the operational amplifier obtains the direct current component of the signal.
Preferably, the model of the operational amplifier is AD 8065.
The invention also provides an intrinsic stable coding method for automatically calibrating the input polarization state, which comprises the following steps:
s1: light output by the laser enters an electric control polarization controller, and the electric control polarization controller is used for changing the polarization state of the light on the optical fiber channel and then is emitted into a first port of the optical circulator;
s2: the light injected into the first port of the optical circulator is emitted out of the second port of the optical circulator;
s3: the light emitted from the second port of the optical circulator enters the polarization beam splitter through the first port of the polarization beam splitter, and the polarization beam splitter divides the light into two horizontal beams and two vertical beams according to the polarization state and then outputs the two beams from the second port and the third port of the polarization beam splitter respectively;
s4: a second port of the polarization beam splitter outputs horizontal light to the first beam splitter, and light output by one output end of the first beam splitter rotates the polarization state by 90 degrees through the second Faraday rotation mirror and is reflected back to a light beam; the light emitted by the fourth port is emitted by the fourth port after being emitted by the second port of the polarization beam splitter, and the light emitted by the fourth port rotates the polarization state by 90 degrees through the first Faraday rotation mirror and is reflected back to the light beam; the light beam is emitted from the third port after being emitted from the fourth port of the polarization beam splitter, is output from one output end of the second beam splitter after passing through the second beam splitter, is rotated by 90 degrees in polarization state by pulling the third rotating mirror through the phase modulator, and is reflected back to the light beam; the phase modulator is used for applying different phases to different light beams passing through twice, then enters the polarization beam splitter through a third port of the polarization beam splitter, and is emitted out of a first port of the polarization beam splitter;
the third port of the polarization beam splitter outputs vertical light to the second beam splitter, the vertical light is output from one output end of the second beam splitter after passing through the second beam splitter, the polarization state of the vertical light is rotated by 90 degrees by pulling the first rotating mirror through the third method after passing through the phase modulator, the vertical light is reflected back to the light beam, and the phase modulator is used for applying different phases to different light beams passing through twice; the light emitted by the fourth port is emitted by the fourth port after being emitted by the third port of the polarization beam splitter, and the light emitted by the fourth port is rotated by 90 degrees in polarization state through the first Faraday rotation mirror and is reflected back to a light beam; light is emitted from the fourth port and then is output to the first beam splitter from the second port, and light output from one output end of the first beam splitter is rotated by 90 degrees in polarization state through the second Faraday rotator mirror and is reflected back to a light beam; then enters the polarization beam splitter through the second port of the polarization beam splitter and is emitted out of the first port of the polarization beam splitter;
s5: two paths of light emitted from the first port of the polarization beam splitter are superposed and then emitted into the second port of the optical circulator and output from the third port of the optical circulator;
s6: and the other output end of the first beam splitter and the other output end of the second beam splitter are both connected to a deviation feedback controller, and the deviation feedback controller calculates a control signal required by the electric control polarization controller and transmits the control signal to the electric control polarization controller, so that the polarization state of light output by the electric control polarization controller is within a preset range.
Preferably, step S6 specifically includes the following steps:
s601: the other output end of the first beam splitter and the other output end of the second beam splitter are both connected to the input end of the balanced light detector; the balance light detector performs photoelectric conversion by taking the light intensity received from the first beam splitter and the second beam splitter as a feedback quantity and outputs an analog signal to the analog-to-digital conversion module;
s602: the analog-to-digital conversion module converts an analog signal output by the balanced light detector into a digital signal and outputs the digital signal to the field programmable gate array module;
s603: the field programmable gate array module calculates the deviation between the actual polarization value and the preset target polarization value according to the digital signal corresponding to the detected polarization state, calculates a control signal required by the electric control polarization controller by using a PID algorithm and transmits the control signal to the electric control polarization controller, so that the polarization state of the light output by the electric control polarization controller is within a preset range.
Preferably, the method further comprises: the steps S601-S603 are repeated continuously to ensure that the input polarization state of the encoding device is always stabilized at 45 °.
Preferably, in step S1, the light output from the laser passes through the optical isolator before entering the electrically controlled polarization controller.
Preferably, the first beam splitter and the second beam splitter split the light into two beams of equal light intensity.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that: the coding device and the coding method for automatically calibrating the input polarization state provided by the invention realize the stabilization of the input coding device in a new mode, namely, a beam splitter is used for splitting a light beam output by the polarization beam splitter into two beams, wherein one beam is used for feedback. The device provided by the invention can reduce the error rate because the input polarization state of the coding device is stable in a required state, and the coding can not be realized without the compensation. The compensation device can be stabilized for a period of time to ensure that the receiving and transmitting polarization states are always similar, so that the reduction of the error rate in the period of time can be ensured to be stable. For the control time, the control time of the automatic calibration control method provided by the invention is far shorter than the polarization change time, and if the control time is longer than the polarization change time, the system is always in the control stage, and the whole system cannot realize successful coding.
Drawings
FIG. 1 is a schematic diagram of an intrinsically stable encoding apparatus for automatically calibrating an input polarization state according to embodiment 1.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent;
for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product;
it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
Example 1
As shown in fig. 1, the present embodiment provides an intrinsically stable encoding apparatus for automatically calibrating an input polarization state, comprising: an electronic control polarization controller EPC, an optical circulator CIR, a polarization beam splitter PBS, a first beam splitter BS-1, a second beam splitter BS-2, a phase modulator PM, a first Faraday rotation mirror FM-1, a second Faraday rotation mirror FM-2, a third Faraday rotation mirror FM-3 and a deviation feedback controller;
the input end of the electronic control polarization controller EPC receives light output by the laser LD, the electronic control polarization controller EPC is used for changing the polarization state of the light on the optical fiber channel, and the output end of the electronic control polarization controller EPC is connected with the optical circulator CIR;
the optical circulator CIR comprises a first port, a second port and a third port, the first port is used for receiving light output by the electronic control polarization controller EPC, the second port is connected with the polarization beam splitter PBS, and the third port is used as an output end of the intrinsic stable coding device for automatically calibrating the input polarization state;
the polarization beam splitter PBS comprises a first port, a second port, a third port and a fourth port, wherein the first port of the polarization beam splitter PBS receives light output by the second port of the light receiving circulator CIR, and the light is divided into two horizontal beams and two vertical beams according to the polarization state and then is respectively output from the second port and the third port of the polarization beam splitter PBS; the second port of the PBS is connected with the input end of the first beam splitter BS-1; the third port of the PBS is connected with the input end of the second beam splitter BS-2; the fourth port of the PBS is connected with a first Faraday rotator FM-1, and the first Faraday rotator FM-1 is used for rotating the polarization state by 90 degrees and reflecting the light beam;
the first beam splitter BS-1 comprises two output ends, one output end of the first beam splitter BS-1 is connected with a second Faraday rotation mirror FM-2, and the second Faraday rotation mirror FM-2 is used for rotating the polarization state by 90 degrees and reflecting light beams back;
the second beam splitter BS-2 comprises two output ends, one output end of the second beam splitter BS-2 is connected with one end of a phase modulator PM, the other end of the phase modulator PM is connected with a third Faraday rotation mirror FM-3, and the third Faraday rotation mirror FM-3 is used for rotating the polarization state by 90 degrees and reflecting the light beam; the phase modulator PM is used to apply different phases to the two passes of different light beams;
and the other output end of the first beam splitter BS-1 and the other output end of the second beam splitter BS-2 are both connected to a deviation feedback controller, and the deviation feedback controller is used for calculating a control signal required by the electronically controlled polarization controller EPC and transmitting the control signal to the electronically controlled polarization controller EPC, so that the polarization state of light output by the electronically controlled polarization controller EPC is within a preset range.
More specifically, the deviation feedback controller comprises a balanced light detector BPD, an analog-to-digital conversion module A/D and a field programmable gate array module FPGA;
the other output end of the first beam splitter BS-1 and the other output end of the second beam splitter BS-2 are both connected to the input end of the balanced light detector BPD; the balance light detector BPD is used for performing photoelectric conversion on light intensity received from the first beam splitter BS-1 and the second beam splitter BS-2 as feedback quantity and outputting an analog signal to the analog-to-digital conversion module A/D;
the analog-to-digital conversion module A/D is used for converting analog signals output by the balanced light detector BPD into digital signals and outputting the digital signals to the FPGA;
the FPGA is used for calculating a control signal required by the EPC according to the detected digital signal corresponding to the polarization state by using a PID algorithm and transmitting the control signal to the EPC, so that the polarization state of light output by the EPC is within a preset range.
More specifically, the electrically controlled polarization controller EPC keeps controlling the polarization state of light to be maintained at 45 °
More specifically, the first beam splitter BS-1 and the second beam splitter BS-2 are 50:50 beam splitters for splitting light into two beams of equal light intensity.
More specifically, an optical isolator ISO is also provided between the output of the laser LD and the input of the electronically controlled polarization controller EPC, which optical isolator ISO allows only one-way light to pass.
More specifically, the analog-to-digital conversion module a/D includes an attenuation circuit that controls the signal within a range that the analog-to-digital conversion module a/D is subjected to, and an operational amplifier that then takes a direct current component of the signal.
More specifically, the model of the operational amplifier adopts AD 8065.
Example 2
The present embodiment provides an encoding method for automatically calibrating intrinsic stability of input polarization state, which includes the following steps:
s1: light output by the laser LD enters an electronic control polarization controller EPC, and the electronic control polarization controller EPC is used for changing the polarization state of the light on the optical fiber channel and then enters a first port of the optical circulator CIR;
s2: light injected into the first port of the optical circulator CIR is emitted out of the second port of the optical circulator CIR;
s3: light emitted from the second port of the CIR enters the PBS through the first port of the PBS, and the PBS divides the light into two horizontal beams and two vertical beams according to the polarization state and then outputs the two beams from the second port and the third port of the PBS respectively;
s4: a second port of the PBS outputs horizontal light to the first beam splitter BS-1, and light output by one output end of the first beam splitter BS-1 is rotated by 90 degrees in polarization state through the second Faraday rotation mirror FM-2 and is reflected back to a light beam; the light emitted by the fourth port is emitted by the fourth port after being emitted by the second port of the PBS, and the light emitted by the fourth port is rotated by 90 degrees in polarization state through the first Faraday rotation mirror FM-1 and is reflected back to a light beam; the light beam is emitted from a third port after being emitted from a fourth port of the PBS, is output from an output end of the BS-2 after passing through the BS-2, passes through the PM of the phase modulator, is rotated by 90 degrees in polarization state by pulling a FM-3 rotating mirror through a third method, and is reflected back to the light beam; the phase modulator PM is used for applying different phases to different light beams passing through twice, then enters the polarization beam splitter PBS through a third port of the polarization beam splitter PBS, and is emitted out of a first port of the polarization beam splitter PBS;
a third port of the polarization beam splitter PBS outputs vertical light to a second beam splitter BS-2, the vertical light is output from one output end of the second beam splitter BS-2 after passing through the second beam splitter BS-2, the vertical light passes through a phase modulator PM, the third rotating mirror FM-3 is pulled by a third method to rotate the polarization state by 90 degrees and reflect the polarization state back to a light beam, and the phase modulator PM is used for applying different phases to different light beams passing through twice; the light emitted by the fourth port is emitted by the fourth port after being emitted by the third port of the polarizing beam splitter PBS, and the light emitted by the fourth port is rotated by 90 degrees in polarization state through the first Faraday rotation mirror FM-1 and is reflected back to a light beam; light is emitted from the fourth port and then is output to the first beam splitter BS-1 from the second port, and light output from one output end of the first beam splitter BS-1 is rotated by 90 degrees in polarization state through the second Faraday rotation mirror FM-2 and is reflected back to a light beam; then enters the PBS through the second port of the PBS and is emitted out of the first port of the PBS;
s5: two paths of light emitted from the first port of the PBS are superposed and then emitted into the second port of the CIR and output from the third port of the CIR;
s6: and the other output end of the first beam splitter BS-1 and the other output end of the second beam splitter BS-2 are both connected to a deviation feedback controller, and the deviation feedback controller calculates a control signal required by the electronically controlled polarization controller EPC and transmits the control signal to the electronically controlled polarization controller EPC, so that the polarization state of light output by the electronically controlled polarization controller EPC is within a preset range.
More specifically, step S6 specifically includes the following steps:
s601: the other output end of the first beam splitter BS-1 and the other output end of the second beam splitter BS-2 are both connected to the input end of the balanced light detector BPD; the balance light detector BPD takes the light intensity received from the first beam splitter BS-1 and the second beam splitter BS-2 as feedback quantity to carry out photoelectric conversion and output an analog signal to the analog-to-digital conversion module A/D;
s602: the analog-to-digital conversion module A/D converts an analog signal output by the balance light detector BPD into a digital signal and outputs the digital signal to the FPGA;
s603: and the FPGA calculates the deviation between the actual polarization value and a preset target polarization value according to the digital signal corresponding to the detected polarization state, calculates a control signal required by the EPC by using a PID algorithm and transmits the control signal to the EPC, so that the polarization state of the light output by the EPC is within a preset range.
In step S603, a preset target value is first stored in a target variable, then a difference between the target value and a target value is obtained through an acquisition amount of an analog-to-digital conversion module a/D, and the difference is stored in a distance variable, the electronically controlled polarization controller EPC is controlled to change db by four voltage amounts of the control amount, that is, db is db-distance/D, D is a parameter, then the acquisition amount of the analog-to-digital conversion module a/D is analyzed, a quadratic difference 2 is calculated, and if the requirement of an error is met, the next step is performed.
The steps S601-S603 are repeated continuously to ensure that the input polarization state of the encoding device is always stabilized at 45 °.
If the polarization state on the optical fiber channel is under various disturbance conditions such as burst, rapid and the like, the input polarization state of the polarization coding device is unstable, so that the coding device is unstable, and the error rate is increased.
More specifically, in step S1, the light output from the laser LD first passes through the optical isolator ISO and then enters the electrically controlled polarization controller EPC.
More specifically, the first beam splitter BS-1 and the second beam splitter BS-2 split the light into two beams of equal light intensity.
The coding device and the coding method for automatically calibrating the input polarization state provided by the invention realize the stabilization of the input coding device in a new mode, namely, a beam splitter is used for splitting a light beam output by a PBS into two beams, wherein one beam is used for feedback. The device provided by the invention can reduce the error rate because the input polarization state of the coding device is stable in a required state, and the coding can not be realized without the compensation. The compensation device can be stabilized for a period of time to ensure that the receiving and transmitting polarization states are always similar, so that the reduction of the error rate in the period of time can be ensured to be stable. For the control time, the control time of the automatic calibration control method provided by the invention is far shorter than the polarization change time, and if the control time is longer than the polarization change time, the system is always in the control stage, and the whole system cannot realize successful coding.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. An encoding apparatus for automatically calibrating intrinsic stability of an input polarization state, comprising: the device comprises an electric control polarization controller, an optical circulator, a polarization beam splitter, a first beam splitter, a second beam splitter, a phase modulator, a first Faraday rotator mirror, a second Faraday rotator mirror, a third Faraday rotator mirror and a deviation feedback controller;
the input end of the electric control polarization controller receives light output by the laser, the electric control polarization controller is used for changing the polarization state of the light on the optical fiber channel, and the output end of the electric control polarization controller is connected with the optical circulator;
the light circulator comprises a first port, a second port and a third port, wherein the first port is used for receiving light output by the electric control polarization controller, the second port is connected with the polarization beam splitter, and the third port is used as an output end of the intrinsic stable coding device for automatically calibrating and inputting the polarization state;
the polarization beam splitter comprises a first port, a second port, a third port and a fourth port, the first port of the polarization beam splitter receives light output by the second port of the light circulator, and the light is divided into two horizontal beams and two vertical beams according to the polarization state and then is output from the second port and the third port of the polarization beam splitter respectively; the second port of the polarization beam splitter is connected with the input end of the first beam splitter; the third port of the polarization beam splitter is connected with the input end of the second beam splitter; the fourth port of the polarization beam splitter is connected with a first Faraday rotator mirror, and the first Faraday rotator mirror is used for rotating the polarization state by 90 degrees and reflecting the light beam;
the first beam splitter comprises two output ends, one output end of the first beam splitter is connected with a second Faraday rotator mirror, and the second Faraday rotator mirror is used for rotating the polarization state by 90 degrees and reflecting the light beam;
the second beam splitter comprises two output ends, one output end of the second beam splitter is connected with one end of the phase modulator, the other end of the phase modulator is connected with a third normal-pulling first rotating mirror, and the third normal-pulling first rotating mirror is used for rotating the polarization state by 90 degrees and reflecting the light beam; the phase modulator is used for applying different phases to different light beams passing through the two times;
and the other output end of the first beam splitter and the other output end of the second beam splitter are both connected to a deviation feedback controller, and the deviation feedback controller is used for calculating a control signal required by the electric control polarization controller and transmitting the control signal to the electric control polarization controller, so that the polarization state of light output by the electric control polarization controller is within a preset range.
2. The apparatus of claim 1, wherein the bias feedback controller comprises a balanced photodetector, an analog-to-digital conversion module, and a field programmable gate array module;
the other output end of the first beam splitter and the other output end of the second beam splitter are both connected to the input end of the balanced light detector; the balance light detector is used for performing photoelectric conversion on light intensity received from the first beam splitter and the second beam splitter as feedback quantity and outputting an analog signal to the analog-to-digital conversion module;
the analog-to-digital conversion module is used for converting the analog signal output by the balanced light detector into a digital signal and outputting the digital signal to the field programmable gate array module;
the field programmable gate array module is used for calculating a control signal required by the electric control polarization controller by using a PID algorithm according to the detected digital signal corresponding to the polarization state and transmitting the control signal to the electric control polarization controller, so that the polarization state of light output by the electric control polarization controller is within a preset range.
3. The device of claim 2, wherein the electronically controlled polarization controller maintains the polarization of the control light at 45 °.
4. The apparatus of claim 2, wherein the first and second beam splitters are 50:50 beam splitters for splitting light into two beams of equal intensity.
5. The device of claim 1, wherein an optical isolator is disposed between the output of the laser and the input of the electronically controlled polarization controller, the optical isolator allowing only one-way light to pass through.
6. The apparatus of claim 1, wherein the ADC module comprises an attenuator circuit and an operational amplifier, the attenuator circuit controls the signal within a range of the ADC module, and the operational amplifier obtains the DC component of the signal.
7. The apparatus according to claim 4, wherein the operational amplifier is AD8065 in type.
8. An intrinsic stable encoding method for automatically calibrating input polarization state, comprising the steps of:
s1: light output by the laser enters an electric control polarization controller, and the electric control polarization controller is used for changing the polarization state of the light on the optical fiber channel and then is emitted into a first port of the optical circulator;
s2: the light injected into the first port of the optical circulator is emitted out of the second port of the optical circulator;
s3: the light emitted from the second port of the optical circulator enters the polarization beam splitter through the first port of the polarization beam splitter, and the polarization beam splitter divides the light into two horizontal beams and two vertical beams according to the polarization state and then outputs the two beams from the second port and the third port of the polarization beam splitter respectively;
s4: a second port of the polarization beam splitter outputs horizontal light to the first beam splitter, and light output by one output end of the first beam splitter rotates the polarization state by 90 degrees through the second Faraday rotation mirror and is reflected back to a light beam; the light emitted by the fourth port is emitted by the fourth port after being emitted by the second port of the polarization beam splitter, and the light emitted by the fourth port rotates the polarization state by 90 degrees through the first Faraday rotation mirror and is reflected back to the light beam; the light beam is emitted from the third port after being emitted from the fourth port of the polarization beam splitter, is output from one output end of the second beam splitter after passing through the second beam splitter, is rotated by 90 degrees in polarization state by pulling the third rotating mirror through the phase modulator, and is reflected back to the light beam; the phase modulator is used for applying different phases to different light beams passing through twice, then enters the polarization beam splitter through a third port of the polarization beam splitter, and is emitted out of a first port of the polarization beam splitter;
the third port of the polarization beam splitter outputs vertical light to the second beam splitter, the vertical light is output from one output end of the second beam splitter after passing through the second beam splitter, the polarization state of the vertical light is rotated by 90 degrees by pulling the first rotating mirror through the third method after passing through the phase modulator, the vertical light is reflected back to the light beam, and the phase modulator is used for applying different phases to different light beams passing through twice; the light emitted by the fourth port is emitted by the fourth port after being emitted by the third port of the polarization beam splitter, and the light emitted by the fourth port is rotated by 90 degrees in polarization state through the first Faraday rotation mirror and is reflected back to a light beam; light is emitted from the fourth port and then is output to the first beam splitter from the second port, and light output from one output end of the first beam splitter is rotated by 90 degrees in polarization state through the second Faraday rotator mirror and is reflected back to a light beam; then enters the polarization beam splitter through the second port of the polarization beam splitter and is emitted out of the first port of the polarization beam splitter;
s5: two paths of light emitted from the first port of the polarization beam splitter are superposed and then emitted into the second port of the optical circulator and output from the third port of the optical circulator;
s6: and the other output end of the first beam splitter and the other output end of the second beam splitter are both connected to a deviation feedback controller, and the deviation feedback controller calculates a control signal required by the electric control polarization controller and transmits the control signal to the electric control polarization controller, so that the polarization state of light output by the electric control polarization controller is within a preset range.
9. The method according to claim 8, wherein step S6 comprises the following steps:
s601: the other output end of the first beam splitter and the other output end of the second beam splitter are both connected to the input end of the balanced light detector; the balance light detector performs photoelectric conversion by taking the light intensity received from the first beam splitter and the second beam splitter as a feedback quantity and outputs an analog signal to the analog-to-digital conversion module;
s602: the analog-to-digital conversion module converts an analog signal output by the balanced light detector into a digital signal and outputs the digital signal to the field programmable gate array module;
s603: the field programmable gate array module calculates the deviation between the actual polarization value and the preset target polarization value according to the digital signal corresponding to the detected polarization state, calculates a control signal required by the electric control polarization controller by using a PID algorithm and transmits the control signal to the electric control polarization controller, so that the polarization state of the light output by the electric control polarization controller is within a preset range.
10. The method of claim 9, further comprising: the steps S601-S603 are repeated continuously to ensure that the input polarization state of the encoding device is always stabilized at 45 °.
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