CN112558332A - Automatic phase compensation device and use method thereof - Google Patents
Automatic phase compensation device and use method thereof Download PDFInfo
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- CN112558332A CN112558332A CN202011643234.XA CN202011643234A CN112558332A CN 112558332 A CN112558332 A CN 112558332A CN 202011643234 A CN202011643234 A CN 202011643234A CN 112558332 A CN112558332 A CN 112558332A
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0305—Constructional arrangements
- G02F1/0311—Structural association of optical elements, e.g. lenses, polarizers, phase plates, with the crystal
Abstract
The invention provides an automatic phase compensation device and a using method thereof, wherein the device comprises a first polarization analysis system, a first lambda/2 wave plate, a second lambda/2 wave plate, a first lambda/4 wave plate, a lithium niobate crystal, a second lambda/4 wave plate, a second polarization analysis system, a pressure control module, a phase difference calculation module and an optical system, wherein a lambda/4-lithium niobate crystal-lambda/4 combination is utilized to fix the fast axes of the first lambda/4 wave plate and the second lambda/4 wave plate at an angle of 45 degrees with the x axis, and any phase difference is compensated by adjusting the included angle between the fast axis and the x axis of the lithium niobate crystal, so that the device can be applied to various optical experiments and has higher adaptability; in addition, the transverse electro-optic effect of the lithium niobate crystal is utilized to compensate any phase difference through piezoelectric control, so that automation is realized, errors caused by artificial participation are reduced, and the precision is greatly improved.
Description
Technical Field
The invention relates to the technical field of polarization maintaining, in particular to an automatic phase compensation device and a using method thereof.
Background
In the field of quantum communication or optical fiber communication, the photon polarization state is adopted for information coding and communication, so the requirement on the photon polarization state is higher. Various optical polarization devices exist in an optical system, and when light passes through the devices, the polarization state of the light is changed due to phase difference, so that the experimental result is seriously influenced.
At present, phase compensation is realized by adopting three forms of a phase retarder, a birefringent crystal, a half-wave plate and a quarter-wave plate group:
1. when compensating for the phase using the phase retarder, it is necessary to determine the thickness of the single wafer according to the retardation amount required for a specific wavelength. After the thickness of the single wafer is determined, the optimal material needs to be selected for manufacturing, and the manufacturing process is strict. However, after complicated calculation and design, the phase difference that can be compensated by the phase retarder can only be obtained for a specific wavelength and cannot be used for other wavelengths, which makes the method have great limitation in practicality and also greatly affects the accuracy.
2. The method of using the birefringent crystal to split the light beam and then using the parallel beam splitter to couple the two polarized lights needs to change the thickness of the parallel beam splitter, and has the problems of low precision and poor practicability.
3. In the method for compensating the phase delay by using the optical phase difference generated by the half-wave plate and the quarter-wave plate set, firstly, the Jones vector modulated by the wave plate set is compared with the Jones vector corresponding to the polarization state of the emergent light wave, the angle required to be adjusted of each wave plate is calculated, and then, the angle adjustment is carried out on different wave plates. Although the method can make up for the defects of the two methods, the process of completing the compensation is very complicated and time-consuming, and meanwhile, different wave plates can be adjusted manually, so that the phase compensation precision is low.
Disclosure of Invention
In order to solve the defects and shortcomings of the prior art, the automatic phase compensation device and the use method thereof are provided, so that the problems of poor practicability and low precision of the phase compensation device can be solved.
The automatic phase compensation device comprises a first polarization analysis system, a first lambda/2 wave plate, a second lambda/2 wave plate, a first lambda/4 wave plate, a lithium niobate crystal, a second lambda/4 wave plate, a second polarization analysis system, a pressure control module, a phase difference calculation module and an optical system, wherein the first polarization analysis system and the first lambda/2 wave plate are sequentially arranged in the normal incidence direction of the optical system, the second lambda/2 wave plate, the first lambda/4 wave plate, the lithium niobate crystal, the second lambda/4 wave plate and the second polarization analysis system are sequentially arranged in the emergent beam direction of the optical system, the first polarization analysis system and the second polarization analysis system are connected with the information input end of the phase difference calculation module through wires, so that the phase information of input and output light is transmitted to the phase difference calculation module for calculation to obtain a phase offset theta The information output end of the phase difference calculation module is connected with the information input end of the voltage control module through a lead so as to convert the phase offset theta into a voltage signal, and the signal output ends 1 and 2 of the voltage control module are correspondingly connected with the electrode plates 1 and 2 of the lithium niobate crystal.
As a further improvement of the scheme, the included angle beta between the fast axis and the x axis of the first lambda/4 wave plate and the second lambda/4 wave plate is fixed to be 45 degrees.
The use method of the automatic phase compensation device is characterized in that:
the method comprises the following steps: adjusting the first lambda/2 wave plate and the second lambda/2 wave plate to enable the light transmission directions of the two wave plates to be consistent so as to calibrate line polarization;
step two: measuring the polarization states of input light and output light by using a first polarization analysis system and a second polarization analysis system to respectively obtain the phase theta of the input light1And output light phase θ2。
Step three: measuring the phase theta of the input light1And output light phase θ2And feeding back to the phase difference calculation module to obtain the phase shift amount theta of the output light relative to the input light.
Step four: the phase difference calculation module transmits the phase offset theta to the voltage control module, and the voltage control module generates a corresponding voltage signal according to the phase offset theta.
Step five: the voltage control module transmits the voltage signal to the electrode plates at two ends of the lithium niobate crystal to form transverse voltage, so that automatic adjustment of optical phase compensation is realized.
The invention has the beneficial effects that:
compared with the prior art, the automatic phase compensation device and the use method thereof provided by the invention utilize the combination of the lambda/4-lithium niobate crystal and the lambda/4, the fast axes and the x axis of the two lambda/4 wave plates in the combination are fixed to form an angle of 45 degrees, and any phase difference is compensated by adjusting the included angle between the fast axis and the x axis of the lithium niobate crystal, so that the device can be applied to various optical experiments and has higher adaptability; in addition, the transverse electro-optic effect of the lithium niobate crystal is utilized to compensate any phase difference through piezoelectric control, so that automation is realized, errors caused by artificial participation are reduced, and the precision is greatly improved.
Drawings
FIG. 1 is a schematic diagram of an automatic phase compensation device according to the present invention;
FIG. 2 is a schematic view of an included angle between a fast axis and an x axis of a wave plate and a lithium niobate crystal according to the present invention.
Wherein: the system comprises a 1-first polarization analysis system, a 2-first lambda/2 wave plate, a 3-second lambda/2 wave plate, a 4-first lambda/4 wave plate, a 5-lithium niobate crystal, a 6-second lambda/4 wave plate, a 7-second polarization analysis system, an 8-pressure control module, a 9-phase difference calculation module and a 10-optical system.
Detailed Description
The following detailed description of embodiments of the invention is provided in conjunction with the appended drawings:
with reference to fig. 1-2, the automatic phase compensation device provided by the present invention includes a first polarization analysis system 1, a first λ/2 wave plate 2, a second λ/2 wave plate 3, a first λ/4 wave plate 4, a lithium niobate crystal 5, a second λ/4 wave plate 6, a second polarization analysis system 7, a pressure control module 8, a phase difference calculation module 9, and an optical system 10, wherein the first polarization analysis system 1 and the first λ/2 wave plate 2 are sequentially disposed in a normal incidence direction of the optical system 10, the second λ/2 wave plate 3, the first λ/4 wave plate 4, the lithium niobate crystal 5, the second λ/4 wave plate 6, and the second polarization analysis system 7 are sequentially disposed in an emergent beam direction of the optical system 10, the first polarization analysis system 1 and the second polarization analysis system 7 are connected to an information input end of the phase difference calculation module 9 through a wire, the phase information of input and output light is transmitted to a phase difference calculation module 9 to be calculated to obtain a phase offset amount theta, an information output end of the phase difference calculation module 9 is connected with an information input end of a pressure control module 8 through a lead to convert the phase offset amount theta into a voltage signal, signal output ends 1 and 2 of the pressure control module 8 are correspondingly connected with electrode plates 1 and 2 of a lithium niobate crystal 5, and a first lambda/2 wave plate 2, a second lambda/2 wave plate 3, a first lambda/4 wave plate 4, the lithium niobate crystal 5 and a second lambda/4 wave plate 6 are matched together to realize automatic compensation of a phase device, wherein an included angle beta between a fast axis and an x axis of the first lambda/4 wave plate 4 and the second lambda/4 wave plate 6 is fixed to be 45 degrees.
The use method of the automatic phase compensation device is characterized in that:
the method comprises the following steps: the first lambda/2 wave plate 2 and the second lambda/2 wave plate 3 are adjusted to enable the light transmission directions of the two wave plates to be consistent so as to calibrate line polarization;
step two: measuring the polarization states of the input light and the output light by using the first polarization analysis system 1 and the second polarization analysis system 7 to respectively obtain the phase theta of the input light1And output light phase θ2。
Step three: measuring the phase theta of the input light1And output light phase θ2The phase difference is fed back to the phase difference calculation module 9, and the phase shift amount θ of the output light relative to the input light is obtained.
Step four: the phase difference calculation module 9 transmits the phase offset θ to the voltage control module 8, and the voltage control module 8 generates a corresponding voltage signal according to the phase offset θ.
Step five: the voltage control module 8 transmits the voltage signal to the electrode plates at two ends of the lithium niobate crystal 5 to form a transverse voltage, thereby realizing the automatic adjustment of optical phase compensation.
The invention provides an automatic phase compensation device and a using method thereof, and the principle is as follows: firstly, an optical system to be phase-compensated is used as a reference, and a rectangular coordinate system is established by taking the fast axis direction as an x-axis coordinate and the slow axis direction as a y-axis coordinate. The polarization direction of a light wave component propagating fast in an optical system is the fast axis, and the vertical direction thereof is the slow axis direction. Due to the fact that the propagation speeds of the fast axis and the slow axis in the optical system are different, the refractive indexes are different, components of incident light in two directions generate phase difference, and therefore the polarization state is changed. The wave plate can generate phase delay between two linearly polarized light which are perpendicular to each other, so that the polarization state of the light is changed. The wave plate is also used for distinguishing a fast axis from a slow axis, and light with a high relative propagation speed has a light vector direction which is the fast axis direction and a slow axis which is the direction perpendicular to the fast axis direction. Various devices that linearly convert the polarization state of light can be represented by a 2x2 matrix, called the jones matrix for polarizing devices.
Represented as jones matrices of 1/2 and 1/4 wave plates with fast and x axes respectively,
the rotation matrix is represented as
Then the jones matrix for a λ/4 plate at any angle can be expressed as:
wherein theta is the included angle between the fast axis of the lambda/4 wave plate and the x axis.
And a Jones matrix of the lambda/2 wave plate arranged at any angle can be obtained:
wherein delta is the included angle between the fast axis of the lambda/2 wave plate and the x axis.
When phase compensation is carried out, the lambda/4-lambda/2-lambda/4 wave plate set is arranged in front of and behind the optical path to be compensated and is perpendicular to the light beam. At the moment, the included angle between the fast axis of the lambda/4 wave plate and the x axis is adjusted to be 45 degrees, and the Jones matrix is obtained
If the polarized light of the incident wave plate group is in the initial state
The initial Jones matrix is sequentially multiplied by the Jones matrix of the passed wave plate to obtain a phase-compensated Jones matrix
Therefore, the arbitrary phase difference can be compensated by rotating the included angle delta between the fast axis of the lambda/2 wave plate and the x axis.
The transverse electro-optic effect of the lithium niobate crystal is utilized to act as a lambda/2 wave plate. Lithium niobate is used as a nonlinear optical crystal material and has wide application in the field of optical communication. When an electric field is applied to the lithium niobate crystal perpendicular to the propagation direction of a light beam therein, a transverse electro-optic effect occurs. Namely: when light wave passes through lithium niobate crystal, a phase difference is generated
Where l is the length in the light-passing direction, d is the thickness in the direction of applied voltage, and V is the applied voltage.
This phase retardation is due solely to birefringence caused by the electro-optic effect and is therefore referred to as electro-optic phase retardation.
When the electro-optic crystal and the wavelength of the propagating light are determined, the phase difference changes only depending on the applied voltage, i.e. the phase changes proportionally by changing the voltage.
Using 4 parameters S0、S1、S2、S3To describe a light waveIntensity and polarization state of (c). The components of the electric vector in the x and y axes are, according to the equation of the transmission of light in space:
s parameters are respectively expressed as
Wherein
Further elaboration of the S parameter into the form of spherical coordinates
Thereby constructing a structure S1、S2、S3A space sphere with coordinates, on which the rectangular coordinate of any point P is S1，S2，S3And 2 χ and 2 ψ are the spherical coordinates of the point correspondence.
And obtaining the phase difference of the front light and the rear light by the feedback of the polarization state measurement of the input and output light. According to the phase difference, a transverse voltage can be applied to the lithium niobate crystal, so that the phase is compensated through a transverse electro-optic effect, and the automatic adjustment of optical phase compensation is realized.
The above embodiments are not limited to the technical solutions of the embodiments themselves, and the embodiments may be combined with each other into a new embodiment. The above embodiments are only for illustrating the technical solutions of the present invention and are not limited thereto, and any modification or equivalent replacement without departing from the spirit and scope of the present invention should be covered within the technical solutions of the present invention.
Claims (3)
1. An automatic phase compensation device, characterized by: the polarization analysis device comprises a first polarization analysis system (1), a first lambda/2 wave plate (2), a second lambda/2 wave plate (3), a first lambda/4 wave plate (4), a lithium niobate crystal (5), a second lambda/4 wave plate (6), a second polarization analysis system (7), a pressure control module (8), a phase difference calculation module (9) and an optical system (10), wherein the first polarization analysis system (1) and the first lambda/2 wave plate (2) are sequentially arranged in the normal incidence direction of the optical system (10), the second lambda/2 wave plate (3), the first lambda/4 wave plate (4), the lithium niobate crystal (5), the second lambda/4 wave plate (6) and the second polarization analysis system (7) are sequentially arranged in the emergent beam direction of the optical system (10), and the first polarization analysis system (1) and the second polarization analysis system (7) are connected with the information input end of the phase difference calculation module (9) through wires, the phase information of input and output light is transmitted to a phase difference calculation module (9) to be calculated so as to obtain a phase offset theta, an information output end of the phase difference calculation module (9) is connected with an information input end of a voltage control module (8) through a lead so as to convert the phase offset theta into a voltage signal, and signal output ends 1 and 2 of the voltage control module (8) are correspondingly connected with electrode plates 1 and 2 of a lithium niobate crystal (5).
2. The method of claim 1, further comprising: and the included angle beta between the fast axis of the first lambda/4 wave plate (4) and the fast axis of the second lambda/4 wave plate (6) and the x axis is fixed to be 45 degrees.
3. The use method of the automatic phase compensation device is characterized in that:
the method comprises the following steps: adjusting the first lambda/2 wave plate (2) and the second lambda/2 wave plate (3) to enable the light transmission directions of the two wave plates to be consistent so as to calibrate line polarization;
step two: the polarization states of input light and output light are measured by using a first polarization analysis system (1) and a second polarization analysis system (7) to respectively obtain the phase theta of the input light1And output light phase θ2。
Step three: measuring the phase theta of the input light1And output light phase θ2The phase difference is fed back to a phase difference calculation module (9) to obtain the phase shift amount theta of the output light relative to the input light.
Step four: the phase difference calculation module (9) transmits the phase offset theta to the voltage control module (8), and the voltage control module (8) generates a corresponding voltage signal according to the phase offset theta.
Step five: the voltage control module (8) transmits the voltage signal to the electrode plates at two ends of the lithium niobate crystal (5) to form transverse voltage, so that automatic adjustment of optical phase compensation is realized.
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