CN210201850U - Polarization encoding device and quantum key distribution light source - Google Patents
Polarization encoding device and quantum key distribution light source Download PDFInfo
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- CN210201850U CN210201850U CN201921590693.9U CN201921590693U CN210201850U CN 210201850 U CN210201850 U CN 210201850U CN 201921590693 U CN201921590693 U CN 201921590693U CN 210201850 U CN210201850 U CN 210201850U
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Abstract
A polarization encoding device and a quantum distribution light source based on the device are provided, the device comprises: the optical splitter, the first polarization piece, the second polarization piece and the phase modulator; the optical beam splitter comprises an input port, a reflection output port, a transmission output port and an output port; the first polarization piece and the second polarization piece are connected with the phase modulator through polarization maintaining optical fibers to form a bidirectional loop light path meeting the Sagnac effect; the input port receives input light through a polarization maintaining fiber. The device can avoid the problems of polarization mode delay, poor stability and the like of the traditional polarization modulator caused by the difference of optical fiber paths, and is simplified and simple to operate. The quantum key distribution can be quickly, accurately and stably realized by the quantum distribution light source based on the device.
Description
Technical Field
The utility model relates to a quantum communication field especially relates to a polarization encoding device and quantum key distribution light source.
Background
At present, the encoding method of polarization state modulation of Quantum Key Distribution (QKD) light source mainly includes the following two methods.
First, it is implemented using a polarization modulator. The polarization modulator is equivalent to an equal-arm interferometer, and the arm lengths of two arms of the interferometer must be strictly equal to ensure the interference effect. However, because of the difference in the refractive indices of the two polarization components of H, V, Polarization Mode Delay (PMD) phenomena may occur after passing through the modulator, and this amount of delay is typically on the order of 10ps for lithium niobate crystal based modulators. The presence of PMD can greatly limit the performance of the modulator, which typically requires compensation using schemes such as high index fibers, and the system is complex and performance limited. And because the two arms of the interferometer are influenced by the change of environmental conditions such as external temperature, mechanics and the like, the influence on the two arms is different, the polarization modulation result gradually drifts, and the long-term stability is poor.
Second, a polarization modulation method based on a circulator + sagnac loop is realized. The method is generally realized by adopting a circulator + Sagnac ring structure. Specifically, the method uses a polarization controller to realize polarization state control of incident linearly polarized light, uses single-mode fiber transmission, transmits the light to a Polarization Beam Splitter (PBS) after passing through a circulator, ensures that the light incident on the PBS is 45-degree linearly polarized light and uniformly outputs the light from two arms of the PBS, the light components of the two arms interfere at the PBS again through a Sagnac ring structure, uses a phase modulator on one arm to add an additional phase component, generates different polarization states after the light interferes on the PBS, and returns the light to the circulator for output. Because single-mode optical fiber is used between the circulator and the PBS for transmission, a polarization controller is needed to modulate the polarization state of incident light, so that the system is more complex and has poorer integration level. Meanwhile, the scheme needs to perform a calibration process before implementation, ensures that 45-degree linearly polarized light is uniformly projected onto two arms of the PBS, is complex in calibration process, needs a calibration process before each polarization encoding device is used, and is poor in practicability.
SUMMERY OF THE UTILITY MODEL
Problem (A)
Problem to prior art existence, the utility model provides a polarization encoding device and quantum key distribution light source for at least part is solved above-mentioned technical problem.
(II) technical scheme
The utility model provides an aspect a polarization encoding device, include: the optical splitter, the first polarization piece, the second polarization piece and the phase modulator; the optical beam splitter comprises an input port, a reflection output port, a transmission output port and an output port; the first polarization plate and the second polarization plate are connected with the phase modulator through polarization maintaining optical fibers to form a bidirectional loop optical path meeting the Sagnac effect; the input port receives input light through a polarization maintaining fiber; the input light enters the optical beam splitter after rotating through the polarization maintaining optical fiber, the optical beam splitter splits the rotated input light into a first light component and a second light component, the first light component is transmitted to the first polarizer through the reflection output port, the fast axis is cut off and coupled to the slow axis of the polarization maintaining optical fiber through the first polarizer, the first light component is transmitted to the phase modulator in a clockwise direction to be subjected to phase modulation and then transmitted back to the optical beam splitter, the second light component is transmitted to the second polarizer through the transmission output port, the fast axis is cut off and coupled to the slow axis of the polarization maintaining optical fiber through the second polarizer, the second light component is transmitted back to the optical beam splitter in an anticlockwise direction, and two beams of light transmitted back to the optical beam splitter are interfered and then output through the output port.
Optionally, an angle between the first polarization plate and the horizontal direction is 0 °, and an angle between the second polarization plate and the horizontal direction is 90 °.
Optionally, lengths of the polarization maintaining fibers between the first polarization plate, the second polarization plate and the phase modulator may be adjustable.
Optionally, the input light is horizontally linearly polarized light, and the polarization maintaining fiber of the input port is further configured to rotate the horizontally linearly polarized light by 45 ° to obtain 45 ° linearly polarized light.
Optionally, an optical signal is transmitted between the reflection output port and the first polarization plate through a free space, and an optical signal is transmitted between the transmission output port and the second polarization plate through a free space.
Optionally, the additional phase of the first light component after being modulated by the phase modulator is 0, pi/2, pi, or 3 pi/2.
Optionally, the output port is connected to a single-mode optical fiber, and is configured to output an optical signal obtained by interfering two beams of light transmitted back to the optical splitter.
The utility model provides an on the other hand quantum key distribution light source based on above-mentioned polarization encoding device, include: a laser for generating a narrow optical pulse signal; the intensity modulator is used for carrying out intensity modulation on the narrow optical pulse signal to generate an intensity state signal required by quantum key distribution; the polarization encoding device is used for carrying out polarization encoding on the intensity state signal to generate a polarization state signal required by quantum key distribution; and the attenuator is used for attenuating the polarization state signal to a single photon magnitude required by quantum key distribution and outputting the single photon magnitude.
Optionally, the quantum key distribution light source further includes: and the pulse generator is used for sending out a pulse signal so as to drive the laser, the intensity modulator and the polarization encoding device.
Optionally, the pulse generator generates a periodic electrical pulse signal to drive the laser; the pulse generator generates a random pulse signal to drive the intensity modulator and the polarization encoding device.
(III) advantageous effects
The utility model provides a polarization coding device and quantum key distribution light source adopts the polarization modulation scheme based on Sagnac ring, because positive and negative two-way light component polarization state is the same in the phase modulator, and has walked the optic fibre of the same length, has eliminated the optic fibre path difference to avoid traditional polarization modulator because the polarization mode that the optic fibre path difference caused delays, the relatively poor scheduling problem of stability. Meanwhile, compared with a polarization modulation method based on a circulator and a sagnac ring, the polarization coding device simplifies the use of the circulator and a polarization controller, uses the polarization-maintaining optical fiber to realize the 45-degree incidence of linearly polarized light, avoids the complicated initial polarization state calibration process, simplifies the realization device of the system, and can quickly, accurately and stably realize the quantum key distribution.
Drawings
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
FIG. 1 schematically illustrates a block diagram of a polarization encoding apparatus according to an embodiment of the present invention;
fig. 2 schematically shows a structure diagram of a quantum key distribution light source according to an embodiment of the present invention.
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be understood that the description is intended to be illustrative only and is not intended to limit the scope of the present invention. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It may be evident, however, that one or more embodiments may be practiced without these specific details. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms "comprises," "comprising," and the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.
All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It is noted that the terms used herein should be interpreted as having a meaning that is consistent with the context of this specification and should not be interpreted in an idealized or overly formal sense.
Fig. 1 schematically shows a structure diagram of a polarization encoding apparatus according to an embodiment of the present invention. As shown in fig. 1, the polarization encoding apparatus includes:
a Beam Splitter (BS), a first polarizer (Pola1), a second polarizer (Pola2) and a Phase Modulator (PM).
An optical splitter (BS) includes an input port, a reflective output port, a transmissive output port, and an output port. Input light (Input) is connected to the Input port through an Input optical fiber, which is a polarization maintaining fiber. The Output light (Output) is connected to the Output port through an Output fiber, which is a single mode fiber.
As shown in fig. 1, the optical splitter (BS) includes a first port a, a second port B, a third port C and a fourth port D. The specific input port, reflective output port, transmissive output port, and output port may be more practical. For example:
when the first port a is an input port, the second port B is a reflective output port, and the third port C is a transmissive output port.
When the second port B is an input port, the first port a is a reflection output port, and the fourth port D is a transmission output port.
When the third port C is an input port, the fourth port D is a reflection output port, and the first port a is a transmission output port.
The first polarization plate (Pola1), the second polarization plate (Pola2) and the Phase Modulator (PM) are connected through polarization-maintaining optical fibers based on Sagnac effect (Sagnac) loop to form a bidirectional loop light path. The length of the polarization-maintaining fiber between the first polarizer (Pola1), the second polarizer (Pola2) and the Phase Modulator (PM) is adjustable, and the delay of the Sagnac loop reaching the Phase Modulator (PM) in the clockwise direction and the counter-clockwise direction can be made different by adjusting the length of the polarization-maintaining fiber from the Phase Modulator (PM) to the first polarizer (Pola1) and the second polarizer (Pola 2). Wherein the included angle between the first polarizer (Pola1) and the horizontal direction is 0 degree, and the included angle between the second polarizer (Pola2) and the horizontal direction is 90 degrees.
The polarization encoding process of the polarization encoding device comprises the following steps: the input light enters an optical Beam Splitter (BS) after rotating through a polarization maintaining optical fiber, the optical Beam Splitter (BS) evenly splits the rotated input light into a first light component and a second light component, the first light component is transmitted to a first polarizer (Pola1) through a reflection output port, the first light component is cut off at a fast axis and coupled to a slow axis of the polarization maintaining optical fiber through a first polarizer (Pola1), the first light component is transmitted to a Phase Modulator (PM) along a clockwise direction to be subjected to phase modulation and then transmitted back to the optical Beam Splitter (BS), the second light component is transmitted to a second polarizer (Pola2) through a transmission output port, the fast axis is cut off through a second polarizer (Pola2) and coupled to the slow axis of the polarization maintaining optical fiber, the second light component is transmitted back to the optical Beam Splitter (BS) along a counterclockwise direction, and two beams of light transmitted back to the optical Beam Splitter (BS) are output through the output port after being interfered.
Specifically, with the first port a as an input port, the second port B as a reflection output port, the third port C as a transmission output port, and the fourth port D as an output port, the polarization encoding process is as follows:
and S1, horizontally inputting linearly polarized light, rotating the input optical fiber by 45 degrees through the polarization maintaining optical fiber, enabling the input horizontally polarized light to be linearly polarized light of 45 degrees, enabling the linearly polarized light to be incident on a port A of the BS, uniformly dividing the linearly polarized light of 45 degrees into a first light component and a second light component by the BS, and respectively outputting the first light component and the second light component from the reflection output port B and the transmission output port C. Wherein, the polarization state of the incident polarized light can be expressed as:
s2, the reflective output port B of BS outputs the first light component into the Pola1 through free space, with Pola1 placed at 0 °, and fast axis cut-off is achieved through Pola1, allowing the first light component to couple into the slow axis of the polarization maintaining fiber, propagating clockwise in the bidirectional ring path.
And S3, outputting a second light component to Pola2 through free space by a transmission output end C of the BS, placing Pola2 at 90 degrees, realizing fast axis cut-off through Pola2, coupling the second light component to the slow axis of the polarization-maintaining fiber after passing through the polarization plate, and transmitting in a bidirectional ring light path along the counterclockwise direction. At this time, the corresponding polarization state is:
where | S > refers to polarization along the slow axis in polarization-maintaining light, and subscripts c and a refer to clockwise and counterclockwise propagation, respectively.
S4, the first light component output clockwise is acted by the electric signal loaded on PM when passing through PM, and an extra phase is added
When the second light component output counterclockwise passes through the PM, the electrical signal loaded on the PM is zero, and no additional phase is superimposed. At this time, the corresponding polarization state is:
s5, the first light component arrives clockwise at Pola2 and is transmitted through free space to the BS 'S transmissive output port C, and the second component arrives counter-clocked at Pola1 and is transmitted through free space to the BS' S reflective output port B. The two pulse components are output through an output port D after interference occurs on the BS. At this time, the corresponding polarization state is:
wherein the extra phase
Can be 0 or pi/2 or pi or 3 pi/2, and the 4 corresponding output quantum states are respectively
The quantum states of the two groups of basis vectors can be directly used for BB84 protocol coding.
In addition, a polarization controller is additionally added behind the output port D, a unitary transformation is applied, the | L >, | R > quantum states are adjusted to | H >, | V > quantum states, meanwhile, | + >, | - > quantum states are kept unchanged, and the original BB84 protocol coding can be realized.
The polarization encoding device provided by the embodiment adopts a polarization modulation scheme based on the Sagnac loop, and because the forward and backward bidirectional light components have the same polarization state in the phase modulator and pass through the optical fibers with the same length, the optical fiber path difference is eliminated, so that the problems of polarization mode delay, poor stability and the like of the traditional polarization modulator caused by the optical fiber path difference are solved. Meanwhile, compared with a polarization modulation method based on a circulator and a sagnac ring, the polarization coding device simplifies the use of the circulator and a polarization controller, realizes the 45-degree incidence of linearly polarized light by using a polarization-maintaining optical fiber, avoids a complicated initial polarization state calibration process, and simplifies a system realization device.
Fig. 2 schematically shows a structure diagram of a quantum key distribution light source according to an embodiment of the present invention. As shown in fig. 2, the quantum key distribution light source includes a laser, an intensity modulator, the polarization encoding device, an attenuator, and a pulse generator.
And the laser is used for generating a narrow optical pulse signal. Specifically, the laser emits a periodic narrow optical pulse signal under the driving of a periodic electrical pulse generated by a pulse generator.
And the intensity modulator is used for carrying out intensity modulation on the narrow optical pulse signal to generate an intensity state signal required by quantum key distribution. Specifically, the intensity modulator modulates the input narrow optical pulse signal under the action of random pulses generated by the pulse generator to generate three intensity states, namely a signal state, a decoy state, a vacuum state and the like, required by quantum key distribution.
And the polarization encoding device is used for carrying out polarization encoding on the intensity state signal to generate a polarization state signal required by quantum key distribution. Specifically, the optical signal after intensity modulation enters a polarization encoding device, and under the action of random pulses generated by a pulse generator, the polarization encoding device modulates the input narrow optical pulse signal to generate four polarization states of +, -, L, R and the like required by quantum key distribution.
And the attenuator is used for attenuating the polarization state signal to the single photon magnitude required by quantum key distribution and then outputting the signal.
The quantum key distribution light source provided by the embodiment can avoid the problems of polarization mode delay, poor stability and the like of the traditional polarization modulator caused by the difference of optical fiber paths by adopting the polarization encoding device provided by the embodiment. And the method is simple to operate, and can quickly generate four polarization states of +, -, L, R and the like required by quantum key distribution, thereby realizing accurate, stable and quick distribution of the quantum key.
It will be understood by those skilled in the art that while the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. Accordingly, the scope of the present invention should not be limited to the above-described embodiments, but should be defined not only by the appended claims, but also by equivalents thereof.
Claims (10)
1. A polarization encoding device, comprising:
the optical splitter, the first polarization piece, the second polarization piece and the phase modulator;
the optical beam splitter comprises an input port, a reflection output port, a transmission output port and an output port;
the first polarization piece and the second polarization piece are connected with the phase modulator through polarization-maintaining optical fibers to form a bidirectional loop optical path meeting the Sagnac effect;
the input port receives input light through a polarization maintaining optical fiber;
the input light enters the optical beam splitter after rotating through the polarization maintaining optical fiber, the optical beam splitter splits the rotated input light into a first light component and a second light component, the first light component is transmitted to the first polarizer through the reflection output port, the first polarizer realizes fast axis cutoff and is coupled into a slow axis of the polarization maintaining optical fiber and then is transmitted to the phase modulator clockwise for phase modulation, the phase modulator then transmits the phase modulated phase back to the optical beam splitter, the second light component is transmitted to the second polarizer through the transmission output port, the second polarizer realizes fast axis cutoff and is coupled into the slow axis of the polarization maintaining optical fiber and then is transmitted back to the optical beam splitter along the counterclockwise direction, and two beams of light transmitted back to the optical beam splitter are output through the output port after being interfered.
2. The polarization encoding device of claim 1, wherein the first polarizer is at an angle of 0 ° to the horizontal and the second polarizer is at an angle of 90 ° to the horizontal.
3. The polarization encoding device of claim 1, wherein a length of polarization maintaining fiber between the first polarization plate, the second polarization plate, and the phase modulator is adjustable.
4. The polarization encoding device of claim 1, wherein the input light is horizontally linearly polarized light, and the polarization maintaining fiber of the input port is further configured to rotate the horizontally linearly polarized light by 45 ° to obtain 45 ° linearly polarized light.
5. The polarization encoding device of claim 1, wherein the reflective output port transmits optical signals through free space with the first polarizer and the transmissive output port transmits optical signals through free space with the second polarizer.
6. The polarization encoding device of claim 1, wherein the additional phase after modulation of the first light component by the phase modulator is 0 or pi/2 or pi or 3 pi/2.
7. The polarization encoding device of claim 1, wherein the output port is connected to a single-mode fiber for outputting an optical signal obtained by interfering two beams of light transmitted back to the optical splitter.
8. A quantum key distribution light source based on the polarization encoding device of any one of claims 1 to 7, comprising:
a laser for generating a narrow optical pulse signal;
the intensity modulator is used for carrying out intensity modulation on the narrow optical pulse signal and generating an intensity state signal required by quantum key distribution;
the polarization encoding device is used for carrying out polarization encoding on the intensity state signal to generate a polarization state signal required by quantum key distribution;
and the attenuator is used for attenuating the polarization state signal to a single photon magnitude required by quantum key distribution and then outputting the signal.
9. The quantum key distribution light source of claim 8, further comprising:
and the pulse generator is used for sending out a pulse signal so as to drive the laser, the intensity modulator and the polarization encoding device.
10. The quantum key distribution optical source of claim 9, wherein the pulse generator generates a periodic electrical pulse signal to drive the laser;
the pulse generator generates a random pulse signal to drive the intensity modulator and the polarization encoding device.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110545180A (en) * | 2019-09-23 | 2019-12-06 | 中国科学技术大学 | Polarization encoding device and quantum key distribution light source |
| CN114465725A (en) * | 2022-04-11 | 2022-05-10 | 北京中科国光量子科技有限公司 | Quantum key distribution coding device |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110545180A (en) * | 2019-09-23 | 2019-12-06 | 中国科学技术大学 | Polarization encoding device and quantum key distribution light source |
| CN114465725A (en) * | 2022-04-11 | 2022-05-10 | 北京中科国光量子科技有限公司 | Quantum key distribution coding device |
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