CN212231469U - Two-stage polarization encoding device and quantum key distribution light source - Google Patents
Two-stage polarization encoding device and quantum key distribution light source Download PDFInfo
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- CN212231469U CN212231469U CN202020917877.8U CN202020917877U CN212231469U CN 212231469 U CN212231469 U CN 212231469U CN 202020917877 U CN202020917877 U CN 202020917877U CN 212231469 U CN212231469 U CN 212231469U
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Abstract
A polarization encoding device comprises a two-stage Sagnac ring and specifically comprises a circulator 1, a polarization beam splitter PBS1, a phase modulator PM1, a circulator 2, a polarization beam splitter PBS2 and a phase modulator PM2, wherein the circulator 1 and the circulator 2 respectively comprise a first port a, a second port b and a third port c; PBS1 and PBS2 each included first port 1, second port 2, and third port 3; the PBS1 and the second port 2 and the third port 3 of the PBS2 are connected through polarization-maintaining optical fibers based on a Sagnac ring to form a bidirectional ring optical path; input light is connected to a first port a of the circulator 1 through an input optical fiber, and the input optical fiber is a polarization maintaining optical fiber; the output light is connected to the third port c of the circulator 2 through an output optical fiber, which is a single mode optical fiber. The utility model discloses use the pulse signal drive of two passageways, single amplitude, satisfied the demand that 4 polarization states were prepared in polarization encoding QKD experiment, avoided the technical problem that the pulse signal of single channel, multiple amplitude produced, realize that the degree of difficulty is little, the reliability is high.
Description
Technical Field
The present invention relates to the field of optical polarization encoding, and more particularly to a polarization encoding device and a quantum key distribution light source for use in, for example, a quantum key distribution system.
Background
Quantum communication is one of the leading-edge fields of current physics, and the basic physical principle based on quantum mechanics ensures the unconditional safety of information transmission, and is a development direction of quantum informatics to practical application. The core of Quantum communication is Quantum Key Distribution (QKD), which can realize that two communication parties far away from each other share unconditionally safe Quantum keys, and in combination with a one-time pad encryption method, can realize safe communication proved by strict mathematics of information theory. The BB84 protocol is the first QKD protocol proposed by Bennett et al, 1984, and electricity is one of the most widely used QKD so far. In the QKD experiment in free space and satellite-ground, because the fidelity of atmosphere to the polarization state is better, encoding is mostly performed based on the polarization state, and correspondingly, the polarization state modulation of the QKD light source needs to be performed to realize random encoding of four polarization states of two orthogonal basis vectors.
There are two main methods of polarization encoding that are commonly used. One is based on inputting the polarization modulator based on lithium ion crystal or gallium arsenide material after passing through the 45 degree rotation axis with external linearly polarized light, H, V two polarization components are respectively transmitted along two axial directions of the modulator crystal, and by applying a voltage signal on the modulator, an extra phase difference is introduced between H, V two polarization components, and interference occurs at the output port of the modulator crystal, so that different polarization states are generated. The other method is a polarization modulation method based on a circulator and a Sagnac ring, wherein an interference ring of a Sagnacx structure is constructed, an extra phase difference is introduced between a clockwise component and a counterclockwise component through a phase modulator, and finally different polarization states are generated through interference.
For the polarization encoding methods reported so far, a single-stage polarization encoding scheme is adopted. To generate the 4 polarization states required for the polarization encoded QKD experiment, it is necessary to generate the amplitudes of 0 and 1/2V, respectivelyπ、Vπ、3/2VπPulse signals of four voltage values, where VπIs a half-wave voltage of a polarization modulator or a phase modulator. Considering that the typical half-wave voltage of the modulator is about 5V, pulse signals with amplitudes of 0, 2.5V, 5V, 7.5V and other four voltage values are respectively generated to drive the modulator to realize preparation of a target polarization state, and meanwhile, in order to ensure the fidelity of the prepared polarization state, the requirement of low jitter is also provided for the pulse signals. With the gradual increase of the repetition frequency from MHz to GHz, the generation of the pulse signals with multiple amplitude, low jitter and large voltage puts a very high demand on driving electronics, and has the advantages of complex technology, high implementation difficulty and low reliability, thereby limiting the application prospect of the single-stage polarization encoding device to a certain extent.
SUMMERY OF THE UTILITY MODEL
In view of the above, the present invention provides a two-stage polarization encoding device and a quantum key distribution light source, so as to partially solve at least one of the above technical problems.
In order to achieve the above object, as an aspect of the present invention, there is provided a polarization encoding apparatus comprising a two-stage Sagnac loop, specifically comprising a circulator 1, a polarization beam splitter PBS1, a phase modulator PM1, a circulator 2, a polarization beam splitter PBS2, a phase modulator PM2, wherein,
the circulator 1 and the circulator 2 respectively comprise a first port a, a second port b and a third port c;
PBS1 and PBS2 each included first port 1, second port 2, and third port 3;
PBS1 and PBS2 are connected between second port 2 and third port 3 by Sagnac loop-based polarization maintaining fiber to form a bi-directional loop optical path, and the delays of Sagnac loop reaching PM1 and PM2 in clockwise and counterclockwise directions are made different by adjusting the lengths of PM1 and PM2 to the polarization maintaining fibers of second port 2 and third port 3;
the input light is connected to a first port a of the circulator 1 through an input optical fiber;
the output light is connected to the third port c of the circulator 2 through an output optical fiber.
The input light is linearly polarized light and horizontally input, and the input optical fiber rotates for 45 degrees to enable the input light to be linearly polarized light for 45 degrees; the input optical fiber is a polarization maintaining optical fiber, and the output optical fiber is a single mode optical fiber.
Wherein, the ports of the circulator 1 and the circulator 2 are set as follows:
when the first port a is an input port, the second port b is an output port;
when the second port b is an input port, the third port c is an output port.
Wherein the ports of PBS1 and PBS2 are configured to:
when the first port 1 is an input port, the second port 2 is a reflection output end, and the third port 3 is a transmission output end;
when the second port 2 is an input end, the first port 1 is a reflection output end;
when the third port 3 is an input port, the first port 1 is a transmission output port.
As another aspect of the present invention, there is provided a quantum key distribution light source using the above two-stage polarization encoding apparatus, including a pulse generator, a laser, an intensity modulator, a polarization encoding apparatus, and an attenuator; wherein the content of the first and second substances,
the pulse generator is used for sending out a specific pulse signal so as to respectively drive the laser, the intensity modulator and the polarization encoding device;
the laser emits periodic narrow light pulse signals under the driving of periodic electric pulses generated by the pulse generator;
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 and a vacuum state, which are required by quantum key distribution;
the light signal after intensity modulation enters a polarization coding device, the polarization coding device adopts the polarization coding device, a pulse generator respectively generates voltage pulse signals with two channels and binary amplitudes, the voltage pulse signals respectively act on a first-stage Sagnac ring and a second-stage Sagnac ring of the polarization coding device, the input narrow light pulse signals are modulated, and four polarization states of +, -, L, R required by quantum key distribution are generated;
and the optical signal after the polarization coding is finished is attenuated to the single photon magnitude required by the quantum key distribution and then output after passing through the attenuator.
Based on the above technical scheme can know, the utility model discloses a two-stage polarization coding device, coding method and quantum key distribution light source have one of following beneficial effect at least for prior art:
(1) through the scheme of the two-stage polarization encoding device, the requirement of preparing 4 polarization states in a polarization encoding QKD experiment can be met by using pulse signals with two channels and single amplitude value for driving, the technical problem caused by pulse signals with single channel and multiple amplitude values is avoided, the technology is simple, the realization difficulty is small, and the reliability is high;
(2) the requirement on the amplitude of a driving electric pulse signal is reduced by the scheme of the two-stage polarization encoding device, and 3/2V of the single-stage polarization encoding deviceπReduced to Vπ(VπHalf-wave voltage of the phase modulator), the pulse amplitude requirement on the driving electronics is reduced;
(3) according to the polarization modulation scheme based on the two-stage Sagnac ring, due to the fact that forward and reverse bidirectional light components are in the same polarization state in the phase modulator and pass through the optical fibers with the same length, the problems of polarization mode delay, poor stability and the like of a traditional polarization modulator caused by optical fiber path difference can be solved, a complex initial polarization state calibration process is also avoided, and the polarization modulation scheme has high stability and reliability.
Drawings
Fig. 1 is a schematic diagram of the structure and method of the polarization encoding apparatus of the present invention;
fig. 2 is a schematic diagram of the application of the polarization encoding apparatus of the present invention in quantum key distribution.
Detailed Description
The utility model discloses to traditional single-stage polarization encoding's scheme, provided a two-stage polarization encoding device's scheme, use the pulse signal drive of two-channel, single amplitude, can satisfy the demand of polarization encoding QKD experiment preparation 4 kinds of polarization states, reduced the demand to driving electric pulse signal range, avoided the technical problem that single channel, multiple amplitude's pulse signal produced, simple technique, realization degree of difficulty are little, the reliability is high.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings.
The utility model discloses a polarization encoding device, as shown in fig. 1, mainly constitute by two-stage Sagnac ring, specifically include circulator 1, polarization beam splitter PBS1, phase modulator PM1, circulator 2, polarization beam splitter PBS2, several parts of phase modulator PM2, wherein:
the circulator 1(2) includes a first port a, a second port b and a third port c;
when the first port a is an input port, the second port b is an output port;
when the second port b is an input port, the third port c is an output port;
PBS1(2) includes first port 1, second port 2, and third port 3;
when the first port 1 is an input port, the second port 2 is a reflection output end, and the third port 3 is a transmission output end;
when the second port 2 is an input end, the first port 1 is a reflection output end;
when the third port 3 is an input port, the first port 1 is a transmission output port;
the second port 2 and the third port 3 of the PBS1(2) are connected through polarization-maintaining optical fibers based on Sagnac loop to form a bidirectional loop optical path, and the lengths of the polarization-maintaining optical fibers from the PM1(2) to the second port 2 and the third port 3 are adjusted to ensure that the delays of the Sagnac reaching the PM1(2) in the clockwise direction and the anticlockwise direction are different;
an Input light Input is connected to a first port a of the circulator 1 through an Input optical fiber, and the Input optical fiber is a polarization maintaining optical fiber;
the Output light Output is connected to the third port c of the circulator 2 through an Output optical fiber, and the Output optical fiber is a single mode optical fiber;
as shown in fig. 1, the flowchart of the encoding method based on the polarization encoding apparatus is shown, and specifically includes the following steps:
the Input light Input is linearly polarized light and horizontally Input, the Input optical fiber is rotated by 45 degrees, the Input light becomes 45-degree linearly polarized light, the linearly polarized light is incident on the first port a of the circulator 1, and then the linearly polarized light is output from the second port b of the circulator 1.
The 45 ° linearly polarized light is output from the second port b of the circulator 1 to the first port 1 of the polarization beam splitter PBS1, and the 45 ° linearly polarized light is uniformly divided into a first component | H > and a second component | V > from the PBS1, and output from the reflection end 2 and the transmission end 3, respectively.
The reflective end 2 of the PBS1 achieves a fast axis cutoff for the first component and then couples into the slow axis of the polarization maintaining fiber, propagating clockwise in the bi-directional ring optical path.
The transmissive end 3 of PBS1 achieves a fast axis cut-off for the second component and is then coupled into the slow axis of the polarization maintaining fiber, propagating in a counter-clockwise bi-directional loop path.
The first component optical pulse which is output clockwise is acted by an electric signal loaded on PM1 when passing through PM1, and an extra phase is added
When the second component optical pulse output anticlockwise passes through the PM1, the electric signal loaded on the PM1 is zero, and no additional phase is superposed.
The first component is transmitted clockwise to port 3 of PBS 1; the second component inverse clock pulse is transmitted to port 2 of PBS 1. The two pulse components interfere at PBS1 and are output through port 1.
The light pulse output from port 1 of PBS1 is input to second port b of circulator 1, and then output from third port c of circulator 1.
The light pulse output from the third port c of the circulator 1 is input to the first port a of the circulator 2, and then output from the second port b of the circulator 2.
The second port b of circulator 2 outputs to the first port 1 of polarization beam splitter PBS2, splitting the | H >, | V > polarization components from PBS2, respectively, the first component | H > and the second component | V > output from reflective port 2 and transmissive port 3, respectively.
The reflective end 2 of the PBS2 achieves a fast axis cutoff for the first component and then couples into the slow axis of the polarization maintaining fiber, propagating clockwise in the bi-directional ring optical path.
The transmissive end 3 of PBS2 achieves a fast axis cut-off for the second component and is then coupled into the slow axis of the polarization maintaining fiber, propagating in a counter-clockwise bi-directional loop path.
The first component optical pulse which is output clockwise is acted by an electric signal loaded on PM2 when passing through PM2, and an extra phase is added
When the second component optical pulse output anticlockwise passes through the PM2, the electric signal loaded on the PM2 is zero, and no additional phase is superposed.
The first component is transmitted clockwise to port 3 of PBS 2; the second component inverse clock pulse is transmitted to port 2 of PBS 2. The two pulse components interfere at PBS2 and are output through port 1.
The polarization state of the output pulsed light can be expressed as
When extra phase
And
00, pi and 0,
When the output 4 quantum states are respectively
And
the preparation of four polarization states required by the BB84 protocol is completed through the combination of two-stage polarization encoding.
The light pulse output from port 1 of PBS2 is input to second port b of circulator 2, and then output from third port c of circulator 2.
And the third port c of the circulator 2 outputs, and is finally coupled to the Output optical fiber Output and outputs.
Based on the polarization encoding device, the quantum key distribution light source can be realized, and the polarization encoding device is applied to quantum key distribution. As shown in fig. 2, the light source mainly includes a pulse generator, a laser, an intensity modulator, a polarization encoding device, an attenuator, and so on:
the pulse generator is used for emitting specific pulse signals to drive the laser, the intensity modulator and the polarization encoding device respectively.
The laser emits periodic narrow optical pulse signals under the drive of periodic electric pulses generated by the pulse generator.
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 optical signal after the intensity modulation enters a polarization encoding device. The polarization encoding device adopts a two-stage polarization encoding scheme provided by the patent, and the pulse generator respectively generates two-channel voltage pulse signals with binary amplitudes, and the two-channel voltage pulse signals respectively act on a first-stage Sagnac ring and a second-stage Sagnac ring of the polarization encoding device to modulate the input narrow light pulse signals and generate four polarization states of +, -, L, R and the like required by quantum key distribution.
And after the optical signal subjected to intensity modulation and polarization coding passes through the attenuator, the optical signal is attenuated to a single photon magnitude required by quantum key distribution and then output.
The above-mentioned embodiments, further detailed description of the objects, technical solutions and advantages of the present invention, it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (5)
1. A polarization encoding device is characterized by comprising two stages of Sagnac rings, and particularly comprising a circulator 1, a polarization beam splitter PBS1, a phase modulator PM1, a circulator 2, a polarization beam splitter PBS2 and a phase modulator PM2, wherein,
the circulator 1 and the circulator 2 respectively comprise a first port a, a second port b and a third port c;
PBS1 and PBS2 each included first port 1, second port 2, and third port 3;
PBS1 and PBS2 are connected between second port 2 and third port 3 by Sagnac loop-based polarization maintaining fiber to form a bi-directional loop optical path, and the delays of Sagnac loop reaching PM1 and PM2 in clockwise and counterclockwise directions are made different by adjusting the lengths of PM1 and PM2 to the polarization maintaining fibers of second port 2 and third port 3;
the input light is connected to a first port a of the circulator 1 through an input optical fiber;
the output light is connected to the third port c of the circulator 2 through an output optical fiber.
2. The polarization encoding device of claim 1, wherein the input light is linearly polarized light horizontal input, and the input optical fiber is rotated by 45 ° to make the input light be linearly polarized light of 45 °; the input optical fiber is a polarization maintaining optical fiber, and the output optical fiber is a single mode optical fiber.
3. The polarization encoding device of claim 1, wherein the ports of the circulator 1 and circulator 2 are configured as follows:
when the first port a is an input port, the second port b is an output port;
when the second port b is an input port, the third port c is an output port.
4. The polarization encoding device of claim 1, wherein the ports of PBS1 and PBS2 are configured as:
when the first port 1 is an input port, the second port 2 is a reflection output end, and the third port 3 is a transmission output end;
when the second port 2 is an input end, the first port 1 is a reflection output end;
when the third port 3 is an input port, the first port 1 is a transmission output port.
5. A quantum key distribution light source employing a polarization encoding apparatus as claimed in any one of claims 1 to 4, wherein the light source comprises a pulse generator, a laser, an intensity modulator, a polarization encoding apparatus and an attenuator; wherein the content of the first and second substances,
the pulse generator is used for sending out a specific pulse signal so as to respectively drive the laser, the intensity modulator and the polarization encoding device;
the laser emits periodic narrow light pulse signals under the driving of periodic electric pulses generated by the pulse generator;
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 and a vacuum state, which are required by quantum key distribution;
the optical signal after intensity modulation enters a polarization coding device, the polarization coding device adopts the polarization coding device as claimed in any one of claims 1 to 4, a pulse generator respectively generates two-channel voltage pulse signals with binary amplitudes, the two-channel voltage pulse signals respectively act on a first-stage Sagnac ring and a second-stage Sagnac ring of the polarization coding device to modulate the input narrow optical pulse signals, and four polarization states of +, -, L, R required by quantum key distribution are generated;
and the optical signal after the polarization coding is finished is attenuated to the single photon magnitude required by the quantum key distribution and then output after passing through the attenuator.
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| CN114338020B (en) * | 2022-03-15 | 2022-06-24 | 浙江九州量子信息技术股份有限公司 | Quantum key distribution coding device |
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