A quantum key distribution light source

Abstract

A quantum key distribution light source comprises: a laser (1) for generating an optical pulse signal; a filter (2) for performing narrow-band filtering on the optical pulse signal to obtain a narrow optical pulse signal, wherein the filter (2) is an FP cavity filter; an intensity modulator (3) for performing intensity modulation on the narrow optical pulse signal to generate an intensity state required for quantum key distribution; a polarization modulator (4) for performing polarization modulation on the intensity state to generate four orthogonal polarization states required for quantum key distribution; an attenuator (5) for performing energy attenuation on the four orthogonal polarization states; and a pulse generator (6) for generating a driving pulse signal to drive the laser (1), the intensity modulator (3) and the polarization modulator (4). The quantum key distribution light source can realize a narrow linewidth quantum key distribution light source with a linewidth of about 10 pm.

Description

Technical Field

[0001] The invention relates to the field of quantum communication, and in particular to a quantum key distribution light source. Background Art

[0002] Quantum key distribution uses single photons to load polarization information for transmission. It cannot amplify the signal like optical communication, and the quantum light signal received at the receiving end is very weak. It is necessary to improve the signal-to-noise ratio of the system by reducing background noise to complete effective security coding. In long-distance satellite-to-ground quantum communication systems, the key to successfully realizing quantum key distribution in a high-noise environment is to effectively suppress environmental background noise through optical filtering.

[0003] In existing quantum key distribution systems, especially in free space and satellite-to-ground quantum key distribution systems, the quantum key distribution light source at the transmitter generally uses a gain switch-based method to drive the semiconductor laser to generate light pulses. The line width of the optical signal is about 0.1nm, and no additional spectral filtering is performed. In order to achieve system filtering with a narrower line width (about 10pm), the line width of the quantum key distribution light source must first be much lower than 0.1nm, so that the corresponding filter can be used for filtering at the receiving end, and finally the line width requirement of the system can be met. Existing optical filters, generally including coherent filters, grating-based filters or atomic filters, are difficult to meet the application requirements of narrow line width quantum key distribution light sources. Coherent filters and grating-based filters are difficult to achieve a line width of 10pm or less. Although atomic filtering technology can achieve ultra-narrowband filtering, and the filtering line width can reach several pm, it is only applicable to specific atomic spectral lines and has a narrow application range; at the same time, since atomic filtering technology is polarization-dependent, it is difficult to be applied in polarization-encoded quantum key distribution systems. Summary of the invention

[0004] 1. Technical issues

[0005] In view of the problems existing in the prior art, the present invention proposes a quantum key distribution light source for at least partially solving the above technical problems.

[0006] (II) Technical solution

[0007] The present invention provides a quantum key distribution light source, comprising: a laser 1, used to generate an optical pulse signal; a filter 2, used to perform narrow-band filtering on the optical pulse signal to obtain a narrow optical pulse signal, wherein the filter 2 is an FP cavity filter; an intensity modulator 3, used to perform intensity modulation on the narrow optical pulse signal to generate an intensity state required for quantum key distribution; a polarization modulator 4, used to perform polarization modulation on the intensity state to generate four orthogonal polarization states required for quantum key distribution; an attenuator 5, used to perform energy attenuation on the four orthogonal polarization states; and a pulse generator 6, used to generate a driving pulse signal to drive the laser 1, the intensity modulator 3 and the polarization modulator 4.

[0008] Optionally, the filter 2 includes: an input collimator 21, used to expand the optical pulse signal and transmit it through free space; an FP cavity 22, used to perform narrow-band filtering on the optical pulse signal transmitted by the input collimator 21 to obtain the narrow optical pulse signal; a semiconductor refrigerator 23, used to control the ambient temperature of the FP cavity 22; a thermistor 24, used to collect the ambient temperature; and an output collimator 25, used to output the filtered narrow optical pulse signal.

[0009] Optionally, the input collimator 21 and the output collimator 25 are optical fiber collimators, and the semiconductor cooler 23 is a semiconductor cooler based on the Peltier effect.

[0010] Optionally, the thermistor 24 and the FP cavity 22 are integrated on the semiconductor refrigerator 24 .

[0011] Optionally, the filter 2 and the intensity modulator 3 as well as the intensity modulator 3 and the polarization modulator 4 are connected via polarization-maintaining optical fibers.

[0012] Optionally, the pulse generator 6 is connected to the laser 1 , the intensity modulator 3 , and the polarization modulator 4 respectively through radio frequency cables.

[0013] Optionally, the polarization modulator 4 and the attenuator 5 are connected via a single-mode optical fiber.

[0014] Optionally, the intensity modulator 3 is an intensity modulator based on lithium niobate crystal.

[0015] Optionally, the polarization modulator 4 is a polarization modulator based on lithium niobate crystal or gallium arsenide material.

[0016] Optionally, the attenuator 5 is an electro-optical variable attenuator.

[0017] (III) Beneficial effects

[0018] The present invention provides a quantum key distribution light source, which generates light pulses by driving a semiconductor laser through a pulse generator, and filters the light signal with an FP cavity filter, thereby generating a light signal with a narrower linewidth, and finally realizing a quantum key distribution light source with a linewidth of about 10pm. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For a more complete understanding of the present invention and its advantages, reference will now be made to the following description taken in conjunction with the accompanying drawings, in which:

[0020] Figure 1 A schematic diagram of a structure of a quantum key distribution light source according to an embodiment of the present invention is shown;

[0021] Figure 2 The structure of a quantum key distribution light source according to another embodiment of the present invention is schematically shown.

[0022] [Reference Signs]

[0023] 1-Laser

[0024] 2-Filter

[0025] 21-Input collimator

[0026] 22-FP cavity

[0027] 23-Semiconductor Refrigerator

[0028] 24-Thermistor

[0029] 25-Output collimator

[0030] 3-Intensity Modulator

[0031] 4-Polarization Modulator

[0032] 5-Attenuator

[0033] 6-Pulse Generator DETAILED DESCRIPTION

[0034] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0035] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0036] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0037] Figure 1 The structure of a quantum key distribution light source according to an embodiment of the present invention is schematically shown. Figure 1 As shown, the quantum key distribution light source includes:

[0038] The laser 1 is used to generate an optical pulse signal.

[0039] Filter 2 is used to perform narrow-band filtering on the optical pulse signal to obtain a narrow optical pulse signal, wherein filter 2 is a Fabry-Perot cavity filter (FP cavity filter).

[0040] FP cavity filter is one of the important devices in modern fiber optic communication and fiber optic sensing. The FP cavity is generally composed of a glass plate with a high reflective film on the inner surface and an anti-reflective film on the outer surface. The incident light beam can produce a multi-beam interference effect in the cavity, and the light waves that meet the phase matching conditions produce constructive interference to form a filter output. The light waves that do not meet the phase conditions produce destructive interference and are reflected and output by one side of the FP cavity. By optimizing the parameter design of the FP cavity, a FP cavity narrowband filter with high transmittance and narrow linewidth can be achieved. Compared with other filters based on atomic filtering, grating filtering, etc., the FP cavity filter can achieve the advantages of a wide range of working filter segments, tunable central wavelength, narrow filter linewidth, and high optical efficiency.

[0041] The intensity modulator 3 is used to perform intensity modulation on the narrow optical pulse signal to generate the intensity state required for quantum key distribution.

[0042] The polarization modulator 4 is used to perform polarization modulation on the intensity state to generate four orthogonal polarization states required for quantum key distribution.

[0043] The attenuator 5 is used to attenuate the energy of four orthogonal polarization states.

[0044] The pulse generator 6 is used to generate a specific driving pulse signal to drive the laser 1 , the intensity modulator 3 and the polarization modulator 4 .

[0045] Specifically, the working process of the quantum key distribution light source is as follows: driven by the pulse signal generated by the pulse generator 6, the laser 1 generates an optical pulse signal, which is coupled and output after spectral filtering by the filter 2 to generate an optical pulse signal with a narrow line width. Under the action of the pulse signal generated by the pulse generator 6, the intensity modulator 3 modulates the intensity of the narrow optical pulse signal output by the filter 2 to generate three intensity states required for quantum key distribution, namely, the signal state, the decoy state, and the vacuum state. Under the action of the pulse signal generated by the pulse generator 6, the polarization modulator 4 polarization modulates the optical signal output by the intensity modulator 3 to generate four orthogonal polarization states required for quantum key distribution. The attenuator 5 is used to attenuate the energy of the four orthogonal polarization states and output them after attenuation to the single photon level required for quantum key distribution, so as to realize a narrow line width quantum key distribution light source with a line width of about 10pm.

[0046] Figure 2 The structure of a quantum key distribution light source according to another embodiment of the present invention is schematically shown. Figure 2 As shown, the quantum key distribution light source includes:

[0047] Laser 1, filter 2, intensity modulator 3, polarization modulator 4, attenuator 5 and pulse generator 6.

[0048] The pulse generator 6 is used to send out specific pulse signals to drive the laser 1, the intensity modulator 3, and the polarization modulator 4 respectively.

[0049] The laser 1 is used to emit a periodic optical pulse signal under the drive of the periodic electrical pulse generated by the pulse generator; the laser can be, for example, a high-bandwidth distributed feedback laser (DFB) or a vertical cavity surface emitting laser (VCSEL). The time width of the laser output optical pulse is less than 100ps, and the spectral line width is generally less than 0.1nm.

[0050] The filter 2 is used for spectrally filtering the optical pulse signal emitted by the laser 1.

[0051] Specifically, the filter 2 includes an input collimator 21, an FP cavity 22, a semiconductor cooler 23, a thermistor 24 and an output collimator 25. The input collimator 21 is used to expand the optical pulse signal and transmit it through free space. The FP cavity 22 is used to perform narrow-band filtering on the optical pulse signal transmitted by the input collimator 21 to obtain a narrow optical pulse signal and transmit it through free space. The semiconductor cooler 23 is used to control the ambient temperature of the FP cavity 22; the thermistor 24 is used to collect the ambient temperature. The output collimator 25 is used to couple and output the above-mentioned narrow optical pulse signal. Among them, the FP cavity 22 and the thermistor 24 are both integrated on the semiconductor cooler 23.

[0052] The input collimator 21 and the output collimator 25 may be, for example, G-lens fiber collimators, but the present invention does not limit this.

[0053] The semiconductor cooler 23 may be, for example, a semiconductor cooler based on the Peltier effect, but the present invention does not impose any specific limitation thereto.

[0054] The thermistor 24 may be, for example, a thermistor with a negative temperature coefficient or a positive temperature coefficient, which is not specifically limited in the present invention.

[0055] The intensity modulator 3 is used to modulate the narrow optical pulse signal output by the filter 2 under the action of the random pulse generated by the pulse generator 6, and generate three intensity states such as the signal state, the decoy state, and the vacuum state required for quantum key distribution. The intensity modulator 3 can, for example, be an intensity modulator based on a lithium niobate crystal with a bandwidth of more than 10 GHz. The pulse generator 6 generates three electrical pulse signals with different voltage amplitudes to drive the intensity modulator 3. By adjusting the DC bias of the intensity modulator 3, when the pulse generator 6 is loaded with a vacuum state electrical pulse signal, the maximum extinction is achieved, with a value of -30 dB; when the pulse generator 6 is loaded with a signal state electrical pulse signal, the minimum extinction is achieved, with a value of 0 dB; when the pulse generator 6 is loaded with a decoy state electrical pulse signal, a specific value of extinction is achieved, with a value of -6 dB.

[0056] The narrow optical pulse signal after intensity modulation by the intensity modulator 3 enters the polarization modulator 4. The polarization modulator 4 is used to modulate the input narrow optical pulse signal under the action of the random pulse generated by the pulse generator 6, and generate the four polarization states of +, -, L, and R required for quantum key distribution. The polarization controller 4 can, for example, use a polarization modulator based on lithium niobate crystal or gallium arsenide material with a bandwidth of more than 10 GHz. The pulse generator 6 generates four electrical pulse signals with different voltage amplitudes, which correspond to the four specific voltage values ​​of the polarization modulator, namely 0, Vπ / 2, Vπ, and 3Vπ / 2, and can generate four polarization states of +, -, L, and R.

[0057] The attenuator 5 is capable of receiving the intensity modulated and polarization modulated optical signal, and outputting the optical signal after attenuating it to the single photon level required for quantum key distribution. The attenuator 5 may be, for example, an electro-optical variable attenuator, and a DC voltage is used to control the attenuation of the attenuator. Typically, the average number of photons per pulse of the attenuated optical signal is generally between 0.1 and 1.

[0058] In the embodiment of the present invention, the pulse generator 6 is connected to the laser 1, the intensity modulator 3 and the polarization modulator 4 via a radio frequency cable; the laser 1 is connected to the filter 2 (input collimator 21) using a polarization-maintaining optical fiber; the filter 2 (output collimator 25) is connected to the intensity modulator 3 using a polarization-maintaining optical fiber; the intensity modulator 3 is connected to the polarization modulator 4 using a polarization-maintaining optical fiber; and the polarization modulator 4 is connected to the attenuator 5 using a single-mode optical fiber.

[0059] The quantum key distribution light source of this embodiment can realize narrow linewidth quantum key distribution with a linewidth of about 10pm.

[0060] It will be appreciated by those skilled in the art that, although the present invention has been shown and described with reference to specific exemplary embodiments of the present invention, it will be appreciated by those skilled in the art that, without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents, various changes in form and detail may be made to the present invention. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be determined not only by the appended claims, but also by the equivalents of the appended claims.

Claims

1. A quantum key distribution light source, which realizes a narrow linewidth quantum key distribution light source with a linewidth of the order of 10 pm, comprising: A laser (1) for generating an optical pulse signal; A filter (2) is used to perform narrow-band filtering on the optical pulse signal to obtain a narrow optical pulse signal, wherein the filter (2) is an FP cavity filter; An intensity modulator (3) is used to perform intensity modulation on the narrow optical pulse signal to generate an intensity state required for quantum key distribution; A polarization modulator (4) is used to perform polarization modulation on the intensity state to generate four orthogonal polarization states required for quantum key distribution; An attenuator (5), used for attenuating energy of the four orthogonal polarization states; a pulse generator (6) for generating a driving pulse signal to drive the laser (1), the intensity modulator (3) and the polarization modulator (4), Wherein, the filter (2) comprises: An input collimator (21) is used to expand the optical pulse signal and transmit it through free space; The FP cavity (22) is used to perform narrow-band filtering on the optical pulse signal transmitted by the input collimator (21) to obtain a narrow optical pulse signal; A semiconductor refrigerator (23) for controlling the ambient temperature of the FP chamber (22); A thermistor (24), used for collecting the ambient temperature; An output collimator (25), used for outputting the narrow optical pulse signal; The time width of the laser output light pulse is less than 100ps, and the spectral line width is less than 0.1nm.

2. The quantum key distribution light source according to claim 1, wherein: The input collimator (21) and the output collimator (25) are optical fiber collimators, and the semiconductor cooler (23) is a semiconductor cooler based on the Peltier effect.

3. The quantum key distribution light source according to claim 1, wherein: The thermistor (24) and the FP cavity (22) are integrated on the semiconductor refrigerator (23).

4. The quantum key distribution light source according to claim 1, wherein: The filter (2) and the intensity modulator (3), as well as the intensity modulator (3) and the polarization modulator (4), are connected via polarization-maintaining optical fibers.

5. The quantum key distribution light source according to claim 2, wherein: The pulse generator (6) is respectively connected to the laser (1), the intensity modulator (3), and the polarization modulator (4) via radio frequency cables.

6. The quantum key distribution light source according to claim 1, wherein: The polarization modulator (4) and the attenuator (5) are connected via a single-mode optical fiber.

7. The quantum key distribution light source according to claim 1, wherein: The intensity modulator (3) is an intensity modulator based on lithium niobate crystal or silicon.

8. The quantum key distribution light source according to claim 1, wherein: The polarization modulator (4) is a polarization modulator based on lithium niobate crystal, silicon-based or gallium arsenide material.

9. The quantum key distribution light source according to claim 3, wherein: The attenuator (5) is an electro-optical variable attenuator or a mechanical variable attenuator.

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