A quantum-classical signal co-fiber transmission device

Abstract

This invention relates to a quantum-classical signal co-fiber transmission device, comprising: a first classical signal transmitter transmitting a classical signal to a first channel; a first channel selector transmitting the classical signal from the first channel to a second channel; a second channel selector transmitting the classical signal from the second channel to a fifth channel; a first classical signal receiver receiving the classical signal from the fifth channel; a quantum signal transmitter transmitting a quantum signal to a fourth channel; wherein the quantum signal from the fourth channel is transmitted to the second channel by the second channel selector; the quantum signal from the second channel is transmitted to a third channel by the first channel selector; and a quantum signal receiver receiving the quantum signal from the third channel. This invention automatically eliminates classical noise during co-fiber transmission and requires no modification to the classical and quantum system equipment, making it easy to implement and reducing technical implementation difficulty and production costs.

Description

Technical Field

[0001] This invention relates to the field of quantum and classical signal co-fiber transmission technology, and in particular to a quantum-classical signal co-fiber transmission device. Background Technology

[0002] Currently, the main schemes for co-fiber transmission of quantum and classical signals include wavelength division multiplexing (WDM), time division multiplexing (TDM), and space division multiplexing (SDM). Among them, WDM utilizes wavelength freedom to achieve the multiplexing and demultiplexing of quantum and classical signals based on WDM multiplexers. This co-fiber transmission technology is the most mature and widely used. Time division multiplexing utilizes time freedom, based on precise control of transmission time, to achieve the transmission of quantum and classical signals at different times in the same optical fiber. This scheme is the most complex to implement because it requires significant modifications to both quantum and classical communication equipment and necessitates tight coupling between the two. Space division multiplexing utilizes spatial freedom, using few-mode or multi-core optical fibers to couple quantum and classical signals into the same fiber. The practical application of this scheme depends on the large-scale deployment of few-mode or multi-core optical fibers. The main drawbacks of existing quantum-classical co-fiber transmission schemes are: (1) Wavelength division multiplexing scheme: requires significant modifications to classical equipment, quantum equipment, and optical devices, and requires quantum signals and classical signals to have different wavelengths; (2) Time division multiplexing scheme: requires stable and precise control of the transmission and reception timing of quantum and classical signals, which is particularly difficult to implement for high-speed systems. It also involves significant modifications to the equipment; (3) Space division multiplexing scheme: requires replacing the already widely deployed standard single-mode fiber with few-mode fiber or multi-core fiber, involving significant modifications to the optical transmission line medium.

[0003] Since time-division multiplexing (TDM) and space-division multiplexing (SDM) schemes are rarely used in practical applications, this patent focuses on analyzing wavelength-division multiplexing (WDM) schemes. For WDM co-fiber transmission schemes, crosstalk noise, spontaneous Raman scattering noise, and four-wave mixing noise generated by classical signals transmitted in the same fiber can significantly impact the signal-to-noise ratio (SNR) of quantum communication systems. Measures are needed to suppress these classical noises (i.e., noise generated by the interaction between classical signals and the optical fiber). For example, existing schemes employ noise reduction methods such as reducing the transmission power of classical signal light, optimizing wavelength allocation, adding narrowband filters, and reducing the gate width of single-photon detectors. However, these noise reduction solutions typically require modifications to classical communication equipment, quantum communication equipment, and optical devices. For example, reducing the transmitted optical power of classical signals requires adding an adjustable optical attenuator to the transmitter of classical communication equipment and an optical amplifier to the receiver, which necessitates modifying the optical power control unit in classical communication equipment. Adding a narrowband filter requires adding an optical filter before the receiver of quantum communication equipment. Reducing the gate width of a single-photon detector requires modifying the gating circuit of the single-photon detector in quantum communication equipment. Optimizing wavelength allocation requires modifying a standard wavelength division multiplexer to support optical devices with specific input wavelengths. All of these factors increase the technical difficulty and cost of co-fiber transmission of quantum signals and classical signals. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a quantum-classical signal co-fiber transmission device that can automatically immunize classical noise during co-fiber transmission, and does not require modification of classical and quantum system equipment, is easy to implement, and reduces the difficulty of technical implementation and production costs.

[0005] According to the technical solution provided by the present invention, the quantum-classical signal co-fiber transmission device includes:

[0006] The first classical signal transmitter transmits the first classical signal to the first channel;

[0007] The first channel selector transmits the first classical signal in the first channel to the second channel;

[0008] The second channel selector transmits the first classical signal in the second channel to the fifth channel;

[0009] The first classical signal receiver receives the first classical signal in the fifth channel;

[0010] A quantum signal transmitter transmits quantum signals to the fourth channel;

[0011] The quantum signal in the fourth channel is transmitted to the second channel by the second channel selector; the quantum signal in the second channel is transmitted to the third channel by the first channel selector.

[0012] A quantum signal receiver receives quantum signals from the third channel;

[0013] The second classical signal transmitter transmits the second classical signal.

[0014] The second classical signal receiver receives the second classical signal.

[0015] In one embodiment of the present invention, both the first channel selector and the second channel selector include three ports. The three ports of the first channel selector are respectively connected to the first channel, the second channel and the third channel, and the three ports of the second channel selector are respectively connected to the second channel, the fourth channel and the fifth channel.

[0016] In one embodiment of the present invention, a first dichroic mirror is further included, which is connected between the first channel selector and the quantum signal transmitter.

[0017] In one embodiment of the present invention, the wavelength of the quantum signal is within the transmission wavelength range of the first dichroic mirror.

[0018] In one embodiment of the present invention, the first classical signal transmitter and the quantum signal receiver are located on the same side of the second transmission channel, and the first classical signal receiver and the quantum signal transmitter are located on the other side of the second transmission channel.

[0019] In one embodiment of the present invention, the second channel is a co-fiber channel, which is fabricated from single-mode optical fiber.

[0020] In one embodiment of the present invention, both the first channel selector and the second channel selector are optical circulators.

[0021] In one embodiment of the invention, an optical filter is further included, which is connected between the first channel selector and the quantum signal transmitter.

[0022] In one embodiment of the present invention, the wavelength of the quantum signal is within the transmission wavelength range of the optical filter.

[0023] The present invention also provides a quantum-classical signal co-fiber transmission device, comprising:

[0024] The first classical signal transmitter transmits the first classical signal to the first channel;

[0025] The first channel selector transmits the first classical signal in the first channel to the third dichroic mirror;

[0026] The second dichroic mirror transmits the first classical signal from the third dichroic mirror through the second channel and then transmits it to the second dichroic mirror.

[0027] The second channel selector transmits the first classical signal transmitted through the second dichroic mirror to the fifth channel;

[0028] The first classical signal receiver receives the first classical signal in the fifth channel;

[0029] A quantum signal transmitter transmits quantum signals to the fourth channel;

[0030] The quantum signal in the fourth channel is transmitted to the second dichroic mirror by the second channel selector; the quantum signal is transmitted to the second channel after passing through the second dichroic mirror; the quantum signal in the second channel is transmitted to the third channel by the first channel selector after passing through the third dichroic mirror.

[0031] A quantum signal receiver receives quantum signals from the third channel;

[0032] The second classical signal transmitter transmits a second classical signal to the second dichroic mirror, and the second classical signal is reflected by the second dichroic mirror to the second channel;

[0033] The second classical signal receiver receives the second classical signal reflected by the third dichroic mirror in the second channel.

[0034] The technical solution of the present invention has the following advantages compared with the prior art:

[0035] 1. Configure the first and second channel selectors to automatically immunize against crosstalk noise and forward spontaneous Raman scattering noise during co-fiber transmission;

[0036] 2. The first dichroic mirror is set to automatically select the direction of light transmission based on wavelength, and automatically eliminates reverse spontaneous Raman scattering noise and four-wave mixing noise.

[0037] 3. Achieve co-fiber transmission of quantum and classical signals based on path degrees of freedom; no human intervention is required, and the main classical noise intensity can be suppressed to the minimum in principle. Compared with existing solutions, no modification is required to the classical and quantum system equipment, which is easy to implement and reduces the difficulty of technical implementation and production costs.

[0038] 4. In the co-fiber transmission of the device of the present invention, the quantum signal and the classical signal can have the same wavelength or different wavelengths. Attached Figure Description

[0039] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0040] Figure 1This is a schematic diagram of the structure of one embodiment of the quantum-classical signal co-fiber transmission device of the present invention;

[0041] Figure 2 This is a schematic diagram of another embodiment of the quantum-classical signal co-fiber transmission device of the present invention. Detailed Implementation

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0043] Example 1:

[0044] Reference Figure 1 As shown, in order to achieve co-fiber transmission of quantum-classical signals without modifying quantum and classical communication devices, and to automatically immunize against crosstalk noise and forward spontaneous Raman scattering noise during co-fiber transmission, the present invention includes:

[0045] The first classical signal transmitter transmits the first classical signal to the first channel;

[0046] The first channel selector transmits the first classical signal in the first channel to the second channel;

[0047] The second channel selector transmits the first classical signal in the second channel to the fifth channel;

[0048] The first classical signal receiver receives the first classical signal in the fifth channel;

[0049] A quantum signal transmitter transmits quantum signals to the fourth channel;

[0050] The quantum signal in the fourth channel is transmitted to the second channel by the second channel selector; the quantum signal in the second channel is transmitted to the third channel by the first channel selector.

[0051] A quantum signal receiver receives quantum signals from the third channel;

[0052] The second classical signal transmitter transmits the second classical signal.

[0053] The second classical signal receiver receives the second classical signal.

[0054] Both the first channel selector and the second channel selector are optical circulators.

[0055] Both the first channel selector and the second channel selector include three ports. The three ports of the first channel selector are connected to the first channel, the second channel, and the third channel, respectively. The three ports of the second channel selector are connected to the second channel, the fourth channel, and the fifth channel, respectively.

[0056] Specifically, taking the two-fiber bidirectional system commonly used in classical optical communication as an example, this illustrates how quantum signals can be transmitted along the same fiber as classical signals in one of the fibers. Figure 1 As shown, TX1 represents the first classical signal transmitter, RX1 represents the first classical signal receiver, CIR1 represents the first channel selector, CIR2 represents the second channel selector, QKD-T represents the quantum signal transmitter, and QKD-R represents the quantum signal receiver. The classical signal is a two-fiber, bidirectional system, with one transmitter and one receiver on each side. Without loss of generality, the quantum signal and the first classical signal in the fiber below are transmitted together. The quantum signal receiver QKD-R is on the same side as the first classical signal transmitter TX1, and the quantum signal transmitter QKD-T is on the same side as the first classical signal receiver RX1. According to the working principle of an optical circulator, it only allows unidirectional transmission, i.e., from 1->2->3. The optical circulator selects to separate or couple the classical / quantum signals based on the transmission direction of the two optical signals, enabling the quantum and classical signals to be transmitted in the same fiber without affecting the normal operation of their respective devices.

[0057] Classical Communication: The first classical signal transmitter TX1 transmits the first classical signal and inputs it into one port of the first optical circulator CIR1. Then, it enters the quantum-classical signal co-fiber through the other port, i.e., into the second channel. It is transmitted through the optical fiber to one port of the second optical circulator CIR2, and then outputs from the other port to the first classical signal receiver RX1, completing the classical communication process.

[0058] Quantum communication: The quantum signal transmitter QKD-T emits a quantum signal and inputs it into the second optical circulator CIR2, then into the optical fiber containing both quantum and classical signals, i.e., into the second channel. The signal is then transmitted through the fiber to the first optical circulator CIR1, and finally output to the quantum signal receiver QKD-R, completing the quantum communication process.

[0059] In this context, the wavelengths of quantum signals and classical signals can be the same or different.

[0060] The aforementioned co-fiber transmission device can achieve automatic immunity to crosstalk noise: the characteristic of an optical circulator is its unidirectional nature, meaning that a signal input from the first port can only be output from the second port, and similarly, a signal input from the second port can only be output from the third port. Therefore, automatic immunity to crosstalk noise is achieved through path selection.

[0061] The aforementioned co-fiber transmission device can achieve automatic immunity to forward spontaneous Raman scattering noise: this is divided into forward spontaneous Raman scattering and backward spontaneous Raman scattering noise, where forward refers to noise propagation in the same direction as the classical signal, and backward refers to noise propagation in the opposite direction to the classical signal. For forward spontaneous Raman scattering noise, in Figure 1 Its transmission direction is opposite to that of the quantum signal, and due to the path differentiation of the first optical circulator CIR1, the forward spontaneous Raman scattering noise generated between the first classical signal transmitter TX1 and the first optical circulator CIR1 will naturally not enter the quantum signal receiver QKD-R from the first optical circulator CIR1, thus achieving automatic immunity to forward spontaneous Raman scattering noise through path selection.

[0062] Furthermore, in order to automatically immunize against reverse spontaneous Raman scattering noise and four-wave mixing noise during co-fiber transmission, the present invention also includes a first dichroic mirror, which is connected between the first channel selector and the quantum signal transmitter.

[0063] The wavelength of the quantum signal is within the transmission wavelength range of the first dichroic mirror.

[0064] Specifically, for reverse spontaneous Raman scattering noise, in Figure 1 Its transmission direction is the same as the quantum signal, and it enters the quantum signal receiver QKD-R through the output of the first circulator CIR1. However, by adding a first dichroic mirror DM1 before the quantum signal receiver QKD-R, light with the same wavelength as the quantum signal can be completely transmitted, while light of other wavelengths is completely reflected. That is, by using the first dichroic mirror based on wavelength path selection, most of the back spontaneous Raman scattering noise can be blocked, thereby achieving automatic immunity to back Raman scattering noise.

[0065] For four-wave mixing noise, assume the classical optical frequency of the co-fiber is v1, and the synchronization optical frequency emitted by the quantum system is v2. Without loss of generality, assume v2 > v1, then there are two frequencies of the generated four-wave mixing noise: v3 = 2v1 - v2 and v4 = 2v1 - v2. If the frequency of the quantum signal is chosen to be different from v3 and v4, then light of the same wavelength as the quantum signal will be transmitted through the first dichroic mirror DM1, while noise light of different wavelengths will be reflected. This completely and automatically isolates the four-wave mixing noise from the quantum signal receiver QKD-R, thus achieving automatic immunity against the four-wave mixing noise.

[0066] Furthermore, the first dichroic mirror can be set to be immune to reverse spontaneous Raman scattering noise and four-wave mixing noise, or the optical filter can be set to be immune to reverse spontaneous Raman scattering noise and four-wave mixing noise.

[0067] The table below compares the ease of implementation of different noise reduction schemes and their impact on the modification of quantum / classical communication devices.

[0068]

[0069] The analysis of the table above shows that the solution of this invention is not only easy to implement, but also has no impact on the modification of quantum / classical communication equipment, belonging to the category of modification-free co-fiber transmission solutions. Furthermore, although solution 2 in the table is also easy to implement and has minimal impact, it needs to be used in conjunction with other solutions to achieve good results, and it cannot effectively suppress in-band classical noise. In contrast, the solution of this invention can be used alone and can effectively suppress most in-band classical noise.

[0070] Example 2:

[0071] like Figure 2 As shown, to enable co-fiber transmission of quantum signals and classical signals from two fibers in a bidirectional two-fiber classical signal transmission, the present invention includes:

[0072] The first classical signal transmitter transmits the first classical signal to the first channel;

[0073] The first channel selector transmits the first classical signal in the first channel to the third dichroic mirror;

[0074] The second dichroic mirror transmits the first classical signal from the third dichroic mirror through the second channel and then transmits it to the second dichroic mirror.

[0075] The second channel selector transmits the first classical signal transmitted through the second dichroic mirror to the fifth channel;

[0076] The first classical signal receiver receives the first classical signal in the fifth channel;

[0077] A quantum signal transmitter transmits quantum signals to the fourth channel;

[0078] The quantum signal in the fourth channel is transmitted to the second dichroic mirror by the second channel selector; the quantum signal is transmitted to the second channel after passing through the second dichroic mirror; the quantum signal in the second channel is transmitted to the third channel by the first channel selector after passing through the third dichroic mirror.

[0079] A quantum signal receiver receives quantum signals from the third channel;

[0080] The second classical signal transmitter transmits a second classical signal to the second dichroic mirror, and the second classical signal is reflected by the second dichroic mirror to the second channel;

[0081] The second classical signal receiver receives the second classical signal reflected by the third dichroic mirror in the second channel.

[0082] Specifically, Figure 2 The difference lies in the addition of two dichroic mirrors, DM2 and DM3, which enable both the first classical signal and the second classical signal to be transmitted along the same fiber as the quantum signal. The transmission wavelength ranges of the second dichroic mirror DM2 and the third dichroic mirror DM3 are selected such that the wavelengths of the first classical signal between the first classical signal transmitter Tx1 and the first classical signal receiver Rx1 can transmit along with the wavelengths of the quantum signal, while the wavelengths of the second classical signal between the second classical signal transmitter Tx2 and the second classical signal receiver Rx2 are reflected when passed through the second dichroic mirror DM2 and the third dichroic mirror DM3.

[0083] Classical Communication: The first classical signal transmitter Tx1 transmits a classical signal, which is input to one port of the first optical channel selector CIR1. The signal then travels from the other port through the third dichroic mirror DM3, and into the co-fiber of the quantum and classical signals. It is then transmitted through the fiber to the second dichroic mirror DM2 on the side of the first classical signal receiver Rx1, where it is transmitted through the second channel selector CIR2. Finally, the output of the second channel selector CIR2 reaches the first classical signal receiver Rx1.

[0084] The second classical communication transmitter Tx2 emits a second classical signal, which is reflected by the second dichroic mirror DM2. After reflection, the signal enters the optical fiber containing both quantum and classical signals. It is then transmitted through the optical fiber to the second classical signal receiver Rx2, where it is reflected by the third dichroic mirror DM3, completing the classical communication process.

[0085] Quantum communication: The quantum signal transmitter QKD-T emits a quantum signal and inputs it to the second channel selector CIR2. The signal is then transmitted through the second dichroic mirror DM2 and into the co-fiber of the quantum and classical signals. It is then transmitted through the fiber to the third dichroic mirror DM3 on the same side as the quantum signal receiver, transmitted through it, and enters the first channel selector CIR1. The signal is then output from the first channel selector CIR1, transmitted through the first dichroic mirror DM1, and finally enters the quantum signal receiver QKD-R, completing the quantum communication process.

[0086] In this case, the wavelength of the quantum signal can be the same as that of the first classical signal.

[0087] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A quantum-classical signal co-fiber transmission device, characterized in that, include: The first classical signal transmitter transmits the first classical signal to the first channel; The first channel selector transmits the first classical signal in the first channel to the second channel; The second channel selector transmits the first classical signal in the second channel to the fifth channel; The first classical signal receiver receives the first classical signal in the fifth channel; A quantum signal transmitter transmits quantum signals to the fourth channel; The quantum signal in the fourth channel is transmitted to the second channel by the second channel selector; the quantum signal in the second channel is transmitted to the third channel by the first channel selector; both the first channel selector and the second channel selector include three ports, the three ports of the first channel selector are respectively connected to the first channel, the second channel and the third channel, and the three ports of the second channel selector are respectively connected to the second channel, the fourth channel and the fifth channel; A quantum signal receiver receives quantum signals from the third channel; A first dichroic mirror is connected between the first channel selector and the quantum signal receiver; The second classical signal transmitter transmits the second classical signal. The second classical signal receiver receives the second classical signal.

2. The quantum-classical signal co-fiber transmission device according to claim 1, characterized in that: The wavelength of the quantum signal is within the transmission wavelength range of the first dichroic mirror.

3. The quantum-classical signal co-fiber transmission device according to claim 1, characterized in that: The first classical signal transmitter and the quantum signal receiver are located on the same side of the second channel, and the first classical signal receiver and the quantum signal transmitter are located on the other side of the second channel.

4. The quantum-classical signal co-fiber transmission device according to claim 1, characterized in that: The second channel is a co-fiber channel, which is made of single-mode optical fiber.

5. The quantum-classical signal co-fiber transmission device according to claim 1, characterized in that: Both the first channel selector and the second channel selector are optical circulators.

6. The quantum-classical signal co-fiber transmission device according to claim 1, characterized in that: It also includes an optical filter connected between the first channel selector and the quantum signal transmitter.

7. The quantum-classical signal co-fiber transmission device according to claim 6, characterized in that: The wavelength of the quantum signal is within the transmission wavelength range of the optical filter.

8. A quantum-classical signal co-fiber transmission device, characterized in that, include: The first classical signal transmitter transmits the first classical signal to the first channel; The first channel selector transmits the first classical signal in the first channel to the third dichroic mirror; The second dichroic mirror transmits the first classical signal from the third dichroic mirror through the second channel and then through the second dichroic mirror. The second channel selector transmits the first classical signal transmitted through the second dichroic mirror to the fifth channel; The first classical signal receiver receives the first classical signal in the fifth channel; A quantum signal transmitter transmits quantum signals to the fourth channel; The quantum signal in the fourth channel is transmitted to the second dichroic mirror by the second channel selector; the quantum signal is transmitted to the second channel after passing through the second dichroic mirror; and the quantum signal in the second channel is transmitted to the third channel by the first channel selector after passing through the third dichroic mirror. A quantum signal receiver receives quantum signals from the third channel; The first dichroic mirror transmits the output of the first channel selector to the quantum signal receiver; The second classical signal transmitter transmits a second classical signal to the second dichroic mirror, and the second classical signal is reflected by the second dichroic mirror to the second channel; The second classical signal receiver receives the second classical signal reflected by the third dichroic mirror in the second channel.

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