Polarization controlling encoding method, encoder and quantum key dispatching system

[0035] Example 1:

[0036] The first composition structure of the polarization control encoder in the quantum key distribution system of the present invention is as figure 1 Shown: It is composed of two 2×2 3dB polarization-maintaining beam splitters 3 and 6, a polarization-maintaining phase modulator 5 and a polarization-maintaining delay line 4, which together form a polarization-maintaining Mach-Zenter interferometer. One of the two ports 1 and 2 on one side of the 3dB polarization-maintaining beam splitter 3 is used as the input end of the polarization control encoder, and one of the two ports 7 and 8 on the other side of the 3dB polarization-maintaining beam splitter 6 is used as the output end. , The polarization-maintaining phase modulator 5 and the polarization-maintaining delay line 4 (in any order) are inserted into either arm of the above-mentioned Mach-Zehnder interferometer, or both are inserted into the two arms of the above-mentioned Mach-Zehnder interferometer. In operation, the optical pulse enters the polarization-maintaining beam splitter 3 through port 1 or 2 of the polarization-maintaining beam splitter 3 and is divided into two paths. One path is phase-modulated by the polarization-maintaining phase modulator 5, and the other path is extended by the polarization-maintaining delay line 4. At this time, the two relatively delayed paths are combined by the polarization-maintaining beam splitter 6 into a routing port 7 or 8 for output. Because all optical paths are polarization-maintaining optical paths, the polarization states of the two pulses output from this are the same. When the polarization-maintaining phase modulator 5 and the polarization-maintaining delay line 4 are located in the same arm of the polarization-maintaining Mach-Zenter interferometer, the above result is not affected.

[0037] Example 2:

[0038] The second composition structure of the polarization control encoder in the quantum key distribution system of the present invention is as follows: figure 2 Shown: it is composed of a 2×2 3dB polarization-maintaining beam splitter 11, two mirrors 13 and 15, a polarization-maintaining phase modulator 12 and a polarization-maintaining delay line 14. The two ports 9 and 10 on one side of the 3dB polarization-maintaining beam splitter 11 can be used as the input and output ends of the polarization control encoder. One of the two ports on the other side of the 3dB polarization-maintaining beam splitter 11 is connected to the polarization-maintaining in turn The phase modulator 12 and the mirror 13, the other port on the same side is connected to the polarization maintaining delay line 14 and the mirror 15 in sequence. A slightly changed but functionally identical structure is to connect the polarization maintaining delay line 14 to the polarization maintaining phase The modulator 12 (regardless of order) is connected in series at the same port at the same time, while the other port is connected to only one mirror. In operation, the light pulse enters the polarization-maintaining beam splitter 11 through port 9 of the polarization-maintaining beam splitter 11 and is divided into two paths. One path is delayed by the polarization-maintaining delay line 14 and reflected by the reflector 15, and the other path is phase-maintained by the polarization. The modulator 12 undergoes phase modulation and then is reflected by the mirror 13, the reflected two optical pulses are combined by the polarization-maintaining beam splitter 11 into a routing port 10 for output. Because all optical paths are polarization-maintaining optical paths, the output from 10 is The polarization states of the two pulses are the same. When the polarization-maintaining delay line 14 and the polarization-maintaining phase modulator 12 (regardless of the order) are serially connected to the same port, and the other port is connected to only one mirror, the above result is not affected. The optical pulse is input from port 10 and output from port 9 is the same as when port 9 or 10 is used as input and output at the same time.

[0039] Example 3:

[0040] The third composition structure of the polarization control encoder in the quantum key distribution system of the present invention is as image 3 Shown: it consists of a 2×2 3dB beam splitter 18, two 90-degree rotating Faraday mirrors 20 and 22, a phase modulator 19 and a delay line 21. The two ports 16 and 17 on one side of the 3dB beam splitter 18 are respectively used as the input and output ends of the polarization control encoder. One of the two ports on the other side of the 3dB beam splitter 18 is connected to the phase modulator 19 and 90 degrees in turn. The Faraday mirror 20 is rotated, and the other port on the same side is connected to the delay line 21 and the 90-degree rotating Faraday mirror 22 in sequence. During operation, the light pulse enters the beam splitter 18 through the port 16 of the beam splitter 18 and is divided into two paths. One path is delayed by the delay line 21, reflected by the 90-degree rotating Faraday mirror 22, and the other path is performed by the phase modulator 19. After phase modulation, they are reflected by the 90-degree rotating Faraday mirror 20, and the reflected two optical pulses are combined by the beam splitter 18 into a routing port 17 for output. Because the two optical paths are both reflected by the 90-degree rotating Faraday mirror and undergo their respective The optical path is even number of times, so the polarization states of the two pulses output from this are the same. The optical pulse is input from port 17 and output from port 16 is the same as when port 16 or 17 is used as input and output at the same time.