Hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3

Abstract

A hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3. At the input end of the LiNbO3 chip, the input optical fiber is connected to a 3dB coupler through a LiNbO3 waveguide. The two output ends of the 3dB coupler are respectively connected to two high-speed phase modulators through LiNbO3 waveguides. At the output end of the LiNbO3 chip, the two high-speed phase modulators are respectively connected to two waveguide coupling regions through LiNbO3 waveguides. At the input end of the PLC chip, two PLC waveguides are respectively connected to two LiNbO3 waveguides in the LiNbO3 chip segment through two waveguide coupling regions. One PLC waveguide is connected to a PLC delay line, and the other PLC waveguide is connected to a thermo-optic phase modulator. The PLC delay line and the thermo-optic phase modulator are respectively connected to two input ends of a directional coupler, and the two output ends of the directional coupler are connected to two output optical fibers. Compared with the prior art, the present invention combines the advantages of LiNbO3 and PLC materials, uses the LiNbO3 material to make high-speed phase modulators, uses the PLC waveguide for low-loss delay, realizes chip-level integration of AMZI, and realizes high-speed phase encoding.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum phase encoding, and particularly to a hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3. Background Art

[0002] Quantum information technology originated in the 1980s and is mainly divided into two major research directions: quantum communication and quantum computing. With the continuous progress of science and technology, due to the limitations of the underlying basic principles of classical information-based encryption technology, there are inherent security risks. Quantum secure communication has unconditional physical security due to the basic laws of quantum mechanics. Therefore, the application of Quantum Key Distribution (QKD) technology is becoming more and more widespread.

[0003] The prerequisite for quantum key distribution technology is the preparation of quantum bits. A quantum bit utilizes a 2-dimensional Hilbert space for encoding, and its commonly used encoding methods mainly include polarization encoding and phase encoding. The currently commonly used phase-encoded quantum key distribution schemes are mostly built by using traditional discrete optical components through technologies such as fiber splicing. Traditional phase-encoded QKD systems are as shown in Figure 1 . Among them, the phase encoding and phase decoding devices are unbalanced Mach-Zehnder interferometers (AMZIs), which are composed of 3dB couplers, phase modulators, fiber delay lines, etc. The encoders at the sending end (Alice) and the decoders at the receiving end (Bob) are required to have equal arm length differences. Because the consistency of the AMZI arm length differences at the sending end and the receiving end directly affects the key generation rate of the QKD system. To ensure the key generation rate of QKD, in actual production, the process accuracy of fiber cutting is usually required to reach the level of hundreds of micrometers or even lower, which is often difficult to guarantee. This is the key difficulty restricting the practical application and productization of phase-encoded QKD.

[0004] To solve this problem, as shown in Figure 1 , units such as NEC in Japan proposed to use PLC waveguides to fabricate unbalanced Mach-Zehnder interferometers. However, the unbalanced Mach-Zehnder interferometers fabricated by PLC waveguides cannot achieve high-speed phase modulation. Summary of the Invention

[0005] The purpose of the present invention is to provide a hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 to solve the technical problem that the process consistency of the unbalanced MZI interferometer in the traditional phase-encoded QKD system is poor, resulting in a low key generation rate of the QKD system.

[0006] The technical solution of the present invention is realized as follows:

[0007] A hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3, comprising an input optical fiber, a LiNbO 3 chip, a PLC chip, and an output optical fiber connected in sequence. The LiNbO 3 chip includes a LiNbO 3 waveguide, a 3dB coupler, and two high-speed phase modulators. At the input end of the LiNbO 3 chip, the input optical fiber is connected to the 3dB coupler through the LiNbO 3 waveguide. The two output ends of the 3dB coupler are respectively connected to the two high-speed phase modulators through the LiNbO 3 waveguide. At the output end of the LiNbO 3 chip, the two high-speed phase modulators are respectively connected to a first waveguide coupling region and a second waveguide coupling region through the LiNbO 3 waveguide. The first waveguide coupling region and the second waveguide coupling region are both connected to the PLC chip;

[0008] The PLC chip includes PLC waveguides, a PLC delay line, and a directional coupler. At the input end of the PLC chip, the two PLC waveguides are respectively connected to the two LiNbO 3 waveguides of the LiNbO 3 chip segment through the first waveguide coupling region and the second waveguide coupling region; one PLC waveguide is connected to the PLC delay line, and the other PLC waveguide is connected to a thermo-optic phase modulator; the PLC delay line and the thermo-optic phase modulator are respectively connected to the two input ends of the directional coupler, and the two output ends of the directional coupler are connected to the two output optical fibers.

[0009] Preferably, the 3dB coupler is any one of a Y-type optical power splitter, a 2x2 directional coupler, and a multimode interferometer.

[0010] Preferably, the LiNbO 3 waveguide is fabricated by proton exchange or titanium diffusion manufacturing process.

[0011] Preferably, the refractive index difference of the PLC waveguide is 0.5%-2%.

[0012] Preferably, the polishing angles of the input and output ends of the LiNbO 3 chip are 10-15°.

[0013] Preferably, the polishing angle of the input end of the PLC chip is 8-15°, and the polishing angle of the output end is 8°.

[0014] Preferably, the manufacturing process of the PLC waveguide is to deposit materials on a silicon-based chip using chemical vapor deposition, then form a mask pattern for the delay waveguide using ultraviolet lithography, and finally transfer the mask pattern to the deposited materials using inductively coupled plasma etching to form the PLC waveguide.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. A hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 proposed by the present invention combines the advantages of LiNbO3 and PLC materials. It uses LiNbO3 material to fabricate a high-speed phase modulator and PLC waveguide for low-loss delay, realizing chip-level integration of AMZI, with advantages such as small loss, high phase encoding rate, low device cost, small size, and large-scale production feasibility.

[0017] 2. A hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 provided by the present invention uses semiconductor processes to ensure the consistency of the arm length difference of AMZI, solving the problem that it is difficult to guarantee the fiber cutting accuracy in traditional phase encoding QKD systems.

[0018] 3. A hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 provided by the present invention has two high-speed phase modulators for encoding and decoding AMZI, and can realize 0, π / 2, π, 3π / 2, 4 kinds of phase encodings through digital modulation combination, achieving high-speed phase encoding.

[0019] 4. A hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 of the present invention has very small transmission loss (about 0.1 dB) in the PLC delay waveguide, and the losses of the two arms of AMZI are the same. There is no need to add additional devices or processes to adjust the optical power balance of the two arms. At the same time, the insertion loss at the receiving end (Bob) is smaller than that of traditional systems, and a greater transmission distance can be achieved;

[0020] 5. A hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 provided by the present invention has exactly the same structure for the encoding chip and the decoding chip, which can realize device unity and save R & D and manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of a phase encoding QKD system in the prior art;

[0022] Figure 2 It is a schematic diagram of the principle of a hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 of the present invention.

[0023] In the figure: 10 - single - photon source, 11 - 3dB coupler, 12 - optical fiber, 13 - optical fiber delay line, 14 - phase modulator, 15 - 3dB coupler, 16 - optical fiber channel, 17 - 3dB coupler, 18 - optical fiber, 19 - optical fiber delay line, 110 - phase modulator, 111 - 3dB coupler, 112 - single - photon detector, 113 - single - photon detector, 21 - input optical fiber, 22 - LiNbO 3 waveguide, 23 - 3dB coupler, 24 - first high - speed phase modulator, 25 - second high - speed phase modulator, 26 - LiNbO 3 chip, 27 - first waveguide coupling region, 28 - second waveguide coupling region, 29 - thermo - optic phase modulator, 210 - PLC delay line, 211 - PLC waveguide, 212 - directional coupler, 213 - PLC chip, 214 - output optical fiber. Detailed implementation mode

[0024] Next, the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0025] As Figure 2 shown, a hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 of the present invention includes an input optical fiber 21, a LiNbO 3 chip 26, a PLC chip 213, and an output optical fiber 214 connected in sequence. The output optical fiber 214 includes two paths. The LiNbO 3 chip 26 includes a LiNbO 3 waveguide 22, a 3dB coupler 23, and two high - speed phase modulators, which are the first high - speed phase modulator 24 and the second high - speed phase modulator 25; at the input end of the LiNbO 3 chip 26, the first high - speed phase modulator 24 and the second high - speed phase modulator 25 are respectively connected to the first waveguide coupling region 27 and the second waveguide coupling region 28 through the LiNbO 3 waveguide 22. The first waveguide coupling region 27 and the second waveguide coupling region 28 are both connected to the PLC chip 213;

[0026] The PLC chip 213 includes a PLC waveguide 211, a PLC delay line 210, and a directional coupler 212; at the input end of the PLC chip 213, two PLC waveguides 211 are respectively connected to the two LiNbO 3 chip 26 segments through the first waveguide coupling region 27 and the second waveguide coupling region 28, and the two LiNbO 3The waveguide 22 is connected; one PLC waveguide 211 is connected to the PLC delay line 210, and the other PLC waveguide 211 is connected to the thermo-optic phase modulator 29; the PLC delay line 210 and the thermo-optic phase modulator 29 are respectively connected to the two input ends of the directional coupler 212, and the two output ends of the directional coupler 212 are connected to the two output optical fibers 214.

[0027] LiNbO 3 The chip 26 and the PLC chip 213 are connected through a waveguide coupling region, and inside the waveguide coupling region, LiNbO 3 The waveguide 22 and the PLC waveguide 211 are coupled and aligned through a high-precision alignment process.

[0028] The input optical fiber 21 is used to couple the quantum optical signal into the hybrid integrated quantum phase encoding or decoding chip of PLC and LiNbO 3 .

[0029] The LiNbO 3 The chip 26 and the PLC chip 213 form an AMZI with high-speed phase encoding or decoding function. When encoding, a specific phase difference among 0, π / 2, π, and 3π / 2 is realized between the two arms of the AMZI, and when decoding, a specific phase difference among 0 and π / 2 is realized.

[0030] For the two output optical fibers 214, when the chip performs the encoding function, one of the output optical fibers 214 is connected to the optical fiber channel; when the chip performs the decoding function, the two output optical fibers 214 are respectively connected to two single-photon detectors.

[0031] The 3dB coupler 23 is designed as a Y-shaped optical power splitter to split the input light into two beams of the same intensity and respectively couple them to the first high-speed phase modulator 24 and the second high-speed phase modulator 25.

[0032] The first high-speed phase modulator 24 and the second high-speed phase modulator 25 respectively realize 0, π / 2 and 0, π phase modulations. This implementation method can reduce the requirement of the high-speed phase modulator for the driving voltage.

[0033] The first waveguide coupling region 27 and the second waveguide coupling region 28 realize the optical coupling connection between the LiNbO 3 chip 26 and the PLC chip 213.

[0034] The PLC delay line 210 realizes the delay of the optical pulse signal.

[0035] The thermo-optic phase modulator 29 realizes the initial phase bias and feedback regulation of the AMZI.

[0036] The described directional coupler 212 realizes the beam combination of the two arms of the AMZI.

[0037] The described LiNbO 3 The polishing angles of the input and output ends of the chip 26 are 10°.

[0038] The polishing angle of the input end of the described PLC chip 213 is 15°, and the polishing angle of the output end is 8°.

[0039] The described LiNbO 3 The manufacturing process of the waveguide 22 is proton exchange.

[0040] The refractive index difference of the described PLC waveguide 211 is 0.75%.

[0041] The working process of the hybrid integrated quantum phase encoding chip of PLC and LiNbO 3 is as follows: The photon signal generated by the single photon source is coupled to the phase encoding chip through the input optical fiber 21. The thermo-optic phase modulator is adjusted to modulate the initial phase difference of the AMZI to π phase. The first high-speed phase modulator 24 and the second high-speed phase modulator 25 are combined to randomly load 4 different phase differences (0, π / 2, π, 3π / 2) to realize the output of 4 different phase states, and are output to the optical fiber channel through any one of the output optical fibers 214 or 215. Among them, 0 and π are a set of orthogonal bases, and π / 2 and 3π / 2 are another set of orthogonal bases. The phase encoding process is shown in Table 1.

[0042] The working process of the hybrid integrated quantum phase decoding chip of PLC and LiNbO 3 is as follows: The photon signal in the optical fiber channel is coupled to the phase decoding chip through the input optical fiber 21. The thermo-optic phase modulator is adjusted to modulate the initial phase difference of the AMZI to 0 phase. One of the combinations of the first high-speed phase modulator 24 and the second high-speed phase modulator 25 is randomly loaded with 2 different phase differences (0, π / 2) to realize 2 different measurement basis phase states. The decoded optical signal is output and coupled to two single photon detectors through the two output optical fibers 214. The phase decoding process is shown in Table 2.

[0043] Table 1 Phase Encoding Example

[0044]

[0045] Table 2 Phase Decoding Example

[0046]

[0047] Based on the structure and principle of the present invention, it can be seen that the hybrid integrated quantum phase encoding and decoding system of the present invention based on PLC and LiNbO3 combines LiNbO 3The advantages of two materials, LiNbO and PLC, are utilized. A high-speed phase modulator is fabricated using the LiNbO 3 material, and a low-loss delay is achieved using a PLC waveguide, realizing chip-level integration of the AMZI and high-speed phase encoding.

Claims

1. A hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3, comprising an input optical fiber, a LiNbO3 chip, a PLC chip and an output optical fiber connected in sequence, characterized in that: The LiNbO3 chip includes a LiNbO3 waveguide, a 3dB coupler and two high-speed phase modulators. At the input end of the LiNbO3 chip, the input optical fiber is connected to the 3dB coupler through the LiNbO3 waveguide. The two output ends of the 3dB coupler are respectively connected to the two high-speed phase modulators through the LiNbO3 waveguide. At the output end of the LiNbO3 chip, the two high-speed phase modulators are respectively connected to the first waveguide coupling region and the second waveguide coupling region through the LiNbO3 waveguide. The first waveguide coupling region and the second waveguide coupling region are both connected to the PLC chip. The PLC chip includes a PLC waveguide, a PLC delay line, and a directional coupler; at the input end of the PLC chip, two PLC waveguides are connected to the two LiNbO3 waveguides of the LiNbO3 chip segment through a first waveguide coupling region and a second waveguide coupling region respectively; one PLC waveguide is connected to the PLC delay line, and the other PLC waveguide is connected to a thermo-optical phase modulator; the PLC delay line and the thermo-optical phase modulator are respectively connected to the two input ends of the directional coupler, and the two output ends of the directional coupler are connected to two output optical fibers; the 3dB coupler is any one of a Y-type optical power divider, a 2x2 directional coupler, and a multi-mode interferometer; the LiNbO3 waveguide is manufactured using proton exchange and titanium diffusion processes.

2. The hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 as claimed in claim 1, characterized in that: The refractive index difference of the PLC waveguide is 0.5% - 2%.

3. The hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 as claimed in claim 1, characterized in that: The polishing angles of the input and output ends of the LiNbO3 chip are 10-15°.

4. The hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 as claimed in claim 1, characterized in that: The polishing angle of the input end of the PLC chip is 8-15°, and the polishing angle of the output end is 8°.

5. The hybrid integrated quantum phase encoding and decoding system based on PLC and LiNbO3 as claimed in claim 1, characterized in that: The manufacturing process of the PLC waveguide is to deposit the material on a silicon-based chip using chemical vapor deposition, then use ultraviolet photolithography to form a mask pattern of the delay waveguide, and finally use an inductively coupled plasma etching process to transfer the mask pattern to the deposited material to form the PLC waveguide.

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