CN1199388C - Optical fiber single photon routing control device - Google Patents

Abstract

The present invention relates to an optical fibre single photon routing manipulation device which comprises a single photon incidence port 1, a circulator 2, an optical fiber coupler 3, an optical fiber 4, polarization controllers 5, 7, a phase modulator 6, a delay signal generator 8, an electrical signal input end 9 and single photon radiation ports 23, 34, wherein the beam splitting ratio of the optical fiber coupler 3 is 50% to 50%; the maximum length of the optical fiber 4 is 30 km; an optical path is composed of the single photon incidence port 1, the circulator 2, the optical fiber coupler 3, the optical fiber 4, the polarization controllers 5, 7 and the phase modulator 6; a circuit is composed of the phase modulator 6 and the delay signal generator 8. The present invention can realize the optical single photon routing manipulation of the optical fiber. The present invention manipulates the single photon which is entered from the single photon incidence port 1 to radiate from the single photon radiation ports 23, 34, the routing manipulation successful rate exceeds 92%, and therefore, the present invention is particularly suitable for optical fiber single photon routing manipulation in the quantum secrecy communication.

Description

Optical fiber single photon routing control device

                      

The invention relates to an optical fiber single-photon routing control device, which realizes the single-photon routing control in the optical fiber, and belongs to the technical field of quantum security communication.

Background technique

Quantum secure communication is communication based on light quantum. Information is loaded on and transmitted by a single photon. The unknown quantum state cannot be cloned. Measuring the quantum will change the quantum state, so that it is impossible for an eavesdropper to obtain the communication information without being caught. It is found that, therefore, quantum secure communication can realize the absolute secrecy of communication. This will be widely used in military confidential transmission and commercial information authentication. Similar to existing optical communication, quantum secure communication also has the problem of routing and manipulating quantum information, that is, single photons. Among the existing optical communication technologies, the development of routing components and technologies is relatively mature, and there are various routing methods and technologies. Quantum secure communication requires routing and manipulation of single photons. At present, there are few studies in this area. Single-photon routing manipulation devices can be divided into two categories: space and fiber optics. The Chinese patent application number 02111395.5 relates to a spatial single photon routing control device, which is completed by a spatial Mach-Zehnder interferometer and a phase modulator. As for the optical fiber single photon routing control device, there is no patent yet. Long-distance single-photon routing manipulation can be realized through single-photon interference in optical fibers. The simplest single-photon interference in optical fibers can be accomplished by fiber-optic Mach-Zehnder interferometers and phase modulators. However, since the fiber is greatly affected by the environment, the single-photon interference in the fiber cannot be kept stable when the fiber length reaches several meters.

Contents of invention

From the perspective of quantum theory, whether the photon carries the information of "which path" is the key condition for whether interference can occur. There are two light paths in a general interferometer. At a certain moment, the photons in the interferometer will only choose one path, but the other path that exists at the same time will also affect it. In fact, it is the optical path difference, or phase difference, of the two possible paths that determines the interference of each single photon. Due to the influence of the environment, slight fluctuations in the length of the fiber will cause changes in the phase difference. This fluctuation is intensified with the increase of the length of the fiber, which brings great difficulties to the realization of stable long-distance single-photon routing control.

The present invention aims to introduce a fiber optic single-photon routing control device, which can solve the problems of short single-photon interference distance and unstable interference in optical fiber, and realize long-distance stable single-photon interference, thereby realizing optical fiber single-photon routing control and finally For quantum secure communication.

The device of the present invention adopts the following structure to achieve the above object. The structure of the device of the present invention is now described in detail in conjunction with the accompanying drawings: a fiber single photon routing control device, including a single photon incident port 1, a circulator 2, a fiber coupler 3, an optical fiber 4, a first polarization controller 5 and a second Polarization controller 7, phase modulator 6, delay signal generator 8, first electrical signal input terminal 9, first single photon output port 23 and second single photon output port 34, circulator 2 has three ports, incident port 20 , exit port 21, return exit port 22, fiber coupler 3 has four ports, the first bidirectional port 30, the second bidirectional port 31, the 3rd bidirectional port 32 and the 4th bidirectional port 33, the beam splitting of fiber optic coupler 3 The ratio is 50%: 50%, the optical fiber 4 has two ports, the fifth bidirectional port 40 and the sixth bidirectional port 41, the first polarization controller 5 and the second polarization controller 7 each have two ports, and the seventh bidirectional port 50, the eighth bidirectional port 51 and the ninth bidirectional port 70, the tenth bidirectional port 71, the phase modulator 6 has three ports, the eleventh bidirectional port 60 and the twelfth bidirectional port 61, and the second electrical signal input terminal 62 , delay signal generator 8 has two ports, the 3rd electric signal input end 80 and electric signal output end 81, it is characterized in that, the maximum length of optical fiber 4 is 30km, circulator 2, optical fiber coupler 3, optical fiber 4, the first A polarization controller 5, a second polarization controller 7, and a phase modulator 6 are optical components whose operating wavelength is equal to the wavelength of the single-photon pulse 10. The single-photon incident port 1, the circulator 2, the fiber coupler 3, and the optical fiber 4 , the first polarization controller 5, the second polarization controller 7, and the phase modulator 6 form an optical circuit, and the phase modulator 6 and the delay signal generator 8 form a circuit, and the connections between the optical circuit and the circuit are respectively completed by optical fibers and cables, and the optical circuit inside Connection: the single photon incident port 1 is connected to the incident port 20, the outgoing port 21 is connected to the first bidirectional port 30, the fourth bidirectional port 33 is connected to the fifth bidirectional port 40, the sixth bidirectional port 41 is connected to the seventh bidirectional port 50, The eighth bidirectional port 51 is connected to the eleventh bidirectional port 60, the twelfth bidirectional port 61 is connected to the ninth bidirectional port 70, the tenth bidirectional port 71 is connected to the third bidirectional port 32, and returns to the outgoing port 22 and the second bidirectional port 31 are respectively connected with the first single-photon output port 23 and the second single-photon output port 34, and the circuit is internally connected: the first electrical signal input end 9 is connected with the third electrical signal input end 80, and the electrical signal output end 81 is connected with the second electrical signal input end 80. The signal input 62 is connected.

working principle. The single photon pulse 10 is incident from the photon incident port 1, and passes through the circulator 2 to the first bidirectional port 30, because the beam splitting ratio of the fiber coupler 3 is 50%:50%, so the single photon passes through the third bidirectional port 32 with the same probability Or the fourth bidirectional port 33 enters the ring optical path made up of the optical fiber 4, the first polarization controller 5 and the second polarization controller 7, and the phase modulator 6:

1. The clockwise path single photon a3 enters the ring optical path from the fourth bidirectional port 33, successively passes through the optical fiber 4, the first polarization controller 5, the phase modulator 6, the second polarization controller 7, and returns through the third bidirectional port 32 Fiber coupler 3;

2. The counterclockwise path single photon a2 enters the ring optical path from the third bidirectional port 32, successively passes through the second polarization controller 7, the phase modulator 6, the first polarization controller 5, and the optical fiber 4, and returns through the fourth bidirectional port 33 Fiber coupler3.

其中V_光纤是光在光纤中的传播速度)，且t₁＜＜t₂，t₂≈T_环形光路。单光子脉冲宽度为τ，延迟信号发生器8加至相位调制器6的调制脉冲的上升沿时刻为t_m，Δt是调制脉冲脉宽，V_m是调制脉冲电压幅度，t₀是延迟时间，T_光脉冲是单光子脉冲的重复周期。As shown in Figure 2, the moment when the single photon a2 in the counterclockwise path reaches the phase modulator 6 is t ₁ , and the moment when the single photon a3 in the clockwise path reaches the phase modulator 6 is t ₂ , there is t ₁ +t ₂ ≈ T _{ring light path} ( The time required for a single photon to go around the ring light path,

Where V _fiber is the propagation speed of light in the fiber), and t ₁ << t ₂ , t ₂ ≈ _{T ring light path} . The single-photon pulse width is τ, and the rising edge moment of the modulated pulse added to the phase modulator 6 by the delay signal generator 8 is _tm , Δt is the modulated pulse width, _Vm is the modulated pulse voltage amplitude, and _t0 is the delay time, A T _{light pulse} is a repeating period of a single photon pulse.

When the single photon pulse 10 is incident, the synchronous electrical signal 11 is transmitted from the first electrical signal input end 9 to the third electrical signal input end 80, and after a delay time _t0 , the delay signal generator 8 generates a modulated pulse with a voltage amplitude of V _m , arrive at and drive the phase modulator 6 through the electrical signal output terminal 81 and the second electrical signal input terminal 62, at the same time, the single photon a3 in the clockwise path or the single photon a2 in the counterclockwise path in the optical path just passes through the phase modulator 6, Thus subject to phase modulation of the modulating pulse.

By adjusting the delay time t ₀ and the modulation pulse width Δt, the single photon a3 in the clockwise path or the single photon a2 in the counterclockwise path can be selected to be modulated:

When t ₀ =t ₁ and τ<Δt<t ₂ , the counterclockwise path single photon a2 is modulated;

When (t ₁ +τ)<t ₀ <t ₂ and (t ₂ −t ₀ +τ)<Δt<(T _{light pulse} −t ₂ ), the clockwise path single photon a3 is modulated.

Adjust the modulation pulse voltage amplitude V _m , and add modulation pulses of different voltage amplitude V _m within the Δt time, and the phase difference Δφ of the corresponding two photons can be obtained: $\mathrm{\&Delta;\&phi;}=\frac{V_m}{V_{\mathrm{\&pi;}}}\mathrm{\&pi;},$ Where Vπ is the half-wave voltage of the phase modulator 6, that is, the absolute value of the voltage corresponding to the phase difference π, which is inherent to the phase modulator 6 at the corresponding wavelength.

When V _m =2nVπ, phase difference Δφ=2nπ, n=0, 1, 2,...;

When V _m =(2n+1)Vπ, the phase difference Δφ=(2n+1)π, n=0, 1, 2,...;

when $V_m=(2\mathrm{no}+1)\frac{\mathrm{V\&pi;}}{2}$ , the phase difference $\mathrm{\&Delta;\&phi;}=(2\mathrm{no}+1)\frac{\mathrm{\&pi;}}{2},\mathrm{no}=0,\mathrm{1,2},\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;.$ The clockwise path single photon a3 and the counterclockwise path single photon a2 undergo single photon interference at the fiber coupler 3:

When the two-way single-photon phase difference Δφ is an even multiple of π, the interference is constructive, and the single photon passes through the first bidirectional port 30 and returns to the exit port 22, and finally exits from the first single-photon exit port 23;

When the two-way single-photon phase difference Δφ is an odd multiple of π, the interference cancels, and the single photon passes through the second bidirectional port 31, and finally exits from the second single-photon exit port 34;

的奇数倍时，单光子以相同的概率从第一单光子出射端口23或第二单光子出射端口34出射。When the two-way single-photon phase difference Δφ is

When an odd multiple of , the single photons are emitted from the first single photon exit port 23 or the second single photon exit port 34 with the same probability.

This completes the time-division modulation of single photons in the ring light path. This device only uses one phase modulator 6, and according to the difference in the arrival time of the single photons a3 and a2 in the clockwise and anticlockwise paths to the phase modulator 6, by adjusting the delay time t ₀ , the pulse width Δt and the modulation pulse voltage amplitude V _m , it can be Arbitrary and precise modulation of the single photon a3 and a2 phases in the forward and counterclockwise paths, so as to realize the long-distance routing control of single photons in the optical fiber. The single-photon pulse source is a light pulse emitted by a laser, which is attenuated to the single-photon pulse level. The first and second polarization controllers 5 and 7 are corresponding to the incident single photon wavelength, and can adjust the polarization direction of the single photon in the phase modulator 6 to improve the stability of single photon interference.

The outstanding effect of the present invention is that it can realize single-photon long-distance stable interference and stable single-photon routing control that can be used in optical fibers; the phase modulator 6 is directly connected to the electronic circuit, which is easy to integrate; the success rate of single-photon routing control exceeds 92%.

Description of drawings

Figure 1 is a schematic diagram of the structure of an optical fiber single-photon routing control device, wherein 1 is a single-photon incident port, 2 is a circulator, 3 is a fiber coupler, 4 is an optical fiber, 5 is a first polarization controller, 6 is a phase modulator, 7 is the second polarization controller, 8 is the delay signal generator, 9 is the first electrical signal input port, 23 and 34 are the first and second photon output ports, 10 is the single photon pulse, 11 is the synchronous electrical signal.

Fig. 2 is the timing diagram of selecting the trigger moment of the phase modulator 6 modulation pulse and the pulse width of the modulation pulse, wherein the four coordinate systems are under the same time axis t, the ordinate of "single photon pulse" is single photon pulse amplitude A, and "synchronization The ordinate of "signal" is the amplitude V of the synchronous electrical signal, and the ordinate of "delayed signal" is the amplitude V of the modulation voltage. The time when _the single photon a2 in the counterclockwise path reaches the phase modulator 6 is t ₁ , and the time when the single photon a3 in the clockwise path reaches the _{phase modulator 6} is t ₂ . One week), and t ₁ << t ₂ , the single-photon pulse width is τ, t _m is the rising edge moment of the modulation pulse added by the delay signal generator 8 to the phase modulator 6, and Δt is the modulation pulse width , V _m is the modulation pulse voltage amplitude, t ₀ is the delay time, and T _{light pulse} is the repetition period of the single-photon pulse 10.

Detailed ways

Example 1

An optical fiber single-photon routing control device with the above-mentioned structure is characterized in that the average number of photons per pulse of the incident single-photon pulse 10 is ≤0.5, the wavelength is 1550nm, the phase modulator 6 is Aeroflex 10G type, and the delay signal generator 8 It is a DG535 type, and the length of the optical fiber 4 is 5km.

Example 2

An optical fiber single-photon routing control device with the above structure or the structure described in Embodiment 1 is characterized in that the length of the optical fiber 4 is 28 km.

The single-photon source that generates single-photons and the instrument that detects single-photons: Agilent 33250A pulse signal generator, which modulates New Focus-Vortex 6000 series semiconductor lasers (LD) to generate light pulses with a wavelength of 1550nm, and the generated light pulses are attenuated Attenuate the chip to the single photon level, and at the same time output the synchronous pulse signal to the SR400 photon counter and the DG535 delay signal generator, and the single photon detector InGaAs avalanche diode detects the Single photon, the detected signal is sent to the SR400 photon counter, and the latter completes the single photon counting.

The pulse signal generator modulates the semiconductor laser with a repetition frequency of 10KHz, and the optical power is about 5nW at this time. When the attenuation is -75dB, the average number of photons <n>=0.1, that is, each pulse contains 0.1 photons on average. The pulse signal generator modulates the semiconductor laser with a repetition frequency of 3.33KHz, and the optical power is about 7nW at this time. When the attenuation is -75dB, the average number of photons <n>=0.5, that is, each pulse contains 0.5 photons on average.

The time t ₁ ≈ 0 for a single photon a2 in the counterclockwise path to reach the phase modulator 6, the time required for a single photon to circle _{the ring optical path} T ≈ t ₂ , the single photon pulse width τ ≈ 10 ns, and the phase modulator 6 operates at a wavelength of 1550 nm The half-wave voltage Vπ is 5 volts.

By changing the single photon a3 phase of the clockwise path, the single photon routing control is performed. The length of the fiber 4 and the average number of photons <n> are respectively 5Km, 0.1 and 28Km, and the respective delay time t ₀ of 0.5, the pulse width Δt of the modulation pulse, and the modulation pulse The selection of the voltage amplitude V _m is shown in Table 1.

Table 1 Fiber length (Km) Single photon pulse width τ(μs) t ₂ ≈ _{T ring light path} (μs) Single photon pulse repetition period T _{light pulse} (μs) Delay time t ₀ (μs) Modulation pulse width Δt(μs) Modulation pulse voltage amplitude V _m (volts) single photon exit port Single photon routing manipulation success rate (%) 5 0.01 25 100 24.50 1 0 twenty three >95 5 34 >98 28 0.01 140 333 139.50 1 0 twenty three >92 5 34 >94

By changing the single-photon phase of the counterclockwise path, the single-photon routing control is performed. The length of the fiber 4 and the average number of photons <n> are respectively 5Km, 0.1 and 28Km, 0.5, and the respective delay times t ₀ , modulated pulse pulse width Δt, modulated pulse The selection of the voltage amplitude V _m is shown in Table 2.

Table 2 Fiber length (Km) Single photon pulse width τ(μs) t ₂ ≈ _{T ring light path} (μs) Single photon pulse repetition period T _{light pulse} (μs) Delay time t ₀ (μs) Modulation pulse width Δt(μs) Modulation pulse voltage amplitude V _m (volts) single photon exit port Single photon routing manipulation success rate (%) 5 0.01 25 100 0 1 0 twenty three >95 5 34 >98 28 0.01 140 333 0 1 0 twenty three >92 5 34 >95

In summary, the present invention only uses one phase modulator 6 through time-sharing modulation of single photons in the annular optical path, and realizes long-distance stable optical fiber single photon routing control, and the interference contrast, that is, the success rate of single photon routing control is greater than 92%.

Claims (3)

1. optical fiber single-photon router device, comprise single-photon incident port (1), circulator (2), fiber coupler (3), optical fiber (4), first Polarization Controller (5) and second Polarization Controller (7), phase-modulator (6), delayed signal generator (8), first electric signal input end (9), the first single photon exit ports (23) and the second single photon exit ports (34), circulator (2) has three ports, incident port (20), exit ports (21), return exit ports (22), fiber coupler (3) has four ports, first bidirectional port (30), second bidirectional port (31), the 3rd bidirectional port (32) and the 4th bidirectional port (33), the splitting ratio of fiber coupler (3) is 50%: 50%, optical fiber (4) has two ports, the 5th bidirectional port (40) and the 6th bidirectional port (41), first Polarization Controller (5) and second Polarization Controller (7) respectively have two ports, the 7th bidirectional port (50), the 8th bidirectional port (51) and the 9th bidirectional port (70), the tenth bidirectional port (71), phase-modulator (6) has three ports, the 11 two-way port (60) and the 12 bidirectional port (61), with second electric signal input end (62), delayed signal generator (8) has two ports, the 3rd electric signal input end (80) and electrical signal (81), it is characterized in that, the maximum length of optical fiber (4) is 30km, circulator (2), fiber coupler (3), optical fiber (4), first Polarization Controller (5) and second Polarization Controller (7), phase-modulator (6) is the optical component that operation wavelength equates with the wavelength of single photon pulses (10), single-photon incident port (1), circulator (2), fiber coupler (3), optical fiber (4), first Polarization Controller (5) and second Polarization Controller (7), phase-modulator (6) is formed light path, phase-modulator (6) and delayed signal generator (8) built-up circuit, light path and being connected respectively of circuit inside are finished by optical fiber and cable, light path is inner to be connected: single-photon incident port (1) is connected with incident port (20), exit ports (21) is connected with first bidirectional port (30), the 4th bidirectional port (33) is connected with the 5th bidirectional port (40), the 6th bidirectional port (41) is connected with the 7th bidirectional port (50), the 8th bidirectional port (51) is connected with the 11 two-way port (60), the 12 bidirectional port (61) is connected with the 9th bidirectional port (70), the tenth bidirectional port (71) is connected with the 3rd bidirectional port (32), returning exit ports (22) is connected with the second single photon exit ports (34) with the first single photon exit ports (23) respectively with second bidirectional port (31), circuit is inner to be connected: first electric signal input end (9) is connected with the 3rd electric signal input end (80), and electrical signal (81) is connected with second electric signal input end (62).

2. optical fiber single-photon router device according to claim 1, it is characterized in that, average every pulsed light subnumber≤0.5 of incident single photon pulses (10), wavelength is 1550nm, phase-modulator (6) is an Aeroflex 10G type, Time Delay Generator (8) is the DG535 type, and the length of optical fiber (4) is 5km.

3. optical fiber single-photon router device according to claim 1 and 2 is characterized in that the length of optical fiber (4) is 28km.

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