KR101573867B1 - On-demand single-photon source for quantum communication - Google Patents

Abstract

Disclosed is a customized single-photon light source for quantum communication. According to an embodiment of the present invention, the single-photon light source includes: a photon-pair light source which uses a voluntary parametric down-conversion or spontaneous four-wave mixing phenomenon to generate a pair of photons; an announcing photon detector which detects one of the photons generated as a pair; and an optical buffer which executes a variable optical delay operation by using the other photon not detected by the announcing photon detector and outputs the photon. A single photon with a high probability at a desired point in time can be obtained by using a time multiplexing method combining the photon-pair light source, announcing photon detector, and variable optical buffer to implement highly secure quantum communication while reducing noise.

Description

≪ Desc / Clms Page number 1 > ON-DEMAND SINGLE-PHOTON SOURCE FOR QUANTUM COMMUNICATION <

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a customized single photon source for quantum communication, and more particularly to a custom single photon source for quantum communication using a single photon as a medium of transmission of information.

Conventional optical communication technologies based on multiple photons always involve security problems, and software - based security technologies based on complex algorithms are used to overcome them. However, the software method has security factors such as the hardware development and the reliability problem of the hardware provider. Therefore, a quantum communication technology that can solve the security problem more fundamentally based on the physical law is being developed.

A single photon source is a key element for quantum communication, and if there is an ideal single photon source that generates only one photon at a desired time, it is possible to eliminate the possibility that the eavesdropper intercepts some signals in the middle of the communication line, There is no single photon source.

In conventional quantum communication, weak laser pulses or nonlinear optics based photon pair light sources are mainly used. Generally, they have a photon generation efficiency of 10% or less, and when two or more photons are simultaneously output in order to increase the photon generation efficiency And the security is seriously deteriorated. In addition, a single photon source based on so-called single emitters using quantum dots or single atoms has also been developed, but a sufficient single photon generation efficiency has not been obtained due to the limit of the photon collection efficiency commonly.

A problem to be solved by the present invention is to increase the probability that a single photon is generated at a desired time through a time multiplexing method combining a photon pair light source, a preliminary photon detector and a variable optical buffer, and reduce noise caused by generation of two or more photons In this case, it is possible to provide a customized single photon source for quantum communication, which can be put to practical use by utilizing a conventional photon pair light source and a technically feasible optical buffer structure.

A single photon source according to an embodiment of the present invention includes a photon pair light source for generating a pair of photons by using a spontaneous-parameter down conversion or an eigen-emission light wave mixing phenomenon; A preliminary photon detector for detecting any one of the pair of photons; And an optical buffer for outputting the photon after applying a variable optical delay to the remaining one photon not detected by the predictor photon detector.

The photon pair light source includes a nonlinear optical medium that causes spontaneous parameter down conversion or self-emission light wave mixing; And a pump light source incident on the nonlinear optical medium to generate the pair of photons.

In the nonlinear optical medium, one of the pair of photons may have a wavelength in a visible light or a near-infrared region, and the other one of the photons may have a communication wavelength band.

The pump light source is a pulsed laser having a constant period, and the period may correspond to a distance corresponding to a minimum unit of the magnitude of the optical delay within a pulse width and a time during which the light passes.

Wherein the optical buffer includes an electro-optic modulator for changing polarization of the remaining one photon not detected by the predictive photon detector; A polarization beam splitter for splitting the optical path according to the polarization of the photon passed through the all-optical modulator; And an optical delay line for applying different optical delays to the photons in accordance with the optical path divided by the polarization beam splitter.

N total number of the all-optical modulators, and the difference in distance between the two optical paths selected by each of the N optical modulators is L, 2L, 4L, ... , ^2N- 1L (where L is a distance corresponding to the minimum unit of the magnitude of the optical delay).

The optical path may include an optical fiber.

The single photon source may further include a signal processing unit for generating a driving signal based on a time when the predicted photon detector detects the photon and applying the driving signal to the all-optical modulator.

The signal processing unit may include a field programmable gate array.

The optical buffer may adjust the optical delay value so as to output the photon at a predetermined time by compensating for the difference between the time when the predicted photon detector detected the photon and the reference time.

According to an embodiment of the present invention, a time multiplexing method combining a photon pair light source, a preliminary photon detector, and a variable optical buffer increases the probability of generating a single photon at a desired time, and reduces noise caused by generation of two or more photons have. At this time, it is possible to increase the possibility of practical use by utilizing the existing photon pair light source and the optical buffer structure having technological feasibility.

1 is a diagram illustrating a single photon source according to an embodiment of the present invention.
FIG. 2 is a view illustrating a principle of fixing a time at which a photon is output in a single photon source according to an exemplary embodiment of the present invention. Referring to FIG.

The present invention may have various embodiments, and particular embodiments are illustrated and described in the drawings. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all variations that fall within the spirit and scope of the invention.

Unless otherwise defined, terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Also, terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the contextual meaning of the related art, and should not be construed as an ideal or overly formal sense.

Terms including ordinals, such as first, second, etc., may be used to describe various elements, but the elements are not limited to these terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but there may be other elements in between . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention, the singular forms of which shall be construed as including plural referents unless the context clearly dictates otherwise. In particular, the terms "comprise" or "having" are used to specify that a feature, a number, a step, an operation, an element, a component, or a combination thereof, , Steps, operations, elements, components, or combinations thereof, as a matter of principle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals are used for the same components, although they are shown in different drawings.

1 is a diagram illustrating a single photon source according to an embodiment of the present invention.

Referring to FIG. 1, a time-multiplexed single photon source according to an exemplary embodiment of the present invention includes a pump light source 110 and a nonlinear optical medium 120. The spon- taneous parametric down-conversion (SPDC) A photon pair light source for generating a pair of photons using a spontaneous four-wave mixing (SFWM) phenomenon, a preliminary photon detector 130 for detecting any one of the pair of photons, An optical buffer 150 for outputting the photon after applying a tunable optical delay to the remaining one photon not detected by the predictive photon detector 130 and a predictive photon detector 130 for detecting the photon And a signal processing unit 140 that determines the magnitude of the optical delay of the optical buffer 150 based on one time.

The pump light source 110 is incident on the nonlinear optical medium 120 causing SPDC or SFWM to generate a pair of photons at the same time, Lt; / RTI > At this time, the period T corresponds to a distance L corresponding to the minimum unit of the magnitude of the optical delay controlled by the optical buffer 150 within the pulse width and the time during which the light passes.

The nonlinear optical medium 120 can simultaneously generate two photons at the same time by a quantum mechanical principle called spontaneous down conversion (SPDC) or self-emission wave mixing (SFWM) when the pump light source 110 is incident. At this time, the wavelength and the traveling direction of the two photons are determined by the momentum conservation law and the energy conservation law. However, the generation of a photon pair is very low in efficiency, unlike a conventional classical optical phenomenon, so that most photon pairs are generated intermittently, and the generation time is not deterministic but random.

The photon pair light source is basically a random light source, but using the fact that two photons are always made, it is possible to construct a definite photon source that outputs photons at a fixed time. More specifically, any one of the two photons travels to the preliminary photon detector 130, and when the preliminary photon detector 130 detects one photon, the remaining one photon, which coincides with the detected photon, 150). At this time, the optical buffer 150 may apply a light delay to the photons to compensate for the detection time of the preliminary photon detector 130, so that the output time of the photon may be constant.

On the other hand, in the nonlinear optical medium 120 in which the pump light source 110 is incident, one of the pair of photons has a wavelength in a visible light or near-infrared region, and the other one has a communication wavelength band A non-overlapping photon pair source can be constructed.

The optical buffer 150 includes an electro-optic modulator (EOM-1 to EOM-N), an electrooptic modulator (EOM-1 to EOM-1) for changing the polarization of the remaining one photon not detected by the preliminary photon detector 130, N divided by polarizing beam splitters (PBS-1 to PBS-N) and polarizing beam splitters PBS-1 to PBS-N that divide the optical path according to the polarization of the photons passing through the polarizing beam splitter And an optical delay line for applying different optical delays to the photons in accordance with the path.

In particular, the optical buffer 150 adjusts the total optical delay value so as to output the photon at a predetermined time by compensating for the difference between the time when the notice photon detector 130 detects the photon and the reference time, 1 to EOM-N) and polarization beam splitters PBS-1 to PBS-N, respectively.

The optical modulators EOM-1 to EOM-N change the polarization of the photons by the Pockel's effect. Each of the optical modulators EOM-1 to EOM-N modulates the photons by an optical delay Length can be selected to be sent to any one of two different optical paths. At this time, the distance difference between the two optical paths selected by the all-optical modulators (EOM-1 to EOM-N) has a value corresponding to a power of 2 such as L, 2L, 4L, . That is, the distance difference between the two optical paths selected by the Nth all-optical modulator (EOM-N) is ^2N- 1L (where L is a distance corresponding to the minimum unit of the optical delay) have.

Meanwhile, a method for causing the optical buffer 150 to have a desired optical delay value is as follows. The first electro-optical modulator (EOM-1) can keep the polarization of the photon as it is or rotate 90 degrees according to the driving signal of the signal processing unit 140. [ Next, the first polarized beam splitter PBS-1 causes the horizontal polarized light to proceed to the first light path OP-1A and the vertical polarized light to the second light path OP-1B . That is, the first polarizing beam splitter (PBS-1) can transmit photons of horizontal polarization and reflect photons of vertical polarization, and vice versa. In other words, the photon, which is vertically polarized light, proceeds to the first optical path OP-1A and the horizontally polarized photon proceeds to the second optical path OP-1B.

Here, the optical path of the transmitted or reflected photons is again combined by the first polarizing beam splitter (PBS-1), and the distance traveled until the optical paths of the two polarized components are merged becomes L difference. That is, the first all-optical modulator (EOM-1) can apply any one optical delay of two optical paths having a distance difference of L to the photons traveling according to the driving signal, -1A) or the second optical path OP-1B can function as an optical delay line.

Also, the second all-optical modulator (EOM-2), like the first all-optical modulator (EOM-1), can either maintain the polarization of the photon or rotate it 90 degrees. The progress path of the photon is divided into either the first optical path OP-2A or the second optical path OP-2B, which is divided by the second polarized beam splitter PBS-2 and has a distance difference of 2L from each other And this process is continued until the Nth all-optical modulator (EOM-N) and the polarization beam splitter PBS-N.

Thus, the path differences of the two paths selected by the all-optical modulators EOM-1 to EOM-N are L, 2L, 4L, ... , ^2N- 1L, one of 2N kinds of optical paths can be selected according to driving signals applied to N light modulators (EOM-1 to EOM-N). In this case, The first optical paths OP-1A to OP-NA and the second optical paths OP-1B to OP-NB may include optical fibers.

In the figure, the path differences selected by the all-optical modulators EOM-1 to EOM-N are arranged in increasing order, but the order of the all-optical modulators EOM-1 to EOM- Can be obtained. It is also intended to provide the largest number of optical paths within the given number of all-optical modulators (EOM-1 to EOM-N), so that the difference in distance between the respective optical paths has a value corresponding to a power of 2 , The distance difference of each light path may be changed to other values as necessary.

Particularly, when the basic unit L of the optical path difference of the optical buffer 150 is adjusted to the distance that the photon advances during the period T of the pump light source 110, the apparatus shown in this figure has a jitter Lt; RTI ID = 0.0 > photonic < / RTI > However, if there is no particular relationship between the period T of the pulse and the basic unit L of the optical path difference, or if the pump light source 110 is a continuous oscillation laser, The principles of operation are valid, and a single photon source according to an embodiment of the present invention can be utilized for quantum communication.

The signal processing unit 140 receives a signal from the advance photon detector 130 and outputs an operation voltage of the all-optical modulators EOM-1 to EOM-N. The signal processing unit 140 generates a signal based on the detection time of the photon by the advance photon detector 130 And can apply the generated driving signals to the electrooptic modulators EOM-1 to EOM-N. In this case, the signal processing unit 140 may include a field-programmable gate array (FPGA).

On the other hand, the wavelength of the photons detected by the preliminary photon detector 130 to be efficiently detected by the silicon-based detector is a visible light or near infrared region, and the wavelength of the output photon is a communication wavelength band between 1.5 m and 1.6 m When the photon pair light source is designed, not only the efficiency of the preliminary photon detector 130 but also the applicability of the outputted photon can be increased.

FIG. 2 is a view illustrating a principle of fixing a time at which a photon is output in a single photon source according to an exemplary embodiment of the present invention. Referring to FIG.

Referring to FIG. 2, when the pump light source is composed of a pulse train having a period T and a number of pulses N, if a preliminary photon detector detects a photon generated in the nth pulse, a photon input to the optical buffer The optical delay can be adjusted to Nn before arrival. In this way, even if n changes to an arbitrary value, the time during which the photon is output from the optical buffer is fixed to the time of the N-th pulse.

According to the single photon source of the present invention described above, a single photon output can be obtained with a high probability at a desired time through a time multiplexing method combining a photon pair light source, a preliminary photon detector, and a variable optical buffer, This makes it possible to implement quantum communication with low noise and high security.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken in conjunction with the present invention. It will be understood that various modifications and changes may be made without departing from the scope of the present invention.

110: pump light source
120: nonlinear optical medium
130: preliminary photon detector
140: Signal processor
150: Optical buffer
EOM-1 ~ EOM-N: All-optical modulator
PBS-1 to PBS-N: Polarizing beam splitter
OP-1A to OP-NA: the first light path
OP-1B to OP-NB: Second optical path

Claims (10)

A photon pair light source for generating a pair of photons using spontaneous parameter down conversion or self-emission light wave mixing;
A preliminary photon detector for detecting any one of the pair of photons; And
And an optical buffer for outputting the photon after applying a variable optical delay to the remaining one photon not detected by the preliminary photon detector,
The optical buffer includes:
An all-optical modulator for changing the polarization of the remaining one photon not detected by the predictive photon detector;
A polarization beam splitter for splitting the optical path according to the polarization of the photon passed through the all-optical modulator; And
And an optical delay line for applying different optical delays to the photons in accordance with the optical path divided by the polarization beam splitter.
The method according to claim 1,
Wherein the photon pair light source comprises:
A nonlinear optical medium causing spontaneous parameter downconversion or self-emission optical wave mixing; And
And a pump light source incident on the nonlinear optical medium to generate the pair of photons.
3. The method of claim 2,
Wherein the nonlinear optical medium is such that any one of the pair of photons has a wavelength in the visible or near infrared region and the other has a communication wavelength band.
3. The method of claim 2,
The pump light source is a pulsed laser having a constant period,
Wherein the period matches a distance corresponding to a minimum unit of the magnitude of the optical delay within a pulse width and a time during which the light passes.
delete The method according to claim 1,
N total number of all-optical modulators are provided,
The difference in distance between the two optical paths selected by each of the N optical modulators is L, 2L, 4L, ... , ^2N- 1L (where L is a distance corresponding to the smallest unit of the magnitude of the optical delay).
The method according to claim 1,
The optical path includes a single photon source including an optical fiber.
The method according to claim 1,
Further comprising: a signal processor for generating a drive signal based on a time at which the predicted photon detector detected the photon and applying the drive signal to the all-optical modulator.
9. The method of claim 8,
The signal processing unit includes a field programmable gate array.
The method according to claim 1,
Wherein the optical buffer adjusts the optical delay value so as to compensate for a difference between a time when the predictive photon detector detected the photon and a reference time to output the photon at a predetermined time.

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