JP2004264097A - Photon detector unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quicken an apparent response speed of a photon detecting element. <P>SOLUTION: This photon detector unit is provided with a light deflector 12 for deflecting incident light, an array type APD photon detector 14 having the plurality of photon detecting elements 14-1 to 14-n for detecting photons, a light deflector driving means 13 for driving the light deflector 12 to sweep upper sides of the plurality of photon detecting elements 14-1 to 14-n by output light from the light deflector 12, a bias impressing means 15 for impressing a gate pulse as a bias voltage to each of the photon detecting elements 14-1 to 14-n to be met to timing when the output light from the light deflector 12 gets incident into the each of the photon detecting elements 14-1 to 14-n, and a data processing means for converting detection signals from the plurality of photon detecting elements 14-1 to 14-n into time serial signals. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a photon detection device used for quantum information processing such as transmission of quantum cryptography using a single photon light source, and more particularly to a photon detection device capable of performing photon detection at a single photon level at high speed. .
[0002]
[Prior art]
In recent years, single-photon detectors have become an essential technology in the field of quantum information processing such as quantum cryptography and quantum computation, in addition to their use in conventional high-sensitivity optical measurement. is there. In particular, in quantum cryptography and quantum communication, a high-speed and high-detection-efficiency photon receiving device is required in order to increase the communication speed and extend the communication distance, as in ordinary optical communication.
[0003]
In ultra-high-sensitivity optical measurement receiving single-photon level signal light, a photon using a cooled avalanche photodiode (APD: avalanche photodiode) or a photomultiplier tube (PMT: photomultiplier tube) is usually used. A detector is used. In particular, in a communication wavelength band of 1.5 μm, PMT has almost no sensitivity, and therefore, it is a general method to use a photon detector using a cooled APD.
[0004]
For photon detection in the 1.5 μm band, an indium-gallium-arsenic-based (INGaAs) -based APD is often used due to sensitivity problems. As a conventional technique relating to photon detection using an indium-gallium-arsenic-based (INGaAs) -based APD, for example, see Non-Patent Document 1.
[0005]
In Non-Patent Document 1, an APD used for photon detection is driven under a special bias condition called a Geiger operation mode. In the Geiger operation mode, a reverse bias voltage is applied slightly higher than the breakdown voltage VB of the APD, and an avalanche caused by the incidence of photons is observed as a pulse signal. When the incident photons periodically fly in synchronization with the clock signal, a reverse bias voltage (gate pulse) larger than the breakdown voltage VB of the APD is sequentially applied in accordance with the timing at which the signal photons are incident. A driving method called a gated Geiger operation mode in which periodic application is performed is used. That is, if a photon is just incident at the moment when the reverse bias voltage becomes higher than the breakdown voltage VB, a signal pulse is generated in the output signal with a constant detection efficiency. If no photon can be detected, nothing is output.
[0006]
When such a photon detector is used, for example, for quantum cryptography communication, the communication speed can be increased by shortening the time interval T during which photons fly. However, for example, as described in Non-Patent Document 1 described above, in a photon detector using an APD driven in a gated Geiger operation mode, a phenomenon called after pulse occurs, and after a photon is detected, a clock signal is generated. When a gate pulse is applied to the APD synchronously, an electron avalanche may occur and an incorrect signal pulse may be output even though no photon is incident. The after-pulse generation interval decreases as the elapsed time after photon detection increases. Note that the after pulse is caused by carriers remaining in the element during the previous avalanche amplification in the APD.
[0007]
FIG. 5 is a schematic diagram showing the relationship between the photon detection, the after-pulse generation probability, and the gate pulse train when the intensity of the incident light is very weak and photons are sparsely detected with respect to the gate pulse train.
[0008]
FIG. 5A shows a case where the time interval T of the gate pulse train is short. After the photon detection, the next gate pulse is applied while the after-pulse count rate Pafter (Δt) is large, so that no photon is incident. However, the probability that the detection signal is output erroneously increases.
[0009]
On the other hand, FIG. 5B shows a case where the time interval T ′ of the gate pulse train is long, and after a sufficient time has elapsed after the photon detection, the next gate pulse is applied. No longer occurs.
[0010]
FIG. 6 shows experimental data obtained by observing the after-pulse generation probability Pafter (t) when the time t has elapsed from the photon detection. As can be seen from FIG. 6, there is a probability that an after pulse is generated at about 10 ⁻² even after 0.5 μms has elapsed from the photon detection. Therefore, the shorter the interval at which photons fly in order to increase the communication speed, the greater the probability that an error signal will occur. For example, when an APD photon detector having the characteristics shown in FIG. 6 is used, an error of about 1% occurs when T = 0.5 μm.
[0011]
To remove the effects of the after-pulse described above, if the intensity of the incident light is extremely weak and photons are sparsely detected with respect to the gate pulse period, apply a gate pulse for a certain period of time after the photon detection. For example, a method has been proposed in which the application of a gate pulse is restarted after the after-pulse counting rate is sufficiently reduced by providing a non-performing time (for example, see Non-Patent Document 2).
[0012]
However, in this method, when photons fly frequently, the dead time caused by stopping the application of the gate pulse becomes longer and the efficiency of detection decreases, so that this method is not a practical method.
[0013]
[Non-patent document 1]
D. Stucki et al. J., "Photon counting for quantum key distribution with Peltier cooled InGaAs APDs," Mod. Opt. 48, 1967 (2001))
[Non-patent document 2]
D. Stucki et al. , "Quantum key distribution over 67 km with a plug & play system," New J. Phys. Phys 4, 41.1-41.8 (2002); Yoshizawa et al. , "A Method of Discarding After-Pulses in Single-Photon Detection for Quantum Key Distribution," Jpn. J. Appl. Phys. 41, 6016-6017 (2002))
[0014]
[Problems to be solved by the invention]
The conventional photon detector described above has a problem that it is difficult to sufficiently increase the response speed of photon detection due to the influence of the after pulse.
[0015]
Further, in addition to the response time limitation of the photon detector caused by the influence of the after pulse as described above, the response speed is also inherently limited by the element characteristics of the APD. Usually, in the APD, there is a trade-off between the response speed and the quantum efficiency. Therefore, there is a problem that it is difficult to obtain a sufficient response speed in a photon detector requiring high quantum efficiency.
[0016]
The present invention has been made in view of the above, and an object of the present invention is to provide a high-speed photon detection device capable of significantly improving an apparent response speed as compared with a case where a single photon detector is used.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, a photon detection device according to the present invention includes a light deflector that deflects incident light, a photon detector having a plurality of photon detection elements that detect photons, and an output light of the light deflector. An optical deflector driving means for driving the optical deflector so as to sweep over the plurality of photon detecting elements, and each of the optical deflectors so that output light of the optical deflector is synchronized with a timing of being incident on each of the photon detecting elements. It is characterized by comprising bias applying means for applying a gate pulse as a bias voltage to a photon detecting element, and data processing means for converting detection signals from the plurality of photon detecting elements into time-series signals.
[0018]
According to the present invention, the incident photon pulse train is deflected by the optical deflector so as to sequentially sweep the plurality of photon detection elements, thereby increasing the apparent response speed of each photon detection element. This makes it possible to perform photon detection at high speed even when a low-speed photon detection element is used.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a photon detection device according to the present invention will be described in detail with reference to the accompanying drawings.
[0020]
Embodiment 1 FIG.
FIG. 1 is a conceptual diagram illustrating a configuration of the photon detection device according to the first embodiment. The photon detecting device according to the first embodiment includes an optical deflector 12 that changes the traveling direction of each incident photon of the incident photon pulse train 11, an optical deflector driving unit 13 that drives the optical deflector based on a synchronization signal, and An array-type APD photon detector 14 in which a plurality of photon detecting elements (for example, cooled avalanche photodiodes (APDs)) 14-1 to 14-n are arranged in a row (array), and an array-type APD photon detector 14 A bias application means 15 for sequentially and periodically applying a reverse bias voltage (gate pulse) greater than the breakdown voltage VB of the APD to each of the APDs 14-1 to 14-n, and the APDs 14-1 to 14-n of the array type APD photon detector 14. And a data processing means 16 for converting the detection signal output from 14-n into a time-series signal (serial signal).
[0021]
Let T be the time interval (period) of each incident photon in the incident photon pulse train 11. The array-type APD photon detector 14 includes a plurality of APDs 14-1 to 14-n, and a plurality of APDs 14-1 to 14-n are arranged in an array or a matrix.
[0022]
The optical deflector 12 is driven by an optical deflector driving unit 13 that operates in synchronization with a clock signal as a synchronization signal, and deflects each incident photon of the incident photon pulse train 11. The optical deflector driving unit 13 controls the voltage applied to the optical deflector 12 to adjust the deflection angle and the deflection speed of each incident photon of the incident photon pulse train 11. In other words, the optical deflector driving means 13 generates a plurality of output lights of the optical deflector 12 so that a pulse train is sequentially incident on each of the APDs 14-1 to 14-n on the array type APD photon detector 14. The voltage applied to the optical deflector 12 is controlled so as to sweep over the APD.
[0023]
As the light deflector 12, an acousto-optic deflector (AOD: Acoustic-optical reflector) using an acousto-optic effect may be used. The AOD uses an effect that an acousto-optic wave generated in the acousto-optic element causes an optical refractive index change, and the generated diffraction grating diffracts incident light. The deflection angle Δθ by AOD is given as follows using the wavelength λ of the incident photon, the acoustic velocity Va in the acousto-optic element, and the applied acoustic frequency Δf.
[0024]
Δθ = λ · Δf / Va
As can be seen from the above equation, the deflection angle Δθ is proportional to the acoustic frequency Δf applied to the AOD. Therefore, by changing the modulation frequency of the output voltage of the optical deflector driving means 13, the deflection angle Δθ can be freely selected. The deflection angle Δθ can be swept at a sweep speed on the order of MHz.
[0025]
Further, as the light deflector 12, an electro-optical deflector (EOD: Electro-optical reflector) using an electro-optical effect can be used. In EOD, incident light is deflected using a change in the refractive index caused by the electro-optic effect. In this case, the deflection angle Δθ is determined by the type and size of the electro-optical element used, the applied voltage, the polarization direction of the incident light, and the like.
[0026]
Further, as the optical deflector 12, a mechanical deflector using a reflecting mirror such as a galvanometer mirror or a polygonal mirror can be used. The mechanical deflector is inferior in terms of speed and integration as compared with the case of using AOD or EOD, but can realize an optical deflector with low loss and simple.
[0027]
FIG. 2 schematically shows a state of a gate pulse train (reverse bias voltage) applied by the bias applying means 15 to each of the APDs 14-1 to 14-n of the array-type APD photon detector 14. FIG. 3 shows the relationship between the voltage Vbias of the gate pulse train and the APD current. Id in FIG. 3 represents the dark current of the APD.
[0028]
As shown in FIG. 2, based on the synchronization signal, the bias applying unit 15 applies a gate to each of the n APDs 14-1 to 14-n at a period nT that is n times the time interval T of the incident photon pulse train 11. Apply a pulse train. Further, as shown in FIG. 3, each gate pulse (reverse bias voltage) applied to each of the APDs 14-1 to 14-n at the time interval nT by the bias applying means 15 is a voltage VB + ΔV larger than the breakdown voltage VB of the APD. , APD between the voltages VB-ΔV smaller than the breakdown voltage VB of the APD.
[0029]
As described above, the n APDs 14-1 to 14-n are used, and a gate pulse is applied to the n APDs 14-1 to 14-n at a time interval nT which is n times the time interval T of the incident photon pulse train 11. The response speed required for each of the APDs 14-1 to 14-n can be reduced to 1 / n.
[0030]
The outputs of the plurality of APDs 14-1 to 14-n of the array type APD photon detector 14 are input to the data processing unit 16, and the data processing unit 16 outputs the outputs from the plurality of APDs 14-1 to 14-n. While maintaining the chronological order of the photon detection signals, the photon detection signals are subjected to data processing such as conversion into chronological serial signals and output.
[0031]
According to such a configuration, the incident photon pulse train 11 arriving at a constant time interval T is incident on the optical deflector 12. Note that the incident photon pulse train 11 only needs to synchronize the flight period of the pulse train with the synchronization signal (clock signal). When the light intensity is extremely weak, each pulse train does not necessarily include a photon. Good. That is, the photons may randomly fly in a toothless state as long as the intervals are arbitrary integer multiples of the time T.
[0032]
The first incident photon of the incident photon pulse train 11 incident on the optical deflector 12 is deflected by the optical deflector 12 and is one of a plurality of APDs 14-1 to 14-n of the array type APD photon detector 14. (For example, the first APD 14-1). At this point of incidence, a gate pulse (reverse bias voltage) is applied from the bias applying means 15 to all the APDs 14-1 to 14-n, whereby the APDs to which the first photon is incident are output. At the output, a signal pulse is generated by the avalanche effect. No signal pulse is generated at the output of another APD to which no photon has been incident.
[0033]
Here, the incident photon pulse is incident on the optical deflector 12 at a certain time interval T, but the next photon is incident on the APD on which the first photon is incident on the first photon. Is after the time nT which is n times the time interval T of the incident photon pulse train 11 after the light is incident.
[0034]
The signal pulse output from the first APD on which the photon is incident is input to the data processing unit 16.
[0035]
When a time T elapses after the first photon is incident on the optical deflector 12, the second photon is incident on the optical deflector 12. The second photon is deflected by the optical deflector 12 and enters, for example, the second APD 14-2. As a result, a signal pulse is generated at the output of the second APD 14-2 in the same manner as described above. The signal pulse output from the second APD on which the photon is incident is input to the data processing unit 16. As described above, the next photon is incident on the APD on which the second photon is incident after a time nT from the incidence of the second photon.
[0036]
Such an operation is repeatedly executed each time an incident photon pulse is incident on the optical deflector 12 with a time interval T. The data processing unit 16 converts the photon detection signals output from the plurality of APDs 14-1 to 14-n into time-series serial signals, and outputs the serial signals.
[0037]
With such a configuration, for example, when n APDs 14-1 to 14-n are arranged in the array-type APD photon detector 14, the apparent appearance of each photon detection element (APD) is ideal. It is possible to increase the response speed by n times.
[0038]
As described above, in the first embodiment, the plurality of APDs 14-1 to 14-n are provided in the array-type APD photon detector 14, and the light deflection is performed so as to sequentially sweep over the plurality of APDs 14-1 to 14-n. Since the incident photon pulse train 11 is deflected by the detector 12, the interval between the gate pulses (reverse bias voltage) applied to each of the APDs 14-1 to 14-n is n times the time interval T of the incident photon pulse train 11. nT is sufficient. Therefore, in the first embodiment, it becomes possible to increase the apparent response speed of each of the photon detecting elements (APDs) 14-1 to 14-n to n times, and to use a low-speed photon detecting element. However, photon detection can be performed at high speed.
[0039]
Embodiment 2 FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the photon detection device of the first embodiment is applied to a quantum cryptography receiver in quantum cryptography communication.
[0040]
The quantum cryptography communication system shown in FIG. 4 includes a quantum cryptography transmission device 51 and a quantum cryptography reception device 56. The quantum cryptography transmission device 51 includes a quantum cryptography modulator 52 that modulates a signal photon in accordance with a quantum cryptography protocol, a multiplexer (not shown) that multiplexes a clock signal light having a higher light intensity than a signal photon and a signal photon, and the like. Have.
[0041]
The quantum cryptography receiver 56 includes a quantum cryptography demodulator 54 for demodulating a received signal received via the transmission path 53, a clock extracting unit 55 for extracting a clock signal from the received signal, and the photon detector 20 according to the first embodiment. And The photon detecting device 20 has the same optical deflector 12, optical deflector driving unit 13, array type APD photon detector 14, bias applying unit 15, and data processing unit 16 as those described in the first embodiment. ing.
[0042]
In such a quantum cryptography communication system, a signal photon modulated according to a quantum cryptography protocol by a quantum cryptography modulator 52 of a quantum cryptography transmission device 51 is multiplexed with a clock signal light, and then transmitted through a transmission path 53 to a quantum cryptography. The light enters the receiving device 56.
[0043]
The signal photons incident on the quantum cryptography demodulator 54 of the quantum cryptography receiver 56 are demodulated by the quantum cryptography demodulator 54 and then incident on the optical deflector 12. Further, the clock extraction unit 55 receives the clock signal light demultiplexed from the signal photons by the quantum encryption demodulator 54, and extracts a clock signal (synchronization signal) for synchronization from the clock signal light.
[0044]
The synchronization signal extracted by the clock extracting unit 55 is input to the optical deflector driving unit 13 and the bias applying unit 15 as in the first embodiment. The optical deflector driving means 13 and the bias applying means 15 operate in the same manner as in the first embodiment. The signal photons incident on the optical deflector 12 are deflected by the optical deflector 12, and then incident on an array-type APD photon detector 14 in which a plurality of APDs 14-1 to 14-n are arranged. The detection signal of the array type APD photon detector 14 is converted into a time series signal by the data processing means 16 and output from the data processing means 16.
[0045]
Note that the signal photons demodulated by the quantum cryptographic demodulator 54 may be branched into a plurality of paths. In such a case, the photon detectors 20 may be installed one by one on each path.
[0046]
【The invention's effect】
As described above, according to the present invention, the incident photon pulse train is deflected by the optical deflector so as to sequentially sweep the plurality of photon detection elements, so that the apparent response speed of each photon detection element is increased. It is possible to perform high-speed photon detection even when a low-speed photon detection element is used.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a photon detection device according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a time chart of a gate pulse output from a bias applying unit.
FIG. 3 is a diagram showing a relationship between a voltage of a gate pulse train and an APD current.
FIG. 4 is a diagram showing a configuration of a second embodiment in which the present invention is applied to a quantum cryptographic communication device.
FIG. 5 is a diagram showing a relationship among photon detection, an after-pulse count rate, and a gate pulse.
FIG. 6 is a diagram showing a time change of an after-pulse counting rate of the APD photon detector.
[Explanation of symbols]
Reference Signs List 11 incident photon pulse train, 12 optical deflector, 13 deflector driving means, 14 array type photon detector, 14-1 to 14-n photon detector, 15 bias applying means, 16 data processing means, 51 quantum cryptographic transmitter, 52 quantum encryption modulator, 53 transmission line, 54 quantum encryption demodulator, 55 clock extraction means, 56 quantum encryption receiving device.

Claims (6)

An optical deflector for deflecting incident light,
A photon detector having a plurality of photon detection elements for detecting photons,
Optical deflector driving means for driving the optical deflector, so that the output light of the optical deflector sweeps over the plurality of photon detection elements,
Bias applying means for applying a gate pulse as a bias voltage to each photon detection element so as to match the timing at which the output light of the optical deflector is incident on each photon detection element,
Data processing means for converting a detection signal from the plurality of photon detection elements into a time-series signal,
A photon detection device comprising: The photon detector according to claim 1, wherein the photon detector includes the plurality of photon detection elements arranged in a row. The photon detecting device according to claim 1, wherein the plurality of photon detecting elements are avalanche photodiodes. The photon detection device according to claim 1, wherein the light deflector comprises an acousto-optic element. The photon detection device according to claim 1, wherein the light deflector is made of an electro-optic crystal. The photon detection device according to claim 1, wherein the light deflector comprises a reflecting mirror.

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