TWI866470B - Generating method of polarized single photon and polarized single photon light source system - Google Patents

Abstract

Generating method of polarized single photon light source includes generating pulse signal from a pulse signal generating element to a light emitting diode, and a voltage of the pulse signal is lower than a nominal working voltage of the light emitting diode. The method further includes generating a first light beam by the light emitting diode based on the pulse signal, and the first light beam has a first light intensity. The method further includes transforming the first light beam into a polarized light beam and adjusting the first light intensity by a polarizer. The method further includes detecting photon number by a photon counter.

Description

Method for generating polarized single photons and polarized single photon light source system

The present disclosure relates to a method for generating polarized single photons and a polarized single photon light source system.

With the development of quantum technology, quantum communication, quantum optics and other technologies are the main research directions. Applications of scientific education such as photo sensor calibration and quantum phenomenon demonstration all require single-photon light sources. However, the current single-photon light source manufacturing method uses semiconductor quantum dots, quantum wells, single-molecule luminescence, single-atom luminescence and other methods. The above methods still have the disadvantages of difficult manufacturing methods and high costs.

In view of this, how to provide a single-photon light source with low manufacturing difficulty and low cost is still a goal that urgently needs research.

A technical aspect of the present disclosure is a method for generating polarized single photons.

In one embodiment, a method for generating polarized single photons includes generating a pulse signal to a photodiode by a pulse signal generating element; the photodiode generates a first light beam with a first light intensity according to the pulse signal, and the first light beam includes less than ten non-polarized photons; converting the first light beam into a polarized light beam by a polarizer set and adjusting the first light intensity; and detecting the number of photons by a photon counter.

In one embodiment, the voltage of the pulse signal is lower than the nominal operating voltage of the photodiode.

In one embodiment, the duration of the pulse signal is less than 100 nanoseconds.

In one embodiment, converting the first light beam into a polarized light beam by a polarizer set and adjusting the first light intensity further includes adjusting the angle between the first polarizer and the second polarizer of the polarizer set to obtain a change in the number of photoelectrons of the polarized light beam.

In one embodiment, converting the first light beam into a polarized light beam by a polarizer set and adjusting the first light intensity also includes determining the polarization angle according to the change in the number of photoelectrons.

In one embodiment, converting the first light beam into a polarized light beam and adjusting the first light intensity by a polarizer set further includes fixing the polarization angle between the first polarizer and the second polarizer and adjusting the pulse signal to enable the photodiode to generate a second light beam, wherein the second light beam has a second light intensity less than the first light intensity.

In one embodiment, the method for generating polarized single photons further includes calculating the average number of photoelectrons in the polarized light beam received by the photon counter according to an approximate model.

One technical aspect of the present disclosure is a polarized single-photon light source system.

In one embodiment, a polarized single-photon light source system includes a photodiode, a pulse signal generating element, a photon counter, and a polarizer set. The photodiode is configured to emit a first light beam. The pulse signal generating element is electrically connected to the photodiode and configured to generate a pulse signal to the photodiode. The polarizer set is located between the photodiode and the photon counter and configured to convert the first light beam into a polarized light beam.

In one embodiment, the polarized single-photon light source system further includes an attenuator disposed between the photodiode and the polarizer assembly.

In one embodiment, the photon counter is a photomultiplier tube.

In the above-mentioned embodiment, a light source with a small number of photons in a non-polarized state can be first generated by a low-cost light-emitting diode and a pulse signal generating element that provides a pulse signal. The manufacturing difficulty and cost of the equipment used in this step are lower than the existing practice. Then, by providing polarization characteristics and controlling the light intensity through a polarizer set to screen the polarized single-photon light source, the effect of the change in polarization angle on the average number of photoelectrons can be clearly seen. Therefore, the method and system for generating polarized single photons disclosed in the present invention can effectively generate polarized single photons, and has the advantages of low difficulty and low cost in element manufacturing.

The following will disclose multiple embodiments of the present invention with drawings. For the purpose of clarity, many practical details will be described together in the following description. However, it should be understood that these practical details should not be used to limit the present invention. That is to say, in some embodiments of the present invention, these practical details are not necessary. In addition, in order to simplify the drawings, some commonly used structures and components will be depicted in the drawings in a simple schematic manner. And for the sake of clarity, the thickness of the layers and regions in the drawings may be exaggerated, and the same element symbols represent the same elements in the description of the drawings.

FIG. 1 is a schematic diagram of a polarized single-photon light source system 100 according to an embodiment of the present disclosure. The polarized single-photon light source system 100 includes a photodiode 110, a pulse signal generating element 112, a polarizer set 120, and a photon counter 130. The photodiode 110 is configured to emit a first light beam L1, and the first light beam L1 is non-polarized light. The pulse signal generating element 112 is electrically connected to the photodiode 110 and configured to generate a pulse signal S to the photodiode 110. The polarizer set 120 is located between the photodiode 110 and the photon counter 130. The polarizer set 120 includes a first polarizer 122 and a second polarizer 124. The polarizer set 120 is configured to convert the first light beam L1 into a polarized light beam P1.

The photodiode 110 is controlled by a pulse signal generating element 112 to generate a light beam. The pulse signal generating element 112 can be a function generator, a quartz oscillator, or other equipment or device that can generate a pulse square wave. In this embodiment, a function generator is used as an example. The pulse signal generating element 112 provides a pulse signal S to the photodiode 110, so that the photodiode 110 generates a first light beam L1 containing a plurality of (e.g., less than ten) non-polarized photons, which is then screened by the polarizer assembly 120 into a polarized light beam P1 containing polarized single photons.

The first light beam L1 is defined as a non-polarized light beam entering the polarizer assembly 120. In some embodiments, the first light beam L1 may be a light beam emitted by the photodiode 110 and then generated by other components. In this embodiment, the photon counter 130 is exemplified by a photomultiplier (PMT), but the disclosure is not limited thereto. The photomultiplier in this embodiment converts photons into photoelectrons at a ratio of about 4 to 1, that is, the quantum efficiency (QE) is about 25%.

Compared to the technology of directly generating polarized photons, the present disclosure has the advantages of low difficulty and low cost in device manufacturing through the combination of the photodiode 110, the pulse signal generating element 112 and the polarizer assembly 120.

FIG. 2 is a flow chart of a method for generating polarized single photons according to an embodiment of the present disclosure. Refer to FIG. 1 and FIG. 2. The method starts at step S1, where a pulse signal generating element 112 generates a pulse signal S to a photodiode 110. In this embodiment, the voltage of the pulse signal S is lower than the nominal operating voltage of the photodiode 110, but the present disclosure is not limited thereto. Continuing to step S2, the photodiode 110 generates a first light beam L1 according to the pulse signal S, and the first light beam L1 has a first light intensity. In steps S3 to S5, the first light beam L1 is converted into a polarized light beam P1 by a polarizer assembly 120, and the first light intensity is adjusted. The detailed steps may include step S3, adjusting the angle between the first polarizer 122 and the second polarizer 124 of the polarizer set 120 to obtain the variation of the number of photoelectrons of the polarized light beam P1. Then, step S4 is performed to determine the polarization angle according to the variation of the number of photoelectrons. Optionally, step S5 is performed to fix the polarization angle and adjust the pulse signal S so that the photodiode 110 generates a second light beam, wherein the second light beam has a second light intensity less than the first light intensity. Finally, in step S6, the number of photons is detected by the photon counter 130.

It should be understood that step S6 can be performed in any of steps S2 to S5 to confirm the effect of adjusting the pulse signal S, polarization angle and other parameters on generating a single photon light source. The execution order of step S6 is not limited to the final step of the method, and the execution number of step S6 is not limited.

In step S1, by adjusting the voltage (square wave amplitude) and width (square wave time length, period) of the pulse signal S of the pulse signal generating element 112, the photodiode 110 can be switched continuously and rapidly with a weak intensity to emit a single to several photons.

For example, in this embodiment, the voltage of the pulse signal S is 1500 mV, which is much lower than the nominal operating voltage of 3000 mV of the photodiode 110. In other embodiments, the voltage of the pulse signal S may be higher than the nominal operating voltage, as long as the photodiode 110 can emit a first light beam L1 including a plurality of non-polarized photons, and the first light beam L1 then enters the polarizer assembly 120.

In addition, the duration of the pulse signal S needs to be as short as 10 nanoseconds (ns) to enable the photodiode 110 to produce a rapid and continuous switching effect. In other words, the duration corresponding to the width of the pulse signal S needs to be at least less than 100 nanoseconds.

Referring to step S2 of FIG. 2 , the photodiode 110 generates a first light beam L1 according to the pulse signal S, and the first light beam L1 has a first light intensity. The effect of making the emitted first light beam L1 have only a single to several (less than ten) photons is illustrated by FIGS. 3A to 3D . FIGS. 3A to 3D are spectrums of a photon counter under different pulse signals S according to an embodiment of the present disclosure. In the embodiments of FIGS. 3A to 3D , the width of the pulse signal S is fixed at 10 nanoseconds, and the voltages are 1550 mV, 1570 mV, 1590 mV, and 1610 mV, respectively. It should be understood that the actual values of the width and voltage of the pulse signal S may vary with different system architectures and are not intended to limit the present invention.

From the peak values in Figures 3A to 3D, it can be seen that the first light beam L1 generated by the photodiode 110 controlled by the pulse signal generating element 112 has a first light intensity detected by the photon counter 130 of about 1 to 3 photoelectrons, or less than 3 photoelectrons. When the light intensity (number of photoelectrons) is to be reduced, the voltage of the pulse signal S can be reduced, and vice versa. Similarly, when the light intensity is to be reduced, the voltage of the pulse signal S can be fixed and the width of the pulse signal S can be reduced. Therefore, in step S1 to step S2, the desired first light intensity can be dynamically approached.

Referring to step S3 of FIG. 2, the angle between the first polarizer 122 and the second polarizer 124 of the polarizer assembly 120 is adjusted to obtain the variation in the number of photoelectrons of the polarized light beam P1. The relationship between the variation in the number of photoelectrons and the polarization angle is illustrated in FIGS. 4A to 4F. FIGS. 4A to 4F are spectrums of a photon counter at different polarization angles according to an embodiment of the present disclosure. FIGS. 4A to 4F respectively represent the spectrum of the photon counter when the angle between the first polarizer 122 and the second polarizer 124 is 0 degrees, 30 degrees, 60 degrees, 90 degrees, 120 degrees, and 180 degrees, and the pulse signal S is fixed. Polarization angle between the first polarizer 122 and the second polarizer 124 The relationship with light intensity satisfies the relationship: ,in is the light intensity when the polarization angle is 0 degrees.

From the peaks in Figures 4A to 4F, it can be seen that the change in the first light intensity is related to the polarization angle. The polarization angle in Figure 4A is 0 degrees, and the spectrum of the photon counter shows that there are mainly about one to three photoelectrons, mainly three photoelectrons. The polarization angle in Figure 4B is 30 degrees, and there are mainly about one to two photoelectrons. The polarization angle in Figure 4C is 60 degrees, and there are about one to two photoelectrons. The polarization angle in Figure 4D is 90 degrees, and there is mainly one photoelectron. The trends shown in the spectra in Figures 4E and 4F are similar to those in Figures 4C and 4A, respectively. It can be clearly seen that the change in the first light intensity conforms to the relationship that is proportional to the square of the cosine function.

It should be understood that the actual values of the photon counters in FIGS. 4A to 4F may vary with different system architectures, are not intended to limit the present invention, and have no corresponding relationship with the values in FIGS. 3A to 3D.

Referring to step S4 of FIG. 2, the polarization angle is determined according to the variation of the number of photoelectrons. After detecting multiple different polarization angles in step S3, it can be concluded that the spectrum variation is most obvious when the polarization angle is 80 degrees. FIG. 5 is a spectrum of a photon counter when the polarization angle is 80 degrees according to an embodiment of the present disclosure. FIG. 5 shows an obvious single photon peak.

Referring to step S6 of FIG. 2 , the average number of photoelectrons of the polarized light beam P1 received by the photon counter is calculated according to the approximate model. The average number of photoelectrons calculated by the approximate model when the polarization angle is 80 degrees is about 0.216, and it can be seen that the average number of photons is less than one. Therefore, it can be seen that the first light beam L1 provides a light beam with a high probability of having single photons. The polarizer set 120 can provide the first light beam L1 with polarization characteristics and further screen out the polarized light beam P1 that meets the requirements of the single-photon light source.

FIG. 6 is a graph showing the relationship between the average number of photoelectrons and the polarization angle according to an embodiment of the present disclosure. The average number of photoelectrons is proportional to the square of the cosine function. From the aforementioned steps and FIG. 6, it can be seen that a polarization single photon light source can be generated under the condition that the polarization angle is close to 80 degrees.

Referring to step S5 of FIG. 2 , step S5 is selectively performed. In step S5 , the polarization angle is fixed, and the pulse signal S is adjusted to make the photodiode 110 generate a second light beam, wherein the second light beam has a second light intensity less than the first light intensity.

FIG. 7A and FIG. 7B are spectrums of a photon counter under the same polarization angle and different pulse signals S according to an embodiment of the present disclosure. The polarization angles in FIG. 7A and FIG. 7B are both 0 degrees, which is only an example. In other embodiments, after the polarization angle of step S4 is determined, step S5 can be performed to further adjust the polarized light beam P1 to obtain a polarized light beam with lower light intensity.

The pulse signal S voltage in FIG. 7A is smaller than the pulse signal S voltage in FIG. 7B. The peak in FIG. 7A is mainly single photons. FIG. 8A to FIG. 8F are the spectrum of the photon counter of the embodiment in FIG. 7A when the polarization angle is 20 degrees, 60 degrees, 90 degrees, 120 degrees, 160 degrees and 180 degrees, respectively.

Refer to Figures 8A to 8F and Figure 5 at the same time. Figure 5 represents the polarized light beam P1 with a polarization angle of 80 degrees in step S4, with an average photoelectron number of 0.216. The second light intensity in Figures 8A to 8F is less than the first light intensity in Figure 5 at different polarization angles. It can be seen that the average photoelectron number of the second light intensity of the second light beam obtained by step S5 can be lower than 0.216. Therefore, further adjusting the polarized light beam P1 by step S5 produces a more reliable polarized single-photon light source.

When the polarized single-photon light source system 100 is used as a light source, the photon counter 130 can be used to first confirm whether the polarized light beam P1 meets the requirements, and then the polarized light beam P1 is directed to the optical system of the actual application. Therefore, the polarized light beam P1 is defined as the light beam entering the photon counter 130, and is also the light beam provided by the polarized single-photon light source system 100 as a light source.

FIG. 9 is a schematic diagram of a polarized single-photon light source system 100a according to another embodiment of the present disclosure. The polarized single-photon light source system 100a is similar to the polarized single-photon light source system 100 of FIG. 1, except that the polarized single-photon light source system 100a further includes an attenuator 140 disposed between the photodiode 110 and the polarizer assembly 120.

The attenuator 140 helps to increase the probability of generating single photons. In the present embodiment, the photodiode 110 emits an initial light beam L0, which forms a first light beam L1 having a single to several non-polarized photons after passing through the attenuator 140. In summary, through the method and system disclosed herein, a non-polarized light source having a small number of photons can be first generated by a low-cost light-emitting diode and a pulse signal generating element that provides a pulse signal. The manufacturing difficulty and cost of the equipment used in this step are lower than the existing practices. Then, by providing polarization characteristics and controlling the light intensity through a polarizer set to screen the polarized single-photon light source, the effect of changes in the polarization angle on the average number of photoelectrons can be clearly seen. Therefore, the method and system for generating polarized single photons disclosed herein can effectively generate polarized single photons and have the advantages of low difficulty and low cost in device manufacturing.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present disclosure. Anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be determined by the scope of the attached patent application.

100,100a: Polarized single-photon light source system 110: Photodiode 112: Pulse signal generating element 120: Polarizer set 122: First polarizer 124: Second polarizer 130: Photon counter 140: Attenuator L0: Initial beam L1: First beam P1: Polarized beam S: Pulse signal S1~S6: Steps

FIG. 1 is a schematic diagram of a polarized single-photon light source system according to an embodiment of the present disclosure. FIG. 2 is a flow chart of a method for generating polarized single photons according to an embodiment of the present disclosure. FIG. 3A to FIG. 3D are spectrums of a photon counter under different pulse signals according to an embodiment of the present disclosure. FIG. 4A to FIG. 4F are spectrums of a photon counter under different polarization angles according to an embodiment of the present disclosure. FIG. 5 is a spectrum of a photon counter when the polarization angle is 80 degrees according to an embodiment of the present disclosure. FIG. 6 is a graph showing the relationship between the average number of photoelectrons and the polarization angle according to an embodiment of the present disclosure. FIG. 7A and FIG. 7B are spectrums of a photon counter under the same polarization angle and different pulse signals according to an embodiment of the present disclosure. Figures 8A to 8F are the spectrum of the photon counter of the embodiment in Figure 7A when the polarization angle is 20 degrees, 60 degrees, 90 degrees, 120 degrees, 160 degrees and 180 degrees. Figure 9 is a schematic diagram of a polarized single-photon light source system according to another embodiment of the present disclosure.

S1~S6: Steps

Claims (10)

A method for generating a polarized single photon comprises: generating a pulse signal to a photodiode by a pulse signal generating element; the photodiode generates a first light beam according to the pulse signal, wherein the first light beam has a first light intensity and contains less than ten non-polarized photons; converting the first light beam into a polarized light beam by a polarizer set and adjusting the first light intensity; and detecting the number of photons by a photon counter. A method for generating polarized single photons as described in claim 1, wherein the voltage of the pulse signal is lower than the nominal operating voltage of the photodiode. A method for generating polarized single photons as described in claim 1, wherein the duration of the pulse signal is less than 100 nanoseconds. The method for generating polarized single photons as described in claim 1, wherein the first light beam is converted into the polarized light beam by the polarizer set, and the first light intensity is adjusted, further comprising: Adjusting an angle between a first polarizer and a second polarizer of the polarizer set to obtain a photoelectron number change of the polarized light beam. The method for generating polarized single photons as described in claim 4, wherein the first light beam is converted into the polarized light beam by the polarizer set, and the first light intensity is adjusted, further comprising: Determining at least one polarization angle according to the variation in the number of photoelectrons. The method for generating polarized single photons as described in claim 5, wherein the first light beam is converted into the polarized light beam by the polarizer set, and the adjustment of the first light intensity further comprises: fixing the polarization angle between the first polarizer and the second polarizer; and adjusting the pulse signal so that the photodiode generates a second light beam, wherein the second light beam has a second light intensity less than the first light intensity. The method for generating polarized single photons as described in claim 4 further comprises: Calculating an average number of photoelectrons of the polarized light beam received by the photon counter according to an approximate model. A polarized single-photon light source system, using the method for generating polarized single photons of claim 1, wherein the polarized single-photon light source system comprises: a photodiode, configured to emit a first light beam; a pulse signal generating element, electrically connected to the photodiode, configured to generate a pulse signal to the photodiode; a photon counter; and a polarizer set, located between the photodiode and the photon counter, configured to convert the first light beam into a polarized light beam. The polarized single-photon light source system as described in claim 8 further comprises: An attenuator disposed between the photodiode and the polarizer assembly. A polarized single-photon light source system as described in claim 8, wherein the photon counter is a photomultiplier tube.