Apparatus and method for measuring wavelength of single photon

Abstract

The present invention relates to an apparatus and method for measuring the wavelength of a single photon, the apparatus comprising: a light source for emitting light; a light distributor for distributing the light emitted from the light source at a predetermined ratio; a first single-photon detector for detecting single photons in first light distributed by the light distributor; a filter for filtering second light distributed by the light distributor; a second single-photon detector for detecting single photons in the second light filtered by the filter; a calculation unit for calculating a first photon count value and a second photon count value from the single photons detected by the first single-photon detector and the single photons detected by the second single-photon detector, respectively; and a measurement unit for deriving the ratio of the photon count values according to the difference between the first photon count value and the second photon count value calculated by the calculation unit, and measuring the wavelengths of the single photons according to the ratio of the photon count values.

Description

Device and method for measuring the wavelength of a single photon

[0001] The present invention claims the benefit of the filing dates of Korean Patent Application No. 10-2024-0187267 filed with the Korean Intellectual Property Office on December 16, 2024, and Korean Patent Application No. 10-2025-0048004 filed with the Korean Intellectual Property Office on April 14, 2025, the entire contents of which are incorporated into the present invention.

[0002] The present invention relates to an apparatus and method for measuring the wavelength of a single photon using a response flattening filter.

[0003]

[0004] Single-photon detection technology is utilized in various fields, including quantum information science, biology, astronomy, and remote sensing. This technology enables the precise detection of individual photons, allowing for the generation of high-resolution images even under conditions of minute light intensity. Consequently, it has become possible to observe biological processes at the molecular level in fields such as medical imaging, fluorescence microscopy, and remote sensing. Recently, alongside advancements in quantum information science—including quantum communication, quantum sensing, and quantum computing—the demand for measurement equipment capable of measuring at the photon level has surged. In this context, single-photon detector (SNSPD, photomultiplier tube, SPAD, etc.) technologies are advancing, with different technologies being employed for various purposes.

[0005] Furthermore, to achieve various objectives, single-photon detection technology utilizes not only single-photon detectors but also advanced infrastructure equipment such as spectroscopic filters, Time-Correlation Number Measurement (TCSPC) devices, and Electron Multiplying Charge-Coupled Device (EMCCD) image measurement instruments. The combination of these devices provides a method to measure light wavelengths at the photon level, which can ensure more reliable measurement results in fields requiring single-photon detection technology.

[0006] Existing single-photon detector technologies and wavelength measurement methods face technical limitations and cost issues. Specifically, technologies utilizing spectrometer-mounted EMCCDs and spectroscopic filters are expensive, and the complexity and large size of the equipment impose restrictions on mobility and installation. Furthermore, these technologies have limitations in terms of practicality across various environments, and accurate measurements can be challenging, particularly when high-speed and precise wavelength measurement are required for the realization of quantum technology.

[0007] Furthermore, advanced applications such as quantum communication require more precise and practical wavelength measurement techniques, which conventional methods may struggle to meet. In particular, more sophisticated measurement methods compared to existing techniques are necessary to support complex technologies, such as the construction of quantum networks and the development of quantum repeaters.

[0008] The aforementioned background technology is technical information that the inventor possessed or acquired during the process of deriving the embodiments of the present invention, and it cannot be considered as prior art disclosed to the general public prior to the filing of the embodiments of the present invention.

[0009]

[0010] To solve the above problem, the present invention provides an apparatus and method for measuring the wavelength of a single photon according to the ratio of photon count values ​​by passing light from one of two optical paths through a response flattening filter.

[0011]

[0012] An apparatus for measuring the wavelength of a single photon according to one embodiment of the present invention may include: a light source that irradiates light; a light splitter that distributes the light irradiated from the light source at a predetermined ratio; a first single photon detector that detects a single photon of the first light distributed by the light splitter; a filter that filters the second light distributed by the light splitter; a second single photon detector that detects a single photon of the second light filtered by the filter; a calculation unit that calculates a first photon count value and a second photon count value, respectively, using the single photon detected by the first single photon detector and the single photon detected by the second single photon detector; and a measurement unit that derives the ratio of photon count values ​​based on the difference between the first photon count value and the second photon count value calculated by the calculation unit, and measures the wavelength of the single photon according to the ratio of photon count values.

[0013] According to one embodiment of the present invention, the optical splitter may be an optical fiber splitter.

[0014] According to one embodiment of the present invention, the optical splitter may be a beam splitter.

[0015] According to one embodiment of the present invention, a predetermined ratio of the optical splitter may be 50:50.

[0016] According to one embodiment of the present invention, the filter may be a flat-response filter.

[0017] According to one embodiment of the present invention, the filter may be coated on the sensor window of the second single photon detector.

[0018] According to one embodiment of the present invention, the first single photon detector and the second single photon detector may be a SPAD (Single Photon Avalanche Diode).

[0019] According to one embodiment of the present invention, the first single-photon detector and the second single-photon detector may have the same spectral sensitivity.

[0020] A method for measuring the wavelength of a single photon according to one embodiment of the present invention may include: a step of distributing light irradiated from a light source through a light splitter at a predetermined ratio; a step of detecting a single photon from the first light distributed from the light splitter using a first single photon detector; a step of filtering the second light distributed from the light splitter using a filter; a step of detecting a single photon from the second light filtered by the filter using a second single photon detector; a step of calculating a first photon count value and a second photon count value, respectively, using the single photon detected by the first single photon detector and the single photon detected by the second single photon detector; and a step of deriving a ratio of photon count values ​​based on the difference between the first photon count value and the second photon count value, and measuring the wavelength of the single photon based on the ratio of photon count values.

[0021]

[0022] An apparatus and method for measuring the wavelength of a single photon according to one embodiment of the present invention has the advantage of being able to measure wavelengths at the photon level.

[0023] In addition, the present invention has the advantage of enabling measurements at a fast picosecond level and at the real photon level.

[0024] In addition, the present invention is economical because it can be implemented relatively simply and inexpensively.

[0025] The effects obtainable from the invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the invention belongs from the description below.

[0026]

[0027] FIG. 1 illustrates a schematic diagram of an apparatus for measuring the wavelength of a single photon according to one embodiment of the present invention.

[0028] FIG. 2 illustrates a schematic diagram of an apparatus for measuring the wavelength of a single photon according to another embodiment of the present invention.

[0029] FIG. 3 illustrates the spectral sensitivity according to wavelength using a response flattening filter in a device for measuring the wavelength of a single photon according to one embodiment of the present invention.

[0030] FIG. 4 illustrates a flowchart of a method for measuring the wavelength of a single photon according to one embodiment of the present invention.

[0031] ※ Explanation of symbols

[0032] 1: Device for measuring the wavelength of a single photon

[0033] 10: Light source 20: Optical splitter

[0034] 21: Fiber optic splitter 22: Beam splitter

[0035] 30: Single photon detector 31: First single photon detector

[0036] 32: Second single-photon detector 40: Filter

[0037] 50: Output section

[0038]

[0039] The present invention will become clear from the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Meanwhile, the terms used in this specification are for describing the embodiments and are not intended to limit the present invention.

[0040] Throughout this specification, the singular form includes the plural form unless specifically stated otherwise in the text.

[0041] Throughout this specification, the terms “comprises” and / or “comprising” as used mean that the mentioned components, steps, actions and / or elements do not exclude the presence or addition of one or more other components, steps, actions and / or elements, and that, unless specifically stated otherwise, they do not exclude other components but may include additional components.

[0042] Additionally, terms such as “...part” as used throughout this specification refer to a unit that processes at least one function or operation, which may be implemented in hardware or software, or a combination of hardware and software.

[0043] Furthermore, throughout this specification, when a part is described as being “connected” to another part, this includes not only cases where they are “directly connected” but also cases where they are connected “with other components in between.”

[0044]

[0045] The present invention will be described in more detail below.

[0046] FIG. 1 illustrates a schematic diagram of an apparatus (1) for measuring the wavelength of a single photon according to one embodiment of the present invention, FIG. 2 illustrates a schematic diagram of an apparatus (1) for measuring the wavelength of a single photon according to another embodiment of the present invention, and FIG. 3 illustrates the spectral sensitivity according to wavelength by using a response flattening filter in an apparatus for measuring the wavelength of a single photon according to one embodiment of the present invention.

[0047] Referring to FIGS. 1 and 2, an apparatus (1) for measuring the wavelength of a single photon according to one embodiment of the present invention may include a light source (10), a light splitter (20), a first single photon detector (31), a filter (40), a second single photon detector (32), a calculation unit (50), and a measurement unit (not shown).

[0048] The light source (10) is configured to irradiate light (L), and it is particularly preferable that it be configured to irradiate a single photon using a single-photon source. To effectively irradiate such a single photon, it may further include a collimator that aligns the optical axis. Additionally, it may further include an ultrafast laser or a pulse modulator to emit single photons at regular intervals.

[0049] Light (L) irradiated from a light source (10) can be distributed at a constant ratio and irradiated into multiple paths. Here, the present invention may further include a light splitter (20) to distribute the irradiated light (L). That is, light irradiated from a light source (10) can be distributed at a predetermined ratio through the light splitter (20), and preferably can be distributed into two paths.

[0050] The light splitter (20) can be appropriately selected according to the path where the light (L) travels.

[0051] In one embodiment, the optical splitter (20) may be an optical fiber splitter (21). Referring to FIG. 1 (a) and (b), when the process of distributing light (L) occurs inside an optical fiber, the light (L) traveling in one optical fiber can be distributed to multiple output ports. In one embodiment, the optical fiber splitter (21) may be an optical fiber coupler (21).

[0052] In another embodiment, the light splitter (20) may be a beam splitter (22). Referring to FIG. 2 (a) and (b), if the process of distributing light (L) does not occur within a special medium, a portion of the incident light (L) can be reflected and transmitted to distribute it into multiple paths.

[0053] This light splitter (20) can distribute one light (L) irradiated from a light source (10) into a plurality of lights, preferably two lights, in a predetermined ratio.

[0054] In one embodiment, if the optical splitter (20) is an optical fiber coupler (21), the distribution ratio of light (L) can be adjusted through the spacing between the cores of the optical fibers, the difference in refractive index, etc. In another embodiment, if the optical splitter (20) is a beam splitter (22), the distribution ratio of light (L) can be adjusted by adjusting the thickness of the reflective and transmissive coating on the surface of the beam splitter (22), the refractive index inside the beam splitter (22), etc.

[0055] Here, the 'predetermined ratio' is not specifically limited, but preferably can be 50:50. That is, after calculating the photon count value in the calculation unit (50) using the single photon detected by the two single photon detectors (30) described below, it is desirable to distribute the light in the same ratio to measure the wavelength of the single photon by deriving the ratio of the photon count values ​​through the difference between these photon count values.

[0056] A single-photon detector (SPD, 30) is a photodetector capable of detecting a single photon at very low light intensity. When a photon is incident, it is converted into an electrical signal and then amplified to detect the presence of a single photon.

[0057] In one embodiment, the single photon detector (30) may be a SPAD (Single Photon Avalanche Diode). In the SPAD, a photoelectric effect occurs due to an incident photon, generating an electron-hole pair, and a large signal is output due to the avalanche effect by a high voltage (Geiger mode), which can be converted into a binary signal to detect the presence or absence of a single photon.

[0058] In the apparatus (1) for measuring the wavelength of a single photon according to one embodiment of the present invention, each light distributed from the light splitter (20), namely the first light and the second light, can be received to detect a single photon. Preferably, the first light distributed from the light splitter (20) can detect a single photon through the first single photon detector (31), and the second light distributed from the light splitter (20) can detect a single photon through the second single photon detector (32). However, the second light described below may be incident with a portion of the light blocked by a filter (40) before being incident on the second single photon detector (32).

[0059] The filter (40) is configured to filter the second light distributed from the light splitter (20), and can control the photon count by selectively allowing only a portion of the light to pass through (i.e., filtering). Accordingly, the photon count of the second light that has passed through the filter (40) and is detected through the second single photon detector (32) differs from the photon count of the first light detected through the first single photon detector (31).

[0060] In particular, in the present invention, the filter (40) is not subject to any special limitations if it is formed such that the difference in photon counts generated by the filter (40) increases or decreases at a predetermined rate. In one embodiment, the filter (40) of the present invention may be a flat-response filter.

[0061] The response flattening filter (40) is a filter (40) designed to maintain the intensity of light evenly according to the wavelength of the light. Accordingly, with reference to FIG. 3, when the second light passes through the filter (40), particularly the response flattening filter (40), it can be filtered so that the intensity does not vary according to the wavelength of the second light and is irradiated with a uniform intensity. This second light can be incident on the second single-photon detector (32).

[0062] In addition, for the first light and the second light distributed 50:50 in the light splitter (20) to have their photon counts controlled only by the filter (40), the spectral sensitivity of the first single photon detector (31) and the second single photon detector (32) may be provided equally.

[0063] Referring to FIG. 3(a), the spectral responsivity of the single photon detector (30) varies depending on the type of product, the diameter of the detection area, etc. Therefore, when the spectral responsivity of the plurality of single photon detectors (30), particularly the first single photon detector (31) and the second single photon detector (32), is made the same, the photon count is controlled only by the filter (40), so the ratio of spectral responsivity according to the wavelength of light can be formed consistently.

[0064] Meanwhile, referring to FIG. 1 (a) and FIG. 2 (a), the position of the filter (40) may be placed on the path where the second light distributed from the light splitter (20) is irradiated to the second single-photon detector (32). It does not matter where it is placed on the path of the second light.

[0065] In particular, the filter (40) may be provided integrally with the second single-photon detector (32) in one embodiment. More specifically, referring to FIG. 1 (b) and FIG. 2 (b), the filter (40) may be provided by coating it on the sensor window, which is the part where the second light is incident on the second single-photon detector (32). In this case, the filter (40) may be coated by depositing it on the surface of the sensor window using materials such as glass, silicon, metal oxide, and organic material, and then heat treating. This has the advantage of miniaturizing the device (1) for measuring the wavelength of a single photon.

[0066] The calculation unit (50) is configured to calculate a photon count value from a single photon detected by a single photon detector. This can record the signal pulse generated when a single photon reaches the single photon detector at an accurate time, convert it into digital data, and store it. With this digital data, a photon count value, which is the number of single photons detected during a specific time, can be calculated. In one embodiment, the calculation unit (50) may be a TCSPC (Time-Correlated Single Photon Counting).

[0067] That is, the output unit (50) of the present invention can calculate a first photon count value using a single photon detected by the first single photon detector (31), and calculate a second photon count value using a single photon detected by the second single photon detector (32).

[0068] In addition, a measuring unit (not shown) for measuring the wavelength of a single photon according to the ratio of photon count values ​​may be further included.

[0069] The measuring unit can derive the ratio of photon count values ​​through the first photon count value (see Fig. 3 (a)) and the second photon count value (see Fig. 3 (b)) received from the output unit (50). This is because the second light, which has passed through the filter (40), particularly the response flattening filter (40), has its photon count constant according to the wavelength by filtering, and accordingly, the photon count values ​​detected by the first single photon detector (31) and the second single photon detector (32) differ at a constant ratio according to the wavelength (see Fig. 3 (c)). Therefore, if this ratio is stored in a database, even if a different light source (10) is used in the device according to the present invention, the wavelength of the single photon of the irradiated light can be measured by deriving the ratio of the photon count values.

[0070] FIG. 4 illustrates a flowchart of a method for measuring the wavelength of a single photon according to one embodiment of the present invention.

[0071] Referring to FIG. 4, a method (S1) for measuring the wavelength of a single photon according to one embodiment of the present invention may include the steps of: distributing light at a predetermined ratio through a light splitter (20) (S10); detecting a single photon of the first light with a first single photon detector (31) (S20); filtering the second light with a filter (40) (S30); detecting a single photon of the second light with a second single photon detector (32) (S40); calculating a first photon count value and a second photon count value, respectively (S50); and measuring the wavelength of a single photon according to the ratio of the photon count values ​​(S60).

[0072] The step (S10) of distributing light at a predetermined ratio through a light splitter (20) is a step of passing light irradiated from a light source (10) through a light splitter (20) to distribute it at a predetermined ratio so that it is irradiated into multiple paths.

[0073] The step (S20) of detecting a single photon of the first light with the first single photon detector (31) is a step of detecting a single photon of the first light, which is one of the lights distributed by the light splitter (20), through the first single photon detector (31).

[0074] The step (S30) of filtering the second light with a filter (40) is a step of filtering the second light, which is the remaining one of the lights distributed by the light splitter (20), by passing it through the filter (40).

[0075] The step (S40) of detecting a single photon of the second light with the second single photon detector (32) is a step of detecting a single photon of the second light through the second single photon detector (32) of the second light that has passed through the filter (40).

[0076] The step (S50) of calculating the first photon count value and the second photon count value, respectively, is to calculate the first photon count value using a single photon detected by the first single photon detector (31) and to calculate the second photon count value using a single photon detected by the second single photon detector (32), respectively.

[0077] The step (S60) of measuring the wavelength of the single photon according to the ratio of the photon count values ​​is a step of deriving the ratio of the photon count values ​​through the received first photon count value and the second photon count value. This allows the wavelength of the single photon of the irradiated light to be measured by deriving the ratio of the photon count values ​​even when using a different light source (10).

[0078] A method (S1) for measuring the wavelength of a single photon according to one embodiment of the present invention may include all configurations and features of an apparatus (1) for measuring the wavelength of a single photon according to one embodiment of the present invention described above.

[0079]

[0080] Although the present invention has been described above by limited embodiments, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

Claims

1. As a device for measuring the wavelength of a single photon, A light source that emits light; A light splitter that distributes light irradiated from the above light source at a predetermined ratio; A first single-photon detector that detects a single photon of the first light distributed from the above-mentioned light splitter; A filter that filters the second light distributed from the above-mentioned light splitter; A second single-photon detector that detects a single photon of the second light filtered by the filter above; A calculation unit that calculates a first photon count value and a second photon count value, respectively, using a single photon detected by the first single photon detector and a single photon detected by the second single photon detector; and An apparatus for measuring the wavelength of a single photon, comprising: a measuring unit that derives the ratio of photon count values ​​based on the difference between the first photon count value and the second photon count value calculated by the above-mentioned calculation unit, and measures the wavelength of the single photon based on the ratio of the photon count values.

2. In Paragraph 1, The above optical splitter is, A device for measuring the wavelength of a single photon, characterized by being a fiber optic splitter.

3. In Paragraph 1, The above optical splitter is, A device for measuring the wavelength of a single photon characterized by being a beam splitter.

4. In Paragraph 1, The predetermined ratio of the above optical splitter is, A device for measuring the wavelength of a single photon characterized by being 50:

50.

5. In Paragraph 1, The above filter is, An apparatus for measuring the wavelength of a single photon characterized by being a flat-response filter.

6. In Paragraph 1, The above filter is, A device for measuring the wavelength of a single photon, characterized by being coated on the sensor window of the second single photon detector.

7. In Paragraph 1, The first single-photon detector and the second single-photon detector above are, A device for measuring the wavelength of a single photon characterized by being a SPAD (Single Photon Avalanche Diode).

8. In Paragraph 1, The first single-photon detector and the second single-photon detector above are, A device for measuring the wavelength of a single photon characterized by having the same spectral sensitivity.

9. As a method for measuring the wavelength of a single photon, A step of distributing light irradiated from a light source at a predetermined ratio through a light splitter; A step of detecting a single photon using a first single photon detector of the first light distributed from the above light splitter; A step of filtering the second light distributed from the above light splitter with a filter; A step of detecting a single photon using a second single photon detector of the second light filtered by the above filter; A step of calculating a first photon count value and a second photon count value, respectively, using a single photon detected by the first single photon detector and a single photon detected by the second single photon detector; and A method for measuring the wavelength of a single photon, comprising the step of deriving a ratio of photon count values ​​based on the difference between the first photon count value and the second photon count value, and measuring the wavelength of the single photon based on the ratio of photon count values.

Images