CN111308453A - Device for measuring optical fiber length by using entangled photons - Google Patents
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- CN111308453A CN111308453A CN202010172728.8A CN202010172728A CN111308453A CN 111308453 A CN111308453 A CN 111308453A CN 202010172728 A CN202010172728 A CN 202010172728A CN 111308453 A CN111308453 A CN 111308453A
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 40
- 239000000835 fiber Substances 0.000 claims abstract description 15
- 230000003287 optical effect Effects 0.000 claims abstract description 5
- 239000013078 crystal Substances 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 238000005086 pumping Methods 0.000 claims description 3
- 230000002269 spontaneous effect Effects 0.000 claims description 3
- 238000005259 measurement Methods 0.000 abstract description 22
- 238000000034 method Methods 0.000 description 20
- 238000002281 optical coherence-domain reflectometry Methods 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 2
- 238000005314 correlation function Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000002310 reflectometry Methods 0.000 description 2
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- 230000009286 beneficial effect Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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- G01S11/12—Systems for determining distance or velocity not using reflection or reradiation using electromagnetic waves other than radio waves
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Abstract
The invention provides a device for measuring the length of an optical fiber by using entangled photons, which comprises an entangled light source, a single photon detector and an event timer, wherein the entangled light source generates entangled photon pairs, one path of the entangled photon pairs is signal light, and the other path of the entangled photon pairs is idle light; the signal light and the idle light are respectively detected by the single-photon detectors D1 and D2, and the event timer records the time { t } t of the photon reaching the single-photon detectors D1 and D21jAnd t2jJ represents the jth photon, and t is obtained through second-order correlation operation2‑t1Indicating the time difference of arrival of the signal light and the idle light; adding the optical fiber with the length to be measured into the idle optical path, and recording the time { t 'of the photons reaching the single photon detectors D1 and D2 again by the event timer'1jAnd { t'2jT 'is obtained through second-order correlation operation'2‑t′1Calculating the length l ═ v of the optical fiberg·[(t′2‑t′1)‑(t2‑t1)]，vgIs the group velocity of the entangled photons in the fiber. Hair brushIt is clear that high measurement accuracy and a large measurement range can be simultaneously achieved.
Description
Technical Field
The invention belongs to the field of test and measurement, and particularly relates to an optical fiber length measurement technology.
Background
With the rapid development of optical fiber sensing technology, the requirement for the measurement accuracy of the optical fiber length is increasing day by day. The accurate measurement of the length of the optical fiber is of great importance to the development, production and maintenance of the optical fiber. The following methods are currently used to measure the length of an optical fiber:
the currently widely adopted method for measuring the length of the optical fiber is a time domain reflectometry (OTDR), but the method has a blind zone, namely when the length of the optical fiber is less than a certain value, the method cannot measure the length of the optical fiber, and the measurement precision can only reach the meter level.
Low Coherence Reflectometry (OLCR) is often used for high precision fiber length measurements, primarily to monitor small variations in fiber length. The method has high test precision which can reach 10 mu m, and has the defects of smaller dynamic range and the maximum measurable range which is only a few centimeters.
An Optical Frequency Domain Reflectometer (OFDR) is used for measuring the length of the optical fiber, and the measurement precision of the Optical Frequency Domain Reflectometer (OFDR) is higher than that of an OTDR and can reach millimeter level; the measurement range is larger than that of OLCR, and can reach several kilometers, and the method has higher practicability. However, OFDR cannot effectively measure the back-scattered light, and the system has very high requirements on the laser light source to achieve good coherence and stability; in addition, the coherent function of the source performs uncertain modulation on the received spectrum, so that the spatial variation of the scattering signal to be observed generates distortion, and the real spatial information is damaged; together with the non-linearity of the frequency sweep and the phase noise of the interferometer, its application is therefore limited.
Optical Coherence Domain Reflectometry (OCDR) is also a more commonly used method of measuring fiber length with high precision. The optical coherence domain reflectometry method has the advantages of high precision which can reach 10 mu m, large measurement range, signal-to-noise ratio which is more than 100dB and high sensitivity. However, similar to OFDR, the system has high requirements for light source and is not suitable for measuring long optical fibers to ensure good coherence of the system.
All-fiber interferometric systems developed from velocity interferometers can also be used to make fiber length measurements. The principle and the structure for measuring the length of the optical fiber by using the all-fiber interference system are simple, and the length measurement without a blind area can be realized. However, the measurement accuracy is not high, and the error is mainly derived from the counting of the interference fringes and the determination of the reference fiber length L.
The principle of measuring the length of the optical fiber based on the frequency shift asymmetric Sagnac interferometer is simple: the phase delay caused by the propagation of a lightwave signal in an optical fiber depends on the frequency of the light and the length of the optical fiber, i.e., the phase delay caused by the transmission of light of different frequencies in the same optical fiber is different. This difference can be easily analyzed by interference phenomena. The method for measuring the length of the optical fiber based on the frequency shift asymmetric Sagnac interferometer has high resolution and can reach micron level, the measurement range is large, and the length of the optical fiber from a few meters to dozens of kilometers can be measured. The error of this method is mainly derived from the reading error of the frequency of the minimum point in the interference signal.
The methods for measuring the length of the optical fiber are either low in precision or small in measurement range, or have high requirements on equipment and complex structures. By utilizing the characteristic that quantum entangled photon pairs have non-localized and non-classical strong association, a novel optical fiber length measuring method based on a quantum entangled light source is provided for the first time. The method utilizes the characteristic that the second order correlation function of the entangled photon pair takes the time difference as a variable, and utilizes the single photon detector and the coincidence measuring device to measure the time difference t. The length of the optical fiber can be calculated by l ═ c · t, where c is the speed of light.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides an optical fiber length measuring device based on a quantum entangled photon pair by utilizing the characteristics of non-localized and non-classical strong correlation of the quantum entangled photon pair, and the time difference t is measured by a single photon detector and a coincidence measuring device by utilizing the characteristic that a second order correlation function of the entangled photon pair takes the time difference as a variable; the length of the fiber, l ═ vt, is then calculated, where v is the velocity of the photon in the fiber.
The technical scheme adopted by the invention for solving the technical problems is as follows: an apparatus for measuring the length of optical fiber by using entangled photons includes an entangled light source, a single photon detector and an event timer.
The entanglement light source generates entanglement photon pairs, wherein one path of the entanglement light source is signal light, and the other path of the entanglement light source is idle light; the signal light and the idle light are respectively detected by the single-photon detectors D1 and D2, and the event timer records the time { t } t of the photon reaching the single-photon detectors D1 and D21jAnd t2jJ represents the jth photon, and t is obtained through second-order correlation operation2-t1Indicating the time difference of arrival of the signal light and the idle light; adding the optical fiber with the length to be measured into the idle optical path, and recording the time { t 'of the photons reaching the single photon detectors D1 and D2 again by the event timer'1jAnd { t'2jAnd, t 'is obtained by second order correlation calculation'2-t′1Calculating the length l ═ v of the optical fiberg·[(t′2-t′1)-(t2-t1)]，vgIs the group velocity of the entangled photons in the fiber.
The entanglement light source adopts 780nm laser pumping 10mm long PPKTP crystal to obtain entanglement photon pair through spontaneous parametric down-conversion.
The invention has the beneficial effects that: theoretically, t2-t1The measurement error of the method is 100fs, so the precision of the optical fiber length which can be measured by the method is dozens of microns, and the measurement range is not limited by increasing the pump laser power and increasing the brightness of the entanglement source. The method can simultaneously realize high measurement precision and large measurement range.
Drawings
FIG. 1 is a schematic diagram of the principle of using entangled photons versus the length of a fiber;
in the figure, 1-entangled photon pair generation device, 2-signal light, 3-idle light, 4-single photon detector D1, 5-single photon detector D2, 6-event timer, 7-cable for transmitting electric signals, and 8-optical fiber with length to be measured.
Detailed Description
The present invention will be further described with reference to the following drawings and examples, which include, but are not limited to, the following examples.
The invention designs a method for measuring the length of an optical fiber by using entangled photons, the principle of which is shown in figure 1, and the method comprises two parts of preparation and detection of an entangled light source.
The method adopts 780nm laser pumping 10mm long PPKTP crystal to obtain entangled photon pairs through spontaneous parametric down-conversion, wherein one is called signal light, and the other is called idle light. The signal light and the idle light in the entangled photon pair are respectively detected by the single photon detectors D1 and D2, and the event timer records the arrival time { t } of the photons1jAnd t2jJ represents the jth photon, and t is obtained through second-order correlation operation2-t1And represents the time difference between the arrival of the signal light and the arrival of the idle light. Adding an optical fiber with the length to be measured into an idle light path of the entangled photon pair, and recording the arrival time { t 'of the photon at the moment by an event timer'1jAnd { t'2jT 'at this time is obtained by second-order correlation calculation'2-t′1. Time delay delta t ═ t ' (t ') due to the addition of optical fiber '2-t′1)-(t2-t1) So that the length l of the fiber is equal to vg·Δt＝vg·[(t′2-t′1)-(t2-t1)]In the formula vgIs the group velocity of the entangled photons in the fiber.
In the embodiment of the invention, a 780nm laser pump 10mm long PPKTP crystal is adopted to obtain an entanglement light source, a superconducting single photon detector is adopted to detect the entanglement light source, and an event timer is used for measuring the arrival time of photons. The method is limited by the time jitter of the single-photon detector in experiments, and the measurement error of the time difference is dozens of picoseconds, so the measurement precision of the optical fiber length is millimeter magnitude.
Claims (2)
1. The utility model provides an utilize entanglement photon to the device of measuring optical fiber length, includes entanglement light source, single photon detector and event timer, its characterized in that: the entanglement light source generates entanglement photon pairs, wherein one path of the entanglement light source is signal light, and the other path of the entanglement light source is idle light; the signal light and the idle light are respectively detected by the single-photon detectors D1 and D2, and the event timer records the time when the photons reach the single-photon detectors D1 and D2M { t }1jAnd t2jJ represents the jth photon, and t is obtained through second-order correlation operation2-t1Indicating the time difference of arrival of the signal light and the idle light; adding the optical fiber with the length to be measured into the idle optical path, and recording the time { t 'of the photons reaching the single photon detectors D1 and D2 again by the event timer'1jAnd { t'2jT 'is obtained through second-order correlation operation'2-t′1Calculating the length l ═ v of the optical fiberg·[(t′2-t′1)-(t2-t1)]And vg is the group velocity of the entangled photons in the fiber.
2. The apparatus for measuring a length of an optical fiber using entangled photon pairs according to claim 1, wherein: the entanglement light source adopts 780nm laser pumping 10mm long PPKTP crystal to obtain entanglement photon pair through spontaneous parametric down-conversion.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114499671B (en) * | 2022-01-26 | 2024-02-06 | 中国科学院国家授时中心 | Microwave frequency anti-distortion and anti-dispersion measurement method based on quantum entanglement light source |
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|---|---|---|---|---|
| US20050199812A1 (en) * | 2004-03-15 | 2005-09-15 | University Of Maryland | System and method for clock synchronization and position determination using entangled photon pairs |
| CN103675801A (en) * | 2013-12-02 | 2014-03-26 | 上海交通大学 | Navigation and distance measurement system on basis of quantum entanglement light and method for implementing navigation and distance measurement system |
| CN108718218A (en) * | 2018-05-09 | 2018-10-30 | 中国科学院国家授时中心 | Two-way quantum method for synchronizing time based on frequency entanglement light source |
| CN109547144A (en) * | 2018-12-30 | 2019-03-29 | 华南师范大学 | A kind of clock system and method based on quantum entanglement |
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- 2020-03-12 CN CN202010172728.8A patent/CN111308453A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20050199812A1 (en) * | 2004-03-15 | 2005-09-15 | University Of Maryland | System and method for clock synchronization and position determination using entangled photon pairs |
| CN103675801A (en) * | 2013-12-02 | 2014-03-26 | 上海交通大学 | Navigation and distance measurement system on basis of quantum entanglement light and method for implementing navigation and distance measurement system |
| CN108718218A (en) * | 2018-05-09 | 2018-10-30 | 中国科学院国家授时中心 | Two-way quantum method for synchronizing time based on frequency entanglement light source |
| CN109547144A (en) * | 2018-12-30 | 2019-03-29 | 华南师范大学 | A kind of clock system and method based on quantum entanglement |
Non-Patent Citations (1)
| Title |
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| 季玲玲,吴令安: "光学超晶格中级联参量过程制备纠缠光子对" * |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114499671B (en) * | 2022-01-26 | 2024-02-06 | 中国科学院国家授时中心 | Microwave frequency anti-distortion and anti-dispersion measurement method based on quantum entanglement light source |
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