Light velocity measuring device based on FPGA (Field Programmable Gate Array)

Abstract

The utility model belongs to the technical field of light velocity measurement, and particularly discloses an FPGA-based light velocity measurement device, which comprises an FPGA-based digital lock-in amplifier, a first light path part, a position adjusting mechanism and a photoelectric detector, the first light path part sequentially comprises a modulatable laser light source, a beam splitter, a cube-corner prism and a focusing lens along the optical axis. According to the invention, the digital lock-in amplifier based on the FPGA is adopted to replace an oscilloscope in the traditional scheme. On one hand, the light velocity is measured by using a phase-locked amplification technology, so that a laser signal can be distinguished more stably and accurately, interference of an external environment is reduced, and light velocity measurement in a longer distance is realized; and on the other hand, high-precision measurement of the light velocity can be realized without using an oscilloscope, and the problems of complexity and high cost of a traditional light velocity measurement device can be solved.

Description

Technical Field

[0001] The present application belongs to the technical field of light speed measurement, and more specifically, relates to a light speed measurement device based on FPGA. Background Art

[0002] In physics, the speed of light is an important basic parameter. The measurement of the wavelength of light waves, the mass-energy relationship in relativity, the motion mass of elementary particles, etc. are all related to the speed of light. This parameter is widely used in many fields such as scientific research, precision measurement, engineering technology, aerospace, data communication, etc. Therefore, the correct measurement of the speed of light is of great significance.

[0003] The traditional light speed measuring instrument includes: a modulated laser light source, an oscilloscope, a signal generator and a photodetector. It measures the speed of light by the phase method. The red light emitted by the light emitting diode is modulated in the instrument and then divided into two paths. One beam is input into the X channel of the dual-trace oscilloscope; the other beam is emitted from the exit hole. The exit light changes its propagation direction through a right-angle reflector, enters the instrument from the receiving hole, and is input into the Y channel of the oscilloscope. These two intensity modulated wave signals with the same frequency are coherent in the oscilloscope, and a Lissajous figure is obtained on the screen.

[0004] Generally speaking, this figure is an ellipse. If the phase difference between the two signals is 0 or π, the Lissajous figure is a straight line. The two straight lines corresponding to the phase difference of 0 and π should have different directions, one in the first and third quadrants, and the other in the second and fourth quadrants. The phase difference between the two modulated signals is related to the distance the outgoing light propagates in the air. If the right-angle reflector is close to the exit hole, the phase difference between the two signals is equal (which can be achieved by adjusting the phase knob on the instrument), and a straight line is obtained on the oscilloscope. In the process of moving the reflector away, the Lissajous figure changes to an ellipse. The orientation and ellipticity of the ellipse also change with distance. When a straight line appears on the oscilloscope again, it means that the phase of the Y component in the oscilloscope has changed by π. That is, the modulated light path has changed by half a wavelength. The speed of light can be calculated by the calculation formula: c=λf, where c is the speed of light, λ is the laser wavelength, and f is the modulation frequency.

[0005] However, traditional light speed measuring instruments have the problems of complex equipment and high cost. Summary of the invention

[0006] In view of the defects of the prior art, the purpose of this application is to provide a light speed measurement device based on FPGA, aiming to solve the problems of complexity and high cost of traditional light speed measurement devices.

[0007] To achieve the above-mentioned purpose, in a first aspect, the present application provides a light speed measurement device based on FPGA, comprising: a digital phase-locked amplifier based on FPGA, a first optical path portion, a position adjustment mechanism and a photodetector;

[0008] The first optical path portion includes, in sequence along the optical axis: a modulated laser light source, a beam splitter, a corner cube prism and a focusing lens, wherein:

[0009] The laser output by the modulated laser light source is split by a beam splitter and then enters a corner cube prism; the corner cube prism reflects the incident laser in parallel to the beam splitter, and then reflects it again by the beam splitter; the reflected light reflected by the beam splitter is focused by a focusing lens to the active area of ​​the photodetector;

[0010] The output channel of the FPGA-based digital lock-in amplifier is connected to the input end of the modulated laser light source, and is used to output an analog signal to the modulated laser light source, so that the laser to be measured obtains a characteristic frequency. When receiving the photoelectric signal returned by the photodetector at different flight distances, the phase of the modulated laser at different flight distances is demodulated to calculate the speed of the modulated laser.

[0011] The position adjustment mechanism is used to change the position of the corner cube prism relative to the beam splitter, thereby changing the flight distance of the laser;

[0012] The output end of the photodetector is connected to the input channel of the FPGA-based digital lock-in amplifier for collecting the photoelectric signal focused on the active area.

[0013] Preferably, the output channel of the FPGA-based digital lock-in amplifier and the modulated laser light source, and the photodetector and the input channel of the FPGA-based digital lock-in amplifier are respectively connected via coaxial cables.

[0014] Preferably, the modulatable laser light source is a DML modulatable laser light source.

[0015] Preferably, the focusing lens is a plano-convex lens with a focal length of 30 mm.

[0016] Preferably, the position adjustment mechanism is a slide rail, and the corner cube prism is arranged on the slide rail.

[0017] To achieve the above-mentioned purpose, in a second aspect, the present application provides a light speed measurement device based on FPGA, comprising: a digital phase-locked amplifier based on FPGA, a second optical path portion, a position adjustment mechanism and a photodetector;

[0018] The second optical path portion includes, in sequence along the optical axis: a modulatable laser light source and a focusing lens, wherein:

[0019] The laser output from the modulated laser light source flies for a certain distance and then is focused by a focusing lens onto the active area of ​​the photodetector.

[0020] The output channel of the FPGA-based digital lock-in amplifier is connected to the input end of the modulated laser light source, and is used to output an analog signal to the modulated laser light source, so that the laser to be measured obtains a characteristic frequency. When receiving the photoelectric signal returned by the photodetector at different flight distances, the phase of the modulated laser at different flight distances is demodulated to calculate the speed of the modulated laser.

[0021] The position adjustment mechanism is used to change the position of the photoelectric detector, thereby changing the laser flight distance;

[0022] The output end of the photodetector is connected to the input channel of the FPGA-based digital lock-in amplifier for collecting the photoelectric signal focused on the active area.

[0023] Preferably, the output channel of the FPGA-based digital lock-in amplifier and the modulated laser light source, and the photodetector and the input channel of the FPGA-based digital lock-in amplifier are respectively connected via coaxial cables.

[0024] Preferably, the modulatable laser light source is a DML modulatable laser light source.

[0025] Preferably, the focusing lens is a plano-convex lens with a focal length of 30 mm.

[0026] Preferably, the position adjustment mechanism is a slide rail, and the photoelectric detector is arranged on the slide rail.

[0027] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the prior art:

[0028] This application proposes a light speed measurement device based on FPGA, which uses a digital phase-locked amplifier based on FPGA to replace the oscilloscope in the traditional solution. On the one hand, using phase-locked amplification technology to measure the speed of light can more stably and accurately distinguish laser signals, reduce interference from the external environment, and achieve longer-distance light speed measurement; on the other hand, high-precision measurement of the speed of light can be achieved without using an oscilloscope, which can solve the problem of complexity and high cost of traditional light speed measurement devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the structure of a light speed measurement device based on FPGA provided in Example 1 of the present application.

[0030] Figure 2 This is a schematic diagram of the structure of a light speed measurement device based on FPGA provided in Example 2 of the present application.

[0031] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0032] 1-phase-locked amplifier output channel; 2-modulatable laser light source; 3-beam splitter; 4-corner cone prism; 5-focusing lens; 6-photodetector; 7-phase-locked amplifier input channel; 8-FPGA-based digital phase-locked amplifier; 9-position adjustment mechanism. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0034] like Figure 1 As shown, the present application provides a light speed measurement device based on FPGA, comprising: a digital phase-locked amplifier 8 based on FPGA, a first optical path portion, a position adjustment mechanism 9 and a photodetector 6;

[0035] The first optical path portion includes, in sequence along the optical axis: a modulated laser light source 2, a beam splitter 3, a corner cube prism 4 and a focusing lens 5, wherein:

[0036] The laser output by the modulated laser light source 2 is split by the beam splitter 3 and then enters the corner cube 4; the corner cube 4 reflects the incident laser in parallel to the beam splitter 3, and is reflected again by the beam splitter 3; the reflected light reflected by the beam splitter 3 is focused by the focusing lens 5 to the active area of ​​the photodetector 6;

[0037] The output channel 1 of the digital phase-locked amplifier 8 based on FPGA is connected to the input end of the modulated laser light source 2, and is used to output an analog signal to the modulated laser light source, so that the laser to be measured obtains a characteristic frequency, and when receiving the photoelectric signal returned by the photodetector at different flight distances, demodulates to obtain the phase of the modulated laser at different flight distances, so as to calculate the speed of the modulated laser;

[0038] The position adjustment mechanism 9 is used to change the position of the corner cube prism 4 relative to the beam splitter 3, thereby changing the flight distance of the laser;

[0039] The output end of the photodetector 6 is connected to the input channel 7 of the FPGA-based digital phase-locked amplifier 8 for collecting the photoelectric signal focused on the active area.

[0040] A phase-locked amplifier is a device used to detect weak signals, and has the advantages of strong detection capability, strong versatility, and high reliability. Digital phase-locked amplifiers overcome the temperature drift and other non-ideal low-frequency characteristics of analog phase-locked amplifiers, greatly improving the performance of phase-locked amplifiers, and greatly improving the research, development, and application of phase-locked amplifiers. FPGA (Field Programmable Gate Array) is a programmable logic gate array. This application uses a digital phase-locked amplifier based on FPGA, which is a device that uses the programmability and parallel processing capabilities of FPGA to implement the function of a phase-locked amplifier in the form of a digital circuit. It has higher flexibility than traditional phase-locked amplifiers. The digital signal acquisition and signal processing function based on FPGA can collect the photoelectric signal data generated by the photodetector at a speed of up to 125MHz / s, with high accuracy and fast speed.

[0041] Preferably, the output channel of the FPGA-based digital lock-in amplifier and the modulated laser light source, and the photodetector and the input channel of the FPGA-based digital lock-in amplifier are respectively connected via coaxial cables.

[0042] Preferably, the modulatable laser light source is a DML (direct modulation) modulatable laser light source.

[0043] Preferably, the beam splitter has a beam splitting ratio of 5:5, which can split the incident light into two and refract and reflect them.

[0044] Preferably, the focusing lens 5 is a plano-convex lens with a focal length of 30 mm.

[0045] A plano-convex lens is an optical element that features a flat surface and a convex surface. When parallel light rays pass through a plano-convex lens, they are focused into a single point, which is the focal point of the lens. When using a plano-convex lens, the convex surface is usually facing the incident light, because the incident light on the two sides of the plano-convex lens has a slight difference in refractive index, resulting in a difference in focal length on the two sides. In order to reduce spherical aberration, the light beam should be incident on a curved surface as much as possible, so that the direction of the light and the focusing effect can be better controlled.

[0046] The photodetector 6 can convert light signals into electrical signals. When incident light shines on the active area, the change in the detector resistance value will cause a change in voltage.

[0047] Preferably, the position adjustment mechanism 9 is a slide rail, and the corner cube prism 4 is arranged on the slide rail.

[0048] In this embodiment, the analog signal is an analog signal with a fixed frequency of 100 kHz.

[0049] It should be noted that after demodulating the phase of the modulated laser at different flight distances, the speed of the modulated laser can be calculated based on the phase and distance. In this embodiment, the flight distance refers to the sum of all distances traveled during the period from the laser output from the modulated laser light source 2 to the active area of ​​the photodetector 6.

[0050] The calculation formula of laser light speed is as follows:

[0051]

[0052] Among them, c is the speed of light, Δd is the change in the distance light flies, f is the characteristic frequency of light, and Δφ is the phase change of light.

[0053] The above calculation formula belongs to the prior art and is not within the scope of protection of this application. It can be calculated manually by the user or by the calculation unit. Taking the average value of multiple measurements can obtain a more accurate result.

[0054] like Figure 2 As shown, the present application provides a light speed measurement device based on FPGA, comprising: a digital phase-locked amplifier 8 based on FPGA, a second optical path portion, a position adjustment mechanism 9 and a photodetector 6;

[0055] The second optical path portion includes, in sequence along the optical axis: a modulatable laser light source 2 and a focusing lens 5, wherein:

[0056] The laser outputted by the modulated laser light source 2 flies for a certain distance and is then focused by the focusing lens 5 onto the active area of ​​the photodetector 6;

[0057] The output channel 1 of the digital phase-locked amplifier 8 based on FPGA is connected to the input end of the modulated laser light source 2, and is used to output an analog signal to the modulated laser light source, so that the laser to be measured obtains a characteristic frequency, and when receiving the photoelectric signal returned by the photodetector at different flight distances, demodulates to obtain the phase of the modulated laser at different flight distances, so as to calculate the speed of the modulated laser;

[0058] The position adjustment mechanism 9 is used to change the position of the photodetector 6, thereby changing the laser flight distance;

[0059] The output end of the photodetector 6 is connected to the input channel 7 of the FPGA-based digital phase-locked amplifier 8 for collecting the photoelectric signal focused on the active area.

[0060] The program Figure 1 Based on the scheme shown, the optical path is simplified, and the light speed measurement is realized through the FPGA-based phase-locked amplifier, modulated laser, and photodetector, and an oscilloscope is also not required, which can save costs and simplify experimental operations.

[0061] Preferably, the output channel of the FPGA-based digital lock-in amplifier and the modulated laser light source, and the photodetector and the input channel of the FPGA-based digital lock-in amplifier are respectively connected via coaxial cables.

[0062] Preferably, the modulatable laser light source is a DML modulatable laser light source.

[0063] Preferably, the beam splitting ratio of the beam splitter is 5:5.

[0064] Preferably, the focusing lens 5 is a plano-convex lens with a focal length of 30 mm.

[0065] Preferably, the position adjustment mechanism 9 is a slide rail, and the photoelectric detector 6 is arranged on the slide rail.

[0066] It should be understood that expressions such as "including" and "may include" that may be used in the present application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In the present application, terms such as "including" and / or "having" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0067] In addition, in the present application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0068] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the relative position relationship after connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0069] In addition, in the embodiments of the present application, the mathematical concepts mentioned are symmetry, equality, parallelism, verticality, etc. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense, and allow a small amount of deviation, approximation to symmetry, approximation to equality, approximation to parallelism, approximation to verticality, etc. are all possible. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0070] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A light speed measurement device based on FPGA, characterized in that: include: A digital phase-locked amplifier (8) based on FPGA, a first optical path portion, a position adjustment mechanism (9) and a photodetector (6); The first optical path portion comprises, in sequence along the optical axis: a modulatable laser light source (2), a beam splitter (3), a corner cube prism (4) and a focusing lens (5), wherein: The laser light output by the modulated laser light source (2) is split by a beam splitter (3) and then enters a corner cube prism (4); the corner cube prism (4) reflects the incident laser light in parallel to the beam splitter (3), and then reflects the incident laser light again by the beam splitter (3); the reflected light reflected by the beam splitter (3) is focused by a focusing lens (5) to an active area of ​​a photoelectric detector (6); The output channel (1) of the FPGA-based digital phase-locked amplifier (8) is connected to the input end of the modulated laser light source (2) and is used to output an analog signal to the modulated laser light source so that the laser to be measured obtains a characteristic frequency. When receiving the photoelectric signal returned by the photoelectric detector at different flight distances, the phase of the modulated laser at different flight distances is demodulated to calculate the speed of the modulated laser. The position adjustment mechanism (9) is used to change the position of the corner cube prism (4) relative to the beam splitter (3), thereby changing the flight distance of the laser; The output end of the photodetector (6) is connected to the input channel (7) of the FPGA-based digital lock-in amplifier (8) for collecting the photoelectric signal focused on the active area.

2. The light speed measuring device according to claim 1, characterized in that: The output channel of the FPGA-based digital lock-in amplifier and the modulated laser light source, and the photodetector and the input channel of the FPGA-based digital lock-in amplifier are respectively connected through coaxial cables.

3. The light speed measuring device according to claim 1, characterized in that: The modulatable laser light source is a DML modulatable laser light source.

4. The light speed measuring device according to claim 1, characterized in that: The focusing lens (5) is a plano-convex lens with a focal length of 30 mm.

5. The light speed measuring device according to claim 1, characterized in that: The position adjustment mechanism (9) is a slide rail, and the corner cube prism (4) is arranged on the slide rail.

6. A light speed measurement device based on FPGA, characterized in that: include: A digital phase-locked amplifier (8) based on FPGA, a second optical path portion, a position adjustment mechanism (9) and a photodetector (6); The second optical path portion includes, in sequence along the optical axis: a modulatable laser light source (2) and a focusing lens (5), wherein: The laser light outputted by the modulated laser light source (2) flies for a certain distance and is then focused by a focusing lens (5) onto the active area of ​​a photodetector (6); The output channel of the FPGA-based digital phase-locked amplifier (8) is connected to the input end of the modulated laser light source (2) and is used to output an analog signal to the modulated laser light source so that the laser to be measured obtains a characteristic frequency. When receiving the photoelectric signal returned by the photoelectric detector at different flight distances, the phase of the modulated laser at different flight distances is demodulated to calculate the speed of the modulated laser. The position adjustment mechanism (9) is used to change the position of the photoelectric detector (6), thereby changing the flying distance of the laser; The output end of the photodetector (6) is connected to the input channel of the FPGA-based digital lock-in amplifier (8) for collecting the photoelectric signal focused on the active area.

7. The light speed measuring device according to claim 6, characterized in that: The output channel of the FPGA-based digital lock-in amplifier and the modulated laser light source, and the photodetector and the input channel of the FPGA-based digital lock-in amplifier are respectively connected through coaxial cables.

8. The light speed measuring device according to claim 6, characterized in that: The modulatable laser light source is a DML modulatable laser light source.

9. The light speed measuring device according to claim 6, characterized in that: The focusing lens (5) is a plano-convex lens with a focal length of 30 mm.

10. The light speed measuring device according to claim 6, characterized in that: The position adjustment mechanism (9) is a slide rail, and the photoelectric detector (6) is arranged on the slide rail.

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