An apparatus for frequency shift detection

Abstract

The utility model provides a kind of device for frequency shift detection, including polarized laser emission unit, polarized beam splitting unit, λ / 2 wave plate, amplifier unit, polarized separation coupling unit, optical lens unit, λ / 4 wave plate, the polarized separation coupling unit has port A6, port A7, port A8 and port A9, the circular polarized light beam scattered back by measured medium is converted into horizontal linear polarization backscattering light by λ / 4 wave plate, the horizontal linear polarization backscattering light is collected after optical lens unit and returns port A7 and is received;The horizontal linear polarization reference beam received by port A8 and the horizontal linear polarization backscattering light received by port A7 interfere in polarized separation coupling unit and generate difference frequency signal, the difference frequency signal is output by the port A9, and frequency shift signal is detected.The device for frequency shift detection of the application simplifies device structure, saves device manufacturing time and cost.

Description

Technical Field

[0001] This utility model relates to the field of frequency shift detection technology, and in particular, to a device for frequency shift detection. Background Technology

[0002] Laser Doppler velocimetry / anemometry (LDV / LDA) uses laser light to irradiate moving particles (such as tracer particles in a fluid), and the scattered light generates a Doppler frequency shift. The velocity is calculated by measuring the frequency shift through interferometry.

[0003] Traditional laser Doppler velocimeters typically involve complex interferometric optical paths and numerous optical components, which increases their production costs. For example, patent application FR2939202A1 discloses a biaxial laser blood sampling probe that includes three beam splitters and one beam combiner, significantly increasing the complexity of its optical path structure. Furthermore, existing laser Doppler velocimeters suffer from suboptimal signal-to-noise ratios.

[0004] Therefore, there is an urgent need to propose a device for frequency shift detection that can perform frequency shift detection using only a single unit that maintains the polarization state of the input light, which simplifies the device structure and saves device manufacturing time and cost. Utility Model Content

[0005] Traditional laser Doppler velocimeters typically include complex interferometric optical paths and a large number of optical components, which increases the production cost of laser Doppler velocimeters to some extent. In addition, existing laser Doppler velocimeters have the technical problem of unsatisfactory signal-to-noise ratio. This utility model proposes a device for frequency shift detection to solve at least one of the above-mentioned technical problems.

[0006] In a preferred embodiment of this utility model, an apparatus for frequency shift detection is provided, comprising:

[0007] A polarized laser emitting unit that generates a horizontally linearly polarized laser beam;

[0008] A polarization beam splitter unit has ports A1, A2 and A3. Port A1 receives the horizontally linearly polarized laser beam, port A2 outputs a horizontally linearly polarized reference beam, and port A3 outputs a horizontally linearly polarized signal beam. The horizontally linearly polarized reference beam enters the reference optical path, and the horizontally linearly polarized signal beam enters the signal optical path.

[0009] A λ / 2 waveplate is disposed in the signal optical path to rotate a horizontally linearly polarized signal beam into a vertically linearly polarized signal beam.

[0010] An amplifier unit is disposed in the signal optical path. The amplifier unit has a port A4 and a port A5. The port A4 receives the vertically polarized signal beam, and the port A5 outputs the vertically polarized signal beam with enhanced power.

[0011] A polarization separation coupling unit has ports A6, A7, A8, and A9. Port A7 is a bidirectional input / output port. Port A6 receives the power-enhanced vertically polarized signal beam, port A7 outputs the power-enhanced vertically polarized signal beam, and port A8 receives the horizontally polarized reference beam.

[0012] An optical lens unit that focuses the power-enhanced vertically polarized signal beam output from port A7;

[0013] A λ / 4 waveplate is used to focus and enhance the power of a vertically linearly polarized signal beam, which is then converted into a circularly polarized beam and irradiates the medium under test.

[0014] in,

[0015] The circularly polarized beam scattered back by the measured medium is converted into horizontally linearly polarized backscattered light by a λ / 4 waveplate. The horizontally linearly polarized backscattered light is collected by an optical lens unit and returns to port A7 for reception.

[0016] The horizontally polarized reference beam received at port A8 and the horizontally polarized backscattered light received at port A7 interfere in the polarization separation coupling unit and generate a difference frequency signal. The difference frequency signal is output through port A9 and the frequency shift signal is detected.

[0017] Preferably, the device for frequency shift detection further includes a photoelectric conversion unit, which converts the difference frequency signal output from port A9 into an electrical signal.

[0018] Preferably, the device for frequency shift detection further includes a signal amplification unit that amplifies the electrical signal.

[0019] Preferably, the device for frequency shift detection further includes a filtering unit that filters out noise from the amplified electrical signal.

[0020] Preferably, the device for frequency shift detection further includes a signal conditioning unit that shapes and biases the noise-filtered electrical signal.

[0021] Preferably, the device for frequency shift detection further includes a signal digitization unit that converts the shaped and bias-adjusted electrical signal into a digital signal.

[0022] Preferably, the device for frequency shift detection further includes a frequency shift extraction and analysis unit, which is used to calculate the frequency shift and output the result.

[0023] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0024] 1. The device for frequency shift detection of this application rotates a horizontally linearly polarized signal beam into a vertically linearly polarized signal beam by means of a λ / 2 waveplate, which is strictly orthogonal to the horizontally linearly polarized reference beam. Physical isolation between the interference signal and the crosstalk light is achieved in the polarization separation coupling unit, which significantly improves the signal-to-noise ratio. An amplifier unit is set in the signal optical path. By pre-amplifying the amplifier unit, the accumulation of noise in the subsequent link is avoided.

[0025] 2. The device for frequency shift detection in this application simplifies the device structure and saves device manufacturing time and cost by replacing the traditional complex interference optical path with a polarization separation coupling unit (e.g., additional beam splitters can be omitted). Attached Figure Description

[0026] The preferred embodiments will now be described in a clear and easy-to-understand manner, with reference to the accompanying drawings, to further explain the above-mentioned characteristics, technical features, advantages, and implementation methods.

[0027] Figure 1 This invention illustrates a device for frequency shift detection in one embodiment of the present invention. Detailed Implementation

[0028] The following provides a more detailed description of various aspects of this utility model.

[0029] Unless otherwise defined or stated, all technical and scientific terms used herein have the same meaning as are familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention.

[0030] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the specific implementation methods of this utility model will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of this utility model. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0031] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The drawings only show components related to this application and are not drawn according to the actual number, shape, and size of the components in the actual implementation. In the actual implementation, the form, quantity, and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex. For example, the thickness of the elements in the drawings may be exaggerated for clarity.

[0032] Example 1

[0033] As attached Figure 1 As shown, this utility model provides a device for frequency shift detection, comprising:

[0034] Polarized laser emitting unit 1, which generates a horizontally linearly polarized laser beam;

[0035] The polarization beam splitter 2 has ports A1, A2 and A3. Port A1 receives the horizontally polarized laser beam, port A2 outputs a horizontally polarized reference beam, and port A3 outputs a horizontally polarized signal beam. The horizontally polarized reference beam enters the reference optical path, and the horizontally polarized signal beam enters the signal optical path.

[0036] λ / 2 waveplate 3, which is disposed in the signal optical path, is used to rotate the horizontally linearly polarized signal beam into a vertically linearly polarized signal beam;

[0037] Amplifier unit 4 is disposed in the signal optical path. Amplifier unit 4 has port A4 and port A5. Port A4 receives the vertically polarized signal beam, and port A5 outputs the vertically polarized signal beam with enhanced power.

[0038] The polarization separation coupling unit 5 has ports A6, A7, A8 and A9. Port A7 is a bidirectional input / output port. Port A6 receives the power-enhanced vertically polarized signal beam, port A7 outputs the power-enhanced vertically polarized signal beam, and port A8 receives the horizontally polarized reference beam.

[0039] Optical lens unit 6, which focuses the power-enhanced vertically polarized signal beam output from port A7;

[0040] The vertically linearly polarized signal beam, after being focused and enhanced by power, is converted into a circularly polarized beam 14 by the λ / 4 waveplate 7 and then irradiates the medium under test 16.

[0041] in,

[0042] The circularly polarized beam 15, scattered and returned by the medium under test 16, is converted into horizontally polarized backscattered light by the λ / 4 waveplate 7. The horizontally polarized backscattered light is collected by the optical lens unit 6 and returned to port A7 for reception.

[0043] The horizontally polarized reference beam received at port A8 and the horizontally polarized backscattered light received at port A7 interfere in the polarization separation coupling unit 5 and generate a difference frequency signal. The difference frequency signal is output through port A9 and the frequency shift signal is detected.

[0044] In a preferred embodiment, the polarization laser emitting unit 1 is a 1550nm wavelength single-mode polarization-maintaining fiber laser with a polarization extinction ratio ≥25dB.

[0045] In a preferred embodiment, port A6 receives the power-enhanced vertically polarized signal beam, wherein the power value is enhanced to not less than 30 dBm. It should be noted that enhancing the power value of the vertically polarized signal beam output from the λ / 2 waveplate 3 to not less than 30 dBm via amplifier unit 4 can compensate for losses in subsequent optical paths (optical lenses, λ / 4 waveplate, scattering by the measured medium), ensuring that backscattered light can be effectively detected.

[0046] In a preferred embodiment, the polarization beam splitter 2 is a polarization-preserving fiber beam splitter with three ports: port A1 is the input port, and ports A2 and A3 are the output ports. The splitting ratio of the horizontally polarized reference beam and the horizontally polarized signal beam is 1:9, ensuring that the reference light power is moderate and the signal light is amplified to meet the transmission requirements.

[0047] In a preferred embodiment, the λ / 2 waveplate 3 is a zero-order λ / 2 waveplate to reduce the influence of temperature drift; the polarization rotation accuracy is ±0.5°, the aperture covers the diameter of the signal beam, and it is placed at 45° to the optical axis in the signal optical path.

[0048] In a preferred embodiment, amplifier unit 4 is an erbium-doped fiber amplifier (EDFA) or a ytterbium-doped fiber amplifier (YDFA). Input port A4 receives vertically polarized signals, and output port A5 outputs vertically polarized signals with enhanced power, with an output power ≥30dBm.

[0049] In a preferred embodiment, the polarization separation coupling unit 5 is a fiber-optic four-port polarization separation coupler. Port A6 receives the vertically linearly polarized signal beam and transmits it to A7 (bidirectional port); port A8 receives the horizontally linearly polarized reference beam; port A7 receives the horizontally linearly polarized backscattered light, which interferes with the horizontally linearly polarized reference beam input from A8, and outputs the difference frequency signal through port A9. The polarization isolation of the polarization separation coupling unit 5 is ≥30dB, ensuring that there is no crosstalk between V / horizontal linearly polarized light.

[0050] In a preferred embodiment, the optical lens unit 6 is an achromatic focusing lens group, the focal length of which is adapted to the distance of the measured medium.

[0051] In a preferred embodiment, the λ / 4 waveplate 7 is a zero-order λ / 4 waveplate, and the working wavelength matched polarization laser emitting unit 1 is placed at 45° to the direction of the outgoing vertically polarized signal beam to achieve linear polarization to circular polarization conversion. On the return journey, the circularly polarized beam is converted into horizontally linearly polarized backscattered light (perpendicular to the outgoing vertically polarized signal beam) by the λ / 4 waveplate, with a polarization conversion efficiency ≥99% and a phase delay accuracy of λ / 4±λ / 100.

[0052] In a preferred embodiment, the device for frequency shift detection further includes a photoelectric conversion unit 8, which converts the difference frequency signal output from port A9 into an electrical signal. It should be noted that the photoelectric conversion unit 8 can be selected as an avalanche photodiode (APD) in low-power scenarios (such as weak scattered echoes) to improve sensitivity through avalanche gain; and can be selected as a high-speed photodiode (PD) in high-frequency scenarios (such as GHz-level frequency shifts) to ensure that the response bandwidth matches the difference frequency signal frequency.

[0053] Preferably, the device for frequency shift detection further includes a signal amplification unit 9, which amplifies the electrical signal. It should be noted that the signal amplification unit 9 employs a low-noise amplifier (LNA) to avoid introducing excessive noise while amplifying the signal, especially for weak difference frequency signals.

[0054] Preferably, the device for frequency shift detection further includes a filtering unit 10, which filters out noise from the amplified electrical signal. It should be noted that the filtering unit 10 is a bandpass filter (BPF) with a center frequency adapted to the expected frequency shift range (e.g., kHz to GHz), a bandwidth of ±10% of the center frequency, and noise suppression.

[0055] Preferably, the device for frequency shift detection further includes a signal conditioning unit 11, which performs waveform shaping and bias adjustment on the noise-filtered electrical signal. It should be noted that the waveform shaping involves converting the sinusoidal difference frequency signal into a square wave using a comparator, facilitating direct processing by a counter or digital circuit (especially suitable for frequency measurement using counting methods); the bias adjustment involves superimposing a DC bias onto the AC difference frequency signal to ensure that the overall signal is within the effective input range of the processing module (e.g., to prevent negative voltage from exceeding the ADC's range).

[0056] Preferably, the device for frequency shift detection further includes a signal digitization unit 12, which converts the shaped and bias-adjusted electrical signal into a digital signal. It should be noted that the signal digitization unit 12 is an analog-to-digital converter (ADC).

[0057] Preferably, the device for frequency shift detection further includes a frequency shift extraction and analysis unit 13, which is used to calculate the frequency shift and output the result.

[0058] It should be noted that the frequency shift extraction and analysis unit 13 can perform digital domain processing, including:

[0059] Fast Fourier Transform (FFT): It finds the frequency corresponding to the peak of a signal through spectral analysis, namely the Doppler frequency shift Δf (unit: Hz). It is suitable for static or slowly changing frequency shifts, such as blood flow velocity measurement.

[0060] If the velocity of the object being measured is v, the laser wavelength is λ, and θ is the angle between the beam and the direction of motion of the object being measured, then the relationship between frequency shift and velocity is: Δf = 2vcosθ / λ, from which the velocity value can be calculated.

[0061] Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspect set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or practice the method can be implemented using other structures and / or functionalities besides one or more of the aspects set forth herein.

[0062] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of this utility model. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this utility model, and these improvements and modifications should also be considered within the protection scope of this utility model.

[0063] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing description of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A device for frequency shift detection, characterized in that, include: A polarized laser emitting unit that generates a horizontally linearly polarized laser beam; A polarization beam splitter unit has ports A1, A2 and A3. Port A1 receives the horizontally linearly polarized laser beam, port A2 outputs a horizontally linearly polarized reference beam, and port A3 outputs a horizontally linearly polarized signal beam. The horizontally linearly polarized reference beam enters the reference optical path, and the horizontally linearly polarized signal beam enters the signal optical path. A λ / 2 waveplate is disposed in the signal optical path to rotate a horizontally linearly polarized signal beam into a vertically linearly polarized signal beam. An amplifier unit is disposed in the signal optical path. The amplifier unit has a port A4 and a port A5. The port A4 receives the vertically polarized signal beam, and the port A5 outputs the vertically polarized signal beam with enhanced power. A polarization separation coupling unit has ports A6, A7, A8, and A9. Port A7 is a bidirectional input / output port. Port A6 receives the power-enhanced vertically polarized signal beam, port A7 outputs the power-enhanced vertically polarized signal beam, and port A8 receives the horizontally polarized reference beam. An optical lens unit that focuses the power-enhanced vertically polarized signal beam output from port A7; A λ / 4 waveplate is used to focus and enhance the power of a vertically linearly polarized signal beam, which is then converted into a circularly polarized beam and irradiates the medium under test. in, The circularly polarized beam scattered back by the measured medium is converted into horizontally linearly polarized backscattered light by a λ / 4 waveplate. The horizontally linearly polarized backscattered light is collected by an optical lens unit and returns to port A7 for reception. The horizontally polarized reference beam received at port A8 and the horizontally polarized backscattered light received at port A7 interfere in the polarization separation coupling unit and generate a difference frequency signal. The difference frequency signal is output through port A9 and the frequency shift signal is detected.

2. The device for frequency shift detection as described in claim 1, characterized in that, The device for frequency shift detection also includes a photoelectric conversion unit that converts the difference frequency signal output from port A9 into an electrical signal.

3. The device for frequency shift detection as described in claim 2, characterized in that, The device for frequency shift detection also includes a signal amplification unit that amplifies the electrical signal.

4. The apparatus for frequency shift detection as described in claim 3, characterized in that, The device for frequency shift detection also includes a filtering unit that filters out noise from the amplified electrical signal.

5. The apparatus for frequency shift detection as described in claim 4, characterized in that, The device for frequency shift detection also includes a signal conditioning unit that shapes and biases the noise-filtered electrical signal.

6. The apparatus for frequency shift detection as described in claim 5, characterized in that, The device for frequency shift detection also includes a signal digitization unit that converts the shaped and bias-adjusted electrical signal into a digital signal.

7. The apparatus for frequency shift detection as described in claim 6, characterized in that, The device for frequency shift detection also includes a frequency shift extraction and analysis unit, which is used to calculate the frequency shift and output the result.

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